A Review of Multi-material and Composite Parts Production by Modified Additive Manufacturing Methods
---
paper_title: Additive Manufacturing Technologies: Rapid Prototyping to Direct Digital Manufacturing

paper_content:

Additive Manufacturing Technologies: Rapid Prototyping to Direct Digital Manufacturing deals with various aspects of joining materials to form parts. Additive Manufacturing (AM) is an automated technique for direct conversion of 3D CAD data into physical objects using a variety of approaches. Manufacturers have been using these technologies in order to reduce development cycle times and get their products to the market quicker, more cost effectively, and with added value due to the incorporation of customizable features. Realizing the potential of AM applications, a large number of processes have been developed allowing the use of various materials ranging from plastics to metals for product development. Authors Ian Gibson, David W. Rosen and Brent Stucker explain these issues, as well as: Providing a comprehensive overview of AM technologies plus descriptions of support technologies like software systems and post-processing approaches Discussing the wide variety of new and emerging applications like micro-scale AM, medical applications, direct write electronics and Direct Digital Manufacturing of end-use components Introducing systematic solutions for process selection and design for AM Additive Manufacturing Technologies: Rapid Prototyping to Direct Digital Manufacturing is the perfect book for researchers, students, practicing engineers, entrepreneurs, and manufacturing industry professionals interested in additive manufacturing.
---
paper_title: Modeling and Fabrication of Heterogeneous Three-Dimensional Objects Based on Additive Manufacturing

paper_content:

Heterogeneous object modeling and fabrication has been studied in the past few decades. Recently the idea of digital materials has been demonstrated by using Additive Manufacturing (AM) processes. Our previous study illustrated that the mask-image-projection based Stereolithography (MIP-SL) process is promising in fabricating such heterogeneous objects. In the paper, we present an integrated framework for modeling and fabricating heterogenous objects based on the MIP-SL process. Our approach can achieve desired grading transmission between different materials in the object by considering the fabrication constraints of the MIP-SL process. The MIP-SL process planning of a heterogeneous model and the hardware setup for its fabrication are also presented. Test cases including physical experiments are performed to demonstrate the possibility of using heterogeneous materials to achieve desired physical properties. Future work on the design and fabrication of objects with heterogeneous materials is also discussed.Copyright © 2013 by ASME
---
paper_title: Modelling for randomly oriented multi material additive manufacturing component and its fabrication

paper_content:

Abstract Additive Manufacturing (AM) is one of the advanced manufacturing processes, which was initially used only for visualization purpose as Rapid Prototype (RP) components. In later stages due to the advancement of materials processing in AM technology it is also used to manufacture tools and functional parts. In material science field AM is very much useful in the development of multi material component such as functionally gradient materials, heterogeneous material structures and porous material structures. These structures have tremendous applications in the field of aeronautical, automobile and medical industries. But some of the traditional techniques, which are used for fabrication of these structures, have difficulties such as uniform & random distribution, size and shape control and maximum percentage of secondary materials to the primary materials. In this work a novel methodology is introduced for the fabrication of randomly oriented multi material (ROMM) using Polyjet 3D Printing (3DP) machine, which takes into account for the distribution of plastic reinforcement in matrix elastomer as modelled using Computer Aided Design (CAD) software. CATIA VB SCRIPT has been used for ROMM CAD modelling. Stress–strain behaviour of Polyjet 3DP component (with pure elastomer and with randomly oriented plastic reinforced elastomer) is carried out in Universal Testing Machine (UTM). It has been found that ROMM with plastic reinforcement provides significantly improved stiffness compared to pure elastomer component. In addition, the stiffness is consistent among different ROMM Polyjet 3DP components, which were taken at three different orientations (Horizontal, Inclined and Vertical) from the ROMM rectangular plate domain. It shows that reinforcement is uniformly distributed. Normal distribution curve and volumetric analysis is carried out in ROMM to verify uniform and random distribution of plastic reinforcement in elastomer. Based on the experimental results, this modelling and manufacturing technique can be used for the spatial orientation of reinforcement in the ROMM component and its fabrication with better stiffness for form & fit and functional parts applications.
---
paper_title: Fabrication and mechanical properties of homogeneous zirconia toughened alumina ceramics via cyclic solution infiltration and in situ precipitation

paper_content:

Abstract Alumina ceramic composites toughened with various contents of fine-sized zirconia particulates were fabricated via cyclic infiltrating pre-sintered alumina preforms with zirconium oxychloride solution and immersion in ammonia solution to induce in situ precipitation. Homogeneous distribution of zirconia throughout the bulk material has been substantiated by line-scan analysis and backscattering images taken from sections with different distances from surface. It was found that a higher drying temperature and increase in infiltration numbers lead to a greater zirconia content and bigger grain size. The hardness of fabricated zirconia toughened alumina composite was firstly improved probably due to the microstructure refining effect, while a further increase in zirconia content results in the decrease of hardness. A significantly higher indentation toughness has been observed for samples containing >10 wt.% zirconia compared with other specimens, which could be attributed to the coarser zirconia grain size and the related greater tendency to transformation into monoclinic phase.
---
paper_title: Preparation of zirconia–mullite composites by an infiltration route

paper_content:

Abstract In order to improve the mechanical properties of pure mullite ceramics, a process has been developed that incorporates Zr(Y)O 2 into mullite by infiltrating partially reaction sintered (porous) mullite compacts with mixed ZrOCl 2 ·8H 2 O and YCl 3 ·6H 2 O solutions, corresponding to ZrO 2 /Y 2 O 3 = 97/3 (mol.%). The infiltration of small amount (∼7.2 wt.%) of Zr(Y)O 2 significantly improved the densification behavior and mechanical properties of mullite bodies sintered at 1620 °C, for 10 h. The mocrostructure contained a few elongated mullite crystals (aspect ratio > 6) which were embedded in a fine-grained matrix. The relatively large Zr(Y)O 2 inclusions were mainly dispersed intergranularly in the matrix, but small ( 2 O 3 content than that of stoichiometric mullite composition formed at triple points of the mullite/mullite grains.
---
paper_title: Stereolithography of spatially controlled multi-material bioactive poly(ethylene glycol) scaffolds.

paper_content:

Abstract Challenges remain in tissue engineering to control the spatial, mechanical, temporal and biochemical architectures of scaffolds. Unique capabilities of stereolithography (SL) for fabricating multi-material spatially controlled bioactive scaffolds were explored in this work. To accomplish multi-material builds, a mini-vat setup was designed allowing for self-aligning X–Y registration during fabrication. The mini-vat setup allowed the part to be easily removed and rinsed, and different photocrosslinkable solutions to be easily removed and added to the vat. Two photocrosslinkable hydrogel biopolymers, poly(ethylene glycol) dimethacrylate (PEG-dma, MW 1000) and poly(ethylene glycol) diacrylate (PEG-da, MW 3400), were used as the primary scaffold materials. Multi-material scaffolds were fabricated by including controlled concentrations of fluorescently labeled dextran, fluorescently labeled bioactive PEG or bioactive PEG in different regions of the scaffold. The presence of the fluorescent component in specific regions of the scaffold was analyzed with fluorescent microscopy, while human dermal fibroblast cells were seeded on top of the fabricated scaffolds with selective bioactivity and phase contrast microscopy images were used to show specific localization of cells in the regions patterned with bioactive PEG. Multi-material spatial control was successfully demonstrated in features down to 500 μm. In addition, the equilibrium swelling behavior of the two biopolymers after SL fabrication was determined and used to design constructs with the specified dimensions at the swollen state. The use of multi-material SL and the relative ease of conjugating different bioactive ligands or growth factors to PEG allows for the fabrication of tailored three-dimensional constructs with specified spatially controlled bioactivity.
---
paper_title: Fabrication of fine-grained alumina ceramics by a novel process integrating stereolithography and liquid precursor infiltration processing

paper_content:

Abstract In this study, we report a novel approach, integrating stereolithography and liquid precursor infiltration techniques, to fabricate fine-grained alumina ceramics. The XRD patterns of the sample immersed with Zr 4+ or Zr 4+ (Y 3+ ) show that the sintered body contains Al 2 O 3 and t-ZrO 2 as the major phase and minor phase, respectively. Moreover, the t-ZrO 2 phase in the sample immersed with Zr 4+ (Y 3+ ) shows intense peaks compared to the composite immersed with Zr 4+ . On the other hand, the sample immersed with Mg 2+ contained Al 2 O 3 and MgAl 2 O 4 as the major phase and minor phase, respectively. The microstructure of the sample immersed with Zr 4+ shows that ZrO 2 particles are homogeneously distributed in the Al 2 O 3 matrix, thus inhibiting the grain growth of alumina particles. Moreover, the sample immersed with Mg 2+ shows a more dense and fine-grained structure. Compared to the non-infiltrated sample, the average grain size of the alumina sample immersed with Zr 4+ or Mg 2+ decreased. The sample infiltrated with Zr 4+ (Y 3+ ) had the smallest alumina average grain size of 1.14 µm. The ceramics prepared by infiltration showed a higher hardness (19.54 GPa), but a slightly lower fracture toughness (4.02 MPa m 1/2 ) compared to the samples (17.2 GPa, 4.13 MPa m 1/2 ) without infiltration.
---
paper_title: A novel quasicrystal-resin composite for stereolithography

paper_content:

Abstract Laser stereolithography (SL) is an additive manufacturing technology which is increasingly being used to produce customized end-user parts of any complex shape. It requires the use of a photo-curable resin which can be loaded with ceramic powders or carbon fibers to produce composite parts. However, the range of available materials compatible with the SL process is rather limited. In particular, photo-curable resins reinforced by metal particles are difficult to process, because of fundamental limitations related to the high reflectivity of intermetallics in the UV–visible range. In this work, the unique properties of Al-based quasicrystalline alloys are being used to develop a new UV-curable resin reinforced by such metal particles. The optical properties of the quasicrystalline particles and of the filled resin are studied and they are found to be compatible with the SL process. The volume fraction of the filler particles in the liquid resin is optimized to increase the polymerization depth while preserving suitable rheological behaviour. Finally, 3D composite parts are being built by SL. The composite parts have improved mechanical properties compared to the unfilled resin (higher hardness, reduced wear losses and lower friction coefficient) and compete favourably with the other commercial photo-curable resins.
---
paper_title: Structure property relationship of metal matrix syntactic foams manufactured by a binder jet printing process

paper_content:

Abstract The present research work has investigated the synthesis of ceramic structures based on inorganic, spherical-hollow microballoons using a binder jet printing process. Binder jet printing is a process that allows the synthesis process of complex and intricate parts with minimal waste of the feedstock material. The ceramic microballoons here investigated were based on a mullite derivative. The printed ceramic parts were cured and sintered as the precursor templates for metal matrix syntactic foams (MMSFs). The MMSFs were manufactured by infiltrating the printed ceramic templates by molten aluminum. The flexural strength of the cured, sintered, and infiltrated structures were also investigated. It is proposed that binder jet printing followed by a sintering and pressureless infiltration process represents an advantageous technology for designing complex MMSF structures.
---
paper_title: Fabrication of functionally graded reaction infiltrated SiC–Si composite by three-dimensional printing (3DP™) process

paper_content:

Carbon performs have been fabricated using the three-dimensional printing (3DP™) process for reaction-infiltrated SiC–Si composites. Starting with glassy carbon powders of 45–105 μm sizes, the preform was produced by printing acetone-based furfuryl resin binder. The bulk density and open porosity of the resulting preform was 0.6 g cm−3 and 48%, respectively. The binder printing conditions during preform fabrication mostly determined the preform microstructure. Pressureless reactive infiltration of such preforms at 1450°C in nitrogen atmosphere formed a SiC–Si composite with a coarse-SiC grain structure. Some residual carbon remained inside the SiC grains in this reaction bonded SiC–C due to sluggish reactivity of the larger carbon powder particles. Relatively complex-shaped carbon preforms with overhang, undercut, and inner channel structures were produced, demonstrating the capability of the 3DP process. A functionally graded SiC–Si composite was also fabricated, by varying carbon-yielding binder dosage during the preform fabrication, in order to control the spatial SiC concentration within the SiC–Si composite.
---
paper_title: Fabrication of Al2O3-based composites by indirect 3D-printing

paper_content:

Abstract A powder mixture of alumina and dextrin was used as a precursor material for fabrication of porous alumina preforms by indirect three-dimensional printing. Post-pressureless infiltration of the fabricated preforms with copper alloys resulted in dense composites with interpenetrating microstructure. The fabrication procedure involves four steps: a) freeze-drying of Al2O3/dextrin blends, b) three-dimensional printing of the green bodies, c) drying, dextrin decomposition and sintering of the printed bodies and d) post-pressureless infiltration of Cu-alloy into as-fabricated Al2O3 porous preforms. As result of the dextrin decomposition and Al2O3 sintering an average linear shrinkage of 17.7% was measured. After sintering the Al2O3 preforms with ∼36 vol.% porosity were obtained. A post-infiltration with copper alloy at 1300 °C for 1.5 h led to formation of dense Al2O3/Cu parts. X-ray analysis showed the presence of α-Al2O3, Cu and Cu2O only. Al2O3/Cu composite exhibits a fracture toughness of ∼5.5 MPa m1 / 2 and bending strength of ∼236 MPa. Fractographic analysis showed that crack bridging by plastically deformed metal phase may control the fracture toughness of this composite.
---
paper_title: A new physics-based model for equilibrium saturation determination in binder jetting additive manufacturing process

paper_content:

Abstract In binder jetting additive manufacturing (BJ-AM) process, the features are created through the interaction between droplets of the liquid binding agent and the layered powder bed. The amount of binder, which is termed binder saturation, depends strongly on the liquid binder and powder bed interaction including the spreading (i.e. lateral migration) and penetration (vertical migration) of the binder in powder bed, and is of crucial importance for determining the accuracy and strength of the printed parts. In the present study, a new physics-based model is developed to predict the optimal saturation levels for the green part printing, which is realized via capillary pressure estimation that is based on the binder and powder bed interactions in the equilibrium state. The proposed model was evaluated by both the Ti-6Al-4V and 420 stainless steel powders that exhibit different powder characteristics and packing densities. In order to estimate the equilibrium saturation using the proposed model, the physical characteristics such as average contact angle between the binder and powder material, specific surface area of powder particles, saturation and capillary pressure characterization curve were determined. Features with various degrees of dimensions (1-D, 2-D, 3-D) were printed out using M-Lab ExOne printer for determining the equilibrium saturation. Good agreement was observed between the theoretical predictions and experimentally measured saturation levels for the Ti-6Al-4V powder. On the other hand, the model underestimated the optimal saturation level for the 420 stainless steel powder, which was likely caused by the micro-surface areas from powder particle surface that do not contribute to the binder-powder bed interactions.
---
paper_title: Mechanical modeling based on numerical homogenization of an Al2O3/Al composite manufactured via binder jet printing

paper_content:

Abstract The present research work takes advantage of a recently published numerical homogenization implementation in MATLAB to find the elasticity tensor of a ceramic–metallic composite (CMC) system to be compared to an experimental data. Numerical homogenization is an efficient way to determine effective macroscopic properties of a composite material. This technique represents an effective means to model a two-phase composite. In this work, an extension of a previously published numeric homogenization code was investigated in order to model the compressive elastic modulus of the ceramic–metallic composites. The extension to the numerical code makes use of physical micrograph images to accurately describe the phase distribution of the composite. Multiple micrographs were taken from each sample, to subsequently better represent the actual microstructure of the composite as a whole. The composites were created using a binder jet 3D printing technology, where a ceramic precursor material was initially assembled, followed by a molten metal infiltration process. It was found that the studied numerical homogenization yielded an elastic modulus approximately 11.5% lower than the experimental data, suggesting a reliable modeling technique for predicting the elastic tensor of CMCs.
---
paper_title: Fabricating a pearl/PLGA composite scaffold by the low-temperature deposition manufacturing technique for bone tissue engineering

paper_content:

Here we developed a composite scaffold of pearl/poly(lactic-co-glycolic acid) (pearl/PLGA) utilizing the low-temperature deposition manufacturing (LDM). LDM makes it possible to fabricate scaffolds with designed microstructure and macrostructure, while keeping the bioactivity of biomaterials by working at a low temperature. Process optimization was carried out to fabricate a mixture of pearl powder, PLGA and 1,4-dioxane with the designed hierarchical structures, and freeze-dried at a temperature of −40 °C. Scaffolds with square and designated bone shape were fabricated by following the 3D model. Marrow stem cells (MSCs) were seeded on the pearl/PLGA scaffold and then cultured in a rotating cell culture system. The adhesion, proliferation and differentiation of MSCs into osteoblasts were determined using scanning electronic microscopy, WST-1 assay, alkaline phosphatase activity assay, immunofluorescence staining and real-time reverse transcription polymerase chain reaction. The results showed that the composite scaffold had high porosity (81.98 ± 3.75%), proper pore size (micropores: <10 µm; macropore: 495 ± 54 µm) and mechanical property (compressive strength: 0.81 ± 0.04 MPa; elastic modulus: 23.14 ± 0.75 MPa). The pearl/PLGA scaffolds exhibited better biocompatibility and osteoconductivity compared with the tricalcium phosphate/PLGA scaffold. All these results indicate that the pearl/PLGA scaffolds fulfill the basic requirements of bone tissue engineering scaffold.
---
paper_title: Low-temperature deposition manufacturing: A novel and promising rapid prototyping technology for the fabrication of tissue-engineered scaffold

paper_content:

Abstract Developed in recent years, low-temperature deposition manufacturing (LDM) represents one of the most promising rapid prototyping technologies. It is not only based on rapid deposition manufacturing process but also combined with phase separation process. Besides the controlled macropore size, tissue-engineered scaffold fabricated by LDM has inter-connected micropores in the deposited lines. More importantly, it is a green manufacturing process that involves non-heating liquefying of materials. It has been employed to fabricate tissue-engineered scaffolds for bone, cartilage, blood vessel and nerve tissue regenerations. It is a promising technology in the fabrication of tissue-engineered scaffold similar to ideal scaffold and the design of complex organs. In the current paper, this novel LDM technology is introduced, and its control parameters, biomedical applications and challenges are included and discussed as well.
---
paper_title: Multinozzle Low-Temperature Deposition System for Construction of Gradient Tissue Engineering Scaffolds

paper_content:

Tissue engineering is a technology that enables us to construct complicated hominine organs composed of many different types of cells. One of the key points to achieve this goal is to control the material composition and porous structure of the scaffold accurately. A disposable syringe based volume-driven injecting (VDI) nozzle was proposed and designed to extrude both natural derived and synthetic polymers. A multinozzle low-temperature deposition and manufacturing (M-LDM) system is proposed to fabricate scaffolds with heterogeneous materials and gradient hierarchical porous structures. PLGA, collagen, gelatin, chitosan can be extruded without leaking to form hierarchical porous scaffolds for primary study. Composite scaffolds with two kinds of materials were fabricated via two different nozzles to get both hydrophilic and mechanical properties. The results from scanning electron microscopy (SEM) demonstrated that the natural-derived biomaterials were strongly absorbed onto the synthetic biomaterials to form a stable network. Several gradient PLGA/TCP scaffolds were also fabricated to supply several samples. © 2008 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2009
---
paper_title: A Novel Osteochondral Scaffold Fabricated via Multi-nozzle Low-temperature Deposition Manufacturing

paper_content:

A functional-region/separate-interface/single-cell-type of tissue engineering pathway was evaluated to regenerate osteochondral defects that are deep in the marrow cavity. A gradient osteochondral scaffold fabricated via a rapid prototyping technology, called multi-nozzle low-temperature deposition manufacturing, was composed of three parts with different materials and pore-structures, respectively, for bone, cartilage and a separate interface between them. The separate interface was composed of micro-pores, that were less than 5 urn and with low porosity, to reduce or to avoid the destruction of the micro-environment in vivo by preventing blood and cells and reducing the amount of oxygen and nutrients moving from the marrow cavity to the articulate marrow. The preliminary results after 6 weeks of implantation into 4 mm diameter osteochondral defects in the knee joints of rabbits showed that the defects with the scaffold/cells composition had bone-like or cartilage-like tissue filling the defects with smo...
---
paper_title: Dynamic Analysis of a Bi-stable Buckled Structure for Vibration Energy Harvester

paper_content:

Vibration energy harvesting offers a viable alternative to batteries for powering sensors in remote locations. In the past decade, the energy harvesting community has turned to nonlinear structures as an effective means for creating high-performance devices. In particular, researchers have used buckled structures to improve vibration scavenging power production at low frequencies (<100 Hz) and to broaden device operational bandwidths. To achieve these ends, accurate structural models are needed. These models are critical for carrying out a systematic and quantitative device design process. Specifically, the models enable the user to optimize device geometries, arrive at meaningful estimates of power production, and estimate device lifetimes, etc. This work focuses on the dynamic behavior of a bi-stable switching energy harvester made from a buckled beam structure, coupled to two cantilever beams with tip masses via a torsional rod. Results from experimental testing of the energy harvesting structure under different forced vibration conditions are compared with a nonlinear model created of the structure. For the model, linear equations of motion for free vibration of each component have been derived using Hamilton’s principle, and shape functions for each individual component are determined by applying boundary conditions for the linear vibration. Nonlinear dynamic behavior effects are integrated through consideration of large deformation of the main beam. The effects of different parameters on the vibrational system, including the geometry of the structure, buckling load and natural frequency of the cantilever arms, have been investigated. These parameters can play an important role in the optimization process of energy harvesters. Finally, parametric results obtained from the presented method are compared with the experimental data in different aspects.
---
paper_title: Feedstock material property – process relationships in fused deposition of ceramics (FDC)

paper_content:

Fused deposition of ceramics (FDC) is a solid freeform fabrication technique based on extrusion of highly loaded polymer systems. The process utilizes particle loaded thermoplastic binder feedstock in the form of a filament. The filament acts as both the piston driving the extrusion and also the feedstock being deposited. Filaments can fail during FDC via buckling, when the extrusion pressure needed is higher than the critical buckling load that the filament can support. Compressive elastic modulus determines the load carrying ability of the filament and the viscosity determines the resistance to extrusion (or extrusion pressure). A methodology for characterizing the compressive mechanical properties of FDC filament feedstocks has been developed. It was found that feedstock materials with a ratio (E/ηa) greater than a critical value (3×105 to 5×105 s‐1) do not buckle during FDC while those with a ratio less than this range buckle.
---
paper_title: Fabrication of Piezoelectric Ceramic / Polymer Composite Transducers using Fused Deposition of Ceramics

paper_content:

The Fused Deposition of Ceramics (FDC) technique was used to fabricate ceramic skeletons for development of piezoelectric composite transducers for medical imaging. The green parts were designed in order to have 30 vol% of PZT-5H ceramic in the final composites. Physical characterization of the sintered samples revealed that 96% of the theoretical density was achieved. Optical microscopy showed that defects, such as small roads and bubbles were eliminated due to powder processing improvements. The electromechanical properties of the final composites were found to be similar to properties obtained for conventionally made composites.
---
paper_title: Extrusion-based additive manufacturing of ZrO2 using photoinitiated polymerization

paper_content:

Abstract Thanks to the exceptional combination of mechanical, thermal, chemical and biological properties, engineering ceramics are becoming increasingly important in the nowadays-industrial landscape. Traditionally, ceramic components are produced via near net-shape techniques, involving labor and expensive processing routes that use molds or dies such as injection molding, green machining, firing, sintering and finish machining. Hence, traditional ceramic manufacturing technologies lack the ability to compete in a customized and small series market, as it exists for e.g. aerospace and biomedical applications. The fabrication of miniature and complex parts as well as small features is also a limitation. In this context, Additive Manufacturing provides an important contribution, given the large design freedom and decoupling of production cost and complexity. Especially, nozzle based techniques offer new opportunities thanks to the efficient usage of material and economical advantage in prototyping and single/small series component production. In this work, a novel processing route for the production of AM ceramics components is proposed. It combines the advantages of AM syringe extrusion and UV curing into a single 3D printing technique, along with the potential for multi-material, complex and miniature ceramic component production. Different dispersions of ZrO 2 and commercially available UV resins (containing from 22.5 to 55 vol.% ZrO 2 ) are prepared using two different mixing techniques. The homogeneity, rheology and printability of those dispersions are subsequently investigated, along with firing and sintering trials. A sample density of about 92.1% has been obtained after sintering, proving the potential of the technology in development. A novel methodology for the process assessment is also proposed.
---
paper_title: Multinozzle Low-Temperature Deposition System for Construction of Gradient Tissue Engineering Scaffolds

paper_content:

Tissue engineering is a technology that enables us to construct complicated hominine organs composed of many different types of cells. One of the key points to achieve this goal is to control the material composition and porous structure of the scaffold accurately. A disposable syringe based volume-driven injecting (VDI) nozzle was proposed and designed to extrude both natural derived and synthetic polymers. A multinozzle low-temperature deposition and manufacturing (M-LDM) system is proposed to fabricate scaffolds with heterogeneous materials and gradient hierarchical porous structures. PLGA, collagen, gelatin, chitosan can be extruded without leaking to form hierarchical porous scaffolds for primary study. Composite scaffolds with two kinds of materials were fabricated via two different nozzles to get both hydrophilic and mechanical properties. The results from scanning electron microscopy (SEM) demonstrated that the natural-derived biomaterials were strongly absorbed onto the synthetic biomaterials to form a stable network. Several gradient PLGA/TCP scaffolds were also fabricated to supply several samples. © 2008 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2009
---
paper_title: An accurate mathematical study on the free vibration of stepped thickness circular/annular Mindlin functionally graded plates

paper_content:

Abstract An analytical solution based on a new exact closed form procedure is presented for free vibration analysis of stepped circular and annular FG plates via first order shear deformation plate theory of Mindlin. The material properties change continuously through the thickness of the plate, which can vary according to a power-law distribution of the volume fraction of the constituents, whereas Poisson’s ratio is set to be constant. Based on the domain decomposition technique, five highly coupled governing partial differential equations of motion for freely vibrating FG plates were exactly solved by introducing the new potential functions as well as using the method of separation of variables. Several comparison studies were presented by those reported in the literature and the FEM analysis, for various thickness values and combinations of stepped thickness variations of circular/annular FG plates to demonstrate highly stability and accuracy of present exact procedure. The effect of the geometrical and material plate parameters such as step thickness ratios, step locations and the power law index on the natural frequencies of FG plates is investigated.
---
paper_title: Melt electrospinning of poly(ε-caprolactone) scaffolds: Phenomenological observations associated with collection and direct writing

paper_content:

Melt electrospinning and its additive manufacturing analogue, melt electrospinning writing (MEW), are two processes which can produce porous materials for applications where solvent toxicity and accumulation in solution electrospinning are problematic. This study explores the melt electrospinning of poly(e-caprolactone) (PCL) scaffolds, specifically for applications in tissue engineering. The research described here aims to inform researchers interested in melt electrospinning about technical aspects of the process. This includes rapid fiber characterization using glass microscope slides, allowing influential processing parameters on fiber morphology to be assessed, as well as observed fiber collection phenomena on different collector substrates. The distribution and alignment of melt electrospun PCL fibers can be controlled to a certain degree using patterned collectors to create large numbers of scaffolds with shaped macroporous architectures. However, the buildup of residual charge in the collected fibers limits the achievable thickness of the porous template through such scaffolds. One challenge identified for MEW is the ability to control charge buildup so that fibers can be placed accurately in close proximity, and in many centimeter heights. The scale and size of scaffolds produced using MEW, however, indicate that this emerging process will fill a technological niche in biofabrication.
---
paper_title: Toward fast and cost-effective ink-jet printing of solid electrolyte for lithium microbatteries

paper_content:

Abstract Ink-jet printing of ionogel for low-cost microbattery is presented. Such an approach allows to provide liquid-like electrolyte performances for all-solid microdevices. Ink-jet printing process is possible thanks to sol precursor of the ionogel. This full silica based ionogels confining ionic liquid are known to be thermal resistant, serving safety and technologies requiring solder reflow. High ionic conductivity and compatibility with porous composite electrodes allow reaching good electrochemical cycling performance: full Li-ion cell with LiFePO 4 and Li 4 Ti 5 O 12 porous composite electrodes shows a surface capacity of 300 μAh cm −2 for more than 100 cycles. Such surface capacities are very competitive as compared to those obtained for microdevices based on expensive PVD processes.
---
paper_title: Laser melting functionally graded composition of Waspaloy® and Zirconia powders

paper_content:

An approach for fabricating functionally graded specimens of supernickel alloy and ceramic compositions via Selective Laser Melting (SLM) is presented. The focus aimed at using the functionally graded material (FGM) concept to gradually grade powdered compositions of Zirconia within a base material of Waspaloy®. A high power Nd:YAG laser was used to process the material compositions to a high density with gradual but discrete changes between layered compositions. The graded specimens initially consisted of 100% Waspaloy® with subsequent layers containing increased volume compositions of Zirconia (0–10%). Specimens were examined for porosity and microstructure. It was found that specimens contained an average porosity of 0.34% with a gradual change between layers without any major interface defects.
---
paper_title: Additive manufacturing of star poly(ε-caprolactone) wet-spun scaffolds for bone tissue engineering applications

paper_content:

Three-dimensional fibrous scaffolds made of a three-arm star poly(e-caprolactone) were developed by employing a novel computer-aided wet-spinning apparatus to precisely control the deposition patte...
---
paper_title: Metal nanoparticle direct inkjet printing for low-temperature 3D micro metal structure fabrication

paper_content:

Inkjet printing of functional materials is a key technology toward ultra-low-cost, large-area electronics. We demonstrate low-temperature 3D micro metal structure fabrication by direct inkjet printing of metal nanoparticles (NPs) as a versatile, direct 3D metal structuring approach representing an alternative to conventional vacuum deposition and photolithographic methods. Metal NP ink was inkjet-printed to exploit the large melting temperature drop of the nanomaterial and the ease of the NP ink formulation. Parametric studies on the basic conditions for stable 3D inkjet printing of NP ink were carried out. Furthermore, diverse 3D metal microstructures, including micro metal pillar arrays, helices, zigzag and micro bridges were demonstrated and electrical characterization was performed. Since the process requires low temperature, it carries substantial potential for fabrication of electronics on a plastic substrate.
---
paper_title: Electrospinning of Polymeric Nanofibers for Tissue Engineering Applications: A Review

paper_content:

Interest in electrospinning has recently escalated due to the ability to produce materials with nanoscale properties. Electrospun fibers have been investigated as promising tissue engineering scaffolds since they mimic the nanoscale properties of native extracellular matrix. In this review, we examine electrospinning by providing a brief description of the theory behind the process, examining the effect of changing the process parameters on fiber morphology, and discussing the potential applications and impacts of electrospinning on the field of tissue engineering.
---
paper_title: Frontiers of 3D Printing/Additive Manufacturing: from Human Organs to Aircraft Fabrication†

paper_content:

It has been more than three decades since stereolithography began to emerge in various forms of additive manufacturing and 3D printing. Today these technologies are proliferating worldwide in various forms of advanced manufacturing. The largest segment of the 3D printing market today involves various polymer component fabrications, particularly complex structures not attainable by other manufacturing methods. Conventional printer head systems have also been adapted to selectively print various speciated human cells and special molecules in attempts to construct human organs, beginning with skin and various tissue patches. These efforts are discussed along with metal and alloy fabrication of a variety of implant and bone replacement components by creating powder layers, which are selectively melted into complex forms (such as foams and other open-cellular structures) using laser and electron beams directed by CAD software. Efforts to create a “living implant” by bone ingrowth and eventual vascularization within these implants will be discussed briefly. Novel printer heads for direct metal droplet deposition as in other 3D printing systems are briefly described since these concepts will allow for the eventual fabrication of very large and complex products, including automotive and aerospace structures and components.
---
paper_title: Interfacial characterization of SLM parts in multi-material processing: Metallurgical diffusion between 316L stainless steel and C18400 copper alloy

paper_content:

Abstract Multi-material processing in selective laser melting using a novel approach, by the separation of two different materials within a single dispensing coating system was investigated. 316L stainless steel and UNS C18400 Cu alloy multi-material samples were produced using selective laser melting and their interfacial characteristics were analyzed using focused ion beam, scanning electron microscopy, energy dispersive spectroscopy and electron back scattered diffraction techniques. A substantial amount of Fe and Cu element diffusion was observed at the bond interface suggesting good metallurgical bonding. Quantitative evidence of good bonding at the interface was also obtained from the tensile tests where the fracture was initiated at the copper region. Nevertheless, the tensile strength of steel/Cu SLM parts was evaluated to be 310 ± 18 MPa and the variation in microhardness values was found to be gradual along the bonding interface from the steel region (256 ± 7 HV 0.1 ) to the copper region (72 ± 3 HV 0.1 ).
---
paper_title: Markov Decision Process for Image-Guided Additive Manufacturing

paper_content:

Additive manufacturing (AM) is a process to produce three-dimensional parts with complex and free-form geometries layer by layer from computer-aided-design models. However, real-time quality control is the main challenge that hampers the wide adoption of AM. Advancements in sensing systems facilitate AM monitoring and control. Realizing full potentials of sensing data for AM quality control depends to a great extent on effective analytical methods and tools that will handle complicated imaging data, and extract pertinent information about defect conditions and process dynamics. This letter considers the optimal control problem for AM parts whose layerwise defect states can be monitored using advanced sensing systems. Specifically, we formulate the in situ AM control problem as a Markov decision process and utilize the layerwise imaging data to find an optimal control policy. We take into account the stochastic uncertainty in the variations of layerwise defects and aim at mitigating the defects before they reach the nonrecoverable stage. Finally, the model is used to derive an optimal control policy by utilizing the defect-state signals estimated from layerwise images in a metal AM application.
---
paper_title: Inkjet-Printed Flexible Graphene-Based Supercapacitor

paper_content:

Abstract A flexible supercapacitor is being developed for integrating with and powering flexible electronics for military and commercial applications. Graphene oxide dispersed in water was used as an ink for inkjet printing the electrode active material onto metal film on Kapton current collectors. After printing, the graphene oxide was thermally reduced at 200 °C to produce conductive graphene electrodes. These electrodes were heat sealed together with added electrolyte and separator, and the assembled supercapacitor performance was evaluated. The specific capacitance of the graphene is good, and the overall performance of the packaged device serves as a proof of concept. But in the future, thicker graphene electrodes and further package optimization will be required to obtain good device-level performance. A number of issues associated with using Kapton for packaging these devices are identified and discussed.
---
paper_title: Macrostructures with hierarchical porosity produced from alumina–aluminum hydroxide–chitosan wet-spun fibers

paper_content:

Abstract This paper reports on the development of macrostructures with hierarchical porosity produced from Al 2 O 3 –Al(OH) 3 –chitosan wet-spun fibers. Aqueous suspensions (13 vol% of solids, 1.3 vol% of chitosan, 0.1 M acetic acid, pH–4) containing different Al 2 O 3 –Al(OH) 3 ratios were extruded through a 500 μm diameter syringe needle into a 2 M NaOH coagulation bath. After washing and drying, these continuous fibers were controllably chopped into 5 mm long staples and shaped under vacuum into 40×40 mm 2 cylindrical macroelements, using 2 wt% chitosan solution as binder. By varying the Al 2 O 3 –Al(OH) 3 content (100–0, 50–50 and 0–100 vol%) and sintering temperature (1100–1500 °C), structures with different levels of porosity (up to 84%), specific surface area (up to 7 m 2 g −1 ) and mechanical strength (up to 9 MPa in uniaxial compression) were obtained. The ratio between the porosity inside the solid part of the structure and the interfilament space was also affected by these parameters and was adjusted according to the numerous potential applications of this system.
---
paper_title: Fabrication of inkjet printed organic photovoltaics on flexible Ag electrode with additives

paper_content:

Abstract In this paper, we describe organic photovoltaics (OPVs) based on flexible thin film Ag anodes that are fabricated using a controlled deposition of photoactive layer by inkjet printing. The inkjet printed OPV photo-active layer is a P3HT:PCBM blend incorporated with a high boiling point additive, 1,6-hexanedithiol which serves to allow improved morphology. The devices show comparable power conversion efficiency to those fabricated using spin-coating techniques. Optimization of procedures for OPV fabrication without ITO electrodes or spin-coating of the active layer is a vital step towards realizing the potential of OPVs for mass production.
---
paper_title: Fabrication of Functionally Graded Materials Via Inkjet Color Printing

paper_content:

A new method for fabricating functionally graded materials (FGMs) via inkjet color printing is reported in this paper. Al 2 O 3 and ZrO 2 aqueous suspensions were stabilized electrostatically and placed in different color reservoirs in inkjet cartridges. The volume and composition of the suspensions printed in droplets at a small area were controlled by the inkjet cyan-magenta-yellow-black color printing principle. The analysis of energy-dispersive spectrometry shows that with multi-layer printing, the composition profile of the printed FGM is consistent with the designed profile. The new method shows the potential for fabricating FGMs with arbitrarily designed three-dimensional composition profiles.
---
paper_title: Inkjet Printing Resolution Study for Multi-Material Rapid Prototyping

paper_content:

In addition to its application in media printing, inkjet printing is becoming an increasingly attractive option for the distribution and patterning of materials for a wide variety of applications. In this study a commercial inkjet printer was modified to study the resolution of fluid dot placement required to fabricate 3D multi-material patterns layer by layer. A Java-based computer program was developed to convert stereolithography (STL) data layer by layer, control ink cartridges individually and print ink with customized fluid dot placement arrangements. The study found that complement printing between nozzles which are 30µm in diameter and 144µm apart is essential to achieve a sufficiently dense 3D pattern. When printed with 36µm vertical spacing a layer thickness of 1.30µm is achievable, and when printing layer by layer, the thickness increases almost at a linear rate.
---
paper_title: 3D printed microfluidic circuitry via multijet-based additive manufacturing

paper_content:

The miniaturization of integrated fluidic processors affords extensive benefits for chemical and biological fields, yet traditional, monolithic methods of microfabrication present numerous obstacles for the scaling of fluidic operators. Recently, researchers have investigated the use of additive manufacturing or “three-dimensional (3D) printing” technologies – predominantly stereolithography – as a promising alternative for the construction of submillimeter-scale fluidic components. One challenge, however, is that current stereolithography methods lack the ability to simultaneously print sacrificial support materials, which limits the geometric versatility of such approaches. In this work, we investigate the use of multijet modelling (alternatively, polyjet printing) – a layer-by-layer, multi-material inkjetting process – for 3D printing geometrically complex, yet functionally advantageous fluidic components comprised of both static and dynamic physical elements. We examine a fundamental class of 3D printed microfluidic operators, including fluidic capacitors, fluidic diodes, and fluidic transistors. In addition, we evaluate the potential to advance on-chip automation of integrated fluidic systems via geometric modification of component parameters. Theoretical and experimental results for 3D fluidic capacitors demonstrated that transitioning from planar to non-planar diaphragm architectures improved component performance. Flow rectification experiments for 3D printed fluidic diodes revealed a diodicity of 80.6 ± 1.8. Geometry-based gain enhancement for 3D printed fluidic transistors yielded pressure gain of 3.01 ± 0.78. Consistent with additional additive manufacturing methodologies, the use of digitally-transferrable 3D models of fluidic components combined with commercially-available 3D printers could extend the fluidic routing capabilities presented here to researchers in fields beyond the core engineering community.
---
paper_title: Laser and electron-beam powder-bed additive manufacturing of metallic implants: A review on processes, materials and designs

paper_content:

Additive manufacturing (AM), also commonly known as 3D printing, allows the direct fabrication of functional parts with complex shapes from digital models. In this review, the current progress of two AM processes suitable for metallic orthopaedic implant applications, namely selective laser melting (SLM) and electron beam melting (EBM) are presented. Several critical design factors such as the need for data acquisition for patient-specific design, design dependent porosity for osteo-inductive implants, surface topology of the implants and design for reduction of stress-shielding in implants are discussed. Additive manufactured biomaterials such as 316L stainless steel, titanium-6aluminium-4vanadium (Ti6Al4V) and cobalt-chromium (CoCr) are highlighted. Limitations and future potential of such technologies are also explored. © 2015 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 34:369–385, 2016.
---
paper_title: Multi-materials drop-on-demand inkjet technology based on pneumatic diaphragm actuator

paper_content:

Micro-droplet jetting belongs to the field of precision fluid dispensing techniques. Unlike traditional subtraction manufacture process, micro-droplet jetting as an additive fabrication technique with features of non-contact and data-driven represents a new development trend of modern manufacturing process. In this paper, the design, fabrication and performance of a multi-materials drop-on-demand (DOD) inkjet system based on pneumatic diaphragm actuator were described. For capturing the droplet ejection process and measuring the droplet dimension, a self-made in situ imaging system based on time delayed external trigger was set up. The performance of the generator was studied by adjusting the structure and control parameters. Furthermore, the influence of fluid properties on the droplet ejection process was experimentally investigated. Micro-solderballs of 160.5 μm in diameter and UV curing adhesive micro-bumps of 346.94 μm in contact diameter with the substrate were produced. The results demonstrated that the DOD inkjet generator possesses characteristics of robust, easy to operate and maintain, and able to withstand high temperature as well as applicability to a wide variety of materials including polymers, low melting point resin and high melting point metal. The system has a great potential of being used in the fields of IC and MEMS packaging, 3D printing, organic semiconductor fabrication, and biological and chemical analysis.
---
paper_title: Three-dimensional printed millifluidic devices for zebrafish embryo tests

paper_content:

Implementations of Lab-on-a-Chip technologies for in-situ analysis of small model organisms and embryos (both invertebrate and vertebrate) are attracting an increasing interest. A significant hurdle to widespread applications of microfluidic and millifluidic devices for in-situ analysis of small model organisms is the access to expensive clean room facilities and complex microfabrication technologies. Furthermore, these resources require significant investments and engineering know-how. For example, poly(dimethylsiloxane) soft lithography is still largely unattainable to the gross majority of biomedical laboratories willing to pursue development of chip-based platforms. They often turn instead to readily available but inferior classical solutions. We refer to this phenomenon as workshop-to-bench gap of bioengineering science. To tackle the above issues, we examined the capabilities of commercially available Multi-Jet Modelling (MJM) and Stereolithography (SLA) systems for low volume fabrication of optical-grade millifluidic devices designed for culture and biotests performed on millimetre-sized specimens such as zebrafish embryos. The selected 3D printing technologies spanned a range from affordable personal desktop systems to high-end professional printers. The main motivation of our work was to pave the way for off-the-shelf and user-friendly 3D printing methods in order to rapidly and inexpensively build optical-grade millifluidic devices for customized studies on small model organisms. Compared with other rapid prototyping technologies such as soft lithography and infrared laser micromachining in poly(methyl methacrylate), we demonstrate that selected SLA technologies can achieve user-friendly and rapid production of prototypes, superior feature reproduction quality, and comparable levels of optical transparency. A caution need to be, however, exercised as majority of tested SLA and MJM resins were found toxic and caused significant developmental abnormalities in zebrafish embryos. Taken together, our data demonstrate that SLA technologies can be used for rapid and accurate production of devices for biomedical research. However, polymer biotoxicity needs to be carefully evaluated.
---
paper_title: Flexible organic phototransistors based on a combination of printing methods

paper_content:

Abstract Highly photosensitive organic phototransistors (OPTs) are successfully demonstrated on a flexible substrate using all-solution process as well as a combination of printing methods which consist of roll-to-plate reverse offset printing (ROP), inkjet printing and bar coating. Excellent electrical switching characteristics are obtained from heterogeneous interfacial properties of the reverse-offset-printed silver nanoparticle electrode and the inkjet-printed p -channel polymeric semiconductor. In particular, the OPTs exhibit remarkably photosensitivity with a photo-to-dark current ratio exceeding 5 orders. This optoelectronic properties of the combinational printed OPTs are theoretically and experimentally studied, and found the comparable tendency. In addition, excellent mechanical stability is observed with up to 0.5% of strain applied to the OPTs. Hence, by manufactured with a combination of various graphic art printing methods such as roll-to-plate ROP, inkjet printing, and bar coating, these devices are very promising candidates for large-area and low-cost printed and flexible optoelectronics applications.
---
paper_title: Biomimetic wet-stable fibres via wet spinning and diacid-based crosslinking of collagen triple helices

paper_content:

One of the limitations of electrospun collagen as bone-like fibrous structure is the potential collagen triple helix denaturation in the fibre state and the corresponding inadequate wet stability even after crosslinking. Here, we have demonstrated the feasibility of accomplishing wet-stable fibres by wet spinning and diacid-based crosslinking of collagen triple helices, whereby fibre ability to act as bonemimicking mineralisation system has also been explored. Circular dichroism (CD) demonstrated nearly complete triple helix retention in resulting wet-spun fibres, and the corresponding chemically crosslinked fibres successfully preserved their fibrous morphology following 1-week incubation in phosphate buffer solution (PBS). The presented novel diacid-based crosslinking route imparted superior tensile modulus and strength to the resulting fibres indicating that covalent functionalization of distant collagen molecules is unlikely to be accomplished by current state-of-the-art carbodiimide-based crosslinking. To mimic the constituents of natural bone extra cellular matrix (ECM), the crosslinked fibres were coated with carbonated hydroxyapatite (CHA) through biomimetic precipitation, resulting in an attractive biomaterial for guided bone regeneration (GBR), e.g. in bony defects of the maxillofacial region. © 2015 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY license
---
paper_title: Hybrid printing of mechanically and biologically improved constructs for cartilage tissue engineering applications

paper_content:

Bioprinting is an emerging technique used to fabricate viable, 3D tissue constructs through the precise deposition of cells and hydrogels in a layer-by-layer fashion. Despite the ability to mimic the native properties of tissue, printed 3D constructs that are composed of naturally-derived biomaterials still lack structural integrity and adequate mechanical properties for use in vivo, thus limiting their development for use in load-bearing tissue engineering applications, such as cartilage. Fabrication of viable constructs using a novel multi-head deposition system provides the ability to combine synthetic polymers, which have higher mechanical strength than natural materials, with the favorable environment for cell growth provided by traditional naturally-derived hydrogels. However, the complexity and high cost associated with constructing the required robotic system hamper the widespread application of this approach. Moreover, the scaffolds fabricated by these robotic systems often lack flexibility, which further restrict their applications. To address these limitations, advanced fabrication techniques are necessary to generate complex constructs with controlled architectures and adequate mechanical properties. In this study, we describe the construction of a hybrid inkjet printing/electrospinning system that can be used to fabricate viable tissues for cartilage tissue engineering applications. Electrospinning of polycaprolactone fibers was alternated with inkjet printing of rabbit elastic chondrocytes suspended in a fibrin?collagen hydrogel in order to fabricate a five-layer tissue construct of 1?mm thickness. The chondrocytes survived within the printed hybrid construct with more than 80% viability one week after printing. In addition, the cells proliferated and maintained their basic biological properties within the printed layered constructs. Furthermore, the fabricated constructs formed cartilage-like tissues both in vitro and in vivo as evidenced by the deposition of type II collagen and glycosaminoglycans. Moreover, the printed hybrid scaffolds demonstrated enhanced mechanical properties compared to printed alginate or fibrin?collagen gels alone. This study demonstrates the feasibility of constructing a hybrid inkjet printing system using off-the-shelf components to produce cartilage constructs with improved biological and mechanical properties.
---
paper_title: Ink-jet printed porous composite LiFePO4 electrode from aqueous suspension for microbatteries

paper_content:

This work demonstrates ink-jet printed LiFePO4-based composite porous electrodes for microbattery application. As binder and dispersant, we found that aqueous inks with more suitable rheological properties with respect to ink-jet printing are prepared with the low molecular weight poly-acrylic-co-maleic acid copolymer, rather than with the carboxymethyl cellulose standard binder of the lithium-ion technology. The ink-jet printed thin and porous electrode shows very high rate charge/discharge behavior, both in LiPF6/ethylene carbonate-dimethyl carbonate (LP30) and lithium bis(trifluoromethane)sulfonylimide salt (Li-TFSI) in N-methyl-N-propylpyrrolidinium bis(trifluoromethane)suflonylimide ionic liquid (PYR13-TFSI) electrolytes, as well as good cyclability.
---
paper_title: Inkjet printed polymeric electron blocking and surface energy modifying layer for low dark current organic photodetectors

paper_content:

Abstract The reduction of dark current is required to enhance the signal-to-noise ratio and decrease the power consumption in photodetectors. This is typically achieved by introducing additional functional layers to suppress carrier injection, a task that proves to be challenging especially in printed devices. Here we report on the successful reduction of dark current below 100 nA cm −2 (at −1 V bias) in an inkjet printed photodetector by the insertion of an electron blocking layer based on poly[3-(3,5-di-tert-butyl-4-methoxyphenyl)-thiophene], while preserving a high quantum yield. Furthermore, the electron blocking layer strongly increases the surface energy of the hydrophobic photoactive layer, therefore simplifying the printing of transparent top electrodes from water based formulations without the addition of surfactants.
---
paper_title: Process-level modeling and simulation for HP's Multi Jet Fusion 3D printing technology

paper_content:

The 3D printing technology is expected to revolutionize part manufacturing by enabling rapid and inexpensive production at a small scale. HP's Multi Jet Fusion 3D printing technology is developed to provide new levels of part quality in a fast and inexpensive way compared to existing 3D printing technologies. The printed part quality is determined by the interplay of the printing device and materials used for printing. Thus, it is essential to have a proper cyber-physical system model for the printing system for process-level simulation of the HP's Multi Jet Fusion technology. In this paper, we propose an approach for the process-level modeling and simulation of HP's Multi Jet Fusion technology. Our approach can be used to carry out simulation of the 3D printing system, to provide guidance for optimization and development of the printing process and exploration of materials. Preliminary results potentially indicate that the simulation of our proposed model is significantly faster than the finite element method, which is a widely used technique for 3D printing simulation.
---
paper_title: Electrospun cartilage‐derived matrix scaffolds for cartilage tissue engineering

paper_content:

Macroscale scaffolds created from cartilage-derived matrix (CDM) demonstrate chondroinductive or chondro-inductive properties, but many fabrication methods do not allow for control of nanoscale architecture. In this regard, electrospun scaffolds have shown significant promise for cartilage tissue engineering. However, nanofibrous materials generally exhibit a relatively small pore size and require techniques such as multilayering or the inclusion of sacrificial fibers to enhance cellular infiltration. The objectives of this study were (1) to compare multilayer to single-layer electrospun poly(ɛ-caprolactone) (PCL) scaffolds for cartilage tissue engineering, and (2) to determine whether incorporation of CDM into the PCL fibers would enhance chondrogenesis by human adipose-derived stem cells (hASCs). PCL and PCL–CDM scaffolds were prepared by sequential collection of 60 electrospun layers from the surface of a grounded saline bath into a single scaffold, or by continuous electrospinning onto the surface of a grounded saline bath and harvest as a single-layer scaffold. Scaffolds were seeded with hASCs and evaluated over 28 days in culture. The predominant effects on hASCs of incorporation of CDM into scaffolds were to stimulate sulfated glycosaminoglycan synthesis and COL10A1 gene expression. Compared with single-layer scaffolds, multilayer scaffolds enhanced cell infiltration and ACAN gene expression. However, compared with single-layer constructs, multilayer PCL constructs had a much lower elastic modulus, and PCL–CDM constructs had an elastic modulus approximately 1% that of PCL constructs. These data suggest that multilayer electrospun constructs enhance homogeneous cell seeding, and that the inclusion of CDM stimulates chondrogenesis-related bioactivity. © 2014 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 102A: 3998–4008, 2014.
---
paper_title: Selective Laser Melting of Polymer Powder – Part Mechanics as Function of Exposure Speed☆

paper_content:

Abstract The selective laser melting of polymer powders is a well-established technology for additive manufacturing applications, although there is still a deficit in basic process knowledge. Considering the demands of series production, the technique of selective laser melting of polymers is faced with various challenges concerning suitable material systems, process strategies and part properties. Consequently, basic research is necessary to understand and optimize processes in order to enable a shift from prototyping applications to serial production of small-lot sized series. A better understanding of the interaction between the sub-processes of selective laser melting and the resulting part properties is necessary for the derivation of new process strategies for increased part quality. Selective laser melting of polymers is mainly divided in the three phases of powder feeding, tempering and geometry exposure. By the interaction of these sub-processes, the resulting temperature fields determine the part properties through microstructural changes in the pore number and distribution. In addition to absolute temperature values, the time dependency of the thermal fields has an influence on the porosity of the molten parts. Current process strategies aim for a decrease in building time by increasing scan speed and laser power, although the absolute energy input into the material does not change when scan speed and laser power are increased at a constant ratio. In prior investigations, the authors showed a correlation between the heating rate and the shape of the resulting melt pool. Based on this correlation, the interaction between heating rates (on a fixed level of exposure energy) and mechanical part properties (tensile test) is analyzed within the paper. The study also implies additional results for other levels of energy input during geometry exposure, which allow for a cross-check of the results. Furthermore, part positioning in the build chamber as well as part density are taken into account. Based on these basic investigations, new process strategies considering the time dependent material behavior can be derived.
---
paper_title: Additive Manufacturing of Ceramic‐Based Materials

paper_content:

This paper offers a review of present achievements in the field of processing of ceramic-based materials with complex geometry using the main additive manufacturing (AM) technologies. In AM, the geometrical design of a desired ceramic-based component is combined with the materials design. In this way, the fabrication times and the product costs of ceramic-based parts with required properties can be substantially reduced. However, dimensional accuracy and surface finish still remain crucial features in today's AM due to the layer-by-layer formation of the parts. In spite of the fact that significant progress has been made in the development of feedstock materials, the most difficult limitations for AM technologies are the restrictions set by material selection for each AM method and aspects considering the inner architectural design of the manufactured parts. Hence, any future progress in the field of AM should be based on the improvement of the existing technologies or, alternatively, the development of new approaches with an emphasis on parts allowing the near-net formation of ceramic structures, while optimizing the design of new materials and of the part architecture.
---
paper_title: Interfacial characterization of SLM parts in multi-material processing: Intermetallic phase formation between AlSi10Mg and C18400 copper alloy

paper_content:

Abstract Multi-material processing in selective laser melting (SLM) using AlSi10Mg and UNS C18400 copper alloy was carried out. The interfacial characteristics were analyzed with FIB, SEM, XRD, EDS and EBSD techniques. Al 2 Cu intermetallic compound was formed at the Al/Cu bond interface after the SLM process. The tensile strength of Al/Cu SLM parts was evaluated to be 176 ± 31 MPa and flexural strength under a 3 point bending test was evaluated to be around 200 MPa for Cu at root and 500 MPa for Al at root. Further analysis suggested that the formation of intermetallic compounds translated the fracture mechanism at the interface from ductile to brittle cleavage. The microhardness values also varied along the interface with high microhardness at the interface due to the intermetallic compounds.
---
paper_title: Additive manufacturing technologies: state of the art and trends

paper_content:

The rapid prototyping has been developed from the 1980s to produce models and prototypes until the technologies evolution today. Nowadays, these technologies have other names such as 3D printing or additive manufacturing, and so forth, but they all have the same origins from rapid prototyping. The design and manufacturing process stood the same until new requirements such as a better integration on production line, a largest series of manufacturing or the reduce weight of products due to heavy costs of machines and materials. The ability to produce complex geometries allows proposing of design and manufacturing solutions in the industrial field in order to be ever more effective. The additive manufacturing (AM) technology develops rapidly with news solutions and markets which sometimes need to demonstrate their reliability. The community needs to survey some evolutions such as the new exchange format, the faster 3D printing systems, the advanced numerical simulation or the emergence of new use. This review is addressed to persons who wish have a global view on the AM and improve their understanding. We propose to review the different AM technologies and the new trends to get a global overview through the engineering and manufacturing process. This article describes the engineering and manufacturing cycle with the 3D model management and the most recent technologies from the evolution of additive manufacturing. Finally, the use of AM resulted in new trends that are exposed below with the description of some new economic activities.
---
paper_title: Combined micro and macro additive manufacturing of a swirling flow coaxial phacoemulsifier sleeve with internal micro-vanes.

paper_content:

Microstereolithography (microSL) technology can fabricate complex, three-dimensional (3D) microstructures, although microSL has difficulty producing macrostructures with micro-scale features. There are potentially many applications where 3D micro-features can benefit the overall function of the macrostructure. One such application involves a medical device called a coaxial phacoemulsifier where the tip of the phacoemulsifier is inserted into the eye through a relatively small incision and used to break the lens apart while removing the lens pieces and associated fluid from the eye through a small tube. In order to maintain the eye at a constant pressure, the phacoemulsifier also includes an irrigation solution that is injected into the eye during the procedure through a coaxial sleeve. It has been reported, however, that the impinging flow from the irrigation solution on the corneal endothelial cells in the inner eye can damage these cells during the procedure. As a result, a method for reducing the impinging flow velocities and the resulting shear stresses on the endothelial cells during this procedure was explored, including the design and development of a complex, 3D micro-vane within the sleeve. The micro-vane introduces swirl into the irrigation solution, producing a flow with rapidly dissipating flow velocities. Fabrication of the sleeve and fitting could not be accomplished using microSL alone, and thus, a two-part design was accomplished where a sleeve with the micro-vane was fabricated with microSL and a threaded fitting used to attach the sleeve to the phacoemulsifier was fabricated using an Objet Eden 333 rapid prototyping machine. The new combined device was tested within a water container using particle image velocimetry, and the results showed successful swirling flow with an ejection of the irrigation fluid through the micro-vane in three different radial directions corresponding to the three micro-vanes. As expected, the sleeve produced a swirling flow with rapidly dissipating streamwise flow velocities where the maximum measured streamwise flow velocities using the micro-vane were lower than those without the micro-vane by 2 mm from the tip where they remained at approximately 70% of those produced by the conventional sleeve as the flow continued to develop. It is believed that this new device will reduce damage to endothelial cells during cataract surgery and significantly improve patient outcomes from this procedure. This unique application demonstrates the utility of combining microSL with a macro rapid prototyping technology for fabricating a real macro-scale device with functional, 3D micro-scale features that would be difficult and costly to fabricate using alternative manufacturing methods.
---
paper_title: Developing Gradient Metal Alloys through Radial Deposition Additive Manufacturing

paper_content:

Interest in additive manufacturing (AM) has dramatically expanded in the last several years, owing to the paradigm shift that the process provides over conventional manufacturing. Although the vast majority of recent work in AM has focused on three-dimensional printing in polymers, AM techniques for fabricating metal alloys have been available for more than a decade. Here, laser deposition (LD) is used to fabricate multifunctional metal alloys that have a strategically graded composition to alter their mechanical and physical properties. Using the technique in combination with rotational deposition enables fabrication of compositional gradients radially from the center of a sample. A roadmap for developing gradient alloys is presented that uses multi-component phase diagrams as maps for composition selection so as to avoid unwanted phases. Practical applications for the new technology are demonstrated in low-coefficient of thermal expansion radially graded metal inserts for carbon-fiber spacecraft panels.
---
paper_title: An analytical closed-form solution for free vibration of stepped circular/annular Mindlin functionally graded plate

paper_content:

An exact solution based on a unique procedure is presented for free vibration of stepped circular and annular functionally graded (FG) plates via first-order shear deformation plate theory of Mindlin. A power-law distribution of the volume fraction of the components is considered for the Young's Modulus and Poisson's ratio of the studied FG plate. Free vibration of the plate is solved by introducing some new potential functions and the use of separation of variables method. Finally, several comparisons of the developed model were presented with the FEA analysis, to demonstrate the accuracy of the proposed exact procedure. The effect of the geometrical parameters such as step thickness ratios and step locations on the natural frequencies of FG plates is also investigated.
---
paper_title: Development of nickel‐titanium graded composition components

paper_content:

Purpose – Three layer‐additive manufacturing methods were evaluated to producing nickel‐titanium graded composition material. One potential application is fabrication of attachment clips that join thermal protection systems to launch vehicle structure. Thermal gradients during flight generate excessive bending and shear loads that limit the service lifetime of the Inconel clips currently used. It is envisioned that a graded composition component could be tailored to reduce the stress concentrations.Design/methodology/approach – Deposits with nearly continuous composition grade were built from Ti‐6‐4 and Inconel 718 powder using laser direct metal deposition. Layered deposits were produced by flat wire welding from Ti‐6‐4 and Inconel 718 wire. Ultrasonic consolidation was used to produce layered deposits from pure nickel and commercially pure titanium foils. Microstructure, bond line morphology, chemical composition, and reaction phases were characterized.Findings – All three manufacturing methods require ...
---
paper_title: Laser deposition of compositionally graded titanium–vanadium and titanium–molybdenum alloys

paper_content:

Compositionally graded binary titanium–vanadium and titanium–molybdenum alloys have been deposited using the laser engineered net-shaping (LENS™) process. A compositional gradient, from elemental Ti to Ti–25at.% V or Ti–25at.% Mo, has been achieved within a length of ∼25 mm. The feedstock used for depositing the graded alloy consists of elemental Ti and V (or Mo) powders. Though the microstructural features across the graded alloy correspond to those typically observed in α/β Ti alloys, the scale of the features is refined in a number of cases. Microhardness measurements across the graded samples exhibit an increase in hardness with increasing alloying content up to a composition of ∼12% in case of Ti–xV and up to a composition of ∼10% in case of the Ti–xMo alloys. Further increase in the alloying content resulted in a decrease in hardness for both the Ti–xV as well as the Ti–xMo alloys. A notable feature of these graded deposits is the large prior β grain size resulting from the directionally solidified nature of the microstructure. Thus, grains ∼10 mm in length grows in a direction perpendicular to the substrate. The ability to achieve such substantial changes in composition across rather limited length makes this process a highly attractive candidate for combinatorial materials science studies.
---
paper_title: Direct laser deposition of Ti-6Al-4V from elemental powder blends

paper_content:

Purpose ::: ::: ::: ::: ::: This paper aims to achieve Ti-6Al-4V from Ti, Al and V elemental powder blends using direct laser deposition (DLD) and to understand the effects of laser transverse speed and laser power on the initial fabrication of deposit’s microstructure and Vickers hardness. ::: ::: ::: ::: ::: Design/methodology/approach ::: ::: ::: ::: ::: Two sets of powder blends with different weight percentage ratio for three elemental powder were used during DLD process. Five experiments with different processing parameters were performed to evaluate how microstructure and Vickers hardness change with laser power and laser transverse speed. Energy dispersive X-ray spectroscopy, optical microscopy and Vickers hardness test were used to analyze deposits’ properties. ::: ::: ::: ::: ::: Findings ::: ::: ::: ::: ::: This paper reveals that significant variance of elemental powder’s size and density would cause lack of weight percentage of certain elements in final part and using multiple coaxial powder nozzles design would be a solution. Also, higher laser power or slower laser transverse speed tend to benefit the formation of finer microstructures and increase Vickers hardness. ::: ::: ::: ::: ::: Originality/value ::: ::: ::: ::: ::: This paper demonstrates a new method to fabricate Ti-6Al-4V and gives out a possible weight percentage ratio 87:7:6 for Ti:Al:V at powder blends during DLD process. The relationship between microstructure and Vickers hardness with laser power and laser transverse speed would provide valuable reference for people working on tailoring material properties using elemental powder method.
---
paper_title: Functionally graded Co-Cr-Mo coating on Ti-6Al-4V alloy structures.

paper_content:

Abstract Functionally graded, hard and wear-resistant Co–Cr–Mo alloy was coated on Ti–6Al–4V alloy with a metallurgically sound interface using Laser Engineering Net Shaping (LENS™). The addition of the Co–Cr–Mo alloy onto the surface of Ti–6Al–4V alloy significantly increased the surface hardness without any intermetallic phases in the transition region. A 100% Co–Cr–Mo transition from Ti–6Al–4V was difficult to produce due to cracking. However, using optimized LENS™ processing parameters, crack-free coatings containing up to 86% Co–Cr–Mo were deposited on Ti–6Al–4V alloy with excellent reproducibility. Human osteoblast cells were cultured to test in vitro biocompatibility of the coatings. Based on in vitro biocompatibility, increasing the Co–Cr–Mo concentration in the coating reduced the live cell numbers after 14 days of culture on the coating compared with base Ti–6Al–4V alloy. However, coated samples always showed better bone cell proliferation than 100% Co–Cr–Mo alloy. Producing near net shape components with graded compositions using LENS™ could potentially be a viable route for manufacturing unitized structures for metal-on-metal prosthetic devices to minimize the wear-induced osteolysis and aseptic loosening that are significant problems in current implant design.
---
paper_title: Friction Stir Additive Manufacturing: Route to High Structural Performance

paper_content:

Aerospace and automotive industries provide the next big opportunities for additive manufacturing. Currently, the additive industry is confronted with four major challenges that have been identified in this article. These challenges need to be addressed for the additive technologies to march into new frontiers and create additional markets. Specific potential success in the transportation sectors is dependent on the ability to manufacture complicated structures with high performance. Most of the techniques used for metal-based additive manufacturing are fusion based because of their ability to fulfill the computer-aided design to component vision. Although these techniques aid in fabrication of complex shapes, achieving high structural performance is a key problem due to the liquid–solid phase transformation. In this article, friction stir additive manufacturing (FSAM) is shown as a potential solid-state process for attaining high-performance lightweight alloys for simpler geometrical applications. To illustrate FSAM as a high-performance route, manufactured builds of Mg-4Y-3Nd and AA5083 are shown as examples. In the Mg-based alloy, an average hardness of 120 HV was achieved in the built structure and was significantly higher than that of the base material (97 HV). Similarly for the Al-based alloy, compared with the base hardness of 88 HV, the average built hardness was 104 HV. A potential application of FSAM is illustrated by taking an example of a simple stiffener assembly.
---
paper_title: A study of subgrain formation in Al 3003 H-18 foils undergoing ultrasonic additive manufacturing using a dislocation density based crystal plasticity finite element framework

paper_content:

A novel dislocation density based crystal plasticity finite element model (DDCP-FEM) framework has been extended to predict subgrain formation during ultrasonic additive manufacturing of Al 3003 H-18 tempered foils. The present study identifies various microstructural transitions such as recrystallization and dislocation density evolutions that occur during the processing of these foils as a function of input processing parameters such as normal force, ultrasonic oscillation amplitude, and initial microstructure. Furthermore, changes in average grain sizes in the Al 3003 H-18 foils have been calculated before and after processing from both microstructures and the simulation study. The simulation predictions were in good agreement with experimental results. This provides evidence that DDCP-FEM can be used as a tool for optimizing input processing parameters so that minimal grain fragmentation occurs during processing leading to better mechanical properties for 3 dimensional components made using ultrasonic...
---
paper_title: Characterization of the laminated object manufacturing (LOM) process

paper_content:

Laminated object manufacturing (LOM) is a rapid prototyping process where a part is built sequentially from layers of paper. Studied in the present paper are the precision and accuracy of the LOM process and the dimensional stability of LOM parts. The process was found to exhibit both constant and random sources of error in the part dimensions. The dimensional error was the largest normal to the plane of the paper, exacerbated by the moisture absorption and subsequent swelling. The key process parameters were identified and optimized for sufficient bonding and cutting accuracy.
---
paper_title: Ultrasonic Additive Manufacturing – A Hybrid Production Process for Novel Functional Products

paper_content:

Ultrasonic Additive Manufacturing (UAM), or Ultrasonic Consolidation as it is also referred, is a hybrid form of manufacture, primarily for metal components. The unique nature of the process permits extremely novel functionality to be realised such as multi-material structures with embedded componentry. UAM has been subject to research and investigation at Loughborough University since 2001. This paper introduces UAM then details a number of key findings in a number of areas that have been of particular focus at Loughborough in recent years. These include; the influence of pre-process material texture on interlaminar bonding, secure fibre positioning through laser machined channels, and freeform electrical circuitry integration.
---
paper_title: Dissimilar metal friction welding of austenitic–ferritic stainless steels

paper_content:

Abstract Continuous drive friction welding studies on austenitic–ferritic stainless steel combination has been attempted in this investigation. Parameter optimization, microstructure–mechanical property correlation and fracture behaviour is a major contribution of the study. Sound welds are obtained at certain weld parameter combinations only. The mechanical properties of dissimilar metal welds are comparable to those of ferritic stainless steel welds. Evaluation of the joints for resistance to pitting corrosion revealed that the dissimilar welds exhibit lower resistance to pitting corrosion compared to the ferritic and austenitic stainless steel welds. Interface on the austenitic stainless steel side exhibited higher residual stress possibly due to its higher flow stress and higher coefficient of thermal expansion.
---
paper_title: Statistical Characterization of Ultrasonic Additive Manufacturing Ti/Al Composites

paper_content:

Ultrasonic additive manufacturing (UAM) is an emerging solid-state fabrication process that can be used for layered creation of solid metal structures. In UAM, ultrasonic energy is used to induce plastic deformation and nascent surface formation at the interface between layers of metal foil, thus creating bonding between the layers. UAM is an inherently stochastic process with a number of unknown facets that can affect the bond quality. In order to take advantage of the unique benefits of UAM, it is necessary to understand the relationship between manufacturing parameters (machine settings) and bond quality by quantifying the mechanical strength of UAM builds. This research identifies the optimum combination of processing parameters, including normal force, oscillation amplitude, weld speed, and number of bilayers for the manufacture of commercially pure, grade 1 titanium+1100-O aluminum composites. A multifactorial experiment was designed to study the effect of the above factors on the outcome measures ultimate shear strength and ultimate transverse tensile strength. Generalized linear models were used to study the statistical significance of each factor. For a given factor, the operating levels were selected to cover the full range of machine capabilities. Transverse shear and transverse tensile experiments were conducted to quantify the bond strength of the builds. Optimum levels of each parameter were established based on statistical contrast trend analyses. The results from these analyses indicate that high mechanical strength can be achieved with a process window bounded by a 1500 N normal force, 30 μm oscillation amplitude, about 42 mm/s weld speed, and two bilayers. The effects of each process parameter on bond strength are discussed and explained.
---
paper_title: Characterization of interfacial microstructures in 3003 aluminum alloy blocks fabricated by ultrasonic additive manufacturing

paper_content:

Ultrasonic additive manufacturing (UAM) is a solid-state processing technique that uses ultrasonic vibrations to bond metal tapes into near net-shaped components. The benefits of UAM include the production of complex geometries and the incorporation of smart materials to produce functional composites and join dissimilar metals. The majority of the current research focuses on processing parameter optimization to eliminate macroscopic void formation at the interface. The present study utilizes ion-channeling contrast imaging from a focused ion beam, electron backscattered diffraction and transmission electron microscopy to examine microstructural changes induced during the UAM process. The results indicate that there is a bonding mechanism due to localized plastic deformation of asperities that undergo recrystallization and grain growth across the interface. Evidence for localized solidification microstructures, generated due to frictional sliding between the sonotrode horn and the tape material, is also presented.
---
paper_title: Rapid laminated tooling

paper_content:

Abstract Rapid laminating methods predates rapid prototyping by several years, indeed the first work on laminated tooling by Professor Nakagawa was initially published in the late 1980s. Since then, Nakagawa’s team has been joined by a number of other research groups, with interest being boosted by the advent of rapid prototyping. This paper presents some of the finding of a 3 years study undertaken to investigate the use of laminated steel tooling for a range of automotive and aerospace production processes. The results of the programme are illustrated using production tooling for injection moulding of automotive components. The benefits of laminated tooling are shown, not just in terms of reduced cost and lead-times but perhaps more importantly, through reduced cycle times and improved part quality by the use of conformal cooling.
---
paper_title: NiTi–Al interface strength in ultrasonic additive manufacturing composites

paper_content:

Abstract Ultrasonic Additive Manufacturing (UAM) is a new rapid prototyping process for creating metal-matrix composites at or near room temperature. The low process temperatures enable composite materials that have tailored CTEs through utilizing recovery stresses generated by highly prestrained Shape Memory Alloy (SMA) fibers embedded within the matrix. The strength of the fiber–matrix interface, which is the limiting factor in UAM composites, has not been characterized. In this study, we characterize the shear strength of the fiber–matrix interface and study the bonding between the fiber and matrix in composites fabricated with prestrained NiTi embedded in an Al 3003-H18 matrix. In heating the composite, stresses develop due to the blocked behavior of NiTi and the difference in CTE of the matrix and fiber. Differential scanning calorimetry is used to observe composite failure temperatures; an average interface shear strength of 7.28 MPa is determined using constitutive models of the NiTi element and Al matrix. The constitutive models describe the thermally-induced strain of the composite, showing an effective CTE of zero at 135 °C. The models show that by increasing the embedded fiber length, interface failure temperatures can be increased so that zero CTE behaviors can be utilized without irreversibly changing the NiTi prestrain. Results from energy dispersive X-ray spectroscopy indicate that the bonding between the fiber and interface is mechanical in nature with no evidence to support chemical or metallurgical bonding.
---
paper_title: Characterization of Process for Embedding SiC Fibers in Al 6061 O Matrix Through Ultrasonic Consolidation

paper_content:

In this paper, continuous SiC fibers were embedded in an Al 6061 O matrix through ultrasonic consolidation at room temperature. The optimum embedding parameters were determined through peel tests and metallographic analysis. The influence of the embedded fiber volume fraction and base metal thickness on the interface bond strength was studied, and the fiber/matrix bond strength was tested through fiber pullout test. The results showed that embedding ≥0.8% volume fraction of SiC fiber in a 6061 O matrix could significantly increase and even its interfacial strength, but there is a threshold for embedded fiber volume fraction at specific parameters, over which the plastic flow and friction may be insufficient to have a strong bond at foil/foil interfaces between fibers. The study also showed that base metal thickness did not have significant influence on the interfacial strength with an exception of samples with a base metal thickness of 500 μm. Based on the results, it was proposed that microfriction at consolidation interfaces plays an important role for joint formation, and localized plastic flow around fibers is important to have fibers fully and safely embedded.
---
paper_title: Interfacial shear strength estimates of NiTi–Al matrix composites fabricated via ultrasonic additive manufacturing

paper_content:

The purpose of this study is to understand and improve the interfacial shear strength of metal matrix composites fabricated via ultrasonic additive manufacturing (UAM). NiTi–Al composites can exhibit dramatically lower thermal expansion compared to aluminum, yet blocking stresses developed during thermal cycling have been found to degrade and eventually cause interface failure in these composites. In this study, the strength of the interface was characterized with pullout tests. Since adhered aluminum was consistently observed on all pullout samples, the matrix yielded prior to the interface breaking. Measured pullout loads were utilized as an input to a finite element model for stress and shear lag analysis. The aluminum matrix experiences a calculated peak shear stress near 230 MPa, which is above its ultimate shear strength of 150–200 MPa thus corroborating the experimentally-observed matrix failure. The influence of various fiber surface treatments and consolidation characteristics on bond mechanisms was studied with scanning electron microscopy, energy dispersive X-ray spectroscopy, optical microscopy, and focused ion beam microscopy.
---
paper_title: 3D bioprinting of tissues and organs

paper_content:

Additive manufacturing, otherwise known as three-dimensional (3D) printing, is driving major innovations in many areas, such as engineering, manufacturing, art, education and medicine. Recent advances have enabled 3D printing of biocompatible materials, cells and supporting components into complex 3D functional living tissues. 3D bioprinting is being applied to regenerative medicine to address the need for tissues and organs suitable for transplantation. Compared with non-biological printing, 3D bioprinting involves additional complexities, such as the choice of materials, cell types, growth and differentiation factors, and technical challenges related to the sensitivities of living cells and the construction of tissues. Addressing these complexities requires the integration of technologies from the fields of engineering, biomaterials science, cell biology, physics and medicine. 3D bioprinting has already been used for the generation and transplantation of several tissues, including multilayered skin, bone, vascular grafts, tracheal splints, heart tissue and cartilaginous structures. Other applications include developing high-throughput 3D-bioprinted tissue models for research, drug discovery and toxicology.
---
paper_title: Biofabrication of multi-material anatomically shaped tissue constructs

paper_content:

Additive manufacturing in the field of regenerative medicine aims to fabricate organized tissue-equivalents. However, the control over shape and composition of biofabricated constructs is still a challenge and needs to be improved. The current research aims to improve shape, by converging a number of biocompatible, quality construction materials into a single three-dimensional fiber deposition process. To demonstrate this, several models of complex anatomically shaped constructs were fabricated by combined deposition of poly(vinyl alcohol), poly(e-caprolactone), gelatin methacrylamide/gellan gum and alginate hydrogel. Sacrificial components were co-deposited as temporary support for overhang geometries and were removed after fabrication by immersion in aqueous solutions. Embedding of chondrocytes in the gelatin methacrylamide/gellan component demonstrated that the fabrication and the sacrificing procedure did not affect cell viability. Further, it was shown that anatomically shaped constructs can be successfully fabricated, yielding advanced porous thermoplastic polymer scaffolds, layered porous hydrogel constructs, as well as reinforced cell-laden hydrogel structures. In conclusion, anatomically shaped tissue constructs of clinically relevant sizes can be generated when employing multiple building and sacrificial materials in a single biofabrication session. The current techniques offer improved control over both internal and external construct architecture underscoring its potential to generate customized implants for human tissue regeneration. (Some figures may appear in colour only in the online journal)
---
paper_title: Creating Perfused Functional Vascular Channels Using 3D Bio-Printing Technology

paper_content:

We developed a methodology using 3D bio-printing technology to create a functional in vitro vascular channel with perfused open lumen using only cells and biological matrices. The fabricated vasculature has a tight, confluent endothelium lining, presenting barrier function for both plasma protein and highmolecular weight dextran molecule. The fluidic vascular channel is capable of supporting the viability of tissue up to 5 mm in distance at 5 million cells/mL density under the physiological flow condition. In static-cultured vascular channels, active angiogenic sprouting from the vessel surface was observed whereas physiological flow strongly suppressed this process. Gene expression analysis was reported in this study to show the potential of this vessel model in vascular biology research. The methods have great potential in vascularized tissue fabrication using 3D bio-printing technology as the vascular channel is simultaneously created while cells and matrix are printed around the channel in desired 3D patterns. It can also serve as a unique experimental tool for investigating fundamental mechanisms of vascular remodeling with extracellular matrix and maturation process under 3D flow condition.
---
paper_title: Bioprinting technology and its applications

paper_content:

Bioprinting technology has emerged as a powerful tool for building tissue and organ structures in the field of tissue engineering. This technology allows precise placement of cells, biomaterials and biomolecules in spatially predefined locations within confined three-dimensional (3D) structures. Various bioprinting technologies have been developed and utilized for applications in life sciences, ranging from studying cellular mechanisms to constructing tissues and organs for implantation, including heart valve, myocardial tissue, trachea and blood vessels. In this article, we introduce the general principles and limitations of the most widely used bioprinting technologies, including jetting- and extrusion-based systems. Application-based research focused on tissue regeneration is presented, as well as the current challenges that hamper clinical utility of bioprinting technology.
---
paper_title: Low temperature additive manufacturing of three dimensional scaffolds for bone-tissue engineering applications: Processing related challenges and property assessment

paper_content:

Abstract In the last two decades, additive manufacturing (AM) has made significant progress towards the fabrication of biomaterials and tissue engineering constructs. One direction of research is focused on the development of mechanically stable implants with patient-specific size/shape and another direction has been to fabricate tissue-engineered scaffolds with designed porous architecture to facilitate vascularization. Among AM techniques, three dimensional powder printing (3DPP) is suitable for fabrication of bone related prosthetic devices, while three dimensional plotting (3DPL) is based on extrusion of biopolymers to create artificial tissues. In the present review, we aim to develop a better understanding of the science and engineering aspects of these low temperature AM techniques (3DPP and 3DPL) in the context of the bone-tissue engineering applications. While recognizing multiple property requirements of a 3D scaffold, the central theme is to discuss the critical roles played by the binder and powder properties together with the interplay among processing parameters in the context of the physics of binder-material interaction for the fabrication of implants with predefined architecture having structural complexity. An effort also has been exerted to discuss the existing challenges to translate the design concepts and material/binder formulations to develop implantable scaffolds with a more emphasis on bioceramics and biopolymers. Summarizing, this review highlights the need to adopt intelligent processing approaches and targeted application-specific biocompatibility characterization, while fabricating mechanically stable and biologically functionalized 3D tissue equivalents.
---
paper_title: Bioprinting technology and its applications

paper_content:

Bioprinting technology has emerged as a powerful tool for building tissue and organ structures in the field of tissue engineering. This technology allows precise placement of cells, biomaterials and biomolecules in spatially predefined locations within confined three-dimensional (3D) structures. Various bioprinting technologies have been developed and utilized for applications in life sciences, ranging from studying cellular mechanisms to constructing tissues and organs for implantation, including heart valve, myocardial tissue, trachea and blood vessels. In this article, we introduce the general principles and limitations of the most widely used bioprinting technologies, including jetting- and extrusion-based systems. Application-based research focused on tissue regeneration is presented, as well as the current challenges that hamper clinical utility of bioprinting technology.
---
paper_title: Surface and Shape Deposition Manufacturing for the Fabrication of a Curved Surface Gripper

paper_content:

Biological systems such as the gecko are complex, involving a wide variety of materials and length scales. Bio-inspired robotic systems seek to emulate this complexity, leading to manufacturing challenges. A new design for a membrane-based gripper for curved surfaces requires the inclusion of microscale features, macroscale structural elements, electrically patterned thin films, and both soft and hard materials. Surface and shape deposition manufacturing (S2DM) is introduced as a process that can create parts with multiple materials, as well as integrated thin films and microtextures. It combines SDM techniques, laser cutting and patterning, and a new texturing technique, surface microsculpting. The process allows for precise registration of sequential additive/subtractive manufacturing steps. S2DM is demonstrated with the manufacture of a gripper that picks up common objects using a gecko-inspired adhesive. The process can be extended to other integrated robotic components that benefit from the integration of textures, thin films, and multiple materials.
---
paper_title: Biomimetic Robotic Mechanisms via Shape Deposition Manufacturing

paper_content:

At small scales, the fabrication of robots from off-the-shelf structural materials, sensors and actuators becomes increasingly difficult. New manufacturing methods such as Shape Deposition Manufacturing offer an alternative approach in which sensors and actuators are embedded directly into three-dimensional structures without fasteners or connectors. In addition, structures can be fabricated with spatially varying material properties such as specific stiffness and damping. These capabilities allow us to consider biomimetic designs that draw their inspiration from crustaceans and insects. Recent research on insect physiology has revealed the importance of passive compliance and damping in achieving robustness and simplifying control. We describe the design and fabrication of small robot limbs with locally varying stiffness and embedded sensors and actuators. We discuss the process planning issues associated with creating such structures and present results obtained via Shape Deposition Manufacturing.
---
paper_title: Shape Deposition Manufacturing of a Soft, Atraumatic, and Deployable Surgical Grasper

paper_content:

Laparoscopic pancreaticoduodenectomy (also known as the Whipple procedure) is a highly-complex minimallyinvasive surgical (MIS) procedure used to remove cancer from the head of the pancreas. While mortality rates of the MIS approach are comparable with those of open procedures, morbidity rates remain high due to the delicate nature of the pancreatic tissue, proximity of high-pressure vasculature, and the number of complex anastomoses required [1]. The sharp, rigid nature of the tools and forceps used to manipulate these structures, coupled with lack of haptic feedback, can result in leakage or hemorrhage, which can obfuscate the surgeon’s view and force the surgeon to convert to an open procedure. We present a deployable atraumatic grasper with onboard pressure sensing, allowing a surgeon to grasp and manipulate soft tissue during laparoscopic pancreatic surgery. Created using shape deposition manufacturing, with pressure sensors embedded in each finger enabling real-time grip force monitoring, the device offers the potential to reduce the risk of intraoperative hemorrhage by providing the surgeon with a soft, compliant interface between delicate pancreatic tissue structures and metal laparoscopic forceps that are currently used to manipulate and retract these structures on an ad-hoc basis. Initial manipulation tasks in a simulated environment have demonstrated that the device can be deployed though a 15mm trocar and develop a stable grasp on a pancreas analog using Intuitive Surgical’s daVinci robotic end-effectors.
---
paper_title: Multimechanism oral dosage forms fabricated by three dimensional printing.

paper_content:

Four types of complex oral drug delivery devices have been fabricated using the three dimensional printing process. Immediate-extended release tablets were fabricated which were composed of two drug-containing sections of different pH-based release mechanisms. Pulsed release of chlorpheniramine maleate occurred after a lag time of 10 min followed by extended release of the compound over a period of 7 h. Breakaway tablets were fabricated composed of three sections. An interior fast-eroding section separating two drug-releasing sub-units eroded in 30-45 min in simulated gastric fluid. Enteric dual pulsatory tablets were constructed of one continuous enteric excipient phase into which diclofenac sodium was printed into two separated areas. These samples showed two pulses of release during in vitro USP dissolution at 1 and 8 h with a lag time between pulses of about 4 h. Dual pulsatory tablets were also fabricated. These samples were composed of two erosion based excipient sections of opposite pH based solubility. One section eroded immediately during the acid dissolution stage releasing diclofenac during the first 30 min, and the second section began eroding 5 h later during the high pH stage.
---
paper_title: Inkjet printing for pharmaceutics – A review of research and manufacturing

paper_content:

Global regulatory, manufacturing and consumer trends are driving a need for change in current pharmaceutical sector business models, with a specific focus on the inherently expensive research costs, high-risk capital-intensive scale-up and the traditional centralised batch manufacturing paradigm. New technologies, such as inkjet printing, are being explored to radically transform pharmaceutical production processing and the end-to-end supply chain. This review provides a brief summary of inkjet printing technologies and their current applications in manufacturing before examining the business context driving the exploration of inkjet printing in the pharmaceutical sector. We then examine the trends reported in the literature for pharmaceutical printing, followed by the scientific considerations and challenges facing the adoption of this technology. We demonstrate that research activities are highly diverse, targeting a broad range of pharmaceutical types and printing systems. To mitigate this complexity we show that by categorising findings in terms of targeted business models and Active Pharmaceutical Ingredient (API) chemistry we have a more coherent approach to comparing research findings and can drive efficient translation of a chosen drug to inkjet manufacturing.
---
paper_title: Three-Dimensional Printing of Carbamazepine Sustained-Release Scaffold.

paper_content:

Carbamazepine is the first-line anti-epileptic drug for focal seizures and generalized tonic-clonic seizures. Although sustained-release formulations exist, an initial burst of drug release is still present and this results in side effects. Zero-order release formulations reduce fluctuations in serum drug concentrations, thereby reducing side effects. Three-dimensional printing can potentially fabricate zero-order release formulations with complex geometries. 3D printed scaffolds with varying hole positions (side and top/bottom), number of holes (4, 8, and 12), and hole diameters (1, 1.5, and 2 mm) were designed. Dissolution tests and high performance liquid chromatography analysis were conducted. Good correlations in the linear release profiles of all carbamazepine-containing scaffolds with side holes (R(2) of at least 0.91) were observed. Increasing the hole diameters (1, 1.5, and 2 mm) resulted in increased rate of drug release in the scaffolds with 4 holes (0.0048, 0.0065, and 0.0074 mg/min) and 12 holes (0.0021, 0.0050, and 0.0092 mg/min), and the initial amount of carbamazepine released in the scaffolds with 8 holes (0.4348, 0.7246, and 1.0246 mg) and 12 holes (0.1995, 0.8598, and 1.4366 mg). The ultimate goal of this research is to improve the compliance of patients through a dosage form that provides a zero-order drug release profile for anti-epileptic drugs, so as to achieve therapeutic doses and minimize side effects.
---
paper_title: 3D printing of tablets containing multiple drugs with defined release profiles.

paper_content:

We have employed three-dimensional (3D) extrusion-based printing as a medicine manufacturing technique for the production of multi-active tablets with well-defined and separate controlled release profiles for three different drugs. This 'polypill' made by a 3D additive manufacture technique demonstrates that complex medication regimes can be combined in a single tablet and that it is viable to formulate and 'dial up' this single tablet for the particular needs of an individual. The tablets used to illustrate this concept incorporate an osmotic pump with the drug captopril and sustained release compartments with the drugs nifedipine and glipizide. This combination of medicines could potentially be used to treat diabetics suffering from hypertension. The room temperature extrusion process used to print the formulations used excipients commonly employed in the pharmaceutical industry. Attenuated Total Reflectance Fourier Transform Infrared Spectroscopy (ATR-FTIR) and X-ray powder diffraction (XRPD) were used to assess drug-excipient interaction. The printed formulations were evaluated for drug release using USP dissolution testing. We found that the captopril portion showed the intended zero order drug release of an osmotic pump and noted that the nifedipine and glipizide portions showed either first order release or Korsmeyer-Peppas release kinetics dependent upon the active/excipient ratio used.
---
paper_title: Analytical analysis of buckling and post-buckling of fluid conveying multi-walled carbon nanotubes

paper_content:

Abstract In this work, buckling and post-buckling analysis of fluid conveying multi-walled carbon nanotubes are investigated analytically. The nonlinear governing equations of motion and boundary conditions are derived based on Eringen nonlocal elasticity theory. The nanotube is modeled based on Euler–Bernoulli and Timoshenko beam theories. The Von Karman strain–displacement equation is used to model the structural nonlinearities. Furthermore, the Van der Waals interaction between adjacent layers is taken into account. An analytical approach is employed to determine the critical (buckling) fluid flow velocities and post-buckling deflection. The effects of the small-scale parameter, Van der Waals force, ends support, shear deformation and aspect ratio are carefully examined on the critical fluid velocities and post-buckling behavior.
---
paper_title: Adaptation of pharmaceutical excipients to FDM 3D printing for the fabrication of patient-tailored immediate release tablets.

paper_content:

This work aims to employ fused deposition modelling 3D printing to fabricate immediate release pharmaceutical tablets with several model drugs. It investigates the addition of non-melting filler to methacrylic matrix to facilitate FDM 3D printing and explore the impact of (i) the nature of filler, (ii) compatibility with the gears of the 3D printer and iii) polymer: filler ratio on the 3D printing process. Amongst the investigated fillers in this work, directly compressible lactose, spray-dried lactose and microcrystalline cellulose showed a level of degradation at 135°C whilst talc and TCP allowed consistent flow of the filament and a successful 3D printing of the tablet. A specially developed universal filament based on pharmaceutically approved methacrylic polymer (Eudragit EPO) and thermally stable filler, TCP (tribasic calcium phosphate) was optimised. Four model drugs with different physicochemical properties were included into ready-to-use mechanically stable tablets with immediate release properties. Following the two thermal processes (hot melt extrusion (HME) and fused deposition modelling (FDM) 3D printing), drug contents were 94.22%, 88.53%, 96.51% and 93.04% for 5-ASA, captopril, theophylline and prednisolone respectively. XRPD indicated that a fraction of 5-ASA, theophylline and prednisolone remained crystalline whilst captopril was in amorphous form. By combining the advantages of thermally stable pharmaceutically approved polymers and fillers, this unique approach provides a low cost production method for on demand manufacturing of individualised dosage forms.
---
paper_title: Dropwise additive manufacturing of pharmaceutical products for solvent-based dosage forms.

paper_content:

In recent years, the US Food and Drug Administration has encouraged pharmaceutical companies to develop more innovative and efficient manufacturing methods with improved online monitoring and control. Mini-manufacturing of medicine is one such method enabling the creation of individualized product forms for each patient. This work presents dropwise additive manufacturing of pharmaceutical products (DAMPP), an automated, controlled mini-manufacturing method that deposits active pharmaceutical ingredients (APIs) directly onto edible substrates using drop-on-demand (DoD) inkjet printing technology. The use of DoD technology allows for precise control over the material properties, drug solid state form, drop size, and drop dynamics and can be beneficial in the creation of high-potency drug forms, combination drugs with multiple APIs or individualized medicine products tailored to a specific patient. In this work, DAMPP was used to create dosage forms from solvent-based formulations consisting of API, polymer, and solvent carrier. The forms were then analyzed to determine the reproducibility of creating an on-target dosage form, the morphology of the API of the final form and the dissolution behavior of the drug over time. DAMPP is found to be a viable alternative to traditional mass-manufacturing methods for solvent-based oral dosage forms.
---
paper_title: Control of the non-linear static deflection experienced by a fluid-carrying double-walled carbon nanotube using an external distributed load

paper_content:

In this work, an external distributed line load is used to control the postbuckled static deflection of a double-walled carbon nanotube within which a continuous non-viscous fluid flows at a constant velocity. The non-linear equation of motion and boundary conditions are derived using the non-local Timoshenko beam model for the double-walled carbon nanotube, incorporating Von Karman-type geometric non-linear behavior and taking account of the Van der Waals interaction between adjacent layers. First, in the absence of the control force, an analytical approach is used to determine the buckling fluid flow velocities and steady state non-linear static deflection at velocities greater than the buckling velocity for both the cases of a simple-simple and a simple-clamped end support. Then, the control force participates as an indeterminate parameter in the equations. The control force is obtained by resolving equations in which the postbuckled configuration is considered to be an exponential function of time wit...
---
paper_title: 3-dimensional (3D) fabricated polymer based drug delivery systems.

paper_content:

Drug delivery from 3-dimensional (3D) structures is a rapidly growing area of research. It is essential to achieve structures wherein drug stability is ensured, the drug loading capacity is appropriate and the desired controlled release profile can be attained. Attention must also be paid to the development of appropriate fabrication machinery that allows 3D drug delivery systems (DDS) to be produced in a simple, reliable and reproducible manner. The range of fabrication methods currently being used to form 3D DDSs include electrospinning (solution and melt), wet-spinning and printing (3-dimensional). The use of these techniques enables production of DDSs from the macro-scale down to the nano-scale. This article reviews progress in these fabrication techniques to form DDSs that possess desirable drug delivery kinetics for a wide range of applications.
---
paper_title: Hot-melt extruded filaments based on pharmaceutical grade polymers for 3D printing by fused deposition modeling.

paper_content:

Fused deposition modeling (FDM) is a 3D printing technique based on the deposition of successive layers of thermoplastic materials following their softening/melting. Such a technique holds huge potential for the manufacturing of pharmaceutical products and is currently under extensive investigation. Challenges in this field are mainly related to the paucity of adequate filaments composed of pharmaceutical grade materials, which are needed for feeding the FDM equipment. Accordingly, a number of polymers of common use in pharmaceutical formulation were evaluated as starting materials for fabrication via hot melt extrusion of filaments suitable for FDM processes. By using a twin-screw extruder, filaments based on insoluble (ethylcellulose, Eudragit(®) RL), promptly soluble (polyethylene oxide, Kollicoat(®) IR), enteric soluble (Eudragit(®) L, hydroxypropyl methylcellulose acetate succinate) and swellable/erodible (hydrophilic cellulose derivatives, polyvinyl alcohol, Soluplus(®)) polymers were successfully produced, and the possibility of employing them for printing 600μm thick disks was demonstrated. The behavior of disks as barriers when in contact with aqueous fluids was shown consistent with the functional application of the relevant polymeric components. The produced filaments were thus considered potentially suitable for printing capsules and coating layers for immediate or modified release, and, when loaded with active ingredients, any type of dosage forms.
---
paper_title: A flexible-dose dispenser for immediate and extended release 3D printed tablets

paper_content:

The advances in personalised medicine increased the demand for a fast, accurate and reliable production method of tablets that can be digitally controlled by healthcare staff. A flexible dose tablet system is presented in this study that proved to be suitable for immediate and extended release tablets with a realistic drug loading and an easy-to-swallow tablet design. The method bridges the affordable and digitally controlled Fused Deposition Modelling (FDM) 3D printing with a standard pharmaceutical manufacturing process, Hot Melt Extrusion (HME). The reported method was compatible with three methacrylic polymers (Eudragit RL, RS and E) as well as a cellulose-based one (hydroxypropyl cellulose, HPC SSL). The use of a HME based pharmaceutical filament preserved the linear relationship between the mass and printed volume and was utilized to digitally control the dose via an input from computer software with dose accuracy in the range of 91-95%. Higher resolution printing quality doubled the printing time, but showed a little effect on in vitro release pattern of theophylline and weight accuracy. Physical characterization studies indicated that the majority of the model drug (theophylline) in the 3D printed tablet exists in a crystal form. Owing to the small size, ease of use and the highly adjustable nature of FDM 3D printers, the method holds promise for future individualised treatment.
---
paper_title: 3D printing in pharmaceutics: A new tool for designing customized drug delivery systems.

paper_content:

Three-dimensional printing includes a wide variety of manufacturing techniques, which are all based on digitally-controlled depositing of materials (layer-by-layer) to create freeform geometries. Therefore, three-dimensional printing processes are commonly associated with freeform fabrication techniques. For years, these methods were extensively used in the field of biomanufacturing (especially for bone and tissue engineering) to produce sophisticated and tailor-made scaffolds from patient scans. This paper aims to review the processes that can be used in pharmaceutics, including the parameters to be controlled. In practice, it not straightforward for a formulator to be aware of the various technical advances made in this field, which is gaining more and more interest. Thus, a particular aim of this review is to give an overview on the pragmatic tools, which can be used for designing customized drug delivery systems using 3D printing.
---
paper_title: Integration of additive manufacturing and inkjet printed electronics: a potential route to parts with embedded multifunctionality

paper_content:

Additive manufacturing, an umbrella term for a number of different manufacturing techniques, has attracted increasing interest recently for a number of reasons, such as the facile customisation of parts, reduced time to manufacture from initial design, and possibilities in distributed manufacturing and structural electronics. Inkjet printing is an additive manufacturing technique that is readily integrated with other manufacturing processes, eminently scalable and used extensively in printed electronics. It therefore presents itself as a good candidate for integration with other additive manufacturing techniques to enable the creation of parts with embedded electronics in a timely and cost effective manner. This review introduces some of the fundamental principles of inkjet printing; such as droplet generation, deposition, phase change and post-deposition processing. Particular focus is given to materials most relevant to incorporating structural electronics and how post-processing of these materials has been able to maintain compatibility with temperature sensitive substrates. Specific obstacles likely to be encountered in such an integration and potential strategies to address them will also be discussed.
---
paper_title: Metal-based Inkjet Inks for Printed Electronics

paper_content:

A review on applications of metal-based inkjet inks for printed electronics with a particular focus on inks con- taining metal nanoparticles, complexes and metallo-organic compounds. The review describes the preparation of such inks and obtaining conductive patterns by using various sintering methods: thermal, photonic, microwave, plasma, electri- cal, and chemically triggered. Various applications of metal-based inkjet inks (metallization of solar cell, RFID antennas, OLEDs, thin film transistors, electroluminescence devices) are reviewed.
---
paper_title: 3D Printing for the Rapid Prototyping of Structural Electronics

paper_content:

In new product development, time to market (TTM) is critical for the success and profitability of next generation products. When these products include sophisticated electronics encased in 3D packaging with complex geometries and intricate detail, TTM can be compromised - resulting in lost opportunity. The use of advanced 3D printing technology enhanced with component placement and electrical interconnect deposition can provide electronic prototypes that now can be rapidly fabricated in comparable time frames as traditional 2D bread-boarded prototypes; however, these 3D prototypes include the advantage of being embedded within more appropriate shapes in order to authentically prototype products earlier in the development cycle. The fabrication freedom offered by 3D printing techniques, such as stereolithography and fused deposition modeling have recently been explored in the context of 3D electronics integration - referred to as 3D structural electronics or 3D printed electronics. Enhanced 3D printing may eventually be employed to manufacture end-use parts and thus offer unit-level customization with local manufacturing; however, until the materials and dimensional accuracies improve (an eventuality), 3D printing technologies can be employed to reduce development times by providing advanced geometrically appropriate electronic prototypes. This paper describes the development process used to design a novelty six-sided gaming die. The die includes a microprocessor and accelerometer, which together detect motion and upon halting, identify the top surface through gravity and illuminate light-emitting diodes for a striking effect. By applying 3D printing of structural electronics to expedite prototyping, the development cycle was reduced from weeks to hours.
---
paper_title: Hybrid additive manufacturing of 3D electronic systems

paper_content:

A novel hybrid additive manufacturing (AM) technology combining digital light projection (DLP) stereolithography (SL) with 3D micro-dispensing alongside conventional surface mount packaging is presented in this work. This technology overcomes the inherent limitations of individual AM processes and integrates seamlessly with conventional packaging processes to enable the deposition of multiple materials. This facilitates the creation of bespoke end-use products with complex 3D geometry and multi-layer embedded electronic systems. Through a combination of four-point probe measurement and non-contact focus variation microscopy, it was identified that there was no obvious adverse effect of DLP SL embedding process on the electrical conductivity of printed conductors. The resistivity maintained to be less than 4 × 10−4 Ω centerdot cm before and after DLP SL embedding when cured at 100 °C for 1 h. The mechanical strength of SL specimens with thick polymerized layers was also identified through tensile testing. It was found that the polymerization thickness should be minimised (less than 2 mm) to maximise the bonding strength. As a demonstrator a polymer pyramid with embedded triple-layer 555 LED blinking circuitry was successfully fabricated to prove the technical viability.
---
paper_title: Inkjet printing for flexible electronics: Materials, processes and equipments

paper_content:

Inkjet printing, known as digital writing technique, can directly deposit functional materials to form pattern onto substrate. This paper provides an overview of inkjet printing technologies for flexible electronics. Firstly, we highlight materials challenges in implementing flexible devices into practical application, especially for inkjet printing process. Then the micro/nano-patterning technologies of inkjet printing are discussed, including conventional inkjet printing techniques and electrohydrodynamic printing techniques. Thirdly, the related equipments on inkjet printing are shown. Finally, challenges for its future development are also discussed. The main purpose of the work is to condense the basic knowledge and highlight the challenges associated with the burgeoning and exciting field of inkjet printing for flexible electronics.
---
paper_title: Aerosol based direct-write micro-additive fabrication method for sub-mm 3D metal-dielectric structures

paper_content:

The fabrication of 3D metal-dielectric structures at sub-mm length scale is highly important in order to realize low-loss passives and GHz wavelength antennas with applications in wearable and Internet-of-Things (IoT) devices. The inherent 2D nature of lithographic processes severely limits the available manufacturing routes to fabricate 3D structures. Further, the lithographic processes are subtractive and require the use of environmentally harmful chemicals. In this letter, we demonstrate an additive manufacturing method to fabricate 3D metal-dielectric structures at sub-mm length scale. A UV curable dielectric is dispensed from an Aerosol Jet system at 10–100 µm length scale and instantaneously cured to build complex 3D shapes at a length scale <1 mm. A metal nanoparticle ink is then dispensed over the 3D dielectric using a combination of jetting action and tilted dispense head, also using the Aerosol Jet technique and at a length scale 10–100 µm, followed by the nanoparticle sintering. Simulation studies are carried out to demonstrate the feasibility of using such structures as mm-wave antennas. The manufacturing method described in this letter opens up the possibility of fabricating an entirely new class of custom-shaped 3D structures at a sub-mm length scale with potential applications in 3D antennas and passives.
---
paper_title: Synthesis of Ag/RGO composite as effective conductive ink filler for flexible inkjet printing electronics

paper_content:

Abstract The inkjet printing technology has been an attractive alternative to conventional photolithography to fabricate flexible electronics, owing to its advantages including easy control and low cost. However, development of an appropriate ink possessing low cost, high conductivity and good dispersivity for inkjet printing is still a big challenge. In this work, the well dispersed Ag/RGO composite was obtained by anchoring silver nanoparticles (Ag NPs) on the surface of reduced graphene oxide (RGO) sheet, which served as one of promising conductive ink fillers for printable flexible electronics. The synthesized Ag/RGO composite improved the conductivity of ink with Ag NPs and promoted the dispersivity of RGO to avoid nozzle jam, which offered a proper solution to the two critical issues of conductive ink: conductivity and dispersivity. The Ag/RGO composite was attested to be a suitable material for fabricating printable flexible electronics at 100 °C and developing graphene-based functional electronic devices.
---
paper_title: Aerosol Jet Printing of Nano Particle Based Electrical Chip Interconnects

paper_content:

Abstract Mask less fabricated 3D interconnects may have a big potential in future microelectronic applications by enhancing freedom of device design or power- and footprint saving capabilities along with performance improvements. Within this paper research activities are reported about evaluation of Aerosol Jet Printing (AJP) for feasibility of fabricating non-planar nano particle based electrical chip interconnects on a 3D-integrated System in a Package (SiP) including MEMS that is capable to wake up integrated electronics from power down mode using piezoelectric MEMS components. 3D-stacked multi-chip modules with a footprint of 9 mm x 10 mm are functional connected by AJP after single chips are mounted to printed circuit board (PCB) using underfiller adhesives. AJP, morphology of printed paths, and electrical resistances are investigated. Several challenging factors like printed line width, printed layer thickness, focus limiting standoff height of printhead, thermo-mechanical properties of printed interconnects along with SiP layout were identified and discussed during process development.
---
paper_title: Formulation and processing of novel conductive solution inks in continuous inkjet printing of 3-D electric circuits

paper_content:

One of the greatest challenges for the inkjet printing electrical circuits is formulation and processing of conductive inks. In the present investigation, two different formulations of particle-free conductive solutions are introduced that are low in cost, easy to deposit, and possess good electrical properties. A novel aqueous solution consisting of silver nitrate and additives is initially described. This solution demonstrates excellent adherence to glass and polymers and has an electrical resistivity only 2.9 times that of bulk silver after curing. A metallo-organic decomposition (MOD) ink is subsequently introduced. This ink produces a close-packed silver crystal microstructure after low-temperature thermolysis and subsequent high-temperature annealing. The electrical conductance of the final consolidated trace produced with the MOD ink is very close to bulk silver. In addition, the traces produced with the MOD material exhibit excellent wear and fracture resistance. When utilized in a specialized continuous inkjet (CIJ) printing technology system, both particle-free solution inks are able to produce conductive traces in three dimensions. The importance of three-dimensional (3-D) printing of conductive traces is finally discussed in relation to the broad range of applications in the freeform fabrication industry.
---
paper_title: Inkjet printed System-in-Package design and manufacturing

paper_content:

Additive manufacturing technology using inkjet offers several improvements to electronics manufacturing compared to current non-additive masking technologies. Manufacturing processes can be made more efficient, straightforward and flexible compared to subtractive masking processes, several time-consuming and expensive steps can be omitted. Due to the additive process, material loss is minimal, because material is never removed as with etching processes. The amounts of used material and waste are smaller, which is advantageous in both productivity and environmental means. Furthermore, the additive inkjet manufacturing process is flexible allowing fast prototyping, easy design changes and personalization of products. Additive inkjet processing offers new possibilities to electronics integration, by enabling direct writing on various surfaces, and component interconnection without a specific substrate. The design and manufacturing of inkjet printed modules differs notably from the traditional way to manufacture electronics. In this study a multilayer inkjet interconnection process to integrate functional systems was demonstrated, and the issues regarding the design and manufacturing were considered.
---
paper_title: Printed optics: 3D printing of embedded optical elements for interactive devices

paper_content:

We present an approach to 3D printing custom optical elements for interactive devices labelled Printed Optics. Printed Optics enable sensing, display, and illumination elements to be directly embedded in the casing or mechanical structure of an interactive device. Using these elements, unique display surfaces, novel illumination techniques, custom optical sensors, and embedded optoelectronic components can be digitally fabricated for rapid, high fidelity, highly customized interactive devices. Printed Optics is part of our long term vision for interactive devices that are 3D printed in their entirety. In this paper we explore the possibilities for this vision afforded by fabrication of custom optical elements using today's 3D printing technology.
---
paper_title: Three dimensional printing of high dielectric capacitor using projection based stereolithography method

paper_content:

Abstract We report that efficient high dielectric polymer/ceramic composite materials can be optically printed into three-dimensional (3D) capacitor by the projection based stereolithography (SLA) method. Surface decoration of Ag on Pb(Zr,Ti)O 3 (PZT@Ag) particles were used as filler to enhance the dielectric permittivity. Polymer nanocomposites were fabricated by incorporating PZT@Ag particles into the photocurable polymer solutions, followed by exposure to the digitally controlled optical masks to generate 3D structures. The dielectric permittivity of Flex/PZT@Ag composite reaches as high as 120 at 100 Hz with 18 vol% filler, which is about 30 times higher than that of pure Flex. Furthermore, the dielectric loss is as low as 0.028 at 100 Hz. The results are in good agreement with the effective medium theory (EMT) model. The calculated specific capacitance of our 3D printed capacitor is about 63 F g −1 at the current density of 0.5 A g −1 . Cyclic voltammetry (CV) curves indicate 3D printed capacitors possess low resistance and ideal capacitive properties. These results not only provide a tool to fabricate capacitor with complex shapes but lay the groundwork for creating highly efficient polymer-based composites via 3D printing method for electronic applications.
---
paper_title: Printing conformal electronics on 3D structures with Aerosol Jet technology

paper_content:

Fabrication of 3D mechanical structures is sometimes achieved by layer-wise printing of inks and resins in conjunction with treatments such as photonic curing and laser sintering. The non-treated material is typically dissolved leaving the final 3D part. Such techniques are generally limited to a single material which makes it difficult to integrate high resolution, conformal electronics over part surfaces. In this paper, we demonstrate a novel, non-contact technique for printing conformal circuits called Aerosol Jet printing. This technique creates a collimated jet of aerosol droplets that extend 2–5 mm from the nozzle to the target. The deposited features can be as small as 10 microns or as large as a centimeter wide. A variety of materials can be printed such as metal nanoparticle inks, polymers, adhesives, ceramics, and bio-active matter. The print head direction and XYZ positioning is controlled by CAD/CAM software which allows conformal printing onto 3D substrates having a high level of surface topography. For example, metallic traces can be printed into 3D shapes such as trenches and via holes, as well as onto sidewalls and convex and concave surfaces. We discuss the fabrication of a conformal phase array antenna, embedded circuitry and sensors, and electronic packaging.
---
paper_title: Integrating stereolithography and direct print technologies for 3D structural electronics fabrication

paper_content:

Purpose – The purpose of this paper is to present a hybrid manufacturing system that integrates stereolithography (SL) and direct print (DP) technologies to fabricate three‐dimensional (3D) structures with embedded electronic circuits. A detailed process was developed that enables fabrication of monolithic 3D packages with electronics without removal from the hybrid SL/DP machine during the process. Successful devices are demonstrated consisting of simple 555 timer circuits designed and fabricated in 2D (single layer of routing) and 3D (multiple layers of routing and component placement).Design/methodology/approach – A hybrid SL/DP system was designed and developed using a 3D Systems SL 250/50 machine and an nScrypt micro‐dispensing pump integrated within the SL machine through orthogonally‐aligned linear translation stages. A corresponding manufacturing process was also developed using this system to fabricate 2D and 3D monolithic structures with embedded electronic circuits. The process involved part de...
---
paper_title: Aerosol jet printed top grids for organic optoelectronic devices

paper_content:

Abstract Aerosol jet deposited metallic grids are very promising as transparent electrodes for large area organic solar cells and organic light emitting diodes. However, the homogeneity and the printing speed remain a challenge. We report homogeneous and rapidly printed metallic lines based on a complex-based metal–organic silver ink using a processing temperature of 140 °C. We show that inhomogeneities, which are present in printed structures at increased printing speeds and mainly caused by drying effects, can be improved by adding high boiling point solvents. We demonstrate solution processed highly conductive and transparent hybrid electrodes on inverted organic solar cells comprising digitally printed top silver grids.
---
paper_title: A facile method for integrating direct-write devices into three-dimensional printed parts

paper_content:

Integrating direct-write (DW) devices into three-dimensional (3D) printed parts is key to continuing innovation in engineering applications such as smart material systems and structural health monitoring. However, this integration is challenging because: (1) most 3D printing techniques leave rough or porous surfaces if they are untreated; (2) the thermal sintering process required for most conductive inks could degrade the polymeric materials of 3D printed parts; and (3) the extensive pause needed for the DW process during layer-by-layer fabrication may cause weaker interlayer bonding and create structural weak points. These challenges are rather common during the insertion of conductive patterns inside 3D printed structures. As an avoidance tactic, we developed a simple ‘print-stick-peel’ method to transfer the DW device from the polytetrafluoroethylene or perfluoroalkoxy alkanes film onto any layer of a 3D printed object. This transfer can be achieved using the self-adhesion of 3D printing materials or applying additional adhesive. We demonstrated this method by transferring Aerosol Jet® printed strain sensors into parts fabricated by PolyJet™ printing. This report provides an investigation and discussion on the sensitivity, reliability, and influence embedding the sensor has on mechanical properties.
---
paper_title: Application of 3D Printing for Smart Objects with Embedded Electronic Sensors and Systems

paper_content:

Applications of a 3D printing process are presented. This process integrates liquid-state printed components and interconnects with IC chips in all three dimensions, various orientations, and multiple printing layers to deliver personalized system-level functionalities. As an example application, a form-fitting glove is demonstrated with embedded programmable heater, temperature sensor, and the associated control electronics for thermotherapeutic treatment.
---
paper_title: 3-dimensional circuit device fabrication process using stereolithography and direct writing

paper_content:

Additive manufacturing (AM) technology is a method to fabricate a 3-dimensional structure by stacking thin layers. Among AM technologies, it is known that stereolithography (SL) technology can fabricate a structure having high dimensional accuracy. Recently, this technology is being applied for real manufacturing. Meanwhile, direct writing (DW) technology has been used to apply a lowviscosity liquid material on a substrate. In this regards, in this research, we applied the DW technology to deposit a conductive material on the surface of a three-dimensional structure. Moreover, a three-dimensional circuit device (3DCD) which is different from conventional two-dimensional PCBs can be fabricated by the hybrid process of SL and DW technologies. An insulated structure of circuit board having high precision was fabricated using stereolithography. Furthermore, a circuit is fabricated on the several layers using DW. And the 3DCD sample that detects a light was fabricated, successfully.
---
paper_title: Hybrid additive manufacturing of 3D electronic systems

paper_content:

A novel hybrid additive manufacturing (AM) technology combining digital light projection (DLP) stereolithography (SL) with 3D micro-dispensing alongside conventional surface mount packaging is presented in this work. This technology overcomes the inherent limitations of individual AM processes and integrates seamlessly with conventional packaging processes to enable the deposition of multiple materials. This facilitates the creation of bespoke end-use products with complex 3D geometry and multi-layer embedded electronic systems. Through a combination of four-point probe measurement and non-contact focus variation microscopy, it was identified that there was no obvious adverse effect of DLP SL embedding process on the electrical conductivity of printed conductors. The resistivity maintained to be less than 4 × 10−4 Ω centerdot cm before and after DLP SL embedding when cured at 100 °C for 1 h. The mechanical strength of SL specimens with thick polymerized layers was also identified through tensile testing. It was found that the polymerization thickness should be minimised (less than 2 mm) to maximise the bonding strength. As a demonstrator a polymer pyramid with embedded triple-layer 555 LED blinking circuitry was successfully fabricated to prove the technical viability.
---
paper_title: Integration of Direct-Write (DW) and Ultrasonic Consolidation (UC) Technologies to Create Advanced Structures with Embedded Electrical Circuitry.

paper_content:

In many instances conductive traces are needed in small, compact and enclosed areas. However, with traditional manufacturing techniques, embedded electrical traces or antenna arrays have not been a possibility. By integrating Direct Write and Ultrasonic Consolidation technologies, electronic circuitry, antennas and other devices can be manufactured directly into a solid metal structure and subsequently completely enclosed. This can achieve a significant reduction in mass and volume of a complex electronic system without compromising performance.
---
paper_title: Approaches for Additive Manufacturing of 3D Electronic Applications

paper_content:

Abstract Additive manufacturing processes typically used for mechanical parts can be combined with enhanced technologies for electronics production to enable a highly flexible manufacturing of personalized 3D electronic devices. To illustrate different approaches for implementing electrical and electronic functionality, conductive paths and electronic components were embedded in a powder bed printed substrate using an enhanced 3D printer. In addition, a modified Aerosol Jet printing process and assembly technologies adapted from the technology of Molded Interconnect Devices were applied to print circuit patterns and to electrically interconnect components on the surface of the 3D substrates.
---
paper_title: Printing Three-Dimensional Electrical Traces in Additive Manufactured Parts for Injection of Low Melting Temperature Metals

paper_content:

While techniques exist for the rapid prototyping of mechanical and electrical components separately, this paper describes a method where commercial additive manufacturing (AM) techniques can be used to concurrently construct the mechanical structure and electronic circuits in a robotic or mechatronic system. The technique involves printing hollow channels within 3D printed parts that are then filled with a low melting point liquid metal alloy that solidifies to form electrical traces. This method is compatible with most conventional fused deposition modeling and stereolithography (SLA) machines and requires no modification to an existing printer, though the technique could easily be incorporated into multimaterial machines. Three primary considerations are explored using a commercial fused deposition manufacturing (FDM) process as a testbed: material and manufacturing process parameters, simplified injection fluid mechanics, and automatic part generation using standard printed circuit board (PCB) software tools. Example parts demonstrate the ability to embed circuits into a 3D printed structure and populate the surface with discrete electronic components. [DOI: 10.1115/1.4029435]
---
paper_title: Exploring the mechanical strength of additively manufactured metal structures with embedded electrical materials

paper_content:

Abstract Ultrasonic Additive Manufacturing (UAM) enables the integration of a wide variety of components into solid metal matrices due to the process induced high degree of metal matrix plastic flow at low bulk temperatures. Exploitation of this phenomenon allows the fabrication of previously unobtainable novel engineered metal matrix components. The feasibility of directly embedding electrical materials within UAM metal matrices was investigated in this work. Three different dielectric materials were embedded into UAM fabricated aluminium metal-matrices with, research derived, optimal processing parameters. The effect of the dielectric material hardness on the final metal matrix mechanical strength after UAM processing was investigated systematically via mechanical peel testing and microscopy. It was found that when the Knoop hardness of the dielectric film was increased from 12.1 HK/0.01 kg to 27.3 HK/0.01 kg, the mechanical peel testing and linear weld density of the bond interface were enhanced by 15% and 16%, respectively, at UAM parameters of 1600 N weld force, 25 µm sonotrode amplitude, and 20 mm/s welding speed. This work uniquely identified that the mechanical strength of dielectric containing UAM metal matrices improved with increasing dielectric material hardness. It was therefore concluded that any UAM metal matrix mechanical strength degradation due to dielectric embedding could be restricted by employing a dielectric material with a suitable hardness (larger than 20 HK/0.01 kg). This result is of great interest and a vital step for realising electronic containing multifunctional smart metal composites for future industrial applications.
---
paper_title: Exploring the mechanical performance and material structures of integrated electrical circuits within solid state metal additive manufacturing matrices

paper_content:

Ultrasonic Additive Manufacturing (UAM) enables the integration of a wide variety of components into solid metal matrices due to a high degree of metal plastic flow at low matrix bulk temperatures. ...
---
paper_title: Ink-jet printed nanoparticle microelectromechanical systems

paper_content:

Reports a method to additively build three-dimensional (3-D) microelectromechanical systems (MEMS) and electrical circuitry by ink-jet printing nanoparticle metal colloids. Fabricating metallic structures from nanoparticles avoids the extreme processing conditions required for standard lithographic fabrication and molten-metal-droplet deposition. Nanoparticles typically measure 1 to 100 nm in diameter and can be sintered at plastic-compatible temperatures as low as 300/spl deg/C to form material nearly indistinguishable from the bulk material. Multiple ink-jet print heads mounted to a computer-controlled 3-axis gantry deposit the 10% by weight metal colloid ink layer-by-layer onto a heated substrate to make two-dimensional (2-D) and 3-D structures. We report a high-Q resonant inductive coil, linear and rotary electrostatic-drive motors, and in-plane and vertical electrothermal actuators. The devices, printed in minutes with a 100 /spl mu/m feature size, were made out of silver and gold material with high conductivity,and feature as many as 400 layers, insulators, 10:1 vertical aspect ratios, and etch-released mechanical structure. These results suggest a route to a desktop or large-area MEMS fabrication system characterized by many layers, low cost, and data-driven fabrication for rapid turn-around time, and represent the first use of ink-jet printing to build active MEMS.
---
paper_title: Exploring the mechanical strength of additively manufactured metal structures with embedded electrical materials

paper_content:

Abstract Ultrasonic Additive Manufacturing (UAM) enables the integration of a wide variety of components into solid metal matrices due to the process induced high degree of metal matrix plastic flow at low bulk temperatures. Exploitation of this phenomenon allows the fabrication of previously unobtainable novel engineered metal matrix components. The feasibility of directly embedding electrical materials within UAM metal matrices was investigated in this work. Three different dielectric materials were embedded into UAM fabricated aluminium metal-matrices with, research derived, optimal processing parameters. The effect of the dielectric material hardness on the final metal matrix mechanical strength after UAM processing was investigated systematically via mechanical peel testing and microscopy. It was found that when the Knoop hardness of the dielectric film was increased from 12.1 HK/0.01 kg to 27.3 HK/0.01 kg, the mechanical peel testing and linear weld density of the bond interface were enhanced by 15% and 16%, respectively, at UAM parameters of 1600 N weld force, 25 µm sonotrode amplitude, and 20 mm/s welding speed. This work uniquely identified that the mechanical strength of dielectric containing UAM metal matrices improved with increasing dielectric material hardness. It was therefore concluded that any UAM metal matrix mechanical strength degradation due to dielectric embedding could be restricted by employing a dielectric material with a suitable hardness (larger than 20 HK/0.01 kg). This result is of great interest and a vital step for realising electronic containing multifunctional smart metal composites for future industrial applications.
---
paper_title: A MEMS-scale vibration energy harvester based on coupled component structure and bi-stable states

paper_content:

Due to the rapid growth in demand for power for sensing devices located in remote locations, scientists' attention has been drawn to vibration energy harvesting as an alternative to batteries. As a result of over two decades of micro-scale vibration energy harvester research, the use of mechanical nonlinearity in the dynamic behavior of the piezoelectric power generating structures had been recognized as one of the promising solutions to the challenges presented by chaotic, low-frequency vibration sources found in common application environments. In this study, the design and performance of a unique MEMS-scale nonlinear vibration energy harvester based on coupled component structures and bi-stable states are investigated. The coupled-components within the device consist of a main buckled beam bonded with piezoelectric layers, a torsional rod, and two cantilever arms with tip masses at their ends. These arms are connected to the main beam through the torsional rod and are designed to help the main beam snap between its buckled stable states when subjected to sufficient vibration loading. The fabrication of the device will be discussed, including use of plasma-enhanced chemical vapor deposition (PECVD) of silicon nitride under an alternating power field to control compressive stress development within the main buckled beam. After completing the fabrication process, the next step would be testing the device under a variety of vibration loading conditions for its potential use as a vibration energy harvester.
---

Title: A Review of Multi-material and Composite Parts Production by Modified Additive Manufacturing Methods

Section 1: Introduction
Description 1: Provide an overview of the unique capabilities of Additive Manufacturing (AM) in producing multi-material parts and composite materials, including examples and significant achievements.

Section 2: Multi-material and composite additive manufacturing methods
Description 2: Describe various modifications of AM techniques combined with other methods to produce multi-material and composite products.

Section 3: Stereolithography methods
Description 3: Discuss the adaptations of Stereolithography (SLA) for multi-material and composite production, including specific processes and applications.

Section 4: Binder jetting methods
Description 4: Explain the binder jetting process for creating multi-material composites, focusing on techniques to achieve the desired material properties and structures.

Section 5: Extrusion-based printing methods
Description 5: Cover the use of extrusion-based AM methods for multi-material components with tailored porosities, including examples in biomedical applications.

Section 6: Material jetting printing methods
Description 6: Explore the principles and applications of material jetting for multi-material production, including innovative combinations with other techniques.

Section 7: Directed energy deposition (DED) methods
Description 7: Review the DED process for multi-material and composite production, focusing on metallic parts and the methods for mixing and depositing different materials.

Section 8: Laminating metallic parts
Description 8: Discuss Laminated Object Manufacturing (LOM) and other lamination methods for creating metallic parts with layers bonded by various approaches.

Section 9: Bioprinting methods
Description 9: Outline bioprinting techniques that allow for the fabrication of structures with multiple cells and biomaterials, noting specific applications in tissue engineering.

Section 10: Shape deposition methods
Description 10: Describe Shape Deposition Manufacturing (SDM) and its capability to produce multi-material structures by combining additive and subtractive processes.

Section 11: 3D printed drug delivery systems
Description 11: Examine the use of 3D printing for creating drug delivery systems tailored to specific release profiles and patient needs, including various AM techniques.

Section 12: Electronics embedded 3D printed components
Description 12: Cover the integration of electronic components within 3D printed parts, including methods for printing conductive traces and embedding active/passive components.

Section 13: Summary and Conclusions
Description 13: Summarize the reviewed AM processes, their modifications, and their applications in different industries. Discuss the potential and current limitations of AM in multi-material and composite production.