3D Printed Sensors for Biomedical Applications: A Review
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paper_title: An integrated optic ethanol vapor sensor based on a silicon-on-insulator microring resonator coated with a porous ZnO film

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Optical structures fabricated on silicon-on-insulator technology provide a convenient platform for the implementation of highly compact, versatile and low cost devices. In this work, we demonstrate the promise of this technology for integrated low power and low cost optical gas sensing. A room temperature ethanol vapor sensor is demonstrated using a ZnO nanoparticle film as a coating on an SOI micro-ring resonator of 5 µm in radius. The local coating on the ring resonators is prepared from colloidal suspensions of ZnO nanoparticles of around 3 nm diameter. The porous nature of the coating provides a large surface area for gas adsorption. The ZnO refractive index change upon vapor adsorption shifts the microring resonance through evanescent field interaction. Ethanol vapor concentrations down to 100 ppm are detected with this sensing configuration and a detection limit below 25 ppm is estimated.
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paper_title: Wearable Flexible Sensors: A Review

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This paper provides a review on some of the significant research work done on wearable flexible sensors (WFSs). Sensors fabricated with the flexible materials have been attached to a person along with the embedded system to monitor a parameter and transfer the significant data to the monitoring unit for the further analyses. The use of wearable sensors has played a quite important role to monitor the physiological parameters of a person to minimize any malfunctioning happening in the body. This paper categorizes the work according to the materials used for designing the system, the network protocols, and different types of activities that were being monitored. The challenges faced by the current sensing systems and future opportunities for the WFSs regarding its market values are also briefly explained in this paper.
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paper_title: Silicon carbide coated MEMS strain sensor for harsh environment applications

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We present poly-SiC coating and subsequent operation of a Si-based double-ended tuning fork (DETF) resonant strain sensor fabricated in the Bosch commercial foundry process. The coating is applied post release and, hence, has minimal impact on the front end of the microfabrication process. The deposition thickness of nanometer-thin SiC coating was optimized to provide enhanced corrosion resistance to silicon MEMS without compromising the electrical and mechanical performance of the original device. The coated DETF achieves a strain resolution of 0.2 mue in a 10 Hz to 20 kHz bandwidth, which is comparable to the uncoated device. The coated DETF is locally heated with an IR lamp and is shown to operate up to 190 degC in air with a temperature sensitivity of -7.6 Hz/degC. The devices are also dipped in KOH at 80 degC for 5 minutes without etching the structures, confirming the poly-SiC coating provides a sufficient chemical barrier to the underlying silicon. The results demonstrate that SiC-coated poly-Si devices are an effective bridge between poly-Si and full poly-SiC films for applications requiring a high level of corrosion resistance and moderate operating temperatures (up to 200 degC) without compromising the performance characteristics of the original poly-Si device.
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paper_title: Piezoresistive silicon thin film sensor array for biomedical applications

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Abstract N-type hydrogenated nanocrystalline silicon thin film piezoresistors, with gauge factor − 28, were deposited on rugged and flexible polyimide foils by Hot-wire chemical vapor deposition using a tantalum filament heated to 1750 °C. The piezoresistive response under cyclic quasi-static and dynamical (up to 100 Hz) load conditions is reported. Test structures, consisting of microresistors having lateral dimensions in the range from 50 to 100 μm and thickness of 120 nm were defined in an array by reactive ion etching. Metallic pads, forming ohmic contacts to the sensing elements, were defined by a lift-off process. A readout circuit for the array consisting in a mutiplexer on each row and column of the matrix is proposed. The digital data will be processed, interpreted and stored internally by an ultra low-power micro controller, also responsible for the communication of two-way wireless data, e.g. from inside to outside the human body.
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paper_title: Silicon-Nanowire-Based CMOS-Compatible Field-Effect Transistor Nanosensors for Ultrasensitive Electrical Detection of Nucleic Acids

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We herein report the design of a novel semiconducting silicon nanowire field-effect transistor (SiNW-FET) biosensor array for ultrasensitive label-free and real-time detection of nucleic acids. Highly responsive SiNWs with narrow sizes and high surface-to-volume-ratios were "top-down" fabricated with a complementary metal oxide semiconductor compatible anisotropic self-stop etching technique. When SiNWs were covalently modified with DNA probes, the nanosensor showed highly sensitive concentration-dependent conductance change in response to specific target DNA sequences. This SiNW-FET nanosensor revealed ultrahigh sensitivity for rapid and reliable detection of 1 fM of target DNA and high specificity single-nucleotide polymorphism discrimination. As a proof-of-concept for multiplex detection with this small-size and mass producible sensor array, we demonstrated simultaneous selective detection of two pathogenic strain virus DNA sequences (H1N1 and H5N1) of avian influenza.
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paper_title: Wireless sensor network survey

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A wireless sensor network (WSN) has important applications such as remote environmental monitoring and target tracking. This has been enabled by the availability, particularly in recent years, of sensors that are smaller, cheaper, and intelligent. These sensors are equipped with wireless interfaces with which they can communicate with one another to form a network. The design of a WSN depends significantly on the application, and it must consider factors such as the environment, the application's design objectives, cost, hardware, and system constraints. The goal of our survey is to present a comprehensive review of the recent literature since the publication of [I.F. Akyildiz, W. Su, Y. Sankarasubramaniam, E. Cayirci, A survey on sensor networks, IEEE Communications Magazine, 2002]. Following a top-down approach, we give an overview of several new applications and then review the literature on various aspects of WSNs. We classify the problems into three different categories: (1) internal platform and underlying operating system, (2) communication protocol stack, and (3) network services, provisioning, and deployment. We review the major development in these three categories and outline new challenges.
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paper_title: Design and fabrication of a hybrid silicon three-axial force sensor for biomechanical applications

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This paper presents the design and development of a silicon-based three-axial force sensor to be used in a flexible smart interface for biomechanical measurements. Normal and shear forces are detected by combining responses from four piezoresistors obtained by ion implantation in a high aspect-ratio cross-shape flexible element equipped with a 525 m high silicon mesa. The mesa is obtained by a subtractive dry etching process of the whole handle layer of an SOI wafer. Piezoresistor size ranges between 6 and 10m in width, and between 30 and 50m in length. The sensor configuration follows a hybrid integration approach for interconnection and for future electronic circuitry system integration. The sensor ability to measure both normal and shear forces with high linearity ( ∼99%) and low hysteresis is demonstrated by means of tests performed by applying forces from 0 to 2 N. In this paper the packaging design is also presented and materials for flexible sensor array preliminary assembly are described. © 2005 Elsevier B.V. All rights reserved.
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paper_title: 3D printed microfluidic devices: enablers and barriers

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3D printing has the potential to significantly change the field of microfluidics. The ability to fabricate a complete microfluidic device in a single step from a computer model has obvious attractions, but it is the ability to create truly three dimensional structures that will provide new microfluidic capability that is challenging, if not impossible to make with existing approaches. This critical review covers the current state of 3D printing for microfluidics, focusing on the four most frequently used printing approaches: inkjet (i3DP), stereolithography (SLA), two photon polymerisation (2PP) and extrusion printing (focusing on fused deposition modeling). It discusses current achievements and limitations, and opportunities for advancement to reach 3D printing's full potential.
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paper_title: A SiC MEMS Resonant Strain Sensor for Harsh Environment Applications

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In this paper, we present a silicon carbide MEMS resonant strain sensor for harsh environment applications. The sensor is a balanced-mass double-ended tuning fork (BDETF) fabricated from 3C-SiC deposited on a silicon substrate. The SiC was etched in a plasma etch chamber using a silicon oxide mask, achieving a selectivity of 5:1 and etch rate of 2500 Aring/min. The device resonates at atmospheric pressure and operates from room temperature to above 300degC. The device was also subjected to 10 000 g shock (out-of-plane) without damage or shift in resonant frequency. The BDETF exhibits a strain sensitivity of 66 Hz/muepsiv and achieves a strain resolution of 0.11 muepsiv in a bandwidth from 10 to 20 kHz, comparable to state-of-the-art silicon sensors
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paper_title: A review of 3D-printed sensors

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ABSTRACTNowadays, sensors play an important role in human life. Among the many manufacturing methods used in the fabrication of sensors, three-dimensional (3D) printing has gradually shown its advantages, particularly with commercial products. Physical sensors, biosensors, and chemical sensors can all be fabricated via 3D printing technology, through either directly printing sensing components, printing molds for casting sensors, or printing platforms to be integrated with commercial sensors. In this article, the varieties of features and applications of 3D printing technologies used in the fabrication of sensors are reviewed. Several types of 3D printing technologies are compared for better understanding of the tools. With the development of new or hybrid manufacturing methods and materials used in the 3D printing technology, this technology will show its great advantages and potential in the fabrication of highly sensitive nanosensors or compound sensors with 3D intricate structures.
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paper_title: Novel Sensing Approach for LPG Leakage Detection—Part II: Effects of Particle Size, Composition, and Coating Layer Thickness

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Prominent research has been going on to develop a low-cost, efficient gas sensing system. This paper presents a continuation of our earlier research work done to develop a new sensing approach for gas detection at ambient conditions. This paper exhibits the optimization of the response time of the sensor by inhabiting characteristic changes such as variation in the concentration of the dispersion medium, thickness of the coating, and the size of the dispersed medium. Different concentrations of the dispersion medium in the coated suspension were tested to determine the optimal composition required to achieve the highest sensitivity of the tin oxide (SnO2) layer toward the tested gas. The control over adsorption and desorption of the gas molecules in the coated layer was achieved by investigating the particle size of the dispersed medium. The response time of the coated sensor was encouraging and owns a promising potential to the development of a more efficient gas sensing system.
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paper_title: Stretchable, Skin‐Mountable, and Wearable Strain Sensors and Their Potential Applications: A Review

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There is a growing demand for flexible and soft electronic devices. In particular, stretchable, skin-mountable, and wearable strain sensors are needed for several potential applications including personalized health-monitoring, human motion detection, human-machine interfaces, soft robotics, and so forth. This Feature Article presents recent advancements in the development of flexible and stretchable strain sensors. The article shows that highly stretchable strain sensors are successfully being developed by new mechanisms such as disconnection between overlapped nanomaterials, crack propagation in thin films, and tunneling effect, different from traditional strain sensing mechanisms. Strain sensing performances of recently reported strain sensors are comprehensively studied and discussed, showing that appropriate choice of composite structures as well as suitable interaction between functional nanomaterials and polymers are essential for the high performance strain sensing. Next, simulation results of piezoresistivity of stretchable strain sensors by computational models are reported. Finally, potential applications of flexible strain sensors are described. This survey reveals that flexible, skin-mountable, and wearable strain sensors have potential in diverse applications while several grand challenges have to be still overcome.
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paper_title: Wireless sensor networks: a survey

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This paper describes the concept of sensor networks which has been made viable by the convergence of micro-electro-mechanical systems technology, wireless communications and digital electronics. First, the sensing tasks and the potential sensor networks applications are explored, and a review of factors influencing the design of sensor networks is provided. Then, the communication architecture for sensor networks is outlined, and the algorithms and protocols developed for each layer in the literature are explored. Open research issues for the realization of sensor networks are also discussed.
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paper_title: Tactile Sensing From Laser-Ablated Metallized PET Films

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This paper reports the design, fabrication, and implementation of a novel sensor patch developed from commercial polyethylene terephthalate films metallized with aluminum on one side. The aluminum was ablated with laser to form interdigitated electrodes to make sensor prototypes. The interdigitated electrodes were patterned on the substrate with a laser cutter. Characterization of the prototypes was done to determine their operating frequency followed by experimentation. The prototypes have been used as a tactile sensor showing promising results for using these patches in applications with contact pressures considerably lesser than normal human contact pressure.
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paper_title: Novel Sensing Approach for LPG Leakage Detection: Part I—Operating Mechanism and Preliminary Results

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Gas sensing technology has been among the topical research work for quite some time. This paper showcases the research done on the detection mechanism of leakage of domestic cooking gas at ambient conditions. Micro-electro mechanical systems-based interdigital sensors were fabricated on oxidized single-crystal silicon surfaces by the maskless photolithography technique. The electrochemical impedance analysis of these sensors was done to detect liquefied petroleum gas (LPG) with and without coated particles of tin oxide (SnO2) in form of a thin layer. A thin film of SnO2 was spin-coated on the sensing surface of the interdigital sensor to induce selectivity to LPG that consists of a 60/40 mixture of propane and butane, respectively. This paper reports a novel strategy for gas detection under ambient temperature and humidity conditions. The response time of the coated sensor was encouraging and own a promising potential to the development of a complete efficient gas sensing system.
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paper_title: Selective Ultrathin Carbon Sheath on Porous Silicon Nanowires: Materials for Extremely High Energy Density Planar Micro-Supercapacitors

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Microsupercapacitors are attractive energy storage devices for integration with autonomous microsensor networks due to their high-power capabilities and robust cycle lifetimes. Here, we demonstrate porous silicon nanowires synthesized via a lithography compatible low-temperature wet etch and encapsulated in an ultrathin graphitic carbon sheath, as electrochemical double layer capacitor electrodes. Specific capacitance values reaching 325 mF cm–2 are achieved, representing the highest specific ECDL capacitance for planar microsupercapacitor electrode materials to date.
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paper_title: Advances in Optical Sensing and Bioanalysis Enabled by 3D Printing.

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The recent explosion of 3D printing applications in scientific literature has expanded the speed and effectiveness of analytical technological development. 3D printing allows for manufacture that is simply designed in software and printed in-house with nearly no constraints on geometry, and analytical methodologies can thus be prototyped and optimized with little difficulty. The versatility of methods and materials available allows the analytical chemist or biologist to fine-tune both the structural and functional portions of their apparatus. This flexibility has more recently been extended to optical-based bioanalysis, with higher resolution techniques and new printing materials opening the door for a wider variety of optical components, plasmonic surfaces, optical interfaces, and biomimetic systems that can be made in the laboratory. There have been discussions and reviews of various aspects of 3D printing technologies in analytical chemistry; this Review highlights recent literature and trends in their applications to optical sensing and bioanalysis.
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paper_title: The Boom in 3D-Printed Sensor Technology

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Future sensing applications will include high-performance features, such as toxin detection, real-time monitoring of physiological events, advanced diagnostics, and connected feedback. However, such multi-functional sensors require advancements in sensitivity, specificity, and throughput with the simultaneous delivery of multiple detection in a short time. Recent advances in 3D printing and electronics have brought us closer to sensors with multiplex advantages, and additive manufacturing approaches offer a new scope for sensor fabrication. To this end, we review the recent advances in 3D-printed cutting-edge sensors. These achievements demonstrate the successful application of 3D-printing technology in sensor fabrication, and the selected studies deeply explore the potential for creating sensors with higher performance. Further development of multi-process 3D printing is expected to expand future sensor utility and availability.
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paper_title: 3D printing: an emerging technology for sensor fabrication

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Purpose ::: ::: ::: ::: ::: This study aims to provide a technical insight into sensors fabricated by three-dimensional (3D) printing methods. ::: ::: ::: ::: ::: Design/methodology/approach ::: ::: ::: ::: ::: Following an introduction to 3D printing, this article first discusses printed sensors for strain and allied variables, based on a diverse range of principles and materials. It then considers ultrasonic and acoustic sensor developments and provides details of a sensor based on 3D printed electronic components for monitoring food quality in real-time. Finally, brief concluding comments are drawn. ::: ::: ::: ::: ::: Findings ::: ::: ::: ::: ::: Several variants of the 3D printing technique have been used in the fabrication of a range of sensors based on many different operating principles. These exhibit good performance and sometimes unique characteristics. A key benefit is the ability to overcome the limitations of conventional manufacturing techniques by creating complex shapes from a wide range of sensing materials. ::: ::: ::: ::: ::: Originality/value ::: ::: ::: ::: ::: 3D printing is a new and potentially important sensor fabrication technology, and this article provides details of a range of recently reported developments.
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paper_title: A 3D-printed device for a smartphone-based chemiluminescence biosensor for lactate in oral fluid and sweat

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Increasingly, smartphones are used as portable personal computers, revolutionizing communication styles and entire lifestyles. Using 3D-printing technology we have made a disposable minicartridge that can be easily prototyped to turn any kind of smartphone or tablet into a portable luminometer to detect chemiluminescence derived from enzyme-coupled reactions. As proof-of-principle, lactate oxidase was coupled with horseradish peroxidase for lactate determination in oral fluid and sweat. Lactate can be quantified in less than five minutes with detection limits of 0.5 mmol L−1 (corresponding to 4.5 mg dL−1) and 0.1 mmol L−1 (corresponding to 0.9 mg dL−1) in oral fluid and sweat, respectively. A smartphone-based device shows adequate analytical performance to offer a cost-effective alternative for non-invasive lactate measurement. It could be used to evaluate lactate variation in relation to the anaerobic threshold in endurance sport and for monitoring lactic acidosis in critical-care patients.
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paper_title: Paper-based enzymatic reactors for batch injection analysis of glucose on 3D printed cell coupled with amperometric detection

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Abstract This report describes for the first time the development of paper-based enzymatic reactors (PERs) for the detection of glucose (Glu) in artificial serum sample using a 3D printed batch injection analysis (BIA) cell coupled with electrochemical detection. The fabrication of the PERs involved firstly the oxidation of the paper surface with a sodium periodate solution. The oxidized paper was then perforated with a paper punch to create microdisks and activated with a solution containing N -hydroxysuccinimide (NHS) and N -(3-dimethylaminopropyl)- N ′-ethylcarbodiimide hydrochloride (EDC). Glucose oxidase (GOx) enzyme was then covalently immobilized on paper surface to promote the enzymatic assay for the detection of Glu in serum sample. After the addition of Glu on the PER surface placed inside a plastic syringe, the analyte penetrated through the paper surface under vertical flow promoting the enzymatic assay. The reaction product (H 2 O 2 ) was collected with an electronic micropipette in a microtube and analyzed in the 3D BIA cell coupled with screen-printed electrodes (SPEs). The overall preparation time and the cost estimated per PER were 2.5 h and $0.02, respectively. Likewise the PERs, the use of a 3D printer allowed the fabrication of a BIA cell within 4 h at cost of $5. The coupling of SPE with the 3D printed cell exhibited great analytical performance including repeatability and reproducibility lower than 2% as well as high sampling rate (30 injections h −1 ) under low injection volume (10 μL). The limit of detection (LD) and linear range achieved with the proposed approach was 0.11 mmol L −1 and 1–10 mmol L −1 , respectively. Lastly, the glucose concentration level was successfully determined using the proposed method and the values found were not statistically different from the data achieved by a reference method at confidence level of 95%.
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paper_title: 3D-printed biosensor with poly(dimethylsiloxane) reservoir for magnetic separation and quantum dots-based immunolabeling of metallothionein

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Currently, metallothioneins (MTs) are extensively investigated as the molecular biomarkers and the significant positive association of the MT amount was observed in tumorous versus healthy tissue of various types of malignant tumors, including head and neck cancer. Thus, we proposed a biosensor with fluorescence detection, comprising paramagnetic nanoparticles (nanomaghemite core with gold nanoparticles containing shell) for the magnetic separation of MT, based on affinity of its sulfhydryl groups toward gold. Biosensor was crafted from PDMS combined with technology of 3D printing and contained reservoir with volume of 50 μL linked to input (sample/detection components and washing/immunobuffer) and output (waste). For the immunolabeling of immobilized MT anti-MT antibodies conjugated to CdTe quantum dots through synthetic heptapeptide were employed. After optimization of fundamental conditions of the immunolabeling (120 min, 20°C, and 1250 rpm) we performed it on a surface of paramagnetic nanoparticles in the biosensor reservoir, with evaluation of fluorescence of quantum dots (λexc 400 nm, and λem 555 nm). The developed biosensor was applied for quantification of MT in cell lines derived from spinocellular carcinoma (cell line 122P-N) and fibroblasts (122P-F) and levels of the biomarker were found to be about 90 nM in tumor cells and 37 nM in fibroblasts. The proposed system is able to work with low volumes (< 100 μL), with low acquisition costs and high portability.
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paper_title: Enzyme-Immobilized 3D-Printed Reactors for Online Monitoring of Rat Brain Extracellular Glucose and Lactate

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In this study we constructed a highly sensitive system for in vivo monitoring of the concentrations of rat brain extracellular glucose and lactate. This system involved microdialysis (MD) sampling and fluorescence determination in conjunction with a novel sample derivatization scheme in which glucose oxidase and lactate oxidase were immobilized in ABS flow bioreactors (manufactured through low-cost three-dimensional printing (3DP)), via fused deposition modeling, for online oxidization of sampled glucose and lactate, respectively, in rat brain microdialysate. After optimizing the experimental conditions for MD sampling, the manufacture of the designed flow reactors, the enzyme immobilization procedure, and the online derivatization scheme, the available sampling frequency was 15 h(-1) and the system's detection limits reached as low as 0.060 mM for glucose and 0.059 mM for lactate, based on a 20-μL conditioned microdialysate; these characteristics were sufficient to reliably determine the concentrations of extracellular glucose and lactate in the brains of living rats. To demonstrate the system's applicability, we performed (i) spike analyses of offline-collected rat brain microdialysate and (ii) in vivo dynamic monitoring of the extracellular glucose and lactate in living rat brains, in addition to triggering neuronal depolarization by perfusing a high-K(+) medium from the implanted MD probe. Our analytical results and demonstrations confirm that postprinting functionalization of analytical devices manufactured using 3DP technology can be a powerful strategy for extending the diversity and adaptability of currently existing analytical configurations.
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paper_title: 3D printed chip for electrochemical detection of influenza virus labeled with CdS quantum dots

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In this study, we report a new three-dimensional (3D), bead-based microfluidic chip developed for rapid, sensitive and specific detection of influenza hemagglutinin. The principle of microfluidic chip is based on implementation of two-step procedure that includes isolation based on paramagnetic beads and electrochemical detection. As a platform for isolation process, streptavidin-modified MPs, which were conjugated via biotinylated glycan (through streptavidin–biotin affinity) followed by linkage of hemagglutinin to glycan, were used. Vaccine hemagglutinin (HA vaxi) was labeled with CdS quantum dots (QDs) at first. Detection of the isolation product by voltammetry was the end point of the procedure. The suggested and developed method can be used also for detection of other specific substances that are important for control, diagnosis or therapy of infectious diseases.
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paper_title: Customizable 3D Printed ‘Plug and Play’ Millifluidic Devices for Programmable Fluidics

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Three dimensional (3D) printing is actively sought after in recent years as a promising novel technology to construct complex objects, which scope spans from nano- to over millimeter scale. Previously we utilized Fused deposition modeling (FDM)-based 3D printer to construct complex 3D chemical fluidic systems, and here we demonstrate the construction of 3D milli-fluidic structures for programmable liquid handling and control of biological samples. Basic fluidic operation devices, such as water-in-oil (W/O) droplet generators for producing compartmentalized mono-disperse droplets, sensor-integrated chamber for online monitoring of cellular growth, are presented. In addition, chemical surface treatment techniques are used to construct valve-based flow selector for liquid flow control and inter-connectable modular devices for networking fluidic parts. As such this work paves the way for complex operations, such as mixing, flow control, and monitoring of reaction / cell culture progress can be carried out by constructing both passive and active components in 3D printed structures, which designs can be shared online so that anyone with 3D printers can reproduce them by themselves.
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paper_title: 3D-printed supercapacitor-powered electrochemiluminescent protein immunoarray.

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Herein we report a low cost, sensitive, supercapacitor-powered electrochemiluminescent (ECL) protein immunoarray fabricated by an inexpensive 3-dimensional (3D) printer. The immunosensor detects three cancer biomarker proteins in serum within 35 min. The 3D-printed device employs hand screen printed carbon sensors with gravity flow for sample/reagent delivery and washing. Prostate cancer biomarker proteins, prostate specific antigen (PSA), prostate specific membrane antigen (PSMA) and platelet factor-4 (PF-4) in serum were captured on the antibody-coated carbon sensors followed by delivery of detection-antibody-coated Ru(bpy)3(2+) (RuBPY)-doped silica nanoparticles in a sandwich immunoassay. ECL light was initiated from RuBPY in the silica nanoparticles by electrochemical oxidation with tripropylamine (TPrA) co-reactant using supercapacitor power and ECL was captured with a CCD camera. The supercapacitor was rapidly photo-recharged between assays using an inexpensive solar cell. Detection limits were 300-500f gmL(-1) for the 3 proteins in undiluted calf serum. Assays of 6 prostate cancer patient serum samples gave good correlation with conventional single protein ELISAs. This technology could provide sensitive onsite cancer diagnostic tests in resource-limited settings with the need for only moderate-level training.
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paper_title: Application of 3D Printing Technology in Increasing the Diagnostic Performance of Enzyme-Linked Immunosorbent Assay (ELISA) for Infectious Diseases

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Enzyme-linked Immunosorbent Assay (ELISA)-based diagnosis is the mainstay for measuring antibody response in infectious diseases and to support pathogen identification of potential use in infectious disease outbreaks and clinical care of individual patients. The development of laboratory diagnostics using readily available 3D printing technologies provides a timely opportunity for further expansion of this technology into immunodetection systems. Utilizing available 3D printing platforms, a '3D well' was designed and developed to have an increased surface area compared to those of 96-well plates. The ease and rapidity of the development of the 3D well prototype provided an opportunity for its rapid validation through the diagnostic performance of ELISA in infectious disease without modifying current laboratory practices for ELISA. The improved sensitivity of the 3D well of up to 2.25-fold higher compared to the 96-well ELISA provides a potential for the expansion of this technology towards miniaturization and Lab-On-a-Chip platforms to reduce time, volume of reagents and samples needed for such assays in the laboratory diagnosis of infectious and other diseases including applications in other disciplines.
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paper_title: Smartphone-interfaced 3D printed toxicity biosensor integrating bioluminescent “sentinel cells”

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Abstract In this work, we report the design, fabrication, and preliminary assessment of analytical performance of a smartphone-based bioluminescence (BL) whole-cell toxicity biosensor. Genetically engineered human embryonic kidney cells, constitutively expressing a powerful green-emitting luciferase mutant, were used as “sentinel cells” and integrated into 3D printed ready-to-use cartridges, also containing assay reagents. Customizable, low-cost smartphone adaptors were created using a desktop 3D printer to provide a mini-darkbox and an aligned optical interface between the smartphone camera and the cell cartridge for BL signals acquisition. The developed standalone compact device, which also includes disposable droppers for sample and reagents addition, allows the user to perform the toxicity assay within 30 min following the procedure provided by a custom-developed application running on Android (Tox-App). As proof-of-concept we analyzed real samples including ubiquitous products used in everyday life. The results showed good correlation with those obtained with laboratory instrumentation and commercially available toxicity assays, thus supporting potential applications of the proposed device for portable real-life needs.
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paper_title: A Simple, Low-Cost Conductive Composite Material for 3D Printing of Electronic Sensors

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3D printing technology can produce complex objects directly from computer aided digital designs. The technology has traditionally been used by large companies to produce fit and form concept prototypes (‘rapid prototyping’) before production. In recent years however there has been a move to adopt the technology as full-scale manufacturing solution. The advent of low-cost, desktop 3D printers such as the RepRap and Fab@Home has meant a wider user base are now able to have access to desktop manufacturing platforms enabling them to produce highly customised products for personal use and sale. This uptake in usage has been coupled with a demand for printing technology and materials able to print functional elements such as electronic sensors. Here we present formulation of a simple conductive thermoplastic composite we term ‘carbomorph’ and demonstrate how it can be used in an unmodified low-cost 3D printer to print electronic sensors able to sense mechanical flexing and capacitance changes. We show how this capability can be used to produce custom sensing devices and user interface devices along with printed objects with embedded sensing capability. This advance in low-cost 3D printing with offer a new paradigm in the 3D printing field with printed sensors and electronics embedded inside 3D printed objects in a single build process without requiring complex or expensive materials incorporating additives such as carbon nanotubes.
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paper_title: Application of fusion deposition modelling for rapid investment casting – a review

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The rapid prototyping technologies are being used in the various fields of engineering. The ability of producing very small and intricate details makes the rapid prototyping technologies suitable for making patterns for investment casting. Moreover, by using rapid prototyping technologies the patterns can be produced without the necessity of costly hard tooling. The rapid prototyping technologies are considered very useful when only limited numbers of pieces are promptly required as in making prototypes, design iterations and design optimisations. The fusion deposition modelling (FDM) is a rapid prototyping technology that can use a number of materials which can be effectively used for making patterns for investment casting. Different non-wax materials are available which can be used for making patterns and can be burnt easily during autoclaving/firing. This paper reviews the suitability of FDM for making patterns for investment casting. The direct and indirect methods of producing casting patterns along ...
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paper_title: A portable low-cost long-term live-cell imaging platform for biomedical research and education

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Abstract Time-resolved visualization and analysis of slow dynamic processes in living cells has revolutionized many aspects of in vitro cellular studies. However, existing technology applied to time-resolved live-cell microscopy is often immobile, costly and requires a high level of skill to use and maintain. These factors limit its utility to field research and educational purposes. The recent availability of rapid prototyping technology makes it possible to quickly and easily engineer purpose-built alternatives to conventional research infrastructure which are low-cost and user-friendly. In this paper we describe the prototype of a fully automated low-cost, portable live-cell imaging system for time-resolved label-free visualization of dynamic processes in living cells. The device is light-weight (3.6 kg), small (22×22×22 cm) and extremely low-cost (
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paper_title: Simple, Cost-Effective 3D Printed Microfluidic Components for Disposable, Point-of-Care Colorimetric Analysis

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The fabrication of microfluidic chips can be simplified and accelerated by three-dimensional (3D) printing. However, all of the current designs of 3D printed microchips require off-chip bulky equipment to operate, which hindered their applications in the point-of-care (POC) setting. In this work, we demonstrate a new class of movable 3D printed microfluidic chip components, including torque-actuated pump and valve, rotary valve, and pushing valve, which can be operated manually without any off-chip bulky equipment such as syringe pump and gas pressure source. By integrating these components, we developed a user-friendly 3D printed chip that can perform general colorimetric assays. Protein quantification was performed on artificial urine samples as a proof-of-concept model with a smartphone used as the imaging platform. The protein was quantified linearly and was within the physiologically relevant range for humans. We believe that the demonstrated components and designs can expand the functionalities and ...
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paper_title: Automated 3D-printed unibody immunoarray for chemiluminescence detection of cancer biomarker proteins

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A low cost three-dimensional (3D) printed clear plastic microfluidic device was fabricated for fast, low cost automated protein detection. The unibody device features three reagent reservoirs, an efficient 3D network for passive mixing, and an optically transparent detection chamber housing a glass capture antibody array for measuring chemiluminescence output with a CCD camera. Sandwich type assays were built onto the glass arrays using a multi-labeled detection antibody-polyHRP (HRP = horseradish peroxidase). Total assay time was ∼30 min in a complete automated assay employing a programmable syringe pump so that the protocol required minimal operator intervention. The device was used for multiplexed detection of prostate cancer biomarker proteins prostate specific antigen (PSA) and platelet factor 4 (PF-4). Detection limits of 0.5 pg mL-1 were achieved for these proteins in diluted serum with log dynamic ranges of four orders of magnitude. Good accuracy vs. ELISA was validated by analyzing human serum samples. This prototype device holds good promise for further development as a point-of-care cancer diagnostics tool.
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paper_title: Review of Rapid Prototyping-Technology for the Future

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The term “Rapid Prototyping” (RP) refers to a class of technologies that can automatically construct physical models from computer-Aided Design (CAD) data or is a group of techniques used to quickly fabricate a scale model of a physical part or assembly using three-dimensional computer aided design (CAD) data. The “three dimensional printers” allow designers to quickly create tangible prototypes of their designs rather than two dimensional pictures. Such models have numerous uses. They make excellent visual aids for communicating ideas with co-workers or customers apart from design testing. For example Aerospace Engineer might mount a model aerofoil in a wind tunnel to measure lift and drag forces. Across the world, Engineering has the common language and common goal-“Improving the Quality of Life” of mankind without any boundary restrictions. To bring about this much needed change, we require the services of the fraternity of Engineers to work on the challenges posed by our times. The need of the hour is to bring together globally this fraternity to collaborate with each other.
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paper_title: Development of Aptamer-Based Point-of-Care Diagnostic Devices for Malaria Using Three-Dimensional Printing Rapid Prototyping

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We present the adaption of an aptamer-tethered enzyme capture (APTEC) assay into point-of-care device prototypes with potential for malaria diagnosis. The assay functions by capturing the malaria biomarker Plasmodium falciparum lactate dehydrogenase (PfLDH) from samples and using its intrinsic enzymatic activity to generate a visualizable blue color in response to Plasmodium positive samples. Using three-dimensional (3D) printing rapid prototyping, a paper-based syringe test and magnetic bead-based well test were developed. Both were found to successfully detect recombinant PfLDH at ng mL–1 concentrations using low sample volumes (20 μL) and could function using purified or spiked whole blood samples with facile sample preparation. The syringe test was found to be more analytically sensitive but required more additional preparation steps, while the well test required fewer steps and hence may be better suited for future clinical testing. Additionally, the development reagents required for the color respon...
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paper_title: Disposable electrochemical sensor prepared using 3D printing for cell and tissue diagnostics

paper_content:

Abstract In this paper we present a novel electrochemical sensor with a unique 3D architecture allowing for direct measurements on contact, or in close proximity, to biological samples. For biomedical applications, the all-polymer architecture can be mounted on special probes that can access the region under test with no need for biopsy as is done today with the conventional 2D electrodes. The chip consists of a biocompatible substrate comprised of an electrochemical cell with two gold electrodes (working and counter) and an Ag/AgCl quasi-reference electrode. The metal electrodes on the biochip front (sensing) side are fabricated by conventional electroplating and patterning methods. The chip itself is made from PDMS cast from a polymer master fabricated by 3D printing. The electrical communication between the biochip front and backside is enabled by through-hole via -contacts filled with conductive PDMS containing 60 wt% graphite powder. The electroactivity of working electrodes was verified by cyclic voltammetry of ferrocyanide/ferricyanide redox reaction. Amperometric in-vitro detection of the biomarker alkaline phosphatase from three different colon cancer cell lines directly in a cell culture plate while maintaining their biological environment was successfully demonstrated. The sensor exhibit stable voltammetric signatures and significant amperometric response to the enzyme in repeated tests. This approach paves the way to perform direct, non-invasive diagnostics on top of an exposed cell layer for both in-vivo and in-vitro applications.
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paper_title: Ultrarapid detection of pathogenic bacteria using a 3D immunomagnetic flow assay.

paper_content:

We developed a novel 3D immunomagnetic flow assay for the rapid detection of pathogenic bacteria in a large-volume food sample. Antibody-functionalized magnetic nanoparticle clusters (AbMNCs) were magnetically immobilized on the surfaces of a 3D-printed cylindrical microchannel. The injection of a Salmonella-spiked sample solution into the microchannel produced instant binding between the AbMNCs and the Salmonella bacteria due to their efficient collisions. Nearly perfect capture of the AbMNCs and AbMNCs-Salmonella complexes was achieved under a high flow rate by stacking permanent magnets with spacers inside the cylindrical separator to maximize the magnetic force. The concentration of the bacteria in solution was determined using ATP luminescence measurements. The detection limit was better than 10 cfu/mL, and the overall assay time, including the binding, rinsing, and detection steps for a 10 mL sample took less than 3 min. To our knowledge, the 3D immunomagnetic flow assay described here provides the fastest high-sensitivity, high-capacity method for the detection of pathogenic bacteria.
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paper_title: Applications of additive manufacturing in dentistry: A review

paper_content:

Additive manufacturing (AM) or 3D printing has been hailed as the third industrial revolution as it has caused a paradigm shift in the way objects have been manufactured. Conventionally, converting a raw material to a fully finished and assembled, usable product comprises several steps which can be eliminated by using this process as functional products can be created directly from the raw material at a fraction of the time originally consumed. Thus, AM has found applications in several sectors including automotive, aerospace, printed electronics, and healthcare. AM is increasingly being used in the healthcare sector, given its potential to fabricate patient-specific customized implants with required accuracy and precision. Implantable heart valves, rib cages, and bones are some of the examples where AM technologies are used. A vast variety of materials including ceramics, metals, polymers, and composites have been processed to fabricate intricate implants using 3D printing. The applications of AM in dentistry include maxillofacial implants, dentures, and other prosthetic aids. It may also be used in surgical training and planning, as anatomical models can be created at ease using AM. This article gives an overview of the AM process and reviews in detail the applications of 3D printing in dentistry. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2017.
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paper_title: 3D-printed microfluidic automation

paper_content:

Microfluidic automation - the automated routing, dispensing, mixing, and/or separation of fluids through microchannels - generally remains a slowly-spreading technology because device fabrication requires sophisticated facilities and the technology's use demands expert operators. Integrating microfluidic automation in devices has involved specialized multi-layering and bonding approaches. Stereolithography is an assembly-free, 3D-printing technique that is emerging as an efficient alternative for rapid prototyping of biomedical devices. Here we describe fluidic valves and pumps that can be stereolithographically printed in optically-clear, biocompatible plastic and integrated within microfluidic devices at low cost. User-friendly fluid automation devices can be printed and used by non-engineers as replacement for costly robotic pipettors or tedious manual pipetting. Engineers can manipulate the designs as digital modules into new devices of expanded functionality. Printing these devices only requires the digital file and electronic access to a printer.
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paper_title: 3D printed modules for integrated microfluidic devices

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Due to the ever increasing demand for integrated microfluidic devices, an advanced fabrication method is required to expand their capabilities in many research areas. We propose a three-dimensional (3D) printing technique for production of functional modules and demonstrate their assembly into integrated microfluidic device for non-expert users.
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paper_title: 3D printed stratospheric probe as a platform for determination of DNA damage based on carbon quantum dots/DNA complex fluorescence increase

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We present a utilization of carbon quantum dots (CQDs), passivated with polyethylene glycol as a fluorescent recognition probe for DNA damage. Synthesized CQDs were characterized in detail, using optical and electrochemical methods. Further, fluorescent behavior of CQDs was monitored in the presence of genomic DNA, isolated from Staphylococcus aureus. In laboratory conditions, after 30 min of exposure to UV irradiation (λ = 254 nm), the DNA/CQDs complex significantly increased its fluorescence. Further, stratospheric probe was suggested and crafted by using technology of 3D printing (acrylonitrile–butadiene–styrene as a material). CQDs were exploited to evaluate the DNA damage in stratospheric conditions (up to 20,000 m) by determination of fluorescence increase (λexc = 245 nm, λem = 400 nm), together with other parameters (temperature, humidity, altitude, pressure, UV intensity, and X-ray irradiation). The obtained data showed that the sensor utilizing the DNA/CQDs was able to identify the DNA damage, together with external conditions. It was shown the proposed concept is able to operate at temperatures lower than −70 °C. The proposed protocol may by applicable as a biosensor for long-term space missions, like international space station, missions to the Moon or Mars.
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paper_title: Processing Issues and the Characterization of Soft Electrochemical 3D Sensor

paper_content:

Abstract In this work we present the process and characterization issues of 3D electrochemical sensor made on a polymeric substrate using through-substrate via contacts filled with a conductive polymer. In this paper we highlight and demonstrate the main purpose of this architecture for a “touch” sensing applications. The chip consists of a PDMS substrate comprising an electrochemical cell with two gold electrodes (working and counter) and an Ag/AgCl quasi-reference electrode. In the present 3D architecture the electrodes are located on one side of the substrate while the contacts are located at the back side, allowing electrical signals to flow vertically to the potentiostat and signal processing units. The electrical communication between the bio-chip front and backside is enabled by conducting vias fabricated by cast molding. The via-contacts are filled with conductive PDMS containing 60 wt% graphite powder. Electrochemical characterization of the chip is carried by measuring the redox behavior ferricyanide/ferrocyanide couple in a cyclic voltammetry analysis. The 3D sensor exhibits stable voltammetric signatures in repeated tests. Enzymatic activity of alkaline phosphatase in two cell lines was detected and quantified by chronoamperometric assay. These results showing that the described system is suitable for non-invasive diagnostics both for in-vitro & in-vivo applications.
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paper_title: Simple, Cost-Effective 3D Printed Microfluidic Components for Disposable, Point-of-Care Colorimetric Analysis

paper_content:

The fabrication of microfluidic chips can be simplified and accelerated by three-dimensional (3D) printing. However, all of the current designs of 3D printed microchips require off-chip bulky equipment to operate, which hindered their applications in the point-of-care (POC) setting. In this work, we demonstrate a new class of movable 3D printed microfluidic chip components, including torque-actuated pump and valve, rotary valve, and pushing valve, which can be operated manually without any off-chip bulky equipment such as syringe pump and gas pressure source. By integrating these components, we developed a user-friendly 3D printed chip that can perform general colorimetric assays. Protein quantification was performed on artificial urine samples as a proof-of-concept model with a smartphone used as the imaging platform. The protein was quantified linearly and was within the physiologically relevant range for humans. We believe that the demonstrated components and designs can expand the functionalities and ...
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paper_title: Automated 3D-printed unibody immunoarray for chemiluminescence detection of cancer biomarker proteins

paper_content:

A low cost three-dimensional (3D) printed clear plastic microfluidic device was fabricated for fast, low cost automated protein detection. The unibody device features three reagent reservoirs, an efficient 3D network for passive mixing, and an optically transparent detection chamber housing a glass capture antibody array for measuring chemiluminescence output with a CCD camera. Sandwich type assays were built onto the glass arrays using a multi-labeled detection antibody-polyHRP (HRP = horseradish peroxidase). Total assay time was ∼30 min in a complete automated assay employing a programmable syringe pump so that the protocol required minimal operator intervention. The device was used for multiplexed detection of prostate cancer biomarker proteins prostate specific antigen (PSA) and platelet factor 4 (PF-4). Detection limits of 0.5 pg mL-1 were achieved for these proteins in diluted serum with log dynamic ranges of four orders of magnitude. Good accuracy vs. ELISA was validated by analyzing human serum samples. This prototype device holds good promise for further development as a point-of-care cancer diagnostics tool.
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paper_title: A 3D Printed Fluidic Device that Enables Integrated Features

paper_content:

Fluidic devices fabricated using conventional soft lithography are well suited as prototyping methods. Three-dimensional (3D) printing, commonly used for producing design prototypes in industry, allows for one step production of devices. 3D printers build a device layer by layer based on 3D computer models. Here, a reusable, high throughput, 3D printed fluidic device was created that enables flow and incorporates a membrane above a channel in order to study drug transport and affect cells. The device contains 8 parallel channels, 3 mm wide by 1.5 mm deep, connected to a syringe pump through standard, threaded fittings. The device was also printed to allow integration with commercially available membrane inserts whose bottoms are constructed of a porous polycarbonate membrane; this insert enables molecular transport to occur from the channel to above the well. When concentrations of various antibiotics (levofloxacin and linezolid) are pumped through the channels, approximately 18-21% of the drug migrates through the porous membrane, providing evidence that this device will be useful for studies where drug effects on cells are investigated. Finally, we show that mammalian cells cultured on this membrane can be affected by reagents flowing through the channels. Specifically, saponin was used to compromise cell membranes, and a fluorescent label was used to monitor the extent, resulting in a 4-fold increase in fluorescence for saponin treated cells.
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paper_title: 3D-printed fluidic devices enable quantitative evaluation of blood components in modified storage solutions for use in transfusion medicine

paper_content:

A fluidic device constructed with a 3D-printer can be used to investigate stored blood components with subsequent high-throughput calibration and readout with a standard plate reader.
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paper_title: A 3D printed dry electrode for ECG/EEG recording

paper_content:

Abstract In this paper, the design, fabrication and testing of a 3D printed dry electrode is proposed. 3D printing represents an authentic breakthrough for the development and mass production of dry medical electrodes. In fact, it allows a fast and low cost production of high precision tridimensional shapes. This technique is reliable and efficient, and facilitates controllability over the whole process. Initially, 3D capable design software is used to draw the electrode model. The resulting file is simply loaded in a 3D printer whose resolution is 42 μm on x- and y-axes, and 16 μm on z-axis. The electrode is made by an insulating acrylic-based photopolymer. It consists of 180 conical needles (distance = 250 μm) on a truncated conical base. The metallization process undergoes two steps: sputtering of titanium as adhesion promotion layer and evaporation of gold to lower the impedance and prevent oxidation of the electrode. After electrode characterization, experimental results are presented and compared with planar wet Ag/AgCl electrodes for recording ECG–EEG.
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paper_title: Challenges and limitations of patient-specific vascular phantom fabrication using 3D Polyjet printing

paper_content:

Additive manufacturing (3D printing) technology offers a great opportunity towards development of patient-specific vascular anatomic models, for medical device testing and physiological condition evaluation. However, the development process is not yet well established and there are various limitations depending on the printing materials, the technology and the printer resolution. Patient-specific neuro-vascular anatomy was acquired from computed tomography angiography and rotational digital subtraction angiography (DSA). The volumes were imported into a Vitrea 3D workstation (Vital Images Inc.) and the vascular lumen of various vessels and pathologies were segmented using a “marching cubes” algorithm. The results were exported as Stereo Lithographic (STL) files and were further processed by smoothing, trimming, and wall extrusion (to add a custom wall to the model). The models were printed using a Polyjet printer, Eden 260V (Objet-Stratasys). To verify the phantom geometry accuracy, the phantom was reimaged using rotational DSA, and the new data was compared with the initial patient data. The most challenging part of the phantom manufacturing was removal of support material. This aspect could be a serious hurdle in building very tortuous phantoms or small vessels. The accuracy of the printed models was very good: distance analysis showed average differences of 120 μm between the patient and the phantom reconstructed volume dimensions. Most errors were due to residual support material left in the lumen of the phantom. Despite the post-printing challenges experienced during the support cleaning, this technology could be a tremendous benefit to medical research such as in device development and testing.
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paper_title: 3D-printed microfluidic automation

paper_content:

Microfluidic automation - the automated routing, dispensing, mixing, and/or separation of fluids through microchannels - generally remains a slowly-spreading technology because device fabrication requires sophisticated facilities and the technology's use demands expert operators. Integrating microfluidic automation in devices has involved specialized multi-layering and bonding approaches. Stereolithography is an assembly-free, 3D-printing technique that is emerging as an efficient alternative for rapid prototyping of biomedical devices. Here we describe fluidic valves and pumps that can be stereolithographically printed in optically-clear, biocompatible plastic and integrated within microfluidic devices at low cost. User-friendly fluid automation devices can be printed and used by non-engineers as replacement for costly robotic pipettors or tedious manual pipetting. Engineers can manipulate the designs as digital modules into new devices of expanded functionality. Printing these devices only requires the digital file and electronic access to a printer.
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paper_title: 3D printed microfluidic devices with integrated versatile and reusable electrodes

paper_content:

We report two 3D printed devices that can be used for electrochemical detection. In both cases, the electrode is housed in commercially available, polymer-based fittings so that the various electrode materials (platinum, platinum black, carbon, gold, silver) can be easily added to a threaded receiving port printed on the device; this enables a module-like approach to the experimental design, where the electrodes are removable and can be easily repolished for reuse after exposure to biological samples. The first printed device represents a microfluidic platform with a 500 × 500 μm channel and a threaded receiving port to allow integration of either polyetheretherketone (PEEK) nut-encased glassy carbon or platinum black (Pt-black) electrodes for dopamine and nitric oxide (NO) detection, respectively. The embedded 1 mm glassy carbon electrode had a limit of detection (LOD) of 500 nM for dopamine and a linear response (R2 = 0.99) for concentrations between 25–500 μM. When the glassy carbon electrode was coated with 0.05% Nafion, significant exclusion of nitrite was observed when compared to signal obtained from equimolar injections of dopamine. When using flow injection analysis with a Pt/Pt-black electrode and standards derived from NO gas, a linear correlation (R2 = 0.99) over a wide range of concentrations (7.6–190 μM) was obtained, with the LOD for NO being 1 μM. The second application showcases a 3D printed fluidic device that allows collection of the biologically relevant analyte adenosine triphosphate (ATP) while simultaneously measuring the release stimulus (reduced oxygen concentration). The hypoxic sample (4.8 ± 0.5 ppm oxygen) released 2.4 ± 0.4 times more ATP than the normoxic sample (8.4 ± 0.6 ppm oxygen). Importantly, the results reported here verify the reproducible and transferable nature of using 3D printing as a fabrication technique, as devices and electrodes were moved between labs multiple times during completion of the study.
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paper_title: New perspectives in shake flask pH control using a 3D-printed control unit based on pH online measurement

paper_content:

Abstract Online pH control during microbial shake flask cultivation has not been established due to the lack of a practical combination of an online sensor system and an appropriate control unit. The objective of this investigation was to develop a minimum scale dosage apparatus, namely shake flask controller (“SFC”), which can control the pH during a complete cultivation and serves as technical example for the application of small liquid dispensing lab devices. A well evaluated optical, chemosensor based, noninvasive, multisensory platform prototype for online DO (dissolved oxygen)-, pH- and biomass measurement served as sensor. The SFC was designed as cap-integrated, semi-autarkical control unit. Minimum scale working parts like the commercial mp6 piezoelectric micropumps and miniature solenoid valves were combined with a selective laser sintering (SLS) printed backbone. In general it is intended to extend its application range on the control of enzymatic assays, polymerization processes, cell disruption methods or the precise dispense of special chemicals like inducers or inhibitors. It could be proved that pH control within a range of 0.1 pH units could be maintained at different cultivation conditions. A proportional-integral-derivative- (PID) controller and an adaptive proportional controller were successfully applied to calculate the balancing solution volume. SLS based 3D printing using polyamide combined with state-of-the-art micro pumps proved to be perfectly adaptable for minimum size, autoclavable lab devices.
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paper_title: Selective laser sintering: A qualitative and objective approach

paper_content:

This article presents an overview of selective laser sintering (SLS) work as reported in various journals and proceedings. Selective laser sintering was first done mainly on polymers and nylon to create prototypes for audio-visual help and fit-to-form tests. Gradually it was expanded to include metals and alloys to manufacture functional prototypes and develop rapid tooling. The growth gained momentum with the entry of commercial entities such as DTM Corporation and EOS GmbH Electro Optical Systems. Computational modeling has been used to understand the SLS process, optimize the process parameters, and enhance the efficiency of the sintering machine.
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paper_title: A review on selective laser sintering/melting (SLS/SLM) of aluminium alloy powders: Processing, microstructure, and properties

paper_content:

Manufacturing businesses aiming to deliver their new customised products more quickly and gain more consumer markets for their products will increasingly employ selective laser sintering/melting (SLS/SLM) for fabricating high quality, low cost, repeatable, and reliable aluminium alloy powdered parts for automotive, aerospace, and aircraft applications. However, aluminium powder is known to be uniquely bedevilled with the tenacious surface oxide film which is difficult to avoid during SLS/SLM processing. The tenacity of the surface oxide film inhibits metallurgical bonding across the layers during SLS/SLM processing and this consequently leads to initiation of spheroidisation by Marangoni convection. Due to the paucity of publications on SLS/SLM processing of aluminium alloy powders, we review the current state of research and progress from different perspectives of the SLS/SLM, powder metallurgy (P/M) sintering, and pulsed electric current sintering (PECS) of ferrous, non-ferrous alloys, and composite powders as well as laser welding of aluminium alloys in order to provide a basis for follow-on-research that leads to the development of high productivity, SLS/SLM processing of aluminium alloy powders. Moreover, both P/M sintering and PECS of aluminium alloys are evaluated and related to the SLS process with a view to gaining useful insights especially in the aspects of liquid phase sintering (LPS) of aluminium alloys; application of LPS to SLS process; alloying effect in disrupting the surface oxide film of aluminium alloys; and designing of aluminium alloy suitable for the SLS/SLM process. Thereafter, SLS/SLM parameters, powder properties, and different types of lasers with their effects on the processing and densification of aluminium alloys are considered. The microstructure and metallurgical defects associated with SLS/SLM processed parts are also elucidated by highlighting the mechanism of their formation, the main influencing factors, and the remedial measures. Mechanical properties such as hardness, tensile, and fatigue strength of SLS/SLM processed parts are reported. The final part of this paper summarises findings from this review and outlines the trend for future research in the SLS/SLM processing of aluminium alloy powders.
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paper_title: Metal Additive Manufacturing: A Review

paper_content:

This paper reviews the state-of-the-art of an important, rapidly emerging, manufacturing technology that is alternatively called additive manufacturing (AM), direct digital manufacturing, free form fabrication, or 3D printing, etc. A broad contextual overview of metallic AM is provided. AM has the potential to revolutionize the global parts manufacturing and logistics landscape. It enables distributed manufacturing and the productions of parts-on-demand while offering the potential to reduce cost, energy consumption, and carbon footprint. This paper explores the material science, processes, and business consideration associated with achieving these performance gains. It is concluded that a paradigm shift is required in order to fully exploit AM potential.
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paper_title: 3D Printed Stretchable Capacitive Sensors for Highly Sensitive Tactile and Electrochemical Sensing

paper_content:

Developments of innovative strategies for the fabrication of stretchable sensors are of crucial importance for their applications in wearable electronic systems. In this work, we report the successful fabrication of stretchable capacitive sensors using a novel 3D printing method for highly sensitive tactile and electrochemical sensing applications. Unlike conventional lithographic or templated methods, the programmable 3D printing technique can fabricate complex device structures in a cost-effective and facile manner. We designed and fabricated stretchable capacitive sensors with interdigital and double-vortex designs and demonstrated their successful applications as tactile and electrochemical sensors. Especially, our stretchable sensors exhibited a detection limit as low as 1 × 10−6 M for NaCl aqueous solution, which could have significant potential applications when integrated in electronics skins.
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paper_title: Temperature sensor realized by inkjet printing process on flexible substrate

paper_content:

Abstract The objective of this study is to realize a printed and flexible temperature sensor to achieve surface temperature measurement of the human body. The sensor is a thermistor composed silver (Ag) deposited on a Polyimide substrate (Kapton HN). The meander was patterned by inkjet printing with a drop-on-demand Jetlab4 (Microfab Technologies Inc.). The resistance temperature coefficients have been studied in the temperature range of 20–60 °C with a range of voltage between 0 and 1 V. The stability versus time has also been measured without a sensor layer protection. The sensitive area of the sensor, silver lines width and the gap between the electrical conductors were, respectively 6.2 cm 2 , 300 μm, 60 μm. The mean temperature sensor sensitivity found was 2.23 × 10 −3 °C −1 . The results show a good linearity and less than 5% hysteresis in the extended measurement.
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paper_title: 3D multifunctional integumentary membranes for spatiotemporal cardiac measurements and stimulation across the entire epicardium

paper_content:

Tools for cardiac physiological mapping are important for basic and clinical cardiac research. Here the authors use 3D printing to create a thin, elastic silicone sheath that fits tightly around the entire epicardium and contains sensors to measure a variety of physiological parameters of the beating heart ex vivo.
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paper_title: Biocompatible inkjet printing technique for designed seeding of individual living cells.

paper_content:

Inkjet printers are capable of printing at high resolution by ejecting extremely small ink drops. Established printing technology will be able to seed living cells, at micrometer resolution, in arrangements similar to biological tissues. We describe the use of a biocompatible inkjet head and our investigation of the feasibility of microseeding with living cells. Living cells are easily damaged by heat; therefore, we used an electrostatically driven inkjet system that was able to eject ink without generating significant heat. Bovine vascular endothelial cells were prepared and suspended in culture medium, and the cell suspension was used as "ink" and ejected onto culture disks. Microscopic observation showed that the endothelial cells were situated in the ejected dots in the medium, and that the number of cells in each dot was dependent on the concentration of the cell suspension and ejection frequency chosen. After the ejected cells were incubated for a few hours, they adhered to the culture disks. Using our non-heat-generating, electrostatically driven inkjet system, living cells were safely ejected onto culture disks. This microseeding technique with living cells has the potential to advance the field of tissue engineering.
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paper_title: Development and validation of a 3D-printed interfacial stress sensor for prosthetic applications.

paper_content:

a b s t r a c t A novel capacitance-based sensor designed for monitoring mechanical stresses at the stump-socket inter- face of lower-limb amputees is described. It provides practical means of measuring pressure and shear stresses simultaneously. In particular, it comprises of a flexible frame (20 mm × 20 mm), with thickness of 4 mm. By employing rapid prototyping technology in its fabrication, it offers a low-cost and versatile solution, with capability of adopting bespoke shapes of lower-limb residua. The sensor was first ana- lysed using finite element analysis (FEA) and then evaluated using lab-based electromechanical tests. The results validate that the sensor is capable of monitoring both pressure and shear at stresses up to 350 kPa and 80 kPa, respectively. A post-signal processing model is developed to induce pressure and shear stresses, respectively. The effective separation of pressure and shear signals can be potentially advantageous for sensor calibration in clinical applications. The sensor also demonstrates high linearity (approx. 5-8%) and high pressure (approx. 1.3 kPa) and shear (approx. 0.6 kPa) stress resolution perfor- mance. Accordingly, the sensor offers the potential for exploitation as an assistive tool to both evaluate prosthetic socket fitting in clinical settings and alert amputees in home settings of excessive loading at the stump-socket interface, effectively preventing stump tissue breakdown at an early stage.
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paper_title: A digital light processing 3D printer for fast and high-precision fabrication of soft pneumatic actuators

paper_content:

Abstract In this paper, we built up a desktop digital light processing (DLP) 3D printer and fabricated multiple size soft pneumatic actuators integrally with fast speed and high precision. The printing process is based on the projection microstereolithography method. The composition of the printing system and key parameters during the printing process were presented. Evaluation experiments demonstrate that our printer can print objects with as small as 87.5 μm size features. We first printed single pneumatic net-works (pneu-net) actuators integrally and conducted a series of actuation experiments and finite element method analyses to test the actuators’ deformation capability. We further designed a soft pneumatic gripper containing three micro pneu-net actuators with 0.4 mm wide square air channels as well as 0.2 mm thick chamber walls and fabricated the gripper integrally in less than 30 min using our printer. The grasping capability of the gripper was verified through experiments as well. Results presented in this work prove the performance of the DLP printer we build up and show the convenience of fabricating micro soft pneumatic actuators integrally using DLP 3D printing approach with fast speed and high precision.
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paper_title: Digital Light Processing for high-brightness high-resolution applications

paper_content:

Electronic projection display technology for high-brightness applications had its origins in the Gretag Eidophor, an oil film-based projection system developed in the early 1940s. A number of solid state technologies have challenged the Eidophor, including CRT-addressed LCD light valves and active-matrix-addressed LCD panels. More recently, in response to various limitations of the LCD technologies, high-brightness systems have been developed based on Digital Light Processing technology. At the heart of the DLP projection display is the Digital Micromirror Device, a semiconductor-based array of fast, reflective digital light switches that precisely control a light source using a binary pulsewidth modulation technique. This paper describes the design, operation, performance, and advantages of DLP- based projection systems for high-brightness, high- resolution applications. It also presents the current status of high-brightness products that will soon be on the market.
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paper_title: Fabrication of biocompatible lab-on-chip devices for biomedical applications by means of a 3D-printing process

paper_content:

A new microfluidic assembly method for semiconductor-based biosensors using 3D-printing technologies was proposed for a rapid and cost-efficient design of new sensor systems. The microfluidic unit is designed and printed by a 3D-printer in just a few hours and assembled on a light-addressable potentiometric sensor (LAPS) chip using a photo resin. The cell growth curves obtained from culturing cells within microfluidics-based LAPS systems were compared with cell growth curves in cell culture flasks to examine biocompatibility of the 3D-printed chips. Furthermore, an optimal cell culturing within microfluidics-based LAPS chips was achieved by adjusting the fetal calf serum concentrations of the cell culture medium, an important factor for the cell proliferation.
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paper_title: Flexible three-dimensional measurement technique based on a digital light processing projector

paper_content:

A new method of 3D measurement based on a digital light processing (DLP) projector is presented. The projection model of the DLP projector is analyzed, and the relationship between the fringe patterns of the DLP and the fringe strips projected into the 3D space is proposed. Then the 3D shape of the object can be obtained by this relationship. Meanwhile a calibration method for this model is presented. Using this calibration method, parameters of the model can be obtained by a calibration plate, and there is no requirement for the plate to move precisely. This new 3D shape measurement method does not require any restrictions as that in the classical methods. The camera and projector can be put in an arbitrary position, and it is unnecessary to arrange the system layout in parallel, vertical, or other stringent geometry conditions. The experiments show that this method is flexible and is easy to carry out. The system calibration can be finished quickly, and the system is applicable to many shape measurement tasks.
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paper_title: Autonomous Chemical Sensing Interface for Universal Cell Phone Readout

paper_content:

Exploiting the ubiquity of cell phones for quantitative chemical sensing imposes strong demands on interfacing devices. They should be autonomous, disposable, and integrate all necessary calibration and actuation elements. In addition, a single design should couple universally to a variety of cell phones, and operate in their default configuration. Here, we demonstrate such a concept and its implementation as a quantitative glucose meter that integrates finger pumps, unidirectional valves, calibration references, and focusing optics on a disposable device configured for universal video acquisition.
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paper_title: Research of a Novel 3D Printed Strain Gauge Type Force Sensor †

paper_content:

A 3D printed force sensor with a composite structure developed by combining digital light processing (DLP) based printing and inkjet printing technologies is described in this paper. The sensor has cost effectiveness and time-saving advantages compared to the traditional sensor manufacturing process. During this work, the substrate of the force sensor was printed by a DLP based 3D printer using a transparent high-temperature resin, and the strain gauge of the force sensor was inkjet printed using poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT/PSS) conductive ink. Finite element (FE) simulation was conducted to find the print origin of the strain gauge. The relationship between the mechanical properties of the post-cured resin and the curing time was investigated and the resistance of the printed strain gauges was characterized to optimize process parameters. Afterward, the force sensor was characterized. Experimental results show that the sensitivity of the sensor is 2.92% N−1 and the linearity error is 3.1485% full scale (FS) within the range from 0 mN–160 mN, and the effective gauge factor of the strain gauge is about 0.98. The resistance drifting is less than 0.004 kΩ within an hour. These figures prove that the device can perform as a force sensor and 3D printing technology may have great applied potential in sensor fabrication.
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paper_title: Piezoelectric microphone via a digital light processing 3D printing process

paper_content:

In nature sensors possess complex interlocking 3D structures and extremely localized material properties that allow processing of incredibly complex information in a small space. Acoustic sensor design is limited by fabrication processes, often MEMS based, where there is limited scope for fully 3D creations due to planer fabrication methods. Here we investigate the application of 3D printing via digital light processing (DLP) to integrate piezoelectric, conductive and structural polymer layers to create a complete electro-mechanical device. We demonstrate a working piezoelectric acoustic sensor, capable of sending electric signals that can be picked up by pre-amp circuitry fabricated using a commercially available 3D printer. We show that the 3D printing of mechanically sensitive membranes with thicknesses down to 35 μm and tunable resonant frequencies is possible and further show it is possible to create a fully working electro-acoustic device by embedding 3D printed piezoelectric and conductive parts. Realizing this design opens up the possibility of generating truly 3D structured functional prints that may be used in bio-inspired design.
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paper_title: 3D Printing of Carbon Nanotubes-Based Microsupercapacitors

paper_content:

A novel 3D printing procedure is presented for fabricating carbon-nanotubes (CNTs)-based microsupercapacitors. The 3D printer uses a CNTs ink slurry with a moderate solid content and prints a stream of continuous droplets. Appropriate control of a heated base is applied to facilitate the solvent removal and adhesion between printed layers and to improve the structure integrity without structure delamination or distortion upon drying. The 3D-printed electrodes for microsupercapacitors are characterized by SEM, laser scanning confocal microscope, and step profiler. Effect of process parameters on 3D printing is also studied. The final solid-state microsupercapacitors are assembled with the printed multilayer CNTs structures and poly(vinyl alcohol)-H3PO4 gel as the interdigitated microelectrodes and electrolyte. The electrochemical performance of 3D printed microsupercapacitors is also tested, showing a significant areal capacitance and excellent cycle stability.
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paper_title: 4D Printing: Multi‐Material Shape Change

paper_content:

How might 4D printing overcome the obstacles that are hampering the rolling out and scaling up of 3D printing? Skylar Tibbits, Director of the Self-Assembly Lab at the Massachusetts Institute of Technology (MIT), describes how the Lab has partnered up with Stratasys Ltd, an industry leader in the development of 4D Printing, and is making the development of self-assembly programmable materials and adaptive technologies for industrial application in building design and construction its focus.
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paper_title: Occupancy Detection at Smart Home Using Real-Time Dynamic Thresholding of Flexiforce Sensor

paper_content:

Monitoring of the activities of the occupant is paramount important in the field of ambient-assisted living environment. Sensors are widely used to collect, store, and analyze on the continuous stream of data of the observation of their day-to-day activities. The output of any sensor may gradually change with time. It may come to a point where it becomes difficult to make a distinction between different situations from the sensor’s output. Due to the change of sensor’s output with time, it is hard for the system to discriminate very accurately between the regular states and the irregular states. This paper deals with the problems faced with the output of flexiforce sensors that happens when the sensor is in operation for a long period to monitor the activities of the inhabitant. A real-time dynamic thresholding has been designed and introduced to identify different situations clearly and avoid confusions regarding the output of the sensor used.
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paper_title: 4D printing smart biomedical scaffolds with novel soybean oil epoxidized acrylate

paper_content:

Photocurable, biocompatible liquid resins are highly desired for 3D stereolithography based bioprinting. Here we solidified a novel renewable soybean oil epoxidized acrylate, using a 3D laser printing technique, into smart and highly biocompatible scaffolds capable of supporting growth of multipotent human bone marrow mesenchymal stem cells (hMSCs). Porous scaffolds were readily fabricated by simply adjusting the printer infill density; superficial structures of the polymerized soybean oil epoxidized acrylate were significantly affected by laser frequency and printing speed. Shape memory tests confirmed that the scaffold fixed a temporary shape at -18 °C and fully recovered its original shape at human body temperature (37 °C), which indicated the great potential for 4D printing applications. Cytotoxicity analysis proved that the printed scaffolds had significant higher hMSC adhesion and proliferation than traditional polyethylene glycol diacrylate (PEGDA), and had no statistical difference from poly lactic acid (PLA) and polycaprolactone (PCL). This research is believed to significantly advance the development of biomedical scaffolds with renewable plant oils and advanced 3D fabrication techniques.
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paper_title: Active origami by 4D printing

paper_content:

Recent advances in three dimensional (3D) printing technology that allow multiple materials to be printed within each layer enable the creation of materials and components with precisely controlled heterogeneous microstructures. In addition, active materials, such as shape memory polymers, can be printed to create an active microstructure within a solid. These active materials can subsequently be activated in a controlled manner to change the shape or configuration of the solid in response to an environmental stimulus. This has been termed 4D printing, with the 4th dimension being the time-dependent shape change after the printing. In this paper, we advance the 4D printing concept to the design and fabrication of active origami, where a flat sheet automatically folds into a complicated 3D component. Here we print active composites with shape memory polymer fibers precisely printed in an elastomeric matrix and use them as intelligent active hinges to enable origami folding patterns. We develop a theoretical model to provide guidance in selecting design parameters such as fiber dimensions, hinge length, and programming strains and temperature. Using the model, we design and fabricate several active origami components that assemble from flat polymer sheets, including a box, a pyramid, and two origami airplanes. In addition, we directly print a 3D box with active composite hinges and program it to assume a temporary flat shape that subsequently recovers to the 3D box shape on demand.
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paper_title: Biomimetic 4D printing

paper_content:

Printed hydrogel composites with plant-inspired architectures dynamically change shape on immersion in water to yield prescribed complex morphologies.
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paper_title: 3D–4D Printed Objects: New Bioactive Material Opportunities

paper_content:

One of the main objectives of 3D printing in health science is to mimic biological functions. To reach this goal, a 4D printing might be added to 3D-printed objects which will be characterized by their abilities to evolve over time and under external stimulus by modifying their shape, properties or composition. Such abilities are the promise of great opportunities for biosensing and biomimetic systems to progress towards more physiological mimicking systems. Herein are presented two 4D printing examples for biosensing and biomimetic applications using 3D-printed enzymes. The first one is based on the printing of the enzymatic couple glucose oxidase/peroxidase for the chemiluminescent detection of glucose, and the second uses printed alkaline phosphatase to generate in situ programmed and localized calcification of the printed object.
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Title: 3D Printed Sensors for Biomedical Applications: A Review

Section 1: Introduction
Description 1: Introduce the importance of sensors and 3D printing in biomedical applications and provide a background context.

Section 2: Fused Deposition Modelling
Description 2: Discuss the process of Fused Deposition Modelling (FDM) and its applications in fabricating 3D printed sensors for biomedical use, with examples from recent research.

Section 3: Stereolithography
Description 3: Describe the Stereolithography (SLA) method, its advantages, and specific biomedical sensor applications, supported by examples from the literature.

Section 4: Polyjet Process
Description 4: Explain the Polyjet printing process, the materials used, and its specific applications in 3D printed biomedical sensors, with relevant examples.

Section 5: Selective Laser Sintering
Description 5: Explore the Selective Laser Sintering (SLS) process, the range of materials it can process, and its applications in creating biomedical sensors, citing recent studies.

Section 6: 3D Inkjet Printing
Description 6: Detail the 3D Inkjet Printing process, types of inks used, and its applications in biomedical sensing, with specific examples of research work.

Section 7: Digital Light Processing
Description 7: Cover the Digital Light Processing (DLP) technique, its photocuring process, and applications in biomedical sensors, along with examples from recent research.

Section 8: Current Challenges and Future Opportunities
Description 8: Analyze the current challenges in 3D printed biomedical sensors, discuss potential solutions, and explore opportunities for future research and development.

Section 9: Conclusions
Description 9: Summarize the key points discussed in the review, highlight the major findings, and provide final thoughts on the future prospects of 3D printed sensors in biomedical applications.