As electromechanical devices become increasingly small and complex, the number of required components becomes a limiting factor. Researchers have tapped into the potential of hydrogels driven by oscillating chemical reactions to create a self-actuated, single-component pump. This device could act as a practical power source for microfluidic systems and highlights the potential of soft, bio-inspired machinery in mechatronic devices.

Modern mechatronic devices, from industrial machinery to robots, have seen a drastic increase in complexity and intricacy. With sophisticated functionalities, there has been a rise in the number of components that the devices need. The sheer bulkiness and large number of components are a major hindrance to the miniaturization and cost-effectiveness of these devices.

Instead of using multiple bulky components, the researchers explored the possibility of various components of an electromechanical device — like the power supply, actuators, and control system — being reduced to a single piece of hydrogel. In doing this, they created a self-actuated microfluidic pump driven only by an oscillatory chemical reaction, which successfully produced “pressurized oil” (representing mechanical work).

They focused on a unique type of oscillatory chemical reaction that belongs to the Belousov–Zhabotinsky (BZ) class of reactions. Conventionally, a chemical reaction involves a reactant that gives rise to a product to reach a state of equilibrium. But BZ reactions, which involve bromine and an oxidizing agent, produce a system that never reaches chemical equilibrium; instead, it goes back and forth between various states.

Previously, researchers had observed that hydrogels and other polymers housing a BZ reaction (termed BZ gels) were capable of autonomous motion because the reaction caused slight and periodic structural changes, thus showing potential in mechatronic applications. But their practical use has been challenging until now. Previously reported BZ gels showed very small displacement and were only tested while submerged inside chemical baths, which clearly limits their potential applications.

The researchers overcame this hurdle by first producing BZ gels and pre-stretching them, which increases the mechanical work that can be extracted at each BZ cycle. Then, the whole gel and its surrounding chemical solution are completely encapsulated. Finally, the mechanical work produced by the swelling and contraction of the gel is transferred to an external oil through the deformation of a stretchable membrane. The result is a self-actuating pump solely driven by the oscillating reaction that can move fluids back and forth like an artificial “heart” for machines and that can produce mechanical work in the form of pressurized oil. The team tested the approach both virtually and experimentally, showing that the proposed concept holds potential.

This work helps bridge the technological gap that exists for converting oscillating chemical energy into mechanical energy to power useful devices. Examples of long-term applications of pumps made using BZ gels are in the field of microfluidics including drug delivery systems, DNA microarrays for biomedical research, and many other biotechnological and nanotechnological tools. The self-actuating pump could act as a single-component power source in microfluidic systems, thereby simplifying their design, reducing their cost, and broadening their applicability.

Future work will involve the optimization of the design through chemical and mechanical methods. The self-actuating pumps could solve the problem of complexity faced by robotic systems with an increasing number of functions, enabling the development of truly smart multifunctional machines.

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