Scientists from the Smart Materials Laboratory at Shibaura Institute of Technology and the Soft Transducers Laboratory at the Institute of Microengineering, École Polytechnique Fédérale de Lausanne, have developed a method for transforming bulky components in industrial machinery into a piece of hydrogel, thereby making miniaturization possible for such devices.

To demonstrate, the scientists used a single piece of hydrogel to serve as typically bulky components such as the power supply, actuators and control systems, to construct a self-actuated microfluidic pump powered by an oscillatory chemical reaction, which subsequently produced pressurized oil.

"We propose a novel method to realize a simple pumping function using a single-component self-oscillating hydrogel and a membrane," said professor Shingo Maeda from the Shibaura Institute of Technology .

Belousov–Zhabotinsky hydrogel in solution. Source: Shibaura Institute of TechnologyBelousov–Zhabotinsky hydrogel in solution. Source: Shibaura Institute of Technology

To achieve this, the scientists relied on a type of oscillatory chemical reaction derived from the Belousov-Zhabotinsky (BZ) class of reactions. Generally, a chemical reaction relies on a reactant that encourages a product to achieve a state of equilibrium. However, the BZ reactions, which include bromine and an oxidizing agent, generate a system that never achieves chemical equilibrium, alternating between different states, instead. However, the team previously observed hydrogels and other polymers playing host to a BZ reaction (called BZ gels) capable of autonomous movement due to the reaction producing subtle and frequent structural changes, showing significant potential in mechatronic applications, which had previously been a challenge.

According to Professor Maeda: "Previously reported BZ gels showed very small displacement and were only tested while submerged inside chemical baths, which clearly limits their potential applications."

As such, the scientists settled on a new approach. "First, we produce BZ gels and pre-stretch 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," explained Maeda. The outcome of their research is the self-actuating pump driven entirely by the oscillating reaction that moves the fluids back and forth, producing mechanical work in the shape of pressurized oil.

Some potential examples of applications of BZ gel pumps include use cases in the microfluidics field, including drug delivery systems, DNA microarrays for biomedical research and other biotechnological and nanotechnological tools.

The research appears in the journal Scientific Reports.

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