Less is more: A soft, self-actuated pump to simplify mechatronic devices

Modern mechatronic devices, right from industrial machinery to robots, have seen a drastic increase in complexity and intricacy. With sophisticated functionalities being unlocked with each passing day, there has been an inevitable rise in the number of components that the devices need. And although these advancements are undeniably impressive, the sheer bulkiness and large number of components are a major hindrance to the “miniaturization” and cost-effectiveness of these devices.

But what if, instead of using multiple bulky components, we find a smarter way to build them? This is what scientists, including Prof Shingo Maeda, Dr Zebing Mao (Smart Materials Laboratory, Shibaura Institute of Technology) and Dr. Vito Caccuciolo (Soft Transducers Laboratory, Institute of Microengineering, École Polytechnique Fédérale de Lausanne), have worked on, in a recent study published in Scientific Reports. The scientists 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 succeeded in creating a self-actuated microfluidic pump driven only by an oscillatory chemical reaction, which successfully produced “pressurized oil” (representing mechanical work). Prof Maeda, who led the study, says, “We propose a novel method to realize a simple pumping function using a single-component self-oscillating hydrogel and a membrane.”

In their study, the scientists 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 a lot of potential in mechatronic applications. But, their practical use has been challenging until now. Prof Maeda explains, “Previously reported BZ gels showed very small displacement and were only tested while submerged inside chemical baths, which clearly limits their potential applications.”

In this new study, the scientists overcame this hurdle using a new approach, which is much more promising thanks to an innovative implementation. Prof Maeda explains their methodology, “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.” The result of this 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 produce mechanical work in the form of pressurized oil. The scientists tested the approach both virtually and experimentally, showing that the proposed concept holds potential.

This study sheds light on the fundamental physical mechanisms of BZ gels and indicates a way to improve their mechanical performance. It is an important step toward bridging the technological gap that exists for converting oscillating chemical energy into mechanical energy to power useful devices. Some noteworthy examples of feasible 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 proposed by the scientists could act as a single-component power source in microfluidic systems, thereby simplifying their design, reducing their cost, and broadening their applicability.

The research team is optimistic about taking their work to the next level in the future, which will involve the optimization of their design through chemical and mechanical methods. This will be key for bringing forth a paradigm shift in the design of electromechanical devices by taking on a more bio-inspired turn. In this regard, Prof Maeda concludes, “Self-actuating pumps bode to break the wall of complexity faced by certain robotic systems with an increasing number of functions, enabling the development of truly smart multi-functional machines.”

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Title of original paper: Autonomous oil flow generated by self-oscillating polymer gels

Journal: Scientific Reports

DOI: 10.1038/s41598-020-69804-3

Shibaura Institute of Technology (SIT) is a private university with campuses in Tokyo and Saitama. Since the establishment of its predecessor, Tokyo Higher School of Industry and Commerce, in 1927, it has maintained “learning through practice” as its philosophy in the education of engineers. SIT was the only private science and engineering university selected for the Top Global University Project sponsored by the Ministry of Education, Culture, Sports, Science and Technology and will receive support from the ministry for 10 years starting from the 2014 academic year. Its motto, “Nurturing engineers who learn from society and contribute to society,” reflects its mission of fostering scientists and engineers who can contribute to the sustainable growth of the world by exposing their over 8,000 students to culturally diverse environments, where they learn to cope, collaborate, and relate with fellow students from around the world.

Website: https://www.shibaura-it.ac.jp/en/

Shingo Maeda received BS, MS, and PhD degrees in Applied Physics from Waseda University, Japan. During 2015-2016, he worked with Prof Cecilia Laschi’s group at the BioRobotics Institute of the Scuola Superiore Sant’Anna in Pisa, Italy, as a visiting professor. He is currently an Associate Professor at the Department of Engineering Science and Mechanics in Shibaura Institute of Technology, Japan, where he heads the Smart Materials Laboratory. His research interests include chemical robotics, soft robotics, and smart materials.

The study was supported by the Japan Society for the Promotion of Science under Grants-in-Aid for Scientific Research programs (Grant-in-Aid for Scientific Research (B), project no. JP16H04306 and Grant-in-Aid for Scientific Research on Innovative Areas [Research in a proposed research area] 18H05473).