Evolution of self-oscillating polymer gels as autonomous polymer systems

Abstract

We have developed ‘self-oscillating’ gels that undergo spontaneous cyclic swelling–deswelling changes without any on–off switching of external stimuli, as with heart muscle. The self-oscillating gels were designed by utilizing the Belousov–Zhabotinsky (BZ) reaction, an oscillating reaction, as a chemical model of the tricarboxylic acid cycle. We have systematically studied these polymer gels since they were first reported in 1996. Our studies represent innovative research, creating new concepts of functional gels and expanding their potential, and they have attracted attention in many research fields and have inspired related studies. Here, our recent progress on self-oscillating polymer gels is summarized. We developed ‘self-oscillating’ polymer gels that undergo spontaneous cyclic swelling–deswelling changes without any on–off switching of external stimuli like a heart muscle. Here, our recent progress on the self-oscillating polymer gels was summarized. Muscles and other soft tissues in the body experience spontaneous rhythmic changes, such as a heartbeat, hormonal secretion and the cell cycle, without requiring external stimulation. Ryo Yoshida and Takeshi Ueki from the University of Tokyo, Japan, review their team's progress to develop polymer gels that freely undergo cyclic swelling and shrinking. Although tremendous efforts to mimic biological systems have generated numerous synthetic responsive materials for smart tissue engineering and therapeutic applications, these existing systems lack autonomy and depend on induced pH, temperature and other environmental fluctuations to operate. In contrast, the team's gels rely on the oscillating Belousov–Zhabotinsky reaction — a metal-catalyzed oxidation reaction that exhibits spontaneous periodic temporal and spatial patterns. The self-oscillating gels have applications that include biomimetic actuators and tubular intestine-like mass transport systems, providing new perspectives for materials science, robotics and biophysics.