Ryo Yoshida1
The University of Tokyo1
Many kinds of stimuli-responsive polymer gels that exhibit reversible swelling-deswelling change in response to environmental changes have been developed. New functional gels called “intelligent” or “smart” gels have been created, and their applicationsto bio- or biomimetic materials such as actuator (artificial muscle), drug delivery systems, tissue engineering, purification or separation systems, biosensor, shape memory materials, molecular recognition systems, etc. has been exploited. Other than stimuli-responsive function, one of characteristic and important behaviors in living systems is autonomous oscillation such as heartbeat. However, there are few studies on polymer and gel systems undergoing self-oscillation under constant condition without any on-off switching of external stimuli. If such autonomous systems can be realized by using completely synthetic polymers, unprecedented biomimetic materials may be created. From this viewpoint, we developed “self-oscillating” polymer 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 an oscillating reaction called the Belousov-Zhabotinsky reaction, as a chemical model of the TCA cycle in living systems. We have systematically studied these self-oscillating polymer gels since they were first reported in 1996 (JACS). Potential applications of the self-oscillating polymers and gels include several kinds of functional material systems such as biomimetic actuators, mass transport systems and functional fluids. Recently, amoeba-like motion with autonomous sol-gel oscillation was realized. In the BZ reaction, the external addition of an oxidant is required to initiate the oxidation process; in living systems, it is realized by intracellular moieties such as ubiquinone. For further evolution of self-oscillating polymers into autonomous bio-inspired materials, a design imparting macroscopic physical property changes via built-in oxidation systems is key. We achieved an amoeba-like autonomous sol-gel oscillation without the external addition of oxidants by introducing an oxidizing moiety in a self-oscillating triblock terpolymer and coupling the oscillation of macroscopic physical properties with that of the microscopic structure due to spontaneous oxidation. The achievement reported here can pave the way to the creation of artificial life systems. In this talk, our recent progress on the self-oscillating polymer gels is summarized.