Autonomous and Life-Like “Self-Oscillating” Polymer Gels as Novel Functional Softmaterials

Several types of stimuli-responsive polymer gels that reversibly swell and deswell in response to environmental changes have been developed by many researchers. By using these gels as “intelligent” or “smart” gels, many applications in soft actuators as artificial muscles, drug delivery systems, cell culture systems in tissue engineering, purification or separation systems, biosensors, shape memory materials, and molecular recognition systems, etc. have been explored.<br/>On the other hand, in 1996, the author reported “self-oscillating” polymer gels that spontaneously repeat swelling–deswelling changes in a closed solution without any on–off switching by external stimuli, such as heart muscle. They have attracted considerable attention as a new type of gel with an autonomous function that is clearly different from conventional stimuli-responsive gels. The autonomy in the gel is provided by the design, which creates a dissipative structure in the material. The gel has an energy-conversion system involving an oscillatory chemical reaction (called the Belousov–Zhabotinsky (BZ) reaction) which allows periodic mechanical motion of the polymer chain. Since the first report, the author has systematically developed self-oscillating polymer gels from fundamental behavior to construction and demonstration of material systems for potential applications in biomimetic materials, such as autonomous soft actuators, automatic transport systems, and functional fluids exhibiting autonomous sol–gel oscillations similar to those of the ameba. Recently, BZ gels with similar properties have sometimes been called “Yoshida gels”. In this presentation, the research developments and recent progress on self-oscillating polymer gels from the author’s group are summarized.