Self-Oscillating Polymer Gels, Vesicles, Micelles, Coacervates, Linear Polymers Exhibiting Life-Like Autonomous Behaviors

In 1996 [1], 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. 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 amoeba [2]. BZ gels with similar properties have sometimes been called “Yoshida gels” [3]. Further optimal design such as direction control of movement were carried out. In particular, the myocardium repeats expansion and contraction in a uniaxial direction. In order to give the self-oscillating gel such anisotropic deformation, by introducing a layered structure like muscle fibers, the direction of contraction was controlled [4].<br/>Further, by cyclically applying external mechanical stimulation to the BZ gels, it was possible to find resonance, either with the stimulation’s fundamental frequency or an n × or (1/n) × harmonic of it, and then the system kept a “memory” of the resonant oscillation period and maintained it post stimulation, demonstrating an entrainment effect [5]. These findings help bridge the functions of biological systems with nonequilibrium chemical physics and pave the pathway to study the complicated biological problems using simpler biomimicking chemophysical systems.<br/>Cell membranes in living organisms exhibit a fluctuating phenomenon with marginal undulations. Since this phenomenon is closely related to many important life phenomena such as cell motility, transport of intercellular substances, and cell division, many attempts have been made to artificially reproduce and understand the membrane fluctuation phenomenon. When a large hollow capsule-type self-oscillating gel is fabricated, the propagation of chemical waves on the surface causes a unique cell-like fluctuation and buckling of the gel [6]. By analyzing the fluctuation in detail, we will explore the meaning of the biomembrane fluctuation phenomenon and its application as an artificial cell.<br/>References<br/>[1] R. Yoshida, T. Takahashi, T. Yamaguchi and H. Ichijo: <i>J. Am. Chem. Soc.</i>, <b>118</b>, 5134 (1996).<br/>[2] R. Yoshida: <i>Polym. J.</i>, <b>54</b>, 827 (2022).<br/>[3] I.L. Mallphanov and V.K. Vanag: <i>Russ. Chem. Rev.</i>, <b>90</b>, 1263 (2021).<br/>[4] W.S. Lee, T. Enomoto, A.M. Akimoto and R. Yoshida: <i>Chem. Mater.,</i> <b>36</b>, 2007 (2024).<br/>[5] T. Geher-Herczegh, Z. Wang, T. Masuda, N. Vasudevan, R. Yoshida and Y. Hayashi: <i>PNAS</i>, <b>121</b>, e2320331121 (2024).<br/>[6] W.S. Lee, T. Enomoto, A.M. Akimoto and R. Yoshida: <i>Mater. Horiz,</i> <b>10</b>, 1332 (2023).