High-Frequency Swelling/Deswelling Oscillation of Poly(Oligoethylene Glycol) Methacrylate-Based Hydrogel Microspheres with a Tris(2,2′-bipyridyl)ruthenium Catalyst

The swelling/deswelling oscillation of autonomously oscillating hydrogel microspheres (microgels) at a frequency close to that of the human heartbeat was accomplished. In this study, poly(oligoethylene glycol) methacrylate (pOEGMA)-based microgels that contain a tris(2,2′-bipyridyl)ruthenium catalyst were used to create oscillatory chemical systems via the Belousov–Zhabotinsky (BZ) reaction. The oscillating pOEGMA microgels can undergo the BZ reaction without irreversible aggregation at elevated temperatures or high substrate concentrations. By optimizing the chemical composition of the microgels and the BZ reaction conditions, a short swelling/deswelling oscillation period of ∼1.3 s was achieved in the dispersed state. Furthermore, in the assembled state, the microgels exhibited fast swelling/deswelling on the order of seconds (oscillation period: ∼6.2 s). The central concept of this study, that is, “high-frequency oscillation”, can be expected to benefit the development of advanced bioinspired actuators that imitate the human heartbeat.