Novel oscillating swelling-deswelling dynamic behaviour for pH-sensitive polymer gels

Novel dynamics for polymer gel membranes demonstrating rhythmic swelling-deswelling oscillations were achieved by coupling temperature and pH-sensitive poly (N-isopropylacrylamide-co-acrylicacid-co-butylmethacrylate) gels with non-linear oscillating chemical reactions. In a pH-oscillating solution these gels exhibited a repetitive pulsatile mechanical motion with a constant period and amplitude similar to that of a heartbeat. The oscillating swelling and deswelling kinetics of gels have been analysed theoretically for characteristic response times for gel swelling and deswelling and for external pH changes. The experimentally observed oscillation profiles are well simulated by superposition of theoretical equations modified by introduction of an external pH change to the intrinsic swelling-deswelling behaviour for the gels. The novel gel dynamics generating rhythmical pulsatile motion may create new possibilities for applying polymer gels as a functional materials that work under dynamic oscillating states similar to autonomous phenomena in living systems.