Self-oscillating gel

Here we report a novel polymeric gel which autonomously swells and deswells periodically in a closed homogeneous solution without any external stimuli, similar to autonomic phenomena in life such as heartbeat. The mechanical oscillation is achieved by inducing the Belousov-Zhabontinsky (BZ) reaction within the gel. We prepare a copolymer gel of N-isopropylacrylamide (IPAAm) in which ruthenium(II) tris(2,2'-bipyridine) (Ru(bpy)32+), a catalyst for the BZ reaction is covalently bonded to the polymer chain. The poly(IPAAm-co-Ru(bpy)3) gel swells and deswells at the oxidized and reduced states of Ru(bpy)3, respectively. The BZ reaction in the gel generates periodic redox changes of Ru(bpy)3, and the chemical oscillation induces mechanical oscillation of the polymer network.