Contraction waves in self-oscillating polymer gels

As one type of active soft matter, polymer gels coupled mechanical and chemical oscillations, such as Belousov–Zhabotinsky (BZ) gels are widely researched and developed into biomimetic actuators. In the previous literature, the self-oscillating BZ cylindrical gels can generate swelling waves along their longitudinal direction when they are operated without external stimuli. Here, we explore the contraction waves of BZ gels by the means of changing the external mechanical boundary. We firstly synthesize the self-oscillating gel, which is composed of N-isopropyl acrylamide (NIPAAm) gel and a covalently bound metal catalyst of the ruthenium complex. Then, the stress-curve of the gels is investigated to evaluate the elastic modulus of each state of the BZ gel and verified our method. Finally, we investigate the effects of several factors including initial diameters of the gel, various strain, and measuring process on the generation of contraction waves in gels undergoing the BZ reaction by experiments.