Chemomechanics of Self-Oscillating Gels

Biological materials such as cardiac and skin tissue exhibit the unique capacity to transduce mechanical stimuli into propagating electrical and chemical signals throughout the body. Few synthetic materials have been engineered to produce communicative chemical signals in response to mechanical input, though such synthetic material analogues could enable devices that mimic biological tissues and pressure sensitive processes whereby molecular mechanoreceptors enable rapid and localized transmission of chemical signals. In this thesis, self-oscillating polymer gels comprising N-isopropylacrylamideco-Ru(bpy)3 are synthesized in order to elucidate chemical and mechanical (chemomechanical) coupling in synthetic, stimuli-responsive materials, and to design mechanically induced, oscillatory signaling systems. N-isopropylacrylamide-co-Ru(bpy)3 gels represent a unique class of polymeric materials known as BZ gels, that are capable of undergoing the BelousovZhabotinsky (BZ) self-oscillating reaction. When submerged in stagnant solution containing chemical reactants, and in the absence of continuously applied external perturbation, the BZ gels exhibit sustained, colorful oscillations due to the changing oxidation state of Ru(bpy)3 transition metal complex. By measuring temperature profiles of the BZ gel, we showed that the swelling behavior and hydrophobicity of the gel depend on the oxidation state of covalently bound Ru(bpy)3. Using timelapse microscopy, we recorded the BZ oscillations and tracked the far from equilibrium chemical behavior exhibited by the gels. At constant system temperature, the BZ reaction induced cyclic changes in the osmotic pressure of the gel, resulting in periodic gel swelling and shrinking. Such volumetric changes, driven by the BZ reaction, are largest (22 %) when the edge length of the gel is relatively short (0.6 mm), and pattern formation is dominated by slow kinetics. Therefore, by quantifying the chemomechanical behavior of BZ gels, we demonstrated that the gels convert chemical oscillations into mechanical actuation. Next, we sought to design novel stimuli-responsive behavior in BZ gels by devising methods for mechanically triggering oscillations in quiescent gels. When sufficient macroscopic compressive stress was applied to submerged, non-oscillating gels, BZ oscillations were triggered and persisted until the stress was removed. To our knowledge, BZ gels represent the first synthetic hydrogel capable of producing oscillations in response to mechanical stimuli. To establish the conditions conducive to mechanical triggering, we quantified the chemical regimes for which BZ gels spontaneously oscillate or fail to oscillate. In doing so, we demonstrated that such regimes are governed