Adaptive hydrogels with spatiotemporal stiffening using pH-modulating enzymes

Abstract

Biological systems achieve adaptive mechanical responses through reaction-diffusion processes that couple chemical wave propagation to structural transitions. Although synthetic hydrogels with enzymatic reactions offer a platform for replicating such autonomous behavior, the mechanistic principles governing chemomechanical transduction remain poorly understood. Here, we present a glucose oxidase-embedded polyacrylamide-alginate hydrogel with slower transduction kinetics that enable independent resolution of chemical waves and mechanical adaptation. Enzymatic pH waves propagate at 15-44 um/min, triggering calcium-mediated alginate crosslinking through pH-responsive calcium-EDTA dissociation. Independent tracking of chemical and mechanical waves reveals that mechanical wavefronts (12 um/min) lag behind chemical propagation, establishing transduction as the rate-limiting step in this chemomechanical coupling. Remarkably, the enzymatic system must continuously supply chemical energy to both propagate the chemical wave and drive ongoing mechanical transitions, imposing energetic costs on reaction-diffusion beyond kinetic constraints alone. Our adaptive system achieves up to 2.1-fold increase in stiffness and enables autonomous conversion of localized stimuli into system-wide mechanical responses. These mechanistic insights establish design principles for engineering adaptive materials with predictable spatiotemporal control in soft robotics and biomedical applications.