Living organisms exhibit unique homeostatic abilities, maintaining tight control of their local environment through inter-conversions of chemical and mechanical energy and self-regulating feedback loops organized hierarchically across many length scales. In contrast, most synthetic materials are incapable of undergoing continuous self-monitoring and self-regulating behavior. Applying the concept of homeostasis to the design of autonomous materials would have transformative impacts in areas ranging from medical implants that help stabilize bodily functions to smart materials that regulate energy usage. We have explored a versatile strategy for creating self-regulating, self-powered, homeostatic materials capable of precisely tailored chemo-mechano-chemical feedback loops at the nano/microscale.
We design a bilayer system with hydrogel-supported, catalyst-bearing microstructures, which are separated from a reactant-containing “nutrient” layer. Reconfiguration of the gel in response to a stimulus induces the reversible actuation of the microstructures in and out of the nutrient layer and serves as a highly precise “on/off” switch for chemical reactions. We apply this design to trigger a variety of processes—fluorescence quenching, catalytic decomposition of hydrogen peroxide, or a complex enzymatic reaction—that undergo reversible, repeatable cycles synchronized with the motion of the microstructures and the driving external chemical stimulus.
In this manner, we create exemplary internally-regulated, self-sustained homeostatic systems, SMARTS (Self-regulated Mechano-chemical Adaptively Reconfigurable Tunable System), that maintain a user-defined parameter—temperature—by exploiting a continuous feedback loop between various exothermic catalytic reactions in the nutrient layer and the mechanical action of the temperature-responsive gel. The experimental results were validated using computational modeling that qualitatively captured the essential features of the self-regulating behavior and provided additional criteria for the optimization of the homeostatic function, subsequently confirmed experimentally. This design is highly customizable due to the broad choice of chemistries, tunable mechanics, and physical simplicity, thus promising exciting applications in autonomous systems with chemo-mechano-chemical transduction at their core.
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