Synthetic homeostatic materials with chemo-mechano-chemical self-regulation

Abstract

Living organisms exhibit unique homeostatic abilities, maintaining tight control of their local environment through inter-conversions of chemical and mechanical energy and selfregulating feedback loops organized hierarchically across many length scales 1-7 . In contrast, most synthetic materials are incapable of undergoing continuous self-monitoring and self-regulating behavior due to their limited single-directional chemo-mechanical 7-12 or mechano-chemical 13, 14 modes. Applying the concept of homeostasis to the design of autonomous materials 15 would have transformative impacts in areas ranging from medical implants that help stabilize bodily functions to smart materials that regulate energy usage 2, 16, 17 . Here we present 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 organic, inorganic and biochemical reactions that undergo reversible, repeatable cycles synchronized with the motion of the microstructures and the driving external chemical stimulus. By exploiting a continuous feedback loop between various exothermic catalytic reactions in the nutrient layer and the mechanical action of the temperature-responsive gel, we then create exemplary autonomous, self-sustained homeostatic systems that maintain a user-defined parameter-temperature-in a narrow range. 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 chemomechano-chemical transduction at their core.The survival of organisms relies on homeostatic functions such as the maintenance of stable body temperature, blood pressure, pH, and sugar levels 1,3,[5][6][7] . This remarkable self-

Colossal positive and negative thermal expansion and thermosalient effect in a pentamorphic organometallic martensite

“…The isotropic expansion of form b results in large volumetric expansion with a V ¼ 255.5(3) Â 10 -6 K -1 , which, together with a, is among the largest values reported thus far. Indeed, the volumetric and some axial thermal expansion coefficients of the PHA polymorphs are higher than the coefficients that are deemed colossal, reported for Ag 3 [Co(CN) 6 ] (a V ¼ 160 Â 10 -6 K -1 , a a ¼ 150 Â 10 -6 K -1 and a c ¼ -130 Â 10 -6 K -1 ) by Goodwin et al 13,14 , and are comparable to those of a MOF (metal organic framework) material under vacuum (a V ¼ 300 Â 10 -6 K -1 , a a ¼ 230 Â 10 -6 K -1 and a c ¼ -170 Â 10 -6 K -1 ) reported by Omary and colleagues 15 , and of (S,S)-octa-3,5-diyn-2,7-diol (a V ¼ 47-241 Â 10 -6 K -1 , a a ¼ 515-156 Â 10 -6 K -1 , a b ¼ À 85 to À 63 Â 10 -6 K -1 and a c ¼ À 204 to À 45 Â 10 -6 K -1 ) reported by Barbour and colleagues 16 .…”

“…B iogenic mechanical processes in living organisms present important mechanistic and kinematic models for the design of biomimetic actuators [1][2][3] . The capability of rapid energy transfer through the dense and ordered packing of molecular single crystals evolves as a new platform for efficient actuation.…”

Biomimicry, Biofabrication, and Biohybrid Systems: The Emergence and Evolution of Biological Design

“…Inspired by the homeostatic abilities of biological systems, Aizenberg and co-workers have developed a hydrogel system with an internally modulated chemomechanical feedback loop that allows for self-monitoring and regulation. [27] This system, termed self-regulated mechanochemical adaptively reconfigurable tunable system, is composed of an array of microscale hydrogel pillars, or microfins, immersed in a liquid bilayer ( Figure 1B). Chemical stimulation of a catalyst in the top layer results in a change in the swelling properties of the hydrogel, "turning on" or triggering a conformation change in the microfins from an upright to a bent state.…”

Quantifying the bending of bilayer temperature-sensitive hydrogels

“…Stimuli-responsive hydrogels have been the subject of much scientific attention recently [1][2][3][4][5]. This category of hydrogels can respond to very small changes in temperature, pH, humidity, etc.…”