Artificial Perspiration Membrane by Programmed Deformation of Thermoresponsive Hydrogels

Abstract

Thermal management is essential for living organisms and electronic devices to survive and maintain their own functions. However, developing flexible cooling devices for flexible electronics or biological systems is challenging because conventional coolers are bulky and require rigid batteries. In nature, skins help to maintain a constant body temperature by dissipating heat through perspiration. Inspired by nature, an artificial perspiration membrane that automatically regulates evaporation depending on temperature using the programmed deformation of thermoresponsive hydrogels is presented. The thermoresponsive hydrogel is patterned into pinwheel shapes and supported by a polymeric rigid frame with stable adhesion using copolymerization. Both shape of the valve and mechanical constraint of the frame allow six times larger evaporation area in the open state compared to the closed state, and the transition occurs at a fast rate (≈1 s). A stretchable membrane is selectively coated to prevent unintended evaporation through the hydrogel while allowing swelling or shrinking of the hydrogel by securing path of water. Consequently, a 30% reduction in evaporation is observed at lower temperature, resulting in regulation of the skin temperature at the thermal model of human skins. This simple, small, and flexible cooler will be useful for maintaining temperature of flexible devices.

Highly Sensitive On‐Skin Temperature Sensors Based on Biocompatible Hydrogels with Thermoresponsive Transparency and Resistivity

“…[10] Numerous previous works have been devoted to fabricating wearable temperature sensors based on hydrogels that can vary their electrical resistance as a result of changes in ion conductivity [11][12][13][14][15]24,25] or volume due to swelling/contraction with temperature. [16][17][18] Thermoresponsive hydrogels (TRHs) have played a crucial role in a variety of temperature-adaptive applications for actuators, [19] membranes, [20] displays, [21] and electrolytes [22] due to their intelligent thermo-responsive transitions. TRHs are classified by the two types of volume transition that they can undergo the lower critical solution temperature (LCST) or the upper critical solution temperature (UCST).…”

Smart and Biomimetic 3D and 4D Printed Composite Hydrogels: Opportunities for Different Biomedical Applications

“…In the field of actuator applications, stimulus-responsive materials have been highly enticed by the reversible change of form, which can be initiated by diverse external inputs. A number of actuators have been employed as hinges and valves in combination with 4D printing technologies [ 334 , 335 ]. Roach et al used the hybrid print of liquid crystal elastomers (LCE), soft substrates, and conductive wires, which collected and positioned a ball when the current was on and off [ 336 ].…”

Recent Impact of Microfluidics on Skin Models for Perspiration Simulation

“…Kim et al [ 53 ] also used a hydrogel to fabricate an artificial perspiration membrane. However, their aim was to create a refrigeration system inspired in the sweating mechanism.…”

“…( c ) Schematic of the artificial perspiration membrane for heat dissipation developed by Kim et al [ 53 ]. Adapted with permission from [ 53 ]. Copyright 2020, John Wiley and Sons.…”