Surface Microcolumn-Structured PAMg-Based Hydrogels with Superior Weather Resistance for Flexible Pressure Sensors

Abstract

Accompanying the rapid growth of wearable electronics, flexible hydrogel pressure sensors have garnered significant attention due to their promising application in health monitoring and human–machine interfaces. However, traditional hydrogels suffer from water evaporation under ambient conditions, resulting in structural changes and functional decline. In this work, a series of polyacrylamide/gelatin (PAMg) hydrogels with different diameters of microcolumn structure were fabricated via a straightforward template method. The obtained PAMg hydrogels were further treated with composite polyols to improve weather resistance. Using the as-prepared PAMg hydrogel as a sensing medium, sandwich-structured hydrogel pressure sensors were assembled. Combined with equivalent circuit simulation and in situ structural characterization, the obvious variations in electric double-layer capacitance at the hydrogel–electrode interface and induced capacitance between electrodes, which originate from the microcolumn deformation under loading, effectively enhance the capacitance sensing performance of the sensors. Investigations of the effect of microcolumn diameter on sensing performance reveal that the decrease in microcolumn diameter can improve the sensitivity of the sensor. Nevertheless, an excessively small microcolumn diameter leads to insufficient mechanical strength of the microcolumns and results in collapse during tests. Notably, the sensor based on PAMg hydrogels with 600 μm microcolumn diameter exhibits a stable capacitance response over a wide strain and pressure range from 0.01% strain (0.15 kPa) to 50% strain (150 kPa) as well as excellent fatigue resistance (1000 cycles). Moreover, these sensors illustrate precise electrical response to various external stimuli, including static force, temperature, joint movement, etc. Meanwhile, the sensors possess outstanding environmental tolerance and anti-overload capability, thereby enhancing their practical utility.