Skin-Inspired Patterned\nHydrogel with Strain-Stiffening\nCapability for Strain Sensors

Abstract

Flexible materials with ionic conductivity and stretchability\nare\nindispensable in emerging fields of flexible electronic devices as\nsensing and protecting layers. However, designing robust sensing materials\nwith skin-like compliance remains challenging because of the contradiction\nbetween softness and strength. Herein, inspired by the modulus-contrast\nhierarchical structure of biological skin, we fabricated a biomimetic\nhydrogel with strain-stiffening capability by embedding the stiff\narray of poly(acrylic acid) (PAAc) in the soft polyacrylamide (PAAm)\nhydrogel. The stress distribution in both stiff and soft domains can\nbe regulated by changing the arrangement of patterns, thus improving\nthe mechanical properties of the patterned hydrogel. As expected,\nthe resulting patterned hydrogel showed its nonlinear mechanical properties,\nwhich afforded a high strength of 1.20 MPa while maintaining a low\ninitial Young’s modulus of 31.0 kPa. Moreover, the array of\nPAAc enables the patterned hydrogel to possess protonic conductivity\nin the absence of additional ionic salts, thus endowing the patterned\nhydrogel with the ability to serve as a strain sensor for monitoring\nhuman motion.