Anisotropic strain sensors to realize skin‐comparable performances

Abstract Conductive hydrogels (CHs) are promising candidates for wearable devices. However, it remains challenging for traditional CHs to realize a combination of self‐adhesive and skin‐comparable performances. Herein, a stretch‐induced orientation strategy was demonstrated to achieve this goal. The hydrogel was fabricated from poly(vinyl alcohol), aluminum sulfate, tannin acid, and deionized water, which exhibited skin‐comparable elastic modulus (26.3 kPa), stretchability (180%), and water content (87.6%). Meanwhile, it had anisotropic properties. For instance, the mechanical and anisotropy ratios between parallel and orthogonal directions were 1.77 and 2.02, respectively. Furthermore, the presence of free ions within regular conductive channels imparted stable conductivity (gauge factor of 2.2 within 200% strains), fast response (0.2 s), and low detect limit (a strain of 0.2%). Additionally, the existence of catechol groups from tannin acid enabled self‐adhesion ability (adhesion strength of 73.9 kPa). All of these merits show promising potential in wearable devices and electronic skins.