Physically retained charge-dense interfaces enhance piezoionic sensing under physiologically relevant ionic...

Piezoionic hydrogels convert mechanical deformation into ionic signals through pressure-driven ion migration, offering self-powered operation and mechanical compliance suitable for integration with biological tissues. However, conventional piezoionic systems rely on the redistribution of freely mobile ions, making their output strongly dependent on maintaining an optimized internal electrolyte composition and potentially attenuated under physiologically relevant ionic conditions. Here, we report a piezoionic hydrogel designed to retain charge-dense interfaces within a hydrated polymer network. Polyamine-looped silica (PLS) nanoparticles are retained within a polyacrylamide (PAM) scaffold with no detectable particle loss under the tested hydration conditions, while their surface-loop architecture is proposed to promote topological interpenetration with the surrounding polymer network. The positively charged interfaces are proposed to favor the local association of anionic species, thereby contributing to asymmetric ion redistribution during compression. Comparisons with bare silica and amine-functionalized silica (AFS) nanoparticles indicate that the enhanced response is associated with both the charge characteristics and retention of the PLS-containing interfaces. The PLS-containing architecture maintains mechanical recoverability over the tested 20 compression cycles and produces reproducible piezoionic responses over 100 cycles. The PAM/PLS hydrogel exhibits a piezoionic voltage coefficient of 62 mV kPa^-1 in 0.1 M NaCl and generates an approximately 20-fold higher voltage than pristine PAM under a 1.5 kPa load. It also distinguishes the tested pressure levels and retains a detectable voltage during short-term hold loading for up to 20 s. Proof-of-concept measurements further demonstrate repeatable pressure-correlated voltage responses over an approximately 6000-s test period in a 1× PBS bath and detectable responses through porcine-skin barriers. These findings establish the retention of charge-dense interfaces as a material design strategy for enhancing piezoionic sensing under physiologically relevant ionic conditions.