Stimuli-Responsive Ion-Diffusive Ultrasoft Hydrogel for Zero-Powered Bioelectronics

Bioelectronics are emerging devices applied for human that are a promising solution for self-care and smart healthcare. Among them, non-invasive bioelectronics such as electrical stimulation patches are considered as the realistic and feasible medical applications for minimizing anxiety in patients with low immune responses or toxicity problems. Accordingly, multifunctional soft materials, for instances, skin-adhesive, conductive hydrogel for application to non-invasive bioelectronics are essential. Moreover, the number of self-powered system without using extra power source for bioelectronics also has been reported, however, there are still have limitations that require specific movement or environment.<br/>Here in, we introduce a 1) stimuli-responsive ion-diffusive hydrogel (IDH) with optimized softness, skin-adhesive for bioelectronics and 2) a system capable of tissue vitalization by accumulating energy generated and lost spontaneously from humans contact with in daily life using. The IDH was synthesized by using polyacrylamide (PAAM), oxidized hyaluronic acid (OHA) and PEDOT:PSS with schiff-base and hydrogen bonding-based triple network. By tuning the oxidation rate of OHA, optimized the mechanical property of IDH which has similar elastic modulus with human skin (~ 19.24 kPa) and shear adhesion strength (~ 57 J/m2) which is optimized mechanical properties for patients comfortability. Furthermore, the IDH has electrical stimuli-responsive ion loading/releasing properties because of reduction/oxidation of PEDOT:PSS which is capable for iontophoretic drug releasing bioelectronics. The IDH shows higher ion loading efficeincy inside to IDH when DC electric field is applied, and also shows higher ion releasing and penetration to porcine skin when the opposite DC electric field is applied.<br/>The zero-powered system, called body-mediated energy loss conversion (BELC), is structurally designed system of stacked conductors and insulators. The BELC can convert energy loss from electronic devices and physical activity to usable energy via transfer through the human body as a medium. By applying IDH and the BELC system, body-mediated bioelectronics (BMB) patch was designed and fabricated. The BMB patch can internally concentrate electric field and various outputs during human activity (walking, running, typing on labtop, etc.) was measured (14.3 mV/mm of electric field output during running). Furthermore, iontophoretic ion-penetration through porcine skin during human activity was also investigated. The proposed multifunctional IDH is belived to be widely used for non-invasive bioelectronics and also BMB is expected to overcome the drawbacks of conventional bioelectronics and can pave the path to zero-powered bioelectronics with permanent operation.