Percolation-controlled mixed ionic-electronic transport in chitosan/agarose/polypyrrole hydrogels for metal-free...

Designing soft materials that simultaneously achieve skin-matching mechanics, electronic functionality, and sustainable processing remains a central challenge in biointegrated electronics. Here, we report a dual biopolymer hydrogel composed of chitosan and agarose in which polypyrrole (PPy) is polymerized in situ to generate a percolated mixed ionic-electronic network for metal-free hydrogen peroxide (H₂O₂) sensing. By systematically varying the PPy content (0.5-12.5 wt%), we demonstrate a composition-dependent transition from ionically dominated transport to a percolated PPy conductive pathway, as evidenced by cyclic voltammetry, conductivity measurements, and impedance spectroscopy. Concurrently, increasing PPy content induces controlled pore compaction, reduced swelling, enhanced hydrolytic stability, and significant mechanical reinforcement, with Young's modulus values (1.73-3.41 MPa) within the physiological range of human skin. The optimized hydrogel exhibits a sensitivity of 146.3 ± 5.9 μA cm^-2 mM^-1, a detection limit of 6.3 ± 0.2 μM, and excellent linearity (R² = 0.9967) over 0-10 mM H₂O₂ concentration range. Moreover, the hydrogel selectivity toward H₂O₂ as well as its reusability and long-term storage were confirmed. This work establishes design principles for integrating percolated conducting polymer networks within sustainable biopolymer matrices to engineer mechanically compliant, high-performance electrochemical sensing platforms.