Preparation and Sensing Performance of Camellia Saponin-based Conductive Hydrogel

Abstract

Eco-friendly, natural, biodegradable, and economical camellia saponin (S) was utilized as raw material to prepare a conductive hydrogel with excellent mechanical properties. First, camellia saponin was dissolved in a water/glycerol (G) mixture, followed by the addition of polyvinyl alcohol (PVA) and stirring at 105°C for 3 h. The solution was then subjected to freeze-thaw cycling at −20°C and 25°C to obtain polyvinyl alcohol-glycerol-camellia saponin (PGS) hydrogel. Subsequently, an iron chloride solution was added to undergo a metal chelation reaction, resulting in the formation of polyvinyl alcohol-glycerol-camellia saponin-ferric ion (PGSF) hydrogel consisting of polyvinyl alcohol, glycerol, camellia saponin, and Fe³⁺. In parallel, neat PVA (P), PVA/glycerol (PG) and PVA/camellia-saponin (PS) hydrogels were fabricated as benchmarks to compare mechanical, electrical and sensing characteristics. Coordination between ferric ions and camellia saponin markedly boosted both the mechanical robustness and charge-transport ability of the network. The optimised hydrogel sustained an ultimate elongation of 1 038 % and a tensile strength of 1.28 MPa. Under cyclic loading—150 % tensile strain and 50 % compressive strain—it displayed minimal hysteresis, evidencing excellent elastic stability. Electrically, the material exhibited a conductivity of 1.99 S m⁻¹ and a gauge factor of 2.48. When integrated into a flexible wearable sensor, it produced stable, reproducible relative-resistance profiles during flexion of the fingers, wrists, elbows and knees, demonstrating reliable real-time monitoring of human joint motion.