Wrinkled structure conductive hydrogels of chitosan-Fe³⁺-Polyacrylic acid for sensors

Chitosan-based conductive hydrogels have been applied in the fields of electronic skin and biomedical devices due to their antibacterial and conductivity properties. It is demanded that conductive hydrogels process excellent mechanical properties and sensing sensitivity in practical applications. In this work, ferric chloride aqueous solution was dripped into a solution of chitosan and acrylic acid, after which the acrylic acid was in situ polymerized to synthesis the chitosan-Fe³⁺-polyacrylic acid hydrogels (CS-Fe³⁺-PAA). The differential swelling behavior between chitosan ferric ion microgels and polyacrylic acid was used to construct a wrinkled structure of CS-Fe³⁺-PAA. The energy dissipation effect of chitosan ferric ion microgels and the resulting wrinkled structure enabled CS-Fe³⁺-PAA to exhibited excellent mechanical properties and high sensitivity. In the large strain range of 800%~1000%, the sensitivity factor (GF) of CS-Fe³⁺-PAA reached a value of 25.32. The toughness of hydrogels was 2.54 MJ·m⁻³, with elongation at break of 1100% and tensile strength of 0.6 MPa. The CS-Fe³⁺-PAA strain sensor has been successfully used to detect various human activities, including bending movements of joints such as fingers, elbows, and knees, as well as subtle actions such as speaking and swallowing. The unique wrinkled structure provides design ideas and methods for chitosan-based conductive hydrogels with high toughness and sensitivity.