Multifunctional Strain/Pressure Sensor Based on Ag@Polydopamine Nanohybrid Methacrylamide Chitosan/Polyacrylamide Hydrogel for Healthcare Monitoring

Hydrogels have emerged as promising candidates for flexible sensors due to their softness, biocompatibility, and tunable physicochemical properties. However, achieving synchronous satisfaction of conformality, conductivity, and diverse biological functions in hydrogel sensors remains a challenge. Here, we proposed a multifunctional hydrogel sensor by incorporating silver-loaded polydopamine nanoparticles (Ag@PDA) into a thermally cross-linked methacrylamide chitosan (CSMA) and acrylamide network, namely, Ag@PDA/(CSMA-PAM). The Ag@PDA/(CSMA-PAM) hydrogel showed the capability to respond effectively to both strain and pressure, enabling its independent application as either a strain sensor or a pressure sensor. The sensitivity of the hydrogel can reach 2.13 within the strain range of 65 to 150%, exhibiting a response and recovery time of 550 ms when utilized as a strain sensor. In contrast, its sensitivity was 0.07 kPa^-1 during pressures ranging from 0 to 2.15 kPa, with a response and recovery time of 136 ms when employed as a pressure sensor. Additionally, the hydrogel sensor demonstrated high linearity (0.998 for strain and 0.98 for pressure), stable cycling ability (500 cycles), and low detection limit (0.5% for strain and 150 Pa for pressure). Moreover, the Ag@PDA/(CSMA-PAM) hydrogel exhibited good stability and reliability for a variety of practical applications, including the detection of subtle and large deformations, as well as real-time physiological activity monitoring. Further, owing to the bioactive components of chitosan and Ag@PDA present in the hydrogel, the Ag@PDA/(CSMA-PAM) sensor exhibited satisfactory biocompatibility along with excellent antioxidant and antibacterial activities, making it highly promising for applications as wearable sensors in personalized healthcare.