Chitosan/Poly( <i>N</i> -isopropylacrylamide- <i>co</i> -acrylamide) Near-Infrared-Responsive Hydrogel: Preparation, Characterization, and Performance Analysis

In order to enhance the actuation performance of photoresponsive hydrogels in view of their slow response rate and limited functionality, a photoresponsive hydrogel was prepared in this study. The hydrogel was constructed with a thermo-responsive poly(N-isopropylacrylamide-co-acrylamide) (P(NIPAM-AM)) matrix cross-linked by chitosan (CS) and incorporated a photothermal conversion component based on the Fe3+/tannic acid (TA) complex. We characterized the hydrogel’s microscopic morphology and measured its water absorption/desorption rates, mechanical properties, temperature sensitivity, photothermal conversion ability, actuation performance, and sensing performance. Results show that adding chitosan and acrylamide together produced a more tightly cross-linked structure. This improved the hydrogel’s mechanical strength, water retention, and actuation performance. Key performance values include a maximum stress of 101 kPa, maximum strain of 100%, and maximum bending angle of 104.8°. The hydrogel achieved a fast actuation response time of 0.732 s, a bending rate of 0.22 mm/s, and a conductivity of 1.154 (Ω·m)−1. It also demonstrated efficient photothermal conversion, NIR-responsive actuation, and conductive sensing performance. This work provides a useful strategy for developing high-performance light-responsive smart materials and a practical solution for multifunctional flexible actuators.