Thermal-/Light-Tunable Hydrogels Showing Reversible Widening and Closing Actuations Based on Predesigned Interpenetrated Networks

Poly(N-isopropylacrylamide) (PNIPAM) is a well-known biocompatible temperature-sensitive polymer. To enhance the biocompatibility of the artificial iris developed in our previous work, in this study, we demonstrate the syntheses of a series of cross-linked and interpenetrated poly(NIPAM-co-AM) hydrogel networks. Elasticities and mechanical properties of the synthesized hydrogels were investigated. Based on the results, the N3A1-N3A1 interpenetrated network (IPN) hydrogel was selected as a functional material for the fabrication of thermally tunable and light-tunable iris-like actuators. Fabrication of both gradient- and double-layer hydrogels was also carried out. Thermally responsive curling of the synthesized hydrogels was studied. Fabrication of thermal-/light-tunable IPN hydrogels showing actuation of widening and closing was achieved. The synthesized iris-like IPN hydrogels were further coated with polydopamine to promote light sensitivity. Both thermally sensitive actuation and light-sensitive actuation of widening and closing were demonstrated for the fabricated iris-like hydrogels. Stimulated variations in the inner diameter and the outer diameter surrounding the iris-like hydrogels were estimated. The results showed that poly(NIPAM-co-AM) IPN hydrogels are available for the design of thermal-/light-responsive actuators.