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

Abstract

Poly(N-isopropylacrylamide) (PNIPAM) is a wellknown 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.

Responsive Acrylamide-Based Hydrogels: Advances in Interpenetrating Polymer Structures

“…For example, Liu et al created a bilayer structure with a IPN PNIPAm/PAAm hydrogel on a PAAm substrate. This bilayer structure demonstrates reversible opening and closing actions under NIR illumination, similar to the human iris's response to light changes [74].…”

Biomedical applications of stimuli-responsive “smart” interpenetrating polymer network hydrogels

“…Polydopamine (PDA) is a recognized near-infrared-sensitive material proficient in converting near-infrared energy into thermal energy. Liu and co-researchers [ 119 ] applied a coating of PDA onto the surface of a pre-synthesized thermo-responsive IPN hydrogel. When exposed to NIR irradiation, the PDA-coated thermo-responsive IPN hydrogel undergoes reversible swelling and de-swelling transitions.…”

“…The different swelling behaviors of these two layers upon exposure to external stimulus lead to uneven anisotropic expansion and subsequent shape transformation [ 316 , 317 ]. Liu and colleagues [ 119 ] synthesized a bilayer structure by polymerizing a cross-linked and interpenetrating thermo-sensitive poly(NIPAM- co -AM) hydrogel on a PAM gel substrate. Notably, the PAM hydrogel lacks thermo-responsive hydrophilic properties, while the interpenetrating network contracts and solidifies when exposed to hot water due to the presence of pNIPAM.…”

“…The actuator constructed through the principles of light response and moisture absorption can be applied to artificial iris and object grasping and lifting respectively. Adapted with permission [ 119 , 319 ]. Copyright © 2022, American Chemical Society.…”

Extension of the stimulus expansion model for photo‐thermo‐sensitive hydrogels

“…for sensor applications [2] as well as for soft-actuators [3], [4] and within civil engineering [5]. There are different possible stimuli, such as pH [6] or chemical concentrations [7], temperature [8] and light [9], [10]. Within this large variety of possible stimuli, light represents an excellent stimulus.…”