Preparation of high tenacity bilayer hydrogel with rapid thermal response based on the introduction of sodium alginate and porogen

Bilayer hydrogels composed of poly(N-isopropylacrylamide) (PNIPAm) and poly(acrylic acid-co-acrylamide) (P(AAc-co-AAm)) are commonly utilized as anisotropic hydrogels with temperature and pH sensitivity. Nonetheless, PNIPAm is known to possess poor mechanical properties, a slow thermal response, and brittleness, which greatly restricts its application for temperature sensitivity. In order to overcome these limitations, a semi-interpenetrating network (semi-IPN) structure was created by combining PNIPAm with sodium alginate. This structure effectively addressed the issue of PNIPAm's brittleness, increased its tensile stress, and improved its tensile strain. Notably, a porogen such as sodium carbonate was incorporated to increase the porosity of the thermo-sensitive layer hydrogel, resulting in a faster thermal response rate. The bilayer hydrogel obtained can be used as a bidirectional hydrogel driver with both temperature and pH sensitivity. Mechanical manipulation through temperature changes or pH shifts can cause significant deformation in the hydrogel, making it a promising material for soft actuator applications.