UV-mediated synthesis of pNIPAM-crosslinked double-network alginate hydrogels: Enhanced mechanical and shape-memory properties by metal ions and temperature

Allyl-substituted alginate (Alg) underwent gelation with N-isopropylacrylamide (NIPAM) monomers via UV-mediated radical reactions, resulting in a multi-responsive double-network hydrogel. The amount of NIPAM available for crosslinking affected several properties of the resulting Alg-NIPAM hydrogels. As more NIPAM was incorporated, the volume phase transition temperature (VPTT) and swelling properties of the Alg-NIPAM hydrogels decreased. Metal-ion addition caused increased crosslinking of the Alg-NIPAM hydrogels, allowing shape-memory of the materials due to their dual responsiveness to temperature and metal ions. Additional crosslinking caused the hydrogels to become stiffer, showing the ability to regulate the mechanical properties of the hydrogels. As a proof-of-concept, reversible shape changes under temperature and ionic cycling were demonstrated.