Shape Memory Hydrogel Based on Gelatin and Its Derivatives/Hydroxyethyl Methacrylate/Sodium Sulfate

Double network (DN) hydrogel was prepared by photoinitiated polymerization with gelatin (Gel) and hydroxyethyl methacrylate (HEMA) as monomers, methacryloylated gelatin (GelMA) as a cross-linking agent, and 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylphenylacetone (I2959) as an initiator. Then the DN hydrogel was soaked into saturated Na₂SO₄ solution to prepare DN/SO₄²⁻ hydrogel. Tensile property was tested by universal material testing machine. Results showed that when the mass fraction of Gel, HEMA, GelMA was 20%, 40%, and 10%, respectively, and the immersion time was 16 h, the tensile strength of the hydrogel could reach 0.94 MPa, and the elongation at break was 496%. Loading-unloading test showed that the hydrogel had good self-recovery performance. The hydrogel also had biodegradability because of the degradable cross-linking agent GelMA. It could be completely degraded after soaking in trypsin solution for 4 h. The molecular chains in the hydrogel network contracted in the high mass fraction salt solution and stretched in the low mass fraction salt solution, giving the shape memory of the hydrogel by ion stimulation response. The hydrogel with fixed shape (knotting, folding, twisting) could be recovered to its original shape within 5 min after soaking in low mass fraction Na₂SO₄ solution (w=2%). In addition, nontoxic components endowed the hydrogel with excellent biocompatibility, which had been confirmed by MTT method. After co-culture with different mass concentrations of DN/SO₄²⁻ hydrogel extract solution, the viabilities of L929 cells were more than 80%.