Facile preparation of low swelling, high strength, self-healing and pH-responsive hydrogels based on the triple-network structure

A polyacrylic acid (PAA)/gelatin (Gela)/polyvinyl alcohol (PVA) hydrogel was prepared by copolymerization, cooling, and freezing/thawing methods. This triple-network (TN) structure hydrogel displayed superior mechanical properties, low swelling ratio and self-healing properties. The superior mechanical properties are attributed to the triple helix association of Gela and PVA crystallites by reversible hydrogen bonding. The characterization results indicated that the fracture stress and the strain were 808 kPa and 370% respectively, while the compression strength could reach 4443 kPa and the compressive modulus was up to 39 MPa under the deformation of 90%. The hydrogen bonding in PVA contributed to maintain and improve the self-healing ability of hydrogels. Every type of hydrogels exhibited a higher swelling ratio under alkaline conditions, and the swelling ratios of PAA, PAA/PVA and PAA/Gela hydrogels were 27.71, 12.30 and 9.09, respectively. The PAA/Gela/PVA TN hydrogel showed the lowest swelling ratio (6.57) among these hydrogels. These results indicate that the novel TN hydrogels possess good environmental adaptability and have potential applications in the biomedical engineering and sensor field.