Rapid synthesis of biocompatible bilayer hydrogels via frontal polymerization

Hydrogels have been attracting much attention as smart soft materials. The exploration of methods allowing hydrogels to have anisotropic composition, structure, and properties would benefit the fabrication of smart materials with versatile multi-functions. Here we report the rapid frontal polymerization (FP) of bilayer hydrogels possessing good water swelling, mechanical strength, self-healing, biocompatibility, and antibacterial capabilities. The bilayer hydrogels, consisting of poly(AM-co-AMPS) (G-1) and poly(AM-co-HPA) (G-2) (AM, acrylamide; AMPS, 2-acrylamide-2-methylpropanesulfonic acid; HPA, hydroxypropyl acrylate), are synthesized in one step within 6 minutes (min) by horizontal FP. These polymer hydrogels have hierarchical porous morphology with pore sizes of several micrometers and several hundreds of micrometers respectively, equilibrium swelling ratio up to 3371% in water, tensile strength up to 0.204 MPa, and self-healing ability. The good cytocompatibility and low toxicity of the hydrogels are demonstrated through cell culture of L929 fibroblasts in vitro experiments. The tests of hydrogels with Escherichia coli and Staphylococcus aureus reveal their antibacterial property. The results demonstrate that biocompatible anisotropic hydrogels with versatile functions could be fabricated via the rapid and energy-saving approach of FP.