Versatile Bilayer Hydrogel for Wound Dressing through PET-RAFT Polymerization

Multifunctional hydrogel-based wound dressings have been explored for decades due to their huge potential in multifaceted medical intervention to wound healing. However, it is usually not easy to fabricate a single hydrogel with all of the desirable functions at one time. Herein, a bilayer model with an outer layer for hydrogel wound dressing was proposed. The inner layer (H_m-PN_n) was a hybrid hydrogel prepared by N-isopropylacrylamide and chitosan-N-2-hydroxypropyl trimethylammonium chloride (HACC), and the outer layer (PVA_o-PAm_p) was prepared by polyvinyl alcohols and acrylamide. The two hydrogel layers of the bilayer model were covalently connected with excellent interfacial strength by photoinduced electron/energy transfer-reversible addition-fragmentation chain transfer (PET-RAFT) polymerization. The outer layer exposed to the ambient environment exhibited good stretchability and toughness, while the inner-layer hydrogel adhered to the skin exhibited excellent softness, antibacterial activity, thermoresponsivity, and biocompatibility. In particular, the inner layer of a hydrogel demonstrated excellent antibacterial capability toward both Staphylococcus aureus as Gram-positive bacteria and Escherichia coli as Gram-negative bacteria. Cell cytotoxicity showed that the cell viability of all H_m-PN_n layer hydrogels exceeds 80%, confirming that the hydrogels bear excellent biocompatibility. In vivo experimental results indicated that the H_m-PN_n/PVA_o-PAm_p bilayer hydrogel has a significant effect on the acceleration of wound healing, which was demonstrated in a full-thickness skin defect model showing improved collagen disposition and granulation tissue thickness. With these results, the established multifunctional bilayer hydrogel exhibits potential as an excellent wound dressing for wound healing applications, especially for open and infected traumas.