Green synthesis of mechanically robust and antibacterial chitosan colloidal hydrogels under near-neutral conditions for wound dressing.

Chitosan hydrogels are promising biopolymer systems for wound dressing applications, but their effectiveness is often limited by insufficient mechanical properties. Although chemical crosslinking can improve these properties, it typically involves the use of toxic compounds. Additionally, the solubility of chitosan in acidic conditions restricts its broader applications. Herein, we present a facile method using pH adjustment to near-neutral levels (6.4-6.6) followed by shear homogenization to self-assemble chitosan colloidal particles (CCPs) into a robust hydrogel. Silver nanoparticles (AgNPs) are generated in situ via a novel diffusion-controlled, chitosan-mediated reduction of silver nitrate (AgNO3). The resulting CCP-AgNP hydrogel exhibits an anisotropic layered network and excellent mechanical properties, with AgNPs uniformly dispersed throughout the matrix. The compressive fracture stress and strain reached 0.7-1.35 MPa and 50 %-75 %, respectively, likely due to the coordination between the chitosan and silver species. The CCP-AgNP hydrogel exhibited strong antibacterial activity against both Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli). In an in vivo S. aureus-infected full-thickness wound healing model, the hydrogel significantly enhanced wound healing with no cytotoxicity detected as shown by cell viability assays. These findings suggest that CCP-AgNP hydrogels, prepared through this simple, environmentally friendly method, have significant potential as robust and effective wound dressings.