Reductant-free biosynthesis of silver nanoparticle-functionalized bacterial nanocellulose composites via...

Bacterial nanocellulose (BNC) is a structurally pure and biocompatible polysaccharide with excellent moisture retention and mechanical robustness, making it a promising wound care material; however, its lack of intrinsic antimicrobial activity limits clinical applicability. Here, we report a reductant-free, dual-phase biosynthetic strategy for fabricating silver nanoparticle (SNP)-functionalized BNC composites using a silver-tolerant Acetobacter intermedius G7. During cultivation in AgNO₃-supplemented medium, the strain produced BNC along with acetan and extracellular proteins. These macromolecules mediated the in situ reduction of Ag⁺ to Ag⁰. Subsequent alkaline post-treatment further enhanced SNP generation and their homogeneous incorporation into the BNC network. Instrumental analyses confirmed ultrasmall (∼3.2 nm), crystalline SNPs in the BNC matrix and revealed complementary redox contributions of acetan and proteins to SNP formation. The nanocomposites showed strong swelling, durable moisture retention, and fibroblast cytocompatibility. They also showed broad-spectrum antimicrobial activity (minimum inhibitory concentrations ≤5 μg/mL) against three common human pathogens. This study elucidates a molecular-level biosynthesis mechanism involving structurally defined polysaccharides and proteins, and provides a sustainable, green platform for functional macromolecular biomaterials. This is the first report to utilize a silver-tolerant Acetobacter and integrate in-cultivation and post-treatment stages for fabricating SNP-BNC composites entirely driven by microbial and endogenous biopolymer activity, without the use of external reductants.