Steam-sterilizable cationic nanodiamond-silver composites with enhanced antibacterial activity

Hydrogenated nanodiamonds (H-NDs) combine high biocompatibility with a positive ζ-potential, yet exhibit only weak and medium-dependent antibacterial effects. Here, we engineer H-NDs (median sizes 18 and 125 nm) into Ag-decorated composites (H-ND-Ag) without suppressing their positive surface charge (cationic character) by adsorbing a thin chitosan layer, followed by mild polyethyleneimine-assisted AgNP formation. We evaluate how steam sterilization by autoclaving affects the surface chemistry and dispersion of both pristine H-NDs and H-ND-Ag. Autoclaving perturbs the neat H-ND, leading to decreased ζ-potential and eventual aggregation. In contrast, the chitosan-Ag shell preserves the positive charge and long-term colloidal stability of H-ND-Ag. The H-ND-Ag composites suppress the growth of Escherichia coli and Staphylococcus aureus at low loadings, matching or exceeding the performance of reported, protein-stabilized ND-Ag benchmarks. The results support a contact-mediated "Ag-patch" delivery mechanism in which carrier size and Ag distribution - rather than surface charge alone - dominate antibacterial efficacy, and establish a protein-free, autoclave-sterilization-compatible route to durable antibacterial nanodiamond formulations.