Balancing Cytocompatibility and Bacterial Resistance: Insights from Silver-Modified Ti6Al4V Co-Culture Studies

The efficacy of silver's antibacterial properties in biomedical applications depends on the balance with cytocompatibility, influenced by its chemical form. Cysteine, a thiol-containing molecule, can bind silver and link it to surfaces, while reducing cytotoxicity. In this study, Ti6Al4V alloy was chemically pre-treated to enhance bioactivity and subsequently functionalized with a cysteine–silver solution (CT_cysAg).

The functionalization solution was analyzed using DLS, UV–Vis, and FTIR-ATR spectroscopy, evidencing the formation of cysteine-Ag complex compounds. Surface properties were examined through zeta potential measurements, FE-SEM coupled with EDS, XPS analysis, and silver release evaluation. The results of the chemical-physical characterization showed that the CT_cysAg surface contained silver ions (58%), Ag–S bonds (22%), and a limited fraction of silver nanoparticles (20%) with minimum release. CT_cysAg promoted the adhesion of human mesenchymal stem cells (hMSCs) and maintained normal cell morphology, while limiting bacterial clustering and biofilm development (Staphylococcus epidermidis, Staphylococcus aureus, and Escherichia coli). Additionally, CT_cysAg, in a co-culture model, sustained cell viability of hMSCs, in the presence of S. aureus bacteria while maintaining the inherent antimicrobial response.

In conclusion, this study reports the development of a cytocompatible, bacteriostatic Ti6Al4V surface obtained by chemical pre-treatment and cysteine–silver functionalization. With the co-culture test, we demonstrated a protective effect against S. aureus, supporting its potential for multifunctional implant applications.