Silver and Biomedical Implants: The Challenging Balance Between Antibacterial Efficacy and Cytocompatibility

Titanium and its alloys are widely employed for orthopaedic and dental implants due to their excellent mechanical properties, corrosion resistance, and biocompatibility. However, implant-associated infections remain a major clinical challenge, often resulting from bacterial adhesion and biofilm formation on the biomaterial surface. Surface functionalisation with silver has emerged as a promising strategy to impart antibacterial and antifouling properties, although optimisation of silver content and chemical state is crucial to preserve cytocompatibility. In this work, titanium-based substrates were functionalized with silver in distinct chemical forms, including ions, nanoparticles, and covalently bound silver-containing moieties, to investigate the relationship between surface chemistry, silver release, antibacterial efficacy, and biological response.

The modified surfaces were characterised by Field-Emission Scanning Electron Microscopy (FESEM), zeta potential titration curves, silver release measurements, and X-ray Photoelectron Spectroscopy (XPS), providing information on morphology, surface zeta potential, silver distribution, and chemical composition. Antibacterial activity was evaluated using inhibition halo tests against Staphylococcus epidermidis, while the ability to prevent bacterial colonisation was assessed by biofilm formation assays using Staphylococcus aureus. The biological response was investigated through both direct and indirect culture experiments with human mesenchymal stem cells, using Ti6Al4V and tissue culture plastic as control substrates.

The results highlight the strong influence of the silver chemical state on both antibacterial performance and cellular response. While higher silver availability enhances bactericidal and antibiofilm activity, direct contact with silver may negatively affect cell viability. These findings emphasise the importance of carefully tuning surface functionalisation strategies to achieve an optimal balance between infection prevention and host cell compatibility in next-generation titanium-based biomedical implants.