Electrochemical Deposition and Characterisation of Silver-Containing Hydroxyapatite Coatings on Zinc: Influence of Silver Addition on the Functional Properties of a Biodegradable Implant System.

Abstract

Zinc-based materials are promising candidates for biodegradable orthopaedic implants; however, their limited bioactivity and insufficient antibacterial performance restrict broader clinical application. Although Ag-containing hydroxyapatite (HA) coatings have been extensively investigated, most studies have focused on chemically stable substrates, while considerably less attention has been paid to highly reactive biodegradable zinc, for which the effects of silver addition remain insufficiently understood. Therefore, this study investigated how the introduction of silver influences a previously optimised electrochemically deposited hydroxyapatite coating system on zinc. Silver-containing hydroxyapatite (HA-Ag) coatings were prepared by electrochemical deposition and characterised in terms of morphology, chemical composition, phase structure, corrosion behaviour, tribological performance and preliminary biological response. The applied deposition conditions resulted in the formation of a porous and dendritic HA-Ag coating with an average thickness of 45 ± 6.8 μm. SEM and AFM analyses revealed increased surface roughness and dendritic morphology of the coating. XRD, FTIR, EDX and XPS results confirmed the formation of calcium phosphate phases together with the presence of silver-containing species within the coating. The obtained results suggest that silver was present both as metallic particles and in oxidised form associated with the hydroxyapatite layer. Electrochemical measurements performed in Hank's solution indicated a reduced corrosion rate of HA-Ag-coated samples compared to bare zinc. Tribological testing demonstrated altered friction and wear behaviour due to the presence of the ceramic coating. Platelet adhesion assay revealed predominantly spherical platelet morphology, suggesting limited platelet activation under the tested conditions. Antibacterial test performed using the disc diffusion method showed pronounced inhibition zones against E. coli and S. aureus for the HA-Ag-coated samples. Overall, this study contributes to a better understanding of Ag-containing hydroxyapatite coatings formed directly on biodegradable zinc and demonstrates that introducing silver into a previously optimised hydroxyapatite coating system influences not only the coating characteristics but also the overall coating-substrate system, as evidenced by the formation of AgZn and AgZn₃ intermetallic phases. Nevertheless, further in vitro and in vivo studies are required to comprehensively assess the biomedical applicability of the developed coating system.