Antimicrobial and osteoconductive properties of two different types of titanium silver coating

In prosthetic joint surgery, Ag coating of implant areas in direct contact with bone has been met with hesitation for fear of compromising osseointegration. The physicochemical, antibacterial and osteoconductive properties of three different Ti samples were studied: Ti6Al4V alloy that was grit-blasted (GB), Ti6Al4V alloy with an experimental Ti-Ag-nitride layer (SN) applied by physical vapour deposition (PVD) and commercially available PVD-coated Ti6Al4V alloy with a base Ag layer and a surface Ti-Ag-nitride layer (SSN, clinically known as PorAg®). Ag content on the surface of experimental SN and SSN discs was 27.7 %wt and 68.5 % wt, respectively. At 28 d, Ag release was 4 ppm from SN and 26.9 ppm from SSN substrates. Colonisation of discs by Staphylococcus aureus was the highest on GB [944 (± 91) × 104 CFU/mL], distinctly lower on experimental SN discs [414 (± 117) × 104 CFU/mL] and the lowest on SSN discs [307 (± 126) × 104 CFU/mL]. Primary human osteoblasts were abundant 28 d after seeding on GB discs but their adhesion and differentiation, measured by alkaline-phosphatase production, was suppressed by 73 % on SN and by 96 % on SSN discs, in comparison to GB discs. Thus, the PVD-applied Ag coatings differed considerably in their antibacterial effects and osteoconductivity. The experimental SN coating had similar antibacterial effects to the commercially available SSN coating while providing slightly improved osteoconductivity. Balancing the Ag content of Ti implants will be vital for future developments of implants designed for cementless fixation into bone.