Antibacterial and biological characteristics of silver containing and strontium doped plasma sprayed hydroxyapatite coatings

Abstract

Infection in primary total joint prostheses is estimated to occur in up to 3% of all surgery. As a measure to improve the antimicrobial properties of implant materials silver (Ag) was incorporated into plasma sprayed hydroxyapatite (HA) coatings. To offset potential cytotoxic effects of Ag in the coatings strontium (Sr) was also added as a binary dopant. HA powder was doped with 2.0wt.% Ag2O, 1.0wt.% SrO and was then heat treated at 800°C. Titanium substrates were coated using a 30kW plasma spray system equipped with a supersonic nozzle. X-ray diffraction confirmed the phase purity and high crystallinity of the coatings. Samples were evaluated for mechanical stability by adhesive bond strength testing. The results show that the addition of dopants did not affect the overall bond strength of the coatings. The antibacterial efficacies of the coatings were tested against Pseudomonas aeruginosa. Samples that contained the Ag2O dopant were found to be highly effective against bacterial colonization. In vitro cell–material interactions using human fetal osteoblast cells were characterized by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay for cell viability, field emission scanning electron microscopy for cell morphology and confocal imaging for the important differentiation marker alkaline phosphatase (ALP). Our results showed evidence of cytotoxic effects of the Ag–HA coatings, characterized by poor cellular morphology and cell death and nearly complete loss of functional ALP activity. The addition of SrO to the Ag–HA coatings was able to effectively offset these negative effects and improve performance compared with pure HA-coated samples.