The Antibacterial Properties and Biocompatibility of Silver and Hydroxyapatite Nanoparticles Coating on Dental Implants

Introduction:\nInfection associated with dental implants is the most common cause of their failure. The aim of this study was to discover a new coating for dental implants that has a good antibacterial and antibiofilm activity against an early colonizer on implant surfaces: Streptococcus sanguinis. Furthermore, the coating should have a good biocompatibility with bone. \nMethods:\t\nDifferent coatings were prepared on the surface of titanium alloy (Ti4Al6V) discs. Silver, titanium dioxide, and hydroxyapatite nanoparticles, as well as hydroxyapatite microparticles were used to coat titanium discs. Three techniques were used to coat the titanium discs; (i) Solution deposition and heating for hydroxyapatite micro and nanoparticles, (ii) silver plating, and (iii) anodization to coat the discs with titanium dioxide. The antibacterial effect of these coating was investigated against the clinically relevant microbe, Streptococcus sanguinis. End point assays such as lactate production and a live/dead staining kit were used to check for bacterial growth inhibition. The bacterial growth was also qualitatively assessed by scanning electron microscopy. The total concentration of silver, calcium and phosphorus in the media was measured to check the stability of the coatings. Then the biocompatibility of the coatings with good antibacterial activity was evaluated using primary human osteoblast cells; toxicity assays such as lactate dehydrogenase leak and cell protein concentration were used for this purpose. The total concentration of silver and electrolytes (K+ and Na+) were measured in the media and in the cell homogenates. Uncoated titanium discs were used as a control group in both experiments.\nResults: \nThis study revealed that silver plus hydroxyapatite nanoparticles (Ag+nHA) and silver plus hydroxyapatite microparticles (Ag+mHA) coatings have an excellent antibacterial activity against S. sanguinis compared to uncoated titanium discs. , This observation was also confirmed by SEM images. Furthermore, the stability of the coating was confirmed by ICP-MS measurement, as the silver release from these two coatings was low (<0.5 mg/l). However, the biocompatibility test showed that these coatings reduced the viability of osteoblast cells, as measured by less LDH activity and alkaline phosphatase activity in the cell homogenates compared to the control. The activity of these enzymes in the cell homogenates was about 75 % lower than the control. In addition, the silver ion release from these coatings into the cell culture media (DMEM) was 30-fold higher compared to the silver release in the bacterial test.\nConclusion: \nThe antibacterial activity of Ag+nHA and Ag+mHA coatings was confirmed against Streptococcus sanguinis. These coatings could be of great use clinically to prevent the bacterial infection of dental implant. However, this study raise concerns regarding the biosafety of silver-releasing implantable materials, because they may compromise the biocompatibility of the bone cells in certain conditions. Hence, more investigations are needed to ensure the biocompatibility of these two coatings before their clinical application.