Strontium-polydopamine hybrid coating to improve antibacterial ability and osseointegration of titanium implants

Poor osseointegration and implant-associated infection of titanium implants have prompted their urgent development. Strontium (Sr) is widely recognized to promote osteoblast differentiation and inhibit osteoclast growth. To this end, this study aimed to develop a Sr-containing polydopamine (PDA)-coated implant with practical antibacterial ability and excellent osseointegration ability to meet clinical applications. This hybrid coating used PDA as an adhesion layer and a carrier for Sr ions. The effects of Sr contents on shear bond strength, in vitro stability, antibacterial ability, and in vitro osteogenic activity of the implant were evaluated. The Sr-doped PDA surface was soaked in simulated body fluid (SBF) at pH 7.4 or 5.0 for a long time (up to 90 days) to evaluate the in vitro stability. The antimicrobial ability of the hybrid coating against E. coli and S. aureus was examined, while its cellular function was assessed using RAW 264.7 and MG63 cells. The current phase and chemical composition results indicated the presence of Sr ions on the surface of PDA. When Sr was added to PDA, the initial shear strength values were comparable to those of the PDA coating. Soaking time reduced the strength values of Sr-containing coatings, especially for 90 days. However, Sr coating significantly reduced the growth of the two bacteria in a dose-dependent manner. Likewise, Sr coating had a significant dose-dependent inhibitory effect on the development of RAW 264.7 cells but improved MG63 osteogenesis. In conclusion, 40 % Sr-containing PDA hybrid coating on titanium implants may be a potential implant in terms of in vitro stability, antibacterial ability, and osteogenic activity.