Effects of magnesium-substituted nanohydroxyapatite coating on implant osseointegration

Objective: The objective of this study was to compare magnesium-substituted and pure hydroxyapatite coatings on the promotion of osteogenesis in vitro and on the osseointegration in vivo. Methods: Electrochemically deposited pure hydroxyapatite (EDHA) or electrochemically deposited magnesium-substituted hydroxyapatite (EDMHA) coatings were formed on the surface of pure titanium disks or implants. MC3T3-E1 preosteoblasts were cultured in the EDHA and EDMHA coated disks, and cell growth, alkaline phosphatase (ALP) activity, and osteocalcin secretion were measured at various time points. For studies on osseointegration, 30 roughened implants coated either with EDHA or EDMHA (n=15 for each coating) were implanted in the femurs of 15 NZW rabbits. After 2, 4, and 8weeks, femurs were retrieved and prepared for histomorphometric evaluation (n=5 for each coating at each time point). Results: MC3T3-E1 cells cultured on EDMHA coated disks showed increased cell number, ALP, and osteocalcin secretion compared with the EDHA coated disks at all time points (P<0.05 for all). Histologic observation of the coated implants showed woven bone in direct contact with both implant surfaces after 2weeks and mature bone after 8weeks. While there were no differences in the amount of bone between the threads at any time point, the percentage of implant in direct contact with bone (bone implant contact) was slightly higher along the EDMHA coated implants at 2weeks (P=0.086), although this difference was no longer seen at 4 and 8weeks. Conclusion: Mg-substituted HA coated surfaces promote osteogenic differentiation of preosteoblasts in vitro and may improve implant osseointegration during the early stages of bone healing compared with pure EDHA coated surfaces.