The Role of Implant Surface Geometry on Mineralization In Vivo and In Vitro; A Transmission and Scanning Electron Microscopic Study

The purpose of th.is study was to examine the effect of substratum surface topography on bone formation in vivo and in vitro. Precise control over substratum topography was achieved using micromachining, a technique developed from the fabrication of microelectronic components. In the in vivo studies, titanium-coated epoxy replicas of micromachined surfaces were implanted subcutaneously in the parietal area of rats. After 6 weeks, bone-like tissue was found adjacent to some micromachined surfaces. Detailed observation of this tissue with the transmission electron microscope revealed osteoblast/osteocyte-like cells and a fully or partially mineralized collagenous matrix. Mineralized matrix and collagen bundles were found contacting the titanium coating without any intervening material. Mineralized tissue was not found adjacent to smooth surfaces. In vitro, enzymatically released osteogenic cells from calvarial bone produced large ( ~ 10 μm) and small ( ~ 0.5-3 μm) mineralized globules on the micromachined surfaces, whereas only small mineralized globules formed on the smooth control surfaces after 4 weeks of culture. The mineralized nature of the globules was confirmed by energy dispersive X-ray analysis. In a second osteogenic culture system, micromachined or smooth control surfaces were placed on calvarial explants. After 4 weeks, partially mineralized globules ( ~ 5 μm) were noted interspersed between cells and extracellular matrix on the micromachined surfaces but not on the smooth surfaces. This study suggests that the surface topography of an implant influences bone formation in vivo and in vitro and that micromachined surfaces of the dimensions used in these experiments promote mineralized tissue formation