The effects of the surface topography of micromachined titanium substrata on cell behavior in vitro and in vivo

Surface properties, including topography and chemistry, are of prime import ance in establishing the response of tissues to biomaterials. Microfabricat ion techniques have enabled the production of precisely controlled surface topographies that have been used as substrata for cells in culture and on d evices implanted in vivo. This article reviews aspects of cell behavior inv olved in tissue response to implants with an emphasis on the effects of top ography. Microfabricated grooved surfaces produce orientation and directed locomotion of epithelial cells in vitro and can inhibit epithelial downgrow th on implants. The effects depend on the groove dimensions and they are mo dified by epithelial cell-cell interactions. Fibroblasts similarly exhibit contact guidance on grooved surfaces, but fibroblast shape in vitro differs markedly from that found in vivo. Surface topography is important in estab lishing tissue organization adjacent to implants, with smooth surfaces gene rally being associated with fibrous tissue encapsulation. Grooved topograph ies appear to have promise in reducing encapsulation ii in the short term, but additional studies employing three-dimensional reconstruction and diver se topographies are needed to understand better the process of connective-t issue organization adjacent to implants. Microfabricated surfaces can incre ase the frequency of mineralized bone-like tissue nodules adjacent to subcu taneously implanted surfaces in rats. Orientation of these nodules with gro oves occurs both in culture and on implants. Detailed comparisons of cell b ehavior on micromachined substrata in vitro and in vivo are difficult becau se of the number and complexity of factors, such as population density and micromotion, that cart differ between these conditions.