Osteoblast responses to different oxide coatings produced by the sol–gel process on titanium substrates

In order to improve the osseointegration of endosseous implants made from titanium, the structure and composition of the surface were modified. Mirror-polished commercially pure (cp) titanium substrates were coated by the sol–gel process with different oxides: TiO2, SiO2, Nb2O5 and SiO2–TiO2. The coatings were physically and biologically characterized. Infrared spectroscopy confirmed the absence of organic residues. Ellipsometry determined the thickness of layers to be approximately 100 nm. High resolution scanning electron microscopy (SEM) and atomice force microscopy revealed a nanoporous structure in the TiO2 and Nb2O5 layers, whereas the SiO2 and SiO2–TiO2 layers appeared almost smooth. The Ra values, as determined by white-light interferometry, ranged from 20 to 50 nm. The surface energy determined by the sessile-drop contact angle method revealed the highest polar component for SiO2 (30.7 mJ m−2) and the lowest for cp-Ti and 316L stainless steel (6.7 mJ m−2). Cytocompatibility of the oxide layers was investigated with MC3T3-E1 osteoblasts in vitro (proliferation, vitality, morphology and cytochemical/immunolabelling of actin and vinculin). Higher cell proliferation rates were found in SiO2–TiO2 and TiO2, and lower in Nb2O5 and SiO2; whereas the vitality rates increased for cp-Ti and Nb2O5. Cytochemical assays showed that all substrates induced a normal cytoskeleton and well-developed focal adhesion contacts. SEM revealed good cell attachment for all coating layers. In conclusion, the sol–gel-derived oxide layers were thin, pure and nanostructured; consequent different osteoblast responses to those coatings are explained by the mutual action and coadjustment of different interrelated surface parameters.