Mesenchymal stem cell response to conformal sputter deposited calcium phosphate thin films on nanostructured titanium surfaces.

Biomaterial surfaces that can directly induce the osteogenic differentiation of mesenchymal stem cells (MSCs) present an exciting strategy for bone tissue engineering and offers significant benefits for improving the repair or replacement of damaged or lost bone tissue. In this study, titanium nanostructures with distinctive topographical features were produced by radio frequency magnetron sputtering. The response of MSCs to the nanostructured titanium (Ti) surfaces before and after augmentation by a sputter deposited calcium phosphate (CaP) coating has been investigated. The sputtered CaP has the characteristics of a calcium enriched hydroxyapatite surface layer, as determined by X-ray photoelectron spectroscopy and X-ray diffraction studies. The sputter deposited Ti has a polycrystalline surface morphology, as confirmed by atomic force microscopy, and CaP layers deposited thereon (TiCaP) conform to this topography. The effects of these surfaces on MSC focal adhesion formation, actin cytoskeleton organization and Runx2 gene expression were examined. The Ti and TiCaP surfaces were found to promote changes in MSC morphology and adhesion known to be associated with subsequent downstream osteogenic differentiation; however, the equivalent events were not as pronounced on the CaP surface. A significant increase in Runx2 expression was observed for CaP compared to Ti, but no such difference was seen between either Ti and TiCaP, nor CaP and TiCaP. Importantly, the Ti surface engendered the expected contribution of nanoscale features to the MSC response; moreover, the CaP layer when used in combination with this topography has been found to cause no adverse effects in respect of MSC behavior.