Bone marrow derived mesenchymal stem cell response to the RF magnetron sputter deposited hydroxyapatite coating on AZ91 magnesium alloy

The aim of this study was to investigate adhesion of bone marrow stromal cells (BMSCs) and in vitro degradation of hydroxyapatite (HA) coatings deposited on the surface of magnesium alloy (AZ91). The uniform and pore-free HA coating was successfully obtained via RF magnetron sputter deposition at the substrate bias of −25 and substrate bias of −100 V followed by post-deposition annealing. The structural features of the HA coating have been characterized and biological performance of the HA coating has been examined via in vitro test. The X-ray diffraction and Energy dispersive X-ray analysis data revealed that the phase and elemental composition of the deposited HA coatings were similar, but the surface roughness and morphology were influenced by the substrate bias voltage. The coating deposited at −25 V consists of multiple grain-boundaries. In contrast, no grain boundary but rather flat surface was observed for the sample deposited at −100 V. Atomic force microscopy (AFM) was used to obtain topographic images of the obtained coatings and quantitative assessment of the surface roughness. The roughness parameters of the deposited coatings were found to display nanometer scale surface roughness (Sa and Sq) from 92 to 130 nm over areas of 5 × 5 μm2. The in vitro direct culture experiment showed that the HA coating deposited at the substrate bias of −100 V significantly reduced the release of Mg ions in post-culture media and revealed higher BMSCs adhesion density than that on the HA coating deposited at the bias of −25 V and the uncoated AZ91 alloy. Thus, this study demonstrated that the negative pulse substrate bias applied for HA coating deposition allows to improve the surface features of the AZ91 magnesium alloy and enhance BMSCs adhesion in vitro.