Silicon-substituted hydroxyapatite: The next generation of bioactive coatings

Silicon-substituted hydroxyapatite (Si-HA) coatings with three different Si compositions (0.8, 2.2 and 4.9 wt.%) were produced as thin films on titanium substrates by magnetron co-sputtering. Following heat-treatment, a crystalline, single-phase apatite structure was obtained for all coatings, as evidenced by the presence of characteristic peaks for HA in X-ray diffraction traces, and infrared absorption P-O and O-H bands. A human osteoblast-like (HOB) cell model was employed to assess the biocompatibility of these Si-HA coatings. Unsubstituted HA thin coatings were used as a control. The results demonstrated that Si-HA elicited a significantly more rapid growth response by the HOBs as compared to HA, although cells spread well on both coatings, with the formation of extracellular matrix. The cytoskeletons on Si-HA showed clear and distinct actin filaments that were parallel to the long axis of the cells. In contrast, a more diffuse actin cytoskeleton organisation was observed on HA. Biomineralisation was seen on both coatings after 42 days of culturing, with a higher level observed on the Si-HA samples. In conclusion, Si-HA offers great potential as a coating material for future medical applications in hard and soft tissue replacements. (c) 2006 Elsevier B.V. All rights reserved.