Characterization of hydroxyapatite thin films prepared by right angle magnetron sputtering for biomedical applications

One of the current goals in the biomaterials research is to develop implants with improved osteoconductivity and long-term stability. Thanks to its chemical similarity to the mineral phase of natural bone, hydroxyapatite (HA) has been extensively studied and clinically tested as a coating on metallic substrates, to obtain bioactive implants with excellent mechanical properties. At present, HA coatings prepared by the commercially available plasma spraying and other deposition techniques have some major drawbacks such as nonstoichiometry, poor adhesion, etc. In this thesis we develop a novel right angle magnetron sputtering (RAMS) approach to deposit high quality HA thin films.;HA coatings were prepared on various substrates with flat and patterned surfaces. The influence of various sputtering parameters on film growth and properties was studied. X-ray reflectivity (XRR) atomic force microscopy (AFM) and surface profiler measurements were used to determine film roughness and thickness. X-ray diffraction was used to characterize the crystallographic structure of the film. Fourier transform infrared spectroscopy (FTIR) and Raman spectroscopy were performed to characterize the functional groups. The surface micromorphology was examined using Scanning Electron Microscopy (SEM). X-ray photoelectron spectroscopy (XPS) was used to characterize the surface chemistry. The bulk chemical composition was analyzed by energy dispersive x-ray spectroscopy (EDS). The mechanical properties of the HA films were evaluated using nanoindentation. Collectively these results show that using this alternative RF magnetron geometry, as-sputtered HA films are phase pure, nearly stoichiometric, highly crystalline, and strongly bound to the substrate.;The as-sputtered HA coatings induced calcium phosphate precipitation when immersed in simulated body fluid, suggesting in vivo bioactive behavior. In vitro experiments, using murine osteoblasts, showed that cells rapidly adhere, spread and proliferate over the thin coating surface, while simultaneously generating strong in-plane stresses. Proliferation tests using the MC3T3-E1 cell line showed that HA RAMS-coated titanium substrates markedly promote osteoblast proliferation. Osteoblast adhesion tests performed with human osteoblasts also showed that the highest adhesion cell density was achieved on HA RAMS-coated titanium substrates. These experiments demonstrate that RAMS is a promising technique to produce high quality HA coatings on metallic implants for biomedical applications.