| Calcium phosphate/metal composite, which may simultaneously achieve good biocompatibility and good mechanical properties, is expected as one of the most suitable systems for hard tissue repair and replacement. It is reported that calcium phosphate bioceramic coatings on metals with reliable and long-life performances cannot be easily obtained by using some developed technologies, such as plasma spray, ion beam assistant deposition, thermal spray deposition, and sol-gel method. Due to their simple preparation arts and the ability of obtaining uniform composite biocoatings on substrates, the electrochemical methods, which include electrocrystallization, electrophoretic deposition, electro-codeposition, and anodization, are considered to be useful for the application as artificial implant materials.In this study, pure Al thin film was PVD-deposited on medical titanium to form Al-Ti substrate. Al-Ti substrate was then applied to the hybrid technique of anodization and hydrothermal treatment to fabricate nanometric calcium phosphate/Al2O3 porous biocomposite coating on Al-Ti substrate. In addition, calcium phosphate/Al2O3-Al composite was prepared via a multi-step method, that is Al-Ti substrates with Al as the surface layer were anodized firstly, and then were subsequently immersed in NaH2PO4 and Ca(OH)2 solutions, respectively, followed by a biomimetic process conducted in a simulated body fluid (SBF). Techniques, such as scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive X-ray analysis (EDAX), and X-ray diffraction (XRD), were employed to study the microstructures and compositions of Al thin film, porous alumina films (PAFs) and calcium phosphate/Al2O3 biocomposite coatings. The results are indicated as bellows:(1) Pure Al films, thickness 1-5 n m, were deposited on Ti after PVD process. The thickness of Al films was correlated with bias voltage, deposition time, Al target current, and the substrates' conductivity. The deposition time and Al target current had strong effects on Al film thickness than other factors. The roughness of Al film mainly depended on the topography of Ti discs and the thickness of Al films.(2) The hybrid technique of anodization and hydrothermal treatment has led to the successful fabrication of calcium phosphate-Al2O3/Al-Ti biocomposite. During theanodization of Al-Ti substrates in electrolytes containing calcium acetate (CA) and beta -Glycerol phosphate disodium(beta -GP), the elements Ca and P were incorporated into the PAFs layer with columnar pores in the rage of 10~50nm. Additionally, cell voltages between 30V and 60V are the optimal voltage for getting high anodization degree PAFs. It is also found that after hydrothermal treatment, acidic calcium phosphate (Ca4H2(P3O10)2) and monetite formed bioceramic coatings with a specific compact-bottom and loose-top structure.It seems that 8h is a suitable growth time of as-prepared cloddy crystals, and that the nucleation rate of this kind of ceramic coating crystals is close to their growth rate in deionized water.(3) By increasing the concentrations of Ca and P sources in the anodization electrolyte, PAFs containing much more Ca and P elements were synthesized. After hydrothermally treated at 212癈 and 2.0MPa in a diluted phosphorous acid (1 I 800) for 8h, bioceramic coatings consisted of needle-like brushite and monetite were prepared. And the needle-like crystals cross-linked together resulted in the formation of biomimetic coatings with specific microstructures.It is also found that concentration gradient and potential difference are the main driving forces for the incorporation of Ca and P into PAFs layer. It seems that Ca and P existed in PAFs were in the forms of CaO and [PO4] groups, and some related chemical reactions were proposed. Further on, it is demonstrated that the acidic media is essential for the growth of needle-like calcium phosphate crystals.(4) During galvanostatic anodized in phosphorous acid, several processes happened on Al thin films: the form... |
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