| Surface topology and chemical composition of a biomaterial play an important role in the regulation of biological behaviors including protein adsorption, cell adhesion, migration, spreading, proliferation and differentiation. Titanium and titanium alloys have been widely used as orthopedic, dental implants and cardiovascular stents owing to their superior physical properties. However, titanium surface is inherently bio-inert, thus could not form efficient osseointegration with surrounding bone tissue. Therefore, to improve the surface property of titanium implant is significantly important in clinical application. A desired hydroxyapatite composite coatings could not only retain the good mechanical property of a titanium implant, but also improve its property in a specific clinical application, such as biocompatibility and osseointegration. In this study, five types of composite coatings, FHAP/ZrO2, Sr FHAP, Sr-Ca-P/GLT, MnHAP, and HAP/Ca SiO3 were prepared and the processing parameters was optimized. The crystal structure and morphology of the composite coatings were characterized with XRD, FTIR, SEM and EDS. Main contents and conclusion of this study were listed as follows:A novel method of electrolytic fluorine-doped hydroxyapatite/ZrO2 double-layer coating was conducted on medical titanium in ZrO(NO3)2 aqueous solution and subsequently in the mixed solution of Ca(NO3)2 、 NH4H2PO4 and Na F. The microstructure, phase composition, bond strength, dissolution rate and corrosion resistance of the films were studied. Results revealed that the additions of F- reduced the crystallite and increased the crystallinity of hydroxyapatite, structure of apatite was changed from micro-petal-like crystals to nano-needle-like crystals, which aligned vertically to the substrate. The approximately 10 μm thick layers was much denser and uniform. Addition of ZrO2 buffer layer could improve the bond strength between the fluorine-doped hydroxyapatite layer and the substrate. The bond strength of the double-layer coating was found to be significantly higher than that of pure hydroxyapatite coating even after soaking in normal saline for two weeks. In physiological solution, the double-layer coating showed lower dissolution rate and stronger corrosion resistance than pure hydroxyapatite coating.To improve the corrosion resistance and biocompatibility of biomedical titanium, strontium(Sr) and fluorine(F) were simultaneously incorporated in hydroxyapatite(HAP) to form Sr FHAP coating on titanium(Ti) via electrodeposition. The microstructure, phase composition, corrosion resistance, and cytocompatibility of the films were studied. Results revealed that by incorporating F- and Sr2+ ions in HAP, the density of the coating markedly increased, i.e., a lower porosity than common HAP coating. The Sr FHAP layer was dense and uniform, with nano-needle-like crystals of apatite, which aligned vertically to the substrate. The SrFHAP crystals were calcium-deficient apatite, and Sr2+ ions and F- ions were homogeneously distributed in the coating. The Sr FHAP coating showed lower dissolution rate than HAP coating. Potentiodynamic polarization test manifested that the SrFHAP-coated titanium exhibited superior corrosion resistance than HAP single-coated sample. In addition, osteoblasts cellular tests revealed that the SrFHAP coating was more effective to improve the in vitro biocompatibility of Ti compared with HAP coating.To improve coating corrosion resistance and bioactivity, strontium(Sr) and gelatin(GLT) were simultaneously incorporated in calcium phosphate(Ca-P) to form Sr-Ca-P/GLT composite coating on titanium(Ti) by electrodeposition. The surface morphology, chemical composition, phase identification, bond strength, corrosion resistance, and cytocompatibility of the films were studied. Results revealed that the Sr-Ca-P/GLT layer was rough and inhomogeneous, with floral-like crystals or flake agglomerate morphology. The Sr-Ca-P crystals were Sr-doped apatite(hydroxyapatite and brushite), and Sr2+ ions and GLT were homogeneously distributed in the Ca-P coating. The thickness of the composite coating was almost 10 μm without delamination and/or cracking at the interface. The bond strength of the composite coating was 5.6 ± 1.8 MPa. The Sr-Ca-P/GLT coated Ti had lower corrosion rates than bare Ti, suggesting a protective character of the composite coating. Osteoblast cellular tests demonstrated that the Sr-Ca-P/GLT composite coating better enhanced the in vitro biocompatibility of Ti than Ca-P coating.This work elucidated the corrosion resistance and in vitro bioactivity of electroplated manganese-doped hydroxyapatite(MnHAP) film on Na OH-treated titanium(Ti). The Na OH treatment process was performed on Ti surface to enhance the adhesion of the MnHAP coating on Ti. Scanning electron microscopy images showed that the MnHAP coating had needle-like apatite crystals, and the approximately 10 μm-thick layer was denser than HAP. Energy-dispersive X-ray spectroscopy analysis revealed that the MnHAP crystals were Ca-deficient and the Mn/P molar ratio was 0.048. X-ray diffraction confirmed the presence of single-phase MnHAP, which was aligned vertically to the substrate. Fourier transform infrared spectroscopy indicated the presence of phosphate bands ranging from 500 cm-1 to 650 cm-1 and 900 cm-1 to 1100 cm-1, and a hydroxyl band at 3571 cm-1, which was characteristic of HAP. Bond strength test revealed that adhesion for the MnHAP coating was more enhanced than that of the HAP coating. Potentiodynamic polarisation test showed that the MnHAP-coated surface exhibited superior corrosion resistance over the HAP single-coated surface. Bioactivity test conducted by immersing the coatings in simulated body fluid showed that MnHAP coating can rapidly induce bone-like apatite nucleation and growth. Osteoblast cellular tests revealed that the MnHAP coating was better at improving the in vitro biocompatibility of Ti than the HAP coating.A novel method of electrolytic porous hydroxyapatite/calcium silicate(HAP/Ca SiO3) composite coating was conducted on pure titanium in a mixed solution of nano-SiO2、Ca(NO3)2 and NH4H2PO4. SEM observation showed that the composite layer was porous, thereby providing abundant sites for the osteoblast adhesion. XRD results showed that the composite coating was mainly composed of HAP and CaSiO3. Bond strength testing exhibited that HAP-Ca SiO3/Ti had higher bond strength than HAP/Ti. The HAP/CaSiO3 coating was more corrosion resistant than the HAP coating based on the polarization tests. In vitro cell experiments demonstrated that both the HAP and HAP/Ca SiO3 coatings showed better cell response than the bared titanium. In addition, the proliferation of MC3T3-E1 osteoblast cells grown on the HAP/CaSiO3 coating were remarkably higher than those on the bared Ti and pure HAP coating.In summary, various ions doped calcium phosphate composite coatings were prepared by electrodeposition, and electrodeposition technique were studied theoretically and experimentally. The effect of the fluoride ions, strontium ions, manganese ions, silicon ions and gelatin on the physical properties, chemical properties and biological activity of the composite coating were studied. A variety of trace elements in bone required(such as fluorine, strontium, manganese, silicon) was successfully introduced into the Ca-P coating, which provided a preliminary experimental basis for further clinical application of calcium phosphate composite coatings in repairing bone defects. |
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