Fabrication Of Corrosion Resistant Coatings On Titanium Surface And Their Biological Responses

Titanium and its alloys are the most common used medical metals in clinic application. Due to their good mechanical property and biocompatibility, titanium-based implants were widely used in hard tissue repair such as bone, joint and tooth. Although titanium could spontaneously form protective dioxide layer on its surface in atmosphere so as to endow itself with good corrosion resistant property, while under complicated physiological erosion environment in human body, the thin oxide layer(about few nanometers) could be easily peeled off by force, and the low oxygen content in the host would further limit the re-formation of then broken oxide layer. Above issues would become even severe when bacteria infection or inflammation response occurs around the implant, because bacteria infection or inflammation response usually leads to local acidicity on the implant surface, in turn accerlating the erosion process. Therefore, it is essentially important to surface modify titanium so as to promote its corrosion resistance. Appropriate surface modification could not only retain good mechanical properties of titanium substrate, but also endow it with desired surface properties based on practical demands, such as corrosion resistance, wear resistance, biocompatibility and anti-bacterial properties etc.In this study, we employed polymer assistant deposition(PAD) and micro arc oxidation(MAO) technique to construct a series of corrosion resistant coating on titanium substrate surface with osteogenic, anti-bacterial and anti-abrasion properties. We also preliminarily evaluated the biological response of the coatings in vitro. The main contents and conclusions of the study are listed as follows: 1. Fabrication of tantalum oxide coatings with good corrosion resistance and biocompatibility on the titanium substrates by polymer assistant deposition techniqueIn order to increase its corrosion resistance of titanium surface, we constructed corrosion resistant tantalum oxide coatings on titanium by PAD technique. The physical/chemical properties of coatings were characterized by scanning electronic microscopy(SEM), atomic force microscopy(AFM), X-ray photoelectron spectroscopy(XPS), and contact-angle measurement. Electrochemical workstation and scratch tester were used to determine the dynamic potential polarization curve and adhesion strength of the coatings. The results suggest that the coatings displayed good corrosion resistance and relatively high adhesion strength. In addition, the effect of the coatings on the osteoblasts was evaluated in vitro. The results indicate that titanium substrates with tantalum oxide coatings were more beneficial for promoting the proliferation and differentiation of osteoblasts when comparing with those of pure titanium. This study provides an alternative for the construction of titanium materials with good corrosion resistance and biocompatibility. 2. Fabrication of tantalum oxide/titanium oxide composite coatings with good corrosion resistance and biocompatibility on titanium substrates by micro arc oxidation techniqueIn order to improve the fabrication efficiency and reduce costs, tantalum oxide/titanium oxide composite coatings were constructed on titanium substrates by MAO technique. SEM, AFM, X-ray diffraction(XRD), X-ray energy dispersive spectroscopy(EDS), XPS, contact-angle measurement and electrochemical workstation were employed to characterize the surface morphology, chemical composition, crystal structure and corrosion resistance of the composite coatings. The results suggest that the coatings was mainly composed of tantalum oxide and titanium oxide and the micro pores generating by MAO process were sealed by the coatings, thus the corrosion resistance of titanium substrates was improved. Moreover, in vitro cell experiments, including cell viability(CCK-8), ALP activity, mineralization, and PCR, suggest that titanium with tantalum oxide/titanium oxide composite coatings greatly promoted the proliferation and differentiation of osteoblasts when comparing with those of titanium substrates. This study presents a promising approach to efficiently fabricate corrosion resistant coatings with good biocompatibility. 3. Construction of mesoporous silica nanoparticles composite coatings with good corrosion resistance and biocompatibility on titanium substrates with MAO techniqueBacteria infection of an implant is one of the most severe postsurgical complications, and it is also the primary reason leading to implant failure. The 4-6 h after surgery was usually considered as the ‘decisive period' of bacteria infection. Considering that, we deposited the mesoporous silica nanoparticles(MSNs) onto titanium substrates by MAO technique to fabricate MSNs containing composite coatings, which were acting as reservoirs to load ionic bactericide of octenidine(OCT). Thus, we finally obtained antibacterial coatings with good corrosion resistance. The physicochemical properties of the composite coatings were characterized by transmission electron microscopy(TEM), SEM, AFM, XPS, EDS, electrochemical workstation and contact-angle measurement, respectively.The results indicate that MSNs were uniformly deposited onto titanium surface and most of them retained their shape integrity. Electrochemical analysis suggests that titanium substrates with composite coatings had higher corrosion resistance than that of pure titanium substrates. Furthermore, Escherichia coli and Staphylococcus aureus were used as model bacteria to investigate the antibacterial property of titanium substrates with composite coatings. Meanwhile, the influences of the composite coatings on the proliferation and differentiation of osteoblasts was also evaluated in vitro by CCK-8, ALP activity, mineralization. The results confirm that OCT loaded MSNs composite coatings had good anti-bacterial property and biocompatibility. The study provides a new technique for the fabrication of corrosion resistant coatings with good anti-bacterial property. 4. Fabrication of solid silica nanoparticles incorporated composite coatings with good corrosion resistance and anti-abrasion property with MAO techniqueAbrasion of an implant in a host is inevitable. The abrasion resulting in wear debris would aggregrate around surrounding tissue, in trun inducing chronic inflammation reaction and osteolysis around the implant, even leading to aseptic loosening of the implant. Thus, to enhance the anti-abrasion property of titanium substrates, we incorporated solid silica nanoparticles into titanium oxide layer to fabricate composite coatings with MAO technique. TEM, SEM, AFM, XPS and contact angle measurement were used to characterize the titanium substrates. The results indicate that most nanoparticles were uniformly incorporated into the oxide layer. The electrochemical and tribological tests display that the solid silica nanoparticles incorporation significantly improved the corrosion resistance and anti-abrasion properties of titanium substrates. Cell tests indicate that the composite coating had similar biocompatibility to that of pure titanium substrates. The study offers a new alternative for improving the anti-abrasion property of titanium substrates.