Preparation And Properties Of Multifunctional Composite Coating On The Surface Of Degradable Magnesium Alloy

Compared with traditional permanent metal implant materials?such as stainless steel,cobalt chromium alloy,and titanium alloy?,magnesium?Mg?and its alloys have good mechanical properties,degradability,and biocompatibility.However,the degradation rate of Mg alloys in the human body environment is too fast and unpredictable,which will lead to premature mechanical failure of the implants before tissues have adequate time to heal.In addition,hydrogen bubbles generated during the degradation of Mg alloys will cause separation between the tissue and the implant interface,and delay the repair of bone tissue.Therefore,enhancing the corrosion resistance of Mg and its alloys is the key to achieving their clinical application.Surface modification is the most commonly used method to improve the corrosion resistance of Mg alloys.It can not only maintain the good mechanical properties of Mg alloys,but also can impart certain biological functions to Mg alloys,such as biocompatibility,blood compatibility and antibacterical property.In the present paper,a variety of multifunctional composite coatings were prepared on the surface of Mg alloys by chemical conversion,sol-gel,dipping and cyclic voltammetry.The performance of the multifunctional composite coating was systematically evaluated through in vitro degradation tests,biocompatibility tests and antibacterial activity tests.The main studies are as follows:?1?A multifunctional composite coating composed of hydroxyapatite?HA?and titanium dioxide?TiO₂?was prepared on the surface of Mg alloy by chemical conversion and sol-gel methods.As a sealing layer,the TiO₂ sol-gel coating can seal the cracks and pores in the HA coating,thereby improving the corrosion resistance of the coating.By changing the number of TiO₂ sol-gel coatings,the best sealing effect was achieved.The surface morphology and electrochemical test results showed that when the number of TiO₂ sol-gel coatings is 15 layers,the composite coating had the best sealing effect and corrosion resistance.At the same time,the composite coating maintained the top flake-like structure of HA coating which provided binding point for cell growth and adhesion,and significantly improved the biocompatibility of the Mg alloy.The results of in vitro antibacterial tests showed that the antibacterial rate of the composite coating against E.coli and S.aureus reached 99.5±0.3%and 99.8±0.2%,respectively.?2?A multifunctional composite coating composed of calcium phosphate?CaP?and collagen?Col?was prepared on the surface of Mg alloy by chemical conversion and dipping coating.The surface morphology,chemical composition and corrosion resistance of the CaP/Col composite coating were systematically studied.The results showed that the collagen coating effectively sealed the defects on the surface of the CaP coating,and significantly improved the corrosion resistance and in vitro biomineralization ability of the Mg alloy.In addition,the composition of the composite coating was similar to that of natural bones,which provided a more favorable interface for cell growth and adhesion.In vitro biocompatibility studies showed that the composite coating significantly promoted cell attachment,proliferation,and differentiation.?3?A multifunctional composite coating composed of polydopamine?PDA?,dicalcium phosphate dihydrate?DCPD?,collagen?Col?was prepared by two-step chemical conversion method.The surface morphology,chemical composition,thickness,corrosion performance,and cytocompatibility of the coating were analyzed.The results showed that the PDA/DCPD/Col coating significantly improved the corrosion resistance and in vitro biomineralization ability of Mg alloys.Moreover,the PDA/DCPD/Col coating has a similar composition to natural bone,and the surface of the coating has a network structure composed of fibrous calcium phosphate and collagen,which provides a more favorable interface and microenvironment for cell viability and adhesion.Compared with Mg alloy and PDA/DCPD coating,the PDA/DCPD/Col coating had excellent cytocompatibility.?4?A multifunctional composite coating composed of polypyrrole?Ppy?and nano zinc oxide?ZnO?was prepared on the surface of Mg alloy by cyclic voltammetry method.Nano-sized ZnO particles can be doped into the defects of the Ppy coating structure to prolong the service life of the coating.The electrochemical and immersion tests indicated that the corrosion resistance of the Mg alloy was improved significantly by the Ppy/ZnO composite coating.The results of in vitro biocompatibility tests showed that the Ppy/ZnO composite coating significantly promoted the adhesion and proliferation of cells.In addition,in vitro antibacterials tests showed that the Ppy/ZnO composite coating can effectively inhibit the adhesion and growth of E.coli,and the antibacterial effects against planktonic bacteria in the medium reached 96.5±2.6%.