Controlling The Biodegradation Rate Of Magnesium Alloy By Biomimetic Coatings

Biomaterials not only have important social effect in bettering the living quality of human beings, improving their health and saving their lives, but also become a new growth point in economic and scientific-technological areas in recent decades. Magnesium biomaterials have more advantages than other biomaterials It is well known that the magnesium alloy has properties of light weight; similar mechanical properties to natural bone, absorbable biodegradation in vivo, and magnesium ions are one of necessary ions for human body, which make magnesium alloy to be an ideal bone substitute material. However, the high corrosion rate of magnesium alloys badly confined their clinical applications. Hydroxyapatite (HA) is the main ingredient of bone and other hard tissue essence; it has excellent biocompatibility and biological activity. However, the mechanical property of HA is poor and can not be used as implant materials for load-bearing alone. Mg-based apatite coating bio-composites material can make full use of HA and magnesium alloy as a great superiority of biological materials, and effectively resolve the problem of magnesium’s severe corrosion in vivo.In this paper, depending on biocompatibility, biocompatibility, degradability, zinc and calcium elements are chosen as alloying elements to develop Mg-2.0Zn-1.0Ca alloy by squeezing casting and hot extrusion technology, and its microstructure, mechanical properties have been systematic studied. HA was coated on surfaces of AZ31and Mg-Zn-Ca alloy by biomimetic technique, and coatings were studied by X-ray diffraction, energy dispersive spectroscopy and scanning electron microscopy. The corrosion properties of two kinds of magnesium alloy with and without coatings were researched by corrosion tests in simulated body fluid. The results show that:(1) Developed Mg-Zn-Ca alloy has good properties, whose tensile strength is365MPa, compression strength can reach to338.06MPa, yield strength can reach to360MPa, elongation rate maximum is10.25%, elastic modulus is41.69Gpa, hardness value is59.20HV, density is1.751g/cm3,(2) The coatings on the surface of AZ31and Mg-Zn-Ca alloys were produced using biomimetic technique. The coatings are mainly composed of Caio(P04)6(OH)2(abbreviated to be HA) by X-ray diffraction, and with prolonging coating time, the coating thickness is increased.(3) The coating on the surface of AZ31magnesium alloy was coated in48h by biomimetic technique, about35μm in thickness, and coating surface is smooth and dense. The shear strength between matrix and coating was1MPa.(4) The corrosion test shows that:the degradation rate of coatings samples was slower than without coating samples, and it confirmed that the feasibility to control degradation rate of magnesium alloy by changing the morphology and thickness of coatings. The corrosion resistance property of Mg-Zn-Ca alloy is inferior to AZ31magnesium alloy. The corrosion resistance property of Mg-Zn-Ca alloy needs to be further promoted.