Abstract
In order to decrease the degradation rate of magnesium (Mg) alloys for the potential orthopedic applications, manganese-calcium phosphate coatings were prepared on an Mg-Ca-Zn alloy in calcium phosphating solutions with different addition of Mn2+. Influence of Mn content on degradation behaviors of phosphate coatings in the simulated body fluid was investigated to obtain the optimum coating. With the increasing Mn addition, the corrosion resistance of the manganese-calcium phosphate coatings was gradually improved. The optimum coating prepared in solution containing 0.05 mol/L Mn2+ had a uniform and compact microstructure and was composed of MnHPO4·3H2O, CaHPO4·2H2O, and Ca3(PO4)2. The electrochemical corrosion test in simulated body fluid revealed that polarization resistance of the optimum coating is 36273 Ωcm2, which is about 11 times higher than that of phosphate coating without Mn addition. The optimum coating also showed the most stable surface structure and lowest hydrogen release in the immersion test in simulated body fluid.
Highlights
Orthopedic surgery in recent times depends profoundly on the development of biomaterials used for fixation of fractures and joint replacement [1]
Among the three main kinds of biological implant materials, metallic materials, ceramic materials, and polymeric materials, biodegradable metals and polymers have gained interest for their advantages of being gradually dissolved, absorbed, consumed, or excreted in the human body, so there is no need for the secondary surgery to remove implants after the surgery regions have healed [2]
The rapid decomposition speed of Mg alloys hinders the implants to fulfill their surgical function before being discharged, the inhomogeneous local corrosion starting from the surface of Mg alloys makes the corrosion behavior uncontrollable, and too much hydrogen evolved can be accumulated in gas pockets next to the corroding Mg implant, which will delay healing of the surgery region and lead to inflammatory reaction
Summary
Orthopedic surgery in recent times depends profoundly on the development of biomaterials used for fixation of fractures and joint replacement [1]. Among the three main kinds of biological implant materials, metallic materials, ceramic materials, and polymeric materials, biodegradable metals and polymers have gained interest for their advantages of being gradually dissolved, absorbed, consumed, or excreted in the human body, so there is no need for the secondary surgery to remove implants after the surgery regions have healed [2]. Current biodegradable implants made of polymers have an unsatisfactory mechanical strength [3] and limited applications. The rapid decomposition speed of Mg alloys hinders the implants to fulfill their surgical function before being discharged, the inhomogeneous local corrosion starting from the surface of Mg alloys makes the corrosion behavior uncontrollable, and too much hydrogen evolved can be accumulated in gas pockets next to the corroding Mg implant, which will delay healing of the surgery region and lead to inflammatory reaction. Ca was a preferable addition element for its capability of refining microstructure and biomimetic mineralization behavior during alloy biodegradable process [18]; Zn is next to aluminum in strengthening effectiveness as an alloying element in Mg, and adding Zn can improve both the tensile strength and the corrosion resistance of Mg alloys
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