COMPARATIVE MECHANICAL AND CORROSION STUDIES ON MAGNESIUM, ZINC AND IRON ALLOYS AS BIODEGRADABLE METALS

In this paper, selected magnesium, zinc and iron biodegradable alloys were studied as prospective biomaterials for temporary medical implants like stents and fixation devices for fractured bones. Mechanical properties of the alloys were characterized with hardness and tensile tests. In-vitro corrosion behavior was studied using immersion tests in a simulated physiological solution (SPS, 9 g/L NaCl) to roughly estimate the in-vivo biodegradation rates of implants. It was found that the Mg and Zn alloys were limited by a tensile strength of 370 MPa, while the tensile strength of the Fe alloys achieved 530 MPa. The main advantage of the Mg alloys is that their Young's modulus of elasticity is similar to that of the human bone. However, the corrosion tests revealed that the Mg-based alloys showed the highest corrosion rates in the SPS, ranging between 0.6 mm and 4.0 mm per year, which is above the tolerable degradation rates of implants. The corrosion rates of the Zn alloys were between 0.3 mm and 0.6 mm per year and the slowest corrosion rates of approximately 0.2 mm per year were observed for the Fe alloys. The results indicate that all three kinds of alloys meet the mechanical requirements for the load-bearing implants. From the corrosion-behavior point of view, the Zn-and Fe-based slowly corroding alloys appear as promising alternatives to the Mg-based alloys.