Improving the mechanical properties and corrosion resistance of biodegradable Mg–Zn–Ca–Mn alloy bone screw through structural optimization

Bone screw is a representative device for internal fixation. However, Mg alloy bone screw is subjected to complex loads after implantation and leads to stress concentration in specific site, resulting in rapid local degradation. In order to alleviate the local stress concentration of bone screw, structural optimization was carried out through finite element analysis method in this work. The models related to the size parameters of screw such as inner diameter, pitch and tooth angle, were established to explore the influence of them on the stress concentration through orthogonal experiment in loading conditions of three-point bending, torsion and pull-out. The stress state of the screw under the action of multi-factor coupling was analyzed, and the optimal size parameters of the screw were obtained, that is, the inner diameter was 2.5 mm, the pitch was 1.15 mm, the tooth type angle α was 5°, and the tooth type angle β was 40°. In addition, the mechanical properties and corrosion behavior of the screw before and after optimization were verified by experiments. The experimental results showed that the mechanical properties of the screw after optimization were improved, and the screw after optimization had better corrosion resistance than that of the screw before optimization.