Experimental Study of Stress Effects on the Degradation Rate in vitro of Novel Magnesium Alloy Bone Screws / 医用生物力学

ABSTRACT

Objective To study the effect of stress on the degradation rate in vitro of novel magnesium alloy bone screw. Methods A three-dimensional （3D） model of the tibia fracture was established using the reverse engineering method. Then, based on the FE model, the in vitro degradation experimental device for bone screws was designed. The stress distribution of the screw by finite element calculation was used as the in vitro experimental load, which effectively improved the accuracy and efficiency of the experiment. The experimental samples were divided into four groups. Group A was treated as control group without force application, while Groups B, C and D were subjected to 150, 250 and 350 N axial forces. The influence of different mechanical environment on the degradation rate in vitro of bone screws was investigated. Finally, combining the stress distributions with the degradation experiment results in vitro, the curve between the stress and the degradation rate in vitro of novel magnesium alloy bone screws was obtained. Results Degradation experiments in vitro showed that Group A had the lowest weight loss and hydrogen production, and the average degradation rate was (0.315±0.005) mm/a. While in the stress groups, the weight loss and hydrogen production increased gradually with the axial force increasing. The average degradation rates of Groups B, C and D were (0.379±0.006), (0.469±0.007) and (0.547±0.009) mm/a, respectively. Conclusions When the novel magnesium alloy bone screw was degraded in mechanical environment, the greater stress on the screw would cause the faster degradation rate in vitro. The obtained relationship between the maximum stress and the average degradation rate in vitro of the novel megnesium alloy bone screw provided data support and theoretical guidance for material selection, design and clinical application of magnesium alloy bone screws.