Henan University of Science and Technology
目的 研究应力对新型镁合金骨钉体外降解速率的影响。方法 根据逆向建模方法建立的胫骨骨折三维模型设计体外降解实验装置，用有限元计算得到的骨钉应力分布加载实验载荷，有效提高实验的准确性及效率。A组作为对照组不加力，B、C和D组分别施加150N、250N和350N的轴向压力，研究不同力学环境对骨钉体外降解速率的影响程度。将应力分布与体外降解实验结果结合分析，得到应力与新型镁合金骨钉体外降解速率的变化曲线。结果 有限元分析结果表明：II区和IV区应力水平较大，III区次之，I区和V区较低。体外降解实验表明：A组失重最小，产生氢气最少，平均降解速率为（0.315±0.005）mm/a；有应力组随着施加载荷的增大，失重、产氢量逐渐增加，B、C、D组平均降解速率分别为（0.379±0.006）mm/a、（0.469±0.007）mm/a、（0.547±0.009）mm/a。结论 得到新型镁合金骨钉所受的最大应力与平均体外降解速率之间的关系曲线，为镁合金骨钉的选材、设计及临床应用提供数据支撑和理论指导。
Objective To study the effect of stress on the degradation rate in vitro of new magnesium alloy bone screw. Methods A three-dimensional model of the tibia was established using a reverse engineering method, the stress distribution of the bone screws were calculated by finite element (FE) analysis. Then, based on the FE model, the in vitro degradation experimental device for bone screws in mechanical environment was designed, the stress distribution of the screw was used to load the in vitro experimental load, which effectively improved the accuracy and efficiency of the experiment. The experimental samples were divided into four groups, A, B, C, and D, Group A was treated as a control group with no additional force, while Groups B, C, and D were subjected to axial forces of 150, 250, and 350 N. In the experiments, H2 was collected, weight loss was measured, and the surface topography was observed to study the influence of the different mechanical environments on the degradation rate of the bone screws in vitro. Finally, combined the stress distribution with the degradation experiment results in vitro, the curve between stress and the degradation rate of new magnesium alloy bone screws in vitro was obtained. Results The results of FE analysis showed that the stress was mainly concentrated to parts II and IV, followed by part III, parts I and V were lower. Degradation experiments in vitro showed that the 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 group, the weight loss and hydrogen production were increased gradually with the increase of axial force. The average degradation rates of Group B, C and D were (0.379±0.006) mm/a, (0.469±0.007) mm/a and (0.547±0.009) mm/a, respectively. The degradation rate increased with the increase of axial force. Conclusions When the new magnesium alloy bone screw was degraded in mechanical environment, the greater stress on the screw was, the faster the degradation rate in vitro was. The relationship between the maximum stress and the average degradation rate in vitro of the new magnesium alloy bone screws was obtained, which provided data support and theoretical guidance for material selection, design and clinical application of magnesium alloy bone screws.