应力作用下医用镁合金及其器械的腐蚀降解行为与调控机制研究

Applications of magnesium alloys as biomedical implants are crucially dependent on the understanding and controling of the unexpected overfast biodegradation as well as loss of mechanical integrity. Although it's so important to draw attention, few research has been studied on the biodegradation behaviors of magnesium alloys under the action of stress. As a fact, the biodegradable magnesium implants will be surrounded by the complex stress distribution in the clinical appliations. It is well known that the industrial magnesium alloys are highly susceptible to stress corrosion cracking (SCC) especially in the environments containg Cl-. So it is insufficient to study the biodegradation behaviors of magnesium in biological system, which is also full of Cl- ions, without considering the stress condition. Therefore, it is nessesary to fully study and establish the relationship between stress and biodegradation behavior of magnesium. This project proposes to investigate the degradation rate and cracking behavior changes under different stress effects, using the MgZn alloy as the main research group. It foucus on building connections between the stress and the in vitro biodegradation of Mg by getting mechanical test results, e.g. critical stress, to select the appropriate alloy composition and better microstucture. Meanwhile, the computer simulation will be carried out to establish the modelling of stress distribution effects on Mg cracking in the physiological environmet, which will mainly select the wire or sheet implants of magensium. Finally, in order to support the theoretical research, the animal experiments will also be taken to research the mechanical decreasing and fracture mode of magnesium implants in the in vivo stress environment, thus providing the design principles for implant devices.

调控医用镁的腐蚀降解速率和力学衰减达到临床要求是其实用化的关键问题，但目前针对医用镁的腐蚀降解研究还很少涉及到应力作用下的情况，这与医用镁实际使用中存在的复杂应力条件不相符合。由于镁合金是应力腐蚀敏感的材料，尤其在含有Cl-离子环境中，所以，未考虑应力作用下的腐蚀研究对人体这种富含Cl-离子的环境来说是很不充分的，结果科学性也值得怀疑。因此，系统开展应力作用下医用镁合金的腐蚀降解行为及其调控机制的研究就显得非常必要。本课题拟采用镁锌合金为研究组，研究不同应力作用下医用镁的体外降解速率和断裂模式，建立起应力与模拟体液中镁的腐蚀降解的关联数据曲线，优选出应力腐蚀敏感性最低的镁锌合金成分和显微结构，并确定其临界应力大小。对丝材和薄板类镁合金典型器械进行应力数值模拟计算，建立植入物应力分布图。进行镁合金植入物的动物体内植入实验，研究体内应力环境下的力学衰减和断裂模式，为相关器械设计提供理论依据。

调控医用镁的腐蚀降解速率和力学衰减以达到临床要求是其实用化的关键问题。医用镁在实际使用过程中一直处于人体内复杂的应力环境中，然而目前还很少有针对医用镁金属在应力作用下的腐蚀降解行为方面的研究。因此本课题系统地开展应力作用下医用镁合金的腐蚀降解行为及其调控机制的研究具有重要意义。本研究首先筛选出应力腐蚀敏感性较低的高纯镁，并探究了以高纯镁制成的镁丝和镁板在应力作用下的腐蚀降解行为。研究发现镁丝的腐蚀速率随着加载静拉力的增加而显著增加，同时断裂时间显著缩短；镁板在三点弯曲加载下的腐蚀降解没有明显变化，而在四点弯曲加载下其腐蚀速率则随着弯曲载荷的增加而增加。针对三种典型镁金属植入医疗器械开展了应力分布特征的模拟计算和结构优化设计，完成了动物植入试验的验证。采用镁丝材所制备的吻合钉植入动物体内研究其降解情况，结果表明镁金属吻合钉的不同结构会产生不同的应力分布，导致不同的腐蚀降解和失效断裂，优化的镁吻合钉在动物体内能够保持良好的闭合。研究了镁板材所制备的金属夹在动物体内降解的情况，发现镁金属夹的应力集中区域腐蚀降解相对严重。同时，对镁螺钉在骨折力学模型中的腐蚀降解情况进行了研究，发现镁螺钉在固定骨折因拉伸应力存在，其腐蚀降解速率有所加快。