Magnesium (Mg) based materials are the focus of research for use as degradable materials in orthopedics and cranio-maxillofacial surgery. However, corrosion rate control and biosecurity are still the key issues that need to be solved prior to their clinical applications. In the present study, as-rolled high-purity magnesium (HP Mg, 99.99 wt%) screws were implanted in rabbit tibiae for up to 52 weeks in order to investigate their long-term in vivo degradation and the local and systemic effects of their degradation products. A series of long-term monitoring were performed at various time points (4w, 12w, 26w and 52w) after implantation using numerous investigations such as micro-CT assay, histomorphometric analysis, local micro-environment testing and biochemical analysis of serum and urine. It was revealed that HP Mg screws had a uniform degradation morphology and a slow degradation rate in vivo during the period of 52 weeks. Their degradation products not only increased the local pH values but also changed the local Mg²⁺ ions concentration and gas cavity area in the peri-implant tissues in a dynamic manner. More importantly, both the new bone formation and bone-implant contact rate were increased at bone-implant interfaces at 26 weeks and 52 weeks post-implantation. Furthermore, neither abnormal elevation of serum magnesium and urine magnesium level, nor liver and kidney dysfunction were detected during the monitoring period of 26 weeks. All these results of long-term investigation suggest that HP Mg screws possess a slow degradation rate, desirable bone repair capacity and long-term local/systemic biosafety, and consequently may have good potential for application as bone fixation devices.

Statement of significance

The corrosion resistance control and biosecurity issues of Mg alloys limited their clinical applications in some extent. Mg purification is another effective way to improve corrosion resistance of Mg-based materials. However, the long-term in vivo degradation of high-purity magnesium (HP Mg) and the local and systemic effects of its degradation products have not been fully investigated yet, which are the key factors to determine the clinical application prospect of HP Mg. Especially the changes in peri-implant microenvironment may greatly influence the local physiological response and bone repair. In this study, the long-term evolution tendency of in vivo degradation behavior of HP Mg screws was discovered from the view of space-time. Furthermore, not only the dynamic changes of local microenvironment and the long-term evolution process of bone repair, but also the dynamic systemic responses were systematically revealed. Conclusions of this study may help us to further understand the long-term in vivo evolution of HP Mg degradation and the local/systemic effects of its degradation products and help to guide the design of biodegradable bone fixation material.

中文翻译：

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高纯度镁螺杆降解的长期体内进化—镁降解产物的局部和全身作用

镁（Mg）基材料是在骨科和颅颌面外科手术中用作可降解材料的研究重点。但是，腐蚀速率控制和生物安全性仍然是临床应用之前需要解决的关键问题。在本研究中，将经碾压的高纯度镁（HP Mg，99.99 wt％）螺钉植入兔胫骨中长达52周，以研究其在体内的长期作用。降解及其降解产物的局部和全身作用。在植入后的各个时间点（4w，12w，26w和52w）进行了一系列的长期监测，使用了许多研究，例如微CT分析，组织形态分析，局部微环境测试以及血清和尿液的生化分析。结果表明，HP Mg螺钉在52周内的体内降解形态均匀，降解速度缓慢。它们的降解产物不仅增加了局部pH值，而且改变了周围Mg ²⁺离子的浓度和气腔面积。-以动态方式植入组织。更重要的是，在植入后26周和52周，新的骨形成和骨-植入物接触率在骨-植入物界面处均增加了。此外，在26周的监测期内，未检测到血清镁和尿液镁水平异常升高，也未检测到肝肾功能异常。长期研究的所有这些结果表明，HP Mg螺钉具有较慢的降解速度，理想的骨修复能力和长期的局部/全身生物安全性，因此可能具有作为骨固定装置的良好潜力。

重要声明

镁合金的耐蚀性控制和生物安全性问题在一定程度上限制了其临床应用。镁净化是提高镁基材料耐腐蚀性的另一种有效方法。然而，高纯度镁（HP Mg）的长期体内降解及其降解产物的局部和全身作用尚未得到充分研究，这是确定HP Mg临床应用前景的关键因素。尤其是植入物周围微环境的变化可能会极大地影响局部的生理反应和骨骼修复。在这项研究中，体内的长期演变趋势从时空的角度发现了HP Mg螺杆的降解行为。此外，不仅系统地揭示了局部微环境的动态变化和骨修复的长期演变过程，而且还系统地揭示了动态的系统反应。这项研究的结论可能有助于我们进一步了解HP Mg降解的长期体内进化及其降解产物的局部/全身作用，并有助于指导可生物降解骨固定材料的设计。