[In vivo degradation of magnesium alloys and poly (lactic-co-glycolic acid) and degradation evaluation of magnesium alloys using micro-ct]

To explore the degradation of AZ31 magnesium alloy and poly (lactic-co-glycolic acid) (PLGA) in the femoral condyle, and then evaluate the laws of degradation of AZ31 magnesium alloy by Micro-CT images and data.?Forty 3-month-old male New Zealand white rabbits (weighing, 2.5 kg) were randomly divided into 4 groups, 10 rabbits each group. Forty micro-arc-oxidized AZ31 magnesium alloy pins and 40 PLGA pins were implanted into the right and left femoral condyle, respectively. Micro-CT images and data analysis were used to evaluate the degradation at 4, 8, 12, and 16 weeks after operation (n=10). Degradation was evaluated by weight difference between pre-and post-implantation. The inflammatory response was observed around the implants by HE staining. The weight loss of magnesium alloy and Micro-CT results were compared.?The Micro-CT images showed that PLGA pins had gray low signal, which was similar to the soft tissue around. At 4 weeks after operation, no signs of degradation were observed, and there were little corrosion pitting on the magnesium alloy. At 8 weeks, corrosion pitting gradually expanded, the boundary between the longitudinal axis and the cross section became blurred; at 16 weeks, corrosion pitting became bigger, and the boundary was discontinuous. Micro-CT quantitative analysis showed that the volume fraction of magnesium pins decreased slowly at 4 and 8 weeks; it was significantly lower at 12 and 16 weeks than 4 and 8 weeks (P0.05). The magnesium cylinder mineral density continuously decreased during the study period, it had a rapidly speed from 12 to 16 weeks (P0.05). However, the magnesium CT image density showed a slight change (P0.05). The surface-to-volume ratio of the pins constantly increased, and the ratio was significantly larger at 12 and 16 weeks than 4 and 8 weeks, and at 16 weeks than 12 weeks (P0.05). There was more and more corrosion pitting on the surface with time, which resulted in a decrease in the radius that mean trabecular thickness gradually decreased, showing significant difference between different time points after 8 weeks (P0.05). The weight loss detection showed that the degradation of magnesium pin and PLGA gradually increased with time (P0.05), and the degradation rate of magnesium pin was significantly lower than that of PLGA at 8-12 weeks (P0.05), but the degradation rate of magnesium pin was higher than that of PLGA at 16 weeks. At each time point, the weight loss of magnesium alloy was similar to that by Micro-CT, but mass fraction was lower than volume fraction and had significant differences at 8, 12, and 16 weeks (P0.05). HE staining revealed that slight inflammatory response was observed around the magnesium pins at 4 weeks, and inflammatory reaction gradually reduced with time and disappeared at 16 weeks, but no inflammatory reaction was seen around PLGA.?Micro-CT has the advantages of non-trauma, in vivo detection, quantitative analysis, and precise data in evaluating the degradation of AZ31 magnesium alloy. Regarding the degradation of the magnesium alloy and PLGA in vivo, the degradation rate is slow in the early stage, and then increases with time. The degradation of PLGA is faster and earlier but it is then overtaken by AZ31 magnesium alloy at 16 weeks. During the degradation, the density of the magnesium has almost no change. The biomaterials can not firmly attach to the surrounding tissues due to inadequate holding forces.比较镁合金与聚乳酸-羟基乙酸共聚物[poly（lactic-co-glycolic acid），PLGA]在体内降解情况，同时采用Micro-CT深入研究镁合金体内降解规律。.取3月龄雄性新西兰大白兔40只，分别于右侧和左侧股骨髁钻孔植入40个表面微弧氧化处理的AZ31镁合金棒（镁棒）和40个PLGA棒。术后4、8、12、16周各处死10只动物，取出双侧股骨髁，采用Micro-CT扫描及生成数据定量评价植入物降解情况；然后取出植入物清洗、烘干后称重，与术前重量差值作为植入物降解量；HE染色观察局部炎性反应情况。并将镁合金的失重情况与Micro-CT的评价结果进行对比。.Micro-CT扫描示，PLGA棒不显影。术后4周镁棒几乎无降解痕迹，有少量腐蚀点；术后8周在4周原有腐蚀点基础上逐步扩大，纵轴与横截面交界边缘变得模糊；至术后16周镁棒表面腐蚀面积更大，边缘已不连续。Micro-CT定量分析示：术后4、8周镁棒体积分数下降缓慢；术后12、16周较术后4、8周降低明显，16周最低，差异均有统计学意义（P0.05）。术后随时间延长镁矿物密度持续降低，12～16周降低速度最快，第8周后各时间点间比较差异均有统计学意义（P0.05）；而镁CT图像密度随术后时间延长变化很小（P0.05）。术后随时间延长镁棒表面积与体积比持续增加，术后12、16周明显高于4、8周，且16周高于12周（P0.05）。术后随时间延长，镁棒表面腐蚀点越来越多，导致横截面半径减小，即平均骨小梁厚度逐渐降低，8周后各时间点间差异均有统计学意义（P0.05）。失重法检测示：术后随时间延长，两种材料降解量均逐渐增加（P0.05）；术后8、12周，镁棒降解量均显著低于PLGA棒（P0.05），但术后16周时镁棒降解量已超过PLGA棒。将各时间点镁棒质量分数与Micro-CT方法得出的体积分数进行比较，结果显示两个指标的变化趋势相近，但各时间点镁棒质量分数均低于体积分数，且在第8、12、16周差异有统计学意义（P0.05）。HE染色示，术后4周镁棒周围可见轻度炎性反应，但随时间延长炎性反应逐渐减轻，至16周时已未见炎性反应；而PLGA周围一直无炎性反应。.采用Micro-CT检测镁合金降解情况具有无创、可活体检测、定量、精确的优势。镁合金和PLGA在体内均随时间推移而逐步腐蚀，经历先缓慢后加速的持续降解过程；PLGA在体内降解则更早、更快，至16周时镁合金降解量已超过PLGA，镁合金密度在降解过程中无明显变化。镁合金在金属与原骨之间产生新生骨桥欠充分，仍缺乏足够的无缝连接能力。.