Reparation of femoral defects with a Ca-P coated magnesium alloy scaffold carrying sustained release microspheres

doi:10.3969/j.issn.2095-4344.0689

Abstract

Abstract:

BACKGROUND: Previous studies often discuss that magnesium alloy or core-shell microspheres containing growth factors can promote bone regeneration, but there are no relevant reports on the bone regeneration effect of magnesium alloy scaffolds combined with core-shell microspheres containing fibroblast growth factor-2 (FGF-2) and bone morphogenetic protein-2 (BMP-2).

OBJECTIVE: To investigate the effect of Ca-P coated ZK60 magnesium alloy scaffolds combined with core-shell microspheres in the rats with femoral defects.

METHODS: The poly(lactic-co-glycolic acid) and poly-L-lactic acid core-shell sustained release microspheres loaded with FGF-2 and BMP-2 were prepared by means of coaxial electrostatic spraying, and they were filled into the hollow tubular scaffolds of ZK60 magnesium alloy. Ca-P coating was applied to the surface of the magnesium alloy. The Ca-P coated ZK60 magnesium alloy scaffolds and uncoated ZK60 magnesium alloy scaffolds were immersed in Hanks solution for 30 days, and then the corrosion resistance of the alloys was tested. Eighteen Sprague-Dawley rats were randomly divided into six groups, and the model of femoral defects was established in each rat. The defects were implanted with nothing (Blank group), Ca-P coating ZK60 magnesium (ZK group), Ca-P coating ZK60+FGF microspheres (FGF group), Ca-P coating ZK60+BMP microspheres (BMP group), Ca-P coating ZK60+FGF+BMP microspheres (DUAL group, release of the growth factor at the same time), or Ca-P coating ZK60+FGF/BMP microspheres (SEQ group, sequential release). The rats were sacrificed at 8 weeks postoperatively. The defects were evaluated by gross observation, Micro-CT and bone tissue pathological observation.

RESULTS AND CONCLUSION: (1) After 30 days of immersion in Hanks solution, there was a significant corrosion pit on the surface of uncoated ZK60 magnesium alloy, while only corrosion cracks were visible on the surface of Ca-P coated ZK60 magnesium alloy. (2) The Micro-CT results showed that the bone defect of the BLANK group was obvious, and was only covered with a layer of soft tissue. The defect site of ZK group was repaired, but not completely. The repair of FGF group was better than that of the ZK group, but the repair was still incomplete. The defects of BMP and DUAL groups were filled with new tissues, and the tissue density was higher in the DUAL group than the BMP group. The repair effect of SEQ group was the best with the highest density of the new tissues. (3) The histopathological sections of bone tissues showed that the bone defect was obvious in the BLANK group, and the defect was somewhat repaired in the ZK group. The defect repair of FGF group, BMP group and DUAL group was better than that of ZK group, and the repair effect of SEQ group was the best. To conclude, Ca-P coated magnesium alloy scaffolds carrying sustained release FGF-2/BMP-2 microspheres can promote bone regeneration.

中国组织工程研究杂志出版内容重点：生物材料；骨生物材料; 口腔生物材料; 纳米材料; 缓释材料; 材料相容性；组织工程

Key words: Bone Morphogenetic Proteins, Fibroblast Growth Factors, Bone Regeneration, Microspheres, Tissue Engineering

CLC Number:

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Lu Yanqin, Yi Fang, Ju Wei, Li Wenjie, Lei Lei. Reparation of femoral defects with a Ca-P coated magnesium alloy scaffold carrying sustained release microspheres[J]. Chinese Journal of Tissue Engineering Research, 2019, 23(2): 232-238.

Figures/Tables 4

2.2 Ca-P涂层镁合金体外抗腐蚀性实验结果各材料样本的腐蚀速率通过测量Hanks溶液pH值和电化学腐蚀测试结果确定。各组Hanks溶液pH值随浸泡时间的变化，见图2A。所有组的pH值都有增加，Ca-P涂层ZK60镁合金溶液 pH值的变化明显低于无涂层ZK60镁合金。前6 d无涂层ZK60镁合金pH值从8.20增加到10.25，Ca-P涂层ZK60镁合金的pH值从7.50增加到8.25。Hanks溶液中pH值的增加主要是由于Mg或其合金的腐蚀，因此涂层合金的腐蚀速率低于无涂层样品的腐蚀速率[14]。此后，所有溶液的pH值保持10.25左右，这是由于此时镁合金表面己形成一定的保护层，且Hanks溶液里离子已达到一定平衡。耐腐蚀是使用镁合金作为骨科生物材料的关键问题，Ca-P涂层ZK60镁合金可满足这一要求，具有更好的耐蚀性。无涂层和Ca-P涂层ZK60镁合金样本的电化学腐蚀测试结果，见图2B所示。Ca-P涂层后样本自腐蚀电压(Ecorr)值从-1.55 V变成-1.38 V，自腐蚀电流(Icorr)从55.54 μA变为38.19 μA，这表明采用Ca-P涂层改善了ZK60镁合金的耐蚀性。无涂层和Ca-P涂层ZK60镁合金样品浸泡在Hanks溶液中30 d后的表面形态，见图2C，D所示。可以看出无涂层ZK60合金样本腐蚀严重，表面出现了明显大腐蚀坑，腐蚀产物沉积在Hanks溶液和材料表面上；而Ca-P涂层ZK60的表面仅可见腐蚀裂痕未见腐蚀坑，并且在表面生成了白色晶体。通过对Ca-P涂层金属表面灰色晶体和白色晶体X射线能谱分析表明，其主要由O、Mg、P、Ca、Zn和C元素组成，如图2E，F；白色晶体相晶体的Ca/P比为1.0，黑色部分约为0.9，都比羟基磷灰石Ca/P比1.67小，接近二水磷酸钙(的Ca/P比1.0。这表明Ca-P涂层ZK60镁合金浸泡在Hanks溶液中后在材料表面上可能产生羟基磷灰石的前体二水磷酸钙[15]。这些都表明，表面上形成了类骨磷灰石[16]。"

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