Mechanical and biodegradable properties of absorbable hydroxyapatite/
poly-DL-lactide screws

doi:10.3969/j.issn.2095-4344.2013.38.002

Abstract

Abstract:

BACKGROUND: Through compounding hydroxyapatite and poly-DL-lactide, the mechanical properties, physical and chemical properties of the implants can be enhanced.
OBJECTIVE: To detect the effect of hydroxyapatite/poly-DL-lactide composite internal fixation screws in canine femoral condyle cancellous bone fracture repair.
METHODS: Forty-two beagle dogs were operated to bilateral femoral condyle fracture models. The left side was fixed using hydroxyapatite/poly-DL-lactide screws as experimental group; while the right side was fixed with pure poly-DL-lactide screws as control group. After 2, 4, 8, 12, 24, 36 and 48 weeks, conditions of fracture were observed using X-ray, femoral and screw specimens were observed histopathologically, and the bending strength and the average molecular weight were detected. The biological absorption rate, intensity decay rate and biodegradation rate were calculated.
RESULTS AND CONCLUSION: After 2-48 weeks, bilateral fractures were fixed well and new bone grew well, but the biological absorption rate of the screws in the experimental group was lower than that in the control group (P ≤0.01). In the first 2, 4 weeks, the bending strength of the experimental screws was higher than that of the control screw (P ≤0.05), but the biodegradable speed was slower in the former one (P ≤ 0.05 or P ≤ 0.01). The pathological changes were similar in the two groups. After 48 weeks, the fractures were healed and bone tissue reconstruction was completed. Compared with the pure poly-DL-lactide screws, the hydroxyapatite/poly-DL-lactide composite internal fixation screws have better fixation effects, biocompatibility, mechanical properties and biodegradability.

Key words: absorbable implants, tissue engineering, hydroxyapatites, peri-implantitis

CLC Number:

R318

Fu Rong, You Xiao-bo, Zhong Zhen-dong, Li Yan. Mechanical and biodegradable properties of absorbable hydroxyapatite/
poly-DL-lactide screws[J]. Chinese Journal of Tissue Engineering Research, doi: 10.3969/j.issn.2095-4344.2013.38.002.

Figures/Tables 4

由表3可以看出，聚-DL-乳酸螺钉和可吸收复合螺钉的初始重均分子质量差别不大，均从置入后2周起逐渐降低，8周后降解加快，至48周时，两组螺钉重均分子质量均降至最低。聚-DL-乳酸螺钉的重均分子质量较可吸收复合螺钉降低速度快，生物降解率在各个时间段高于可吸收复合螺钉(P ≤ 0.05或P ≤ 0.01)。 2.7 各组组织学观察结果骨折愈合：两组骨折均固定良好，无移位。置入后解剖观察实验组骨折处缝隙较小，随置入时间延长，骨折线逐渐模糊，直至基本消失，提示骨折愈合良好，无延迟愈合及不愈合情况。两组螺钉置入钉道清晰，提示螺钉固定良好。螺钉观察：实验组螺钉初始外观呈乳白色，不透明，对照组螺钉初始外观呈透明状，光泽度良好。置入后2周时，两组螺钉固定良好，未出现断裂、弯曲现象，容易从固定部位完整取出，螺钉外观无明显变化。置入后4周时，两组螺钉固定良好，无断裂弯曲，能完整取出，对照组螺钉表面开始变白。置入后8周时，两组螺钉固定良好，无断裂弯曲，表面螺纹吸收变钝，螺杆表面稍粗糙，对照组螺钉变白。随植入时间延长，两组螺钉表面螺纹吸收缺损明显，螺杆表面明显粗糙，对照组螺钉透明度明显降低呈白色。置入后12周时，两组螺钉表面粗糙，螺纹吸收缺损，对照组螺钉表面明显变白。置入后24周时，两组螺钉表面明显粗糙，螺纹缺损，光泽度差，对照组螺钉透明度明显降低，呈乳白色，出现断裂。置入后36周时，两组螺钉取出困难，均出现断裂，表面明显粗糙，螺纹缺损明显，断裂面不平整，无光泽，对照组螺钉呈乳白色。置入后48周时，两组螺钉取出困难，断裂现象明显，表面螺纹缺损明显，无光泽，对照组螺钉呈明显乳白色。骨组织光镜观察：两组置入后2周均可见炎症反应，肉芽组织内充满成纤维细胞，可见中性粒细胞，实验组炎症反应较轻。置入后4周少量小梁状新骨形成，可见大量成骨细胞，纤维组织增生，见透明软骨组织，类骨质薄。置入后8周成骨活跃，成骨细胞紧贴类骨质表面，类骨质丰富，透明软骨逐渐被小梁骨替代。置入后12周新生骨小梁趋于成熟，互相连接，排列有序。骨小梁内骨细胞排列整齐，软骨基本被小梁骨取代。置入后24周新生骨小梁成熟，互相连接，排列有序。可见较多的新生骨质和多核骨巨细胞，类骨质覆盖均匀，骨小梁内骨细胞排列整齐。置入后36周骨小梁成熟，粗大，互相连接，排列有序。置入后48周，骨小梁成熟，有序排列，螺钉置入区新生骨组织和纤维组织浸入，骨组织重建良好。两组呈现相似病理变化，骨折愈合，骨组织重建良好，见图1。"

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