聚-DL-乳酸生物降解腰椎融合器的设计及材料学特点

Design and fabrication of poly DL-lactic acid biodegradable fusion cage of the lumbar vertebrae

背景:金属椎间融合器存在应力遮挡、融合器下沉、骨吸收、脱出、骨塌陷所带来的并发症和假关节形成等,影响融合效果。生物降解可吸收材料制成的椎间融合器将有可能避免了上述并发症,但目前可吸收腰椎间融合器的材料学性能与设计关系的研究尚属空白。目的:设计并研制聚-DL-乳酸矩形生物降解腰椎间融合器,分析其材料学特性。设计、时间及地点:材料学制备,动物体内植入实验,于2003-01/2006-12在中科院成都有机化学所完成。材料:12月龄家犬20只,由四川大学华西动物实验室提供。聚-DL-乳酸生物降解腰椎间融合器由中科院成都有机化学所生产。方法:根据腰椎间盘的解剖特点及其测量数据,设计聚-DL-乳酸生物降解腰椎间融合器为矩形,长度23和25mm两种规格,宽度为13mm,厚度(前壁)有9、10、11、12四种规格,由前向后厚度呈小弧形变薄,后壁比前壁薄1.5mm,以适应腰椎间盘的形状变化。融合器四壁厚度一致均为2.5mm,两侧壁有数个1mm直径小孔,后壁有3.5mm直径带螺纹孔,用于与植入工具连接。采用精密注塑成型加工工艺,其生产工艺流程是:DL-乳酸→原料贮存→丙交酯制备→丙交酯纯化→聚合→干燥包裹→产品。20只犬全身麻醉后切开双大腿,将该融合器各1枚植入大腿肌肉内,进行体内降解过程抗压强度和黏度试验。主要观察指标:融合器制备情况。动物体内降解过程中融合器的抗压强度和黏度。结果:生产出23mm×13mm×10mm规格的成品,上下两面均呈锯齿状,增强融合的防滑作用,提高了融合器与椎体骨界面之间的锚固力;两侧壁有数个小孔,有助于血管的长入和营养液的交换,以促进骨性融合。植入体内3,6,9个月,尽管随时间的延长该融合器的抗压强度、黏度逐渐降低(r=0.961,P=0.009),但至12个月时仍还有足够的抗压强度和较好的黏度,分别为163MPa和0.66dl/g。结论:聚-DL-乳酸矩形生物降解腰椎间融合器具有较大的装载植骨量及较高的防滑稳定性,融合器的完整性和支撑作用满足促进骨性融合的基本条件。

BACKGROUND： Metal vertebral fusion cage can induce some disadvantages and pseudoarticulation formation such as stress dodge, fusion cage subsidence, bone resorption, prolapse and bone collapse. Biodegradable absorbing material-made vertebral fusion cage can avoid disadvantages mentioned above. There are no studies on correlation of material function to design of absorbing fusion cage of lumbar vertebrae. OBJECTIVE： To design and fabricate the poly DE-lactic acid biodegradable fusion cage of lumbar vertebrae, and to analyze the material characteristics. DESIGN, TIME AND SETTING： The material in vivo experiment was performed at the Chengdu Institute of Organic Chemistry of Chinese Academy of Sciences from January 2003 to December 2006. MATERIALS： Twenty dogs aged 12 months were obtained from Animal Laboratory of West China, Sichuan University. Poly DE-lactic acid biodegradable fusion cage of lumbar vertebrae was produced by the Chengdu Institute of Organic Chemistry of Chinese Academy of Sciences. METHODS： According to the anatomical characters and measured data of lumbar intervertebral disc, we designed the poly DE-lactic acid biodegradable fusion cage of lumbar vertebrae. The rectangle cage consists of two styles： 23 mm and 25 mm, 13 mm in width, and 9, 10, 11 and 12 in depth （anterior wall）. The depth was small half-moon shape from anterior to posterior, and the posterior wall was thinner than anterior wall about 1.5mm to accord with the shape of intervertebral discs. The depth of four walls of the fusion cage was 2.5 mm, with several 1-mm diameter holes on bilateral walls. The posterior wall had 3.5-mm diameter spiral hole, which was used for connecting with the implanted tool. Using precise shaping processing craft, the produce process was DE-lactic acid→raw material storage→lactide preparation→lactide purification→polymerization→drying package→product. After general anesthesia, bilateral thighs were incised in 20 dogs, and then a fusion cage was implanted into each dog to detect compressive strength and viscosity in the process of biodegradation. MAIN OUTCOME MEASURES： Preparation of fusion cage; compressive strength and viscosity in the process of biodegradation in vivo. RESULTS： The size of the products is 23 mm× 13 mm×10 mm and the appearance of the products were saw tooth shape, which could prevent the slide, enhance the solid strength between fusion cage and the surface of vertebra. Small holes on the bilateral wall were beneficial for vascular growth and nutrient fluid exchange, resulting in bony fusion. Compressive strength and viscosity decreased at 3, 6 and 9 months after implantation （r=-0.961, P=0.009）, but compressive strength and viscosity were good at 12 months （163 MPa and 0.66 dl/g）. CONCLUSION： Poly DL-lactic acid biodegradable fusion cage has a big loading implanted bone mass and high stability. The integrity and supportive effect of the fusion cage can meet the requirement of bony fusion.