摘要
骨组织工程修复材料作为骨修复材料中的重要部分一直受到广泛的关注。伴随着科技的发展,骨组织工程修复材料由单一的天然材料,人工合成材料,逐渐转向多孔复合材料。
多孔羟基磷灰石(HA)/β-磷酸三钙(β-TCP)是多孔双相钙磷(Biphasic calcium phosphate)生物活性陶瓷的一种。因其具有良好的生物相容性,生物活性和骨诱导性,己在临床上用作骨缺损的修复。然而,强度低、力学性能不佳等缺陷限制了其应用范围。将HA/β-TCP与活性生物玻璃(Bioactive glass)复合,可以将两者的优良性能结合起来,在保证其具有良好的生物活性的前提下,增强材料的力学强度。
本文以四水硝酸钙(Ca(NO_3)_2 .4H_2O)和磷酸氢二铵((NH_4)_2HPO_4)为原料,采用微波辅助化学沉淀法制备了HA/β-TCP的前躯体缺钙羟基磷灰石(d-HA);用正硅酸盐乙酯和磷酸三乙酯为前驱物,采用溶胶-凝胶法制备出具有良好生物活性的生物玻璃58S(58% SiO_2,33% CaO and 9% P_2O_5,w%)的前躯体。用XRD、IR对所制备出的粉体进行表征,用SEM观察d-HA粉体。
本文改进了多孔HA/β-TCP/58S支架的制备方法。在58S未形成凝胶之前,就加入液相的d-HA悬浊液,待形成凝胶状混合体形成后进行热处理,采用注浆成型法制备出多孔支架。通过对d-HA/58S用量比及致孔剂添加量的控制,来调整多孔支架的孔隙率、显孔隙率、吸水率及力学强度,并与干压成型法制备出的多孔支架做比较。使用XRD、IR等分析手段和化学物理分析方法,对复合材料的成分,孔隙率,显孔隙率,吸水率,抗压强度做出分析和表征。利用SEM观察不同成型方法制备出的多孔支架的微观结构。
研究结果表明,致孔剂含量为50%~60%,采用注浆成型法制备出来的支架其孔隙率在60%~70%,显孔隙率为40%~50%,吸水率为40%~50%;采用干压成型法制备出来的多孔支架,在相同致孔剂含量下,其孔隙率为40%~50%,显孔隙率为30%~35%,吸水率为20%~30%。通过电镜扫描发现,采用注浆成型法制备的多孔支架内部孔隙相互连通,大孔与小孔分布均匀;其孔壁表面结构粗糙,有利于细胞的吸附。结果说明,采用注浆成型法制备出的多孔支架有着较好的内部连通性,因而其生物学性能可能更好。研究还发现,添加了58S后,复合支架的力学强度远高于HA/β-TCP支架,在孔隙率为33.2%时,复合支架的力学强度为6 Mpa,而HA/β-TCP为2.5Mpa,随着58S量的增多,复合支架力学强度有进一步提升。尽管采用注浆成型法制备出的多孔支架其力学强度低于干压成型法制备出多孔支架,但在孔隙率为46.9%时,仍达到4.1 Mpa,基本满足骨组织工程修复材料的力学要求。模拟体液体外降解实验表明,复合支架的溶液pH值随着时间的增长而略有增加,这可能更有利益支架表面的类骨磷灰石增长。
综上所述,采用注浆成型法来制备多孔复合支架,是一种制备方法简便,能有效的提高支架的强度,基本构建满足组织工程需求的支架方法。
Bone tissue engineering material plays an important role in bone repair materials and always receive broad attention from all related fields. With the development of technology,the bone tissue engineering material has developed from the only natural materials, to synthetics materials, and gradually to porous composites.
As one kind of porous biphasic calcium phosphate, porous hydroxyapatite(HA)/β-tricalcium phosphate(β-TCP) has excellent bioactivity, osteogenic induciblity and fine biocompatibility for bone defect repair in clinic. However, its own weakness like low-impact, poor mechanical property limit the scope of application. HA/β-TCP composite with bioactive-glass, may unite the advantages of both sides.That means the Composition may has good bioactivity as well as better compressive strength.
In this experiment, we used Ca(NO_3)_2 .4H_2O and (NH_4)_2HPO_4 as raw materials for prepareing HA/β-TCP’s precursor d-HA by the method of microwave-aided chemical precipitation; took orthosilicate ethylester and triethylphosphate as precursors, adopted sol-gel method to produce bioactive 58S which has better bioactive properties. We characterized the produced powder by XRD and IR, and observed d-HA powder by SEM.
We modified the process of HA/β-TCP/58S preparation. Before 58S formed gel, we added suspension of d-HA.Then, took heat treament after the composite became gel hybrid bulk , adopted slip casted method to cast porous scaffolds. By controling the usage raito of d-HA/58S and porogen amount, we adjusted the porosity, pore-porosity, water absorption, compressive strength of the porous scaffolds, and compared these with porous scaffolds made by presse shaped method. The characters of composites, such as composition ,microstructure, pore-porosity, porosity water absorption ,compressive strength were analyzed with IR,XRD,SEM and some chemistry methods.
The results show that, when porogen reached 50% to 60%,(mass fractions) in green body, scaffolds had high porosity about 60% to 70%, pore-porosity about 40% to 50%, water absorption about 40% to 50% by the method of slip casting; however, at the same weight of porogen, scaffolds shaped by press method just reached porosity about 40% to 50%, pore-porosity about 30% to 35%, water absorption about 20% to 30%. SEM indicated that scaffold has connected inner pore with homogeneous pore distribution by the slip casted method and the surface of pore wall of scaffold was rough so that cells may easily get absorbed. Therefore, porous scaffolds made by slip casted method may have better biological properties .Meanwhile, compositing 58S with HA/β-TCP, the scaffolds’s compressive strength improved greatly.When the porosity was about 33.2%, the compound’s compressive strength was about 6 Mpa, but HA/β-TCP just obtained 2.5Mpa.With the the ratio of 58S in scaffold increased, the better compressive strength was achieved. Even though the compressive strength of porous scaffolds made by the slip casted method could not reach the same level of scaffolds by press casted method, they were still up to 4.1 Mpa with porosity about 46.9%, basically satisfy the compressive requirements of bone-tissue engineering. SBF soaking experiment showed, the pH value of SBF solution had slight increase with time growth,which may benefit for bone apatite growth on scaffold surface.
In conclusion, slip casted method is a simple preparation method, can effectively improve the strength of scaffolds, basically meet the needs of tissue engineering method.
引文
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