【作者】 黄苏萍；

【导师】 黄伯云； 周科朝；

【作者基本信息】 中南大学 ， 材料学， 2006， 博士

【摘要】 针对羟基磷灰石（Hydroxyapatite,简称HA）/高密度聚乙烯（HighDensityPolyethylene,简称HDPE）骨替代材料的力学性能低和生物相容性差等问题,本文通过优化微观结构和制备工艺,对HA/HDPE复合材料的力学性能、生物相容性及强韧化机理进行了系统研究,获得如下结论:1.依据人体骨的结构特征,首次对HA/HDPE骨替代材料进行了多尺度结构设计:从原子尺度上——提高材料界面结合强度;纳米尺度上——实现纳米HA颗粒在HDPE基体中的均匀分散;微米尺度上——形成定向排列的HA/HDPE复合纤维织构;从而通过多尺度的协同作用来达到提高HA/HDPE骨替代材料力学性能的目的。2.阐明了HA矿化机理,并确定出诱导HA矿化的最佳有机功能团结构-COOH和矿化液成分。结果表明:以-COOH、-NH₂为功能团的有机分子膜通过静电聚集、立体化学互补和晶格匹配三种界面识别作用调控无机晶体在有机膜上的形核与生长,使HA晶体定向生长。矿化液中的无机离子和氨基酸分子通过与HA晶体的晶格离子发生交换或在HA晶体表面吸附来控制HA晶体的生长与形貌。HA晶体在矿化液中的生长过程遵循表面扩散的螺旋生长机理,并依此确定出诱导HA矿化的最佳有机功能团结构-COOH和矿化液成分。3.首次采用原位矿化复合技术,模拟人体骨的矿化过程,通过枝接在HDPE表面的-COOH功能团从分子水平调控HA晶体在HDPE上的形核与生长,制备出纳米HA/HDPE复合粉末,从而有效改善了纳米HA颗粒在HDPE基体中的分散状态,并提高了HA/HDPE界面结合强度,解决了HA在基体中易团聚和界面结合强度低的技术难关。4.采用固相挤出技术成功制备出了纳米HA颗粒均匀分散、HA/HDPE复合纤维定向排列的多尺度结构HA/HDPE复合材料:其拉伸强度为245MPa,抗弯强度为165MPa,拉伸模量为18.1GPa,达到了皮质骨力学性能的要求。分析表明,该复合材料中HA与HDPE之间以化学键结合,界面结合强度很高,因此在HDPE结晶过程中在HA周围形成网络结构的伸直链晶,该结构的存在显著提高了材料的强度。另一方面,材料中形成了定向排列的复合纤维,这是复合材料强度提高的重要原因。5.阐明了HA/HDPE多尺度复合材料的强韧化机理。研究表明:多尺度结构HA/HDPE复合材料的增强增韧是通过纳米HA颗粒和HA/HDPE复合纤维在不同尺度上协同作用的结果。在纳米尺度,纳米HA颗粒的均匀分散和高的HA/HDPE界面结合强度显著提高了HDPE的结晶度,细化了HDPE晶粒尺寸,并在HA颗粒表面形成取向结晶层,从而使材料在断裂过程中通过HDPE取向结晶层的基体形变和HA脱粘过程对微裂纹起钝化和钉扎作用,并扩大能量耗散的区域,以阻滞微孔隙和银纹的长大和破断,抑制大裂纹的早期形成。在微米尺度,由于HA/HDPE复合纤维的定向排列,使体系的活化体积显著降低,大大增加了材料的断裂热激活能,从而显著提高材料的强度。另一方面,复合纤维在应力作用过程中通过纤维断裂、纤维拔出、裂纹偏转机制使材料在形变与破坏过程中耗散更多的能量,从而显著提高材料的强度和韧性。6.体外模拟实验、体外细胞毒性实验和体内植入实验结果表明:HA/HDPE复合材料有利于碳酸羟基磷灰石（HCA）的矿化沉积,对微环境的Ca²⁺浓度和酸碱度影响微小;无细胞毒性,且植入后的炎性细胞程度和囊壁形成均符合生物材料评价标准,说明多尺度结构HA/HDPE复合材料具有良好的成骨性能和生物相容性。更多还原

【Abstract】 In order to enhance mechanical properties and improve the biocompatibility, the HA/HDPE composite with multi-scale structure was prepared by the process of structure design, surface modification, in situ biomineralization, and solid-state extrusion. And its microstructure, mechanical properties, biocompatibility and the mechanism of toughening and reinforcement were investigated systematically in this paper.1. Based on the microstructure characteristics of human being’s bone, the HA/HDPE composite structure was designed from multi-scale structure: on the atom scale, the interfacial strength was high; the HA nanoparticles dispersed in the HDPE matrix homogeneously on the nano-scale; and on the micro-scale, the oriented and arrayed HA/HDPE composite fibers were formed. Its aims were to enhance the mechanical properties by the co-operate action on the multi-scales.2. The biomineralization mechanism of HA was studied systematically, results showed that the -COOH and the -NH₂ functional groups had high polarity and charged density, which led to increase supersatuation and lower the interfacial energy, they controlled the nucleation and crystal growth of HA by the "interfacial molecular recognization" of electrostatic accumulation, structural correspondence and stereochemical requirements. The inorganic ions and amine acids controlled the crystal growth and morphology of HA by absorbing on the surface of HA or exchanging with the lattice ions of HA. And the crystal growth of HA followed the surface diffusion controlled screw growth mechanism.3. The process of in situ biomineralization was applied to prepare HA/HDPE powders for the first time. FTIR analysis indicated that the HA nanoparticles grew on the HDPE with chemical bond and dispersed in polymer on the level of nanometer dimension, which improved the dispersion of HA in the HDPE matrix and efficiently enhanced the interfacial strength.4. The process of solid-state extrusion was applied to prepare the HA/HDPE composite, and its effect on microstructure and mechanical properties of HA/ HDPE composite was investigated by means of Fourier transformed infrared spectroscopy （FTIR）, scanning electron microscope （SEM）, Instron testing machine and Ceast Impact tester at room temperature. Results show that: （1） The HA/HDPE was a multi-scale microstructure composite. On the nano-scale, the HA particles dispersed in the matrix homogeneously; the HA/HDPE composite fibers was oriented and arrayed on the micro-scale. （2） HA/HDPE composite has the better mechanical properties. The bend strength, tensile strength and Yong’s modulus reach 165MPa, 245MPa and 18.1GPa, respectively, which meet the mechanical requirements for cortical bone. Tensile fracture analysis and energy dispersive X-ray analysis （EDX） results indicated that the interfacial bonding strength was high, in the higher interfacial bonding strength condition, the produced interfacial stress from the contraction of matrix can strain-induces the crystallization of matrix to forming the extended-chain crystal structure in the area surrounding the filler, as a result, the mechanical properties of composite were improved greatly. On the other hand, the oriented and allied HA/HDPE fibers were formed, which was the main role to enhance the mechanical properties.5. The toughening and reinforcement mechanism of HA/HDPE composite was investigated. Results show that the co-operate actions of multi-scale was the main role to enhance the mechanical properties. On the nano-scale, homogeneous dispersion of HA and high interfacial strength between HA and HDPE leads to the high crystalline, litter crystal size and the formation of oriented extended-chain crystal structure. Its result in the HDPE deformation and HA deadhesion during the fracture process, which can pin the development of microcracks, expend large energies and prohibit the formation of large crack. On the micro-scale, the formation of oriented HA/HDPE fibers can reduce greatly the activity volume and crease the fracture energy, which leads to the strength high. On the other hand, the composite fiber can expend energies largely by fracture, pullout and crackbowing, which enhance the strength and toughening to a great extend.6. The simulating experiment in vitro was operated. Results show that the HA/HDPE composite can induce the carbonic-hydroxyapatite mineralize on the composite, and its influence on the concentration and acid/alkali value of simulate body fluid was very little, which indicate that the composite have good osteoinduction and osteoconduction. The biocompatibility of the HA/HDPE composite was evaluated by flow cytometry after L929 incubated with extraction of the HA/HDPE composite, implanted in animal, compared with the materials applied in clinch. The results showed that there are no significant differences between two groups （P>0.05）, which demonstrated that the HA/HDPE composite had a good biocompatibility.更多还原