【作者】 谢雷；

【导师】 王小祥； 郦剑；

【作者基本信息】 浙江大学 ， 材料加工工程， 2009， 博士

【摘要】 珍珠质是一种天然的生物复合材料,它是由大约95%的文石碳酸钙和5%的有机基质交替叠加,层层复合而成,形成高度有序的微观结构,类似于建筑上的砖墙。得益于这种高度有序的无机-有机复合结构,珍珠质表现出优异的机械性能,尤其是抗断裂韧性,比合成的文石高3000倍。不但如此,珍珠质还具有较高的生物相容性和成骨活性,是一种理想的骨修复和骨替代材料。因此,珍珠质的结构和性能以及其生物矿化机制吸引了众多科学工作者的关注。本文采用扫描电镜(SEM),透射电镜(TEM),X-ray衍射分析(XRD),电子能谱(EDS),喇曼光谱(Raman spectrum),光学金相显微镜等分析测试方法,系统地研究了三角帆蚌贝壳的珍珠质层微观结构和生长方式,并用气氛扩散法体外模拟珍珠质的形成过程。本文利用贝壳的珍珠囊,成功地在钛金属牙种植体表面制备出珍珠质生物活性涂层。对贝壳珍珠质微观结构的广泛观察发现,正常的珍珠结构具有有机-无机层层交叠的高度有序结构,无机相为文石碳酸钙构成。有机基质层的厚度和文石板片的厚度分别为20nm和500nm。TEM研究发现相邻板片的晶体取向存在一定的差异。除了正常的珍珠质结构外,还存在3种比较常见的异常结构带,包括柱状珍珠质结构带,针状晶体结构带和球状晶体结构带。柱状珍珠质结构带中,柱状珍珠质形貌酷似鲍鱼贝壳的珍珠质形貌,但是单个板片的厚度在1000-1300nm之间,为文石单晶。针状晶体结构带和球状晶体结构带由文石多晶构成。球状晶体结构带与鲍鱼贝壳的生长线结构非常相似,球状晶体由棒状文石晶体以放射状方式组装而成,SAD分析表明球状晶体为文石多晶构成。异常结构的形成可能跟有机质异常分泌,导致文石晶体c轴方向生长失控有关。而从相应的贝壳中取得的珍珠的珍珠质微观结构中却未观察到类似的异常结构,这个可能是由矿化微环境的不同导致的。文石板片的形核位置一般在下层文石板片的边缘区域或者位于板片的边界处。形核后,单个文石板片迅速呈现层状结构。这种结构特征伴随文石板片生长的整个过程。HRTEM分析发现,文石板片的晶体内部存在许多晶格缺陷,而且这些缺陷都发生在文石晶体的(001)晶面上,结合前人的研究后,我们认为这些晶格缺陷可能是由于文石板片生长过程中包埋进晶体内部的有机大分子引起的,并且跟文石板片的层状结构有一定的关联。在体外模拟碳酸钙沉积中,未经去有机质处理的珍珠质表面沉积的碳酸钙晶体由文石构成,取向与珍珠质的文石晶体一致,而且呈现出板层结构;而在去有机质处理的珍珠质表面,尽管沉积的碳酸钙晶体的晶型和取向都与珍珠质的文石一致,但是其晶体形貌呈现出屋脊状,而非板层状;载波片基底上沉积的碳酸钙是方解石、文石和球文石晶体的混合物。这些结果表明,有机大分子能吸附到文石晶体的(001)晶面上,控制文石晶体沿c轴方向生长,从而导致板层结构的文石晶体的形成。在本文的研究中,开发了一种新的涂层制备方法,即用生物法在钛金属牙种植体表面制备出天然的珍珠质涂层。将钛金属种植体植入到三角帆蚌的圆形珍珠囊中45天后,可以在种植体的表面沉积上珍珠质涂层。但是观察发现,珍珠质涂层表面有飞边的现象,而且涂层与钛螺钉的界面处存在空隙,说明涂层与种植体的界面处未到达紧密结合。改用圆柱状珍珠囊作为珍珠质涂层制备“反应室”后,可以得到光滑的珍珠质涂层,无飞边现象,而且钛金属螺钉表面和珍珠质涂层紧密结合,无空隙存在。这可能是圆柱状珍珠囊的外套膜与钛金属螺钉的拓扑表面能达到高度匹配的结果。更多还原

【Abstract】 Nacre （mother of pearl）, a natural biocomposite material, is composed of about 95% inorganic aragonite, with only a few percent of organic biopolymer. It has high ordered microstructures in which the crystals and organic matrix exhibit interdigitating array like brick-mortar in architecture. Nacre has excellent mechanical properties due to its laminated microstructures, particularly in its toughness （work of fracture） being 3000 times higher than that of the artificial aragonite. On the other hand, nacre has a high biocompatibility and an ability of inducing growth of bone, and thus is believed to be a new material for bone repairing and substitution. Therefore, nacre has attracted many scientists to study its microstructure and mechanical properties aiming to unveil the biomineralization mechanism by which nacre is formed in mollusk shell.In the present study, SEM, TEM, XRD, EDS, Raman spectrum and optical microscope were used to systemically research the microstructures and formation process of the nacre of freshwater H. cumingii Lea shells and the corresponding pearls. Based on the studies, a formation mechanism of nacre was suggested. Nacreous biocoatings were fabricated successfully on surface of titanium implants by inserting titanium implants into mantle sacs of shells.SEM observations showed that the cross-section of the normal nacre in the shells exhibits the interdigitating array of tablets and organic biopolymer matrix, about 500nm and 30nm in thickness, respectively. XRD analysis showed that nacre was composed of aragonite crystals with a preferential orientation in [001] direction. SAD showed that the individual tablet was diffracted as aragonite single crystal pattern. However, the disorientation of a- and b-axis exists between adjacent tablets of aragonite in normal nacre. Beside the normal nacre, three kinds of abnormal structure band, columnar nacre structure, needle-like structure and spherulitic structure, were frequently observed to be sandwiched inside the nacreous layer on the cross section of shells. The columnar nacre structure band whose structure is similar with the nacre of abalone is proved to be composed of aragonite tablets with preferential orientation of [001] direction, which is identical with the aragonite tablets in normal nacre. Needle-like structure band and spherulitic structure band were composed of aragonite polycrystals. A spherulitic crystal in spherulitic structure band, whose structure is similar with the growth line of abalone shell, is composed of rod-like crystals. The abnormal structure observed in preset study may be induced by abnormal secretion of organic matrix. To our surprise, the similar abnormal structure bands have never been observed in the nacre of pearls which were obtained from the corresponding shells. This may result from the fact that the formation of pearls’ nacre occurs in closed space of mantle sacs.Nucleation of aragonite tablets occurs at the edge of underlying tablets or the boundary region of adjacent tablets. At various stage of growth, the individual aragonite tablets all exhibit laminated structure. The sub-layers are about 20-50nm in thickness. HRTEM showed that many lattice defects existed on the （001） plane of aragonite crystal. These lattice defects are isolated and the spacing in the [001] direction between two neighboring defects is about 5-20nm, a dimension comparable with the thickness of sub-layers, indicating that the laminated structure of individual aragonite tablet may be closely related with these lattice defects. It is believed that these lattice defects may result from the adsorption of organic macromolecules on the （001） plane of aragonite crystal during the growth of individual aragonite tablet. Simulated growth of CaCO₃ in vitro showed that the deposits formed on the native nacre surface were composed of aragonite crystals with laminated structure, while the deposits formed on nacre surfaces which were pre-treated with sodium hypochlorite were composed of aragonite crystals with ridge-like morphology. In the control experiment, the deposits formed on the glass slices were composed of mixture of calcite, aragonite and vaterite. In control experiment, the deposits forming on glass slices were composed of mixture of calcite, aragonite and vaterite. These results suggest that some kind of organic macromolecules that have property to stabilize the （001） plane of aragonite crystals in order to regulate the growth along the c-axis of aragonite crystals, and consequently, form individual aragonite tablet with laminated structure.A new coating technique was developed to fabricate the nacreous biocoatings on titanium implants. All specimens were found to be coated with a layer of natural nacre after implantation for 45 days in spherical mantle sac. However, the mismatching between the local topography of titanium implant surface and spherical mantle sac not only resulted in the formation of a fin along the long-axis of implant, but also led to formation of a gap between the coating and the implant. To solve these problems, we designed a cylindrical pearl sac in order to match the cylindrical titanium implant. Using this cylindrical pearl sac as a reaction room, the nacreous coatings grew smoothly around the whole cylindrical surface of titanium implant. Moreover, the gap between the coating and the titanium implant was disappeared when nacreous coating was fabricated in cylindrical sac, indicating that the close apposition between the coating and the titanium implant was achieved.更多还原