CNTs/磷酸钙骨水泥复合材料的快速凝固成型及机理研究

【作者】 孙晓宁；

【导师】 孙康宁；

【作者基本信息】 山东大学 ， 材料学， 2007， 硕士

【摘要】 磷酸钙骨水泥使用过程中操作简便，可任意成形，可以原位固化，植入体内后，在体内环境下自行结晶，固化后产物的化学成分与骨组织的无机成分相似，晶相结构亦与骨组织相近，植入骨缺损后可被逐渐降解吸收，降解释放的钙和磷也能够参与缺损区骨组织形成，是理想的骨替换及修复材料。但磷酸钙骨水泥凝固速度慢，强度低、力学性能差，力学性能仅介于松质骨与皮质骨之间，脆性大且承受载荷的能力差，大大限制了它的应用，常见的改善方法包括：固体粉料方面，不同的磷酸钙之间相互搭配，向粉料中加入外加剂等；调和液方面，选用柠檬酸、衣康酸、苹果酸、磷酸钠盐等有机及无机调和液；传统的增强方法：与晶须、有机高分子材料、短纤维等形成复合材料。本文采用固相烧结法制备所需的磷酸钙粉体，系统观察了不同冷却方式对磷酸钙粉体纯度的影响，选取合适的冷却方式，制备出了高纯度的磷酸钙粉体。利用纳米碳管尺度小、强度高、弹性模量大、比表面积大、力学性能优异等特点，将纳米碳管作为增强相，通过球磨混合的方式，将纳米碳管分散到磷酸钙粉体中，添加不同含量的纳米碳管，通过SEM观察纳米碳管在粉体中的分散情况，通过测量复合粉体成型后力学性能，不同纳米碳管含量时的压缩及弯曲强度，最终得到纳米碳管分散较为均匀，成型后力学性能较高的纳米碳管／磷酸钙复合材料粉体。系统研究原始颗粒粒度、液固比、HA晶种对复合材料粉体成型后凝固时间及力学性能的影响。实验表明减小颗粒粒径，加入晶种HA，降低液固比都可以缩短复合材料的凝固时间，凝固时间最短出现在颗粒粒径最小时：T_I=5.5min，T_F=6.4min。复合材料的力学性能与参数的选取有关，当液固比为0.35时得到弯曲强度的最大值16.81MPa。对微观结构观察发现，加入晶种HA会促使水化后产物成颗粒状。采用两种添加方式加入添加剂壳聚糖，断口SEM分析表明加入壳聚糖后水化后产物多为棒状，但有部分片层状产物；壳聚糖含量0.5％时，凝固时间较短而力学性能比较高。将壳聚糖温敏凝胶作为液相与磷酸钙粉体混合，力学性能较纯磷酸钙骨水泥有所提高，SEM图片显示复合材料为蜂窝状网络结构，可以考虑用来制备组织工程支架材料。对复合材料的凝固机理进行探索，利用固相反应动力学和不均匀扩散的有关原理，进一步证明原始颗粒粒径越小，凝固时间越短；固液比的变化会改变固体颗粒间的距离，造成颗粒间相互搭接所需的时间发生变化。加入HA品种能够降低成核势垒，加快成核速度，因此凝固时间缩短。添加剂壳聚糖通过改变液相的粘度，减缓成核速率，因此凝固时间延长；分析认为：壳聚糖的分子链带有多种官能团，对HA晶体的生长有定向引导作用，因此水化产物部分呈现片层状。更多还原

【Abstract】 Calcium phosphate cement can be easily operated and shaped at will, it is a self-setting cement which can solidify in-situ. When implanted in human body, it grow spontaneously, the chemical component of the products are similar to the inorganic component of the bone, the structure of the crystals are also similar to the bone structure. The hydrated products have biodegradability, after injection, they are absorbed by the human body gradually, the Ca and P ions take part in the formation of the damaged bone, so it is a perfect material for bone substitution and repair. But calcium phosphate cement has low strength and mechanical properties, it can’t endure load because of its brittleness, which restrict its use. Researches are carried out to resolve these problems. First is solid powder, including the arrangement in-group for different calcium phosphate and the addition of additives. Second is liquid, including citric acid, malic acid and phosphate natrium. Crystal whisker, organic materials, chopped fiber were also used to strengthen the materials.In this paper, calcium phosphate powders were prepared by solid-state sintering, the influence of the cooling method on the purity of the powder was studied. We choose a proper cooling method to prepare powder with high purity.Carbon nanotubes possess unique properties such as small measure, high strength, the great modulus of elasticity and specific surface area. The CNTs, which were used to strength the materials, were added to the powders by ball milling. Different content of CNTs were added, the disperse condition were studied by SEM photographs, the flexural strength and the compressive strength of the composite with different content of CNTs were also compared. At last, we got CNTs/CPC composite powder with uniform dispersion of CNTs and high mechanics strength after setting.We did research about the influence of the granularity of raw powder, the ratio of liquid to solid and the content of HA crystal seed on the setting time and the mechanics strength of the composites. The experiments showed that reducing the diameter of the powder, adding HA crystal seeds and reducing the ratio of liquid to solid can shorten the setting time of the composite, the shortest setting time is T_I=5.5min, T_F=6.4min when the diameter of the powder is the minimum. The mechanics strength changed with the parameter and when the ratio of the liquid to solid is 0.35, we got the maximum of flexural strength, which was 16.81MPa. Observing the microstructure, we found that the addition of HA crystal seed will induce the morphology of the hydrated product to become grain-like.Two method were used to add chitosan, the result showed that the hydrated product have rod-like morphology, part showed plate-like. When the content of the chitosan is 0.5%, we got short setting time but high mechanics strength. Thermosensitive chitosan-based hydrogel were used as liquid and mixed with calcium phosphate powder, compared with pure calcium phosphate cement, the mechanics strength was improved. The SEM photographs showed that the structure is net-like, which can be used to prepare tissue engineering scaffold material.The setting mechanism of the composite were studied, we used solid reaction kinetics and principle of nonhomogeneous diffusion to explain that the smaller of the raw powder, the shorter of the setting time. The variety of ratio of liquid to solid will change the distance of the powders, which cause the change of the reaction time between powders. The addition of HA crystal seeds could decrease the potential barrier for nucleation and therefore accelerate nucleation and growth of the product. The addition of chitosan will increase the viscosity of the liquid, decelerate nucleation, therefore the setting time is prolonged. It showed that chitosan molecule have kinds of functions, which lead the product to grow to a certain direction, therefore part of hydrated product show plate-like.更多还原