Organic Template Modified In Situ Synthesis And Characterization Of Biomimetic Calcium Salts Composites

Biominerals is an important component of living organisms, almost all the natural biological minerals are self-assembly biomacromolecules/inorganic composite materials. The structure of biominerals is far more complex than conventional materials. The main feature of biomineral is that the organic template always induces the formation of the inorganic mineral. Mediated by organic templates, phases, size, morphology, orientation, texture and content of each component of inorganic minerals can been controlled precisely. Few natural biominerals is made up of pure inorganic mineral, such as bones, teeth, shells and pearls are natural composite materials. Nearly all biominerals make the use of biomacromolecules to control the growth of inorganic phase. At same time, these natural organic matters in the composite materials also serve as the framework of the structure. Using the principle of biomineralization is a new biomimetic synthesis of the field of materials synthesis, especially the growth control of the inorganic minerals by organic templates and the synthesis of the organic/inorganic composites under the framework of the organic templates, has been the hot research area of biomimetic synthesis. In recent years, based on above studies, researchers have carried many significant works in the area of biomaterials, and make some great progresses in biomedical materials.Referring to relative literatures, we use several different natural polymer hydrogels as organic template to control the in situ precipitation of the hydroxyapatite in the hydrogel. In addition, some other polymers are added in the original natural polymer hydrogel systems in order to achieve the dual effect of template control and the organic/inorganic composite can be prepared with a special structure and excellent performance for bone repair and bone tissue engineering; Secondly, this paper also studies the mediation of different organic matrix on the growth of calcium carbonate minerals, and obtains calcium carbonate minerals with multi-level structure in sub-micro level and the mesoscopic scale. The results provide the necessary physical and chemical parameters and basis for the further study of biomineralization of organic template system and the relationship between structure and function of organic templates and inorganic minerals. The main contents of this dissertation are as following:1. Homogeneous gelatin-poly(acrylic acid)/hydroxyapatite nanocomposites, chitosan-polylactic acid/hydroxyapatite nanocomposites and chitosan-silk fibroin/hydroxyapatite nanocomposites were respectively prepared by an approach of in situ precipitation through a multiple-order template-driven. The morphological and componential characteristics of the nanocomposite were performed by means of scanning electron microscope (SEM), transmission electron microscope (TEM), X-ray diffraction analyzer (XRD) and fourier transformed infrared spectroscopy (FTIR), mechanical properties of nanocomposite was characterized by universal testing machine. The experimental results indicate that natural organic hydrogel template and other polymer additives played obvious dual mediation effects during the fabrication of inorganic/organic nanocomposite. The compartment effect from three-dimensional networks of natural polymer hydrogel can control the size and decentralization degree of inorganic particles in organic matrices. Moreover, addition of other polymer additives in the natural polymer hydrogel can further mediate the morphology and structure of the inorganic particles and also enhance the mechanical property of the inorganic/organic composite. Based on above homogeneous hydroxyapatite/organic hydrogel nanocomposite, scaffolds with hierarchical porosity were prepared by a multilevel lyophilization, the scaffold mimic the structure of natural bone from micro- to sub micro-scale which make it more useful in the bone biomimetic applications at different level. The present study may further enhance the understanding of biomineralization and shed light on the development of new biomaterials for bone tissue engineering.2,. The purpose of this part is to fabricating porous biomaterial scaffolds with optimized pore architecture for load-bearing bone sites in bone repair. We develop a novel fabrication technique of porous scaffold which was inspired by the phenomenon of dialysis. Here we employ this process of dialysis into the in situ precipitation and develop a smart strategy to integrate composite synthesis and pores fabrication into one step by an improved in situ precipitation method based on our previous work. Briefly, unidirectional pores come forth through a spontaneous process that occurs simultaneously with the in situ precipitation of HA into the CS matrix. Use this method, we have successfully fabricated orientation-structured porous CS/HA scaffold exhibiting highly anisotropic porous structure, uniform and optimal pore sizes, high porosity, unidirectional interconnected network, and excellent anisotropic mechanical properties, which have met many of the key requirements for bone tissue engineering. This novel one-step fabrication method opens up a new field for the traditional technique of porous structure fabrication, especially for anisotropic porous structure fabrication. It is expected that the fabrication technique could be extended to a variety of other polymers as matrix materials. In addition, the in vitro cell culture experiments indicated that orientation-structured porous CS/HA scaffold (40/60 in weight ratio) showed excellent cell biocompatibility, in which the MG63 cells could spread and cluster along the macroporous walls of the scaffold, and deeply penetrate into the tube-like pores. This unidirectional tubular structure would probably facilitate cell ingrowth and further tissue formation after implantation in vivo. Based on the biomimetic conception of bone tissue in anisotropic structure and properties, it is worth pointing out that the anisotropic porous scaffolds may have more advantages than traditional random porous scaffolds as bone substitutes and have a better potential for application in bone tissue engineering.3. Calcium carbonate crystals were induced by gelatin and chitosan natural polymers respectively. Moreover, aspartic acid small organic molecules are also added to the biomacromolecular template for dual mediations. From the characteristics of biomineralization of calcium carbonate mineral, we improve the in situ precipitation technique developed by our research group from the perspective of biomimetic synthesis. Hydrothermal decomposition of urea solution can produce carbon dioxide in situ, and carbon dioxide combines with calcium ions in solution to precipitate calcium carbonate in situ. In addition, the temperature and pressure of hydrothermal reaction can be controlled, and the reaction can be artificially controlled in a different time. From the analysis and observation of the products induced by organic template at different time, we can further understand the different roles of mediation factors in the complex organic template system in order to provide new ideas and research model for the synthesis of some complex morphology with special characteristics of the inorganic mineral crystals.