Hydrogel Template Modified In Situ Synthesis And Characterization Of Calcium Phosphates Composites For Bone Tissue Engineering

In natural world, biominerals such as ivories, fish otoliths, magnetosomes, bones, eggshells, teeth, pearls and so on, possess excellent biological, physical and chemical properties. It is helpful for developing and utilizing the novel materials to further study the formation mechanism of these biominerals and the characteristics of biomineralization. Biomineralization is a research direction of regenerative medicine and tissue engineering, and plays an important role on the study of hard tissues. Using the principle of biomineralization is a new biomimetic synthesis of the field of materials synthesis, especially 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, making use of organic matrice in the field of the biomimetic materials synthesis, has recevied some encouraging results, and promoted the development of biomedical materials.Referring to relative literatures, this paper firstly selected several different natural polymer hydrogels as organic template to control the in situ precipitation of the hydroxyapatite in the hydrogel. In addition, some other functional molecules 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; Next, we used in situ chemical crosslinking and biomimetic method to prepare organic/inorganic composite. The results provide the necessary basis for the further study of biomineralization of organic template system. The concrete contents of this dissertation are as follows:1. Homogeneous collagen/hydroxyapatite nanocomposites and collagen-silk fibroin/hydroxyapatite nanocomposites were respectively prepared by an approach of in situ precipitation through a double template based on collagen hydrogel and functional molecular additives. The componential and morphological characteristics of the nanocomposite were performed by using fourier transformed infrared spectroscopy (FTIR), X-ray diffraction analyzer (XRD), scanning electron microscope (SEM), and transmission electron microscope (TEM). The mechanical properties of nanocomposite were measured by universal testing machine. The cytocompatibility of nanocomposite was finally evaluated based on osteoblast cells morphologic changes and the CKK-8assay evaluation. The experimental results indicated that collagen hydrogel template played obvious dual mediation effects during the in situ precipitation. The compartment effect from three-dimensional networks of collagen hydrogel can control the size and decentralization degree of inorganic particles in organic matrices. Besides, addition of other functional molecular additives (silk fibroin) in the collagen hydrogel can enhance the mechanical property of the inorganic/organic composite. Due to this double template, organic polymer/hydroxyapatite nanocomposite which combined excellent mechanical property with good cytocompatibility can be obtained.Based on above homogeneous hydroxyapatite/collagen hydrogel nanocomposite, nanocomposite scaffolds with hierarchical porosity were prepared by means of a multilevel lyophilization, the nanocomposite scaffold mimic structures of bone from microcosmic to sub microcosmic scale which make it more appropriate to bone biomimetic applications at different structural level. The sizes of the pores and porosity can be controlled by changing the various parameters in this multilevel lyophilization.2. Homogeneous chitosan-multi-walled carbon nanotube/hydroxyapatite nanocomposites and chitosan-silk sericin/hydroxyapatite nanocomposites were respectively prepared by an approach of in situ precipitation through a double template based on chitosan hydrogel and functional molecular additives. The componential and morphological characteristics of the nanocomposite were performed by using fourier transformed infrared spectroscopy (FTIR), X-ray diffraction analyzer (XRD), scanning electron microscope (SEM), and transmission electron microscope (TEM). The mechanical properties of nanocomposite were measured by universal testing machine. The cytocompatibility of nanocomposite was finally evaluated based on osteoblast cells morphologic changes and the CKK-8assay evaluation. The experimental results indicated that chitosan hydrogel template and other functional molecular additives played obvious dual mediation effects on the nucleation and growth of hydroxyapatite. During the in situ precipitation, the compartment effect from three-dimensional networks of chitosan hydrogel can control the size and decentralization degree of inorganic particles in organic matrices. Besides, addition of other functional molecular additives (multi-walled carbon nanotube and silk sericin) in the chitosan hydrogel can further mediate the morphology and structure of the inorganic particles and also enhance the mechanical property of the composite. The organic polymer/hydroxyapatite nanocomposite based on chitosan hygrogel exhibited better mechanical property than that of collagen/hydroxyapatite nanocomposite. Moreover, different ways of alkali diffusion also effected the morphology of chitosan-silk sericin/hydroxyapatite nanocomposites.Based on above homogeneous hydroxyapatite/chitosan hydrogel nanocomposite, nanocomposite scaffolds with hierarchical porosity were prepared by means of a multilevel lyophilization, the nanocomposite scaffold mimic structures of bone from microcosmic to sub microcosmic scale which make it more appropriate to bone biomimetic applications at different structural level. The sizes of the pores and porosity can be controlled by changing the various parameters in this multilevel lyophilization.3. Chitosan-hyaluronic acid composite hydrogel was fabricated through in situ chemical crosslinking method. This in situ forming hydrogel is moderate in reaction and requires no extraneous chemical crosslinking agents which are toxic. Then biomimetic method was adopted to synthesis hydroxyapatite on the chitosan-hyaluronic acid composite hydrogel. The experimental results indicated the number and size of hydroxyapatite crystals became more and bigger with the extension of mineralization time. Furthemore, hyaluronic acid promoted the attachment, growth and proliferation of osteoblasts.