| During the process of biomineralization, the organic matters can mediate the polymorphs, morphology, size, orientation and arrangement of the biomineral, contributing a lot to the special functions of the material. For example, the oriented growth of hydroxyapatite (HAP) along the fibril was induced by the pre-built collagen scaffold and the acidic proteins/glycoproteins, leading to the formation of bone or teeth, which are the highly ordered organic/inorganic hybrid materials. In nacre, the acidic proteins, insoluble β-chitin fibrils and soluble hydrated gel structure formed by silk-like proteins of β-sheet conformation, cooperate closely to regulate the growth of arrgonite, which can develop the highly ordered multilayer hybrid materials. Therefore, people are inspired to design and make such high performed materials, by learning the lessons from nature.Amorphous calcium phosphate (ACP), with excellent biocompatibility, osteoconduction and biodegradability, shows poor stability in solution and can be transformed easily to a more stable polymorph - HAP. As a kind of soluble and biocompatible additives, silk fibroin can mediate the growth of inorganic crystals. If the silk fibroin could stabilize the ACP, it would be desirable to expand its application to the areas such as bone repair. Meanwhile, a lot of studies that investigate the influence of negatively charged organic additives on the biomineralization of CaCO3 have been reported, leading it to quite a mature study field. However, for the positively charged organic additives also exist widely in the natural biominerals, it would be meaningful to pay attention on as well. The main results obtained in this research are listed as following.1. Based on the gas diffusion, the pH value of the mineralization solution increased slowly when the ammonia gas diffused into the solution, leading to the precipitation of calcium phosphate. The morphology and polymorph of calcium phosphates were characterized by SEM, TEM, SAED, XRD and FTIR. Generally, the spherical particles were ACP and the adhesive sheets were HAP in our work. The results also showed that ACP could be obtained by adjusting the mineralization time, the weight concentration of RSF, the molar concentrations of calcium ion and phosphate ion. When the Ca2+/PO43- concentrations increased, a higher RSF concentration would be needed to induce the growth of ACP. Furthermore, it was found that RSF with higher molecular weight could induce the growth of ACP in a lower concentration under the same condition. The regulation property of silk fibroin (fibrous protein) was much better than bull serum albumin (globular protein); while GCS (polysaccharide) showed a poor stability than protein. The unfold space structure and the abundant calcium ion chelating sites of silk fibroin contributed a lot to its desirable performance of stabilizing ACP.2. We introduced the polycation (TMC) to mediate the crystallization of CaCO3. Various vaterites with special superstructure could be obtained by changing the concentration of calcium ion. By TEM results, we thought that the superstructures were formed through oriented attachment, the basic unit of which was the nanoparticle and platelet that shared the same crystallographic orientation. The (001) face of the vaterite could be exposed at the presence of the TMC, inhibiting the growth of crystal along this direction. This could be attributed to the attachment of the positively charged TMC to the negatively charged (001) face. Besides, for TMC could stabilize the primary nanoparticles and platelets, it played a key role during the assembling. |
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