Biomimetic Calcium Phosphate-based Organic-inorganic Hybrid Materials

The synthesis of biomimetic materials has become the emerging areas in the fields of materials, chemistry and biomedicine et.al. With the excellent structure design procedure, the general organic component and inorganic phase can be well integrated to ensure amazing functions like mechanical, optic properties. It should be noted that the ordered arrangement of organic and inorganic component is the key fact to bring attractive functions to biomaterials. In the artificial design of biometic materials, the bottom-up strategy through the assembly of both organic and inorganic phase is considered as one of the most efficient ways which are close to the biological condition. However, the strict requirement of assembly needs the tight integration between organic molecule itself and organic-inorganic phase at nano or micro-scale. Accordingly, the essential issue that the ordered arrangement of organic phase and inorganic phase at such small scale is a great chellagen for fabrication of biomimetic materials. In this work, we investigate the biological conditions that give rise to the order of distinc organic and inorganic phase and design a simple model system containing amphiphilic molecules and model protein. After adding additional calcium ions and phosphate ions, organic-inorganic hybrid plates and helix spontennously generats in the solution via self-assembly process. Both organic and inorganic phase are tightly integrated at nanoscle with ordered arrangement.We note that thse hybrid plates have interesting mechanical properties as bone. We also invesitigate the influence of different concentrations of reaction components on the morphology of hybrid plates, and synthesize the homochial nano-helix clusters consisted with organic-inorganic hybrid helix with same chiratlity. A physicochemicalmodel based on the chirality of organic molecules and the elastic free energy is suggested to explain the formation of chiral helix and the proliferation of chirality. The thesis is composed of five chapters:In chapter1, we briefly introduce the typical properties of biomaterials and their. We focus on the composition-structure-function relationship of biomaterials. Then, the fundamental mechanisms and the recent developments during the crystallization and growth model of biominerals are also described. We review the essencial role of organic molecules, especially matrix macromolecules and molecules in the crystallization process. Finally, we suggest the crucial relationship of organic molecules and inorganic phase in the assembly of high order structure and inspire us to design reasonable reaction system to achieve the goal.In chapter2, we design a model system to mimic the special relationships of organic molecules and inorganic phase. Here a model amphiphilic molecules Bis(2-ethylhexyl) sulfosuccinate (AOT) and Bovine Serum Albumin (BSA) in a supersatuated calcium phosphate solution. Organic-inorganic hybrid plates can spontaneously form and own alternative stacking of ultrathin organic layers and inorganic layers.Interestingly, the modulus and hardness is close to the natural bone in human body, which can be considered as a calcium phosphate based bone-like materaisl.In chapter3, we further investigate the role of different reaction components (AOT. BSA and calcium/phosphate ions) on the morphology of resulted hybrid plates, which can be considered as a kind of hybrid mesocrystal. We suggest the different concentration of AOT, BSA and calcium/phosphate ions have various effects on the morphology especially the aspect ratio of hybrid plates. However, the internal lamellar structure maintains inspite of the change of reaction components. The increase of AOT leads to smaller aspect ratio while the larger BSA concentrations give rise to elongated ones. Apart from the organic components, the aspect ratio can also increase with more calcium/phosphate ions in reaction solutions.In chapter4we investigate the formation mechanism of these bone-like organic-inorganic hybrid mesocrystal. With the observation of the morphology of surface steps on the hybrid mesocrystal, we suggest that the classical step growth model of crystals dominate its formation process. The growth step is hybrid consisted by two AOT bilayers and two thin CaP layers. Through the movement of hybrid steps, the AOT molecules and CaP phase are carefully arranged into ordered structure while the anisotropic absorbtion behavior of BSA can control the morphology of steps and then the morphology of hybrid mesocrystal.In chapter5, we obain chiral organic-inorganic hybrid helix by decreasing the concentration of AOT molecules with similar internal structure as above hybrid plates. Interestingly, the helix with same chirality can form homochiral clusters, and these homochiral clusters are proliferated from single chiral helix as matrix. We suggest that the chirality determined free elastic energy ensure the homichiral proliferation process. This means the biomimetic hybrid materials can spontenneously amplify their chiral strucrures to later generations. This is very similar as the chiral selection of mollusk shell and proliferation process.In chapter6, we sumerize the key points for biomimetic fabrication of hybrid mateirals. Our investigation of hybrid crystal formation via co-assembly of organic and inorganic phase in a classical step growth of inorganic crystals offer a new strategy to orderly integrate organic-inorganic phase at nanoscale. In addition, we also indicate that materials-based spontenneous amplification can occure in our simple model system. This interesting phenomenon offers a novel insight in the synthesis of highly regulated or self-similar materials. Finally, we also describe the shortages of our work and unsolved issues for further investigation.