Biomimetic Polymer Fibrils Containing Cholic Acid Derivatives

Biomimetics is the science of imitating nature. Biomimetic mineralization generally is stipulated an organic molecules as a matrix to induce nucleation, growth of inorganic crystal in vitro. Here, the organic molecules are used to mimic biomacromolecules, and the supersaturated solution is used to mimic biological media. The progresses on the research of biomimetic mineralization are very important for material science and biomedicine. Among those, the mineralization of polymeric fibril with helicity has the comprehensive significance for exploring biomimatic mineralization mechanism. This is because that collagen molecule widely distributed in nature possesses a tripo-stranded helical structure. Using a polymeric fibril to mimic the behavior of collagen in vivo is a biomimetic strategy. The core is to develop a polymeric structure with helicity, rigidity and the capability to induce mimeral formation. We found that the polymer of cholic acid directives have helical conformation and rigid chain. Its diameter is about 1.5 nm and the length dependent on the molecular weight. The fibrils are hydrophobic, but using selected hydrolysis to remove the methyl ester in side chain, gained the core-shell type hydrophiphile structure. The hydrophobic chain mainly drives the assembly in aqueous solution. The hydrophilic group is used to induce inorganic mineral.An acellular simulated body fluid has inorganic ion concentrations similar to those of human extracellular fluid, in order to reproduce formation of apatite on bioactive materials in vitro. This fluid can be used for not only evaluation of bioactivity of artificial materials in vitro, but also coating of apatite on various materials under biomimetic conditions. In our work, we found that there are an amount of nanocrystals (ca. 6-8 nm) in SBF and no obvious aggregation occurred in 60 day time period.In this thesis, we found the mineralization behavior of the polymeric fibrils in SBF is speculated on the changes of the extinction efficient of samples solution. Formation of plate-like hydroxyapatite on the surface of the polymeric fibrils was observed by HRTEM. The SAED pattern taken from the plate-like crystal phase indicates that it is a single crystal of hydroxyapatite and the [001] direction of hydroxyapatite is vertical to the surface of the plate-like fibril assembly. Author believes that the model combining the polymeric fibril and SBF solution provided the key information and experiment data.