Synthetic Polysaccharide-Mediated Biomimetic Syntheses Of Inorganic Materials
Despite the importance of polysaccharides in biomineralization, their specific roles are not well understood and they have received very little attention in studies of biomimetic mineralization and the synthesis of biomimetic materials. The experiments reported in this dissertation were designed to advance the knowledge and understanding of the role of acid polysaccharides in biomineralization and biomimetic materials. In the first experiment, maleic chitosan was synthesized using methanesulfonic/tolunesulfonic chitosan salts as organic-soluble precursors either in formamide or DMSO. The acid polysaccharide was then used as an organic template for the biomimetic mineralization of calcium carbonate. Amorphous calcium carbonate (ACC) films were produced and stabilized in the presence of maleic chitosan. The films were formed through a process of colloidal self-organization, with nanoparticles less than 10nm being responsible for the selforganization. This study may provide insights into how ACC films are formed in the presence of additive/template systems and contribute to the understanding of biological mechanisms in ACC stabilization. It was also found that maleic chitosan-mediated CaCO3 spherulites with amorphous cores were obtained through a two-step process: First, ACC films were formed from which amorphous nanoparticles were deposited and stabilized to form ACC cores. The cores then acted as nuclei for the radial growth of needle-like calcite subunits. The crystals thus combine the coexistence of calcite and ACC found in composite skeletal elements and the radially-ordered structure of spherulitic biominerals. These findings may provide new insights into spherulitic crystallization, particularly the formation of spherulitic biominerals in nature and lead to increased understanding and potential treatment of diseases in which amorphous cores have already been observed in spherulites, such as Alzheimer's disease and kidney stones. In the second experiment, maleic chitosan-based hydrogels were prepared via photopolymerization and used as an organic matrix template for the growth of carbonated hydroxyaptite. Porous bonelike biocomposites were produced by using maleic chitosan/PEGDA hydrogels as 3D templates in conjunction with a modified simulated body fluid (SBF) mineralization approach. The study suggested that maleic chitosan-based hydrogel not only provides reactive sites for the binding of mineral phase, but also plays an important role in stabilizing amorphous inorganic nanophase at the early stage. It also implies that polysaccharide macromolecules, particularly acid polysaccharides like maleic chitosan, are potential scaffolds for the design of new bonelike biocomposites.
dissertation or thesis