Synthesis And Characterization Of Collagen Mimic Peptides And Collagen-hydroxyapatite Composite Materials

Collagen is the most abundant and widely distributed protein in mammals.As the main component of the extracellular matrix,collagen is widely spread in various tissues and organs as insoluble fibers,providing a molecular scaffold for supporting organs and protecting human body.Collagen possesses the characteristic(Gly-X-Y)n repetitive sequence pattern and triple helix structure,and a single Gly mutation in collagen results in connective tissue disorders.Collagen displays excellent biological properties,including low immunogenicity,biodegradability and biocompatibility,and it thus has broad applications in biomaterials.In this thesis,we focus on the synthesis and characterization of collagen mimic peptides and collagen-hydroxyapatite composite materials.The main work of this thesis is summarized as follows:1.Triple helcial peptides provide a well controlled system with reasonable size to investigate the structure and function of collagen.We have developed Fmoc-based solid state synthesis as well as recombinant expression methods to synthesize triple helical collagen mimic peptides.The solid state synthesis apporach is suitable for the synthesis of collagen mimic peptide with mediate size with no or few isotopic labels,while the recombinant expression technique is appropriate for long peptides with uniform isotopic labels for NMR structure determination.2.We compare a Gly-Ala mutation and a similar natural interruption to understand the molecular mechanism of Osteogenesis Imperfecta.Two peptides,one modeling a natural G5 G interruption(POALO)and the other one mimicking a pathological Gly-to-Ala substitution(LOAPO),are designed.Circular Dichroism(CD),NMR,and computational simulation studies have discovered significant differences in stability,conformation,and folding between the two peptides.We have discovered that the conserved hydrophobic residues at the specific sites of interruptions may play critical roles in collagen stability and local conformation,and may therefore provide a molecular basis of different biological roles of natural interruptions and Gly substitutions.3.Compared with natural collagen,our constructed recombinant collagen has several advantages such as high purity,stable quality,good solubility,easy processing,and low immunity.We use recombinant collagen,CaCl2,and phosphate as raw materials,and particularly collagen as the biotemplate,to synthesize recombinant collagen-HA hybrid nanomaterials at room temperature.We have investigated the effect of reaction time and phosphate concentration on the system,and characterized the crystal phase,chemical bond structure,morphology and composition of the hybrid materials using techniques such as XRD,FTIR,SEM and TGA.We have discovered that the reaction time and the phosphate concentration can well mediate the morphology of synthesized recombinant collagen-HA hybrid nanomaterials.