Study On The Preparation And Propeties Of Polyphosphazene/Gelatin Composite Scaffold For Tissue Engineering

PART ONE STUDY ON THE PREPARATION AND PROPETIES OF POLYPHOSPHAZENE/GELATIN COMPOSITE SCAFFOLD FOR TISSUE ENGINEERINGBiomaterials are widely used in artificial organ, tissue engineering, drug releasing system and other fields due to theirs good biocompatibility and biodegradability. Application and research fields expand with increasing varities of biomaterials. As we have known, there is a wide variety of biocompatible materials which include bioceramics, synthetic and natural biopolymers available for tissue engineering. Each material has its own characteristics, and within each family of materials there is a range of properties and characteristics. There seems to be less emphasis on new materials, but rather on the combination, processing or other treatment of established systems in novel ways. Composite materials were proved to be one of the best ways to obtain a kind of ideal tissue engineering scaffold. Composite biomaterials can produce properties that exactly fit the requirements for a particular structure for a particular purpose.In this study, two kinds of polyphosphazenes were synthesized and blended or crosslinked with gelatin, to improve the hydrophilicity, bioactivity and rates of degradability. At first, amino acid ester substituted polyphosphazene was synthesized and coelectrospun with gelatin at different weight ratios. These polyphosphazene/gelatin composite nanofibers were suhjected to 5 times simulated body fluid (5-SBF) to induce biomineralization. In the traditional 5-SBF, in which the pH value increased continuously, homogeneous nucleation occurred and apatite deposite on composite fibers from the beginning. In contrast, in the improved 5-SBF which was balanced with gassy carbon dioxide all the time at a pH of 6.4±0.02, flaky-like apatie crystals were resulted finally. The mineralization rate in t-5SBF incubation was faster than mineralization rate in i-5SBF. In i-5SBF, the mineralization rate was slow at the beginning but increased with prolonged incubation time. And apatite obtained by i-5SBF was mainly brushite (DCPD) at the initial stage and subsequently changed into HA. Biomineralization results confimed that polyphosphazenes/gelatin composite materials have better bioactivity and hydrophilicity than pure polyphosphazenes materials and also have better structural stability than pure gelatin.By incorporating unsaturated acrylate groups onto polyphosphazene backone and thiol groups onto gelatin backbone, respectively, the polyphosphazene/gelatin composite was also attempt through Michael addition. It was envisoned a good solution to avoid the use of small molecular agent for gelatin crosslinking to prevent the possible biocompatibility issue. PART TWO SELF-ASSEMBLED GELS OF AMPHIPHILIC SEQUENTIAL PEPTIDE IN WATER AND ORGANIC SOLVENTSArising from the abundant protein self-assemblies existing in nature, recently, the self-assembly of peptides has been a research focus. Through rational designing the molecular structures of peptides and altering the external environment, peptides can spontaneously or induced self-assemble into specific-shape aggregates via noncovalent forces, such as hydrogen bonding, hydrophobic and S-stacking interactions etc. Due to well biocompatibility and controlled degradation, functional materials constructed from the self-assembly of peptides present a great potential in many biomedical fields.An amphiphilic peptide designed with serine as a polar residue showed gelation in both water and organic solvents. This sequential peptide has a strong tendency to adoptβ-sheet conformation in these solvents. Such gels ofβ-sheet peptide based on hierarchical self-assembly consist of nanofiber construction because of theβ-sheet structure, and because of crosslinking attributable to hydrogen bonding among hydroxyl groups of the serine side chain.