The Studies On Materials Preparation, Construction And Evaluation For Tissue Engineering Scaffold

In the past decade, tissue engineering has attracted many attentions from the researchers. It is very important to fabricate scaffold and to introduce bioactive agents (such as growth factors, DNA, etc) into scaffold.In this dissertation, the terpolymers of polyester-polycarbonate and polyester-polycarbonate-polyether were designed and prepared and fabricated into porous tube by solvent casting/particulate leaching. The tubes were implanted in rats to evaluate the potential application for nerve guide conduit. Then, PLGA, collagen-coating PLGA scaffold and rhBMP-2-containing PLGA scaffold were obtained by emulsion/freeze-drying method. The effects of those scaffolds on the adhesion and proliferation of osteoblasts and bone regeneration were estimated in vitro and in vivo. Finally, nanofibers scaffolds of rigid polysaccharide were fabricated by coaxial electrospinning, and the core-shell structured nanofibers scaffolds composed of polycaprolactone as shell and BSA-loaded dextran as core were also obtained. All the above are summarized as follows:(1) Biodegradable terpolymers of poly(2, 2-dimethyl trimethylene carbonate-co-ε-caprolactone-co-glycolide) and poly(2, 2-dimethyl trimethylene carbonate-co-ε-caprolactone)-block-poly(ethylene glycol) were synthesized by the bulk copolymerization of using stannous octanoate as catalyst. The products were characterized by ¹H-NMR, ¹³C-NMR, FT-IR, and GPC. It was found that the most terpolymers have the T_g below -50°C and present rubber state both at room temperature and body temperature (37℃). The tensile strength and elastic modulus of most terpolymers were more than 6.2 MPa and 25 MPa, respectively. The water absorptions of the terpolymers were less than 10%. The hydrophilicity and degradability could be adjusted by changing the content of the PEG or glycolide. These materials are expected to be useful for nerve reconstruction and other biomedical applications.Solvent casting/particulate leaching was used to fabricated the terpolymers intoporous tube, which have low degree of swelling and excellent elasticity and toughness. The tubes were used to bridge a 10 mm gap in the right sciatic nerve of rats. There were no collapse and oppression occurred in the first 10 weeks. The porous tube disintegrated since the 16th weeks after surgery. It was showed that the porous tube could induce the nerve stump across the gap by electrophysiological and histological evaluation. The degradation rate of the porous tube was consistent with the regeneration rate of the impaired nerve. The preliminary study results in vivo indicate that these materials are very promising as nerve guides.(2) PLGA, collagen-coating PLGA scaffold and rhBMP-2-containing PLGA scaffold were obtained by emulsion/freeze drying method. The pore size were 100-270 urn and the porosity was 92%. The release profiles in vitro showed a burst release within the first day, followed by relatively steady release. The cumulative release percentage of rhBMP-2 at the first day and 30 days were 30% and 80.6%, respectively. The activity of the released rhBMP-2 was not damaged.The effects of the rhBMP-2-containing scaffolds on the adhesion and proliferation of osteoblasts and bone regeneration were superior to that of the PLGA and collagen-coating scaffolds by the in vitro and in vivo experiments.(3) Nanofibers scaffolds of chitosan, sodium alginate and hyaluronic acid were fabricated by coaxial electrospinning using PEO as shell and rigid polysaccharide as core. The pure nanofibers scaffolds of the polysaccharide were obtained after removing the PEO by chloroform. The diameters of the fibers were about 160-330 nm. The chitosan scaffold could be stable in the water without crosslinking.The core-shell structured nanofibers scaffolds composed of polycaprolactone as shell and BSA-loaded dextran as core were also obtained. The steady and sustained release of BSA was attained. The release rate could be easily modulated by the feed rate of the inner solution. The introduction of PEG into shell layer accelerated the release of BSA, but it also resulted in a burst release. The degradation rate of the scaffold increased with the increasing content of dextran or PEG. Compared with the solvent casting/particulate leaching and emulsion/freeze-drying methods, the electrospinning method is much promising in the scaffold fabricating and theincorporation of bioactive agents because of its high loading efficiency/capacity, mild loading condition and relatively steady release characteristics. The coaxial electrospinning technique present a significant method for fabricating scaffold.