Several Applications Of Cross-linked Carboxymethyl Chitosan In Tissue Engineering

A novel carboxymethyl chitosan (CMC) material system for tissue engineering was designed and fabricated. The properties including biodegradability, mechanical properties and biocompatibility were studied on the applications in repairing various tissues. Following are the major subjects of the thesis:(1) Fabrication and characterization of bimodal CMC scaffold system. CMC was prepared by chitosan reacting with monochloroacetic acid under various conditions, and the structure was investigated by Fourier-transformed infrared spectrometer, nuclear magnetic resonance spectrometer and X-ray diffraction. Afterwards, dissolvable CMC was cross-linked by 1-ethyl-3(3-dimethylaminopropyl) carbodiimide hydrochloride (EDC). The cross-linking conditions were optimized based on physical properties. Thereafter, EDC cross-linked CMC was used to form scaffolds with varying ratios of high to low molecular weight distribution (MWD) while maintaining the mechanical properties. The degradation rate of the novel materials was found to be fairly accelerated and to some extent controllable.(2) Peripheral nerve regeneration using bimodal CMC tubes. The nerve affinity was initially assessed by seeding with Neuro-2a cells: cells cultured on novel CMC system showed better spreading and improved axon growth. Moreover, 10 mm rat sciatic nerve defects were used to further evaluate the effectiveness and biodegradability of bimodal CMC nerve conduits on peripheral nerve regeneration. The results showed that after a postoperative survival period of 12 weeks, the CMC conduits were partly degraded and absorbed. Results from histological morphology and histomorphometry analysis both demonstrated that the regenerated axons had bridged the defect gap and grown into the distal nerve tissue. The CMC tubes had better nerve regeneration behaviors than the chitosan tubes and demonstrated equivalence to nerve autografts which is the current"gold"standard.(3) Collagen nanofiber coated porous CMC microcarriers (CMC-MC) for use as injectable cell microcarriers for cartilage regeneration. A modified phase separation method combined with freeze-extraction was employed for formulating the CMC-MC. Collagen nanofibers were immobilized onto the surfaces of the CMC-MC via covalently anchoring collagen molecules in the matrix structure of the spheres and subsequently more molecules self-assembling into nano-scaled fibrous networks. Scanning electron microscopy and hydroxyproline analysis revealed that larger amount of collagen was immobilized on the CMC-MC with initial treatment. In vitro cell culture revealed that chondrocytes could adhere, proliferate and retain differentiated on the CMC-MC.(4) CMC/collagen nanofibers composite scaffolds for bone tissue engineering. Novel scaffold were designed and fabricated to mimic the structure of natural bone. A compact chitosan membrane layer could prevent fibrous tissue invasion and increase the mechanical properties. Then the scaffolds were implanted into a rabbit fibula defect model to evaluate the biodegradability and bioactivity of bone repair. The results indicated that the CMC/collagen scaffolds degraded faster than chitosan/collagen scaffolds, and they could facilitate bone regeneration. Osteogenesis center was formed in the interior of the scaffold and affluent blood vessels for the nutrition transportation were found. Bimodal MWD could further increase the degradation rate of the scaffolds, and marrow-like tissue was found within the regenerated bone.