Chitosan-Based Biomaterials for Bone Tissue Engineering Applications
|關鍵字:||幾丁聚醣;骨生長因子;化學固定;氫氧基磷灰石;骨組織工程;chitosan;bone growth factor;chemical immobilization;hydroxyapatite;tissue engineering||公開日期:||2007||摘要:||骨創傷的修復在臨床醫學上是個很重要的課題，藉由組織工程的發展，我們得以發展出能夠引導骨缺陷修復的人工植入材料。本論文的主軸乃是設計及開發以幾丁聚醣天然高分子為主之生醫材料，藉由不同形式之基材設計與生物活性分子之導入，欲發展出能夠取代現今骨修復之填充材料，使其具有臨床應用性之價值。本論文主要包括了以下之幾部分:
Tissue engineering has shown great promise as a viable alternative to current bone graft solutions due to its use of biocompatible, biodegradable scaffolds as support systems for cellular attachment, proliferation, migration, and maintenance of normal phenotypic expression. The overall goal of this thesis was to design and develop biodegradable, biocompatible chitosan-based scaffolds that will be practical alternatives to current bone repair materials. The first specific aim was to develop a new method to prepare an osteoinductive-osteoconductive bioimplant based on chitosan and recombinant human bone morphogenetic protein-2 (rhBMP-2). BMP-2 was chemically immobilized on the chitosan membrane in order to provide a bioactive surface that can enhance bone-regeneration capacity. Cellular evaluation demonstrated this novel rhBMP-2-immbilized membrane to be biocompatible and osteoionductive, with evidence of enhanced cellular proliferation and early alkaline phosphatase expression. Accelerated bone healing observed histologically and radiographically in the rabbit radius critical-sized defect indicated that it would seen to be applicable for inducing significant and localized bone formation in future guided tissue regeneration. The next objective was to develop 3-dimensional chitosan scaffolds. The macroporous chitosan sponges were fabricated by the modified method based on thermally induced phase separation. A combination of solid-liquid phase separation/solvent-extraction/neutralization/freeze drying paths were successfully developed to fabricate highly anisotropic chitosan scaffolds with high porosities (>90%) and macropores (>100µm) which may favor cell growth, migrate, nutrient transportation and further bone tissue regeneration. When implanted in a segmental long bone defect, however, macroporous chitosan sponges did not show sufficient osteoconductivity for complete bone defect healing. It was therefore another aim of this thesis to chemically immobilize rhBMP-2 on macroporous chitosan scaffolds in order to provide osteoinductivity for quick and promoted bone regeneration. Bone defect bridging and union was achieved within 4 weeks in 8 of 10 specimens. Such a high bone healing efficiency of rhBMP-2-immobilized chitosan sponges revealed that they are good candidate bioimplants for guided tissue regeneration application. A trial related to implantation of pure chitosan sponge in the tooth extraction socket was also made in this thesis. Surprisingly, unlike long-bone defect model, the alveolar bone was preserved and regenerated when the extraction socket was implanted with pure chitosan sponge. It could be concluded that osteoconductivity of chitosan has much to do with the implanted site. Pure chitosan sponge has great potential to be used as a socket filler to prevent adsorption of alveolar bone after tooth extraction. In spite of the promising performance of the chitosan scaffolds, they could not be applied in the load-bearing bone defects because polymer themselves are mechanically too weak. Consequently, a final aim was to prepare chitosan/hydroxyapatite composites designed to mimic the properties of bone, which itself is a composite. The mechanical properties were significantly improved as hydroxyapatite was incorporated. In vivo animal studies in male New Zealand white rabbits showed that composite scaffolds provided a suitable structure for new cellular infiltration throughout the scaffold pore structure. Composite scaffolds also supported the vascularization of new tissue within the defect site, as well as newly mineralized bone tissue at the margins of the defect. In summary, this dissertation demonstrates the successful generation of a biomimetic scaffold capable of localizing growth factor delivery which indicates significant potentials in tissue engineering and regenerative medicine.
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