Cell Based And Non-Cell Based Tissue Engineering Of Bone And Related Research

Bone defects caused by trauma, infection and tumor always present a dilemma for orthopaedic surgeons. Therapies for bone defects include autografts, allografts and artificial bone substitutes. However, all of these methods have inherent problems and limitations. Autografts are limited by a lack of adequate supply and by donor site morbidity. Allgrafts have the potential danger of tansmission of infectious diseases. The problems and limitations have promoted the development of new biomaterials for bone substitutes. People have been interested in developing and improving delivery systems for BMPs to heal bony defects since Mr. Urist discovered this osteoinductive growth factor in 1965. On the other hand, cell-based bone tissue engineering has emerged as an promising alternative for bone repair. Tissue engineering of bone in abroad sense includes the non cell-based strategy, delivery systems for BMPs, and cell-based strategy of bone tissue engineering. Both approaches are correlative with and at the same time independent of each other. In common, an ideal biomaterial is critical and quite demanded of as a carrier for BMPsor temporary extracellular matrix (ECM) for osteoblasts. Hydroxyapatite/collagen (HAC) sandwich composite was produced to mimic thenatural extracellular matrix of bone, with the collagen serving as a template for apatite formation. A three-dimensional highly porous scaffold had been developed by mixing HAC with poly(L-lactic acid) (PLA) using a thermally induced phase??separation technique(TIPS). The scaffold obtained was utilized as a carrier for BMPsdelivery system as well as ECM for cell-based strategy. In addition, the biologicaland cytological effects of low intensity pulsed ultrasound(LIPUS) and cyclicmechanical stimulation on the commonly used osteoblast progenitor cells was alsostudied.This thesis consists of four parts:1. The synthesis of three-dimensional highly porous HAC-PLA scaffold and its properties.2. Non cell-based strategy for bone tissue engineering: the application of HAC-PLA scaffold as a carrier of BMPs deliver}' system.3. Cell-based strategy for bone tissue engineering: the application of HAC-PLA scaffold as ECM for osteoblast progenitor cells.4. The cytological and biological studies of human periosteal cells and bone marrow stromal cells.Conclusions:1. Using type I collagen to template mineralization of calcium and phosphate in solution, we got HA/collagen sandwich composite, mimicking the natural bone both in composition and microstructure.2. The three-dimensional HAC-PLA scaffold synthesized by TIPS had a high porosity of up to 90%, with pore size varying from SO^im to 300p.m. The HAC-PLA scaffold proved biocompatible as exhibited by in vivo implantation and co-culture study with cells in vitro.3. Followed by incorporation with bovine BMPs, HAC-PLA porous scaffolds were used to treat 15mm segmental defects of radii in rabbits. Radiological and histological examination indicated that the defects healed in 12 weeks but there were still some remnants of the material retained at the center of pre-existing defects.4. Pre-wetting of porous PLA scaffold with pure ethanol significantly improved its hydrophilicity. SEM showed BMP flocci were well dispersed inside the prewet scaffold.5. The prewet HAC-PLA scaffold was loaded with bovine BMP and then the??composites were implanted in 2cm diaphyseal defects in radii of adult beagel dogs. All defects healed after treatment with BMP loaded HAC-PLA, and HMD measurements of the reparative tissue in the pre-existing defects were higher than those of intact radii. Histological observation indicated that the presence of BMP not only had promoted osteogenesis but also had accelerated degradation of the biomaterials.6. The pre-digested and combined treatment was more effective than traditional techniques such as ''outgrowth" and ''digestion"methods.7. Treatment of human bone marrow stromal cells with 10~7M dexametheson...