Osteognenesis Of Stems Cells Induced By Muti-level Construction And Drug Delivery Microspherical Scaffolds

Controlled organ regenerational and fuction construction is always a dram for human being . The development of tissue engineering offer a path for this dream. The aim of this thesis is developing a functional controlled release tissue engineering scaffold for bone repair.The current replacement procedures for bone defect therapy mainly depended on autologous tissue which is the golden standard. Unfortunately, the origination of autologous bone is often limited in supply, and the allogenous bone takes an increased risk of disease transmission. Tissue engineering strategy, which utilizes an alternative approach to assist tissue repair via forming a microenvironment that effectively promotes cellular growth and proliferation in a synthetic or natural scaffold to produce extracellular matrix and regenerate tissue, can overcome the limitations that were induced by autologous and allogenous tissuetransplantation for bone repair.Microsphere sintering technique was used in this thesis for fabricating the scaffolds with muti-component and muti-structure (nano scale-micro scale-macro scale). PLGA based microspherical sintering scaffolds were developed in this studies. These scaffolds possess regulated biodegradation, drug controlled release, as well as good mechanical property.(1) Muti-level construction of cntrolled release tissue engineering scaffoldsFirstly, as a synthetic polymer, PLGA lacks functional groups, and the improvement of biocompatibility is also demanded. Many approaches have been carried out to enhance the bio-functionality of PLGA, and blending PLGA with biomolecules or nano bioceramic particles provides a simple and effective pathway for this purpose. In this work, two methods were applied to modify PLGA scaffold: modification with natural biomolecules and blending with nano particles. (1) Modification with natural biomolecules: lecithin was introduing into PLGA scaffold, and the results indicated that the scaffold with 5% lecithin showed better cell biological properties such as higher alkaline phosphatase (ALP) activity, higher calcium secretion and stronger type I colllagen gene expression. Howerver, the rising lecithin content in the scaffolds produced a lower cell biological properties, which may be due to the higher hydrophilicity of scaffold surfaces. (2) Modification with nano particles: Mesoporous silica-HA (MSH), nano TiO2, and HA were introducing into PLGA scaffolds respectively. The results demonstrated that after modifiaction by nano particles, the scaffolds showed improved mechanical propertes, trapping protein and cell biliogical properties. Additionally, PLGA-MSH scaffolds also exhibited beneficial drug delivery property. After a comprison among PLGA-MSH, PLGA-HA and PLGA-TiO2 scaffolds, PLGA-MSH and PLGA-HA scaffolds showed better properties than PLGA-TiO2, therefore our following studies will focus on these scaffolds.(2) controlled release tissue engineering scaffolds for cell differentiationIn this work, dexamethasone (Dex), ascorbic acid (AA) andβ-glycerophosphate (GP) , the key components of ostoegenic media, were loaded into PLGA micropspherical scaffolds, and the osteogenesis in situ of mesenchymal stem cells (MSCs) on the scaffolds were evaluated. Ther results indicated that, after 14 days and 28 days of culture, MSCs on the drug laden scaffold exhibited strong osteoblastic properties. In-vitro osteogenesis was induced in the mesenchymal stem cells from the highly chondrogenic synovium mesenchymal stem cells (SMSCs) and the bone marrow (BMSCs), and also the effect on macrophages and osteoblasts by controlled release of a nitrogenous bisphosphonate additive - alendronate (AL) from PLGA/MSH and PLGA/HA scaffolds were assessed. AL is a nitrogenous bisphosphonate (BP) consisting of stable analogues of natural pyrophosphate compounds that inhibit bone resorption by osteoclasts. The resulted demonstrated that AL can inhibite the activity of macroiphages and also promote tha activity of osteoblast. In addition, AL and Dex laden PLGA/MSH microspheres was successfully induced in-vitro osteogenesis in SMSCs. AL and Dex laden PLGA/HA also exhibited the similar effect on BMSCs osteogenic commitment in vitro and in vivo. BMSCs laden PLGA/HA-AL-SMS and PLGA/HA-Com-SMS were also implanted into the back subcutis of mice and bone defects surgically created on rabbit femurs. The histology and immunohistochemistry results indicated that the scaffolds promoted MSCs osteogenic commitment and also the new bone formation in vivo. In addtion, these in situ AL delivery systems could effectively inhibit the growth of macrophage while enhance the proliferation and commitment of osteoblasts.