The aim of the present study was to use chitosan (CS) based microparticles (MPs) to treat critical sized bone defects in rat models. The advantage of MPs over scaffolds is that MPs can be easily injected into the defect site using minimally invasive technique. CS based MPs ionically cross-linked with sodium tri-polyphospahte (TPP) were fabricated using emulsification technique. We have optimized the cross-linking density that is required to give particles with spherical morphology in 1X batches (approximate yield: 110 g MPs) and scaled up the process to fabricate 4X batches (approximate yield: 400 g MPs). Scale up of the fabrication process was necessary to produce larger quantities of MPs from each batch.
We have also used three other formulations to fabricate hybrid CS MPs by incorporating either 10%, 20% calcium phosphate (CaHPO4), or 10% calcium carbonate (CaCO3) to the optimized 4X batches. We have studied the attachment and proliferation of mesenchymal stem cells (MSCs) on these hybrid MPs. MSCs seeded on the hybrid MPs have shown good attachment and proliferation. MSCs seeded on the MPs showed differentiation towards osteoblasts as evident from the expression of alkaline phosphatase (ALP), osteocalcin (OC), and collagen I (COL I) on days 7, 14, 21, and 28.
Finally, MSCs seeded CS MPs were evaluated for in vivo bone formation using a rat femur model. In vivo bone formation was examined using x-ray imaging, micro computed tomography (µ-CT), and histology at 4 and 8 weeks after the implantation. The in vivo studies showed that the group of rats that received the implant had better bone healing compared to the control groups.
It is known that macrophages play an important role in wound healing. To test the appropriateness of macrophages in bone healing we have studied the expression of growth factors like transforming growth factor (TGF-β) and bone morphogenic proteins (BMPs) in macrophages. We have also co-cultured the macrophages and osteoblasts (OBs) on the hybrid MPs to look at the influence of macrophages on bone regeneration in vitro. Macrophages expressed TGF-β and BMPs when seeded on the MPs. Co-culture studies showed that the expression of ALP and COLLI was up regulated on day 7.
|Advisor:||Jayasuriya, Ambalangodagae C.|
|School:||The University of Toledo|
|School Location:||United States -- Ohio|
|Source:||DAI-B 71/03, Dissertation Abstracts International|
|Keywords:||Bone regeneration, Chitosan, Mesenchymal stem cells|
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