(392g) "Graduate Student Award Session:"Investigating the Concurrent Effect of Encapsulation and Perfusion on Chondrogenic Differentiation of Mesenchymal Stem Cells

Every year millions of people are diagnosed with osteoarthrosis which happens largely due to joint injuries, obesity, lack of movement and trauma. Cartilage is an avascular tissue with a low regeneration capacity. There are multiple treatments for cartilage repair including microfracture, osteochondral grafts transplantation and autologous chondrocytes transplantation. Beside their high rate of success, these methods still possess multiple drawbacks including formation of fibrous tissue which lack the structure of the native tissue and the damage to the healthy cartilage due to biopsies that is required for isolation of autologous chondrocytes. Bone marrow mesenchymal stem cells (bMSCs) are a promising cell source for variety of tissue engineering applications due to their pluripotency and differentiation capacities. The ability of MSCs to differentiate into chondrocytes has also made them the foremost option in cartilage repair studies. Using MSC aggregates which are differentiated prior to implantation, can overcome the drawbacks of the current treatment methods. Creating an in-vitro microenvironment for cells which can mimic the in-vivo conditions will facilitate the differentiation process. In addition, cell fate and function in-vitro are greatly affected by the composition of the extracellular matrix in which for cartilage is made of different type of glycosaminoglycans (GAGs). Capsules are a great tool for this purpose which provide cell zonation, structural organization and protect the cells from the shear stress of perfusion models. Since capsules wall acts as a diffusion barrier for nutrients and growth factors, employing the microcapsules in a perfusion chip will facilitate the cell access to nutrients and growth factors required for MSCs differentiation. In this research, the simultaneous effect of microencapsulation and perfusion on the differentiation of MSCs to chondrocytes has been investigated. Microcapsules with a size range of 300-400µm were made using electrospraying technique. To make microcapsules, MSCs were added to a solution containing hyaluronic acid at concentration of 1.5% and chondroitin sulfate A at concentration of 4%. This solution was then electrosprayed into a stirring chitosan solution. The electrostatic force between negatively charged GAGs and positively charged chitosan forms the microcapsules. Furthermore, hollow structure of microcapsules will permit tuning of their inner environment. For this purpose, the second type of capsules were made by addition of collagen type I at a concentration of 1.5mg/ml to the GAG solution containing MSCs. These two types of capsules were then analyzed quantitively and qualitatively to investigate and compare their differentiation capacity after 4 weeks of culture in chondrogenic medium. GAG content, Cell proliferation and total collagen content were analyzed by using dimethyl methylene blue, Hoechst and hydroxyproline assays, respectively. In all these tests, it was observed that microcapsules containing collagen, had higher GAG content, cell proliferation and total collagen content after four weeks of culture in static conditions compared to microcapsules without collagen. These results suggest that the presence of collagen inside the capsules will facilitate the growth and differentiation of MSCs. Qualitative analysis of MSC differentiation to chondrocytes in microcapsules was also done by staining collagen type II and GAG using immunohistochemistry and toluidine blue staining respectively. Same results were observed here as microcapsules containing collagen showed higher collagen type II and GAG content. To analyze the effect of perfusion, the microcapsules containing collagen were transferred to a 3D perfusion chip. The results were compared with microcapsules in a static culture. Same set of analysis were done, and it was observed that the perfusion will accelerate the rate of differentiation compared to static culture. This is mainly due to better access of cells to nutrients and growth factors inside microcapsules. These results show the advantages of MSC encapsulation toward their differentiation ability to chondrocytes compared to non-encapsulated MSCs. These microcapsules have multiple applications in modular tissue engineering especially for treating articular cartilage damage.