Tubular Perfusion System Bioreactor for the Dynamic Culture of Human Mesenchymal Stem Cells

Title of Document: TUBULAR PERFUSION SYSTEM BIOREACTOR FOR THE DYNAMIC CULTURE OF HUMAN MESENCHYMAL STEM CELLS Andrew Bryan Yeatts, Doctor of Philosophy, 2012 Directed By: Associate Professor John P. Fisher, Fischell Department of Bioengineering In vitro culture techniques must be improved in order to increase the feasibility of cell based tissue engineering strategies. Limitations of current techniques are largely a result of the slow diffusion of molecules such as oxygen into the interior of three dimensional scaffolds in static culture. In order to enhance nutrient transport we have developed a novel bioreactor, the tubular perfusion system (TPS), to culture human mesenchymal stem cells (hMSCs) in three dimensional scaffolds. In our design, hMSCs are cultured on scaffolds tightly packed in a tubular growth chamber. Media is perfused by a peristaltic pump through the growth chamber and around the tightly packed scaffolds. In the first part of the work hMSCs are encapsulated in alginate scaffolds and results demonstrate bioreactor culture enhances late osteoblastic differentiation of hMSCs. An investigation into shear stress in the system revealed that osteogenic markers increase with increasing shear stress and that the differentiation of hMSCs is dependent on cell radial position within scaffolds. In order to enhance the ability to implant these constructs in vivo, a method to create an aggregated cell containing construct in vitro in a bioreactor system was developed. In this part of the work hMSCs are cultured in individual alginate beads in the TPS bioreactor and the beads are aggregated to form one large construct. Following this the TPS bioreactor was investigated to culture synthetic poly-L-lactic acid scaffolds which were fabricated using supercritical carbon dioxide gel drying. In addition to investigating the effects of perfusion on hMSC growth in these scaffolds, the effect of microporosity was investigated. In the final part of the work, a study was completed to determine how TPS culture influenced in vivo bone regeneration. Here alginate beads as well as synthetic PLGA/PCL constructs were used as scaffolds. Results revealed the efficacy of using the tubular perfusion system for bone tissue engineering and demonstrated increased bone formation as a result of hMSC implantation in both alginate and PLGA/PCL scaffolds. These studies highlighted the need for bioreactor culture in vitro as well as scaffolds to support in vivo tissue interaction. TUBULAR PERFUSION SYSTEM BIOREACTOR FOR THE DYNAMIC CULTURE OF HUMAN MESENCHYMAL STEM CELLS