Development and Application of a 3-D Perfusion Bioreactor Cell Culture System for Bone Tissue Engineering
Porter, Blaise Damian
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Tissue engineering strategies that combine porous biomaterial scaffolds with cells capable of osteogenesis or bioactive proteins have shown promise as effective bone graft substitutes. Attempts to culture bone tissue-engineering constructs thicker than 1mm in vitro often result in a shell of viable cells and mineralized matrix surrounding a necrotic core. To address this limitation, we developed a perfusion bioreactor system that improves mass transport throughout large cell-seeded constructs. Additionally, we established and validated 3-D computational methods to model flow and shear stresses within the microporosity of perfused constructs. Micro-CT scanning and analysis techniques were used to non-destructively monitor mineral development over time in culture. CFD modeling of axial perfusion through cylindrical scaffolds with a regular microarchitecture revealed a uniform flow field distributed throughout the scaffold. Perfusion resulted in a 140-fold increase in mineral deposition at the interior of 3 mm thick polymer scaffolds seeded with rat bone marrow stromal cells. The total detected mineral volume tripled as the construct length was increased from 3 to 9 mm. Increasing scaffold length to 9 mm did not affect the mineral volume fraction (MVF) within the full volume of each construct. Mineral volume, spatial distribution, density, particle size and particle number were then quantified on cell-seeded constructs in 5 different culture environments. The effect of time varying flow conditions was compared with continuous perfusion as well as two different control cell culture methods in an attempt to enhance mineralized matrix within the constructs. Intermittent elevated perfusion and dynamic culture in an orbital rocker plate produced the greatest amount of mineral within 9 mm long constructs compared to low continuous flow and high continuous flow cases. Together, these studies indicate that dynamic culture conditions enhance construct development with regards to cell viability, mineralized matrix deposition, growth rate, and distribution. Furthermore, these techniques provide a rational approach to selecting perfusion culture conditions that optimize the amount and distribution of mineralized matrix production. Finally, the established perfusion bioreactor, in combination with micro-CT analysis, provides a foundation for evaluating new scaffolds and cell types that may be useful for the development of effective bone graft substitutes.