(443a) Modular Tissue Engineering System for Characterization of Oxygen Gradients, hMSC Differentiation, and Pre-Vascularization

Tissue engineering is currently limited by the inability to adequately vascularize tissues in vitro or in vivo. Fundamental issues of nutrient perfusion and mass transport limitations, especially oxygen diffusion, restrict construct development to smaller than clinically relevant dimensions and limit the ability for in vivo integration. Here we present a bioreactor culture system for a ?modular' approach to tissue engineering, where scaffold size, tissue type, transport issues, and surgical implantation in vivo are considered from the outset. Using human mesenchymal stem cells (hMSCs) differentiated into adipogenic and chondrogenic lineages as the model cell and tissue types, we examined the differences in the expression profiles of hMSCs under different oxygen tensions, as well as the development of oxygen gradients in hMSC-seeded collagen hydrogels in static culture or perfused by porous silk microtubes. Perfusion with porous silk tubes enhanced oxygen transport in the gels and, in turn, cell viability and differentiation. This experimental data, combined with modeling of oxygen transport, defined the required capillary spacing and dimensions of the minimally-sized unit on a tissue-specific basis. The outcomes of this study represent a generic strategy that can be employed by any laboratory, where specific variables (cell density, metabolic rate, etc.) can be imported into the design matrix to determine minimally-sized units for any cell type, biomaterial matrix, or target tissue.