Transport and Mechanical Property Enhancements for Tissue Engineered Vascular Grafts

Previous research established a fibrin-based tissue-engineered blood vessel to provide an alternative source to autologous vasculature, which is considered the standard course of treatment in many vascular diseases. The focus of this research was to investigate methods of improving the mechanical properties of these engineered tissues with three focus areas: (1) improved nutrient and metabolite transport, (2) matrix cross-linking using a ruthenium catalyst and tyrosine residues inherent to fibrin and many extracellular matrix molecules, and (3) cell-signal induced increases in collagen production via culture in low oxygen environments.;The first focus area implemented transmural flow to improve nutrient and metabolite transport with mathematical analysis of dissolved oxygen (DO) transport. The DO transport and consumption models demonstrated improved transport when controlled transmural flow was combined with axial flow during bioreactor operation. The predicted DO concentrations were elevated and the profiles in the tissue were more uniform and demonstrated agreement with physical system measurements. These results have been extended to a pulsatile.;The second method evaluated a ruthenium-catalyzed method of cross-linking and was shown to significantly increase the strength and stiffness of viable engineered tissue. This method cross-linked tyrosine residues inherent to fibrin and cell-deposited extracellular matrix proteins and provided increases in mechanical strength and stiffness after cross-linking to physiological levels. These effects were also found to be tunable with culture duration or light exposure time. Subcutaneous implantation of cross-linked tissue demonstrated a mild inflammatory response similar to control tissues. Thus, the ruthenium catalyzed cross-linking method was shown to be rapid, non-toxic, minimally inflammatory, and capable of increasing stiffness and strength of engineered tissues.;The third method investigated the impact of low environmental oxygen concentration and insulin on the fibrin-based tubular constructs. Tissues that were cultured under hypoxic conditions with insulin supplementation demonstrated increased mechanical strength and stiffness, collagen density and collagen deposited on a per-cell basis. The combined effect of these treatments showed interacting effects on these measures due to increases in chronologically distinct collagen processing steps, namely increased Akt phosphorylation and prolyl-4-hydroxylase (P4H). These proteins promote collagen transcription and post-translational modification, respectively. The multi-faceted approach of these methods provides the potential to yield a unique, fully biological tissue-engineered vascular graft capable of arterial implantation.