Metabolic Requirements of Blood Vessels in a Perfusion Bioreactor

Small caliber vessel grafts are one of the major challenges of vascular tissue engineering. A variety of proc- esses have been developed to create vascular grafts from scaf- folds and donor cells in bioreactors. In order to optimize such processes, this study focused on monitoring vessel metabolism under conditions typically used in perfusion protocols. Bovine veins were perfused in a bioreactor for four days. Group 1 vessels served as controls and were perfused with standard medium. Medium of group 2 was adjusted to the viscosity of blood. Group 3 vessels were additionally challenged with ele- vated luminal pressure. Contractile function was assessed in an organ bath. Tissue viability was determined by tetrazolium dye reduction. Oxygen gradients, dextrose consumption, and lac- tate production were monitored using a blood gas analyzer. KCl induced contractions did not differ between days 0 and 4. Norepinephrine dose-response curves of group 3 vessels achieved a higher maximum contraction on day 4, with no changes of EC50. Tissue viability was not altered by any of the perfusion conditions. Oxygen gradients across the vessels did not change with time but were elevated in group 2, with no signs of oxygen depletion. Dextrose consumption and lactate formation of group 1 and 2 vessels appeared to be stoichiomet- ric. In contrast, group 3 vessels produced more lactate than dextrose could supply. These results indicate that conven- tional oxygenation of culture media is sufficient to meet the oxygen consumption of a functional vessel. Elevated shear forces increased the oxygen demand without affecting dextrose consumption. Elevated shear forces and luminal pressure caused the utilization of alternative energy sources. Thus online monitoring of key metabolic parameters appears to be a desirable feature of perfusion bioreactors for vascular tissue engineering.