Bovine saphenous veins (BSV) were incubated in a perfusion bioreactor to study vessel wall metabolism and wall structure under tissue engineering conditions. Group 1 vessels were perfused for 4 or 8 days. The viscosity of the medium was increased to that of blood in group 2.Group 3 vessels were additionally strained with luminal pressure. Groups 1-d through 3-d were similar except that BSV were endothelium-denuded before perfusion. Groups 1-a through 3-a used native vessels at elevated flow rates. Group 3 vessels responded significantly better to noradrenaline on day 4, whereas denuded vessels showed attenuated responses (p<0.001). Tetrazolium dye reduction did not depend on perfusion conditions or time except for denuded vessels. pO 2 gradients across the vessels were independent of time and significantly higher in group 2 (p<0.001). BSV converted glucose stoichiometrically to lactate except vessels of groups 3, 1-d, and 3-d which released more lactate than glucose could supply (p<0.001). Group 1 vessels as well as all vessels perfused with elevated flow rates showed a loss of endothelial cells after 4 days, whereas group 2 and 3 vessels retained most of the endothelium. These data suggest that vessel metabolism was not limited by oxygen supply. Shear forces did not affect glucose metabolism but increased oxygen consumption and endothelial cell survival. Luminal pressure caused the utilization of energy sources other than glucose, as long as the endothelium was intact. Therefore, vessel metabolism needs to be monitored during tissue engineering procedures which challenge the constructs with mechanical stimuli.

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Abstract-Small caliber vessel grafts are one of the major challenges of vascular tissue engineering. A variety of processes have been developed to create vascular grafts from scaffolds 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 elevated luminal pressure. Contractile function was assessed in an organ bath. Tissue viability was determined by tetrazolium dye reduction. Oxygen gradients, dextrose consumption, and lactate 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 EC 50 . 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 stoichiometric. In contrast, group 3 vessels produced more lactate than dextrose could supply. These results indicate that conventional 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.