A collaboration of researchers has succeeded in growing functional arteries from cells derived from a biopsy of cow vascular tissue. By growing the arteries in a novel bioreactor system, they have engineered arteries that are much more resistant to rupture by blood pressure/shear than arteries produced by other methods. To create the vessels, a constant stream of culture medium was pulsed over tube-shaped polymer scaffolds infiltrated with smooth muscle cells. After eight weeks of culture, the vessels were seeded with endothelial cells to mimic the morphology of native vessels. According to Laura Niklason of Duke University (Durham, NC), senior author on the paper ( Science, 284, 489–493, 1999), "To the naked eye, the vessels looked exactly like native vessels." Immunohistological studies confirmed arterial markers were present on the vessels, which contracted properly in response to pharmacological agents. To validate that the arteries were functional, they were grafted into the femoral artery of miniature pigs and their performance compared with grafts prepared using a static system. "The nonpulsed vessels began to show signs of thrombosis by the third week," Niklason observes. "[But] the pulsed vessels remained open for [all] four weeks [of the study]." The approach holds promise as an alternative source of vessels for bypasses in vascular disease.