When patients need a vascular graft, as during heart bypass surgery, surgeons often use blood vessels from elsewhere in the body, but these are not always available.As an alternative, Yale researchers led by Yibing Qyang, PhD, associate professor of medicine (cardiology) and of pathology, are developing grafts in the lab using human induced pluripotent stem cells differentiated into smooth muscle cells, which are then seeded onto tube-shaped scaffolds and grown into blood vessels in a bioreactor.In the past, vessels generated this way were weak and often swelled. To generate stronger vessels, Qyang and colleagues applied surges of radial pressure to the developing vessels, stretching them as if they were pulsing with blood. When grafted onto the aortas of rats, as reported in Cell Stem Cell, these grafts carried blood without bloating and proved nearly as strong as grafts used in the clinic today.Next, Qyang plans to develop grafts that are stronger still and universally compatible, i.e. able to avoid immune rejection. These could be ready for clinical use within five to 10 years, Qyang says.