Replacement skin could save the lives of severely burned patients and spare them from painful skin-graft-harvesting operations. But today's "artificial skin" products are used only as temporary dressings for wounds, not permanent grafts for burns, in part because they're made without something vital to the survival of skin grafts-blood vessels. A handful of researchers are working to change that.

One method combines several types of cells with genetic engineering. Yale University dermatologist Jeffrey Schechner starts with dermis-the skin's bottom layer-from organ donors. He strips cells from this tissue and adds keratinocytes-the cells that make up the top layer of skin-from the foreskins of circumcised baby boys. Next he adds endothelial cells that come from the lining of veins in umbilical cords and have been genetically engineered to produce a growth-promoting protein. These cells multiply and line the channels left by the dermis's original blood vessels.

All this may sound a bit ghastly, but it seems to work as Schechner described last spring at the annual meeting of the Society for Investigative Dermatology. Schechner grafted the new skin onto the back of a mouse, and two weeks later he found red blood cells in the channels of the graft-an indication that the mouse's blood vessels had linked with the synthetic ones.

Schechner is now fine-tuning his system.