One of the problems with artificial skin is its vulnera­bility to infection. Synthetic skin is used in burn treatment and plastic surgery, but blood vessels, which carry the immune system's machinery, may not connect to the new dermis for a week or two. "Without blood vessels, bacteria can grow and cause infection," says ­Ioannis Yannas, a bioengineer and materials scientist at MIT who helped develop the first artificial-skin product, approved by the U.S. Food and Drug Administration in the mid-1990s. In a new approach, cultured skin cells are genetically modified to produce higher levels of an antibacterial protein. The cells multiply in the lab and are injected into a collagen matrix of artificial skin. "We're using genetic modification to try to get the cultured skin to behave more like normal skin," says Dorothy Supp, a researcher at the Cincinnati Shriners Hospital for Children in Ohio, who led the project. Supp cautions that the engineered cells are far from clinical use: the true test of their bacteria-fighting properties will come in the complex environment of a real wound. The researchers are planning experiments in animal models. The technique could eventually be used to make skin that can sweat and tan after implantation.