In a "scratch assay," a researcher scratches a 2 millimeter gash through a layer of skin tissue, simulating a cut in real skin. Over time, with the addition of proteins called "growth factors" the skin cells will migrate into the gap and multiply, closing it up. This takes place in a matter of hours. Preliminary scratch assays at Stanford show that an engineered version of epidermal growth factor (EGF) can close the gap in 48 hours compared to 72 hours with natural EGF. If you'd like more information, e-mail David Orenstein, Manager, Communications and P.R.