A.J. Welch can turn skin transparent but, no, he explains with a laugh, he cannot make you look like one of those old "Visible Man" science toys. What Welch, a biomedical engineer at the University of Texas at Austin, and his colleagues can do is nonetheless amazing: They can create temporary windows where they can see right through the outer skin of rats and guinea pigs.
The trick is an injection of glycerol under the animals' epidermis. Glycerol drives out the water molecules that normally scatter light and render skin opaque. Because glycerol has nearly the same index of refraction as collagen, the common protein in skin, light travels in a straighter line through treated cells. In a few minutes, the skin becomes transparent up to a millimeter or two deep far enough to make blood vessels visible. Water gradually seeps back into the cells, so the skin fogs up again after about 20 minutes.
Before Welch tries this method on human skin, he'll need to know the health effects of high doses of glycerol although he thinks other, more innocuous molecules, such as glucose, will work. But the potential of the technique is clear. "There will be medical applications anywhere you'd want to improve visibility through the tissue. Brain surgery, for example, or delineating the depth of tumors below the skin," Welch says. His colleagues have already used glycerol treatment to render the white of the eye transparent to improve laser surgery for glaucoma.
|Rat skin, stretched over test markings, turns clear in 20 minutes.|
Photo by G. Vagas, E.K. Chan, J.K. Barton, H.G. Rylander, A.J. Welch/Surgery and Medicine, Volume 24, Issue 2, pp. 133-141, 1999 Wiley-Liss Inc.;