Making Skin from Sharks

Early tests offer new hope for burn victims

Each year, thousands of Americans die from fires. In too many of the cases, death occurs because so much skin is burned away that vital body functions are disrupted. Essential fluids ooze out, and natural defenses are too weakened to fight off bacterial infection. To prevent these complications, doctors try to cover burn sites with skin grafts from undamaged portions of the patient's body, but often there is too little skin left and they have to resort to using skin from pigs or cadavers. Being foreign tissue, these grafts are usually rejected in three to 25 days. The ideal solution would be artificial skin, a goal that has eluded scientists. But last week a team of Boston researchers announced they had a successful skin substitute made from a startling mixture of ingredients: cowhide, shark cartilage and plastic.

Developed over the past decade by Surgeon John F. Burke of Massachusetts General Hospital and Mechanical Engineer Ioannis V. Yannas of the Massachusetts Institute of Technology, the artificial skin has so far been used on ten patients, ranging in age from three to 60. All had third-degree burns over 50% to 90% of their bodies. Says Burke: "They were very badly burned. On a scale of 1 to 10, they were 11." In the 16 months since the first graft, the ersatz skin has not been rejected by any of the patients, nor have infections developed in the grafted areas. The body's natural defense system does not recognize it as foreign, like animal and cadaver skin. Thus there is no need to use drugs to help prevent rejection. The wounds heal with little scarring. Says Burke: "We are firmly convinced that the artificial skin is better than anything else now available for the management of acute burns."

Like natural skin, the man-made version is composed of two main layers. The innermost, corresponding to the dermis, is a mixture of a protein from cowhide and a complex carbohydrate derived from shark cartilage. When mixed with an acidic solution, the two ingredients become short white fibers. Freeze-dried and vacuum treated to remove moisture, the fibers form a light and highly porous white sheet of material, which is placed in an oven at a high temperature. The topmost layer, equivalent to the epidermis, is made by bonding a viscous plastic onto the cowhide-shark sheet. The completed skin is then freeze-dried and stored in sterile, closed containers at room temperature.

About as thick as kitchen paper toweling, artificial skin is soft, pliable and handles very much like the real thing, though it is not quite so sturdy. It is draped on burn sites in patches as large as 6 in. by 10 in. Says Burke: "The nerve fibers from below, which are still alive, grow up into the new material, just like blood vessels and connective tissue. So these patients have the same kind of sensations as with a skin graft. It isn't perfect, but it is very good." The artificial dermis breaks down as new natural tissue forms. The plastic top layer acts solely as a temporary protective covering; beginning as early as ten days after the artificial skin graft, postage-stamp size patches of plastic are peeled away and replaced by slivers of the patient's own epidermal tissue.

Man-made skin is still experimental, and more clinical testing will be needed before it is available for widespread use. Says Yannas: "We want to develop a membrane that will cover the wound and let it change over to natural skin without any more treatment or procedures. We don't want to use the patient's own skin at all."

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