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A second skin

Scientists are creating artificial tissues to quickly and seamlessly patch burns and wounds. Their goal: the perfect skin substitute.

January 30, 2006|Linda Marsa | Special to The Times

SKIN doesn't get any respect. We heedlessly scratch, scrape and bruise it, and intentionally scorch it in the summer sun in our quest for the perfect tan.

Yet consider what it does. The largest organ in the body, this 1.8-square-meter network of nerves, blood vessels, pigments, fibrous cells and sweat and oil glands keeps fluids in and bacteria out, cools us down, holds our other organs neatly inside our bodies and senses the environment, warning us of dangers such as extreme heat or cold.

Without the skin's protective barrier, victims of massive burns are vulnerable to an onslaught of disease-carrying microbes and potentially fatal dehydration and shock. They lose their sense of touch and ability to regulate their body temperature. And when people age or develop diabetes, their skin loses resilience, leaving them prone to hard-to-heal wounds that can turn gangrenous, necessitating amputation.

To help curtail the annual 10,000 deaths from burn-related infections and 100,000 amputations needed because of diabetic foot ulcers, researchers are developing new artificial skin technologies in tissue engineering laboratories across the country, with the goal of creating substitute skin that looks and functions like normal skin -- with the same soft, smooth texture, strength, durability and color pigmentation.

If these synthetic skins can knit with the surrounding tissue and spur the growth of sweat glands, hair follicles and the blood vessels that nourish the skin cells with oxygen and nutrients, patients should heal more quickly, and with greatly reduced scarring.

These new skins aren't perfect -- they lack blood vessels and pigment-forming cells, for example -- and for now the gold standard remains taking grafts from the patient's body whenever possible. Artificial skins are only used when sufficient quantities of such skin grafts aren't available, such as when someone sustains massive burns over more than half his or her body.

But in the not too distant future, scientists hope that artificial skin technology may advance to the point where it can replace the real thing, and we'll be able to quickly and seamlessly patch burns and wounds without harvesting skin from other sites on our hides, and produce grafts that are even more functional.

"The holy grail is to develop a wound-healing technique that is even better than what the body does," says biochemist Richard A. Ikeda, program director for wound healing at the National Institute of General Medical Sciences in Bethesda, Md.

A delicate procedure

Even under the best of circumstances, the healing of wounds is an imperfect process. The body doesn't generate exact replicas of the skin that has been lost.

The problem lies with the response to injury of the lower part of the skin, called the dermis. Made primarily of proteins called collagen that give skin its firmness and pliability, the dermis is constantly being turned over, with new networks of collagen replacing the old.

But when it is damaged, a super-dense form of collagen is created to quickly cover over the wound -- so thick that no hair roots, sweat glands and few nerves can grow in it, and the skin loses functionality. And as the collagen heals, it shrinks, which pulls on the surrounding skin.

Such scarring is reduced with traditional skin grafts, but although this technology has improved, there are still serious problems with infections and getting those grafts to take. And, depending on the thickness of the graft, the replacement skin can lack certain features of skin, such as pigment, nerves or hairs.

Even so, can artificial skin ever hope to come close?

To be sure, some artificial skin products already exist, and have been available for more than a decade. Consisting of a fabric of human or other mammalian cells combined with synthetic or biocompatible materials, these fake skins are placed on a wound to provide a protective barrier against infection and prevent leakage of vital fluids. This gives the underlying tissue a chance to heal.

Some of the products slough off over time, while others become part of the permanent skin. But all fall far short of the goal of fully functional skin with all its complex bells and whistles.

Up to half of the grafts of these skins don't take, for example. And the ones that do can thicken as they heal, forming scars that contract over time, leading to a loss of motion in joints and permanent disfigurement.

Plus, the skin that forms is not as strong or durable as real skin and can be painful long after the initial injury has healed, says Dr. Robert L. Sheridan, codirector of the Adult Burn Service at Massachusetts General Hospital and a surgeon at Harvard Medical School in Boston.

"These are not true replacements -- essentially they're high-tech bandages that jump-start the healing process," Ikeda says.

Scientists hope that the next wave of synthetic skins will do more.

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