Skin Substitutes Used In Many Cases

Mon, May 09, 2011

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KMUW / Fletcher Powell

With sunny days and summer months approaching, many people might begin thinking about how to protect their skin from the sun’s rays. But the way we consider our skin must include far more than simple concern about sunscreen. As the body’s largest organ, the skin protects us, helps us stay hydrated, regulates our temperature, and retains nutrients. As part of our Sound Mind and Body health series, KMUW’s Fletcher Powell takes a look at what doctors can do to help a person whose skin can no longer serve these functions.

Remember this?

(Masterpiece Theatre music)

Many people probably recognize that music as being used as the theme song for the enduring PBS show, “Masterpiece Theatre.” Some might even remember that show’s long-time host, British-American journalist Alistair Cooke.

But what a lot of people might not know is that, not long after his death in 2004, Cooke became part of a major scandal involving the sale of stolen body parts to medical technology companies. Basically, what happened was, a firm in New Jersey was taking cadavers that were meant to be cremated and stealing tissue from them. That tissue was then sold to companies like the LifeCell Corporation, who would use that tissue to engineer substitute tissue grafts for use in medical procedures. Cooke’s body was one of the victims of the theft.

Now, this is actually a pretty common thing. Not the stealing of body parts, of course, but the use of tissue from cadavers as a sort of artificial version of, say, a person’s own skin. That artificial skin can then be used to treat burn victims when more traditional techniques might not be available.

Ashish Mahajan is a plastic surgeon working with the Buncke Clinic in San Francisco.

Mahajan: If you burn 80 to 90 percent of your body, there aren’t areas to take a skin graft. You’d have to take little pieces and do it over and over and during that time a person can become severely ill and might not even survive their therapy.

This skin grafting involves taking a section of skin from one part of a person’s body, and literally placing it over another area that no longer has functioning skin. But, in the case of burn victims, there sometimes isn’t enough unaffected skin to graft over the burns. And a person without functioning skin is in big trouble.

Mahajan: There are several kinds of infections that someone who’s had burns can develop, one is in their lungs, another is in their skin or their wounds. They can have problems with their kidneys; their immune function is generally decreased because of the severe injury. The skin is a large portion of our body, and an injury to that much of the skin affects the entire body.

So the goal, Mahajan says, is to find a way of healing the wounds quickly and effectively, even when traditional skin grafts aren’t feasible, which means a short-term substitute will be needed that will serve the same purpose that skin does.

Mahajan: Skin has two general functions. Two layers:  the epidermis—which you can think of as kind of a barrier to losing water and a barrier to bacterial contamination to your body. That’s a barrier to infection. And then, under that is the dermis. It’s thicker, more elastic, and it gives skin its mechanical properties, more or less.

Many skin substitutes are made with a silicon sheet on the outside, to serve as that epidermal barrier, under which is placed a collection of substances that contribute to the function of the dermis—collagen, for instance. And the idea is that, over time, your own cells will migrate to the area and start to take over the function of the artificial skin.

Mahajan is quick to point out that, in nearly all cases, the substitute will probably need to be removed and replaced with an actual skin graft—the substitute is there to help the healing process along more quickly and to buy more time when a skin graft is difficult. How much time it buys, and how much of the substitute needs to be removed, depends on what the artificial skin is made out of.

Mahajan: The general way to categorize these substitutes is, either they’re autografts, derived from the person themselves; they’re allografts, they’re still human but from some other human; and xenografts, xenografts are from some other species… the most common xenografts are pig dermis.

He says these xenografts tend to produce a response from a person’s immune system within 10 days or so. The other kind, the allografts, are the sort that are sometimes taken from cadavers—as in the case of a skin substitute called Alloderm, which is made by LifeCell, one of those companies that was duped by the New Jersey tissue thieves. Generally, allografts will also eventually produce an immune reaction in a person’s body and need to be removed. But, in the case of Alloderm, for example, manufacturers actually go in and take out the cells in the tissue that will produce that reaction, allowing the substitute skin to be more or less incorporated by the body.

And it’s these kinds of advances that are making skin substitutes even more useful and more attractive as time goes on. Some researchers are even trying to engineer substitutes that also act as an antibiotic, which would, of course, greatly decrease the risk of infection when using artificial skin. Not only that, but these skin substitutes are already being used for far more than just burn victims.

Mahajan: When you put in a breast implant under the skin of the breast after a mastectomy, there’s not much over it except that skin, and sometimes the implant can cause trouble for the skin, it can cause it to break down, and the implant we’ll have to remove… using substituted dermal acellular… human dermal matrix around the implant can help prevent that. That’s another really common use where we’ve seen some success.

Mahajan says, ultimately, the ideal skin substitute would be one that’s non-toxic, won’t cause any immune reactions, is durable, and doesn’t present any risk of disease transmission. And while nothing meets that ideal just yet, the fact that researchers are constantly working to improve skin substitutes might mean it’s not far away.

Mahajan: The first goal is to get these substitutes to function like human skin. The second goal might be to get them to function better than human skin.