 |
|
|||||||||||||||||||
|
||||||||||||||||||||
|
|
 
 
click here to see the photos and captions for this article In the art and science of building artificial body parts, our largest, most exposed organ has proved most difficult to design. A laboratory visit to the consumer-minded researchers who are fleshing it out. Without skin, we would be puddles. The body's largest organ keeps our insides from leaking out and the world from oozing in: Skin shields us from germs, injury, and the sun. We are more than 90 percent water, and without the supportive, water-repellent membrane that is skin, we'd be mere masses of fluid on the floor. Our outermost surface, the epidermis, is actually an unglamorous wall of dead cells. The real skin action is in the second layer, the dermis, which we see only in cases of injury. Skin seems like it should be a relatively easy organ to imitate--at least aesthetically. After all, it's what we most present to others: skin shows. But creating convincing synthetic skin--whether for the manufacture of artificial body parts or for filmmaking animatronics--has proved difficult for exactly that reason. We know all too well what the real thing looks like. And while we have demanding expectations for how skin should appear in a movie or a painting, we're even tougher when it comes to our own bodies. We may accept a heart from another person, or an artificial valve, but we will wear only our own skin--no one else's will do. This is not just a matter of elitism. The standard procedure for treating severe burns is to apply cadaver skin to the victim to protect the body from germs. But in a matter of days, that skin dies. No person-to-person skin transplant has ever held. Although the epidermis can be approximated with a believable outline, a base color, and perhaps some artful shading, capturing what transpires underneath, in the dermis, is another matter. To make skin appear live, tiny pores, shadows of blood vessels, and hints of furrows that correspond to the dermis below must be there. Even if viewers aren't consciously aware of such details, without this subsurface intricacy, artificial skin looks flat and dead. This is why, for example, the movements of the computer-generated dancing baby on Ally McBeal are more human than its flesh, which is eerily dense; real babies have fine, almost translucent skin. In Thomas Mann's The Magic Mountain, the director of the Swiss sanitorium paints as a hobby. A doctor who understands the complicated structure of skin, he is particularly boastful about his mastery of it in a portrait. "That human hide there is a matter of science... you'll see not just the horny and mucous layer of the outer skin, but... the imagined reticular layer with its sebacious glands, sweat glands, blood vessels, papillae." A patient who is already smitten with the portrait's subject then becomes obsessed with her skin. (Later, the woman in the painting wears a sleeveless dress, revealing more skin than ever before, which inspires the single love scene of the book--and leads to the patient's seven-year stay at the sanitorium.) Creating skin details lovely enough to inspire ardor is something that Jean Bolte, a senior viewpainter at Lucasfilm's Industrial Light & Magic in San Rafael, California, has struggled with for about a decade in both the model shop (where effects are created on puppets) and on the computer (where effects are created digitally). In the shop, Bolte, who has worked on films including Men in Black and Jumanji, found silicon to be the best medium for imparting depth to big-screen skin, but she now electronically paints effects onto digitized images. "Before Jurassic Park, the best we could do was the T2 [Terminator 2] man, the mercury man," says Bolte. "He was pretty cool, but he had no surface texture. He was completely reflective. To have what seems like real skin, you need a painter. Now we can paint with software." The medical industry has also been a source of inspiration, materials, and tools for Bolte and others in special effects. "I worked with a guy who designed artificial eyes," she says. "And the best glue I've ever seen came from work done with prosthetics." Although artificial limbs and heart valves, organ transplants, and blood transfusions have been part of the medical world for the last few decades, man-made skin appeared only a few years ago. It is the deep dermis underlayer--which provides strength, elasticity, and most of all, comfort--that biotechnology firms have finally conquered with synthetic and natural products. Anyone who has scraped a knee or superficially sliced themselves in the kitchen takes it for granted that the epidermis easily replaces itself when damaged. But the dermis is unable to do that. Once destroyed, it is gone forever. Not only is a person scarred, but because the scar tissue is rigid, the freedom of movement afforded by the flexible dermis is lost. Healthy skin that is pinched or pulled can resume its regular form; scar tissue cannot. Nor can it grow, which is especially damaging for children because the rest of their body gets bigger while the scar tissue doesn't. In cases of extensive second- and third-degree burns, the buildup of such tissue can be crippling. In a jar in my refrigerator is a piece of synthetic skin that's designed to do what the human body cannot: regenerate dermal cells. Roughly the size of a slice of American cheese and the width of two stacked quarters, it's a rubbery, transparent patch lined on one side with silicon, the other with collagen. The silicon is slippery and water-repellent, while the collagen has the texture of a fine sponge; the whole piece is submerged in an alcohol solution that smells like nail-polish remover. My skin patch is a gift from the lab that manufactured it, a biotech firm called Integra LifeSciences Corporation, based in Plainsboro, New Jersey. But the Integra patch is not skin itself; it's more like skin real estate, a tract of collagen sponge that human cells find inviting. They move in and colonize the Integra material, and it becomes, after a few weeks, part of the body. For $1,000, you can have an eight- by 10-inch vacant lot, guaranteed to attract your own cells. Integra is proud that its product has a two-year shelf life, and though it should be refrigerated, it doesn't have to be. The generic, foil-wrapper packaging--similar to that used for freeze-dried food--seems intended as reassurance that even though the contents promote an aberrant response in the body, there is no reason for alarm. And the skin patch itself has a blank, anonymous quality. Such anonymity is intentional, for once sewed or stapled onto the patient, it begins to absorb the person's cells: blood vessels, pigment, and then sweat glands, nerve endings, and hair follicles. In short, a purely synthetic material becomes natural skin. To biotech designers, the Integra patch is an attractive, mass-manufactured ideal: one product, long shelf life, many consumers. This kind of Alien-style, protean substance exemplifies strategies now evolving in commercial medicine: manufacturing goods that the body not only incorporates as its own, facilitating healing, but that also allow future movement and growth. Kent Ritzel, who as medical section chair of the Industrial Designers Society of America administers its Medical Design Excellence Award, sees products like Integra as a break from the static engineering that was characteristic of the postwar era. "We are constantly in motion, and we have to see how medical products interact with us as we move," explains Ritzel. "You can't just apply skin. You have to understand the forces that work on the body." Integra contains no human cells, while other types of synthetic skin--Apligraf, manufactured by Organogenesis, based in Canton, Massachusetts, and Dermagraft made by Advanced Tissue Sciences in San Diego--do incorporate human skin cells. (Apligraf is harvested from infant foreskins.) Because of the perishable nature of organic cells, Apligraf and Dermagraft have a shelf life of only one week. While skin cells surrounding traumas like burns are responsive to Integra, when it comes to chronic problems like venous and diabetic ulcers (in which the body's healing process is already severely compromised), the hybrid products are needed. But all of them are based on the principle that subtle physiological intervention promises a more successful outcome than wholesale replacement with a foreign or artificial object. In many ways, products like Integra--which is essentially a blank slate allowing patients to impose their own order upon it--represent a vast improvement over transplanted organs, which require a severe damping down of the immune system to prevent rejection. The new, synthetic skins trick the body into thinking that the replacement tissue is relatively normal and that the damaged site doesn't require emergency action. Simon Archibald, an Integra biologist who helped create the skin patch, sees these products as a reversal of biomedical convention. "People in the field spent years treating the patient like an object, something you do something to, not someone you cooperate with," Archibald says. "We try to cooperate with what the body wants." Healthy dermis has a three-dimensional structure that provides a congenial home for cells. But scar tissue is almost two-dimensional. Skin cells adjacent to the damaged area produce collagen in rows, as if they were sandbagging a river, but because the rows are so tight, no living skin cells can survive within scar tissue. Without the teeming, three-dimensional matrix of skin, you get only hard and unyielding flat tissue. Integra therefore set out to re-create the skin matrix while simultaneously convincing the body not to produce scar tissue. Instead of attempting to ape skin cells, Integra researchers concentrated on providing a comfortable environment for them. The Integra collagen has a matrix form that dermal cells surrounding the injury recognize as familiar--what Integra scientists call "keeping cells happy." Cheerful cells feel comfortable replicating and migrating through the matrix. After a few weeks, human dermal cells have colonized the Integra patch; the protective layer of silicon is removed, and epidermal cells taken from other parts of the patient's body are used to seed the top layer of skin. The Integra production laboratory is a cross between a busy delicatessen (practical) and an intensive care unit (sterile). There's the tendon prep room, which contains a freezer full of neatly shrink-wrapped yard-long cow tendons (raw collagen). Next door is the tendon processor--a glorified meat grinder. There, the ground tendons are mixed with shark cartilage and then with water. The resulting slurry is poured into metal pans and freeze-dried into sheets, which are then lined with silicon. A thin gray thread is sewn into the silicon side as a visual marker; the telltale was introduced after a surgeon installed a patch wrong side out during clinical trials. At Integra, the concept of devising materials that enlist the body in healing itself is combined with an assembly-line mentality. One area is devoted to making collagen straws that promote the regrowth of nerves by providing a "ladder" through which the broken ends of the nerve can reconnect (once damaged, they won't heal themselves). The straws, which come in handy plastic packs, are now being considered for approval by the FDA. Integra, as well as other firms that manufacture tissues and organs, aspires to create products that are medical Levittowns: innocuous, unassuming, a trustworthy guarantee in a nonthreatening package. "We design for cells, not for people," says George McKinney III, Integra's chief operating officer. "So you get your own skin eventually. If the patch is on the face where skin is thin, then over the next few months, that skin will develop thinly. On the feet it would be thicker. We just get it close enough to let you take over." Because the patient's own cells supply the final merchandise with individuality, the healed organ is as productive as what nature builds. Perhaps in the future, the best biomedical design will be the opposite of body parts--empty shells within which the body itself will detail its own form. WENDY MARSTON is a writer based in New York City. Her book, The Hypo-chondriac's Handbook, was published this fall by Chronicle Books. |
BACK TO TOP