Temporary dressings are used for a variety of reasons on serious burn wounds. One new product is called OrCel and uses layers of human skin cells (from someone other the donor) and collagen (a tough connective tissue) from cows to make a dressing that can be applied to a burn wound or donor graft site for two to three weeks and then removed. A study compared the effectiveness of OrCel with a product that has been in use for decades and is composed of layers of silicone, nylon, and collagen from pigs. The researchers concluded that partial thickness donor sites healed more quickly with OrCel dressings than with the standard product. One advantage of early healing is that a donor site can potentially be reused for another graft after the area heals. Burns. 2003 Dec; 29(8): 837-41.
Researchers investigating hypertrophic scars (scars that grow above or outside the wound) have been limited because animals do not form hypertrophic scars. As a result, experiments using animals rather than people are not helpful in developing new treatments for people (regardless of one’s beliefs about animal experimentation). Researchers in Lebanon evaluated whether different types of wound dressings may help prevent hypertrophic scarring. The wounds that were treated were either donor sites for partial thickness skin grafts or wounds that were allowed to heal without grafting or surgical closure. The researchers concluded that patients treated with moist exposed burn ointment (MEBO) had less hypertrophic scarring than patients treated with dressings, Tegaderm, or antibiotic ointment. Aesthetic Plastic Surgery. 2003 Dec 4.
Because of the cosmetic importance of skin on the face, facial burns are a particular challenge. For 15 to 20 years the study researchers followed 18 patients who had received full thickness skin grafts for facial burns. The grafted skin was able to sweat, had oil glands, and was elastic. Partial thickness grafts don’t have sweat or sebaceous (oil) glands. When looked at under a microscope, the grafted skin looked more like regular facial skin than skin from the area of the donor site. The researchers suggested that full thickness grafts for facial burns may produce the best results. Zhonghua Zheng Xing Wai Ke Za Zhi. 2003 Jul; 19(4): 276-8.
French researchers studied the use of a product called Integra Dermal Regeneration Template for deep hand burns. Integra was used to cover the wounds either immediately after hospitalization or later during reconstructive surgery. Integra has two layers: 1) a permanent bottom collagen layer (from cows) that is a substitute for the dermal layer of the skin (the layer beneath the epidermis, which is the top layer of the skin); and 2) a top silicone layer that is a temporary substitute for normal epidermal skin. Two to three weeks after the wound is covered with Integra, the silicone layer is removed and replaced with a very thin donor graft of epidermal skin. Using thin epidermal skin grafts instead of thicker split thickness grafts has two potential advantages. The donor site looks more like normal skin after it has healed because there is less scarring when a thinner graft is removed. The donor site also heals much more quickly and can thus be “re-harvested” more quickly for additional grafts. The layer of collagen is left in place as a substitute dermal layer of skin and supports the donor epidermal graft (hence the name “regeneration template”).The researchers found that Integra worked well. There was a 100% “take” of the grafts and the grafted skin was flexible and supple enough to allow easy use of the joints in the fingers and hands. The cosmetic result was judged to be satisfactory. British Journal of Plastic Surgery. 2003 Dec; 56(8): 764-74.
A new dressing product is being investigated in France. It has been tested on patients with second degree wounds. None of the patients developed infections and for those patients who had grafts, all of the grafts “took.” The product saturates a new type of dressing (lipidocolloid) with sulfasalazine, which has long been used in burn units to prevent infections. J Wound Care. 2004 Apr; 13(4): 145-8.
One way of growing additional skin is with tissue “expanders.” A surgeon (usually a plastic surgeon) places a balloon under the skin and then gradually inflates the balloon with salt water. As the balloon gets bigger, the skin covering the balloon expands by growing new skin. After the skin expands, a “flap” of the expanded skin is used to cover a nearby area of skin that needs to be replaced. There are several advantages of tissue expansion. First, the expanded skin will be a good match in terms of color, texture, thickness, and the amount of hair. This is particularly important in areas such as the scalp and face. Second, because the skin doesn’t need to be moved, there is usually less visible scarring. Third, the blood supply for the skin flap remains intact and so the likelihood that the flap will take is higher than when skin is moved from a graft site. Fourth, the nerve supply in the flap is not cut and so the person will have feeling in the flap. The disadvantages of tissue expanders include the time it takes to expand the skin (up to three or four months); the unsightly bulge that occurs as the balloon is inflated; the possibility that the expander will rupture and require additional surgery; and the possibility of infection in the area of the expander. The article discusses the use of tissue expanders in children, including burn survivors. Because of the time tissue expansion requires, use in burn patients is limited to reconstructing scarred areas with healthy nearby skin. J Craniofac Surg. 2003 Nov; 14(6): 866-72.
A “contracture” is a shortening or shrinking of tissue. Grafted skin and scars shrink. When shrinkage occurs near joints and other moving body parts, such as the fingers and the eyelids, it can make movement much more difficult. Contractures can also occur when a part of the body isn’t used normally. For example, burn survivors who must keep a limb in a particular position to allow for healing of a graft or wound may experience shortening of the tendons or ligaments in that limb. When tendons and ligaments shorten, normal range of motion in the limb is lost. Such contractures may have to be “released” surgically. Exercise is one important way to prevent contractures. The author reports on the exercises used by a patient who had developed contractures requiring surgery to regain flexibility and prevent contractures from recurring following the surgery. J Burn Care Rehabil. 2003 Nov-Dec; 24(6): 378-81.
When burns occur there are very complicated responses by the body, some of which are poorly understood. One chemical produced by the body in larger amounts than normal following a burn injury is nitrous oxide, which can potentially cause further damage to wounded tissues. One hypothesis is that increased nitrous oxide may reduce blood supply to injured tissue by increasing the tendency of blood to clot. Researchers have investigated whether naturally occurring substances may help with wound healing. One such substance is thymus oil, which is known to have antiseptic and antioxidant properties. It was found that thymus oil decreased the levels of nitrous oxide in burn patients and promoted the formation of new skin. J Burn Care Rehabil. 2003 Nov-Dec; 24(6): 395-9.
Wound healing is usually a much bigger problem for people with diabetes than for people who don’t have diabetes. Diabetes affects blood vessels and can reduce the blood supply to the body’s tissues. Because blood transports oxygen, nutrients, and cells that are important for wound healing, a reduction in blood supply slows healing, including healing of burns. Researchers in Saudi Arabia performed experiments to determine whether a particular type of light (polychromatic light emitting diodes (LED)) stimulated healing of burn wounds in diabetic rats and nondiabetic rats. They concluded that LED light encouraged wound healing for the diabetic rats but not for rats without diabetes. Journal of Clinical Laser Medicine and Surgery. 2003 Oct; 21(5): 249-58.
Swiss researchers are investigating why cultured epithelial autografts (CEA’s) don’t always “take.” A CEA is produced by removing living, unburned skin cells from a burn patient and using those cells to grow thin sheets of new cells in a laboratory. A CEA is then grafted back onto the burn patient. There are two major advantages of CEA’s. First, “autografts” (grafts from the patient’s own skin) are not limited to areas of the patient’s unburned skin. New “skin” can be grown. This is particularly important for patients with extensive burns. Second, the grafts are not rejected by the patient’s immune system because the grafts are “recognized” by the immune system as being part of the person’s own body. One problem with the grafts has been that, on average, about 35% of CEA’s don’t end up taking; i.e., they don’t bond with the tissue beneath the graft. The Swiss researchers focused on the percentage of the cells in a CEA that continue to live following the grafting procedure. They found that more than 90% of the cells survived, leading them to conclude that early death of the cultured cells is not a good explanation for the failure of a CEA to take. The researchers did find that other biological processes occurring in cells varied a great deal between individuals and might explain why CEA’s take in some patients and not in others. International Journal of Artificial Organs. 2003 Sep; 26(9): 793-803.
Skin regeneration is an important field of tissue engineering. Especially in larger burns and chronic wounds, present treatments are insufficient in preventing scar formation and promoting healing. Initial screening of potentially interesting products for skin substitution is usually done by in vitro tests. Before entering the clinic, however, in vivo studies in immunocompetent animals are necessary to prove efficacy and provide information on safety aspects.
We have obtained extensive experience using the domestic pig as test animal for studies on skin replacement materials, including tissue engineered skin substitutes, and burn wound treatment.
Two models are described: an excisional wound model for testing of dermal
and epidermal substitutes and a burn wound model for contact and scald burns,
which allows testing of modern wound dressings in comparison to the present
gold standards in burn treatment. The results of these experiments show
that in vivo testing was able to reveal (dis)advantages of the treatments
which were not detected during in vitro studies.
Biomaterials. 2004 April Pages 1559-1567
