Skin Substitutes

What are Skin Substitutes?

Skin substitutes are natural, synthetic or biosynthetic materials that are used to cover large wounds to restore at least some of the functions of the skin. Skin substitutes provide temporary or permanent wound closure and protect the wound from infection, further damage and water loss, and reduce pain. They facilitate the growth of the normal skin over the wound.

Wounds that are associated with a lot of skin loss can easily develop infections besides being unsightly to look at. Such wounds are commonly observed following burns, trauma, or diabetes or venous ulcers in the leg.

Once the initial infection is treated and the wound appears healthy, attempts are made to cover large wounds with skin grafts. The graft is usually taken from another part of the body and may be a partial-thickness or a full-thickness graft. Full-thickness grafts consist of both the layers of the skin, the epidermis as well as the dermis. On the other hand, partial-thickness grafts consist of the epidermis and a part of the dermis. Once the graft is placed over the wound, it attaches itself to the wound in a few weeks. Blood vessels from below the wound grow into the graft and ensure that the graft is taken up, and the grafting is successful. Wound care is extremely important during this period to prevent graft rejection.

In some cases during wound management, the adequate amount of skin for grafting may not be available, or the patient may not want to create another wound. In these cases, skin substitutes are used. Skin substitutes are today an important requirement of plastic surgery.

When are Skin Substitutes used?

Skin substitutes are used in the treatment of conditions like burns, trauma wounds, diabetes or venous ulcers, where skin grafts may not be possible. In some cases, skin substitutes are used as a permanent solution. In other cases, they may be used as a temporary measure. Some of the conditions in which temporary skin substitutes are used are as follows:

• On superficial wounds till skin healing occurs
• On donor sites of skin grafts
• To temporarily cover wounds till skin grafting can be done

What are the Types of Skin Substitutes?

Depending on the source, skin substitutes can be biological or synthetic. Some of the synthetic substitutes also contain biological material and may be referred to as biosynthetic skin substitutes.

Biological skin substitutes include tissues that are obtained from biological sources. These include:

• Skin grafts obtained from pigs, which are sometimes used after introduction of some modifications
• Skin grafts obtained from cadavers. Just like people can donate their organs after death, they can also donate their skin, which can be used for grafting.
• Amnion, which is a fetal tissue that is obtained from the placenta and used only after being subjected to several preservation techniques. It is used as a temporary skin substitute.

• Cultured epithelial autografts. These are produced by growing skin cells obtained from a small biopsy from the patient in the laboratory. They are expanded into sheets, which can be placed over the wound. They can be used as permanent skin substitutes.

Synthetic or bioengineered or biosynthetic skin substitutes are artificially produced. Some of them contain skin cells while others do not. Those which do not contain skin cells and are therefore classified as acellular include:

• Biobrane®, which consists of a nylon mesh and an outer layer of silastic.
• Integra®, which consists of bovine collagen, chondroitin-6-sulphate and a silastic membrane.
• Matriderm® which consists of bovine type I collagen with elastin.

Cellular skin substitutes contain some types of skin cells. These include keratinocytes, which are the most common cells of the skin, and fibroblasts, which produce fibrous tissue. The cells are often obtained from the foreskin of the penis obtained from babies undergoing circumcision. Some of the cellular skin substitutes are:

• Apligraf®, which consists of type I bovine collagen, and keratinocytes and fibroblasts form the cellular component.
• TransCyte®, which consists of a nylon mesh and outer silastic layer, with fibroblasts as the cellular component.
• OrCel® which consists of skin cells in two layers and type I bovine collagen sponge.
• Hyalomatrix®, which consists of hyaluronan base, fibroblasts and an outer silicone membrane.
• Dermagraft®, which is a bioabsorbable polyglactin mesh with fibroblast cells.

What are the Advantages and Disadvantages of Skin Substitutes?

Some of the advantages of using skin substitutes are as follows:

• They can be used in conditions where adequate skin grafts are not available, for example, in extensive burns.
• They prevent the creation of additional wounds, as in skin grafting.
• They provide temporary protection to the wound till skin grafting can be done.
• Synthetic skin substitutes can be made available in large quantities.

The main disadvantages of skin substitutes are:

• The high cost, makes them unaffordable for several people. Biological skin grafts may be comparatively cheaper to synthetic grafts.
• The availability of plastic surgeons who are experienced in using them.
• Since some of the tissues or cells in skin substitutes may originate from cows, pigs or infants, these may not be culturally acceptable to all individuals. Therefore, it is necessary to inform the recipient of the contents of the skin substitute before it can be used.
• Tissues from other species can result in a reaction in allergic individuals.