Skin substitutes as a form of wound closure have been found useful since the earliest centuries of medical science. Skin is made up of epidermis (upper) and dermis (lower) skin layers, and is the largest organ in the human body. It is in direct and constant contact with the outside environment, so it is the most susceptible to injury and damage. Thus, a substitute is necessary in many cases of skin wounds.
Types and Uses of Skin Substitutes
Skin substitutes are used to aid in wound closure, control associated pain and replace the skin function to promote healing of the wound. A skin substitute can be either temporary or permanent:
Temporary substitutes are used as a short-term wound covering to protect the wound area from risks posed by the outside environment (such as bacterial contamination or external trauma), and provide a clean healthy and moist environment to promote wound healing. It is usually removed after three to four weeks. Temporary skin substitutes can be categorized as follows:
Natural substitutes, formed from live cells that require proper processing and preparation before usage, such as:
- Human allograft: The best choice among temporary skin substitutes, it is human skin taken from human cadavers, consisting of both epidermal and dermal skin layers. It is used for temporary coverage of large excised wounds.
- Pig skin xenograft: This is pig skin that has been specially treated and contains only the dermis layer. It is mainly used in the coverage of partial thickness burns and excised wounds prior to skin grafting.
- Human amnion: This is a thin transparent membrane that covers a fetus inside the mother's womb. Because this is made from human placenta, it is one of the most effective substitutes to be used in healing or covering partial thickness burns, as well as covering some other types of superficial wounds.
- Oasis wound matrix®: This skin substitute is a natural product derived from mucosal cells found in the small intestinal walls. It is used mainly in hard to heal non-burn wounds, but can also be used for superficial burn wounds and skin graft sites in donors.
Synthetic substitutes, formed from synthesized materials that are made on demand with specific characteristics required in each case, such as:
- Biobrane™: Is a synthetic substitute made up of a thin layer of silicone with small pore-like holes (that allow exudate material to come out and topical antibiotics to go in), and an inner nylon triple layer with a thin water layer in between to provide a moist environment for wound healing. It’s mainly used for closing clean superficial burns and excised wounds.
- TransCyte™: Is a double-layered skin substitute with an outer silicone layer (with no pores) and an inner layer lined with human neonatal foreskin fibroblast. This is used to close or cover clean superficial to moderately deep burn wounds, especially in children. It is also used for temporary closure of wounds before skin grafting.
Permanent skin substitutes are used to replace the full thickness of skin layers and improve the quality of skin at the wound or burn sites permanently. These skin substitutes include:
- Epicel: Also known as cultured epithelial autograft (CEA), it only provides the epithelial (outermost) layer of skin. It is made from the patient’s own skin cells by taking a small skin biopsy and culturing it for two to three weeks to "grow" the necessary graft size. It’s mainly used for very large burn wounds that cover more than 30 percent of the total body surface area.
- Alloderm: This permanent substitute consists of a treated dermis layer of human cadavers skin, which is mainly used as a dermal implant to replace soft tissue defects. It also can be used for deep partial and full thickness burn wounds. It cannot be used on large areas. This substitute still requires a thin epithelial layer to cover it. It has a long shelf life and requires re-hydration before applying.
- Integra: This synthetic permanent substitute is made of an inner dermal analog layer (similar to skin dermis) with material that joins the wound's existing cells, promotes cell growth and helps in the formation of new blood vessels. It provides an outer epithelial layer that covers and protects the wound until the dermal analog layer is well incorporated. This process takes about two to three weeks, and then the outer layer must be replaced with either CEA or a skin graft from the patient.
Advantages of Skin Substitutes
Using skin substitutes has been shown to accelerate wound healing with fewer complications from infection and dehydration. Additionally, skin substitutes are more cosmetically attractive and provide more functionality and flexibility to wound sites.
Who Is a Candidate for Skin Substitutes
Precautions When Skin Substitutes are Used
Whenever skin substitutes are used precautions should be taken to avoid movement of the wound area, especially in the first two to three weeks of healing. When skin substitutes are still fresh, they are fragile and can be easily broken from any pressure or movement. Proper wound care, healthy diet and compliance with medication and treatment can help promote the healing process.
Recovery of wounds with skin substitutes depends on the wound site, size, depth, patient’s medical history and overall condition. Each case is unique, but it usually takes several weeks for a wound to regenerate and replace lost tissue and regain acceptable function and flexibility.