Autologous and Allogenic Skin Replacement
The
best way to cover large surface wounds is the transplantation of the
patient's own skin (ie, split-thickness skin grafts) from an adjacent
undamaged area that matches closely in terms of texture, color, and
thickness. This surgical procedure inflicts an injury on the donor site
analogous to a superficial second-degree burn, allowing spontaneous
healing in 2-3 weeks, usually without scarring.
Autograft is the method of choice to achieve definitive coverage of burned skin with good quality of healed skin. This technique has been improved by expanding the surface of the skin graft with a mesh apparatus, depending on the needs of the patient. Recently, as much as 25-30 times expansion has been described. However, excessive meshing usually results in healed skin that is more susceptible to infections and has a basketlike pattern, a major drawback for aesthetic appearance. An alternative is the Meek island graft or sandwich graft. This method allows easier handling of widely expanded autografts than meshed skin. In addition, because the autograft islands are not mutually connected, failure of a few of them does not affect the overall graft take. The Meek technique has been reported to be superior to the mesh procedure for expansion ratios of more than 1:6.
In large surface burns, early closure of burn wounds with autologous skin grafts is limited by the lack of adequate donor sites. A delay of 2-3 weeks is necessary to wait for healing of donor sites before harvesting them again. The split-skin graft from the initial donor site can usually be reharvested 2-3 times and healed autografted wounds. This coverage process is time consuming and, thus, induces high risks of morbidity and mortality, mainly due to bacterial invasion.
Cuono and coworkers[3] proposed a 2-step procedure using composite autologous-allogenic skin replacement (de-epidermized skin allografts for dermis substitution and autologous, in vitro–reconstructed epidermis for surface covering) in burns. Compton et al[4] , as well as Hefton and coworkers[5] , preferred the use of both autologous, in vitro–reconstructed and allogenic, in vitro–reconstructed epidermal grafts for large-surface wounds.
Although the use of epidermal autografts has markedly advanced the management of extensive burns and saved lives, this technique has major limitations, as follows: (1) at least 3 weeks is needed for growth of cultured epidermal sheets in the laboratory, thus delaying the coverage of wounds; (2) epidermal sheets need to be grafted on a clean wound bed because they are highly sensible to bacterial infection and toxicity of residual antiseptics; (3) the success of the treatment strongly depends on the dexterity of the laboratory and surgical teams, from the production of the sheets to their graft and care after grafting because this material is very fragile; (4) the regeneration of the dermal compartment underneath the epidermis is a lengthy process, and skin remains fragile for at least 3 years and usually blisters; and (5) the aesthetic aspect of the healed skin is less acceptable than the one obtained with a split-thickness graft.
It was recognized early that any successful artificial skin or skinlike material must replace all of the functions of skin and, therefore, consist of a dermal portion and an epidermal portion. It was clinically apparent that a deep burn or other deep and/or large-surface wounds could not be completely closed promptly after injury by using the patient's available autograft donor sites. Moreover, in certain clinical situations (eg, elderly and young individuals), the donor sites themselves (if taken at standard thickness) create new wounds that often take a long time to heal and create additional metabolic stress, infection risk, and scarring.
After early debridement of deep and extensive burns, temporary closure of the wound is usually achieved with cadaver allograft before autografting with cultured epidermal sheets. Instead of completely removing cadaver skin before sheet transplantation, an excision of allogeneic epidermis can be performed with a dermatome to only maintain the allogeneic dermis on the wound. Because nonliving dermis alone may not be rejected, autologous cultured epidermal sheets can be grafted onto it, thus greatly enhancing healing. Indeed, cultured epidermal sheets grafted onto homograft dermis display early rete ridge development and anchoring fibril regeneration, in addition to a graft take of 95%.
Knowing that devitalization of allografts reduces their antigenicity, the use of allogeneic cadaver skin as a biologic dressing is now widely accepted and is usually preferred to synthetic dressings. The preservation of allografts can be performed by different techniques, such as freeze-drying, glutaraldehyde fixation, or glycerolization.
Cryopreservation of homografts with glycerol is the most popular method of cadaver skin processing because freeze-drying is too expensive and glutaraldehyde fixation has proven less efficient. Moreover, skin preservation can reduce the risk of virus transmission from skin grafting, providing time to rid the donor skin of pathogens. Indeed, incubation of cadaver skin for several hours at 37°C in glycerol displays a significant virucidal and bactericidal effect. To provide sufficient cadaver skin instantly accessible for the patient with a burn, skin banks, such as the Euro Skin Bank in Beverwijk, The Netherlands, have been well developed through the years. However, allogenic skin banking has a significantly higher cost compared with xenogeneic skin banking and biologic dressings.
Autograft is the method of choice to achieve definitive coverage of burned skin with good quality of healed skin. This technique has been improved by expanding the surface of the skin graft with a mesh apparatus, depending on the needs of the patient. Recently, as much as 25-30 times expansion has been described. However, excessive meshing usually results in healed skin that is more susceptible to infections and has a basketlike pattern, a major drawback for aesthetic appearance. An alternative is the Meek island graft or sandwich graft. This method allows easier handling of widely expanded autografts than meshed skin. In addition, because the autograft islands are not mutually connected, failure of a few of them does not affect the overall graft take. The Meek technique has been reported to be superior to the mesh procedure for expansion ratios of more than 1:6.
In large surface burns, early closure of burn wounds with autologous skin grafts is limited by the lack of adequate donor sites. A delay of 2-3 weeks is necessary to wait for healing of donor sites before harvesting them again. The split-skin graft from the initial donor site can usually be reharvested 2-3 times and healed autografted wounds. This coverage process is time consuming and, thus, induces high risks of morbidity and mortality, mainly due to bacterial invasion.
Cuono and coworkers[3] proposed a 2-step procedure using composite autologous-allogenic skin replacement (de-epidermized skin allografts for dermis substitution and autologous, in vitro–reconstructed epidermis for surface covering) in burns. Compton et al[4] , as well as Hefton and coworkers[5] , preferred the use of both autologous, in vitro–reconstructed and allogenic, in vitro–reconstructed epidermal grafts for large-surface wounds.
Although the use of epidermal autografts has markedly advanced the management of extensive burns and saved lives, this technique has major limitations, as follows: (1) at least 3 weeks is needed for growth of cultured epidermal sheets in the laboratory, thus delaying the coverage of wounds; (2) epidermal sheets need to be grafted on a clean wound bed because they are highly sensible to bacterial infection and toxicity of residual antiseptics; (3) the success of the treatment strongly depends on the dexterity of the laboratory and surgical teams, from the production of the sheets to their graft and care after grafting because this material is very fragile; (4) the regeneration of the dermal compartment underneath the epidermis is a lengthy process, and skin remains fragile for at least 3 years and usually blisters; and (5) the aesthetic aspect of the healed skin is less acceptable than the one obtained with a split-thickness graft.
It was recognized early that any successful artificial skin or skinlike material must replace all of the functions of skin and, therefore, consist of a dermal portion and an epidermal portion. It was clinically apparent that a deep burn or other deep and/or large-surface wounds could not be completely closed promptly after injury by using the patient's available autograft donor sites. Moreover, in certain clinical situations (eg, elderly and young individuals), the donor sites themselves (if taken at standard thickness) create new wounds that often take a long time to heal and create additional metabolic stress, infection risk, and scarring.
Wound coverage with allogenic skin
One of the main differences between the cultured epidermal sheet and a split-thickness autograft is the lack of the dermal structure from the cultured autograftable sheets. The absence of dermis is perceived as the major cause for a lower percentage of graft takes and higher fragility and blistering after epidermal sheet transplantation compared to split-thickness autograft. A dermal component protects the basal layer of the epidermis and has a significant impact on the postgrafting biologic responses of the epithelial cells to the differentiation and wound-healing processes.After early debridement of deep and extensive burns, temporary closure of the wound is usually achieved with cadaver allograft before autografting with cultured epidermal sheets. Instead of completely removing cadaver skin before sheet transplantation, an excision of allogeneic epidermis can be performed with a dermatome to only maintain the allogeneic dermis on the wound. Because nonliving dermis alone may not be rejected, autologous cultured epidermal sheets can be grafted onto it, thus greatly enhancing healing. Indeed, cultured epidermal sheets grafted onto homograft dermis display early rete ridge development and anchoring fibril regeneration, in addition to a graft take of 95%.
Knowing that devitalization of allografts reduces their antigenicity, the use of allogeneic cadaver skin as a biologic dressing is now widely accepted and is usually preferred to synthetic dressings. The preservation of allografts can be performed by different techniques, such as freeze-drying, glutaraldehyde fixation, or glycerolization.
Cryopreservation of homografts with glycerol is the most popular method of cadaver skin processing because freeze-drying is too expensive and glutaraldehyde fixation has proven less efficient. Moreover, skin preservation can reduce the risk of virus transmission from skin grafting, providing time to rid the donor skin of pathogens. Indeed, incubation of cadaver skin for several hours at 37°C in glycerol displays a significant virucidal and bactericidal effect. To provide sufficient cadaver skin instantly accessible for the patient with a burn, skin banks, such as the Euro Skin Bank in Beverwijk, The Netherlands, have been well developed through the years. However, allogenic skin banking has a significantly higher cost compared with xenogeneic skin banking and biologic dressings.
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