An autograft can refer to tissue transplanted from one part of an individual's body (e.g., a “donor site”) to another part (e.g., a “recipient site”). Autografts can be used, for example, to replace missing skin and other tissue and/or to accelerate healing resulting from trauma, wounds, burns, surgery and birth defects. Availability of tissue for autografting can be limited by characteristics of candidate donor sites, including a number and/or total area of tissue grafts, healing behavior of the donor site, similarity of the donor and recipient sites, aesthetic considerations, etc.
Skin grafting can be performed surgically. For example, a conventional autograft procedure may include excision or surgical removal of burn injured tissue, choosing a donor site, which may be an area from which healthy skin is removed to be used as cover for the cleaned burned area, and harvesting, where the graft may be removed from the donor site, e.g., using an instrument similar to an electric shaver. Such instrument (e.g., a dermatome) can be structured to gently shave a piece of tissue, which may be, e.g., about 10/1000 of an inch thick for a split-thickness graft, from the skin at the unburned donor site to use as a skin graft. The skin graft can then be placed over the cleaned wound so that it can heal. Donor skin tissue can be removed to such a depth that the donor site can heal on its own, in a process similar to that of healing of a second degree burn.
Two conventional types of autografts which may be used for a permanent wound coverage include sheet grafts and meshed grafts. A sheet graft can refer to a piece of skin tissue removed from an undamaged donor site of the body, in a process that may be referred to as harvesting. The size of the donor skin piece that is used may be about the same size as the damaged area. The sheet graft can be laid over the excised wound, and stapled or otherwise fastened in place. The donor skin tissue used in sheet grafts may not stretch significantly, and a sheet graft can be obtained that is slightly larger than the damaged area to be covered because there may often be a slight shrinkage of the graft tissue after harvesting.
Sheet grafts can provide an improved appearance of the repaired tissue site. For example, sheet grafts may be preferred for use on large areas of the face, neck and hands if they are damaged, so that these more visible parts of the body can appear less scarred after healing. A sheet graft may be used to cover an entire burned or damaged region of skin, e.g., if the damaged site is small. Small areas of a sheet graft can be lost after placement because of a buildup of fluid (e.g., a hematoma) can occur under the sheet graft following placement the sheet graft.
Sheet grafts may be full-thickness or split-thickness. For example, split-thickness skin grafts can be used to cover wounds in burn and skin ulcer patients. A conventional split-thickness graft can be formed, e.g., by harvesting a sheet of epidermis and upper dermal tissue from a donor site, in a procedure similar to that of peeling an apple. The split-thickness graft can then be placed on the location of the burn or ulcer. The skin tissue may then grow back at the donor site following a generally extended healing time. Split-thickness grafts may be preferable to full-thickness grafts because removing large amounts of full-thickness skin tissue from the donor site can lead to scarring and extensive healing times at the donor site, as well as an increased risk of infection. However, skin tissue removed from the donor site for a split-thickness skin autograft can include only a thin epithelial layer, which can lack certain elements of the dermis that improve structural stability and normal appearance in the recipient site.
Full-thickness skin grafts can be formed using sheets of tissue that include the entire epidermis layer and a dermal component of variable thickness. Because the dermal component can be preserved in full-thickness grafts, more of the characteristics of normal skin can be maintained following the grafting procedure. Full-thickness grafts can contain a greater collagen content, dermal vascular plexus, and epithelial appendages as compared to split-thickness grafts. However, full-thickness grafts can require more precise conditions for survival because of the greater amount of tissue requiring revascularization.
Full-thickness skin grafts can be preferable for repairing, e.g., visible areas of the face that may be inaccessible by local flaps, or for graft procedures where local flaps are contraindicated. Such full-thickness skin grafts can retain more of the characteristics of normal skin including, e.g., color, texture, and thickness, as compared to split-thickness grafts. Full-thickness grafts may also undergo less contraction while healing. These properties can be important on more visible areas such as the face and hands. Additionally, full-thickness grafts in children can be more likely to grow with the individual. However, application of conventional full-thickness skin grafts can be limited to relatively small, uncontaminated, well-vascularized wounds, and thus may not be appropriate for as many types of graft procedures as split-thickness grafts. Additionally, donor sites for full-thickness grafts can require surgical closure or resurfacing with a split-thickness graft.
A meshed skin graft can be used to cover larger areas of open wounds that may be difficult to cover using sheet grafts because of, e.g., a lack of a sufficient area of healthy donor sites. Meshing of a skin graft can facilitate skin tissue from a donor site to be expanded to cover a larger area. It also can facilitate draining of blood and body fluids from under the skin grafts when they are placed on a wound, which may help prevent graft loss. The expansion ratio (e.g., a ratio of the unstretched graft area to the stretched graft area) of a meshed graft may typically be between about 1:1 to 1:4. For example, donor skin can be meshed at a ratio of about 1:1 or 1:2 ratio, whereas larger expansion ratios may lead to a more fragile graft, scarring of the meshed graft as it heals, and/or extended healing times.
A conventional graft meshing procedure can include running the donor skin tissue through a machine that cuts slits through the tissue, which can facilitate the expansion in a pattern similar to that of fish netting or a chain-link fence. Healing can occur as the spaces between the mesh of the stretched graft, which may be referred to as gaps or interstices, fill in with new epithelial skin growth. However, meshed grafts may be less durable graft than sheet grafts, and a large mesh can lead to permanent scarring after the graft heals.
To help the graft heal and become secure, the area of the graft can preferably not be moved for at least about five days following each surgery. During this immobilization period, blood vessels can grow from underlying tissue into the skin graft, and can help to bond the two tissue layers together. About five days after the graft is placed, exercise therapy programs, tub baths, and other normal daily activities can often be resumed. Deep second-degree and full-thickness burns may require skin graft surgery for quick healing and minimal scarring. Large burn sizes can lead to more than one grafting procedure during a hospital stay, and may require long periods of immobilization for healing.
As an alternative to autografting, skin tissue obtained from recently-deceased people (which may be referred to, e.g. as a homograft, an allograft, or cadaver skin) can be used as a temporary cover for a wound area that has been cleaned. Unmeshed cadaver skin can be put over the excised wound and stapled in place. Post-operatively, the cadaver skin may be covered with a dressing. Wound coverage using cadaveric allograft can then be removed prior to permanent autografting.
A xenograft or heterograft can refer to skin taken from one of a variety of animals, for example, a pig. Heterograft skin tissue can also be used for temporary coverage of an excised wound prior to placement of a more permanent autograft, and may be used because of a limited availability and/or high expense of human skin tissue. In some cases religious, financial, or cultural objections to the use of human cadaver skin may also be factors leading to use of a heterograft. Wound coverage using a xenograft or an allograft is generally a temporary procedure which may be used until harvesting and placement of an autograft is feasible.
Epithelial appendages can preferably be regenerated following a grafting procedure. For example, hair can be more likely to grow from full-thickness grafts than from split-thickness grafts, but such hair growth may be undesirable based on the location of the wound. Accordingly, donor sites for full-thickness grafts can be carefully selected based in part, e.g., on patterns of hair growth at the time of surgery. Further, certain hair follicles may not be oriented perpendicular to the skin surface, and they can be transected if an incision provided to remove graft tissue is not oriented properly.
Sweat glands and sebaceous glands located in graft tissue may initially degenerate following grafting. These structures can be more likely to regenerate in full-thickness grafts than in split-thickness grafts because full-thickness grafts can be transferred as entire functional units. For example, sweat gland regeneration can depend in part on reinnervation of the skin graft with recipient bed sympathetic nerve fibers. Once such ingrowth has occurred, the skin graft can assume the sweating characteristics of the recipient site, rather than retaining the characteristics of the donor site. In contrast, sebaceous gland regeneration may be independent of graft reinnervation and can retain the characteristics of the donor site. Prior to the regeneration, the skin graft tissue may lack normal lubrication of sebum produced by these glands, which can make such grafts more susceptible to injury.
In general, grafting procedures may be limited by the amount of tissue which can be removed from the donor site without causing excessive adverse effects. Full-thickness grafts can provide improved tissue quality at the wound site, but the donor site may be more severely disfigured as described above. Split-thickness grafts can be a compromise between healing times and aesthetic and functional properties of the donor and recipient sites, whereas meshing can provide more extensive graft coverage at the expense of visible scarring.
Harvesting of graft tissue from the donor site generally can generate undesirable large-scale tissue damage to the donor site. On the other hand, small areas of skin wounding adjacent to healthy tissue can be well-tolerated and may heal quickly. Such healing of small wounds can occur in techniques such as “fractional photothermolysis” or “fractional resurfacing,” in which patterns of damage having a small dimension can be created in skin tissue. These exemplary techniques are described, e.g., in U.S. Pat. No. 6,997,923 and U.S. Patent Publication No. 2006/0155266. Small-scale damage patterns can heal quickly by regrowth of healthy tissue, and can further provide desirable effects such as skin tightening without visible scarring.
In view of the shortcomings of the above described procedures for tissue grafting, it may be desirable to provide exemplary embodiments of method and apparatus that can provide tissue suitable for grafting while minimizing unwanted damage to the donor sites.
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