The last component of wound bed preparation is Edges – facilitating re-epithelialization by paying special attention to the edges of the wound. Are the edges flat and even with the granulation tissue so that the epithelial cells can migrate across the wound? Or are they rolled (termed epibole) with the epidermis encasing the basement membrane so that the epithelial cells cannot migrate? (Photo 1)
The tissue changes that occur at the edges of the wound (while the necrotic tissue, infection, and moisture are being managed) provide valuable information about wound prognosis. For example, tiny islands of epithelium that pop up in the midst of the wound bed are indicators that the wound is only partial thickness and epithelial cells are migrating from the hair follicles. Re-epithelialization will progress more rapidly and skin grafting may be avoided, as was the case of the patient whose lower leg is shown in Photo 2 (below). The presence of undermining at the edges is a result of loss of connective tissue in the subcutaneous layer; wound closure cannot occur until the undermined area has filled in with granulation tissue that is level with the edges so that it can support epithelial migration. And when that condition is achieved, one can sometimes see the basement membrane, looking like a translucent film, migrating across the wound bed before the epithelial cells – a visible miracle occurring!
The strategies available to the clinician to facilitate epithelial migration at the edges can be quite simple or very advanced, depending on availability of products, other processes occurring in the wound bed, and size of the wound. First, any epibole, callus, senescent cells, or hypergranulation must be removed, either by debridement or by application of silver nitrate. When the edge is level with the granulation, a dressing can be applied just to the edges to allow epithelial migration, and applied in such a way that dressings on the central part of the wound will not inhibit the process. For example, foams used with negative pressure wound therapy can macerate edges and destroy fragile epithelium; however, a ½ to 1 inch strip of Xeroform over the edges prior to application of the foam will protect the edges and allow epithelial migration (see below).
Dressings that contain collagen attract the cells needed for tissue repair and provide the scaffolding for these cells, as well as reducing the amount of matrix metalloproteases (MMPs) in the wound bed. Because the collagen attracts the cells with which it is in contact, overlapping the collagen dressing slightly over the wound edge is advised in order to facilitate epithelial migration. The collagen products are only placed on clean and/or granulating parts of the wound, not on slough or eschar, so in some cases thin strips are placed on the edges while other dressings are placed on the remainder of the wound.
Another dressing that is excellent in facilitating re-epithelialization is X-Cell (Medline Industries, Inc., Chicago, IL). This dressing is composed of hydrofiber that is partially saturated with saline, thus it is moist enough to prevent dessication of the edges and is non-adherent so that new epithelium is not disrupted with removal.
Advanced biological dressings for wound closure can be classified as acellular or cellular and can be derived from human or animal tissue. More than 100 skin substitutes have been approved for use in the US, and are coded as either “wound dressings” or as Human Cells, Tissues, and Cellular and Tissue-based Products. Examples of acellular products are the collagen dressings which are derived from animal collagen that is processed, sterilized, and treated to remove any cells, lipids, carbohydrates, and non-collagenous proteins; cellular products include the bioengineered living cellular construct Apligraf (Organogenesis Inc., Canton MA) and the human fibroblast-derived dermal substitute Dermagraft (Organogenesis Inc., Canton MA).1 A study by Fitzgerald on diabetic foot ulcers (DFU) concluded that “the proportion of patients whose DFU wounds were treated with human fibroblast-derived substitutes was significantly higher and that their time until healing was lower than patients whose wounds were treated with the nonviable collagen matrix.”1
Other acellular skin substitutes that have been studied and found effective in promoting healing of DFUs include a human acellular dermal matrix (DermACELL, LifeNet Health, Virginia Beach, VA), a human amniotic allograft (AmnioExcel, Integra Lifesciences, Plainsboro, NJ), , and acellular fish skin graft (Kerecis Omega3, Kerecis, Isafjordur, Iceland). Note that these are termed “skin substitutes” but do not replace autologous split-thickness skin grafts which are still considered the gold-standard of wound closure by many clinicians.
While the skin substitutes must be applied by or under the supervision of an MD or DPM, the products listed as wound dressings can be incorporated into the care by any wound care clinician. Careful observation of the wound edges and facilitating re-epithelialization as early in the healing process as possible is a vital component of evidence-based wound care and gives hope to both the patient and the clinician.
 Fitzgerald RH, Sabolinski ML, Skornicki M, Parsons NB. Evaluation of wound closure rates using a human fibroblast-derived dermal substitute versus a fetal bovine collagen dressing: A retrospective study. Wound Management and Prevention. 2019;65(9):26-34.
 Cazzell S, Moyer PM, Samsell B, Dorsch K, McLean J, Moore MA. A prospective, multicenter, single-arm clinical trial for treatment of complex diabetic foot ulcers with deep exposure using acellular dermal matrix. Advances in Skin and Wound Care. 2019;32(9):409-415.
 Thompson P, Hanson DS, Langemo D, Anderson J. Comparing human amniotic allograft and standard wound care when using total contact casting in the treatment of patients with diabetic foot ulcers. Advances in Skin and Wound Care. 2019;32(6):272-277.
 Mowry KC, Vonvallet PP, Bellis SL. Enhanced skin regeneratin using a novel amniotic-derived tissue graft. Wounds. 2017;29(9):277-285.
 Michael S, Winters C, Khan M. Acellular fish skin graft use for diabetic lower extremity wound healing: A retrospective study of 58 ulcerations and a literature review. Wounds. 2019;31(10):262-271.
Further information on dressings of all types can be found at the following:
Weir D, Brindle CT. Wound dressings. In Hamm R (Ed), Text and Atlas of Wound Diagnosis and Treatment: 2nd edition. New York: McGraw Hill Education. 2019, 373-418. Available at.