Fractional Skin Harvesting: Autologous Skin Grafting without Donor-site Morbidity

Skin wounds that are too extensive to heal by primary closure often require reconstruction by autologous grafting or flap transplantation,1 which in turn requires harvesting of donor skin, causing morbidities—including pain, risk of infection, discoloration, and scarring—that are frequently more troublesome for patients than the primary wounds themselves.2,3 Split-thickness skin grafting (STSG), the current “gold standard” for closing large skin wounds,4 involves harvesting the epidermis and the upper portion of dermis from donor sites, and then transplanting the grafts onto the wound(s). STSGs are generally less damaging to donor sites (although donor-site morbidities are still substantial), and have higher “take” rates, than full-thickness grafts. However, because deep dermal structures such as hair follicles and sweat glands are not harvested, the STSG is aesthetically and functionally abnormal and scar-like. In addition, STSGs are usually meshed and expanded before grafting, which increases area coverage and facilitates fluid drainage but also causes a permanent, unsightly “fish-net” appearance in the grafted skin. Much effort has been invested in finding/developing exogenous graft materials, such as cadaveric skin, xenografts, and artificial skin substitutes.5 At present, these options can only provide temporary wound coverage, and eventual autologous grafting remains necessary. Alternative wound closure technologies that minimize donor-site morbidity, provide STSG-like graft reliability without unsightly texture, and can be performed easily in practice would be very beneficial. Scarring at the donor and/or graft site is one of the most problematic morbidities associated with autologous skin grafting. Scarring is nature’s way of quickly filling large voids in tissue, with a haphazard arrangement of connective tissue elements. Scar tissue is stiff, often painful, dysfunctional, and tends to contract over time, causing deformities. The arrangement of extracellular matrix and specialized dermal structures that confer function to normal tissue is missing.6 In contrast to scarring, a process that haphazardly replaces grossly missing tissue, remodeling is a process that replaces tissue while maintaining tissue architecture on the microscopic scale. Remodeling occurs in every organ as we age and grow, and it is abundantly clear that almost every tissue has the capacity for local remodeling without scarring. While scarring is stimulated by large-scale tissue damage, remodeling is stimulated by microscopic tissue damage. This principle became clear when we developed fractional photothermolysis (FP),7 which is now in widespread clinical use to improve photoaged skin and various lesions including wound scars.8 In FP, laser microbeams are used to produce hundreds to thousands of microscopic thermal burns per cm2 of skin surface, creating very thin columns of thermal damage or tissue removal, called “microthermal zones.” Microthermal zones less than about 300 µm in diameter heal rapidly without scarring.9 The differences between FP and third-degree skin burns are striking. Both involve extensive, full-thickness (ie, including complete epidermis and dermis) thermal damage, but third-degree burns heal slowly with scarring, whereas after FP the epidermis closes within 1 day, and the dermal injury is repaired in about 2 weeks, followed by continued tissue remodeling without scarring.9 Amazingly, up to 50% of the volume of normal skin can be killed or removed by FP—followed by rapid replacement of the lost tissue by remodeling, resulting in new skin tissue that is both functionally and aesthetically normal.9 Since our experience with FP established that millions of small, full-thickness columns of skin tissue can be removed without causing scarring, we hypothesized that similarly large numbers of full-thickness microscopic skin tissue columns (MSTCs) could be harvested from healthy skin with negligible donor-site morbidity and that these MSTCs could serve as a graft to improve skin wound healing. The current study was performed to test these hypotheses in the swine, a commonly used model for human skin.10,11