Accelerated epithelialization and improved wound healing metrics in porcine full‐thickness wounds transplanted with full‐thickness skin micrografts

Abstract

Split-thickness skin grafting (STSG) is the current gold standard for treatment of extensive burn and traumatic skin injuries. However, STSG is limited by donor-site morbidity and availability, and often leads to scarring and wound contracture. Furthermore, these thin grafts lack dermal elements such as nerves and adnexa which are important in recapitulating normal skin function. Methods of fractional skin replacement either as minced STSGs or microscopic skin tissue columns have been proposed, though these techniques have not been fully characterized and lack evidence of regenerated adnexal structures. Here, we describe an alternative method of fractional skin replacement using full-thickness skin micrografts containing deep dermal components and intact adnexa. Full-thickness wounds measuring 3 cm in diameter and 2 cm apart were created on adult female Yorkshire swine. Full-thickness skin tissue columns (FTSTCs) 1.5 mm in diameter with intact adnexa and subcutaneous tissue were obtained using a suction-assisted device. Explant culture was initiated to demonstrate the capacity of FTSTCs to act as reservoirs of viable and proliferative epidermal and dermal cells. FTSTCs were applied directly to excisional wounds at three different expansion ratios (1:16, 1:40, 1:100) in fibrin sealant. Biopsies were collected at defined time points postwounding and processed for histology and immunohistochemistry. Wounds grafted with FTSTCs showed enhanced reepithelialization and epidermal differentiation over untreated control wounds in a dosage dependent manner. Adnexal structures such as hair follicles and sweat glands were only evident in FTSTC-treated wounds. Furthermore, whereas ungrafted wounds were marked by extensive infiltration of α-Smooth Muscle Actin (α-SMA ) myofibroblasts at POD 60, α-SMA expression was sparse and largely limited to perivascular cells in FTSTC-treated wounds. The number of Ki67 cells was also greatly reduced in FTSTC-treated wounds. Transplantation of FTSTCs containing intact adnexa improved wound healing parameters in porcine full-thickness wounds and may have implications for the treatment of large, traumatic wounds.

Full‐thickness skin columns: A method to reduce healing time and donor site morbidity in deep partial‐thickness burns

“…At this high harvest density, the native vascular tree may be damaged, yielding poor healing outcomes as the importance of an intact vascular tree prevents ischemia and allows for the migration of inflammatory and proliferative mediators, which are key to healing. 34 Though not previously reported in the literature, harvest density does indeed impact healing at the donor site, with previous reports of donor site healing around 1 week, and very little to no scarring visualised after 1 month, it's likely that these studies used a lower harvest density 12,13 We were able to compare this morbidity to the donor site data in our first objective, which was harvested at 7%-10%. At this harvest density, we saw 100% re-epithelialisation by day 7, faster than STSG donor sites, and less dyspigmentation compared to STSGs, visualised in Figure 5..…”

“…To our best knowledge, this present study was the first to examine the results of directly implanting FTSCs into small incisions made in the wound bed, albeit deep partial‐thickness burns, maintaining their natural orientation. The primary method to applying FTSCs to wound beds previously published involve a ‘scatter’ method, where skin columns are randomly laid onto a wound bed 12–14,29 . Results from this method thus far have been promising, showing increased re‐epithelialisation and less wound contraction compared to healing by secondary intent.…”

The pig as a model system for investigating the recruitment and contribution of myofibroblasts in skin healing

“…78 Similarly, in Yorkshire pigs, Rettinger et al, 2017, showed myofibroblast populations persist at Day 14 and Day 28 postwounding, although immunoreactivity for α-SMA was reduced by the addition of microscopic skin tissue columns. 80 Our own analysis of the healing of 2 cm diameter wounds in Yorkshire pigs found persistence of myofibroblasts at Day 28, although immunoreactivity was reduced compared to Day 7 (Figure 2). Yorkshire pigs, although they do persist in burns at this timepoint.…”

Evaluation of Donor Site Pain After Fractional Autologous Full-Thickness Skin Grafting

“…Although autologous skin grafts are clinically proven to enhance wound healing, 11 all skin grafting techniques are implicated in some degree of donor site trauma. 18 Significant drawbacks of current harvesting techniques include pain at the donor site, limited donor skin availability, 19 scarring, and an inability to restore complete skin function and architecture. 12 There have been several attempts to reduce the trauma from donor site harvesting.…”