Laser Micropatterning Promotes Rete Ridge Formation and Enhanced Engineered Skin Strength without Increased Inflammation.

Rete ridges play multiple important roles in native skin tissue function, including enhancing skin strength, but they are largely absent from engineered tissue models and skin substitutes. Laser micropatterning of fibroblast-containing dermal templates prior to seeding of keratinocytes was shown to facilitate rete ridge development in engineered skin (ES) both in vitro and in vivo. However, it is unknown whether rete ridge development results exclusively from the microarchitectural features formed by ablative processing or whether laser treatment causes an inflammatory response that contributes to rete ridge formation. In this study, laser-micropatterned and non-laser- treated ES grafts were developed and assessed during culture and for four weeks post grafting onto full-thickness wounds in immunodeficient mice. Decreases in inflammatory cytokine secretion were initially observed in vitro in laser-treated grafts compared to non-treated controls, although cytokine levels were similar in both groups five days after laser treatment. Post grafting, rete ridge-containing ES showed a significant increase in vascularization at week 2, and in collagen deposition and biomechanics at weeks 2 and 4, compared with controls. No differences in inflammatory cytokine expression after grafting were observed between groups. The results suggest that laser micropatterning of ES to create rete ridges improves the mechanical properties of healed skin grafts without increasing inflammation.

A role for vitamin D and the vitamin D receptor in keloid disorder.

Keloids are disfiguring fibroproliferative lesions that can occur in susceptible individuals following any skin injury. They are extremely challenging to treat, with relatively low response rates to current therapies and high rates of recurrence after treatment. Although several distinct genetic loci have been associated with keloid formation in different populations, there has been no single causative gene yet identified and the molecular mechanisms guiding keloid development are incompletely understood. Further, although it is well known that keloids are more commonly observed in populations with dark skin pigmentation, the basis for increased keloid risk in skin of colour is not yet known. Because individuals with dark skin pigmentation are at higher risk for vitamin D deficiency, the role of vitamin D in keloid pathology has gained interest in the keloid research community. A limited number of studies have found lower serum vitamin D levels in patients with keloids, and reduced expression of the vitamin D receptor (VDR) in keloid lesions compared with uninjured skin. Vitamin D has documented anti-inflammatory, anti-proliferative and pro-differentiation activities, suggesting it may have a therapeutic role in suppression of keloid fibrosis. Here we review the evidence supporting a role for vitamin D and VDR in keloid pathology.

Scar Management and Dyschromia: A Summary Report from the 2021 American Burn Association State of the Science Meeting.

Burn scars, and in particular, hypertrophic scars, are a challenging yet common outcome for survivors of burn injuries. In 2021, the American Burn Association brought together experts in burn care and research to discuss critical topics related to burns, including burn scars, at its State of the Science conference. Clinicians and researchers with burn scar expertise, as well as burn patients, industry representatives, and other interested stakeholders met to discuss issues related to burn scars and discuss priorities for future burn scar research. The various preventative strategies and treatment modalities currently utilized for burn scars were discussed, including relatively noninvasive therapies such as massage, compression, and silicone sheeting, as well as medical interventions such as corticosteroid injection and laser therapies. A common theme that emerged is that the efficacy of current therapies for specific patient populations is not clear, and further research is needed to improve upon these treatments and develop more effective strategies to suppress scar formation. This will necessitate quantitative analyses of outcomes and would benefit from creation of scar biobanks and shared data resources. In addition, outcomes of importance to patients, such as scar dyschromia, must be given greater attention by clinicians and researchers to improve overall quality of life in burn survivors. Herein we summarize the main topics of discussion from this meeting and offer recommendations for areas where further research and development are needed.

Myofibroblasts Are Not Characteristic Features of Keloid Lesions.

Keloids are disfiguring, scar-like lesions that are challenging to treat, with low response rates to current interventions and frequent recurrence. It has been widely reported that keloids are characterized by myofibroblasts, specialized contractile fibroblasts that express alpha-smooth muscle actin (α-SMA). However, evidence supporting a role for myofibroblasts in keloid pathology is inconclusive, with conflicting reports in the literature. This complicates development of more effective therapies, as the benefit of interventions targeting myofibroblasts is unclear. This study was undertaken to determine whether myofibroblasts can be considered characteristic of keloids. Methods: Myofibroblasts in tissue sections from keloids, hypertrophic scars (HTSs), and normal skin were localized by α-SMA immunostaining. Expression of α-SMA mRNA (ACTA2 gene) in normal skin and keloid tissue, and in fibroblasts from normal skin, keloid, and HTSs, was measured using quantitative polymerase chain reaction. Results: Normal skin did not exhibit α-SMA-expressing myofibroblasts, but myofibroblasts were identified in 50% of keloids and 60% of HTSs. No significant differences in ACTA2 expression between keloid and normal skin tissue were observed. Mean ACTA2 expression was higher in HTS (2.54-fold, P = 0.005) and keloid fibroblasts (1.75-fold, P = 0.046) versus normal fibroblasts in vitro. However, α-SMA expression in keloids in vivo was not associated with elevated ACTA2 in keloid fibroblasts in vitro. Conclusions: Despite elevated ACTA2 in cultured keloid fibroblasts, myofibroblast presence is not a consistent feature of keloids. Therefore, therapies that target myofibroblasts may not be effective for all keloids. Further research is required to define the mechanisms driving keloid formation for development of more effective therapies.

Advantages and Disadvantages of Using Small and Large Animals in Burn Research: Proceedings of the 2021 Research Special Interest Group.

Multiple animal species and approaches have been used for modeling different aspects of burn care, with some strategies considered more appropriate or translatable than others. On April 15, 2021, the Research Special Interest Group of the American Burn Association held a virtual session as part of the agenda for the annual meeting. The session was set up as a pro/con debate on the use of small versus large animals for application to four important aspects of burn pathophysiology: burn healing/conversion, scarring, inhalation injury, and sepsis. For each of these topics, two experienced investigators (one each for small and large animal models) described the advantages and disadvantages of using these preclinical models. The use of swine as a large animal model was a common theme due to anatomic similarities with human skin. The exception to this was a well-defined ovine model of inhalation injury; both of these species have larger airways which allow for incorporation of clinical tools such as bronchoscopes. However, these models are expensive and demanding from labor and resource standpoints. Various strategies have been implemented to make the more inexpensive rodent models appropriate for answering specific questions of interest in burns. Moreover, modeling burn-sepsis in large animals has proven difficult. It was agreed that the use of both small and large animal models has merit for answering basic questions about the responses to burn injury. Expert opinion and the ensuing lively conversations are summarized herein, which we hope will help inform experimental design of future research.

sEH-derived metabolites of linoleic acid drive pathologic inflammation while impairing key innate immune cell function in burn injury.

Fatty acid composition in the Western diet has shifted from saturated to polyunsaturated fatty acids (PUFAs), and specifically to linoleic acid (LA, 18:2), which has gradually increased in the diet over the past 50 y to become the most abundant dietary fatty acid in human adipose tissue. PUFA-derived oxylipins regulate a variety of biological functions. The cytochrome P450 (CYP450)­formed epoxy fatty acid metabolites of LA (EpOMEs) are hydrolyzed by the soluble epoxide hydrolase enzyme (sEH) to dihydroxyoctadecenoic acids (DiHOMEs). DiHOMEs are considered cardioprotective at low concentrations but at higher levels have been implicated as vascular permeability and cytotoxic agents and are associated with acute respiratory distress syndrome in severe COVID-19 patients. High EpOME levels have also correlated with sepsis-related fatalities; however, those studies failed to monitor DiHOME levels. Considering the overlap of burn pathophysiology with these pathologies, the role of DiHOMEs in the immune response to burn injury was investigated. 12,13-DiHOME was found to facilitate the maturation and activation of stimulated neutrophils, while impeding monocyte and macrophage functionality and cytokine generation. In addition, DiHOME serum concentrations were significantly elevated in burn-injured mice and these increases were ablated by administration of 1-trifluoromethoxyphenyl-3-(1-propionylpiperidin-4-yl) urea (TPPU), a sEH inhibitor. TPPU also reduced necrosis of innate and adaptive immune cells in burned mice, in a dose-dependent manner. The findings suggest DiHOMEs are a key driver of immune cell dysfunction in severe burn injury through hyperinflammatory neutrophilic and impaired monocytic actions, and inhibition of sEH might be a promising therapeutic strategy to mitigate deleterious outcomes in burn patients.

Isolation and feeder-free primary culture of four cell types from a single human skin sample.

Four types of primary cells-dermal fibroblasts, dermal microvascular endothelial cells, epidermal keratinocytes, and epidermal melanocytes-can be isolated simultaneously from a single human skin sample, without the use of xenogeneic murine feeder cells. This protocol describes the procedures for isolation of these cells from adult full-thickness skin obtained from surgical discard tissue. The cells isolated using this protocol contain stem cell populations and are competent to form functional skin tissue in three-dimensional reconstructed skin models. For complete details on the use and execution of this profile, please refer to Supp et al. (2002), Boyce et al. (2015), Boyce et al. (2017a), Boyce et al. (2017b), and Supp et al. (2019).

TPPU treatment of burned mice dampens inflammation and generation of bioactive DHET which impairs neutrophil function.

Oxylipins modulate the behavior of immune cells in inflammation. Soluble epoxide hydrolase (sEH) converts anti-inflammatory epoxyeicosatrienoic acid (EET) to dihydroxyeicosatrienoic acid (DHET). An sEH-inhibitor, TPPU, has been demonstrated to ameliorate lipopolysaccharide (LPS)- and sepsis-induced inflammation via EETs. The immunomodulatory role of DHET is not well characterized. We hypothesized that TPPU dampens inflammation and that sEH-derived DHET alters neutrophil functionality in burn induced inflammation. Outbred mice were treated with vehicle, TPPU or 14,15-DHET and immediately subjected to either sham or dorsal scald 28% total body surface area burn injury. After 6 and 24 h, interleukin 6 (IL-6) serum levels and neutrophil activation were analyzed. For in vitro analyses, bone marrow derived neutrophil functionality and mRNA expression were examined. In vivo, 14,15-DHET and IL-6 serum concentrations were decreased after burn injury with TPPU administration. In vitro, 14,15-DHET impaired neutrophil chemotaxis, acidification, CXCR1/CXCR2 expression and reactive oxygen species (ROS) production, the latter independent from p38MAPK and PI3K signaling. We conclude that TPPU administration decreases DHET post-burn. Furthermore, DHET downregulates key neutrophil immune functions and mRNA expression. Altogether, these data reveal that TPPU not only increases anti-inflammatory and inflammation resolving EET levels, but also prevents potential impairment of neutrophils by DHET in trauma.

Analysis of HOX gene expression and the effects of HOXA9 overexpression in fibroblasts derived from keloid lesions and normal skin.

Keloids are fibroproliferative lesions resulting from an abnormal wound healing process due to pathological mechanisms that remain incompletely understood. Keloids tend to occur more frequently in anterior versus posterior body regions (e.g., ears, face, upper torso); this has been attributed to higher skin tension in those areas, although this has not yet been conclusively proven. Previous studies reported reduced expression of multiple homeobox (HOX) genes in keloid versus normal fibroblasts, suggesting a role for HOX genes in keloid pathology. However, HOX genes are differentially expressed along the anterior-posterior axis. Hypothetically, differential HOX expression may be due to differences in body sites, as matched donor sites are often unavailable for keloids and normal skin. To better understand the basis for differential HOX gene expression in cells from keloids compared with normal skin, we compared HOXA7, HOXA9, HOXC8 and HOXC11 expression in keloid and normal skin-derived fibroblasts from various body sites. When keloid (N = 20) and normal (N = 12) fibroblast cell strains were evaluated, expression of HOXA7, HOXA9 and HOXC8 was significantly lower in keloid versus normal fibroblasts. However, HOX gene expression was lower in fibroblasts from more anterior versus posterior body sites. When keloid and normal cells from similar body sites were compared, differential HOX expression was not observed. To investigate the phenotypic relevance of HOX expression, HOXA9 was overexpressed in keloid and normal fibroblasts. HOXA9 overexpression did not affect proliferation but significantly reduced fibroblast migration and altered gene expression. The results suggest that differential HOX expression may be due to differences in positional identity between keloid and normal fibroblasts. However, HOX genes can potentially regulate fibroblast phenotype, suggesting that differential HOX gene expression may play a role in keloid development in anterior body sites.

Coming to Consensus: What Defines Deep Partial Thickness Burn Injuries in Porcine Models?

Deep partial thickness burns are clinically prevalent and difficult to diagnose. In order to develop methods to assess burn depth and therapies to treat deep partial thickness burns, reliable, accurate animal models are needed. The variety of animal models in the literature and the lack of precise details reported for the experimental procedures make comparison of research between investigators challenging and ultimately affect translation to patients. They sought to compare deep partial thickness porcine burn models from five well-established laboratories. In doing so, they uncovered a lack of consistency in approaches to the evaluation of burn injury depth that was present within and among various models. They then used an iterative process to develop a scoring rubric with an educational component to facilitate burn injury depth evaluation that improved reliability of the scoring. Using the developed rubric to re-score the five burn models, they found that all models created a deep partial thickness injury and that agreement about specific characteristics identified on histological staining was improved. Finally, they present consensus statements on the evaluation and interpretation of the microanatomy of deep partial thickness burns in pigs.

Direct comparison of reproducibility and reliability in quantitative assessments of burn scar properties.

INTRODUCTION: Determining the efficacy of anti-scar technologies can be difficult as qualitative, subjective assessments are often utilized instead of systematic, objective measures. Perceptions regarding the reliability of instruments for quantitative measurements along with their high cost and increased data collection time may discourage their use, leading to use of scar scales which are relatively quick and low-cost. To directly evaluate the reliability of instruments for quantitative measurements of scar properties, instruments and two qualitative scales were compared by assessing a variety of cutaneous scars. METHODS: Scar height and surface texture were evaluated using a 3D scanner and a mold/cast technique. Scar color was evaluated by using a spectroscopy-based tool, the Mexameter®, and digital photography with image analysis. Scar biomechanics were evaluated using the BTC-2000™, Dermal Torque Meter (DTM®), and ballistometer®. The Vancouver Scar Scale (VSS) and Patient and Observer Scar Assessment Scale (POSAS) were used to qualitatively evaluate the same scar properties. Intraclass correlation coefficients (ICC) were used to determine inter- and intra-user reliability (poor, moderate, good, excellent) with all instruments and the kappa reliability statistic was used to asses inter-user reliability (poor, fair, moderate, good, very good) for VSS and POSAS. Time for measurement collection and after collection analysis was also recorded. RESULTS: The Mexameter® was the most reliable method for evaluating erythema and pigmentation compared to digital photography and image processing, POSAS and VSS. Digital photography and analysis was more reliable than POSAS and VSS. Assessment of scar height was significantly more reliable when using a 3D scanner versus VSS and POSAS. The 3D scanner and mold-cast techniques also offered an additional benefit of providing an absolute value of scar height relative to the surrounding tissue. Intra-user reliability for all mechanical tests was moderate to good. Inter-user reliability was greater when using the BTC-2000™ and ballistometer® versus the DTM®. All quantitative measurements took less than 90 s for collection, with the exception of the mold/cast technique. CONCLUSION: Non-invasive instruments allow scar properties to be quantitatively assessed with high sensitivity and as a function of time and/or treatment without the need for biopsy collection. Overall, the reliability of scar assessments was significantly improved when quantitative instruments were utilized versus scar scales. Quantitative assessment of color and biomechanics were swift, requiring less than 90 s per measurement while assessments of texture and height required additional analysis time after collection. With proper training of clinical staff and well-defined protocols for measurement collection, reliable, quantitative assessments of scar properties can be collected with little disruption to the clinical workflow.

Inherited DNA Repair Defects Disrupt the Structure and Function of Human Skin.

Squamous cell carcinoma (SCC) is a global public health burden originating in epidermal stem and progenitor cells (ESPCs) of the skin and mucosa. To understand how genetic risk factors contribute to SCC, studies of ESPC biology are imperative. Children with Fanconi anemia (FA) are a paradigm for extreme SCC susceptibility caused by germline loss-of-function mutations in FA DNA repair pathway genes. To discover epidermal vulnerabilities, patient-derived pluripotent stem cells (PSCs) conditional for the FA pathway were differentiated into ESPCs and PSC-derived epidermal organotypic rafts (PSC-EORs). FA PSC-EORs harbored diminished cell-cell junctions and increased proliferation in the basal cell compartment. Furthermore, desmosome and hemidesmosome defects were identified in the skin of FA patients, and these translated into accelerated blistering following mechanically induced stress. Together, we demonstrate that a critical DNA repair pathway maintains the structure and function of human skin and provide 3D epidermal models wherein SCC prevention can now be explored.

Disease-associated KIF3A variants alter gene methylation and expression impacting skin barrier and atopic dermatitis risk.

Single nucleotide polymorphisms (SNPs) in the gene encoding kinesin family member 3A, KIF3A, have been associated with atopic dermatitis (AD), a chronic inflammatory skin disorder. We find that KIF3A SNP rs11740584 and rs2299007 risk alleles create cytosine-phosphate-guanine sites, which are highly methylated and result in lower KIF3A expression, and this methylation is associated with increased transepidermal water loss (TEWL) in risk allele carriers. Kif3aK14∆/∆ mice have increased TEWL, disrupted junctional proteins, and increased susceptibility to develop AD. Thus, KIF3A is required for skin barrier homeostasis whereby decreased KIF3A skin expression causes disrupted skin barrier function and promotes development of AD.

Cultured Epithelial Autograft Combined with Micropatterned Dermal Template Forms Rete Ridges In Vivo.

For patients with large, full-thickness burn wounds, sufficient donor sites for autografting are not available, and thus, alternate strategies must be used to close these wounds. Cultured epithelial autografts (CEAs) can aid in closing these wounds but are often associated with slow deposition of basement membrane proteins, leading to blistering and graft loss. Rete ridges and dermal papillae present at the dermal-epidermal junction (DEJ) play a key role in epidermal adhesion and skin homeostasis. Promoting the development of an interdigitated DEJ may enhance basement membrane protein deposition and provide enhanced physical interlock of the epidermis and dermis. To develop a dermal template with stable dermal papillae, an electrospun collagen scaffold was seeded with human dermal fibroblasts. Ridged topographies were patterned into the cell-seeded dermal template using laser ablation, creating wide and shallow (ActiveFX) or narrow and deep (DeepFX) wells. Micropatterned or flat (control) dermal templates were combined with CEAs immediately before grafting to full-thickness excisional wounds on immunodeficient mice. CEAs grafted in conjunction with ridged templates showed rete ridge formation at 2 weeks after grafting and led to increased epidermal thickness, proliferation, and stemness compared to templates with a flat DEJ. As this technology is further developed, the dermal papilla-containing dermal templates may be utilized in combination with CEAs to improve adhesion and clinical function. Impact statement Cultured epithelial autografts (CEAs) serve as an adjunct to conventional split-thickness autograft in patients with very large burns, but they are susceptible to blistering that can reduce engraftment. Blistering results, in part, from relatively slow basement membrane deposition after grafting. This study demonstrates that basement membrane deposition and rete ridge formation are enhanced by combination of CEAs with a micropatterned, cell-seeded dermal template. These findings may lead to improved treatment and increased survival in patients with very large burns.

Pirfenidone inhibits epithelial-mesenchymal transition in keloid keratinocytes.

BACKGROUND: Keloids are benign fibroproliferative skin lesions that are difficult to treat and become a lifetime predicament for patients. Several treatment modalities have been put forth, but as yet no satisfactory approach to the prevention or treatment of keloids has been identified. The process of epithelial-to-mesenchymal transition (EMT) has been implicated in keloid scarring, as keloid keratinocytes display an EMT-like phenotype. This study investigated the potential of pirfenidone, an antifibrotic agent, to counteract EMT-like alterations in keloid keratinocytes, including gene expression, cell migratory and proliferative functions. METHODS: Normal and keloid keratinocytes were isolated from discarded normal skin tissues and from resected keloid tissues, respectively. Cells were quiesced for 24 h without epidermal growth factor DS-Qi1MCDigital and were exposed to transforming growth factor-beta1 (TGF-ß1; 10 ng/mL), with or without pirfenidone (400 µg/mL), for an additional 24 h. The effects of pirfenidone on cytotoxicity, cell migration, cell proliferation, and on expression of genes and proteins involved in EMT were assayed. Statistical significance was determined by two-way ANOVA using Sigma Plot. RESULTS: We found that pirfenidone did not elicit any cytotoxic effect at concentrations up to 1000 µg/mL. A statistically significant dose-dependent decrease in basal cell proliferation rate was noted in both normal and keloid keratinocytes when exposed to pirfenidone at concentrations ranging from 200 to 1000 µg/mL. Pirfenidone significantly decreased basal cell migration in both normal and keloid keratinocytes, but a significant decrease in TGF-ß1-induced cell migration was seen only in keloid keratinocytes. Significant inhibition of the expression of TGF-ß1-induced core EMT genes, namely hyaluronan synthase 2, vimentin, cadherin-11, and wingless-type MMTV integration site family, member 5A along with fibronectin-1, was observed in both normal and keloid keratinocytes treated with pirfenidone. In addition, the protein levels of vimentin and fibronectin were significantly reduced by pirfenidone (400 µg/mL) in both normal and keloid keratinocytes. CONCLUSIONS: For the first time, this study shows the efficacy of pirfenidone in inhibiting the EMT-like phenotype in keratinocytes derived from keloids, suggesting that pirfenidone may counteract a critical contributor of keloid progression and recurrence.

Improved Scar Outcomes with Increased Daily Duration of Pressure Garment Therapy.

Objective: Despite the development of a number of treatment modalities, scarring remains common postburn injury. To reduce burn scarring, pressure garment therapy has been widely utilized but is complicated by low patient adherence. To improve adherence, reduced hours of daily garment wear has been proposed. Approach: To examine the efficacy of pressure garment therapy at reduced durations of daily wear, a porcine burn-excise-autograft model was utilized. Grafted burns were treated with pressure garments (20 mmHg) for 8, 16, or 24 h of daily wear with untreated burns serving as controls. Scar area, thickness, biomechanical properties, and tissue structure were assessed over time. Results: All treatment groups reduced scar thickness and contraction versus controls and improved scar pliability and elasticity. Pressure garments worn 24 h per day significantly reduced contraction versus the 8- and 16-h groups and prevented alignment of collagen within the dermis. Innovation: Though pressure garment therapy is prescribed for use 23 h per day, the need for almost continuous use has not been previously examined. Adjustable, low-fatigue pressure garments were developed for this porcine study to examine the role of daily duration of wear without confounding factors such as garment fatigue and patient adherence. Conclusion: For maximum efficacy, pressure garments should be worn 23 to 24 h per day; however, garments worn as little as 8 h per day significantly improve scar outcomes versus no treatment.

Light or Dark Pigmentation of Engineered Skin Substitutes Containing Melanocytes Protects Against Ultraviolet Light-Induced DNA Damage In Vivo.

Engineered skin substitutes (ESS) containing autologous fibroblasts and keratinocytes provide stable wound closure in patients with large, full-thickness burns, but are limited by hypopigmentation due to absence of added melanocytes. DNA damage caused by ultraviolet radiation (UV) increases risk for skin cancer development. In human skin, melanocytes provide pigmentation that protects skin from UV-induced DNA damage. This study investigated whether inclusion of human melanocytes (hM) affects the response of ESS to UV in vivo. Specifically, pigmentation and formation of cyclobutane pyrimidine dimers (CPDs), the most prevalent UV-induced DNA photoproduct, were analyzed. Three groups of ESS were prepared with fibroblasts and keratinocytes, ± melanocytes, and grafted orthotopically to immunodeficient mice: ESS without melanocytes (ESS-hM), ESS with light skin-derived (Caucasian) melanocytes (ESS+hM-L), and ESS with dark skin-derived (African-American) melanocytes (ESS+hM-D). Pigmentation of ESS+hM-L and ESS+hM-D increased significantly after grafting; pigmentation levels were significantly different among groups. Mean melanocyte densities in ESS+hM-L and ESS+hM-D were similar to each other and to densities in normal human skin. After 8 weeks in vivo, grafts were irradiated with 135 mJ/cm2 UV; non-UV-treated mice served as controls. UV modestly increased pigmentation in the ESS+hM groups. UV significantly increased CPD levels in ESS-hM, and levels in ESS-hM were significantly greater than in ESS+hM-L or ESS+hM-D. The results demonstrate that light or dark melanocytes in ESS decreased UV-induced DNA damage. Therefore, melanocytes in ESS play a photoprotective role. Protection against UV-induced DNA damage is expected to reduce skin cancer risk in patients grafted with ESS containing autologous melanocytes.

Exogenous Keratinocyte Growth Factor Is Not Required for Pigmentation of Skin Substitutes with Three Isogeneic Cell Types.

Engineered skin substitutes (ESS) containing human fibroblasts (hF) and human keratinocytes (hK) provide significant medical benefits for treatment of acute and chronic skin wounds, including, but not limited to, burns, burn scars, congenital skin lesions, and cutaneous ulcers. However, anatomic deficiencies, such as lack of pigment, can contribute to long-term morbidity, including hypopigmentation and reduced solar protection. To address the deficiency of hypopigmentation, ESS were populated sequentially with cultured hF, human melanocytes (hM), and hK to generate ESS with pigment (ESS-P). Constructs were incubated in media containing 0.0, 1.5, or 5.0 ng/mL keratinocyte growth factor (KGF), which promotes survival and differentiation of hM in ESS-P, and had media changed at 24 or 48 h intervals. ESS-P were evaluated in vitro for surface hydration, surface color, and distribution of hM. Proliferation was assessed by measuring incorporation of 5-bromo-2'-deoxyuridine into replicating DNA in basal epidermal cells. ESS-P from test conditions were grafted to immunodeficient mice, and were assessed over 12 weeks for pigmented area, pigment density, and distribution of hM in healed human grafts. The in vitro data showed differences among test groups, including increase in hydration of the epidermal surface with higher KGF, increase of surface pigmentation with 24 h media changes, increase of hM density with higher KGF and 24 h media changes, and time-dependent decrease of proliferation. At 12 weeks after grafting, differences among groups were found for pigment density, but not for distribution of hM or percentage of pigmented area. These differences demonstrate that a higher concentration of KGF (5 ng/mL) in the maturation medium of ESS-P and more frequent media changes (24 h interval) promote higher viability and hM differentiation of ESS-P before grafting, but are not required for full pigmentation (pigmented area, pigment density, hM distribution) of grafted wounds. Based on these results, reductions of the concentration of KGF (i.e., 1.5 ng/mL) in the maturation medium, and of the frequency of medium changes (48 h intervals) would be expected to support survival, continued replication, and restoration of skin color by hM in therapeutic transplantation of ESS-P. Impact Statement Restoration of skin color after traumatic injury affects personal identity and provides protection from exposure to solar radiation. Keratinocyte growth factor (KGF) and nutrient supply are known to regulate survival of melanocytes before transplantation in engineered skin substitutes with pigment (ESS-P). This report demonstrates that exogenous KGF is not required to restore skin color and that replacement of the nutrient medium at lower frequency (48 versus 24 h) does not inhibit development of skin color after melanocyte transplantation. These results offer new alternatives to conserve resources in fabrication of ESS-P and to maintain efficacy for restoration of skin color.

Fractional CO2 laser micropatterning of cell-seeded electrospun collagen scaffolds enables rete ridge formation in 3D engineered skin.

Rete ridges are interdigitations of the epidermis and dermis of the skin that play multiple roles in homeostasis, including enhancing adhesion via increased contact area and acting as niches for epidermal stem cells. These structures, however, are generally absent from engineered skin (ES). To develop ES with rete ridges, human fibroblast-seeded dermal templates were treated with a fractional CO2 laser, creating consistently spaced wells at the surface. Constructs with and without laser treatment were seeded with keratinocytes, cultured for 10 days, and grafted onto athymic mice for four weeks. Rete-ridge like structures were observed in the laser-patterned (ridged) samples at the time of grafting and were maintained in vivo. Ridged grafts displayed improved barrier function over non-lasered (flat) grafts at the time of grafting and 4 weeks post-grafting. Presence of ridges in vivo corresponded with increased keratinocyte proliferation, epidermal area, and basement membrane length. These results suggest that this method can be utilized to develop engineered skin grafts with rete ridges, that the ridge pattern is stable for at least 4 weeks post-grafting, and that the presence of these ridges enhances epidermal proliferation and establishment of barrier function. STATEMENT OF SIGNIFICANCE: Rete ridges play a role in epidermal homeostasis, enhance epidermal-dermal adhesion and act as niches for epidermal stem cells. Despite their role in skin function, these structures are not directly engineered into synthetic skin. A new method to rapidly and reproducibly generate rete ridges in engineered skin was developed using fractional CO2 laser ablation. The resulting engineered rete ridges aided in the establishment of epidermal barrier function, basement membrane protein deposition and epidermal regeneration. This new model of engineered skin with rete ridges could be utilized as an in vitro system to study epidermal stem cells, a testbed for pharmaceutical evaluation or translated for clinical use in full-thickness wound repair.