The female, red Duroc pig as an animal model of hypertrophic scarring and the potential role of the cones of skin

Hypertrophic scarring occurs after deep dermal wounds. Our understanding of the etiology is poor; one reason is the lack of an animal model. In 1972, Silverstein described scarring in the Duroc pig but the model was never confirmed nor disproved. Another reason, as we previously suggested, is that hypertrophic scarring only occurs within regions of human skin that contain cones and the cones have not been studied in relation to hypertrophic scarring. We, therefore (i) explored healing in the female, red Duroc model for similarities to human hypertrophic scarring, studying wound thickness, appearance, healing status at 3 weeks, histology, and immunocytochemical localization of decorin, versican, TGFbeta1 and IGF-1; and (ii) examined Duroc skin for cones. We found that healing after deep wounds in Duroc pigs is similar, but not identical, to human hypertrophic scarring. We also found that Duroc skin contains cones. Healing in the female, red Duroc pig is sufficiently similar to human hypertrophic scarring to warrant further study so that it can be accepted or rejected as a model of human hypertrophic scarring. In addition, the relationship of the cones to hypertrophic scarring needs further detail and can be studied in this model.     

105Changes in Nitric Oxide Levels After Deep Dermal injury in the Female,Red Duroc Pig (FRDP)

Introduction : Hypertrophic scar is a devastating sequel to burns and other tangential skin injuries. It follows deep dermal injuries and does not occur after superficial injuries. Nitric oxide (NO) plays many important roles in wound healing from inflammation to scar remodeling. Studies have shown that expression of nitric oxide synthase and nitric oxide production are decreased in human hypertrophic scar. However little is known about NO involvement in the early stages of hypertrophic scarring, because of the lack of an animal model. It was recently reported that the female red Duroc pig (FRDP) makes thick scar, which is similar to human hypertrophic scar. We hypothesized that NO production in wounds on the female, red Duroc pig is similar to that of human hypertrophic scar and that NO involvement in deep wounds is different from that in superficial wounds. Methods : Superficial (0.015” to 0.030”) and deep (0.045” to 0.060”) wounds were created on the backs of four FRDPs. Biopsies were collected at weeks 1.5, 4, 8 and 21 post wounding including samples of uninjured skin. Nitric oxide levels were measured with the Griess reaction assay and normalized with tissue protein level. Results : Superficial wounds healed with an invisible scar whereas the deep wounds healed with scar resembling mild hypertrophic scar. The thickness of the scars from the deep wounds was significantly greater than uninjured skin and healed superficial wounds (p < 0.01). NO levels were increased at 1.5 weeks in deep wounds compared to superficial wounds and uninjured skin (p < 0.05). At 8 weeks, NO levels in deep wounds had returned to the level of uninjured tissue and superficial wounds. By 21 weeks, NO levels had decreased significantly when compared to superficial wounds (p < 0.01). There were no differences in NO levels between uninjured skin and superficial wounds at any time point (p > 0.05). Conclusions : NO production is similar in late, deep wounds on the female, red Duroc pig to that reported in the literature for human hypertrophic scar further validating this animal model. NO production is quite different after deep wounds as compared to superficial wounds in the FRDP. Early elevation in nitric oxide production might account for excessive inflammation in deep wounds that become thick scars in the FRDP. Nitric oxide regulators and effects at early stages of scar formation should be elucidated further and the FRDP appears to be a useful model.     

Nerve quantification in female red Duroc pig (FRDP) scar compared to human hypertrophic scar

A significant impediment to studying hypertrophic scar is the lack of an animal model. We have confirmed similarities between scarring in the female red Duroc pig (FRDP) and human hypertrophic scar and conclude that this model warrants validation. Reports have suggested that the cutaneous nervous system may play a role in hypertrophic scar development and several studies have shown nerve density in hypertrophic scar to be increased. The purpose of this study was to further validate the FRDP model of hypertrophic scar by quantifying nerves in FRDP tissue and comparing the findings to human hypertrophic scar. Wounds of varying depth were created on the backs of two FRDP and tissue samples were harvested at 10 days, 1 month and 5 months post-wounding. Human specimens were obtained from six burn patients. Immunohistochemistry was performed and digital images were captured. Color subtractive computer-assisted image analysis was used to quantify nerve density and nerve area fraction. The results demonstrate that nerve tissue is increased in FRDP scar tissue and is quite similar to that in human hypertrophic scar and to that described in the literature. These data provide additional evidence that the FRDP model may be useful for studying hypertrophic scarring.     

Changes in VEGF and nitric oxide after deep dermal injury in the female, red Duroc pig-further similarities between female, Duroc scar and human hypertrophic scar

Despite decades of research, our understanding of human hypertrophic scar is limited. A reliable animal model could significantly increase our understanding. We previously confirmed similarities between scarring in the female, red, Duroc pig and human hypertrophic scarring. The purpose of this study was to: (1) measure vascular endothelial growth factor (VEGF) and nitric oxide (NO) levels in wounds on the female Duroc; and (2) to compare the NO levels to those reported for human hypertrophic scar. Shallow and deep wounds were created on four female Durocs. VEGF levels were measured using ELISA and NO levels with the Griess reagent. VEGF and NO levels were increased in deep wounds at 10 days when compared to shallow wounds (p < 0.05). At 15 weeks, VEGF and NO levels had returned to the level of shallow wounds. At 21 weeks, VEGF and NO levels had declined below baseline levels in deep wounds and the NO levels were significantly lower (p < 0.01). We found that VEGF and NO exhibit two distinctly different temporal patterns in shallow and deep wounds on the female Durocs. Furthermore, NO is decreased in female, Duroc scar as it is in human, hypertrophic scar further validating the usefulness of the model.     

建立一种兔耳增生性瘢痕的动物模型

目的　建立由动物自身产生的与人增生性瘢痕类似的增生性动物模型。方法　选用2 4只新西兰大耳白兔 ,分别在兔耳腹侧、背侧面作直径 1.5cm的全层皮肤缺损各 14 4个、72个 ,对创面愈合后形成的增生块进行组织病理学、层黏连蛋白 (LN)mRNA及整合素 β1mRNA检测等检查。结果　兔耳腹侧创面可产生类似人增生性瘢痕样的过度增生 ,其发生率为 71% ,以兔耳腹侧面中部为著 ,增生块最长持续时间超过伤口愈合后 15 0d ,而兔耳背侧面的创面增生块发生率不到3 0 % ,且增生块持续时间短 ,为 76d。切片镜下显示 ,增生块的真皮层存在大量成纤维细胞 ,与人增生性瘢痕结构类似。结论　兔耳腹侧面尤其腹侧面的中部可产生类似人增生性瘢痕样病理改变 ,可望成为研究瘢痕的动物模型。     

Scar formation following excisional and burn injuries in a red Duroc pig model

Scar research is challenging because rodents do not naturally form excessive scars, and burn depth, size, and location cannot be controlled in human longitudinal studies. The female, red Duroc pig model has been shown to form robust scars with biological and anatomical similarities to human hypertrophic scars. To more closely mimic the mode of injury, recreate the complex chemical milieu of the burn wound environment and enhance scar development, an animal model of excessive burn‐induced scarring was developed and compared with the more commonly used model, which involves excisional wounds created via dermatome. Standardized, full‐thickness thermal wounds were created on the dorsum of female, red Duroc pigs. Wounds for the dermatome model were created using two different total dermatome settings: ～1.5 mm and ≥ 1.9 mm. Results from analysis over 150 days showed that burn wounds healed at much slower rate and contracted more significantly than dermatome wounds of both settings. The burn scars were hairless, had mixed pigmentation, and displayed fourfold and twofold greater excess erythema values, respectively, compared with ～1.5 mm and ≥ 1.9 mm deep dermatome injuries. Burn scars were less elastic, less pliable, and weaker than scars resulting from excisional injuries. Decorin and versican gene expression levels were elevated in the burn group at day 150 compared with both dermatome groups. In addition, transforming growth factor‐beta 1 was significantly up‐regulated in the burn group vs. the ～1.5 mm deep dermatome group at all time points, and expression remained significantly elevated vs. both dermatome groups at day 150. Compared with scars from dermatome wounds, the burn scar model described here demonstrates greater similarity to human hypertrophic scar. Thus, this burn scar model may provide an improved platform for studying the pathophysiology of burn‐related hypertrophic scarring, investigating current anti‐scar therapies, and development of new strategies with greater clinical benefit.     

皮肤圆锥体结构损伤致增生性瘢痕的病理学观察

目的探讨皮肤圆锥体结构受损与增生性瘢痕(HS)形成的关系,寻找HS形成的原因及适合HS研究的动物模型。方法将2只雌性杜洛克猪(FRDP)背部去毛后,取正常皮肤1块, 行皮肤圆锥体结构观察;然后用气动取皮机造成皮肤缺损深度为0．38、0．76、1．14、1．52 mm的创面, 每个创面面积7．0 cm×7．0 cm,每只猪的背部共8个创面。根据上述创面深度将其分为4组,每组4 个创面。将0．38、0．76 mm组视为浅创面组;1．14、1．52 mm组视为深创面组。伤后不处理,让创面自然愈合。分别在伤后即刻(0)、10、30、60、90、150 d,切取创面组织标本行HE和弹性纤维(VVG)染色。行正常FRDP皮肤组织及受损圆锥体结构观察;大体观察不同深度FRDP创面愈合及瘢痕形成情况;用组织学方法观察HS的形态;VVG染色测定瘢痕组织的厚度并计分。结果正常FRDP背部皮肤存在圆锥体结构,与人类的皮肤圆锥体结构相似。浅创面组伤后3周内愈合,愈合的创面较为平整,无瘢痕组织形成;深创面组伤后4周以上愈合,愈合的创面较厚,无毛发,挛缩,质地坚硬,局部色素变浅或加深。浅创面组皮肤圆锥体结构的上半部分受损,但脂肪穹隆及腺体完好;深创面组皮肤圆锥体结构的下半部分受损,伤及脂肪穹隆及腺体。伤后150 d浅创面组的组织学结构与正常皮肤相似;深创面组圆锥体结构消失,并被大量堆积、没有特定方向、排列紊乱的胶原纤维束充盈。深创面组瘢痕组织厚度评分可见时间越长瘢痕越厚,伤后150 d瘢痕增生达高峰。结论皮肤圆锥体结构受损可导致HS的形成,FRDP可作为HS研究的动物模型。     

The effect of the angiogenesis inhibitor, angiostatin, on hypertrophic scarring

Introduction: Hypertrophic scarring is commonly seen by plastic surgeons in China. Since the etiology of hypertrophic scarring is still unknown, the only reliable treatment is surgical excision. To understand if angiogenesis plays an important role in the formation of hypertrophic scars, we investigated the effect of angiostatin, a potent angiogenesis inhibitor, on hypertrophic scar formation. Our hypothesis is that angiogenesis is required for increased scar formation and angiogenesis inhibition may be one of the methods that can be used to prevent the formation of hypertrophic scars. Methods: We have developed a reliable model in rabbits that results in hypertrophic scarring by creating a 6mm x 6mm full thickness skin wound on both ears. The cDNA for angiostatin is cloned into the pcDNA 3.1 mammalian expression vector. After the wounds re-epithelialized but prior to excessive scarring, the angiostatin expression vector was injected with Lipofectin 2000 once every two days. The expression of angiostatin was confirmed by RT-PCR. The scar tissue was harvested 14 days after injection and processed for histology and total protein. Histology was examined with routine stains, the amount of collagen deposition in the scar tissue was detected by proline assay, and TGF-β1 and VEGF expression was detected by western blot. Results: Compared to the control injection scar, the injection of angiostatin led to a much more normal-looking of scar in the rabbit ear. The proline assay demonstrated that the injection of the angiostatin expression vector resulted in much less collagen in the scar tissue. Western blot analysis showed there was less TGF-β1 and VEGF protein expression in the treated ear compared to the control. Conclusion: The introduction of a vector over-expression angiostatin can result in the decreased formation of hypertrophic scars in a rabbit ear model. This is corroborated by evidence of decreased collagen deposition, the primary extracellular matrix component of scars. In addition, we demonstrate the decreased expression of τηε pro-fibrosis growth factor, TGF-1, and the potent angiogenic factor, VEGF. These data suggest that angiogenesis inhibitors may have a potential role in the treatment of hypertrophic scarring.     

Recombinant human decorin inhibits cell proliferation and downregulates TGF-beta1 production in hypertrophic scar fibroblasts

Hypertrophic scarring remains a major problem for patients who have suffered deep burns. The pathophysiology underlying hypertrophic scar formation may be driven by the biological activity of transforming growth factor beta1 (TGF-beta(1)). Decorin is a human proteoglycan that inactivates the effect of TGF-beta(1) and therefore displays a beneficial effect of antifibrosis in various tissues. Hypertrophic scarring is a fibroproliferative disorder of the dermis that occurs following wounding. This study investigated the effects of decorin on cell proliferation, TGF-beta(1) production, and collagen synthesis in hypertrophic scar fibroblasts. The cell proliferation rates, cell cycle distribution, low-molecular-weight apoptotic DNA and TGF-beta(1) levels, and contents of type I and type III collagen amino-terminal propeptide (PINP, PIIINP) in supernatants were assessed. Fibroblast proliferation was significantly (P<0.05) inhibited by decorin, and this effect was dose-dependent. The fibroblast population became stationary at decorin concentrations of 100 and 200 nM. Decorin inhibited fibroblast proliferation by inducing cell growth arrest but not apoptosis. TGF-beta(1) and PINP levels were significantly (P<0.05) lower in fibroblasts treated with 10, 50, 100, 200 nM of decorin compared with fibroblasts without decorin addition. However, there was no significant difference in PIIINP concentration between the decorin-treated group and the control group. These results suggest that decorin has a down-regulatory effect on cell proliferation, TGF-beta(1) production, and collagen synthesis in hypertrophic scar fibroblasts. Improved understanding of such a regulatory mechanisms may eventually be of therapeutic significance in the control of hypertrophic scarring.     

Temporal expression of the transforming growth factor-Beta pathway in the rabbit ear model of wound healing and scarring

BACKGROUND: Despite numerous studies that have investigated the cellular and molecular mechanisms underlying scar formation, this process still remains poorly understood. The importance of transforming growth factor-beta (TGF-beta) in these processes has been well recognized, and this study sought to define the temporal expression of the key members in this pathway in a well-established, clinically relevant, rabbit ear model of hypertrophic scarring. STUDY DESIGN: Seven-millimeter (hypertrophic) and 5-mm (nonhypertrophic) punch wounds were made on the ears of 12 rabbits. Wounds were harvested at days 0, 7, 15, 28, and 40. RESULTS: There were no appreciable histologic differences between the 5- and 7-mm wounds at days 7 and 15. At day 28, however, the 7-mm scars were considerably more hypertrophic compared with the 5-mm control scars (p<0.001). The mRNA levels of TGF-beta1 and collagen Ialpha2 were notably higher in the hypertrophic 7-mm scars at day 28 than in the nonhypertrophic 5-mm scars (p<0.03). Although not pronounced, levels of TGF-beta2 were higher in the hypertrophic scars. There were no other statistically significant differences between the 7- and 5-mm scars. CONCLUSIONS: Elevated levels of TGF-beta1, and possibly TGF-beta2, are associated with hypertrophic scar formation.     

增生性瘢痕动物实验模型的建立与应用

目的建立由动物自身产生的增生性瘢痕实验模型.方法选用47只日本大耳白兔,在耳腹侧面制作6mm圆形全层皮肤缺损创面、1.5cm×4.5cm长方形创面以及耳背圆形创面共388个,进行组织学等多项观察.结果70%兔耳圆形创面可发生与人增生性瘢痕类似的增生块,增生块持续时间最长为150d;长方形创面增生块发生率为80%以上,持续时间已超过262d.增生块内有特征性的结节或漩涡状结构.创基注入TGF-β1、IFN-y,可以促进或抑制增生块的发生.原位杂交,查明内源性TGF-β1mRNA为强阳性表达.利用此模型证实成纤维细胞凋亡在病理性瘢痕发生、发展过程中起着重要的调控作用.结论兔耳可以产生与人增生性瘢痕类似的病理改变,可以用作瘢痕研究的实验模型.     

Recombinant human decorin inhibits TGF-β1-induced contraction of collagen lattice by hypertrophic scar fibroblasts

Decorin was reported to bind transforming growth factor-beta (TGF-β₁) and neutralise some of its activity as a key regulator of wound contraction and hypertrophic scar formation. In this study, we investigated whether recombinant human decorin affected TGF-β₁-induced fibroblast contractile activity, by using fibroblast-populated collagen lattice with decorin added to the collagen gel. Hypertrophic scar fibroblasts showed greater basal contraction of collagen gels than normal fibroblasts, and the addition of TGF-β₁ significantly enhanced this. Decorin inhibited both the basal and TGF-β₁-enhanced contraction of collagen gel by both normal and hypertrophic scar fibroblasts. Decorin also inhibited TGF-β₁-induced α-smooth muscle actin (α-SMA), plasminogen activator inhibitor-1 (PAI-1) protein and mRNA expressions in normal and hypertrophic scar fibroblasts. These results suggest that decorin may have therapeutic potential for excessive skin contraction as observed in hypertrophic scarring.     

A porcine deep dermal partial thickness burn model with hypertrophic scarring

We developed a reproducible model of deep dermal partial thickness burn injury in juvenile Large White pigs. The contact burn is created using water at 92 degrees C for 15s in a bottle with the bottom replaced with plastic wrap. The depth of injury was determined by a histopathologist who examined tissue sections 2 and 6 days after injury in a blinded manner. Upon creation, the circular wound area developed white eschar and a hyperaemic zone around the wound border. Animals were kept for 6 weeks or 99 days to examine the wound healing process. The wounds took between 3 and 5 weeks for complete re-epithelialisation. Most wounds developed contracted, purple, hypertrophic scars. On measurement, the thickness of the burned skin was approximately 1.8 times that of the control skin at week 6 and approximately 2.2 times thicker than control skin at 99 days after injury. We have developed various methods to assess healing wounds, including digital photographic analysis, depth of organising granulation tissue, immunohistochemistry, electron microscopy and tensiometry. Immunohistochemistry and electron microscopy showed that our porcine hypertrophic scar appears similar to human hypertrophic scarring. The development of this model allows us to test and compare different treatments on burn wounds.     

Inhibition of procollagen C-proteinase reduces scar hypertrophy in a rabbit model of cutaneous scarring

Hypertrophic scarring, which results from excessive collagen deposition at sites of dermal wound repair, can be functionally and cosmetically debilitating to the surgical patient. Pharmacological regulation of collagen synthesis and deposition is a direct approach to the control of scar tissue formation. One of the key steps in collagen stabilization is the cleavage of the C-terminal propeptide from the precursor molecule to form collagen fibrils, a reaction catalyzed by procollagen C-proteinase (PCP). We tested the ability of a PCP inhibitor to reduce hypertrophic scar formation in a rabbit ear model. After the placement of four, 7-mm dermal wounds on each ear, New Zealand white rabbits received PCP inhibitor subcutaneously in the left ear at four time points postwounding: days 7, 9, 11, 13 (early treatment; n=20 wounds) or days 11, 13, 15, 17 (late treatment; n=20 wounds). The right ear of each animal served as a control (vehicle alone). Wounds were harvested on postoperative day 28 and scar hypertrophy quantified by measurement of the scar elevation index. Early treatment of wounds with PCP inhibitor did not reduce scar formation compared with controls (p>0.05). However, late treatment resulted in a statistically significant reduction in the scar elevation index (p<0.01). Our results point not only to the potential use of PCP inhibitors to mitigate hypertrophic scarring but also to the temporal importance of drug delivery for antiscarring therapy.     

Prophylactic treatment of deep dermal burn scar to prevent hypertrophic scarring using the pulsed dye laser: a preliminary study

The pulsed dye laser, by selectively targeting blood vessels, has been used to treat established hypertrophic scars with good effect. This prospective clinical study aims to assess the feasibility of treating deep dermal burn wounds prophylactically before the formation of hypertrophic scars. Patients with burn wounds that took longer than 2 weeks to heal were primarily recruited. Each patient's burn area was divided into a treated area and a negative control. The area was laser treated with the pulsed dye laser (Chromos 585; SLS, Wales) twice at 6 weekly intervals. The appearance of the wound at both sites was inspected visually and scored at 6 weeks, and at 3, 6, and 9 months. Five patients with six burn sites (forearm, arm, and back) were treated. Treated areas achieved better scarring at 6 weeks ( = 0.04, paired -test) and at 3 months ( = 0.003, paired -test). The difference, however, became insignificant at 6 and 9 months. No notable side effects were seen in all patients. Prophylactic treatment of burn wounds with the pulsed dye laser is effective in hastening the resolution of scarring. In the authors' opinion, this treatment may revolutionize the traditional method of hypertrophic burn scar prevention, and should be considered early, especially for patients who are prone to hypertrophic scarring, and in areas where hypertrophic scarring are common.     

Adenovirus-mediated METH1 gene expression inhibits hypertrophic scarring in a rabbit ear model

Hypertrophic scarring remains a major problem for patients who have suffered from surgeries or burns. Vascularization plays an important role in the early phase of hypertrophic scarring. Therefore, the inhibition of angiogenesis might be used as a preventive strategy. In this study, we assessed the effect of anti-angiogenesis resulting from adenovirus-mediated METH1 (metalloprotease and thrombospondin1) gene expression on the hypertrophic scar formation in a rabbit ear model of hypertrophic scarring. We first investigated the number of microvessel and microcirculatory perfusion in untreated scars on days 10, 30, 60, and 90 after epithelialization. Then, we examined the effect of anti-angiogenesis by adenovirus-mediated METH1 expression on hypertrophic scar formation by calculating the scar elevation index, counting the microvessel and argyrophilic nucleolar organizer region particle, and detecting the amount of collagen on days 30 and 60 after treatment. We found that untreated scar tissues at the proliferative phase (days 10–60 after epithelialization) had a significantly higher density of microvessel and microcirculatory perfusion than those at the mature phase (day 90 after epithelization) (both p <0.05). On days 30 and 60 after treatment, the hypertrophic scar formation was significantly inhibited in the treatment group. There was significantly reduced scar elevation index, microvessel count, number of argyrophilic nucleolar organizer region, and total collagen content for treated scars. Our results demonstrate that METH1 has a markedly inhibitive effect on the formation of hypertrophic scar, and may thus have a promising application in the prevention of human hyperthropic scars.     

Effect of chymase activity on skin thickness in the Clawn miniature pig hypertrophic scarring model

Objective: The female red Duroc pig, a heavy and cumbersome animal, is routinely used as an animal model for hypertrophic scarring. Chymase, a chymotrypsin-like serine protease, plays an important role in skin fibrosis. This study aimed to create a lightweight pig hypertrophic scarring model using Clawn miniature pigs, and to investigate the role of chymase in hypertrophic scarring.

Methods: After creating four skin wounds (7.5?×?7.5?cm, depth?=?0.15?cm) in each pig, skin biopsies were performed after 15, 30, 60, 90, 120, and 150?days. Skin thickness, water content, hydroxyproline percentage, chymase activity, and transforming growth factor-beta 1 concentration were measured, and pathological analyses were performed.

Results and conclusions: Both tissue thickness and chymase activity were increased in scar tissue, peaked on day 90 after injury, and then gradually decreased. Peripheral scar tissue showed higher chymase activity than central scar tissue. Neither chymase activity nor transforming growth factor-beta 1 was detected in the surrounding normal skin, whereas central scar tissue showed a high transforming growth factor-beta 1 concentration, peaking on day 15, and decreasing to normal by day 120. We found the Clawn miniature pig to be a useful model for hypertrophic scarring. Chymase activity and skin thickness were well-correlated, suggesting that scars thicken when chymase activity is high.     

Homeostasis of the epidermal barrier layer: A theory of how occlusion reduces hypertrophic scarring

The mechanism of hypertrophic scar reduction using silicone gel sheeting remains elusive. We hypothesize that the decrease in scar formation is due to occlusion and homeostasis of the barrier layer. Using an established model of hypertrophic scarring, rabbits were divided into four groups and scars were tape-stripped or occluded with Kelocote, Cavilon, or Indermil, with each rabbit serving as its own internal control. All wounds were harvested on day 28 and examined histologically to measure the scar elevation index (SEI), epithelial thickness, and cellularity. Immunohistochemistry fluorescence was used to quantify inflammation in the dermis. Transepidermal water loss (TEWL) was measured for each occlusive agent and tape stripping. Ultrastructural analysis was performed by electron microscopy. Kelocote, Cavilon, and Indermil all significantly decreased SEI when compared with controls. Each of the occlusive treatments was shown to decrease TEWL while tape stripping increased TEWL. Tape stripping significantly increased the SEI, epithelial thickness, and cellularity. Immunostaining for macrophages showed increased density of inflammatory cells in the tape-stripped scars. Under electron microscopy, the tape-stripped wounds displayed extensive inflammation and keratinocyte damage. Both unwounded skin and occlusion-treated scars did not display these characteristics. In conclusion, hypertrophic scarring was reduced regardless of occlusive method used. Furthermore, repeated disruption of the permeability barrier by tape stripping led to an increase in scarring. Ultrastructural analysis suggests that occluded wounds may be in an advanced state of wound repair. Occlusion may mediate its effects through establishing homeostasis of the epidermal barrier layer.