Role and innocuity of Tisseel, a tissue glue, in the grafting process and in vivo evolution of human cultured epidermis

Air-Pressure-Supported Application of Cultured Human Keratinocytes in a Fibrin Sealant Suspension as a Potential Clinical Tool for Large-Scale Wounds

The treatment of large-scale skin wounds remains a therapeutic challenge. In most cases there is not enough autologous material available for full coverage. Cultured epithelial autografts are efficient in restoring the lost epidermal cover; however, they have some disadvantages, such as difficult application and protracted cell cultivation periods. Transplanting a sprayed keratinocyte suspension in fibrin sealant as biological carrier is an option to overcome those disadvantages. Here, we studied different seeding techniques regarding their applicability and advantages on cell survival, attachment, and outgrowth in vitro and thereby improve the cell transfer to the wound bed. Human primary keratinocytes were suspended in a fibrin sealant. WST-8 assay was used to evaluate the vitality for 7 days. Furthermore, the cells were labeled with CellTracker™ CM-Di-I and stained with a life/dead staining. Cell morphology, shape, and distribution were microscopically analyzed. There was a significant increase in vitality while cultivating the cells in fibrin. Sprayed cells were considerably more homogenously distributed. Sprayed cells reached the confluent state earlier than dripped cells. There was no difference in the vitality and morphology in both groups over the observation period. These findings indicate that the sprayed keratinocytes are superior to the application of the cells as droplets. The sprayed application may offer a promising therapeutic option in the treatment of large chronic wounds.

Human adipose stromal vascular cell delivery in a fibrin spray

BACKGROUND AIMS

Adipose tissue represents a practical source of autologous mesenchymal stromal cells (MSCs) and vascular-endothelial progenitor cells, available for regenerative therapy without in vitro expansion. One of the problems confronting the therapeutic application of such cells is how to immobilize them at the wound site. We evaluated in vitro the growth and differentiation of human adipose stromal vascular fraction (SVF) cells after delivery through the use of a fibrin spray system.

METHODS

SVF cells were harvested from four human adult patients undergoing elective abdominoplasty, through the use of the LipiVage system. After collagenase digestion, mesenchymal and endothelial progenitor cells (pericytes, supra-adventitial stromal cells, endothelial progenitors) were quantified by flow cytometry before culture. SVF cells were applied to culture vessels by means of the Tisseel fibrin spray system. SVF cell growth and differentiation were documented by immunofluorescence staining and photomicrography.

RESULTS

SVF cells remained viable after application and were expanded up to 3 weeks, when they reached confluence and adipogenic differentiation. Under angiogenic conditions, SVF cells formed endothelial (vWF+, CD31+ and CD34+) tubules surrounded by CD146+ and α-smooth muscle actin+ perivascular/stromal cells.

CONCLUSIONS

Human adipose tissue is a rich source of autologous stem cells, which are readily available for regenerative applications such as wound healing, without in vitro expansion. Our results indicate that mesenchymal and endothelial progenitor cells, prepared in a closed system from unpassaged lipoaspirate samples, retain their growth and differentiation capacity when applied and immobilized on a substrate using a clinically approved fibrin sealant spray system.

Enhanced cryoprecipitate for skin graft and donor site wound healing in pigs

Due to similarities in skin characteristics, the authors hypothesise that a pig model would most accurately show the ability of autologous, enhanced cryoprecipitate (eCryo) to improve the wound healing of split-thickness skin grafts (STSGs) and corresponding donor sites. Fifty-two STSGs (5 × 5 cm) were fashioned and treated according to a randomised protocol with an autologous eCryo-treated and a control group. Macroscopic assessment, histological evaluation and cellular composition were completed at days 7, 14, 21 and 28. Thirty-two donor sites were also created and assessed in a similar manner. Histologic analysis showed enhancement of healing over all time points for eCryo-treated donor sites. All other results showed no statistically significant improvement with the use of eCryo. Autologous cryoprecipitate appears to be a safe, inexpensive and easy-to-use alternative to fibrin glue, which carries risks and is, in many cases, prohibitively expensive. Further studies are necessary to evaluate the full potential of eCryo. Interestingly, eCryo application may improve donor site aesthetic appearance. We believe that a pig model most reliably simulates eCryo's behaviour in humans to accurately reflect its future clinical applicability.

Intra-myocardial biomaterial injection therapy in the treatment of heart failure: Materials, outcomes and challenges

Heart failure initiated by coronary artery disease and myocardial infarction (MI) is a widespread, debilitating condition for which there are a limited number of options to prevent disease progression. Intra-myocardial biomaterial injection following MI theoretically provides a means to reduce the stresses experienced by the infarcted ventricular wall, which may alter the pathological remodeling process in a positive manner. Furthermore, biomaterial injection provides an opportunity to concurrently introduce cellular components and depots of bioactive agents. Biologically derived, synthetic and hybrid materials have been applied, as well as materials designed expressly for this purpose, although optimal design parameters, including degradation rate and profile, injectability, elastic modulus and various possible bioactivities, largely remain to be elucidated. This review seeks to summarize the current body of growing literature where biomaterial injection, with and without concurrent pharmaceutical or cellular delivery, has been pursued to improve functional outcomes following MI. The literature to date generally demonstrates acute functional benefits associated with biomaterial injection therapy across a broad variety of animal models and material compositions. Further functional improvements have been reported when cellular or pharmaceutical agents have been incorporated into the delivery system. Despite these encouraging early results, the specific mechanisms behind the observed functional improvements remain to be fully explored and future studies employing hypothesis-driven material design and selection may increase the potential of this approach to alleviate the morbidity and mortality of heart failure.

Reconstructive Surgery with Integra Dermal Regeneration Template: Histologic Study, Clinical Evaluation, and Current Practice

BACKGROUND

Yannas and Burke developed the concept of the dermal regeneration template in the 1970s. It is now a widely accepted tool in the treatment of burns as well as in reconstructive surgery.

METHODS

The authors present a previously published study of Integra used in 20 consecutive patients to reconstruct 30 anatomical sites and then analyze the histologic and clinical outcomes. Wound healing was evaluated by examination of weekly punch biopsy specimens with standard and immunohistochemical stains. Patient satisfaction was assessed using a visual analogue scale, and scar appearance was assessed using a modified Vancouver Scar Scale.

RESULTS

Four distinct phases of dermal regeneration could be demonstrated histologically: imbibition, fibroblast migration, neovascularization, and remodeling and maturation. Full vascularization of the neodermis occurred at 4 weeks. Patients reported increased range of movement and improvement in appearance compared with their preoperative states.

CONCLUSIONS

The color of the matrix reflected the stage of neodermal vascularization. No adnexa, nerve endings, or elastic fibers were seen in any of the specimens. The new collagen was histologically indistinguishable from normal dermal collagen. The authors also present their current protocol and experience with using Integra for a range of reconstructive procedures.

Novel techniques to improve split-thickness skin graft viability during vulvo-vaginal reconstruction

BACKGROUND

Split-thickness skin grafts are often utilized for vulvo-vaginal reconstruction. Unfortunately, infection and sloughing may occur in up to 22% of patients with standard techniques especially at irradiated recipient sites.

CASES

We report seven cases of vulvo-vaginal reconstruction using split-thickness skin grafts. In this series, we used fibrin tissue adhesives with and without vacuum-assisted closure devices to augment graft adherence and viability. We briefly describe the clinical history, surgical techniques, and outcomes of the cohort.

CONCLUSION

Fibrin tissue adhesives and wound vacuum-assisted closure devices may improve the viability of split-thickness skin grafts during vulvo-vaginal reconstruction.

MBCP biphasic calcium phosphate granules and tissucol fibrin sealant in rabbit femoral defects: the effect of fibrin on bone ingrowth

An ageing population implies an increase in bone and dental diseases, which are in turn a source of numerous handicaps. These pathologies are an expensive burden for the European health system. As no specific bioactive materials are efficient enough to cope with this burden, we have to develop an injectable, mouldable, self-hardening bone substitute to support bone tissue reconstruction and augmentation. New, highly bioactive and suitable biomaterials have been developed to replace bone grafts in orthopedic revision and maxillofacial surgery for bone augmentation. These mouldable, self-hardening materials are based on the association of MBCP Biphasic Calcium Phosphate Granules and Tissucol Fibrin Sealant. The in vivo evaluation of ingrowth in relation to the composite was made in an experiment on rabbits. The results indicate that in the presence of fibrin sealant, newly-formed bone developed at a small distance from the surface of the calcium phosphate ceramic. Two different bone apposition processes were identified. Without the fibrin component (MBCP group), bone rested directly on the surface of the granules. This observation is commonly described as osteoconduction in calcium phosphate materials. On the contrary, the presence of the fibrinogen component seemed to modify this standard osteoconduction phenomenon: the newly-formed bone essentially grew at a distance from the surface of the granules, on the fibrillar network, and could be considered as an inductive phenomenon for osteogenic cell differentiation from mesenchymal stem cells.

Fibrin as an inducer of fibrosis in the tunica albuginea of the rat: a new animal model of Peyronie's disease

OBJECTIVES

To investigate the role of fibrin in inducing fibrosis in the tunica albuginea (TA) of the rat penis, to develop a new animal model for Peyronie's disease (PD).

MATERIALS AND METHODS

The TA of rats (five per group per period) were injected with either saline, fibrin, transforming growth factor-beta1 (TGF-beta1) or TGF-beta1 plus fibrin; the rats were killed at 1, 3, and 6 weeks after injection. Images were analysed quantitatively from tissue sections stained for collagen (Masson trichrome), fibrin (Verhoeff's stain) and elastin (Hart's stain), and immunostained for TGF-beta1, inducible nitric oxide synthase (iNOS), heme oxygenase 1 (HO1), alpha-smooth muscle actin (ASMA), apoptosis (TUNEL) and plasminogen activator inhibitor (PAI). Collagen fibre organization was characterized by electron microscopy. Human PD plaque tissue and normal human TA were assayed for fibrin by immunohistochemistry in nine samples.

RESULTS

At 1 week after injection of fibrin into the rat TA, only oedema was present; at 3 weeks, the oedema developed into a characteristic fibrotic PD-like plaque. The injection of TGF-beta1 into the TA also induced oedema in the TA at 1 and 3 weeks but there was very little evidence of a recognisable plaque at either time. Injection with TGF-beta1 plus fibrin resulted in oedema at 1 week but at 3 weeks there was a smaller plaque than with fibrin only. At 6 weeks the induced plaques in the fibrin-only and fibrin + TGF-beta1 groups persisted, and were comparable with those elicited at this time by TGF-beta1 alone. The control animals showed no pathology at any of the sample times. At 3 weeks the PD plaque induced by injection with fibrin alone had not only greater expression of TGF-beta1 than the TA of the animals receiving TGF-beta1 alone, but also greater levels of other markers of fibrosis, e.g. HO1 (reactive oxygen species), ASMA (presence of myofibroblasts), apoptosis, and PAI (inhibitor of fibrinolysis). iNOS, a known antifibrotic agent, was also increased. In human PD plaque tissue, fibrin was detected by immunohistochemistry in all nine specimens.

CONCLUSIONS

These results suggest that fibrin, when introduced into the TA of the rat penis, acts as a potential profibrotic protein, possibly via the local release of TGF-beta1, and induces a plaque not only histologically similar to that induced by TGF-beta1 but to that of the human condition. Because fibrin can extravasate from the blood into the human TA after an injury to the TA, and because fibrin persists in the plaque tissue, we hypothesise that fibrin may play a key role in the pathogenesis of human PD.

Reconstructed human skin produced in vitro and grafted on athymic mice

BACKGROUND

The best alternative to a split-thickness graft for the wound coverage of patients with extensive burns should be in vitro reconstructed autologous skin made of both dermis and epidermis and devoid of exogenous extracellular matrix proteins and synthetic material. We have designed such a reconstructed human skin (rHS) and present here its first in vivo grafting on athymic mice.

METHODS

The rHS was made by culturing newborn or adult keratinocytes on superimposed fibrous sheets obtained after culturing human fibroblasts with ascorbic acid. Ten days after keratinocyte seeding, reconstructed skins were either cultured at the air-liquid interface or grafted on athymic mice. We present the macroscopic, histologic, and phenotypic properties of such tissues in vitro and in vivo after grafting on nude mice.

RESULTS

After maturation in vitro, the reconstructed skin exhibited a well-developed human epidermis that expressed differentiated markers and basement membrane proteins. Four days after grafting, a complete take of all grafts was obtained. Histological analysis revealed that the newly generated epidermis of newborn rHS was thicker than that of adult rHS after 4 days but similar 21 days after grafting. The basement membrane components (bullous pemphigoid antigens, laminin, and type IV and VII collagens) were detected at the dermo-epidermal junction, showing a continuous line 4 days after grafting. Ultrastructural studies revealed that the basement membrane was continuous and well organized 21 days after transplantation. The macroscopic aspect of the reconstructed skin revealed a resistant, supple, and elastic tissue. Elastin staining and elastic fibers were detected as a complex network in the rHS that contributes to the good elasticity of this new reconstructed tissue.

CONCLUSIONS

This new rHS model gives supple and easy to handle skins while demonstrating an adequate wound healing on mice. These results are promising for the development of this skin substitute for permanent coverage of burn wounds.

The use of fibrin glue in skin grafts and tissue-engineered skin replacements: a review

Fibrin glue has been widely used as an adhesive in plastic and reconstructive surgery. This article reviews the advantages and disadvantages of its use with skin grafts and tissue-engineered skin substitutes. Fibrin glue has been shown to improve the percentage of skin graft take, especially when associated with difficult grafting sites or sites associated with unavoidable movement. Evidence also suggests improved hemostasis and a protective effect resulting in reduced bacterial infection. Fibrin, associated with fibronectin, has been shown to support keratinocyte and fibroblast growth both in vitro and in vivo, and may enhance cellular motility in the wound. When used as a delivery system for cultured keratinocytes and fibroblasts, fibrin glue may provide similar advantages to those proven with conventional skin grafts. Fibrin glue has also been shown to be a suitable delivery vehicle for exogenous growth factors that may in the future be used to accelerate wound healing.

Mechanisms of wound reepithelialization: hints from a tissue-engineered reconstructed skin to long-standing questions

Wound closure of epithelial tissues must occur efficiently to restore rapidly their barrier function. We have developed a tissue-engineered wound-healing model composed of human skin keratinocytes and fibroblasts to better understand the mechanisms of reepithelialization. It allowed us to quantify the reepithelialization rate, which was significantly accelerated in the presence of fibrin or platelet-rich plasma. The reepithelialization of these 6 mm excisional wounds required the contribution of keratinocyte proliferation, migration, stratification, and differentiation. The epidermis regenerated progressively from the surrounding wound margins. After 3 days, the neoepidermis showed a complete spectrum of changes. Near the wound margin, the differentiation of the neoepidermis (keratins 1/10, filaggrin, and loricrin) and regeneration of the dermoepidermal junction (laminin 5 and collagen IV) were more advanced than toward the wound center, where the proliferative index was significantly increased. The spatial distribution of keratinocytes distinguished by particular features suggests two complementary mechanisms of reepithelialization: 1) the passive displacement of the superficial layers near the wound margin that would rapidly regenerate a barrier function and 2) the crawling of keratinocytes over each other at the tip of the progressing neoepidermis. Therefore, this study brings a new perspective to long-standing questions concerning wound reepithelialization.

Aerosolization of Epidermal Cells with Fibrin Glue for the Epithelialization of Porcine Wounds with Unfavorable Topography

Aerosolized epidermal cell suspension was previously found to be effective for the epithelialization of full-thickness wounds. This suspension is less expensive than and requires a shorter preparation time than the currently used cultured epithelial autografts. Still, convex and irregular wounds present unfavorable conditions for homogenous dispersion of the aerosolized cell suspension. The authors hypothesized that the addition of fibrin glue to the aerosol of cells would reduce cell movement and ensure homogenous dispersion of the cells, thereby promoting wound epithelialization. The objectives of the study were to evaluate the healing of wounds with unfavorable topography after autotransplantation of an epidermal cell aerosol with and without fibrin glue. Six Yorkshire piglets were studied. An epidermal suspension was made from full-thickness groin skin. Dispase was used to separate the epidermis from the dermis, and trypsin was used to separate the epidermal cells from one another. Twenty-four hours later, full-thickness wounds with unfavorable topography were created adjacent to the vertebral column of six pigs. Twelve wounds were treated with an aerosol of epidermal cell suspension mixed with fibrin glue (study group), and 12 wounds were treated with the same suspension without the fibrin glue (control group). The percentages of total wound contraction and the epithelialized and nonepithelialized areas were evaluated 1, 2, 3, and 4 weeks after aerosolization. The histologic characteristics of the newly formed skin were examined by light microscopy using slides stained with hematoxylin and eosin. Study wounds were characterized by central epithelialization, whereas control wounds were characterized by peripheral epithelialization. Study wounds contracted at a slower rate than control wounds, but wound size was the same in both groups after 4 weeks. The addition of fibrin glue facilitated epithelialization: Study wounds showed 75.5 +/- 22.4 percent (mean +/- SD) and 94.2 +/- 8.8 percent epithelialization after 3 and 4 weeks, respectively, compared with 46.3 +/- 9.5 percent and 47.9 +/- 13.1 percent epithelialization of the control wounds at the same times. These differences between the study and control groups were statistically significant (p < 0.001, paired t test). The addition of fibrin glue to an aerosol of epidermal cells significantly enhances the epithelialization of wounds with unfavorable topography in pigs.

Fibrin sealant in wound repair: a systematic survey of the literature

Fibrin sealants have recently been approved for clinical use in the US by the FDA and have been available for clinical use in Europe for years. The indication for use in the US is haemostasis. Nevertheless, both commercial and non-commercial fibrin sealant preparations are also for wound healing and for prevention of abdominal adhesions in the US and Europe. To the non-cognoscenti of fibrin sealants, their use to promote wound repair and to prevent abdominal adhesions appears contradictory since an agent that promotes connective tissue repair might be expected to promote abdominal adhesion rather than prevent them. In this systematic survey of the animal and clinical data evidence is presented that supports both off-label uses. However there is much inconsistency in the data secondary to the use of various fibrin sealant preparations, different animal models and clinical situations and different application techniques. It is clear from this survey that standard preparation and application of fibrin sealant for a particular surgical setting are needed to resolve the many apparent discrepancies in the literature. A corollary to this is the likelihood that different fibrin sealant preparations may be preferred for different clinical situations.

Multistep production of bioengineered skin substitutes: sequential modulation of culture conditions

Many studies are being conducted to define the role of growth factors in cutaneous physiology in order to add cytokines in a timely fashion for optimal tissue engineering of skin. This study is aimed at developing a multistep approach for the production of bioengineered skin substitutes, taking into account the effects of various growth factors according to the culture time. The use of a serum-supplemented medium throughout the whole culture period of skin substitutes was compared to the sequential use of specific additives at defined culture steps. Histological analysis revealed that serum was necessary for keratinocyte proliferation and migration on dermal substitutes during the first 2 d after their seeding. However, the serum-free medium presented some advantages when supplemented with different additives at specific culture steps. Interestingly, ascorbic acid added to the dermal substitutes before and after keratinocyte seeding maintained their cuboidal morphology in the basal epidermal layer. In the absence of serum, collagen matrix degradation slowed down, and a better multilayered epidermal organization was obtained, notably with retinoic acid. Stratum corneum formation was also enhanced by fatty acids. Thus, sequential addition of exogenous factors to the medium used to produce skin substitutes can improve their structural features and functional properties in vitro.

Large surface of cultured human epithelium obtained on a dermal matrix based on live fibroblast-containing fibrin gels

The aim of this study was to develop a new keratinocyte culture system on a dermal equivalent suitable for skin wound closure. Our dermal matrix is based on a fibrin gel from plasma cryoprecipitate containing live human fibroblast (from human foreskin). Keratinocytes obtained from primary culture according to the Rheinwald and Green method, were seeded on the gel at different seeding ratios. In all cases, the keratinocytes plated on the dermal equivalent grew to confluence and stratified epithelium was obtained within 10-15 days in culture. Early expression of basal membrane proteins was detected by immunostaining with laminin and type IV collagen antibodies. Cell proliferation was detected both in the epidermal layer and in the fibroblast embedded in the gel as assessed by BrdU incorporation. Detachment of composite cultures from dishes or flasks is a simple and quick procedure without the need for dispase treatment. Grafting of composite cultures to nude mice gave rise to an orderly stratified, orthokeratinized epithelium resembling human epidermis. A number of advantages including a large expansion factor without the need of 3T3 feeder layer, the availability of fibrin/plasma cryoprecipitate from blood banks and the versatile manipulation of composite cultures suggest that this system could be suitable for the definitive coverage of severely burned patients.

Use of in vitro reconstructed skin To cover skin flap donor site

BACKGROUND

The skin flap technique is widely used in reconstructive surgery for the coverage of deep burns of the face, neck, and joints. Facial deformities and joint contractures are avoided by transplanting vascularized full-thickness skin on wounds. The major drawback of this technique is the injury inflicted upon the donor site, which corresponds to a third degree burn. The usual technique to cover the flap donor site is the transplantation of split-thickness autografts. In the case of patients with deep and extensive burns, the harvesting of good quality autografts is often difficult because of multiple scars. In order to avoid additional trauma to the patient by split-thickness skin harvesting, we have experimented the use of a new model of in vitro reconstructed skin graft for flap donor site coverage in a mouse model.

MATERIALS AND METHODS

The reconstructed skin was grafted on the back of nude mice at the skin flap donor site, while flap was used to cover a wound generated on joint of the posterior leg.

RESULTS

A 100% graft take was achieved (16 mice were used) and a limited contraction of the reconstructed skin was observed 30 days posttransplantation (78% of the initial surface area of the graft remained). Histological analysis of the graft demonstrated healing of a well differentiated epidermis laying on a dense dermis.

CONCLUSIONS

Since this technique would prevent additional trauma to the patient while achieving a good healing of the wound, it may be a useful approach in the coverage of skin flap donor site in humans.

Grafting on nude mice of living skin equivalents produced using human collagens

Autologous epidermal transplantation for human burn management is an example of a significant breakthrough in tissue engineering. However, the main drawback with this treatment remains the fragility of these grafts during and after surgery. A new human bilayered skin equivalent (hSE) was produced in our laboratory to overcome this problem. The aim of the present work was to study skin regeneration after hSE grafting onto nude mice. A comparative study was carried out over a period of 90 days, between anchored bovine skin equivalent, hSE and hSE+, the latter containing additional matrix components included at concentrations similar to those in human skin in vivo. The addition of a dermal layer to the epidermal sheet led to successful graft take, enhanced healing, and provided mechanical resistance to the grafts after transplantation. In situ analysis of the grafts showed good ultrastructural organization, including the deposition of a continuous basement membrane 1 week after surgery.

Cultured epidermal sheet grafting with Hemaseel HMN fibrin sealant on nude mice

Grafting of cultured epidermal sheets is a promising technique for skin restoration in extensive burns, but the technique has some limitations, resulting in variable graft takes. These experiments were designed to evaluate the innocuity of Hemaseel HMN fibrin sealant in the grafting process and in vivo evolution of cultured epidermis. A total of 30 mice were grafted, 15 were controls, 15 received tissue sealant application before the deposition of the cultured human epidermal sheets. Seven days after transplantation, compared to controls, the percentage of graft take over the total surface area grafted was greater in animals that had received the tissue sealant application. No difference was found 14 and 21 days postgrafting. In contrast, the percentage of graft take over the bony area (spinal) was significantly increased in animals grafted with previous application of sealant compared to controls at 7, 14 and 21 days postgrafting. Immunohistological and ultrastructural analysis showed that the evolution of the cultured human epidermis after transplantation was similar in both groups. The basement membrane was well structured 21 days after transplantation. The sealant was present at 4 days but not at 21 days postgrafting. Therefore, we conclude that the application of fibrin sealant before cultured epidermal sheet deposition on nude mouse graft bed is innocuous and enhances their mechanical stability. Since in this nude mouse system Hemaseel HMN fibrin sealant increased the percentage of graft take over areas difficult to engraft, we think that it may be advantageous in cultured epidermal sheet grafting on burn patients.

Skin equivalent produced with human collagen

Several studies have recently been conducted on cultured skin equivalent (SE), prepared using human keratinocytes seeded on various types of dermal equivalents (DE). We previously showed the advantages of our anchorage method in preventing the severe surface reduction of DE due to fibroblast contractile properties in vitro. A new anchored human SE was established in our laboratory in order to obtain a bioengineered tissue that would possess the appropriate histological and biological properties. In order to compare the effects of different collagen origins on the evolution of SE in vitro, human keratinocytes were seeded on three types of anchored DE. A comparative study was carried out between bovine SE (bSE), human SE (hSE), and human skin equivalent containing additional dermal matrix components (hSE+). Immunohistological analysis showed that hSE and hSE+ presented good structural organization, including the deposition of several basement membrane constituents. Higher amounts of transglutaminase, ceramides, and keratin 1 were detected in the epidermal layers of all SE when cultured at the air-liquid interface. However, a 92 kDa gelatinase activity was higher in bovine skin equivalent (bSE) compared to hSE cultures. The use of human collagens comparatively to bovine collagen as SE matricial component delayed the degradation of the dermal layer in culture.

Early basement membrane formation following the grafting of cultured epidermal sheets detached with thermolysin or Dispase

The basement membrane zone is important for graft adhesion and stability. The aim of the present study was to visualize the regeneration of the basement membrane and determine the sequential appearance of its constituents in the early postgrafting period of cultured human epidermal sheets. A keratinocyte single cell suspension, devoid of dermal fibroblast contamination, was obtained from human skin by a two-step tissue digestion method with thermolysin and trypsin. After culturing, epidermal sheets were generated, detached enzymatically by incubating with thermolysin (for 20-30 min) or Dispase (for 45-60 min), and deposited on a muscular graft bed of athymic mice. Immunohistochemistry and ultrastructural analyses were performed on biopsies harvested 2, 4 and 21 days postgrafting. Bullous pemphigoid antigens and laminin were detected at the dermo-epidermal junction, showing an almost continuous line 2 days postgrafting. Type IV collagen was generally absent at this time, but it was detected 4 days postgrafting. Type VII collagen was labelled as a discontinuous line of increasing intensity from 2 to 21 days postgrafting. Ultrastructural analysis revealed hemidesmosomes and a discontinuous lamina densa 2 days postgrafting, and a complete basement membrane with a continuous lamina densa, hemidesmosomes and anchoring fibrils 21 days postgrafting. The sequence of appearance of major basement membrane components was similar for cultured sheets detached with thermolysin or Dispase. However, it differed from that of other wound healing models. Results are discussed in terms of the variable keratinocyte migration requirement between various wound healing models.