Advantage of the presence of living dermal fibroblasts within in vitro reconstructed skin for grafting in humans

Les substituts cutanés reconstruits en laboratoire : application au traitement des brûlés

The development of skin substitutes started 25 years ago with the cultivation of keratinocytes to replace the epidermis of extensively burned patients. It is now possible to reproduce in vitro the two layers of skin, epidermis and dermis. Cultured epidermises are now usually used in burn centers dealing with the more severe patients. They are provided by hospital or private laboratories. Dermal substrates are some collagen matrices, which act in vivo as a guide for the reconstruction of a neodermis. Living dermis include living fibroblasts. Different models are now available for clinical use. Living skin equivalent is obtained by coculturing fibroblast and keratinocytes on a collagen support. Clinical essays are going on for chronic wounds. We present the different skin equivalent models and their clinical applications.

Congenital Melanocytic Nevus and the Internet: An Evaluation of Available Web-Based Resources

The Internet has become an increasingly used tool for patient education and the coordination of support groups. For families with children diagnosed with congenital melanocytic nevus, this is also the case. To evaluate the quality of congenital melanocytic nevus-related information on the Internet, a standardized assessment of web sites was used. The overall Internet informational and support resources regarding congenital melanocytic nevus were found to be accurate and user friendly but limited. The authors recommend practitioners direct patient families to www.nevusnetwork.org as a starting point, and supplement an interest in pictures and information regarding support groups with visits to www.dermatlas.org and http://groups.MSN.com/AussieNevusSupportGroup.

Fibroblast populated dense collagen matrices: cell migration, cell density and metalloproteinases expression

Dense collagen matrices obtained by using the property of type I collagen to form liquid crystals at high concentrations, were shown to be colonized by human dermal fibroblasts (Biomaterials 23 (2002) 27). In order to evaluate them as possible tissue substitutes, we investigated in this study the mechanism of cell colonization. Fibroblasts were seeded at the surface of collagen matrices at concentrations of 5 and 40 b mg/ml. Cell density and migration were estimated from histological sections over 28 days within 500 microm thick matrices. At day 14, migration started in the 40 mg/ml matrices, attaining 320 microm in distance and 5500 cell/mm(3) in density at day 28. As zymography and western blot techniques demonstrated production of collagenase 1 (MMP1) and gelatinase A (MMP2) in culture medium, collagen hydrolysis was required for cells to penetrate the collagen network. Furthermore, the presence of MMP1 and MMP2 and their tissue inhibitors TIMP1 and TIMP2 was revealed by immunohistochemistry. We presently show that 40 mg/ml collagen matrices are colonized by human dermal fibroblasts and reach, at day 28, a density close to that measured in human dermis.

A review of keratinocyte delivery to the wound bed

Over the last 20 years, confluent sheets of cultured epithelial autograft have been used for patients with major burns. Problems with the lack of "take" and long-term durability, as well as the time delay to produce such grafts, have led to the development of delivery systems to transfer keratinocytes to the wound bed. This review article describes the problems of using cultured epithelial autograft and the advantages of using preconfluent keratinocytes. Despite the numerous delivery systems that have been reported, most studies are limited to animal wound bed models. There are a few small clinical studies that have demonstrated enhanced healing using mainly subjective methods. There is a need for controlled, randomized clinical trials to prove the efficacy of keratinocyte delivery systems. Proposals for the use of this technology are made.

Substance P axons and sensory threshold increase in burn-graft human skin

BACKGROUND

Our knowledge of afferent nerve fiber reinnervation of grafted skin following third-degree burn is limited by a lack of quantitative histological and psychophysical assessment from the same cutaneous area. The current study compares fiber profile and functional recovery measurements in injured and control skin from the same subject.

MATERIALS AND METHODS

Nerve regeneration and modality-specific sensory thresholds were compared using immunocytochemical labeling with protein gene product 9.5 antibody to stain all axons and anti-substance P to label substance P axons (which are predominantly unmyelinated), as well as computerized instrumentation to obtain psychophysical estimates.

RESULTS

Compared to control skin, threshold measures of pinprick (P < 0.001), warming (P < 0.001), touch (P < 0.001), and vibration (P < 0.01) were significantly elevated in burn-graft skin and correlated with histological analysis of skin biopsies obtained from the same site. Immunohistochemical staining of all axons innervating the dermis and epidermis revealed a significant reduction in burn-graft relative to control skin (54% decrease, P < 0.0001). In contrast, the incidence of substance P nerve fibers was significantly elevated in burn-graft (177% increase, P < 0.05) and appeared to correlate with patient reports of pruritus and pain.

CONCLUSIONS

Observations support the hypothesis that sensory regeneration is fiber-size-dependent in burn-graft skin. The findings that substance P fiber growth increased while total fiber count decreased and that thermal threshold showed the greatest degree of functional recovery suggest that unmyelinated neurons have the greater ability to transverse scar tissue and reinnervate grafted skin following third-degree burn injury.

Autologous cultured keratinocytes on porcine gelatin microbeads effectively heal chronic venous leg ulcers

We have established a specific bioreactor microcarrier cell culture system using porcine gelatin microbeads as carriers to produce autologous keratinocytes on a large scale. Moreover, we have shown that autologous keratinocytes can be cultured on porcine collagen pads, thereby forming a single cell layer. The objective of this study was to compare efficacy and safety of autologous cultured keratinocytes on microbeads and collagen pads in the treatment of chronic wounds. Fifteen patients with recalcitrant venous leg ulcers were assigned to three groups in a single-center, prospective, uncontrolled study: five underwent a single treatment with keratinocyte monolayers on collagen pads (group 1); another five received a single grafting with keratinocyte-microbeads (group 2); and the last five received multiple, consecutive applications of keratinocyte-microbeads 3 days apart (group 3). All patients were followed for up to 12 weeks. By 12 weeks, there was a mean reduction in the initial wound area of 50, 83, and 97 percent in the three groups, respectively. The changes in wound size were statistically significant between the first and third groups (p= 0.0003). Keratinocyte-microbeads proved to be more effective than keratinocyte monolayers on collagen pads when the former were applied every 3 days. Rapid availability within 10-13 days after skin biopsy and easy handling represent particular advantages.

Construction of large area organotypical cultures of oral mucosa and skin

BACKGROUND

Skin and oral mucosal keratinocytes grown in vitro usually lose their normal patterns of differentiation, unless grown as organotypical cultures that are constructed by allowing collagen gels containing fibroblasts to contract before they are plated with keratinocytes and raised to the air/medium interface. However, the contraction process tends to produce small irregular cultures.

METHODS

To generate uniformly differentiating large cultures, we have investigated several aspects of the factors involved in the culture construction. By adjusting the number of fibroblasts used and by plating the matrices with keratinocytes prior to contraction, cultures of up to 72 cm2 were constructed.

RESULTS

The cultures retained almost the full surface areas of the original matrices and showed uniform patterns of epithelial plating and differentiation. Immunostaining for cytokeratins and integrins indicated restoration of in vitro phenotypes similar to those of the epithelial tissues of origin.

CONCLUSIONS

These methods successfully generate cultures required for certain types of investigations and tissues that are suitable for clinical use as grafts.

Validation of a morphometric method for evaluating fibroblast numbers in normal and pathologic tissues

The aim of this work was to validate an image analysis method, based on cell nuclei form factor determination, for counting fibroblasts within human dermis. We first used reconstructed dermal equivalents in which fibroblasts can also be counted directly after lysis of the collagen matrix. We found a good correlation between the results of direct counting and those of image analysis from day 10 to day 28 of culture. When applied to young normal donors' skin biopsies fixed in Bouin's solution and embedded in paraffin, the image analysis method yielded mid-dermis fibroblast counts of between 2100 and 4100 per mm3 of fresh tissue. A nuclear form factor (FF) comprised between 0.35 and 0.84 was found to be a biologic marker of fibroblasts. This was confirmed after fibroblast discrimination from other cell types, which had rounder nuclei (FF >/= 0.85) and were identified either by their location (e.g. endothelial cells) or by labeling with specific antibodies (e.g. lymphocytes and monocytes/macrophages). Similar results were obtained with seven healthy donors' skin biopsies that had been frozen in nitrogen liquid and cryostat-sectioned, showing that this counting method is independent of the histologic procedure. Finally, analysis of samples of hypertrophic scars from two patients revealed that fibroblast density in some parts of the dermis was more than twice the value found in other parts presenting a fibroblast density almost normal, showing that this cell counting method can also be used to assess fibroblast heterogeneity within a given tissue.

Long-term remodeling of a bilayered living human skin equivalent (Apligraf) grafted onto nude mice: immunolocalization of human cells and characterization of extracellular matrix

Type I collagen is a clinically approved biomaterial largely used in tissue engineering. It acts as a regenerative template in which the implanted collagen is progressively degraded and replaced by new cell-synthesized tissue. Apligraf, a bioengineered living skin, is composed of a bovine collagen lattice containing living human fibroblasts overlaid with a fully differentiated epithelium made of human keratinocytes. To investigate its progressive remodeling, athymic mice were grafted and the cellular and the extracellular matrix components were studied from 0 to 365 days after grafting. Biopsies were analyzed using immunohistochemistry with species-specific antibodies and electron microscopy techniques. We observed that this bioengineered tissue provided living and bioactive cells to the wound site up to 1 year after grafting. The graft was rapidly incorporated within the host tissue and the bovine collagen present in the graft was progressively replaced by human and mouse collagens. A normal healing process was observed, i.e., type III collagen appeared transiently with type I collagen, the major collagen isoform present at later stages. New molecules, such as elastin, were produced by the living human cells contained within the graft. This animal model combined with species-specific immunohistochemistry tools is thus very useful for studying long-term tissue remodeling of bioengineered living tissues.

Effect of fibroblasts on epidermal regeneration

BACKGROUND

There is little information on specific interactions between dermal fibroblasts and epidermal keratinocytes. The use of engineered skin equivalents consisting of organotypic cocultures of keratinocytes and fibroblasts offers an attractive approach for such studies.

OBJECTIVES

To examine the role fibroblasts play in generation and maintenance of reconstructed epidermis.

METHODS

Human keratinocytes were seeded on collagen matrices populated with increasing numbers of fibroblasts and cultured for 2 weeks at the air-liquid interface.

RESULTS

In the absence of fibroblasts, stratified epidermis with only three or four viable cell layers was formed. In the presence of fibroblasts, keratinocyte proliferation was stimulated and epidermal morphology was improved. Epidermal morphogenesis was also markedly improved in epidermis generated in organotypic keratinocyte monocultures grown in medium derived from dermal equivalents or from organotypic keratinocyte-fibroblast cocultures. These observations clearly indicate the proliferation-stimulating activity of soluble factors released from fibroblasts. Under all experimental conditions, onset of keratinocyte differentiation was shown by the expression of keratin 10 in all suprabasal cell layers. With increasing numbers of fibroblasts incorporated into the collagen matrix, the expression of markers associated with keratinocyte activation, e.g. keratins 6, 16 and 17 and the cornified envelope precursor SKALP decreased, and involucrin localization shifted toward the granulosum layer. This fibroblast-mediated effect was even more pronounced when the fibroblasts were precultured in the collagen matrices for 1 week instead of overnight. The basement membrane proteins collagen VII and laminin 5 were present at the epithelial-matrix border. The expression of integrin alpha 6 beta 4 and of E-cadherin was comparable with that seen in native skin and was not significantly modulated by fibroblasts. Under all experimental conditions the expression of integrin subunits alpha 2, alpha 3 and beta 1 was upregulated, indicating keratinocyte activation.

CONCLUSIONS

Our results illustrate that numbers of fibroblasts in the collagen matrix and their functional state is a critical factor for establishment of normal epidermal morphogenesis.

Production of ordered collagen matrices for three-dimensional cell culture

The aim of this study was to produce collagen gels with controlled fibrillar order as matrices for cell culture. Their structural characterization and colonization by human dermal fibroblasts arc presently reported. Ordered matrices are obtained by using the property of type I collagen monomers to self-assemble in liquid crystalline arrays by slow evaporation of acidic solutions at high concentrations. Induction of fibrillogenesis concomittent with the stabilization of the supramolecular order is then obtained, within petri dishes, by gelation of the viscous preparations under ammoniac vapours. For comparison, dermal equivalents, in which collagen compaction depends on fibroblasts contraction, are made according to the method of Bell et al. (Proc. Natl. Acad. Sci. 76(3) (1979) 1274). The fibrillar arrangement of the collagen network in the samples is determined by polarizing optical microscopy and by transmission electron microscopy. Whereas dermal equivalents exhibit heterogeneous distributions of fibrils, two differents types of order are obtained in the stabilized liquid crystalline collagen samples, namely aligned, i.e. nematic, at 20 mg/ml, or crimped, i.e. precholesteric, at 40 mg/ml. The morphology and behaviour of fibroblasts seeded on the surface of the matrices are analysed from day 1 to day 21. The cells are viable, proliferate at the surface of ordered matrices and migrate up to 400 microm in depth. Production of concentrated and ordered collagen matrices provides new perspectives to study the behaviour of cells in a valorized three-dimensional context where the fibrillar organization becomes close to in vivo situations.

A study to evaluate primary dressings for the application of cultured keratinocytes

Despite the recent improvements in cell culture and dermal regeneration methods, tissue engineering of skin has yet to receive widespread acceptance in the management of burn injuries. The reasons for this are complex and include not only the inherent costs of (particularly) setting up and running such a system but also the continuing difficulties in achieving successful engraftment of the neoepidermis. The latter has previously been addressed in a number of ways, including improving the recipient bed and using pre-confluent delivery systems to allow earlier application of cells to that wound bed. One area that has received little attention is that of the optimal wound dressing to use with this technology; the cells are very poorly attached at early time points, and, in this context, the traditional dressing of paraffin gauze has never been formally assessed in comparison with newer materials. Using a porcine acute wound chamber model, we performed a prospective randomised trial to assess four different wound dressings with reference to the amount of epidermal cover gained and the histological quality of the regenerated skin after 3 weeks. Out of the four materials tested, polyurethane foam (Allevyn) was superior histologically (although equal in take rate with paraffin gauze), whilst polythene sheet (Opsite) and silicone sheet were substantially inferior. We conclude that the traditional dressing used with this technology should be compared with polyurethane foam in a clinical trial. In the future, novel dressings should be formally tested against traditional methods before being adopted.

Reconstructive surgery using an artificial dermis (Integra): results with 39 grafts

Integra was initially developed for the primary coverage of acute burns. It acts as a network for dermal reconstruction. An epidermal graft overlay is necessary after 3 weeks to achieve the in vivo reconstruction of a full-thickness skin equivalent. The quality of the functional and aesthetic results achieved led us to evaluate the potential of Integra in the treatment of burn scars and for general reconstructive surgery. We present a series of 31 patients who underwent Integra grafting for reconstructive surgery at a total of 39 operational sites. The average area grafted per procedure was 267 cm(2). Complications (silicone detachment, failure of the graft, haematoma) were observed in nine cases. The length of follow-up ranged from 0.5 year to 4 years. Two patients (two sites) were lost to follow-up; the final results in the remaining patients were considered to be good in 28 cases, average in six cases and poor in three cases. The disadvantages of using Integra in reconstructive surgery are the necessity of two operations, the risks of infection under the silicone layer, of the silicone becoming detached and of recurrence of contraction. On the other hand, Integra has many advantages including its immediate availability, the availability of large quantities, the simplicity and reliability of the technique, and the pliability and the cosmetic appearance of the resulting cover. In the light of these preliminary results, Integra appears as a new alternative to full-thickness skin grafting, skin expansion and even skin flaps for reconstructive surgery.

Collagen fibril network and elastic system remodeling in a reconstructed skin transplanted on nude mice

Wound healing of deep and extensive burns can induce hypertrophic scar formation, which is a detrimental outcome for skin functionality. These scars are characterized by an impaired collagen fibril organization with fibril bundles oriented parallel to each other, in contrast with a basket weave pattern arrangement in normal skin. We prepared a reconstructed skin made of a collagen sponge seeded with human fibroblasts and keratinocytes and grown in vitro for 20 days. We transplanted it on the back of nude mice to assess whether this reconstructed skin could prevent scar formation. After transplantation, murine blood vessels had revascularized one-third of the sponge thickness on the fifth day and were observed underneath the epidermis at day 15. The reconstructed skin extracellular matrix was mostly made of human collagen I, organized in loosely packed fibrils 5 days after transplantation, with a mean diameter of 45 nm. After 40-90 days, fibril bundles were arranged in a basket weave pattern while their mean diameter increased to 56 nm, therefore exactly matching mouse skin papillary dermis organization. Interestingly, we showed that an elastic system remodeling was started off in this model. Indeed, human elastin deposits were organized in thin fibrils oriented perpendicular to epidermis at day 90 whereas elastic system usually took years to be re-established in human scars. Our reconstructed skin model promoted in only 90 days the remodeling of an extracellular matrix nearly similar to normal dermis (i.e. collagen fibril diameter and arrangement, and the partial reconstruction of the elastic system).

Grafting of large pieces of human reconstructed skin in a porcine model

Present techniques can save about 25% of patients burnt over more than 90% of their body surface. However, problems of functional and aesthetic repair arise, which are often resolved only by major therapeutic procedures. Current advances in skin substitutes permit the cultivation, from a skin biopsy, of large surfaces of in vitro human reconstructed skin (HRS). Our model, obtained by the co-culture of fibroblasts and keratinocytes on a dermal substrate composed of collagen-glycosaminoglycan-chitosan, reproduces, in vitro, a tissue close to human skin, which could play a role in reconstructive surgery. The objectives of this experiment were to assess whether it is possible to perform large HRS grafts and to evaluate the preliminary cosmetic results. We used four immunosuppressed female pigs. Full-thickness skin resections of 50-100 cm(2)were performed on the dorsa of the animals. The defects were grafted with between one and six pieces of HRS under tied-over dressings. At day 14, we found a soft and smooth surface of good transparent healthy pink skin, which was very easy to distinguish from the surrounding tissues. The junctions between different pieces of living skin were not visible. Immunohistological studies with specific anti-human keratin 14 antibodies confirmed the graft take: 7 days after grafting the human epidermis was attached to the living dermis and showed good organisation with a basal cell layer and suprabasal cells; 28 days after grafting the human epidermis seemed to be replaced by pig epidermis. This study highlights the possibility of grafting large surfaces with HRS using a routine operating technique.

An improved and rapid method to construct skin equivalents from human hair follicles and fibroblasts

To produce sufficient amounts of high quality skin equivalents (SE), either allogenic for dermatopharmacological and dermatotoxicological studies or autologous for transplantation purposes, we established a rapid, easy and cost effective three-dimensional SE model on the basis of human dermal fibroblasts, collagen and freshly plucked hair follicles. Acidic liquid collagen was polymerized with sodium hydroxide in the presence of fibroblasts to form a dermal equivalent (DE) resembling normal human dermis. At 24 h later, freshly plucked hair follicles were implanted into the surface of these DEs after cutting their bulbs off. Another 48 h later, the surface of the SEs was lifted to the air-liquid interface. Fourteen days after implantation, outgrowing keratinocytes from the outer root sheath of the hair follicles completely covered the surface of the SE and built a fully developed, multi-layered and cornified epidermis. Histology and immunofluorescence studies with specific antibodies directed against components of keratinocytes, fibroblasts, cell-adhesion molecules, different extracellular matrix and basement membrane proteins revealed the similarity of our three-dimensional SEs to the in vivo situation in normal human skin. Using autologous cell sources and cell culture media enriched with serum from the respective cell donor, it will be possible to use these SEs for autologous transplantation, thereby reducing the risk of transplant rejection.

Development of composite cultured oral mucosa utilizing collagen sponge matrix and contracted collagen gel: a preliminary study for clinical applications

A new type of cultured mucosa was developed as a mucosal substitute. This composite cultured oral mucosa (CCOM) was composed of (1) a lamina propria in which fibroblasts were embedded in contacted collagen gel and honeycomb structured collagen sponge and (2) stratified epithelial cell layers on the surface of the cultured lamina propria. CCOM had a well-stratified and differentiated epithelial cell layer, and its involucrin and laminin expression resembled that of normal oral mucosa. Desmosomes were recognizable with transmission electron microscopic examination. In the lamina propria, contracted collagen gel had pooled away from the sponge wall, leaving a sparse structure inside the collagen sponge. Transplantation of CCOM to nude mice was performed by creating full-thickness wound and then applying CCOM (n = 12). Murine skin allograft (n = 4) and no-graft conditions (n = 5) served as controls. The mice were sacrificed for histological evaluation and assessed for wound contraction 28 days after transplantation. The epithelium of the CCOM-treated group had five to 10 cell layers, and the dermis contained many fibroblasts and a large amount of collagen bundles. The wound contraction of the CCOM-treated group was statistically less than that of the no-graft group. These results indicate that CCOM has barrier functions against various stresses and can induce a fibrovascular ingrowth from the surrounding wound bed, and that CCOM could be applied in a clinical setting.

Long-term regeneration of human epidermis on third degree burns transplanted with autologous cultured epithelium grown on a fibrin matrix

BACKGROUND

Extensive third degree burn wounds can be permanently covered by the transplantation of autologous cultured keratinocytes. Many modifications to Green and colleagues' original technique have been suggested, including the use of a fibrin matrix. However, the properties of the cultured cells must be assessed using suitable criteria before a modified method of culture for therapeutic purposes is transferred to clinical use, because changes in culture conditions may reduce keratinocyte lifespan and result in the loss of the transplanted epithelium.

METHODS

To evaluate the performances of human keratinocytes grown on a fibrin matrix, we assay for their colony-forming ability, their growth potential and their ability to generate an epidermis when grafted onto athymic mice. The results of these experiments allowed us to compare side by side the performance for third degree burn treatment of autologous cultured epithelium grafts grown according to Rheinwald and Green on fibrin matrices with that of grafts grown directly on plastic surfaces.

RESULTS

We found that human keratinocytes cultured on a fibrin matrix had the same growth capacity and transplantability as those cultured on plastic surfaces and that the presence of a fibrin matrix greatly facilitated the preparation, handling, and surgical transplantation of the grafts, which did not need to be detached enzymatically. The rate of take of grafts grown on fibrin matrices was high, and was similar to that of conventionally cultured grafts. The grafted autologous cells are capable of generating a normal epidermis for many years and favor the regeneration of a superficial dermis.

CONCLUSION

We have demonstrated that: 1) fibrin matrices have considerable advantages over plastic for the culture of skin cells for grafting and that it is now possible to generate and transplant enough cultured epithelium from a small skin biopsy to restore completely the epidermis of an adult human in 16 days; and 2) the generated epidermis self-renews itself for years. The use of fibrin matrices thus significantly improves the transplantation of cultured epithelium grafts for extensive burns as recently demonstrated in a follow-up work.

Artificial skin

The skin is a complex organ that is difficult to replace when it is irreversibly damaged by burns, trauma, or disease. Although autologous skin transplantation remains the most common form of treatment in patients with significant skin loss, there are now a number of commercially available products that can be used to replace the skin temporarily or permanently. Here we describe several such products under the rubric "artificial skin," focusing on two types of technology that have been applied to the problem of permanent skin replacement.

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.

Novel living skin replacement biotherapy approach for wounded skin tissues

A novel living skin replacement (LSR) biotherapy concept, addressing the challenging problems related to tissue regeneration and wound healing, is presented for the treatment of skin burns, traumatic injuries and ulcerations. LSR combines elements of cell therapy along with those of tissue engineering to allow for the regeneration of wounded skin. It takes advantage of biodegradable microspheres onto which donor skin epidermal and dermal cells can be attached and expanded in vitro for subsequent direct application down to the deepest recesses of the wound bed. The key element of the biotherapy is the ability of the skin cells to migrate freely from the microspheres into the wound for regeneration of the tissues. The large surface to volume ratio of the microspheres allows for the delivery of appropriate cell numbers while minimizing the amount of biomaterial to be resorbed. This novel approach presents a number of advantages over existing therapies including facilitated cell manipulations, ease of storage and transportation, rapid clinical intervention due to the elimination of any surgical suturing or stapling, and a more natural three-dimensional tissue remodeling and anatomical compliance. Preliminary in vitro and in vivo evidence of the LSR functionality and its potential benefits is presented.