Living skin substitutes: survival and function of fibroblasts seeded in a dermal substitute in experimental wounds

Quantitative analysis of cell adhesion on aligned micro- and nanofibers

In this study, we quantitatively analyzed the affinity of cell adhesion to aligned nanofibers composed of composites of poly(glycolic acid) (PGA) and collagen. Electrospun composite fibers were fabricated at various PGA/collagen weight mixing ratio (7, 18, 40, 67, and 86%) to generate fibers that ranged in diameter from 10 mum to 500 nm. Scanning electron microscopy (SEM) observation revealed that the PGA/collagen fibers were long and uniformly aligned, irrespective of the PGA/collagen weight mixing ratio. In addition, it was observed that a significantly higher number of NIH3T3 fibroblasts adhered to nanofibers with smaller diameters in comparison to fibers with larger diameters. The highest affinity of cell adhesion was observed in the PGA/collagen fibers with diameter of 500 nm and PGA/collagen weight mixing ratio of 40%. Furthermore, the adherent cells were more elongated on fibers with smaller diameters. Thus, based on the results here, PGA/collagen composite fibers are suitable for tissue culture studies and provide an attractive material for tissue engineering applications.

High yields of autologous living dermal equivalents using porcine gelatin microbeads as microcarriers for autologous fibroblasts

Permanent skin replacement requires a dermal component to ensure adequate long-term graft stability and to prevent wound contraction. This study was to construct a bioreactor microcarrier cell culture system (Bio-MCCS) to produce autologous living dermal equivalents on a large scale. Autologous fibroblasts were isolated from split-thickness skin biopsy from a leg ulcer patient, inoculated onto macroporous porcine gelatin microbeads, and incubated in a bioreactor (Cellspin) in serum-free fibroblast growth medium or in DMEM medium containing 10% fetal calf serum (FCS). Fibroblasts rapidly adhered to and actively proliferated on the microbeads in the bioreactor in both serum-free and serum-containing medium. MTT assay showed the number of fibroblasts on the microbeads reached up to 5.3- or 4.0-fold the cells seeded in DMEM medium containing 10% FCS or serum-free medium, respectively. When removed from Bio-MCCS and cultured under static conditions, fibroblasts were able to leave the microbeads and proliferate to confluence on the bottom of tissue culture flasks. When stored at room temperature in DMEM containing 10% FBS, fibroblast cultured on the microbeads retained highest viabilities for at least 3 weeks, up to 82% of originals. This Bio-MCCS using porcine gelatin microbeads as carriers for fibroblasts offers a new option of mass production of autologous living dermal equivalents.

Impact of Transforming Growth Factor-β1 on Atrioventricular Node Conduction Modification by Injected Autologous Fibroblasts in the Canine Heart

Background— Atrioventricular (AV) nodal ablation for management of atrial fibrillation (AF) is irreversible and requires permanent pacemaker implantation. We hypothesized that as an alternative, implantation of autologous fibroblasts in the perinodal region would focally modify AV nodal conduction and that this modulation would be enhanced by pretreatment with transforming growth factor-β1 (TGF-β1), a stimulant of fibroblasts.

Methods and Results— Skin biopsies were taken from 12 mongrel dogs, and derived fibroblasts were dissociated and grown in culture for 2 weeks. Multiple injections (0.25 mL) were made through an 8F NOGA catheter along the fast/slow AV nodal pathways as guided by an electroanatomic mapping system. Seven dogs received fibroblasts alone (1×10 6 cells/mL), 7 dogs received TGF-β1 (5 μg), 4 dogs received fibroblasts and TGF-β1 (1×10 6 cells/mL+5 μg), and 4 dogs received saline only. AV node function was assessed at baseline and after 4 weeks. Saline (80 mL) with assigned therapy (0.25 mL per injection) was injected into the peri-AV nodal region in each dog. At baseline, the AH interval (66±3 ms) and the average RR interval (331±17 ms) in pacing-induced AF were similar in each cohort. The increase in AH interval in normal sinus rhythm was longer after fibroblast (23±4 versus 5±5 ms; P =0.05) and fibroblast plus TGF-β1 (50±5 versus 5±5 ms; P <0.001) injections than with saline alone, with similar findings during high right atrium and distal coronary sinus pacing. The AH interval was not significantly increased after TGF-β1 injections. The AH interval was significantly longer after fibroblast plus TGF-β1 injections than with either therapy (TGF-β1 or fibroblasts) alone. The RR interval during AF was increased in dogs that received fibroblasts alone (110±36 versus −41±34 ms) and to a greater extent with the addition of TGF-β1 (294±108 versus −41±34 ms). No AV block was seen in any cohort at 4 weeks. Labeled fibroblasts that expressed vimentin were identified in all dogs that received cell injections at 4 weeks.

Conclusions— AV nodal modification can be achieved with injected fibroblasts without the creation of AV block. The effect on AV node conduction is substantially enhanced by pretreatment of fibroblasts with TGF-β1. These data have therapeutic potential for the management of rapid ventricular rate during AF without pacemaker implantation.

Human CD46-transgenic mice in studies involving replication-incompetent adenoviral type 35 vectors

Wild-type strains of mice do not express CD46, a high-affinity receptor for human group B adenoviruses including type 35. Therefore, studies performed to date in mice using replication-incompetent Ad35 (rAd35) vaccine carriers may underestimate potency or result in altered vector distribution. Here, it is reported that CD46 transgenic mice (MYII-strain) express CD46 in all major organs and that it functions as a receptor for rAd35 vectors. Similar to monkeys and humans, MYII mice highly express CD46 in their lungs and kidneys and demonstrate low expression in muscle. Upon intravenous administration, rAd35 vector genomes as well as expression are detected in lungs of MYII mice, in contrast to wild-type littermates. Expression was predominantly detected in lung epithelial cells. Upon intramuscular administration, the initial level of luciferase expression is higher in MYII mice as compared with wild-type littermates, in spite of the fact that CD46 expression is low in muscle of MYII mice. The higher level of expression in muscle of MYII mice results in prolonged gene expression as assessed by CCD camera imaging for luciferase activity. Finally, a significant dose-sparing effect in MYII mice as compared with wild-type littermates on anti-SIVgag CD8+ T-cell induction following intramuscular vaccination with an rA35.SIVgag vaccine was observed. This dose-sparing effect was also observed when reinfusing dendritic cells derived from MYII mice after exposure to rAd35.SIVgag vaccine as compared with rAd35.SIVgag exposed dendritic cells from wild-type littermates. It was concluded that MYII mice represent an interesting preclinical model to evaluate potency and safety of rAd35 vectors.

Improved enzymatic isolation of fibroblasts for the creation of autologous skin substitutes

The number of medical applications using autologous fibroblasts is increasing rapidly. We investigated thoroughly the procedure to isolate cells from skin using the enzymatic tissue dissociation procedure. Tissue digestion efficiency, cell viability, and yield were investigated in relation to size of tissue fragments, digestion volume to tissue ratio, digestion time, and importance of other protease activities present in Clostridium histolyticum collagenase (CHC) (neutral protease, clostripain, and trypsin). The results showed that digestion was optimal with small tissue fragments (2-3 mm3) and with volumes tissue ratios > or =2 ml/g tissue. For incubations < or =10 h, the digestion efficiency and cell isolation yields were significantly improved by increasing the collagenase, neutral protease, or clostripain activity, whereas trypsin activity had no effects. However, a too high proteolytic activity of one of the proteases present in CHC digestion solution or long exposure times interfered with cell viability and cell culture yields. The optimal range of CHC proteases activities per milliliter digestion solutions was determined for digestions < or =10 h (collagenase 2700-3900 Mandl U/ml, neutral protease 5100-10,000 caseinase U/ml, and clostripain 35-48 BAEE U/ml) and for longer digestions (>14 h) (collagenase 1350- 3000 U/ml, neutral protease 2550-7700 U/ml, and clostripain 18-36 U/ml). Using these conditions, a maximum fibroblast expansion was achieved when isolated cells were seeded at 1 x 10(4) cells/cm2. These results did not only allow selection of optimal CHC batches able to digest dermal tissue with an high cell viability but also significantly increased the fibroblast yields, enabling us to produce autologous dermal tissue in a clinically acceptable time frame of 3 wk.

Viability and Function of Autologous and Allogeneic Fibroblasts Seeded in Dermal Substitutes after Implantation

BACKGROUND

Fibroblast-seeded collagen sponges have been used for the treatment of skin defects and skin ulcers. However, the viability of the fibroblasts after implantation is still unknown. The objective of this study was to investigate the viability and distribution of autologous and allogeneic fibroblasts after implantation and to clarify which type is more effective for wound healing.

MATERIALS AND METHODS

Skin samples of Hartley guinea pigs were retrieved and autologous fibroblasts were isolated and cultured. Fibroblasts isolated from the skin of a Strain2 guinea pig were used as allogeneic fibroblasts. Three full-thickness wounds were created on the backs of guinea pigs and an acellular collagen sponge, a collagen sponge seeded with autologous fibroblasts, and a collagen sponge seeded with allogeneic fibroblasts were transplanted. Before implantation, fibroblasts were labeled with PKH26. The guinea pigs were sacrificed 1, 2, and 3 weeks after implantation. The epithelization and contraction of the wounds were assessed, and the viability and distribution of the seeded fibroblasts were observed in cross sections.

RESULTS

Three weeks after implantation, the PKH26-labeled autologous and allogeneic fibroblasts remained viable. In the wounds covered with the autologous fibroblast-seeded collagen sponge, the epithelization was fastest, and the percent wound contraction was smallest. In contrast, in the wounds covered with allogeneic fibroblasts, the epithelization was slowest and the percent contraction was largest.

CONCLUSION

The allogeneic fibroblasts seeded in the collagen sponge survived and remained viable on the grafted area, but did not accelerate wound healing.

Synthetic scaffold morphology controls human dermal connective tissue formation

Engineering tissues in bioreactors is often hampered by disproportionate tissue formation at the surface of scaffolds. This hinders nutrient flow and retards cell proliferation and tissue formation inside the scaffold. The objective of this study was to optimize scaffold morphology to prevent this from happening and to determine the optimal scaffold geometric values for connective tissue engineering. After comparing lyophilized crosslinked collagen, compression molded/salt leached PEGT/PBT copolymer and collagen-PEGT/PBT hybrid scaffolds, the PEGT/PBT scaffold was selected for optimization. Geometric parameters were determined using SEM, microcomputed tomography, and flow permeability measurements. Fibroblast were seeded and cultured under dynamic flow conditions for 2 weeks. Cell numbers were determined using CyQuant DNA assay, and tissue distribution was visualized in H&E- and Sirius Red-stained sections. Scaffolds 0.5 and 1.5 mm thick showed bridged connected tissue from top-to-bottom, whereas 4-mm-thick scaffolds only revealed tissue ingrowth until a maximum depth of 0.6-0.8 mm. Rapid prototyped scaffold were used to assess the maximal void space (pore size) that still could be filled with tissue. Tissue bridging between fibers was only found at fiber distances < or =401 +/- 60 microm, whereas filling of void spaces in 3D-deposited scaffolds only occurred at distances < or =273 +/- 55 microm. PEGT/PBT scaffolds having similar optimal porosities, but different average interconnected pore sizes of 142 +/- 50, 160 +/- 56 to 191 +/- 69 microm showed comparable seeding efficiencies at day 1, but after 2 weeks the total cell numbers were significantly higher in the scaffolds with intermediate and high interconnectivity. However, only scaffolds with an intermediate interconnectivity revealed homogenous tissue formation throughout the scaffold with complete filling of all pores. In conclusion, significant amount of connective tissue was formed within 14 days using a dynamic culture process that filled all void spaces of a PEGT/PBT scaffolds with the following geometric parameters: thickness 1.5-1.6 mm, pore size range 90-360 microm, and average interconnecting pore size of 160 +/- 56 microm.

Modulation of scar tissue formation using different dermal regeneration templates in the treatment of experimental full-thickness wounds

The recovery of skin function is the goal of each burn surgeon. Split-skin graft treatment of full-thickness skin defects leads to scar formation, which is often vulnerable and instable. Therefore, the aim of this study was to analyze wound healing and scar tissue formation in acute full-thickness wounds treated with clinically available biopolymer dermal regeneration templates. Full-thickness wounds (3 x 3 cm) on both flanks of Gottingen mini pigs (n= 3) were treated with split-thickness skin graft alone or in combination with a 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide (EDC) cross-linked-collagen scaffold, Integra, or a polyethyleneglycol terephthalate-polybutylene terephthalate (PEGT/PBT) scaffold. The wounds (n= 12 per group) were examined weekly for six weeks to evaluate graft take, contraction (planimetry), and cosmetic appearance. Histologic samples taken after one and six weeks were used to assess scaffold angiogenesis, biocompatibility, and scar tissue quality. In all wounds, one week postwounding graft take was between 93 and 100 percent. The control wound, treated with split-skin graft, showed little granulation tissue formation, whereas the EDC-collagen treated wounds showed two to three times more granulation tissue formation. The collagen scaffold was completely degraded within one week. The Integra and PEGT/PBT scaffolds showed angiogenesis only through two-thirds of the scaffold, which resulted in loss of integrity of the epidermis. Only basal cells survived, proliferated, and regenerated a fully differentiated epidermis within three weeks. Granulation thickness was comparable to collagen scaffold-treated wounds. After six weeks, control wounds showed a wound contraction of 27.2 +/- 6.1 percent, Integra-treated wounds 34.6 +/- 6.4 percent, collagen scaffold-treated wounds 38.1 +/- 5.0 percent, and PEGT/PBT scaffold-treated wounds 54.5 +/- 3.9 percent. The latter wounds had significantly more contraction than wounds of other treatment groups. Microscopically, the control and collagen scaffold-treated wounds showed an immature scar tissue that was two times thicker in the EDC-collagen treated wounds. The Integra-treated wounds showed nondegraded collagen scaffold fibers with partly de novo dermal tissue formation and partly areas with giant cells and other inflammatory cells. The PEGT/PBT scaffold was almost completely degraded. Scaffold particles were phagocytosized and degraded intracellularly by clusters of macrophages. The scar tissue was in the early phase of ECM remodeling. In conclusion, this study showed that the rate of dermal tissue formation and scarring is influenced by the rate of scaffold angiogenesis, degradation, and host response induced by the scaffold materials.

Upside-down transfer of porcine keratinocytes from a porous, synthetic dressing to experimental full-thickness wounds

Currently, the use of cultured epithelial autografts as an alternative to split-thickness skin autografts for coverage of full-thickness wounds is limited due to fragility of the sheet and variability in the outcome of healing. This could be circumvented by the transfer of proliferating keratinocytes, instead of differentiated sheets, to the wound bed and the "in vivo" regeneration of epidermis. The aim of this study was to achieve re-epithelialization on experimental full-thickness wounds in the pig using a porous, synthetic carrier seeded with proliferating keratinocytes. Porcine keratinocytes were isolated by enzymatic digestion and cultured in Optimem basal medium with mitogens. In a full-thickness wound model, carriers with different seeding densities were transplanted upside down onto the wound bed. Keratinocytes were labeled using a fluorescent red membrane marker, PKH-26 GL. Transfer of keratinocytes and re-epithelialization were recorded macroscopically and histologically. On day 4 after transplantation, transfer of fluorescently labeled keratinocytes was shown by their presence in the granulation tissue. An immature epidermis, as well as epithelial cords and islands, formed as early as day 8. At day 12 a stratified epidermis and wound closure were established and epithelial cysts were formed by differentiation of epithelial islands. Wounds treated with seeding densities as low as 50,000 cells/cm(2) showed wound closure within 12 days, whereas wounds treated with 10,000 cells/cm(2) or the nonseeded (acellular) carriers did not show complete re-epithelialization before day 17 after treatment. This study showed that porcine keratinocytes, transplanted "upside down" in experimental full-thickness wounds using a synthetic carrier, continued to proliferate and started to differentiate, enabling the formation of a new epidermis in a time frame of 12 days.

The role of allogenic fibroblasts in an acute wound healing model

Skin is the first tissue-engineered organ to have been successfully developed in the laboratory, and it has been clinically available for use as epidermal sheets for some time. As refinements in this field of tissue engineering continue, several key issues give cause for concern. One issue is the need to form a more complete dermal analogue before grafting. To this end, fibroblasts may be used in vitro to deposit extracellular matrix components within a basic scaffold, laying down those molecules not endogenous to the material and thereby improving the quality of the skin replacement. Many studies have shown the benefits of in vitro seeding with fibroblasts, but there has been some debate regarding the longevity of such cells after allotransplantation into an immunocompetent host. In this study, the authors set out to determine the longevity of transplanted cells in an immunocompetent porcine model. A total of 24 wounds were made on four female animals, 12 of which were covered with acellular hyaluronic acid dermal matrices, and the remainder of which were covered with matrices seeded with allogenic (male) fibroblasts. After a week in vivo, the wounds were grafted with either split-thickness skin grafts or cultured epithelial autograft. Biopsy specimens were obtained from wounds at varying time intervals and assessed using genetic analysis to determine the survival of allotransplanted cells. No cells were detectable by polymerase chain reaction analysis (sensitivity, 1:100,000) after 7 days in vivo. Subsequent histologic examination demonstrated little difference in wound morphology. The authors conclude that allogenic fibroblasts do not survive transplantation in a porcine wound model.

Porcine wound models for skin substitution and burn treatment

Skin regeneration is an important field of tissue engineering. Especially in larger burns and chronic wounds, present treatments are insufficient in preventing scar formation and promoting healing. Initial screening of potentially interesting products for skin substitution is usually done by in vitro tests. Before entering the clinic, however, in vivo studies in immunocompetent animals are necessary to prove efficacy and provide information on safety aspects. We have obtained extensive experience using the domestic pig as test animal for studies on skin replacement materials, including tissue engineered skin substitutes, and burn wound treatment. Two models are described: an excisional wound model for testing of dermal and epidermal substitutes and a burn wound model for contact and scald burns, which allows testing of modern wound dressings in comparison to the present gold standards in burn treatment. The results of these experiments show that in vivo testing was able to reveal (dis)advantages of the treatments which were not detected during in vitro studies.

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.

Nerve regeneration in a collagen-chitosan tissue-engineered skin transplanted on nude mice

A reconstructed skin made of a collagen-chitosan sponge seeded with human fibroblasts and keratinocytes and grown in vitro for 31 days was developed for the treatment of deep and extensive burns. The aim of this study was to assess whether this tissue-engineered skin could promote nerve regeneration in vivo, since recovery of sensation is a major concern for burnt patients. The human reconstructed skin was transplanted on the back of nude mice and the growth of nerve fibres within it was assessed 40, 60, 90 and 120 days after graft. Nerve growth was monitored by confocal microscopy using immunohistochemical staining of PGP 9.5 and 150 kD neurofilament, while Schwann cell migration was observed using protein S100 expression and laminin deposition. Nerve growth was first detected 60 days after transplantation and was more abundant 90 and 120 days after graft. Linear arrangements of Schwann cells were observed in the graft as early as 40 days after graft. Nerve growth was observed along these Schwann cell extensions 60 days after transplantation. We conclude that the three-dimensional architecture of the collagen-chitosan tissue-engineered skin sponge encourages nerve growth. This result provides new perspectives to increase nerve regeneration within the tissue-engineered skin by linkage of neurotrophic factors in the sponge before transplantation.

Allogeneic fibroblasts in dermal substitutes induce inflammation and scar formation

In the present study, we compared the use of autologous versus allogeneic fibroblasts in dermal skin substitutes in a porcine wound model. The allogeneic fibroblast populations were isolated from female and a male pig (allo-1, - 2 and - 3) and the controls, autologous fibroblasts, from female graft-recipient pigs (control). The histocompatibility of the three donor pigs with the recipient pigs was determined with a mixed lymphocyte reaction. In two pigs, full-thickness wounds were treated with the fibroblast-seeded dermal substitutes (n = 5 per animal) and immediately overgrafted with meshed split-skin autografts. After 6 weeks, wound contraction was measured by planimetry and scar formation was scored. At 2, 4, and 6 weeks biopsies were taken and evaluated for the presence of inflammatory reactions, myofibroblasts, and scar formation. The mixed lymphocyte reaction of both recipient pigs showed the highest responses on peripheral blood mononuclear cells of the allo-3 donor pig, and was low or negative for allo-1 and allo-2. In all "allogeneic" wounds, more inflammatory cells were observed over time along with inflammatory foci consisting of a mix of lymphocytes and granulomatous cells. After 4 weeks, myofibroblasts were absent in the control wounds, whereas in "allogeneic" wounds, myofibroblasts colocalized with inflammation foci. The final scar tissue of the "allogeneic" wounds showed granulating areas with thin, immature collagen bundles. In contrast, the control wounds showed a dermal tissue with mature collagen bundles organized randomly like in normal skin. The wounds treated with allo-3 fibroblasts showed in both pigs a significant increase in scar formation and wound contraction when compared with control wounds. In conclusion, for optimal restoration of dermal skin function with minimal scar formation, skin substitutes containing autologous fibroblasts are preferred over skin substitutes with allogeneic fibroblasts.

Exploiting the natural diversity in adenovirus tropism for therapy and prevention of disease

Since targeting of recombinant adenovirus vectors to defined cell types in vivo is a major challenge in gene therapy and vaccinology, we explored the natural diversity in human adenovirus tissue tropism. Hereto, we constructed a library of Ad5 vectors carrying fibers from other human serotypes. From this library, we identified vectors that efficiently infect human cells that are important for diverse gene therapy approaches and for induction of immunity. For several medical applications (prenatal diagnosis, artificial bone, vaccination, and cardiovascular disease), we demonstrate the applicability of these novel vectors. In addition, screening cell types derived from different species revealed that cellular receptors for human subgroup B adenoviruses are not conserved between rodents and primates. These results provide a rationale for utilizing elements of human adenovirus serotypes to generate chimeric vectors that improve our knowledge concerning adenovirus biology and widen the therapeutic window for vaccination and many different gene transfer applications.

Cultured autologous fibroblasts augment epidermal repair

BACKGROUND

Autologous dermal fibroblasts may be useful in the treatment of skin wounds and for the enhancement of keratinocyte proliferation. This paper addressed the following questions: (1) can cultured fibroblasts (CF) be transplanted as suspensions to full-thickness skin wounds and do they influence wound healing; (2) will the transplanted CF be integrated into the new dermis; (3) can a transgene that encodes a secretable marker, human epidermal growth factor (hEGF), be expressed in the wound fluid by the transplanted CF; and (4) do CF cotransplanted with cultured keratinocytes (CK) influence the rate of wound healing?

METHODS

Suspensions of CF were transplanted alone or together with CK to full-thickness wounds covered with liquid-containing chambers in an established porcine model.

RESULTS

Transplantation of CF accelerated reepithelialization as determined from wound histologies and sequential measurements of protein efflux over the wound surface. CF transfected with a marker gene, beta-galactosidase, resulted in in vivo gene expression and demonstrated that transplanted CF integrated into the developing dermis. Transplantation of hEGF gene-transfected CF resulted in significant hEGF expression in wound fluid. The hEGF levels peaked at day 1 (2450 pg/ml) and then sharply decreased to low levels on day 6. CF cotransplanted with CK led to greater number of keratinocyte colonies in the wound and accelerated reepithelialization as compared with CK alone.

CONCLUSIONS

Transplanted CF integrated into the dermis, accelerated reepithelialization, and improved the outcome of CK transplantation. CF may also be used for the expression of transgenes in wound and wound fluid.

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).

Innocuousness and intracellular distribution of PKH67: a fluorescent probe for cell proliferation assessment

PKH dyes were initially developed by Horan et al. to provide appropriate probes for in vitro and in vivo cell tracking. It has been reported for many cell types that PKH bind irreversibly to the cell membrane without significantly affecting cell growth. Thus, these probes provide an opportunity for long-term cell monitoring and the identification of cells of interest among a heterogeneous cell population. An important feature is that upon cell division, the probe is partitioned equally between each daughter cell, making it possible to quantify tell fluorescence by flow cytometry. In this situation. the flow cytometric study of PKH67 characteristics shows that this probe does not affect the main cell-functions such as viability or proliferation. Moreover, the intracellular distribution of PKH67 is demonstrated by following its kinetics of internalization by confocal microscopy. These results present PKH67 as a probe suitable for dynamic analysis of cell proliferation as well as the study of intracellular localization and membrane recycling mechanisms.

In vitro characterization of an artificial dermal scaffold

The treatment of extensive burn injuries has been enhanced by the development of artificial skin substitutes. Integra Artificial Skin, an acellular collagen-glycosaminoglycan (C-GAG) dermal equivalent requires a two-stage grafting procedure. However, preseeding the C-GAG dermal equivalent with cultured fibroblasts and keratinocytes, with the aim of performing a single-stage grafting procedure, may be beneficial in terms of replacing the requirement for traditional split-skin grafts. In this comparative in vitro study, the interactions of cultured human dermal fibroblasts and epidermal keratinocytes in Integra Artificial Skin in comparison to cadaver deepidermalized dermis (DED) was investigated. An increase in cell proliferation and migration in the C-GAG dermal equivalent was observed over time. Cocultures of fibroblasts and keratinocytes on both dermal equivalents showed positive expression of proliferation, differentiation, and extracellular matrix (ECM) protein markers. Organization of keratinocytes in the epidermal layers of DED composites were better compared to the C-GAG composites. Deposition of ECM proteins was enhanced in the presence of keratinocytes in both dermal equivalents. Results demonstrate that in vitro the C-GAG dermal equivalent is biocompatible for cell attachment, migration, proliferation, and differentiation. Preseeding Integra Artificial Skin with cultured autologous fibroblasts and keratinocytes for in vivo application, as a single-stage grafting procedure, warrants testing. A better clinical outcome may be achieved as shown by our in vitro results of the coculture composites.

Autologous keratinocyte suspensions accelerate epidermal wound healing in pigs

BACKGROUND

Tissue culture techniques enable in vitro expansion of keratinocytes that can be used to treat burns and chronic wounds. These keratinocytes are commonly grafted onto the wounds as differentiated sheets of mature epithelium. Less is however known about the effects of transplanting the cells as suspensions. This study evaluated epidermal regeneration in fluid-treated skin wounds treated with suspensions of cultured and noncultured autologous keratinocytes.

MATERIALS AND METHODS

Eighty-seven full-thickness excisional skin wounds were created on the back of 6 pigs and then transplanted with either cultured or noncultured autologous keratinocytes. The wounds were enclosed with liquid-tight chambers containing saline to provide a hydrated and standardized environment.

RESULTS

Keratinocyte transplantation resulted in several cell colonies within the granulation tissue of the wound. These colonies progressively coalesced and contributed to a new epithelium. The origin of the transplanted keratinocytes was confirmed by histochemical staining of wounds transplanted with transfected keratinocytes expressing beta-galactosidase. Transplantation of 0.125 x 10(6), 0.5 x 10(6), and 2.0 x 10(6) cultured keratinocytes, and 0.5 x 10(6) and 5.0 x 10(6) noncultured keratinocytes, increased reepithelialization dose dependently over saline-treated controls. The epithelial barrier function recovered faster in transplanted wounds as demonstrated by less protein leakage over the wound surface on Days 7-10 as compared to control wounds. Wound reepithelialization and the number of keratinocyte colonies observed in granulation tissue were significantly less in wounds transplanted with noncultured keratinocytes compared to wounds seeded with cultured keratinocytes.

CONCLUSION

Our study demonstrates successful transplantation of keratinocyte suspensions and their dose-dependent acceleration of wound repair. Selection of proliferative cells during culture and higher colony-forming efficiency may explain the greater effects observed with cultured keratinocytes.

In vivo cultured skin composed of two-layer collagen sponges with preconfluent cells

Although various kinds of cultured skin substitutes have been developed, it takes several weeks to produce them before grafting. In their previous study, the authors succeeded in producing cultured skin easily in a short period of time by layering two collagen sponges. In the current study, to shorten this period even further, they grafted the cell-preconfluent artificial skin immediately after seeding the cells. They used two collagen sponges with different pore sizes and crosslink densities. They seeded 1,000,000 cells per square centimeter of fibroblasts and 1,000,000 cells per square centimeter of keratinocytes on the respective collagen sponges and grafted them on a full-thickness, excised wound on the back of severe combined immunodeficient mice. Two weeks after grafting, epithelium and dermislike tissue were formed. They then decreased the number of keratinocytes and grafted them. Four weeks after grafting, at seeding densities of 50,000 to 1,000,000 cells per square centimeter of keratinocytes, the preconfluent artificial skin took histologically, and human type IV and type VII collagen were stained immunohistochemically. This cell-preconfluent artificial skin composed of two-layer collagen sponges seems promising for widespread clinical use.

Dermal fibroblasts do not enhance the graft take rate of autologous, cultured keratinocyte suspension on full-thickness wounds in rats

Dermal fibroblasts are known to play an important role in wound healing. In this study, cultured autologous keratinocyte suspension was applied with fibrin glue to the full-thickness wounds in rats (N = 20). Histological analysis on day 14 showed regenerated epithelium in 10 wounds (50%). Keratinocytes were also premixed with allogeneic dermal fibroblasts in a ratio of 3:1 and 5:1 before application to other full-thickness wounds (N = 20) with fibrin glue. Regeneration of epithelium was observed in 10 (50%) and 9 (45%) wounds respectively. Acute inflammatory reaction and mild to moderate proliferation of fibroblasts in the subepithelial layer of the allogeneic fibroblasts were noted. The addition of dermal fibroblasts to keratinocytes/fibrin glue does not enhance the take rate of the cultured keratinocyte suspension.

Higher numbers of autologous fibroblasts in an artificial dermal substitute improve tissue regeneration and modulate scar tissue formation

Cultured skin substitutes are increasingly important for the treatment of burns and chronic wounds. The role of fibroblast numbers present in a living-skin equivalent is at present unknown. The quality of dermal tissue regeneration was therefore investigated in relation to the number of autologous fibroblasts seeded in dermal substitutes, transplanted instantaneously or precultured for 10 days in the substitute. A full-thickness porcine wound model was used to compare acellular dermal substitutes (ADS) with dermal substitutes seeded with fibroblasts at two densities, 1x10(5) (0-DS10) and 5x10(5) cells/cm(2) (0-DS50), and with dermal substitutes seeded 10 days before operation at the same densities (10-DS10 and 10-DS50) (n=7 for each group, five pigs). After transplantation of the dermal substitutes, split-skin mesh grafts were applied on top. Wound healing was evaluated blind for 6 weeks. Cosmetic appearance was evaluated and wound contraction was measured by planimetry. The wound biopsies taken after 3 weeks were stained for myofibroblasts (alpha-smooth muscle actin), and after 6 weeks for scar tissue formation (collagen bundles organized in parallel and the absence of elastin staining). Collagen maturation was investigated with polarized light. For wound cosmetic parameters, the 10-DS50 and 0-DS50 treatments scored significantly better than the ADS treatment, as did the 10-DS50 treatment for wound contraction (p<0.05, paired t-test). Three weeks after wounding, the area with myofibroblasts in the granulation tissue, determined by image analysis, was significantly smaller for 0-DS50, 10-DS10, and 10-DS50 than for the ADS treatment (p<0.04, paired t-test). After 6 weeks, the wounds treated with 0-DS50, 0-DS10, and 10-DS50 had significantly less scar tissue and significantly more mature collagen bundles in the regenerated dermis. This improvement of wound healing was correlated with the higher numbers of fibroblasts present in the dermal substitute at the moment of transplantation. In conclusion, dermal regeneration of experimental full-skin defects was significantly improved by treatment with dermal substitutes containing high numbers of (precultured) autologous fibroblasts.