Single-Cell Suspensions of Cultured Human Keratinocytes in Fibrin–Glue Reconstitute the Epidermis

Growth factors IGF-1 and KGF and adipose-derived stem cells promote migration and viability of primary human keratinocytes in an in vitro wound model

Introduction

In the field of plastic surgery, epidermal transplantation is a potential treatment for chronic wounds that results in only minor donor site morbidity. Improving the regenerative capacities of epidermal grafts or single-cell suspensions and therefore accelerating healing processes would be of significant interest.

Methods

In the present study, we analyzed the effects of growth factors and adipose-derived stem cells (ADSCs) on keratinocyte properties. For optimum translation into the clinical setting, primary human keratinocytes and patient-matched ADSCs were isolated and used in an in vitro wound model.

Results

The keratinocyte migration and viability increased after treatment with the growth factors insulin-like growth factor 1 (IGF-1) and keratinocyte growth factor (KGF). A similar effect was observed with the use of a concentrated ADSC-conditioned medium (ADSC-CM). It was further possible to isolate the keratinocytes in a xenogen-free medium, which is essential for clinical translation. Importantly, a patient-dependent influence on the effects of the growth factors and ADSC-CM was observed.

Discussion

This study provides potential for the improvement of epidermal transplantation in the treatment of chronic wounds using xenogen-free isolated and cultivated keratinocytes, growth factors, and ADSC. Translating these results into clinical application may help accelerate wound healing and shorten the time until patients can return to everyday life.

Self-Organization of Long-Lasting Human Endothelial Capillary-Like Networks Guided by DLP Bioprinting

Tissue engineering holds great promise for regenerative medicine, drug discovery, and as an alternative to animal models. However, as soon as the dimensions of engineered tissue exceed the diffusion limit of oxygen and nutriments, a necrotic core forms leading to irreversible damage. To overcome this constraint, the establishment of a functional perfusion network is essential. In this work, digital light processing bioprinting is used to encapsulate endothelial progenitor cells (EPCs) in 3D light-cured hydrogel scaffolds to guide them toward vascular network formation. In these scaffolds, EPCs proliferate and self-organize within a few days into branched tubular structures with predefined geometry, forming capillary-like vascular tubes or trees of diameters in the range of 10 to 100 µm. Presenting a confluent monolayer wall of cells strongly connect by tight junctions around a central lumen-like space, these structures can be microinjected with a fluorescent dye and are stable for several weeks in vitro. These endothelial structures can be recovered and manipulated in an alginate patch without altering their shape or viability. This approach opens new opportunities for future applications, such as stacking with other cell sheets or multicellular constructs to yield bioengineered tissue with higher complexity and functionality.

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.

Evolution of a concept with enzymatic debridement and autologous in situ cell and platelet-rich fibrin therapy (BroKerF)

BACKGROUND

Deep partial-thickness burns are traditionally treated by tangential excision and split thickness skin graft (STSG) coverage. STSGs create donor site morbidity and increase the wound surface in burn patients. Herein, we present a novel concept consisting of enzymatic debridement of deep partial-thickness burns followed by co-delivery of autologous keratinocyte suspension and plated-rich fibrin (PRF) or fibrin glue.

MATERIAL AND METHODS

In a retrospective case study, patients with deep partial-thickness burns treated with enzymatic debridement and autologous cell therapy combined with PRF or fibrin glue (BroKerF) between 2017 and 2018 were analysed. BroKerF was applied to up to 15% total body surface area (TBSA); larger injuries were combined with surgical excision and skin grafting. Exclusion criteria were age <18 or >70 years, I°, IIa°-only, III° burns and loss of follow-up.

RESULTS

A total of 20 patients with burn injuries of 16.8% ± 10.3% TBSA and mean Abbreviated Burn Severity Score 5.45 ± 1.8 were identified. Of the patients, 65% (n = 13) were treated with PRF, while 35% (n = 7) were treated with fibrin glue. The mean area treated with BroKerF was 7.5% ± 0.05% TBSA, mean time to full epithelialization was 21.06 ± 9.2 days and mean hospitalization time was 24.7 ± 14.4 days. Of the patients, 35% (n = 7) needed additional STSG, 43% (n = 3) of whom had biopsy-proven wound infections.

CONCLUSION

BroKerF is an innovative treatment strategy, which, in our opinion, will show its efficacy when higher standardization is achieved. The combination of selective debridement and autologous skin cells in a fibrin matrix combines regenerative measures for burn treatment.

LAY SUMMARY

Patients suffering from large burn wounds often require the use of large skin grafts to bring burned areas to heal. Before the application of skin grafts, the burned skin must be removed either by surgery or using enzymatic agents. In this article, we describe a method where small areas of skin are taken and skin cells are extracted and sprayed on wound areas that were treated with an enzymatic agent. The cells are held in place by a substance extracted from patients' blood (PRF) that is sprayed on the wound together with the skin cells. We believe this technique can be helpful to reduce the need of skin grafts in burned patients and improve the healing process.

Transplantation of autologous cells and porous gelatin microcarriers to promote wound healing

Definitive treatment to achieve wound healing in major burns frequently include skin transplantation, where split-thickness skin grafts is considered gold standard. This method is associated with several drawbacks. To overcome these hurdles, efforts have been made to develop tissue engineered skin substitutes, often comprised of a combination of cells and biomaterials. In the present study, we aimed to investigate transplantation of autologous keratinocytes and fibroblasts seeded on porous gelatin microcarriers using a porcine wound model. Pre-seeded microcarriers were transplanted to a total of 168 surgical full-thickness wounds (2cm diameter) on eight adult female pigs and covered with occlusive dressings. The experimental groups included wounds transplanted with microcarriers seeded with the combination of keratinocytes and fibroblasts, microcarriers seeded with each cell type individually, microcarriers without cells, each cell type in suspension, and NaCl control. Wounds were allowed to heal for one, two, four or eight weeks before being excised and fixated for subsequent histological and immunohistochemical analysis. In vitro, we confirmed that viable cells populate the surface and the pores of the microcarriers. In vivo, the microcarriers were to a large extent degraded after two weeks. After one week, all treatment groups, with the exception of microcarriers alone, displayed significantly thicker neo-epidermis compared to controls. After two weeks, wounds transplanted with microcarriers seeded with cells displayed significantly thicker neo-epidermis compared to controls. After four weeks there was no difference in the thickness of neo-epidermis. In conclusion, the experiments performed illustrate that autologous cells seeded on porous gelatin microcarriers stimulates the re-epithelialization of wounds. This method could be a promising candidate for skin transplantation. Future studies will focus on additional outcome parameters to evaluate long-term quality of healing following transplantation.

Bioengineering of a Full-Thickness Skin Equivalent in a 96-Well Insert Format for Substance Permeation Studies and Organ-On-A-Chip Applications

The human skin is involved in protecting the inner body from constant exposure to outer environmental stimuli. There is an evident need to screen for toxicity and the efficacy of drugs and cosmetics applied to the skin. To date, animal studies are still the standard method for substance testing, although they are currently controversially discussed Therefore, the multi-organ chip is an attractive alternative to replace animal testing. The two-organ chip is designed to hold 96-well cell culture inserts (CCIs). Small-sized skin equivalents are needed for this. In this study, full-thickness skin equivalents (ftSEs) were generated successfully inside 96-well CCIs. These skin equivalents developed with in vivo-like histological architecture, with normal differentiation marker expressions and proliferation rates. The 96-well CCI-based ftSEs were successfully integrated into the two-organ chip. The permeation of fluorescein sodium salt through the ftSEs was monitored during the culture. The results show a decreasing value for the permeation over time, which seems a promising method to track the development of the ftSEs. Additionally, the permeation was implemented in a computational fluid dynamics simulation, as a tool to predict results in long-term experiments. The advantage of these ftSEs is the reduced need for cells and substances, which makes them more suitable for high throughput assays.

Fibrin/Schwann Cell Matrix in Poly-Epsilon-Caprolactone Conduits Enhances Guided Nerve Regeneration

The goal of this study was to investigate if a three dimensional matrix, loaded homogeneously with Schwann cells and the neurotrophic factor LIF (leukemia inhibitory factor), enhances regeneration in a biodegradable nerve guidance channel as compared to non-structured cell suspensions. Therefore a 10 mm nerve gap in the buccal branch of the rat's facial nerve was bridged with tubular PCL (poly-epsilon-caprolactone) conduits filled with no matrix, Schwann cells, the three dimensional fibrin/Schwann cell matrix or the fibrin/Schwann cell matrix added with LIF. Four weeks after the nerve defects were bridged histological and morphometric analyses of the implants were performed. In conclusion, the three dimensional fibrin/Schwann cells matrix enhanced the quantity and the quality of peripheral nerve regeneration through PCL conduits. The application of LIF prevented hyperneurotization. Therefore, tissue engineered fibrin/Schwann cells matrices are new invented biocompatible and biodegradable devices for enhancing peripheral nerve regeneration as compared to non-structured cell suspensions without neurotrophic factors.

Lipoxin A4 encapsulated in PLGA microparticles accelerates wound healing of skin ulcers

Lipoxin A₄ (LXA₄) is involved in the resolution of inflammation and wound healing; however, it is extremely unstable. Thus, to preserve its biological activities and confer stability, we encapsulated LXA₄ in poly-lactic-co-glycolic acid (PLGA) microparticles (LXA₄-MS) and assessed its application in treating dorsal rat skin lesions. Ulcers were sealed with fibrin adhesive and treated with either LXA₄-MS, unloaded microparticles (Un-MS), soluble LXA₄, or PBS/glue (vehicle). All groups were compared at 0, 2, 7, and 14 days post-lesions. Our results revealed that LXA₄-MS accelerated wound healing from day 7 and reduced initial ulcer diameters by 80%. Soluble LXA₄, Un-MS, or PBS closed wounds by 60%, 45%, and 39%, respectively. LXA₄-MS reduced IL-1β and TNF-α, but increased TGF-β, collagen deposition, and the number of blood vessels. Compared to other treatments, LXA₄-MS reduced inflammatory cell numbers, myeloperoxidase (MPO) concentration, and metalloproteinase-8 (MMP8) mRNA in scar tissue, indicating decreased neutrophil chemotaxis. In addition, LXA₄-MS treatment increased macrophages and IL-4, suggesting a positive impact on wound healing. Finally, we demonstrated that WRW4, a selective LXA₄ receptor (ALX) antagonist, reversed healing by 50%, indicating that LXA₄ must interact with ALX to induce wound healing. Our results show that LXA₄-MS could be used as a pharmaceutical formulation for the treatment of skin ulcers.

A Novel Bioreactor Microcarrier Cell Culture System for High Yields of Proliferating Autologous Human Keratinocytes

Rapid and efficient resurfacing of various skin defects by autologous keratinocyte transplantation is significant in skin wound healing. We developed a novel bioreactor microcarrier cell culture system (Bio-MCCS) to produce autologous human keratinocytes on a large scale. In this Bio-MCCS we used porcine gelatin microbeads as microcarriers for autolgous keratinocytes and spinning bottles as fermentation tanks. First, the microbeads were modified by culturing them with autologous dermal fibroblasts that were subsequently killed when they proliferated to confluence on the microbeads. We then performed the Bio-MCCS by expanding ketatinocytes on the microbeads in spinning bottles at 37°C, 5% CO2. Our results showed that keratinocytes rapidly attached to and actively proliferated on the modified microbeads in the Bio-MCCS, achieving high cell densities on the modified microbeads (MTT assay and PI staining). Keratinocytes cultured on the modified microbeads in the Bio-MCCS remained proliferating potentials as shown by positive PCNA staining and BrdU labeling. In contrast, keratinocytes cultured on nonmodified microbeads in the Bio-MCCS proliferated slowly, rapidly ceased to proliferate, and finally dislodged from the microbeads. When removed from the Bio-MCCS and cultured under static conditions, keratinocytes were able to leave the modified microbeads and formed a multilayered epidermal equivalent on the culture surfaces. While stored at room temperature, keratinocytes remained at higher viabilities on the modified microbeads when compared to those on nonmodified microbeads. The achievement of high yields of proliferating autologous keratinocytes by this Bio-MCCS offers a practical potential of resurfacing various skin defects by direct administration of autologous keratinocyte microbeads on various skin defects.

Bioreactor Microcarrier Cell Culture System (Bio-MCCS) for Large-Scale Production of Autologous Melanocytes

Restoration of cutaneous pigmentation can be achieved in stable vitiligo by autologous cultured melanocyte transplantation. It was the goal of this study to construct a bioreactor microcarrier cell culture system (Bio-MCCS) to produce autologous melanocytes in large scale. In this Bio-MCCS, porcine gelatin microbeads were used as microcarriers, spinning bottle as fermented tank. Autologous melanocytes were able to attach to and proliferate on the gelatin microbeads in serum-free melanocyte medium in the Bio-MCCS, reaching up to 24-fold the cells seeded on day 15 (MTT assay). These autologous melanocytes cultured on gelatin microbeads could leave the microbeads and proliferate on the bottom of tissue culture flasks. Although Pluronic F68 has been widely used to protect animal cells from hydrodynamic stress in animal cell bioreactors, Pluronic F68 at a concentration of 0.25–1.0% showed no significant protective effects on the autologous melanocytes cultured on the microbeads and subjected to mechanical stress in the Bio-MCCS. This Bio-MCCS using porcine gelatin microbeads as microcarriers enabled large-scale production of autologous mela-nocytes, offering a potential treatment for large-area stable vitiligo by direct administration of the melanocytes cultured on the gelatin microbeads to the vitiliginous site.

Treatment of standardised wounds with pure epidermal micrografts generated with an automated device

In this study, we analysed the effects of pure epidermal micrografts generated with an automated device in a standardised human wound model. Epidermal micrografts were harvested using an automated device. Micrografts were then transplanted onto split-skin donor sites. The target area was only partially covered with transplants to create an intra-individual control area. Wounds were evaluated by subjective assessment as well as measurements with combined laser and white light spectroscopy and cutometry. The epidermal graft sites remained completely stable, whereas control sites offered partially unstable and blistering areas. Statistically, no measurable difference in the speed of initial reepithelialisation could be shown. However, there was an increased pliability and softness of the treated areas that correlated with the subjective impression of both investigators and patients. There was a significantly higher relative haemoglobin concentration, measurable in treated and untreated areas at 4 weeks and 6 months. Cutometry showed no differences in skin properties between treated and untreated areas. This study shows an effect of epidermal micrografts in a standardised human wound model and supports the positive impact of keratinocytes on early wound healing as described in literature. Long-term effects of epidermal grafting deserve further studies.

Cutaneous Tissue Engineering and Lower Extremity Wounds (Part 1)

Tissue-engineered skin is a novel therapeutic with which difficult-to-heal lower extremity wounds may be treated. Such skins are products of cutaneous tissue engineering that provide an alternative for autologous or allogeneic tissue transplantation, thereby avoiding problems associated with donor site availability, the risk of infection, and scarring. Recently developed tissue-engineered skin equivalents have shown to be superior in certain ways to compression therapy for refractory venous ulcers and acute wounds. These biologic products behave similarly to autografts.

Buried Chip Skin Grafting in Neuropathic Diabetic Foot Ulcers Following Vacuum-Assisted Wound Bed Preparation: Enhancing a Classic Surgical Tool with Novel Technologies

In patients with diabetes mellitus, complications such as polyneuropathy and peripheral angiopathy inevitably lead to diabetic foot complications including foot ulcers, gangrene, and osteoarthropathy. These conditions necessitate minor or major amputation as part of treatment. In patients with Charcot’s arthropathy and predominant neuropathy, recurrent foot ulcers are common in areas of high pressure. Such high pressure is caused by the degrading of the architecture of the foot and inadequate footwear. These patients are a clinical challenge. A select group of such patients may benefit from free surgical tissue transfer, though free or local flap surgery is often difficult or even impossible owing to an impaired arterial circulation. In such wounds, surgical debridement followed by skin grafts often fail due to bacterial burden in the wounds. To circumvent these problems, the authors developed a therapeutic approach using buried chip skin grafting to close granulation wound beds in diabetic feet. Locally applied vacuum therapy (VAC®) for wound bed preparation of chronic, nonresponsive foot ulcers and subsequent grafting using the burying technique with a minute fraction of skin was used. Firm closure was achieved. The closed wound was resistant to mechanical irritation.

Successful application of keratinocyte suspension using autologous fibrin spray

OBJECTIVE

The back is a challenging anatomical area to resurface in acute burns due to its large surface area, its dependent position with the patient lying down and the shearing forces applied to any method of resurfacing employed. This case study presents the use of Vivostat^® (Vivostat A/S, Lillerød, Denmark) in resurfacing the back in conjunction with Recell^® regenerative epithelial suspension. Vivostat^® (Vivostat A/S, Lillerød, Denmark) is a "novel patented biotechnological process that enables reproducible preparation of autologous fibrin sealant or platelet rich fibrin without cryoprecipitation or a separate thrombin component" [1].

METHODS

A 29-year-old female sustained 27% total body surface area (TBSA) flame burns, including the whole back. This area was initially grafted with the sandwich autograft/allograft technique on day four after injury, with approximately 80% graft take on day eight. Unfortunately, there was subsequent significant graft loss on the back proving to be a stubborn area to treat despite further grafting sessions. This challenge led to the decision to use Vivostat^® (Vivostat A/S, Lillerød, Denmark) and Recell^® to resurface the back.

RESULTS

The patient underwent one session of resurfacing with Vivostat^® (Vivostat A/S, Lillerød, Denmark) and Recell^® and went on to have full healing on the back.

CONCLUSIONS

NICE (The National Institute for Health and Care Excellence) states that Recell^® shows potential to improve healing in acute burns and we believe that its co-delivery with fibrin via Vivostat^® (Vivostat A/S, Lillerød, Denmark) allows for precise delivery of the fibrin suspended cells while minimising loss in the "run off" encountered when Recell^® is just simply sprayed on, assisting the anchoring of keratinocytes to the wound surface and thus aiding in the treatment of challenging areas.

Fibrin matrices: The versatile therapeutic delivery systems

Fibrin sealants, that have been employed for over a century by surgeons to stop post surgery bleeding, are finding novel applications in the controlled delivery of antibiotics and several other therapeutics. Fibrinogen can be easily purified from blood plasma and converted by thrombolysis to fibrin that undergoes spontaneous aggregation to form insoluble clot. During the gelling, fibrin can be formulated into films, clots, threads, microbeads, nanoconstructs and nanoparticles. Whole plasma clots in the form of beads and microparticles can also be prepared by activating endogenous thrombin, for possible drug delivery. Fibrin formulations offer remarkable scope for controlling the porosity as well as in vivo degradability and hence the release of the associated therapeutics. Binding/covalent-linking of therapeutics to the fibrin matrix, crosslinking of the matrix with bifunctional reagents and coentrapment of protease inhibitors have been successful in regulating both in vitro and in vivo release of the therapeutics. The release rates can also be remarkably lowered by preentrapment of therapeutics in insoluble particles like liposomes or by anchoring them to the matrix via molecules that bind them as well as fibrin.

Mesenchymal stem cell therapy and delivery systems in nonhealing wounds

OBJECTIVE

The objective of the study was to inform wound care practitioners of mesenchymal stem cell application for nonhealing wounds. Recent advances in delivery systems are also discussed in order to highlight potential improvements toward clinical application of stem cell therapy for chronic wounds.

DATA SOURCES

MEDLINE and PubMed Central were searched for scientific studies regarding the use of mesenchymal stem cells and delivery systems in wound healing.

STUDY SELECTION

Preclinical studies using stem cells as therapeutic modality for chronic wounds were selected for this review.

DATA EXTRACTION

Information on study design, sample size and characteristics, stem cell source, type of delivery systems, and rate and time of wound closure was abstracted.

DATA SYNTHESIS

Application of mesenchymal stem cells improved wound healing in experimental and clinical settings. Advances in stem cell therapy and delivery vehicles offer promising alternatives to current limited therapeutic modalities for chronic wounds.

CONCLUSIONS

Stem cell therapy has recently emerged as a promising therapeutic strategy for nonhealing wounds. Further research is needed to evaluate the relationship between the various delivery systems and stem cells in order to maximize their therapeutic effects. Development of novel delivery vehicles for stem cells can open new opportunities for more effective cell therapy of chronic wounds.

Fibrin acts as biomimetic niche inducing both differentiation and stem cell marker expression of early human endothelial progenitor cells

OBJECTIVES

Transplantation of endothelial progenitor cells (EPCs) is a promising approach for revascularization of tissue. We have used a natural and biocompatible biopolymer, fibrin, to induce cell population growth, differentiation and functional activity of EPCs.

MATERIALS AND METHODS

Peripheral blood mononuclear cells were cultured for 1 week to obtain early EPCs. Fibrin was characterized for stiffness and capability to sustain cell population expansion at different fibrinogen-thrombin ratios. Viability, differentiation and angiogenic properties of EPCs were evaluated and compared to those of EPCs grown on fibronectin.

RESULTS

Fibrin had a nanometric fibrous structure forming a porous network. Fibrinogen concentration significantly influenced fibrin stiffness and cell growth: 9 mg/ml fibrinogen and 25 U/ml thrombin was the best ratio for enhanced cell viability. Moreover, cell viability was significantly higher on fibrin compared to being on fibronectin. Even though no significant difference was observed in expression of endothelial markers, culture on fibrin elicited marked induction of stem cell markers OCT 3/4 and NANOG. In vitro angiogenesis assay on Matrigel showed that EPCs grown on fibrin retain angiogenetic capability as EPCs grown on fibronectin, but significantly better release of cytokines involved in cell recruitment was produced by EPC grown on fibrin.

CONCLUSION

Fibrin is a suitable matrix for EPC growth, differentiation and angiogenesis capability, suggesting that fibrin gel may be very useful for regenerative medicine.

Paracrine factors from fibroblast aggregates in a fibrin-matrix carrier enhance keratinocyte viability and migration

Efficient re-epithelialization of skin lesions is dependent on paracrine support from connective tissue fibroblasts. In deep skin defects, the supporting growth factor incentive is lacking. Current methods of keratinocyte transplantation with compromised attachment, spread, and cell proliferation warrant improvement and refinement. We describe here how human keratinocytes can be stimulated by matrix-embedded factors from a novel process of fibroblast activation: nemosis. Interestingly, the unique set of mediators released in this process also plays a key role in normal wound healing. To develop a system for targeted delivery of nemosis-derived paracrine effectors, herein designated as Finectra, we combined them with fibrin to establish a controlled-release gel. Keratinocytes seeded to cover this active matrix showed better adherence, outgrowth, and viability than did cells on control matrix. The matrix incorporating Finectra supported viability of both primary keratinocytes and green fluorescent protein (GFP)-labeled HaCaT cells, as evaluated by MTT assay and persistence of GFP-fluorescence. The fibrin-Finectra matrix promoted migration of keratinocytes to cover a larger area on the matrix, suggesting better wound coverage on transplantation. An inhibitor of EGFR/c-Met receptor tyrosine kinases abolished keratinocyte responses to fibrin-Finectra matrix. This matrix can thus deliver biologically relevant synergistic stimuli to keratinocytes and hasten re-epithelialization.

Fibrin gels and their clinical and bioengineering applications

Fibrin gels, prepared from fibrinogen and thrombin, the key proteins involved in blood clotting, were among the first biomaterials used to prevent bleeding and promote wound healing. The unique polymerization mechanism of fibrin, which allows control of gelation times and network architecture by variation in reaction conditions, allows formation of a wide array of soft substrates under physiological conditions. Fibrin gels have been extensively studied rheologically in part because their nonlinear elasticity, characterized by soft compliance at small strains and impressive stiffening to resist larger deformations, appears essential for their function as haemostatic plugs and as matrices for cell migration and wound healing. The filaments forming a fibrin network are among the softest in nature, allowing them to deform to large extents and stiffen but not break. The biochemical and mechanical properties of fibrin have recently been exploited in numerous studies that suggest its potential for applications in medicine and bioengineering.

Comparison of autologous full-thickness gingiva and skin substitutes for wound healing

Ideally tissue-engineered products should maintain the characteristics of the original tissue. For example, skin represents orthokeratinized epithelium and oral gingiva represents parakeratinized epithelium. The aim of this study was to develop an autologous full-thickness gingiva substitute suitable for clinical applications and to compare it with our autologous full-thickness skin substitute that is routinely used for healing chronic wounds. Autologous full-thickness skin and gingiva substitutes were constructed under identical culture conditions from 3-mm punch biopsies isolated from the upper leg or gingiva tissue, respectively. Both consisted of reconstructed epithelia on acellular dermis repopulated with fibroblasts. To compare the characteristics of the original and reconstructed tissue, differential morphological observations and expression of differentiation markers (keratins 6, 10, and 17 and stratum corneum precursors involucrin, loricrin, and SKALP) were determined. Skin and gingiva substitutes were transplanted onto therapy-resistant leg ulcers or tooth extraction sites in order to determine their effects on wound healing. The tissue-engineered constructs maintained many of the differential histological and immunohistochemical characteristics of the original tissues from which they were derived. The skin substitute was orthokeratinized, and the gingiva substitute was parakeratinized. Transplantation of skin (n = 19) and gingiva substitutes (n = 3) resulted in accelerated wound healing with no adverse effects. As identical culture systems were used to generate both the skin and gingiva substitutes, the differences observed in tissue (immuno)histology can be attributed to intrinsic properties of the tissues rather than to environmental factors (e.g., air or saliva). This study emphasizes the importance of closely matching donor sites with the area to be transplanted. Our results represent a large step forward in the area of clinical applications in oral tissue engineering, which have until now greatly lagged behind skin tissue engineering.

The value of debridement and Vacuum-Assisted Closure (V.A.C.) Therapy in diabetic foot ulcers

BACKGROUND

Treatment of diabetic foot ulcers includes a number of different regimes such as glycaemic control, re-vascularization, surgical, local wound treatment, offloading and other non-surgical treatments. Although considered the standard of care, the scientific evidence behind the various debridements used is scarce. This presentation will focus on debridement and V.A.C. Therapy, two treatments widely used in patients with diabetes and foot ulcers.

METHODS

A review of existing literature on these treatments in diabetic foot ulcers, with focus on description of the various types of debridements used, the principles behind negative pressure wound therapy (NPWT) using the V.A.C. Therapy system and level of evidence.

RESULTS

Five randomized controlled trials (RCT) of debridement were identified; three assessed the effectiveness of a hydrogel as a debridement method, one evaluated surgical debridement and one evaluated larval therapy. Pooling the three hydrogel RCTs suggested that hydrogels are significantly more effective than gauze or standard care in healing diabetic foot ulcers. Surgical debridement and larval therapy showed no significant benefit. Other debridement methods such as enzyme preparations or polysaccharide beads have not been evaluated in RCTs of people with diabetes. More than 300 articles have been published on negative pressure wound therapy, including several small RCTs and a larger multi-centre RCT of diabetic foot ulcers. Negative pressure wound therapy seems to be a safe and effective treatment for complex diabetic foot wounds, and could lead to a higher proportion of healed wounds, faster healing rates, and potentially fewer re-amputations than standard care.

CONCLUSIONS

Although debridement of the ulcer is considered a prerequisite for healing of diabetic foot ulcers, the grade of evidence is quite low. This may be due to a lack of studies rather than lack of effect. Negative pressure wound therapy seems to be safe and effective in the treatment of some diabetic foot ulcers, although there is still only one well-performed trial that evaluates the effect.

Decellularized dermis in combination with cultivated keratinocytes in a short- and long-term animal experimental investigation

Decellularized human dermis as a potentially ideal scaffold for dermal substitution in severe burns was examined in a two-staged animal experiment. In an initial step, an in vitro generated composite graft consisting of human keratinocytes and decellularized dermis (AlloDerm) was transplanted onto nude mice in a short-term trial (n = 20, 14 days). Subsequently, a combined one-step grafting of full thickness wounds with both decellularized dermis (in part preincubated with fibroblasts) and cultivated autologous keratinocytes as a cell suspension in fibrin glue was done in a long-term porcine animal model (n = 10, 6 months). In both series, macroscopic wound healing was evaluated by planimetry. Histological investigations included morphological as well as immunohistochemical parameters. The short-term study showed both successful integration of the composite grafts and reduction of wound contraction compared with the control group (epithelial grafts). The long-term porcine study displayed reduced myofibroblast formation and contraction in the wounds that had been treated with fibroblast-preincubated dermis. After 4 weeks, a decline of the structural integrity of the dermal matrix could be noticed. The utility of decellularized dermis as template for both dermal reconstitution and keratinocyte delivery vehicle was shown. The closure of full thickness wounds by a single-step combination of an autologous keratinocyte fibrin sealant suspension and acellular dermis in a pig animal model could be shown. Incorporation of fibroblasts led to reduced wound contraction but could not prevent the loss of dermal integrity. The engineered 'skin' remained viable and stable over a period of 6 months.

Tissue engineering of tendons and ligaments by human bone marrow stromal cells in a liquid fibrin matrix in immunodeficient rats: results of a histologic study

INTRODUCTION

The original complex structure and mechanical properties are not fully restored after ligament and tendon injuries. Due to their high proliferation rate and differentiation potential, Bone Marrow Stromal Cells (BMSC) are considered to be an ideal cell source for tissue engineering to optimize the healing process. Ideal matrices for tissue engineering of ligaments and tendons should allow for homogenous cell seeding and offer sufficient stability.

MATERIAL AND METHODS

A mixture of human BMSC and liquid fibrin glue was injected into a standardized full-thickness window defect of the patellar tendon of immunodeficient rats (BMSC group). The histology of the tissue was analysed 10 and 20 days postoperatively and compared to four control groups. These groups consisted of a cohort with a mixture of human fibroblasts and fibrin glue, fibrin glue without cells, a defect group without treatment, and a group with uninjured patellar tendon tissue.

RESULTS

Tendon defects in the BMSC group revealed dense collagen fibres and spindle-shaped cells, which were mainly orientated along the loading axis. Histologic sections of the control groups, especially of untreated defects and of defects filled with fibrin glue only, showed irregular patterns of cell distribution, irregular formed cell nucleoli and less tissue maturation. Compared to healthy tendon tissue, higher numbers of cells and less intense matrix staining was observed in the BMSC group. No ectopic bone or cartilage formation was observed in any specimen.

CONCLUSIONS

Injection of human BMSC in a fibrin glue matrix appears to lead to more mature tissue formation with more regular patterns of cell distribution. Advantages of this "in-vivo" tissue engineering approach are a homogenous cell-matrix mixture in a well-known and approved biological matrix, and simple, minimally-invasive application by injection.

Tissue engineering in head and neck reconstructive surgery: what type of tissue do we need?

Craniofacial tissue loss due to congenital defects, disease or injury is a major clinical problem. The head and neck region is composed of several tissues. The most prevalent method of reconstruction is autologous grafting. Often, there is insufficient host tissue for adequate repair of the defect side, and extensive donor site morbidity may result from the secondary surgical procedure. The field of tissue engineering has the potential to create functional replacements for damaged or pathologic tissues.

[A comparison of the gene expression patterns of human chondrocytes and chondrogen differentiated mesenchymal stem cells for tissue engineering]

BACKGROUND

Tissue engineering is a promising method for the generation of chondrogenic grafts for reconstructive surgery. In cultured chondrocytes, the dedifferentiation of cells seems unavoidable for multiplication.

METHODS

In this study, we investigated the expression of distinct markers during the dedifferentiation of human chondrocytes (HC) harvested during septoplasty and human mesenchymal stem cells (hMSC) from cartilage biopsies in cell culture using the microarray technique.

RESULTS

The genes for collagen 1alpha1, 2alpha1, 3alpha1, 4alpha1, 11alpha1, biglycan, fibromodulin and lumican were activated during the dedifferentiation of the HCs, collagen 9alpha2, 9alpha3, 10alpha1 and chondroadherin were inactivated. During chondrogenic differentiation of hMSCs, the genes for collagen 3alpha1, 9alpha2, 9alpha3, 10alpha1, 11alpha1 were activated, collagen 4alpha1 and fibromodulin inactivated and the genes for Col 1alpha1, biglycan und chondroadherin constantly expressed.

CONCLUSION

The genetic profile for the investigated markers in human chondrocytes generated from hMSCs resembles the profile in differentiated chondrocytes. Collagen 2alpha1, 9alpha2, 9alpha3, 10alpha1 could represent markers for the differentiation of chondrocytes, Col 1alpha1, 3alpha1 und 4alpha1, biglycan, fibromodulin and lumican markers for the dedifferentiation into a more fibroblastoid cell type.

Number and proliferative capacity of human mesenchymal stem cells are modulated positively in multiple trauma patients and negatively in atrophic nonunions

Mesenchymal stem cells (MSCs) participate in regenerative osteogenesis by generating bone-forming cells. To examine the proliferative capacity of MSC populations from bone marrow and their relationship to trauma severity (multiple trauma, monofracture, atrophic nonunion), we quantified colony properties of human MSCs in vitro. Serum levels of mediators associated with bone formation were also assessed. Fifty-five individuals were enrolled in this study (13 multiple trauma patients, 15 patients with monofracture, 20 patients with atrophic nonunions, 7 healthy volunteers). The colony forming unit-fibroblast (CFU-F) assay was used to quantify total colony number, mean cell density per colony, and mean colony area. MSC phenotype was established using flow cytometry and osteogenic differentiation. MSCs obtained from multiple-trauma patients yielded the highest reservoir. Significant differences in colony numbers of MSCs in female subjects were found between multiple-trauma patients (mean +/- SD 48 +/- 21 CFU-F/culture) and healthy volunteers (18.7 +/- 3.3 CFU-F/culture, P < 0.05), patients with monotrauma (15 +/- 10 CFU-F/culture, P < 0.05), and patients with atrophic nonunions (6.3 +/- 4.1 CFU-F/culture, P < 0.05). In male participants, significant differences were found between patients with nonunions (14 +/- 14 CFU-F/culture) and healthy volunteers (54 +/- 17 CFU-F/culture, P < 0.05) as well as multiple-trauma patients (59 +/- 25 CFU-F/culture, P < 0.05). The highest proliferative capacity (cell density) was seen in multiple-trauma patients. These data suggest that trauma severity and gender affect the reservoir and proliferation capacity of bone marrow-derived MSCs.

Optimized delivery of skin keratinocytes by aerosolization and suspension in fibrin tissue adhesive

Aerosolized suspensions of keratinocytes provide a potential therapy for wounds, but the effects of aerosolization on cell viability remain unclear. Likewise, little is known of the resulting cell distribution pattern and how this compares to the density required for epithelialization. The potential benefits of cospraying cells in the presence of fibrin adhesive are equally uncertain. Thus, in the present study we have optimized conditions for the aerosolization of cultured keratinocytes using a device (Tissomat) that supports the option for coapplication with fibrin (Tisseel). Cell viability was unaffected when sprayed at 10 psi, but a significant reduction in metabolic activity, as determined by the methylthiazoyldiphenol-tetrazolium assay, was observed at higher pressure. Bursts of 0.2 mL cell suspension (1.5x10(6)/mL) delivered from a height of 10 cm was sufficient to epithelialize an area of 10-15 cm2 within 7 days in vitro. Confluent areas corresponded to those with a density of 5,000-10,000 cells/cm2 at 24 hours. Optimal cell growth in Tisseel was achieved through dilution of fibrinogen (1-3 mg/mL) and thrombin (2-5 IU/mL). This optimized formulation eliminated fluid run-off postspraying and stimulated a twofold increase in cellular response. Therefore, our in vitro data supports the theory that aerosolized suspensions of keratinocytes in fibrin will benefit healing.

Transduction of beta3 integrin subunit cDNA confers on human keratinocytes the ability to adhere to gelatin

alphavbeta3 is a multiligand integrin receptor that interacts with fibrinogen (FG), fibrin (FB), fibronectin (FN), vitronectin (VN), and denatured collagen. We previously reported that cultured normal human keratinocytes, like in vivo keratinocytes, do not express alphavbeta3 on the cell surface, and do not adhere to and migrate on FG and FB. Furthermore, we reported that human keratinocytes transduced with beta3 integrin subunit cDNA by a retrovirus-mediated transduction method express alphavbeta3 on the cell surface and adhere to FG, FB, FN, and VN significantly compared with beta-galactosidase (beta-gal) cDNA-transduced keratinocytes (control). In this study, we determined whether these beta3 integrin subunit cDNA-transduced keratinocytes or normal human keratinocytes adhere to denatured collagen (gelatin) using a 1 h cell adhesion assay. beta3 cDNA-transduced keratinocytes adhered to gelatin, whereas no significant adhesion was observed with the control cells (beta-gal cDNA-transduced keratinocytes and normal human keratinocytes). The adhesion to gelatin was inhibited by LM609, a monoclonal antibody to alphavbeta3, and RGD peptides but not by normal mouse IgG1 nor RGE peptides. Thus, transduction of beta3 integrin subunit cDNA confers on human keratinocytes the ability to adhere to denatured collagen (gelatin) as well as to FG, FB, VN, and FN. Otherwise, normal human keratinocytes do not adhere to gelatin. These data support the idea that beta3 cDNA-transduced human keratinocytes can be a good material for cultured epithelium to achieve better take rate with acute or chronic wounds, in which FG, FB, and denatured collagen are abundantly present.

Synergistic effect of keratinocyte transplantation and epidermal growth factor delivery on epidermal regeneration

Both keratinocyte transplantation and epidermal growth factor (EGF) delivery stimulate epidermal regeneration. In this study, we hypothesized that the combined therapy of keratinocyte transplantation and EGF delivery accelerates epidermal regeneration compared to the single therapy of either keratinocyte transplantation or EGF delivery. To test this hypothesis, we utilized fibrin matrix as a keratinocyte/EGF delivery vehicle for epidermal regeneration. Full-thickness wounds were created on the dorsum of athymic mice, and human keratinocytes and EGF in fibrin matrix were sprayed onto the wounds to regenerate epidermal layers (group 1). As controls, human keratinocytes in fibrin matrix (group 2), EGF in fibrin matrix (group 3), or fibrin matrix alone (group 4) was sprayed onto the wounds. Spraying keratinocytes suspended in fibrin matrix did not affect the keratinocyte viability, as the cell viabilities before and after spraying were not different. EGF was released from fibrin matrix for 3 days. The wounds were analyzed with histology and immunohistochemistry at 1 and 3 weeks after treatments. Compared with the control groups, initial wound closure rate was highest in group 1. Histological analyses indicated that group 1 exhibited faster and better epidermal regeneration than the other groups. Immunohistochemical analyses showed that regenerated epithelium in groups 1 and 2 stained positively for human involucrin at 3 weeks, whereas the tissue sections of the groups 3 and 4 stained negatively. Human laminin was detected at the dermal-epidermal junction of the regenerated tissues in groups 1 and 2 at 3 weeks and was not detected in groups 3 and 4. The epidermal thickness of the regenerated tissues in group 1 was significantly thicker than that of the other groups at all time points. These results suggest that the combined therapy of keratinocyte transplantation and EGF delivery is more efficacious for epidermal regeneration than each separate therapy alone.

Authentic fibroblast matrix in dermal equivalents normalises epidermal histogenesis and dermoepidermal junction in organotypic co-culture

Besides medical application as composite skin grafts, in vitro constructed skin equivalents (SEs) or organotypic co-cultures represent valuable tools for cutaneous biology. Major drawbacks of conventional models, employing collagen hydrogels as dermal equivalents (DEs), are a rather poor stability and limited life span, restricting studies to early phases of skin regeneration. Here we present an improved stabilised in vitro model actually providing the basis for skin-like homeostasis. Keratinocytes were grown on dermal equivalents (DEs) reinforced by modified hyaluronic acid fibres (Hyalograft-3D) and colonised with skin fibroblasts, producing genuine dermis-type matrix. These SEs developed a superior epidermal architecture with regular differentiation and ultrastructure, which occurred also faster than in SEs based on collagen-DEs. Critical aspects of differentiation, still unbalanced in early stages, were perfectly re-normalised, most strikingly the co-expression of keratins K1/K10 and downregulation of regeneration-associated keratins such as K16. The restriction of integrin and K15 distribution as well as keratinocyte proliferation to the basal layer underlined the restored tissue polarity, while the drop of growth rates towards physiological levels implied finally accomplishment of homeostasis. This correlated to faster basement membrane (BM) formation and ultrastructurally defined dermo-epidermal junction including abundant anchoring fibrils for strong tissue connection. Whereas the fibroblasts in the scaffold initially secreted a typical provisional regenerative matrix (fibronectin, tenascin), with time collagens of mature dermis (type I and III) were accumulating giving rise to an in vivo-like matrix with regularly organised bundles of striated collagen fibrils. In contrast to the more catabolic state in conventional DEs, the de novo reconstruction of genuine dermal tissue seemed to be a key element for maintaining prolonged normal keratinocyte proliferation (followed up to 8 wks), fulfilling the criteria of tissue-homeostasis, and possibly providing a stem cell niche.

Skin Grafting of Venous Ulcers: A Review of its Current Role

As a therapeutic option, grafting of venous ulcers has not been very successfully received despite the different types of grafting methods. Currently, there are only a few controlled randomized trials offering clear guidance to clinicians. The development of artificially bioengineered skin constructs has led to a renewed interest in wound bed preparation, and preliminary successes suggest that the role of skin grafting could be studied in the current context.

Permanent restoration of human skin treated with cultured epithelium grafting--wound healing by stem cell based tissue engineering--

The technique of epidermal cell culture developed by Green and colleagues made a breakthrough in the treatment of massive wounds in vivo with grown cells in vitro. In the past two decades, progress of culture methods and clinical practice have been made and now it is possible to treat extensive skin defect with large amounts of cultured epithelium. Since 1985, we have been successfully used cultured epidermis as autografts for the permanent coverage of full-thickness burn wounds or excised burn scars, giant nevi, tattoos and so on. Furthermore, cultured epidermis has been available as allografts to promote the healing of chronic skin ulcers or deep dermal burn. In this paper we describe our clinical experience of cultured epithelium grafting for the treatment of wounds and predict new trial of wound management and regeneration based on tissue engineering concept.

Overexpression of vascular endothelial growth factor accelerates early vascularization and improves healing of genetically modified cultured skin substitutes

Cultured skin substitutes (CSS) lack a vascular plexus, leading to slower vascularization after grafting than split-thickness skin autograft. CSS containing keratinocytes genetically modified to overexpress vascular endothelial growth factor (VEGF) were previously shown to exhibit enhanced vascularization up to 2 weeks after grafting to athymic mice. The present study examines whether enhanced vascularization compared with controls persists after stable engraftment is achieved and analyzes VEGF expression, wound contraction, and engraftment. Control and VEGF-modified (VEGF+) CSS were grafted onto full-thickness wounds in athymic mice. VEGF expression was detected in VEGF+ CSS 14 weeks after grafting. Graft contraction was significantly lower in VEGF+ CSS compared with controls, suggesting more stable engraftment and better tissue development. Positive HLA-ABC staining, indicating persistence of human cells, was seen in 86.7% (13/15) of grafted VEGF+ CSS, compared with 58.3% (7/12) of controls. Differences in dermal vascularization between control and VEGF+ grafts were significant 1 week after surgery, but not at later times. However, the distribution of vessels was different, with more vessels in the upper dermis of VEGF+ grafts. These results suggest that VEGF overexpression in genetically modified CSS acts to accelerate early graft vascularization and can contribute to improved healing of full-thickness skin 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.

Tissue engineering in plastic reconstructive surgery

Tissue engineering (TE) is a new interdisciplinary field of applied research combining engineering and biosciences together with clinical application, mainly in surgical specialities, to develop living substitutes for tissues and organs. Tissue engineering approaches can be categorized into substitutive approaches, where the aim is the ex vivo construction of a living tissue or organ similar to a transplant, vs. histioconductive or histioinductive concepts in vivo. The main successful approaches in developing tissue substitutes to date have been progresses in the understanding of cell-cell interactions, the selection of appropriate matrices (cell-matrix interaction) and chemical signalling (cytokines, growth factors) for stimulation of cell proliferation and migration within a tissue-engineered construct. So far virtually all mammalian cells can be cultured under specific culture conditions and in tissue specific matrices. Future progress in cell biology may permit the use of pluripotent stem cells for TE. The blueprint for tissue differentiation is the genome: for this it is reasonable to combine tissue engineering with gene therapy. The key to the progress of tissue engineering is an understanding between basic scientists, biochemical engineers, clinicians, and industry.

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.

Growth modulation of fibroblasts by chitosan-polyvinyl pyrrolidone hydrogel: implications for wound management?

Wounds in adults and fetuses differ in their healing ability with respect to scar formation. In adults, wounds lacking the epidermis exhibit excess collagen production and scar formation. Fibroblasts synthesize and deposit a collagen rich extracellular matrix. The early migration and proliferation of fibroblasts in the wound area is implicated in wound scarring. We have synthesized a hydrogel from chitosan-polyvinyl pyrrolidone (PVP) and examined its effect on fibroblast growth modulation in vitro. The hydrogel was found to be hydrophilic as seen from its octane contact angle (141.2+/-0.37 degrees). The hydrogel was non-toxic and biocompatible with fibroblasts and epithelial cells as confirmed by the 3(4,5-dimethylthiazolyl-2)-2, 5-diphenyl tetrazolium bromide (MTT) as-say. It showed dual properties by supporting growth of epithelial cells (SiHa) and selectively inhibiting fibro-blast (NIH3T3) growth. Growth inhibition of fibroblasts resulted from their inability to attach on to the hydrogel. These findings are supported by image analysis, which revealed a significant difference (P<0.05) between the number of fibroblasts attached to the hydrogel in tissue culture as compared to tissue culture treated polystyrene (TCPS) controls. However, no significant difference was observed (P>0.05) in the number of epithelial (SiHa) cells attached on to the hydrogel as compared to the TCPS control. Although in vivo experiments are awaited, these findings point to the possible use of chitosan-PVP hydrogels in wound-management.