Vascularized collagen-glycosaminoglycan matrix provides a dermal substrate and improves take of cultured epithelial autografts

Advancements in cell-based therapies for thermal burn wounds: a comprehensive systematic review of clinical trials outcomes

BACKGROUND

Burn trauma is one of the major causes of morbidity and mortality worldwide. The standard management of burn wounds consists of early debridement, dressing changes, surgical management, and split-thickness skin autografts (STSGs). However, there are limitations for the standard management that inclines us to find alternative treatment approaches, such as innovative cell-based therapies. We aimed to systematically review the different aspects of cell-based treatment approaches for burn wounds in clinical trials.

METHODS

A systematic search through PubMed, Medline, Embase, and Cochrane Library databases was carried out using a combination of keywords, including "Cell transplantation", "Fibroblast", "Keratinocyte", "Melanocyte", or "Stem Cell" with "Burn", "Burn wound", or "Burn injury". Firstly, titles and abstracts of the studies existing in these databases until "February 2024" were screened. Then, the selected studies were read thoroughly, and considering the inclusion and exclusion criteria, final articles were included in this systematic review. Moreover, a manual search was performed through the reference lists of the included studies to minimize the risk of missing reports.

RESULTS

Overall, 30 clinical trials with 970 patients were included in our study. Considering the type of cells, six studies used keratinocytes, nine used fibroblasts, eight used combined keratinocytes and fibroblasts, one study used combined keratinocytes and melanocytes, five used combined keratinocytes and fibroblasts and melanocytes, and one study used mesenchymal stem cells (MSCs). Evaluation of the preparation type in these studies showed that cultured method was used in 25 trials, and non-cultured method in 5 trials. Also, the graft type of 17 trials was allogeneic, and of 13 other trials was autologous.

CONCLUSIONS

Our study showed that employing cell-based therapies for the treatment of burn wounds have significant results in clinical studies and are promising approaches that can be considered as alternative treatments in many cases. However, choosing appropriate cell-based treatment for each burn wound is essential and depends on the situation of each patient.

FEATURES OF QUALITY CONTROL STRATEGY FOR DRUGS BASED ON VIABLE SKIN CELLS

The aim of the study was to research the international experience in quality assurance of the products based on skin cells in order to identify the features of the quality control strategy in the development, production, as well as during an expert quality assessment as a part of the state registration procedure in the Russian Federation.

Materials and methods. The article provides an analysis of the materials presented in the assessment reports of the USA and Japanese regulatory authorities, as well as on the official websites of manufacturers, in review and scientific papers on the study of the structure and properties of tissue-engineered skin analogs.

Results. The manufacture of products containing human skin cells is associated with such risks as the possibility of contamination of the preparation with infective agents transmitted by materials of the animal origin, feeder cells, donor cells, or during the manufacturing process; a small amount of biopsy materials; a complexity of a three-dimensional product structure when combining cells with a scaffold; continuity of the manufacture process and a short product expiry date. The raw materials and reagents control, the creation of cell banks, using animal feeder cells only from qualified cell banks, an in-process control and release testing in accordance with the requirements of the finished product specification, make it possible to obtain a preparation with a reproducible quality. The specification should contain information about the identity, safety and potency of the product. For each preparation, the choice of approaches for assessing the quality is individual and depends on its composition and mode of action.

Conclusion. The features of the quality control strategy for the drugs based on human skin cells, consist in the implementation of control measures in order to obtain a proper quality of cellular (viability, sterility, identity, potency, et al) and non-cellular (physico-chemical scaffold properties) components or the whole graft (bioburden, barrier properties). The approaches and methods for determining the potency should be selected individually for each product and reflect the number, viability and identity of cells, a proliferative activity and secretable ability of the cellular component.

Large full-thickness wounded skin regeneration using 3D-printed elastic scaffold with minimal functional unit of skin

Traditional tissue engineering skin are composed of living cells and natural or synthetic scaffold. Besize the time delay and the risk of contamination involved with cell culture, the lack of autologous cell source and the persistence of allogeneic cells in heterologous grafts have limited its application. This study shows a novel tissue engineering functional skin by carrying minimal functional unit of skin (MFUS) in 3D-printed polylactide-co-caprolactone (PLCL) scaffold and collagen gel (PLCL + Col + MFUS). MFUS is full-layer micro skin harvested from rat autologous tail skin. 3D-printed PLCL elastic scaffold has the similar mechanical properties with rat skin which provides a suitable environment for MFUS growing and enhances the skin wound healing. Four large full-thickness skin defects with 30 mm diameter of each wound are created in rat dorsal skin, and treated either with tissue engineering functional skin (PLCL + Col + MFUS), or with 3D-printed PLCL scaffold and collagen gel (PLCL + Col), or with micro skin islands only (Micro skin), or without treatment (Normal healing). The wound treated with PLCL + Col + MFUS heales much faster than the other three groups as evidenced by the fibroblasts migration from fascia to the gap between the MFUS dermis layer, and functional skin with hair follicles and sebaceous gland has been regenerated. The PLCL + Col treated wound heals faster than normal healing wound, but no skin appendages formed in PLCL + Col-treated wound. The wound treated with micro skin islands heals slower than the wounds treated either with tissue engineering skin (PLCL + Col + MFUS) or with PLCL + Col gel. Our results provide a new strategy to use autologous MFUS instead "seed cells" as the bio-resource of engineering skin for large full-thickness skin wound healing.

A Gelatin-sulfonated Silk Composite Scaffold based on 3D Printing Technology Enhances Skin Regeneration by Stimulating Epidermal Growth and Dermal Neovascularization

One of the key problems hindering skin repair is the deficiency of dermal vascularization and difficulty of epidermis regeneration, which makes it challenging to fabricate scaffolds that can biologically fulfill the requirements for skin regeneration. To overcome this problem, three-dimensional printing was used to fabricate a gelatin-sulfonated silk composite scaffold that was incorporated with basic fibroblast growth factor 2 (FGF-2) through binding with a sulfonic acid group (SO₃) (3DG-SF-SO₃-FGF). The efficacy and mechanism by which the 3DG-SF-SO₃-FGF scaffolds promote skin regeneration were investigated both within in vitro cell culture and in vivo with a full-thickness skin defect model. The histological results showed that the gelatin-sulfonated silk composite scaffolds promoted granulation, and that incorporation of FGF-2 significantly enhanced the regeneration of skin-like tissues after implantation in rat skin defects for 14 and 28 days. Further investigations demonstrated that 3DG-SF-SO₃-FGF scaffolds might stimulate dermal vascularization. These findings thus suggest that incorporation of FGF-2 into the 3D printed scaffolds is a viable strategy for enhancing skin regeneration.

Cross-linked Collagen Hydrogel Matrix Resisting Contraction To Facilitate Full-Thickness Skin Equivalents

Full-thickness skin equivalents are gathering increased interest as skin grafts for the treatment of large skin defects or chronic wounds or as nonanimal test platforms. However, their fibroblast-mediated contraction and poor mechanical stability lead to disadvantages toward their reproducibility and applicability in vitro and in vivo. To overcome these pitfalls, we aimed to chemically cross-link the dermal layer of a full-thickness skin model composed of a collagen type I hydrogel. Using a noncytotoxic four-arm succinimidyl glutarate polyethylene glycol (PEG-SG), cross-linking could be achieved in cell seeded collagen hydrogels. A concentration of 0.5 mg of PEG-SG/mg of collagen led to a viability comparable to non-cross-linked collagen hydrogels and no increased release of intracellular lactate dehydrogenase. Cross-linked collagen hydrogels were more mechanically stable and less prone to enzymatic degradation via collagenase when compared with non-cross-linked collagen hydrogels. Remarkably, during 21 days, cross-linked collagen hydrogels maintain their initial surface area, whereas standard dermal models contracted up to 50%. Finally, full-thickness skin equivalents were generated by seeding human epidermal keratinocytes on the surface of the equivalents and culturing these equivalents at an air-liquid interface. Immunohistochemical stainings of the cross-linked model revealed well-defined epidermal layers including an intact stratum corneum and a dermal part with homogeneously distributed human dermal fibroblasts. These results indicate that cross-linking of collagen with PEG-SG reduces contraction of collagen hydrogels and thus increases the applicability of these models as an additional tool for efficacy and safety assessment or a new generation of skin grafts.

Multifaceted role of hair follicle dermal cells in bioengineered skins

BACKGROUND

The method of generating bioengineered skin constructs was pioneered several decades ago; nowadays these constructs are used regularly for the treatment of severe burns and nonhealing wounds. Commonly, these constructs are comprised of skin fibroblasts within a collagen scaffold, forming the skin dermis, and stratified keratinocytes overlying this, forming the skin epidermis. In the past decade there has been a surge of interest in bioengineered skins, with researchers seeking alternative cell sources, or scaffolds, from which constructs can be established, and for more biomimetic equivalents with skin appendages.

OBJECTIVES

To evaluate whether human hair follicle dermal cells can act as an alternative cell source for engineering the dermal component of engineered skin constructs.

METHODS

We established in vitro skin constructs by incorporating into the collagenous dermal compartment: (i) primary interfollicular dermal fibroblasts, (ii) hair follicle dermal papilla cells or (iii) hair follicle dermal sheath cells. In vivo skins were established by mixing dermal cells and keratinocytes in chambers on top of immunologically compromised mice.

RESULTS

All fibroblast subtypes were capable of supporting growth of overlying epithelial cells, both in vitro and in vivo. However, we found hair follicle dermal sheath cells to be superior to fibroblasts in their capacity to influence the establishment of a basal lamina.

CONCLUSIONS

Human hair follicle dermal cells can be readily interchanged with interfollicular fibroblasts and used as an alternative cell source for establishing the dermal component of engineered skin both in vitro and in vivo.

Skin tissue engineering advances in severe burns: review and therapeutic applications

Current advances in basic stem cell research and tissue engineering augur well for the development of improved cultured skin tissue substitutes: a class of products that is still fraught with limitations for clinical use. Although the ability to grow autologous keratinocytes in-vitro from a small skin biopsy into sheets of stratified epithelium (within 3 to 4 weeks) helped alleviate the problem of insufficient donor site for extensive burn, many burn units still have to grapple with insufficient skin allografts which are used as intermediate wound coverage after burn excision. Alternatives offered by tissue-engineered skin dermal replacements to meet emergency demand have been used fairly successfully. Despite the availability of these commercial products, they all suffer from the same problems of extremely high cost, sub-normal skin microstructure and inconsistent engraftment, especially in full thickness burns. Clinical practice for severe burn treatment has since evolved to incorporate these tissue-engineered skin substitutes, usually as an adjunct to speed up epithelization for wound closure and/or to improve quality of life by improving the functional and cosmetic results long-term. This review seeks to bring the reader through the beginnings of skin tissue engineering, the utilization of some of the key products developed for the treatment of severe burns and the hope of harnessing stem cells to improve on current practice.

Advanced therapies of skin injuries

The loss of tissue is still one of the most challenging problems in healthcare. Efficient laboratory expansion of skin tissue to reproduce the skins barrier function can make the difference between life and death for patients with extensive full-thickness burns, chronic wounds, or genetic disorders such as bullous conditions. This engineering has been initiated based on the acute need in the 1980s and today, tissue-engineered skin is the reality. The human skin equivalents are available not only as models for permeation and toxicity screening, but are frequently applied in vivo as clinical skin substitutes. This review aims to introduce the most important recent development in the extensive field of tissue engineering and to describe already approved, commercially available skin substitutes in clinical use.

Dermal matrices and bioengineered skin substitutes: a critical review of current options

Background:

Over recent decades, scientists and surgeons have collaborated to develop various bioengineered and synthetic products as an alternative to skin grafts. Despite the numerous articles and reviews written about dermal skin substitutes, there is no general consensus.

Methods:

This article reviews dermal skin scaffolds used in clinical applications and experimental settings. For scaffold evaluation, we focused on clinical and/or histological results, and conclusions are listed. Explanations for general trends were sought based on existing knowledge about tissue engineering principles and wound healing mechanisms.

Results:

Decellularized dermis seems to remain the best option with no other acellular scaffold being clinically proven to gain better results yet. In general, chemically cross-linked products were seen to be less effective in skin tissue engineering. Biocompatibility could be enhanced by preseeding substitutes with fibroblasts to allow some natural scaffold remodeling before product application.

Conclusions:

Skin substitutes are a useful tool in plastic and reconstructive surgery practices as an alternative to skin grafts. In the choice of substitute, the general plastic surgery principle of replacing like tissue with like tissue seems to be still standing, and products most resembling the natural dermal extracellular matrix should be preferred.

Dermal papilla cells improve the wound healing process and generate hair bud-like structures in grafted skin substitutes using hair follicle stem cells

Tissue-engineered skin represents a useful strategy for the treatment of deep skin injuries and might contribute to the understanding of skin regeneration. The use of dermal papilla cells (DPCs) as a dermal component in a permanent composite skin with human hair follicle stem cells (HFSCs) was evaluated by studying the tissue-engineered skin architecture, stem cell persistence, hair regeneration, and graft-take in nude mice. A porcine acellular dermal matrix was seeded with HFSCs alone and with HFSCs plus human DPCs or dermal fibroblasts (DFs). In vitro, the presence of DPCs induced a more regular and multilayered stratified epidermis with more basal p63-positive cells and invaginations. The DPC-containing constructs more accurately mimicked the skin architecture by properly stratifying the differentiating HFSCs and developing a well-ordered epithelia that contributed to more closely recapitulate an artificial human skin. This acellular dermal matrix previously repopulated in vitro with HFSCs and DFs or DPCs as the dermal component was grafted in nude mice. The presence of DPCs in the composite substitute not only favored early neovascularization, good assimilation and remodeling after grafting but also contributed to the neovascular network maturation, which might reduce the inflammation process, resulting in a better healing process, with less scarring and wound contraction. Interestingly, only DPC-containing constructs showed embryonic hair bud-like structures with cells of human origin, presence of precursor epithelial cells, and expression of a hair differentiation marker. Although preliminary, these findings have demonstrated the importance of the presence of DPCs for proper skin repair.

Early kinetics of integration of collagen-glycosaminoglycan regenerative scaffolds in a diabetic mouse model

BACKGROUND

Collagen-glycosaminoglycan scaffolds, originally designed to treat severe burns, are now commonly used in patients with complex wounds associated with diabetes mellitus. In this study, the authors investigated how the thickness of the scaffold would affect cellular integration with the diabetic host and whether this can be accelerated using subatmospheric pressure wound therapy devices.

METHODS

Collagen-glycosaminoglycan scaffolds, 500 to 2000-μm thick, were applied to dorsal wounds in genetically diabetic mice. In addition, 1000-μm collagen-glycosaminoglycan scaffolds with and without silicone were treated with a subatmospheric pressure device (-125 mmHg). On days 5 and 10, cellular and vascular integration of tissues was studied by histology, immunohistochemistry, corrosion casting, and qRT-polymerase chain reaction.

RESULTS

Cells and vessels from the wound surface populated the scaffold to form layers with varying cellular density. Areas of high cell density and proliferation were noted at the bottom of the scaffold. Increasing the thickness of the scaffold did not affect the extent of cellular ingrowth, so that thicker scaffolds had a thicker residual acellular layer on the surface. The thickness of cellular ingrowth was stable between days 5 and 10, whereas vessels seen in the scaffolds on day 10 were not yet present on day 5. Subatmospheric pressure devices applied to silicone-covered collagen-glycosaminoglycan scaffolds minimized the granulation tissue formation beneath the scaffold, which enhanced vessel ingrowth.

CONCLUSIONS

The early kinetics of cellular integration into collagen-glycosaminoglycan scaffolds is independent of scaffold thickness in a diabetic wound model. Scaffold adherence to the wound and integration can be improved using a subatmospheric pressure device.

Sandwich-type fiber scaffolds with square arrayed microwells and nanostructured cues as microskin grafts for skin regeneration

The paper reports the fabrication of sandwich-type scaffolds consisting of radially-aligned nanofibers at the bottom, nanofiber membranes with square arrayed microwells and nanostructured cues at the top, and microskin tissues in between as microskin grafts for use in skin regeneration. This class of nanofiber scaffolds was able to confine the microskin tissues in the square arrayed wells and simultaneously present nanotopographic cues to the cultured NIH 3T3 fibroblasts and primary rat skin cells, guiding and facilitating their migration in vitro. More importantly, we demonstrated that the sandwich-type transplants exhibited an even distribution of microskin grafts, greatly improved the 'take' rate of microskin tissues, and promoted re-epithelialization on wound in vivo. In addition, the void area in the scaffolds was well suitable for exudate drainage in wound. The sandwich-type scaffolds show great potential as microskin grafts for repairing extensive burn injuries and may provide a good solution for the treatment of acute skin defects and chronic wounds including diabetic ulcer, pressure ulcer, and venous stasis ulcer.

Nanotopography-guided tissue engineering and regenerative medicine

Human tissues are intricate ensembles of multiple cell types embedded in complex and well-defined structures of the extracellular matrix (ECM). The organization of ECM is frequently hierarchical from nano to macro, with many proteins forming large scale structures with feature sizes up to several hundred microns. Inspired from these natural designs of ECM, nanotopography-guided approaches have been increasingly investigated for the last several decades. Results demonstrate that the nanotopography itself can activate tissue-specific function in vitro as well as promote tissue regeneration in vivo upon transplantation. In this review, we provide an extensive analysis of recent efforts to mimic functional nanostructures in vitro for improved tissue engineering and regeneration of injured and damaged tissues. We first characterize the role of various nanostructures in human tissues with respect to each tissue-specific function. Then, we describe various fabrication methods in terms of patterning principles and material characteristics. Finally, we summarize the applications of nanotopography to various tissues, which are classified into four types depending on their functions: protective, mechano-sensitive, electro-active, and shear stress-sensitive tissues. Some limitations and future challenges are briefly discussed at the end.

Development of a vascularized skin construct using adipose-derived stem cells from debrided burned skin

Large body surface area burns pose significant therapeutic challenges. Clinically, the extent and depth of burn injury may mandate the use of allograft for temporary wound coverage while autografts are serially harvested from the same donor areas. The paucity of donor sites in patients with burns involving large surface areas highlights the need for better skin substitutes that can achieve early and complete coverage and retain normal skin durability with minimal donor requirements. We have isolated autologous stem cells from the adipose layer of surgically debrided burned skin (dsASCs), using a point-of-care stem cell isolation device. These cells, in a collagen—polyethylene glycol fibrin-based bilayer hydrogel, differentiate into an epithelial layer, a vascularized dermal layer, and a hypodermal layer. All-trans-retinoic acid and fenofibrate were used to differentiate dsASCs into epithelial-like cells. Immunocytochemical analysis showed a matrix- and time-dependent change in the expression of stromal, vascular, and epithelial cell markers. These results indicate that stem cells isolated from debrided skin can be used as a single autologous cell source to develop a vascularized skin construct without culture expansion or addition of exogenous growth factors. This technique may provide an alternative approach for cutaneous coverage after extensive burn injuries.

Bioengineered skin constructs and their use in wound healing

BACKGROUND

Over the past two decades, the field of wound healing and tissue repair has witnessed tremendous advances resulting from the biological sciences, biomedical and tissue engineering, and greater clinical understanding of wounds and their pathophysiology. In large part because of these advances, clinicians are now able to offer and deliver more sophisticated and effective treatments to patients with acute wounds, chronic wounds, burns, and other types of injuries.

METHODS

This report relies on published information focused on bioengineered skin and the authors' perspectives on the application of this technology in wound healing. In some cases, off-label applications of certain bioengineered skin constructs have been used to illustrate the spectrum of usefulness of these constructs.

RESULTS

Bioengineered skin (including acellular and cellular products; living and nonliving constructs; and epidermal, dermal, and bilayered therapeutic adjuncts) has resulted in very substantial and demonstrable improvements in wound care. Some of the constructs are U.S. Food and Drug Administration approved for treatment of burns and for impaired healing situations, including venous and diabetic foot ulcers.

CONCLUSIONS

The advances that have occurred in testing and proving the efficacy of bioengineered skin hold great promise for further improvements in the way this technology is used in the surgical field and in wound care. Advances in therapeutic agents have also led to greater understanding of pathophysiology. Thus, wound bed preparation as a concept and as an approach is in fact the result of the need to maximize the benefits of advanced therapies.

Effect of 3D-scaffold formation on differentiation and survival in human neural progenitor cells

BACKGROUND

3D-scaffolds have been shown to direct cell growth and differentiation in many different cell types, with the formation and functionalisation of the 3D-microenviroment being important in determining the fate of the embedded cells. Here we used a hydrogel-based scaffold to investigate the influences of matrix concentration and functionalisation with laminin on the formation of the scaffolds, and the effect of these scaffolds on human neural progenitor cells cultured within them.

METHODS

In this study we used different concentrations of the hydrogel-based matrix PuraMatrix. In some experiments we functionalised the matrix with laminin I. The impact of concentration and treatment with laminin on the formation of the scaffold was examined with atomic force microscopy. Cells from a human fetal neural progenitor cell line were cultured in the different matrices, as well as in a 2D culture system, and were subsequently analysed with antibody stainings against neuronal markers. In parallel, the survival rate of the cells was determined by a live/dead assay.

RESULTS

Atomic force microscopy measurements demonstrated that the matrices are formed by networks of isolated PuraMatrix fibres and aggregates of fibres. An increase of the hydrogel concentration led to a decrease in the mesh size of the scaffolds and functionalisation with laminin promoted aggregation of the fibres (bundle formation), which further reduces the density of isolated fibres. We showed that laminin-functionalisation is essential for human neural progenitor cells to build up 3D-growth patterns, and that proliferation of the cells is also affected by the concentration of matrix. In addition we found that 3D-cultures enhanced neuronal differentiation and the survival rate of the cells compared to 2D-cultures.

CONCLUSIONS

Taken together, we have demonstrated a direct influence of the 3D-scaffold formation on the survival and neuronal differentiation of human neural progenitor cells. These findings emphasize the importance of optimizing 3D-scaffolds protocols prior to in vivo engraftment of stem and progenitor cells in the context of regenerative medicine.

A review of tissue-engineered skin bioconstructs available for skin reconstruction

Situations where normal autografts cannot be used to replace damaged skin often lead to a greater risk of mortality, prolonged hospital stay and increased expenditure for the National Health Service. There is a substantial need for tissue-engineered skin bioconstructs and research is active in this field. Significant progress has been made over the years in the development and clinical use of bioengineered components of the various skin layers. Off-the-shelf availability of such constructs, or production of sufficient quantities of biological materials to aid rapid wound closure, are often the only means to help patients with major skin loss. The aim of this review is to describe those materials already commercially available for clinical use as well as to give a short insight to those under development. It seeks to provide skin scientists/tissue engineers with the information required to not only develop in vitro models of skin, but to move closer to achieving the ultimate goal of an off-the-shelf, complete full-thickness skin replacement.

The use of a non-cultured autologous cell suspension and Integra® dermal regeneration template to repair full-thickness skin wounds in a porcine model: A one-step process

Integra is a skin substitute used for dermal reconstruction. Current clinical practice consists of two procedures, first applying Integra to the wound and then replacing the silicone pseudo-epidermis with an epidermal autograft 3 weeks later. This two-step repair limits the clinical use of the product. An effective one-step procedure could reduce the time taken to repair and decrease the number of procedures for use of Integra. This study examined the effects of simultaneous application of a non-cultured autologous suspension of cells, isolated using the ReCell autologous cell harvesting device, in combination with Integra, to achieve a one-step skin repair. In two female Yorkshire swine, 10 full-thickness wounds were created. Wounds were treated with Integra seeded with cell suspension and compared to controls of Integra alone and cell suspension alone. Weekly macroscopic and histological assessment demonstrated that the wounds treated simultaneously with Integra and non-cultured autologous cells had enhanced epithelialization at an early time-point compared to controls. Wounds treated simultaneously with Integra and cell suspension demonstrate that cells remain viable, migrate through the Integra template and self-organize into differentiated epidermis. The results indicate that combining Integra with autologous cells facilitates one-step skin reconstruction of a full-thickness skin wound.

Cultured epithelial autograft (CEA) in burn treatment: three decades later

Methods for handling burn wounds have changed in recent decades and increasingly aggressive surgical approach with early tangential excision and wound closure is being applied. Split-thickness skin (STSG) autografts are the "gold standard" for burn wound closure and remain the mainstay of treatment to provide permanent wound coverage and achieve healing. In some massively burned patients, however, the burns are so extensive that donor site availability is limited. Fortunately, considerable progress has been made in the culture of human keratinocytes and it is now possible to obtain large amounts of cultured epithelium from a small skin biopsy within 3-4 weeks. Questions related to optimal cell type for culture, culture techniques, transplantation of confluent sheets or non-confluent cells, immediate and late final take, carrier and transfer modality, as well as final outcome, ability to generate an epithelium after transplantation, and scar quality are still not fully answered. Progress accomplished since Reinwald and Green first described their keratinocyte culture technique is reviewed.

Preparation and characterization of biodegradable anti-adhesive membrane for peritoneal wound healing

Postoperative adhesions remain a significant complication of abdominal surgery although the wide variety of physical barriers has been developed to reduce the incidence of adhesion. In this study, the bilayered composite membrane formed by the association of a methoxy poly (ethylene glycol)-poly (L-lactide-co-glycolide) (mPEG-PLGA) film and a crosslinked collagen-hyaluronic acid (Col-HA) membrane with fibronectin (FN) coating was prepared for promoting wound healing and providing tissue adhesion resistance simultaneously. In vitro adhesion test revealed that fibroblasts attached better on Col-HA membrane compared to those on mPEG-PLGA film, PLGA film or Interceed (oxidized cellulose) while mPEG-PLGA film had the lowest cell adhesive property. In confocal microscopic observation, the actin filaments were significantly further polymerized when 50 or 100 microg/cm(3) fibronectin was incorporated on the COL-HA membranes. After 7-day culture, fibroblasts penetrated throughout the Col-HA-FN network and the cell density increased whereas very few cells were found attached on the surface of the mPEG-PLGA film. In vivo evaluation test showed that the composite membrane could remain during the critical period of peritoneal healing and did not provoke any inflammation or adverse tissue reaction.

The effect of gelatin–chondroitin sulfate–hyaluronic acid skin substitute on wound healing in SCID mice

Tissue-engineered skin substitutes provided a feasibility to overcome the shortage of skin autograft by culturing keratinocytes and dermal fibroblasts in vitro. In this study, we applied bi-layer gelatin-chondrointin-6-sulfate-hyaluronic acid (gelatin-C6S-HA) biomatrices onto the severe combined immunodeficiency (SCID) mice to evaluate its effect on promoting wound healing. Human foreskin keratinocytes and dermal fibroblasts were cultured with reconstructed skin equivalent (rSE) for 7 days. The rSE was then grafted to the dorsum of SCID mice to evaluate its biocompatibility by histologic and immunohistochemistry analysis. The results showed that human epidermis were well-developed with the expression of differentiated markers and basement membrane-specific proteins at 4 weeks. After implantation, the percentages of skin graft take were satisfactory, while cell-seeded group was better than non-cell-seeded one. The basement membrane proteins including laminin, type IV collagen, type VII collagen, integrin alpha6, and integrin beta4 were all detected at the dermal-epidermal junction, which showed a continuous structure in the 4 weeks after grafting. This bi-layer gelatin-C6S-HA skin substitute not only has positive effect on promoting wound healing, but also has high rate of graft take. This rSE would have the potential to be applied on the extensively and deeply burned patients who suffer from severe skin defect in the near future.

[In vitro three-dimensional reconstruction of human bladder mucosa]

OBJECTIVE

The purpose of this study is to apply the in vitro keratinocyte culture techniques and the tissue engineering principles to human urothelium, to reconstruct an in vitro three-dimensional human bladder mucosa, suitable for grafting.

MATERIAL AND METHODS

Biopsy specimens of human bladder mucosa were obtained from patients undergoing suprapubic prostatectomy, in vitro cultured and finally, an immunohistochemical study was made.

RESULTS

A three-dimensional in vitro tissue was obtained, composed of a bio-artificial submucosa (fibrin gel and fibroblast) where the uroepithelial cells were seeding. We used a biodegradable polyglycolic acid mesh to facilitate the tissue manipulation and implantation. An immature epithelium was obtained with a weak immunostaining to cytokeratins. The immunohistochemical study could not demonstrate the development of basement membrane.

CONCLUSIONS

In vitro keratinocyte culture techniques could be applied to other epithelial tissues like the urothelium. We obtained a three-dimensional in vitro tissue suitable for grafting in a relatively short time, which needs the matrix interactions in order to mature.

Therapeutic neovascularization: contributions from bioengineering

A number of pathological entities and surgical interventions could benefit from therapeutic stimulation of new blood vessel formation. Although strategies designed for promoting neovascularization have shown promise in preclinical models, translation to human application has met with limited success when angiogenesis is used as the single therapeutic mechanism. While clinical protocols continue to be optimized, a number of exciting new approaches are being developed. Bioengineering has played an important role in the progress of many of these innovative new strategies. In this review, we present a general outline of therapeutic neovascularization, with an emphasis on investigations using engineering principles to address this vexing clinical problem. In addition, we identify some limitations and suggest areas for future research.

Culturing of skin fibroblasts in a thin PLGA-collagen hybrid mesh

A thin biodegradable hybrid mesh of synthetic poly(DL-lactic-co-glycolic acid) (PLGA) and naturally derived collagen was used for three-dimensional culture of human skin fibroblasts. The hybrid mesh was constructed by forming web-like collagen microsponges in the openings of a PLGA knitted mesh. The behaviors of the fibroblasts on the hybrid mesh and PLGA knitted mesh were compared. The efficiency of cell seeding was much higher and the cells grew more quickly in the hybrid mesh than in the PLGA mesh. The fibroblasts in the PLGA mesh grew from the peripheral PLGA fibers toward the centers of the openings, while those in the hybrid mesh also grew from the collagen microsponges in the openings of the mesh resulting in a more homogenous growth. The proliferated cells and secreted extracellular matrices were more uniformly distributed in the hybrid mesh than in the PLGA mesh. Histological staining of in vitro cultured fibroblast/mesh implants indicated that the fibroblasts were distributed throughout the hybrid mesh and formed a uniform layer of dermal tissue having almost the same thickness as that of the hybrid mesh. However, the tissue formed in the PLGA mesh was thick adjacent to the PLGA fibers and thin in the center of the openings. Fibroblasts cultured in the hybrid mesh were implanted in the back of nude mouse. Dermal tissues were formed after 2 weeks and became epithelialized after 4 weeks. The results indicate that the web-like collagen microsponges formed in the openings of the PLGA knitted mesh increased the efficiency of cell seeding, improved cell distribution, and therefore facilitated rapid formation of dermal tissue having a uniform thickness. PLGA-collagen hybrid mesh may be useful for skin tissue engineering.

Reduction of adhesions with composite AlloDerm/polypropylene mesh implants for abdominal wall reconstruction

Ventral hernia repair often includes the use of structural prosthetic materials, such as polypropylene mesh, that can induce dense abdominal adhesions to peritoneal structures. AlloDerm (LifeCell Corp., Branchburg, N.J.), a commercially available decellularized human dermal analogue with its native basement membrane components intact, is gradually revascularized and replaced with autologous tissue after implantation. The authors hypothesized that AlloDerm integrated with polypropylene mesh would reduce adhesions and provide a biodegradable scaffold to generate an autologous vascularized tissue layer separating the abdominal viscera from the mesh. Ventral hernia defects (3 x 1 cm) in 19 guinea pigs were repaired using an inlay technique with polypropylene mesh alone (n = 6) or with composite implants constructed by integrating polypropylene mesh and AlloDerm with its basement membrane surface oriented toward (polypropylene/AlloIn, n = 7) or away from (polypropylene/ AlloOut, n = 6) the peritoneal cavity. At 4 weeks, the authors determined the amount of mesh implant surface area covered by adhesions, the strength of the adhesions [graded from 0 (none) to 3], and the incidence of bowel adhesions. Histologic analyses were performed on full-thickness tissue sections from the repair sites. The mean surface areas affected by adhesions and mean adhesion strength were significantly lower in the polypropylene/AlloIn (area, 12.4 percent; mean grade, 1.0) and polypropylene/AlloOut (area, 9.5 percent; mean grade, 0.5) groups than in the polypropylene group (area, 79.5 percent; mean grade, 2.9); there were no such differences between the polypropylene/AlloIn and polypropylene/AlloOut groups. The bowel was adherent to 67 percent of polypropylene repairs and 0 percent of the composite mesh repairs. The AlloDerm was remodeled to form a vascularized tissue layer beneath the mesh in composite repairs, unlike the significantly thinner, dense scar layer that formed in the polypropylene repairs. Immunohistochemical labeling for factor VIII showed neovascularization throughout the AlloDerm. The AlloDerm thus functioned as a biodegradable tissue scaffold, guiding the formation of a thick, well-vascularized tissue layer separating the polypropylene mesh from intraperitoneal structures. This significantly reduced both the amount of surface area covered by adhesions and adhesion strength. Basement membrane orientation had no effect. Composite mesh implants composed of structural prosthetic materials integrated with AlloDerm may have useful clinical applications for abdominal wall reconstruction by reducing adhesions and providing a vascularized tissue layer to separate and protect the peritoneal structures from polypropylene mesh fibers.

Plastic Surgery

The range of casualties treated by the Defence Medical Services in the recent Gulf conflict has reaffirmed the important role of plastic surgery within the military. This review seeks to highlight some areas of recent innovation and improvement within the realms of plastic surgery generally, of which some, such as the introduction of Flammacerium and the availability of skin substitutes, have direct military relevance.

Selective differentiation of neural progenitor cells by high-epitope density nanofibers

Neural progenitor cells were encapsulated in vitro within a three-dimensional network of nanofibers formed by self-assembly of peptide amphiphile molecules. The self-assembly is triggered by mixing cell suspensions in media with dilute aqueous solutions of the molecules, and cells survive the growth of the nanofibers around them. These nanofibers were designed to present to cells the neurite-promoting laminin epitope IKVAV at nearly van der Waals density. Relative to laminin or soluble peptide, the artificial nanofiber scaffold induced very rapid differentiation of cells into neurons, while discouraging the development of astrocytes. This rapid selective differentiation is linked to the amplification of bioactive epitope presentation to cells by the nanofibers.

Synthesis of Tissues and Organs

Symbolism that describes the synthetic processes for chemical compounds has been used to describe, in qualitative terms, the synthesis of tissues and organs at the correct anatomical site. The synthetic process is summarized in the reaction diagram, a shorthand representation of the reactants, reactor, and products. Analysis of a large number of independent protocols has led to identification of the simplest synthetic pathways for two organs that have been studied extensively: skin and peripheral nerves. These apparently irreducible reaction diagrams for the two organs are not only simple but surprisingly similar, a fact suggesting the existence of general rules for the synthesis of other organs as well. The only two reactants that are required are an active scaffold (a macromolecular network synthesized as a highly porous analogue of the extracellular matrix) and a seeding of epithelial cells of the organ being synthesized. Scaffolds possessed biological (regenerative) activity provided that they were capable of blocking the contraction process that leads to closure of the injured site. Such activity requires that the density of ligands for binding of contractile cells on the scaffold maintains a sufficiently high level over the period of synthesis.

Clinical applications of tissue engineered constructs

The reconstruction of soft tissue defects poses a challenge for plastic surgeons and tissue engineers. The construction of a biologically, functionally, and cosmetically successful replacement part will involve the combination of a composite that contains endoderm, mesoderm, and ectoderm. It will be active in immune surveillance and function. It must be durable to withstand the stress and strain encountered by the skin. Such a composite will involve the use of bone, cartilage, muscle, blood vessels, nerves, connective tissue, dermis, and epidermis. Fortunately, many of these tissues are among the best studied by tissue engineers. The future of this field will likely involve to some degree the co-mingling of current reconstructive modalities, including the techniques of prefabrication and pre-lamination, with more aggressive and successful tissue engineering technology and the rapidly developing science of stem cell biology. Tissues synthesized in vitro with better structure, color, and texture can be pre-laminated to a site that has already been prefabricated. Prefabrication of a bio-absorbable matrix can create a well perfused scaffold onto which larger subunits can be prelaminated. The future of this field of endeavor is exciting, and, with further research, experience, and interdisciplinary collaboration, bioengineered tissue constructs will become a reality.

A guide to biological skin substitutes

The role of artificial skin substitutes in burn surgery and the treatment of chronic wounds is constantly evolving. New products are regularly being produced and approved for clinical use. Studies on existing products clarify their efficacy and effectiveness in different clinical scenarios. This review is aimed at busy clinicians in order to bring them up to date with the latest developments in the field of artificial skin substitutes. It examines the components, structure, performance and comparative costs of the main commercial skin substitutes, and reviews briefly technologies under development that have not yet become widely available.

Regeneration of neomucosa using cell-seeded collagen-GAG matrices in athymic mice

Tissue engineering of oral mucosa could allow improved reconstructive options for intraoral tissue defects. Porous collagen-glycosaminoglycan (CG) matrices coated with a silicone elastomer were seeded by centrifugation with cultured human oral mucosal epithelial cells (strain OKG4 gingival keratinocytes) at a density of 250,000 cells per square centimeter. Full-thickness dorsal wounds (1.5 x 1.5 cm) were created surgically on each athymic mouse and were treated with either a seeded matrix or an unseeded matrix, or they were left open as a control. The CG matrices reduced the degree of wound contraction at day 14 compared with open wounds. The epithelial thickness of seeded matrices at day 14 was significantly greater (p = 0.0001) than that of unseeded matrices. Seeded matrices had more rapid degradation at 14 days compared with unseeded matrices. Human oral mucosal cells seeded into CG matrices contribute to form a stratified and differentiated epithelial layer during revascularization, cellular infiltration, and degradation of the CG matrix.

Effects of collagen matrix containing transforming growth factor (TGF)-beta(1) on wound contraction

We evaluated the effectiveness of transforming growth factor (TGF)-beta(1) on wound contraction, both alone and in combination with collagen matrix, using an in vivo delayed wound healing type model. To clarify the mechanisms involved in the effectiveness of TGF-beta(1), we also used a fibroblast-populated collagen gel contraction in vitro model. Although we found that TGF-beta(1) significantly accelerated contraction of the fibroblast-populated collagen gel in vitro, we demonstrated that both collagen matrix alone and 1.0 microg of TGF-beta(1) alone significantly inhibited wound contraction in the in vivo model. In addition, the combination of TGF-beta(1) and collagen matrix was much more effective than TGF-beta(1) alone, a finding which was supported by histopathological examination. Wounds treated with collagen matrix containing TGF-beta(1) showed horizontal rearrangement of collagen fibers in the dermal part as well as evidence of active fibroblast proliferation, which was not observed in the scar regions of controls. These results show that the application of TGF-beta(1) treated collagen matrix is effective for preventing contraction producing so called "neodermis" in treating a delayed healing type model and may be highly beneficial for treating chronic wounds.

Heparin in the treatment of burns: a review

Burns are difficult to treat, wounds with complex local and systemic pathology and high mortality, that often heal slowly with scars and contractures. Glycosaminoglycans (GAGs) have been used in parenteral and topical application studies. These studies have uncovered anticoagulative, antiinflammatory and neoangiogenic properties, which may stimulate tissue repair and reepithelializing effects. The endogenous GAGs utilized in treating burns are heparin, dermatan sulfate, heparan sulfate, keratin sulfate, chondroitin-4- and chondroitin-6-sulfate, and hyaluronic acid. Heparin, the most sulfated and acidic GAG, has been used parenterally, topically, by inhalation, in pellet, and in bioengineered membranes. Heparin relieved pain, inhibited clotting and inflammation, restored blood flow, and enhanced healing. Heparin effects that improved and reduced burn care were time, dose, pH, site, source and duration related in studies. Potential adverse effects with heparin use are bleeding, thrombocytopenia and allergy. Heparin preserved lung and improved function. Heparin preserved intestinal integrity and reduced bacterial translocation. Collagen restoration was enhanced. The healed skin was smooth. Heparin reduced needs for pain medicine, topical antibiotics, resuscitation fluids, blood, water baths, debridement, surgery and grafts. Cost of treatments were reduced. Although not as yet fully substantiated, topical heparin therapy of burns may be a useful addition to the range of available treatments for burn wounds.

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.

Reduction of abdominal adhesions using composite collagen-GAG implants for ventral hernia repair

Structural biomaterials can restore abdominal wall integrity but may cause adhesions to the underlying viscera. Collagen-glycosaminoglycan (CG) matrices induce the formation of connective tissue and may reduce adhesion formation to permanent biomaterials such as polypropylene (PP) mesh. Composite implants were created by interposing PP mesh within a porous CG matrix created composite implants. The implants were cross-linked with glutaraldehyde one group (CG-G/PP) or left untreated (CG-nG/PP) and compared to PP mesh. At 4 weeks, the abdominal wall was assessed for the degree of adhesions. The composite implants developed a nascent connective tissue-like structure that reduced adhesions to the bowel. The thickest connective tissue developed in the CG-G/PP group (0.7 +/- 0.1 mm) and thinnest in the PP mesh (0.05 +/- 0.01 mm). The surface area covered with adhesions was greatest in the PP group (72 +/- 17%) compared with the CG-G/PP group (28 +/- 15%) or the CG-nG/PP group (21 +/- 8%). Bowel preferentially adhered to the PP mesh, whereas omentum had some adherence to all constructs. Integrating a biodegradable extracellular matrix analog with a permanent structural biomaterial reduced adhesions in this animal model. Alterations in cross-linking of the CG matrix altered the biological response. This technology may be useful in reconstructive surgery by reducing adhesion formation, while maintaining the strength of permanent structural biomaterials.

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

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

Use of porcine acellular dermal matrix as a dermal substitute in rats

OBJECTIVE

To examine porcine acellular dermal matrix (ADM) as a xenogenic dermal substitute in a rat model.

SUMMARY BACKGROUND DATA

Acellular dermal matrix has been used in the treatment of full-thickness skin injuries as an allogenic dermal substitute providing a stable wound base in human and animal studies.

METHODS

Xenogenic and allogenic ADMs were produced by treating porcine or rat skin with Dispase and Triton X-100. Full-thickness skin defects (225 mm2) were created on the dorsum of rats (n = 29), porcine or rat ADMs were implanted in them, and these were overlain with ultrathin split-thickness skin grafts (STSGs). In two adjacent wounds, 0.005- or 0.017-inch-thick autografts were implanted. In other experiments, the antimicrobial agent used during ADM processing (azide or a mixture of antibiotics) and the orientation of the implanted ADM (papillary or reticular side of ADM facing the STSG) were studied. Grafts were evaluated grossly and histologically for 30 days after surgery.

RESULTS

Significant wound contraction was seen at 14, 20, and 30 days after surgery in wounds receiving xenogenic ADM, allogenic ADM, and thin STSGs. Contraction of wounds containing xenogenic ADM was significantly greater than that of wounds containing allogenic ADM at 30 days after surgery. Graft take was poor in wounds containing xenogenic ADM and moderately good in those containing allogenic ADM. Wound healing was not significantly affected by the antimicrobial agent used during ADM preparation or by the ADM orientation.

CONCLUSION

Dispase-Triton-treated allogenic ADM was useful as a dermal substitute in full-thickness skin defects, but healing with xenogenic ADM was poor.

Effects of a collagen matrix containing prostaglandin E(1) on wound contraction

In this study, we evaluated the effectiveness of prostaglandin (PG) E(1) in inhibiting wound contraction, both alone and in combination with collagen matrix, using a in vivo full thickness skin defect model. To clarify the mechanisms involved in this inhibition we also used a fibroblast-populated collagen gel contraction in vitro model. We demonstrated that collagen matrix alone significantly inhibited wound contraction PG E(1) alone did not. Interestingly, their combination was much more effective than either collagen matrix or PG E(1) alone, a finding which was also supported by histopathological examination. Wounds treated with collagen matrix, but not control wounds, showed horizontal rearrangement of collagen fibers in the dermal part as well as evidence of active fibroblast proliferation which was not observed in scar regions surrounded by normal dermis. With the fibroblast-populated collagen gel contraction in vitro model, we found that PG E(1) significantly inhibited contraction at a high dose. It was concluded that collagen matrix combined with PG E(1) is effective for preventing contracture producing so called neodermis than collagen matrix alone, which remains one of the most challenging problems in treating full thickness type wounds.

Take percentage and conditions of cultured epithelium were improved when basement membrane of the graft was maintained and anchoring mesh was added

To achieve a higher take rate for epithelial grafts, this study investigated grafting techniques. Seventy-seven nude mice received flap grafting in which cultured human epithelium was grafted inside the flap, and 55 nude rats received transplantation of epithelium to a full-thickness skin defect. In each group, four models were studied, including model 1, in which epithelium was cultured with the conventional method; model 2, in which epithelium was cultured with fibrin gel to avoid sheet damage, then absorptive mesh was incorporated into the epithelium for anchoring to the graft bed; model 3, in which epithelium was cultured with fibrin gel and combined with absorptive mesh and artificial dermis containing fibroblasts; and model 4, in which the model 2 epithelium was grafted after artificial dermis was transplanted. The take for these models was evaluated grossly and histologically. The results show that the take percentage of models 2 and 3 was significantly higher than that of model 1 (conventional epithelium) and that there was no significant difference between model 3 (simultaneous grafting) and model 4 (two-step grafting). The difference in the take percentages of the grafts to the flap and to the full-thickness skin defect was also insignificant. In immunohistochemistry, human keratin appeared in all epidermis layers and diversification of the layer was observed in models 2, 3, and 4. In these three models, type IV collagen appeared in the basal layer and the formation of basal membrane was confirmed. These findings suggest that epithelia cultured on fibrin gel and combined with absorptive mesh could be used in a new technique for better, more stable take.

Carbohydrates in transplantation

Carbohydrate materials have become increasingly utilized in transplantation and cell/tissue engineering within the past year. This has been well documented in recent applications of immobilized or soluble alpha-galactosyl epitopes (i.e. oligosaccharides with a terminal Galalpha1-3Gal sequence) in preventing hyperacute rejection in pig-to-primate xenotransplantation. In addition, alpha-galactosyl polymers have been shown to exhibit much greater activity (up to 10(4) times) than alpha-galactosyl monomers in inhibiting the binding of anti-galactosyl antibodies to pig kidney epithelial cells and assisting in the prevention of cytotoxicity in human serum.