Skin substitutes: a review

Silver nanoparticle loaded collagen/chitosan scaffolds promote wound healing via regulating fibroblast migration and macrophage activation

Treatment of full-thickness skin defects poses significant clinical challenges including risk of infection and severe scaring. Silver nanoparticle (NAg), an effective antimicrobial agent, has provided a promising therapeutic method for burn wounds. However, the detailed mechanism remains unknown. Hence, we constructed a metallic nanosilver particles-collagen/chitosan hybrid scaffold (NAg-CCS) and investigated its potential effects on wound healing. In vitro scratch assay, immunofluorescence staining and antibacterial activity of the scaffold were all studied. In vivo NAg-CCS was applied in full-thickness skin defects in Sprague-Dawley (SD) rats and the therapeutic effects of treatment were evaluated. The results showed that NAg at a concentration of 10 ppm accelerated the migration of fibroblasts with an increase in expression of α-smooth muscle actin (α-SMA). Furthermore, in vivo studies showed increased levels of pro-inflammatory and scar-related factors as well as α-SMA, while markers for macrophage activation were up-regulated. On day 60 post transplantation of ultra-thin skin graft, the regenerated skin by NAg-CCS had a similar structure to normal skin. In summary, we demonstrated that NAg-CCS was bactericidal, anti-inflammatory and promoted wound healing potentially by regulating fibroblast migration and macrophage activation, making it an ideal dermal substitute for wound regeneration.

Novel bilayer wound dressing based on electrospun gelatin/keratin nanofibrous mats for skin wound repair

A bilayer membrane (GKU) with a commercial polyurethane wound dressing as an outer layer and electrospun gelatin/keratin nanofibrous mat as an inner layer was fabricated as a novel wound dressing. Scanning electron micrographs showed that gelatin/keratin nanofibers had a uniform morphology and bead-free structure with average fiber diameter of 160.4nm. 3-(4,5-Dimethylthiazolyl)-2,5-diphenyltetrazolium bromide assay using L929 fibroblast cells indicated that the residues released from the gelatin/keratin composite nanofibrous mat accelerated cell proliferation. Cell attachment experiments revealed that adhered cells spread better and migrated deeper into the gelatin/keratin nanofibrous mat than that into the gelatin nanofibrous mat. In animal studies, compared with the bilayer membrane without keratin, gauze and commercial wound dressing, Comfeel®, GKU membrane gave much more number of blood vessels and a greater reduction in wound area at 4days, and better wound repair at 14days with a thicker epidermis and larger number of newly formed hair follicles. GKU membrane, thus, could be a good candidate for wound dressing applications.

An easy-to-use wound dressing gelatin-bioactive nanoparticle gel and its preliminary in vivo study

Beyond promoting hard tissue repairing, bioactive glasses (BGs) have also been proved to be beneficial for wound healing. Nano-scale BGs prepared by sol-gel method were found to have a better performance as they have a larger specific surface area. In this work, bioactive nanoparticles (nBPs) with mean diameter of 12 nm (BP-12) instead of conventional BGs were mixed with gelatin to form an easy-to-use hydrogel as a dressing for skin wound. It was found that the composite of BP-12 and gelatin could form a hydrogel (BP-12/Gel) under 25 °C, which showed pronounced thixotropy at a practically accessible shear rate, therefore become easy to be used for wound cover. In vitro, the composite hydrogel of BP-12 and gelatin had good biocompatibility with the fibroblast cells. In vivo, rapid cutaneous-tissue regeneration and tissue-structure formation within 7 days was observed in the wound-healing experiment performed in rats. This hydrogel is thus a promising easy-to-use wound dressing material.

Platelet-Rich Plasma-Loaded Poly(d,l-lactide)-Poly(ethylene glycol)-Poly(d,l-lactide) Hydrogel Dressing Promotes Full-Thickness Skin Wound Healing in a Rodent Model

Traditional therapeutic methods for skin wounds have many disadvantages, and new wound dressings that can facilitate the healing process are thus urgently needed. Platelet-rich plasma (PRP) contains multiple growth factors (GFs) and shows a significant capacity to heal soft tissue wounds. However, these GFs have a short half-life and deactivate rapidly; we therefore need a sustained delivery system to overcome this shortcoming. In this study, poly(d,l-lactide)-poly(ethylene glycol)-poly(d,l-lactide) (PDLLA-PEG-PDLLA: PLEL) hydrogel was successfully created as delivery vehicle for PRP GFs and was evaluated systematically. PLEL hydrogel was injectable at room temperature and exhibited a smart thermosensitive in situ gel-formation behavior at body temperature. In vitro cell culture showed PRP-loaded PLEL hydrogel (PRP/PLEL) had little cytotoxicity, and promoted EaHy926 proliferation, migration and tube formation; the factor release assay additionally indicated that PLEL realized the controlled release of PRP GFs for as long as 14 days. When employed to treat rodents’ full-thickness skin defects, PRP/PLEL showed a significantly better ability to raise the number of both newly formed and mature blood vessels compared to the control, PLEL and PRP groups. Furthermore, the PRP/PLEL-treated group displayed faster wound closure, better reepithelialization and collagen formation. Taken together, PRP/PLEL provides a promising strategy for promoting angiogenesis and skin wound healing, which extends the potential of this dressing for clinical application.

Secretion of wound healing mediators by single and bi-layer skin substitutes

Limitations of current treatments for skin loss caused by major injuries leads to the use of skin substitutes. It is assumed that secretion of wound healing mediators by these skin substitutes plays a role in treating skin loss. In our previous study, single layer keratinocytes (SK), single layer fibroblast (SF) and bilayer (BL; containing keratinocytes and fibroblasts layers) skin substitutes were fabricated using fibrin that had shown potential to heal wounds in preclinical studies. This study aimed to quantify the secretion of wound healing mediators, and compare between single and bi-layer skin substitutes. Skin samples were digested to harvest fibroblasts and keratinocytes, and expanded to obtain sufficient cells for the construction of skin substitutes. Acellular fibrin (AF) construct was used as control. Substitutes i.e. AF, SK, SF and BL were cultured for 2 days, and culture supernatant was collected to analyze secretion of wound healing mediators via multiplex ELISA. Among 19 wound healing mediators tested, BL substitute secreted significantly higher amounts of CXCL1 and GCSF compared to SF and AF substitute but this was not significant with respect to SK substitute. The BL substitute also secreted significantly higher amounts of CXCL5 and IL-6 compared to other substitutes. In contrast, the SK substitute secreted significantly higher amounts of VCAM-1 compared to other substitutes. However, all three skin substitutes also secreted CCL2, CCL5, CCL11, GM-CSF, IL8, IL-1α, TNF-α, ICAM-1, FGF-β, TGF-β, HGF, VEGF-α and PDGF-BB factors, but no significant difference was seen. Secretion of these mediators after transplantation may play a significant role in promoting wound healing process for the treatment of skin loss.

In vivo and in vitro studies of borate based glass micro-fibers for dermal repairing

Full-thickness skin defects represent urgent clinical problem nowadays. Wound dressing materials are hotly needed to induce dermal reconstruction or to treat serious skin defects. In this study, the borate bioactive glass (BG) micro-fibers were fabricated and compared with the traditional material 45S5 Bioglass(®) (SiG) micro-fibers. The morphology, biodegradation and bioactivity of BG and SiG micro-fibers were investigated in vitro. The wound size reduction and angiogenic effects of BG and SiG micro-fibers were evaluated by the rat full-thickness skin defect model and Microfil technique in vivo. Results indicated that the BG micro-fibers showed thinner fiber diameter (1 μm) and better bioactivity than the SiG micro-fibers did. The ionic extracts of BG and SiG micro-fibers were not toxic to human umbilical vein endothelial cells (HUVECs). In vivo, the BG micro-fiber wound dressings obviously enhanced the formation of blood vessel, and resulted in a much faster wound size reduction than the SiG micro-fibers, or than the control groups, after 9 days application. The good skin defect reconstruction ability of BG micro-fibers contributed to the B element in the composition, which results in the better bioactivity and angiogenesis. As shown above, the novel bioactive borate glass micro-fibers are expected to provide a promising therapeutic alternative for dermal reconstruction or skin defect repair.

Evaluation of commonly used temporary skin dressings and a newly developed collagen matrix for treatment of superficial wounds

OBJECTIVE

In the authors' experience, extended superficial-thickness wounds often were treated with the application of synthetic temporary wound dressings. There is a broad range of expensive products available in this market. The aim of this study was to compare commonly used temporary skin dressings with a newly developed collagen matrix.

METHODS

A total of 56 standardized superficial skin defects were generated on the back of 28 adult male Lewis rats using a skin dermatome. The wounds were treated with Biobrane (Smith & Nephew, St Petersburg, Florida) (n = 14), Suprathel (PolyMedics, Denkendorf, Germany) (n = 14), and newly developed Collagen Cell Carrier (Naturin Viscofan, Weinheim, Germany) (CCC; n = 14). Histological evaluation was performed at 3 months' postoperative in regard to quality of newly formed skin.

RESULTS

In regard to epidermal cell count and thickness of skin, Biobrane and Suprathel demonstrated comparable values, whereas CCC demonstrated higher epidermal cell count and thicker neoepidermis. The epidermal thickness of CCC was comparable to untreated, healthy skin.

CONCLUSIONS

The presented results reveal the potential of CCC in the treatment of superficial skin defects and encourages further evaluation of CCC in surgical applications and regenerative medicine.

Wound dressings composed of copper-doped borate bioactive glass microfibers stimulate angiogenesis and heal full-thickness skin defects in a rodent model

There is a need for better wound dressings that possess the requisite angiogenic capacity for rapid in situ healing of full-thickness skin wounds. Borate bioactive glass microfibers are showing a remarkable ability to heal soft tissue wounds but little is known about the process and mechanisms of healing. In the present study, wound dressings composed of borate bioactive glass microfibers (diameter = 0.4-1.2 μm; composition 6Na2O, 8K2O, 8MgO, 22CaO, 54B2O3, 2P2O5; mol%) doped with 0-3.0 wt.% CuO were created and evaluated in vitro and in vivo. When immersed in simulated body fluid, the fibers degraded and converted to hydroxyapatite within ∼7 days, releasing ions such as Ca, B and Cu into the medium. In vitro cell culture showed that the ionic dissolution product of the fibers was not toxic to human umbilical vein endothelial cells (HUVECs) and fibroblasts, promoted HUVEC migration, tubule formation and secretion of vascular endothelial growth factor (VEGF), and stimulated the expression of angiogenic-related genes of the fibroblasts. When used to treat full-thickness skin defects in rodents, the Cu-doped fibers (3.0 wt.% CuO) showed a significantly better capacity to stimulate angiogenesis than the undoped fibers and the untreated defects (control) at 7 and 14 days post-surgery. The defects treated with the Cu-doped and undoped fibers showed improved collagen deposition, maturity and orientation when compared to the untreated defects, the improvement shown by the Cu-doped fibers was not markedly better than the undoped fibers at 14 days post-surgery. These results indicate that the Cu-doped borate glass microfibers have a promising capacity to stimulate angiogenesis and heal full-thickness skin defects. They also provide valuable data for understanding the role of the microfibers in healing soft tissue wounds.

Comparison studies of the in vivo treatment of full-thickness excisional wounds and burns by an artificial bilayer dermal equivalent and J-1 acellular dermal matrix

The effects upon skin repair were compared between a homemade bilayer dermal equivalent (BDE), composed of a collagen/chitosan porous scaffold and a silicone membrane, and J-1 acellular dermal matrix (ADM), a commercial ADM that is used widely in China to treat various skin defects. Full-thickness excisional and burn wounds were prepared on the backs of pigs and then treated with the BDE and J-1 ADM. Biopsy specimens were harvested on days 7, 14, and 21 after surgery for gross, biochemical, and molecular examinations. In comparison with the burn wounds, the excisional wounds showed accelerated granular tissue formation and superior integration with the equivalents, regardless of their type. Immunohistochemical, immunofluorescence, real time quantitative polymerase chain reaction and Western blotting analyses showed that the vascularization rates in the excisional wounds group were also significantly faster than those of the burn group for both dermal equivalents. There was no significant difference between J-1 ADM and BDE treatment on the formation of newly formed blood vessels for the excisional wounds at days 7, 14, and 21. However, there was a significant difference in the number of nascent blood vessels formed in the burn wounds after treatment with J-1 ADM compared with BDE. The highest numbers of newly formed and mature blood vessels were present in the J-1 ADM-treated excisional wounds after 21 days. Ultrathin skin grafts were further transplanted on to the regenerated dermis for 28 days, resulting in the repair of the full-thickness wounds and production of a structure similar to normal skin.

Current wound healing procedures and potential care

In this review, we describe current and future potential wound healing treatments for acute and chronic wounds. The current wound healing approaches are based on autografts, allografts, and cultured epithelial autografts, and wound dressings based on biocompatible and biodegradable polymers. The Food and Drug Administration approved wound healing dressings based on several polymers including collagen, silicon, chitosan, and hyaluronic acid. The new potential therapeutic intervention for wound healing includes sustained delivery of growth factors, and siRNA delivery, targeting microRNA, and stem cell therapy. In addition, environment sensors can also potentially utilize to monitor and manage microenvironment at wound site. Sensors use optical, odor, pH, and hydration sensors to detect such characteristics as uric acid level, pH, protease level, and infection - all in the hopes of early detection of complications.

Glyaderm(®) dermal substitute: clinical application and long-term results in 55 patients

INTRODUCTION

Glycerol preserved acellular dermis (Glyaderm(®)) consists of collagen and elastin fibers and is the first non-profit dermal substitute derived from glycerol-preserved, human allogeneic skin. It is indicated for bi-layered skin reconstruction of full thickness wounds.

METHODS

A protocol for clinical application and optimal interval before autografting with split thickness skin graft (STSG) was developed in a pilot study. A phase III randomized, controlled, paired, intra-individual study compared full thickness defects engrafted with Glyaderm(®) and STSG versus STSG alone. Outcome measures included percentage of Glyaderm(®) take, STSG take, and scar quality assessment.

RESULTS

Pilot study (27 patients): Mean take rates equaled 91.55% for Glyaderm(®) and 96.67% for STSG. The optimal autografting interval was 6 days (±1 day). Randomized trial (28 patients): Mean Glyaderm(®) take rate was 88.17%. STSG take rates were comparable for both research groups (p=0.588). One year after wound closure, Glyaderm(®)+STSG was significantly more elastic (p=0.003) than STSG alone. Blinded observers scored Glyaderm(®) treated wounds better in terms of scar quality.

DISCUSSION

The efficacy of Glyaderm(®) as a suitable dermal substitute for full thickness wounds is attested. Currently a procedure for simultaneous application of Glyaderm(®) and STSG is adopted, allowing for further widespread use of Glyaderm(®).

Spray-assisted layer-by-layer assembly on hyaluronic acid scaffolds for skin tissue engineering

Tissue engineering approaches for the development of a single epidermal-dermal scaffold to treat full-thickness skin defects have been limited by difficulties in the fabrication of a bilayer scaffold combining the specific properties of the epidermis and the dermis. Here we present an innovative approach to developing a scaffold that holds promise for skin tissue engineering. We utilize the spray-assisted layer-by-layer assembly technique to deposit a polyelectrolyte multilayer film composed of hyaluronic acid and poly-L-lysine (the epidermal component) on a porous hyaluronic acid scaffold (the dermal component), in a rapid and controlled manner. The multilayer film promotes cell adhesion, contributing to regeneration of the epidermal barrier functions of skin. While human keratinocytes attached and proliferated on the coated porous scaffolds, they did not invade the porous dermal component, thus leaving room for seeding of relevant fibroblast cell types in this scaffold. This scaffold therefore holds promise for co-culture of different cells, which may be useful for treatment of full-thickness skin defects as well as other tissue engineering applications.

A novel biomaterial: bacterial cellulose and its new era applications

Bacterial cellulose (BC) is a promising natural polymer that is produced by bacteria and that has unique and desirable structural, physical, and chemical properties. From the time when the remarkable properties of BC were found 15 years ago compared with plant cellulose, interest has grown in BC and it has become an article of trade in diverse applications. Following this trend, this paper reviews the progress of relevant studies, including general information about cellulose, production by microorganisms as well as BC cultivation, and its properties. The applications reviewed in the present article comprise biological and nonbiological fields. The latest use of BC in the biomedical, environmental, agricultural, electronic, food, and industrial fields is discussed with its applications in composite form. The present article attempts to amass the assorted uses of BC under one umbrella. Thus, recent advances in BC applications in different fields are thoroughly reviewed. This article concludes with the need for future research of BC to make it commercialized as vital biomaterial.

Biological skin substitutes for wound cover and closure

In the past 30 years, the development and use of artificial skin in the treatment of acute and chronic wounds has advanced from an experimental concept to a working reality. However, while there have been an increasing number of artificial skin substitutes licensed for clinical use, they have yet to supplant the current gold standard of an autologous tissue graft for most applications. This article reviews the advantages and disadvantages of the currently available, biologically based substitutes, with special emphasis on their relative efficacy and suitability for treatment of particular wound types. Economic considerations, desirable improvements of currently available materials and the potential impact of future advances in the field will also be discussed.

Scab-inspired cytophilic membrane of anisotropic nanofibers for rapid wound healing

This work investigates the influence of cytophilic and anisotropic nanomaterials on accelerated cell attachment and directional migration toward rapid wound healing. Inspired by the anisotropic protein nanofibers in scab, a polyurethane (PU) nanofibrous membrane with an aligned structure was fabricated. The membrane showed good affinity for wound-healing-related cells and could guide cell migration in the direction of PU nanofibers. Also, the morphology and distribution of F-actin and paxillin of attached cells were influenced by the underlying nanofibers. The randomly distributed PU nanofibers and planar PU membrane did not show a distinct impact on cell migration. This scab-inspired cytophilic membrane is promising in applications as functional interfacial biomaterials for rapid wound healing, bone repair, and construction of neural networks.

Application of acellular dermal xenografts in full-thickness skin burns

The aim of this study was to explore the clinical value of the porcine acellular dermal xenograft (ADX) in combination with autologous split-thickness skin and pure autologous split-thickness skin grafting applied in deep full-thickness burns and scar wounds. A total of 30 patients with deep burns were randomly divided into experimental and control groups following escharectomy. The patients were separately treated with porcine acellular dermal xenograft (ADX) in combination with autologous split-thickness skin and pure autologous split-thickness skin graft. The wound healing was observed routinely and the scores were evaluated using Vancouver scar scale at different times following transplant surgery. The samples of cograft regions and the control group (pure transplant split-thickness skin autograft) were observed using light microscopy and electron microscopy, and the follow-up results were recorded. No conspicuous rejections on the cograft wound surface were observed. Compared with the control group, the cograft wounds were smooth, presented no scar contracture and exhibited good skin elasticity and recovery of the joint function. The cografted skin combined well and displayed a clear and continuous basal membrane, as well as gradually combined skin structure, a mature stratum corneum, downward extended rete pegs, a mainly uniform dermal collagen fiber structure, regular alignment, and fewer blood capillaries. Clear desmosome cograft regions were identified among heckle cells, as well as a clear and continuous basal membrane. The cografted skin of the combined split-thickness autograft and the acellular heterologous (porcine) dermal matrix showed an improved shape and functional recovery compared with the pure split-thickness skin autograft. The combination of the meshed ADX and the split-thickness skin autograft applied in deep full-thickness burns and scar wounds may induce tissue regeneration via dermis aiming. This method also has superior shape and functional recovery, and has an extensive clinical application value.

Epithelial mechanobiology, skin wound healing, and the stem cell niche

Skin wound healing is a vital process that is important for re-establishing the epithelial barrier following disease or injury. Aberrant or delayed skin wound healing increases the risk of infection, causes patient morbidity, and may lead to the formation of scar tissue. One of the most important events in wound healing is coverage of the wound with a new epithelial layer. This occurs when keratinocytes at the wound periphery divide and migrate to re-populate the wound bed. Many approaches are under investigation to promote and expedite this process, including the topical application of growth factors and the addition of autologous and allogeneic tissue or cell grafts. The mechanical environment of the wound site is also of fundamental importance for the rate and quality of wound healing. It is known that mechanical stress can influence wound healing by affecting the behaviour of cells within the dermis, but it remains unclear how mechanical forces affect the healing epidermis. Tensile forces are known to affect the behaviour of cells within epithelia, however, and the material properties of extracellular matrices, such as substrate stiffness, have been shown to affect the morphology, proliferation, differentiation and migration of many different cell types. In this review we will introduce the structure of the skin and the process of wound healing. We will then discuss the evidence for the effect of tissue mechanics in re-epithelialisation and, in particular, on stem cell behaviour in the wound microenvironment and in intact skin. We will discuss how the elasticity, mechanical heterogeneity and topography of the wound extracellular matrix impact the rate and quality of wound healing, and how we may exploit this knowledge to expedite wound healing and mitigate scarring.

The Effectiveness of Porcine Dermal Collagen (Permacol(®)) on Wound Healing in the Rat Model

Porcine acellular dermal collagen (PDC), which is a biological material derived from processing porcine dermis, has already been used for urologic, gynecologic, plastic, and general surgery procedures up to now. The aim of this study is to investigate the effectiveness of PDC on wound healing as a dermal substitute in the rat model. Twenty Wistar albino rats were divided into two groups. Standard full-thickness skin defects were created on the back of the rats. In the control group (Group 1), the dressings moisturized with saline were changed daily. In the study group (Group 2), porcine dermal collagen was implanted onto each wound and fixed with 4-0 polypropylene sutures. Contraction percentages of wound areas were calculated on the third, seventh, tenth, and fourteenth days by using the planimetric program. On fourteenth day, the wound areas were excised for histopathological examination, inflammatory scoring, and evaluation of collagen deposition. The study group was superior to the control group in terms of inflammatory scoring, type I/type III collagen ratio, and wound contraction rates. Porcine dermal collagen may be used effectively and safely on full-thickness wounds as a current dermal substitute.

Evaluation of an amniotic membrane-collagen dermal substitute in the management of full-thickness skin defects in a pig

Background

To minimize the inflammatory reaction and improve healing, a new modified dermal substitute composed of an atelocollagen, chondroitin-6-sulfate, and amniotic membrane (AM) was applied to full-thickness skin defects in a pig. Atelocollagen was extracted from bovine skin, and two modified dermal substitutes were generated according to the cross-linking type.

Methods

The AM-collagen dermal substitutes were characterized and compared with currently used dermal substitutes in a pig skin defect model. There were five experimental groups: dehydrothermal (DHT) cross-linking atelocollagen with the AM on the top (AM-DHT), DHT and chemical cross-linking atelocollagen with the AM on the top (AM-DHT/chemical), Terudermis, Integra, and AlloDerm. After 3×3 cm full-thickness skin defects on the back of a pig were created, each dermal substitutes dermal substitutes was randomly grafted on the defects. Two weeks after grafting, autologous partial-thickness skin was over-grafted on the neodermis. The take rate of the dermal substitutes, skin, and histological sections were all assessed at 1, 2, and 4 weeks postoperatively.

Results

More rapid healing and a higher take rate were evident in the AM-DHT and Terudermis groups. Histological examination revealed fewer inflammatory cells and more fibroblast hyperplasia in these two groups. Four weeks after surgery, the amount of newly formed collagen was significantly more appropriate in the AM-DHT group.

Conclusions

These observations provide supporting evidence that a newly developed amniotic-collagen dermal substitute may inhibit inflammatory reactions and promote wound healing.

Electrospun synthetic human elastin:collagen composite scaffolds for dermal tissue engineering

We present an electrospun synthetic human elastin:collagen composite scaffold aimed at dermal tissue engineering. The panel of electrospun human tropoelastin and ovine type I collagen blends comprised 80% tropoelastin+20% collagen, 60% tropoelastin+40% collagen and 50% tropoelastin+50% collagen. Electrospinning efficiency decreased with increasing collagen content under the conditions used. Physical and mechanical characterization encompassed fiber morphology, porosity, pore size and modulus, which were prioritized to identify the optimal candidate for dermal tissue regeneration. Scaffolds containing 80% tropoelastin and 20% collagen (80T20C) were selected on this basis for further cell interaction and animal implantation studies. 80T20C enhanced proliferation and migration rates of dermal fibroblasts in vitro and were well tolerated in a mouse subcutaneous implantation study where they persisted over 6 weeks. The 80T20C scaffolds supported fibroblast infiltration, de novo collagen deposition and new capillary formation.

Stricture prevention after extended circumferential endoscopic mucosal resection by injecting autologous keratinocytes in the sheep esophagus

BACKGROUND

During the past decades, endoscopic mucosal resection (EMR) has been developed to treat early intramucosal esophageal cancers and dysplastic Barrett's esophagus. The primary drawback of this method is severe postsurgical esophageal stricture formation. The purpose of this preclinical study was to assess strategies for prevention of this major complication by injecting autologous keratinocytes in the EMR mucosal defect in the sheep model.

METHODS

Circumferential, 6-cm-long EMRs were performed in the esophagus of nine sheep. Autologous keratinocytes were harvested 2 weeks before EMR and cultured. Circumferential resection consisted of two opposite hemicircumferential mucosectomies allowing a widespread resection of 24 cm(2). Immediately after EMR, autologous keratinocytes were endoscopically injected in the mucosal defect. Animals were sacrificed after 6 months.

RESULTS

Circumferential EMRs were successfully performed in all animals. There were no intra- or postoperative complications. None of the animals developed strictures. All animals were sacrificed at 6 months as planned. Histological examinations showed fibrotic changes in 10 % (range 0-25 %) of the circumferential muscularis propria interna layer and 7.2 % (range 0-25 %) in the muscularis propria externa layer at the midportion of the EMR. No circumferential transmural fibrosis was identified.

CONCLUSIONS

Prevention of stricture formation after extensive (6-cm long) circumferential EMR of the sheep esophagus can be achieved by injecting autologous keratinocytes into the wound of the resected mucosal segment.

Shelf-life evaluation of bilayered human skin equivalent, MyDerm™

Skin plays an important role in defense against infection and other harmful biological agents. Due to its fragile structure, skin can be easily damaged by heat, chemicals, traumatic injuries and diseases. An autologous bilayered human skin equivalent, MyDerm™, was engineered to provide a living skin substitute to treat critical skin loss. However, one of the disadvantages of living skin substitute is its short shelf-life, hence limiting its distribution worldwide. The aim of this study was to evaluate the shelf-life of MyDerm™ through assessment of cell morphology, cell viability, population doubling time and functional gene expression levels before transplantation. Skin samples were digested with 0.6% Collagenase Type I followed by epithelial cells dissociation with TrypLE Select. Dermal fibroblasts and keratinocytes were culture-expanded to obtain sufficient cells for MyDerm™ construction. MyDerm™ was constructed with plasma-fibrin as temporary biomaterial and evaluated at 0, 24, 48 and 72 hours after storage at 4°C for its shelf-life determination. The morphology of skin cells derived from MyDerm™ remained unchanged across storage times. Cells harvested from MyDerm™ after storage appeared in good viability (90.5%±2.7% to 94.9%±1.6%) and had short population doubling time (58.4±8.7 to 76.9±19 hours). The modest drop in cell viability and increased in population doubling time at longer storage duration did not demonstrate a significant difference. Gene expression for CK10, CK14 and COL III were also comparable between different storage times. In conclusion, MyDerm™ can be stored in basal medium at 4°C for at least 72 hours before transplantation without compromising its functionality.

Hydrogen-bonding-driven spontaneous gelation of water-soluble phospholipid polymers in aqueous medium

It has been found that mixing of two kinds of water-soluble phospholipids polymers, such as poly(2-methacryloyloxyethyl phosphorylcholine-co-methacrylic acid) (PMA) and poly(2-methacryloyloxyethyl phosphorylcholine-co-n-butyl methacrylate) (PMB), spontaneously forms a hydrogel in aqueous medium at room temperature without any chemical treatment. However, the mechanism of spontaneous gelation has not been clarified yet. The purpose of this study is to investigate the gelation mechanism of the hydrogel. Moreover, effects of ions on gelation and dissolution behavior were observed. We investigated the mechanism of the hydrogel formation by spectroscopic techniques and a rheological method with attention to the interactions between polymer chains. Both Raman spectroscopic analysis and FT-IR analysis revealed that carboxyl groups in methacrylic acid (MA) formed dimer when two polymer solutions were mixed, and the results of the rheological study showed dissociation of carboxyl groups caused dissolution of the hydrogel. Thus, the gelation occurred due to the formation of dimers by hydrogen bonding which acts as a physical cross-linking of polymer chains. The hydrogel dissolved in a large amount of aqueous medium. We also observed the addition of inorganic salts during the preparation of the hydrogel affected the gelation and dissolution behaviors by a rheological and a weight measuring method, respectively. The gelation period became longer in the presence of NaCl and CaCl2 compared with that in the absence of these salts. NaCl and CaCl2 disturbed the formation of hydrogen bonding between carboxyl groups by stabilization of carboxylate anion of the MA units. On the other hand, addition of FeCl3 made the gelation period shorter and stabilized the hydrogel in the aqueous medium. This is because FeCl3 can suppress dissociation of the carboxyl groups by acidic condition of FeCl3 aqueous solution and cross-link the carboxylate anions in the PMA effectively.

Evaluation of functions and tissue compatibility of poly (D,L-lactic-co-glycolic acid) seeded with human dermal fibroblasts

In tissue engineering and wound-healing applications, dermal substitutes are used to provide fibroblasts with the mechanical support for their growth and then to facilitate the skin formation. In this study, three-dimensional porous poly(lactic-co-glycolic acid) (PLGA) 65/35 scaffolds were prepared and then the composites of the scaffolds and human fetal dermal fibroblasts were fabricated as a tissue-engineered dermal substitute. The function and tissue compatibility of the artificial dermal substitute were evaluated at the levels of gene expression (by RT-PCR) and protein expression (total collagen quantities), as well as by histological and immunohistochemical analysis. The PCR products indicated that the mRNA of type-I collagen, mainly secreted by the fibroblasts onto the PLGA scaffolds, was clearly expressed after 4 weeks. The amount of total collagen synthesized from the cells was shown to increase gradually during the initial culture period and slightly decreased afterwards. After 8 weeks of culture, the fibroblasts were well attached and migrated entirely throughout the pores of the PLGA scaffold with normal function. Furthermore, the positively stained type-I collagen was intensively detected throughout the pores. These results suggest that the function and tissue compatibility may be important criteria in evaluating an artificial tissue-engineered skin.

Evaluation of two commonly used temporary skin dressings for the treatment of acute partial-thickness wounds in rats

OBJECTIVES

There is a broad range of expensive temporary wound dressings that promise better results in wound management. The aim of this study was to compare two commonly used temporary dressings for the treatment of partial-thickness wounds in a rat model.

METHODS

Forty-two partial thickness wounds were created on the back of Lewis rats and treated with the dressings; control wounds remained without treatment. Wound size was determined daily by measuring the scabbed area. Three months after the wounds were created, skin elasticity was measured and a histologic evaluation was performed.

RESULTS

Wound appearance in the animals in the treated groups did not differ significantly. Wound closure was slower in the control group than in the dressing groups. There was no histologic evidence of inflammation and no suggestion of epidermal changes in any group.

CONCLUSION

Using both skin dressings, we observed satisfying results without any significant differences. Because of rising health care expenses, cost should play an essential role in the clinical application of these dressings.

Fabrication and characterization of poly(L-lactide-co-glycolide) knitted mesh-reinforced collagen-chitosan hybrid scaffolds for dermal tissue engineering

Mechanical properties are essential considerations for the design of porous scaffolds in the field of tissue engineering. To develop a well-supported hybrid dermal substitute, poly(L-lactide-co-glycolide) (PLGA) yarns were knitted into a mesh with relative fixed loops, followed by incorporation into collagen-chitosan scaffolds (CCS) to obtain PLGA knitted mesh-reinforced CCS (PLGAm/CCS). The morphology and tensile strength in both the dry and wet state of PLGAm/CCS were investigated in vitro. To characterize the tissue response, specifically angiogenesis and tissue regeneration, PLGAm/CCS was embedded subcutaneously in Sprague-Dawley rats and compared with two control implants, i.e., PLGA mesh (PLGAm) and CCS. At weeks 1, 2, and 4 post surgery, tissue specimens were harvested for histology, immunohistochemistry, real-time quantitative PCR and Western blot analysis. These results demonstrated that the incorporation of PLGA knitted mesh into CCS can improve the mechanical strength with little influence on its mean pore size and porosity. After implantation, PLGAm/CCS can resist contraction and promote cell infiltration, neotissue formation, and blood vessel ingrowth, effectively. In conclusion, the mechanical strength of scaffolds can play a synergetic role in tissue regeneration and vascularization by maintaining its 3D microstructure. The ability of PLGAm/CCS to promote angiogenesis and induce in situ tissue formation demonstrates its strong potential in the field of skin tissue engineering.

Promotion of angiogenesis by sustained release of rhGM-CSF from heparinized collagen/chitosan scaffolds

A novel dermal substitute of combining recombinant human granulocyte-macrophage colony-stimulating factor (rhGM-CSF) with a porous heparinized collagen/chitosan scaffolds was developed, considering the inadequate angiogenesis during repair of full-thickness skin defects. The physicochemical properties of heparinized collagen/chitosan scaffolds were examined and in vitro release pattern of rhGM-CSF from scaffolds was measured by ELISA. Four groups of composite scaffolds (heparinized or unheparinized scaffolds loaded with or without rhGM-CSF) were fabricated for subcutaneous implantation in young adult male Sprague-Dawley (SD) rats. Tissue specimens were harvested at different time points after implantation for histopathological, immunohistochemical observation, and Western blotting analysis. The heparinized scaffolds (H(1)E) showed slower biodegradation and sustained release of rhGM-CSF in vitro, although no significantly different release pattern was observed between the H(1)E and unheparinized scaffolds (H(0)E). In vivo investigation revealed that the heparinized scaffolds loaded with rhGM-CSF (H(1)E/rhGM-CSF) had the best cellular adhesion and migration, new vessel formation, and highest expression of VEGF and TGF-β1, indicating promoted angiogenesis. This study demonstrated that composite dermal substitute of combining rhGM-CSF with a porous heparinized collagen/chitosan scaffolds could be a potential therapeutic agent for full-thickness skin defects because of its sustained delivery of rhGM-CSF.

A clinical evaluation of Biobrane(®) and Suprathel(®) in acute burns and reconstructive surgery

BACKGROUND

In the treatment of superficial partial-thickness burns, various skin substitutes and temporary dressings offer potential advantages over traditional treatments. Nonetheless, the search for an ideal temporary skin substitute or biosynthetic wound dressing is still a continuous quest. This research aimed to provide objective data on the long-term outcome of Biobrane(®) and Suprathel(®).

METHODS

Eight months after the initial burn treatment of Biobrane(®) and Suprathel(®), skin elasticity was measured objectively using a Cutometer(®) and the scarring process was quantified using the Vancouver Scar Scale (VSS).

RESULTS

The median healing time for patients treated with Biobrane(®) was up to 1.8 days shorter then the Suprathel(®) group. Regarding the Vancouver Scar Scale (VSS), neither the single parameter, nor the total score were significantly different in both groups. In comparison, the Biobrane(®) group demonstrated superior Cutometer(®) parameters in regards to maximal extension, elasticity, retraction and pliability. Despite higher levels of Biobrane(®) group, the differences in the viscoelastic analysis of both substitutes did not vary significantly.

CONCLUSION

Using both substitutes, we observed satisfying results in superficial partial-thickness burn treatment, without any significant differences. Since the treatment of burned patients is associated with high socioeconomic load, the cost factor should be one of the most important criteria in dermal substitute selection.

Evaluation of sericin/collagen membranes as prospective wound dressing biomaterial

Sericin, a silk protein, has high potential for use in biomedical applications. In this study, wound dressing membranes of Sericin (S) and Collagen (C) were prepared by glutaraldehyde cross-linking at S/C; 2:1, 1:1, 1:2, and 0:1 weight ratios. They were stable in water for 4 weeks. However, increasing the proportion of sericin had decreasing effect on the membrane stability. Water swelling property of membranes was enhanced with sericin. The highest water swelling was obtained in 1:1 group (9.06 g/g), but increasing collagen or sericin content in the membranes had a diminishing effect. Highest water vapor transmission rate was obtained with 1:2 group (1013.80 g/m(2)/day). Oxygen permeability results showed that 1:2 (7.67 mg/L) and 2:1 (7.85 mg/L) S/C groups were better than the other groups. While sericin decreased the tensile strength and elongation of membranes, it increased modulus. Sericin also increased brittleness of membranes, but their UTS range (24.93-44.92 MPa) was still suitable for a wound dressing. Membranes were not penetrable to microorganisms. Cytotoxicity studies showed that fibroblasts and keratinocytes attached and gained their characteristic morphologies. They also proliferated on membranes significantly. After 1 week of subcutaneous implantation, a fibrous capsule formed around all membranes with an acute inflammation. Sericin containing membranes showed signs of degradation (at 2nd week), while collagen only membranes remained largely intact. Eventually, sericin containing membranes degraded in 3 weeks with moderate inflammatory response. Overall results suggest that sericin/collagen membranes would be favorable as wound dressing material when sericin ratio is less than or equal to the collagen component.