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

Oxygen transmission rates of skin substitutes and graft survival

AIM

Oxygen is required for cell migration into the scaffold and for the survival of the overlying graft in the use of a single-layer scaffold. In the absence of diffusion from the avascular wound base, such as in areas above the bone/tendon, oxygen delivery from the lateral edges of the scaffold is important. This study compared the oxygen permeability of skin scaffolds, currently commercially available in Turkey (Nevelia®, MatriDerm®, and Pelnac®), in the lateral plane.

MATERIALS AND METHODS

To measure oxygen permeability, an interconnected closed system was created. Oxygen permeability was evaluated based on the color change that occurred as a result of the reaction of iron with oxygen. After the dermal matrices placed in the closed system were exposed to oxygen, the color change on the surface of the dermal matrices was measured, and electron microscopic images were recorded to compare deformation before and after the procedure.

RESULTS

Two scaffolds did not show deformation after the procedure while Pelnac® had minimal deformation. The oxygen rates on the nitrogen side of the test apparatus were found to be 29%, 34%, and 27% for Nevelia®, MatriDerm®, and Pelnac®, respectively; and the oxygen transmission lengths (length of color change) of these scaffolds in the lateral plane were 1, 2, and 0.5 cm, respectively.

CONCLUSION

Although none of the scaffolds showed significant deformation, and all continued to exhibit their scaffold properties after the procedure, MatriDerm® was determined to be the most suitable scaffold for use in avascular areas, with a 2-cm oxygen transmission length in terms of lateral oxygenation.

Bilayer Hydrogel Composed of Elastin-Mimetic Polypeptides as a Bio-Actuator with Bidirectional and Reversible Bending Behaviors

Biologically derived hydrogels have attracted attention as promising polymers for use in biomedical applications because of their high biocompatibility, biodegradability, and low toxicity. Elastin-mimetic polypeptides (EMPs), which contain a repeated amino acid sequence derived from the hydrophobic domain of tropoelastin, exhibit reversible phase transition behavior, and thus, represent an interesting starting point for the development of biologically derived hydrogels. In this study, we succeeded in developing functional EMP-conjugated hydrogels that displayed temperature-responsive swelling/shrinking properties. The EMP-conjugated hydrogels were prepared through the polymerization of acrylated EMP with acrylamide. The EMP hydrogel swelled and shrank in response to temperature changes, and the swelling/shrinking capacity of the EMP hydrogels could be controlled by altering either the amount of EMP or the salt concentration in the buffer. The EMP hydrogels were able to select a uniform component of EMPs with a desired and specific repeat number of the EMP sequence, which could control the swelling/shrinking property of the EMP hydrogel. Moreover, we developed a smart hydrogel actuator based on EMP crosslinked hydrogels and non-crosslinked hydrogels that exhibited bidirectional curvature behavior in response to changes in temperature. These thermally responsive EMP hydrogels have potential use as bio-actuators for a number of biomedical applications.

Vessel-Derived Decellularized Extracellular Matrices (VdECM): Novel Bio-Engineered Materials for the Wound Healing

BACKGROUND

Decellularized extracellular matrix (dECM) is a non-cellular scaffold with various functions in tissue engineering and regenerative medicine. Elastin is related to tissue elasticity and scarless wound healing, abundantly found in lung and blood vessel tissues. We studied the characteristics of blood vessel-derived dECM (VdECM) and its effect in wound healing.

METHODS

VdECM was prepared from porcine blood vessel tissue. Weight percentages of elastin of VdECM and atelocollagen were analyzed. Migratory potential of VdECM was tested by scratch assay. VdECM in hydrogel form was microscopically examined, tested for fibroblast proliferation, and examined for L/D staining. Cytokine array of various growth factors in adipocyte-derived mesenchymal stem cell (ASC) media with VdECM was done. Animal wound model showed the wound healing effect of VdECM hydrogel in comparison to other topical agents.

RESULTS

VdECM contained 6.7 times more elastin than atelocollagen per unit weight. Microscopic view of 0.35% VdECM hydrogel showed consistent distribution. Compared to 3% atelocollagen, 0.35% VdECM showed superior results in fibroblast migration. Fluorescent microscopic findings of L/D assay had highest percentage of cell survival in 1% VdECM compared to atelocollagen. Growth factor expression was drastically amplified when VdECM was added to ASC media. In the animal study model, epithelialization rate in the VdECM group was higher than that of control, oxytetracycline, and epidermal growth factor ointments.

CONCLUSION

VdECM contains a high ratio of elastin to collagen and amplifies expressions of many growth factors. It promotes fibroblast migration, proliferation, and survival, and epithelialization comparable to other topical agents.

Basic Quality Controls Used in Skin Tissue Engineering

Reconstruction of skin defects is often a challenging effort due to the currently limited reconstructive options. In this sense, tissue engineering has emerged as a possible alternative to replace or repair diseased or damaged tissues from the patient's own cells. A substantial number of tissue-engineered skin substitutes (TESSs) have been conceived and evaluated in vitro and in vivo showing promising results in the preclinical stage. However, only a few constructs have been used in the clinic. The lack of standardization in evaluation methods employed may in part be responsible for this discrepancy. This review covers the most well-known and up-to-date methods for evaluating the optimization of new TESSs and orientative guidelines for the evaluation of TESSs are proposed.

Protein Hydrogels: The Swiss Army Knife for Enhanced Mechanical and Bioactive Properties of Biomaterials

Biomaterials are dynamic tools with many applications: from the primitive use of bone and wood in the replacement of lost limbs and body parts, to the refined involvement of smart and responsive biomaterials in modern medicine and biomedical sciences. Hydrogels constitute a subtype of biomaterials built from water-swollen polymer networks. Their large water content and soft mechanical properties are highly similar to most biological tissues, making them ideal for tissue engineering and biomedical applications. The mechanical properties of hydrogels and their modulation have attracted a lot of attention from the field of mechanobiology. Protein-based hydrogels are becoming increasingly attractive due to their endless design options and array of functionalities, as well as their responsiveness to stimuli. Furthermore, just like the extracellular matrix, they are inherently viscoelastic in part due to mechanical unfolding/refolding transitions of folded protein domains. This review summarizes different natural and engineered protein hydrogels focusing on different strategies followed to modulate their mechanical properties. Applications of mechanically tunable protein-based hydrogels in drug delivery, tissue engineering and mechanobiology are discussed.

A Study of Combining Elastin in the Chitosan Electrospinning to Increase the Mechanical Strength and Bioactivity

While electrospun chitosan membranes modified to retain nanofibrous morphology have shown promise for use in guided bone regeneration applications in in vitro and in vivo studies, their mechanical tear strengths are lower than commercial collagen membranes. Elastin, a natural component of the extracellular matrix, is a protein with extensive elastic property. This work examined the incorporation of elastin into electrospun chitosan membranes to improve their mechanical tear strengths and to further mimic the native extracellular composition for guided bone regeneration (GBR) applications. In this work, hydrolyzed elastin (ES12, Elastin Products Company, USA) was added to a chitosan spinning solution from 0 to 4 wt% of chitosan. The chitosan-elastin (CE) membranes were examined for fiber morphology using SEM, hydrophobicity using water contact angle measurements, the mechanical tear strength under simulated surgical tacking, and compositions using Fourier-transform infrared spectroscopy (FTIR) and post-spinning protein extraction. In vitro experiments were conducted to evaluate the degradation in a lysozyme solution based on the mass loss and growth of fibroblastic cells. Chitosan membranes with elastin showed significantly thicker fiber diameters, lower water contact angles, up to 33% faster degradation rates, and up to seven times higher mechanical strengths than the chitosan membrane. The FTIR spectra showed stronger amide peaks at 1535 cm^-1 and 1655 cm^-1 in membranes with higher concentrated elastin, indicating the incorporation of elastin into electrospun fibers. The bicinchoninic acid (BCA) assay demonstrated an increase in protein concentration in proportion to the amount of elastin added to the CE membranes. In addition, all the CE membranes showed in vitro biocompatibility with the fibroblasts.

Inclusion of Cross-Linked Elastin in Gelatin/PEG Hydrogels Favourably Influences Fibroblast Phenotype

The capacity of a biomaterial to innately modulate cell behavior while meeting the mechanical property requirements of the implant is a much sought-after goal within bioengineering. Here we covalently incorporate soluble elastin into a gelatin–poly (ethylene glycol) (PEG) hydrogel for three-dimensional (3D) cell encapsulation to achieve these properties. The inclusion of elastin into a previously optimized gelatin–PEG hydrogel was then evaluated for effects on entrapped fibroblasts, with the aim to assess the hydrogel as an extracellular matrix (ECM)-mimicking 3D microenvironment for cellular guidance. Soluble elastin was incorporated both physically and covalently into novel gelatin/elastin hybrid PEG hydrogels with the aim to harness the cellular interactivity and mechanical tunability of both elastin and gelatin. This design allowed us to assess the benefits of elastin-containing hydrogels in guiding fibroblast activity for evaluation as a potential dermal replacement. It was found that a gelatin–PEG hydrogel with covalently conjugated elastin, supported neonatal fibroblast viability, promoted their proliferation from 7.3% to 13.5% and guided their behavior. The expression of collagen alpha-1(COL1A1) and elastin in gelatin/elastin hybrid gels increased 16-fold and 6-fold compared to control sample at day 9, respectively. Moreover, cells can be loaded into the hydrogel precursor solution, deposited, and the matrix cross-linked without affecting the incorporated cells adversely, thus enabling a potential injectable system for dermal wound healing.

Overview of natural hydrogels for regenerative medicine applications

Hydrogels from different materials can be used in biomedical field as an innovative approach in regenerative medicine. Depending on the origin source, hydrogels can be synthetized through chemical and physical methods. Hydrogel can be characterized through several physical parameters, such as size, elastic modulus, swelling and degradation rate. Lately, research is focused on hydrogels derived from biologic materials. These hydrogels can be derived from protein polymers, such as collage, elastin, and polysaccharide polymers like glycosaminoglycans or alginate among others. Introduction of decellularized tissues into hydrogels synthesis displays several advantages compared to natural or synthetic based hydrogels. Preservation of natural molecules such as growth factors, glycans, bioactive cryptic peptides and natural proteins can promote cell growth, function, differentiation, angiogenesis, anti-angiogenesis, antimicrobial effects, and chemotactic effects. Versatility of hydrogels make possible multiple applications and combinations with several molecules on order to obtain the adequate characteristic for each scope. In this context, a lot of molecules such as cross link agents, drugs, grow factors or cells can be used. This review focuses on the recent progress of hydrogels synthesis and applications in order to classify the most recent and relevant matters in biomedical field.

Feasibility of repairing full-thickness skin defects by iPSC-derived epithelial stem cells seeded on a human acellular amniotic membrane

Background

Induced pluripotent stem cells (iPSCs) can generate epithelial stem cells (EpSCs) as seed cells for skin substitutes to repair skin defects. Here, we investigated the effects of a human acellular amniotic membrane (hAAM) combined with iPSC-derived CD200⁺/ITGA6⁺ EpSCs as a skin substitute on repairing skin defects in nude mice.

Methods

Human urinary cells isolated from a healthy donor were reprogrammed into iPSCs and then induced into CD200⁺/ITGA6⁺ epithelial stem cells. Immunocytochemistry and RT-PCR were used to examine the characteristics of the induced epithelial stem cells. iPSC-derived EpSCs were cultured on a hAAM, and cytocompatibility of the composite was analyzed by CCK8 assays and scanning electron microscopy. Then, hAAMs combined with iPSC-derived EpSCs were transplanted onto skin defects of mice. The effects of this composite on skin repair were evaluated by immunohistochemistry.

Results

The results showed that CD200⁺/ITGA6⁺ epithelial stem cells induced from iPSCs displayed the phenotypes of hair follicle stem cells. After seeding on the hAAM, iPSC-derived epithelial stem cells had the ability to proliferate. After transplantation, CD200⁺/ITGA6⁺ epithelial stem cells on the hAAM promoted the construction of hair follicles and interfollicular epidermis.

Conclusions

These results indicated that transplantation of a hAAM combined with iPS-derived EpSCs is feasible to reconstruct skin and skin appendages, and may be a substantial reference for iPSC-based therapy for skin defects.

A fibrinous and allogeneic fibroblast-enriched membrane as a biocompatible material can improve diabetic wound healing

The novel fibroblast-loaded fibrin membrane was prepared to promote diabetic wound healing.

Biomaterials for Skin Substitutes

Patients with extensive burns rely on the use of tissue engineered skin due to a lack of sufficient donor tissue, but it is a challenge to identify reliable and economical scaffold materials and donor cell sources for the generation of a functional skin substitute. The current review attempts to evaluate the performance of the wide range of biomaterials available for generating skin substitutes, including both natural biopolymers and synthetic polymers, in terms of tissue response and potential for use in the operating room. Natural biopolymers display an improved cell response, while synthetic polymers provide better control over chemical composition and mechanical properties. It is suggested that not one material meets all the requirements for a skin substitute. Rather, a composite scaffold fabricated from both natural and synthetic biomaterials may allow for the generation of skin substitutes that meet all clinical requirements including a tailored wound size and type, the degree of burn, the patient age, and the available preparation technique. This review aims to be a valuable directory for researchers in the field to find the optimal material or combination of materials based on their specific application.

Tissue Engineered Skin Substitutes

The fundamental skin role is to supply a supportive barrier to protect body against harmful agents and injuries. Three layers of skin including epidermis, dermis and hypodermis form a sophisticated tissue composed of extracellular matrix (ECM) mainly made of collagens and glycosaminoglycans (GAGs) as a scaffold, different cell types such as keratinocytes, fibroblasts and functional cells embedded in the ECM. When the skin is injured, depends on its severity, the majority of mentioned components are recruited to wound regeneration. Additionally, different growth factors like fibroblast growth factor (FGF), epidermal growth factor (EGF), vascular endothelial growth factor (VEGF) are needed to orchestrated wound healing process. In case of large surface area wounds, natural wound repair seems inefficient. Inspired by nature, scientists in tissue engineering field attempt to engineered constructs mimicking natural healing process to promote skin restoration in untreatable injuries. There are three main types of commercially available engineered skin substitutes including epidermal, dermal, and dermoepidermal. Each of them could be composed of scaffold, desired cell types or growth factors. These substitutes could have autologous, allogeneic, or xenogeneic origin. Moreover, they may be cellular or acellular. They are used to accelerate wound healing and recover normal skin functions with pain relief. Although there are a wide variety of commercially available skin substitutes, almost none of them considered as an ideal equivalents required for proper wound healing.

Smart Carriers and Nanohealers: A Nanomedical Insight on Natural Polymers

Biodegradable polymers are popularly being used in an increasing number of fields in the past few decades. The popularity and favorability of these materials are due to their remarkable properties, enabling a wide range of applications and market requirements to be met. Polymer biodegradable systems are a promising arena of research for targeted and site-specific controlled drug delivery, for developing artificial limbs, 3D porous scaffolds for cellular regeneration or tissue engineering and biosensing applications. Several natural polymers have been identified, blended, functionalized and applied for designing nanoscaffolds and drug carriers as a prerequisite for enumerable bionano technological applications. Apart from these, natural polymers have been well studied and are widely used in material science and industrial fields. The present review explains the prominent features of commonly used natural polymers (polysaccharides and proteins) in various nanomedical applications and reveals the current status of the polymer research in bionanotechnology and science sectors.

Attraction factors for Paederus fuscipes ' dispersal, a vector of Paederus dermatitis towards human residential premises

Paederus fuscipes, a vector of Paederus dermatitis in most tropical and subtropical countries of the world have a high prevalence in human dwellings due to their positively phototaxic behaviour which has caused a tremendous impact on human health. In this paper, P. fuscipes dispersal flights were studied for two seasons of the rice cultivation phases in residential premises built close to rice field areas (≈32-60 m and 164 m) in mainland Penang, Malaysia. We examined the effects of different light illuminance, building floor level and their association with rice stages as a focal cause of P. fuscipes dispersion from the rice fields towards human dwellings. The present study showed a significant interaction between different light illuminances and rice cultivation phases in attracting P. fuscipes to disperse and invade human dwellings. The highest number of P. fuscipes was captured near the bright light. P. fuscipes flights increased in line with each floor level, and the highest captures took place at higher building floor levels (levels 2 and 3) compared to lower building floor levels (ground floor and level 1) of a three storey apartment in both rice seasons. This finding not only conveys a better understanding on P. fuscipes dispersal pattern, but also draws public attention on the occurrence of dermatitis linearis caused by the Paederus beetles.

A novel native collagen dressing with advantageous properties to promote physiological wound healing

OBJECTIVE

Chronic hard-to-heal wounds generate high costs and resource use in western health systems and are the focus of intense efforts to improve healing outcomes. Here, we introduce a novel native collagen (90 %):alginate (10 %) wound dressing and compare it with the established oxidised dressings Method: Matrices were analysed by atomic force microscopy (AMF), scanning electron microscopy (SEM), and immunoelectron microscopy for collagen types I, III and V. Viability assays were performed with NIH-3T3 fibroblasts. Matrix metalloproteinase (MMP) binding was analysed, and the effect of the wound dressings on platelet-derived growth factor B homodimer (PDGF-BB) was investigated.

RESULTS

Unlike oxidised regenerated cellulose (ORC)/collagen matrix and ovine forestomach matrix (OFM), the three-dimensional structure of the native collagen matrix (NCM) was found to be analogous to intact, native, dermal collagen. Fibroblasts seeded on the NCM showed exponential growth whereas in ORC/collagen matrix or OFM, very low rates of proliferation were observed after 7 days. MMP sequestration was effective and significant in the NCM. In addition, the NCM was able to significantly stabilise PDGF-BB in vitro.

CONCLUSION

We hypothesise that the observed microstructure of the NCM allows for an effective binding of MMPs and a stabilisation and protection of growth factors and also promotes the ingrowth of dermal fibroblasts, potentially supporting the re commencement of healing in previously recalcitrant wounds.

DECLARATION OF INTEREST

This work was supported by BSN Medical, Hamburg, Germany.

Craniofacial Tissue Engineering

There is substantial need for the replacement of tissues in the craniofacial complex due to congenital defects, disease, and injury. The field of tissue engineering, through the application of engineering and biological principles, has the potential to create functional replacements for damaged or pathologic tissues. Three main approaches to tissue engineering have been pursued: conduction, induction by bioactive factors, and cell transplantation. These approaches will be reviewed as they have been applied to key tissues in the craniofacial region. While many obstacles must still be overcome prior to the successful clinical restoration of tissues such as skeletal muscle and the salivary glands, significant progress has been achieved in the development of several tissue equivalents, including skin, bone, and cartilage. The combined technologies of gene therapy and drug delivery with cell transplantation will continue to increase treatment options for craniofacial cosmetic and functional restoration.

Adhesion and Proliferation of Human Dermal Fibroblasts on Collagen Matrix

The purpose of this study was to evaluate adhesion and growth of human dermal fibroblasts on a 0.150 mm-thick matrix of reconstituted collagen isolated from horse tendon. Collagen was extracted and polymerized according to the standard procedures (Opocrin, Corlo, Modena, Italy). By light microscopy, the bottom surface of the matrix appeared linear and compact, whereas the superficial one was indented and less homogeneous. By scanning electron microscopy, the collagen fibrils had different diameters and the great majority of them was oriented parallel to the surface of the gel. By transmission electron microscopy, collagen fibrils showed the typical banding. Human dermal fibroblasts were seeded on the collagen matrix, previously equilibrated in growth medium. Fibroblast proliferation stopped in the second week and was always significantly lower than that of the same cell strain seeded on plastic and cultured in parallel. By light microscopy, after six days culture, cells formed a confluent multilayer on the surface of the gel. By scanning and transmission electron microscopy, fibroblasts appeared flat and adherent to the matrix. Contacts of cells among themselves and with the collagen fibrils were observed. Fibroblasts never moved into the collagen gel. In conclusion, human dermal fibroblasts can be grown in a three-dimensional matrix made by horse tendon that, on the other hand, seems to condition their proliferation rate.

Cutaneous Wound Healing: Myofibroblastic Differentiation and in Vitro Models

Wound healing is an interactive, dynamic 3-phased process. During the formation of granulation tissue, many fibroblastic cells acquire some morphological and biochemical smooth muscle features and are called myofibroblasts. Myofibroblasts participate in both granulation tissue formation and remodeling phases. Excessive scarring, which is a feature of impaired healing, is a serious health problem that may affect the patient's quality of life. The treatment costs of such lesions are high, and often, the results are unsatisfactory. To understand the wound healing process better and to promote improvement in human healing, models are needed that can predict the in vivo situation in humans. In vitro models allow the study of cell behavior in a controlled environment. Such modeling partitions and reduces to small scales behavior perceived in vivo. This article is focused on `fibroblasts.' In vitro models to study wound healing, the role of (myo)fibroblasts, and skin reconstruction in tissue replacement and promotion of wound healing are discussed.

Double-layered collagen graft to the radial forearm free flap donor sites without skin graft

Background

Radial forearm free flap is the most reliable flap for intraoral soft tissue reconstruction after cancer ablation surgery. However, unesthetic scar of the donor site and the need for a second donor site for skin graft are major disadvantages of the forearm flap. The purpose of this study was to report the clinical results of double-layered collagen graft to the donor site of the forearm free flap without skin graft.

Methods

Twenty-two consecutive patients who underwent oral cancer ablation and forearm reconstruction between April 2010 and November 2013 were included in this study. Male to female ratio was 12:10, and average age was 61.0 years old (27–84). Double-layered collagen was grafted to the donor site of the forearm free flap and healed for secondary intention. Upper silicone had been trimmed at the periphery during secondary intention, and dry dressing was used. Postoperative scar healing and esthetic results and function were evaluated.

Results

An average follow-up period was 34.9 months. The scar area was decreased to 63.9 % in average. The complete healing was obtained between 1.5 and 3 months according to the defect size. There was no functional defect or impairment 3 months after operation. All patients were satisfied with the esthetic results. Three patients died of recurred cancer.

Conclusions

Double-layered collagen graft was successfully performed in this study. Without the thigh skin graft, patients had experienced less painful postoperative healing periods and discomfort.

Ultrastructural investigation on fibroblast interaction with collagen scaffold

Collagen-based scaffolds are used as temporary or permanent coverings to help wound healing. Under natural conditions, wound healing is affected by such factors as cell types, growth factors and several components of the extracellular matrix. Due to the complexity of the cell-to-matrix interaction, many cell based mechanisms regulating wound healing in vivo are not yet properly understood. However, the whole process can be partially simulated in vitro to determine how cells interact with the collagen scaffold in relation to such features as physico-chemical properties, matrix architecture and fiber stability. Under these conditions, cell migration into the collagen matrix can be easily assessed and causally correlated with these features. In this study, we aimed at providing a structural analysis of how NIH3T3 fibroblasts migrate and proliferate in vitro when seeded on a native type-I collagen scaffold. To this end, samples were collected at regular time intervals and analyzed by light microscopy (LM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Through this experimental approach we demonstrate that collagen is gradually frayed into progressively thinner fibrils as fibroblasts migrate into the matrix, embrace the collagen fibers with long filopodia and form large intracellular vacuoles. A key role in this process is also played by microvesicles shed from the fibroblast plasma membrane and spread over long distances inside the collagen matrix. These observations indicate that a native type-I equine collagen provides favorable conditions for simulating collagen processing in vitro and eventually for unraveling the mechanisms controlling cell uptake and intracellular degradation.

Tissue engineering in burn scar reconstruction

Nowadays, most patients with severe burns will survive their injury. This evolution is accompanied by the challenge to cover a large percentage of total body surface area burned. Consequently, more and more patients have to deal with the sequelae of burn scars and require (multiple) reconstructions. This review provides a gross overview of developments in the field of tissue engineering for permanent burn wound coverage and reconstructive burn surgery, focusing on usage and clinical effectiveness. Not only skin substitutes will be discussed but also the replacement of subcutaneous fat tissue and cartilage.

Rapid creation of skin substitutes from human skin cells and biomimetic nanofibers for acute full-thickness wound repair

Creation of functional skin substitutes within a clinically acceptable time window is essential for timely repair and management of large wounds such as extensive burns. The aim of this study was to investigate the possibility of fabricating skin substitutes via a bottom-up nanofiber-enabled cell assembly approach and using such substitutes for full-thickness wound repair in nude mice. Following a layer-by-layer (L-b-L) manner, human primary skin cells (fibroblasts and keratinocytes) were rapidly assembled together with electrospun polycaprolactone (PCL)/collagen (3:1, w/w; 8%, w/v) nanofibers into 3D constructs, in which fibroblasts and keratinocytes were located in the bottom and upper portion respectively. Following culture, the constructs developed into a skin-like structure with expression of basal keratinocyte markers and deposition of new matrix while exhibiting good mechanical strength (as high as 4.0 MPa by 14 days). Treatment of the full-thickness wounds created on the back of nude mice with various grafts (acellular nanofiber meshes, dermal substitutes, skin substitutes and autografts) revealed that 14-day-cultured skin substitutes facilitated a rapid wound closure with complete epithelialization comparable to autografts. Taken together, skin-like substitutes can be formed by L-b-L assembling human skin cells and biomimetic nanofibers and they are effective to heal acute full-thickness wounds in nude mice.

In vivo Quantification of the Effects of Radiation and Presence of Hair Follicle Pores on the Proliferation of Fibroblasts in an Acellular Human Dermis in a Dorsal Skinfold Chamber: Relevance for Tissue Reconstruction following Neoadjuvant Therapy

INTRODUCTION

In neoadjuvant therapy, irradiation has a deleterious effect on neoangiogenesis. The aim of this study was to examine the post-implantation effects of neoadjuvant irradiation on the survival and proliferation of autologous cells seeded onto an acellular human dermis (hAD; Epiflex). Additionally, we examined the influence of dermal hair follicle pores on viability and proliferation. We used dorsal skinfold chambers implanted in rats and in-situ microscopy to quantify cell numbers over 9 days.

METHODS

24 rats received a skinfold chamber and were divided into 2 main groups; irradiated and unirradiated. In the irradiated groups 20Gy were applied epicutaneously at the dorsum. Epiflex pieces were cut to size 5x5mm such that each piece had either one or more visible hair follicle pores, or no such visible pores. Fibroblasts were transduced lentiviral with a fluorescent protein for cell tracking. Matrices were seeded statically with 2.5x104 fluorescent fibroblasts and implanted into the chambers. In each of the two main groups, half of the rats received Epiflex with hair follicle pores and half received Epiflex without pores. Scaffolds were examined in-situ at 0, 3, 6 and 9 days after transplantation. Visible cells on the surface were quantified using ImageJ.

RESULTS

In all groups cell numbers were decreased on day 3. A treatment-dependent increase in cell numbers was observed at subsequent time points. Irradiation had an adverse effect on cell survival and proliferation. The number of cells detected in both irradiated and non-irradiated subjects was increased in those subjects that received transplants with hair follicle pores.

DISCUSSION

This in-vivo study confirms that radiation negatively affects the survival and proliferation of fibroblasts seeded onto a human dermis transplant. The presence of hair follicle pores in the dermis transplants is shown to have a positive effect on cell survival and proliferation even in irradiated subjects.

In vitro and in vivo cytocompatibility of electrospun nanofiber scaffolds for tissue engineering applications

An electrospun polymeric-based nanofibrous scaffold mimicking the extracellular matrix and serving as a temporary support for cell growth, adhesion, migration and proliferation.

Biological and structural characterization of a naturally inspired material engineered from elastin as a candidate for tissue engineering applications

The adoption of a biomimetic approach in the design and fabrication of innovative materials for biomedical applications is encountering a growing interest. In particular, new molecules are being engineered on the basis of proteins present in the extracellular matrix, such as fibronectin, collagen, or elastin. Following this approach scientists expect to be able not only to obtain materials with tailored mechanical properties but also to elicit specific biological responses inherited by the mimicked tissue. In the present work, a novel peptide, engineered starting from the sequence encoded by exon 28 of human tropoelastin, was characterized from a chemical, physical, and biological point of view. The obtained molecule was observed to aggregate at high temperatures, forming a material able to induce a biological effect similar to what elastin does in the physiological context. This material seems to be a good candidate to play a relevant role in future biomedical applications with special reference to vascular surgery.

Proteomic anatomy of human skin

The extracellular matrix is composed of a variety of proteins which are essential for growth, wound healing, and fibrosis. It provides both structural support as well as contributing to the regulation of the local microenvironment. To further characterize the molecular composition of human skin we have undertaken a proteomic approach to identify proteins in three skin regions from two locations. Using laser microdissection, extracellular matrix was obtained from three distinct regions (basement membrane, papillary dermis, and reticular dermis) of formalin-fixed, paraffin embedded tissue from normal human leg and breast skin. The proteome of these regions was determined by mass spectrometric analysis. This study provides a relative quantitative assessment, including protein composition and relative abundance, of the proteins found in different skin regions giving rise to a "proteomic anatomy" of skin. Our findings indicate that there was little difference detected in the subproteomes of the dermal and papillary regions and little difference between the proteomes of leg skin compared to breast skin. One finding of interest is the identification of tenascin-X only in the breast dermis and serum amyloid P-component in the leg dermis. The results of this proteomic analysis corroborate much of the information on the protein composition identified by other methodologies found in the literature but provide additional insight as to localization of skin proteins in the various regions of skin. One potential outcome of this study is that identification of a more global proteomic composition in normal skin may serve as the basis for characterizing and comparing the skin proteomes from a variety of disease states, which may lead to a more complete understanding of the pathology of the disease as well as new therapeutic treatments.

BIOLOGICAL SIGNIFICANCE

This investigation underscores the power of proteomics to bring semiquantitative, non-presumptive molecular characterization to the field of histological anatomy. Traditionally, anatomy relied on visual or histochemical structural characterization which generally involved some level of understanding of the area of interest. With the advent of laser microdissection or laser capture microscopy localization of anatomical structures of interest can be correlated to molecular composition by virtue of mass spectrometric determination of the proteome of that structure. One potential outcome of this study is that identification of a more global proteomic composition in normal skin may serve as the basis for characterizing and comparing the skin proteomes from a variety of disease states, which may lead to a more complete understanding of the pathology of the disease as well as new therapeutic treatments.

Nonsteady state oxygen transport in engineered tissue: implications for design

Engineered tissue constructs are limited in size, and thus clinical relevance, when diffusion is the primary mode of oxygen transport. Understanding the extent of oxygen diffusion and cellular consumption is necessary for the design of engineered tissues, particularly those intended for implantation into hypoxic wound sites. This study presents a combined experimental and computation model to predict design constraints for cellularized fibrin tissues subjected to a step change in the oxygen concentration to simulate transplantation. Nonsteady state analysis of oxygen diffusion and consumption was used to estimate the diffusion coefficient of oxygen (mean±SD, 1.7×10(-9)±8.4×10(-11) m(2)/s) in fibrin hydrogels as well as the Michaelis-Menten parameters, Vmax (1.3×10(-17)±9.2×10(-19) mol·cell(-1)·s(-1)), and Km (8.0×10(-3)±3.5×0(-3) mol/m(3)), of normal human lung fibroblasts. Nondimensionalization of the governing diffusion-reaction equation enabled the creation of a single dimensionless parameter, the Thiele modulus (φ), which encompasses the combined effects of oxygen diffusion, consumption, and tissue dimensions. Tissue thickness is the design parameter with the most pronounced influence on the distribution of oxygen within the system. Additionally, tissues designed such that φ<1 achieve a near spatially uniform and adequate oxygen concentration following the step change. Understanding and optimizing the Thiele modulus will improve the design of engineered tissue implants.

Stem cell therapy for critical limb ischemia: what can we learn from cell therapy for chronic wounds?

Although much progress has been made regarding our knowledge of stem cells and their potential applications for therapeutic angiogenesis, there has been less success with the clinical application of this knowledge to patients with critical limb ischemia (CLI). Patients with CLI often have chronic wounds and newer cell-based therapies for chronic wounds show interesting parallels to stem cell therapy for CLI. Several human-derived wound care products and therapies, including human neonatal fibroblast-derived dermis (Dermagraft®), bilayered bioengineered skin substitute (Apligraf®), recombinant human platelet-derived growth factor and autologous platelet-rich plasma may provide insight into the mechanisms through which differentiated cells can be used as therapy for chronic wounds, and, analogously, by which stem cells might function therapeutically in CLI.

Advances in biomimetic regeneration of elastic matrix structures

Elastin is a vital component of the extracellular matrix, providing soft connective tissues with the property of elastic recoil following deformation and regulating the cellular response via biomechanical transduction to maintain tissue homeostasis. The limited ability of most adult cells to synthesize elastin precursors and assemble them into mature crosslinked structures has hindered the development of functional tissue-engineered constructs that exhibit the structure and biomechanics of normal native elastic tissues in the body. In diseased tissues, the chronic overexpression of proteolytic enzymes can cause significant matrix degradation, to further limit the accumulation and quality (e.g., fiber formation) of newly deposited elastic matrix. This review provides an overview of the role and importance of elastin and elastic matrix in soft tissues, the challenges to elastic matrix generation in vitro and to regenerative elastic matrix repair in vivo, current biomolecular strategies to enhance elastin deposition and matrix assembly, and the need to concurrently inhibit proteolytic matrix disruption for improving the quantity and quality of elastogenesis. The review further presents biomaterial-based options using scaffolds and nanocarriers for spatio-temporal control over the presentation and release of these biomolecules, to enable biomimetic assembly of clinically relevant native elastic matrix-like superstructures. Finally, this review provides an overview of recent advances and prospects for the application of these strategies to regenerating tissue-type specific elastic matrix structures and superstructures.

Novel silk fibroin/elastin wound dressings

Silk fibroin (SF) and elastin (EL) scaffolds were successfully produced for the first time for the treatment of burn wounds. The self-assembly properties of SF, together with the excellent chemical and mechanical stability and biocompatibility, were combined with elastin protein to produce scaffolds with the ability to mimic the extracellular matrix (ECM). Porous scaffolds were obtained by lyophilization and were further crosslinked with genipin (GE). Genipin crosslinking induces the conformational transition from random coil to β-sheet of SF chains, yielding scaffolds with smaller pore size and reduced swelling ratios, degradation and release rates. All results indicated that the composition of the scaffolds had a significant effect on their physical properties, and that can easily be tuned to obtain scaffolds suitable for biological applications. Wound healing was assessed through the use of human full-thickness skin equivalents (EpidermFT). Standardized burn wounds were induced by a cautery and the best re-epithelialization and the fastest wound closure was obtained in wounds treated with 50SF scaffolds; these contain the highest amount of elastin after 6 days of healing in comparison with other dressings and controls. The cytocompatibility demonstrated with human skin fibroblasts together with the healing improvement make these SF/EL scaffolds suitable for wound dressing applications.

Quantitative multispectral imaging of Herovici's polychrome for the assessment of collagen content and tissue remodelling

Bioprosthetic devices, constructed from a variety of materials, are routinely implanted in a variety of anatomical locations. Essential to their success is the formation of a non-destructive interface with the host tissue and appropriate tissue remodelling. Traditionally, the main method of assessing the host-material interface has been qualitative histological evaluation, using pattern recognition and comparative assessment to identify changes in the normal tissue architecture that are characteristic of scar tissue. In the present study, the recently developed technique of multispectral imaging was used to revisit a little-described histological stain, Herovici's polychrome, which is capable of distinguishing between types I and III collagen. Combined, these techniques allowed quantification of collagen content and distribution of collagen types within a tissue sample. Samples of rat tail and human scar tissue were used to optimize the staining, while comparison with immunolabelled samples was used to develop a reproducible quantification system, based on the specific colour profiles for types I and III collagen. Finally the remodelling of rat abdominal wall defects repaired with crosslinked or non-crosslinked extracellular matrix scaffolds derived from porcine urinary bladder was assessed with this technique. Compared to standard histological assessment, the combination of multispectral imaging and Herovici's polychrome staining presents a quick, simple, reliable technique that can provide accurate quantification of tissue remodelling and specifically identify the expression and distribution of types I and III collagen.

[Role of skin substitutes in surgical repair of the sequelae of burn injuries]

The therapeutic management of the sequelae of deep burns always relies in principle on dermal-epidermal grafts. The latter, the price of which to pay is heavy scarring, cannot always be performed because the surface of skin available may not be sufficient. Research pathways have turned towards the creation of skin substitutes to minimise the scarring and improve the cosmetic quality of the grafts. We review the technical characteristics of collagen matrixes (Intégra(®) - Matriderm(®)) and their method of use.

Modern collagen wound dressings: function and purpose

Collagen, which is produced by fibroblasts, is the most abundant protein in the human body. A natural structural protein, collagen is involved in all 3 phases of the wound-healing cascade. It stimulates cellular migration and contributes to new tissue development. Because of their chemotactic properties on wound fibroblasts, collagen dressings encourage the deposition and organization of newly formed collagen, creating an environment that fosters healing. Collagen-based biomaterials stimulate and recruit specific cells, such as macrophages and fibroblasts, along the healing cascade to enhance and influence wound healing. These biomaterials can provide moisture or absorption, depending on the delivery system. Collagen dressings are easy to apply and remove and are conformable. Collagen dressings are usually formulated with bovine, avian, or porcine collagen. Oxidized regenerated cellulose, a plant-based material, has been combined with collagen to produce a dressing capable of binding to and protecting growth factors by binding and inactivating matrix metalloproteinases in the wound environment. The increased understanding of the biochemical processes involved in chronic wound healing allows the design of wound care products aimed at correcting imbalances in the wound microenvironment. Traditional advanced wound care products tend to address the wound's macroenvironment, including moist wound environment control, fluid management, and controlled transpiration of wound fluids. The newer class of biomaterials and wound-healing agents, such as collagen and growth factors, targets specific defects in the chronic wound environment. In vitro laboratory data point to the possibility that these agents benefit the wound healing process at a biochemical level. Considerable evidence has indicated that collagen-based dressings may be capable of stimulating healing by manipulating wound biochemistry.

Single-stage Matriderm® and skin grafting as an alternative reconstruction in high-voltage injuries

This article presents a retrospective analysis of a series of nine patients requiring reconstruction of exposed bone, tendons or joint capsules as a result of acute high-voltage injuries in a single burn centre. As an alternative to free tissue transfer, the dermal substitute Matriderm(®) was used in a one-stage procedure in combination with split-thickness skin grafts (STSG) for reconstruction. Nine patients, in the period between 2005 and 2009 with extensive high-voltage injuries to one or more extremities which required coverage of exposed functional structures as bone, tendons or joint capsule, were included. A total of 11 skin graftings and 2 local flaps were performed. Data including regrafting rate, complications, hospital stays, length of rehabilitation and time until return to work were collected. Eleven STSG in combination with Matriderm(®) were performed on nine patients (success rate 89%). One patient died. One patient needed a free-flap coverage as a secondary procedure. The median follow-up was 30 months (range 6-48 months). The clinical results of these nine treated patients concerning skin-quality and coverage of exposed tendons or joint capsule were very good. In high-voltage injuries free-flap failure occurs between 10% and 30% if performed within the first 4-6 weeks after trauma. The use of single-stage Matriderm(®) and skin grafting for immediate coverage described in this article is a reliable alternative to selected cases within this period.

Fabrication of a nanofibrous scaffold with improved bioactivity for culture of human dermal fibroblasts for skin regeneration

Engineering dermal substitutes with electrospun nanofibres have lately been of prime importance for skin tissue regeneration. Simple electrospinning technology served to produce nanofibrous scaffolds morphologically and structurally similar to the extracellular matrix of native tissues. The nanofibrous scaffolds of poly(L-lactic acid)-co-poly(ε-caprolactone) (PLACL) and PLACL/gelatin complexes were fabricated by the electrospinning process. These nanofibres were characterized for fibre morphology, membrane porosity, wettability and chemical properties by FTIR analysis to culture human foreskin fibroblasts for skin tissue engineering. The nanofibre diameter was obtained between 282 and 761 nm for PLACL and PLACL/gelatin scaffolds; expressions of amino and carboxyl groups and porosity up to 87% were obtained for these fibres, while they also exhibited improved hydrophilic properties after plasma treatment. The results showed that fibroblasts proliferation, morphology, CMFDA dye expression and secretion of collagen were significantly increased in plasma-treated PLACL/gelatin scaffolds compared to PLACL nanofibrous scaffolds. The obtained results prove that the plasma-treated PLACL/gelatin nanofibrous scaffold is a potential biocomposite material for skin tissue regeneration.

Biocompatibility of Collagen Membranes Assessed by Culturing Human J111 Macrophage Cells

We have carried out an in vitro study on the interactions of human macrophages (J111 cell line) with different scaffolds made of type I and II collagen, isolated from horse tendon and from horse articular and trachea cartilage, in order to assess growth properties and biocompatibility of these membranes. We have therefore evaluated cell adhesion and proliferation as well as cytokine production considered an indicator of macrophage activation. The inflammatory response is in fact one of the major causes of collagen destruction thus interfering with cell and tissue behaviour. Moreover, the morphology of cells, seeded on membranes selected for the best characteristics, was described. Results might be relevant for in vivo application such ad “tissue engineering” and/or specialized cells implants.