Tissue engineering of skin

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.

Randomized, Paired-Site Comparison of Autologous Engineered Skin Substitutes and Split-Thickness Skin Graft for Closure of Extensive, Full-Thickness Burns

Stable closure of full-thickness burn wounds remains a limitation to recovery from burns of greater than 50% of the total body surface area (TBSA). Hypothetically, engineered skin substitutes (ESS) consisting of autologous keratinocytes and fibroblasts attached to collagen-based scaffolds may reduce requirements for donor skin, and decrease mortality. ESS were prepared from split-thickness skin biopsies collected after enrollment of 16 pediatric burn patients into an approved study protocol. ESS and split-thickness autograft (AG) were applied to 15 subjects with full-thickness burns involving a mean of 76.9% TBSA. Data consisted of photographs, tracings of donor skin and healed wounds, comparison of mortality with the National Burn Repository, correlation of TBSA closed wounds with TBSA full-thickness burn, frequencies of regrafting, and immunoreactivity to the biopolymer scaffold. One subject expired before ESS application, and 15 subjects received 2056 ESS grafts. The ratio of closed wound to donor areas was 108.7 ± 9.7 for ESS compared with a maximum of 4.0 ± 0.0 for AG. Mortality for enrolled subjects was 6.25%, and 30.3% for a comparable population from the National Burn Repository (P < .05). Engraftment was 83.5 ± 2.0% for ESS and 96.5 ± 0.9% for AG. Percentage TBSA closed was 29.9 ± 3.3% for ESS, and 47.0 ± 2.0% for AG. These values were significantly different between the graft types. Correlation of % TBSA closed with ESS with % TBSA full-thickness burn generated an R value of 0.65 (P < .001). These results indicate that autologous ESS reduce mortality and requirements for donor skin harvesting, for grafting of full-thickness burns of greater than 50% TBSA.

Skin wound healing in humans and mice: Challenges in translational research

Despite the great progress in translational research concerning skin wound healing in the last few decades, no animal model fully predicts all clinical outcomes. The mouse is the most commonly used model, as it is easy to maintain and standardize, and is economically accessible. However, differences between murine and human skin repair, such as the contraction promoted by panniculus carnosus and the role of specific niches of skin stem cells, make it difficult to bridge the gap between preclinical and clinical studies. Therefore, this review highlights the particularities of each species concerning skin morphophysiology, immunology, and genetics, which is essential to properly interpret findings and translate them to medicine.

Immunological challenges associated with artificial skin grafts: available solutions and stem cells in future design of synthetic skin

The repair or replacement of damaged skins is still an important, challenging public health problem. Immune acceptance and long-term survival of skin grafts represent the major problem to overcome in grafting given that in most situations autografts cannot be used. The emergence of artificial skin substitutes provides alternative treatment with the capacity to reduce the dependency on the increasing demand of cadaver skin grafts. Over the years, considerable research efforts have focused on strategies for skin repair or permanent skin graft transplantations. Available skin substitutes include pre- or post-transplantation treatments of donor cells, stem cell-based therapies, and skin equivalents composed of bio-engineered acellular or cellular skin substitutes. However, skin substitutes are still prone to immunological rejection, and as such, there is currently no skin substitute available to overcome this phenomenon. This review focuses on the mechanisms of skin rejection and tolerance induction and outlines in detail current available strategies and alternatives that may allow achieving full-thickness skin replacement and repair.

Electrospun Gelatin/poly(Glycerol Sebacate) Membrane with Controlled Release of Antibiotics for Wound Dressing

BACKGROUND

The most important risk that threatens the skin wounds is infections. Therefore, fabrication of a membrane as a wound dressing with the ability of antibiotic delivery in a proper delivery rate is especially important.

MATERIALS AND METHODS

Poly(glycerol sebacate) (PGS) was prepared from sebacic acid and glycerol with 1:1 ratio; then, it was added to gelatin in the 1:3 ratio and was dissolved in 80% (v/v) acetic acid, and finally, ciprofloxacin was added in 10% (w/v) of polymer solution. The gelatin/PGS membrane was fabricated using an electrospinning method. The membrane was cross-linked using ethyl-3-(3-dimethylaminopropyl) carbodiimide ethyl-3-(3-dimethylaminopropyl)carbodiim (EDC) and N-hydroxysuccinimide (NHS) in different time periods to achieve a proper drug release rate. Fourier-transform infrared (FTIR) spectroscopy was being used to manifest the peaks of polymers and drug in the membrane. Scanning electron microscopy (SEM) was used to evaluate the morphology, fibers diameter, pore size, and porosity before and after crosslinking process. Ultraviolet (UV)-visible spectrophotometry was used to show the ciprofloxacin release from the cross-linked membrane.

RESULTS

FTIR analysis showed the characteristic peaks of gelatin, PGS, and ciprofloxacin without any added peaks after the crosslinking process. SEM images revealed that nanofibers' size increased during the crosslinking process and porosity was higher than 80% before and after crosslinking process. UV-visible spectrophotometry showed the proper rate of ciprofloxacin release occurred from cross-linked membrane that remaining in EDC/NHS ethanol solution for 120 min.

CONCLUSION

The obtained results suggest that this recently developed gelatin/PGS membrane with controlled release of ciprofloxacin could be a promising biodegradable membrane for wound dressing.

Survival of Allogeneic Self-Assembled Cultured Skin

BACKGROUND

Deficiency of autologous skin for reconstruction of severe wounds is a major problem in plastic surgery. Autologous substitutes can provide additional coverage, but due to the duration of production, treatment is significantly delayed. The allogeneic approach offers a potential of having an off-the-shelf solution for the immediate application.

METHODS

In this study, we assess the engraftment and immunogenicity of allogeneic bilayered bioengineered skin prepared by a self-assembly method. Bioengineered skin has the potential immunological advantage of lacking passenger leukocytes including antigen-presenting cells. The skin constructs were transplanted across major histocompatibility complex (MHC) barriers in a porcine animal model. Animals received a second grafting of the same skin construct 7 weeks after the first set of grafts together with MHC-matched constructs to assess for clinical sensitization.

RESULTS

All alloconstructs successfully engrafted with histologic evidence of neovascularization by day 4. Complete cellular rejection and tissue loss occurred by day 8 for most grafts. After the second application, accelerated rejection (<4 days) took place with the development of swine MHC-specific cytotoxic alloantibody.

CONCLUSIONS

These data demonstrate preclinically that self-assembled allogeneic constructs engraft and reject similar to allogeneic skin despite the absence of professional donor antigen-presenting cells.

Insight into skin cell-based osteogenesis: a review

For decades, researchers have been fascinated by the strategy of using cell therapy for bone defects; some progress in the field has been made. Owing to its ample supply and easy access, skin, the largest organ in the body, has gained attention as a potential source of stem cells. Despite extensive applications in skin and nerve regeneration, an increasing number of reports indicate its potential use in bone tissue engineering and regeneration. Unfortunately, few review articles are available to outline current research efforts in skin-based osteogenesis. This review first summarizes the latest findings on stem cells or progenitors in skin and their niches and then discusses the strategies of skin cell-based osteogenesis. We hope this article elucidates this topic and generates new ideas for future studies.

Scientific collaboration: a social network analysis based on literature of animal-derived regenerative implantable medical devices

The collaboration network of English publications on animal-derived regenerative implantable medical devices based on tissue engineering technology and its evolving processes and current states were mapped in this paper. A total of 10 159 English papers published before 1 January 2015 were obtained in eight databases. Social network analysis was conducted on these papers by utilizing UCINET software and Statistical Analysis Software for Informatics researched and developed by Peking University. The collaboration network has evolved from scattered formation to single-core dominated, and then to a core-edge one; collaboration has become more frequent and wider; network density and centrality have decreased; USA, UK and China are the top three countries with Wake Forest University, Harvard University and Tufts University being the top three contributing institutions cooperated mostly during the period between 2010 and 2014; plenty of edge institutes exist. In conclusion, more collaboration among different institutions and countries is needed; Edge institutions and developing countries should expand their scope of collaboration.

Methodologies in creating skin substitutes

The creation of skin substitutes has significantly decreased morbidity and mortality of skin wounds. Although there are still a number of disadvantages of currently available skin substitutes, there has been a significant decline in research advances over the past several years in improving these skin substitutes. Clinically most skin substitutes used are acellular and do not use growth factors to assist wound healing, key areas of potential in this field of research. This article discusses the five necessary attributes of an ideal skin substitute. It comprehensively discusses the three major basic components of currently available skin substitutes: scaffold materials, growth factors, and cells, comparing and contrasting what has been used so far. It then examines a variety of techniques in how to incorporate these basic components together to act as a guide for further research in the field to create cellular skin substitutes with better clinical results.

Current and emerging vascularization strategies in skin tissue engineering

Vascularization is a key process in skin tissue engineering, determining the biological function of artificial skin implants. Hence, efficient vascularization strategies are a major prerequisite for the safe application of these implants in clinical practice. Current approaches include (i) modification of structural and physicochemical properties of dermal scaffolds, (ii) biological scaffold activation with growth factor-releasing systems or gene vectors, and (iii) generation of prevascularized skin substitutes by seeding scaffolds with vessel-forming cells. These conventional approaches may be further supplemented by emerging strategies, such as transplantation of adipose tissue-derived microvascular fragments, 3D bioprinting and microfluidics, miRNA modulation, cell sheet engineering, and fabrication of photosynthetic scaffolds. The successful translation of these vascularization strategies from bench to bedside may pave the way for a broad clinical implementation of skin tissue engineering.

Engineering design of artificial vascular junctions for 3D printing

Vascular vessels, including arteries, veins and capillaries, are being printed using additive manufacturing technologies, also known as 3D printing. This paper demonstrates that it is important to follow the vascular design by nature as close as possible when 3D printing artificial vascular branches. In previous work, the authors developed an algorithm of computational geometry for constructing smooth junctions for 3D printing. In this work, computational fluid dynamics (CFDs) is used to compare the wall shear stress and blood velocity field for the junctions of different designs. The CFD model can reproduce the expected wall shear stress at locations remote from the junction. For large vessels such as veins, it is shown that ensuring the smoothness of the junction and using smaller joining angles as observed in nature is very important to avoid high wall shear stress and recirculation. The issue is however less significant for capillaries. Large joining angles make no difference to the hemodynamic behavior, which is also consistent with the fact that most capillary junctions have large joining angles. The combination of the CFD analysis and the junction construction method form a complete design method for artificial vascular vessels that can be 3D printed using additive manufacturing technologies.

Bioengineered Self-assembled Skin as an Alternative to Skin Grafts

Supplemental Digital Content is available in the text.

For patients with extensive burns or donor site scarring, the limited availability of autologous and the inevitable rejection of allogeneic skin drive the need for new alternatives. Existing engineered biologic and synthetic skin analogs serve as temporary coverage until sufficient autologous skin is available. Here we report successful engraftment of a self-assembled bilayered skin construct derived from autologous skin punch biopsies in a porcine model. Dermal fibroblasts were stimulated to produce an extracellular matrix and were then seeded with epidermal progenitor cells to generate an epidermis. Autologous constructs were grafted onto partial- and full-thickness wounds. By gross examination and histology, skin construct vascularization and healing were comparable to autologous skin grafts and were superior to an autologous bilayered living cellular construct fabricated with fibroblasts cast in bovine collagen. This is the first demonstration of spontaneous vascularization and permanent engraftment of a self-assembled bilayered bioengineered skin that could supplement existing methods of reconstruction.

A synthetic isoflavone, DCMF, promotes human keratinocyte migration by activating Src/FAK signaling pathway

Flavonoids are plant secondary compounds with various pharmacological properties. We previously showed that one flavonoid, trimethoxyisoflavone (TMF), could promote wound healing by inducing keratinocyte migration. Here, we screened TMF derivatives for enhanced activity and identified one compound, 2',6 Dichloro-7-methoxyisoflavone (DCMF), as most effective at promoting migration in a scratch wound assay. Using the HaCaT keratinocyte cell line, we found DCMF treatment induced phosphorylation of both FAK and Src, and increased keratinocyte migration. DCMF-induced Src kinase could promote activation of ERK, AKT, and p38 signaling pathways, and DCMF-induced secretion of matrix metalloproteinase (MMP)-2 and MMP-9 and partial epithelial-mesenchymal transition (EMT), whereas Src inhibition abolished DCMF-induced EMT. Using an in vivo excisional wound model, we observed improved wound closure and re-epithelialization in DCMF-treated mice, as compared to controls. Collectively, our data demonstrate that DCMF induces cell migration and promotes wound healing through activation of Src/FAK, ERK, AKT, and p38 MAPK signaling.

Drug delivery systems for wound healing

Protein, gene, and small molecule therapies hold great potential for facilitating comprehensive tissue repair and regeneration. However, their clinical value will rely on effective delivery systems which maximize their therapeutic benefit. Significant advances have been made in recent years towards biomaterial delivery systems to satisfy this clinical need. Here we summarize the most outstanding advances in drug delivery technology for cutaneous wound healing.

3D Printing of Scaffold for Cells Delivery: Advances in Skin Tissue Engineering

Injury or damage to tissue and organs is a major health problem, resulting in about half of the world’s annual healthcare expenditure every year. Advances in the fields of stem cells (SCs) and biomaterials processing have provided a tremendous leap for researchers to manipulate the dynamics between these two, and obtain a skin substitute that can completely heal the wounded areas. Although wound healing needs a coordinated interplay between cells, extracellular proteins and growth factors, the most important players in this process are the endogenous SCs, which activate the repair cascade by recruiting cells from different sites. Extra cellular matrix (ECM) proteins are activated by these SCs, which in turn aid in cellular migrations and finally secretion of growth factors that can seal and heal the wounds. The interaction between ECM proteins and SCs helps the skin to sustain the rigors of everyday activity, and in an attempt to attain this level of functionality in artificial three-dimensional (3D) constructs, tissue engineered biomaterials are fabricated using more advanced techniques such as bioprinting and laser assisted printing of the organs. This review provides a concise summary of the most recent advances that have been made in the area of polymer bio-fabrication using 3D bio printing used for encapsulating stem cells for skin regeneration. The focus of this review is to describe, in detail, the role of 3D architecture and arrangement of cells within this system that can heal wounds and aid in skin regeneration.

Photocrosslinkable polysaccharide hydrogel composites based on dextran or pullulan–amylose blends with cytokines for a human co-culture model of human osteoblasts and endothelial cells

Polysaccharide hyrogel composites demonstrate fundamental potential as biomaterials for bone regeneration in vitro.

Scaffolds for hand tissue engineering: the importance of surface topography

Tissue engineering is believed to have great potential for the reconstruction of the hand after trauma, congenital absence and tumours. Due to the presence of multiple distinct tissue types, which together function in a precisely orchestrated fashion, the hand counts among the most complex structures to regenerate. As yet the achievements have been limited. More recently, the focus has shifted towards scaffolds, which provide a three-dimensional framework to mimic the natural extracellular environment for specific cell types. In particular their surface structures (or topographies) have become a key research focus to enhance tissue-specific cell attachment and growth into fully functioning units. This article reviews the current understanding in hand tissue engineering before focusing on the potential for scaffold topographical features on micro- and nanometre scales to achieve better functional regeneration of individual and composite tissues.

Stem Cells in Skin Regeneration, Wound Healing, and Their Clinical Applications

The skin is the largest organ of the body and has an array of functions. Skin compartments, epidermis, and hair follicles house stem cells that are indispensable for skin homeostasis and regeneration. These stem cells also contribute to wound repair, resulting in restoration of tissue integrity and function of damaged tissue. Unsuccessful wound healing processes often lead to non-healing wounds. Chronic wounds are caused by depletion of stem cells and a variety of other cellular and molecular mechanisms, many of which are still poorly understood. Current chronic wound therapies are limited, so the search to develop better therapeutic strategies is ongoing. Adult stem cells are gaining recognition as potential candidates for numerous skin pathologies. In this review, we will discuss epidermal and other stem cells present in the skin, and highlight some of the therapeutic applications of epidermal stem cells and other adult stem cells as tools for cell/scaffold-based therapies for non-healing wounds and other skin disorders. We will also discuss emerging concepts and offer some perspectives on how skin tissue-engineered products can be optimized to provide efficacious therapy in cutaneous repair and regeneration.

Preformed gelatin microcryogels as injectable cell carriers for enhanced skin wound healing

Wound dressings of cell-laden bulk hydrogel or scaffold were mainly applied for enhanced cell engraftment in contrast to free cell injection. However, dressing of cells laden in biomaterials on wound surface might not effectively and timely exert functions on deep or chronic wounds where insufficient blood supply exists. Previously, we developed injectable gelatin microcryogels (GMs) which could load cells for enhanced cell delivery and cell therapy. In this study, biological changes of human adipose-derived stem cells (hASCs) laden in GMs were compared in varied aspects with traditional two dimensional (2D) cell culture, such as cell phenotype markers, stemness genes, differentiation, secretion of growth factors, cell apoptosis and cell memory by FACS, QRT-PCR and ELISA, that demonstrated the priming effects of GMs on upregulation of stemness genes and improved secretion of growth factors of hASCs for potential augmented wound healing. In a full-thickness skin wound model in nude mice, multisite injection and dressing of hASCs-laden GMs could significantly accelerate the healing compared to free cell injection. Bioluminescence imaging and protein analysis indicated improved cell retention and secretion of multiple growth factors. Our study suggests that GMs as primed injectable 3D micro-niches represent a new cell delivery methodology for skin wound healing which could not only benefit on the recovery of wound bed but also play direct effects on wound basal layer for healing enhancement. Injectable GMs as facile multisite cell delivery approach potentially provide new minimally-invasive therapeutic strategy for refractory wounds such as diabetic ulcer or radiative skin wound.

STATEMENT OF SIGNIFICANCE

This work applied a type of elastic micro-scaffold (GMs) to load and prime hMSCs for skin wound healing. Due to the injectability of GMs, the 3D cellular micro-niches could simply realize minimally-invasive and multisite cell delivery approach for accelerating the wound healing process superior to free cell injection. The biological features of MSCs has been thoroughly characterized during 3D culture in GMs (i.e. cell proliferation, characterization of cell surface markers, stemness of MSCs in GMs, differentiation of MSCs in GMs, secretion of MSCs in GMs, induced apoptosis of MSCs in GMs). Multiple methods such as bioluminescent imaging, immunohistochemistry, immunofluorescence, qRT-PCR, ELSA and western blot were used to assess the in vivo results between groups.

Fibroblast heterogeneity and its implications for engineering organotypic skin models in vitro

Advances in cell culture methods, multidisciplinary research, clinical need to replace lost skin tissues and regulatory need to replace animal models with alternative test methods has led to development of three dimensional models of human skin. In general, these in vitro models of skin consist of keratinocytes cultured over fibroblast-populated dermal matrices. Accumulating evidences indicate that mesenchyme-derived signals are essential for epidermal morphogenesis, homeostasis and differentiation. Various studies show that fibroblasts isolated from different tissues in the body are dynamic in nature and are morphologically and functionally heterogeneous subpopulations. Further, these differences seem to be dictated by the local biological and physical microenvironment the fibroblasts reside resulting in "positional identity or memory". Furthermore, the heterogeneity among the fibroblasts play a critical role in scarless wound healing and complete restoration of native tissue architecture in fetus and oral mucosa; and excessive scar formation in diseased states like keloids and hypertrophic scars. In this review, we summarize current concepts about the heterogeneity among fibroblasts and their role in various wound healing environments. Further, we contemplate how the insights on fibroblast heterogeneity could be applied for the development of next generation organotypic skin models.

Tumorigenicity Testing in Athymic Mice of Cultured Human Melanocytes for Transplantation in Engineered Skin Substitutes

Autologous engineered skin substitutes (ESS) have been shown to close excised, full-thickness burns, but are consistently hypopigmented due to depletion of human melanocytes (hM) during culture of keratinocytes. Hypothetically, addition of hM to ESS may restore uniform pigmentation, but may also promote neoplasia and tumor formation. To evaluate this risk, 16 strains of hM were isolated and propagated in selective culture medium, then injected subcutaneously into athymic mice (1 χ 107 hM/animal; n = 6/strain) and followed for 24 weeks. Human melanoma cells (SK-Mel-2, SK-Mel-5) served as positive controls. No detectable tumors formed from hM strains derived from normal skin. In contrast, SK-Mel-2 formed tumors in 50% of mice, and SK-Mel-5 formed tumors in 83% of mice. Histopathology confirmed the tumorigenic anatomy of the controls and the presence of hM that were not tumorigenic in the test groups. These results support the safety of cultured hM for transplantation to restore uniform skin pigmentation in wounds closed with ESS.

Evaluation of emulsion electrospun polycaprolactone/hyaluronan/epidermal growth factor nanofibrous scaffolds for wound healing

Wound healing scaffolds provide cells with structural integrity and can also deliver biological agents to establish a skin tissue-specific microenvironment to regulate cell functions and to accelerate the healing process. In this study, we fabricated biodegradable nanofibrous scaffolds with an emulsion electrospinning technique. The scaffolds were composed of polycaprolactone, hyaluronan and encapsulating epidermal growth factor. The morphology and core-sheath structure of the nanofibers were characterized by scanning electron microscopy and transmission electron microscopy. The scaffolds were also characterized for chemical composition and hydrophilicity with a Fourier-transform infrared analysis, energy dispersive spectroscopy and the water contact angle. An in vitro model protein bovine serum albumin and epidermal growth factor release study was conducted to evaluate the sustained release potential of the core-sheath structured nanofibers with and without the hyaluronan component. Additionally, an in vitro cultivation of human skin keratinocytes (HaCaT) and fibroblasts on polycaprolactone/hyaluronan and polycaprolactone/hyaluronan-epidermal growth factor scaffolds showed a significant synergistic effect of hyaluronan and epidermal growth factor on cell proliferation and infiltration. Furthermore, there was an up-regulation of the wound-healing-related genes collagen I, collagen III and TGF-β in polycaprolactone/hyaluronan/epidermal growth factor scaffolds compared with control groups. In the full-thickness wound model, the enhanced regeneration of fully functional skin was facilitated by epidermal regeneration in the polycaprolactone/hyaluronan/epidermal growth factor treatment group. Our findings suggest that bioactivity and hemostasis of the hyaluronan-based nanofibrous scaffolds have the capability to encapsulate and control the release of growth factors that can serve as skin tissue engineering scaffolds for wound healing.

Bioengineering a human plasma-based epidermal substitute with efficient grafting capacity and high content in clonogenic cells

Cultured epithelial autografts (CEAs) produced from a small, healthy skin biopsy represent a lifesaving surgical technique in cases of full-thickness skin burn covering >50% of total body surface area. CEAs also present numerous drawbacks, among them the use of animal proteins and cells, the high fragility of keratinocyte sheets, and the immaturity of the dermal-epidermal junction, leading to heavy cosmetic and functional sequelae. To overcome these weaknesses, we developed a human plasma-based epidermal substitute (hPBES) for epidermal coverage in cases of massive burn, as an alternative to traditional CEA, and set up critical quality controls for preclinical and clinical studies. In this study, phenotypical analyses in conjunction with functional assays (clonal analysis, long-term culture, or in vivo graft) showed that our new substitute fulfills the biological requirements for epidermal regeneration. hPBES keratinocytes showed high potential for cell proliferation and subsequent differentiation similar to healthy skin compared with a well-known reference material, as ascertained by a combination of quality controls. This work highlights the importance of integrating relevant multiparameter quality controls into the bioengineering of new skin substitutes before they reach clinical development.

SIGNIFICANCE

This work involves the development of a new bioengineered epidermal substitute with pertinent functional quality controls. The novelty of this work is based on this quality approach.

Microporous dermal-mimetic electrospun scaffolds pre-seeded with fibroblasts promote tissue regeneration in full-thickness skin wounds

Electrospun scaffolds serve as promising substrates for tissue repair due to their nanofibrous architecture and amenability to tailoring of chemical composition. In this study, the regenerative potential of a microporous electrospun scaffold pre-seeded with dermal fibroblasts was evaluated. Previously we reported that a 70% collagen I and 30% poly(Ɛ-caprolactone) electrospun scaffold (70:30 col/PCL) containing 160 μm diameter pores had favorable mechanical properties, supported fibroblast infiltration and subsequent cell-mediated deposition of extracellular matrix (ECM), and promoted more rapid and effective in vivo skin regeneration when compared to scaffolds lacking micropores. In the current study we tested the hypothesis that the efficacy of the 70:30 col/PCL microporous scaffolds could be further enhanced by seeding scaffolds with dermal fibroblasts prior to implantation into skin wounds. To address this hypothesis, a Fischer 344 (F344) rat syngeneic model was employed. In vitro studies showed that dermal fibroblasts isolated from F344 rat skin were able to adhere and proliferate on 70:30 col/PCL microporous scaffolds, and the cells also filled the 160 μm pores with native ECM proteins such as collagen I and fibronectin. Additionally, scaffolds seeded with F344 fibroblasts exhibited a low rate of contraction (~14%) over a 21 day time frame. To assess regenerative potential, scaffolds with or without seeded F344 dermal fibroblasts were implanted into full thickness, critical size defects created in F344 hosts. Specifically, we compared: microporous scaffolds containing fibroblasts seeded for 4 days; scaffolds containing fibroblasts seeded for only 1 day; acellular microporous scaffolds; and a sham wound (no scaffold). Scaffolds containing fibroblasts seeded for 4 days had the best response of all treatment groups with respect to accelerated wound healing, a more normal-appearing dermal matrix structure, and hair follicle regeneration. Collectively these results suggest that microporous electrospun scaffolds pre-seeded with fibroblasts promote greater wound-healing than acellular scaffolds.

Natural-based nanocomposites for bone tissue engineering and regenerative medicine: a review

Tissue engineering and regenerative medicine has been providing exciting technologies for the development of functional substitutes aimed to repair and regenerate damaged tissues and organs. Inspired by the hierarchical nature of bone, nanostructured biomaterials are gaining a singular attention for tissue engineering, owing their ability to promote cell adhesion and proliferation, and hence new bone growth, compared with conventional microsized materials. Of particular interest are nanocomposites involving biopolymeric matrices and bioactive nanosized fillers. Biodegradability, high mechanical strength, and osteointegration and formation of ligamentous tissue are properties required for such materials. Biopolymers are advantageous due to their similarities with extracellular matrices, specific degradation rates, and good biological performance. By its turn, calcium phosphates possess favorable osteoconductivity, resorbability, and biocompatibility. Herein, an overview on the available natural polymer/calcium phosphate nanocomposite materials, their design, and properties is presented. Scaffolds, hydrogels, and fibers as biomimetic strategies for tissue engineering, and processing methodologies are described. The specific biological properties of the nanocomposites, as well as their interaction with cells, including the use of bioactive molecules, are highlighted. Nanocomposites in vivo studies using animal models are also reviewed and discussed.

Stem cell and tissue engineering in breast reconstruction

Breast cancer worldwide is the most common cancer in women with incidence rate varying from geographic areas. Guidelines for management of breast cancer have been largely established and widely used. Mastectomy is one of the surgical procedures used treating breast cancer. Optionally, after mastectomy, appropriately selected patients could undergo breast reconstruction to create their breast contour. Many techniques have been used for breast reconstructive surgery, mainly implant-based and autologous tissue reconstruction. Even with highly-experienced surgeon and good-quality breast and autologous substitute tissue, still there could be unfilled defect after mastectomy with reconstruction. Stem cell, in particular, adipose-derived stem cell residing within fat tissue, could be used to fill the imperfection providing optimal breast shape and natural feeling of fat tissue. However, whether surgical reconstruction alone or in combination with stem cell and tissue engineering approach be used, the ultimate outcomes are patient safety first and satisfaction second.

Acalvaria

Acalvaria is a rare congenital malformation characterized by an absence of skin and skull. The authors describe a newborn at an estimated 38 weeks gestational age who was delivered via cesarean section from a 32-year-old mother. Upon delivery, the child was noted to have a frontal encephalocele and an absence of calvaria including skull and skin overlying the brain. A thin membrane representing dura mater was overlying the cortical tissue. After multiple craniofacial operations, including repair of the encephalocele and application of cultured keratinocytes over the rostral defect, the patient demonstrated significant closure of the calvarial defect and was alive at an age of more than 17 months with near-average development.

Characterization of fetal keratinocytes, showing enhanced stem cell-like properties: a potential source of cells for skin reconstruction

Epidermal stem cells have been in clinical application as a source of culture-generated grafts. Although applications for such cells are increasing due to aging populations and the greater incidence of diabetes, current keratinocyte grafting technology is limited by immunological barriers and the time needed for culture amplification. We studied the feasibility of using human fetal skin cells for allogeneic transplantation and showed that fetal keratinocytes have faster expansion times, longer telomeres, lower immunogenicity indicators, and greater clonogenicity with more stem cell indicators than adult keratinocytes. The fetal cells did not induce proliferation of T cells in coculture and were able to suppress the proliferation of stimulated T cells. Nevertheless, fetal keratinocytes could stratify normally in vitro. Experimental transplantation of fetal keratinocytes in vivo seeded on an engineered plasma scaffold yielded a well-stratified epidermal architecture and showed stable skin regeneration. These results support the possibility of using fetal skin cells for cell-based therapeutic grafting.

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Properties of fetal and adult keratinocytes are compared in tissue culture and grafts

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Fetal skin cells can be engrafted and show stable human-to-mouse skin regeneration

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Fetal keratinocytes are stem cell rich and need no differentiation before grafting

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Fetal keratinocytes are able to suppress proliferation of stimulated T cells in vitro