Tissue engineering of replacement skin: the crossroads of biomaterials, wound healing, embryonic development, stem cells and regeneration

Advances in keratinocyte delivery in burn wound care

This review gives an updated overview on keratinocyte transplantation in burn wounds concentrating on application methods and future therapeutic cell delivery options with a special interest in hydrogels and spray devices for cell delivery. To achieve faster re-epithelialisation of burn wounds, the original autologous keratinocyte culture and transplantation technique was introduced over 3 decades ago. Application types of keratinocytes transplantation have improved from cell sheets to single-cell solutions delivered with a spray system. However, further enhancement of cell culture, cell viability and function in vivo, cell carrier and cell delivery systems remain themes of interest. Hydrogels such as chitosan, alginate, fibrin and collagen are frequently used in burn wound care and have advantageous characteristics as cell carriers. Future approaches of keratinocyte transplantation involve spray devices, but optimisation of application technique and carrier type is necessary.

Application and Assessment of Allogeneic Fibroblasts for Cell Therapy

BACKGROUND AND OBJECTIVE

In recent years, due to increasing number of patients with non-healing skin ulcers, skin substitutes have been used. Skin substitutes contain living cells causing faster and more effective wound healing. Therefore, research on the use of autologous and allogeneic cells such as fibroblasts in skin substitutes has attracted attentions. However, there are discrepancies in the immune responses to allogeneic fibroblasts. Therefore, we aimed to review the immune responses to allogeneic fibroblasts.

METHODS

Donor fibroblasts were isolated from the skin of three rats. Nine recipient rats which were subcutaneously injected with three different regimens, were divided into three groups: Group 1; phosphate buffered saline (PBS) without cells (control), group 2: allogeneic fibroblasts of one animal source suspended in phosphate buffered saline, and group 3; phosphate buffered saline containing mixed allogeneic fibroblasts of three animal sources. The skin samples were biopsied at 1, 3 and 7 days after injection and studied histopathologically.

RESULTS AND CONCLUSION

No signs of redness and edema were observed in the injection sites. In pathology examination, changes such as vasculitis, eosinophils and lymphocytes accumulation around fibroblasts, fibroblast apoptosis and transplant rejection at the injection site were not observed in either group.Subcutaneous injection of allogeneic fibroblasts in rats can be introduced as a promising approach for wound healing as they do not stimulate the immune system.

3D Bioprinting Technologies for Tissue Engineering Applications

Three-dimensional (3D) printing (rapid prototyping or additive manufacturing) technologies have received significant attention in various fields over the past several decades. Tissue engineering applications of 3D bioprinting, in particular, have attracted the attention of many researchers. 3D scaffolds produced by the 3D bioprinting of biomaterials (bio-inks) enable the regeneration and restoration of various tissues and organs. These 3D bioprinting techniques are useful for fabricating scaffolds for biomedical and regenerative medicine and tissue engineering applications, permitting rapid manufacture with high-precision and control over size, porosity, and shape. In this review, we introduce a variety of tissue engineering applications to create bones, vascular, skin, cartilage, and neural structures using a variety of 3D bioprinting techniques.

Advances in Protein-Based Materials: From Origin to Novel Biomaterials

Biomaterials play a very important role in biomedicine and tissue engineering where they directly affect the cellular activities and their microenvironment . Myriad of techniques have been employed to fabricate a vast number natural, artificial and recombinant polymer s in order to harness these biomaterials in tissue regene ration , drug delivery and various other applications. Despite of tremendous efforts made in this field during last few decades, advanced and new generation biomaterials are still lacking. Protein based biomaterials have emerged as an attractive alternatives due to their intrinsic properties like cell to cell interaction , structural support and cellular communications. Several protein based biomaterials like, collagen , keratin , elastin , silk protein and more recently recombinant protein s are being utilized in a number of biomedical and biotechnological processes. These protein-based biomaterials have enormous capabilities, which can completely revolutionize the biomaterial world. In this review, we address an up-to date review on the novel, protein-based biomaterials used for biomedical field including tissue engineering, medical science, regenerative medicine as well as drug delivery. Further, we have also emphasized the novel fabrication techniques associated with protein-based materials and implication of these biomaterials in the domain of biomedical engineering .

Adipose Tissue-Derived Stromal Cells for Wound Healing

Skin as the outer layer covers the body. Wounds can affect this vital organ negatively and disrupt its functions. Wound healing as a biological process is initiated immediately after an injury. This process consists of three stages: inflammation, proliferation, remodeling. Generally, these three stages occur continuously and timely. However, some factors such as infection, obesity and diabetes mellitus can interfere with these stages and impede the normal healing process which results in chronic wounds. Financial burden on both patients and health care systems, negative biologic effect on the patient's general health status and reduction in quality of life are a number of issues which make chronic wounds as a considerable challenge. During recent years, along with advances in the biomedical sciences, various surgical and non-surgical therapeutic methods have been suggested. All of these suggested treatments have their own advantages and disadvantages. Recently, cell-based therapies and regenerative medicine represent promising approaches to wound healing. Accordingly, several types of mesenchymal stem cells have been used in both preclinical and clinical settings for the treatment of wounds. Adipose-derived stromal cells are a cost-effective source of mesenchymal stem cells in wound management which can be easily harvest from adipose tissues through the less invasive processes with high yield rates. In addition, their ability to secrete multiple cytokines and growth factors, and differentiation into skin cells make them an ideal cell type to use in wound treatment. This is a concise overview on the application of adipose-derived stromal cells in wound healing and their role in the treatment of chronic wounds.

Decellularized bSIS-ECM as a Regenerative Biomaterial for Skin Wound Repair

Tissue engineering-based regenerative applications can involve the use of stem cells for the treatment of non-healing wounds. Multipotent mesenchymal stem cells have become a focus of skin injury treatments along with many other injury types owing to their unprecedented advantages. However, there are certain limitations concerning the solo use of stem cells in skin wound repair. Natural bioactive extracellular matrix-based scaffolds have great potential for overcoming these limitations by supporting the regenerative activity and localization of stem cells. This chapter describes the use of bone marrow mesenchymal stem cells together with decellularized bovine small intestinal submucosa (SIS), for the treatment of a critical-sized full-thickness skin defect in a small animal model.

Nanofibrous artificial skin substitute composed of mPEG–PCL grafted gelatin/hyaluronan/chondroitin sulfate/sericin for 2nd degree burn care: in vitro and in vivo study

The aim of this study was to investigate the efficacy of a skin substitute composed of mPEG–PCL–grafted-gelatin (Bio-Syn)/hyaluronan/chondroitin sulfate/sericin and to study its in vitro biocompatibility with human fibroblasts, human keratinocytes and hMSCs in terms of cellular adhesion and proliferation (∼5–6 fold). mPEG–PCL was grafted into a gelatin backbone via a Michael addition reaction to prepare Bio-Syn and it was characterized using ATR-FTIR, ¹H NMR and TNBS assay. Additionally, keratinocyte–hMSC contact co-culture studies showed that Bio-Syn composite scaffolds loaded with sericin promote hMSCs’ epithelial differentiation with regard to qRT-PCR gene expression (ΔNp63α and keratin 14) and expression of various epithelial markers (Pan-cytokeratin, ΔNp63α and keratin 14). In vivo efficacy studies on a 2^nd degree burn wound model in Wistar rats showed an improved rate of wound contraction, histology (H&E and Van Gieson’s staining) and pro-healing marker (hexosamine, hydroxyproline, etc.) expression in granular tissue compared to using the commercial dressing Neuskin™ and a cotton gauze control.

The paper demonstrates the fabrication of sericin loaded hybrid polymeric composite nanofibrous scaffold and evaluation of its cytocompatibilty in three human monocultures and biocompatibility in second degree burn wound model in Wistar rats.

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.

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.

The Effect of Anti-aging Peptides on Mechanical and Biological Properties of HaCaT Keratinocytes

Atomic force microscopy (AFM) and fluorescence microscopy was applied to determine the influence of the anti-aging peptides on the morphology and the mechanical properties of keratinocytes. Immortalized human keratinocytes (HaCaT) were treated with two anti-aging bioactive peptides: Acetyl Tetrapeptide-2 and Acetyl Hexapeptide-50 (Lipotec). The AFM measurement of the keratinocyte stiffness were carried after 48 h exposure at an indentation depth of 200 nm. AFM analysis showed increase of the cell stiffness for cells treated with Acetyl Tetrapeptide-2 (P1) in concentration range. Acetyl Hexapeptide-50 (P2) at concentration of 0.05 µg/ml also increased the stiffness of HaCaT cells but at higher concentrations 0.5 and 5 µg/ml cell stiffness was lower as compared to untreated control. Fluorescence microscopy revealed remodeling of actin filaments dependent on the concentration of P2 peptide. The mechanical response of HaCaT cells treated with P2 peptide corresponds to change of transcription level of ACTN1 and SOD2 which activity was expected to be modulated by P2 treatment.

Treatment of a burn animal model with functionalized tridimensional electrospun biomaterials

Laminin-functionalized poly-d,l-lactic acid scaffolds were produced. Following this, mesenchymal stem cells and keratinocytes were seeded on biomaterials for the in vivo experiments, where the biomaterials with or without cells were implanted. The analysis is comprised of the visual aspect and mean size of the lesion plus the histology and gene expression. The results showed that the cells occupied all the structure of the scaffolds in all the groups. After nine days of in vivo experiments, the defect size did not show statistical difference among the groups, although the groups with the poly-d,l-lactic acid/Lam biomaterial had the lowest lesion size and presented the best visual aspect of the wound. Gene expression analysis showed considerable increase of tumor growth factor beta 1 expression, increased vascular endothelial growth factor and balance of the BAX/Bcl-2 ratio when compared to the lesion group. Histological analysis showed well-formed tissue in the groups where the biomaterials and biomaterials plus cells were used. In some animals, in which biomaterials and cells were used, the epidermis was formed throughout the length of the wound. In conclusion, these biomaterials were found to be capable of providing support for the growth of cells and stimulated the healing of the skin, which was improved by the use of cells.

Stem Cell Secretome and Its Effect on Cellular Mechanisms Relevant to Wound Healing

Stem cells introduced to site of injury primarily act via indirect paracrine effects rather than direct cell replacement of damaged cells. This gives rise to understanding the stem cell secretome. In this study, in vitro studies demonstrate that the secretome activates the PI3K/Akt or FAK/ERK1/2 signaling cascades and subsequently enhances the proliferative and migratory abilities of various types of skin cells, such as fibroblasts, keratinocytes, and vascular epithelial cells, ultimately accelerating wound contraction. Indeed, inhibition of these signaling pathways with synthetic inhibitors resulted in the disruption of secretome-induced beneficial effects on various skin cells. In addition, major components of the stem cell secretome (EGF, basic FGF, and HGF) may be responsible for the acceleration of wound contraction. Stimulatory effects of these three prominent factors on wound contraction are achieved through the upregulation of PI3K/Akt or FAK/ERK1/2 activity. Overall, we lay the rationale for using the stem cell secretome in promoting wound contraction. In vivo wound healing studies are warranted to test the significance of our in vitro findings.

* Ethical Issues in the Use of Animal Models for Tissue Engineering: Reflections on Legal Aspects, Moral Theory, Three Rs Strategies, and Harm-Benefit Analysis

Animal experimentation requires a solid and rational moral foundation. Objective and emphatic decision-making and protocol evaluation by researchers and ethics committees remain a difficult and sensitive matter. This article presents three perspectives that facilitate a consideration of the minimally acceptable standard for animal experiments, in particular, in tissue engineering (TE) and regenerative medicine. First, we review the boundaries provided by law and public opinion in America and Europe. Second, we review contemporary moral theory to introduce the Neo-Rawlsian contractarian theory to objectively evaluate the ethics of animal experiments. Third, we introduce the importance of available reduction, replacement, and refinement strategies, which should be accounted for in moral decision-making and protocol evaluation of animal experiments. The three perspectives are integrated into an algorithmic and graphic harm-benefit analysis tool based on the most relevant aspects of animal models in TE. We conclude with a consideration of future avenues to improve animal experiments.

Superabsorbent crosslinked carboxymethyl cellulose-PEG hydrogels for potential wound dressing applications

This study focused on the synthesis and comprehensive characterization of environmentally friendly hydrogel membranes based on carboxymethyl cellulose (CMC) for wound dressing and skin repair substitutes. These new CMC hydrogels were prepared with two degrees of functionalization (DS=0.77 and 1.22) and chemically crosslinked with citric acid (CA) for tuning their properties. Additionally, CMC-based hybrids were prepared by blending with polyethylene glycol (PEG, 10wt.%). The results demonstrated that superabsorbent hydrogels (SAP) were produced with swelling degree typically ranging from 100% to 5000%, which was significantly dependent on the concentration of CA crosslinker and the addition of PEG as network modifier. The spectroscopical characterizations indicated that the mechanism of CA crosslinking was mostly associated with the chemical reaction with CMC hydroxyl groups and that PEG played an important role on the formation of a hybrid polymeric network. These hydrogels presented very distinct morphological features depended on the degree of crosslinking and the surface nanomechanical properties (e.g., elastic moduli) were drastically affected (from approximately 0.08GPa to 2.0GPa) due to the formation of CMC-PEG hybrid nanostructures. These CMC-based hydrogels were cytocompatible considering the in vitro cell viability responses of over 95% towards human embryonic kidney cells (HEK293T) used as model cell line.

Materials and techniques in chest wall reconstruction: a review

Extensive chest wall resection and reconstruction are a challenging procedure that requires a multidisciplinary approach, including input from thoracic surgeon, plastic surgeon and oncologist. In particular chest wall neoplastic pathology is associated with high surgical morbidity and can result in full thickness defects hard to reconstruct. The goals of a successful chest wall reconstruction are to restore the chest wall rigidity, preserve pulmonary mechanic and protect the intrathoracic organs minimizing the thoracic deformity. In case of large full thickness defects synthetic, biologic or composite meshes can be used, with or without titanium plate to restore thoracic cage rigidity as like as more recently the use of allograft to reconstruct the sternum. After skeletal stability is established full tissue coverage can be achieved using direct suture, skin graft or local advancement flaps, pedicled myocutaneous flaps or free flaps. The aim of this article is to illustrate the indications, various materials and techniques for chest wall reconstruction with the goal to obtain the best chest wall rigidity and soft tissue coverage.

Failure rates of artificial dermis products in treatment of diabetic foot ulcer: A systematic review and network meta-analysis

Diabetic foot ulcer (DFU) is a frequent complication in diabetic patients, occurring in up to 25% of those affected. Among the treatments available to clinicians, the use of bioengineered skin substitutes is an attractive alternative. Artificial dermis functions as a matrix, covering the wound and supporting healing and reconstruction of the lost tissue. This study was aimed at reviewing the use of five regeneration matrices (namely, Integra, Nevelia, Matriderm, Pelnac, and Renoskin) as reported by clinical trials. We searched Medline, Embase, ISI Web of Science, Scopus, and Cochrane Central Register of Controlled Trials databases for relevant studies. Risk of failure rates was analysed by relative risk ratio method and complete ulcer healing was studied using network meta-analysis. Thirteen studies (12 randomized clinical trials and one cohort study) were eligible for analysis. The network meta-analysis based on a single study for Matriderm and 12 studies for other products showed that Matriderm was statistically inferior in achieving complete ulcer healing, as compared to all other products combined. In the second phase analysis, which was limited to three studies using artificial dermis products, there was a 57% reduction in the risk of reepithelialization failure for DFU patients who used Matriderm or Pelnac, compared to those who used Pelnac with basic fibroblast growth factor spray or skin grafting. The data showed an overall low failure rate suggesting that these bioengineered skin products provide a suitable support and microenvironment for healing of DFUs with low ulcer recurrence rates. This systematic review with meta-analysis highlights the pressing need for more studies investigating the safety, efficacy and failure rates of regeneration matrices in the treatment of DFUs.

Construction of 3D multicellular microfluidic chip for an in vitro skin model

Current in vitro skin models do not recapitulate the complex architecture and functions of the skin tissue. In particular, on-chip construction of an in vitro model comprising the epidermis and dermis layer with vascular structure for mass transport has not been reported yet. In this study, we aim to develop a microfluidic, three-dimensional (3D) skin chip with fluidic channels using PDMS and hydrogels. Mass transport within the collagen hydrogel matrix was verified with fluorescent model molecules, and a transport-reaction model of oxygen and glucose inside the skin chip was developed to aid the design of the microfluidic skin chip. Comparison of viabilities of dermal fibroblasts and HaCaT cultured in the chip with various culture conditions revealed that the presence of flow plays a crucial role in maintaining the viability, and both cells were viable after 10 days of air exposure culture. Our 3D skin chip with vascular structures can be a valuable in vitro model for reproducing the interaction between different components of the skin tissue, and thus work as a more physiologically realistic platform for testing skin reaction to cosmetic products and drugs.

Biomaterials based strategies for rotator cuff repair

Tearing of the rotator cuff commonly occurs as among one of the most frequently experienced tendon disorders. While treatment typically involves surgical repair, failure rates to achieve or sustain healing range from 20 to 90%. The insufficient capacity to recover damaged tendon to heal to the bone, especially at the enthesis, is primarily responsible for the failure rates reported. Various types of biomaterials with special structures have been developed to improve tendon-bone healing and tendon regeneration, and have received considerable attention for replacement, reconstruction, or reinforcement of tendon defects. In this review, we first give a brief introduction of the anatomy of the rotator cuff and then discuss various design strategies to augment rotator cuff repair. Furthermore, we highlight current biomaterials used for repair and their clinical applications as well as the limitations in the literature. We conclude this article with challenges and future directions in designing more advanced biomaterials for augmentation of rotator cuff repair.

Emerging Biofabrication Strategies for Engineering Complex Tissue Constructs

The demand for organ transplantation and repair, coupled with a shortage of available donors, poses an urgent clinical need for the development of innovative treatment strategies for long-term repair and regeneration of injured or diseased tissues and organs. Bioengineering organs, by growing patient-derived cells in biomaterial scaffolds in the presence of pertinent physicochemical signals, provides a promising solution to meet this demand. However, recapitulating the structural and cytoarchitectural complexities of native tissues in vitro remains a significant challenge to be addressed. Through tremendous efforts over the past decade, several innovative biofabrication strategies have been developed to overcome these challenges. This review highlights recent work on emerging three-dimensional bioprinting and textile techniques, compares the advantages and shortcomings of these approaches, outlines the use of common biomaterials and advanced hybrid scaffolds, and describes several design considerations including the structural, physical, biological, and economical parameters that are crucial for the fabrication of functional, complex, engineered tissues. Finally, the applications of these biofabrication strategies in neural, skin, connective, and muscle tissue engineering are explored.

Advances in Skin Regeneration Using Tissue Engineering

Tissue engineered skin substitutes for wound healing have evolved tremendously over the last couple of years. New advances have been made toward developing skin substitutes made up of artificial and natural materials. Engineered skin substitutes are developed from acellular materials or can be synthesized from autologous, allograft, xenogenic, or synthetic sources. Each of these engineered skin substitutes has their advantages and disadvantages. However, to this date, a complete functional skin substitute is not available, and research is continuing to develop a competent full thickness skin substitute product that can vascularize rapidly. There is also a need to redesign the currently available substitutes to make them user friendly, commercially affordable, and viable with longer shelf life. The present review focuses on providing an overview of advances in the field of tissue engineered skin substitute development, the availability of various types, and their application.

Histopathological assessment of OASIS Ultra on critical-sized wound healing: a pilot study

BACKGROUND

Dermatopathologists assess wounds secondary to trauma, infection, or oncologic resection that can be challenging to reconstruct. OASIS Ultra, an extracellular matrix, has been described for use in chronic and burn wounds. The aim of this pilot study is to assess wound healing in post-traumatic and infective wounds treated with OASIS using histological markers of repair.

MATERIALS AND METHODS

Adults with traumatic, infective or iatrogenic wound defects with size precluding primary closure were eligible. Half the wound was randomly assigned to receive OASIS plus standard therapy; the other half received standard of care (SOC) therapy. During dressing changes, standardized-scale photographs were taken and biopsies obtained. Histologic sections were reviewed for degree of acute inflammation and extent of tissue repair. Neutrophils, edema, hemorrhage, necrosis, fibroblasts, collagen density and neovascularization were semi-quantitatively assessed.

RESULTS

Forty-four skin biopsies from 7 patients with 10 acute wounds met eligibility criteria. Histologically, OASIS samples demonstrated improved acute inflammation scores compared to SOC. No patients experienced OASIS-related complications. OASIS-treated wound halves trended toward more wound contraction and improved tissue repair.

CONCLUSION

Our scoring system aids histopathological wound assessment. Treatment of critical-sized, post-traumatic, acute wounds with OASIS resulted in decreased inflammation, and potentially more advanced wound healing, compared to SOC.

Nanotechnology-Driven Therapeutic Interventions in Wound Healing: Potential Uses and Applications

The chronic nature and associated complications of nonhealing wounds have led to the emergence of nanotechnology-based therapies that aim at facilitating the healing process and ultimately repairing the injured tissue. A number of engineered nanotechnologies have been proposed demonstrating unique properties and multiple functions that address specific problems associated with wound repair mechanisms. In this outlook, we highlight the most recently developed nanotechnology-based therapeutic agents and assess the viability and efficacy of each treatment, with emphasis on chronic cutaneous wounds. Herein we explore the unmet needs and future directions of current technologies, while discussing promising strategies that can advance the wound-healing field.

Physicochemical properties of polycaprolactone/collagen/elastin nanofibers fabricated by electrospinning

Collagen and elastin are the two most abundant proteins in the human body, and as biomaterials offer fascinating properties to composite materials. More detailed investigations including these biomaterials within reinforced composites are still needed. This report describes physicochemical properties of fibers composed of collagen type I, collagen III, elastin and polycaprolactone (PCL). Prior to the electrospinning process, PCL was functionalized through covalent attachment of -NH₂ groups by aminolysis reaction with hexamentilendiamine. The fibers were fabricated by electrospinning technique set up with a non-conventional collector. A morphological comparative study was developed at different rations of collagen type I, observing in some cases two populations of fibers. The diameters and morphology were analyzed by SEM, observing a wide array of nanostructures with diameters of ~310 to 693nm. Chemical characterization was assessed by FT-IR spectroscopy and the functionalized PCL was characterized through ninhydrin assay resulting in 0.36mM NH₂/mg fiber. Swelling tests were performed for 24h, obtaining 320% for the majority of the fibers indicating morphological stability and good water uptake. In addition, contact angle analysis demonstrated adequate permeability and differences for each system depending mainly upon the type of biopolymer incorporated and the functionalization of PCL, ranging the values from 108° to 17°. Moreover, differential scanning calorimetry results showed a melting temperature (T_m) of ~60°C. The onset degradation temperatures (T_d,onset) ranged between 115 and 148°C, and were obtained by thermogravimetric analysis. The local mechanical properties of individual fibers were quantified by atomic force acoustic microscopy. These results propose that the physicochemical and mechanical properties of these scaffolds offer the possibility for enhanced biological activity Thus, they have a great potential as candidate scaffolds in tissue engineering applications.

Exendin-4 in combination with adipose-derived stem cells promotes angiogenesis and improves diabetic wound healing

Background

Diminished wound healing is a major complication of diabetes mellitus and can lead to foot ulcers. However, there are limited therapeutic methods to treat this condition. Exendin-4 (Ex-4), a glucagon-like peptide-1 receptor agonist, is known to have many beneficial effects on diabetes. In addition, mesenchymal stem cells are known to have wound healing effects. We investigated the effects of Ex-4 in combination with human adipose tissue-derived stem cells (ADSCs) on diabetic wound healing in a diabetic animal model.

Methods

Diabetic db/db (blood glucose levels, >500 mg/dl) or C57BL/6 mice were subjected to wounding on the skin of the back. One day after wounding, each wound received ADSCs (2.5 × 10⁵ cells) injected intradermally around the wound and/or Ex-4 (50 μl of 100 nM Ex-4) topically applied on the wound with a fine brush daily. Wound size was monitored and wound histology was examined. Human endothelial cells and keratinocyte cells were used to assess angiogenesis and vascular endothelial growth factor expression in vitro.

Results

Topical administration of Ex-4 or injection of ADSCs resulted in a rapid reduction of wound size in both diabetic and normoglycemic animals compared with vehicle treatment. Histological analysis also showed rapid skin reconstruction in Ex-4-treated or ADSC-injected wounds. A combination of Ex-4 and ADSCs showed a significantly better therapeutic effect over either treatment alone. In vitro angiogenesis assays showed that both Ex-4 and ADSC-conditioned media (CM) treatment improved migration, invasion and proliferation of human endothelial cells. ADSC-CM also increased migration and proliferation of human keratinocytes. In addition, both Ex-4 and ADSC-CM increased the expression of vascular endothelial growth factor. Co-culture with ADSCs increased migration and proliferation of these cells similar to that found after ADSC-CM treatment.

Conclusions

We suggest that Ex-4 itself is effective for the treatment of diabetic skin wounds, and a combination of topical treatment of Ex-4 and injection of ADSCs has a better therapeutic effect. Thus, a combination of Ex-4 and ADSCs might be an effective therapeutic option for the treatment of diabetic wounds, such as foot ulcers.

A highly bioactive bone extracellular matrix-biomimetic nanofibrous system with rapid angiogenesis promotes diabetic wound healing

BGN-containing CPB nanofibrous scaffolds with rapid angiogenesis promotes diabetic wound healing.

Cryopreservation of dermal fibroblasts and keratinocytes in hydroxyethyl starch-based cryoprotectants

BACKGROUND

Preservation of human skin fibroblasts and keratinocytes is essential for the creation of skin tissue banks. For successful cryopreservation of cells, selection of an appropriate cryoprotectant agent (CPA) is imperative. The aim of this study was to identify CPAs that minimize toxic effects and allow for the preservation of human fibroblasts and keratinocytes in suspension and in monolayers.

RESULTS

We cryopreserved human fibroblasts and keratinocytes with different CPAs and compared them to fresh, unfrozen cells. Cells were frozen in the presence and absence of hydroxyethyl starch (HES) or dimethyl sulfoxide (DMSO), the latter of which is a commonly used CPA known to exert toxic effects on cells. Cell numbers were counted immediately post-thaw as well as three days after thawing. Cellular structures were analyzed and counted by labeling nuclei, mitochondria, and actin filaments. We found that successful cryopreservation of suspended or adherent keratinocytes can be accomplished with a 10% HES or a 5% HES, 5% DMSO solution. Cell viability of fibroblasts cryopreserved in suspension was maintained with 10% HES or 5% HES, 5% DMSO solutions. Adherent, cryopreserved fibroblasts were successfully maintained with a 5% HES, 5% DMSO solution.

CONCLUSION

We conclude that skin tissue cells can be effectively cryopreserved by substituting all or a portion of DMSO with HES. Given that DMSO is the most commonly used CPA and is believed to be more toxic than HES, these findings are of clinical significance for tissue-based replacement therapies. Therapies that require the use of keratinocyte and fibroblast cells, such as those aimed at treating skin wounds or skin burns, may be optimized by substituting a portion or all of DMSO with HES during cryopreservation protocols.

Experimental wound dressings of degradable PHA for skin defect repair

The present study reports construction of wound dressing materials from degradable natural polymers such as hydroxy derivatives of carboxylic acids (PHAs) and 3-hydroxybutyrate/4-hydroxybutyrate [P(3HB/4HB)] as copolymer. The developed polymer films and electrospun membranes were evaluated for its wound healing properties with Grafts-elastic nonwoven membranes carrying fibroblast cells derived from adipose tissue multipotent mesenchymal stem cells. The efficacy of nonwoven membranes of P(3HB/4HB) carrying the culture of allogenic fibroblasts was assessed against model skin defects in Wistar rats. The morphological, histological and molecular studies revealed the presence of fibroblasts on dressing materials which facilitated wound healing, vascularization and regeneration. Further it was also observed that cells secreted extracellular matrix proteins which formed a layer on the surface of membranes and promoted the migration of epidermal cells from the neighboring tissues surrounding the wound. The wounds under the P(3HB/4HB) membrane carrying cells healed 1.4 times faster than the wounds under the cell-free membrane and 3.5 times faster than the wounds healing under the eschar (control).The complete wound healing process was achieved at Day 14. Thus the study highlights the importance of nonwoven membranes developed from degradable P(3HB/4HB) polymers in reducing inflammation, enhancing angiogenic properties of skin and facilitating better wound healing process.

EGFL7-overexpressing epidermal stem cells promotes fibroblast proliferation and migration via mediating cell adhesion and strengthening cytoskeleton

Epidermal growth factor (EGF)-like family members mediate a wide range of biological activities including cell proliferation and migration. Increasing evidence indicated that EGF plays an important role in the process of wound healing by stimulating fibroblast motility. The aim of this study was to see whether EGF-like domain 7 (EGFL7)-overexpressing epidermal stem cells (EGFL7-ESCs) would promote fibroblast proliferation and migration. We found that mRNA and protein levels of EGFL7 expression were significantly increased in EGFL7-ESCs. The protein expression of EGFL7 was significantly elevated in conditioned media (CM) of EGFL7-ESCs compared to ESCs CM or vector-ESCs CM. The cell count and cell viability of EGFL7-ESCs CM-treated fibroblasts were also significantly increased compared to control. In addition, EGFL7-ESCs CM-treated fibroblasts showed elevated migration compared with control. Moreover, the expressions of β1-integrin, β-tubulin, β-actin, and Vimentin were increased, while that of E-cadherin was decreased in EGFL7-ESCs CM-treated fibroblasts. These results indicate that EGFL7-ESCs contribute towards promoting fibroblast migration through enhancing cell adhesion, strengthening cytoskeleton, and reducing intercellular aggregation. These findings suggest that the stimulating effect of EGFL7-ESCs on fibroblast proliferation and migration may provide a useful strategy for wound healing.

Polymer fiber-based models of connective tissue repair and healing

Physiologically relevant models of wound healing are essential for understanding the biology of connective tissue repair and healing. They can also be used to identify key cellular processes and matrix characteristics critical for the design of soft tissue grafts. Modeling the various stages of repair post tendon injury, polymer meshes of varying fiber diameter (nano-1 (390 nm) < nano-2 (740 nm) < micro (1420 nm)) were produced. Alignment was also introduced in the nano-2 group to model matrix undergoing biological healing rather than scar formation. The response of human tendon fibroblasts on these model substrates were evaluated over time as a function of fiber diameter and alignment. It was observed that the repair models of unaligned nanoscale fibers enhanced cell growth and collagen synthesis, while these outcomes were significantly reduced in the mature repair model consisting of unaligned micron-sized fibers. Organization of paxillin and actin on unaligned meshes was enhanced on micro- compared to nano-sized fibers, while the expression and activity of RhoA and Rac1 were greater on nanofibers. In contrast, aligned nanofibers promoted early cell organization, while reducing excessive cell growth and collagen production in the long term. These results show that the early-stage repair model of unaligned nanoscale fibers elicits a response characteristic of the proliferative phase of wound repair, while the more mature model consisting of unaligned micron-sized fibers is more representative of the remodeling phase by supporting cell organization while suppressing growth and biosynthesis. Interestingly, introduction of fiber alignment in the nanofiber model alters fibroblast response from repair to healing, implicating matrix alignment as a critical design factor for circumventing scar formation and promoting biological healing of soft tissue injuries.

Diversification and enrichment of clinical biomaterials inspired by Darwinian evolution

Regenerative medicine and biomaterials design are driven by biomimicry. There is the essential requirement to emulate human cell, tissue, organ and physiological complexity to ensure long-lasting clinical success. Biomimicry projects for biomaterials innovation can be re-invigorated with evolutionary insights and perspectives, since Darwinian evolution is the original dynamic process for biological organisation and complexity. Many existing human inspired regenerative biomaterials (defined as a nature generated, nature derived and nature mimicking structure, produced within a biological system, which can deputise for, or replace human tissues for which it closely matches) are without important elements of biological complexity such as, hierarchy and autonomous actions. It is possible to engineer these essential elements into clinical biomaterials via bioinspired implementation of concepts, processes and mechanisms played out during Darwinian evolution; mechanisms such as, directed, computational, accelerated evolutions and artificial selection contrived in the laboratory. These dynamos for innovation can be used during biomaterials fabrication, but also to choose optimal designs in the regeneration process. Further evolutionary information can help at the design stage; gleaned from the historical evolution of material adaptations compared across phylogenies to changes in their environment and habitats. Taken together, harnessing evolutionary mechanisms and evolutionary pathways, leading to ideal adaptations, will eventually provide a new class of Darwinian and evolutionary biomaterials. This will provide bioengineers with a more diversified and more efficient innovation tool for biomaterial design, synthesis and function than currently achieved with synthetic materials chemistry programmes and rational based materials design approach, which require reasoned logic. It will also inject further creativity, diversity and richness into the biomedical technologies that we make. All of which are based on biological principles. Such evolution-inspired biomaterials have the potential to generate innovative solutions, which match with existing bioengineering problems, in vital areas of clinical materials translation that include tissue engineering, gene delivery, drug delivery, immunity modulation, and scar-less wound healing.

STATEMENT OF SIGNIFICANCE

Evolution by natural selection is a powerful generator of innovations in molecular, materials and structures. Man has influenced evolution for thousands of years, to create new breeds of farm animals and crop plants, but now molecular and materials can be molded in the same way. Biological molecules and simple structures can be evolved, literally in the laboratory. Furthermore, they are re-designed via lessons learnt from evolutionary history. Through a 3-step process to (1) create variants in material building blocks, (2) screen the variants with beneficial traits/properties and (3) select and support their self-assembly into usable materials, improvements in design and performance can emerge. By introducing biological molecules and small organisms into this process, it is possible to make increasingly diversified, sophisticated and clinically relevant materials for multiple roles in biomedicine.

Generation of an artificial intestine for the management of short bowel syndrome

PURPOSE OF REVIEW

This article discusses the current state of the art in artificial intestine generation in the treatment of short bowel syndrome.

RECENT FINDINGS

Short bowel syndrome defines the condition in which patients lack sufficient intestinal length to allow for adequate absorption of nutrition and fluids, and thus need parenteral support. Advances toward the development of an artificial intestine have improved dramatically since the first attempts in the 1980s, and the last decade has seen significant advances in understanding the intestinal stem cell niche, the growth of complex primary intestinal stem cells in culture, and fabrication of the biomaterials that can support the growth and differentiation of these stem cells. There has also been recent progress in understanding the role of the microbiota and the immune cells on the growth of intestinal cultures on scaffolds in animal models. Despite recent progress, there is much work to be done before the development of a functional artificial intestine for short bowel syndrome is successfully achieved.

SUMMARY

Continued concerted efforts by cell biologists, bioengineers, and clinician-scientists will be required for the development of an artificial intestine as a clinical treatment modality for short bowel syndrome.