Current Status and Future of Skin Substitutes for Chronic Wound Healing

Recent Achievements in the Development of Biomaterials Improved with Platelet Concentrates for Soft and Hard Tissue Engineering Applications

Platelet concentrates such as platelet-rich plasma, platelet-rich fibrin or concentrated growth factors are cost-effective autologous preparations containing various growth factors, including platelet-derived growth factor, transforming growth factor β, insulin-like growth factor 1 and vascular endothelial growth factor. For this reason, they are often used in regenerative medicine to treat wounds, nerve damage as well as cartilage and bone defects. Unfortunately, after administration, these preparations release growth factors very quickly, which lose their activity rapidly. As a consequence, this results in the need to repeat the therapy, which is associated with additional pain and discomfort for the patient. Recent research shows that combining platelet concentrates with biomaterials overcomes this problem because growth factors are released in a more sustainable manner. Moreover, this concept fits into the latest trends in tissue engineering, which include biomaterials, bioactive factors and cells. Therefore, this review presents the latest literature reports on the properties of biomaterials enriched with platelet concentrates for applications in skin, nerve, cartilage and bone tissue engineering.

Dehydrozingerone promotes healing of diabetic foot ulcers: a molecular insight

INTRODUCTION

One of the most common problems of diabetes are diabetic foot ulcers (DFUs). According to National Institute for Health, initial management of DFUs can decrease the complication of limb amputations and can improve the patient's quality of life. DFU treatment can be optimized with the help of multidisciplinary approach. Based on many studies, control of glucose levels in blood, antioxidant activity, reduction in cytokine levels, re-epithelialization, collagen formation, migration of fibroblasts are major phases involved in managing DFU. Dehydrozingerone (DHZ), has been known for its anti-inflammatory, antioxidant and wound healing properties.

METHODOLOGY

Three months high-fat diet and low dose of streptozotocin-induced type-II diabetic foot ulcer model was used to evaluate the effectiveness of dehydrozingerone. DHZ was given orally to rats for 15 days post wounding. TNF-α, IL-1β and antioxidant parameters like lipid peroxidation, glutathione reductase were estimated. Immunoblotting was done to investigate the effect of DHZ on the expression of ERK, JNK, HSP-27, P38, SIRT-1, NFκB, SMA, VEGF and MMP-9 in skin tissue. Histopathology was performed for analyzing DHZ effect on migration of fibroblasts, formation of epithelium, granulation tissue formation, angiogenesis and collagen formation.

RESULTS

DHZ decreased the levels of malondialdehyde, TNF-α, IL-1β and increased glutathione levels in wound tissue. Western blotting results suggested that DHZ activated ERK1/2/JNK/p38 signaling, increased expression of HSP-27, SIRT-1, VEGF, SMA thus facilitating the migration and proliferation of fibroblasts, angiogenesis and decreased inflammation. Masson Trichrome & histopathology showed an increase in collagen, epithelial and granulation tissue formation.

CONCLUSION

DHZ significantly accelerates the healing of diabetic foot ulcers in high fat diet fed plus low dose streptozotocin induced type-II diabetic Wistar rats.

Diabetic wound healing approaches: an update

Diabetic wounds are of profound clinical importance. Despite immense efforts directed towards its management, it results in the development of amputations, following a diagnosis of diabetic foot. With a better understanding of the complexities of the microbalance involved in the healing process, researchers have developed advanced methods for the management of wounds as well as diagnostic tools (especially, for wound infections) to be delivered to clinics sooner. In this review, we address the newer developments that hope to drive the transition from bench to bedside in the coming decade.

Clinical and patient-reported outcomes of tissue engineering strategies for periodontal and peri-implant reconstruction

Scientific advancements in biomaterials, cellular therapies, and growth factors have brought new therapeutic options for periodontal and peri-implant reconstructive procedures. These tissue engineering strategies involve the enrichment of scaffolds with living cells or signaling molecules and aim at mimicking the cascades of wound healing events and the clinical outcomes of conventional autogenous grafts, without the need for donor tissue. Several tissue engineering strategies have been explored over the years for a variety of clinical scenarios, including periodontal regeneration, treatment of gingival recessions/mucogingival conditions, alveolar ridge preservation, bone augmentation procedures, sinus floor elevation, and peri-implant bone regeneration therapies. The goal of this article was to review the tissue engineering strategies that have been performed for periodontal and peri-implant reconstruction and implant site development, and to evaluate their safety, invasiveness, efficacy, and patient-reported outcomes. A detailed systematic search was conducted to identify eligible randomized controlled trials reporting the outcomes of tissue engineering strategies utilized for the aforementioned indications. A total of 128 trials were ultimately included in this review for a detailed qualitative analysis. Commonly performed tissue engineering strategies involved scaffolds enriched with mesenchymal or somatic cells (cell-based tissue engineering strategies), or more often scaffolds loaded with signaling molecules/growth factors (signaling molecule-based tissue engineering strategies). These approaches were found to be safe when utilized for periodontal and peri-implant reconstruction therapies and implant site development. Tissue engineering strategies demonstrated either similar or superior clinical outcomes than conventional approaches for the treatment of infrabony and furcation defects, alveolar ridge preservation, and sinus floor augmentation. Tissue engineering strategies can promote higher root coverage, keratinized tissue width, and gingival thickness gain than scaffolds alone can, and they can often obtain similar mean root coverage compared with autogenous grafts. There is some evidence suggesting that tissue engineering strategies can have a positive effect on patient morbidity, their preference, esthetics, and quality of life when utilized for the treatment of mucogingival deformities. Similarly, tissue engineering strategies can reduce the invasiveness and complications of autogenous graft-based staged bone augmentation. More studies incorporating patient-reported outcomes are needed to understand the cost-benefits of tissue engineering strategies compared with traditional treatments.

The therapeutic and commercial landscape of stem cell vesicles in regenerative dermatology

Extracellular vesicles (EVs) are lipid enveloped nanoparticles that are naturally produced by cells and function in the intercellular transfer of biological material such as proteins, RNAs and metabolites. They have been shown to act in an autocrine and paracrine manner to alter the functions of local and distant recipient cells, with a growing body of evidence highlighting their wide-ranging functions in regenerative processes such as stem cell maintenance, tissue repair and immune modulation. EVs offer several potential advantages over stem cell therapies such as improved safety profiles, scalability, and enhanced storage and quality control of the final product. In fact, many of the pro-regenerative outcomes of stem cell therapies have been attributed to the release of mesenchymal stem cell-derived EVs (MSC-EVs) and their potent effects on extracellular matrix turnover, local cell recruitment, proliferation and angiogenesis is now well described. These positive outcomes have led to clinical trials assessing the safety of MSC-EVs for applications in wound healing and the treatment of cutaneous ulcers, as well as the emergence of multiple commercial MSC-EV sources marketed for topical application in cosmetic medicine. However, regenerative EV therapeutics remain in their infancy and pertinent questions regarding product standardisation, potency and the regulatory landscape surrounding the development of these promising nano-therapeutics must be addressed to ensure safe and effective clinical adoption. In this article we provide an overview of the emerging landscape of MSC-EVs in regenerative dermatology and cosmetic science, highlighting the underlying biological mechanisms pertinent to their application and providing a perspective on current safety considerations, regulation and future directions in the field.

Injectable Crosslinked Genipin Hybrid Gelatin-PVA Hydrogels for Future Use as Bioinks in Expediting Cutaneous Healing Capacity: Physicochemical Characterisation and Cytotoxicity Evaluation

The irregular shape and depth of wounds could be the major hurdles in wound healing for the common three-dimensional foam, sheet, or film treatment design. The injectable hydrogel is a splendid alternate technique to enhance healing efficiency post-implantation via injectable or 3D-bioprinting technologies. The authentic combination of natural and synthetic polymers could potentially enhance the injectability and biocompatibility properties. Thus, the purpose of this study was to characterise a hybrid gelatin−PVA hydrogel crosslinked with genipin (GNP; natural crosslinker). In brief, gelatin (GE) and PVA were prepared in various concentrations (w/v): GE, GPVA3 (3% PVA), and GPVA5 (5% PVA), followed by a 0.1% (w/v) genipin (GNP) crosslink, to achieve polymerisation in three minutes. The physicochemical and biocompatibility properties were further evaluated. GPVA3_GNP and GPVA5_GNP with GNP demonstrated excellent physicochemical properties compared to GE_GNP and non-crosslinked hydrogels. GPVA5_GNP significantly displayed the optimum swelling ratio (621.1 ± 93.18%) and excellent hydrophilicity (38.51 ± 2.58°). In addition, GPVA5_GNP showed an optimum biodegradation rate (0.02 ± 0.005 mg/h) and the highest mechanical strength with the highest compression modulus (2.14 ± 0.06 MPa). In addition, the surface and cross-sectional view for scanning electron microscopy (SEM) displayed that all of the GPVA hydrogels have optimum average pore sizes (100−199 μm) with interconnected pores. There were no substantial changes in chemical analysis, including FTIR, XRD, and EDX, after PVA and GNP intervention. Furthermore, GPVA hydrogels influenced the cell biocompatibility, which successfully indicated >85% of cell viability. In conclusion, gelatin−PVA hydrogels crosslinked with GNP were proven to have excellent physicochemical, mechanical, and biocompatibility properties, as required for potential bioinks for chronic wound healing.

Isolation of Aloe saponaria-Derived Extracellular Vesicles and Investigation of Their Potential for Chronic Wound Healing

A chronic wound is caused by a failure to progress through the normal phases of wound repair in an orderly and timely manner. To induce skin regeneration while inhibiting chronic inflammation, numerous natural products, and in particular, plant-derived biomaterials, have been developed. Aloe saponaria, is known to contain flavonoid and phenolic acid compounds with anti-oxidative and anti-inflammatory properties. Here, we isolated extracellular vesicles (EVs) from Aloe saponaria by polyethylene glycol (PEG)-based precipitation and investigated their potential as a therapeutic for chronic wound healing. The Aloe saponaria-derived EVs (AS-EVs) showed no significant cytotoxicity on several cell types, despite a high level of intracellular uptake. When lipopolysaccharide (LPS)-stimulated RAW264.7 macrophages were treated with AS-EVs, significant reductions in the expression of pro-inflammatory genes, such as interleukin-6 and interleukin-1β, were observed. Proliferation and migration of human dermal fibroblasts, as determined by the water-soluble tetrazolium salt-8 and transwell migration assay, respectively, were shown to be promoted by treatment with AS-EVs. It was also demonstrated that AS-EVs enhanced tube formation in human umbilical vein endothelial cells, indicating a stimulatory activity on angiogenesis; one of the crucial steps for effective wound healing. Collectively, our results suggest the potential of AS-EVs as a natural therapeutic for chronic wound healing.

Therapeutic Effect and Mechanism of Negative Pressure Wound Therapy with Huoxue Shengji Decoction Instillation for Chronic Skin Ulcers

Background

Negative pressure wound therapy (NPWT) with instillation (NPWTi) is a new treatment for chronic skin ulcers (CSUs), but the choice of perfusate is still investigated. The clinical application of Huoxue Shengji (HXSJ) decoction has been proved to promote the formation of granulation. The formation of fresh granulation, angiogenesis, and proliferation of vascular endothelial cells are closely related. The purpose of this study was to observe the clinical efficacy of NWPT with HXSJ decoction instillation in the treatment of CSUs and to explore the potential mechanism by which HXSJ decoction promotes proliferation of vascular endothelial cells at the cellular level.

Methods

In the clinical study, the random number table was used to divide the patients into three groups (patients were numbered by visit time and assigned a random number and grouped by the remainder after the random number was divided by 3, and when the number of patients in one group reached 20, the enrolment of this group is stopped), including NPWT combined with HXSJ decoction instillation (group A), NPWT combined with normal saline instillation (group B), and NPWT (group C). Related indexes were examined, including the wound cavity volume, bacterial culture, histopathology examination, time periods of debridement, repair methods, and the time of ulcer healing. In the basic research, the effect of HXSJ decoction on the proliferation of HUVECs was analysed by CCK-8 assay and RT-PCR and western blot were used to quantify the VEGF and VEGFR-2 expression in the relevant signalling pathway.

Results

There was no significant difference in the improvement rate of invasive cavity volume (P > 0.05) between groups A and B, but a significant difference was observed between groups A and C (P < 0.05). There was no significant difference in microbial reduction among groups (all P > 0.05). Histopathological examination showed that the microvascular count in group A was significantly higher than that in groups B and C (both P < 0.01) and there was no statistical difference between groups B and C (P > 0.05). There were no significant differences in the number of invasive lesions and repair methods among the groups (all P > 0.05). The healing time of group A was significantly faster than those of groups B and C (compared to group B, P < 0.05; compared to group C, P < 0.01), and there was no statistical difference between groups B and C (P > 0.05). In the cellular experiments, concentration screening was performed and 125 μg/mL HXSJ decoction showed the most significant effect on the proliferation of HUVECs and also enhanced the expression of VEGF and VEGFR-2.

Conclusion

HXSJ decoction can enhance the expression of VEGF and VEGFR-2 and promote the proliferation of HUVECs. Treatment with NWPT with HXSJ decoction instillation can further reduce the wound cavity volume; meanwhile, it can promote blood vessel formation in ulcer wounds, thus accelerating the healing of CSUs.

A Prospective Randomized Controlled Multicenter Clinical Trial Comparing Paste-Type Acellular Dermal Matrix to Standard Care for the Treatment of Chronic Wounds

The treatment of chronic wounds remains challenging. Acellular dermal matrix (ADM) has been shown to be effective for various types of wound healing. This study was designed to compare the wound size reduction rate after 12 weeks between patients receiving paste-type ADM and standard wound care. Patients over 19 years old with chronic wounds, deeper than full-thickness skin defects, more than 4 cm² in size that did not heal over the 3 weeks before the study were included. After a screening period of 7 days, patients were randomized to receive either paste-type ADM or standard wound care. The wound status was evaluated at baseline, 1, 2, 4, 8, and 12 weeks. A total of 86 patients were enrolled in this study. The wounds continuously and constantly reduced in size from week 1, and the reduction rate was significantly greater in the study group from week 2 until the end (week 12). In the study group, wound healing was achieved in 29 of 38 wounds (76.3%). Paste-type ADM might be a useful option for wound healing and can be applied safely and efficiently for advanced wound care.

Wound Healing with Electrical Stimulation Technologies: A Review

Electrical stimulation (ES) is an attractive field among clinicians in the topic of wound healing, which is common yet complicated and requires multidisciplinary approaches. The conventional dressing and skin graft showed no promise on complete wound closure. These urge the need for the exploration of electrical stimulation to supplement current wound care management. This review aims to provide an overview of electrical stimulation in wound healing. The mechanism of galvanotaxis related to wound repair will be reviewed at the cellular and molecular levels. Meanwhile, different modalities of externally applied electricity mimicking a physiologic electric field will be discussed and compared in vitro, in vivo, and clinically. With the emerging of tissue engineering and regenerative medicine, the integration of electroconductive biomaterials into modern miniaturised dressing is of interest and has become possible with the advancing understanding of smart biomaterials.

A Beginner's Introduction to Skin Stem Cells and Wound Healing

The primary function of the skin is that of a physical barrier against the environment and diverse pathogens; therefore, its integrity is essential for survival. Skin regeneration depends on multiple stem cell compartments within the epidermis, which, despite their different transcriptional and proliferative capacity, as well as different anatomical location, fall under the general term of skin stem cells (SSCs). Skin wounds can normally heal without problem; however, some diseases or extensive damage may delay or prevent healing. Non-healing wounds represent a serious and life-threatening scenario that may require advanced therapeutic strategies. In this regard, increased focus has been directed at SSCs and their role in wound healing, although emerging therapeutical approaches are considering the use of other stem cells instead, such as mesenchymal stem cells (MSCs). Given its extensive and broad nature, this review supplies newcomers with an introduction to SSCs, wound healing, and therapeutic strategies for skin regeneration, thus familiarizing the reader with the subject in preparation for future in depth reading.

Comparison of Skin Substitutes for Acute and Chronic Wound Management

Chronic and acute wounds, such as diabetic foot ulcers and burns, respectively, can be difficult to treat, especially when autologous skin transplantations are unavailable. Skin substitutes can be used as a treatment alternative by providing the structural elements and growth factors necessary for reepithelialization and revascularization from a nonautologous source. As of 2020, there are 76 commercially available skin substitute products; this article provides a review of the relevant literature related to the major categories of skin substitutes available.

Advances in Skin Tissue Bioengineering and the Challenges of Clinical Translation

Skin tissue bioengineering is an emerging field that brings together interdisciplinary teams to promote successful translation to clinical care. Extensive deep tissue injuries, such as large burns and other major skin loss conditions, are medical indications where bioengineered skin substitutes (that restore both dermal and epidermal tissues) are being studied as alternatives. These may not only reduce mortality but also lessen morbidity to improve quality of life and functional outcome compared with the current standards of care. A common objective of dermal-epidermal therapies is to reduce the time required to accomplish stable closure of wounds with minimal scar in patients with insufficient donor sites for autologous split-thickness skin grafts. However, no commercially-available product has yet fully satisfied this objective. Tissue engineered skin may include cells, biopolymer scaffolds and drugs, and requires regulatory review to demonstrate safety and efficacy. They must be scalable for manufacturing and distribution. The advancement of technology and the introduction of bioreactors and bio-printing for skin tissue engineering may facilitate clinical products' availability. This mini-review elucidates the reasons for the few available commercial skin substitutes. In addition, it provides insights into the challenges faced by surgeons and scientists to develop new therapies and deliver the results of translational research to improve patient care.

Punch Grafting for the Management of Hard-to-Heal Diabetic Foot Ulcers: A Prospective Case Series

Punch grafting is an alternative treatment to enhance wound healing which has been associated with promising clinical outcomes in various leg and foot wound types. We aimed to evaluate the clinical outcomes of punch grafting as a treatment for hard-to-heal diabetic foot ulcers (DFUs). Six patients with chronic neuropathic or neuroischemic DFUs with more than 6 months of evolution not responding to conventional treatment were included in a prospective case series between May 2017 and December 2020. All patients were previously debrided using an ultrasound-assisted wound debridement and then, grafted with 4 to 6 mm punch from the donor site that was in all cases the anterolateral aspect of the thigh. All patients were followed up weekly until wound healing. Four (66.7%) DFUs were located in the heel, 1 (16.7%) in the dorsal aspect of the foot and 1 (16.7%) in the Achilles tendon. The median evolution time was 172 (interquartile range [IQR], 25th-75th; 44-276) weeks with a median area of 5.9 (IQR; 1.87-37.12) cm² before grafting. Complete epithelization was achieved in 3 (50%) patients at 12 weeks follow-up period with a mean time of 5.67 ± 2.88 weeks. Two of the remaining patients achieved wound healing at 32 and 24 weeks, respectively, and 1 patient showed punch graft unsuccessful in adhering. The median time of wound healing of all patients included in the study was 9.00 (IQR; 4.00-28.00) weeks. The wound area reduction (WAR) at 4 weeks was 38.66% and WAR at 12 weeks was 88.56%. No adverse effects related to the ulcer were registered through the follow-up period. Autologous punch graft is an easy procedure that promotes healing, achieving wound closure in chronic DFUs representing an alternative of treatment for hard-to-heal DFUs in which conservative treatment has been unsuccessful.

Mathematical Modeling Can Advance Wound Healing Research

Significance: For over 30 years, there has been sustained interest in the development of mathematical models for investigating the complex mechanisms underlying each stage of the wound healing process. Despite the immense associated challenges, such models have helped usher in a paradigm shift in wound healing research. Recent Advances: In this article, we review contributions in the field that span epidermal, dermal, and corneal wound healing, and treatments of nonhealing wounds. The recent influence of mathematical models on biological experiments is detailed, with a focus on wound healing assays and fibroblast-populated collagen lattices. Critical Issues: We provide an overview of the field of mathematical modeling of wound healing, highlighting key advances made in recent decades, and discuss how such models have contributed to the development of improved treatment strategies and/or an enhanced understanding of the tightly regulated steps that comprise the healing process. Future Directions: We detail some of the open problems in the field that could be addressed through a combination of theoretical and/or experimental approaches. To move the field forward, we need to have a common language between scientists to facilitate cross-collaboration, which we hope this review can support by highlighting progress to date.

Synergistic Effect of Biomaterial and Stem Cell for Skin Tissue Engineering in Cutaneous Wound Healing: A Concise Review

Skin tissue engineering has made remarkable progress in wound healing treatment with the advent of newer fabrication strategies using natural/synthetic polymers and stem cells. Stem cell therapy is used to treat a wide range of injuries and degenerative diseases of the skin. Nevertheless, many related studies demonstrated modest improvement in organ functions due to the low survival rate of transplanted cells at the targeted injured area. Thus, incorporating stem cells into biomaterial offer niches to transplanted stem cells, enhancing their delivery and therapeutic effects. Currently, through the skin tissue engineering approach, many attempts have employed biomaterials as a platform to improve the engraftment of implanted cells and facilitate the function of exogenous cells by mimicking the tissue microenvironment. This review aims to identify the limitations of stem cell therapy in wound healing treatment and potentially highlight how the use of various biomaterials can enhance the therapeutic efficiency of stem cells in tissue regeneration post-implantation. Moreover, the review discusses the combined effects of stem cells and biomaterials in in vitro and in vivo settings followed by identifying the key factors contributing to the treatment outcomes. Apart from stem cells and biomaterials, the role of growth factors and other cellular substitutes used in effective wound healing treatment has been mentioned. In conclusion, the synergistic effect of biomaterials and stem cells provided significant effectiveness in therapeutic outcomes mainly in wound healing improvement.

TGF-β loaded exosome enhances ischemic wound healing in vitro and in vivo

Rationale: With over seven million infections and $25 billion treatment cost, chronic ischemic wounds are one of the most serious complications in the United States. The controlled release of bioactive factor enriched exosome from finbrin gel was a promising strategy to promote wound healing. Methods: To address this unsolved problem, we developed clinical-grade platelets exosome product (PEP), which was incorporate with injectable surgical fibrin sealant (TISSEEL), to promote chronic wound healing and complete skin regeneration. The PEP characterization stimulated cellular activities and in vivo rabbit ischemic wound healing capacity of TISSEEL-PEP were performed and analyzed. Results: PEP, enriched with transforming growth factor beta (TGF-β), possessed exosomal characteristics including exosome size, morphology, and typical markers including CD63, CD9, and ALG-2-interacting protein X (Alix). In vitro, PEP significantly promoted cell proliferation, migration, tube formation, as well as skin organoid formation. Topical treatment of ischemic wounds with TISSEEL-PEP promoted full-thickness healing with the reacquisition of hair follicles and sebaceous glands. Superior to untreated and TISSEEL-only treated controls, TISSEEL-PEP drove cutaneous healing associated with collagen synthesis and restoration of dermal architecture. Furthermore, PEP promoted epithelial and vascular cell activity enhancing angiogenesis to restore blood flow and mature skin function. Transcriptome deconvolution of TISSEEL-PEP versus TISSEEL-only treated wounds prioritized regenerative pathways encompassing neovascularization, matrix remodeling and tissue growth. Conclusion: This room-temperature stable, lyophilized exosome product is thus capable of delivering a bioactive transforming growth factor beta to drive regenerative events.

3D Bioprinting of Functional Skin Substitutes: From Current Achievements to Future Goals

The aim of this review is to present 3D bioprinting of skin substitutes as an efficient approach of managing skin injuries. From a clinical point of view, classic treatments only provide physical protection from the environment, and existing engineered scaffolds, albeit acting as a physical support for cells, fail to overcome needs, such as neovascularisation. In the present work, the basic principles of bioprinting, together with the most popular approaches and choices of biomaterials for 3D-printed skin construct production, are explained, as well as the main advantages over other production methods. Moreover, the development of this technology is described in a chronological manner through examples of relevant experimental work in the last two decades: from the pioneers Lee et al. to the latest advances and different innovative strategies carried out lately to overcome the well-known challenges in tissue engineering of skin. In general, this technology has a huge potential to offer, although a multidisciplinary effort is required to optimise designs, biomaterials and production processes.

Chronic wounds and novel therapeutic approaches

In the past decade, the frequency of chronic wounds in older population has increased, and their impact on quality of life is substantial. Chronic wounds are a public health problem associated with very high economic and psychosocial costs. These wounds result from various pathologies and comorbidities, such arterial and venous insufficiency, diabetes mellitus and continuous skin pressure. Recently, the role of infection and biofilms in the healing of chronic wounds has been the subject of considerable research. This paper presents an overview of various methods and products used to manage chronic wounds and discusses recent advances in wound care. To decide on the best treatment for any wound, it is crucial to holistically assess the patient and the wound. Additionally, multiple strategies could be used to prevent or treat chronic wounds.

From Grafts to Human Bioengineered Vascularized Skin Substitutes

The skin plays an important role in the maintenance of the human's body physiological homeostasis. It acts as a coverage that protects against infective microorganism or biomechanical impacts. Skin is also implied in thermal regulation and fluid balance. However, skin can suffer several damages that impede normal wound-healing responses and lead to chronic wounds. Since the use of autografts, allografts, and xenografts present source limitations and intense rejection associated problems, bioengineered artificial skin substitutes (BASS) have emerged as a promising solution to address these problems. Despite this, currently available skin substitutes have many drawbacks, and an ideal skin substitute has not been developed yet. The advances that have been produced on tissue engineering techniques have enabled improving and developing new arising skin substitutes. The aim of this review is to outline these advances, including commercially available skin substitutes, to finally focus on future tissue engineering perspectives leading to the creation of autologous prevascularized skin equivalents with a hypodermal-like layer to achieve an exemplary skin substitute that fulfills all the biological characteristics of native skin and contributes to wound healing.

Tissue engineering: from the bedside to the bench and back to the bedside

The field of Tissue Engineering and Regenerative Medicine has evolved rapidly over the past thirty years. This review will summarize its history, current status and direction through the lens of clinical need, its progress through science in the laboratory and application back into patients. We can take pride in the fact that much effort and progress began with the surgical problems of children and that many surgeons in the pediatric surgical specialties have become pioneers and investigators in this new field of science, engineering, and medicine. Although the field has yet to fulfill its great promise, there have been several examples where a therapy has progressed from the first idea to human application within a short span of time and, in many cases, it has been applied in the surgical care of children.

Advances in Dermoepidermal Skin Substitutes for Diabetic Foot Ulcers

Diabetic foot ulcers (DFUs) are one of the major complications of diabetes, representing a leading cause of hospitalisation and non-traumatic lower limb amputations. Multidisciplinary management, patient education, glucose control, debridement, off-loading, infection control, and adequate perfusion are the mainstays of standard care. Despite all these, at least 30% of DFUs fail to heal within 20 weeks. Therefore, dermoepidermal skin substitutes (DSS) have been used as a new therapeutic adjunct for DFUs. This brief review outlines the recent advances in DSS for the treatment of DFUs. PubMed and Cochrane databases were systematically searched in May to July 2018 for systematic reviews published after 2013 and for randomised controlled trials (RCTs). A retrospective evaluation of 28 RCTs was performed. Rates of complete wound closure and time to healing were examined for 17 commonly available DSS. Healing rates after 12 weeks and time to complete closure in DFUs are heterogeneous among the 28 RCT. The best healing rates at 12 weeks were accomplished with dermal cellular substitutes (Epifix®, 100% and Amnioband®, 85%) and with dermal acellular substitutes (Allopatch®, 80% and Hyalograft®, 78.8%). Based on these studies, DSS used in conjunction with standard care appear to improve the healing rates of DFUs, as compared with standard care alone. Nonetheless, new studies with more homogeneous samples are needed to ascertain the role of ulcer size, duration, depth and/or type in the efficacy of DSS. Moreover, future RCTs should include patients with severe comorbidities, in order to be more representative of clinical reality.

Bioactive Glasses: A Promising Therapeutic Ion Release Strategy for Enhancing Wound Healing

The morbidity, mortality, and burden of burn victims and patients with severe diabetic wounds are still high, which leads to an extensively growing demand for novel treatments with high clinical efficacy. Biomaterial-based wound treatment approaches have progressed over time from simple cotton wool dressings to advanced skin substitutes containing cells and growth factors; however, no wound care approach is yet completely satisfying. Bioactive glasses are materials with potential in many areas that exhibit unique features in biomedical applications. Today, bioactive glasses are not only amorphous solid structures that can be used as a substitute in hard tissue but also are promising materials for soft tissue regeneration and wound healing applications. Biologically active elements such as Ag, B, Ca, Ce, Co, Cu, Ga, Mg, Se, Sr, and Zn can be incorporated in glass networks; hence, the superiority of these multifunctional materials over current materials results from their ability to release multiple therapeutic ions in the wound environment, which target different stages of the wound healing process. Bioactive glasses and their dissolution products have high potency for inducing angiogenesis and exerting several biological impacts on cell functions, which are involved in wound healing and some other features that are valuable in wound healing applications, namely hemostatic and antibacterial properties. In this review, we focus on skin structure, the dynamic process of wound healing in injured skin, and existing wound care approaches. The basic concepts of bioactive glasses are reviewed to better understand the relationship between glass structure and its properties. We illustrate the active role of bioactive glasses in wound repair and regeneration. Finally, research studies that have used bioactive glasses in wound healing applications are summarized and the future trends in this field are elaborated.

Photodynamic Therapy Delays Cutaneous Wound Healing in Mice

BACKGROUND

Cutaneous wound healing is a complex, dynamic physiological process. Traditional methods of promoting wound healing are not always effective. Consequently, alternative modalities, such as photodynamic therapy (PDT), are needed. We examined the effectiveness and underlying mechanisms of PDT in a murine model of acute wound healing.

METHODS

Two excisional wounds were produced, one on each side of the midline, in C57bL/6J mice. Methyl 5-aminolevulinate hydrochloride (MAL) was applied to the right-side wound. After 1 to 3 hours of incubation, the wound was irradiated with red light. The left-side wound was not treated with MAL or red light. On Day 14, the wounds were excised and subjected to histological and immunohistochemical analysis.

RESULTS

During the first week, no difference was seen between the two sides. However, at week 2, PDT-treated wounds exhibited delayed re-epithelialization. On Day 14, hematoxylin and eosin (HE) staining showed a continuous epithelial lining in untreated wounds. In contrast, PDT-treated wounds partially lacked epithelium in the wound bed. Masson's Trichrome (MTC) staining showed a thicker dermis and more collagen fibers and inflammatory cells in PDT-treated wounds than in untreated wounds. Immunohistochemical analyses showed significantly fewer CD31⁺ blood vessels and greater collagen III density in PDT-treated wounds than in untreated wounds. However, treated and untreated wounds did not differ in collagen I density.

CONCLUSIONS

PDT delayed acute wound healing in a murine model of secondary intention wound healing.

A carrageenan/agarose composite sponge and its immunomodulatory activities toward RAW264.7

A kind of commercial hybrid carrageenan (HC)/agarose composite sponge containing κ-, μ-, ι-, and ν-carrageenan, which could turn into hydrogel and release carrageenan at human body temperature was fabricated for immune stimulation and modulation. Release behavior demonstrated that the hybrid carrageenan contained sponge was mechanically stable and could release carrageenan constantly. RT-PCR and ELISA experiments showed that the leaching liquor of the sponge could stimulate RAW264.7 from M0 state to a polarized state by secreting more anti-inflammatory factor IL-10 than pro-inflammatory ones, such as, IL-6 and TNF-α. Transwell experiments also indicated that the leaching liquor could promote the proliferation of NIH-3T3 by stimulating RAW264.7 of M0 state after 7 days. Results of particle size and intracellular concentration analyses suggested that the released carrageenan might enter into the cellular interior of RAW264.7 in the form of microgels or protein complexes. The sponge would be a promising candidate for skin wound dressing.

Combination product of dermal matrix, human mesenchymal stem cells, and timolol promotes diabetic wound healing in mice

Diabetic foot ulcers are a major health care concern with limited effective therapies. Mesenchymal stem cell (MSC)-based therapies are promising treatment options due to their beneficial effects of immunomodulation, angiogenesis, and other paracrine effects. We investigated whether a bioengineered scaffold device containing hypoxia-preconditioned, allogeneic human MSCs combined with the beta-adrenergic antagonist timolol could improve impaired wound healing in diabetic mice. Different iterations were tested to optimize the primary wound outcome, which was percent of wound epithelialization. MSC preconditioned in 1 μM timolol at 1% oxygen (hypoxia) seeded at a density of 2.5 × 10⁵  cells/cm² on Integra Matrix Wound Scaffold (MSC/T/H/S) applied to wounds and combined with daily topical timolol applications at 2.9 mM resulted in optimal wound epithelialization 65.6% (24.9% ± 13.0% with MSC/T/H/S vs 41.2% ± 20.1%, in control). Systemic absorption of timolol was below the HPLC limit of quantification, suggesting that with the 7-day treatment, accumulative steady-state timolol concentration is minimal. In the early inflammation stage of healing, the MSC/T/H/S treatment increased CCL2 expression, lowered the pro-inflammatory cytokines IL-1B and IL6 levels, decreased neutrophils by 44.8%, and shifted the macrophage ratio of M2/M1 to 1.9 in the wound, demonstrating an anti-inflammatory benefit. Importantly, expression of the endothelial marker CD31 was increased by 2.5-fold with this treatment. Overall, the combination device successfully improved wound healing and reduced the wound inflammatory response in the diabetic mouse model, suggesting that it could be translated to a therapy for patients with diabetic chronic wounds.

Lipid Nanoparticles as a Skin Wound Healing Drug Delivery System: Discoveries and Advances

Chronic wounds are a remarkable cause of morbidity, requiring long-time treatments with a significant impact on the quality of life and high costs for public health. Although there are a variety of topical skin preparations commercially available, they have several limitations that frequently impair wound healing, such as drug instability, toxicity, limited time of action and ineffective skin permeation. In recent years, researchers have focused on the development of new effective treatments for wound healing and shown frequent interest in nanometric drug delivery systems to overcome such obstacles. In dermatology, lipid nanoparticles (LNPs) have received great attention from researchers due to their great functionalities, greater adhesion to the skin and film formation, enabling the hydration and maintenance of skin integrity, as well as present a more effective penetration through the skin barrier. This review provides an update on topical formulations based on Solid Lipid Nanoparticles (SLNs) and Nanostructured Lipid Carriers (NLCs) as wound healing treatments. Both SLNs and NLCs are able to increase solubility and stability of active pharmaceutical ingredients and increase skin penetration compared to the free drugs. Additionally, SLNs and NLCs can increase pharmacological activity, increase the release profile of the drugs, promote synergistic effects and improve the sensory properties of the final formulation. Topical dosage forms containing nanoparticles have been extensively evaluated for wound healing activity, mainly the dressings, films and scaffolds. Therefore, lipid nanoparticles have contributed in improving wound healing therapies when incorporated into other dosage forms with better efficacy and lesser adverse effects than conventional formulations.

Burn injury

Burn injuries are under-appreciated injuries that are associated with substantial morbidity and mortality. Burn injuries, particularly severe burns, are accompanied by an immune and inflammatory response, metabolic changes and distributive shock that can be challenging to manage and can lead to multiple organ failure. Of great importance is that the injury affects not only the physical health, but also the mental health and quality of life of the patient. Accordingly, patients with burn injury cannot be considered recovered when the wounds have healed; instead, burn injury leads to long-term profound alterations that must be addressed to optimize quality of life. Burn care providers are, therefore, faced with a plethora of challenges including acute and critical care management, long-term care and rehabilitation. The aim of this Primer is not only to give an overview and update about burn care, but also to raise awareness of the ongoing challenges and stigmata associated with burn injuries.

Autologous Fat Grafting Promotes Macrophage Infiltration to Increase Secretion of Growth Factors and Revascularization, Thereby Treating Diabetic Rat Skin Defect

BACKGROUND

Diabetic skin defect is difficult to manage in surgical clinics, and there is still lack of effective treatments for diabetic skin defects. Currently, autologous fat grafting (AFG) is promising in the field of reconstructive surgery, while macrophage infiltration in autologous adipose tissue is considered vital for tissue regeneration. But AFG is rarely applied to the treatment of diabetic skin defects, and whether macrophage infiltration assists AFG to promote wound healing is still unknown.

METHODS

Full-thickness skin defect diabetic rats were divided into 3 groups: control group, autologous fat grafting (AFG) group and AFG with macrophage depletion (AFG+MD) group. We examined the amount of macrophages in the wounds bed and the expression level of inflammatory factors IL-10, IL-6, TNF-α, and also growth factors PDGF-β, TGF-β, IGF-1 at the same time. The content of collagen-I and α-smooth muscle actin protein in the wounds were determined by Western blot analysis. Finally, the healing of the wounds was evaluated.

RESULTS

The AFG group showing more rapid healing, secreting more growth factors and more obvious vascularization in the healing process, compared with the control group. But, the secretion of growth factors and the construction of extracellular matrix (ECM) in the wounds were limited when macrophages were depleted after AFG.

CONCLUSION

AFG promotes the infiltration of macrophages to improve the healing environment of diabetic wounds by increasing the secretion of growth factors and revascularization, which provides a potential method for the treatment of diabetic skin defects.

Stromal vascular fraction promotes migration of fibroblasts and angiogenesis through regulation of extracellular matrix in the skin wound healing process

Background

A refractory wound is a typical complication of diabetes and is a common outcome after surgery. Current approaches have difficulty in improving wound healing. Recently, non-expanded stromal vascular fraction (SVF), which is derived from mature fat, has opened up new directions for the treatment of refractory wound healing. The aim of the current study is to systematically investigate the impact of SVF on wound healing, including the rate and characteristics of wound healing, ability of fibroblasts to migrate, and blood transport reconstruction, with a special emphasis on their precise molecular mechanisms.

Methods

SVF was isolated by digestion, followed by filtration and centrifugation, and then validated by immunocytochemistry, a MTS proliferation assay and multilineage potential analysis. A wound model was generated by creating 6-mm-diameter wounds, which include a full skin defect, on the backs of streptozocin-induced hyperglycemic mice. SVF or human adipose-derived stem cell (hADSC) suspensions were subcutaneously injected, and the wounds were characterized over a 9-day period by photography and measurements. A scratch test was used to determine whether changes in the migratory ability of fibroblasts occurred after co-culture with hADSCs. Angiogenesis was observed with human umbilical vein endothelial cells. mRNA from fibroblasts, endotheliocyte, and skin tissue were sequenced by high-throughput RNAseq, and differentially expressed genes, and pathways, potentially regulated by SVF or hADSCs were bioinformatically analyzed.

Results

Our data show that hADSCs have multiple characteristics of MSC. SVF and hADSCs significantly improved wound healing in hyperglycemic mice. hADSCs improve the migratory ability of fibroblasts and capillary structure formation in HUVECs. SVF promotes wound healing by focusing on angiogenesis and matrix remodeling.

Conclusions

Both SVF and hADSCs improve the function of fibroblast and endothelial cells, regulate gene expression, and promote skin healing. Various mechanisms likely are involved, including migration of fibroblasts, tubulogenesis of endothelial cells through regulation of cell adhesion, and cytokine pathways.

Fibronectin precoating wound bed enhances the therapeutic effects of autologous epidermal basal cell suspension for full-thickness wounds by improving epidermal stem cells' utilization

Background

Autologous epidermal basal cell suspension therapy has been proven to be one of the most effective treatments for full-thickness wounds. However, we found there remain obvious defects that significantly confined the utilization and function of the epidermal basal cells (EBCs), especially the epidermal stem cells (ESCs) in it. This study investigated whether precoating fibronectin (FN) on the wound bed before spraying EBCs could overcome these defects and further explored its possible mechanisms.

Methods

In the in vitro study, EBCs were isolated from the donor skin of patients who needed skin grafting. Different concentrations of FN were used to precoat culture dishes before cell culture; the adherent efficiency, proliferation and migration ability of ESCs were analyzed and compared with traditional collagen IV precoating.

In the in vivo study, Sprague–Dawley (SD) rats with full-thickness skin wounds were selected as full-thickness wounds’ model. For the experiment groups, 20 μg/ml FN was precoated on the wound bed 10 min before EBC spray. The quality of wound healing was estimated by the residual wound area rate, wound healing time, and hematoxylin and eosin (H&E) staining. Expression of ESC markers, neovascular markers, inflammation markers, and collagen formation and degradation markers was elucidated by immunohistochemistry (IHC), immunofluorescence (IF), western blot (WB), and RT-qPCR analysis.

Results

The in vitro study showed that the dishes precoated with 20 μg/ml FN had a similar adherent efficiency and colony formation rate with collagen IV, but it could improve the proliferation and migration of ESCs significantly. Similarly, in the in vivo study, precoating FN on wound bed before EBC spray also significantly promote wound healing by improving ESCs’ utilization efficiency, promoting angiogenesis, decreasing inflammations, and regulating collagen formation and degradation.

Conclusion

FN precoating wound bed before EBC spray could significantly promote full-thickness wound healing by improving the utilization and function of the ESCs and further by promoting angiogenesis, decreasing inflammations, and regulating collagen formation and degradation.

Graphical abstract

Biofabrication of thick vascularized neo-pedicle flaps for reconstructive surgery

Wound chronicity due to intrinsic and extrinsic factors perturbs adequate lesion closure and reestablishment of the protective skin barrier. Immediate and proper care of chronic wounds is necessary for a swift recovery and a reduction of patient vulnerability to infection. Advanced therapies supplemented with standard wound care procedures have been clinically implemented to restore aberrant tissue; however, these treatments are ineffective if local vasculature is too compromised to support minimally-invasive strategies. Autologous "flaps", which are tissues equipped with their own hierarchical vascular supply, can be harvested from one region of the patient and transplanted to the wound where it is reperfused upon microsurgical anastomosis to appropriate recipient vessels. Despite the success of autologous flap transfer, these procedures are extremely invasive, incur obligatory donor-site morbidity, and require sufficient donor-tissue availability, microsurgical expertise, and specialized equipment. 3D-bioprinting modalities, such as extrusion-based bioprinting, can be used to address the clinical constraints of autologous flap transfer, primarily addressing donor-site morbidity and tissue availability. This advancement in regenerative medicine allows the biofabrication of heterogeneous tissue structures with high shape fidelity and spatial resolution to generate biomimetic constructs with the anatomically-precise geometries of native tissue to ensure tissue-specific function. Yet, meaningful progress toward this clinical application has been limited by the lack of vascularization required to meet the nutrient and oxygen demands of clinically relevant tissue volumes. Thus, various criteria for the fabrication of functional tissues with hierarchical, patent vasculature must be considered when implementing 3D-bioprinting technologies for deep, chronic wounds.

Peptide-Functionalized Hydrogels Modulate Integrin Expression and Stemness in Adult Human Epidermal Keratinocytes

The extracellular matrix (ECM) controls keratinocyte proliferation, migration, and differentiation through β-integrin signaling. Wound-healing research requires expanding cells in vitro while maintaining replicative capacity; however, early terminal differentiation under traditional culture conditions limits expansion. Here, a design of experiments approach identifies poly(ethylene glycol)-based hydrogel formulations with mechanical properties (elastic modulus, E = 20.9 ± 0.56 kPa) and bioactive peptide sequences that mimic the epidermal ECM. These hydrogels enable systematic investigation of the influence of cell-binding domains from fibronectin (RGDS), laminin (YIGSR), and collagen IV (HepIII) on keratinocyte stemness and β₁ integrin expression. Quantification of 14-day keratin protein expression shows four hydrogels improve stemness compared to standard techniques. Three hydrogels increase β₁ integrin expression, demonstrating a positive linear relationship between stemness and β₁ integrin expression. Multifactorial statistical analysis predicts an optimal peptide combination ([RGDS] = 0.67 mm, [YIGSR] = 0.13 mm, and [HepIII] = 0.02 mm) for maintaining stemness in vitro. Best-performing hydrogels exhibit no decrease in Ki-67-positive cells compared to standards (15% decrease, day 7 to 14; p < 0.05, Tukey Test). These data demonstrate that precisely designed hydrogel biomaterials direct integrin expression and promote proliferation, improving the regenerative capability of cultured keratinocytes for basic science and translational work.

Epidermal stem cells in wound healing and their clinical applications

The skin has important barrier, sensory, and immune functions, contributing to the health and integrity of the organism. Extensive skin injuries that threaten the entire organism require immediate and effective treatment. Wound healing is a natural response, but in severe conditions, such as burns and diabetes, this process is insufficient to achieve effective treatment. Epidermal stem cells (EPSCs) are a multipotent cell type and are committed to the formation and differentiation of the functional epidermis. As the contributions of EPSCs in wound healing and tissue regeneration have been increasingly attracting the attention of researchers, a rising number of therapies based on EPSCs are currently under development. In this paper, we review the characteristics of EPSCs and the mechanisms underlying their functions during wound healing. Applications of EPSCs are also discussed to determine the potential and feasibility of using EPSCs clinically in wound healing.

MicroRNA 155 Downregulation by Vitamin C–Loaded Human Serum Albumin Nanoparticles During Cutaneous Wound Healing in Mice

This study focused on potential of vitamin C loaded human serum albumin (HSA) nanoparticles for treatment of wound. Nanocarrier were prepared and assessed for their effect on growth of 3T3 fibroblast cells, cell migration, wound healing rate and expression of miR-155, TGF-β1 and SMAD 1,2 genes. Wound healing assay was done and wounds were treated with vitamin C loaded HSA nanoparticles. Nanoparticles were prepared with size and zeta potential of 180±6 and -29 mV, respectively. Vitamin C loaded HSA nanoparticles showed controlled release of vitamin C into the buffer solution. Also, yield and encapsulation efficacy of loaded nanoparticles were obtained as 70.6 and 52.1 %, respectively. MTT results showed that the growth of 3T3 fibroblast cells was promoted in culture medium with 20 µg/ml of vitamin C loaded HSA nanoparticles. Cell migration assay indicated the positive effect of loaded nanoparticles on wound healing. The in-vivo results showed that the rate of wound healing was increased after treatment with 20 µg/ml of vitamin C loaded HSA nanoparticles. The wounds were healed faster when treated with vitamin C loaded HSA nanoparticles in comparison with control group. The expression of miR-155 was downregulated after treatment. Furthermore, expression of TGF-β1 and SMAD 1,2 were increased while the wounds were treated with these nanoparticles. In conclusion, these results showed for the first time that wounds were healed after treatment with albumin nanocarrier loaded with vitamin C. This nanocarrier changed expression of miR-155 and TGF-β1 towards faster healing of wounds.

Skin tissue regeneration for burn injury

The skin is the largest organ of the body, which meets the environment most directly. Thus, the skin is vulnerable to various damages, particularly burn injury. Skin wound healing is a serious interaction between cell types, cytokines, mediators, the neurovascular system, and matrix remodeling. Tissue regeneration technology remarkably enhances skin repair via re-epidermalization, epidermal-stromal cell interactions, angiogenesis, and inhabitation of hypertrophic scars and keloids. The success rates of skin healing for burn injuries have significantly increased with the use of various skin substitutes. In this review, we discuss skin replacement with cells, growth factors, scaffolds, or cell-seeded scaffolds for skin tissue reconstruction and also compare the high efficacy and cost-effectiveness of each therapy. We describe the essentials, achievements, and challenges of cell-based therapy in reducing scar formation and improving burn injury treatment.

The discovery and development of topical medicines for wound healing

INTRODUCTION

Chronic, nonhealing skin wounds claim >3% of the health-care budget in industrialized countries, and the incidence is rising. Currently, two parallel trends influence innovations within the field of wound healing: the need to reduce spread of antibiotic resistance and the emerging use of health economy and value-based models. Areas covered: This review focuses on the discovery of drug candidates and development of treatments aiming to enhance wound healing in the heterogeneous group of patients with nonhealing wounds. Expert opinion: Nonhealing wounds are multifaceted and recognized as difficult indications. The majority of products currently in use are medical device dressings, or concepts of negative pressure or hyperbaric oxygen treatment. Global best practice guidelines for the treatment of diabetic foot ulcers recommend debridement, redressing, as well as infection control, and are critical to the lack of coherent clinical evidence for many approved products in active wound care. To accelerate wound healing, there is an emerging trend toward biologics, gene therapy, and novel concepts for drug delivery in research and in the pipeline for clinical trials. Scientific delineation of the therapeutic mechanism of action is, in our opinion, vital for clinical trial success and for an increased fraction of medical products in the pharmaceutical pipeline.

Accelerated Wound Healing by Fibroblasts Differentiated from Human Embryonic Stem Cell-Derived Mesenchymal Stem Cells in a Pressure Ulcer Animal Model

Fibroblasts synthesize and secrete dermal collagen, matrix proteins, growth factors, and cytokines. These characteristics of fibroblasts provide a potential way for fibroblast therapy to treat skin ulcers more effectively than conventional therapies such as cytokine therapy and negative pressure wound therapy. However, the obstacle to the commercialization of fibroblast therapy is the limited supply of cells with consistent quality. In this study, we tested whether human embryonic stem cell-derived mesenchymal stem cells (hESC-MSCs) could be differentiated into fibroblasts considering that they have characteristics of high differentiation rates, unlimited proliferation possibility from a single colony, and homogeneity. As a result, hESC-MSC-derived fibroblasts (hESC-MSC-Fbs) showed a significant increase in the expression of type I and III collagen, fibronectin, and fibroblast-specific protein-1 (FSP-1). Besides, vessel formation and wound healing were enhanced in hESC-MSC-Fb-treated skin tissues compared to PBS- or hESC-MSC-treated skin tissues, along with decreased IL-6 expression at 4 days after the formation of pressure ulcer wound in a mouse model. In view of the limited available cell sources for fibroblast therapy, hESC-MSC-Fbs show a promising potential as a commercial cell therapy source to treat skin ulcers.

Treatment of human chronic wounds with autologous extracellular matrix/stromal vascular fraction gel: A STROBE-compliant study

Stem cell therapy is considered as the most promising treatment for chronic wounds. Extracellular matrix/stromal vascular fraction gel (ECM/SVF gel), an adipose-derived stem cell-based cytotherapy, has shown healing potential in experimental wounds in animal models. However, the effects of ECM/SVF gel on human chronic wounds have not been investigated. The aim of the present study is to investigate the therapeutic effect of ECM/SVF gel on human chronic wounds.Autologous ECM/SVF gel was prepared and used to treat patients with chronic wounds in clinics, with negative pressure wound therapy as the positive control. Wound healing rate per week and histological changes were performed.The average wound healing rate per week in the ECM/SVF gel group was 34.55 ± 11.18% compared with 10.16 ± 2.67% in the negative pressure wound therapy group (P < .001). Histological analysis with hematoxylin and eosin, Masson's trichrome staining, and CD31 immunohistochemistry showed less lymphocyte infiltration, more collagen accumulation, and more newly formed vessels in the ECM/SVF gel group treated skins compared to the control.ECM/SVF gel is an effective therapeutic option for chronic wound healing in clinics.

Self-assembled human osseous cell sheets as living biopapers for the laser-assisted bioprinting of human endothelial cells

A major challenge during the engineering of voluminous bone tissues is to maintain cell viability in the central regions of the construct. In vitro prevascularization of bone substitutes relying on endothelial cell bioprinting has the potential to resolve this issue and to replicate the native bone microvasculature. Laser-assisted bioprinting (LAB) commonly uses biological layers of hydrogel, called 'biopapers', to support patterns of printed cells and constitute the basic units of the construct. The self-assembly approach of tissue engineering allows the production of biomimetic cell-derived bone extracellular matrix including living cells. We hypothesized that self-assembled osseous sheets can serve as living biopapers to support the LAB of human endothelial cells and thus guide tubule-like structure formation. Human umbilical vein endothelial cells were bioprinted on the surface of the biopapers following a predefined pattern of lines. The osseous biopapers showed relevant matrix mineralization and pro-angiogenic hallmarks. Our results revealed that formation of tubule-like structures was favored when the cellular orientation within the biopaper was parallel to the printed lines. Altogether, we validated that human osseous cell sheets can be used as biopapers for LAB, allowing the production of human prevascularized cell-based osseous constructs that can be relevant for autologous bone repair applications.

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.

Functional and Biomimetic Materials for Engineering of the Three-Dimensional Cell Microenvironment

The cell microenvironment has emerged as a key determinant of cell behavior and function in development, physiology, and pathophysiology. The extracellular matrix (ECM) within the cell microenvironment serves not only as a structural foundation for cells but also as a source of three-dimensional (3D) biochemical and biophysical cues that trigger and regulate cell behaviors. Increasing evidence suggests that the 3D character of the microenvironment is required for development of many critical cell responses observed in vivo, fueling a surge in the development of functional and biomimetic materials for engineering the 3D cell microenvironment. Progress in the design of such materials has improved control of cell behaviors in 3D and advanced the fields of tissue regeneration, in vitro tissue models, large-scale cell differentiation, immunotherapy, and gene therapy. However, the field is still in its infancy, and discoveries about the nature of cell-microenvironment interactions continue to overturn much early progress in the field. Key challenges continue to be dissecting the roles of chemistry, structure, mechanics, and electrophysiology in the cell microenvironment, and understanding and harnessing the roles of periodicity and drift in these factors. This review encapsulates where recent advances appear to leave the ever-shifting state of the art, and it highlights areas in which substantial potential and uncertainty remain.

Cultured epidermal stem cells in regenerative medicine

Transplantation of cultured epidermal cell sheets (CES) has long been used to treat patients with burns, chronic wounds, and stable vitiligo. In patients with large area burns this can be a life-saving procedure. The ultimate goal, however, is to restore all normal functions of the skin and prevent scar formation. Increased focus on the incorporation of epidermal stem cells (EpiSCs) within CES transplants may ultimately prove to be key to achieving this. Transplanted EpiSCs contribute to restoring the complete epidermis and provide long-term renewal.Maintenance of the regenerative potential of EpiSCs is anchorage-dependent. The extracellular matrix (ECM) provides physical cues that are interpreted by EpiSCs and reciprocal signaling between cells and ECM are integrated to determine cell fate. Thus, the carrier scaffold chosen for culture and transplant influences maintenance of EpiSC phenotype and may enhance or detract from regenerative healing following transfer.Long-term effectiveness and safety of genetically modified EpiSCs to correct the severe skin blistering disease epidermolysis bullosa has been shown clinically. Furthermore, skin is gaining interest as an easily accessible source of adult epithelial stem cells potentially useful for restoration of other types of epithelia. This review highlights the role of EpiSCs in the current treatment of skin injury and disease, as well as their potential in novel regenerative medicine applications involving other epithelia.

Synergistic effect of human Bone Morphogenic Protein-2 and Mesenchymal Stromal Cells on chronic wounds through hypoxia-inducible factor-1 α induction

Chronic skin ulcers and burns require advanced treatments. Mesenchymal Stromal Cells (MSCs) are effective in treating these pathologies. Bone Morphogenic Protein-2 (BMP-2) is known to enhance angiogenesis. We investigated whether recombinant human hBMP-2 potentiates the effect of MSCs on wound healing. Severe ulceration was induced in rats by irradiation and treated by co-infusion of MSCs with hBMP-2 into the ulcerated area which accelerated wound healing. Potentiation of the effect of MSCs by hBMP-2 on endothelial repair improved skin healing. HBMP-2 and MSCs synergistically, in a supra additive or enhanced manner, renewed tissue structures, resulting in normalization of the epidermis, hair follicles, sebaceous glands, collagen fibre density, and blood vessels. Co-localization of MSCs with CD31 + cells suggests recruitment of endothelial cells at the site of injection. HBMP-2 and MSCs enhanced angiogenesis and induced micro-vessel formation in the dermis where hair follicles were regenerated. HBMP-2 acts by causing hypoxia-inducible factor-1 α (HIF-1α) expression which impacts endothelial tube formation and skin repair. This effect is abolished by siRNA. These results propose that new strategies adding cytokines to MSCs should be evaluated for treating radiation-induced dermatitis, burns, and chronic ulcers in humans.