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There are different types of skin diseases due to chronic injuries that impede the natural healing process of the skin. Tissue engineering has focused on the development of bioengineered skin or skin substitutes that cover the wound, providing the necessary care to restore the functionality of injured skin. There are two types of substitutes: acellular skin substitutes, which offer a low response to the body, and cellular skin substitutes (CSSs), which incorporate living cells and appear as a great alternative in the treatment of skin injuries due to their greater interaction and integration with the rest of the body. For the development of a CSS, it is necessary to select the most suitable biomaterials, cell components, and methodology of biofabrication for the wound to be treated. Moreover, these CSSs are immature substitutes that must undergo a maturing process in specific bioreactors, guaranteeing their functionality. The bioreactor simulates the natural state of maturation of the skin by controlling parameters such as temperature, pressure, or humidity, allowing a homogeneous maturation of the CSSs in an aseptic environment. The use of bioreactors not only contributes to the maturation of the CSSs but also offers a new way of obtaining large sections of skin substitutes or natural skin from small portions acquired from the patient, donor, or substitute. Based on the innovation of this technology and the need to develop efficient CSSs, this work offers an update on bioreactor technology in the field of skin regeneration. Impact Statement The manufacture of functional cellular skin substitutes (CSSs) is one of the current goals in the field of tissue engineering to improve the treatment of chronic skin injuries, thus favoring skin repair and regeneration. The main advances in the development of innovative and effective CSSs are largely focused on the selection of more adequate cellular components, biomaterials, and biofabrication techniques to be used in their biofabrication. However, the maturation of CSSs should be an essential step in obtaining a functional substitute capable of replacing the native skin. The sequential procedure from the design of the CSS to its maturation process will be reviewed. In the context of the manufacturing of novel CSSs, different technologies to biofabricate functional structures and how their maturation can be carried out by specific devices are addressed, as well as key challenges facing the design and development of CSSs.

Diabetic foot ulcers (DFUs) will affect up to one-third of people with diabetes, and not all ulcers heal despite gold standard management. DFUs carry a very high personal and financial cost, but studies of adjunctive wound healing therapies are sparse. Suggested adjuvant topical agents include sucrose octasulfate, placental membrane allografts and autologous patches containing leucocytes, fibrin and platelets. Systemic options are very limited. Promising treatments needing more study include topical oxygen, honey and nitric oxide, growth factors and other bioengineered skin products. Newer technologies may eventually provide more options.

Diabetes is a common disease that potentially interferes with healing processes after lower limb trauma. In our presented case a trimalleolar ankle fracture with undiscovered serious soft-tissue injuries resulted in chronic soft-tissue complications in a diabetic patient, requiring three and a half months of hospitalization in a higher level center and the application of state-of-the-art wound treatment, including vacuum-assisted closure therapy, Integra bioengineered skin substitute, split-thickness skin-grafting, and methods enhancing wound healing, such as polarized light therapy and transdermal CO2 delivery. The presented case emphasizes the importance of soft-tissue care and multidisciplinary approach in diabetic trauma patients with poor compliance.

Diabetic foot ulcers (DFU) are one of the most common diabetes complications and are associated with significant morbidity and mortality. Current DFU standard of care (SOC) involves four principles: (1) pressure relief, (2) debridement, (3) infection management, and (4) revascularization when indicated. Despite the current SOC, many DFU persist, warranting a new approach for the management of these complex wounds. This review aims to summarize the current SOC as well as the latest trends in adjunctive therapies that may become the new SOC in DFU management. These include negative pressure wound therapy and hyperbaric oxygen therapy, bioengineered skin substitutes, growth factors, shockwave therapy, and several others. These novel therapies have shown significant DFU clinical improvement among subsets of DFU patients. However, much of the literature comes from smaller trials with inconsistent patient selection and outcomes measured, making it difficult to assess the true clinical benefit of these treatments. While novel therapies are promising for the interdisciplinary approach to DFU management, many still lack sufficient evidence, and their efficacy remains to be determined.

The use of bioengineered skin has facilitated fundamental and applied research because it enables the investigation of complex interactions between various cell types as well as the extracellular matrix. The predominantly manual fabrication of these living tissues means, however, that their quality, standardization, and production volume are extremely dependent on the technician's experience. Simple laboratory automation could facilitate the use of living tissues by a greater number of research groups. We developed and present here an injection molding technique for the fabrication of bilayered skin equivalents. The tissue was formed automatically by two separate injections into a customized mold to produce the dermal and epidermal skin layers. We demonstrated the biocompatibility of this fabrication process and confirmed the resulting bilayered morphology of the bioengineered skin using histology and immunohistochemistry. Our findings highlight the possibility of fabricating multilayered living tissue by injection molding, suggesting that further investigation into this automation method could result in the rapid and low-cost fabrication of standardized bioengineered skin.

Processed and radiation sterilized allograft tissues that can be banked for use on demand are a precious therapeutic resource for the repair or reconstruction of damaged or injured tissues. Skin dressings or skin substitutes like allograft skin, amniotic membrane and bioengineered skin can be used for the treatment of thermal burns and radiation induced skin injuries. Bone grafts can be employed for repairing fracture defects, filling in destroyed regions of bone, and treatment of spinal and joint injuries. A nuclear scenario would result in a large number of casualties due to the heat, blast and radiation effects of the weapon. Perspective of radiation sterilized biological tissues provided by the tissue banks for management of casualties in a nuclear disaster scenario is presented.

ObjectiveThe gold-standard for the management of patients affected by large-surface third-degree burns is autologous skin graft. There is no way to accurately assess burned area size and predict the number of cells and the time necessary to produce a skin graft.Materials and MethodsWhen burns affect 40% TBSA), the donor site surfaces are insufficient. The alternative grafting strategy uses bioengineered skin substitutes that are generated using the own keratinocytes of the patient after ex vivo expansion. We developed a software for severe burn diagnosis and autologous skin substitute production.ResultsWe developed a software-assisted calculation of the required graft surface and keratinocyte numbers and the time to produce the graft needed, according to patient clinical characteristics. The software also offers assistance to estimate the Baux score, a method that links the severity of burn injuries and the prognosis for the patient.DiscussionOptimal setup of the bioengineering process involved determination of the required graft surface, adjustment of cell quantities, and control of the timing necessary for production. This could be determined and automated by this software. Accordingly, tools to assist the design of personalized protocols will contribute to care quality and cost limitation.ConclusionThis software provides a principle of assisted burned patient diagnose and skin substitute bioengineering process which development may facilitate the design of personalized protocols for skin regenerative cell therapies.

Soft tissue injuries of head and neck are the most common injuries encountered by the maxillofacial surgeons during their clinical practice. Therefore, one must have a sound knowledge of the various types, their mechanisms of injuries and most importantly, the management of the same. This chapter discusses the classification system of all types of soft tissue injuries, and focuses on the principles of management of different types of the injuries, with emphasis on their mechanism and healing process. Numerous figures, box diagrams and case scenarios are added to make the chapter interesting and provide real time information about the topic. A special note on necrotizing fasciitis, one of the most challenging infections in the head and neck region has also been mentioned along with information about wound dressings. Recent advances in the management of soft tissue injuries like use of growth factors, bioengineered skin substitutes and stem cell therapy are enumerated for the readers to encourage them about futuristic approaches. The authors hope that the readership attains a holistic knowledge about various aspects of the soft tissue injuries and their management.

This review aims to be an update of Bioengineered Artificial Skin Substitutes (BASS) applications. At the first moment, they were created as an attempt to replace native skin grafts transplantation. Nowadays, these in vitro models have been increasing and widening their application areas, becoming important tools for research. This study is focus on the ability to design in vitro BASS which have been demonstrated to be appropriate to develop new products in the cosmetic and pharmacology industry. Allowing to go deeper into the skin disease research, and to analyze the effects provoked by environmental stressful agents. The importance of BASS to replace animal experimentation is also highlighted. Furthermore, the BASS validation parameters approved by the OECD (Organisation for Economic Co-operation and Development) are also analyzed. This report presents an overview of the skin models applicable to skin research along with their design methods. Finally, the potential and limitations of the currently available BASS to supply the demands for disease modeling and pharmaceutical screening are discussed.

Autologous skin grafts are used to treat severe burn wounds, however, the availability of adequate donor sites makes this option less practical. Recently, stem cells have been used successfully in tissue engineering and in regenerative medicine. The current study aims to differentiate umbilical cord tissue derived mesenchymal stem cells (CT-MSCs) into skin cells (fibroblasts and keratinocytes) for use to treat severe burn wounds. After isolation, MSCs were characterized and their growth characteristics were determined. The cells were induced to differentiate into fibroblasts and keratinocytes using respective induction medium. Results indicated that CT-MSCs were spindle shaped, plastic adherent and positive for CD29, CD44, CD73, CD90 markers. CT-MSCs also showed high proliferative potential as indicated by cumulative population doubling, doubling time and plating efficiency. The MSCs were successfully differentiated into fibroblast and keratinocytes as indicated by morphological changes and expression of lineage specific genes. We propose that these differentiated skin cells which are derived from CT-MSCs can thus be used for the development of bioengineered skin; however, further studies are required to evaluate the utility of these substitutes.

Chronic venous leg ulcers are responsible for significant morbidity and health care costs worldwide. This pilot study evaluated the effectiveness 2 biologically active grafts, TheraSkin and Apligraf, in conjunction with compression therapy. The study, not industry-sponsored, was designed and conducted as a prospective, head-to-head, single-site, randomized clinical trial to assess differences in healing rates, adverse outcomes, and treatment costs. The healing rates were different but not statistically significant, there were no adverse outcomes, and TheraSkin averaged $2495.33 and Apligraf averaged $4316.67 per subject. This suggests that TheraSkin may provide equivalent or superior outcomes to Apligraf while reducing costs.

Background: Dermal substitutes are currently largely used for the treatment of huge skin loss in patients in critical general health conditions, for the treatment of severe burns and to promote the healing process in chronic wounds. Aims: The authors performed a retrospective assessment of their experience with bioengineered skin to possibly identify the most appropriate clinical indication and management for each substitute. Materials and Methods: The study involved 109 patients with 127 skin defects repaired with dermal substitutes over a 9 years period, from 2007 to 2016. Hyalomatrix® was used in 63 defects, whereas Integra® and Nevelia® were used in 56 and 8 defects, respectively. Results: The statistical analysis failed to reveal a correlation between the choice of a specific dermal substitute and any possible clinical variable except in the soft-tissue defects of the scalp where Hyalomatrix® was electively used. Conclusions: In the authors’ experience, the scalp defects followed a radical excision of skin tumours that included the periosteum. Here, the preliminary cover with a hyaluronan three-dimensional scaffold constantly allowed for the regeneration of a derma-like layer with a rich vascular network fit for supporting a split-thickness skin graft. Nevertheless, the authors still prefer Integra® when the goal is a better cosmetic outcome and Hyalomatrix® when a faster wound healing is required, especially in the management of deep wounds where the priority is a fast obliteration with a newly formed tissue with a rich blood supply. However, these clinical indications still are anecdotally based.

Wound healing is a complex restorative process of the altered cutaneous tissue, which is impaired by numerous local and systemic factors, leading to chronic non-healing lesions with few efficient therapeutic options. Stem cells possess the capacity to differentiate into various types of cell lines. Furthermore, stem cells are able to secrete cytokines and growth factors, modulating inflammation and ultimately leading to angiogenesis, fibrogenesis, and epithelization. Because of their paracrine activity, these cells are able to attract other cell types to the base of the wound, improving the formation of new skin layers. Mesenchymal stem cells derived from the adipose tissue, bone marrow, and placenta, offer numerous ways of implementation. The process of harvesting, growing, and administrating stem cells depends on the site and type of the cells, but recent trial results showed improvement of wound healing independent of the administration site. Bioengineered skin substitutes are validated for treatment of chronic wounds with direct application on the skin surface. These offer physical scaffolding for the migrating cells and promote secretion of growth factors, thus facilitating rapid wound healing. Obtaining further clinical data is essential, but stem cell therapy may become a first-line therapeutic choice for the treatment of non-healing chronic wounds.

Due to the poor regenerative capacity of adult mammalian skin, there is a need to develop effective skin substitutes for promoting skin regeneration after a severe wound. However, the complexity of skin biology has made it difficult to enable perfect regeneration of skin. Thus, animal models are being used to test potential skin substitutes. Murine models are valuable but their healing process involves dermal contraction. We have developed a device called a dome that is able to eliminate the contraction effect of rodent skin while simultaneously housing a bioengineered skin graft. The dome comes in two models, which enables researchers to evaluate the cells that contribute in wound healing from neighboring intact tissue during skin healing/regeneration. This protocol simplifies grafting of skin substitutes, eliminates the contraction effect of surrounding skin, and summarizes a simple method for animal surgery for wound healing and skin regeneration studies.

Significance: Recent generation of bioengineered human skin allowed the efficient treatment of patients with severe skin defects. However, the optical and biomechanical properties of these models are not known. Aim: Three models of bioengineered human skin based on fibrin-agarose biomaterials (acellular, dermal skin substitutes, and complete dermoepidermal skin substitutes) were generated and analyzed. Approach: Optical and biomechanical properties of these artificial human skin substitutes were investigated using the inverse adding-doubling method and tensile tests, respectively. Results: The analysis of the optical properties revealed that the model that most resembled the optical behavior of the native human skin in terms of absorption and scattering properties was the dermoepidermal human skin substitutes after 7 to 14 days in culture. The time-course evaluation of the biomechanical parameters showed that the dermoepidermal substitutes displayed significant higher values than acellular and dermal skin substitutes for all parameters analyzed and did not differ from the control skin for traction deformation, stress, and strain at fracture break. Conclusions: We demonstrate the crucial role of the cells from a physical point of view, confirming that a bioengineered dermoepidermal human skin substitute based on fibrin-agarose biomaterials is able to fulfill the minimal requirements for skin transplants for future clinical use at early stages of in vitro development., Ministry of Science, Innovation and Universities of Spain PGC2018-101904-A-I0, Instituto de Salud Carlos III (ISCIII), Ministry of Science, Innovation and Universities, through AES 2017 AC17/00013, Instituto de Salud Carlos III (ISCIII), Ministry of Science, Innovation and Universities within EuroNanoMed framework, EU AC17/00013, University of Granada A.TEP.280.UGR18, Junta de Andalucía PE-0395-2019, Fundación Benéfica Anticancer San Francisco Javier y Santa Cándida, Granada, Spain, OTRI.35A-07

The skin is a “smart”, multifunctional organ that is protective, self-healing and capable of sensing and many forms of artificial skins have been developed with properties and functionalities approximating those of natural skin. Starting from specific commercial products for the treatment of burns, progress in two fields of research has since allowed these remarkable materials to be viable skin replacements for a wide range of dermatological conditions. This review maps out the development of bioengineered skin replacements and synthetic skin substitutes, including electronic skins. The specific behaviors of these skins are highlighted, and the performances of both types of artificial skins are evaluated against this. Moving beyond mere replication, highly advanced artificial skin materials are also identified as potential augmented skins that can be used as flexible electronics for health-care monitoring and other applications.

Human autologous bioengineered skin has been successfully developed and used to treat skin injuries in a growing number of cases. In current clinical studies, the biomaterial used is fabricated via plastic compression of collagen hydrogel to increase the density and stability of the tissue. To further facilitate clinical adoption of bioengineered skin, the fabrication technique needs to be improved in terms of standardization and automation. Here, we present a one-step mixing technique using highly concentrated collagen and human fibroblasts to simplify fabrication of stable dermal equivalents. As controls, we prepared cellularized dermal equivalents with three varying collagen compositions. We found that the dermal equivalents produced using the simplified mixing technique were stable and pliable, showed viable fibroblast distribution throughout the tissue, and were comparable to highly concentrated manually produced collagen gels. Because no subsequent plastic compression of collagen is required in the simplified mixing technique, the fabrication steps and production time for dermal equivalents are consistently reduced. The present study provides a basis for further investigations to optimize the technique, which has significant promise in enabling efficient clinical production of bioengineered skin in the future.

Clinical use of bioengineered skin in reconstructive surgery has been established for more than 30 years. The limitations and ethical considerations regarding the use of animal models have expanded the application of bioengineered skin in the areas of disease modeling and drug screening. These skin models should represent the anatomical and physiological traits of native skin for the efficient replication of normal and pathological skin conditions. In addition, reliability of such models is essential for the conduction of faithful, rapid, and large-scale studies. Therefore, research efforts are focused on automated fabrication methods to replace the traditional manual approaches. This report presents an overview of the skin models applicable to skin disease modeling along with their fabrication methods, and discusses the potential of the currently available options to conform and satisfy the demands for disease modeling and drug screening., International Journal of Molecular Sciences, 20 (6), ISSN:1422-0067

Producción Científica, Dermo-epidermal equivalents based on plasma-derived fibrin hydrogels have been ex tensively studied for skin engineering. However, they showed rapid degradation and contraction over time and low mechanical properties which limit their reproducibility and lifespan. In order to achieve better mechanical properties, elasticity and biological properties, we incorporated a elastin-like recombinamer (ELR) network, based on two types of ELR, one modified with azide (SKS-N3 ) and other with cyclooctyne (SKS-Cyclo) chemical groups at molar ratio 1:1 at three different SKS (serine-lysine-serine sequence) concentrations (1, 3, and 5 wt.%), into plasma-derived fibrin hydrogels. Our results showed a decrease in gelation time and contraction, both in the absence and presence of the encapsulated human primary fibroblasts (hFBs), higher mechanical properties and increase in elasticity when SKSs content is equal or higher than 3%. However, hFBs proliferation showed an improvement when the lowest SKS content (1 wt.%) was used but started decreasing when increasing SKS concentration at day 14 with respect to the plasma control. Proliferation of human primary keratinocytes (hKCs) seeded on top of the hybrid-plasma hydrogels containing 1 and 3% of SKS showed no differences to plasma control and an increase in hKCs proliferation was observed for hybrid-plasma hydrogels containing 5 wt.% of SKS. These promising results showed the need to achieve a balance between the reduced contraction, the better mechanical properties and biological properties and indicate the potential of using this type of hydrogel as a testing platform for pharmaceutical products and cosmetics, and future work will elucidate their potential., Gobierno Español, (Grant/Award Numbers: FPU15-00448, PID2019-110709RB-100, RED2018-102417-T), Junta de Castilla y León (VA317P18, Infrared2018-UVA06), Interreg. V España-Portugal POCTEP (0624_2IQBIONEURO_6_E), Programa de Actividades de I + D entre Grupos de Investigación de la Comunidad de Madrid (S2018/BAA-4480), Programa Estatal de I + D + i Orientada a los Retos de la So-ciedad (RTI2018-101627-B-I00)

Skin is a very complex organ and hence designing a bioengineered skin model replicating the essential physiological characteristics for replacing the diseased or damaged parts has been a challenging goal for many. Newer technologies for satisfying most of the criteria are being attempted with the copious efforts of biologists, engineers, physiologists, using multitude of features in combination. Amongst them nanotechnology based biomaterials have gained prominence owing to the enhanced pharmacokinetics, bio-distribution profile, extended half-life and reduced side effects. Designing a matrix that can be assimilated into the body during the regeneration and delivering the essential pharmacological agents in a temporal and spatially specific manner is a tremendous goal. This review essentially deals with the various approaches for designing a multidisciplinary translational smart matrix for addressing the various skin related ailments.

Total parenteral nutrition (TPN) can be a lifesaving intervention for premature neonates and it is often delivered through peripheral access in this unique population. However, extravasation and tissue damage can result. Current literature lacks strong evidence regarding the treatment and reconstruction of such injuries in this age group. The authors present a patient with a 30-week gestational age premature newborn whom suffered an extravasation injury with peripherally administered TPN leading to full thickness skin and soft tissue necrosis of the dorsum of the right hand. This was serially debrided and ultimately repaired using Apligraf (Graftskin, Living Skin Equivalent, LSE; Organogenesis Inc, Canton, MA), which rapidly facilitated secondary healing.

This chapter (Bioscience engineering of cell, tissue, and organs) reviews the development of artificially produced cells, tissues, and organs. The cells, tissues, and organs are developed considering the preservation of three-dimensional protein structure. The artificial synthesis of yeast cells promoted by synthetic chromosomes are presented in this chapter. Synthetic bacteria processing the minimum number of synthetic chromosomes is described. The production of artificial livers, lungs, insulin delivery systems, bioengineered skin, antigen-presenting cells, lymph nodes, thymus, spleen, and salivary glands are described in this chapter.

Clinical use of bioengineered skin in reconstructive surgery has been established for more than 30 years. The limitations and ethical considerations regarding the use of animal models have expanded the application of bioengineered skin in the areas of disease modeling and drug screening. These skin models should represent the anatomical and physiological traits of native skin for the efficient replication of normal and pathological skin conditions. In addition, reliability of such models is essential for the conduction of faithful, rapid, and large-scale studies. Therefore, research efforts are focused on automated fabrication methods to replace the traditional manual approaches. This report presents an overview of the skin models applicable to skin disease modeling along with their fabrication methods, and discusses the potential of the currently available options to conform and satisfy the demands for disease modeling and drug screening.

Clinical use of bioengineered skin in reconstructive surgery has been established for more than 30 years. The limitations and ethical considerations regarding the use of animal models have expanded the application of bioengineered skin in the areas of disease modeling and drug screening. These skin models should represent the anatomical and physiological traits of native skin for the efficient replication of normal and pathological skin conditions. In addition, reliability of such models is essential for the conduction of faithful, rapid, and large-scale studies. Therefore, research efforts are focused on automated fabrication methods to replace the traditional manual approaches. This report presents an overview of the skin models applicable to skin disease modeling along with their fabrication methods, and discusses the potential of the currently available options to conform and satisfy the demands for disease modeling and drug screening.

35.2 million annual cases in the U.S. require clinical intervention for major skin loss. To meet this demand, the field of skin tissue engineering has grown rapidly over the past 40 years. Traditionally, skin tissue engineering relies on the "cell-scaffold-signal" approach, whereby isolated cells are formulated into a three-dimensional substrate matrix, or scaffold, and exposed to the proper molecular, physical, and/or electrical signals to encourage growth and differentiation. However, clinically available bioengineered skin equivalents (BSEs) suffer from a number of drawbacks, including time required to generate autologous BSEs, poor allogeneic BSE survival, and physical limitations such as mass transfer issues. Additionally, different types of skin wounds require different BSE designs. MicroRNA has recently emerged as a new and exciting field of RNA interference that can overcome the barriers of BSE design. MicroRNA can regulate cellular behavior, change the bioactive milieu of the skin, and be delivered to skin tissue in a number of ways. While it is still in its infancy, the use of microRNAs in skin tissue engineering offers the opportunity to both enhance and expand a field for which there is still a vast unmet clinical need. Here we give a review of skin tissue engineering, focusing on the important cellular processes, bioactive mediators, and scaffolds. We further discuss potential microRNA targets for each individual component, and we conclude with possible future applications.