Prospective study on the treatment of lower-extremity chronic venous and mixed ulcers using tissue-engineered skin substitute made by the self-assembly approach

The economic burden of burned patients for hospitalization in Canada

BACKGROUND

Burn injuries pose a significant burden on both patients and healthcare systems. Yet, costs arising from the consumption of resources by these patients are rarely examined in Canada.

OBJECTIVE

The objective of this study was to assess real-world costs resulting from the initial hospitalization of patients admitted to a major burn unit in Quebec, Canada.

METHODS

A cost study based on a retrospective cohort was undertaken using in-hospital economic data matched to hospital chart data. Our cohort included all burn-injured patients admitted between April 1, 2017, and March 31, 2021, to the hospital's major burn unit during their initial hospitalization. Descriptive statistics were tabulated for sociodemographic and economic data. Costing data were analyzed unstratified and stratified according to burn severity (i.e., ≥ 20% of total body surface area [TBSA] vs. < 20%). Costs were presented in CAD 2021.

RESULTS

Our cohort included 362 patients, including 65 (18%) with TBSA ≥ 20%. The average initial hospitalization cost was $32,360 ($22,783 for < 20% TBSA and $76,121 for ≥ 20% TBSA).

CONCLUSION

Findings reveal that the total cost of the initial hospitalization, from a public hospital perspective, was $11,714,348. Our study underlines the substantial burden associated with burns and highlights the need for long-term cost evaluations.

Skin-on-a-chip technologies towards clinical translation and commercialization

Skin is the largest organ of the human body which plays a critical role in thermoregulation, metabolism (e.g. synthesis of vitamin D), and protection of other organs from environmental threats, such as infections, microorganisms, ultraviolet radiation, and physical damage. Even though skin diseases are considered to be less fatal, the ubiquity of skin diseases and irritation caused by them highlights the importance of skin studies. Furthermore, skin is a promising means for transdermal drug delivery, which requires a thorough understanding of human skin structure. Current animal andin vitrotwo/three-dimensional skin models provide a platform for disease studies and drug testing, whereas they face challenges in the complete recapitulation of the dynamic and complex structure of actual skin tissue. One of the most effective methods for testing pharmaceuticals and modeling skin diseases are skin-on-a-chip (SoC) platforms. SoC technologies provide a non-invasive approach for examining 3D skin layers and artificially creating disease models in order to develop diagnostic or therapeutic methods. In addition, SoC models enable dynamic perfusion of culture medium with nutrients and facilitate the continuous removal of cellular waste to further mimic thein vivocondition. Here, the article reviews the most recent advances in the design and applications of SoC platforms for disease modeling as well as the analysis of drugs and cosmetics. By examining the contributions of different patents to the physiological relevance of skin models, the review underscores the significant shift towards more ethical and efficient alternatives to animal testing. Furthermore, it explores the market dynamics ofin vitroskin models and organ-on-a-chip platforms, discussing the impact of legislative changes and market demand on the development and adoption of these advanced research tools. This article also identifies the existing obstacles that hinder the advancement of SoC platforms, proposing directions for future improvements, particularly focusing on the journey towards clinical adoption.

Biomaterials used for tissue engineering of barrier-forming cell monolayers in the eye

Cell monolayers that form a barrier between two structures play an important role for the maintenance of tissue functionality. In the anterior portion of the eye, the corneal endothelium forms a barrier that controls fluid exchange between the aqueous humor of the anterior chamber and the corneal stroma. This monolayer is central in the pathogenesis of Fuchs endothelial corneal dystrophy (FECD). FECD is a common corneal disease, in which corneal endothelial cells deposit extracellular matrix that increases the thickness of its basal membrane (Descemet's membrane), and forms excrescences (guttae). With time, there is a decrease in endothelial cell density that generates vision loss. Transplantation of a monolayer of healthy corneal endothelial cells on a Descemet membrane substitute could become an interesting alternative for the treatment of this pathology. In the back of the eye, the retinal pigment epithelium (RPE) forms the blood-retinal barrier, controlling fluid exchange between the choriocapillaris and the photoreceptors of the outer retina. In the retinal disease dry age-related macular degeneration (dry AMD), deposits (drusen) form between the RPE and its basal membrane (Bruch's membrane). These deposits hinder fluid exchange, resulting in progressive RPE cell death, which in turn generates photoreceptor cell death, and vision loss. Transplantation of a RPE monolayer on a Bruch's membrane/choroidal stromal substitute to replace the RPE before photoreceptor cell death could become a treatment alternative for this eye disease. This review will present the different biomaterials that are proposed for the engineering of a monolayer of corneal endothelium for the treatment of FECD, and a RPE monolayer for the treatment of dry AMD.

A Novel Wound Therapy Modality: Autologous Wound Edge Dotted Full-Thickness Skin Grafting Improving Diabetic Foot Ulcer Healing

Aim

To explore the therapeutic efficacy of autologous wound edge-dotted full-thickness skin grafting in improving diabetic foot ulcer healing.

Methods

Sixty-three patients were divided into three groups: conventional wound therapy (CWT) (n = 23), platelet-rich plasma (PRP) (n = 20), and graft (n = 20). All participants were followed up for 12 weeks. The therapeutic efficacy of the three different wound treatment modalities was analyzed.

Results

After follow-up, 37 (58.7%) patients showed complete wound re-epithelialization, of which 10 (43.5%) occurred in the CWT group, 14 (70.0%) in the PRP group, and 13 (65.0%) in the graft group. Multivariate Cox analysis showed that the independent predictive factors for ulcer healing were different treatment modalities (graft: HR = 3.214, 95% CI=1.300-7.945, P < 0.05; platelet-rich plasma: HR = 3.075, 95% CI=1.320-7.161, P < 0.01), ABI (HR = 9.917, 95% CI=2.675-36.760, P < 0.01), and TcPO2 (HR = 1.040; 95% CI=1.005-1.076; P < 0.05). Stratified analysis showed that higher ABI in graft group or PRP group had higher wound healing rate (graft group: HR = 3.748, 95% CI=1.210-11.607, P < 0.05; PRP group: HR = 5.029, 95% CI=1.743-14.509, P < 0.05); higher TcPO2 in the graft group had higher wound healing rate (HR = 15.805, 95% CI=4.414-56.594, P < 0.01). Additionally, the wound healing time (P < 0.0167) and cumulative healing rate (P < 0.05) in both the PRP group and graft group were more advantageous. The graft group promotes wound re-epithelialization earlier and faster than in the CWT group and PRP group (P < 0.05). Meanwhile, the graft group had lower medical costs (P < 0.0167).

Conclusion

Autologous wound edge dotted full-thickness skin grafting has a higher cost-performance ratio than traditional diabetic foot ulcer wound care and is worthy of further clinical application.

In vivo efficacy proof of concept of a large-size bioprinted dermo-epidermal substitute for permanent wound coverage

Introduction: An autologous split-thickness skin graft (STSG) is a standard treatment for coverage of full-thickness skin defects. However, this technique has two major drawbacks: the use of general anesthesia for skin harvesting and scar sequelae on the donor site. In order to reduce morbidity associated with STSG harvesting, researchers have developed autologous dermo-epidermal substitutes (DESs) using cell culture, tissue engineering, and, more recently, bioprinting approaches. This study assessed the manufacturing reliability and in vivo efficacy of a large-size good manufacturing practice (GMP)-compatible bio-printed human DES, named Poieskin®, for acute wound healing treatment. Methods: Two batches (40 cm2 each) of Poieskin® were produced, and their reliability and homogeneity were assessed using histological scoring. Immunosuppressed mice received either samples of Poieskin® (n = 8) or human STSG (n = 8) immediately after longitudinal acute full-thickness excision of size 1 × 1.5 cm, applied on the skeletal muscle plane. The engraftment rate was assessed through standardized photographs on day 16 of the follow-up. Moreover, wound contraction, superficial vascularization, and local inflammation were evaluated via standardized photographs, laser Doppler imaging, and PET imaging, respectively. Histological analysis was finally performed after euthanasia. Results: Histological scoring reached 75% ± 8% and 73% ± 12%, respectively, displaying a robust and homogeneous construct. Engraftment was comparable for both groups: 91.8% (SD = 0.1152) for the Poieskin® group versus 100% (SD = 0) for the human STSG group. We did not record differences in either graft perfusion, PET imaging, or histological scoring on day 16. Conclusion: Poieskin® presents consistent bioengineering manufacturing characteristics to treat full-thickness cutaneous defects as an alternative to STSG in clinical applications. Manufacturing of Poieskin® is reliable and homogeneous, leading to a clinically satisfying rate of graft take compared to the reference human STSG in a mouse model. These results encourage the use of Poieskin® in phase I clinical trials as its manufacturing procedure is compatible with pharmaceutical guidelines.

The Self-Assembled Skin Substitute History: Successes, Challenges, and Current Treatment Indications

The self-assembled skin substitute (SASS) is an autologous bilayered skin substitute designed by our academic laboratory, the Laboratoire d'Organogenèse Expérimentale (LOEX) to offer definitive treatment for patients lacking donor sites (unwounded skin) to cover their burn wounds. This product shows skin-like attributes, such as an autologous dermal and epidermal layer, and is easily manipulable by the surgeon. Its development stems from the need for skin replacement in high total body surface area burned survivors presenting few donor sites for standard split-thickness skin grafting. This review aims to present the history, successes, challenges, and current therapeutic indications of this skin substitute. We review the product's development history, before discussing current production techniques, as well as clinical use. The progression observed since the initial SASS production technique described in 1999, up to the most recent technique expresses significant advances made in the technical aspect of our product, such as the reduction of the production time. We then explore the efficacy and benefits of SASS over existing skin substitutes and discuss the outcomes of a recent study focusing on the successful treatment of 14 patients. Moreover, an ongoing cross-Canada study is further assessing the product's safety and efficacy. The limitations and technical challenges of SASS are also discussed.

Skin Tissue Engineering Advances in Burns: A Brief Introduction to the Past, the Present, and the Future Potential

Burn injuries are a severe form of skin damage with a significant risk of scarring and systemic sequelae. Approximately 11 million individuals worldwide suffer burn injuries annually, with 180,000 people dying due to their injuries. Wound healing is considered the main determinant for the survival of severe burns and remains a challenge. The surgical treatment of burn wounds entails debridement of necrotic tissue, and the wound is covered with autologous skin substitutes taken from healthy donor areas. Autologous skin transplantation is still considered to be the gold standard for wound repair. However, autologous skin grafts are not always possible, especially in cases with extensive burns and limited donor sites. Allografts from human cadaver skin and xenografts from pig skin may be used in these situations to cover the wounds temporarily. Alternatively, dermal analogs are used until permanent coverage with autologous skin grafts or artificial skins can be achieved, requiring staged procedures to prolong the healing times with the associated risks of local and systemic infection. Over the last few decades, the wound healing process through tissue-engineered skin substitutes has significantly enhanced as the advances in intensive care ensuring early survival have led to the need to repair large skin defects. The focus has shifted from survival to the quality of survival, necessitating accelerated wound repair. This special volume of JBCR is dedicated to the discoveries, developments, and applications leading the reader into the past, present, and future perspectives of skin tissue engineering in burn injuries.

Considerations for the clinical use of stem cells in genitourinary regenerative medicine

The genitourinary tract can be affected by several pathologies which require repair or replacement to recover biological functions. Current therapeutic strategies are challenged by a growing shortage of adequate tissues. Therefore, new options must be considered for the treatment of patients, with the use of stem cells (SCs) being attractive. Two different strategies can be derived from stem cell use: Cell therapy and tissue therapy, mainly through tissue engineering. The recent advances using these approaches are described in this review, with a focus on stromal/mesenchymal cells found in adipose tissue. Indeed, the accessibility, high yield at harvest as well as anti-fibrotic, immunomodulatory and proangiogenic properties make adipose-derived stromal/SCs promising alternatives to the therapies currently offered to patients. Finally, an innovative technique allowing tissue reconstruction without exogenous material, the self-assembly approach, will be presented. Despite advances, more studies are needed to translate such approaches from the bench to clinics in urology. For the 21^st century, cell and tissue therapies based on SCs are certainly the future of genitourinary regenerative medicine.

A review of diabetic wound models-Novel insights into diabetic foot ulcer

Diabetic foot ulcer (DFU) is a major debilitating complication of diabetes. Many research investigations have been conducted with the aims to uncover the diabetic wound healing mechanisms, develop novel therapeutics, and screen bioactive wound dressings in order to improve the current management of DFU. These would have not been possible without the utilization of an appropriate wound model, especially in a diabetic wound context. This review focuses on the different in vitro research models used in DFU investigations such as the 2D scratch wound assay, 3D skin model, and 3D angiogenesis model as well as their limitations. The current efforts and challenges to apply the 2D and 3D in vitro models in a hyperglycemic context to provide insights into DFU modeling will be reviewed. Perspectives of utilizing 3D bioprinting and skin-on-the-chip model as a diabetic wound model in the future will also be highlighted. By leveraging knowledge from past experiences and current research, an improved experimental model for DFU is anticipated to be established in near future.

Surviving an Extensive Burn Injury Using Advanced Skin Replacement Technologies

There have been significant improvements in the technology available for treating extensive burns in the past decade. This case presents two unique, skin replacement technologies that were used to treat an 86% surface area flame burn in a pediatric patient. A temporary dermal replacement, known as "Novosorb™ Biodegradable Temporizing Matrix" was first used to stabilize the burn injury and remained in place for approximately three months. Given the large burn size and lack of available donor skin for grafting, a permanent skin replacement product known as "Self-Assembled Skin Substitute (SASS)" was then utilized to cover the burns. SASS is a novel technology that was developed to replace skin as an autologous skin graft and is currently available in Canada through a clinical trial for major burns. Ultimately, the concurrent use of these two technologies allowed for the unprecedented survival of a child following an extensive and life-threatening burn injury.

Cellular human tissue-engineered skin substitutes investigated for deep and difficult to heal injuries

Wound healing is an important function of skin; however, after significant skin injury (burns) or in certain dermatological pathologies (chronic wounds), this important process can be deregulated or lost, resulting in severe complications. To avoid these, studies have focused on developing tissue-engineered skin substitutes (TESSs), which attempt to replace and regenerate the damaged skin. Autologous cultured epithelial substitutes (CESs) constituted of keratinocytes, allogeneic cultured dermal substitutes (CDSs) composed of biomaterials and fibroblasts and autologous composite skin substitutes (CSSs) comprised of biomaterials, keratinocytes and fibroblasts, have been the most studied clinical TESSs, reporting positive results for different pathological conditions. However, researchers' purpose is to develop TESSs that resemble in a better way the human skin and its wound healing process. For this reason, they have also evaluated at preclinical level the incorporation of other human cell types such as melanocytes, Merkel and Langerhans cells, skin stem cells (SSCs), induced pluripotent stem cells (iPSCs) or mesenchymal stem cells (MSCs). Among these, MSCs have been also reported in clinical studies with hopeful results. Future perspectives in the field of human-TESSs are focused on improving in vivo animal models, incorporating immune cells, designing specific niches inside the biomaterials to increase stem cell potential and developing three-dimensional bioprinting strategies, with the final purpose of increasing patient's health care. In this review we summarize the use of different human cell populations for preclinical and clinical TESSs under research, remarking their strengths and limitations and discuss the future perspectives, which could be useful for wound healing purposes.

Three-Dimensional Model of Hypertrophic Scar Using a Tissue-Engineering Approach

Following wound healing, skin is replaced by a specialized tissue called scar. Sometime, this scar can become pathologic, called hypertrophic scar, with a high amount of extracellular matrix, capillaries, and myofibroblast persistence. To understand the mechanisms at the origin of the fibrosis is paramount to treat patients, but despite few animal models and in vitro studies using mainly human pathological cells cultured on plastic on monolayer, the treatment of these fibrotic scars remains unsatisfactory. As in tissue, cells are most often imbedded in extracellular matrix, we have developed, using a tissue engineering method, new in vitro models to study human fibrotic skin pathologies as hypertrophic scars. Human cells isolated from hypertrophic scars are used to reconstitute a three-dimensional fibrotic skin comprising both dermal and epidermal parts. This method called the self-assembly approach is based on the cell capacity to reconstitute their own environment as in vivo. In this chapter, the described methods include extraction and culture of human scar keratinocytes and fibroblasts from cutaneous biopsies as well as the protocols to produce fibrotic skin that can be used to study pathological process.

Advances in generation of three-dimensional skin equivalents: pre-clinical studies to clinical therapies

The inability of two-dimensional cell culture systems to adequately map the structure and function of complex organs like skin necessitates the development of three-dimensional (3D) skin models. A diverse range of 3D skin equivalents have been developed over the last few decades for studying complex properties of skin as well as for drug discovery and clinical applications for skin regeneration in chronic wounds, such as diabetic foot ulcers, where the normal mechanism of wound healing is compromised. These 3D skin substitutes also serve as a suitable alternative to animal models in industrial applications and fundamental research. With the emergence of tissue engineering, new scaffolds and matrices have been integrated into 3D cell culture systems, along with gene therapy approaches, to increase the efficacy of transplanted cells in skin regeneration. This review summarizes recent approaches to the development of skin equivalents as well as different models for studying skin diseases and properties and current therapeutic applications of skin substitutes.

Conditioned medium produced by fibroblasts cultured in low oxygen pressure allows the formation of highly structured capillary-like networks in fibrin gels

Tissue engineering is an emerging and promising concept to replace or cure failing organs, but its clinical translation currently encounters issues due to the inability to quickly produce inexpensive thick tissues, which are necessary for many applications. To circumvent this problem, we postulate that cells secrete the optimal cocktail required to promote angiogenesis when they are placed in physiological conditions where their oxygen supply is reduced. Thus, dermal fibroblasts were cultivated under hypoxia (2% O₂) to condition their cell culture medium. The potential of this conditioned medium was tested for human umbilical vein endothelial cell proliferation and for their ability to form capillary-like networks into fibrin gels. The medium conditioned by dermal fibroblasts under hypoxic conditions (DF-Hx) induced a more significant proliferation of endothelial cells compared to medium conditioned by dermal fibroblasts under normoxic conditions (DF-Nx). In essence, doubling time for endothelial cells in DF-Hx was reduced by 10.4% compared to DF-Nx after 1 week of conditioning, and by 20.3% after 2 weeks. The DF-Hx allowed the formation of more extended and more structured capillary-like networks than DF-Nx or commercially available medium, paving the way to further refinements.

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.

A Cultured Autologous Dermo-epidermal Skin Substitute for Full-Thickness Skin Defects: A Phase I, Open, Prospective Clinical Trial in Children

BACKGROUND

The management of deep partial-thickness and full-thickness skin defects remains a significant challenge. Particularly with massive defects, the current standard treatment, split-thickness skin grafting, is fraught with donor-site limitations and unsatisfactory long-term outcomes. A novel, autologous, bioengineered skin substitute was developed to address this problem.

METHODS

To determine whether this skin substitute could safely provide permanent defect coverage, a phase I clinical trial was performed at the University Children's Hospital Zurich. Ten pediatric patients with acute or elective deep partial- or full-thickness skin defects were included. Skin grafts of 49 cm were bioengineered using autologous keratinocytes and fibroblasts isolated from a patient's small skin biopsy specimen (4 cm), incorporated in a collagen hydrogel.

RESULTS

Graft take, epithelialization, infection, adverse events, skin quality, and histology were analyzed. Median graft take at 21 days postoperatively was 78 percent (range, 0 to 100 percent). Healed skin substitutes were stable and skin quality was nearly normal. There were four cases of hematoma leading to partial graft loss. Histology at 3 months revealed a well-stratified epidermis and a dermal compartment comparable to native skin. Mean follow-up duration was 15 months.

CONCLUSIONS

In the first clinical application of this novel skin substitute, safe coverage of skin defects was achieved. Safety and efficacy phase II trials comparing the novel skin substitute to split-thickness skin grafts are ongoing.

CLINICAL QUESTION/LEVEL OF EVIDENCE

Therapeutic, IV.

Immune tolerance of tissue-engineered skin produced with allogeneic or xenogeneic fibroblasts and syngeneic keratinocytes grafted on mice

Organs are needed for the long-term replacement of diseased or wounded tissues. Various technologies based on cells seeded in synthetic or biomaterial scaffolds, or scaffold-free methods have been developed in order to produce substitutes that mimic native organs and tissues. For cell-based approaches, the use of living allogeneic fibroblasts could potentially lead to the production of "off-the-shelf" bioengineered organs/tissues. However, questions remain regarding the outcome of allogeneic grafts in terms of persistence of allogeneic cells, tolerance and the host immune reaction against the tissue after implantation. To evaluate graft tolerance of engineered-tissues containing non-autologous fibroblasts, tissue-engineered skin substitutes (TESs) produced with syngeneic, allogeneic or xenogeneic fibroblasts associated with syngeneic, allogeneic or xenogeneic epithelial cells were grafted in mice as primary and secondary grafts. The immune response was evaluated by histological analysis and immunodetection of M2 macrophages, CD4- and CD8-positive T cells, 15, 19, 35 and 56 days after grafting. Tissue-engineered skin composed of non-autologous epithelial cells were rejected. In contrast, TESs composed of non-autologous fibroblasts underlying syngeneic epithelial cells were still present 56 days after grafting. This work shows that TES composed of non-autologous fibroblasts and autologous epithelial cells are not rejected after grafting. STATEMENT OF SIGNIFICANCE: We found that tissue-engineered skin substitutes produced by a scaffold-free cell-based approach from allogeneic fibroblasts and autologous epithelial cells are not rejected after grafting and allow for the permanent coverage of a full-thickness skin wounds. In the field of tissue engineering, these findings open the possibility of selecting a human fibroblastic or stromal cell population based on its biological properties and adequate biosafety, banking it, in order to produce "ready-to-use" bioengineered organs/tissues that could be grafted to any patient without eliciting immune reaction after grafting. Our results can be generalized to any organs produced from fibroblasts. Thus, it is a great step with multiple applications in tissue engineering and transplantation.

Skin Stem Cells, Their Niche and Tissue Engineering Approach for Skin Regeneration

Skin is the main organ that covers the human body and acts as a protective barrier between the human body and the environment. Skin tissue as a stem cell source can be used for transplantation in therapeutic application in terms of its properties such as abundant, easy to access, high plasticity and high ability to regenerate. The immunological profile of these cells makes it a suitable resource for autologous and allogeneic applications. The lack of major histo-compatibility complex 1 is also advantageous in its use. Epidermal stem cells are the main stem cells in the skin and are suitable cells in tissue engineering studies for their important role in wound repair. In the last 30 years, many studies have been conducted to develop substitutions that mimic human skin. Stem cell-based skin substitutions have been developed to be used in clinical applications, to support the healing of acute and chronic wounds and as test systems for dermatological and pharmacological applications. In this chapter, tissue specific properties of epidermal stem cells, composition of their niche, regenerative approaches and repair of tissue degeneration have been examined.

Specialized Living Wound Dressing Based on the Self-Assembly Approach of Tissue Engineering

There is a high incidence of failure and recurrence for chronic skin wounds following conventional therapies. To promote healing, the use of skin substitutes containing living cells as wound dressings has been proposed. The aim of this study was to produce a scaffold-free cell-based bilayered tissue-engineered skin substitute (TES) containing living fibroblasts and keratinocytes suitable for use as wound dressing, while considering production time, handling effort during the manufacturing process, and stability of the final product. The self-assembly method, which relies on the ability of mesenchymal cells to secrete and organize connective tissue sheet sustaining keratinocyte growth, was used to produce TESs. Three fibroblast-seeding densities were tested to produce tissue sheets. At day 17, keratinocytes were added onto 1 or 3 (reference method) stacked tissue sheets. Four days later, TESs were subjected either to 4, 10, or 17 days of culture at the air–liquid interface (A/L). All resulting TESs were comparable in terms of their histological aspect, protein expression profile and contractile behavior in vitro. However, signs of extracellular matrix (ECM) digestion that progressed over culture time were noted in TESs produced with only one fibroblast-derived tissue sheet. With lower fibroblast density, the ECM of TESs was almost completely digested after 10 days A/L and lost histological integrity after grafting in athymic mice. Increasing the fibroblast seeding density 5 to 10 times solved this problem. We conclude that the proposed method allows for a 25-day production of a living TES, which retains its histological characteristics in vitro for at least two weeks.

Tissue-engineered 3D melanoma model with blood and lymphatic capillaries for drug development

While being the rarest skin cancer, melanoma is also the deadliest. To further drug discovery and improve clinical translation, new human cell-based in vitro models are needed. Our work strives to mimic the melanoma microenvironment in vitro as an alternative to animal testing. We used the self-assembly method to produce a 3D human melanoma model exempt of exogenous biomaterial. This model is based on primary human skin cells and melanoma cell lines while including a key feature for tumor progression: blood and lymphatic capillaries. Major components of the tumor microenvironment such as capillaries, human extracellular matrix, a stratified epidermis (involucrin, filaggrin) and basement membrane (laminin 332) are recapitulated in vitro. We demonstrate the persistence of CD31+ blood and podoplanin+/LYVE-1+ lymphatic capillaries in the engineered tissue. Chronic treatment with vemurafenib was applied to the model and elicited a dose-dependent response on proliferation and apoptosis, making it a promising tool to test new compounds in a human-like environment.

Are the Effects of the Cholera Toxin and Isoproterenol on Human Keratinocytes' Proliferative Potential Dependent on Whether They Are Co-Cultured with Human or Murine Fibroblast Feeder Layers?

Human keratinocyte culture has provided the means to treat burns, wounds and skin pathologies. To date, to efficiently culture keratinocytes, cells are cultured on an irradiated feeder layer (iFL), either comprising human (iHFL) or murine (i3T3FL) fibroblasts, and the culture medium is supplemented with a cyclic adenosine monophosphate (cAMP) accumulation inducing agent such as isoproterenol (ISO) or cholera toxin (CT). Previous studies have characterized how the feeder layer type and the cAMP inducer type influence epithelial cells' phenotype independently from one another, but it is still unknown if an optimal combination of feeder layer and cAMP inducer types exists. We used sophisticated statistical models to search for a synergetic effect of feeder layer and cAMP inducer types on human keratinocytes' proliferative potential. Our data suggests that, when culturing human keratinocytes, using iHFL over i3T3FL increases population doublings and colony-forming efficiency through signaling pathways involving Ak mouse strain thymoma (Akt, also known as protein kinase B) isoforms 1 to 3, signal transducer and activator of transcription 5 (STAT5), p53, and adenosine monophosphate activated protein kinase α1 (AMPKα1). Both tested cAMP inducers ISO and CT yielded comparable outcomes. However, no significant synergy between feeder layer and cAMP inducer types was detected. We conclude that, to promote human keratinocyte growth in the early passages of culture, co-culturing them with a human feeder layer is preferable to a murine feeder layer.

Use of bilaminar grafts as life-saving interventions for severe burns: A single-center experience

BACKGROUND

Skin coverage remains a significant hurdle in large-sized burns. Recent advances have allowed to grow Bilaminar Cultured Skin Autografts (BCSGs) from patients' own donor sites. The aim of this study was to report long-term outcomes in patients with large-sized burns having received BCSGs.

METHODS

Nine patients received BCSGs from January 2010 to May 2015. Except one patient who died during hospitalization, all patients were contacted. Four agreed to partake in the study. Patients were tested with the Vancouver Scar Scale (VSS), QuickDASH questionnaire and Burn Specific Health Scale (BSHS). Incisional biopsies of BCSGs were compared with patients' autografts.

RESULTS

From nine patients, mean age was 40 years and mean TBSA was 70.3%. For the four patients included, score averaged was 2.25 on the VSS, 29.5 on QuickDASH, 36/36 for psychosocial items and 63/84 for functional abilities on the BSHS. Compared with autografts, BCSGs demonstrated better pliability VSS and functionality. Biopsies showed no evidence of malignancy or atypical changes, but areas of hyperpigmentation.

CONCLUSION

This is the first report investigating the long-term outcome of a newly developed BCSG. BCSGs demonstrated comparable results with patients' autografts, functional outcomes on self-reported questionnaires and excellent psychological states. Precaution given the extensive unexpected hyperpigmentation must be taken and a randomized controlled study is underway.

Engineering Tissues without the Use of a Synthetic Scaffold: A Twenty-Year History of the Self-Assembly Method

Twenty years ago, Dr. François A. Auger, the founder of the Laboratory of Experimental Organogenesis (LOEX), introduced the self-assembly technique. This innovative technique relies on the ability of dermal fibroblasts to produce and assemble their own extracellular matrix, differing from all other tissue-engineering techniques that use preformed synthetic scaffolds. Nevertheless, the use of the self-assembly technique was limited for a long time due to its main drawbacks: time and cost. Recent scientific breakthroughs have addressed these limitations. New protocol modifications that aim at increasing the rate of extracellular matrix formation have been proposed to reduce the production costs and laboratory handling time of engineered tissues. Moreover, the introduction of vascularization strategies in vitro permits the formation of capillary-like networks within reconstructed tissues. These optimization strategies enable the large-scale production of inexpensive native-like substitutes using the self-assembly technique. These substitutes can be used to reconstruct three-dimensional models free of exogenous materials for clinical and fundamental applications.

Synthetic polymeric biomaterials for wound healing: a review

Wounds are of a variety of types and each category has its own distinctive healing requirements. This realization has spurred the development of a myriad of wound dressings, each with specific characteristics. It is unrealistic to expect a singular dressing to embrace all characteristics that would fulfill generic needs for wound healing. However, each dressing may approach the ideal requirements by deviating from the 'one size fits all approach', if it conforms strictly to the specifications of the wound and the patient. Indeed, a functional wound dressing should achieve healing of the wound with minimal time and cost expenditures. This article offers an insight into several different types of polymeric materials clinically used in wound dressings and the events taking place at cellular level, which aid the process of healing, while the biomaterial dressing interacts with the body tissue. Hence, the significance of using synthetic polymer films, foam dressings, hydrocolloids, alginate dressings, and hydrogels has been reviewed, and the properties of these materials that conform to wound-healing requirements have been explored. A special section on bioactive dressings and bioengineered skin substitutes that play an active part in healing process has been re-examined in this work.

Tissue engineering of skin and regenerative medicine for wound care

Engineering of biologic skin substitutes has progressed over time from individual applications of skin cells, or biopolymer scaffolds, to combinations of cells and scaffolds for treatment, healing, and closure of acute and chronic skin wounds. Skin substitutes may be categorized into three groups: acellular scaffolds, temporary substitutes containing allogeneic skin cells, and permanent substitutes containing autologous skin cells. Combined use of acellular dermal substitutes with permanent skin substitutes containing autologous cells has been shown to provide definitive wound closure in burns involving greater than 90% of the total body surface area. These advances have contributed to reduced morbidity and mortality from both acute and chronic wounds but, to date, have failed to replace all of the structures and functions of the skin. Among the remaining deficiencies in cellular or biologic skin substitutes are hypopigmentation, absence of stable vascular and lymphatic networks, absence of hair follicles, sebaceous and sweat glands, and incomplete innervation. Correction of these deficiencies depends on regulation of biologic pathways of embryonic and fetal development to restore the full anatomy and physiology of uninjured skin. Elucidation and integration of developmental biology into future models of biologic skin substitutes promises to restore complete anatomy and physiology, and further reduce morbidity from skin wounds and scar. This article offers a review of recent advances in skin cell thrapies and discusses the future prospects in cutaneous regeneration.

In Vivo Evaluation and Imaging of a Bilayered Self-Assembled Skin Substitute Using a Decellularized Dermal Matrix Grafted on Mice

As time to final coverage is the essence for better survival outcome in severely burned patients, we have continuously strived to reduce the duration for the preparation of our bilayered self-assembled skin substitutes (SASS). These SASS produced in vitro by the self-assembly approach have a structure and functionality very similar to native skin. Recently, we have shown that a decellularized dermal matrix preproduced by the self-assembly approach could be used as a template to further obtain self-assembled skin substitute using a decellularized dermal template (SASS-DM) in vitro. Thus, the production period with patient cells was then reduced to about 1 month. Herein, preclinical animal experiments have been performed to confirm the integration and evolution of such a graft and compare the maturation of SASS and SASS-DM in vivo. Both tissues, reconstructed from adult or newborn cells, were grafted on athymic mice. Green fluorescent protein-transfected keratinocytes were also used to follow grafted tissues weekly for 6 weeks using an in vivo imaging system (IVIS). Cell architecture and differentiation were studied with histological and immunofluorescence analyses at each time point. Graft integration, macroscopic evolution, histological analyses, and expression of skin differentiation markers were similar between both skin substitutes reconstructed from either newborn or adult cells, and IVIS observations confirmed the efficient engraftment of SASS-DM. In conclusion, our in vivo graft experiments on a mouse model demonstrated that the SASS-DM had equivalent macroscopic, histological, and differentiation evolution over a 6-week period, when compared with the SASS. The tissue-engineered SASS-DM could improve clinical availability and advantageously shorten the time necessary for the definitive wound coverage of severely burned patients.

Production of a Bilayered Self-Assembled Skin Substitute Using a Tissue-Engineered Acellular Dermal Matrix

Our bilayered self-assembled skin substitutes (SASS) are skin substitutes showing a structure and functionality very similar to native human skin. These constructs are used, in life-threatening burn wounds, as permanent autologous grafts for the treatment of such affected patients even though their production is exacting. We thus intended to shorten their current production time to improve their clinical applicability. A self-assembled decellularized dermal matrix (DM) was used. It allowed the production of an autologous skin substitute from patient's cells. The characterization of SASS reconstructed using a decellularized dermal matrix (SASS-DM) was performed by histology, immunofluorescence, transmission electron microscopy, and uniaxial tensile analysis. Using the SASS-DM, it was possible to reduce the standard production time from about 8 to 4 and a half weeks. The structure, cell differentiation, and mechanical properties of the new skin substitutes were shown to be similar to the SASS. The decellularization process had no influence on the final microstructure and mechanical properties of the DM. This model, by enabling the production of a skin substitute in a shorter time frame without compromising its intrinsic tissue properties, represents a promising addition to the currently available burn and wound treatments.

Regenerative approaches for the cornea

The cornea is the transparent front part of the eye that transmits light to the back of the eye to generate vision. Loss of corneal transparency, if irreversible, leads to severe vision loss or blindness. For decades, corneal transplantation using human donor corneas has been the only option for treating corneal blindness. Despite recent improvement in surgical techniques, donor cornea transplantation remains plagued by risks of suboptimal optical results and visual acuity, immune rejection and eventually graft failure. Furthermore, the demand for suitable donor corneas is increasing faster than the number of donors, leaving thousands of curable patients untreated worldwide. Here, we critically review the state of the art of biomaterials for corneal regeneration. However, the lessons learned from the use of the cornea as a disease model will allow for extension of the biomaterials and techniques for regeneration of more complex organs such as the heart.

Bioengineered Self-assembled Skin as an Alternative to Skin Grafts

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

The role of radical surgery in the management of CEAP C5/6 and lipodermatosclerosis

Aim Analysis of the radical removing of the dermatosclerotic tissues and ulcer(s) with perforator veins dissection as well as local wound and standard compression treatment of CEAP C5/6 stage in a prospective comparative cohort study. Primary endpoint is to compare the results of the one-year follow-up regarding quality of life, vein clinical severity score, and ulcer healing process. Secondary endpoint is the precise presentation of the surgical technique. Tertiary endpoint is to demonstrate the photo-documented results of the postoperative wound treatment protocol. Method Clinical and statistical comparison of radical surgery versus solely wound care and compression in a cohort of 15 patients in each group (Groups 1, 2). In Group 1, radical removing of the dermatosclerotic pannicule and leg ulcer, perforator vein dissection, great saphenous vein, or small saphenous vein was performed. Quality of life , pain intensity, vein clinical severity score and patients' load capacity were compared. The tissue oxygen saturation changes were monitored via near infra-red spectroscopy. Results Both groups were statistically comparable. Wound healing in the operated group was 100% versus 60% in the second one, the difference was significant, p = 0.006. The quality of life: 45.33 versus 36.8, p < 0.001, intensity of leg restless and pain: 2.28 versus 5.3, p < 0.001, changes of vein clinical severity score: 5.27 versus 20.93, p < 0.001, changes of tO_2sat: 19.00 versus 6.07 in the upper third of the leg p < 0.001, proved significantly better in group 1 compared to 2. Load capacity was significantly better in group 1 than 2 at the end of the study. The average wound healing time was 113 days in group 1. Conclusion The radical surgery provides significantly better results, considering quality of life, vein clinical severity score, load capacity than the conservative treatment in this study.

Role of seaweed laminaran from Saccharina longicruris on matrix deposition during dermal tissue-engineered production

Our laboratory has developed a technique to reconstruct in vitro tissue from human cells using the self-assembly tissue-engineering method, which utilizes the ability of fibroblasts to deposit the matrix they secrete. The time necessary for tissue construction, several weeks, is a drawback for many clinical uses. We hypothesized that the addition of laminaran can increase the deposition of matrix, speeding up the production of the tissue. Laminaran was isolated from the brown seaweed Saccharina longicruris harvested in Canada and its structure was evaluated. Laminaran is a small molecular weight polysaccharide composed of linear glucose chains. Monolayer-cultured human skin fibroblasts were cultured in the presence of laminaran with ascorbate for 7 or 35 days to produce a dermis. Treatment did not induce any variation in the growth rate or alpha smooth muscle actin content but it did increase the deposition of collagen I in a dose-dependent manner. After 35 days, the reconstructed dermal thickness was increased when laminaran was added, and collagen I deposition and MMP activity were also significantly increased. Thus, laminaran can be used to increase the rate of production of reconstructed self-assembled dermis and can also potentially be used in cosmetic or therapeutic creams to stimulate matrix production.

Human urine-derived stem cells in combination with polycaprolactone/gelatin nanofibrous membranes enhance wound healing by promoting angiogenesis

Background

Despite advancements in wound healing techniques and devices, new treatments are needed to improve therapeutic outcomes. This study aimed to evaluate the potential use of a new biomaterial engineered from human urine-derived stem cells (USCs) and polycaprolactone/gelatin (PCL/GT) for wound healing.

Methods

USCs were isolated from healthy individuals. To fabricate PCL/GT composite meshes, twin-nozzle electrospinning were used to spin the PCL and gelatin solutions in normal organic solvents. The morphologies and hydrophilicity properties of PCL/GT membranes were investigated. After USCs were seeded onto a PCL/GT, cell adhesion, morphology, proliferation, and cytotoxicity were examined. Then, USCs were seeded on a PCL/GT blend nanofibrous membrane and transplanted into rabbit full-thickness skin defects for wound repair. Finally, the effect of USCs condition medium on proliferation, migration, and tube formation of human umbilical vein endothelial cells (HUVECs) were performed in vitro.

Results

USCs were successfully isolated from urine samples and expressed specific mesenchymal stem cells markers and could differentiate into osteoblasts, adipocytes, and chondrocytes. PCL/GT membrane has suitable mechanical properties similar with skin tissue and has good biocompatibility. USCs-PCL/GT significantly enhanced the healing of full-thickness skin wounds in rabbits compared to wounds treated with PCL/GT membrane alone or untreated wounds. USCs-PCL/GT-treated wounds closed much faster, with increased re-epithelialization, collagen formation, and angiogenesis. Moreover, USCs could secrete VEGF and TGF-β1, and USC-conditioned medium enhanced the migration, proliferation, and tube formation of endothelial cells.

Conclusion

USCs in combination with PCL/GT significantly prompted the healing of full-thickness skin wounds in rabbits. USCs based therapy provides a novel strategy for accelerating wound closure and promoting angiogenesis.

Using human umbilical cord cells for tissue engineering: a comparison with skin cells

The epithelial cells and Wharton׳s jelly cells (WJC) from the human umbilical cord have yet to be extensively studied in respect to their capacity to generate tissue-engineered substitutes for clinical applications. Our reconstruction strategy, based on the self-assembly approach of tissue engineering, allows the production of various types of living human tissues such as skin and cornea from a wide range of cell types originating from post-natal tissue sources. Here we placed epithelial cells and WJC from the umbilical cord in the context of a reconstructed skin substitute in combination with skin keratinocytes and fibroblasts. We compared the ability of the epithelial cells from both sources to generate a stratified, differentiated skin-like epithelium upon exposure to air when cultured on the two stromal cell types. Conversely, the ability of the WJC to behave as dermal fibroblasts, producing extracellular matrix and supporting the formation of a differentiated epithelium for both types of epithelial cells, was also investigated. Of the four types of constructs produced, the combination of WJC and keratinocytes was the most similar to skin engineered from dermal fibroblasts and keratinocytes. When cultured on dermal fibroblasts, the cord epithelial cells were able to differentiate in vitro into a stratified multilayered epithelium expressing molecules characteristic of keratinocyte differentiation after exposure to air, and maintaining the expression of keratins K18 and K19, typical of the umbilical cord epithelium. WJC were able to support the growth and differentiation of keratinocytes, especially at the early stages of air-liquid culture. In contrast, cord epithelial cells cultured on WJC did not form a differentiated epidermis when exposed to air. These results support the premise that the tissue from which cells originate can largely affect the properties and homoeostasis of reconstructed substitutes featuring both epithelial and stromal compartments.