A guide to biological skin substitutes

Synthesis and Physicochemical Characterization of Gelatine-Based Biodegradable Aerogel-like Composites as Possible Scaffolds for Regenerative Medicine

Regenerative medicine is an interdisciplinary field aiming at restoring pathologically damaged tissues and whole organs by cell transplantation in combination with proper supporting scaffolds. Gelatine-based ones are very attractive due to their biocompatibility, rapid biodegradability, and lack of immunogenicity. Gelatine-based composite hydrogels, containing strengthening agents to improve their modest mechanical properties, have been demonstrated to act as extracellular matrices (ECMs), thus playing a critical role in "organ manufacturing". Inspired by the lysyl oxidase (LO)-mediated process of crosslinking, which occurs in nature to reinforce collagen, we have recently developed a versatile protocol to crosslink gelatine B (Gel B) in the presence or absence of LO, using properly synthesized polystyrene- and polyacrylic-based copolymers containing the amine or aldehyde groups needed for crosslinking reactions. Here, following the developed protocol with slight modifications, we have successfully crosslinked Gel B in different conditions, obtaining eight out of nine compounds in high yield (57-99%). The determined crosslinking degree percentage (CP%) evidenced a high CP% for compounds obtained in presence of LO and using the styrenic amine-containing (CP5/DMAA) and acrylic aldehyde-containing (CPMA/DMAA) copolymers as crosslinking agents. ATR-FTIR analyses confirmed the chemical structure of all compounds, while optical microscopy demonstrated cavernous, crater-like, and labyrinth-like morphologies and cavities with a size in the range 15-261 µm. An apparent density in the range 0.10-0.45 g/cm3 confirmed the aerogel-like structure of most samples. Although the best biodegradation profile was observed for the sample obtained using 10% CP5/DMAA (M3), high swelling and absorption properties, high porosity, and good biodegradation profiles were also observed for samples obtained using the 5-10% CP5/DMAA (M4, 5, 6) and 20% CPMA/DMAA (M9) copolymers. Collectively, in this work of synthesis and physicochemical characterization, new aerogel-like composites have been developed and, based on their characteristics, which fit well within the requirements for TE, five candidates (M3, M4, M5, M6, and M9) suitable for future biological experiments on cell adhesion, infiltration and proliferation, to confirm their effective functioning, have been identified.

Outcomes of Dermal Regeneration Templates in Irradiated and Nonirradiated Scalp Defects

OBJECTIVES

Dermal regeneration templates (DRTs) are frequently used to treat scalp defects. The aim was to compare the time course of healing for DRTs in scalp defects with and without preoperative radiation.

METHODS

The authors conducted a retrospective cohort study of DRT-based scalp reconstruction at 2 academic medical centers between 2013 and 2022. Information was collected on demographic variables, comorbidities, medication use, history of radiation, and DRT outcomes. The primary outcome was DRT loss, defined as exposed calvarium or DRT detachment based on postoperative follow-up documentation. Kaplan-Meier survival analysis and multivariable Cox proportional-hazard regressions were used to compare DRT loss in irradiated and nonirradiated defects. Multivariable logistic regressions were used to compare 30-day postoperative complications (infection, hematoma, or seroma) in irradiated and nonirradiated defects.

RESULTS

In total, 158 cases were included. Twenty-eight (18%) patients had a preoperative history of radiation to the scalp. The mean follow-up time after DRT placement was 2.6 months (SD: 4.5 mo). The estimated probability of DRT survival at 2 months was 91% (95% CI: 83%-100%) in nonirradiated patients and 65% (95% CI: 48%-88%) in irradiated patients. In the 55 patients with a bony wound base, preoperative head radiation was associated with a higher likelihood of DRT loss (hazard ratio: 11). Half the irradiated defects experienced uncomplicated total wound closure using Integra Wound Matrix Dressing with or without second-stage reconstruction.

CONCLUSIONS

Dermal regeneration template can offer durable coverage in nonirradiated scalp defects. Although DRT loss is more likely in irradiated scalp defects, successful DRT-based reconstruction is possible in select cases.

Effects of mesenchymal stem cell culture on radio sterilized human amnion or radio sterilized pig skin in burn wound healing

Deep second and third degree burns treatment requires fibroblasts, keratinocytes and other skin cells in order to grow new dermis and epidermis. Cells can proliferate, secrete growth factors and extracellular matrix required to repair the damaged tissue. Radiosterilized human amnion and radiosterilized pig skin have been used as natural origin skin dressings for burned patients. Adipose-derived mesenchymal stem cells can differentiate into fibroblasts and keratinocytes and improve wound-healing progress. These cells can stimulate vascular tissue formation, release growth factors, synthetize new extracellular matrix and immunoregulate other cells. In this study, we developed mesenchymal stem cells-cellularized skin substitutes based from radiosterilized human amnion or pig skin. Third-degree burns were induced in mice animal models to evaluate the effect of cellularized skin substitutes on burn wound healing. Mesenchymal phenotype was immunophenotypically confirmed by flow cytometry and cell viability was close to 100%. Skin recovery was evaluated in burned mice after seven and fourteen days post-coverage with cellularized and non-cellularized sustitutes. Histological techniques and immunofluorescence were used to evaluate re-epithelization and type I collagen deposition. We determined that cellularized-human amnion or cellularized-pig skin in combination with mesenchymal stem cells improve extracellular matrix deposition. Both cellularized constructs increase detection of type I collagen in newly formed mouse skin and can be potentially used as skin coverage for further clinical treatment of burned patients.

Synthesis and Characterization of Amine and Aldehyde-Containing Copolymers for Enzymatic Crosslinking of Gelatine

In tissue engineering (TE), the support structure (scaffold) plays a key role necessary for cell adhesion and proliferation. The protein constituents of the extracellular matrix (ECM), such as collagen, its derivative gelatine, and elastin, are the most attractive materials as possible scaffolds. To improve the modest mechanical properties of gelatine, a strategy consists of crosslinking it, as naturally occurs for collagen, which is stiffened by the oxidative action of lysyl oxidase (LO). Here, a novel protocol to crosslink gelatine has been developed, not using the commonly employed crosslinkers, but based on the formation of imine bonds or on aldolic condensation reactions occurring between gelatine and properly synthesized copolymers containing amine residues via LO-mediated oxidation. Particularly, we first synthesized and characterized an amino butyl styrene monomer (5), its copolymers with dimethylacrylamide (DMAA), and its terpolymer with DMAA and acrylic acid (AA). Three acryloyl amidoamine monomers (11a-c) and their copolymers with DMAA were then prepared. A methacrolein (MA)/DMAA copolymer already possessing the needed aldehyde groups was finally developed to investigate the relevance of LO in the crosslinking process. Oxidation tests of amine copolymers with LO were performed to identify the best substrates to be used in experiments of gelatine reticulation. Copolymers obtained with 5, 11b, and 11c were excellent substrates for LO and were employed with MA/DMAA copolymers in gelatine crosslinking tests in different conditions. Among the amine-containing copolymers, that obtained with 5 (CP5/DMMA-43.1) afforded a material (M21) with the highest crosslinking percentage (71%). Cytotoxicity experiments carried out on two cell lines (IMR-32 and SH SY5Y) with the analogous (P5) of the synthetic constituent of M21 (CP5/DMAA) had evidenced no significant reduction in cell viability, but proliferation promotion, thus establishing the biocompatibility of M21 and the possibility to develop it as a new scaffold for TE, upon further investigations.

Analysis of bioprinting strategies for skin diseases and injuries through structural and temporal dynamics: historical perspectives, research hotspots, and emerging trends

This study endeavors to investigate the progression, research focal points, and budding trends in the realm of skin bioprinting over the past decade from a structural and temporal dynamics standpoint. Scholarly articles on skin bioprinting were obtained from WoSCC. A series of bibliometric tools comprising R software, CiteSpace, HistCite, and an alluvial generator were employed to discern historical characteristics, evolution of active topics, and upcoming tendencies in the area of skin bioprinting. Over the past decade, there has been a consistent rise in research interest in skin bioprinting, accompanied by an extensive array of meaningful scientific collaborations. Concurrently, diverse dynamic topics have emerged during various periods, as substantiated by an aggregate of 22 disciplines, 74 keywords, and 187 references demonstrating citation bursts. Four burgeoning research subfields were discerned through keyword clustering-namely, #3 'in situbioprinting', #6 'vascular', #7 'xanthan gum', and #8 'collagen hydrogels'. The keyword alluvial map reveals that Module 1, including 'transplantation' etc, has primarily dominated the research module over the previous decade, maintaining enduring relevance despite annual shifts in keyword focus. Additionally, we mapped out the top six key modules from 2023 being 'silk fibroin nanofiber', 'system', 'ionic liquid', 'mechanism', and 'foot ulcer'. Three recent research subdivisions were identified via timeline visualization of references, particularly Clusters #0 'wound healing', #4 'situ mineralization', and #5 '3D bioprinter'. Insights derived from bibliometric analyses illustrate present conditions and trends in skin bioprinting research, potentially aiding researchers in pinpointing central themes and pioneering novel investigative approaches in this field.

3D bioprinting bioglass to construct vascularized full-thickness skin substitutes for wound healing

Constructing three-dimensional (3D) bioprinted skin tissues that accurately replicate the mechanical properties of native skin and provide adequate oxygen and nutrient support remains a formidable challenge. In this study, we incorporated phosphosilicate calcium bioglasses (PSCs), a type of bioactive glass (BG), into the bioinks used for 3D bioprinting. The resulting bioink exhibited mechanical properties and biocompatibility that closely resembled those of natural skin. Utilizing 3D bioprinting technology, we successfully fabricated full-thickness skin substitutes, which underwent comprehensive evaluation to assess their regenerative potential in treating full-thickness skin injuries in rats. Remarkably, the skin substitutes loaded with PSCs exhibited exceptional angiogenic activity, as evidenced by the upregulation of angiogenesis-related genes in vitro and the observation of enhanced vascularization in wound tissue sections in vivo. These findings conclusively demonstrated the outstanding efficacy of PSCs in promoting angiogenesis and facilitating the repair of full-thickness skin wounds. The insights garnered from this study provide a valuable reference strategy for the development of skin tissue grafts with potent angiogenesis-inducing capabilities.

In vitro and in vivo evaluation of electrospun poly (ε-caprolactone)/collagen scaffolds and Wharton's jelly mesenchymal stromal cells (hWJ-MSCs) constructs as potential alternative for skin tissue engineering

Dermal substitutes bear a high clinical demand because of their ability to promote the healing process of cutaneous wounds by reducing the healing time the appearance and improving the functionality of the repaired tissue. Despite the increasing development of dermal substitutes, most of them are only composed of biological or biosynthetic matrices. This demonstrates the need for new developments focused on using scaffolds with cells (tissue construct) that promote the production of factors for biological signaling, wound coverage, and general support of the tissue repair process. Here, we fabricate by electrospinning two scaffolds: poly(ε-caprolactone) (PCL) as a control and poly(ε-caprolactone)/collagen type I (PCol) in a ratio lower collagen than previously reported, 19:1, respectively. Then, characterize their physicochemical and mechanical properties. As we bear in mind the creation of a biologically functional construct, we characterize and assess in vitro the implications of seeding human Wharton's jelly mesenchymal stromal cells (hWJ-MSCs) on both scaffolds. Finally, to determine the potential functionality of the constructs in vivo, their efficiency was evaluated in a porcine biomodel. Our findings demonstrated that collagen incorporation in the scaffolds produces fibers with similar diameters to those in the human native extracellular matrix, increases wettability, and enhances the presence of nitrogen on the scaffold surface, improving cell adhesion and proliferation. These synthetic scaffolds improved the secretion of factors by hWJ-MSCs involved in skin repair processes such as b-FGF and Angiopoietin I and induced its differentiation towards epithelial lineage, as shown by the increased expression of Involucrin and JUP. In vivo experiments confirmed that lesions treated with the PCol/hWJ-MSCs constructs might reproduce a morphological organization that seems relatively equivalent to normal skin. These results suggest that the PCol/hWJ-MSCs construct is a promising alternative for skin lesions repair in the clinic.

Carvacrol-Loaded Phytosomes for Enhanced Wound Healing: Molecular Docking, Formulation, DoE-Aided Optimization, and in vitro/in vivo Evaluation

Background

Despite recent advances in wound healing products, phytochemicals have been considered promising and attractive alternatives. Carvacrol (CAR), a natural phenolic compound, has been reported to be effective in wound healing.

Purpose

This work endeavored to develop novel CAR-loaded phytosomes for the enhancement of the wound healing process.

Methods

Molecular docking was performed to compare the affinities of the different types of phospholipids to CAR. Phytosomes were prepared by three methods (thin-film hydration, cosolvency, and salting out) using Lipoid S100 and Phospholipon 90H with three levels of saturation percent (0%, 50%, and 100%), and three levels of phospholipid molar percent (66.67%, 75%, and 80%). The optimization was performed using Design Expert where particle size, polydispersity index, and zeta potential were chosen as dependent variables. The optimized formula (F1) was further investigated regarding entrapment efficiency, TEM, 1H-NMR, FT-IR, DSC, X-RD, in vitro release, ex vivo permeation, and stability. Furthermore, it was incorporated into a hydrogel formulation, and an in vivo study was conducted to investigate the wound-healing properties of F1.

Results

F1 was chosen as the optimized formula prepared via the thin-film hydration method with a saturation percent and a phospholipid molar percent of zero and 66.67, respectively. TEM revealed the spherical shape of phytosomal vesicles with uniform size, while the results of 1H-NMR, FT-IR, DSC, and X-RD confirmed the formation of the phytosomal complex. F1 demonstrated a higher in vitro release and a slower permeation than free CAR. The wound area of F1-treated animals showed a marked reduction associated with a high degree of collagen fiber deposition and enhanced cellular proliferation.

Conclusion

F1 can be considered as a promising remedy for the enhancement of wound healing and hence it would be hoped to undergo further investigation.

Artificial Skin Therapies; Strategy for Product Development

Significance: Tissue-engineered artificial skin for clinical reconstruction can be regarded as an established practice. Bi-layered skin equivalents are available as established allogenic or autologous therapy, and various acellular skin replacements can support tissue repair. Moreover, there is considerable commonality between the skin and other soft tissue reconstruction products. This article presents an attempt to create a comprehensive global landscape review of advanced replacement materials and associated strategies for skin and soft tissue reconstruction. Recent Advances: There has been rapid growth in the number of commercial and pre-commercial products over the past decade. In this survey, 263 base products for advanced skin therapy have been identified, across 8 therapeutic categories, giving over 350 products in total. The largest market is in the United States, followed by the E.U. zone. However, despite these advances, and the investment of resources in each product development, there are key issues concerning the clinical efficacy, cost-benefit of products, and clinical impact. Each therapeutic strategy has relative merits and limitations. Critical Issues: A critical consideration in developing and evaluating products is the therapeutic modality, associated regulatory processes, and the potential for clinical adoption geographically, determined by regulatory territory, intellectual property, and commercial distribution factors. The survey identifies an opportunity for developments that improve basic efficacy or cost-benefit. Future Directions: The economic pressures on health care systems, compounded by the demands of our increasingly ageing population, and the imperative to distribute effective health care, create an urgent global need for effective and affordable products.

Mutable Collagenous Tissue Isolated from Echinoderms Leads to the Production of a Dermal Template That Is Biocompatible and Effective for Wound Healing in Rats

The mutable collagenous tissue (MCT) of echinoderms possesses biological peculiarities that facilitate native collagen extraction and employment for biomedical applications such as regenerative purposes for the treatment of skin wounds. Strategies for skin regeneration have been developed and dermal substitutes have been used to cover the lesion to facilitate cell proliferation, although very little is known about the application of novel matrix obtained from marine collagen. From food waste we isolated eco-friendly collagen, naturally enriched with glycosaminoglycans, to produce an innovative marine-derived biomaterial assembled as a novel bi-layered skin substitute (Marine Collagen Dermal Template or MCDT). The present work carried out a preliminary experimental in vivo comparative analysis between the MCDT and Integra, one of the most widely used dermal templates for wound management, in a rat model of full-thickness skin wounds. Clinical, histological, and molecular evaluations showed that the MCDT might be a valuable tool in promoting and supporting skin wound healing: it is biocompatible, as no adverse reactions were observed, along with stimulating angiogenesis and the deposition of mature collagen. Therefore, the two dermal templates used in this study displayed similar biocompatibility and outcome with focus on full-thickness skin wounds, although a peculiar cellular behavior involving the angiogenesis process was observed for the MCDT.

Long-term scarring outcomes and safety of patients treated with NovoSorbⓇ Biodegradable Temporizing Matrix (BTM): An observational cohort study

Background/Aim

NovoSorb^Ⓡ Biodegradable Temporizing Matrix (BTM) is a relatively novel, biodegradable polyurethane-based dermal regeneration template. The aim of this study was to evaluate the long-term scarring outcomes and safety of BTM in patients who underwent dermal reconstruction involving ≥5% of the total body surface area.

Methods

This was a postmarket, multicenter, observational cohort study involving evaluation of long-term outcomes in patients treated with BTM. A total of 55 patients (35 from Royal Adelaide Hospital, South Australia, and 20 from Victoria Adult Burns Service, The Alfred, Victoria) who underwent dermal repair with BTM between 2011 and 2017 were screened for inclusion in this study. All patients had BTM implanted for ≥18 months.

Results

Fifteen eligible patients with a mean (SD) age of 49.1 (14.3) years completed study assessments. These patients had a total of 39 areas treated with BTM. Using the Patient and Observer Scar Assessment Scale, scar quality was reported to be good by both observers and patients, with a mean (SD) observer score across all lesions of 3.6 (1.2) and mean (SD) overall opinion of 3.8 (1.2) as well as a mean (SD) patient score of 3.5 (1.2) and overall opinion of 5.0 (2.2). No adverse events or adverse device effects were reported or identified.

Conclusion

The long-term scar quality is comparable to published studies. BTM is safe in the long term with no additional risks or adverse consequences being identified.

Revisiting the Role of Amniotic Membrane Dressing in Acute Large Traumatic Wounds: A Randomized Feasibility Study at a Level 1 Trauma Centre

Introduction

Acute large traumatic wounds require temporary dressing prior to the definitive soft tissue reconstruction, as the physiological derangement during the immediate postinjury period delays the definitive surgical intervention. Selecting an ideal dressing material from numerous available synthetic dressings and skin substitutes poses a challenge. Although amniotic membrane (AM) scaffold has a definitive role in promoting wound healing in burns and chronic wounds, however, its efficacy in acute large traumatic wound is lacking. The present trial aimed to evaluate the safety and efficacy of AM in wound bed preparation before the definitive soft-tissue reconstruction in acute large traumatic wounds.

Methods

Sixty patients with acute large traumatic wounds (>10 cm × 10 cm) were divided into two groups (conventional dressing and AM dressing) using simple mixed block randomization. Wounds were assessed using the Bates Jensen Score at various timelines for the signs of early wound healing. The primary outcome was to evaluate the time taken for the wound bed preparation for definitive soft-tissue reconstruction. The secondary outcome was the pain assessment and complications, if any.

Results

There was significant reduction in the wound exudate as well as peripheral tissue edema in the intervention group (P = 0.01). AM dressing was significantly less painful (P = 0.01). The incidence of wound infection and need for debridement was decreased in the intervention group. However, the time interval to definitive soft-tissue coverage was statistically insignificant and comparable in both the groups. No adverse reactions were seen in either group.

Conclusion

AM dressings are safe and efficacious with significant reduction in wound exudates and peripheral edema. However, these dressings do not hasten the wound maturation as compared to conventional dressings. AM dressings can be used as a less painful alternative to conventional dressing in the management of large acute posttraumatic wounds.

Recent advances in decellularized biomaterials for wound healing

The skin is one of the most essential organs in the human body, interacting with the external environment and shielding the body from diseases and excessive water loss. Thus, the loss of the integrity of large portions of the skin due to injury and illness may lead to significant disabilities and even death. Decellularized biomaterials derived from the extracellular matrix of tissues and organs are natural biomaterials with large quantities of bioactive macromolecules and peptides, which possess excellent physical structures and sophisticated biomolecules, and thus, promote wound healing and skin regeneration. Here, we highlighted the applications of decellularized materials in wound repair. First, the wound-healing process was reviewed. Second, we elucidated the mechanisms of several extracellular matrix constitutes in facilitating wound healing. Third, the major categories of decellularized materials in the treatment of cutaneous wounds in numerous preclinical models and over decades of clinical practice were elaborated. Finally, we discussed the current hurdles in the field and anticipated the future challenges and novel avenues for research on decellularized biomaterials-based wound treatment.

Biodegradable temporising matrix: use of negative pressure wound therapy shows a significantly higher success rate

OBJECTIVE

The purpose of this case series was to evaluate the efficacy of a synthetic biodegradable temporising matrix (BTM; PolyNovo Biomaterials Pty Ltd, Australia) and compare the outcome of BTM patients with and without negative pressure wound therapy (NPWT).

METHOD

A retrospective chart review was conducted on patients admitted with deep full-thickness burns, traumatic or complex wound injuries treated with BTM. Electronic medical records and images were evaluated by a team of clinical professionals. Endpoints included: the measure of successful BTM integration; and comparison between patients treated with and without NPWT. Additional measures were BTM total surface area, BTM sites, timeliness of BTM application and any complications.

RESULTS

A total of 28 patients were evaluated and 23 (82.1%) demonstrated overall successful BTM integration. Patients treated with BTM in conjunction with NPWT (n=16) demonstrated a significantly higher (p=0.046) integration rate compared to patients treated without NPWT (n=12) (93.8% versus 58.3%, respectively). Patients treated with BTM with NPWT continued to successfully integrate and sustain favourable outcomes despite the presence of severe infection or the development of haematomas.

CONCLUSION

A significantly higher integration rate was demonstrated when BTM was used in conjunction with NPWT. The results of this study further support the efficacy of successful integration of BTM as a replacement for tissue loss in the treatment of deep, full-thickness burns, traumatic and complex wound injuries, and particularly favourable outcomes with the use of NPWT. To the best of our knowledge, this is the first reported case series comparing the clinical outcomes of BTM with and without the use of NPWT.

FEATURES OF QUALITY CONTROL STRATEGY FOR DRUGS BASED ON VIABLE SKIN CELLS

The aim of the study was to research the international experience in quality assurance of the products based on skin cells in order to identify the features of the quality control strategy in the development, production, as well as during an expert quality assessment as a part of the state registration procedure in the Russian Federation.

Materials and methods. The article provides an analysis of the materials presented in the assessment reports of the USA and Japanese regulatory authorities, as well as on the official websites of manufacturers, in review and scientific papers on the study of the structure and properties of tissue-engineered skin analogs.

Results. The manufacture of products containing human skin cells is associated with such risks as the possibility of contamination of the preparation with infective agents transmitted by materials of the animal origin, feeder cells, donor cells, or during the manufacturing process; a small amount of biopsy materials; a complexity of a three-dimensional product structure when combining cells with a scaffold; continuity of the manufacture process and a short product expiry date. The raw materials and reagents control, the creation of cell banks, using animal feeder cells only from qualified cell banks, an in-process control and release testing in accordance with the requirements of the finished product specification, make it possible to obtain a preparation with a reproducible quality. The specification should contain information about the identity, safety and potency of the product. For each preparation, the choice of approaches for assessing the quality is individual and depends on its composition and mode of action.

Conclusion. The features of the quality control strategy for the drugs based on human skin cells, consist in the implementation of control measures in order to obtain a proper quality of cellular (viability, sterility, identity, potency, et al) and non-cellular (physico-chemical scaffold properties) components or the whole graft (bioburden, barrier properties). The approaches and methods for determining the potency should be selected individually for each product and reflect the number, viability and identity of cells, a proliferative activity and secretable ability of the cellular component.

Robot-assisted in situ bioprinting of gelatin methacrylate hydrogels with stem cells induces hair follicle-inclusive skin regeneration

Large skin defects caused by accidents or disease can cause fluid loss, water and electrolyte disorders, hypoproteinemia and serious infection and remain a difficult problem in clinical practice. In situ bioprinting is a promising, recently developed technology that involves timely, customized, and morphologically adapted bioprinting of bioink into tissue defects to promote the recovery of human tissues or organs. During this process, bioink is a key factor. In this study, we synthesized a biocompatible, photosensitive hydrogel material comprising gelatin methacrylate (GelMA) for robot-assisted in situ bioprinting of skin wounds. The results showed that GelMA demonstrated good printability of that supported the proliferation of skin-derived precursors (SKPs) and maintained their properties. Furthermore, in situ bioprinting of GelMA hydrogels with epidermal stem cells (Epi-SCs) and SKPs onto skin wounds showed complete wound healing and functional tissue skin regeneration. The regenerated skin contains epidermis, dermis, blood vessels, hair follicles, and sebaceous glands and resembling native skin. These results provide an effective strategy for skin repair through the combined application of GelMA hydrogels, Epi-SCs, SKPs and in situ bioprinting and its promising clinical translational potential for further applications.

Advances in microfabrication technologies in tissue engineering and regenerative medicine

BACKGROUND

Tissue engineering provides various strategies to fabricate an appropriate microenvironment to support the repair and regeneration of lost or damaged tissues. In this matter, several technologies have been implemented to construct close-to-native three-dimensional structures at numerous physiological scales, which are essential to confer the functional characteristics of living tissues.

METHODS

In this article, we review a variety of microfabrication technologies that are currently utilized for several tissue engineering applications, such as soft lithography, microneedles, templated and self-assembly of microstructures, microfluidics, fiber spinning, and bioprinting.

RESULTS

These technologies have considerably helped us to precisely manipulate cells or cellular constructs for the fabrication of biomimetic tissues and organs. Although currently available tissues still lack some crucial functionalities, including vascular networks, innervation, and lymphatic system, microfabrication strategies are being proposed to overcome these issues. Moreover, the microfabrication techniques that have progressed to the preclinical stage are also discussed.

CONCLUSIONS

This article aims to highlight the advantages and drawbacks of each technique and areas of further research for a more comprehensive and evolving understanding of microfabrication techniques in terms of tissue engineering and regenerative medicine applications.

Adaptive multi‐degree‐of‐freedom in situ bioprinting robot for hair‐follicle‐inclusive skin repair: A preliminary study conducted in mice

Skin acts as an essential barrier, protecting organisms from their environment. For skin trauma caused by accidental injuries, rapid healing, personalization, and functionality are vital requirements in clinical, which are the bottlenecks hindering the translation of skin repair from benchside to bedside. Herein, we described a novel design and a proof‐of‐concept demonstration of an adaptive bioprinting robot to proceed rapid in situ bioprinting on a full‐thickness excisional wound in mice. The three‐dimensional (3D) scanning and closed‐loop visual system integrated in the robot and the multi‐degree‐of‐freedom mechanism provide immediate, precise, and complete wound coverage through stereotactic bioprinting, which hits the key requirements of rapid‐healing and personalization in skin repair. Combined with the robot, epidermal stem cells and skin‐derived precursors isolated from neonatal mice mixed with Matrigel were directly printed into the injured area to replicate the skin structure. Excisional wounds after bioprinting showed complete wound healing and functional skin tissue regeneration that closely resembling native skin, including epidermis, dermis, blood vessels, hair follicles and sebaceous glands etc. This study provides an effective strategy for skin repair through the combination of the novel robot and a bioactive bioink, and has a promising clinical translational potential for further applications.

In vivo printing of growth factor-eluting adhesive scaffolds improves wound healing

Acute and chronic wounds affect millions of people around the world, imposing a growing financial burden on patients and hospitals. Despite the application of current wound management strategies, the physiological healing process is disrupted in many cases, resulting in impaired wound healing. Therefore, more efficient and easy-to-use treatment modalities are needed. In this study, we demonstrate the benefit of in vivo printed, growth factor-eluting adhesive scaffolds for the treatment of full-thickness wounds in a porcine model. A custom-made handheld printer is implemented to finely print gelatin-methacryloyl (GelMA) hydrogel containing vascular endothelial growth factor (VEGF) into the wounds. In vitro and in vivo results show that the in situ GelMA crosslinking induces a strong scaffold adhesion and enables printing on curved surfaces of wet tissues, without the need for any sutures. The scaffold is further shown to offer a sustained release of VEGF, enhancing the migration of endothelial cells in vitro. Histological analyses demonstrate that the administration of the VEGF-eluting GelMA scaffolds that remain adherent to the wound bed significantly improves the quality of healing in porcine wounds. The introduced in vivo printing strategy for wound healing applications is translational and convenient to use in any place, such as an operating room, and does not require expensive bioprinters or imaging modalities.

A collagen-silica-based biocomposite for potential application in bone tissue engineering

Bone is a hierarchical material that has inspired the design of biopolymer-derived biocomposites for tissue engineering purposes. The present study sought to synthesize and perform the physicochemical characterization and biocompatibility of a collagen-silica-based biocomposite for potential application in bone tissue engineering. Ultrastructure, biodegradability, swelling behavior, and biocompatibility properties were analyzed to gain insight into the advantages and limitations to the use of this biomaterial as a bone substitute. Scanning electron microscopy analysis showed a packed-collagen fibril matrix and silica particles in the biocomposite three-dimensional structure. As shown by analysis of in vitro swelling behavior and biodegradability, it would seem that the material swelled soon after implantation and then suffered degradation. Biocompatibility properties were analyzed in vivo 14-days postimplantation using an experimental model in Wistar rats. The biocomposite was placed inside the hematopoietic bone marrow compartment of both tibiae (n = 16). Newly formed woven bone was observed in response to both materials. Unlike the pure-collagen-tissue interface, extensive areas of osseointegration were observed at the biocomposite-tissue interface, which would indicate that silica particles stimulated new bone formation. Agglomerates of finely particulate material with no inflammatory infiltrate or multinucleated giant cells were observed in the bone marrow implanted with the biocomposite. The biocomposite showed good biocompatibility properties. Further studies are necessary to evaluate their biological behavior over time.

Application of paste-type acellular dermal matrix in hard-to-heal wounds

OBJECTIVE

The extracellular matrix (ECM) is one of the most important elements in wound healing. Absence or dysfunction of the ECM may impair wound healing. The application of acellular dermal matrix (ADM) as a substitute for ECM has been suggested. This study investigated the clinical application and wound healing effects of a paste-type ADM in patients presenting with hard-to-heal wounds due to various causes.

METHOD

Patients with a hard-to-heal wound for >1 month, from September 2017 to February 2019, were included in this study. After debridement, the paste-type ADM was applied, at zero (baseline), two and four weeks. After application of the paste-type ADM, a conventional dressing was applied using polyurethane foam. Wound size, the formation of granulation tissue, re-epithelialisation, complete healing and adverse events were recorded at zero (baseline), one, two, four, eight and 12 weeks after the initial treatment.

RESULTS

A total of 18 patients took part (eight male, 10 female, mean age of 56±16.16 years). The mean wound area decreased from 17.42±10.04cm² to 12.73±7.60cm² by week one (p<0.05), to 10.16±7.00 by week two (p<0.0005), to 5.56±5.25 by week four (p<0.0001), to 2.77±5.15 by week eight (p<0.0001) and to 2.07±4.78 by week 12 (p<0.0001). The number of patients with >75% re-epithelialisation increased from two (11.1%) at two weeks to five (27.8%) at four weeks, to 11 (61.1%) at eight weeks and to 13 (72.2%) at 12 weeks. The number of patients showing complete wound healing was two (11.1%) at four weeks, nine (50.0%) at eight weeks and 12 (66.7%) at 12 weeks. No adverse events were reported during treatment.

CONCLUSION

The paste-type ADM used in this study is a viable option for facilitating wound healing; it can shorten hospitalisation, and promote a faster recovery and return to normal life activities.

Polysaccharide-based skin scaffolds with enhanced mechanical compatibility with native human skin

We report a custom-made technique to synthesize process-convenient skin scaffolds by tuning the mechanical properties of hydrogels based on a few naturally occurring polysaccharides to match the rheological properties of previously established benchmarks, i.e., the ex vivo native human skins. We studied the mechanical parameters using oscillatory shear rheology. At small strain amplitudes, the intrinsic elastic modulus showed an almost linear dependence in the middle and a changing rate profile at the two ends with concentration of the principal hydrogel component variant, i.e., kappa (κ)-carrageenan. At large strain amplitudes, the hydrogels demonstrated intercycle strain-softening behavior, the onset of which was directly proportional to the κ-carrageenan concentration. We observed a concentration match for the intrinsic elastic modulus of the benchmark within this sigmoidal curve fit. Contextually, we need to explore other potent polymeric hydrogel systems to achieve mechanical affinity in terms of multiple rheological parameters derived from both strain amplitude and angular frequency sweeps. Additionally, we carried out diffusion experiments to study caffeine permeation attributes. The hydrogels show improved barrier features with increasing κ-carrageenan concentration. In terms of the penetration flux and total cumulative amount of permeated caffeine, this enhanced mechanical adherence demonstrates comparable penetration features with the commercial 3D skin model.

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.

3D Bioprinting of Vascularized Tissues for in vitro and in vivo Applications

With a limited supply of organ donors and available organs for transplantation, the aim of tissue engineering with three-dimensional (3D) bioprinting technology is to construct fully functional and viable tissue and organ replacements for various clinical applications. 3D bioprinting allows for the customization of complex tissue architecture with numerous combinations of materials and printing methods to build different tissue types, and eventually fully functional replacement organs. The main challenge of maintaining 3D printed tissue viability is the inclusion of complex vascular networks for nutrient transport and waste disposal. Rapid development and discoveries in recent years have taken huge strides toward perfecting the incorporation of vascular networks in 3D printed tissue and organs. In this review, we will discuss the latest advancements in fabricating vascularized tissue and organs including novel strategies and materials, and their applications. Our discussion will begin with the exploration of printing vasculature, progress through the current statuses of bioprinting tissue/organoids from bone to muscles to organs, and conclude with relevant applications for in vitro models and drug testing. We will also explore and discuss the current limitations of vascularized tissue engineering and some of the promising future directions this technology may bring.

A Prototype Skin Substitute, Made of Recycled Marine Collagen, Improves the Skin Regeneration of Sheep

Simple Summary

Marine ecosystems are a huge source of unexplored “blue” materials for different applications. The edible part of sea urchin is limited, and the vast majority of the product ends up as waste. Our studies intend to fully recycle wastes from the food industry and reconvert them in high added-value products, as innovative biocompatible skin substitutes for tissue regeneration. The aim of the present work is to apply the pioneering skin substitute in in vivo experimental wounds to test its regenerative potential and compare it, in a future study, to the available commercial membranes produced with collagen of bovine, porcine, and equine origin. Results are encouraging since the skin substitute made with marine collagen reduced inflammation, promoted the deposition of granulation tissue, and enhanced a proper re-epithelialization with the adequate development of skin appendages. In summary, our findings might be of great interest for processing industries and biotech companies which transform waste materials in high-valuable and innovative products for Veterinary advanced applications.

Abstract

Skin wound healing is a complex and dynamic process that aims to restore lesioned tissues. Collagen-based skin substitutes are a promising treatment to promote wound healing by mimicking the native skin structure. Recently, collagen from marine organisms has gained interest as a source for producing biomaterials for skin regenerative strategies. This preliminary study aimed to describe the application of a collagen-based skin-like scaffold (CBSS), manufactured with collagen extracted from sea urchin food waste, to treat experimental skin wounds in a large animal. The wound-healing process was assessed over different time points by the means of clinical, histopathological, and molecular analysis. The CBSS treatment improved wound re-epithelialization along with cell proliferation, gene expression of growth factors (VEGF-A), and development of skin adnexa throughout the healing process. Furthermore, it regulated the gene expression of collagen type I and III, thus enhancing the maturation of the granulation tissue into a mature dermis without any signs of scarring as observed in untreated wounds. The observed results (reduced inflammation, better re-epithelialization, proper development of mature dermis and skin adnexa) suggest that sea urchin-derived CBSS is a promising biomaterial for skin wound healing in a “blue biotechnologies” perspective for animals of Veterinary interest.

Reconstruction of intraoral oncologic surgical defects with Integra® bilayer wound matrix

Utilization of biologic skin substitutes for the management of soft tissue defects as an alternative to autologous skin grafts has expanded over the past 2 decades. The purpose of this case series study was to report our experience with Integra® bilayer wound matrix for reconstruction of intraoral oncologic defects. Case records of 6 patients with intraoral oncologic defects reconstructed with Integra® bilayer wound matrix were retrospectively reviewed. The surgical defect location, size, and time to removal of surgical splint varied. Clinically, normal oral epithelialization was noted for all patients. One patient demonstrated a small area of dehiscence and bone exposure after adjuvant radiation therapy which resolved with minimal intervention. Integra bilayer wound matrix is a viable and versatile option for reconstruction of intraoral oncologic surgical defects. Further exploration of wound healing with Integra® matrix, surgical techniques, and cost-effectiveness is advocated.

Development of novel microenvironments for promoting enhanced wound healing

PURPOSE OF REVIEW

Nonhealing wounds are a significant issue facing the healthcare industry. Materials that modulate the wound microenvironment have the potential to improve healing outcomes.

RECENT FINDINGS

A variety of acellular and cellular scaffolds have been developed for regulating the wound microenvironment, including materials for controlled release of antimicrobials and growth factors, materials with inherent immunomodulative properties, and novel colloidal-based scaffolds. Scaffold construction methods include electrospinning, 3D printing, decellularization of extracellular matrix, or a combination of techniques. Material application methods include layering or injecting at the wound site.

SUMMARY

Though these techniques show promise for repairing wounds, all material strategies thus far struggle to induce regeneration of features such as sweat glands and hair follicles. Nonetheless, innovative technologies currently in the research phase may facilitate future attainment of these features. Novel methods and materials are constantly arising for the development of microenvironments for enhanced wound healing.

Complex approach to skin repair in an extensively burned child: a case study

The limited amount of donor sites and loss of dermis are major challenges in the therapy of extensively burned patients. Here, we present a complex treatment approach of an eight-year-old boy with full-thickness burns on 90% of the total body surface area, using simple and efficient techniques of tissue engineering. To obtain sufficient skin for grafting we repeatedly harvested the same anatomical areas. Acceleration of donor site healing was achieved by treatment with a suspension of noncultured autologous skin cells (NASC) and acellular porcine dermis (Xe-Derma (XD), Czech Republic). Moreover, such wound management allowed up to six reharvestings, compared with one-to-three procedures following routine treatment. Bilayer Integra template (Integra LifeSciences Corp., US) was used as the dermal substitute in over 60% of full-thickness burns. Following successful vascularisation of the neodermis in 3-4 weeks, the templates were covered with meshed split-thickness skin grafts (STSG), or Meek autografts, and facilitated by NASC/XD. We may conclude that such a 'sandwich' technique approach, combining four biological covers (Integra, STSG, NASC and XD), significantly contributed to the successful skin repair of the patient.

Advances in the Research of Bioinks Based on Natural Collagen, Polysaccharide and Their Derivatives for Skin 3D Bioprinting

The skin plays an important role in protecting the human body, and wound healing must be set in motion immediately following injury or trauma to restore the normal structure and function of skin. The extracellular matrix component of the skin mainly consists of collagen, glycosaminoglycan (GAG), elastin and hyaluronic acid (HA). Recently, natural collagen, polysaccharide and their derivatives such as collagen, gelatin, alginate, chitosan and pectin have been selected as the matrix materials of bioink to construct a functional artificial skin due to their biocompatible and biodegradable properties by 3D bioprinting, which is a revolutionary technology with the potential to transform both research and medical therapeutics. In this review, we outline the current skin bioprinting technologies and the bioink components for skin bioprinting. We also summarize the bioink products practiced in research recently and current challenges to guide future research to develop in a promising direction. While there are challenges regarding currently available skin bioprinting, addressing these issues will facilitate the rapid advancement of 3D skin bioprinting and its ability to mimic the native anatomy and physiology of skin and surrounding tissues in the future.

Biological characterization of dehydrated amniotic membrane allograft: Mechanisms of action and implications for wound care

There is a growing clinical demand in the wound care market to treat chronic wounds such as diabetic foot ulcers. Advanced cell and tissue-based products (CTPs) are often used to address challenging chronic wounds where healing has stalled. These products contain active biologics such as growth factors and cytokines as well as structural components that support and stimulate cell growth and assist in tissue regeneration. This study addresses the in vitro biologic effects of a clinically available dehydrated amniotic membrane allograft (DAMA). The broad mechanism of action results from DAMA's biologic composition that leads to stimulation of cell migration cell proliferation, and reduction of pro-inflammatory cytokines. Results show that DAMA possesses growth factors and cytokines such as EGF, FGF, PDGFs, VEGF, TGF-β, IL-8, and TIMPs 1 and 2. Furthermore, in vitro experiments demonstrate that DAMA stimulates cell proliferation, cell migration, secretion of collagen type I, and the reduction of pro-inflammatory cytokines IL-1β, IL-6, and TNF-α. This study findings are consistent with the clinical benefits previously published for DAMA and other CTPs in chronic wounds suggesting that the introduction of DAMA to non-healing, complex wounds helps to improve the wound milieu by providing essential structural components, cytokines, and growth factors to create an appropriate environment for wound healing.

Bacterial cellulose micro-nano fibres for wound healing applications

Bacterial cellulose (BC) is cellulose produced by a few limited species of bacteria in given conditions. BC has many remarkable properties such as its attractive mechanical properties, water uptake ability and biocompatibility which makes it a very desirable material to be used for wound healing. Inherently due to these important properties, the material is very resistant to easy processing and thus difficult to produce into useful entities. Additionally, being rate limited by the dependency on bacterial production, high yield is difficult to obtain and thus secondary material processing is sought after. In this review, BC is explained in terms of synthesis, structure and properties. These beneficial properties are directly related to the material's great potential in wound healing where it has also been trialled commercially but ultimately failed due to processing issues. However, more recently there has been increased frequency in scientific work relating to BC processing into hybrid polymeric fibres using common laboratory fibre forming techniques such as electrospinning and pressurised gyration. This paper summarises current progress in BC fibre manufacturing, its downfalls and also gives a future perspective on how the landscape should change to allow BC to be utilised in wound care in the current environment.

Combination of negative pressure wound therapy (NPWT) and integra dermal regeneration template (IDRT) in the lower extremity wound; Our experience with 4 cases

The treatment of de-gloving injuries in the lower limb with exposed tendons, bone, and/or nerve is a challenging reconstruction problem. The standard management of de-gloving injuries involve either direct closure if the skin is viable or immediate grafting with the avulsed skin or full- or split-thickness graft when the skin flap is not viable. Alternative methods are flap coverage especially when the underlying structures are not suitable for grafting such as extensive loss of paratenon and/or exposed bone or open joints The use of negative pressure wound therapy (NPWT) followed by use of Integra dermal regeneration template (IDRT) and subsequent split-thickness skin grafting (STSG) as an alternative to the previously mentioned surgical options has been described. In this series we describe the successful management of four patients with exposed tendons, bones, and joints of the distal lower extremity following road traffic accidents (RTA) using NPWT, Integra and thin split-thickness skin grafts.

Integra in Scalp Reconstruction After Tumor Excision: Recommendations From a Multidisciplinary Advisory Board

Integra is a dermal regeneration template used in the reconstruction of burns, traumatic injuries, or excision lesions in patients who present particular risk factors for traditional surgical procedures. A multidisciplinary advisory board of expert dermatologists and plastic surgeons have discussed the use of Integra in the reconstruction of scalp defects after tumor excision, focusing on the evidence derived from literature and on their experience in the treatment of approximately 400 patients. In this position paper, the authors summarize the main evidence discussed during the board, and the common practice guidelines proposed by the experts. The use of Integra is recommended in elderly patients with multiple comorbidities who have a higher risk for potential complications in traditional surgery; these patients may in fact benefit from a lower anesthetic risk, a less complicated postsurgical care and limited morbidity at the donor site obtained with the dermal template. Integra should also be used in the reconstruction of large and complex wounds and in case of bone exposure, as it helps to overcome the challenges related to wound healing in difficult areas. Notably, Integra has proven to be effective in patients who have undergone previous surgical procedures or adjuvant radiation therapy, in which previous incisions, scarring and radiation damages may hamper the effectiveness of traditional procedures. Finally, Integra is recommended in patients with recurrent and aggressive tumors who need closer tumor surveillance, as it gives easy access to the tumor site for oncologic follow-up examination.

A clinical trial with a novel collagen dermal substitute for wound healing in burn patients

Biomechanical properties of new dermal replacement were very similar than commercial products. Also this replacement can be used for skin regeneration for burn wounds. Therefore, we suggest that new dermal replacement can be used in the medical field.

In situ bioprinting - Bioprinting from benchside to bedside?

Bioprinting technologies have been advancing at the convergence of automation, digitalization, and new tissue engineering (TE) approaches. In situ bioprinting may be favored during certain situations when compared with the conventional in vitro bioprinting when de novo tissues are to be printed directly on the intended anatomical location in the living body. To date, few attempts have been made to fabricate in situ tissues, which can be safely arrested and immobilized while printing in preclinical living models. In this review, we have explained the need and utility for in situ bioprinting with regard to the conventional bioprinting approach. The two main in situ bioprinting approaches, namely, robotic arm and handheld approaches, have been defined and differentiated. The various studies involving in situ fabrication of skin, bone, and cartilage tissues have been elucidated. Finally, we have also discussed the advantages, challenges, and the prospects in the field of in situ bioprinting modalities in line with parallel technological advancements. STATEMENT OF SIGNIFICANCE: In situ bioprinting may be favored during certain situations when compared with the conventional in vitro bioprinting when tissues are to be fabricated or repaired directly on the intended anatomical location in the living body, using the body as a bioreactor. However, the technology requires a lot more improvement to fabricate complex tissues in situ, which could eventually be possible through the multi-disciplinary innovations in tissue engineering. This review explains the need and utility and current approaches by handheld and robotic modes for in situ bioprinting. The latest studies involving in situ fabrication of skin, bone, and cartilage tissues have been elucidated. The review also covers the background studies, advantages, technical and ethical challenges, and possible suggestions for future improvements.

Differentiation of Menstrual Blood Stem Cells into Keratinocyte-Like Cells on Bilayer Nanofibrous Scaffold

Skin tissue engineering is a high-throughput technology to heal the wounds. Already, considerable advances have been achieved using stem cells for wound healing applications. Menstrual blood stem cell (MenSC) is an available and accessible source of stem cells that have differentiation potential into a wide range of lineages like keratinocytes. Extracellular matrix like substratum plays an impressive role in skin regeneration as an attachment site for stem cells by transmitting the bioactive signals and provoking stem cells to differentiate into keratinocyte lineage. The biomimetic nanofibrous scaffold especially in bilayer format has been extensively utilized to develop skin equivalents. This chapter explains detailed protocols of keratinocyte differentiation of MenSCs on bilayer scaffold comprising amniotic membrane and fibroin nanofibers. The isolated MenSCs are seeded on the nanofibers and subsequently differentiated into keratinocyte lineage in co-culture with foreskin-derived keratinocytes. Immunofluorescence staining is used to evaluate the development of seeded MenSCs in bilayer scaffold into keratinocyte-like cells.

Wound Coverage Technologies in Burn Care: Established Techniques

Major advances in burn care have reduced post-burn morbidity and mortality. The development and incorporation of new wound healing modalities into the clinical arena have contributed to this improvement by allowing standard-of-care regimens to be established. These regimens range from early excision to the use of cultured epithelial autograft. Here, we review the wound care options that are now well established and used by many burn surgeons.

Application of acellular human dermis and skin grafts for lower extremity reconstruction

OBJECTIVE

To use both acellular human dermis and skin grafting simultaneously for improved skin grafting without contracture. The study also aims to address the lack of research on the application of an acellular human dermis in diverse clinical cases.

METHOD

The study examined patients who had received acellular human dermis (CGDerm, CGBio, Seoul, Korea) and split-thickness skin grafting (STSG) simultaneously for lower limb, full-thickness skin defects between September 2012 and June 2014. The researchers performed chart reviews retrospectively and examined the patients based on the following factors: gender, age, injury mechanism, size, exposed structure, pre-coverage dressing method, coverage method, post-operational engraftment and total healing period, contracture development, elasticity, and infection development.

RESULTS

A sample of 27 patients with a total of 30 wounds took part in the study. Of these wounds, 29 showed successful engraftment without infection or contracture. In one case, continued seroma was observed and, following new coverage of both the acellular human dermis and STSG, engraftment was successful.

CONCLUSION

Human dermis can play an important role in securing the availability of surrounding tissue and in contracture prevention, both of which are key to lower limb reconstruction. Of the types available, acellular human dermis showed lower infection rates than other human dermis types, and its engraftment rate was higher than in STSG-only cases. These findings suggest that acellular human dermis use in STSG is effective and safe in lower limb reconstruction.

Current Strategies and Future Perspectives of Skin-on-a-Chip Platforms: Innovations, Technical Challenges and Commercial Outlook

The skin is the largest and most exposed organ in the human body. Not only it is involved in numerous biological processes essential for life but also it represents a significant endpoint for the application of pharmaceuticals. The area of in vitro skin tissue engineering has been progressing extensively in recent years. Advanced in vitro human skin models strongly impact the discovery of new drugs thanks to the enhanced screening efficiency and reliability. Nowadays, animal models are largely employed at the preclinical stage of new pharmaceutical compounds development for both risk assessment evaluation and pharmacokinetic studies. On the other hand, animal models often insufficiently foresee the human reaction due to the variations in skin immunity and physiology. Skin-on-chips devices offer innovative and state-of-the-art platforms essential to overcome these limitations. In the present review, we focus on the contribution of skin-on-chip platforms in fundamental research and applied medical research. In addition, we also highlighted the technical and practical difficulties that must be overcome to enhance skin-on-chip platforms, e.g. embedding electrical measurements, for improved modeling of human diseases as well as of new drug discovery and development.