Bioengineering the microanatomy of human skin

Recent advances in the 3D skin bioprinting for regenerative medicine: Cells, biomaterials, and methods

The skin is a tissue constantly exposed to the risk of damage, such as cuts, burns, and genetic disorders. The standard treatment is autograft, but it can cause pain to the patient being extremely complex in patients suffering from burns on large body surfaces. Considering that there is a need to develop technologies for the repair of skin tissue like 3D bioprinting. Skin is a tissue that is approximately 1/16 of the total body weight and has three main layers: epidermis, dermis, and hypodermis. Therefore, there are several studies using cells, biomaterials, and bioprinting for skin regeneration. Here, we provide an overview of the structure and function of the epidermis, dermis, and hypodermis, and showed in the recent research in skin regeneration, the main cells used, biomaterials studied that provide initial support for these cells, allowing the growth and formation of the neotissue and general characteristics, advantages and disadvantages of each methodology and the landmarks in recent research in the 3D skin bioprinting.

Improving stability of human three dimensional skin equivalents using plasma surface treatment

In developing three-dimensional (3D) human skin equivalents (HSEs), preventing dermis and epidermis layer distortion due to the contraction of hydrogels by fibroblasts is a challenging issue. Previously, a fabrication method of HSEs was tested using a modified solid scaffold or a hydrogel matrix in combination with the natural polymer coated onto the tissue culture surface, but the obtained HSEs exhibited skin layer contraction and loss of the skin integrity and barrier functions. In this study, we investigated the method of HSE fabrication that enhances the stability of the skin model by using surface plasma treatment. The results showed that plasma treatment of the tissue culture surface prevented dermal layer shrinkage of HSEs, in contrast to the HSE fabrication using fibronectin coating. The HSEs from plasma-treated surface showed significantly higher transepithelial electrical resistance compared to the fibronectin-coated model. They also expressed markers of epidermal differentiation (keratin 10, keratin 14 and loricrin), epidermal tight junctions (claudin 1 and zonula occludens-1), and extracellular matrix proteins (collagen IV), and exhibited morphological characteristics of the primary human skins. Taken together, the use of plasma surface treatment significantly improves the stability of 3D HSEs with well-defined dermis and epidermis layers and enhanced skin integrity and the barrier functions.

Generation of Porcine and Rainbow Trout 3D Intestinal Models and Their Use to Investigate Astaxanthin Effects In Vitro

Astaxanthin (AST) is a natural compound derived from shellfish, microorganisms, and algae, with several healthy properties. For this reason, it is widely used in the diet of humans and animals, such as pigs, broilers, and fish, where its addition is related to its pigmenting properties. Moreover, AST's ability to reduce free radicals and protect cells from oxidative damage finds application during the weaning period, when piglets are exposed to several stressors. To better elucidate the mechanisms involved, here we generate ad hoc pig and rainbow trout in vitro platforms able to mimic the intestinal mucosa. The morphology is validated through histological and molecular analysis, while functional properties of the newly generated intestinal barriers, both in porcine and rainbow trout models, are demonstrated by measuring trans-epithelial electrical resistance and analyzing permeability with fluorescein isothiocyanate-dextran. Exposure to AST induced a significant upregulation of antioxidative stress markers and a reduction in the transcription of inflammation-related interleukins. Altogether, the present findings demonstrate AST's ability to interact with the molecular pathways controlling oxidative stress and inflammation both in the porcine and rainbow trout species and suggest AST's positive role in prevention and health.

Comparison of photodamage in non-pigmented and pigmented human skin equivalents exposed to repeated ultraviolet radiation to investigate the role of melanocytes in skin photoprotection

Introduction

Daily solar ultraviolet (UV) radiation has an important impact on skin health. Understanding the initial events of the UV-induced response is critical to prevent deleterious conditions. However, studies in human volunteers have ethical, technical, and economic implications that make skin equivalents a valuable platform to investigate mechanisms related to UV exposure to the skin. In vitro human skin equivalents can recreate the structure and function of in vivo human skin and represent a valuable tool for academic and industrial applications. Previous studies have utilised non-pigmented full-thickness or pigmented epidermal skin equivalents to investigate skin responses to UV exposure. However, these do not recapitulate the dermal-epidermal crosstalk and the melanocyte role in photoprotection that occurs in vivo. In addition, the UV radiation used in these studies is generally not physiologically representative of real-world UV exposure.

Methods

Well-characterised pigmented and non-pigmented skin equivalents that contain human dermal fibroblasts, endogenous secreted extracellular matrix proteins (ECM) and a well-differentiated and stratified epidermis have been developed. These constructs were exposed to UV radiation for ×5 consecutive days with a physiologically relevant UV dose and subsequently analysed using appropriate end-points to ascertain photodamage to the skin.

Results

We have described that repeated irradiation of full-thickness human skin equivalents in a controlled laboratory environment can recreate UV-associated responses in vitro, mirroring those found in photoexposed native human skin: morphological damage, tanning, alterations in epidermal apoptosis, DNA lesions, proliferation, inflammatory response, and ECM-remodelling.

Discussion

We have found a differential response when using the same UV doses in non-pigmented and pigmented full-thickness skin equivalents, emphasising the role of melanocytes in photoprotection.

Extra Virgin Olive Oil Phenolic Compounds Modulate the Gene Expression of Biomarkers Involved in Fibroblast Proliferation and Differentiation

Extra virgin olive oil phenolic compounds have been identified as possible biostimulant agents against different pathological processes, including alterations in healing processes. However, there is little evidence on the molecular mechanisms involved in this process. The aim was to analyse the effect of hydroxytyrosol, tyrosol, and oleocanthal on fibroblast gene expression. PCR was used to determine the expression of different differentiation markers, extracellular matrix elements, and growth factors in cultured human fibroblasts CCD-1064Sk treated with different doses of hydroxytyrosol (10-5 M and 10-6 M), tyrosol (10-5 M and 10-6 M), and oleocanthal (10-6 M and 10-7 M). After 24 h of hydroxytyrosol treatment, increased expression of connective tissue growth factor, fibroblast growth factor (FGF), platelet-derived growth factor, vascular endothelial growth factor, transforming growth factor β1 (TGF-β1), and their receptors was observed. Tyrosol and olecanthal modulated the expression of FGF and TGFβR1. All phytochemicals tested modified the expression of differentiation markers and extracellular matrix elements, increasing gene expression of actin, fibronectin, decorin, collagen I, and III. Phenolic compounds present in extra virgin olive could have a beneficial effect on tissue regeneration by modulating fibroblast physiology.

Novel microneedle platforms for the treatment of wounds by drug delivery: A review

The management and treatment of wounds are complex and pose a substantial financial burden to the patient. However, the complex environment of wounds leads to inadequate drug absorption to achieve the desired therapeutic effect. As a novel technological platform, microneedles are widely used in drug delivery because of their multiple drug loading, multistage drug release, and multiple designs of topology. This study systematically summarizes and analyzes the manufacturing methods and limitations of different microneedles, as well as the latest research advances in pain management, drug delivery, and healing promotion, and presents the challenges and opportunities for clinical applications. On this basis, the development of microneedles in external wound repair and management is envisioned, and it is hoped that this study can provide guidelines for the design of microneedle systems in different application contexts, including the selection of materials, preparation methods, and structural design, to achieve better healing and regeneration results.

Silk fibroin-derived electrospun materials for biomedical applications: A review

Electrospinning is a versatile technique for fabricating polymeric fibers with diameters ranging from micro- to nanoscale, exhibiting multiple morphologies and arrangements. By combining silk fibroin (SF) with synthetic and/or natural polymers, electrospun materials with outstanding biological, chemical, electrical, physical, mechanical, and optical properties can be achieved, fulfilling the evolving biomedical demands. This review highlights the remarkable versatility of SF-derived electrospun materials, specifically focusing on their application in tissue regeneration (including cartilage, cornea, nerves, blood vessels, bones, and skin), disease treatment (such as cancer and diabetes), and the development of controlled drug delivery systems. Additionally, we explore the potential future trends in utilizing these nanofibrous materials for creating intelligent biomaterials, incorporating biosensors and wearable sensors for monitoring human health, and also discuss the bottlenecks for its widespread use. This comprehensive overview illuminates the significant impact and exciting prospects of SF-derived electrospun materials in advancing biomedical research and applications.

Damaging effects of UVA, blue light, and infrared radiation: in vitro assessment on a reconstructed full-thickness human skin

Introduction

Exposure to solar radiation can cause a range of skin damage, including sunburn, erythema, skin carcinogenesis, the release of reactive oxygen species (ROS), inflammation, DNA damage, and photoaging. Other wavelengths beyond UVB, such as UVA, blue light, and infrared radiation, can also contribute to the harmful effects of solar radiation. Reconstructed full-thickness human skin has the potential to serve as effective predictive in vitro tools for evaluating the effects of solar radiation on the skin. The aim of this work was to evaluate the damaging effects of UVA, blue light, and infrared radiation in a full-thickness skin model in terms of viability, inflammation, photoaging, tissue damage, photocarcinogenesis.

Methods

Full thickness skin models were purchased from Henkel (Phenion FT; Düsseldorf, Germany), and irradiated with increasing doses of UVA, blue light, or infrared radiation. Different endpoints were analyzed on the tissues: Hematoxylin-eosin staining, inflammation mediators, photoaging-related dermal markers and oxidative stress marker GPX1, evaluated by real-time quantitative PCR, as well as photocarcinogenesis markers by Western Blot.

Results and Discussion

The results showed differential responses in cytokine release for each light source. In terms of photoaging biomarkers, collagen, metalloproteinases 1 and 9, elastin, and decorin were modulated by UVA and blue light exposure, while not all these markers were affected by infrared radiation. Furthermore, exposure to UVA and blue light induced loss of fibroblasts and modulation of the photocarcinogenesis markers p53 and p21. In conclusion, the presented results suggest that the various wavelengths of solar light have distinct and differential damaging effects on the skin. Understanding the differential effects of UVA, blue light, and infrared radiation can serve as a valuable tool to investigate the efficacy of photoprotective agents in full thickness skin models.

The frontline of alternatives to animal testing: novel in vitro skin model application in drug development and evaluation

The FDA Modernization Act 2.0 has brought nonclinical drug evaluation into a new era. In vitro models are widely used and play an important role in modern drug development and evaluation, including early candidate drug screening and preclinical drug efficacy and toxicity assessment. Driven by regulatory steering and facilitated by well-defined physiology, novel in vitro skin models are emerging rapidly, becoming the most advanced area in alternative testing research. The revolutionary technologies bring us many in vitro skin models, either laboratory-developed or commercially available, which were all built to emulate the structure of the natural skin to recapitulate the skin's physiological function and particular skin pathology. During the model development, how to achieve balance among complexity, accessibility, capability, and cost-effectiveness remains the core challenge for researchers. This review attempts to introduce the existing in vitro skin models, align them on different dimensions, such as structural complexity, functional maturity, and screening throughput, and provide an update on their current application in various scenarios within the scope of chemical testing and drug development, including testing in genotoxicity, phototoxicity, skin sensitization, corrosion/irritation. Overall, the review will summarize a general strategy for in vitro skin model to enhance future model invention, application, and translation in drug development and evaluation.

Development of a novel in vitro strategy to understand the impact of shaving on skin health: combining tape strip exfoliation and human skin equivalent technology

Introduction

The removal of unwanted hair is a widespread grooming practice adopted by both males and females. Although many depilatory techniques are now available, shaving remains the most common, despite its propensity to irritate skin. Current techniques to investigate the impact of shaving regimes on skin health rely on costly and lengthy clinical trials, which hinge on recruitment of human volunteers and can require invasive biopsies to elucidate cellular and molecular-level changes.

Methods

Well-characterised human skin equivalent technology was combined with a commonplace dermatological technique of tape stripping, to remove cellular material from the uppermost layer of the skin (stratum corneum). This method of exfoliation recapitulated aspects of razor-based shaving in vitro, offering a robust and standardised in vitro method to study inflammatory processes such as those invoked by grooming practices.

Results

Tape strip insult induced inflammatory changes in the skin equivalent such as: increased epidermal proliferation, epidermal thickening, increased cytokine production and impaired barrier function. These changes paralleled effects seen with a single dry razor pass, correlated with the number of tape strips removed, and were attenuated by pre-application of shaving foam, or post-application of moisturisation.

Discussion

Tape strip removal is a common dermatological technique, in this study we demonstrate a novel application of tape stripping, to mimic barrier damage and inflammation associated with a dry shave. We validate this method, comparing it to razor-based shaving in vitro and demonstrate the propensity of suitable shave- and skin-care formulations to mitigate damage. This provides a novel methodology to examine grooming associated damage and a platform for screening potential skin care formulations.

Requisite instruments for the establishment of three-dimensional epidermal human skin equivalents-A methods review

Human skin equivalents (HSEs) are three-dimensional skin organ culture models raised in vitro. This review gives an overview of common techniques for setting up HSEs. The HSE consists of an artificial dermis and epidermis. 3T3-J2 murine fibroblasts, purchased human fibroblasts or freshly isolated and cultured fibroblasts, together with other components, for example, collagen type I, are used to build the scaffold. Freshly isolated and cultured keratinocytes are seeded on top. It is possible to add other cell types, for example, melanocytes, to the HSE-depending on the research question. After several days and further steps, the 3D skin can be harvested. Additionally, we show possible markers and techniques for evaluation of artificial skin. Furthermore, we provide a comparison of HSEs to human skin organ culture, a model which employs human donor skin. We outline advantages and limitations of both models and discuss future perspectives in using HSEs.

The Progress in the Application of Dissolving Microneedles in Biomedicine

In recent years, microneedle technology has been widely used for the transdermal delivery of substances, showing improvements in drug delivery effects with the advantages of minimally invasive, painless, and convenient operation. With the development of nano- and electrochemical technology, different types of microneedles are increasingly being used in other biomedical fields. Recent research progress shows that dissolving microneedles have achieved remarkable results in the fields of dermatological treatment, disease diagnosis and monitoring, and vaccine delivery, and they have a wide range of application prospects in various biomedical fields, showing their great potential as a form of clinical treatment. This review mainly focuses on dissolving microneedles, summarizing the latest research progress in various biomedical fields, providing inspiration for the subsequent intelligent and commercial development of dissolving microneedles, and providing better solutions for clinical treatment.

Impact of the Physical Cellular Microenvironment on the Structure and Function of a Model Hepatocyte Cell Line for Drug Toxicity Applications

It is widely recognised that cells respond to their microenvironment, which has implications for cell culture practices. Growth cues provided by 2D cell culture substrates are far removed from native 3D tissue structure in vivo. Geometry is one of many factors that differs between in vitro culture and in vivo cellular environments. Cultured cells are far removed from their native counterparts and lose some of their predictive capability and reliability. In this study, we examine the cellular processes that occur when a cell is cultured on 2D or 3D surfaces for a short period of 8 days prior to its use in functional assays, which we term: "priming". We follow the process of mechanotransduction from cytoskeletal alterations, to changes to nuclear structure, leading to alterations in gene expression, protein expression and improved functional capabilities. In this study, we utilise HepG2 cells as a hepatocyte model cell line, due to their robustness for drug toxicity screening. Here, we demonstrate enhanced functionality and improved drug toxicity profiles that better reflect the in vivo clinical response. However, findings more broadly reflect in vitro cell culture practises across many areas of cell biology, demonstrating the fundamental impact of mechanotransduction in bioengineering and cell biology.

Constructing epidermal rete ridges using a composite hydrogel to enhance multiple signaling pathways for the maintenance of epidermal stem cell niche

The undulating microstructure rete ridge (RR) located at the junction between the dermis and epidermis plays a crucial role in improving skin mechanical properties and maintaining skin homeostasis. However, the investigation of RR microstructures is usually neglected in current tissue engineering for skin regeneration. Here, to create an epidermal model with RR microstructures, keratinocytes were cultured on a patterned GelMA-PEGDA hydrogel constructed using molding technology. Furthermore, grafting acryloylated Arg-Gly-Asp (RGD) peptides on the hydrogel surface significantly improved cell adhesion, fusion, and development. RT-PCR, Western blot, and immunofluorescence staining confirmed that cells on RR microstructures exhibited higher gene and protein expression associated with epidermal stem cells. RNA sequencing analysis of cells on RR microstructure showed higher gene expression profiles related to stem cell maintenance, basement membrane formation, and epidermal development. Furthermore, RT-PCR analysis of epidermal models of various dimensions demonstrated that smaller microstructures were more conducive to epidermal stem cell marker gene expression, which is analogous to human skin. Overall, we have successfully developed a method for integrating RR microstructures into an epidermal model that mimics natural skin to maintain epidermal stem cell niche, providing a valuable reference for researching skin regeneration within the fields of tissue engineering and regenerative medicine. STATEMENT OF SIGNIFICANCE: This study presents a method for precisely fabricating microstructures of skin rete ridges using composite hydrogels, thereby creating a skin model that mimics natural human skin. The findings reveal that this microstructure provides a stem cell niche that regulates the pathways and promotes the expression of proteins related to epidermal stem cells. This work advances the functional properties of tissue engineered skin and holds promise for improving the therapeutic efficacy of artificial skin grafts for the skin wounds.

Influence of adalimumab on interleukin 12/23 signalling pathways in human keratinocytes treated with lipopolysaccharide A

Introduction

The interleukin-12/23 (IL-12/23) signalling pathway plays an important role in the pathogenesis of psoriasis. In addition, even molecularly targeted therapy has been reported to lose adequate response to treatment.

Aim

To determine the expression patterns of mRNAs and miRNAs related to IL-12/23 signalling pathways in the human keratinocyte culture exposed to liposaccharide A (LPS) and then adalimumab in comparison with untreated cells.

Material and methods

Human, adult, low-Calcium, high-Temperature keratinocyte (HaCaT) cultures were exposed to 1 µg/ml LPS for 8 h, and then adalimumab was added to the cultures at a concentration of 8 µg/ml and incubated for 2, 8, and 24 h. We used mRNA and miRNA microarray, quantitative reverse transcription polymerase chain reaction, and enzyme-linked immunosorbent assay techniques.

Results

STAT1, STAT3, STAT5, IL-6, IL-6R, SOCS3, and JAK3 genes differentiated HaCaT cultures with the drug from controls regardless of the time the cells were exposed to the drug. The addition of adalimumab to a culture previously exposed to LPS resulted in silencing of SOCS3 and IL-6 expression compared to the control, while for the other transcripts they were found to be overexpressed compared to the control culture. The assessment indicated the strongest connections between JAK3 and hsa-miR-373-5p (target score 96); SOCS3, STAT5, and hsa-miR-1827 (target score 96).

Conclusions

Our study indicates that adalimumab has the strongest modulating effect on mRNA and miRNA expression of JAK/STAT and IL-6-dependent IL-12/23 pathways.

Recent advances in bacterial cellulose-based antibacterial composites for infected wound therapy

Wound infection arising from pathogenic bacteria brought serious trouble to the patient and medical system. Among various wound dressings that are effective in killing pathogenic bacteria, antimicrobial composites based on bacterial cellulose (BC) are becoming the most popular materials due to their success in eliminating pathogenic bacteria, preventing wound infection, and promoting wound healing. However, as an extracellular natural polymer, BC is not inherently antimicrobial, which means that it must be combined with other antimicrobials to be effective against pathogens. BC has many advantages over other polymers, including nano-structure, significant moisture retention, non-adhesion to the wound surface, which has made it superior to other biopolymers. This review introduces the recent advances in BC-based composites for the treatment of wound infection, including the classification and preparation methods of composites, the mechanism of wound treatment, and commercial application. Moreover, their wound therapy applications include hydrogel dressing, surgical sutures, wound healing bandages, and patches are summarized in detail. Finally, the challenges and future prospects of BC-based antibacterial composites for the treatment of infected wounds are discussed.

Generation of a novel three-dimensional scaffold-based model of the bovine endometrium

Bovine in vitro endometrial models that resemble tissue function in vivo are needed to study infertility, long-term uterine alterations induced by pathogens and impact of endocrine disruptor chemicals on reproductive function and other reproductive system complications that cause high economic losses in livestock species. The present study aimed to generate an innovative, reproducible, and functional 3D scaffold-based model of the bovine endometrium structurally robust for long term-culture. We developed a multicellular model containing both endometrial epithelial and stromal cells. Epithelial cells organized to form a luminal-like epithelial layer on the surface of the scaffold. Stromal cells produced their own extracellular matrix forming a stable subepithelial compartment that physiologically resembles the normal endometrium. Both cell types released prostaglandin E2 and prostaglandin F2α following a treatment with oxytocin and arachidonic acid. Additionally signal pathways mediating oxytocin and arachidonic acid stimulation of prostaglandin synthesis were analyzed by real time PCR (RT-PCR). Oxytocin receptor (OXTR), prostaglandin E2 receptor 2 (EP2), prostaglandin E2 receptor 4 (EP4), prostaglandin F receptor (PTGFR), prostaglandin E synthase (PTGES), PGF-synthase (PGFS) and prostaglandin-endoperoxide synthase 2 (COX-2) expression was detected in both control and treatment groups, however, only significant changes in abundance of OXTR mRNA transcripts were found. The results obtained by this study are a step forward in bovine in vitro culture technology. This 3D scaffold-based model provides a platform to study regulatory mechanisms involved in endometrial physiology and can set the basis for a broader tool for designing and testing novel therapeutic strategies for recurrent uterine pathologies.

Effect of stem cell secretome in skin rejuvenation: a narrative review

PURPOSE

Cutaneous aging is an inevitable biological process that develops over time due to cumulative cellular and molecular changes caused by exposure to intrinsic (chronological aging) and extrinsic (photo-aging) factors on the skin. Skin aging is characterized by a decline in the body's capability to sustain senescence, dermal cell apoptosis, and homeostasis. Stem cell secretions (secretome) are defined as the total set of dynamically overlapping paracrine soluble growth factors, cytokines, chemokines, angiogenic factors, extracellular matrix proteins, and antimicrobial peptides known to be responsible for tissue rejuvenation, regeneration, homeostasis, and immunomodulation.

METHODS

In this review, we summarized the molecular and regulatory mechanism of the secretome in preventing the skin aging process, as well as its capacity in inducing skin rejuvenation. Furthermore, we illustrated secretome efficiency as an anti-aging therapeutic strategy based on in vitro and in vivo published studies.

RESULTS

In all reviewed publications, the secretome has been proven to be the most effective treatment for aged skin, capable of reversing the aging process through the action of cytokines, growth factors, and collagen, which are its primary components. The reported mechanism of action involves modulating the signaling pathways of aging and replenishing the skin with collagen, fibronectin, and elastin, ultimately resulting in skin renewal and rejuvenation.

CONCLUSION

In conclusion, compared to available treatments, the secretome shows great promise as an anti-aging therapy.

Bioengineered skin organoids: from development to applications

Significant advancements have been made in recent years in the development of highly sophisticated skin organoids. Serving as three-dimensional models that mimic human skin, these organoids have evolved into complex structures and are increasingly recognized as effective alternatives to traditional culture models and human skin due to their ability to overcome the limitations of two-dimensional systems and ethical concerns. The inherent plasticity of skin organoids allows for their construction into physiological and pathological models, enabling the study of skin development and dynamic changes. This review provides an overview of the pivotal work in the progression from 3D layered epidermis to cyst-like skin organoids with appendages. Furthermore, it highlights the latest advancements in organoid construction facilitated by state-of-the-art engineering techniques, such as 3D printing and microfluidic devices. The review also summarizes and discusses the diverse applications of skin organoids in developmental biology, disease modelling, regenerative medicine, and personalized medicine, while considering their prospects and limitations.

Skin Bank Establishment in Treatment of Severe Burn Injuries: Overview and Experience with Skin Allografts at the Vienna Burn Center

Depending on their extent, burn injuries require different treatment strategies. In cases of severe large-area trauma, the availability of vital skin for autografting is limited. Donor skin allografts are a well-established but rarely standardized option for temporary wound coverage. Ten patients were eligible for inclusion in this retrospective study. Overall, 202 donor skin grafts obtained from the in-house skin bank were applied in the Department of Plastic and Reconstructive and Aesthetic Surgery, Medical University of Vienna. Between 2017 and 2022, we analysed the results in patient treatment, the selection of skin donors, tissue procurement, tissue processing and storage of allografts, as well as the condition and morphology of the allografts before application. The average Abbreviated Burn Severity Index (ABSI) was 8.5 (range, 5-12), and the mean affected total body surface area (TBSA) was 46.1% (range, 20-80%). In total, allograft application was performed 14 times. In two cases, a total of eight allografts were removed due to local infection, accounting for 3.96% of skin grafts. Six patients survived the acute phase of treatment. Scanning electron microscope images and histology showed no signs of scaffold decomposition and intact tissue layers of the allografts. The skin banking program and the application of skin allografts at the Vienna Burn Center can be considered successful. In severe burn injuries, skin allografts provide time by serving as sufficient wound coverage after early necrosectomy. Having an in-house skin banking program at a dedicated burn centre is particularly advantageous since issues of availability and distribution can be minimized. Skin allografts provide a reliable treatment option in patients with extensive burn injuries.

Obacunone Photoprotective Effects against Solar-Simulated Radiation-Induced Molecular Modifications in Primary Keratinocytes and Full-Thickness Human Skin

Solar radiation can cause damage to the skin, leading to various adverse effects such as sunburn, reactive oxygen species production, inflammation, DNA damage, and photoaging. To study the potential of photoprotective agents, full-thickness skin models are increasingly being used as in vitro tools. One promising approach to photoprotection involves targeting the redox-sensitive transcription factor Nrf2, which is responsible for regulating various cellular defense mechanisms, including the antioxidant response, inflammatory signaling, and DNA repair. Obacunone, a natural triterpenoid, has been identified as a potent Nrf2 agonist. The present study aims to evaluate the relevance of full-thickness (FT) skin models in photoprotection studies and to explore the potential photoprotective effects of obacunone on those models and in human keratinocytes. Phenion^® full-thickness skin models and keratinocytes were incubated with increasing concentrations of obacunone and irradiated with solar-simulated radiation (SSR). Various photodamage markers were evaluated, including histological integrity, oxidative stress, apoptosis, inflammation, photoaging-related dermal markers, and photocarcinogenesis markers. Increasing doses of SSR were found to modulate various biomarkers related to sun damage in the FT skin models. However, obacunone attenuated cytotoxicity, inflammation, oxidative stress, sunburn reaction, photoaging, and photocarcinogenesis in both keratinocytes and full thickness skin models exposed to SSR. These results suggest that obacunone may have potential as a photoprotective agent for preventing the harmful effects of solar radiation on the skin.

Microneedle-mediated treatment for superficial tumors by combining multiple strategies

Superficial tumors are still challenging to overcome due to the high risk and toxicity of surgery and conventional chemotherapy. Microneedles (MNs) are widely used in the treatment of superficial skin tumors (SST) due to the high penetration rate of the stratum corneum (SC), excellent biocompatibility, simple preparation process, high patient compliance, and minimal invasion. Most importantly, MNs can provide not only efficient and rarely painful delivery carriers, but also combine multi-model strategies with photothermal therapy (PTT), immunotherapy, and gene therapy for synergistic efficacy. To promote an in-depth understanding of their superiorities, this paper systematically summarized the latest application progress of MNs in the treatment of SST by delivering various types of photosensitizers, immune signal molecules, genes, and chemotherapy drugs. Just as important, the advantages, limitations, and drug release mechanisms of MNs based on different materials are introduced in the paper. In addition, the application of MN technology to clinical practice is the ultimate goal of all the work. The obstacles and possible difficulties in expanding the production of MNs and achieving clinical transformation are briefly discussed in this paper. To be anticipated, our work will provide new insights into the precise and rarely painful treatment of SST in the future.

Design and evaluation of a skin-on-a-chip pumpless microfluidic device

The development of microfluidic culture technology facilitates the progress of study of cell and tissue biology. This technology expands the understanding of pathological and physiological changes. A skin chip, as in vitro model, consisting of normal skin tissue with epidermis and dermis layer (full thickness) was developed. Polydimethylsiloxane microchannels with a fed-batched controlled perfusion feeding system were used to create a full-thick ex-vivo human skin on-chip model. The design of a novel skin-on-a-chip model was reported, in which the microchannel structures mimic the architecture of the realistic vascular network as nutrients transporter to the skin layers. Viabilities of full-thick skin samples cultured on the microbioreactor and traditional tissue culture plate revealed that a precise controlled condition provided by the microfluidic enhanced tissue viability at least for seven days. Several advantages in skin sample features under micro-scale-controlled conditions were found such as skin mechanical strength, water adsorption, skin morphology, gene expression, and biopsy longevity. This model can provide an in vitro environment for localizing drug delivery and transdermal drug diffusion studies. The skin on the chip can be a valuable in vitro model for representing the interaction between drugs and skin tissue and a realistic platform for evaluating skin reaction to pharmaceutical materials and cosmetic products.

Corneal epithelial basement membrane assembly is mediated by epithelial cells in coordination with corneal fibroblasts during wound healing

Purpose

To understand which cell types, either alone or in combination, contribute to the assembly of the epithelial basement membrane (BM) during corneal wound healing.

Methods

A 3D corneal organotypic model and an in situ rabbit photorefractive keratectomy (PRK) model were used in this study. The 3D corneal organotypic model was established by culturing the rabbit corneal epithelial cells with either corneal fibroblasts or myofibroblasts embedded in collagen type I for 18 days. Corneal fibroblasts were isolated from fresh rabbit corneas, and the myofibroblasts were derived either directly from bone marrow or differentiated from corneal fibroblasts. Immunocytochemistry for alpha-smooth muscle actin (SMA), vimentin, desmin, and vinculin markers confirmed well-differentiated myofibroblasts. Immunohistochemistry was performed in cryofixed sections for BM markers, including laminin alpha-5, laminin beta-3, perlecan, nidogen-1, and collagen type IV. Specimens were also examined with transmission electron microscopy (TEM). Corneas were collected from rabbits after -3 diopter (D) PRK at different time points after surgery, with four corneas at each time point in each group. Cryofixed corneal sections were stained for vimentin, alpha-SMA, and nidogen-1.

Results

The formation of an epithelial BM with expression of laminin alpha-5, laminin beta-3, perlecan, nidogen-1, and collagen IV was observed at the interface between the corneal epithelial cells and corneal fibroblasts. TEM images further confirmed the presence of epithelial BM in organotypic cultures of epithelial cells and corneal fibroblasts. No epithelial BM was observed in cultures of corneal epithelial cells and myofibroblasts (cornea or bone marrow derived), corneal epithelial cells alone, or corneal fibroblasts alone. In rabbit corneas after -3D PRK, a strong association was observed between the regenerating epithelial BM and the presence of corneal fibroblasts at the site of epithelial BM generation.

Conclusions

The corneal epithelial BM assembly is mediated by epithelial cells in coordination with corneal fibroblasts during wound healing.

Polycaprolactone Electrospun Nanofiber Membrane with Skin Graft Containing Collagen and Bandage Containing MgO Nanoparticles for Wound Healing Applications

The objective of this study was to create a nanofiber-based skin graft with an antimicrobial bandage that could accelerate the healing of an open wound while minimizing infection. To this end, we prepared a bi-layer construct where the top layer acts as bandage, and the bottom layer acts as a dermal equivalent graft. A collagen (CG) gel was combined without and with an electrospun polycaprolactone (PCL) membrane to prepare CG and CG-PCL dermal equivalent constructs. The antibacterial properties of PCL with and without an antibacterial agent (MgO nanoparticles) against Staphylococcus aureus (ATCC 6538) was also examined. Human dermal fibroblasts were cultured in each construct to make the dermal equivalent grafts. After culturing, keratinocytes were plated on top of the tissues to allow growth of an epidermis. Rheological and durability tests were conducted on in vitro dermal and skin equivalent cultures, and we found that PCL significantly affects CG-PCL graft biological and mechanical strength (rheology and durability). PCL presence in the dermal equivalent allowed sufficient tension generation to activate fibroblasts and myofibroblasts in the presence of transforming growth factor-beta. During culture of the skin equivalents, optical coherence tomography (OCT) showed layers corresponding to dermal and epidermal compartments in the presence or absence of PCL; this was confirmed after fixed specimens were histologically sectioned and stained. MgO added to PCL showed antibacterial activity against S. aureus. In vivo animal studies using a rat skin model showed that a polycaprolactone nanofiber bandage containing a type I collagen skin graft has potential for wound healing applications.

Interactions between Malassezia and New Therapeutic Agents in Atopic Dermatitis Affecting Skin Barrier and Inflammation in Recombinant Human Epidermis Model

Several studies have reported the pathogenic role of Malassezia in atopic dermatitis (AD); the significance of Malassezia’s influence on AD needs to be further investigated. Dupilumab, a monoclonal antibody to anti-Interleukin (IL) 4Rα, and ruxolitinib, a Janus kinase (JAK)1/2 inhibitor, are the first approved biologics and inhibitors widely used for AD treatment. In this study, we aimed to investigate how Malassezia Restricta (M. restricta) affects the skin barrier and inflammation in AD and interacts with the AD therapeutic agents ruxolitinib and anti-IL4Rα. To induce an in vitro AD model, a reconstructed human epidermis (RHE) was treated with IL-4 and IL-13. M. restricta was inoculated on the surface of RHE, and anti-IL4Rα or ruxolitinib was supplemented to model treated AD lesions. Histological and molecular analyses were performed. Skin barrier and ceramide-related molecules were downregulated by M. restricta and reverted by anti-IL4Rα and ruxolitinib. Antimicrobial peptides, VEGF, Th2-related, and JAK/STAT pathway molecules were upregulated by M. restricta and suppressed by anti-IL4Rα and ruxolitinib. These findings show that M. restricta aggravated skin barrier function and Th2 inflammation and decreased the efficacy of anti-IL4Rα and ruxolitinib.

Skin drug delivery using lipid vesicles: A starting guideline for their development

Lipid vesicles can provide a cost-effective enhancement of skin drug absorption when vesicle production process is optimised. It is an important challenge to design the ideal vesicle, since their properties and features are related, as changes in one affect the others. Here, we review the main components, preparation and characterization methods commonly used, and the key properties that lead to highly efficient vesicles for transdermal drug delivery purposes. We stand by size, deformability degree and drug loading, as the most important vesicle features that determine the further transdermal drug absorption. The interest in this technology is increasing, as demonstrated by the exponential growth of publications on the topic. Although long-term preservation and scalability issues have limited the commercialization of lipid vesicle products, freeze-drying and modern escalation methods overcome these difficulties, thus predicting a higher use of these technologies in the market and clinical practice.

Investigation into the effect of skin tone modulators and exogenous stress on skin pigmentation utilizing a novel bioengineered skin equivalent

Human skin equivalents (HSEs) are a popular technology due to limitations in animal testing, particularly as they recapitulate aspects of structure and function of human skin. Many HSEs contain two basic cell types to model dermal and epidermal compartments, however this limits their application, particularly when investigating the effect of exogenous stressors on skin health. We describe the development of a novel platform technology that accurately replicates skin pigmentation in vitro. Through incorporation of melanocytes, specialized pigment producing cells, into the basal layer of the epidermis we are able to re-create skin pigmentation in vitro. We observe apical distribution of melanin within keratinocytes and formation of supranuclear caps (SPNCs), only when the epidermal compartment is co-cultured with a dermal compartment, leading to the conclusion that fibroblast support is essential for correct pigment organization. We also evaluate the commonly observed phenomenon that pigmentation darkens with time in vitro, which we further explore through mechanical exfoliation to remove a build-up of melanin deposits in the stratum corneum. Finally, we demonstrate the application of a pigmented HSE to investigate drug modulation of skin tone and protection from UV-induced damage, highlighting the importance of such a model in the wider context of skin biology.

Regulation of epidermal proliferation and hair follicle cycling by synthetic photostable retinoid EC23

BACKGROUND

Retinoid signaling is an important regulator of the epidermis and skin appendages. Therefore, synthetic retinoids have been developed for therapeutic use for skin disorders such as psoriasis and acne.

AIMS

In previous studies, we showed how the photostable retinoid EC23 induces neuronal differentiation in stem cell-like cell populations, and here, we aim to investigate its ability to influence epidermal and hair follicle growth.

METHODS

EC23 influence on skin biology was investigated initially in cultures of monolayer keratinocytes and three-dimentional in vitro models of skin, and finally in in vivo studies of mice back skin.

RESULTS

EC23 induces keratinocyte hyperproliferation in vitro and in vivo, and when applied to mouse skin increases the number of involucrin-positive suprabasal cell layers. These phenotypic changes are similar in skin treated with the natural retinoid all-trans retinoic acid (ATRA); however, EC23 is more potent; a tenfold lower dose of EC23 is sufficient to induce epidermal thickening, and resulting hyperproliferation is sustained for a longer time period after first dose. EC23 treatment resulted in a disorganized stratum corneum, reduced cell surface lipids and compromised barrier, similar to ATRA treatment. However, EC23 induces a rapid telogen to anagen transition and hair re-growth in 6-week-old mice with synchronously resting back skin follicles. The impact of EC23 on the hair cycle was surprising as similar results have not been seen with ATRA.

CONCLUSIONS

These data suggest that synthetic retinoid EC23 is a useful tool in exploring the turnover and differentiation of cells and has a potent effect on skin physiology.

Mesenchymal stem cells express epidermal markers in an in vitro reconstructed human skin model

Introduction: In skin traumas, such as burns, epidermal homeostasis is affected, often requiring clinical approaches. Different therapeutic strategies can be used including transplantation, besides the use of synthetic or natural materials with allogeneic cells. In this context, tissue engineering is an essential tool for skin regeneration, and using mesenchymal stem cells (MSC) from the umbilical cord appears to be a promising strategy in regenerative medicine due to its renewal and differentiation potential and hypo immunogenicity. We evaluated the transdifferentiation of MSC from umbilical cord into keratinocytes in three-dimensional (3D) in vitro skin models, using dermal equivalents composed by type I collagen with dermal fibroblasts and a commercial porcine skin decellularized matrix, both cultured at air-liquid interface (ALI). Methods: The expression of epidermal proteins cytokeratins (CK) 5, 14 and 10, involucrin and filaggrin was investigated by real-time PCR and immunofluorescence, in addition to the activity of epidermal kallikreins (KLK) on the hydrolysis of fluorogenic substrates. Results and discussion: The cultivation of MSCs with differentiation medium on these dermal supports resulted in organotypic cultures characterized by the expression of the epidermal markers CK5, CK14, CK10 and involucrin, mainly on the 7^th day of culture, and filaggrin at 10^th day in ALI. Also, there was a 3-fold increase in the KLK activity in the epidermal equivalents composed by MSC induced to differentiate into keratinocytes compared to the control (MSC cultivated in the proliferation medium). Specifically, the use of collagen and fibroblasts resulted in a more organized MSC-based organotypic culture in comparison to the decellularized matrix. Despite the non-typical epithelium structure formed by MSC onto dermal equivalents, the expression of important epidermal markers in addition to the paracrine effects of these cells in skin may indicate its potential use to produce skin-based substitutes.

An improved human skin explant culture method for testing and assessing personal care products

BACKGROUND

Cultured human skin models have been widely used in the evaluation of dermato-cosmetic products as alternatives to animal testing and expensive clinical testing. The most common in vitro skin culture approach is to maintain skin biopsies in an airlifted condition at the interface of the supporting culture medium and the air phase. This type of ex vivo skin explant culture is not, however, adequate for the testing of cleansing products, such as shampoos and body washes. One major deficiency is that cleansing products would not remain confined on top of the epidermis and have a high chance of running off toward the dermal side, thus compromising the experimental procedure and data interpretation.

MATERIALS AND METHODS

Here, we describe an improved ex vivo method for culturing full-thickness human skin for the effective testing and evaluation of skin care products by topical application.

RESULTS

This newly developed ex vivo human skin culture method has the ability to maintain healthy skin tissues for up to 14 days in culture. Importantly, the model provides a quick and safe way to evaluate skin care products at different time points after single or repetitive topical applications using a combined regimen of leave-on and wash-off. We found that the results obtained using the new skin culture method are reproducible and consistent with the data collected from clinical testing.

CONCLUSION

Our new ex vivo skin explant method offers a highly efficient and cost-effective system for the evaluation and testing of a variety of personal care products and new formulations.

Development of a Vascularized Human Skin Equivalent with Hypodermis for Photoaging Studies

Photoaging is an important extrinsic aging factor leading to altered skin morphology and reduced function. Prior work has revealed a connection between photoaging and loss of subcutaneous fat. Currently, primary models for studying this are in vivo (human samples or animal models) or in vitro models, including human skin equivalents (HSEs). In vivo models are limited by accessibility and cost, while HSEs typically do not include a subcutaneous adipose component. To address this, we developed an "adipose-vascular" HSE (AVHSE) culture method, which includes both hypodermal adipose and vascular cells. Furthermore, we tested AVHSE as a potential model for hypodermal adipose aging via exposure to 0.45 ± 0.15 mW/cm² 385 nm light (UVA). One week of 2 h daily UVA exposure had limited impact on epidermal and vascular components of the AVHSE, but significantly reduced adiposity by approximately 50%. Overall, we have developed a novel method for generating HSE that include vascular and adipose components and demonstrated potential as an aging model using photoaging as an example.

Modeling human HSV infection via a vascularized immune-competent skin-on-chip platform

Herpes simplex virus (HSV) naturally infects skin and mucosal surfaces, causing lifelong recurrent disease worldwide, with no cure or vaccine. Biomimetic human tissue and organ platforms provide attractive alternatives over animal models to recapitulate human diseases. Combining prevascularization and microfluidic approaches, we present a vascularized, three-dimensional skin-on-chip that mimics human skin architecture and is competent to immune-cell and drug perfusion. The endothelialized microvasculature embedded in a fibroblast-containing dermis responds to biological stimulation, while the cornified epidermis functions as a protective barrier. HSV infection of the skin-on-chip displays tissue-level key morphological and pathophysiological features typical of genital herpes infection in humans, including the production of proinflammatory cytokine IL-8, which triggers rapid neutrophil trans-endothelial extravasation and directional migration. Importantly, perfusion with the antiviral drug acyclovir inhibits HSV infection in a dose-dependent and time-sensitive manner. Thus, our vascularized skin-on-chip represents a promising platform for human HSV disease modeling and preclinical therapeutic evaluation.

Emerging roles of keratinocytes in nociceptive transduction and regulation

Keratinocytes are the predominant block-building cells in the epidermis. Emerging evidence has elucidated the roles of keratinocytes in a wide range of pathophysiological processes including cutaneous nociception, pruritus, and inflammation. Intraepidermal free nerve endings are entirely enwrapped within the gutters of keratinocyte cytoplasm and form en passant synaptic-like contacts with keratinocytes. Keratinocytes can detect thermal, mechanical, and chemical stimuli through transient receptor potential ion channels and other sensory receptors. The activated keratinocytes elicit calcium influx and release ATP, which binds to P2 receptors on free nerve endings and excites sensory neurons. This process is modulated by the endogenous opioid system and endothelin. Keratinocytes also express neurotransmitter receptors of adrenaline, acetylcholine, glutamate, and γ-aminobutyric acid, which are involved in regulating the activation and migration, of keratinocytes. Furthermore, keratinocytes serve as both sources and targets of neurotrophic factors, pro-inflammatory cytokines, and neuropeptides. The autocrine and/or paracrine mechanisms of these mediators create a bidirectional feedback loop that amplifies neuroinflammation and contributes to peripheral sensitization.

Evaluation of native and non-native biomaterials for engineering human skin tissue

A variety of human skin models have been developed for applications in regenerative medicine and efficacy studies. Typically, these employ matrix molecules that are derived from non-human sources along with human cells. Key limitations of such models include a lack of cellular and tissue microenvironment that is representative of human physiology for efficacy studies, as well as the potential for adverse immune responses to animal products for regenerative medicine applications. The use of recombinant extracellular matrix proteins to fabricate tissues can overcome these limitations. We evaluated animal- and non-animal-derived scaffold proteins and glycosaminoglycans for the design of biomaterials for skin reconstruction in vitro. Screening of proteins from the dermal-epidermal junction (collagen IV, laminin 5, and fibronectin) demonstrated that certain protein combinations when used as substrates increase the proliferation and migration of keratinocytes compared to the control (no protein). In the investigation of the effect of components from the dermal layer (collagen types I and III, elastin, hyaluronic acid, and dermatan sulfate), the primary influence on the viability of fibroblasts was attributed to the source of type I collagen (rat tail, human, or bovine) used as scaffold. Furthermore, incorporation of dermatan sulfate in the dermal layer led to a reduction in the contraction of tissues compared to the control where the dermal scaffold was composed primarily of collagen type I. This work highlights the influence of the composition of biomaterials on the development of complex reconstructed skin models that are suitable for clinical translation and in vitro safety assessment.

Design considerations of benchtop fluid flow bioreactors for bio-engineered tissue equivalents in vitro

One of the major aims of bio-engineering tissue equivalents in vitro is to create physiologically relevant culture conditions to accurately recreate the cellular microenvironment. This often includes incorporation of factors such as the extracellular matrix, co-culture of multiple cell types and three-dimensional culture techniques. These advanced techniques can recapitulate some of the properties of tissue in vivo, however fluid flow is a key aspect that is often absent. Fluid flow can be introduced into cell and tissue culture using bioreactors, which are becoming increasingly common as we seek to produce increasingly accurate tissue models. Bespoke technology is continuously being developed to tailor systems for specific applications and to allow compatibility with a range of culture techniques. For effective perfusion of a tissue culture many parameters can be controlled, ranging from impacts of the fluid flow such as increased shear stress and mass transport, to potentially unwanted side effects such as temperature fluctuations. A thorough understanding of these properties and their implications on the culture model can aid with a more accurate interpretation of results. Improved and more complete characterisation of bioreactor properties will also lead to greater accuracy when reporting culture conditions in protocols, aiding experimental reproducibility, and allowing more precise comparison of results between different systems. In this review we provide an analysis of the different factors involved in the development of benchtop flow bioreactors and their potential biological impacts across a range of applications.

The ROC skin model: a robust skin equivalent for permeation and live cell imaging studies

Rat Epidermal Keratinocyte (REK) Organotypic Culture (ROC) is an epidermis model that is robust and inexpensive to develop and maintain, and it has in previous studies been shown to have permeability characteristics close to those of human skin. Here, we characterize the model further by structural comparison to native human and rat skin and by investigating functional characteristics of lipid packing, polarity, and permeability coefficients. We show that the ROC model has structural similarities to native human skin and observe human skin-like permeability coefficients for testosterone and mannitol. We develop a transwell device that allows live cell microscopy of the tissue at the air-liquid interface and establish transgenic cell lines expressing different fluorescently tagged proteins. This enables showing the migration of keratinocytes during the first days after seeding, finding that keratinocytes have a higher mean migration rate in the earlier days of development. Collectively, our results show that the ROC model is an inexpensive and robust epidermis model that works reproducibly across laboratories.

Development, characterization and in vivo evaluation of the ointment containing hyaluronic acid for potential wound healing applications

Wound healing is a complex biological process. In this context, hyaluronic acid (HA) plays an important role in all phases of wound healing, from inflammation to the remodelling process. Nevertheless, its presence in adults decreases by 50% compared to newborns, which drastically reduces tissue regeneration. In this sense, this work presented a new method of extracting HA from chicken combs, as well as the development and in vivo evaluation of an ointment composed of vaseline, lanolin and HA 1% (w/w) for wound healing. The rheological analysis showed that the ointment containing HA has a viscoelastic behaviour. The in vivo test showed on the 7^th day that the group treated with the ointment containing HA had a wound area of 0.07 cm² against 0.09 cm² of the ointment without HA (vaseline, and lanolin). On the other hand, the groups treated with the HA ointment had a higher mean percentage of collagen and better healing on the 14^th day. The results of this paper indicate that the new method used to obtain HA is feasible, low-cost, and easy to obtain. Furthermore, the HA containing ointment improved wound healing. Therefore, the obtained ointment has great potential for use as an effective biomaterial in wound healing.

Reconstructed human pigmented skin/epidermis models achieve epidermal pigmentation through melanocore transfer

The skin acts as a barrier to environmental insults and provides many vital functions. One of these is to shield DNA from harmful ultraviolet radiation, which is achieved by skin pigmentation arising as melanin is produced and dispersed within the epidermal layer. This is a crucial defence against DNA damage, photo‐ageing and skin cancer. The mechanisms and regulation of melanogenesis and melanin transfer involve extensive crosstalk between melanocytes and keratinocytes in the epidermis, as well as fibroblasts in the dermal layer. Although the predominant mechanism of melanin transfer continues to be debated and several plausible models have been proposed, we and others previously provided evidence for a coupled exo/phagocytosis model. Herein, we performed histology and immunohistochemistry analyses and demonstrated that a newly developed full‐thickness three‐dimensional reconstructed human pigmented skin model and an epidermis‐only model exhibit dispersed pigment throughout keratinocytes in the epidermis. Transmission electron microscopy revealed melanocores between melanocytes and keratinocytes, suggesting that melanin is transferred through coupled exocytosis/phagocytosis of the melanosome core, or melanocore, similar to our previous observations in human skin biopsies. We, therefore, present evidence that our in vitro models of pigmented human skin show epidermal pigmentation comparable to human skin. These findings have a high value for studies of skin pigmentation mechanisms and pigmentary disorders, whilst reducing the reliance on animal models and human skin biopsies.

Ciprofloxacin-loaded dissolving polymeric microneedles as a potential therapeutic for the treatment of S. aureus skin infections

Microneedles have been widely studied for many topical and transdermal therapeutics due to their ability to painlessly puncture the skin, thereby bypassing the stratum corneum, the main skin barrier. In this study, ciprofloxacin (CIP) was loaded into dissolving polymeric microneedles prepared by a two-layer centrifugation method as a potential treatment of skin infections such as cellulitis. The polymers used were polyvinyl alcohol (PVA) and polyvinylpyrrolidone (PVP). Two formulations were investigated, namely CIP_MN1, composed of 10 mg ciprofloxacin incorporated into a polymer matrix of PVA and PVP with a weight ratio of (9:1), and CIP_MN2, composed of 10 mg ciprofloxacin incorporated into PVA polymer. CIP_MN1 and CIP_MN2 showed a mean microneedle height of 188 and 179 µm, respectively. Since Parafilm has been proven as a model to examine the perforation of microneedles in skin, it was used to evaluate the ability of microneedles to perforate the skin. CIP_MN1 showed almost complete perforation of Parafilm, 190 pores, compared to CIP_MN2 which created only 85 pores in Parafilm, and therefore CIP_MN1 was used for subsequent studies. Examining CIP_MN1 on agarose gel as an in vitro model of human skin showed that the formula was able to fully perforate the agarose gel. Moreover, this formula showed significantly greater antimicrobial activity (p < 0.0001) compared to a free gel of ciprofloxacin against Staphylococcus aureus in an agarose gel-based model. This was evidenced by a zone of inhibition of 29 mm for the microneedle formulation of ciprofloxacin (CIP_MN1) compared to 2 mm for the free gel of ciprofloxacin. Furthermore, the CIP_MN1 showed complete dissolution in human skin after 60 min from application. Finally, the skin deposition of CIP_MN1 was investigated in ex vivo excised human skin. CIP_MN1 showed significantly more deposition of ciprofloxacin in deeper skin layers compared to the free gel of ciprofloxacin, and the released ciprofloxacin from the microneedles tends to migrate to deeper layers with time. Collectively, these results suggest that CIP_MN1 can be a potential delivery system for the treatment of S. aureus skin infections.

Protective Mechanisms of Liquid Formulations for Gastro-Oesophageal Reflux Disease in a Human Reconstructed Oesophageal Epithelium Model

Purpose

A novel experimental design based on a human-reconstructed oesophageal epithelium (HO2E) model has been applied to quantitively assess the properties of a set of liquid formulations, Device A (Gerdoff^® Protection), Device B (Esoxx^® One), and Device C (Marial^® gel) developed to form a temporary physical barrier on the oesophageal epithelium and modify epithelial permeability so to protect the oesophageal mucosa from refluxate components.

Methods

The formulations were applied to a prewetted HO2E model for 15 min. Then, a 0.5% caffeine solution was applied, and its penetration kinetics was assessed at 1 h and 2 h in acidic environments (pH= 3.3) to mirror exposure of the oesophageal mucosa to acidic reflux in GORD patients. Caffeine permeated into the basolateral compartment (evaluated by HPLC-UV) and Lucifer yellow (LY) permeability were quantified 15 min after application of the caffeine in acidic environments.

Results

At the 15 min timepoint, Device A reduced caffeine permeation by 77.2% and LY flux by 30.4% compared to the untreated control and with a faster mode of action than that of the other liquid formulations. Transepithelial caffeine flux was reduced, albeit with different timing and efficiency, by all three compounds up to the end of the 2 hour experiment. At 1 h, Device A reduced the caffeine flux by 79.2%; Device B, by 67.2%; and Device C, by 37%.

Conclusion

These results confirm the ability of the medical devices tested to interact with the oesophageal epithelium and create a temporary physical protective film for up to 2 hours after their application. The results underline differences in the mechanism of action of the three medical devices, with Device A performing faster than the other formulations. The overall results support the relevance of the reconstructed mucosal model to investigate oesophageal epithelium–product interactions and precisely differentiate liquid formulation performance.

Skin-on-a-Chip Technology: Microengineering Physiologically Relevant In Vitro Skin Models

The increased demand for physiologically relevant in vitro human skin models for testing pharmaceutical drugs has led to significant advancements in skin engineering. One of the most promising approaches is the use of in vitro microfluidic systems to generate advanced skin models, commonly known as skin-on-a-chip (SoC) devices. These devices allow the simulation of key mechanical, functional and structural features of the human skin, better mimicking the native microenvironment. Importantly, contrary to conventional cell culture techniques, SoC devices can perfuse the skin tissue, either by the inclusion of perfusable lumens or by the use of microfluidic channels acting as engineered vasculature. Moreover, integrating sensors on the SoC device allows real-time, non-destructive monitoring of skin function and the effect of topically and systemically applied drugs. In this Review, the major challenges and key prerequisites for the creation of physiologically relevant SoC devices for drug testing are considered. Technical (e.g., SoC fabrication and sensor integration) and biological (e.g., cell sourcing and scaffold materials) aspects are discussed. Recent advancements in SoC devices are here presented, and their main achievements and drawbacks are compared and discussed. Finally, this review highlights the current challenges that need to be overcome for the clinical translation of SoC devices.

Fully Synthetic 3D Fibrous Scaffolds for Stromal Tissues-Replacement of Animal-Derived Scaffold Materials Demonstrated by Multilayered Skin

The extracellular matrix (ECM) of soft tissues in vivo has remarkable biological and structural properties. Thereby, the ECM provides mechanical stability while it still can be rearranged via cellular remodeling during tissue maturation or healing processes. However, modern synthetic alternatives fail to provide these key features among basic properties. Synthetic matrices are usually completely degraded or are inert regarding cellular remodeling. Based on a refined electrospinning process, a method is developed to generate synthetic scaffolds with highly porous fibrous structures and enhanced fiber-to-fiber distances. Since this approach allows for cell migration, matrix remodeling, and ECM synthesis, the scaffold provides an ideal platform for the generation of soft tissue equivalents. Using this matrix, an electrospun-based multilayered skin equivalent composed of a stratified epidermis, a dermal compartment, and a subcutis is able to be generated without the use of animal matrix components. The extension of classical dense electrospun scaffolds with high porosities and motile fibers generates a fully synthetic and defined alternative to collagen-gel-based tissue models and is a promising system for the construction of tissue equivalents as in vitro models or in vivo implants.

Association between the chronology of gestation and the morphometrical skin characteristics at childbirth: a development of predictive model

Objective

The structural maturation of the skin is considered a potential marker of pregnancy dating. This study investigated the correlation between the morphometrical skin characteristics with the pregnancy chronology to propose models for predicting gestational age.

Methods

A cross-sectional analysis selected 35 corpses of newborns. The biopsy was performed up to 48 hours after death in the periumbilical abdomen, palm and sole regions. Pregnancy chronology was based on the obstetric ultrasound before 14 weeks. The dimensions of the skin layers, area of glands and connective fibrous tissue were measured with imaging software support. Univariate and multivariate regression models on morphometric values were used to predict gestational age.

Results

Gestational age at birth ranged from 20.3 to 41.2 weeks. Seventy-one skin specimens resulted in the analysis of 1183 digital histological images. The correlation between skin thickness and gestational age was positive and strong in both regions of the body. The highest univariate correlation between gestational age and skin thickness was using the epidermal layer dimensions, in palm (r=0.867, p<0.001). The multivariate modelling with the thickness of the abdominal epidermis, the dermis and the area of the sebaceous glands adjusted had the highest correlation with gestational age (r=0.99, p<0.001).

Conclusion

The thickness of the protective epidermal barrier is, in itself, a potential marker of pregnancy dating. However, sets of values obtained from skin morphometry enhanced the estimation of the gestational age. Such findings may support non-invasive image approaches to estimate pregnancy dating with various clinical applications.

The biological applications of DNA nanomaterials: current challenges and future directions

DNA, a genetic material, has been employed in different scientific directions for various biological applications as driven by DNA nanotechnology in the past decades, including tissue regeneration, disease prevention, inflammation inhibition, bioimaging, biosensing, diagnosis, antitumor drug delivery, and therapeutics. With the rapid progress in DNA nanotechnology, multitudinous DNA nanomaterials have been designed with different shape and size based on the classic Watson-Crick base-pairing for molecular self-assembly. Some DNA materials could functionally change cell biological behaviors, such as cell migration, cell proliferation, cell differentiation, autophagy, and anti-inflammatory effects. Some single-stranded DNAs (ssDNAs) or RNAs with secondary structures via self-pairing, named aptamer, possess the ability of targeting, which are selected by systematic evolution of ligands by exponential enrichment (SELEX) and applied for tumor targeted diagnosis and treatment. Some DNA nanomaterials with three-dimensional (3D) nanostructures and stable structures are investigated as drug carrier systems to delivery multiple antitumor medicine or gene therapeutic agents. While the functional DNA nanostructures have promoted the development of the DNA nanotechnology with innovative designs and preparation strategies, and also proved with great potential in the biological and medical use, there is still a long way to go for the eventual application of DNA materials in real life. Here in this review, we conducted a comprehensive survey of the structural development history of various DNA nanomaterials, introduced the principles of different DNA nanomaterials, summarized their biological applications in different fields, and discussed the current challenges and further directions that could help to achieve their applications in the future.

The Keratinocyte as a Crucial Cell in the Predisposition, Onset, Progression, Therapy and Study of the Atopic Dermatitis

The keratinocyte (KC) is the main functional and structural component of the epidermis, the most external layer of the skin that is highly specialized in defense against external agents, prevention of leakage of body fluids and retention of internal water within the cells. Altered epidermal barrier and aberrant KC differentiation are involved in the pathophysiology of several skin diseases, such as atopic dermatitis (AD). AD is a chronic inflammatory disease characterized by cutaneous and systemic immune dysregulation and skin microbiota dysbiosis. Nevertheless, the pathological mechanisms of this complex disease remain largely unknown. In this review, we summarize current knowledge about the participation of the KC in different aspects of the AD. We provide an overview of the genetic predisposing and environmental factors, inflammatory molecules and signaling pathways of the KC that participate in the physiopathology of the AD. We also analyze the link among the KC, the microbiota and the inflammatory response underlying acute and chronic skin AD lesions.