The Importance of Mimicking Dermal-Epidermal Junction for Skin Tissue Engineering: A Review

Recombinant human collagen XVII protects skin basement membrane integrity by inhibiting the MAPK and Wnt signaling pathways

Collagen XVII is a key component linking the cytoskeleton to the basement membrane, serving an essential role in maintaining skin integrity. With the advancement of synthetic biology, recombinant human collagen XVII (RHCXVII) has emerged as a promising novel collagen material. The present study aimed to elucidate the efficacy and mechanisms of action of RHCXVII in protecting skin basement membrane integrity. A skin injury model was established using ultraviolet B (UVB) irradiation on human HaCaT keratinocytes treated with RHCXVII. The effects of RHCXVII on cell migration and adhesion were assessed using wound healing assay and hematoxylin and eosin staining, respectively. The expression of key extracellular matrix (ECM) components such as collagen IV, collagen VII, laminin 332 and integrin α6 (ITGA6) were quantified using reverse transcription‑quantitative PCR and western blotting. The mechanism of action of RHCXVII in protecting skin basement membrane integrity was investigated using a phosphorylated‑antibody array and verified by western blotting. RHCXVII significantly increased the migration and adhesion of UVB‑irradiated HaCaT cells (P<0.01). Additionally, RHCXVII significantly upregulated expression levels of collagen type IV α1 chain, collagen type VII α1 chain, laminin subunit β3 and ITGA6 in UVB‑irradiated HaCaT cells (P<0.05). RHCXVII significantly inhibited the phosphorylation of p38 and c‑Jun in the MAPK and Wnt signaling pathways (P<0.01). In conclusion, RHCXVII protected skin basement membrane integrity by enhancing migration and adhesion of keratinocytes, upregulating key ECM components and inhibiting protein phosphorylation in MAPK and Wnt pathways. The present study enhanced the current understanding of RHCXVII as a protector of skin basement membrane integrity. Furthermore, the present study highlighted clinical implications and the broad therapeutic potential of RHCXVII in both medical and cosmetic application.

Long-Term Outcomes of a Cultured Autologous Dermo-Epidermal Skin Substitute in Children: 5-Year Results of a Phase I Clinical Trial

Limited donor sites and poor long-term outcomes with standard treatment for large skin defects remain a huge problem. An autologous, bilayered, laboratory-grown skin substitute (denovoSkin) was developed to overcome this problem and has shown to be safe in 10 pediatric patients in a Phase I clinical trial after transplantation. The goal of this article was to report on 48-month long-term results. The pediatric participants of the phase I clinical trial were followed up at yearly visits up to 5 years after transplantation. Safety parameters, including the occurrence of adverse events, possible deviations of vital signs, and changes in concomitant therapy as well as additional parameters regarding skin stability, scar quality, and tumor formation, were assessed. Furthermore, scar maturation was photographically documented. Of the 10 patients treated with denovoSkin in this phase I clinical trial, 7 completed the 5-year follow-up period. Skin substitutes continued to be deemed safe, remained stable, and practically unchanged, with no sign of fragility and no tumor formation at clinical examination. Scar quality, captured using the Patient and Observer Scar Assessment Scale, was evaluated as close to normal skin. Transplantation of this laboratory-grown skin substitute in children is to date considered safe and shows encouraging functional and aesthetical long-term results close to normal skin. These results are promising and highlight the potential of a life-saving therapy for large skin defects. A multicentre, prospective, randomized, phase II clinical trial is currently ongoing to further evaluate the safety and efficacy of this novel skin substitute. Clinicaltrials.gov identifier NCT02145130.

Functional tissue units in the Human Reference Atlas

Functional tissue units form the basic building blocks of organs and are important for understanding and modeling the healthy physiological function of the organ and changes that occur during disease states. In this comprehensive catalog of 22 anatomically based, nested functional tissue units from 10 healthy human organs, we document the definition, physical dimensions, blood vasculature connections, and cellular composition. All anatomy terms are mapped to the multi-species Uber-anatomy Ontology (Uberon) and cells are mapped to Cell Ontology to support computational access via standardized metadata. The catalog includes datasets, illustrations, and a large printable poster illustrating how the blood vasculature connects the 22 functional tissue units in 10 organs. All data and code are freely available. The work is part of an ongoing international effort to construct a Human Reference Atlas of the 37 trillion cells that make up the healthy human body.

Subcutaneous depth-selective spectral imaging with mμSORS enables noninvasive glucose monitoring

Noninvasive blood glucose monitoring offers substantial advantages for patients, but current technologies are often not sufficiently accurate for clinical applications or require personalized calibration. Here we report multiple μ-spatially offset Raman spectroscopy, which captures Raman signals at varying skin depths, and show that it accurately detects blood glucose levels in humans. In 35 individuals with or without type 2 diabetes, we first determine the optimal depth for glucose detection to be at or below the capillary-rich dermal-epidermal junction, where we observe a strong correlation between specific Raman bands and venous plasma glucose concentrations. In a second study, comprising 230 participants, we then improve accuracy of our regression model to reach a mean absolute relative difference of 14.6%, without personalized calibration, whereby 99.4% of calculated glucose values fall into clinically acceptable zones of the consensus error grid (zones A and B). These findings highlight the ability and robustness of multiple μ-spatially offset Raman spectroscopy for noninvasive blood glucose measurement in a clinical setting.

pH-responsive hydrogel with dual-crosslinked network of polyvinyl alcohol/boric acid for controlled release of salvianolic acid B: novel pro-regenerative mechanisms in scar inhibition and wound healing

This study investigates a novel pH-responsive hydrogel composed of polyvinyl alcohol (PVA) and boric acid (BA) designed for the controlled release of salvianolic acid B (SAB), addressing the critical challenge of scar formation and skin regeneration. The dual-crosslinked network architecture of the hydrogel exhibits remarkable pH sensitivity, enabling it to achieve a peak SAB release within 48 hours in the acidic microenvironment characteristic of early-stage wound healing. In vitro assessments demonstrated that the PVA-BA-SAB hydrogel significantly inhibits fibroblast activation and mitigates abnormal collagen deposition, effectively preventing excessive scar formation. Transcriptome sequencing reveals the potential role of PVA-BA-SAB hydrogel in balancing TGF-β and Wnt signaling pathways. Furthermore, in vivo studies revealed enhanced tissue regeneration, characterized by improved collagen organization and increased vascularization, as well as the promotion of mature hair follicle development. The hydrogel's biocompatibility, mechanical robustness and adhesive properties were also thoroughly evaluated, confirming its suitability for clinical applications. These findings suggest that the PVA-BA-SAB hydrogel fully exerts the excellent characteristics of biomaterials and maximizes the pharmacological effect of SAB. Our innovative drug delivery system not only facilitates enhanced wound healing but also offers a strategic approach to minimize scarring. This research provides valuable insights into innovative therapeutic strategies for effective wound management and tissue repair.

3D Bioprinting a Novel Skin Co-Culture Model Using Human Keratinocytes and Fibroblasts

3D bioprinting can generate the organized structures found in human skin for a variety of biological, medical, and pharmaceutical applications. Challenges in bioprinting skin include printing different types of cells in the same construct while maintaining their viability, which depends on the type of bioprinter and bioinks used. This study evaluated a novel 3D bioprinted skin model containing human keratinocytes (HEKa) and human dermal fibroblasts (HDF) in co-culture (CC) using a high-viscosity fibrin-based bioink produced using the BioX extrusion-based bioprinter. The constructs containing HEKa or HDF cells alone (control groups) and in CC were evaluated at 1, 10, and 20 days after bioprinting for viability, immunocytochemistry for specific markers (K5 and K10 for keratinocytes; vimentin and fibroblast specific protein [FSP] for fibroblasts). The storage, loss modulus, and viscosity properties of the constructs were also assessed to compare the effects of keratinocytes and fibroblasts individually and combined, providing important insights when bioprinting skin. Our findings revealed significantly higher cell viability in the CC group compared to individual keratinocyte and fibroblast groups, suggesting the combined cell presence enhanced survival rates. Additionally, proliferation rates of both cell types remained consistent over time, indicating non-competitive growth within the construct. Interestingly, keratinocytes exhibited a greater impact on the viscoelastic properties of the construct compared to fibroblasts, likely due to their larger size and arrangement. These insights contribute to optimizing bioprinting strategies for skin tissue engineering and emphasize the important role of different cell types in 3D skin models.

Long-Term Histological Evaluation of a Novel Dermal Template in the Treatment of Pediatric Burns

For pediatric patients with full-thickness burns, achieving adequate dermal regeneration is essential to prevent inelastic scars that may hinder growth. Traditional autologous split-thickness skin grafts alone often fail to restore the dermal layer adequately. This study evaluates the long-term effect of using a NovoSorb® Biodegradable Temporizing Matrix (BTM) as a dermal scaffold in four pediatric patients, promoting dermal formation before autografting. Pediatric burn patients treated at the University Children's Hospital Zurich between 2020 and 2022 underwent a two-step treatment involving NovoSorb® BTM application, followed by autografting. Histological analysis, conducted through 22 punch biopsies taken up to 2.6 years post-application, demonstrated robust dermal reorganization, with mature epidermal regeneration and stable dermo-epidermal connections. Immunofluorescence staining showed rapid capillary ingrowth, while extracellular matrix components, including collagen and elastic fibers, gradually aligned over time, mimicking normal skin structure. By 2.6 years, the dermal layer displayed characteristics close to uninjured skin, with remnants of NovoSorb® BTM degrading within five months post-application. This study suggests that NovoSorb® BTM facilitates elastic scar formation, offering significant benefits for pediatric patients by reducing functional limitations associated with inelastic scarring.

Ectoin attenuates cortisone-induced skin issues by suppression GR signaling and the UVB-induced overexpression of 11β-HSD1

BACKGROUND

Accelerated pace of modern work and lifestyles subject individuals to various external and psychological stressors, which, in turn, can trigger additional stress through visible signs of fatigue, hair loss, and obesity. As the primary stress hormone affecting skin health, cortisol connects to the glucocorticoid receptor (GR) to aggravate skin issues induced by stress. This activation depends on the expression of 11β-hydroxysteroid dehydrogenase 1 (11β-HSD1) in skin cells, which locally converts cortisone-produced by the central and peripheral hypothalamic-pituitary-adrenal axis-into its active form.

METHODS

Our study delves deeper into stress's adverse effects on the skin, including the disruption of keratinocyte structural proteins, the loss of basement membrane proteins, and the degradation of collagen.

RESULTS

Remarkably, we discovered that Ectoin, an amino acid derivative obtained from halophilic bacteria, is capable of mitigating the inhibitory impacts of cortisone on the expression of cutaneous functional proteins, including involucrin, loricrin, laminin-5, and claudin-1. Moreover, Ectoin reduces the suppressive effect of stress on collagen and hyaluronic acid synthesis by impeding GR signal transduction. Additionally, Ectoin counterbalances the UVB-induced overexpression of 11β-HSD1, thereby diminishing the concentration of endogenous glucocorticoids.

CONCLUSION

Our findings illuminate the significant potential of Ectoin as a preventative agent against stress-induced skin maladies.

Behavioral biometric optical tactile sensor for instantaneous decoupling of dynamic touch signals in real time

Decoupling dynamic touch signals in the optical tactile sensors is highly desired for behavioral tactile applications yet challenging because typical optical sensors mostly measure only static normal force and use imprecise multi-image averaging for dynamic force sensing. Here, we report a highly sensitive upconversion nanocrystals-based behavioral biometric optical tactile sensor that instantaneously and quantitatively decomposes dynamic touch signals into individual components of vertical normal and lateral shear force from a single image in real-time. By mimicking the sensory architecture of human skin, the unique luminescence signal obtained is axisymmetric for static normal forces and non-axisymmetric for dynamic shear forces. Our sensor demonstrates high spatio-temporal screening of small objects and recognizes fingerprints for authentication with high spatial-temporal resolution. Using a dynamic force discrimination machine learning framework, we realized a Braille-to-Speech translation system and a next-generation dynamic biometric recognition system for handwriting.

Mechanisms of Senescence and Anti-Senescence Strategies in the Skin

The skin is the layer of tissue that covers the largest part of the body in vertebrates, and its main function is to act as a protective barrier against external environmental factors, such as microorganisms, ultraviolet light and mechanical damage. Due to its important function, investigating the factors that lead to skin aging and age-related diseases, as well as understanding the biology of this process, is of high importance. Indeed, it has been reported that several external and internal stressors contribute to skin aging, similar to the aging of other tissues. Moreover, during aging, senescent cells accumulate in the skin and express senescence-associated factors, which act in a paracrine manner on neighboring healthy cells and tissues. In this review, we will present the factors that lead to skin aging and cellular senescence, as well as ways to study senescence in vitro and in vivo. We will further discuss the adverse effects of the accumulation of chronic senescent cells and therapeutic agents and tools to selectively target and eliminate them.

Greater mechanistic understanding of the cutaneous pathogenesis of Stevens-Johnson syndrome/toxic epidermal necrolysis can shed light on novel therapeutic strategies: a comprehensive review

PURPOSE OF REVIEW

Stevens-Johnson syndrome/toxic epidermal necrolysis (SJS/TEN) are severe cutaneous adverse drug reactions (SCARs) characterized by widespread epithelial detachment and blistering, which affects the skin and mucocutaneous membranes. To date, therapeutic interventions for SJS/TEN have focused on systematic suppression of the inflammatory response using high-dose corticosteroids or intravenous immunoglobulin G (IgG), for example. No targeted therapies for SJS/TEN currently exist.

RECENT FINDINGS

Though our understanding of the pathogenesis of SJS/TEN has advanced from both an immunological and dermatological perspective, this knowledge is yet to translate into the development of new targeted therapies.

SUMMARY

Greater mechanistic insight into SJS/TEN would potentially unlock new opportunities for identifying or repurposing targeted therapies to limit or even prevent epidermal injury and blistering.

Culture insert device with perfusable microchannels enhancesin vitroskin model development and barrier function assessment

The ever-stricter regulations on animal experiments in the field of cosmetic testing have prompted a surge in skin-related research with a special focus on recapitulation of thein vivoskin structurein vitro. In vitrohuman skin models are seen as an important tool for skin research, which in recent years attracted a lot of attention and effort, with researchers moving from the simplest 2-layered models (dermis with epidermis) to models that incorporate other vital skin structures such as hypodermis, vascular structures, and skin appendages. In this study, we designed a microfluidic device with a reverse flange-shaped anchor that allows culturing of anin vitroskin model in a conventional 6-well plate and assessing its barrier function without transferring the skin model to another device or using additional contraptions. Perfusion of the skin model through vascular-like channels improved the morphogenesis of the epidermis compared with skin models cultured under static conditions. This also allowed us to assess the percutaneous penetration of the tested caffeine permeation and vascular absorption, which is one of the key metrics for systemic drug exposure evaluation.

Light Sheet-Based Laser Patterning Bioprinting Produces Long-Term Viable Full-Thickness Skin Constructs

Tissue engineering holds great promise for biomedical research and healthcare, offering alternatives to animal models and enabling tissue regeneration and organ transplantation. 3D bioprinting stands out for its design flexibility and reproducibility. Here, an integrated fluorescent light sheet bioprinting and imaging system is presented that combines high printing speed (0.66 mm3 /s) and resolution (9 µm) with light sheet-based imaging. This approach employs direct laser patterning and a static light sheet for confined voxel crosslinking in photocrosslinkable materials. The developed bioprinter enables real-time monitoring of hydrogel crosslinking using fluorescent recovery after photobleaching (FRAP) and brightfield imaging as well as in situ light sheet imaging of cells. Human fibroblasts encapsulated in a thiol-ene click chemistry-based hydrogel exhibited high viability (83% ± 4.34%) and functionality. Furthermore, full-thickness skin constructs displayed characteristics of both epidermal and dermal layers and remained viable for 41 days. The integrated approach demonstrates the capabilities of light sheet bioprinting, offering high speed, resolution, and real-time characterization. Future enhancements involving solid-state laser scanning devices such as acousto-optic deflectors and modulators will further enhance resolution and speed, opening new opportunities in light-based bioprinting and advancing tissue engineering.

Advanced function, design and application of skin substitutes for skin regeneration

The development of skin substitutes aims to replace, mimic, or improve the functions of human skin, regenerate damaged skin tissue, and replace or enhance skin function. This includes artificial skin, scaffolds or devices designed for treatment, imitation, or improvement of skin function in wounds and injuries. Therefore, tremendous efforts have been made to develop functional skin substitutes. However, there is still few reports systematically discuss the relationship between the advanced function and design requirements. In this paper, we review the classification, functions, and design requirements of artificial skin or skin substitutes. Different manufacturing strategies for skin substitutes such as hydrogels, 3D/4D printing, electrospinning, microfluidics are summarized. This review also introduces currently available skin substitutes in clinical trials and on the market and the related regulatory requirements. Finally, the prospects and challenges of skin substitutes in the field of tissue engineering are discussed.

Recent trends and perspectives in reconstruction and regeneration of intra/extra-oral wounds using tissue-engineered oral mucosa equivalents

Many conditions, including cancer, trauma, and congenital anomalies, can damage the oral mucosa. Multiple cultures of oral mucosal cells have been used for biocompatibility tests and oral biology studies. In recent decades, the clinical translation of tissue-engineered products has progressed significantly in developing tangible therapies and inspiring advancements in medical science. However, the reconstruction of an intraoral mucosa defect remains a significant challenge. Despite the drawbacks of donor-site morbidity and limited tissue supply, the use of autologous oral mucosa remains the gold standard for oral mucosa reconstruction and repair. Tissue engineering offers a promising solution for repairing and reconstructing oral mucosa tissues. Cell- and scaffold-based tissue engineering approaches have been employed to treat various soft tissue defects, suggesting the potential clinical use of tissue-engineered oral mucosa (TEOMs). In this review, we first cover the recent trends in the reconstruction and regeneration of extra-/intra-oral wounds using TEOMs. Next, we describe the current status and challenges of TEOMs. Finally, future strategic approaches and potential technologies to support the advancement of TEOMs for clinical use are discussed.

Histological assessment of nanostructured fibrin-agarose skin substitutes grafted in burnt patients. A time-course study

A previously developed fibrin-agarose skin model-UGRSKIN-showed promising clinical results in severely burnt patients. To determine the histological parameters associated to the biocompatibility and therapeutic effects of this model, we carried out a comprehensive structural and ultrastructural study of UGRSKIN grafted in severely burnt patients after 3 months of follow-up. The grafted epidermis was analogue to native human skin from day 30th onward, revealing well-structured strata with well-differentiated keratinocytes expressing CK5, CK8, CK10, claudin, plakoglobin, filaggrin, and involucrin in a similar way to controls, suggesting that the epidermis was able to mature and differentiate very early. Melanocytes and Langerhans cells were found from day 30th onward, together with a basement membrane, abundant hemidesmosomes and lack of rete ridges. At the dermal layer, we found an interface between the grafted skin and the host tissue at day 30th, which tended to disappear with time. The grafted superficial dermis showed a progressive increase in properly-oriented collagen fibers, elastic fibers and proteoglycans, including decorin, similarly to control dermis at day 60-90th of in vivo follow-up. Blood vessels determined by CD31 and SMA expression were more abundant in grafted skin than controls, whereas lymphatic vessels were more abundant at day 90th. These results contribute to shed light on the histological parameters associated to biocompatibility and therapeutic effect of the UGRSKIN model grafted in patients and demonstrate that the bioengineered skin grafted in patients is able to mature and differentiate very early at the epithelial level and after 60-90 days at the dermal level.

3D bioprinting-a model for skin aging

Human lifespan continues to extend as an unprecedented number of people reach their seventh and eighth decades of life, unveiling chronic conditions that affect the older adult. Age-related skin conditions include senile purpura, seborrheic keratoses, pemphigus vulgaris, bullous pemphigoid, diabetic foot wounds and skin cancer. Current methods of drug testing prior to clinical trials require the use of pre-clinical animal models, which are often unable to adequately replicate human skin response. Therefore, a reliable model for aged human skin is needed. The current challenges in developing an aged human skin model include the intrinsic variability in skin architecture from person to person. An ideal skin model would incorporate innate functionality such as sensation, vascularization and regeneration. The advent of 3D bioprinting allows us to create human skin equivalent for use as clinical-grade surgical graft, for drug testing and other needs. In this review, we describe the process of human skin aging and outline the steps to create an aged skin model with 3D bioprinting using skin cells (i.e. keratinocytes, fibroblasts and melanocytes). We also provide an overview of current bioprinted skin models, associated limitations and direction for future research.

Cellular activation pathways and interaction networks in vascularized composite allotransplantation

Vascularized composite allotransplantation (VCA) is an evolving field of reconstructive surgery that has revolutionized the treatment of patients with devastating injuries, including those with limb losses or facial disfigurement. The transplanted units are typically comprised of different tissue types, including skin, mucosa, blood and lymphatic vasculature, muscle, and bone. It is widely accepted that the antigenicity of some VCA components, such as skin, is particularly potent in eliciting a strong recipient rejection response following transplantation. The fine line between tolerance and rejection of the graft is orchestrated by different cell types, including both donor and recipient-derived lymphocytes, macrophages, and other immune and donor-derived tissue cells (e.g., endothelium). Here, we delineate the role of different cell and tissue types during VCA rejection. Rejection of VCA grafts and the necessity of life-long multidrug immunosuppression remains one of the major challenges in this field. This review sheds light on recent developments in decoding the cellular signature of graft rejection in VCA and how these may, ultimately, influence the clinical management of VCA patients by way of novel therapies that target specific cellular processes.

Chronic Wound Healing Models

In this paper, we review and analyze the commonly available wound healing models reported in the literature and discuss their advantages and issues, considering their relevance and translational potential to humans. Our analysis includes different in vitro and in silico as well as in vivo models and experimental techniques. We further explore the new technologies in the study of wound healing to provide an all encompassing review of the most efficient ways to proceed with wound healing experiments. We revealed that there is not one model of wound healing that is superior and can give translatable results to human research. Rather, there are many different models that have specific uses for studying certain processes or stages of wound healing. Our analysis suggests that when performing an experiment to assess stages of wound healing or different therapies to enhance healing, one must consider not only the species that will be used but also the type of model and how this can best replicate the physiology or pathophysiology in humans.

Mechanism of action and therapeutic effects of oxidative stress and stem cell-based materials in skin aging: Current evidence and future perspectives

Aging is associated with multiple degenerative diseases, including atherosclerosis, osteoporosis, and Alzheimer's disease. As the most intuitive manifestation of aging, skin aging has received the most significant attention. Skin aging results from various intrinsic and extrinsic factors. Aged skin is characterized by wrinkles, laxity, elastosis, telangiectasia, and aberrant pigmentation. The underlying mechanism is complex and may involve cellular senescence, DNA damage, oxidative stress (OS), inflammation, and genetic mutations, among other factors. Among them, OS plays an important role in skin aging, and multiple antioxidants (e.g., vitamin C, glutathione, and melatonin) are considered to promote skin rejuvenation. In addition, stem cells that exhibit self-replication, multi-directional differentiation, and a strong paracrine function can exert anti-aging effects by inhibiting OS. With the further development of stem cell technology, treatments related to OS mitigation and involving stem cell use may have a promising future in anti-skin aging therapy.

The Role of Cell-Based Therapies in Acute Burn Wound Skin Repair: A Review

Tissue engineering solutions for skin have been developed over the last few decades with a focus initially on a two-layered structure with epithelial and dermal repair. An essential element of skin restoration is a source of cells capable of differentiating into the appropriate phenotype. The need to repair areas of skin when traditional techniques were not adequate addressed led to cell based therapies being developed initially as a laboratory-based tissue expansion opportunity, both as sheets of cultured epithelial autograft and in composite laboratory-based skin substitutes. The time to availability of the cell-based therapies has been solved in a number of ways, from using allograft cell-based solutions to the use of point of care skin cell harvesting for immediate clinical use. More recently pluripotential cells have been explored providing a readily available source of cells and cells which can express the broad range of phenotypes seen in the mature skin construct. The lessons learnt from the use of cell based techniques has driven the exploration of the use of 3D printing technology, with controlled accurate placement of the cells within a specific printed construct to optimise the phenotypic expression and tissue generation.

A hydrogel-fiber-hydrogel composite scaffold based on silk fibroin with the dual-delivery of oxygen and quercetin

Supplying sufficient oxygen within the scaffolds is one of the essential hindrances in tissue engineering that can be resolved by oxygen-generating biomaterials (OGBs). Two main issues related to OGBs are controlling oxygenation and reactive oxygen species (ROS). To address these concerns, we developed a composite scaffold entailing three layers (hydrogel-electrospun fibers-hydrogel) with antioxidant and antibacterial properties. The fibers, the middle layer, reinforced the composite structure, enhancing the mechanical strength from 4.27 ± 0.15 to 8.27 ± 0.25 kPa; also, this layer is made of calcium peroxide and silk fibroin (SF) through electrospinning, which enables oxygen delivery. The first and third layers are physical SF hydrogels to control oxygen release, containing quercetin (Q), a nonenzymatic antioxidant. This composite scaffold resulted in almost more than 40 mmHg of oxygen release for at least 13 days, and compared with similar studies is in a high range. Here, Q was used for the first time for an OGB to scavenge the possible ROS. Q delivery not only led to antioxidant activity but also stabilized oxygen release and enhanced cell viability. Based on the given results, this composite scaffold can be introduced as a safe and controllable oxygen supplier, which is promising for tissue engineering applications, particularly for bone.

Recent Progress in Bioprinting: From Bioink Design to Applications

Currently, there are more than 100,000 people on the US national transplant waiting list, and 17 people die each day waiting for an organ transplant [...].

Elastomeric, bioadhesive and pH-responsive amphiphilic copolymers based on direct crosslinking of poly(glycerol sebacate)-co-polyethylene glycol

Poly(glycerol sebacate) (PGS), a synthetic biorubber, is characterised by its biocompatibility, high elasticity and tunable mechanical properties; however, its inherent hydrophobicity and insolubility in water make it unsuitable for use in advanced biomaterials like hydrogels fabrication. Here, we developed new hydrophilic PGS-based copolymers that enable hydrogel formation through use of two different types of polyethylene glycol (PEG), polyethylene glycol (PEG2) or glycerol ethoxylate (PEG3), combined at different ratios. A two-step polycondensation reaction was used to produce poly(glycerol sebacate)-co-polyethylene glycol (PGS-co-PEG) copolymers that were then crosslinked thermally without the use of initiators or crosslinkers, resulting in PGS-co-PEG2 and PGS-co-PEG3 amphiphilic polymers. It has been illustrated that the properties of PGS-co-PEG copolymers can be controlled by altering the type and amount of PEG. PGS-co-PEG copolymers containing PEG ≥ 40% showed high swelling, flexibility, stretching, bioadhesion and biocompatibility, and good enzymatic degradation and mechanical properties. Also, the addition of PEG created hydrogels that demonstrated pH-responsive behaviours, which can be used for bioapplications requiring responding to physicochemical dynamics. Interestingly, PGS-co-40PEG2 and PGS-co-60PEG3 had the highest shear strengths, 340.4 ± 49.7 kPa and 336.0 ± 35.1 kPa, and these are within the range of commercially available sealants or bioglues. Due to the versatile multifunctionalities of these new copolymer hydrogels, they can have great potential in soft tissue engineering and biomedicine.

The basement membrane in epidermal polarity, stemness, and regeneration

The epidermis is a specialized epithelium that constitutes the outermost layer of the skin, and it provides a protective barrier against environmental assaults. Primarily consisting of multilayered keratinocytes, the epidermis is continuously renewed by proliferation of stem cells and the differentiation of their progeny, which undergo terminal differentiation as they leave the basal layer and move upward toward the surface, where they die and slough off. Basal keratinocytes rest on a basement membrane at the dermal-epidermal junction that is composed of specific extracellular matrix proteins organized into interactive and mechanically supportive networks. Firm attachment of basal keratinocytes, and their dynamic regulation via focal adhesions and hemidesmosomes, is essential for maintaining major skin processes, such as self-renewal, barrier function, and resistance to physical and chemical stresses. The adhesive integrin receptors expressed by epidermal cells serve structural, signaling, and mechanosensory roles that are critical for epidermal cell anchorage and tissue homeostasis. More specifically, the basement membrane components play key roles in preserving the stem cell pool, and establishing cell polarity cues enabling asymmetric cell divisions, which result in the transition from a proliferative basal cell layer to suprabasal cells committed to terminal differentiation. Finally, through a well-regulated sequence of synthesis and remodeling, the components of the dermal-epidermal junction play an essential role in regeneration of the epidermis during skin healing. Here too, they provide biological and mechanical signals that are essential to the restoration of barrier function.

Analysis of drug efficacy for inflammatory skin on an organ-chip system

Bacterial skin infections cause a variety of common skin diseases that require drugs that are safer than antibiotics and have fewer side effects. However, for evaluating skin disease drugs, human skin tissue in vitro constructed traditionally on Transwell has inefficient screening ability because of its fragile barrier function. With mechanical forces and dynamic flow, the organ-on-a-chip system became an innovative, automatic, and modular way to construct pathological models and analyze effective pharmaceutical ingredients in vitro. In this research, we integrated skin extracellular matrix and skin cells into a microfluidic chip to construct a biomimetic “interface-controlled-skin-on-chip” system (IC-SoC), which constructed a stable air–liquid interface (ALI) and necessary mechanical signals for the development of human skin equivalents. The results demonstrated that in the microfluidic system with a flowing microenvironment and ALI, the skin tissue formed in vitro could differentiate into more mature tissue morphological structures and improve barrier function. Then, following exposing the skin surface on the IC-SoC to the stimulation of Propionibacterium acnes (P.acnes) and SLS (sodium lauryl sulfate), the barrier function decreased, as well as inflammatory factors such as IL-1α, IL-8, and PEG2 increased in the medium channel of the IC-SoC. After this pathological skin model was treated with dexamethasone and polyphyllin H, the results showed that polyphyllin H had a significant repair effect on the skin barrier and a significant inhibition effect on the release of inflammation-related cytokines, and the effects were more prominent than dexamethasone. This automated microfluidic system delivers an efficient tissue model for toxicological applications and drug evaluation for bacterial-infected damaged skin instead of animals.

3D printing of skin equivalents with hair follicle structures and epidermal-papillary-dermal layers using gelatin/hyaluronic acid hydrogels

Recent advances in three-dimensional (3D) bioprinting technologies enabled the fabrication of sophisticated live 3D tissue analogs. Although various hydrogel-based bioink has been reported, the development of advanced bioink materials that can reproduce the composition of native extracellular matrix (ECM) accurately and mimic the intrinsic property of laden cells is still challenging. In this work, 3D printed skin equivalents incorporating hair follicle structures and epidermal-papillary-dermal layers are fabricated with gelatin methacryloyl (GelMA)/hyaluronic acid (HA) MA (HAMA) hydrogel (GelMA/HAMA) bioink. The composition of collagen and glycosaminoglycan (GAG) of native skin was recapitulated by adjusting the combination of GelMA and HAMA. The GelMA/HAMA bioink was proven to have excellent viscoelastic and physicochemical properties, 3D printability, cytocompatibility, and functionality to maintain the hair inductive potency and facilitated spontaneous hair pore development. Overall, we suggest that the GelMA/HAMA hydrogels can be promising candidates as bioinks for the 3D printing of skin equivalents with epidermal-papillary-dermal multi-layers and hair follicle structures, and they might serve as a useful model in skin tissue engineering and regeneration.

Modeling an Optimal 3D Skin-on-Chip within Microfluidic Devices for Pharmacological Studies

Preclinical research remains hampered by an inadequate representation of human tissue environments which results in inaccurate predictions of a drug candidate’s effects and target’s suitability. While human 2D and 3D cell cultures and organoids have been extensively improved to mimic the precise structure and function of human tissues, major challenges persist since only few of these models adequately represent the complexity of human tissues. The development of skin-on-chip technology has allowed the transition from static 3D cultures to dynamic 3D cultures resembling human physiology. The integration of vasculature, immune system, or the resident microbiome in the next generation of SoC, with continuous detection of changes in metabolism, would potentially overcome the current limitations, providing reliable and robust results and mimicking the complex human skin. This review aims to provide an overview of the biological skin constituents and mechanical requirements that should be incorporated in a human skin-on-chip, permitting pharmacological, toxicological, and cosmetic tests closer to reality.

A Multi-Functional Anti-Aging Moisturizer Maintains a Diverse and Balanced Facial Skin Microbiome

AIMS

To assess the effect of a 28-day skincare regimen in healthy female subjects on the facial skin microbiome composition and to determine if the skincare regimen including a gentle cleansing lotion, a multi-functional anti-aging moisturizer formulated with prebiotics and postbiotics at skin neutral pH, and bland sunscreen pushed the microbiome to a healthier state and improved skin aging measured by self-assessment and clinical photography.

METHODS AND RESULTS

The study protocol was in accordance with the EU Scientific Committee on Consumer Safety (SCCS) guidance and met all international standards. Twenty-five female subjects between 35 to 65 years old with Fitzpatrick skin type I - VI, moderate crow's feet wrinkles and global face photodamage were enrolled. After 28 days the skincare regimen improved microbial facial diversity and shifted the microbiota composition when compared to baseline.

CONCLUSIONS

After 28-days, the skincare regimen treatment shifted the distribution of the facial skin microbiome, positively influencing the skin microbiome diversity and balance, to promote long term skin health and protect from further skin aging.

SIGNIFICANCE AND IMPACT OF STUDY

These results suggest that incorporating prebiotics and postbiotics into a skincare regimen may have a positive impact on the facial skin microbiome in healthy women.