Towards an actionable One Health approach.

BACKGROUND: Despite the increasing focus on strengthening One Health capacity building on global level, challenges remain in devising and implementing real-world interventions particularly in the Asia-Pacific region. Recognizing these gaps, the One Health Action Commission (OHAC) was established as an academic community for One Health action with an emphasis on research agenda setting to identify actions for highest impact. MAIN TEXT: This viewpoint describes the agenda of, and motivation for, the recently formed OHAC. Recognizing the urgent need for evidence to support the formulation of necessary action plans, OHAC advocates the adoption of both bottom-up and top-down approaches to identify the current gaps in combating zoonoses, antimicrobial resistance, addressing food safety, and to enhance capacity building for context-sensitive One Health implementation. CONCLUSIONS: By promoting broader engagement and connection of multidisciplinary stakeholders, OHAC envisions a collaborative global platform for the generation of innovative One Health knowledge, distilled practical experience and actionable policy advice, guided by strong ethical principles of One Health.

Cascaded dual-channel broadband SPR fiber optic sensor based on Ag and Ag/ZnO/PDMS film structure.

In order to broaden the sensing bandwidth of surface plasmon resonance (SPR) sensors, we propose and demonstrate a dual-channel SPR fiber optic sensor with wide bandwidth. The sensor is fabricated using no-core fiber (NCF), in which the film consists of a silver film and a ZnO film. The sensing characteristics are investigated by simulation and experiment. The resonance wavelength range of the SPR sensor can be significantly tuned by varying the thickness of the ZnO film. In the experiments, a dual-channel SPR sensor that can be used for simultaneous detection of temperature and refractive index was realized by cascading ZnO/Ag film with Ag film. The experimental results show that the two sensing channels are independent without crosstalk. The sensitivity of this sensor is 3512 nm/RIU in the range of 1.333 ∼ 1.385 and 4.6 nm/°C in the range of 0 ∼ 60 °C, which is better than most of the current dual-channel SPR sensors. In addition, the experimental results show that this sensor has good stability in use. The sensor proposed in this work has the advantages of a wide operating wavelength range, simple and compact structure, and high sensitivity. It has a broad application prospect in the simultaneous measurement of refractive index and temperature of liquids.

Mirrored transformation optics.

A mirrored transformation optics (MTO) approach is presented to overcome the material mismatch in transformation optics. It makes good use of the reflection behavior and introduces a mirrored medium to offset the phase discontinuities. Using this approach, a high-performance planar focusing lens of transmission type is designed, which has a larger concentration ratio than the other focusing lens obtained by the generalized Snell's law. The MTO will not change any functionality of the original lens and has promising potential applications in imaging and light energy harvesting.

Transdermally delivered tolerogenic nanoparticles induced effective immune tolerance for asthma treatment.

Induction of antigen-specific immune tolerance for the treatment of allergic or autoimmune diseases is an attractive strategy. Herein, we investigated the protective effect of a transdermal microneedle patch against allergic asthma by stimulating allergen-specific immune tolerance. We fabricated biodegradable tolerogenic nanoparticles (tNPs) that are loaded with a model allergen ovalbumin (OVA) and an immunomodulator rapamycin, and filled the tNPs into microneedle tips by centrifugation to form sustained-release microneedles. After intradermal immunization, the microneedles successfully delivered the cargos into the skin and sustainedly released them for over 96 h. Importantly, the microneedles induced allergen-specific regulatory T cells (Treg), decreased the levels of pro-inflammatory cytokines and antibodies while increased anti-inflammation cytokines, finally leading to restored immune homeostasis. The lung tissue analysis illustrated that the sustained-release microneedles significantly reduced the infiltration of eosinophils, decreased the accumulation of mucus and collagen, and significantly relived asthma symptoms. Our results suggested that the sustained-release microneedle-based transdermal delivery system can induce antigen-specific immune tolerance with improved compliance and efficacy, providing a new therapeutic strategy for the treatment of allergic and autoimmune diseases.

Deciphering the Kinetics of Spontaneous Generation of H2O2 in Individual Water Microdroplets.

Spontaneous generation of H2O2 in sub-10 µm-sized water microdroplets has received increasing interest since its first discovery in 2019. On the other hand, due to the short lifetime of these microdroplets (rapid evaporation) and lack of suitable tools to real-time monitor the generation of H2O2 in individual microdroplets, such a seemingly thermodynamically unfavorable process has also raised vigorous debates on the origin of H2O2 and the underlying mechanism. Herein, we prepared water microdroplets with a long lifetime (>1 h) by virtue of microwell confinement and dynamically monitored the spontaneous generation of H2O2 in individual microdroplets via time-lapsed fluorescence imaging. It was unveiled that H2O2 was continuously generated in the as-prepared water microdroplets and an apparent equilibrium concentration of ∼3 µM of H2O2 in the presence of a H2O2-consuming reaction can be obtained. Through engineering the geometry of these microdroplets, we further revealed that the generation rates of H2O2 in individual microdroplets were positively proportional to their surface-to-volume ratios. This also allowed us to extract a maximal H2O2 generation rate of 7.7 nmol m-2 min-1 in the presence of a H2O2-consuming reaction and derive the corresponding probability of spontaneous conversion of interfacial H2O into H2O2 for the first time, that is, ∼1 of 65,000 water molecules in 1 s. These findings delivered strong evidence that the spontaneous generation of H2O2 indeed occurs at the surface of microdroplets and provided us with an important starting point to further enhance the yield of H2O2 in water microdroplets for future applications.

Polyoxometalate-loaded hyper-crosslinked nanoparticles as a Pickering interfacial catalyst for solvent-free epoxidation of allyl chloride under static conditions.

Epoxidation of allyl chloride and hydrogen peroxide (H2O2) carried out in heterogeneous catalytic systems suffer from poor reaction efficiency due to their heavy mass transfer resistance present at the liquid-liquid interface. Pickering interfacial catalysis (PIC) provides an elegant solution by involving the design of amphiphilic heterogeneous catalysts, which can act as emulsifiers simultaneously. In this study, interface-active polyoxometalate-loaded hyper-crosslinked nanoparticles (HCNPs) were designed. The structural properties of materials were characterized in detail by elemental analysis, Zeta potential, ICP-OES, SEM, TEM, BET, FT-IR, TGA, and XPS. The prepared nanoparticles can build efficient W/O PIC systems with allyl chloride and H2O2. Systematic experiments indicate that catalysts' surface properties, catalyst dosage, and water/oil volume ratio significantly affect the PIC system's catalytic activity and emulsion properties. Moreover, this PIC system maintains high stability after the reaction and can be reused for at least 8 cycles. Excitingly, these interface-active HCNPs can also efficiently promote allyl chloride epoxidation in the absence of solvent and external stirring, illustrating that this approach holds great potential for developing catalytic systems suitable for multiphase reactions.

Transdermal Microneedles Alleviated Rheumatoid Arthritis by Inducing Immune Tolerance via Skin-Resident Antigen Presenting Cells.

Restoring immune tolerance is the ultimate goal for rheumatoid arthritis (RA) treatment. The most reported oral or intravenous injection routes for the immunization of autoantigens cause gastrointestinal side effects, low patient compliance, and unsatisfied immune tolerance induction. Herein, the use of a transdermal microneedle patch is for the first time investigated to codeliver CII peptide autoantigen and rapamycin for reversing immune disorders of RA. The immunized microneedles efficiently recruit antigen-presenting cells particularly Langerhans cells, and induce tolerogenic dendritic cells at the administration skin site. The tolerogenic dendritic cells further homing to lymph nodes to activate systemic Treg cell differentiation, which upregulates the expression of anti-inflammatory mediators while inhibiting the polarization of Th1/2 and Th17 T cell phenotypes and the expression of inflammatory profiles. As a result, the optimized microneedles nearly completely eliminate RA symptoms and inflammatory infiltrations. Furthermore, it is demonstrated that a low dose of rapamycin is crucial for the successful induction of immune tolerance. The results indicate that a rationally designed microneedle patch is a promising strategy for immune balance restoration with increased immune tolerance induction efficiency and patient compliance.

The effects of hydration on the topographical and mechanical properties of corneocytes.

It is well established that the biomechanical properties of the Stratum Corneum (SC) are influenced by both moisture-induced plasticization and the lipid content. This study employs Atomic Force Microscopy to investigate how hydration affects the surface topographical and elasto-viscoplastic characteristics of corneocytes from two anatomical sites. Volar forearm cells underwent swelling when immersed in water with a 50% increase in thickness and volume. Similarly, medial heel cells demonstrated significant swelling in volume, accompanied by increased cell area and reduced cell roughness. Furthermore, as the water activity was increased, they exhibited enhanced compliance, leading to a decreased Young's modulus, hardness, and relaxation times. Moreover, the swollen cells also displayed a greater tolerance to strain before experiencing permanent deformation. Despite the greater predominance of immature cornified envelopes in plantar skin, the comparable Young's modulus of medial heel and forearm corneocytes suggests that cell stiffness primarily relies on the keratin matrix rather than on the cornified envelope. The Young's moduli of the cells in distilled water are similar to those reported for the SC, which suggests that the corneodesmosomes and intercellular lamellae lipids junctions that connect the corneocytes are able to accommodate the mechanical deformations of the SC.

Characterisation of topographical, biomechanical and maturation properties of corneocytes with respect to anatomical location.

BACKGROUND: The Stratum Corneum (SC) is the first barrier of the skin. The properties of individual cells are crucial in understanding how the SC at different anatomical regions maintains a healthy mechanical barrier. The aim of the current study is to present a comprehensive description of the maturation and mechanical properties of superficial corneocytes at different anatomical sites in the nominal dry state. MATERIALS AND METHODS: Corneocytes were collected from five anatomical sites: forearm, cheek, neck, sacrum and medial heel of 10 healthy young participants. The surface topography was analysed using Atomic Force Microscopy (AFM) and Scanning Electron Microscopy (SEM). The level of positive-involucrin cornified envelopes (CEs) and desmoglein-1 (Dsg1) were used as indirect measures of immature CEs and corneodesmosomes, respectively. In addition, AFM nanoindentation and stress-relaxation experiments were performed to characterise the mechanical properties. RESULTS: Volar forearm, neck and sacrum corneocytes presented similar topographies (ridges and valleys) and levels of Dsg1 (13-37%). In contrast, cheek cells exhibited circular nano-objects, while medial heel cells were characterized by villi-like structures. Additionally, medial heel samples also showed the greatest level of immature CEs (32-56%, p < 0.001) and Dsg1 (59-78%, p < 0.001). A large degree of inter-subject variability was found for the Young's moduli of the cells (0.19-2.03 GPa), which was correlated with the level of immature CEs at the cheek, neck and sacrum (p < 0.05). CONCLUSION: It is concluded that a comprehensive study of the mechanical and maturation properties of corneocytes may be used to understand the barrier functions of the SC at different anatomical sites.

Characterisation of superficial corneocyte properties over category I pressure ulcers: Insights into topographical and maturation changes.

BACKGROUND: Pressure ulcers (PUs) are chronic wounds that are detrimental to the quality of life of patients. Despite advances in monitoring skin changes, the structure and function of skin cells over the site of pressure ulcers are not fully understood. OBJECTIVE: The present study aims to evaluate local changes in the properties of superficial corneocytes in category 1 PU sites sampled from a cohort of hospitalised patients. METHODS: Cells were collected from a PU-compromised site and an adjacent control area and their topographical, maturation and mechanical properties were analysed. RESULTS: Corneocytes at the PU-compromised site were characterised by higher levels of immature cornified envelopes (p < 0.001) and greater amounts of desmoglein-1 (corneodesmosomal protein) (p < 0.001) compared to the adjacent control area. The cells at the control site presented the typical ridges-and-valleys topographical features of sacrum corneocytes. By contrast, the PU cells presented circular nano-objects at the cell surface, and, for some patients, the cell topography was deformed. CEs at the PU site were also smaller than at the control site. Although differences were not observed in the mechanical properties of the cells, those of the elderly patients were much softer compared with young subjects. CONCLUSION: This is the first study investigating the changes in corneocyte properties in category I pressure ulcers. Superficial cells at the PU sites showed altered topographical and maturation characteristics. Further studies are required to elucidate if these changes are a consequence of early loss of skin integrity or a result of mechanical and microclimate insults to the skin surface.

Improvement in CO2 Capture of Polyamine with Micro-Interfacial System.

Polyamines have emerged as a promising class of CO2 absorbents due to their remarkable sequestration capacity. However, their potential industrial application as aqueous absorbents is significantly hindered by a low regeneration efficiency and high energy consumption. To address these issues, this study investigates the use of triethylenetetramine (TETA) and ethylene glycol (EG) to develop a nonaqueous absorbent. The incorporation of EG enhances absorption performance and reduces the regeneration energy needed for TETA, whereas the high viscosity of the absorbent impedes absorption rate, amine efficiency, and regeneration efficiency. In order to enhance CO2 capture, micron-sized reaction units (SiO2@TETA-EG) were developed by encapsulating TETA solution with nanosilica. The SiO2@TETA-EG composite exhibits a large specific surface area (99 m2/g), with a porous shell structure and improved fluidity, which effectively counteracts the negative effects caused by high viscosity. Notably, SiO2@TETA-EG indicates a noticeably higher apparent rate constant of 4.29 min-1 at 323.2 K compared to the TETA-EG solution. Furthermore, SiO2@TETA-EG displays a 28.4% boost in regeneration efficiency while maintaining favorable stability in pore size and shape after regeneration.

Iridium-phosphine ligand complexes as an alternative to rhodium-based catalysts for the efficient hydroformylation of propene.

Expensive rhodium (Rh)-based catalysts have been widely used for the hydroformylation of propene. To find a cheaper and effective alternative to these Rh-based catalysts, herein, a series of phosphine ligands were used to coordinate with iridium, and their catalytic reactivities for the hydroformylation of propene were systematically investigated in this study. The effects of different phosphine ligands, pressures, temperatures, and catalyst dosages on the hydroformylation of propene were investigated. Tripyridyl phosphine iridium Ir2(cod)2Cl2-P(3-py)3 (Ir(I)-L5) and its derivatives exhibit the highest catalytic reactivity. Surprisingly, the catalytic reactivity of Ir(I)-L5 is higher than that of Rh2(cod)2Cl2-P(3-py)3 (Rh(I)-L5). When the Ir(I)-L5 complex is used as the catalyst, reactions performed in a polar solvent gave higher turnover number (TON) values than those in a non-polar solvent. Up to a TON of 503 can be obtained. Different n-butyraldehyde/iso-butyraldehyde (n/i) ratios can be obtained by adjusting the phosphine ligands or the proportion of gas pressure. The catalyst showed good reusability in five recycling experiments. Furthermore, based on DFT theoretical calculations, a probable reaction mechanism was proposed. It is reliable that an Ir-based catalyst can be considered as a highly effective catalyst for the hydroformylation of propylene with CO.

Debiased ambient vibrations optical coherence elastography to profile cell, organoid and tissue mechanical properties.

The role of the mechanical environment in defining tissue function, development and growth has been shown to be fundamental. Assessment of the changes in stiffness of tissue matrices at multiple scales has relied mostly on invasive and often specialist equipment such as AFM or mechanical testing devices poorly suited to the cell culture workflow.In this paper, we have developed a unbiased passive optical coherence elastography method, exploiting ambient vibrations in the sample that enables real-time noninvasive quantitative profiling of cells and tissues. We demonstrate a robust method that decouples optical scattering and mechanical properties by actively compensating for scattering associated noise bias and reducing variance. The efficiency for the method to retrieve ground truth is validated in silico and in vitro, and exemplified for key applications such as time course mechanical profiling of bone and cartilage spheroids, tissue engineering cancer models, tissue repair models and single cell. Our method is readily implementable with any commercial optical coherence tomography system without any hardware modifications, and thus offers a breakthrough in on-line tissue mechanical assessment of spatial mechanical properties for organoids, soft tissues and tissue engineering.

Disrupted intercellular bridges and spermatogenesis in fatty acyl-CoA reductase 1 knockout mice: A new model of ether lipid deficiency.

Peroxisomal fatty acyl-CoA reductase 1 (FAR1) is a rate-limiting enzyme for ether lipid (EL) synthesis. Gene mutations in FAR1 cause a rare human disease. Furthermore, altered EL homeostasis has also been associated with various prevalent human diseases. Despite their importance in human health, the exact cellular functions of FAR1 and EL are not well-understood. Here, we report the generation and initial characterization of the first Far1 knockout (KO) mouse model. Far1 KO mice were subviable and displayed growth retardation. The adult KO male mice had smaller testes and were infertile. H&E and immunofluorescent staining showed fewer germ cells in seminiferous tubules. Round spermatids were present but no elongated spermatids or spermatozoa were observed, suggesting a spermatogenesis arrest at this stage. Large multi-nucleated giant cells (MGC) were found lining the lumen of seminiferous tubules with many of them undergoing apoptosis. The immunofluorescent signal of TEX14, an essential component of intercellular bridges (ICB) between developing germ cells, was greatly reduced and mislocalized in KO testis, suggesting the disrupted ICBs as an underlying cause of MGC formation. Integrative analysis of our total testis RNA-sequencing results and published single-cell RNA-sequencing data unveiled cell type-specific molecular alterations underlying the spermatogenesis arrest. Many genes essential for late germ cell development showed dramatic downregulation, whereas genes essential for extracellular matrix dynamics and cell-cell interactions were among the most upregulated genes. Together, this work identified the cell type-specific requirement of ELs in spermatogenesis and suggested a critical role of Far1/ELs in the formation/maintenance of ICB during meiosis.

DNALI1 interacts with the MEIG1/PACRG complex within the manchette and is required for proper sperm flagellum assembly in mice.

The manchette is a transient and unique structure present in elongating spermatids and required for proper differentiation of the germ cells during spermatogenesis. Previous work indicated that the MEIG1/PACRG complex locates in the manchette and is involved in the transport of cargos, such as SPAG16L, to build the sperm flagellum. Here, using co-immunoprecipitation and pull-down approaches in various cell systems, we established that DNALI1, an axonemal component originally cloned from Chlamydomonas reinhardtii, recruits and stabilizes PACRG and we confirm in vivo, the co-localization of DNALI1 and PACRG in the manchette by immunofluorescence of elongating murine spermatids. We next generated mice with a specific deficiency of DNALI1 in male germ cells, and observed a dramatic reduction of the sperm cells, which results in male infertility. In addition, we observed that the majority of the sperm cells exhibited abnormal morphology including misshapen heads, bent tails, enlarged midpiece, discontinuous accessory structure, emphasizing the importance of DNALI1 in sperm differentiation. Examination of testis histology confirmed impaired spermiogenesis in the mutant mice. Importantly, while testicular levels of MEIG1, PACRG, and SPAG16L proteins were unchanged in the Dnali1 mutant mice, their localization within the manchette was greatly affected, indicating that DNALI1 is required for the formation of the MEIG1/PACRG complex within the manchette. Interestingly, in contrast to MEIG1 and PACRG-deficient mice, the DNALI1-deficient mice also showed impaired sperm spermiation/individualization, suggesting additional functions beyond its involvement in the manchette structure. Overall, our work identifies DNALI1 as a protein required for sperm development.

Inactivation of Cops5 in Smooth Muscle Cells Causes Abnormal Reproductive Hormone Homeostasis and Development in Mice.

COP9 constitutive photomorphogenic homolog subunit 5 (COPS5), also known as Jab1 or CSN5, has been implicated in a wide variety of cellular and developmental processes. By analyzing male germ cell-specific COPS5-deficient mice, we have demonstrated previously that COPS5 is essential to maintain male germ survival and acrosome biogenesis. To further determine the role of Cops5 in peritubular myoid cells, a smooth muscle lineage surrounding seminiferous tubules, we herein derived mice conditionally deficient for the Cops5 gene in smooth muscle cells using transgenic Myh11-Cre mice. Although these conditional Cops5-deficient mice were born at the expected Mendelian ratio and appeared to be normal within the first week after birth, the homozygous mice started to show growth retardation after 1 week. These mice also exhibited a variety of developmental and reproductive disorders, including failure of development of reproductive organs in both males and females, spermatogenesis defects, and impaired skeletal development and immune functions. Furthermore, conditional Cops5-deficient mice revealed dramatic impairment of the endocrine system associated with testicular functions, including a marked reduction in serum levels of gonadotropins (follicle-stimulating hormone, luteinizing hormone), testosterone, insulin-like growth factor 1, and glucose, but not vasopressin. All homozygous mice died before age 67 days in the study. Collectively, our results provide novel evidence that Cops5 in smooth muscle lineage plays an essential role in postnatal development and reproductive functions.

Generation of floxed Spag6l mice and disruption of the gene by crossing to a Hprt-Cre line.

Mouse sperm-associated antigen 6 like (SPAG6L) is an axoneme central apparatus protein, essential for the normal function of the ependymal cell and lung cilia, and sperm flagella. Accumulated evidence has disclosed multiple biological functions of SPAG6L, including ciliary/flagellar biogenesis and polarization, neurogenesis, and neuronal migration. Conventional Spag6l knockout mice died of hydrocephalus, which impedes further investigation of the function of the gene in vivo. To overcome the limitation of the short lifespan of conventional knockout mice, we developed a conditional allele by inserting two loxP sites in the genome flanking exon 3 of the Spag6l gene. By crossing the floxed Spag6l mice to a Hrpt-Cre line which expresses Cre recombinase ubiquitously in vivo, mutant mice that are missing SPAG6L globally were obtained. Homozygous mutant Spag6l mice showed normal appearance within the first week after birth, but reduced body size was observed after 1 week, and all developed hydrocephalus and died within 4 weeks of age. The phenotype mirrored that of the conventional Spag6l knockout mice. The newly established floxed Spag6l model provides a powerful tool to further investigate the role of the Spag6l gene in individual cell types and tissues.

Viscoelastic Properties of Polymeric Microneedles Determined by Micromanipulation Measurements and Mathematical Modelling.

Microneedles, including dissolvable ones made from biocompatible and biodegradable materials, have been widely studied and can potentially be used for transdermal drug delivery, disease diagnosis (sampling), skin care, etc. Characterizing their mechanical properties is essential, as being mechanically strong enough to pierce the skin barrier is one of the most fundamental and crucial requirements for them. The micromanipulation technique was based on compressing single microparticles between two flat surfaces to obtain force and displacement data simultaneously. Two mathematical models had already been developed to calculate the rupture stress and apparent Young's modulus, which can identify variations of these parameters in single microneedles within a microneedle patch. In this study, a new model has been developed to determine the viscoelasticity of single microneedles made of hyaluronic acid (HA) with a molecular weight of 300 kDa loaded with lidocaine by using the micromanipulation technique to gather experimental data. The modelling results from the micromanipulation measurements suggest that the microneedles were viscoelastic and their mechanical behaviour was strain-rate dependent, which implies that the penetration efficiency of viscoelastic microneedles can be improved by increasing their piercing speed into the skin.

Lego-Inspired Glass Capillary Microfluidic Device: A Technique for Bespoke Microencapsulation of Phase Change Materials.

We report a Lego-inspired glass capillary microfluidic device capable of encapsulating both organic and aqueous phase change materials (PCMs) with high reproducibility and 100% PCM yield. Oil-in-oil-in-water (O/O/W) and water-in-oil-in-water (W/O/W) core-shell double emulsion droplets were formed to encapsulate hexadecane (HD, an organic PCM) and salt hydrate SP21EK (an aqueous PCM) in a UV-curable polymeric shell, Norland Optical Adhesive (NOA). The double emulsions were consolidated through on-the-fly polymerization, which followed thiol-ene click chemistry for photoinitiation. The particle diameters and shell thicknesses of the microcapsules were controlled by manipulating the geometry of glass capillaries and fluid flow rates. The microcapsules were monodispersed and exhibited the highest encapsulation efficiencies of 65.4 and 44.3% for HD and SP21EK-based materials, respectively, as determined using differential scanning calorimetry (DSC). The thermogravimetric (TGA) analysis confirmed much higher thermal stability of both encapsulated PCMs compared to pure PCMs. Polarization microscopy revealed that microcapsules could sustain over 100 melting-crystallization cycles without any structural changes. Bifunctional microcapsules with remarkable photocatalytic activity along with thermal energy storage performance were produced after the addition of 1 wt % titanium dioxide (TiO2) nanoparticles (NPs) into the polymeric shell. The presence of TiO2 NPs in the shell was confirmed by higher opacity and whiteness of these microcapsules and was quantified by energy dispersive X-ray (EDX) spectroscopy. Young's modulus of HD-based microcapsules estimated using micromanipulation analysis increased from 58.5 to 224 MPa after TiO2 incorporation in the shell.

Characterisation of superficial corneocytes in skin areas of the face exposed to prolonged usage of respirators by healthcare professionals during COVID-19 pandemic.

INTRODUCTION: During the COVID-19 pandemic healthcare workers (HCWs) have used respiratory protective equipment for prolonged periods, which has been associated with detrimental effects on the underlying skin. The present study aims to evaluate changes in the main cells (corneocytes) of the stratum corneum (SC) following prolonged and consecutive use of respirators. METHODS: 17 HCWs who wore respirators daily during routine hospital practice were recruited to a longitudinal cohort study. Corneocytes were collected via tape stripping from a negative control site (area outside the respirator) and from the cheek which was in contact with the device. Corneocytes were sampled on three occasions and analysed for the level of positive-involucrin cornified envelopes (CEs) and the amount of desmoglein-1 (Dsg1), as indirect measurements of immature CEs and corneodesmosomes (CDs), respectively. These were compared to biophysical measurements (Transepidermal water loss, TEWL, and SC hydration) at the same investigation sites. RESULTS: A large degree of inter-subject variability was observed, with maximum coefficients of variation of 43% and 30% for the level of immature CEs and Dsg1, respectively. Although it was observed that there was not an effect of prolonged respirator usage on the properties of corneocytes, the level of CDs was greater at the cheek than the negative control site (p < 0.05). Furthermore, low levels of immature CEs correlated with greater TEWL values after prolonged respirator application (p < 0.01). It was also noted that a smaller proportion of immature CEs and CDs was associated with a reduced incidence of self-reported skin adverse reactions (p < 0.001). CONCLUSIONS: This is the first study that investigated changes in corneocyte properties in the context of prolonged mechanical loading following respirator application. Although differences were not recorded over time, the levels of CDs and immature CEs were consistently higher in the loaded cheek compared to the negative control site and were positively correlated with a greater number of self-reported skin adverse reactions. Further studies are required to evaluate the role of corneocyte characteristics in the evaluation of both healthy and damaged skin sites.