UVA Exposure Research Articles

Evaluation of the Long-term Cumulative UVA Facial Exposure of Queensland School Teachers derived for an Extended Period from the OMI Satellite Irradiance.

This research presents a novel methodology for deriving the total daily broadband solar UVA (320-400nm) received by school teachers during their working day from Ozone Monitoring Instrument (OMI) satellite solar noon UVA irradiance measurements for a Queensland subtropical site (27.5°S, 152°E). Daily UVA exposures are weighted to the anatomical human cheek (anterior infra-orbital region) for teachers wearing and not wearing broad-brimmed hats. The method utilizes the OMI UVA irradiance data collected daily at high temporal resolution over 2005 to 2016 to derive the total daily UVA exposure to a horizontal plane. These horizontal plane exposures are scaled by factors to take into account the timing of outdoor activity. The relationship between exposures to a horizontal plane and those to a vertical plane and the protection provided by a broad-brimmed hat was assessed to evaluate the total daily UVA exposures to the cheek for classroom and physical education teaching staff expected to be outside at different periods of the day. The developed method enables the total daily UVA exposure to specific anatomical sites to be evaluated from the satellite solar noon irradiance at locations that do not have access to surface-based instrumentation capable of recording in the solar UVA waveband.

Therapeutic implications of extracorporeal photopheresis for rheumatic diseases

Extracorporeal photopheresis (ECP) procedure is based on mononuclear cells (MNC) apheresis and their extracorporeal UVA exposure. It has been applied mainly in hematology and transplantation. Over thirty years of experience confirmed its effectiveness, outstanding safety profile and good tolerance. These observations encourage the implementation of ECP in the treatment of autoimmune connective tissue diseases. The procedure might be considered in refractory cases, when the first line treatment strategies do not control disease activity or immunosuppressants are contraindicated and in the group of patients with high risk of infections. Current literature about using ECP in rheumatology is scarce and most data come from case reports and small observational studies. Systemic sclerosis is the most studied rheumatic disease in the field of ECP use. The disease appeared on the list of clinical applications of ECP therapy according to American Society for Apheresis. However, no European or American guidelines, or recommendations for the treatment in rheumatology suggest ECP as the treatment option. There are no standards in performing ECP in rheumatic diseases concerning indications, length of therapy, concomitant immunosuppressive treatment, follow up or patients characteristic. In this review, we have searched literature concerning ECP use in rheumatic diseases.

9-phenyl acridine photosensitizes A375 cells to UVA radiation

Acridines are an important class of bioactive molecules having varied uses. Its derivative, 9-phenylacridine (ACPH) had been found to exhibit antitumor activity both in cell lines and in vivo model. Its DNA binding ability and absorbance in the ultraviolet range encouraged us to investigate its role as a photosensitizer with UVA radiation. We investigated the effects of ACPH prior to UVA exposure on in vitro DNA through photo-cleavage assay. Effect of such treatment was also studied in cultured A375 melanoma cells. Endpoints studied included morphological changes, evaluation of cellular viability, scratch assay, intracellular reactive oxygen species (ROS) production, DNA damage, lipid peroxidation, glutathione (GSH) level, autophagy, cell cycle progression, depletion of mitochondrial membrane potential (ΔΨmt), induction of apoptosis and Hoechst dye efflux assay. Our findings indicated that ACPH could sensitize damage to DNA induced by UVA both in vitro and in cells. It could also potentiate cell killing by UVA. It arrested cells in G2/M phase and induced apoptotic death through mitochondria mediated pathway. This sensitization was through enhancement of intracellular ROS. Our findings also indicated that the stem cells side population was reduced on such treatment. The findings are important as it indicates ACPH as a promising photosensitizer and indicates its possible role in photodynamic therapy.

Influence of UV Irradiation on Corrosion Behavior of 304L SS in 0.1M H<sub>2</sub>SO<sub>4</sub> and 0.5M NaCl

This paper describes an experimental study on the effect of Ultra-Violet (UV) exposure on the electrochemical corrosion behavior of 304L stainless steel in 0.1M H2SO4 and 0.5M NaCl medium. The results of study demonstrate that in NaCl medium, exposure of both UV-A and UV-C shifts the Open Circuit Potential (OCP) in active direction (less noble) as compared to the specimen without UV exposure which indicates less stable passive film. While in sulphuric acid both UV-A and UV-C shifts OCP in noble direction which reflects the stability nature of passive film. In H2SO4 medium, exposure of both UV-A and UV-C assist in improving passivity which is indicated by lower passive current density. In NaCl medium, exposure of both UV-A and UV-C, decrease the pitting corrosion resistance as indicated by lower Epit (pitting potential) and higher Icorr (corrosion current density). In H2SO4 uniform dissolution was observed after each polarization experiment as shown in optical micrographs. In NaCl medium pitting sites are more under both type UV exposures as revealed by microstructure after polarization experiment. EIS (Nyquist plots) showed that exposure of both UV-A and UV-C in NaCl medium specimens have lower polarization resistance (Rp) than without UV exposure. Lower Rp confirms lesser protectiveness of passive film. In case of H2SO4, higher arc radius (Rp) is observed under UV exposure for both UV-A and UV-C.

Daylight-Active Cellulose Nanocrystals Containing Anthraquinone Structures.

Antimicrobial and antiviral materials have attracted significant interest in recent years due to increasing occurrences of nosocomial infections and pathogenic microbial contamination. One method to address this is the combination of photoactive compounds that can produce reactive oxygen species (ROS), such as hydrogen peroxide and hydroxyl radicals to disinfect microbes, with carrier materials that meet the application requirements. Using anthraquinone (AQ) and cellulose nanocrystals (CNCs) as the photoactive and carrier components, respectively, this work demonstrated the first covalent incorporation of AQ onto CNCs. The morphology and the photoactive properties were investigated, revealing the structural integrity of the CNCs and the high degree of photoactivity of the AQ-CNC materials upon UVA exposure. The AQ-CNCs also exhibited an unexpected persistent generation of ROS under darkness, which adds advantages for antimicrobial applications.

Effects of different dicarboxylic acid on the UV-curable urethane resins made from palm fatty acid distillate

A series of four polyol macromers with similar hydroxyl number was prepared by reacting palm fatty acid distillate with neopentaglycol, pentaerythritol, and separate equimolar amounts of isophthalic acid (IPA), terephthalic acid (TPA), phthalic anhydride (PA), and adipic acid (AA). Each macromer was then copolymerized with 2-hydroxylethyl acrylate (2-HEA) and toluene diisocyanate to produce the UV curable resins labeled as UA–IPA, UA–TPA, UA–PA, and UA–AA, respectively. The glass transition temperature (Tg), pendulum hardness, and adhesion properties of the cured films were studied. In general, all the resins produced coatings with high gloss and good adhesion. When accelerated weathering tests were carried out, films of UA–TPA could withstand UVA exposure up to 1500 h. When subjected to methyl ethyl ketone double rub test, cured films of UA–IPA and UA–TPA could withstand the highest double rubs at 90 times, followed by UA–PA and UA–AA at 45 and 15 times, respectively. Under salt spray corrosion test for 720 h, cured films showed good corrosion resistance with no observable blistering, except for UA–AA that showed slight blistering. Excellent water resistance was achieved by all cured films with good adhesion and minimal gloss reduction.

Susceptibility of SARS-CoV-2 to UV irradiation

The coronavirus SARS-CoV-2 pandemic became a global health burden. We determined the susceptibility of SARS-CoV-2 to irradiation with ultraviolet light. The virus was highly susceptible to ultraviolet light. A viral stock with a high infectious titer of 5 × 106 TCID50/mL was completely inactivated by UVC irradiation after nine minutes of exposure. The UVC dose required for complete inactivation was 1,048 mJ/cm2. UVA exposure demonstrated only a weak effect on virus inactivation over 15 minutes. Hence, inactivation of SARS-CoV-2 by UVC irradiation constitutes a reliable method for disinfection purposes in health care facilities and for preparing SARS-CoV-2 material for research purpose.

Photocatalytic degradation of Amoxicillin in pharmaceutical wastewater: A potential tool to manage residual antibiotics

Abstract The present study investigates the degradation of amoxicillin (AMX) using TiO2 photocatalysis and sono-photocatalysis in aqueous solution under UV-A (365 nm) and sunlight exposure. The photocatalysis, as well as sono-photocatalysis, were coupled with H 2 O2 as well to assess the improvement in the degradation of AMX. Response surface methodology (RSM) based on three-level and four variable Box–Behnken experiment design was used to analyse​ and validate the degradation of AMX. Upon comparison of observed values with predicted, the value of the coefficient of regression (R2) was 0.87 which indicate the good fit of the model. The optimum conditions for maximum degradation (80%) of AMX were AMX - 30mg/l, TiO2 dosage - 450mg/l, H 2 O2 concentration — 150 mg/l and pH — 7.0 under UV irradiation (672 W/m2). Significant improvement in rate kinetics of degradation was observed when photocatalysis was complemented with H 2 O2 and sonication (40 KHz) under optimized condition, but the maximal removal remained almost unaffected. The method proved efficient towards degradation of AMX in real pharmaceutical wastewater with reduced reaction time for targeted level treatment. It was concluded that photocatalysis is a potential method for degradation of AMX under the set optimized conditions, and it may be adopted in-silo since photocatalysis coupled with sonication becomes energy-prohibitive for degradation of AMX.

CaproGlu: Multifunctional tissue adhesive platform

Driven by the clinical need for a strong tissue adhesive with elastomeric material properties, a departure from legacy crosslinking chemistries was sought as a multipurpose platform for tissue mending. A fresh approach to bonding wet substrates has yielded a synthetic biomaterial that overcomes the drawbacks of free-radical and nature-inspired bioadhesives. A food-grade liquid polycaprolactone grafted with carbene precursors yields CaproGlu. The first-of-its-kind low-viscosity prepolymer is VOC-free and requires no photoinitiators. Grafted diazirine end-groups form carbene diradicals upon low energy UVA (365 nm) activation that immediately crosslink tissue surfaces; no pre-heating or animal-derived components are required. The hydrophobic polymeric environment enables metastable functional groups not possible in formulations requiring solvents or water. Activated diazirine within CaproGlu is uniquely capable of crosslinking all amino acids, even on wet tissue substrates. CaproGlu undergoes rapid liquid-to-biorubber transition within seconds of UVA exposure–features not found in any other bioadhesive. The exceptional shelf stability of CaproGlu allows gamma sterilization with no change in material properties. CaproGlu wet adhesiveness is challenged against current unmet clinical needs: anastomosis of spliced blood vessels, anesthetic muscle patches, and human platelet-mediating coatings. The versatility of CaproGlu enables both organic and inorganic composites for future bioadhesive platforms.

Plain polystyrene microplastics reduce the toxic effects of ZnO particles on marine microalgae Dunaliella salina

Abstract A critical literature survey on marine ecotoxicology reveals a lack of comprehensive studies to assess the impact of microplastics on the toxicity of engineered nanomaterials at environmentally relevant doses. Though ZnO and microplastics both are well known to be marine pollutants, the combined toxicity of ZnO particles with plain polystyrene (PS) microplastics are yet to be studied. Preliminary characterization of ZnO particles included examining particle size, morphology, and surface area. The amount of nominal and dissolved ions in the suspensions containing nano-sized ZnO particles was determined. The toxicity of bulk and nano-sized ZnO particles in combination with plain PS microplastics at low concentration (1 mg/ L) was assessed towards marine algae Dunaliella salina at three exposure concentrations 1.22, 12.28 and 122.88 μM under UV-A and dark exposure conditions. As expected, a dose-dependent increment in the toxicity, ROS (extracellular & intracellular) generation and lipid peroxidation were noted for both bulk and nano-sized ZnO particles. The harmful effects of bulk and nano-sized ZnO particles were considerably reduced in the presence of plain PS microplastics. This study opens up new dimensions regarding the positive impact of microplastics at low concentration, where they lessen the toxic effects of co-pollutants in the marine ecosystem.

Effect of UVA radiation on the Nrf2 signalling pathway in human skin cells

The harmful effects of low energy UVA photons (315–400 nm) are associated with the massive production of reactive oxygen species resulting in oxidative stress. In response to oxidative damage, NF-E2-related factor 2 (Nrf2) is translocated to the nucleus and drives the expression of detoxication and antioxidant enzymes. UVA's effect on Nrf2 has been quite well characterised in dermal fibroblasts. However, there is a dearth of such information for keratinocytes. This study aimed to evaluate and compare the effect of UVA radiation on the Nrf2 pathway and oxidative stress related proteins in primary human dermal fibroblasts (NHDF), epidermal keratinocytes (NHEK) and human keratinocyte cell line HaCaT. NHDF were exposed to doses of 2.5–7.5 J/cm2, NHEK and HaCaT to 10–20 J/cm2 using a solar simulator. Effects on Nrf2 translocation were evaluated after 1, 3 and 6 h and Nrf2-controlled proteins (heme oxygenase 1 (HO-1), NAD(P)H:quinone oxidoreductase 1 (NQO1), glutathione reductase (GSR), glutathione-S-transferase (GST), interleukine-6 (IL-6), and matrix metalloproteinases (MMP-1, MMP-2)) after 3, 6 and 24 h. The results showed the fastest Nrf2 translocation was in UVA-irradiated HaCaT (1 h), persisting until the subsequent time interval (3 h), while in primary keratinocytes the effect of radiation was minimal. In NHDF, UVA-stimulated Nrf2 translocation was conspicuous 3 h after UVA treatment. In NHDF, most of the studied proteins (NQO1, HO-1, GSR, GSTM1 and MMP-1) showed the highest level 24 h after UVA exposure, except for MMP-2 and IL-6 which had their highest level at a shorter time incubation interval (3 h). In NHEK, NQO1, HO-1 and GST were increased 6 h after UVA exposure, GSR and MMP-2 level was slightly below or above the control level, and MMP-1 and IL-6 increased at shorter time intervals. When comparing NHEK and HaCaT, these cells displayed contrary responses in most of the Nrf2-controlled proteins. Thus, primary keratinocytes cannot be replaced with HaCaT when studying cell signalling such as the Nrf2 driven pathway and Nrf2-controlled proteins.

Seasonal Variation In Sunlight Exposure, Nitric Oxide Metabolites, And Blood Pressure

A reduced exposure to ultraviolet (UV) radiation in winter can decrease 25-hydroxyvitamin D (25(OH)D) levels, increase cardiovascular risk factors, and inhibit athletic performance. Exposing skin to UV-A light in the laboratory has also been shown to release nitric oxide (NO) metabolites into the circulation; molecules known to regulate multiple cardiovascular and metabolic processes. However, it is presently unclear whether NO availability is influenced by the seasonal variation in UV exposure. PURPOSE: To compare UV exposure, serum 25(OH)D, plasma nitrate and nitrite, and blood pressure between the summer and winter months. METHODS: Thirty-four healthy adults (21 males) residing in Scotland (~55.8o N, 4.1o W) were monitored for 7 days in the summer (June - August) and winter (December - February) in a randomised order. Participants wore a personal UV monitor on the wrist throughout each monitoring phase before visiting the laboratory to provide a venous blood sample and to have blood pressure measured. Serum levels of 25(OH)D were measured using an enzyme-linked immunosorbent assay and plasma nitrate and nitrite analysed using gas-phase chemiluminescence. RESULTS: Total UV-A exposure was higher in summer (17 ± 21 J.cm2) compared to winter (2.5 ± 3.0 J.cm2, P<0.001). Plasma nitrate did not differ between seasons (P=0.57) but nitrite (137 ± 31 nM) and serum 25(OH)D (22 ± 8 ng/ml) were lower (both P<0.001) in the winter compared to summer (200 ± 56 nM and 35 ± 13 ng/ml, respectively). Blood pressure was higher in winter (systolic 126 ± 13 mmHg; diastolic 76 ± 9 mmHg) than in summer (systolic 119 ± 11 mmHg; diastolic 67 ± 8 mmHg; both P<0.001). UV-A exposure was positively associated with plasma nitrite (R=0.41, P<0.01) and 25(OH)D (R=0.43, P<0.01). Plasma nitrite was negatively associated with systolic (R=−0.5, P<0.01) and diastolic blood pressure (R=−0.4, P<0.01). CONCLUSIONS: In a similar fashion to 25(OH)D, circulating levels of plasma nitrite, a marker of NO bioavailability, appear to be influenced by seasonal variations in UV exposure. The negative association between nitrite and blood pressure suggest that a reduced level of NO may increase cardiovascular risk factors in the winter months.

A Lipid-Based Oral Supplement Protects Skin Cells in Culture from Ultraviolet Light and Activates Antioxidant and Anti-Inflammatory Mechanisms

Overexposure to ultraviolet (UV) light is associated with multiple health risks, from sunburn and prematurely aging skin to the development of skin cancers. The ingestion of photoprotective natural compounds through diet or supplementation is one method to increase the skin’s UV-resistance. This study’s primary objective was to determine the cellular photoprotective properties of an ingestible skincare supplement (trade name “Anti-Aging Formula” [AAF]) and compare them to its constituent active ingredients: fish oil-derived omega-3s eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), borage-derived omega-6 gamma-linolenic acid (GLA), paprika- and marigold-derived carotenoids, zeaxanthin and lutein, respectively, and vitamin D3. AAF, but not the separate individual ingredients, significantly increased the viability of primary human dermal fibroblasts after UVA exposure compared to the vehicle control. AAF and EPA/DHA-containing fish oil demonstrated similar UVB photoprotective properties whereas GLA, the carotenoids, and vitamin D3 had no significant effect. The second objective was to explore possible mechanisms of action of AAF’s photoprotective effects. AAF-treatment increased cellular antioxidant activity and the expression of genes in the glutathione and peroxiredoxin (PRDX)/thioredoxin (TXN) antioxidant pathways, suggesting an antioxidant mechanism of action. It also diminished cellular arachidonic acid (AA) levels and decreased the expression of the downstream pro-inflammatory prostaglandin-endoperoxide synthase 2 (PTGS2) gene, suggesting an anti-inflammatory mechanism of action. In conclusion, AAF is UVA/B photoprotective when applied directly to primary human dermal fibroblasts. In addition, its photoprotective effects are mainly due to its EPA/DHA components and may relate to its cellular antioxidant effects and inhibition of the AA/PTGS2 inflammatory pathway.

Role of quorum sensing in UVA-induced biofilm formation in Pseudomonas aeruginosa.

Pseudomonas aeruginosa, a versatile bacterium present in terrestrial and aquatic environments and a relevant opportunistic human pathogen, is largely known for the production of robust biofilms. The unique properties of these structures complicate biofilm eradication, because they make the biofilms very resistant to diverse antibacterial agents. Biofilm development and establishment is a complex process regulated by multiple regulatory genetic systems, among them is quorum sensing (QS), a mechanism employed by bacteria to regulate gene transcription in response to population density. In addition, environmental factors such as UVA radiation (400-315 nm) have been linked to biofilm formation. In this work, we further investigate the mechanism underlying the induction of biofilm formation by UVA, analysing the role of QS in this phenomenon. We demonstrate that UVA induces key genes of the Las and Rhl QS systems at the transcriptional level. We also report that pelA and pslA genes, which are essential for biofilm formation and whose transcription depends in part on QS, are significantly induced under UVA exposure. Finally, the results demonstrate that in a relA strain (impaired for ppGpp production), the UVA treatment does not induce biofilm formation or QS genes, suggesting that the increase of biofilm formation due to exposure to UVA in P. aeruginosa could rely on a ppGpp-dependent QS induction.

In-Flight UV-A Exposure of Commercial Airline Pilots.

INTRODUCTION: Understanding UV exposure is essential for the assessment of its contribution to the occupational risk of pilots developing ocular and skin pathologies. The objective of this observational study was to measure the UV exposure of pilots flying between the United Kingdom and a range of destinations at three different seasons.METHODS: The in-flight UV exposure of pilots was measured on 322 Monarch Airlines short-haul flights on the Airbus A321-231 and Airbus A320-214 to 31 destinations, mostly in Europe, from 4 UK airports in September 2016-August 2017. The erythema effective and UV-A doses were compared with the ICNIRP guidance and typical recreational weekend exposure of UK office workers.RESULTS: The erythema effective radiant doses did not exceed 0.1 SED. For most of the flights, the UV-A exposure was also low. On 27 single sector flights, UV-A exposure could have exceeded the ICNIRP guidance if eye protection was not used.DISCUSSION: The UV exposure in a cockpit is mostly governed by the presence of direct sunlight and the duration of a flight. The average monthly exposures were low and significantly below weekend recreational exposures of UK office workers over a similar period. To assess the contribution of occupational UV exposure to the risk of developing sun-related ocular and cutaneous pathologies, it is important to consider the accumulative flight time, destinations, and UV attenuation of aircraft windshields. Additionally, leisure and recreational outdoor time needs to be considered before meaningful overall risk analysis can be undertaken.Baczynska KA, Brown S, Chorley AC, O'Hagan JB, Khazova M, Lyachev A, Wittlich M. In-flight UV-A exposure of commercial airline pilots. Aerosp Med Hum Perform. 2020; 91(6):501-510.

Antibacterial and Hydrophilic Modification of PET Fabrics by Electron Beam Irradiation Process

Electron beam (EB) irradiation has been utilized to modify materials for various applications due to its remarkable advantages. As an efficient and environmental-friendly way for antibacterial and hydrophilic purposes, EB irradiation was applied to modify polyethylene terephthalate (PET) fabrics by grafting with a N-halamine precursor monomer 3-allyl-5,5-dimethylhydantoin (ADMH) and acrylic acid (AA) in this study. The grafted PET fabrics were loaded with silver ions to further enhance the antimicrobial efficacy. The hydrophilicity of the modified PET fabrics was evaluated by testing the water contact angles with different contact times. The breaking strength and thermal stability of the modified swatches were studied. The UVA light stability results showed the chlorine loading of the modified PET fabrics decreased with the extension of UVA exposure time, and most chlorine loading could be recovered by re-chlorination. The antibacterial test showed that the modified PET swatches can inactivate all inoculated S. aureus and E. coli with short contact times.

Reclamation of agro-wastewater polluted with thirteen pesticides by solar photocatalysis to reuse in irrigation of greenhouse lettuce grown

In Mediterranean countries, reuse of reclaimed water is essential for crop irrigation. The occurrence of pesticides in agro-wastewater may represent a risk for human health and environment owing to their release in soil and translocation to plants. The novelty of this work relies on the reuse of reclaimed agro-wastewater polluted with thirteen pesticides for lettuce irrigation. Removing of pesticide residues in agro-wastewater was carried out using natural sunlight and TiO2/Na2S2O8 in a pilot facility located in Murcia (SE of Spain). The studied pesticides were azoxystrobin, boscalid, chlorpropham, flutolanil, flutriafol, isoxaben, methoxyfenozide, myclobutanil, napropamide, prochloraz, propamocarb, propyzamide and triadimenol, which are commonly used in southeast Spain to treat lettuces grown. Different heterogeneous and homogeneous processes were studied and compared. Previously, the optimization of the process for the selection of the best catalytic system was performed at lab-scale. TiO2+ S2O82− was selected due to the greater effectiveness, achieving almost complete disappearance after about 400 kJ m−2 of cumulative UVA exposure. No significant differences were observed in quality parameters of lettuce grown using treated and non-treated agro-wastewater.

Hormesis ultraviolet radiation and its effects on Drosophila melanogaster performance

Hormesis can be protective as a multifarious response that results in upregulation of genes and organismal performance. The protective effects of hormesis in animal models includes improved survival, mating, extended longevity, and improved performance at old age (i.e. mating); amongst others. The sun is a source of energy used by terrestrial life in many trophic levels allowing for exposure to irradiation (UVR), a natural environmental stressor that increases production of reactive oxygen species (ROS) .This type of environmental stress is damaging by attacking lipids, proteins and DNA. Exposure to prolonged UVR conditions early in life (pupae) leads to changes in performance later in life. This response can be classified as preconditioning, pretreatment, conditioning, or cross tolerance. Previous studies scantily provide appropriate levels of exposure needed for UVR hormesis that would increase production of ROS and antioxidant enzymes. The age of the individual at the time of treatment can have dramatic effects on hormesis with low dose UVR effects that induce protection, an extension of normal life span and improved organismal performance shown in other insects. The vinegar fly, Drosophila melanogaster, was exposed to UVA at different intensities. Vials containing pupae, separated from food and kept in same vial were exposed to 0, 30, 45 or 60 minutes of ultraviolet radiation A (nm = 365). Different rates of UVA exposure (mW/m2), produced by the distance from the source, show slight differences in treatment survival/adult emergence and flight ability. Low doses of UVR lead to protective and beneficial responses, while exposures to high doses are damaging and detrimental. Ultimately, data such as these can be refined to develop a model of dose response that can be used to estimate hormesis, or the biphasic response.Support or Funding InformationNIH RISE 5R25GM061222‐19

Repeat UVA exposure of human skin fibroblasts induces both a transitionary and recovery DNA methylation response.

Aim: UVA radiation drives skin photoaging in the dermis, plausibly via persistent changes to DNA methylation in dermal fibroblasts. Methods: Genome-wide DNA methylation changes after fiverepeated daily UVA doses were determined at 48h (transitionary) and 1week (recovery) post final irradiation. Results: Differential methylation was found at the transitionary time point in active chromatin states near genes that are highly expressed in fibroblasts and are involved in cellular defensive mechanisms; the majority of these methylation differences were restored to control levels after 7day recovery. At the recovery time point, new differential methylation occurred at repressed regions near developmental genes, normally weakly expressed in fibroblasts. Conclusion: UVA irradiation induces transitionary and recovery-associated DNA methylation responses in fibroblasts with contrasting functional characteristics.

Degradation problem in silver nanowire transparent electrodes caused by ultraviolet exposure

Silver nanowire (AgNW) transparent electrode inevitably encounters ultraviolet (UV) irradiation from the environment, leading to stability and durability problems when in operation. Since UVA is the most abundant UV band and highly penetrating to AgNW related optoelectrical devices, it is crucial to understand the UVA damage caused to AgNWs. In this study, transparent electrodes composed of pristine AgNWs and glass substrates were manufactured with optimized processing parameters, and then used as model samples for aging tests. UVA exposure was conducted at elevated temperatures including 45 °C, 60 °C and 75 °C at 12 ± 5.5% relative humidity (RH) conditions. Comparative aging tests using conditions of damp heat (85 °C/85% RH) and 105 °C without UV (dark conditions) were also conducted. The relationship between optoelectrical property degradation, morphological changes and photo-corrosion was discussed. Under UVA exposure, the sheet resistance of electrodes increased gradually in an induction period before an abrupt change occurred. A nominal sheet resistance value of 200 Ω/sq was considered as a predestined failure of electrical property. It took 16, 24 and 60 h for UVA exposure at 75 °C, 60 °C and 45 °C, respectively, and 288 h by damp heat aging to degrade to the same status of predestined failure. Aging results of dark conditions indicated no degradation effect on AgNWs for 126 d aging. Moisture caused a different mechanism in damaging the capping agents on AgNWs. Nanocubes of silver chloride and sodium chloride were prone to precipitate at higher aging temperature such as 75 °C with UVA exposure. Sulfidation accounted for deterioration of optical transmittance, and occurred significantly at 45 °C with UVA irradiation and under damp heat conditions. The synergistic aging effect of UVA irradiance at elevated temperature on AgNW degradation has been unambiguously demonstrated. The results of this study provide guidelines for the design of optoelectronic devices when utilizing AgNW transparent electrodes.