Long-term Ultraviolet Irradiation Research Articles

Robust, Flexible, and Superhydrophobic Fabrics for High-efficiency and Ultrawide-Band Microwave Absorption

Microwave absorption (MA) materials are essential for protecting against harmful electromagnetic radiation. In this study, highly efficient and ultrawide-band microwave-absorbing fabrics with superhydrophobic surface features were developed using a facile dip-coating method involving in situ graphene oxide (GO) reduction, deposition of TiO2 nanoparticles, and subsequent coating of a mixture of polydimethylsiloxane (PDMS) and octadecylamine (ODA) on polyester fabrics. Owing to the presence of hierarchically structured surfaces and low-surface-energy materials, the resultant reduced graphene oxide (rGO)/TiO2-ODA/PDMS-coated fabrics demonstrate superhydrophobicity with a water contact angle of 159° and sliding angle of 5°. Under the synergistic effects of conduction loss, interface polarization loss, and surface roughness topography, the optimized fabrics show excellent microwave absorbing performances with a minimum reflection loss (RLmin) of −47.4 dB and a maximum effective absorption bandwidth (EABmax) of 7.7 GHz at a small rGO loading of 6.9 wt%. In addition, the rGO/TiO2-ODA/PDMS coating was robust, and the coated fabrics could withstand repeated washing, soiling, long-term ultraviolet irradiation, and chemical attacks without losing their superhydrophobicity and MA properties. Moreover, the coating imparts self-healing properties to the fabrics. This study provides a promising and effective route for the development of robust and flexible materials with microwave-absorbing properties.

Characterization of the degradation products of biodegradable and traditional plastics on UV irradiation and mechanical abrasion

Biodegradable plastics are popular alternatives to traditional plastics in packaging, mulch sheets, and other applications. However, there are concerns regarding the potential for pollution as a result of their abiotic degradation. In this study, we investigated the degradation of biodegradable polybutylene adipate terephthalate/polylactic acid (PBAT/PLA) and traditional polyethylene (PE) plastic under two typical abiotic conditions: ultraviolet (UV) irradiation and mechanical abrasion (MA) for up to nine months. The physical and chemical properties of the two plastics during the degradation period were assessed. In addition, quantitative analysis of the degradation products was carried out using a new method called membrane filtration and total organic carbon determination (MF-TOCD). The results revealed that PBAT/PLA underwent a greater number of changes in surface morphology, thermal stability, and mass loss compared to PE when exposed to UV and MA during the test period. Further analysis of the released products revealed that PBAT/PLA released more products than PE. Overall, PE mainly produced microplastics (MPs) larger than 0.22 μm, whereas PBAT/PLA produced products <0.22 μm (nanoplastics and soluble molecules) on UV exposure. In contrast, when subjected to MA, PBAT/PLA produced MPs larger than 0.22 μm, and these accumulated gradually; this behavior is similar to that of PE. By combining the mass loss and the TOC data for the degradation products, we determined that long-term UV irradiation generated a large number of smaller particles from PBAT/PLA that could further degrade rather than accumulate in the environment. In summary, we established a new method to separate and characterize MPs as well as nanoplastics and soluble molecules, and provided new insights into the fate of PBAT/PLA during abiotic degradation.

Continuous ultraviolet irradiation induces the development of irreversible resistance of melanoma cells to anticancer drugs

Introduction. Melanoma belongs to the group of the most malignant tumors characterized by aggressive growth and active metastasis. At the same time, the effectiveness of therapy, primarily targeted therapy, is largely limited by the rapid development of drug resistance.Aim. To study the effect of chronic ultraviolet (UV) irradiation on the formation of a population of radiation-resistant melanoma cells; to study the features of cell signaling and the sensitivity of UV-resistant melanoma cells to the antitumor drugs.Materials and methods. The experiments were carried out on in vitro cultured A375 melanoma cells. Cells were cultured in a standard DMEM + 10 % FBS medium; cell growth rate was analyzed using the MTT assay; cell survival after irradiation was analyzed using a colony-forming test. Determination of the transcriptional activity of the estrogen receptor (ER) was performed by reporter analysis upon transfection into cells of a plasmid containing the luciferase reporter gene controlled by estrogen responsive element. The immunoblotting method was used to analyze the expression of cellular proteins; comparative analysis of ERα and ERβ expression was performed by immunofluorescent method.Results. Long-term UV irradiation leads to the formation of a UV-resistant subpopulation of A375 melanoma cells, which is characterized by decreased sensitivity to targeted (vemurafenib) and hormonal (tamoxifen) drugs, increased expression of Snail, an activator of the epithelial-mesenchymal transition, and in the absence of noticeable changes in the expression of PI3K / mTOR signaling. Metformin reduces Snail expression in both parental and UV-resistant A375 cells and enhances the cytostatic effect in combination with vemurafenib or tamoxifen.Conclusion. The data obtained demonstrate a decrease in the sensitivity of melanoma cells to targeted drugs under the long-term exposure to UV. The ability of metformin to potentiate the action of targeted drugs and inhibit Snail allows us to consider metformin not only as an antitumor agent, but also as a potential inhibitor of the epithelial-mesenchymal transition.

On-demand delivery of therapeutic extracellular vesicles by encapsulating in monodispersed photodegradable hydrogel microparticles using a droplet microfluidic device

Mesenchymal stem cells (MSCs)-derived extracellular vesicles (EVs) have been studied for therapeutic applications due to easier endocytosis and fewer adverse effects than MSCs. However, EVs injected medicinally are diluted by body fluids and inefficiently delivered to the therapeutic target, limiting original therapeutic effects. Therefore, biocompatible carriers such as hydrogels are needed in EVs delivery systems to enhance EVs retention and release EVs sustainably at therapeutic targets. In addition to the advantages of delivering EVs using hydrogels, photodegradable hydrogels provide a controllable degradation process via ultraviolet (UV) irradiation. However, long-term UV irradiation to degrade the photodegradable hydrogel may potentially damage EVs and targets; therefore, a carrier that can be degraded with shorter UV irradiation is required. Herein, we generate photodegradable hydrogel microparticles (PHMPs) that can release encapsulated EVs sustainably within 2 min of UV irradiation by droplet-based microfluidics. By regulating the fluidic resistance of the channels, monodisperse PHMPs, which can avoid undesired variations in EVs release kinetics, were generated. EVs were successfully retained in PHMPs in the absence of external stimuli, and EVs were released from PHMPs and enhanced cell proliferation following UV irradiation. Therefore, PHMPs can overcome the limitations of conventional EVs delivery, including their inability to deliver EVs sustainably and on-demand, and low EVs retention.

Time-dose reciprocity mechanism for the inactivation of Escherichia coli explained by a stochastic process with two inactivation effects

There is a great demand for developing and demonstrating novel disinfection technologies for protection against various pathogenic viruses and bacteria. In this context, ultraviolet (UV) irradiation offers an effective and convenient method for the inactivation of pathogenic microorganisms. The quantitative evaluation of the efficacy of UV sterilization relies on the simple time-dose reciprocity law proposed by Bunsen-Roscoe. However, the inactivation rate constants reported in the literature vary widely, even at the same dose and wavelength of irradiation. Thus, it is likely that the physical mechanism of UV inactivation cannot be described by the simple time-dose reciprocity law but requires a secondary inactivation process, which must be identified to clarify the scientific basis. In this paper, we conducted a UV inactivation experiment with Escherichia coli at the same dose but with different irradiances and irradiation durations, varying the irradiance by two to three orders of magnitude. We showed that the efficacy of inactivation obtained by UV-light emitting diode irradiation differs significantly by one order of magnitude at the same dose but different irradiances at a fixed wavelength. To explain this, we constructed a stochastic model introducing a second inactivation rate, such as that due to reactive oxygen species (ROS) that contribute to DNA and/or protein damage, together with the fluence-based UV inactivation rate. By solving the differential equations based on this model, the efficacy of inactivation as a function of the irradiance and irradiation duration under the same UV dose conditions was clearly elucidated. The proposed model clearly shows that at least two inactivation rates are involved in UV inactivation, where the generally used UV inactivation rate does not depend on the irradiance, but the inactivation rate due to ROS does depend on the irradiance. We conclude that the UV inactivation results obtained to date were simply fitted by one inactivation rate that superimposed these two inactivation rates. The effectiveness of long-term UV irradiation at a low irradiance but the same dose provides useful information for future disinfection technologies such as the disinfection of large spaces, for example, hospital rooms using UV light, because it can reduce the radiation dose and its risk to the human body.

Flexible ZnO Nanoparticle-Poly(methyl methacrylate) Hybrid Films and Their Ultraviolet Shielding Behaviors

Flexible hybrid films are finding increasing applications in functional devices. In this work, transparent ZnO nanoparticle and poly(methyl methacrylate) (PMMA) hybrid films are made for ultraviolet (UV) shielding with significantly higher ZnO contents than what has been reported. The tensile strength increases with the ZnO nanoparticle volume percent, from ~ 10 MPa for the pure PMMA samples to ~ 24 MPa for the 20 vol.% ZnO samples, a 150% increase. The elongation at break also increases with the ZnO content increase until 10 vol.% (a 67% increase), after which the elongation at break stays constant. All the ZnO-PMMA films show UV absorption at ~ 365 nm wavelength, with an increasing degree for higher ZnO content samples and a corresponding light transmittance decrease at longer wavelengths. Long-term UV irradiation leads to a reduction in tensile strength and elongation at break, along with lower UV shielding performance. This work proposes that the optimal ZnO content is 5–10 vol.% for the overall UV shielding performance while maintaining good mechanical properties.

Chemical Aging Resistance of Electrical Insulation Materials for Railway Passenger Train

To further improve the chemical aging resistance of Electrical Insulation Materials (EIM) for railway passenger trains, this paper prepares a modified polyvinyl chloride (PVC) with the UV Absorber (UVA) by the copper catalyzed azide-alkyne addition reaction. By analyzing the H-NMR (Nuclear Magnetic Resonance) and infrared spectrums, it is proved that UVA-modified PVC has been prepared successfully. In the end, based on the curve of the infrared spectroscopy as a function of carbonyl group content, the UV aging resistances of modified and common PVCs are compared. The findings show that the common PVC will turn into yellow after long-term ultraviolet irradiation, and the carbonyl in the compound rapidly increases, developing into severe aging; the insulationand physical structure properties has significantly deteriorated; while the modified PVC basically remains unchangedin color after 200h UV irradiation, and the carbonyl content increases at a rate much lower than the common PVC. Given the above, it is thus clear that the UVA-modified PVC prepared presents a better UV aging resistance.

Changes in the skin extensibility due to long-term ultraviolet irradiation

Changes in the skin extensibility due to long-term ultraviolet irradiation

Investigation of optical fibers for high-repetition-rate, ultraviolet planar laser-induced fluorescence of OH

We investigate the fundamental transmission characteristics of nanosecond-duration, 10kHz repetition rate, ultraviolet (UV) laser pulses through state-of-the-art, UV-grade fused-silica fibers being used for hydroxyl radical (OH) planar laser-induced fluorescence (PLIF) imaging. Studied in particular are laser-induced damage thresholds (LIDTs), nonlinear absorption, and optical transmission stability during long-term UV irradiation. Solarization (photodegradation) effects are significantly enhanced when the fiber is exposed to high-repetition-rate, 283nm UV irradiation. For 10kHz laser pulses, two-photon absorption is strong and LIDTs are low, as compared to those of laser pulses propagating at 10Hz. The fiber characterization results are utilized to perform single-laser-shot, OH-PLIF imaging in pulsating turbulent flames with a laser that operates at 10kHz. The nearly spatially uniform output beam that exits a long multimode fiber becomes ideal for PLIF measurements. The proof-of-concept measurements show significant promise for extending the application of a fiber-coupled, high-speed OH-PLIF system to harsh environments such as combustor test beds, and potential system improvements are suggested.

Altered epidermal lipid layers induced by long‐term exposure to suberythemal‐dose ultraviolet

Although several studies have reported on the biological effects of ultraviolet (UV) radiation, there have been only a few reports on the changes in epidermal lipids following long-term UV irradiation at suberythemal dose (SED), to which people are usually exposed during their lifetime. To investigate the changes of epidermal lipid properties after long-term UV radiation with SED. Hairless mice were irradiated three times weekly for 15 weeks at an SED of UV (UVB: 20 mJ/cm(2) ; UVA: 14 J/cm(2) ). Every three weeks, transepidermal water loss (TEWL) was measured by a Tewameter. The morphological alterations of stratum corneum (SC) lipid lamellae were examined by electron microscopy (EM). Activities of three key enzymes for mRNA of serine palmitoyl transferase, fatty acid synthase, and HMG CoA reductase were analyzed with real time reverse transcriptase-polymerase chain reaction. We also measured the amount of ceramide, cholesterol sulfate, and free fatty acid in the SC by high-performance thin-layer chromatography with exposed times. The SED UV-irradiated group showed increased TEWL after 12 weeks. Following the irradiation period, EM revealed incomplete and separated lamellae at SC intercellular space. mRNA of three key enzymes was increased until six weeks of UV irradiation and decreased thereafter. However, three major lipid amounts gradually decreased throughout the exposed period, with a notable decrease in ceramide. Long-term UV irradiation even with SED influences skin barrier function and structure with prominent ceramide decrease in SC intercellular lipid.

Superhydrophobic and Ultraviolet-Blocking Cotton Textiles

Cotton textile was coated with ZnO@SiO(2) nanorods in order to obtain superhydrophobic and ultraviolet (UV)-blocking properties. The coating process was conducted in mild conditions, which involved the low-temperature preparation of ZnO seeds, hydrothermal growth of ZnO nanorods, bioinspired layer-by-layer deposition of a SiO(2) shell on the surface of ZnO nanorods, and hydrophobic modification of ZnO@SiO(2) nanorods with octadecyltrimethoxysilane. Despite the highly curved morphology of cotton fibers, the ZnO@SiO(2) nanorods coated the textile densely and uniformly. The treated cotton textile was found to have a large UV protection factor (UPF = 101.51) together with UV-durable superhydrophobicity, as determined by contact-angle measurement under long-term UV irradiation. The good UV-blocking property can be ascribed to the high UV absorbance and scattering properties of ZnO nanorods, and the UV-durable superhydrophobicity is a result of suppression of the photoactivity of ZnO nanorods by a SiO(2) shell.

Role of Free Cadmium and Selenium Ions in the Potential Mechanism for the Enhancement of Photoluminescence of CdSe Quantum Dots Under Ultraviolet Irradiation

The present study describes an enhancement of the photoluminescence of CdSe quantum dots under long-term ultraviolet irradiation in organic solvents. The photoenhancement effect followed multiexponential kinetics and was found to depend on several factors: intensity of ultraviolet light, polarity of the solvent, presence of capping agents on the nanocrystal surface, and presence of free Cd and Se ions in the solution. High intensity ultraviolet irradiation provoked a rapid enhancement of the photoluminescence of CdSe nanocrystals, reaching the maximum with subsequent photoluminescence decay. Low-intensity ultraviolet irradiation provoked a comparatively slow enhancement of the photoluminescence of CdSe nanocrystals, reaching saturation after 5-6 hours of irradiation in organic solvents (butanol and chloroform). The photoenhancement effect was reversible or irreversible depending on the additional ingredients. The role of free Cd and Se in these processes was clarified. The results are discussed in the context of ultraviolet induced liberation of free Cd and Se ions from the nanocrystal surface and their hypothetical reversible deposition with trapping of the surface holes and influencing the efficiency of radiative versus nonradiative exciton decay during the enhancement of photoluminescence.

Time-dependent effect of chronic UV irradiation on superoxide dismutase and catalase activity in hairless mice skin

Reactive oxygen species are produced by ultraviolet (UV) exposure and cause oxidative damage. Enzymic antioxidants such as superoxide dismutase (SOD) and catalase (CAT) may play important defensive roles in vivo. The previous studies have focused on the acute effects after single UV irradiation on those enzyme activities. In this study, we investigated the chronic effects of ultraviolet-A (UVA) or ultraviolet-B (UVB) exposure on the skin SOD and CAT activities using hairless mice. Accumulated doses of UVA and UVB after 36-week irradiation conducted 3 times a week were 3240 J/cm 2 and 4320 mJ/cm 2, respectively. SOD activity was increased by UVB irradiation and gradually returned to control levels, but was unaffected by UVA irradiation. In contrast, CAT activity was suppressed by UVA irradiation, indicating that the skin SOD and CAT activities are not coordinately regulated by long-term UV irradiation. These findings suggest that SOD activity is induced by repeated exposures to UVB in response to chronic photooxidative stress. However, continual cumulative stress may overwhelm the capacity of this system. These time-dependent changes of the cutaneous antioxidant system by chronic UV irradiation should provide us with important information on photooxidative events in cutaneous photoaging.

Experimental elastosis induced by chronic ultraviolet exposure. Light- and electron-microscopic study.

The effect of long-term ultraviolet irradiation on the connective tissue of the skin was investigated in 25 naked (Ng/-) mice which received a total daily radiant dose of 40 +/- 2 J/cm2 for a period of 8.5 months. The produced alterations were very similar to those found in actinic elastosis of humans, as assessed by histologic and electron-microscopic criteria.

The Induction Of Melanogenesis By Ultraviolet Light In The Pigmentary System Of Rhesus Monkeys

Except for the face, eyelids, friction surfaces, and lips, the epidermis of the rhesus monkey contains no discernible melanocytes. After ultraviolet irradiation, however, dopa-positive dendritic cells appeared. With daily sequential irradiation, the number of histochemically demonstrable dopa-positive dendritic cells peaked after 30 exposures, then declined to a basal level which was maintained for the duration of the experiment (216 exposures or 43 weeks). Pigment cells can be restimulated by shading part of the irradiated area and then reirradiating after 3 months. While shaded, dopa-positive cells disappeared; but when reirradiated, they reappeared, increased, then declined again to a basal level. These melanocytes, unlike those in other primates, require high threshold levels of irradiation to produce a response, have a definite period during which they are active, and transfer very little melanin to the surrounding keratinocytes. Long-term ultraviolet irradiation has no discernible effect on dermal pigment-containing cells.