UVA Exposure Research Articles

SPR sensors for monitoring the degradation processes of Eu(dbm)3(phen) and Alq3 thin films under atmospheric and UVA exposure

The degradation processes of tris(8-hydroxyquinoline) (Alq3) and tris(dibenzoylmethane) mono(1,10-phenanthroline)europium(III) (Eu(dbm)3(phen)) thin films are investigated by the use of AFM, photoluminescence and SPR spectroscopy. The plasmonic sensors are operated both in air and nitrogen environments, where they are irradiated with controlled doses of UVA radiation. AFM results don’t reveal the formation of heterogeneous phases and crystallization under air exposure. The organic thin films change their refractive index under both types of exposure and act as a protective layer against oxidation for the SiO2/MPTS/metal interface of the plasmonic sensors. SPR measurements reveal a strict correlation between the refractive index increase and quenching of the photoluminescence of the organic thin films. The results are promising for the development of compact plasmonic UVA dosimeters in the surface plasmon coupled emission configuration (SPCE) with lanthanide β-diketonate complex materials (patent pending).

PLGA nanoformulation of sparfloxacin enhanced antibacterial activity with photoprotective potential under ambient UV-R exposure

Sparfloxacin (SPFX) is a broad spectrum antibiotic which inhibits bacterial DNA gyrase enzyme activity. However, photodegradation in the presence of UVA limits its antibacterial activity and induces phototoxicity. Thus, to encounter this problem, we have developed poly d,l-lactic-co-glycolic acid (PLGA) loaded SPFX nanoparticles. Here, we have performed a comparative antibacterial activity of SPFX and its nanoparticles (NPs) through molecular docking and plate sensitivity assay. Under environmental UVA exposure, photoexcited SPFX significantly generates ROS, DNA damage and mitochondrial mediated cell death in comparison to PLGA-SPFX-NPs (nano SPFX) in human skin cell line (HaCaT). In presence of UVA, bulk SPFX induced cell cycle arrest with appearance of sub-G1 peak showing apoptosis while nano SPFX did not show any change. SPFX triggered apoptosis via alteration in membrane integrity of mitochondria and lysosome in comparison to PLGA-SPFX-NPs. Involvement of mitochondrial mediated cell death was confirmed by down-regulation of anti-apoptotic Bcl-2 and procaspase-3 and upregulation of pro-apoptotic Bax, cytochrome-c and caspase-3 proteins expression. Specific caspase inhibitor, Z-VAD-FMK showed involvement of caspase cascade pathway in apoptosis. Our finding suggests that controlled release of SPFX from PLGA-SPFX-NPs can reduce its side effects and enhance its antibacterial activity. Thus, nanotization of fluoroquinolones will be a significant step to reduce the problem of resistance and phototoxicity of this group.

Effects of Developmental Stages and Reduced UVB and Low UV Conditions on Plant Secondary Metabolite Profiles in Pak Choi (Brassica rapa subsp. chinensis).

Pak choi (Brassica rapa subsp. chinensis) is rich in secondary metabolites and contains numerous antioxidants, including flavonoids; hydroxycinnamic acids; carotenoids; chlorophylls; and glucosinolates, which can be hydrolyzed to epithionitriles, nitriles, or isothiocyanates. Here, we investigate the effect of reduced exposure to ultraviolet B (UVB) and UV (UVA and UVB) light at four different developmental stages of pak choi. We found that both the plant morphology and secondary metabolite profiles were affected by reduced exposure to UVB and UV, depending on the plant's developmental stage. In detail, mature 15- and 30-leaf plants had higher concentrations of flavonoids, hydroxycinnamic acids, carotenoids, and chlorophylls, whereas sprouts contained high concentrations of glucosinolates and their hydrolysis products. Dry weights and leaf areas increased as a result of reduced UVB and low UV. For the flavonoids and hydroxycinnamic acids in 30-leaf plants, less complex compounds were favored, for example, sinapic acid acylated kaempferol triglycoside instead of the corresponding tetraglycoside. Moreover, also in 30-leaf plants, zeaxanthin, a carotenoid linked to protection during photosynthesis, was increased under low UV conditions. Interestingly, most glucosinolates were not affected by reduced UVB and low UV conditions. However, this study underlines the importance of 4-(methylsulfinyl)butyl glucosinolate in response to UVA and UVB exposure. Further, reduced UVB and low UV conditions resulted in higher concentrations of glucosinolate-derived nitriles. In conclusion, exposure to low doses of UVB and UV from the early to late developmental stages did not result in overall lower concentrations of plant secondary metabolites.

The Effects of Ultraviolet Radiation on Nucleoside Modifications in RNA.

Ultraviolet radiation (UVR) is a known genotoxic agent. Although its effects on DNA have been well-documented, its impact on RNA and RNA modifications is less studied. By using Escherichia coli tRNA (tRNA) as a model system, we identify the UVA (370 nm) susceptible chemical groups and bonds in a large variety of modified nucleosides. We use liquid chromatography tandem mass spectrometry to identify specific nucleoside photoproducts under in vitro and in vivo conditions, which were then verified by employing stable-isotope labeled tRNAs. These studies suggest that the -amino or -oxy groups of modified nucleosides, in addition to sulfur, are labile in the oxidative environment generated by UVA exposure. Further, these studies document a range of RNA photoproducts and post-transcriptional modifications that arise because of UVR-induced cellular stress.

Trans-cinnamic acid attenuates UVA-induced photoaging through inhibition of AP-1 activation and induction of Nrf2-mediated antioxidant genes in human skin fibroblasts

BackgroundUVA irradiation-induced skin damage/photoaging is associated with redox imbalance and collagen degradation. ObjectiveDermato-protective efficacies of trans-cinnamic acid (t-CA), a naturally occurring aromatic compound have been investigated against UVA irradiation, and elucidated underlying molecular mechanism. MethodsHuman foreskin fibroblast-derived (Hs68) cells and nude mice were treated with t-CA prior to UVA exposure, and assayed the anti-photoaging effects of t-CA. ResultsWe found t-CA (20–100 μM) pretreatment substantially ameliorated UVA (3 J/cm2)-induced cytotoxicity, and inhibited intracellular ROS production in Hs68 cells. UVA-induced profound upregulation of metalloproteinase (MMP)-1/-3 and degradation of type I procollagen in dermal fibroblasts were remarkably reversed by t-CA, possibly through inhibition of AP-1 (c-Fos, but not c-Jun) translocation. The t-CA-mediated anti-photoaging properties are associated with increased nuclear translocation of Nrf2. Activation of Nrf2 signaling is accompanied with induction of HO-1 and γ-GCLC expressions in t-CA-treated fibroblasts. Furthermore t-CA-induced Nrf2 translocation is mediated through PKC, AMPK, CKII or ROS signaling cascades. This phenomenon was confirmed with respective pharmacological inhibitors, GF109203X, Compound C, CKII inhibitor or NAC, which blockade t-CA-induced Nrf2 activation. Silencing of Nrf2 signaling with siRNA showed no anti-photoaging effects of t-CA against UVA-induced ROS production, loss of HO-1 and type I collagen degradation in fibroblasts. In vivo evidence on nude mice revealed that t-CA pretreatment (20 or 100 mM/day) significantly suppressed MMP-1/-3 activation and maintained sufficient type I procollagen levels in biopsied skin tissue against UVA irradiation (3 J/cm2/day for 10-day). Conclusiont-CA treatment diminished UVA-induced photoaging/collagen degradation, and protected structural integrity of the skin.

Effects of UV radiation and rainfall reduction on leaf and soil parameters related to C and N cycles of a Mediterranean shrubland before and after a controlled fire

In the Mediterranean basin, reduction in cloudiness owing to climate change is expected to enhance solar ultraviolet (UV) levels and to decrease rainfall over the coming years, which would be accompanied by more frequent and intense wildfires. The aim of the present study was to investigate the role of solar UV-A and UV-B radiation in C and N pools of a Mediterranean shrubland and whether drier conditions could alter this role before and after a fire. Over a three-year field experiment, 18 plots of 9 m2 were subjected to three UV conditions (UV-A + UV-B exclusion, UV-B exclusion or near-ambient UV-A + UV-B exposure) combined with two rainfall regimes (natural or reduced rainfall). Several parameters related to C and N cycles in the soil and in the leaves and litter of two dominant plant species (Arbutus unedo and Phillyrea angustifolia) were measured before and after an experimental fire. UV-A exposure increased soil moisture throughout the study period, as well as respiration before the fire. The additional presence of UV-B decreased β-glucosidase activity at 5–10 cm depth and soil respiration and pH. UV-B exposure also raised leaf C concentration in P. angustifolia and δ15N values in A. unedo. Reduced rainfall often emphasized the opposite effects of UV-A and UV-B on the studied parameters. After the fire, most of the UV and rainfall effects were lost. UV-A exposure seems to stimulate soil biological activity and, thus, C and N turn-over, while the effect of UV-B would be the opposite. At least in the short term, the “homogenizing influence” of fire would probably have a stronger effect on the C and N cycles than the expected changes in UV and rainfall levels.

Effects of myo-inositol, gymnemic acid, and L-methylfolate in polycystic ovary syndrome patients

Polycystic ovary syndrome (PCOS) is a heterogeneous endocrine and metabolic disorder, characterized by chronic anovulation/oligomenorrhea, hyperandrogenism, and insulin-resistance. Moreover, some studies propose a possible association between insulin resistance and hyperhomocysteinemia, which is a significant long-term risk for factor for atherogenesis and chronic vascular damage, especially in situations where insulin levels are increased. Insulin-sensitizing agents are used in the treatment of PCOS: in fact, inositols were shown to have insulin-mimetic properties. Synergic action to myo-inositol is that of gymnemic acids that have antidiabetic, anti-sweetener, and anti-inflammatory activities. Gymnemic acid formulations have also been found useful against obesity due to their ability to delay the glucose absorption in the blood. L-methyl-folate increases peripheral sensitivity to insulin, maintaining folatemia stable, and thus restoring normal homocysteine levels. Unlike folic acid, L-methyl folate has a higher bioavailability, no drug/food interferences, high absorption, and it is stable to UV-A exposure. The aim of our study is to compare the clinical, endocrine, and metabolic parameters in 100 PCOS women treated with myo-inositol, gymnemic acid, and l-methylfolate (Group A) or myo inositol and folic acid only (Group B), continuously for 6 months. From a clinical point of view, it was noticed a more significant improvement of the menstrual cycle regularity and a more significant reduction of BMI in Group A. Moreover, a more significant decrease of total testosterone and increase of SHBG serum levels were noticed in Group A. The metabolic assessment found a more significant decrease of total cholesterol and homocysteine levels; OGTT glycemia and insulinemia values were significantly more improved after treatment with myo-inositol + gymnemic acid. In conclusion, we can state that a good option for the treatment of PCOS is the combined administration of myo-inositol + gymnemic acid + l-methyl-folate, especially for overweight/obese patients with marked insulin resistance and with associated hyperhomocysteinemia.

Under ambient UVA exposure, pefloxacin exhibits both immunomodulatory and genotoxic effects via multiple mechanisms

Pefloxacin (PFLX) is an antibiotic, which shows broad spectrum antimicrobial activities. It is an important derivative of fluoroquinolones (FLQs) group. Ultraviolet radiation (200–400nm) causes major problem for living being which comes at the earth surface naturally through sunlight and increasing regularly due to ozone depletion. PFLX was photodegraded in 5h and forms photoproduct under UVA exposure. At the non photocytotoxic dose PFLX, shows reduced phagocytosis activity, NO (nitric oxide) production, large vacuole formation and down regulated IL-6, TNF-α and IL-1 in BALB/c macrophages at both genes and proteins levels. At higher doses (photocytotoxic doses), PFLX induced a concentration dependent decrease in cell viability of human keratinocyte cell line (HaCaT) and peritoneal macrophages of BALB/c mice. Our molecular docking suggests that PFLX binds only to the cleaved DNA in the DNA-human TOP2A complex. Topoisomerase assay confirmed that PFLX inhibits human topoisomerase by forming an adduct with DNA. Photosensitized PFLX also caused intracellular ROS mediated DNA damage and formation of micronuclei and cyclobutane pyrimidine dimers (CPDs). Increase intracellular ROS leads to apoptosis which was proved through lysosomal destabilization and reduced mitochondrial membrane potential (MMP). Our present study shows that ambient UVA exposure in the presence of PFLX caused immunomodulatory as well as photogenotoxic effects. Therefore, patients under PFLX drug treatment should avoid sunlight exposure, especially during peak hours for their photosafety.

Phototoxic effect of oxytetracycline on normal human melanocytes

Oxytetracycline is a broad-spectrum antibiotic, used in dermatology and veterinary medicine. Like other tetracyclines, it may evoke skin phototoxic reactions related to generation of reactive oxygen species (ROS). Melanins are biopolymers synthesised in melanocytes – highly specialised cells, localised in the basal layer of epidermis. Production of melanin is a defence mechanism against harmful effects of UV radiation, ROS and many chemical substances, including drugs. In the present study the influence of oxytetracycline and UVA radiation on darkly pigmented melanocytes viability, the melanogenesis process and the activity of antioxidant enzymes were analysed. The obtained results show that oxytetracycline decreases cell viability in a dose-dependent manner. It has also been stated that UVA radiation as well as simultaneous exposure to oxytetracycline and UVA radiation reduce melanocytes viability. The tested drug alone exhibits little effect on antioxidant enzymes activity and has no influence on the synthesis of melanin. However, simultaneous exposure of the cells to oxytetracycline and UVA radiation causes an increase of SOD and GPx activity, a decrease of CAT activity as well as stimulates melanogenesis. The obtained results suggest that phototoxicity of oxytetracycline towards normal human melanocytes depends on both time of UVA exposure and the drug concentration.

Long-term Genoprotection Effect of Sechium edule Fruit Extract Against UVA Irradiation in Keratinocytes.

Photoprotection is essential to prevent the long-term deleterious effects of ultraviolet (UV), including skin cancer and photoaging. So far, there has been an increase in the use of natural bioactive phytochemicals for the development of more effective skin photoprotective agents. However, the molecular mechanisms underlying the photochemoprotection activity of such compounds remain largely unknown. The objective of this study was to investigate the effects of a Sechium edule fruit extract (SEE) in terms of photoprotection against UVA in primary human keratinocytes. We found that SEE protected keratinocytes against UVA-induced cytotoxicity, decreased the intracellular amounts of reactive oxygen species, and reduced oxidatively induced DNA lesions after UVA exposure. Furthermore, SEE decreased the induction of CPD lesions in UVA-irradiated keratinocytes and exhibited increased DNA repair of such photoproducts at 24h postexposure. Finally, using DNA repair biochips, we demonstrated that SEE-treated keratinocytes had DNA enzymatic repair activities more efficient for abasic sites, CPD and thymine glycols. Therefore, the benefits of SEE against UVA could be explained by a combination of antioxidant activity, the reduction in DNA damage, and the enhancement of DNA repair capacities.

Repeated ultraviolet irradiation induces the expression of Toll-like receptor 4, IL-6, and IL-10 in neonatal human melanocytes.

Human melanocytes express Toll-like receptor 4 (TLR4), which regulates ultraviolet (UV)-induced cutaneous immunosuppression in Langerhans cells. Lipopolysaccharide (LPS) stimulation increases melanocyte pigmentation and TLR4 expression, while inducing local innate inflammatory responses. We investigated whether UV radiation induces TLR4 expression in neonatal human melanocytes (NHMs) and how this affects the immune system. We cultured NHMs with LPS treatment or with one-time or repeated UVA or UVB exposure, and investigated and compared the effects on TLR4 expression, melanin contents, and cytokine production. NHMs in the resting state did not express TLR4. LPS stimulation induced TLR4 expression and increased pigmentation. TLR4 expression was not detected after single-dose UVA or UVB treatment, but pigmentation increased. Repeated UV treatment induced TLR4 expression and increased pigmentation. LPS stimulation and repeated UV treatment increased IL-6 secretion, and repeated UVB treatment increased IL-10 secretion. These results suggest that human melanocytes may actively participate in UV-induced immune modulation.

Tolerance of the eriophyid mite Aceria salsolae to UV-A light and implications for biological control of Russian thistle.

Aceria salsolae (Acari: Eriophyidae) is being evaluated as a candidate biological control agent of Russian thistle (Salsola tragus, Chenopodiaceae), a major invasive weed of rangelands and dryland crops in the western USA. Prior laboratory host range testing under artificial lighting indicated reproduction on non-native Bassia hyssopifolia and on a native plant, Suaeda calceoliformis. However, in field tests in the native range, mite populations released on these 'nontarget' plants remained low. We hypothesized that UV-A light, which can affect behavior of tetranychid mites, would affect populations of the eriophyid A. salsolae differently on the target and nontarget plant species, decreasing the mite's realized host range. Plants were infested with A. salsolae under lamps that emitted UV-A, along with broad-spectrum lighting, and the size of mite populations and plant growth was compared to infested plants exposed only to broad-spectrum light. Russian thistle supported 3- to 55-fold larger mite populations than nontarget plants regardless of UV-A treatment. UV-A exposure did not affect mite populations on Russian thistle or S. calceoliformis, whereas it increased populations 7-fold on B. hyssopifolia. Main stems on nontarget plants grew 2- to 6-fold faster than did Russian thistle under either light treatment. The two nontarget plants attained greater volume under the control light regime than UV-A, but Russian thistle was unaffected. Although Russian thistle was always the superior host, addition of UV-A light to the artificial lighting regime did not reduce the ability of A. salsolae to reproduce on the two nontarget species, suggesting that UV-B or other environmental factors may be more important in limiting mite populations in the field.

80 - Lipofuscin Generated by UVA Exposure makes Human Skin Keratinocytes Sensitive to Visible Light

The effects of UV radiation on skin cells are well known, while the effect of other fractions of the solar spectrum remains ignored. Recently, we observed that both neonatal primary normal human keratinocyte (NHK) and in immortalized human keratinocytes (HaCaT) cells exposed to UVA and after exposure to visible light had reduction in cell viability, increasing level of redox misbalance as monitored by the increase in DCF fluorescence, and the generation of singlet oxygen. We also detected strand breaks of nuclear DNA and premutagenic Fpg and Endo III-sensitive DNA lesions by Comet assay. Our data showed that UVA radiation (λ= 366 nm, 12 J.cm-2) generates lipofuscin, which is an autofluorescent visible-photosensitizer and a subproduct of incomplete lysosomal digestion of oxidized biomolecules, organelles, and membranes. Visible light photosensitizes lipofuscin inducing photooxidatives processes through the generation of several oxidizing species, which can damage DNA and generate premutagenic lesions, as 8-oxo-dG. Lipofuscinogenesis was also shown to occur more effectively through specific oxidative damages in lysosomes and mitochondria by with photosensitization of 1,9-dimethyl methylene blue (DMMB) 10 nM with red light (λ= 633 nm, 11 J.cm-2). We have then characterized the lipofuscin from human skin keratinocytes by fluorescence lifetime imaging and fluorescence spectroscopy (fluorescence lifetime = 2 ns; excitation at 450 nm and emission at 640 nm). Concluding, UVA and visible light can be dangerous to skin health, raising the importance of not only protecting ourselves against UV radiation, but also against visible light.

Polymeric Antimicrobial N-Halamine-Surface Modification of Stainless Steel

The surfaces of materials fabricated from stainless steel are challenging to functionalize with antimicrobial moieties. This work demonstrates that stainless steel surfaces can be modified with an N-halamine-based copolymer in order to obtain antimicrobial activity. In this regard, a copolymer (HACM) of 2-acrylamido-2-methyl-1-(5-methylhydantoinyl)propane and 3-cloro-2-hydroxypropyl methacrylate was synthesized and grafted onto a stainless steel surface via covalent attachment. Synthesized monomers and copolymers were characterized by NMR, FTIR, and XPS spectral analyses. Upon treatment with dilute bleach, the stainless steel surfaces were rendered antimicrobial, possessing a sufficient amount of chlorine content and excellent stability and durability. The modified stainless steel samples inactivated 6 logs of Staphylococcus aureus and Escherichia coli O157:H7 bacteria within 15 min of contact time. Stabilities of the coatings toward washing and UVA exposure were also studied. The stainless steel samples ...

623 The influence of photoirradiation on the circadian clock genes in human keratinocytes and melanocytes

Human circadian rhythm is organized in hierarchical structure which composed of central pacemaker in the suprachiasmatic nucleus (SCN) of the ventral hypothalamus and peripheral organs. Visible light enters the retina and stimulates SCN, and then the central master clock in the SCN communicates timing information to the skin via a combination sympathetic innervation and secreted hormones. On the other hands, ultraviolet (UV) B rays directly induces expression of the circadian clock genes, such as Per1, Clock and Bmal1 in cultured human keratinocytes. In this study, we investigated that the influence of visible light and UV on the circadian clock genes in human keratinocytes and melanocytes. Stratified keratinocytes and melanocytes were monochromatically irradiated at 280-310 nm using a multiwavelength irradiation spectral apparatus. In addition, melanocytes were irradiated at 365-940 nm using a light emitting diode (LED). 24 h after irradiation, total RNA was extracted and analyzed by Cap Analysis of Gene Expression (CAGE). In keratinocytes, Per1, Per2, Clock, Cry, Bmal1 and RORA were upregulated by 280-300 nm irradiation compared with sham irradiation. In melanocytes, Per2 was upregulated by 280-310 nm irradiation. There was no remarkable change in 365-940 nm irradiation. In conclusion, the circadian rhythm in the skin cells is regulated by UVB irradiation. Future outlook on research is to investigate that the effect of UVA and visible light exposure on clock gene expression in keratinocytes.

UVA-Induced DNA Damage and Apoptosis in Red Blood Cells of the African Catfish Clarias gariepinus.

Ultraviolet-A light (UVA)-induced DNA damage and repair in red blood cells to investigate the sensitivity of African catfish to UVA exposure is reported. Fishes were irradiated with various doses of UVA light (15, 30, and 60 min day-1 for 3 days). Morphological and nuclear abnormalities in red blood cells were observed in the fish exposed to UVA compared with controls. Morphological alterations such as acanthocytes, crenated cells, swollen cells, teardrop-like cells, hemolyzed cells, and sickle cells were observed. Those alterations were increased after 24 h exposure to UVA light and decreased at 14 days after exposure. The percentage of apoptosis was higher in red blood cells exposed to higher doses of UVA light. No micronuclei were detected, but small nuclear abnormalities such as deformed and eccentric nuclei were observed in some groups. We concluded that exposure to UVA light induced DNA damage, apoptosis, and morphological alterations in red blood cells in catfish; however, catfish were found to be less sensitive to UVA light than wild-type medaka.

Differential modes of photosensitisation in cancer cells by berberine and coralyne

In this study, we demonstrated that the cytotoxicity of the protoberberine alkaloids such as coralyne, berberine and jatrorrhizine to several human cancer cell lines can be improved significantly in combination with UVA exposure. However, the phototoxic property of coralyne was much higher than that of the other two alkaloids. The combination of coralyne and UVA (designated as CUVA) induced oxygen-independent cytotoxicity in the human lung cancer A549 cells by producing more lethal DNA double-strand breaks, and the effect was mediated via the replication machinery. In comparison, the berberine-induced phototoxicity to the A549 cells was mediated by reactive oxygen species generation, mitochondrial membrane permeabilisation and caspase-9/caspase-3 activation.

Light spectral effects on phenolic compounds inPerilla frutescensleaves as related to the leaf age, color and duration of exposure

We aimed to evaluate the effects of light spectral components on the phenolic compounds in young and mature green and red perilla leaves seeking to raise plants with increased antioxidant and nutritional value. Plants were cultivated in phytotron (21/17°C) under experimental light emitting diode (LED) based lighting (18 h, 300 µmol m-2 s-1) the whole 30 days growth cycle (long-term exposure) or transferred from high pressure sodium lighting to experimental LED lighting for the last 3 days of experiment (short-term exposure). Experimental lighting spectra consisted of sole red 638 or 665 nm LED light (300 µmol m-2 s-1) or the combination of red 665 nm with 50 µmol m-2 s-1 of blue 455, yellow 595, green 520 nm or 15 µmol m-2 s-1 of UV-A 385 nm light (total PPFD of 300 µmol m-2 s-1 maintained). Sole red light promoted accumulation of phenolic compounds in young red and green perilla leaves both after short-term and long-term exposure, when supplemental blue light had significant effect only in mature leaves. In young green perilla leaves higher contents of phenolic compounds were determined after short-term UV-A exposure. The higher contents of phenolic compounds under different light spectra exposure correlates with higher 2,2-diphenyl-1-picrylhydrazyl (DPPH) free radical scavenging activity after long-term exposure in green perilla and both after long and short-term exposure in red perilla leaves.

Effect of heat, UV radiation, and moisture on the decohesion kinetics of inverted organic solar cells

Organic solar cells subjected to environmental stressors such as heat, moisture, and UV radiation can undergo significant mechanical degradation, leading to delamination of layers and device failure. This paper reports the effect these stressors have on the mechanical integrity of active layers and interfaces as measured by subcritical debonding tests, and the in situ evolution of defects and fracture processes is characterized. At elevated temperatures below 50°C in inert conditions, significant device weakening was observed, an effect we attributed to a temperature-induced P3HT:PCBM delamination mechanism from the underlying ZnO. At 50°C in ambient conditions with UV exposure—selected to better simulate real-world environments—devices were more resistant to fracture because of an interfacial strengthening effect from increased hydrogen bonding where UV-induced Zn(OH)2 formation reinforced the interface with P3HT:PCBM. This photoinduced hydroxylation mechanism was determined from a decrease in the Zn/O ratio with increased UVA or UVB exposure, and hydroxylation was shown to directly correlate with the resistance to fracture in devices.

Photodegradation stability study of PVDF- and PEI-based membranes for oily wastewater treatment process

In this work, an attempt was made to compare the effects of UV irradiation on the intrinsic and separation properties of membranes made of two different polymeric materials, i.e., polyvinylidene fluoride (PVDF) and polyetherimide (PEI). The changes on membrane structural morphologies and chemical characteristics upon UV-A exposure (up to 60 h) were studied by FESEM and FTIR, respectively. It was found that cracks and fractures were detected on the PVDF-based membrane surface when the membrane was exposed directly to UV light for up to 60 h. Furthermore, the mechanical strength and thermal stability of irradiated PVDF-based membrane was reported to decrease with increasing UV exposure time. The PEI membrane surface meanwhile remained almost intact throughout the entire UV irradiation process. Filtration experiments showed that the permeate flux of UV-irradiated PVDF membrane was significantly increased from approximately 11 to 16 L/m2.h with increasing UV exposure time from zero to 60 h. Oil rejection meanwhile was decreased from 98 to 85%. For the PEI-based membrane, oil rejection of > 97% was recorded and its overall structural integrity was marginally affected throughout the entire UV irradiation process. The findings of this work showed that the PEI-based membrane should be considered as the host for photocatalyts incorporation if the membrane was to be used for UV-assisted wastewater treatment process.