Wavelength Ultraviolet Radiation Research Articles

Determination of the Attenuation Properties of Laboratory Gloves Exposed to an Ultraviolet Transilluminator

The transmission of ultraviolet radiation (UVR) from an ultraviolet transilluminator through three types of laboratory gloves (latex, nitrile, vinyl) was determined using two independent methods. First, transmittance was measured with a radiometer equipped with UVA and actinic UV detectors. Second, a spectrophotometer was used to determine the UVR transmittance vs. wavelength (250–440 nm); this data was then used to compute the effective attenuation of the glove material. The average UVA percent transmittance using the radiometer method with an unstretched glove was 73.4%, 0.18%, and 1.10% for vinyl, nitrile, and latex, respectively. The average actinic percent transmittance for an unstretched glove was 13.3%, 0.015%, and 0.024% for vinyl, nitrile, and latex, respectively. Slight increases in UVR transmittance resulted from stretching the gloves by 30% or wetting them with saline. Six hours of UVR exposure decreased transmittance of vinyl gloves and increased transmittance by latex gloves. Results from the spectrophotometer method and radiometer methods of determining UVR transmittance agreed that vinyl gloves had the highest transmittance; however, the spectrophotometer method greatly overestimated UV glove attenuation due to the effect of light scattering by the glove material. The study suggests that in some circumstances, vinyl gloves will provide inadequate protection against workplace ultraviolet radiation.

Dissolved Organic Matter and Ultraviolet Radiation Penetration in the Laurentian Great Lakes and Tributary Waters

Stations in Lakes Huron, Erie, Ontario, and some associated bays and tributaries were surveyed to better characterize the penetration of ultraviolet radiation (UVR) and its controlling factors. Photic (1%) depths of the more damaging short and medium wavelength UVR (305–340 nm) varied widely, from 6–12 m in Lake Huron to less than 0.25 m in tributaries. Water renewal times were inversely related to vertical attenuation coefficients (K d) and also to total and carbon-specific absorption coefficients (a CDOM, a * CDOM) for dissolved organic matter (DOM), which varied much more than did the bulk concentration of DOM. K d was well correlated with a CDOM but not DOM concentration in lakes. Particulate absorption coefficients were appreciable in magnitude, averaging up to 103% of a CDOM at 380 nm and reflecting significant influence of both algal and detrital particles. Modeling of K d between 305 and 380 nm indicated that absorption by DOM and water accounted for 88–94% of UVR attenuation in tributaries, but only 37–77% in lakes. Scattering and absorption by particles accounted for up to 41 and 52% respectively of attenuation at the longer UVR wavelengths. Longer water renewal times in these large lake systems are associated with changes in optical properties of DOM that favor increased UVR penetration, and particles assume an increasingly important role as the chromophoric intensity of the DOM decreases.

Immunbiologische Effekte der extrakorporalen Photopherese

Die extrakorporale Photopherese (ECP) ist eine Therapiemodalität, bei der mit 8-Methoxypsoralen (8-MOP) behandelte lymphomononukleäre Zellen mit UVA-Licht bestrahlt werden. Die bisher bekannten immunbiologischen Effekte der ECP können in kurz- und längerfristige eingeordnet werden. Unmittelbar nach ECP sind Apoptosevorgänge bei bestrahlten 8-MOP-beladenen Lymphozyten der dominierende Prozess. Daneben kommt es durch den unmittelbaren Kontakt von antigenpräsentierenden Zellen mit dem ECP-Durchfluss-System zu einer Aktivierung und Differenzierung von dendritischen Zellen. Der Differenzierungsprozess wird vermutlich auch durch Zytokininduktion und apoptotische Lymphozyten beeinflusst. Je nach zugrundeliegender Erkrankung beeinflussen die jeweiligen immunologischen Grundsituationen die weitere Wirkung der ECP. Beim kutanen T-Zell-Lymphom kommt dem Vorgang der Transimmunisierung eine besondere Bedeutung zu. Die Aufnahme von malignen apoptotischen Lymphozyten durch unreife dendritische Zellen, die Prozessierung von antigenen Tumorpeptiden und eine nachfolgende spezifische CD8+-Immunantwort sind dabei von zentraler Bedeutung. Das klinische Ansprechen korreliert hierbei mit der Tumorlast an malignen T-Zellen im peripheren Blut. Bei der chronischen GvHD-Reaktion konnte gezeigt werden, dass die ECP die Differenzierung von dendritischen Zellen vom DC2-Typ fördert und damit die Alloreaktivität von zytotoxischen T-Zellen beeinflusst. Die biomodulatorischen Effekte der ECP beeinflussen somit nicht nur Lymphozyten, sondern auch antigenpräsentierende Zellen mit ihren regulatorischen Eigenschaften und ihren Einflüssen auf die Gesamtimmunität des Organismus.

Ultraviolet Radiation and the Snow Alga Chlamydomonas nivalis (Bauer) Wille¶

Aplanospores of Chlamydomonas nivalis are frequently found in high-altitude, persistent snowfields where they are photosynthetically active despite cold temperatures and high levels of visible and ultraviolet (UV) radiation. The goals of this work were to characterize the UV environment of the cells in the snow and to investigate the existence and localization of screening compounds that might prevent UV damage. UV irradiance decreased precipitously in snow, with UV radiation of wavelengths 280-315 nm and UV radiation of wavelengths 315-400 nm dropping to 50% of incident levels in the top 1 and 2 cm, respectively. Isolated cell walls exhibited UV absorbance, possibly by sporopollenin, but this absorbance was weak in images of broken or plasmolyzed cells observed through a UV microscope. The cells also contained UV-absorbing cytoplasmic compounds, with the extrachloroplastic carotenoid astaxanthin providing most of the screening. Additional screening compound(s) soluble in aqueous methanol with an absorption maximum at 335 nm played a minor role. Thus, cells are protected against potentially high levels of UV radiation by the snow itself when they live several centimeters beneath the surface, and they rely on cellular screening compounds, chiefly astaxanthin, when located near the surface where UV fluxes are high.

Extracorporeal photopheresis technical aspects

Extracorporeal photochemotherapy is a monotherapy first developed by Edelson et al. in 1987. It is a therapy in which 8-methoxypsoralen (8-MOP) containing lymphocytes are exposed to a long wavelength ultraviolet radiation (UVA) in an extracorporeal system. The initial design of the treatment was based on the use of the UVAR system (Therakos) for both the collection and photoirradiation of the mononuclear cells. This machine is replaced now by XTS apparatus, which is fully automatic and has integrated the fluid logic module (the “heart” of the system). Another principle is used: the two independent steps technique. It consists in first collection of mononuclear cells by a continuous blood cell separator and secondly irradiation in an independent machine: UV-MATIC irradiator (VILBER LOURMAT). These three techniques are analyzed through numerous parameters: technical, biological, hematological data. In the future, we consider we need to precise our requirements for adequate UVA energy and 8-MOP concentration. We also have to define therapeutic dose of irradiated cells and so standardize the process.

Ultraviolet radiation and the snow alga Chlamydomonas nivalis (Bauer) Wille.

Aplanospores of Chlamydomonas nivalis are frequently found in high-altitude, persistent snowfields where they are photosynthetically active despite cold temperatures and high levels of visible and ultraviolet (UV) radiation. The goals of this work were to characterize the UV environment of the cells in the snow and to investigate the existence and localization of screening compounds that might prevent UV damage. UV irradiance decreased precipitously in snow, with UV radiation of wavelengths 280-315 nm and UV radiation of wavelengths 315-400 nm dropping to 50% of incident levels in the top 1 and 2 cm, respectively. Isolated cell walls exhibited UV absorbance, possibly by sporopollenin, but this absorbance was weak in images of broken or plasmolyzed cells observed through a UV microscope. The cells also contained UV-absorbing cytoplasmic compounds, with the extrachloroplastic carotenoid astaxanthin providing most of the screening. Additional screening compound(s) soluble in aqueous methanol with an absorption maximum at 335 nm played a minor role. Thus, cells are protected against potentially high levels of UV radiation by the snow itself when they live several centimeters beneath the surface, and they rely on cellular screening compounds, chiefly astaxanthin, when located near the surface where UV fluxes are high.

A commercial sunscreen's protection against ultraviolet radiation-induced immunosuppression is more than 50% lower than protection against sunburn in humans.

Ultraviolet radiation (280-400 nm)-induced suppression of cutaneous cell-mediated immunity plays an important part in the development of skin cancer. Sunscreens are widely advocated to protect against skin cancer but if they offer insufficient protection against immunosuppression they may inadvertently increase skin cancer risk. This human study evaluated immunoprotection afforded by a commercial sunscreen preparation (labeled sun protection factor 15) offering primarily ultraviolet B (280-320 nm) protection. Indirectly, it also investigated whether ultraviolet A (320-400 nm) plays a part in ultraviolet radiation-induced immunosuppression. Healthy white-skinned volunteers were used (n=119). Ultraviolet radiation exposures were on previously unexposed buttock skin with an ultraviolet radiation source that complied with European recommendations for sunscreen testing. Ultraviolet radiation dose-response curves for sunburn/erythema and suppression of the contact hypersensitivity response were generated either with or without sunscreen in vivo and protection factors were derived for both end-points. The ultraviolet radiation wavelengths transmitted by the sunscreen were determined in vitro and showed that the sunscreen was primarily an ultraviolet B absorber, with relatively poor absorption in the ultraviolet A region. The sun-screen protected against both erythema and immunosuppression but protection against immunosuppression (IPF=4.9, 95% confidence interval: 2.3-10.6) was less than half that for erythema (Ery-PFg=14.2, 95% confidence interval: 10.2-19.8). Failure of the sunscreen to afford comparable protection against both end-points was probably due to immunosuppression by ultraviolet A, a part of the solar spectrum that does not readily cause sunburn. The sunscreen protected against both end-points, which supports the use of sunscreens to reduce immunosuppression but protection against immunosuppression may be improved if sunscreens are formulated to offer equivalent protection against ultraviolet B and ultraviolet A.

BENEFICIAL AND DETRIMENTAL EFFECTS OF UV ON AQUATIC ORGANISMS: IMPLICATIONS OF SPECTRAL VARIATION

Solar ultraviolet radiation (UVR) may have beneficial as well as detrimental effects on living systems. For example, UV-B radiation (280–320 nm) is generally damaging, while UV-A radiation (320–400 nm) may cause damage or stimulate beneficial photorepair of UV-B damage. The nature of both direct and indirect effects of UVR in nature depends on both the photon flux density and the spectral composition of the radiation incident on aquatic organisms across environmental UVR gradients in space (depth, transparency, elevation) and time (diel, seasonal, interannual). Here we use the common and widespread freshwater cladoceran Daphnia pulicaria as a model organism to demonstrate the potential importance of these wavelength-specific effects of UVR to the ecology of aquatic organisms. UVR-exposure experiments are used to manipulate both natural solar and artificial UVR sources to examine the beneficial as well as detrimental effects of different wavelengths of UVR. Changes in the spectral composition of solar radiation are also examined along several natural environmental gradients including diel gradients, depth gradients, and dissolved organic carbon (DOC) gradients. The implications of variation in the spectral composition of UVR for aquatic organisms are discussed. The first biological weighting function (BWF) for a freshwater cladoceran is presented here. It demonstrates that the shortest UV-B wavelengths in sunlight are potentially the most damaging per photon. However, due to the greater photon flux density of longer wavelength UVR in sunlight, the net potential damage to Daphnia in nature is greatest for the longer wavelength UV-B and shorter wavelength UV-A radiation in the 305–322 nm range. Overall the contribution of UV-B to the total mortality response of Daphnia exposed to full-spectrum solar radiation for 7 h on a sunny summer day is 64% while UV-A contributes 36%. The BWF for Daphnia is used with the transmission spectrum for Mylar D to demonstrate that Mylar D cuts out only about half of the damaging UVR in sunlight. Following exposure to damaging UV-B, Daphnia exhibits a dramatic increase in survival in the presence of longer wavelength UV-A and visible radiation due to the stimulation of photoenzymatic repair. We present data that demonstrate the importance of both atmospheric ozone and DOC in creating strong environmental gradients in the intensity (irradiance) and spectral composition of solar UVR in nature. The light-absorbing component of DOC, chromophoric dissolved organic matter (CDOM), is particularly important in creating depth refugia from damaging UV-B in freshwater ecosystems. CDOM may also cause intense variations in the ratio of potentially beneficial UV-A to detrimental UV-B radiation to which aquatic organisms are exposed. In addition to changes in atmospheric ozone, future changes in CDOM related to climate change or other environmental disturbances may substantially alter the underwater exposure of a variety of aquatic organisms to different wavelengths of solar UVR.

In situ exposure to ultraviolet radiation alters the depth distribution of Daphnia

Damaging solar radiation was one of the first factors proposed to explain zooplankton diel vertical migrations (DVM), yet other factors such as temperature, food, and especially predation have typically been more widely studied and identified as the primary factors inducing DVM. This is true in spite of the fact that recent experiments have shown that ambient levels of solar ultraviolet radiation (UVR) are potentially lethal to zooplankton and negative phototactic behavior has been demonstrated in the laboratory. Here we present the first evidence from in situ experiments demonstrating that UVR wavelengths influence the vertical swimming behavior of zooplankton under full spectrum solar radiation. Cylindrical acrylic columns that transmitted or blocked UVR were used to examine the behavioral responses of Daphnia pulicaria to UVR. Experiments were conducted in the epilimnion of a high‐UV system at midday and in late afternoon. In both experiments, a large proportion of individuals migrated downward in the presence of UVR, whereas those in the UVR‐shielded treatments tended to remain closer to the surface.

Improved method for measuring the ensemble average of strand breaks in genomic DNA.

The cis-syn cyclobutane pyrimidine dimer (CPD) is the major photoproduct induced in DNA by low wavelength ultraviolet radiation. An improved method was developed to detect CPD formation and removal in genomic DNA that avoids the problems encountered with the standard method of endonuclease detection of these photoproducts. Since CPD-specific endonucleases make single-strand cuts at CPD sites, quantification of the frequency of CPDs in DNA is usually done by denaturing gel electrophoresis. The standard method of ethidium bromide staining and gel photography requires more than 10 microg of DNA per gel lane, and correction of the photographic signal for the nonlinear film response. To simplify this procedure, a standard Southern blot protocol, coupled with phosphorimage analysis, was developed. This method uses random hybridization probes to detect genomic sequences with minimal sequence bias. Because of the vast linearity range of phosphorimage detection, scans of the signal profiles for the heterogeneous population of DNA fragments can be integrated directly to determine the number-average size of the population.

The role of PUVA in the treatment of psoriasis. Photobiology issues related to skin cancer incidence.

Photochemotherapy with methoxsalen (8-methoxypsoralen) and long wavelength ultraviolet (UV) radiation (referred to as 'PUVA' for psoralen plus UVA) is commonly used to treat psoriasis and vitiligo. These vastly different diseases respond to the therapy by different mechanisms even though the immediate effects of the therapy--the photomodification of cellular biomolecules--is the same for each. Because psoriasis is not cured by PUVA, patients receive many treatments over their lifetime and have a significantly increased risk for the development of skin cancers (primarily squamous cell carcinomas). In this article the basic aspects of psoralen photobiology are reviewed briefly. Several recent studies describing the incidence of skin cancer in UVA treated psoriasis cohorts are comparatively reviewed. In addition the impact of the analysis of mutations in the tumor suppressor gene, p53, are summarized. An unexpected mutation spectrum (very few PUVA type T-->A transversions and frequent UVB solar signature C-->T transitions) suggest that effects other than direct DNA photoadduct formation may be at play. These analyses suggest that it may be possible to improve the therapeutic efficacy of PUVA by a careful evaluation of the mode of delivery. In this review the science behind PUVA is summarized. In addition, the incidence of skin cancer as a long term consequence of repeated treatments is surveyed. To relate clinical observations to molecular events, the nature of p53 mutations found in skin cancers from psoriasis patients is also analyzed. Finally some suggestions for improving the delivery of PUVA therapy are presented.

Sunscreens, skin photobiology, and skin cancer: the need for UVA protection and evaluation of efficacy.

Sunscreens are ultraviolet radiation (UVR)-absorbing chemicals that attenuate the amount and nature of UVR reaching viable cells in the skin. They are selected and tested for their ability to prevent erythema. No sunscreen prevents photodamage, as it has been demonstrated that suberythemal doses of UVR cause a variety of molecular changes (including DNA damage) in these cells. Furthermore, the spectrum of UVR reaching viable cells is altered by topically applied sunscreen. In this review, the basic aspects of sunscreens and skin photobiology are reviewed briefly. Although there can be no question concerning the efficacy of sunscreens for the prevention of erythema, questions remain because of the possible cumulative effects of chronic suberythemal doses and the increased exposure of skin cells to longer UVR wavelengths. The current major issue surrounding sunscreens involves their ability to protect skin cells against the effects of UVA radiation. These UVA effects may be direct damage (base oxidations) or effects on the skin immune system, yet there is no uniformly accepted method for the evaluation of UVA protection. This review is focused primarily on the latter topic covering action spectra that implicate the need for UVA protection. In addition, in vivo and in vitro methods proposed for the evaluation of candidate sunscreen formulations of UVA protective ability are reviewed. Finally, revisions in the terminology used to describe the protection afforded by sunscreens are suggested. It is proposed that SPF ("sun" protection factor) be renamed "sunburn" protection factor and that "critical wavelength" be designated "long wave index."

Variability of bio-optical factors influencing the seasonal attenuation of ultraviolet radiation in temperate coastal waters of Japan

The study identifies the relative contribution of various bio-optical factors to the total attenuation of ultraviolet radiation (UVR) wavelengths and photosynthetically active radiation (PAR) in temperate coastal waters of Japan by surveying the physical properties of the water column, UVR and PAR penetration, and the absorption characteristics of dissolved and particulate material. Spectral absorbance properties of pigment (aph), detritus (ad) and chromophoric dissolved organic material (aCDOM) displayed both seasonal and wavelength specific variability. On an annual basis, absorbance by aCDOM was the highest absorbing fraction (47-59%) for the UVR wavelengths measured (305, 320, 340 and 380 nm) but decreased (32%) at 450 nm. Contribution of pigments to total absorbance was highest (40-60%) during a spring bloom for both UVR and PAR. A large variability (C.V. > 42%) for annual average attenuation coefficients (Kd[lambda]) at respective wavelengths observed suggests that the spectral composition of the water column changes throughout the year in this region. A significant relationship was observed between Kd(lambda) and aCDOM at 305, 320, 340 and 380 nm only (P < 0.01) but not for 450 nm (PAR) indicating the role of CDOM in regulating variations in Kd(lambda), particularly in the UVR range. The slope S, obtained from a natural-log plot of the absorption coefficient of CDOM against wavelength, ranged between 0.014 and 0.036 nm-1 annually (average = 0.020 +/- 0.007, C.V. = 35%) and suggests seasonal changes in the origin of CDOM between terrestrial (low S) and biogenous (high S) CDOM.

Psoriasis, PUVA, and skin cancer--molecular epidemiology: the curious question of T-->A transversions.

Photochemotherapy with 8-methoxypsoralen and long wavelength ultraviolet radiation (PUVA) is commonly used to treat psoriasis and vitiligo. These vastly different diseases respond to the therapy by different mechanisms even though the immediate effects of the therapy - photoadduct formation - is the same for both. Because psoriasis is not cured by PUVA, patients receive many treatments over their lifetime and develop a significant risk for the development of skin cancers (primarily squamous cell carcinomas). In this review the basic aspects of psoralen photobiology are reviewed briefly. In addition the impact of the analysis of mutations in the tumor suppressor gene, p53, are summarized. An unexpected mutation spectrum (very few T-->A transversions and frequent UVB signature C-->T transitions) suggest that effects other than direct DNA photoadduct formation may be at play. The roles of reactive oxygen species-induced base changes as well as other clastogenic factors are discussed. This analysis suggests that it may be possible to improve the therapeutic efficacy of PUVA by a careful evaluation of the mode of delivery.

The Optical Properties of the Anterior Segment of the Eye: Implications for Cortical Cataract

Epidemiological studies have correlated cortical cataract with exposure to light and have suggested that this is due primarily to relatively short wavelengths of ultraviolet radiation (UV-B). In addition, some cellular and animal models also implicate UV-B. In order to evaluate the likely role of different wavelengths of light in the etiology of cortical cataracts, the optical characteristics of several animal models were ascertained and compared to the primate. This study shows that the mouse model absorbs UV-B almost exclusively whereas other animal models such as the rabbit and the guinea pig also contain chromophores that absorb UV-A. The absorptive characteristics of the human lens varies drastically with age. The young lens absorbs primarily UV-A, whereas with age, there are increases in absorptions at 320 nm and out to wavelengths as long as 550 nm. By sectioning human lenses it was found that these changes in absorption properties increased toward the central and the nuclear regions.These absorptive characteristics were then compared to the amount of light reaching the surface of the lens. It was found that UV-B is a minor component of total energy reaching the surface of the human lens and old human lens proteins absorb 2 orders of magnitude more UV-A and visible light than UV-B. It is concluded that it is premature to exclude UV-A or even visible light in the etiology of human cortical cataracts.

The alexandrite effect of theTavernier diamond caused by fluorescence under daylight

The 56.07-carat Tavernier pear-shaped gem di- In his report, Tavernier described a diamond locality amond not only has an important historical provenance, called the Gani mine. A number of rough diamonds were but also shows a substantial color change between incan- found there, many ranging in weight from 10 - 40 carats, descent light and daylight. This famous diamond exhibits with the largest weighing 900 carats ( 1 caratA 0.2 gram) . a very strong blue fluorescence when exposed to long- He mentioned that the colorless to light yellow diamonds wavelength ultraviolet (UV) radiation. It appears light from this area as having a ''greasy'' appearance in day- brown (an orange hue) under incandescent light, and light. This kind of diamond has since been described as light pink (a purple hue) under daylight. This change in being of ''false color,'' in that the appearance is due to color, or ''alexandrite effect,'' is caused by its very strong the lighting conditions, and is not the true bodycolor. blue fluorescence resulting from the long-wavelength ul- Wade discussed the kind of ''greasy'' diamond reported traviolet component present in daylight.q 1998 John Wiley & by Tavernier, and pointed out that this ''false color'' is Sons, Inc. Col Res Appl, 23, 323 - 327, 1998 caused by a blue fluorescence under daylight. 2 Light yel- low diamonds from the Premier Mine in South Africa

Using Ultraviolet Radiation to Reduce Pilling of Knitted Wool and Cotton

The Siroflash anti-pilling treatment for knitted fabrics is a process involving exposure of the fabric or garment surface to short wavelength ultraviolet radiation (UVC), fol lowed by a mild wet oxidation treatment using, for example, hydrogen peroxide or salts of permonosulphuric acid. UVC exposure is confined to the surface fibers and presensitizes them to the wet oxidation process, which selectively weakens them rel ative to the bulk fibers responsible for fabric strength. Because the surface fibers are much weaker after treatment, no anchor fibers are available to secure pills to the fabric surface. The treatment is a highly effective, chlorine-free method of preventing pilling in wool knitwear, which has now been demonstrated in wear trials. In addition. uv treatment of knitted garments prior to aqueous oxidation can effectively limit facing, up in wool knitwear during garment dyeing. A variation of the Siroflash process can also be used on cotton and cotton/wool blend fabrics by first padding hydrogen per oxide onto the fabric before UV exposure, then treating with continuous uv irradiation with a medium-pressure arc system similar to those used commercially for UV curing of polymer films. However, the continuous process is ineffective on pure wool knitted fabrics. The irradiation times necessary for effective treatment on wool using low power germicidal uv tubes vary depending on fabric or garment construction. Using these sources, however, irradiation times are too long for commercial use, and continuous exposure with a focused medium-pressure mercury arc is only partially effective. More powerful uv sources providing a high level of UVC radiation, for example noncoherent excimers or high-intensity low pressure arcs, or hybrid methods for weakening surface fibers (such as UV/H2O2 with a protease enzyme) may provide a rapid, effective, anti- pilling treatment for wool.

Photochemistry of Ozone: Surprises and Recent Lessons

The hydroxyl radical OH is nature9s detergent--it oxidizes pollutants and removes them from the atmosphere. Hydroxyl is created in the photolysis of atmospheric ozone, and the mechanisms and rates of production of OH are therefore very important. In their commentary, Ravishankara et al. discuss recent research into the details of ozone photolysis, particularly the role of electronically excited oxygen atoms. Surprisingly, long wavelength ultraviolet solar radiation has a greater influence on ozone photodissociation than previously believed.

Small Liquid Crystal Droplet Formation of Polymer-Dispersed Liquid Crystal under Ultraviolet Light Irradiation without Short Wavelength Component

The light scattering properties and polymer morphology of polymer-dispersed liquid crystal films were investigated while adjusting the spectrum of ultraviolet light irradiation with several optical filters in their formation process of photopolymerization-induced phase separation. It is found that the short wavelength light component of less than 355 nm, which is contained in ultraviolet light to be irradiated, slows the phase separation process and results in the formation of large liquid crystal droplets. The morphological changes in the polymer may be due to undesirable decomposition products created in the nematic liquid crystal under the short wavelength ultraviolet irradiation. A spectral arrangement using an optical filter to eliminate the short wavelength light is useful in obtaining small liquid crystal droplets with a strong light-scattering effect, which increases the extinction ratio of polymer-dispersed liquid crystal films. This formation technique will also improve photochemical damage in the phase separation process.

Psoralen and long wavelength ultraviolet radiation as an adjuvant therapy for prevention of intimal hyperplasia and constrictive remodeling after balloon dilation: A study in the rabbit iliac artery

Restenosis after balloon angioplasty is the summated effect of intimal hyperplasia and arterial shrinkage, both caused by hyperproliferation. In the present study, the potential of a photochemotherapeutic modality (Psoralen + UVA: PUVA) for the prevention of angioplasty induced proliferation was explored. In rabbit iliac arteries, balloon dilation followed by PUVA-therapy (H = 1 J/cm2) was performed (n = 15). Contralateral arteries served as control. After 2 and 28 days of survival, the contribution of intimal hyperplasia and remodeling to lumen loss was determined by means of angiography and histological analysis. After 2 days, large parts of the media had become acellular, while proliferation was occurring predominantly in the adventitia in both groups. After 28 days, late loss, arterial shrinkage, but not intimal hyperplasia were larger in the PUVA group (P < 0.05). PUVA-therapy did not prevent intimal hyperplasia following balloon dilation but enhanced luminal narrowing by augmented constrictive remodeling.