Ultraviolet Irradiation Time Research Articles

Amphiphilic Poly(D,L‐lactic acid)/Poly(ethylene glycol)/Poly(D,L‐lactic acid) Nanogels for Controlled Release of Hydrophobic Drugs

Photocrosslinked nanogels with a hydrophobic core and hydrophilic shell are successfully fabricated with the goal of obtaining a biocompatible and biodegradable drug carrier for hydrophobic anticancer drugs. These nanogels are composed of amphiphilic triblock copolymers, poly(D,L-lactic acid)/poly(ethylene glycol)/poly(D,L-lactic acid) (PLA-PEG-PLA), with acrylated groups at the end of the PLA segments. The copolymers are synthesized by ring-opening polymerization and possess a low CMC (49.6 mg x L(-1)), which easily helps to form micelles by self-assembly. The acrylated end groups allow the micelles to be photocrosslinked by ultraviolet irradiation, which turn the micelles into nanogels. These nanogels exhibit excellent stability as a suspension in aqueous media at ambient temperature as compared to the micelles. Moreover, the size of the nanogels is easily manipulated in a range of 150 to 250 nm by changing the concentration of crosslinkers, e.g., ethylene glycol dimethacrylate, and ultraviolet light irradiation time. The nanogels achieve a high encapsulation efficiency and offer a steady and long-term release mechanism for the hydrophobic anticancer drug, CPT. It shows that these nanogels are useful for a hydrophobic anticancer drug-carrier system. [pictures: see text] Formation of the PLA-PEG-PLA nanogels.

PH-sensitive diamond field-effect transistors (FETs) with directly aminated channel surface

We have introduced pH sensors fabricated on diamond thin films through modification of the surface-terminated atom. We directly modified the diamond surface from hydrogen to amine or oxygen with ultraviolet (UV) irradiation under ammonia gas. The quantified amine site based on the spectra obtained by X-ray photoelectron spectroscopy (XPS) is 26% (2.6 × 10 14 cm −2) with UV irradiation for 8 h and its coverage is dependent on the UV irradiation time. This directly aminated diamond surface is stable with long-term exposure in air and electrolyte solution. We fabricated diamond solution-gate field-effect transistors (SGFETs) without insulating layers on the channel surface. These diamond SGFETs with amine modified by direct amination are sensitive to pH (45 mV/pH) over a wide range from pH 2 to 12 and their sensitivity is dependent on the density of binding sites corresponding to UV irradiation time on the channel surface.

Basic study of healing of injuries to the myometrium and amniotic membrane using photocrosslinkable chitosan

We performed in vivo and in vitro adhesion experiments on the use of photocrosslinkable chitosan (PC) for healing of the myometrium and the amniotic membrane to test its usefulness in the perinatal field. To determine the adhesion conditions of PC in the healing of the myometrium and amniotic membrane, we applied two concentrations (30 and 50 mg/mL) of PC to the postpartum amniotic membrane, and radiated it with ultraviolet (UV) light for 10, 20, 30 or 60 s. Next, we created incisions of three sizes (pinhole, 5 mm and 10 mm), and performed PC adhesion followed by pressure application experiments. Subsequently, we laparotomized 12-day-pregnant rats under anesthesia, created a 5-mm incision, applied PC and closed the abdomen. We removed the uterus at 20 days of pregnancy, and histologically examined the site of PC application. The optimal adhesion conditions of PC were 50 mg/mL, and the optimal time of UV irradiation was 30 s or longer. In pressure application experiments, the bonding strength of PC was so high that even 10-mm incisions withstood a mean pressure of 92 mmH2O. The bonding strength of PC was significantly higher than that of fibrin glue that was tested in parallel. Histological examination of the rat myometrium showed a mild foreign body reaction with no inflammatory findings, confirming the usefulness of PC. PC is a wound-healing drug, an improvement on the naturally occurring polysaccharide chitosan, and is safer and has a higher bonding strength than biological adhesives including fibrin, making it promising for fetal surgical and perinatal applications.

Structure and adhesion properties of linear low‐density polyethylene powders grafted with acrylic acid via ultraviolet light

AbstractThe structure and adhesion properties of linear low‐density polyethylene (LLDPE) powder grafted with acrylic acid (AA) via ultraviolet light (UV) were studied by Fourier transform infrared spectroscopy (FTIR), electron spectroscopy for chemical analysis (ESCA), scanning electron microscopy (SEM), and water contact angle, peel strength, and graft degree measurements. The results show that the chemically inert LLDPE powder can be graft‐copolymerized with AA via this photografting method. The graft degree increases with the ultraviolet irradiation time. The hydrophilicity of the grafted LLDPE powder and the peel strength of high‐density polyethylene (HDPE)/steel joint with the grafted LLDPE powder used as hot‐melt adhesive are improved considerably, as compared to that with the ungrafted LLDPE powder. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 2549–2553, 2006

The mechanical properties and in vitro biodegradation and biocompatibility of UV-treated poly(3-hydroxybutyrate- co-3-hydroxyhexanoate)

Strong mechanical properties and controllable biodegradability, together with biocompatibility, are the important requirement for the development of medical implant materials. In this study, an ultraviolet (UV) radiation method was developed to achieve controlled degradation for bacterial biopolyester poly (3-hydroxybutyrate- co-3-hydroxyhexanoate) (PHBHHx) which has a low biodegradation rate that limits its application for many implant applications required quick degradation. When UV radiation was applied directly to PHBHHx powder, significant molecular weight (Mw) losses were observed with the powder, Mw reduction depended on the UV radiation time. At the same time, a broad PHBHHx Mw distribution was the result of inhomogeneous radiation. Interestingly, this inhomogeneous radiation helped maintain the mechanical properties of films made of the UV-radiated powder. In comparison, the PHBHHx films subjected to direct UV radiation became very brittle although their degradation was faster than that of the PHBHHx powders subjected to direct UV radiation. After 15 weeks of degradation in simulated body fluid (SBF), films prepared from 8 and 16 h UV-treated PHBHHx powders maintained 92% and 87% of their original weights, respectively, while the untreated PHBHHx films lost only 1% of its weight. Significant increases in growth of fibroblast L929 were observed on films prepared from UV-radiated powders. This improved biocompatibility could be attributed to increasing hydrophilic functional groups generated by increasing polar groups C–O and C O. In general, UV-treated PHBHHx powder had a broad Mw distribution, which contributed to fast degradation due to dissolution of low Mw polymer fragments, and strong mechanical property due to high Mw polymer chains. Combined with its improved biocompatibility, PHBHHx is one more step close to become a biomedical implant material.

Photocatalytic Dissolution of Two Turkish Lignites in Tetralin: Effects of UV Irradiation, TiO2 and ZnO as Photocatalyst

The effects of ultraviolet (UV) irradiation, photocatalyst, and reaction time on the dissolution of two Turkish lignites (Beypazarı and Tunçbilek lignites) in tetralin have been investigated under ambient conditions. Lignites samples were irradiated in the presence or absence of added photocatalysts (TiO 2 and ZnO) at varying reaction times (1–10 days), constant irradiation power (180 W), and constant solvent/lignite ratio (5/1). The solubility of lignites increased with reaction time under UV light. The liquefaction behaviors of the lignites are different from each other. As the maximum solubility (45%) with Tunçbilek lignite has been achieved at shorter reaction times, it has been reached at longer reaction times for Beypazarı lignite (32%). The solubility values obtained from noncatalytic liquefaction are higher than those obtained from liquefaction with TiO 2 and ZnO.

Physical properties of the crosslinked cellulose catalyzed with nanotitanium dioxide under UV irradiation and electronic field

Four different carboxylic acids (1,2,3,4-butane tetracarboxylic acid (BTCA), maleic acid (MA), succinic acid (SUA), and citric acid (CA)) were used as crosslinking agents for finished cotton fabrics in the presence of nanometer titanium dioxide catalyst under the irradiation of ultraviolet (UV) light and/or an electronic field (EF). We find that the dry crease recovery angle, wet crease recovery angle, and softness improvement percentages of the treated fabrics for all the crosslinking agents are gradually increased with the increasing of irradiation time period, but the TSR values decreased in all cases. The crease recovery and softness properties for the various crosslinking agents are ranked as BTCA > MA > CA > SUA at a given UV irradiation time period. The addition of EF treatment on the UV-irradiated fabrics improves the catalytic effects significantly. The spectra of Fourier transform infrared spectrophotometry reveal the crosslinking reaction between the carboxylic acid group of citric acid and the hydroxyl group of methylcellulose; this reaction could form ester and ether groups in the presence of nanometer TiO 2 catalyst under UV irradiation and UV irradiation and EF treatment. The pictures of scanning electron microscopy and the electron spectroscopy for chemical analysis survey spectra show the surface deposition of acid crosslinking agents on the finished fibers and the crosslinking reaction between citric acid and cellulose molecule catalyzed with nanometer titanium dioxide under the irradiation of UV only and under the irradiation of UV and the treatment of EF separately.

Large area UV casting using diverse polyacrylates of microchannels separated by high aspect ratio microwalls

Large area molding of long and deep microchannels separated by high aspect ratio microwalls is important for high sensitivity and high throughput microfluidic devices. Ultraviolet (UV) casting is a feasible, economical and convenient method of replication of such microstructures in plastics. It is shown that a wide variety of polyacrylates with diverse properties such as those made from epoxy (EP), polyurethane (UR), polyester (ES), poly (ethylene glycol) (EG) and poly(propylene glycol) (PG) can be used for the high aspect ratio (7-9) UV casting of such linear microstructures over a 100 mm diameter, enlarging the range of applications of the replicated microstructures. Some challenges arise. With the EG formulation, wavy microstructures were observed; this can be overcome by stress relaxation. With non-polar PG formulation, poor adhesion between the polyester substrate and resin can lead to delamination of the casting from the substrate during demolding; this can be overcome by pre-coating a partially cured same resin on the polyester substrate. An optimum UV irradiation time was important for cure at the deepest end of the microstructure without excessive crosslinking leading to much increased demolding forces. The viscosity and wetting capability of the formulations were found to affect replication fidelity.

Functionalized low-density polyethylene via a novel photografting method and its adhesion properties

A novel photografting, non-vapor and non-liquid phase method was developed to functionalize low-density polyethylene (LDPE) powder. The structure and adhesion properties of LDPE grafted with methacrylic acid (MAA) by this method were studied by Fourier transform infrared (FTIR) spectroscopy, electron spectroscopy for chemical analysis (ESCA), scanning electron microscopy (SEM) and water contact angle, peel strength and graft degree measurements. The results show that the chemically inert LDPE powder can be graft-copolymerized with MAA via this non-vapor and non-liquid phase photografting method. The graft degree increases with the ultraviolet irradiation time. The hydrophilicity of the grafted LDPE powder and the peel strength of high density polyethylene (HDPE)/steel joint with the grafted LDPE powder used as hot melt adhesive are improved considerably as compared to that with the ungrafted LDPE powder.

Ultraviolet stimulated photocatalytic activity on polycrystalline diamond film surfaces

A photocatalytic reaction produced on polycrystalline diamond film surfaces by ultraviolet (UV) light was studied by micro-Raman spectroscopy. The diamond films were specially prepared for this study by the rf-assisted chemical vapor deposition technique. The photocatalytic activity was analyzed in terms of the sharpness of the typical diamond Raman band at 1332 cm−1 and by the weak nondiamond carbon (NDC) features around 1550 cm−1. The micro-Raman spectra show a decrease of the NDC content originally codeposited on diamond film surfaces during the synthesis. This decreasing is proportional to the UV irradiation time, suggesting that the photocatalytic reaction can be controlled by the UV irradiation dose. Since a selective reduction of the NDC phase was achieved on diamond surfaces. The UV irradiation was applied continuously during 1, 2, and 3 days in open atmosphere at room temperature. The role of oxygen radicals, such as ozone (O3) and atomic oxygen (O*) on the photocatalytic reaction is discussed, as well.

Irradiation time dependence of Mn-doped ZnS nanocrystals with carboxylic acid on radiative and non-radiative transitions

ZnS nanocrystals doped with Mn 2+ ions (ZnS:Mn) have attracted much attention in the past few years due to the changes in their optical properties in accordance with quantum confinement effects. ZnS:Mn nanocrystal systems form a new class of luminescent materials with some kind of applications because of the high fluorescence quantum efficiency. The addition of surface passivators and ultraviolet (UV) irradiation caused an increase of photoluminescence (PL) signal intensity. In this article, we report the UV irradiation time dependence of the optical absorption and PL signal intensities of ZnS:Mn nanocrystals with and without acrylic acid (AA). It is noted that the PL signal intensities of ZnS:Mn nanocrystals with and without AA undergo significant increases. On the contrary, the optical absorption intensities and/or non-radiative transition of ZnS:Mn nanocrystals with and without AA measured by photoacoustic (PA) technique decrease with the increase of UV irradiation. These experimental results suggest that there are possibilities of UV curing of the passivating AA polymer and photochemical reactions around the nanocrystals, which increase the fluorescence quantum efficiency.

Ultraviolet excitation of photoluminescence of porous silica under vacuum conditions

The optical properties of porous sol–gel silica are investigated by measuring the absorbance spectrum in the vacuum ultraviolet energy range and the excited photoluminescence. The emission spectrum shows a luminescence with two maxima at about 3.5 eV and <3.0 eV depending on the excitation energy. We observed a decrease of the 3.5 eV emission band with increasing irradiation time with the samples in vacuum. The modification induced on the material cannot be recovered by exposing the samples to the ambient atmosphere. We ascribed the measured photoluminescence to OH-related surface centers whose structure is modified by the concomitant action of vacuum conditions and ultraviolet irradiation time.

Preparation of chlorinated poly(vinyl chloride)‐g‐poly(N‐vinyl‐2‐pyrrolidinone) membranes and their water permeation properties

AbstractChlorinated poly(vinyl chloride) (CPVC) membranes for microfiltration processes were prepared with the combined process of a solvent evaporation technique and the water‐vapor induced‐phase‐inversion method. CPVC membranes with a mean pore size of 0.7 μm were very hydrophobic. These membranes were subjected to surface modification by ultraviolet (UV)‐assisted graft polymerization with N‐vinyl‐2‐pyrrolidinone (NVP) to increase their surface wettability and decrease their adsorptive fouling. The grafting yields of the modified membranes were controlled by alteration of UV irradiation time and NVP monomer concentration. The changes in chemical structure between the CPVC membrane and the CPVC‐g‐poly(N‐vinyl‐2‐pyrrolidinone) membrane and the variation of the topologies of the modified PVC membranes were characterized by Fourier transform infrared spectroscopy, gel permeation chromatography, and field emission scanning electron microscopy. According to the results, the graft yield of the modified CPVC membrane reached a maximum at 5 min of UV exposure time and 20 vol % NVP concentration. The filtration behavior of these membranes was investigated with deionized water by a crossflow filtration measurement. The surface hydrophilicity and roughness were easily changed by the grafting of NVP on the surface of the CPVC membrane through a simultaneous irradiation grafting method by UV irradiation. To confirm the effect of grafting for filtration, we compared the unmodified and modified CPVC membranes with respect to their deionized water permeation by using crossflow filtration methods. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 3188–3195, 2003

Behavior of fibroblasts on a porous hyaluronic acid incorporated collagen matrix.

A hyaluronic acid (HA) incorporated porous collagen matrix was fabricated at -70 degrees C by lyophilization. The HA incorporated collagen matrix showed increased pore size in comparison with collagen matrix. Biodegradability and mechanical properties of matrices were controllable by varying the ultraviolet (UV) irradiation time for cross-linking collagen molecules. Addition of HA to collagen matrix did not effect ultimate tensile stress after UV irradiation. HA incorporated collagen matrices demonstrated a higher resistance against the collagenase degradation than collagen matrix. In an in vitro investigation of cellular behavior using dermal fibroblasts on the porous matrix, HA incorporated collagen matrix induced increased dermal fibroblast migration and proliferation in comparison with collagen matrix. These results suggest that the HA incorporated collagen porous matrix assumes to enhance dermal fibroblast adaptation and regenerative potential.

Photochemical-spectrofluorimetric method for the determination of benzoylurea insecticides: applications in river water samples and in technical formulations

Ultraviolet (UV) irradiation was used to obtain fluorescent photoproducts from four non-fluorescent benzoylurea (BU) insecticides (flufenoxuron (FLF), lufenuron (LUF), hexaflumuron (HF) and triflumuron (TRF)). The effect of solvent, pH (in aqueous solutions), organic solvent percentage and UV irradiation time on the excitation and emission wavelengths and fluorescence intensity were investigated. The largest fluorescence signals and the shortest UV irradiation time were obtained in methanol, ethanol and 2-propanol. Linear calibration graphs were established in the interval between 0.025 and 1.000 μg ml −1 from FLF and TRF and between 0.050 and 1.000 μg ml −1 from LUF and HF with regression coefficients larger than 0.99. A method based on the use of the first-derivative of the spectra of photoproducts was applied to the determination of BU insecticides in river water samples and in technical formulations. The mean recoveries ranged from 95.0% to 110.0% in river water samples and from 92.0% to 101.0% in technical formulations, according to the compound. A preconcentration step, using LLE, allowed to reach the concentration levels established by the EU directive for pesticides in drinking water.

Copolymers of chosen alkyl methacrylates withN-phenylmaleimide andN-(4-halogenphenyl)maleimides: A UV-aging study

Homopolymers and copolymers of ethyl and butyl methacrylates with N-phenylmaleimide, N-(4-chlorophenyl)maleimide, and N-(4-bromophenyl)maleimide were synthesized by free-radical bulk polymerization with benzoyl peroxide as the initiator. The content of imide in the copolymers was about 5–10 or 7.5 wt %. The homopolymers and copolymers were irradiated with ultraviolet (UV) light in a climatic test chamber for various periods to study their aging behavior. After 100, 250, and 500 h, the structure, thermal stability, chemical resistance, and some physicomechanical properties were examined. The influence of UV radiation time on structure and the investigated properties of the homopolymers and copolymers were studied. The experimental results indicate that all investigated copolymers were resistant to UV radiation after 500 h. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 3244–3250, 2001

Evaluation of calcification in porcine valves treated by ultraviolet ray and glutaraldehyde

Porcine aortic valve, of which tissue structural collagen matrix is cross-linked by glutaraldehyde (GA) to enhance mechanical property, is widely used in clinics, but gradual calcification occurs after implantation. Cross-linking the valve by 24 h of ultraviolet (UV) ray irradiation that induces collagen fibrous cross-link resulted in less calcium deposition than GA-pretreated leaflets. After 3 days, calcium level in GA-treated leaflets was distinctively higher than in leaflets cross-linked by UV irradiation for 24 h and in the non-treated control leaflets. The exposure time of UV irradiation was not significantly correlated with the extent of calcification. In all the test groups, molar [Ca]/[P] ratio gradually decreased as time went by, and UV-irradiated and control leaflets demonstrated molar [Ca]/[P] ratio close to apatite as the predominant mineral phase and GA-treated leaflet reached the similar molar ratio after 30 days. In animal experiment, the leaflet treated by UV irradiation demonstrated a stable surface without calcification after 2 months of implantation.

Calcification of leaflets from porcine aortic valves crosslinked by ultraviolet irradiation.

Glutaraldehyde (GA)-pretreated porcine aortic valves are generally used as a bioprosthetic valve, but gradual calcification of the leaflets often occurs. It has been hypothesized that the crosslinking agent, GA, stabilizes and perhaps modifies phosphorus-rich calcifiable structures in the bioprosthetic tissue. This is supported by our findings that calcium deposition is induced rapidly in GA-pretreated leaflets in comparison with ultraviolet (UV) irradiated leaflets. After 3 days of in vitro calcification test, calcium levels were 257.6 +/- 23.5 microg/cm3 in GA-pretreated, 57.7 +/- 10.2 microg/cm3 in the control, and 108.6 +/- 7.6 microg/cm3 in 24 h UV irradiated leaflets. The calcium level in all test groups increased as time proceeds and the calcium level of GA-pretreated leaflets was significantly higher than the control and UV irradiated leaflets during test. This rapid calcium deposition on the GA-pretreated leaflets may be due to residual aldehyde groups after pretreatment. The exposure time of UV irradiation was not significantly correlated with the extent of calcification. After 14 days of the test, calcium levels in leaflets UV irradiated for 1, 2, 4, and 24 h were 502.6 +/- 12.3 microg/cm3, 547.5 +/- 34.1 microg/cm3, 564.3 +/- 26.1 microg/cm3, and 543.0 +/- 55.5 microg/cm3. In all test groups, [Ca]/[P] molar ratio decreased toward that of hydroxyapatite as the predominant mineral phase as time proceeds. This study suggests that UV irradiation can be considerable as an efficient crosslinking method to surmount the side effects induced by GA-pretreatment and may endow tissue with mechanical property.

Photografting of PVC containingN,N-diethyldithiocarbamate groups with vinyl monomers

Poly(vinyl chloride) (PVC) with pendent N,N-diethyldithiocarbamate groups (PVC–SR) was prepared through the reaction of PVC with sodium N,N-diethyldithiocarbamate (NaSR) in butanone and used as a photoinitiator for the grafting polymerization of three vinyl monomers [styrene (St), methyl methacrylate (MMA), and acrylamide (Am)]. The effects of ultraviolet (UV) irradiation time, PVC–SR amount, and the monomer amount on grafting and grafting efficiency were investigated. The results showed that PVC–SR could initiate the polymerization of three vinyl monomers effectively and obtained crosslinked copolymers. The grafting and grafting efficiency of styrene and methyl methacrylate were higher than those of acrylamide. The polymerization activity of three monomers was acrylamide > methyl methacrylate > styrene. By analyzing the UV spectrum of PVC–SR with a different irradiation time, it was confirmed that PVC–SR was dissociated mainly into macromolecular the sulfur radical PVC–S · and the small molecular carbon radical · C(S)N(C2H5)2; the grafting polymerization mechanism was discussed. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 2569–2574, 2000

?-Irradiated poly(tetrafluoroethylene) particle-filled low-density polyethylene. II. UV stability of LDPE in the presence of 2�-PTFE powder and silane coupling agents

Ultraviolet (UV) stability of γ-irradiated poly(tetrafluoroethylene), 2°-PTFE, powder-filled low-density polyethylene (LDPE) was studied in this work. The mechanical and thermal properties of 2°-PTFE powder-filled LDPE were discussed in our previous work (Akinay and Tincer, 1999). It already has been shown that silane coupling agents (SCAs) result in improvements in mechanical properties. The UV stability of these samples was followed by a comparision between strain at break measured after UV irradiation and the initial strain at break, in terms of their ratio defined as residual elongation. The development of carbonyl index was also determined by infrared measurements. To get further UV stability, a hindered amine light stabilizer (HALS) was also used. Whereas addition of 2°-PTFE slightly enhanced the UV stability of LDPE, mercapto type silane (A-189) treatment appeared to increase the UV stability compared with the other types of silane treatments. HALS highly improved the UV stability of untreated and silane-treated 2°-PTFE-filled LDPE at given UV irradiation time. Although we observed some fluctuations in the experimental data of HALS and SCA treated 2°-PTFE-filled LDPE, the coaddition of HALS and SCAs showed synergetics effects in the UV stability compared with the separate additions.