A novel PVDF-TiO2@g-C3N4 composite electrospun fiber for efficient photocatalytic degradation of tetracycline under visible light irradiation

A novel composite electrospun fiber with high photocatalytic efficiency, good stability, strong hydrophobicity, good pollution resistance, and easy separation and recovery was synthesized. The TiO₂@g-C₃N₄ (TCN) with special core-shell structure (5-10 nm shell) facilitated the separation of photogenerated electron-holes and had high photocatalytic performance. The poly (vinylidene fluoride) (PVDF) electrospun fiber immobilized with TCN was successfully fabricated (PVDF-TCN) with uniform distribution and size of nanofibers by using electrospinning, which was used for degrading tetracycline under visible-light irradiation (> 400 nm). A special rougher surface of electrospun fiber obtained by washing of sacrificial PVP increased the specific surface area, which became more conducive to the adhesion of the catalyst. The water contact angle and FTIR results demonstrated that the electrospun fiber became extremely hydrophilic after adding TCN catalyst, which could effectively mitigate the fiber pollution. The PVDF-TCN-0.2g electrospun fiber exhibited excellent photocatalytic performance and the degradation efficiency of tetracycline was up to 97% in 300 min under visible-light irradiation. The mechanism of PVDF-TCN electrospun fiber degradation of tetracycline in the photocatalytic process was also proposed. In addition, the PVDF-TCN-0.2g exhibited a stable activity after 4 cycles experiments since the degradation efficiency remained about 90%. Therefore, we believed this study provided a new strategy in catalyst immobilization and wastewater treatment.

Surface Modification of PLLA, PTFE and PVDF with Extreme Ultraviolet (EUV) to Enhance Cell Adhesion

Recently, extreme ultraviolet (EUV) radiation has been increasingly used to modify polymers. Properties such as the extremely short absorption lengths in polymers and the very strong interaction of EUV photons with materials may play a key role in achieving new biomaterials. The purpose of the study was to examine the impact of EUV radiation on cell adhesion to the surface of modified polymers that are widely used in medicine: poly(tetrafluoroethylene) (PTFE), poly (vinylidene fluoride) (PVDF), and poly-L-(lactic acid) (PLLA). After EUV surface modification, which has been performed using a home-made laboratory system, changes in surface wettability, morphology, chemical composition and cell adhesion polymers were analyzed. For each of the three polymers, the EUV radiation differently effects the process of endothelial cell adhesion, dependent of the parameters applied in the modification process. In the case of PVDF and PTFE, higher cell number and cellular coverage were obtained after EUV radiation with oxygen. In the case of PLLA, better results were obtained for EUV modification with nitrogen. For all three polymers tested, significant improvements in endothelial cell adhesion after EUV modification have been demonstrated.

A Broadband Polyvinylidene Difluoride-Based Hydrophone with Integrated Readout Circuit for Intravascular Photoacoustic Imaging

Intravascular photoacoustic (IVPA) imaging can visualize the coronary atherosclerotic plaque composition on the basis of the optical absorption contrast. Most of the photoacoustic (PA) energy of human coronary plaque lipids was found to lie in the frequency band between 2 and 15 MHz requiring a very broadband transducer, especially if a combination with intravascular ultrasound is desired. We have developed a broadband polyvinylidene difluoride (PVDF) transducer (0.6 × 0.6 mm, 52 μm thick) with integrated electronics to match the low capacitance of such a small polyvinylidene difluoride element (<5 pF/mm(2)) with the high capacitive load of the long cable (∼100 pF/m). The new readout circuit provides an output voltage with a sensitivity of about 3.8 μV/Pa at 2.25 MHz. Its response is flat within 10 dB in the range 2 to 15 MHz. The root mean square (rms) output noise level is 259 μV over the entire bandwidth (1-20 MHz), resulting in a minimum detectable pressure of 30 Pa at 2.25 MHz.

Photocatalytic applications of paper-like poly(vinylidene fluoride)-titanium dioxide hybrids fabricated using a combination of electrospinning and electrospraying

A paper-like photocatalyst was fabricated by electrospraying an N,N'-dimethylformamide (DMF) dispersion of titanium dioxide (TiO2) nanoparticles (NPs) on a poly(vinylidene fluoride) nanofiber (PVDF NF) mat prepared by electrospinning. Morphological studies revealed that the TiO2 NPs uniformly deposited as clusters on the surface of the PVDF NF mat. The immobilized amount of TiO2 was found to be 2.08, 2.44, 3.80, and 4.73 mg per 45 cm(2) of PVDF-TiO2 hybrids for the electrospraying of 10, 20, 40, and 60 ml of TiO2-DMF, respectively. The hybrid photocatalysts were effective in degrading bisphenol A (BPA), 4-chlorophenol (4-CP), and cimetidine (CMT), which dissolved in both deionized water and secondary wastewater effluents, with activity being proportional to the quantity of TiO2 NPs immobilized. For the highest loading amount of TiO2, BPA, 4-CP, and CMT degraded completely within 100, 100, and 40 min of UV irradiation, respectively. Stable photo-oxidation of CMT was maintained through 10 repeated cycles. During these cycles, it was confirmed that there was no loss of TiO2 NPs by inductively coupled plasma optical emission spectrometry. Our results suggest that effective and stable PVDF-TiO2 hybrid photocatalysts can be fabricated on a large scale by combining electrospinning and electrospraying techniques.

Characterization of modified PVDF membrane by gamma irradiation for non-potable water reuse

Poly(vinylidene fluorine) (PVDF) membranes were grafted by gamma-ray irradiation and were sulfonated by sodium sulfite to modify the surface of the membranes. The characteristics of the modified PVDF membranes were evaluated by the data of Fourier transform infrared (FT-IR), X-ray photoelectron spectroscopy (XPS), field-emission scanning electron microscope (FE-SEM), the contact angle of the membrane surface and the water permeability. From the results of FT-IR, XPS and FE-SEM, it was shown that the modified membranes were successfully grafted by gamma-ray irradiation and were sulfonated. The content of oxygen and sulfur increased with the monomer concentration, while the content of fluorine sharply decreased. The pore size of the modified membranes decreased after gamma-ray irradiation. The contact angle and the water permeability showed that the hydrophilicity of the modified membranes played a role in determining the membrane performance. The feasibility study of the modified PVDF membranes for using non-potable water reuse were carried out using a laboratory-scale microfiltration system. Grey wastewater was used as the influent in the filtration unit, and permeate quality satisfied non-potable water reuse guidelines in the Republic of Korea.

Ultrasound irradiation combined with hydraulic cleaning on fouled polyethersulfone and polyvinylidene fluoride membranes

In this study, an ultrasonic irradiation technique was utilized to mitigate the fouling of polyethersulfone (PES) and polyvinylidene fluoride (PVDF) membranes. The use of ultrasound at 20 kHz was applied to a dead-end microfiltration cell in order to mitigate fouling caused by the presence of colloidal bentonite particles. The effect of ultrasonic power and pulse duration on the permeate flux recovery was examined. Measurements indicate that an increase in ultrasonic power and longer pulse duration results to a higher permeate flux recovery. In order to reduce power consumption, a low to high power shift (LHPS) and pulsation method, were investigated. Methods of cleaning such as ultrasonic irradiation, ultrasonic cleaning with forward flushing and ultrasonic cleaning with backwashing were utilized and their cleaning efficiencies were examined. The cleaning performance was assessed using the clean water flux method and scanning electron microscope analysis of the cleaned membranes. Results showed that LHPS and pulsation method both improve the permeate flux recovery but were not able to attain the 93.97 and 74.88% flux recovery for PES and PVDF that was achieved by constant-15 W ultrasonic cleaning. In addition, forward flushing and backwashing may enhance the performance of ultrasonic cleaning at 9 W but could become disadvantageous at 15 W.

All-optically controllable and highly efficient scattering mode light modulator based on azobenzene liquid crystals and poly(N-vinylcarbazole) films

The present study reports that isothermal phase transition induced by photoisomerization of azobenzene liquid crystals (azo-LCs) from trans- to cis-isomers results in the dissolution of poly(N-vinylcarbazole) (PVK) into azo-LCs. Transparent (scattering) states can be demonstrated using uniform (rough) morphologies of PVK generated by slow (rapid) phase separation of PVK and azo-LCs from cis- to trans-isomers. The PVK films were examined in detail using scanning electron microscopy. Scattering performance resulting from the rough PVK surface induced micron-sized LC domains, and transparent performance resulting from the reformed uniform PVK surface can be optically and reversibly switched. Finally, all-optically controllable and highly efficient (contrast ratio of 370:1) scattering mode light modulators based on azo-LCs and PVK films were demonstrated.

Dynamic swelling of tunable full-color block copolymer photonic gels via counterion exchange

One-dimensionally periodic block copolymer photonic lamellar gels with full-color tunability as a result of a direct exchange of counteranions were fabricated via a two-step procedure comprising the self-assembly of a hydrophobic block-hydrophilic polyelectrolyte block copolymer, polystyrene-b-poly(2-vinyl pyridine) (PS-b-P2VP), followed by sequential quaternization of the P2VP layers in 1-bromoethane solution. Depending on the hydration characteristics of each counteranion, the selective swelling of the block copolymer lamellar structures leads to large tunability of the photonic stop band from blue to red wavelengths. More extensive quaternization of the P2VP block allows the photonic lamellar gels to swell more and red shift to longer wavelength. Here, we investigate the dynamic swelling behavior in the photonic gel films through time-resolved in situ measurement of UV-vis transmission. We model the swelling behavior using the transfer matrix method based on the experimentally observed reflectivity data with substitution of appropriate counterions. These tunable structural color materials may be attractive for numerous applications such as high-contrast displays without using a backlight, color filters, and optical mirrors for flexible lasing.

Dielectric properties of EVA rubber composites at microwave frequencies theory, instrumentation and measurements

This work describes and evaluates a technique for determining the dielectric properties of carbon-black filled Ethylene Vinyl Acetate (EVA) rubber and presents results on the studies of the effect of frequency on the permittivity and microwave conductivity using resonant cavity perturbation method. The measurements are performed with the aid of a Network Analyzer in X-band. The simplicity of this method lies in the fact that the dielectric properties can be obtained directly from the analytical formula without taking recourse to calibration.

Optimization of a quasi-solid-state dye-sensitized solar cell employing a nanocrystal-polymer composite electrolyte modified with water and ethanol

A quasi-solid-state dye-sensitized solar cell employing a poly(ethylene oxide)-poly(vinylidene fluoride) (PEO-PVDF)/TiO2 gel electrolyte modified by various concentrations of water and ethanol is described. It is shown that the introduction of water and ethanol prevents the crystallization of the polymer matrix, and enhances the free I(-)/I(3)(-) concentration and the networks for ion transportation in the electrolyte, thus leading to an improvement in conductivity. A high energy conversion efficiency of about 5.8% is achieved by controlling the additive concentration in the electrolyte. Optimization of the additive-modified electrolyte performance has been obtained by studying the cross-linking behavior of water and ethanol with Fourier transform infrared (FTIR), differential scanning calorimetry (DSC) and viscosity measurements, and the electrical conduction behavior of the electrolyte with impedance spectra measurements.

Excitation of acoustic waves from cylindrical polyvinylidene fluoride (PVDF) film confined in a concentric wall

This paper investigates acoustic wave radiation from cylindrical polyvinylidene fluoride (PVDF) film mounted inside a concentric wall with a small air gap. In such a structure, propagation is allowed only in the gap between the film and the wall surface, and the wave propagates in the axial direction of the cylinder. The radiation impedance of the cylindrical transducer inside the concentric wall has been calculated using a one-dimensional propagation model. After calculating the mechanical impedance of the cylindrical PVDF film, the generated acoustic wave has been calculated as a function of frequency with various air gaps between the PVDF film and the wall. It has been found that the excited acoustic wave becomes stronger for a narrower air gap and shows a maximum at a specific air gap. This phenomenon has been explained as the match between the transducer impedance and the radiation impedance of the air gap. When the gap is too small, the radiation impedance exceeds the transducer's mechanical impedance, the acoustic wave radiation decreases with the decreasing gap, and the resonance frequency increases due to loading by the imaginary part of the excessive radiation impedance. All these theoretical results have been experimentally confirmed.

MAGIC polymer gel for dosimetric verification in boron neutron capture therapy

Radiation sensitive polymer gels are among the most promising three-dimensional dose verification tools developed to date. Polymer gel dosimeter known by the acronym MAGIC has been tested for evaluation of its use in boron neutron capture (BNCT) dosimetry. We irradiated a large (diameter 10 cm, length 20 cm) cylindrical gel phantom in the epithermal neutron beam of the Finnish BNCT facility at the FiR 1 nuclear reactor. Neutron irradiation was simulated with a Monte Carlo radiation transport code MCNP. Gel samples from the same production batch were also irradiated with 6 MV photons from a medical linear accelerator to compare dose response in the two different types of beams. Irradiated gel phantoms were imaged using MRI to determine their relaxation rate R2 maps. The measured and normalized dose distribution in the epithermal neutron beam was compared to the dose distribution calculated by computer simulation. The results support the feasibility MAGIC gel in BNCT dosimetry.

Controlled release of 5-fluorouridine from radiation-crosslinked poly(ethylene-co-vinyl acetate) films

The effect of gamma-radiation doses of 12.5-380 kGy on the infrared spectra, gel content, mechanical properties, and the release of oxobutyl-5-fluoro-2'-deoxyuridine (OfdUrd, an antitumor agent) from poly(ethylene-co-vinyl acetate) (EVA) films was studied. The results showed that the application of radiation doses produced a crosslinking reaction leading to a maximum gel content of about 85% in the case of 150 kGy. Higher doses did not increase the gel content in EVA films. The mechanical properties (tensile strength, percentage elongation at break and Young's modulus) of all studied EVA matrices were affected by the exposure to gamma-radiation. Irradiation doses over 50 kGy caused an increase in the Young's modulus of EVA and at the same time a decrease in the strain per cent. Moreover, the network structure formed after irradiation reduced significantly the OFdUrd release from EVA films. In this manner, the radiation dose applied to the polymeric matrix modulated the release of OFdUrd, avoiding the high concentrations that may cause severe systemic toxicity. The loading of OFdUrd to EVA film triggered a slight hyperemia after implantation, while the inflammatory reaction was only observed during the first two days.

Rheological evaluation of dispersions, prepared with different non- and gamma-irradiated bioadhesive cospray dried powder mixtures

Various polymer mixtures were used to prepare gels: native drum dried waxy maize starch, Amioca starch, Carbopol 974P NF and powder mixtures obtained by cospray drying Amioca starch and Carbopol 974P NF, and by blending Carbopol 974P NF with Amioca starch or drum dried waxy maize starch. Oscillatory rheology was employed to investigate the influence of gamma-irradiation, but also of the different compositions (i.e. Carbopol 974P NF varied from 5 to 25% w/w in the powder mixtures tested) and the preparation procedures of the powder mixtures on the viscoelastic properties of the polymer dispersions. The rheological data showed that gamma-irradiation has a significant influence on the rheological behaviour of the polymers dispersed. More elastic properties were obtained when the concentration of Carbopol 974P NF was increased. The dispersions containing at least an amount of 15% Carbopol 974P NF (w/w) are mainly elastic. Contrary to cospray drying the powders, blending the powders leads to higher elastic and gel properties of the dispersed polymers.

Design, fabrication, and characterization of a tissue-equivalent phantom for optical elastography

We suitably adapt the design of a tissue-equivalent phantom used for photoacoustic imaging to construct phantoms for optical elastography. The elastography phantom we consider should have optical properties such as scattering coefficient, scattering anisotropy factor, and refractive index; mechanical properties such as storage and loss modulus; and acoustic properties such as ultrasound velocity, attenuation coefficient, and acoustic impedance to match healthy and diseased tissues. The phantom is made of poly (vinyl alcohol) (PVA) and its mechanical, optical, and acoustic properties are tailored by physical cross-linking effected through subjecting a suitable mix of PVA stock and water to a number of freeze-thaw cycles and by varying the degree of hydrolysis in the PVA stock. The optical, mechanical, and acoustic properties of the samples prepared are measured by employing different techniques. The measured variations in the values of optical scattering coefficient, scattering anisotropy factor, and refractive index and storage modulus are found to be comparable to those in normal and diseased breast tissues. The acoustic properties such as sound speed, acoustic attenuation coefficient, and density are found to be close to the average values reported in the literature for normal breast tissue.

Dose verification of single shot gamma knife applications using VIPAR polymer gel and MRI

This work describes an experimental procedure with potential to assess the overall accuracy associated with gamma knife clinical applications, from patient imaging and dosimetry planning to patient positioning and dose delivery using the automated positioning system of a Leksell Gamma Knife model C. The VIPAR polymer gel-MRI dosimetry method is employed due to its inherent three-dimensional feature and linear dose response over the range of gamma knife applications. Different polymer gel vials were irradiated with single shot gamma knife treatment plans using each of the four available collimator helmets to deliver a maximum dose of 30 Gy. Percentage relative dose results are presented not only in the form of one-dimensional profiles but also planar isocontours and isosurfaces in three dimensions. Experimental results are compared with corresponding Gammaplan treatment planning system calculations as well as acceptance test radiochromic film measurements. A good agreement, within the experimental uncertainty, is observed between measured and expected dose distributions. This experimental uncertainty is of the order of one imaging pixel in the MRI gel readout session (<1 mm) and allows for the verification of single shot gamma knife applications in terms of acceptance specifications for precision in beam alignment and accuracy. Averaging net R(2) results in the dose plateau of the 4 mm and 18 mm collimator irradiated gel vials, which were MR scanned in the same session, provides a crude estimate of the 4 mm output factor which agrees within errors with the default value of 0.870.

Bleaching Efficacy of Whitening Agents Activated by Xenon Lamp and 960-nm Diode Radiation

OBJECTIVE

This in vitro study examines the efficacy of two different dental whitening agents, Opalescence Xtra and Opus White, by analyzing the change in color achieved by the treatment and the temperature increase induced in the pulpal chamber.

BACKGROUND DATA

Bleaching techniques achieved significant advances with the use of coherent or incoherent radiation sources to activate the bleaching chemicals.

METHODS

The bleaching agents, containing 35% of hydrogen peroxide, were stimulated with 0.9 W of xenon arc lamp and 0.9 W or 2 W of a 960-nm diode laser during 60 sec (0.9 W) and 30 sec (2 W) on 33 extracted human teeth. During irradiation, the temperature in the pulpal cavity was monitored. The color change was evaluated using the CIE L*a*b* color space measurement system.

RESULTS

The treated groups showed an increase in color saturation (DeltaC*) of 3-32% and a change in whiteness (DeltaL*) of 0-8%. This study found that only some of the irradiated groups show statistically significant difference (p < 0.05) in the effectiveness of their treatment when compared to the control, whereas no significant statistical difference was obtained in between the irradiated groups. Temperature increase was 2-4 degrees C when using the xenon arc lamp, 2-8 degrees C and 4-12 degrees C when using the diode laser at 0.9 W and 2 W, respectively.

CONCLUSIONS

The results of this study suggest that Opalescence Extra and Opus White are both effective to provide brighter teeth. However, according to the conditions used in this study, only the xenon arc lamp induced a safer temperature increase.

Branched fluoropolymer-Si hybrids via surface-initiated ATRP of pentafluorostyrene on hydrogen-terminated Si(100) surfaces

Linear, branched, and arborescent fluoropolymer-Si hybrids were prepared via surface-initiated atom transfer radical polymerization (ATRP) from the 4-vinylbenzyl chloride (VBC) inimer and ClSO(3)H-modified VBC that were immobilized on hydrogen-terminated Si(100), or Si-H, surfaces. The simple approach of UV-induced coupling of VBC with the Si-H surface provided a stable, Si-C bonded monolayer of "monofunctional" ATRP initiators (the Si-VBC surface). The aromatic rings of the Si-VBC surface were then sulfonated by ClSO(3)H to introduce sulfonyl chloride (-SO(2)Cl) groups and to give rise to a monolayer of "bifunctional" ATRP initiators. Kinetics study indicated that the chain growth of poly(pentafluorostyrene) from the functionalized silicon surfaces was consistent with a "controlled" or "living" process. The chemical composition and functionality of the silicon surface were tailored by the well-defined linear and branched fluoropolymer brushes. Atomic force microscopy images revealed that the surface-initiated ATRP of pentafluorostyrene (PFS) had proceeded uniformly on the Si-VBC surface to give rise to a dense and molecularly flat surface coverage of the linear brushes. The uniformity of surfaces with branched brushes was controlled by varying the feed ratio of the monomer and inimer (VBC in the present case). The living chain ends on the functionalized silicon surfaces were used as the macroinitiators for the synthesis of diblock copolymer brushes, consisting of the PFS and methyl methacrylate polymer blocks.

Characterization of structural changes of poly(vinyl methyl ether) gamma-irradiated in diluted aqueous solutions

An aqueous deoxygenated dilute PVME solution (cP = 0.5 mass %) was irradiated with gamma-rays at different radiation doses (D = 0.2-10 kGy). At these concentrations and doses contracted molecules are formed but no macroscopic networks. For the analysis of the structural changes, the irradiated samples were analyzed by size exclusion chromatography (SEC) with a triple detector system, static light scattering, and viscometry. SEC measurements necessitate for the application of the universal calibration principle the knowledge of the Kuhn-Mark-Houwink (KMH) parameters. To obtain these parameters commercially available poly(vinyl methyl ether) was fractionated and analyzed by the same means. We found at 30 degrees C a KMH relationship to [eta] = 0.0226 (mL/g) x Mw(0.67) in THF. We observed an increase in molar masses without any significant structural changing for D < 0.5 kGy. With increasing radiation dose, the intramolecular cross-linking reaction becomes more and more important. The results of viscosity measurements show a slight increase in contraction for 1.0 kGy. For irradiation dose higher than D > 1.5 kGy, a strong contraction occurs. For D > 5.0 kGy, the favored intramolecular reactions lead to the formation of microgels.

Leaching of organic acids from irradiated EVA plastic as a function of solution pH and polarity

The leaching of several target organic acids from an irradiated ethylene vinyl acetate material, such as those used as a solution product container, is examined as a function of solution pH and polarity. The targeted compounds included highly soluble weak acids such as acetic and formic acids, and larger, more lipophillic acids such as myristic, palmitic, and stearic acids. The leaching of these compounds was examined over a pH range of 3 to 11 and in various ethanol/water proportions. While pH and solution polarity had only a modest impact on the accumulation of the acetic and formic acids, the accumulation of the fatty acids was greatly affected by both factors. It is suggested that the accumulation of these leachables at high pH is influenced by two processes. The first process, partitioning, the speciation of the acidic leachables (protonated versus dissociated form) contributes to the pH trends observed. In this case, entities that already exist in the plastic partition themselves between the plastic and solution via migration. A second, more important, contributor to the leaching of these acids is a pH-dependent increase in their availability arising from an unspecified reactive process.

Bacteriorhodopsin-based Langmuir-Schaefer films for solar energy capture

The photovoltaic (PV) solar cell, converting incident solar radiation directly into electrical energy, today represents the most common power source for the earth-orbiting spacecraft, and the utilization of organic materials in this context is here explored in comparison with the present state of the art placing emphasis in organic nanotechnology. Poly[3-3'(vinylcarbazole)] (PVK) was synthesized by oxidative polymerization with ferric chloride of N-vinylcarbazole. The resulting polymer was then deposited on solid support by using the Langmuir-Schaefer (LS) technique. The pressure-area isotherm of PVK revealed the possibility of compact monolayer formation at the air-water interface. Different layers of PVK were doped with iodine vapors. The cyclic voltammetry investigation of PVK-doped I2 showed a distinctive electrochemical behavior. The photoinduced charge transfer across a donor/acceptor (D/A) hybrid interface provided an effective method to study the PV properties of the composite LS films. The results are compared with other approaches within the biological framework, such as bacteriorhodopsin (BR), and organic nanostructured materials.

Evaluation of the performance of VIPAR polymer gels using a variety of x-ray and electron beams

The aim of this investigation was the evaluation of the usefulness of N-vinyl pyrrolidone argon (VIPAR) polymer gel dosimetry for relative dose measurements using the majority of types and energies of radiation beams used in clinical practice. For this reason, VIPAR polymer gels were irradiated with the following beams: 6 and 23 MV photons (maximum dose: 15 Gy) and 6, 9, 12, 15, 18 and 21 MeV electrons (90% dose: 15 Gy). Using 6 MV x-rays, a linear gel dose response was verified for doses up to 20 Gy. Assuming linearity of response for the rest of the photon and electron beams used in this study, percentage depth dose measurements were derived. For all beams used and the range of relative doses studied, a satisfying agreement was observed between percentage depth dose measurements performed using the VIPAR gel-MRI method and an ion chamber, validating the assumption that a linear gel dose response holds for all photon and electron beams studied. VIPAR gels, therefore, can be used for relative dose distribution measurements using photons or electrons of any typical energy used in external radiotherapy applications. It is also demonstrated that two-dimensional dose distribution measurements through an irradiated (9 MeV electrons, 3 cm x 3 cm cone) VIPAR gel volume can be easily obtained.

Time-resolved luminescence in conducting polymer/antidot nanocomposites

We report modification of the structure and properties of conjugated polymers through controlled embedding wide-gap nanocrystals (antidots) within the polymer matrix. Investigations were carried out by means of stationary and time-resolved photoluminescence. Antidots strongly modify the luminescence spectrum of poly(p-phenylene vinylene) but have almost no influence on the spectrum of poly(2-(6-cyano-6'-methylheptyloxy)-1, 4-phenylene. We explain this observation with respect to the different chain structure and electron density distribution in these two materials. The temporal evolution of luminescence spectra in polymer/antidot composites contains a series of characteristic times. The shortest of these (0.35-0.6 ns) are independent of antidot material and characterize processes in the polymer matrix. Larger times considerably exceeding 1 ns are composition-sensitive and attributable to carrier capture by nanocrystals. The qualitative character of the modification of luminescence spectra associated with the inclusion of antidots depends strongly on the characteristics of the polymer matrices and more weakly on the antidot material. This suggests that the predominant effect of the nanocrystals relates to the modification of the matrix near the polymer-inorganic interface.

In vitro testing of the bond between soft materials used for maxillofacial prostheses and cast titanium

STATEMENT OF PROBLEM

The choice of soft materials for maxillofacial prostheses is important for covering extraoral defects after tumor surgery or radiation therapy. The use of cast commercially pure titanium as reinforcement seems to be a suitable option.

PURPOSE

Making use of the advantages of titanium frameworks for maxillofacial prostheses requires exploring ways of combining it with soft materials. This study investigated such combinations and evaluated discoloration of the soft material to determine whether it was attributable to the titanium reinforcement.

MATERIAL AND METHODS

Five soft materials used for maxillofacial prostheses and their bond strengths to cast titanium were tested. Different ways of conditioning the titanium surface and different adhesives were used. Plain mechanical retention was also studied. The Gretag SPM 100 was used to determine the potential effects on coloring after 24 hours of radiation in the Suntest rapid exposure unit.

RESULTS

Suitable material combinations for bonding soft materials to titanium were found for all soft materials studied. Bond strength varied depending on the chemical basis of the soft material. Results indicated that maximal bond strengths were obtained by the combinations Supersoft with Super-Bond, Supersoft with subsequent silicoating, and bonding with Dentacolor connector. Few color shifts attributable to the titanium reinforcement were evident in the 2-mm layers of the soft materials applied.

CONCLUSION

The results of this study showed that it is possible to combine a titanium framework and soft silicone materials.

Effect of high-dose electron beam irradiation on the migration of DOA and ATBC plasticizers from food-grade PVC and PVDC/PVC films, respectively, into olive oil

The effect of high-dose irradiation on the migration of dioctyl adipate (DOA) and acetyl tributyl citrate (ATBC) plasticizers from food-grade poly (vinyl chloride) (PVC) and poly (vinylidene chloride/vinyl chloride) (PVDC/PVC) copolymer (Saran) films, respectively, into olive oil was studied. The results showed a significantly higher amount of DOA migrated into olive oil from irradiated versus nonirradiated samples. This difference was more noticeable in oil samples collected during initial periods of contact. The amount of DOA migrating into olive oil was lower for samples irradiated at a dose of 20 kGy in comparison with samples irradiated at a dose of 50 kGy. At a sampling time of 1 h the amount of DOA that migrated into olive oil was 93.9 mg/liter, 141.5 mg/liter, and 183.4 mg/liter for nonirradiated samples, 20-kGy irradiated samples, and 50-kGy irradiated samples, respectively. After 288 hr (12 days) of oil-film contact the respective amounts were 390.8 mg/liter, 409.2 mg/liter, and 430.1 mg/liter. There were no statistically significant differences in migrating amount of ATBC between nonirradiated samples and samples irradiated at a dose of 20 kGy, while in samples irradiated at a dose of 50 kGy the migration of ATBC was increased. After 1 h of oil-film contact no detectable amounts of ATBC had migrated. After 288 h of contact the amounts of ATBC that migrated into olive oil were 3.59 mg/liter, 3.56 mg/liter, and 4.12 mg/liter for nonirradiated samples, 20-kGy irradiated samples, and 50-kGy irradiated samples, respectively. It is suggested that plasticized PVC should not be used in direct contact with high-fat foodstuffs with or without irradiation treatment.

Microfilters for biomedicine obtained by swift ion processing

Swift ions with 50 MeV energy are used to irradiate bio-polymeric films. Lithium, carbon and oxygen beams, with fluencies ranging between 10(8) and 10(13) ions/cm2, are swept on large surfaces of hydrogenated and fluorated polymers. The electronic stopping power of the ion induces high rates of ionization, excitation and radical formation along the ion path with production of chain-scission and cross-linking processes which can be investigated by the molecular emission from the irradiated polymer. The radiation damage increases the chemical solubility of the material around the ion track up to distances of the order of 100 nm. A suitable chemical etching removes the damaged material leaving micrometric holes in the polymeric film. This process gives rise to micro-perforated films which can be used as microfilters, with sub-micrometric pore dimension, high selectivity and controllable porosity. Their use is very interesting for special applications in ultra- and microfiltration of biological liquids.

[The effect of composition and structure of radiological equivalent materials on radiological equivalent]

Morphology of inorganic material powders before and after being treated by ultrafine crush was observed by transformite electron microscope. The length and diameter of granules were measured. Polymers inorganic material powders before and after being treated by ultrafine crush were used for preparing radiological equivalent materials. Blending compatibility of inorganic meterials with polymer materials was observed by scanning electron microscope. CT values of tissue equivalent materials were measured by X-ray CT. Distribution of inorganic materials was examined. The compactness of materials was determined by the water absorbed method. The elastic module of materials was measured by laser speckle interferementry method. The results showed that the inorganic material powders treated by the ultrafine crush blent well with polymer and the distribution of these powders in the polymer was homogeneous. The equivalent errors of linear attenuation coefficients and CT values of equivalent materials were small. Their elastic modules increased one order of magnitude from 6.028 x 10(2) kg/cm2 to 9.753 x 10(3) kg/cm2. In addition, the rod inorganic material powders having rod granule blent easily with polymer. The present study provides a theoretical guidance and experimental basis for the design and synthesis of radiological equivalent materials.

Effect of microwave heating on the migration of dioctyladipate and acetyltributylcitrate plasticizers from food-grade PVC and PVDC/PVC films into olive oil and water

Migration of dioctyladipate (DOA) and acetyltributylcitrate (ATBC) plasticizers from plasticized polyvinylchloride (PVC) and polyvinylidene chloride (PVDC)/PVC (Saran) films into both olive oil and distilled water during microwave heating has been studied. The plasticizer migrating into olive oil and water was determined using an indirect GC method after saponification of the ester-type plasticizer (DOA or ATBC) and subsequent collection of the alcohol component of the ester, namely: 2-ethyl-1-hexanol and 1-butanol, respectively. Migration was dependent on heating time, microwave power setting, the nature of the food simulant and the initial concentration of the plasticizer in the film. Migration of DOA into olive oil reached equilibrium after heating for 10 min at full power (604.6 mg DOA/l). Migration into distilled water was 74.1 mg/l after 8 min of microwave cooking at full power. The amount of ATBC migrating into olive oil reached equilibrium after heating for 10 min at full power (73.9 mg ATBC/l). Migration into distilled water was 4.1 mg/l after heating at full power for 8 min. Control samples containing olive oil gave DOA migration values which were significantly higher than the upper limit for global migration (60 mg/l) set by the European Community. It is proposed that PVC should not be used in direct contact with food in the microwave oven, while Saran may be used with caution in microwave heating and reheating applications, avoiding its direct contact with high fat foodstuffs.

[Graft polymerization onto poly(methylvinylsiloxane)-bonded silica gel by gamma-ray irradiation]

Poly(methylvinylsiloxane)-bonded silica gel was synthesized by condensation reaction between silica gel and the hydrolysis product of methylvinyldichlorosilane. Graft polymerization of styrene or indene onto poly(methylvinylsiloxane)-bonded silica gel was carried out by gamma-ray irradiation and compared with that onto silica gel. Homopolymer was found to be formed through a radical mechanism concurrently with an ionic mechanism in the graft polymerization. Probably genuine graft polymers are formed in the graft polymerization onto poly(methylvinylsiloxane)-bonded silica gel, while the product formed in the graft polymerization onto silica gel may be apparent graft polymers.

Ethylene chlorohydrin formation in radiation- and ethylene oxide-sterilized poly(vinyl chloride)

Published reports on the formation of ethylene chlorohydrin in ethylene oxide-sterilized poly(vinyl chloride) are contradictory. The present paper discusses parameters involved in the ethylene chlorohydrin formation, such as the stabilizer system, plasticizer content and thermal strain during manufacture. It is shown that ethylene chlorohydrin can be formed in ethylene oxide-sterilized poly(vinyl chloride) previously sterilized by irradiation, in amounts dramatically exceeding published 'safe levels'.

In vivo release of testosterone from vinyl polymer composites prepared by radiation-induced polymerization

Polymer-testosterone composites with long periods of controlled slow release were made by radiation-induced polymerization in a supercooled state at low temperature using glass-forming monomers. The in vitro release of testosterone from various vinyl polymer composites was found to follow a matrix-controlled process (Q-t1/2). The rate of drug delivery was accelerated with increasing water content of polymers. In experiments in vivo, the composites were implanted subcutaneously in the back of castrated rats during the 30 day test period. The in vivo release rate of testosterone was a little smaller than in vitro. This difference between two releases also increased with the increase of hydrophilicity of polymer. The physiological response in rats was investigated by measuring the weight of ventral prostate and serum testosterone concentration with testosterone-containing composites. The weight of ventral prostate increased linearly with increasing rate of drug release and the serum testosterone concentration could be correlated with the release and with the weight increase of ventral prostate. It was found from microscopic observation that the used polymer carriers had relatively good biocompatibility to cause little foreign body reaction.

Controlled slow release of chemotherapeutic drugs for cancer from matrices prepared by radiation polymerization at low temperatures

The vinyl polymer-chemotherapeutic agent composites of various shapes (rod, tablet, membrane, microsphere, and powder) were prepared by radiation polymerization at low temperatures for the purpose of durable controlled slow release of drugs from implanted matrices. Bleomycin hydrochloric acid, mitomycin C, and 5-fluorouracil were tested as chemotherapeutic drugs entrapped in poly(diethylene glycol dimethacrylate) including a small quantity of a polymer such as poly(styrene), poly(vinyl formal), poly(vinyl acetate), poly(methyl methacrylate) on polyethylene glycol No. 600. The release rates from the matrices depended much on the kind of polymer, drug, and monomer concentration in polymerization and also on the shape of the composite. The release of these drugs from polymer matrices obeyed the diffusion-controlled release mechanism based on Higuchi's equation and was durable for more than thirty days. It was found that the release rate can be controlled easily by design of the shapes and structures of the polymer matrices.