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PubMed2005

Domain shape relaxation and local viscosity in stratifying foam films.

We studied the dynamics of two different types of domain shape relaxation in a stratifying foam film composed of an anionic polymer and cationic surfactant. Those films thin in stepwise fashion: circular domains of lower film thickness are formed, expand and coalesce until they cover the whole film surface. We found that the shape relaxation of coalescing domains is governed only by 2D dissipation, and the measurement of the time scales allows to determine the ratio between the driving force (line tension) and local film viscosity. Further, we analyzed the withdrawal of stripes and modeled it by a moving disc pulled by an external force. Here, 3D dissipation can not be neglected (Stokes paradox) and the equilibrium velocity depends logarithmically on the viscosity of the surrounding 3D air. The evaluation of both kinds of relaxation events yields the orders of magnitude of film viscosity and line tension. For the investigated system we found that the film viscosity is at least 30 times larger than the bulk viscosity, which can be explained by the local molecular ordering and strong interactions with film surfaces.

Anions↗
PubMed2002

Confinement and processing effects on glass transition temperature and physical aging in ultrathin polymer films: novel fluorescence measurements.

Fluorescence intensity measurements of chromophore-doped or -labeled polymers have been used for the first time to determine the effects of decreasing film thickness on glass transition temperature, T(g), the relative strength of the glass transition, and the relative rate of physical aging below T(g) in supported, ultrathin polymer films. The temperature dependence of fluorescence intensity measured in the glassy state of thin and ultrathin films of pyrene-doped polystyrene (PS), poly(isobutyl methacrylate) (PiBMA), and poly(2-vinylpyridine) (P2VP) differs from that in the rubbery state with a transition at T(g). Positive deviations from bulk T(g) are observed in ultrathin PiBMA and P2VP films on silica substrates while substantial negative deviations from bulk T(g) are observed in ultrathin PS films on silica substrates. The relative difference in the temperature dependences of fluorescence intensity in the rubbery and glassy states is usually reduced with decreasing film thickness, indicating that the strength of the glass transition is reduced in thinner films. The temperature dependence of fluorescence intensity also provides useful information on effects of processing history as well as on the degree of polymer-substrate interaction. In addition, when used as a polymer label, a mobility-sensitive rotor chromophore is demonstrated to be useful in measuring relative rates of physical aging in films as thin as 10 nm.

Journal Article↗
PubMed2003

Glass transition temperature of freely-standing films of atactic poly(methyl methacrylate).

We have used ellipsometry to measure the glass transition temperature T(g) of high molecular weight (M(w)=790 x 10(3)), freely-standing films of atactic poly(methyl methacrylate) (a-PMMA), as well as films of the same polymer supported on two different substrates: the native oxide layer of silicon (Si) and gold-covered Si. We observe linear reductions in T(g) with decreasing film thickness h for the freely-standing PMMA films with 30 nm < h<100 nm, which is qualitatively similar to previous results obtained for freely-standing polystyrene (PS) films. However the magnitude of the T(g) reductions for PMMA is much less than for freely-standing films of PS of comparable molecular weight and thickness. We also find that for films supported on either substrate, with thicknesses as small as 30 nm, the T(g) values do not deviate substantially from the value measured for thick films.

Journal Article↗
PubMed1996

The AAPM/RSNA physics tutorial for residents. Measures of screen-film performance.

The choice of screen-film combination, combined with film-processing conditions, substantially affects radiographic image quality (contrast, blur, and noise) and radiation dose. Film type (single or double emulsion, silver halide content, grain morphology, and spectral sensitivity), processing conditions (chemicals, temperature, time, and agitation), fog level (storage, safelight, light leaks), and characteristics (gradient) determine how the x-ray intensity pattern will be related to the optical density pattern in the radiograph. The type of screen (phosphor layer thickness, light-absorbing dyes and pigments, phosphor particle size), speed of the screen-film processing system (sensitivity), film granularity, screen uniformity, and film contrast affect radiographic noise. Detective quantum efficiency is the basic measure of the efficiency of an imaging system and takes into account the contrast, image blur, speed, and image noise of the system. For radiologists, residents, medical physicists, and technologists involved in medical imaging, it is important to have a basic understanding of the characteristics of screen-film and film-processing systems.

Humans↗
PubMed2003

Population-based mammography screening: comparison of screen-film and full-field digital mammography with soft-copy reading--Oslo I study.

PURPOSE: To compare screen-film and full-field digital mammography with soft-copy reading in a population-based screening program. MATERIALS AND METHODS: Full-field digital and screen-film mammography were performed in 3,683 women aged 50-69 years. Two standard views of each breast were acquired with each modality. Images underwent independent double reading with use of a five-point rating scale for probability of cancer. Recall rates and positive predictive values were calculated. Cancer detection rates determined with both modalities were compared by using the McNemar test for paired proportions. Retrospective side-by-side analysis for conspicuity of cancers was performed by an external independent radiologist group with experience in both modalities. RESULTS: In 3,683 cases, 31 cancers were detected. Screen-film mammography depicted 28 (0.76%) malignancies, and full-field digital mammography depicted 23 (0.62%) malignancies. The difference between cancer detection rates was not significant (P =.23). The recall rate for full-field digital mammography (4.6%; 168 of 3,683 cases) was slightly higher than that for screen-film mammography (3.5%; 128 of 3,683 cases). The positive predictive value based on needle biopsy results was 46% for screen-film mammography and 39% for full-field digital mammography. Side-by-side image comparison for cancer conspicuity led to classification of 19 cancers as equal for probability of malignancy, six cancers as slightly better demonstrated at screen-film mammography, and six cancers as slightly better demonstrated at full-field digital mammography. CONCLUSION: There was no statistically significant difference in cancer detection rate between screen-film and full-field digital mammography. Cancer conspicuity was equal with both modalities. Full-field digital mammography with soft-copy reading is comparable to screen-film mammography in population-based screening.

Aged↗
PubMed2002

In vitro study of drug-loaded bioresorbable films and support structures.

Bioresorbable films can serve simultaneously as anatomic support structures and as drug delivery platforms. In the present study, bioresorbable poly(L-lactic acid) (PLLA) films containing dexamethasone were prepared by solution processing methods. Their in vitro studies focused on the mechanical properties with respect to morphology and degradation and erosion processes. Novel expandable support devices (stents) developed from these films were studied. Such a stent would support conduits, such as the neonatal trachea to treat tracheal malacia, until the airway matures, and would then be totally resorbed, obviating the need for a removal operation. The PLLA films showed good initial mechanical properties. They can accommodate drug incorporation on the film surface and also in the bulk. Water incubation of the films results in a decrease in their tensile mechanical properties, due to chain scission and morphological changes. These changes can vary from degradation and small changes in morphological features to erosion, leading to a microporous structure, depending on the polymer. The cumulative release of dexamethasone from the films is linear. The rate of release is determined by the film's structure (drug location/dispersion). The stents demonstrated good mechanical properties. The initial radial compression strength of the stent is determined mainly by the polymer structure. Drug incorporation has a minor effect on the initial stent strength. Exposure to radial compression stress results in elastic reversible deformation or a sudden brittle fracture, depending on the polymer. A 20-week in vitro study of the stents showed that they are applicable for supporting body conduits, such as the trachea.

Absorbable Implants↗
PubMed2005

Structural properties of biodegradable polyesters and rheological behaviour of their dispersions and films.

This paper focuses on the dependence of the rheological properties of PLA-PEG and PLGA dispersions and films on the polymer structural properties, in order to obtain useful information to predict and explain the performance of polyester films as drug-delivery systems. In this study, one PLA-PEG and three PLGA polymers of different molecular mass were synthesized and characterized by NMR, GPC, DSC and TGA-FT-IR. To characterize the viscoelastic behaviour of concentrated solutions in dichloromethane and of the films obtained by a solvent-casting technique, oscillatory shear rheometry was used. The polymer dispersions showed a characteristic Newtonian viscous behaviour, but with different consistency index depending on the nature of the polymer. Freshly prepared, PLGA and PLA-PEG films had elastic modulus (G') greater than viscous modulus (G"). The decrease in both moduli caused by an increase in temperature from 25 to 37 degrees C was especially marked for the polymers with T(g) below or around 25 degrees C (PLGA 27 kDa and PLA-PEG 27 kDa). After being immersed in pH 7.4 aqueous solution for one week, PLGA films showed a significant increase in both G' and G", due to the promotion of polymer-polymer interactions in a non-solvent medium. In contrast, the PLA-PEG film became softer and more hydrated, due to the amphiphilic character of the polymer. The water taken up by the film acted as a plasticizer and induced the softening of the system. These results suggest that the presence of PEG chains exerts a strong influence on the mechanical properties of polyesters films and, possibly, the performance as coating or matrices of drug-delivery systems.

Biodegradation, Environmental↗
PubMed2005

Suppression of cell attachment and protein adsorption onto amphiphilic polylactide-grafted dextran films.

To develop novel biodegradable biomedical materials, polylactide-grafted dextrans (Dex-g-PLA)s having various lengths, numbers of graft chains and sugar units were synthesized using the trimethylsilyl (TMS) protection method. To explore the possibility of using Dex-g-PLA as a biomedical soft-material, the contact angle, cell attachment and protein adsorption properties of the films prepared from these biodegradable and amphiphilic graft co-polymers were investigated. The poly-L-lactide (PLLA) film did not absorb water at all because of its high hydrophobicity, while the graft co-polymer films started immediately to swell after immersion in PBS. The percentage of water absorption at equilibrium increased with increasing sugar unit content. The receding contact angle of the Dex-g-PLA films against water was smaller than that of the PLLA film. The receding contact angle of Dex-g-PLA films against water decreased with increasing the sugar unit content. The top surface of the Dex-g-PLA film was suggested to be covered with hydrophilic Dex segments by means of annealing in water and to afford the wettable surface. Such a wettable surface led to the suppression of cell attachment and protein adsorption onto the film.

Adsorption↗
PubMed2005

Novel biodegradable films and scaffolds of chitosan blended with poly(3-hydroxybutyrate).

In order to develop a novel biomaterial, films of chitosan blended with poly(3-hydroxybutyrate) (PHB) were prepared by an emulsion blending technique and their properties were characterized. Scanning electron microscopy (SEM) showed that PHB microspheres were formed and were entrapped in chitosan matrices, which made the film surface rough. With increasing PHB content, the roughness of the film surface increased, while the swelling capability of the films decreased. In a wet state, the blended films exhibited a lower elastic modulus, a higher elongation-at-break and a higher tensile strength compared with chitosan films. Cell-culture experiments revealed that the blended films had better cytocompatibility than chitosan films. To explore the potential application of the blended material in tissue engineering, the porous blended scaffolds were fabricated and their pore morphology was observed by SEM. The results revealed that not only pore structure but also pore wall morphology of the blended scaffolds could be controlled by selecting the parameters of the fabrication process. These advantageous properties indicate that the blended chitosan/PHB material is promising for tissue engineering applications.

Absorbable Implants↗
PubMed2004

Temperature effects on resistance of aligned multiwalled carbon nanotube films.

Electrical transport in vertically aligned films of multiwalled carbon nanotubes has been investigated in the -150 degrees C to 300 degrees C temperature range (all the tests were conducted in air at atmospheric pressure). In all the cases, the nanotube film exhibited a semi-conducting behavior, with the film resistance decreasing with increasing temperature. Removal of amorphous carbon contamination (via plasma etching) significantly improved the nanotube film's sensitivity to temperature changes (particularly in the 20 degrees C to 200 degrees C temperature range). All the of films tested in this study showed a consistent, repeatable behavior that was independent of the nanotube film length. The temperature sensitivity of the nanotube films was also found to be independent of the heating/cooling rates and without hysteresis. Because of the excellent repeatability and stability of the results, it is conceived that miniaturized temperature sensors could be designed using such aligned multiwalled nanotube films.

Carbon↗
PubMed2006

Construction and electrochemistry of Langmuir-Blodgett films of fullerene lipid composite/hybrid materials.

Studies of the electrochemistry of Langmuir-Blodgett (LB) films of C70/artificial lipids including tridodecylmethylammonium bromide (3C12N+Br-, 1), didodecylphosphate (2C12PO4H, 2), and dioleoylphosphatidylcholine (DOPC, 3) and of LB films of a fullerene lipid (4) bearing triple alkyl chains on a C60 moiety on electrodes were carried out in aqueous media. Stable Langmuir monolayers of fullerene C70/artificial lipid composites and the fullerene lipid (4) were formed at the air-water interface and these monolayers were transferred onto electrodes as LB films. Here, we focus on the importance of cationic matrix lipid films to the facile electrochemistry of C70 embedded in a LB film of cationic lipids on an electrode in aqueous media. On the basis of the electrolyte dependence and the charge dependence of the matrix lipids, a possible electron-transfer mechanism of the C70/artificial lipid LB film-modified electrodes is presented. Electrochemistry of a LB film of 4 was also obtained in an aqueous medium. We demonstrate that the introduction of the chemistry of lipid bilayer membranes to the LB films of fullerenes guides us toward the construction of fullerene/lipid bilayer devices.

Electrochemistry↗
PubMed2006

A study of nano-mechanical properties and nano-scratch behavior of boron carbonitride films.

Boron carbonitride (BCN) films were deposited by d.c. unbalanced magnetron sputter deposition where a substrate bias ranging from -50 V to -300 V was applied to the sample. X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy were used to confirm the composition and bonding structure of the BCN films. Surface morphology and roughness were analyzed by atomic force microscopy. The nano-mechanical properties and nano-scratch behavior of the prepared films were determined by a nano-indentation system equipped with continuous stiffness measurement and lateral-force measurement attachments. The results indicate that there is little change in the content of B, C, and N. The films deposited are compounds with hybridized B-C-N bonds and the disordered degree of the structure increases with increasing the substrate bias. The substrate biasing can enhance the nanohardness, elastic modulus, nano-scratch resistance, and cohesion strength of the deposited films. During the nano-scratch test, plastic deformation and ploughing wear appears for the BCN films deposited at lower bias. Elastic deformation becomes the dominant deformation mechanism for the films deposited at higher bias. The coefficient of friction between the deposited BCN films and the diamond tip depends on the loading critical load. The increasing of the substrate bias leads to the improvement of the critical load and the elastic deformation proportion.

Adhesiveness↗
PubMed2006

Stable photoinduced charge separation in nanostructured films containing a 1,4,5,8-naphthalenetetracarboxylic diimide and cytochrome c.

Photoinduced electron transfer between 1,4,5,8-naphthalenetetracarboxylic diimides (NDI) and the redox protein cytochrome c (cyt c) was studied in solution and in spin-coated thin films. The NDI derivatives employed in this study were N,N'-bis(butyl)-1,4,5,8-naphthalenetetracarboxylic diimide (BNDI) and N,N'-bis(2-phosphonoethyl)-1,4,5,8-naphthalenetetracarboxylic diimide (PNDI). Irradiation of the NDI in solution with UV light (365 nm), in the presence of cyt c, resulted in the reduction of the heme iron from the Fe3+ to the Fe2+ state. When PNDI and cyt c were co-deposited by spin-coating on quartz, glass, and silicon substrates, photoactive films were obtained. Exposition of the films to a UV lamp or natural sun light resulted in photoreduction of the protein, generating a stable charge-separated state. Thin films containing segregated layers of BNDI and cyt c were also prepared. Irradiation of these films, however, resulted in protein degradation. The results can be explained through the formation of imide radicals, which transfer an electron to cyt c in the co-deposited films. In the case of segregated films, protein photodegradation suggests the formation of singlet oxygen within the films.

Biophysics↗
PubMed2003

Examination of murine tear film.

PURPOSE: To define spatially any free aqueous layer in murine tear film. METHOD: A pre-zeroed microelectrode was touched to the superficial corneal epithelium and then raised in steps of 1 micro m through the murine tear film into the air and then retraced along the same path. Other murine tear films were partially probed with a spatial resolution of 0.1 micro m. The reference microelectrode was placed in a fragment of 3% polyacrylamide gel equilibrated against 154 mM NaCl and located on the nasal quadrant of the scleral conjunctiva. Other murine corneas were quick frozen in melting isopentane and freeze substituted or pretreated with cetylpyridinium chloride and then examined by transmission electron microscopy. RESULTS: The recorded electrical profiles of the tear film were reproducible in each preparation and showed a relatively uniform positive electrical potential throughout their whole thickness, except within 0.5 micro m of the epithelial surface when the potential reversed to negative values. The thickness of mouse tear film averaged 7.4 +/- 0.8 micro m (mean +/- SD, n = 40). The electron microscope images showed the murine tear film to have a relatively uniform positive electron density throughout the thickness. CONCLUSIONS: Electrical profiles of the murine tear film presented no evidence of a separate free aqueous phase. The tear film is observed as an aqueous gel that includes anion-exchanging polyelectrolytes throughout most of its thickness, but within 0.5 micro m of the epithelial surface, it changes to cation-exchanging polyelectrolytes. Electron microscope images provide some supporting evidence.

Animals↗
PubMed1999

Structures of surfactant films: a scanning force microscopy study.

The alveolar lining layer is thought to consist of a continuous duplex layer, i.e., an aqueous hypophase covered by a thin surfactant film which is a monolayer with dipalmitoyl-phosphatidylcholine (DPPC) as its most important component. Findings obtained by electron microscopy and results from in vitro experiments suggest, however, that the structure and hence the structure-function relations of surfactant films are more complex. In order to better define their structures films of surfactants were studied by scanning force microscopy. Four different surfactants were spread on a Langmuir-Wilhelmy balance, and then transferred onto a solid mica plate by the Langmuir-Blodgett technique, under various states of film compression. Imaging of the films by scanning force microscopy was performed in the contact (repulsive) mode in air. The scanning force micrographs revealed that surfactant films are not homogeneous, but rather undergo phase transitions depending on the surface pressures. Even at comparable surface pressures different surfactants show quite different surface patterns. Differences in surface structure can even be observed in films containing surfactant proteins (SP)-B and SP-C. These observations give further evidence that the widely accepted hypothesis of a regular monolayer of phospholipids governing the surface tension probably does not hold true, but that the structure-function relationship of surface active surfactant films is even more complex than hitherto thought.

1,2-Dipalmitoylphosphatidylcholine↗
PubMed2004

Development and characterization of biodegradable chitosan films for local delivery of Paclitaxel.

Intratumoral and local drug delivery strategies have gained momentum recently as a promising modality in cancer therapy. In order to deliver paclitaxel at the tumor site in therapeutically relevant concentrations, chitosan films were fabricated. Paclitaxel could be loaded at 31% wt/wt in films, which were translucent and flexible. Physicochemical characterization of paclitaxel via thermal, spectroscopic, x-ray diffraction, and electron microscopy techniques revealed information on solid-state properties of paclitaxel as well as chitosan in films. While chitosan was in amorphous form, paclitaxel seemed to be present in both amorphous and crystalline forms in film. The polymeric dispersion of paclitaxel in poloxamer formed fibrous structures generating discontinuities in the film matrix, thereby leading to the introduction of perturbations in the packing arrangement of polymer chains. These films released only 10% to 15% of loaded paclitaxel by a burst effect under in vitro testing conditions, with lysozyme having no effect on the release. However, films softened after implantation in mice and lost integrity over time. The implantable delivery system is not only biodegradable but also well tolerated in vivo and hence, biocompatible as revealed by histological studies. The lack of formulation-induced local inflammatory responses of paclitaxel chitosan films suggests a new paradigm for localized chemotherapy based on implantable systems.

Animals↗
PubMed2005

Release and permeation kinetics of caffeine from bioadhesive transdermal films.

The aim of this work was to investigate, in vitro, the kinetics of release and permeation of caffeine, chosen as model drug, from bioadhesive transdermal films. These films are not self-adhesive but become adhesive when applied to wet skin. Permeation experiments were performed from films with different drug loadings using rabbit ear skin as barrier. In order to characterize the release kinetics of caffeine from the film, a polyethylene membrane, impregnated with isopropyl myristate was employed. The data obtained in the present work suggest that caffeine release from transdermal bioadhesive films was controlled either by the permeability characteristics of the skin or by the film itself, depending on drug loading. When drug loading is low (ie, caffeine is dissolved in the polymers constituting the film), the control resides in the skin. When caffeine loading exceeds its solubility in the film, the permeation profile is not linear, but shows a sort of burst effect in the early times of permeation, probably owing to the presence of solid drug and/or to a certain degree of "conserved supersaturation" in the solid phase.

Adhesives↗
PubMed2002

In-vitro release of fluoropyrimidines from PLGA film implants.

The release of two low-molecular weight water-soluble fluoropyrimidines, 5-fluorouracil and 5-fluorouridine, from implants of PLGA films was modulated by varying the area (diameter) and number of layers of film per implant. The aim was to achieve continuous release without burst effect for at least a month. The film implants were prepared by the solvent evaporation technique. Except with 5-fluorouracil films, the in-vitro release profiles were in all cases triphasic, indicating that release proceeds by a combination of diffusion and polymer erosion. The experimental data fit the equation resulting from the sum of two exponentials, one direct and the other inverse. 5-fluorouridine release from simple films presented a relatively minor burst effect (24-28%). In contrast, the delivery of both compounds from sandwich-type implants occurred continuously without a burst effect, and lasted for 17-20 days. During the first phase, both 3- and 5-mm sandwiches released 55% of the dose of 5-fluorouridine, at rate constants of 0.037+/-0.021 h(-1) (n = 3) and 0.009+/-0.003 h(-1) (n=3), respectively. In the second phase, release was gradual from both simple films (k2 = 0.011-0.015 h(-1)) and sandwiches (k2 = 0.018-0.058 h(-1)). According to the analysis-of-variance results, neither the area nor type of implant influenced the rate constants significantly. The release profiles of 5-fluorouracil from simple films showed a severe burst effect (64-71%). Release of 5-fluorouracil was gradual only from sandwiches, 5 mm in diameter, showing a lag time unobserved in the 3-mm sandwiches. In the second phase, release was gradual (k2 = 0.014+/-0.003 h(-1)) from 3-mm implants. However, the high variability in results for 5-mm implants prevents conclusions being drawn about the model parameters. Therefore, the sandwich-type film implants showed their utility for releasing water-soluble drugs for a prolonged time, without burst effect.

Absorbable Implants↗