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PubMed2006

Stability of triglyceride liquid films on hydrophilic and hydrophobic glasses.

Wetting and dewetting of solid surfaces by oily fluids were investigated in terms of the stability of the liquid film formed between an air bubble and the solid surface. With the objective of understanding how molecules with low polarity but relatively complex molecular structure behave at the solid/liquid interface, three liquid triglycerides with different chain length and saturation were chosen, namely, tributyrin, tricaprylin, and triolein. Tributyrin and tricaprylin exist in milkfat while triolein is present in vegetable oils. The stability of the liquid films may be inferred from the shape of the disjoining pressure isotherms, which represent the dependence of the disjoining pressure on the film thickness. Disjoining pressure isotherms for films of the three triglycerides on hydrophilic and hydrophobic glasses were obtained using a recently developed apparatus, based on the interferometric technique. The experimental curves are compared with the theoretical predictions of London-Hamaker. The deviations between theory and experiment are interpreted in terms of a structural component of the disjoining pressure. All triglycerides form metastable films on both hydrophilic and hydrophobic glasses which means that for disjoining pressures higher than a critical value, pi(c), a wetting transition occurs and the film ruptures. The mechanisms for film rupture are discussed and a correlation between film stability and the apolar (Lifshitz-van der Waals) and the polar components of the spreading coefficient is proposed.

Journal Article↗
PubMed2006

Growth of ultrathin films of cadmium telluride and tellurium as studied by electrochemical atomic force microscopy.

Time dependent, cathodic electrodeposition of ultrathin CdTe and Te films has been studied in 50 mM H(2)SO(4) + 1 mM CdSO(4) + 0.1 mM TeO(2) solutions at room temperature under potential control using electrochemical atomic force microscopy (EC-AFM). The films were also characterized electrochemically and with X-ray diffraction. The growth mechanism and the composition of the films depends on the applied potentials. Island-like growth mode was observed for CdTe films when the deposition potential was -0.35 V (SHE). At a more positive deposition potential of 0.138 V (SHE), Cd was not co-deposited into the film but affected the dynamic growth mode of the deposit. At this voltage smooth Te films were obtained. Depending on the applied potential, Cd acts either as a co-deposition element for CdTe film growth, or as a mediator for layer-by-layer growth of Te films.

Journal Article↗
PubMed2006

A novel technique for improving interferometric determination of emulsion film thickness by digital filtration.

Determination of the thickness of emulsion films by using the film interferometric images is usually less accurate than that of foam films, due to the close values of the refractive indices of the liquid film and adjacent liquid phases (hence, low contrast and high level of noise at high magnification). A new technique was developed to improve the thickness determination by obtaining the interferometric images without directly filtering the illuminating light, as is usually done in the classical Scheludko interferometric technique. The new method then uses digital filtration during the off-line image post-processing to obtain monochromatic interferometric images required for the thickness determination. The technique was tested with foam films stabilised by sodium dodecyl sulfate and successfully applied to determine thickness of toluene-water-toluene emulsion films using the green and red digital filters. Results for emulsion film thickness determined by either the green or red digital filtration are comparable, thus validating the new technique developed here for emulsion films.

Letter↗
PubMed2006

Effects of In, Al and Sn dopants on the structural and optical properties of ZnO thin films.

Effect of In, Al and Sn dopants on the optical and structural properties of ZnO thin films have been investigated by X-ray diffraction technique and optical characterization method. X-ray diffraction patterns confirm that the films have polycrystalline nature. The thin films have (002) as the preferred orientation. This (002) preferred orientation is due to the minimal surface energy which the hexagonal structure, c-plane to the ZnO crystallites, corresponds to the densest packed plane. The grain size values of the films are found to be 29.0, 35.2 and 39.5 nm for In, Al and Sn doped ZnO thin films, respectively. The optical band gaps of the films were calculated. The absorption edge shifts to the lower wavelengths with In, Al and Sn dopants. The inclusion of dopant into films expands also width of localized states as E(UIn)>E(UAl)>E(USn). The refractive index dispersion curves obey the single oscillator model. The dispersion parameters and optical constants of the films were determined. These parameters changed with In, Al and Sn dopants.

Aluminum↗
PubMed2003

A review of drainage and spontaneous rupture in free standing thin films with tangentially immobile interfaces.

A review of spontaneous rupture in thin films with tangentially immobile interfaces is presented that emphasizes the theoretical developments of film drainage and corrugation growth through the linearization of lubrication theory in a cylindrical geometry. Spontaneous rupture occurs when corrugations from adjacent interfaces become unstable and grow to a critical thickness. A corrugated interface is composed of a number of waveforms and each waveform becomes unstable at a unique transition thickness. The onset of instability occurs at the maximum transition thickness, and it is shown that only upper and lower bounds of this thickness can be predicted from linear stability analysis. The upper bound is equivalent to the Frenkel criterion and is obtained from the zeroth order approximation of the H3 term in the evolution equation. This criterion is determined solely by the film radius, interfacial tension and Hamaker constant. The lower bound is obtained from the first order approximation of the H3 term in the evolution equation and is dependent on the film thinning velocity. A semi-empirical equation, referred to as the MTR equation, is obtained by combining the drainage theory of Manev et al. [J. Dispersion Sci. Technol., 18 (1997) 769] and the experimental measurements of Radoev et al. [J. Colloid Interface Sci. 95 (1983) 254] and is shown to provide accurate predictions of film thinning velocity near the critical thickness of rupture. The MTR equation permits the prediction of the lower bound of the maximum transition thickness based entirely on film radius, Plateau border radius, interfacial tension, temperature and Hamaker constant. The MTR equation extrapolates to Reynolds equation under conditions when the Plateau border pressure is small, which provides a lower bound for the maximum transition thickness that is equivalent to the criterion of Gumerman and Homsy [Chem. Eng. Commun. 2 (1975) 27]. The relative accuracy of either bound is thought to be dependent on the amplitude of the hydrodynamic corrugations, and a semi-empirical correlation is also obtained that permits the amplitude to be calculated as a function of the upper and lower bound of the maximum transition thickness. The relationship between the evolving theoretical developments is demonstrated by three film thickness master curves, which reduce to simple analytical expressions under limiting conditions when the drainage pressure drop is controlled by either the Plateau border capillary pressure or the van der Waals disjoining pressure. The master curves simplify solution of the various theoretical predictions enormously over the entire range of the linear approximation. Finally, it is shown that when the Frenkel criterion is used to assess film stability, recent studies reach conclusions that are contrary to the relevance of spontaneous rupture as a cell-opening mechanism in foams.

Journal Article↗
PubMed1977

Equilibrium and metastable states in lecithin films.

We have considered whether lecithin surface films below the gel-liquid crystal transition temperature, Tc, are in unique physical states. In general, below Tc, equilibrium films do not exist when surface pressures, pi, exceed about 0.1 dyn/cm. Since surface pressure-surface area isotherms of lecithin films below Tc always encompass pi's much greater than 0.1 dyn/cm, the film states are metastable. We show that the film properties under these conditions depend strongly on the history of the film, particularly the method of film formation. Lecithin surface films below Tc are thus in arbitrary metastable states, so that pi-area isotherms are difficult to interpret. The physical significance of such isotherms remains to be determined. The utility of pure lecithin surface layers below Tc as models for biological systems is also challenged by our results.

Atmospheric Pressure↗
PubMed1978

Equilibrium studies of lecithin-cholesterol interactions. II. Phase relations in surface films: analysis of the "condensing" effect of cholesterol.

From measurements of the equilibrium spreading pressure pie for dispersions of lecithin--dimyristoyl (DML) or dioleoyl (DOL)--and cholesterol (CHOL) in water, we have deduced the phase relations in both the aqueous dispersions and the equilibrium surface films. At 29.5 degrees C, when the mole fraction of cholesterol in the dispersion chi(CHOL) is 0 chi(CHOL) less than chi(CHOL) less than 0.33, pie is constant and equal to the value for pure lecithin (DOL or DML). The phase rule predicts than two bulk lipid phases coexist; these are pure lecithin and lecithin:cholesterol 2:1 complex. The equilibrium surface film contants only lecithin and therefore lecithin and 2:1 complex are immiscible in surface films. When 0.33 less than chi/CHOL) less than 1.0, pie is also contant with a value intermediate between that for pure lecithin and cholesterol. In this range of lipid composition two bulk lipid phases also coexist: lecithin:cholesterol 2:1 complex and pure cholesterol. However, the equilibrium surface film contains only the 2:1 complex and, therefore, 2:1 complex is also immiscible with cholesterol in surface films. When pi less than pie, as in the case of spread films, we deduce that two surface phases may coexist; the composition of the phases will depend on chi(CHOL). When 0 less than chi(CHOL) less than 0.33, both lecithin and 2:1 complex coexist, and when 0.33 less than chi(CHOL) less than 1.0, 2:1 complex and cholesterol coexist. The "condensing" effect of cholesterol in lecithin surface films is reexamined. The effect is attributed to formation of the lecithin:cholesterol 2:1 complex and nonequilibrium conditions in the two-phase surface film.

Cholesterol↗
PubMed1998

Evaluation of polyethylene glycol/polylactic acid films in the prevention of adhesions in the rabbit adhesion formation and reformation sidewall models.

OBJECTIVE: To assess the efficacy of bioresorbable films consisting of various polyethylene glycol 6000 and polylactic acid block copolymers on the formation and reformation of adhesions in rabbit models of adhesion development between the sidewall to the adjacent cecum and bowel. The composition of the different polymers was expressed by the number of monomeric units in the block, namely, ethylene oxide (EO) and lactic acid (LA), respectively. DESIGN: Studies of the efficacy of EO/LA films were conducted in rabbit sidewall adhesion formation studies in the presence and absence of blood and in rabbit adhesion reformation studies. REPEL (Life Medical Sciences, Edison, NJ), a film of EO/LA ratio 3.0 manufactured under commercial conditions, was also tested in these animal models. SETTING: University-based laboratory. ANIMALS: New Zealand white rabbits. INTERVENTION(S): Placement of films of various EO/LA ratios at the site of injury to the parietal peritoneum. MAIN OUTCOME MEASURE(S): Adhesion formation and reformation. RESULT(S): Films of various EO/LA ratios, Seprafilm (Genzyme, Cambridge, MA) and Interceed (Johnson and Johnson Medical, Arlington, TX) placed over an area of excised sidewall at the time of initial injury were highly efficacious in the prevention of adhesion formation. A film of EO/LA ratio 3.7, in contrast with Interceed, was also shown to maintain maximal efficacy in the reduction of adhesion formation in the presence of blood. Further, a film of EO/LA ratio 3.0 produced under commercial conditions, REPEL, was highly efficacious in reducing adhesion development in the rabbit models of adhesion and reformation. CONCLUSION(S): These studies suggest that bioresorbable EO/LA films reduced adhesion development in rabbit models of adhesion formation and reformation.

Abdomen↗
PubMed2000

Effect of oxiplex* films (PEO/CMC) on adhesion formation and reformation in rabbit models and on peritoneal infection in a rat model.

OBJECTIVE: To assess the efficacy of Oxiplex (FzioMed, Inc., San Luis Obispo, CA) barriers. DESIGN: Film of polyethylene oxide and carboxymethylcellulose (Oxiplex) were tested for strength and tissue adherence. Films were selected for evaluation in models for biocompatability and adherence. Three films were selected for evaluation in efficacy studies, and one was evaluated for effects on bacterial peritonitis. Handling characteristics of Oxiplex film were evaluated via laparoscopy. SETTING: University laboratory. PATIENT(S): Rabbits, rats, pigs. INTERVENTION(S): Placement of Oxiplex prototypes at the site of injury. MAIN OUTCOME MEASURE(S): Mechanical properties, biocompatibility, tissue adherence, adhesion development, infection potentiation, and device handling. RESULT(S): Mechanical tests indicated that tensile strength and elongation were inversely correlated. All films tested had excellent tissue adherence properties. Selected films, based on residence time and biocompatibility, prevented adhesion formation in all animals and were highly efficacious in preventing adhesion reformation. The optimal Oxiplex prototype prevented adhesion reformation in 91% of the animals. This Oxiplex film, dyed to allow visualization, prevented adhesion reformation and did not affect bacterial peritonitis. In a laparoscopic model, the Oxiplex film, delivered in FilmSert forceps, via a 5.0-mm trocar, rapidly unfurled and could be easily applied to tissue with strong adherence. CONCLUSION(S): These data show development of an adhesion prevention material that is tissue adherent, can be placed via laparoscopy, and does not affect host resistance.

Absorbable Implants↗
PubMed2001

Preparation and applications of polypyrrole films in solid-phase microextraction.

Polypyrrole (PPY) and poly-N-phenylpyrrole (PPPY) films were prepared and applied for solid-phase microextraction (SPME). The extraction properties of the new films to volatile organic compounds were examined using an SPME device coupled with GC-flame ionization detection. A PPY-coated capillary was applied for in-tube SPME to evaluate its extraction efficiency towards less volatile compounds and ionic species. The porous surface structures of the films, revealed by scanning electron microscopy, provided high surface areas and allowed for high extraction efficiency. Compared with commercial SPME stationary phases, the new phases showed better selectivity and sensitivity toward polar, aromatic, basic and anionic compounds, due to their inherent multifunctional properties. In addition, PPY and PPPY films showed different selectivity to various groups of compounds studied, indicating that the selectivity of the films could be modified by introducing a new functional group (phenyl in PPPY) into the polymer. For in-tube SPME, the PPY-coated capillary showed superior extraction efficiency to commercial capillaries for a variety of compounds, demonstrating its potential applications for a wide range of analytes when coupled with HPLC. The sensitivity and selectivity of the films for SPME could be tuned by changing the film thickness. These results are in line with both the theoretical expectations and the results obtained by other methods, which indicate not only that PPY films can be used as new stationary phases for SPME. but also that SPME method may provide an alternative tool for studying materials like polypyrrole.

Capillary Action↗
PubMed2003

Two liquid adsorptive entrapment of a pluronic polymer into the surface of polyaniline films.

Pluronic triblock copolymers were entrapped on the surface of polyaniline (PANI) films by first immersing the latter in N-methylpyrrolidinone (NMP) solutions of one of the Pluronics for a short time. This softened the surface of the films and allowed the Pluronic molecules to entangle with PANI segments of the swollen film on the surface. Further, the films were taken out from the NMP solution and dipped into water, which is a nonsolvent for PANI. The rapid surface deswelling of PANI by the water resulted in the entrapment of the Pluronic on its surface, with the hydrophilic blocks toward water and the hydrophobic block imbedded in the PANI films. The modified PANI obtained was examined by X-ray photoelectron spectroscopy, water droplets contact angles, scanning electron microscopy, and wide angle X-ray diffraction. The surface of the Pluronic entrapped PANI films became more hydrophilic than the hydrophobic PANI films and decreased the amount of bovine serum albumin protein adsorbed on them. This means that, by reducing the biofouling, the life of the modified polyaniline film can be extended when the latter is employed as a biosensor.

Adsorption↗
PubMed2001

Analysis of tear film breakup on Etafilcon A hydrogel lenses.

PURPOSE: There is a need to understand better the biomaterial characteristics responsible for tear film stability during hydrogel lens wear. The underlying cause of pre-lens tear film instability may be indicated by the distribution of sites of breakup. The purpose of this study was to compare the distribution of rupture sites during wear of a common biomaterial to that without lenses. METHODS: A videokeratography unit, the Topographic Modeling System, was used to capture an image of the tear film at the moment of breakup. Forty measurements were made for each of ten subjects, and the resultant rupture site distributions evaluated. The pre-lens tear film breakup locations were studied for Acuvue (Etafilcon A) disposable contact lenses using the same technique. RESULTS: There was a statistically significant trend for pre-corneal tear film breaks to occur more commonly in parameniscal zones than in areas overlying the central cornea (ANOVA, p = 0.002). With the Etafilcon A lenses, a significant difference in breakup frequency between the two regions was not observed. CONCLUSIONS: The pre-corneal tear film findings are consistent with the meniscus model of tear film stability; however, the biomaterial surface characteristics of Etafilcon A give other factors a more dominant role in tear film rupture.

Biocompatible Materials↗
PubMed2003

Platelet adhesive resistance of segmented polyurethane film surface-grafted with vinyl benzyl sulfo monomer of ammonium zwitterions.

Platelet from human plasma adhered on the segmented poly(ether urethane) (SPEU) film grafted with N,N-dimethyl-N-(p-vinylbenyl)-N-(3-sulfopropyl) ammonium (DMVSA) was studied. SPEU films were hydroxylated by potassium peroxosulfate (KPS) and then grafted with DMVSA using ceric ammonium nitrate (CAN) as initiator. The mixing time of hydroxylated SPEU/CAN and the monomer concentration effect on graft polymerization yield were determined by ATR-FTIR. Surface analysis of the grafted films by ATR-FTIR and ESCA confirmed that DMVSA was successfully grafted onto the SPEU film surface. The grafted film possessed a relatively hydrophilic surface, as revealed by water contact angle measurement. The improved blood compatibility of the grafted films was preliminarily evaluated by a platelet-rich plasma adhesion study and scanning electron microscopy, using original SPEU and hydroxylated SPEU films as the controls. The results showed that platelet attachment was decreased greatly on the segmented polyurethane films grafted with DMVSA. This kind of new biomaterials grafted with sulfo ammonium zwitterionic monomers might have potential for biomedical applications.

Blood Platelets↗
PubMed1997

Preparation of cross-linked hyaluronic acid films of low water content.

Hyaluronic acid (HA) was chemically cross-linked with poly(ethylene glycol) diglycidyl ether, a diepoxy compound (EX-810), to yield low water content and slowly degradable films when brought into contact with water. The cross-linking reaction was performed under acidic and neutral conditions, since the epoxy group is readily hydrolysed in alkaline media. To allow the reaction to proceed at high HA concentrations, a solution casting method was employed for the cross-linking of HA. The lowest water content of the cross-linked HA films obtained was 60 wt% when swollen with buffered saline at 37 degrees C. Alginic acid and poly(vinyl alcohol), which possess hydroxyl groups, similar to HA, were also found to undergo cross-linking with the diepoxy compound. Since IR spectra of the cross-linked films had no significantly new absorption, intermolecular formation of ether bonds between the hydroxyl groups belonging to different polysaccharide molecules was assumed to take place. It seemed too difficult to detect the ether bonds in the cross-linked HA films, because the virgin HA film itself contained ether bonds in the molecule. The cross-linked HA film with a water content of 60 wt% exhibited practically no weight loss after 10 days of immersion in phosphate-buffered saline (pH 7.4), while this film underwent in vivo degradation by 30% weight loss after 7 days of subcutaneous implantation in rats. The inflammation reaction elicited around the implanted film was not significant.

Alginates↗
PubMed1997

Characterization of hydroxyapatite film with mixed interface by Ar+ ion beam enhanced deposition.

Ar+ ion beam enhanced deposition (IBED) was used to produce a hydroxyapatite (HA) film on polished titanium substrates. In this study, the HA ceramic target was sputtered by an argon-ion beam with an energy of 1.5 KeV, and the sputtered film was intermittently bombarded by energetic argon-ions at 60 KeV. An effective Ca-Ti mixed layer produced by the energetic argon-ion bombardment was confirmed by using Auger electron spectroscopy. The characteristics of the deposited films were evaluated by Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, X-ray diffraction (XRD) and scanning electron microscopy (SEM) analyses. XRD analysis revealed that the as-deposited film was amorphous, and a hydroxyapatite-type structure was obtained from the post-heat treatment of the deposited films. SEM observations showed that no distinct difference in surface morphology was found between the as-deposited and heat-treated samples for Ar+ IBED films, suggesting a strongly bonded HA film on the titanium substrate. In comparison with the HA target, some chemistry alterations were brought about in the deposited films, such as the incorporation of CO3, the loss of the OH groups and some distortion of the phosphate lattice.

Argon↗
PubMed2000

Cross-linked hyaluronic acid hydrogel films: new biomaterials for drug delivery.

A new hyaluronic acid (HA)-based hydrogel film was prepared and evaluated for use in drug delivery. This biocompatible material crosslinks and gels in minutes, and the dried film swells and rehydrates to a flexible hydrogel in seconds. HA was first converted to the adipic dihydrazide derivative and then crosslinked with the macromolecular homobifunctional reagent poly(ethylene glycol)-propiondialdehyde to give a polymer network. After gelation, a solvent casting method was used to obtain a HA hydrogel film. The dried film swelled sevenfold in volume in buffer, reaching equilibrium in less than 100 s. Scanning electron microscopy (SEM) of the hydrogel films showed a condensed and featureless structure before swelling, but a porous microstructure when hydrated. The thermal behavior of the hydrogel films was characterized by differential scanning calorimetry. The enzymatic degradation of the HA hydrogel films by hyaluronidase was studied using both SEM and a spectrophotometric assay. Drug release from the hydrogel film was evaluated in vitro using selected anti-bacterial and anti-inflammatory drugs. This novel biomaterial can be employed for controlled release of therapeutic agents at wound sites.

Anti-Infective Agents↗
PubMed1998

Effect of fractal dimension on drug permeation through porous ethylcellulose films.

Fractal geometry was applied to quantify the complexity of an internal structure of a porous film prepared with ethylcellulose (EC) and diethylphthalate (DEP) as a plasticizer. EC was dissolved together with DEP in a water-ethanol mixture solution, and then evaporated on Teflon petri dishes in order to make porous EC films. Boundary lines of the porous structures in the EC film cross section were taken by a confocal laser microscope as image data, and these images were fed into a computer to estimate the fractal dimension. The porous structure in EC film was observed to be a typical fractal and its complexity was quantified as a non-integral fractal dimension. No clear correlation was observed between the fractal dimension and the porosity of EC films, suggesting that they were mutually independent parameters representing the porous structure in the EC films. The permeation of theophylline through the EC films was determined by using two-chamber diffusion cells. A fairly good relationship between the permeability coefficient of theophylline and the fractal dimensions was observed, suggesting the usefulness of the fractal dimension as a novel parameter for evaluating drug permeation through porous films.

Cellulose↗
PubMed2001

Image quality of dry-processed film.

Recently, a lot of dry film processors and its radiographic films have been favorably used in hospitals. We have evaluated the diagnostic capability and measured the image quality of these dry processed films, comparing it with those of conventional wet processed films. It is found that (1) dry processed film has almost the same diagnostic capability to that of wet processed film, and (2) dry film had strong absorption at 804 nm which brought a reddish color tone to dry film and gave radiologists problems in diagnosis. These situations have been improved through this study to some extent.

Humans↗