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PubMed1999

Adsorption of serum albumin to thin films of poly(lactide-co-glycolide).

Protein adsorption has been implicated in the variability of drug release from biodegradable microspheres. We used optical reflectometry to measure the extent and kinetics of bovine serum albumin (BSA) adsorption to smooth spin-cast films prepared from two poly(lactide-co-glycolide) (PLG) samples that have different end-groups, one being a hydrophilic carboxylic end group and the other a hydrophobic ester end group. One of us has previously shown that these end-groups influence microsphere degradation (Tracy et al. , 1998, Factors affecting the degradation rate of poly(lactide-co-glycolide) microspheres in vivo and in vitro. Biomaterials: submitted for publication.). Both films were moderately hydrophobic, and their wettability was independent of the type of end-group. BSA adsorbed readily to both native PLG films, attaining as much as 50% surface coverage by area and was insensitive to the type of end-group. Aging the films in water for 24 h prior to BSA exposure decreased the hydrophobicity of the films and this in turn correlated with a significant decrease in the initial BSA adsorption rate. This was consistent with the often-observed trend that surface hydrophobicity favors protein adsorption. In spite of the lower adsorption affinity revealed by this decreased initial adsorption rate, the final adsorbed amounts on the aged films exceeded those attained on native films, presumably due to the increase in total surface area produced by partial PLG erosion.

Adsorption↗
PubMed2002

Spatial and temporal distribution of solute leaching in heterogeneous soils: analysis and application to multisampler lysimeter data.

Accurate assessment of the fate of salts, nutrients, and pollutants in natural, heterogeneous soils requires a proper quantification of both spatial and temporal solute spreading during solute movement. The number of experiments with multisampler devices that measure solute leaching as a function of space and time is increasing. The breakthrough curve (BTC) can characterize the temporal aspect of solute leaching, and recently the spatial solute distribution curve (SSDC) was introduced to describe the spatial solute distribution. We combined and extended both concepts to develop a tool for the comprehensive analysis of the full spatio-temporal behavior of solute leaching. The sampling locations are ranked in order of descending amount of total leaching (defined as the cumulative leaching from an individual compartment at the end of the experiment), thus collapsing both spatial axes of the sampling plane into one. The leaching process can then be described by a curved surface that is a function of the single spatial coordinate and time. This leaching surface is scaled to integrate to unity, and termed S can efficiently represent data from multisampler solute transport experiments or simulation results from multidimensional solute transport models. The mathematical relationships between the scaled leaching surface S, the BTC, and the SSDC are established. Any desired characteristic of the leaching process can be derived from S. The analysis was applied to a chloride leaching experiment on a lysimeter with 300 drainage compartments of 25 cm2 each. The sandy soil monolith in the lysimeter exhibited fingered flow in the water-repellent top layer. The observed S demonstrated the absence of a sharp separation between fingers and dry areas, owing to diverging flow in the wettable soil below the fingers. Times-to-peak, maximum solute fluxes, and total leaching varied more in high-leaching than in low-leaching compartments. This suggests a stochastic-convective transport process in the high-flow streamtubes, while convection dispersion is predominant in the low-flow areas. S can be viewed as a bivariate probability density function. Its marginal distributions are the BTC of all sampling locations combined, and the SSDC of cumulative solute leaching at the end of the experiment. The observed S cannot be represented by assuming complete independence between its marginal distributions, indicating that S contains information about the leaching process that cannot be derived from the combination of the BTC and the SSDC.

Environmental Monitoring↗
PubMed2002

Using polymer solutions to enhance recovery of mobile coal tar and creosote DNAPLs.

Direct pumping and enhanced recovery of coal tar and creosote dense, non-aqueous phase liquids (DNAPLs) from the subsurface have had mixed results because these DNAPLs are viscous fluids that can potentially alter aquifer wettability. To improve the inefficiencies associated with waterflooding, the research presented here considered the use of a polymer solution that can be added to the injected flood solution to increase the viscosity and decrease the velocity of the flooding solution. Results from one-dimensional, vertically oriented laboratory column experiments that evaluate the recovery of coal-derived DNAPL with both water and polymer flooding solutions are presented. The final DNAPL saturation remaining in the column was assessed in water and oil-wet systems for three viscous DNAPLs. Adding polymer to increase the aqueous solution viscosity did not have a significant impact in water-wet systems. A final DNAPL saturation of approximately 19% was achieved for both water and polymer floods. In contrast, the addition of polymer significantly improved recovery in oil-wet systems. The final saturation was over 40% in oil-wet systems after waterflooding, but approximately 19% with a polymer flushing solution. Although the final saturation produced with polymer flooding was similar between the oil- and water-wet systems, differences in the relative permeability and distribution of DNAPL in the porous matrix caused the DNAPL recovery to be much slower in the oil-wet system.

Coal Tar↗
PubMed2002

Towards a better understanding of tetrachloroethene entry pressure in the matrix of Permo-Triassic sandstones.

The pressure required for a chlorinated solvent to enter a geological medium can be calculated given knowledge of the characteristic pore size of the medium and the interfacial tension (IFT) and contact angle of the solvent-water-rock system. Using a centrifuge-based method, capillary pressure-saturation curves have been determined for 30 water-saturated samples of Permo-Triassic sandstones for the solvent tetrachloroethene (PCE). These curves have been successfully fitted using the van Genuchten function to determine PCE entry pressure for each of the sandstone samples. A plot of PCE entry pressures against average pore diameter shows a linear relationship in log-log space; however, observed values for PCE entry pressure are significantly lower than would be expected theoretically for a sandstone-PCE-water system. This may be explained either by a decrease in the IFT or an increase in the contact angle. The IFT may decrease during contact with sandstones due to hysteresis effects during imbibition and drainage of fluids, but this is unlikely to be sufficient to account for the low entry pressures observed. Therefore, it is inferred that the low observed PCE entry pressures are due to higher than expected PCE contact angles, and that the average pore-throat surface of the sandstones is more solvent wetting than would be expected. A weak acid extraction indicates the presence of calcite and dolomite in the sandstone cores, and a correlation is observed between carbonate content per unit porosity and a reduction in PCE entry pressure. It is suggested that these mineral phases are responsible for observed wettability changes and a conceptual model is proposed. One consequence of the lower observed entry pressures is that solvents are likely to penetrate deeper into the matrix of water-saturated sandstones than previously expected.

Calcium Carbonate↗
PubMed2003

Effects of VOCs on herbaceous plants in an open-top chamber experiment.

A selection of herbaceous plants representing the ground flora around a typical chemical installation in the UK was exposed continuously for 7 weeks to a mixture of six VOCs (acetone, acetonitrile, dichloromethane, ethanol, methyl t-butyl ether and toluene) in open-top chambers. Exposure concentrations were based on predictions of atmospheric dispersion from a single source, at a distance of approximately 2 km. The effects of continuous exposure, representing a worst-case, were measured in terms of uncontrolled water loss from leaves, leaf wettability, chlorophyll content and fluorescence, dry matter production and detailed observations of changes in plant growth and phenology. There were significant effects of VOC exposure on seed production, leaf water content and photosynthetic efficiency in some plant species. Such effects may be detectable in vegetation close to major industrial point sources of VOCs, or as a result of an accidental release of material during manufacture or transport. Some of the species tested e.g. birdsfoot trefoil (Lotus corniculatus L.) seem to be promising as potential bioindicators for VOCs, but there may be other even more sensitive species waiting to be discovered. However, the most obvious and conveniently measured response to VOCexposure in the birdsfoot trefoil (premature senescence i.e. advanced timing of seed pod production) could easily be confused in the field with climatic influences. It is also uncertain at this stage whether any of the effects observed would lead to longer term ecological changes in natural plant communities, through biased competition between sensitive and more tolerant species.

Acetone↗
PubMed2003

Permeation of captan through disposable nitrile glove.

The purpose of this study was to investigate the permeation of an aqueous emulsion of the pesticide, captan, as a wettable powder (48.9% captan) through a disposable nitrile glove material using an American Society for Testing and Materials (ASTM)-type I-PTC-600 permeation cell. The goal was to investigate the protective capability of the gloves against dermatitis. The analytical method was based on gas chromatography-mass spectrometry (GC-MS) and gas chromatography-electron capture detection (GC-ECD). The least quantifiable limit (LQL) was 6 ng for GC-ECD and 30 ng for GC-MS. Testing was conducted using the ASTM F739 closed-loop permeation method and a worst-case aqueous concentration 217 mg/ml of captan 50-WP. The average permeation rates were low, with 12+/-5 ng/(cm(2)min) after 2h, 50+/-25 ng/(cm(2)min) after 4h, and 77+/-58 ng/(cm(2)min) after 8h. The calculated diffusion coefficient was (1.28+/-0.10) x 10(-5)cm(2)/h. No significant swelling or shrinkage occurred at P</=0.05. Infrared (IR) reflectance analysis of pre- and post-exposure glove surfaces confirmed no outer or inner surface degradation. The disposable nitrile glove showed excellent resistance to a highly concentrated aqueous emulsion of captan. Because the ASTM normalized breakthrough detection time of 250 ng/cm(2) was <2h, these gloves should not be reused once worn, and decontamination is not advised. Protection is also advised for agricultural reentry field workers, because captan has been shown to persist on crops with a half-life greater than the current reentry intervals of 1-4 days.

Captan↗
PubMed2000

Hydrophobins, the fungal coat unravelled.

Hydrophobins are among the most surface active molecules and self-assemble at any hydrophilic-hydrophobic interface into an amphipathic film. These small secreted proteins of about 100 amino acids can be used to make hydrophilic surfaces hydrophobic and hydrophobic surfaces hydrophilic. Although differences in the biophysical properties of hydrophobins have not yet been related to differences in primary structure it has been established that the N-terminal part, at least partly, determines wettability of the hydrophilic side of the assemblage, while the eight conserved cysteine residues that form four disulphide bridges prevent self-assembly of the hydrophobin in the absence of a hydrophilic-hydrophobic interface. Three conformations of class I hydrophobins have been identified: the monomeric state, which is soluble in water, the alpha-helical state, which is the result of self-assembly at a hydrophobic solid, and the beta-sheet state, which is formed during self-assembly at the water-air interface. Experimental evidence strongly indicates that the alpha-helical state is an intermediate and that the beta-sheet state is the end form of assembly. The latter state has a typical ultrastructure of a mosaic of 10 nm wide rodlets, which have been shown to resemble the amyloid fibrils.

Air↗
PubMed1985

Substratum topography and cell traction on sulphuric acid treated bacteriological-grade plastic.

Treatment of bacteriological-grade plastic with concentrated sulphuric acid is a well known technique which increases the wettability of the surface and renders it suitable for eukaryotic cell adhesion. We have noticed that these substrata present a distinctive surface topography in the presence of a serum supplement under normal culture conditions. The adsorbed serum layer is comprised of fine furrows and ridges and the influence of adherent cells on this layer leads to minute tears and distortions in the direction of the corrugations. This provides a novel system for the investigation of cell spreading and locomotion by scanning electron microscopy.

Animals↗
PubMed1986

Use of enzymatic solubilization of tissues and direct injection on pre-columns of large volumes for analysing biological samples by high-performance liquid chromatography.

A pre-column technique, which can be used to introduce all types of biological samples into high-performance liquid chromatographic systems, is described. Fluids are injected directly, whereas faeces are homogenized and centrifuged and tissue samples are solubilized by the enzyme subtilisin A. Acetonitrile is added to all samples (no precipitation of proteins is seen), fluids (10%), solubilized tissue (25%) and faeces (20%), to obtain better wettability of the packing and to counteract binding. Samples of up to 50 ml are injected onto a 6 X 4 mm I.D. pre-column from which the compounds are backflushed onto the analytical column. Different packing materials for the pre-column have been used; LiChroprep RP-18 gave the best results. This system has been used for a series of different drugs, using different analytical columns and different detectors. Both gradient and isocratic elution have been used. High recoveries, good reproducibility and low detection limits are seen for routine analysis. For metabolic work, a very large enrichment factor is obtained.

Biotransformation↗
PubMed2001

Agglomeration state and migration of drugs in wet granulations during drying.

Migration of drugs was studied during drying of wet granules, agglomerated at pendular and funicular state (S(3) and S(4)). Granulating liquids of different viscosity (2.5 and 7.5 mPa s) and drugs and diluents of different solubility and wettability were employed and correlation was sought between distribution of the liquid, wet kneading parameters (torque and liquid consumption S%), solid-liquid interactions (work of adhesion and spreading coefficients) and the migration of drugs. It was found that drug migration, expressed as CV% of its content, was strongly dependent on the type of diluent. Also, the type of diluent exerted the strongest effect on torque and liquid consumption during wet kneading and a significant one on moisture content of the final granulations. Viscosity of the granulating liquid and molecular weight of the binder had no effect on liquid consumption but viscosity had a significant one on drug migration. Significant linear relationships were found between spreading coefficients and the liquid consumption (S%) at the mid-state of funicular agglomeration (S(3)+S(4))/2 or the torque at the capillary state S(5). Migration of drug was remarkably lower for drying in the microwave oven and increased from the pendular (S(3)) to the funicular (S(4)) agglomeration state when drying in conventional oven was applied. Linear relationships were found between migration (CV%) and the spreading coefficient of liquid on solid, lambda(LS), for the low and the high viscosity levels of the granulating liquid, with r=0.965, P=0.05 and r=0.901, P=0.10, respectively. Also, a general linear relationship (r=0.903 and P=0.002) accommodating all experimental data was found between migration (CV%) and the ratio lambda(LS)/viscosity. Drug migration increases with solubility and may become a problem in a range higher than 1 g in 148-400 ml of granulating liquid.

Analysis of Variance↗
PubMed2002

Preparation and in vitro evaluation of solid dispersions of halofantrine.

The low aqueous solubility of halofantrine (HF) and its low bioavailability from commercially available tablets (Halfan) suggested the formulation of solid dispersions (SDs) of HF to reduce its particle size and improve its wettability and aqueous solubility. Preformulation studies involved the development of a high performance liquid chromatography (HPLC) method for the analysis of HF. In addition, solubility studies were conducted on HF in aqueous solutions containing different concentrations of various carriers. Formulation studies included the preparation of SDs and physical mixtures (PMs) of HF with different carriers and their physicochemical characterization using differential scanning calorimetry (DSC), Fourier-Transform infra-red (FT-IR) spectroscopy and dissolution studies. A 3-month stability study at elevated temperatures was conducted on representative SDs of HF with selected carriers.

Antimalarials↗
PubMed2002

Dry adsorbed emulsion: 2. Dissolution behaviour of an intricate formulation.

The behaviour of a pharmaceutical form, called dry adsorbed emulsion (DAE), containing a sparingly soluble drug (i.e. theophylline) was studied for dissolution drug release kinetic, in relation with DAE structure characterisation. In vitro dissolution testings were performed under different experimental conditions (medium at pH 1.2 and 7.4, medium with or without surfactant addition, different particle sizes, discrete or densified particles). Discrete DAE particles showed an extended release, in comparison with the native drug powder, depending on both drug solubility in the medium and particle size. The relevance of dissolution data was not improved by surfactant addition (0.1% sodium lauryl sulfate: SLS). After an initial release due to theophylline of the DAE superficial layer, the dissolution followed the Higuchi model. This suggested that DAE behaved as an inert matrix, which controlled drug release by diffusion through the hydrophobic part of the DAE. Densified DAE particles showed a slower dissolution rate than discrete DAE particles, because of their weak wettability and their poor disintegrant properties due to the particulate rearrangement under pressure. Lastly in a technological point of view, DAE could be considered as a potential drug delivery system in capsules or tablets to better control bioavailability of drugs.

Adsorption↗
PubMed2002

Dissolution testing of a poorly soluble compound using the flow-through cell dissolution apparatus.

Dissolution of Pfizer Compound PD198306, a poorly soluble compound, was studied in 25 mM pH 9 sodium phosphate solution with 0.5% SLS using the flow-through cell dissolution apparatus. Unmicronized and micronized drug powders were tested. Several methods of loading the drug powder into the flow-through dissolution cells and their impact on dissolution were investigated. The influence of flow rate of the dissolution medium on the rate and extent of dissolution were studied. PD198306 has poor wettability even in the presence of 0.5% SLS. It was found that loading the drug powder into the dissolution cell in the form of a suspension provided the best dissolution profile in terms of the rate and extent of dissolution. The flow rate of 4 ml/min resulted in good particle size discrimination.

Flow Cytometry↗
PubMed2002

Utilization of supercritical carbon dioxide for complex formation of ibuprofen and methyl-beta-cyclodextrin.

The dissolution rate of a drug into the biological environment can be enhanced by forming complexes with cyclodextrins and their derivatives. In this study, ibuprofen-methyl-beta-cyclodextrin complexes were prepared successfully by passing ibuprofen-laden CO(2) through a methyl-beta-cyclodextrin packed bed. The maximum drug loading obtained in this work was 10.8 wt.%, which was comparable to that of a 1:1 complex (13.6 wt.% of ibuprofen). The complex exhibited instantaneous dissolution profiles in water solution. The enhanced dissolution rate was attributed to the amorphous character and improved wettability of the product.

Anti-Inflammatory Agents, Non-Steroidal↗
PubMed2002

The effect of ethanol on acrylic bone cement.

Prosthesis loosening is a major problem associated with the use of poly(methyl methacrylate) (PMMA) bone cement that may be related to a peri-implant vacuolisation commonly observed at bone-cement interface. Methyl methacrylate (MMA) monomer may be one of the cement components partly responsible for the mentioned vacuolisation due to a cytotoxic effect associated to this compound. Alcoholism has been related to bone necrosis in predisposed individuals. Furthermore, ethanol has been shown to clean material with adherent cement debris during cleaning procedure in laboratory. Consequently, we have decided to study whether ethanol will also be related to an increased liberation of MMA from the polymer matrix. 'In vitro' release studies using PMMA plates were conducted to access the role of ethanol on the liberation of the monomer. Contact angle measurements and surface tension estimation were also carried out in order to find a possible effect of ethanol on surface cement properties. Results suggest that ethanol, even in small quantities, enhances the leaching of the monomer from the polymer matrix, but does not considerably change the wettability properties of the cement surface.

Acrylic Resins↗
PubMed2003

Surface characterisation of bags for total parenteral nutrition by tensiometry and atomic force microscopy.

Bags made of poly-ethylene and poly-vinylchloride and of the copolymer ethylene-vinylacetate were used as containers of perfusion solutions for total parenteral nutrition. The bags were characterised by tensiometry (free energy and its polar and dispersed components) and atomic force microscopy (AFM) before and after various periods of storage of solutions for total parenteral nutrition containing L-aminoacids, electrolytes or glucose. In most of the cases, after storage of these solutions, tensiometric characterisation and atomic force microscopy analysis of the internal surface of bags showed deep modifications which highlight the adsorption of the solutes. The changes of surface characteristics were found to depend on the time of contact, the wettability of the polymer and the compounds present into the solutions, while their concentration has a negligible effect. Generally, the aminoacid solutions produced a higher increase in the polar component even after short storage times. Poly-ethylene and the copolymer ethylene-vinylacetate showed a greater inertia if compared with the poly-vinylchloride bags.

Equipment and Supplies, Hospital↗
PubMed1998

Polymorphism and desolvation of flupirtine maleate.

Crystallizates of the analgesic agent flupirtine maleate (Katadolon; ASTA Medica, Dresden, Germany) obtained from isopropanol are examined by X-ray diffractometry, polarization microscopy and thermoanalysis. Depending on the crystallizing conditions, the modifications A and B as well as an isopropanol solvate are observed. The inversion temperature A-->B of the enantiotropic modifications is 164 degrees C (differential scanning calorimetry (DSC) onset). During thermal desolvation, modification B is formed well below the inversion temperature. In concentrated isopropanol suspensions, the solvate and modification B are rapidly transformed into modification A. It is shown how phase-pure products consisting of modification A, which is better wettable with water and stable at room temperature, can be obtained.

Aminopyridines↗
PubMed2003

Flame treatment for the selective wetting and separation of PVC and PET.

Flame treatment has been used for many years to modify the surface of plastics to allow coatings to be added. The effect of the treatment is to produce hydrophilic species on the surface of the plastic making it water-wettable. The production of hydrophilic plastic surfaces is also required in the selective separation of plastics by froth flotation. For the process to be selective one plastic must be rendered hydrophilic while another remains hydrophobic. In this study the potential for separation of PVC and PET has been investigated. Flame treatment was shown to be very effective in producing a hydrophilic surface on both plastics, although the process was not selective under the conditions investigated. Raising the temperature of the plastics above their softening point produced a hydrophobic recovery. As the softening point of PVC was significantly lower than for PET it was possible to produce a significant difference in hydrophobicity, as judged using contact angle measurement. When immersed in water the contact angle of the PVC was found to be strongly dependent on the pH. Good separation efficiency of the two plastics was achieved by froth flotation from pH 4 to 9. One particular advantage of the technique is that no chemical reagents may be required in the flotation stage. The practicalities of designing a flake treatment system however have to be addressed before considering it to be a viable industrial process.

Conservation of Natural Resources↗