Permeability Character Research Articles

Electrophoretic Characterization of Insulin Growth Factor (IGF-1) Functionalized Magnetic Nanoparticles

The synthesis of composite nanoparticles consisting of a magnetite core coated with a layer of the hormone insulin growth factor 1 (IGF-1) is described. The adsorption of the hormone in the different formulations is first studied by electrophoretic mobility measurements as a function of pH, ionic strength, and time. Because of the permeable character expected for both citrate and IGF-1 coatings surrounding the magnetite cores, an appropriate analysis of their electrophoretic mobility must be addressed. Recent developments of electrokinetic theories for particles covered by soft surface layers have rendered possible the evaluation of the softness degree from raw electrophoretic mobility data. In the present contribution, the data are quantitatively analyzed based on the theoretical model of the electrokinetics of soft particles. As a result, information is obtained on both the thickness and the charge density of the surrounding layer. It is shown that IGF-1 adsorbs onto the surface of citrate-coated magnetite nanoparticles, and adsorption is confirmed by dot-blot analysis. In addition, it is also demonstrated that the external layer of IGF-1 exerts a shielding effect on the surface charge of citrate-magnetite particles, as suggested by the mobility reduction upon contacting the particles with the hormone. Aging effects are demonstrated, providing an electrokinetic fingerprint of changes in adsorbed protein configuration with time.

Pig ear skin as an in-vitro model for human skin permeability.

Pig skin has been shown to have similar histological and physiological properties to human skin and has been suggested as a good model for human skin permeability. In this series of experiments, the in-vitro permeability of pig ear skin was compared with human (abdominal) skin and rat (dorsal) skin using both hydrophilic (water, mannitol, paraquat) and lipophilic (aldrin, carbaryl, fluazifop-butyl) penetrants. Pig skin was found to have a closer permeability character than rat skin to human skin, particularly for lipophilic penetrants. Electrical conductivity measurements across pig skin membranes showed that skin conductivity could be a useful method for assessing the integrity of membranes, particularly when used in conjunction with water permeability assessments.

Permeability of crust is key to crispness retention

Bread loses crispness rapidly after baking because water originating from the wet crumb accumulates in the dry crust. This water accumulation might be increased by the dense and low permeable character of the bread crust. Our objective was to investigate the influence of permeability of the crust on water uptake in the crust and on crispness retention. To achieve this objective, we increased the permeability of the control bread crust by creating small channels through the crust. The water vapour permeability of the crust with and without channels was measured using a newly developed method for brittle materials. Two further properties were measured over time: crispness of bread by analysing acoustic properties and water content of the crust. Control bread crust had low water vapour permeability and functioned as a barrier, leading to increased uptake of water in the crust. Water uptake was halved, however, if the water vapour permeability of the crust was doubled. As a consequence, crispness retention increased eight-fold; breads stored for four hours were as crispy as control breads stored for 30 min. We can conclude, therefore, that permeability of crust is key to crispness retention.

Electrophoretic characterization of gold nanoparticles functionalized with human serum albumin (HSA) and creatine

The synthesis of composite nanoparticles consisting of a gold core coated with a human serum albumin (HSA)/creatine layer is described, and their possible application as novel drug carriers for brain delivery is discussed. In this paper, the effect of the concentration of creatine and HSA in the different formulations is studied by electrophoretic mobility measurements as a function of pH and ionic strength. Due to the permeable character of the coatings surrounding the gold cores, an appropriate analysis of their electrophoretic mobility must be addressed. Recent developments of electrokinetic theories for particles covered by soft surface layers have rendered possible the evaluation of the softness degree from raw electrophoretic mobility data. In the present contribution, the data are quantitatively analyzed on the basis of three theoretical models of the electrokinetics of soft particles. As a result, information is obtained on both the surface potential and the charge density of the surrounding layer. The three models used reproduce properly the experimental behavior, although Duval and Ohshima's calculations appear to yield a more accurate fit of the data. It is shown that the albumin/nanogold particles absorb large amounts of creatine. In addition, the low surface charge and the albumin layer are expected to make it possible to deliver the particles through the blood–brain barrier.

Probing Surface Structures of Shewanella spp. by Microelectrophoresis

Long-range electrostatic forces substantially influence bacterial interactions and bacterial adhesion during the preliminary steps of biofilm formation. The strength of these forces depends strongly on the structure of the bacterium surfaces investigated. The latter may be addressed from appropriate analysis of electrophoretic mobility measurements. Due to the permeable character of the bacterium wall and/or surrounding polymer layer, bacteria may be regarded as paradigms of soft bioparticles. The electrophoretic motion of such particles in a direct-current electric field differs considerably from that of their rigid counterparts in the sense that electroosmotic flow takes place around and within the soft surface layer. Recent developments of electrokinetic theories for soft particles now render possible the evaluation of the softness degree (or equivalently the hydrodynamic permeability) from the raw electrokinetic data. In this article, the electrophoretic mobilities of three Shewanella strains (MR-4, CN32, and BrY) presenting various and well-characterized phenotypes of polymer fringe are reported over a wide range of pH and ionic strength conditions. The data are quantitatively analyzed on the basis of a rigorous numerical evaluation of the governing electrostatic and hydrodynamic equations for soft particles. It is clearly shown how the peculiar surface structures of the bacteria investigated are reflected in their electrohydrodynamic properties.

Investigation of artificial biomembrane systems in biopartitioning micellar chromatography by method of mathematical design

An attempt to create and study an artificial membrane system was realized via biopartitioning micellar liquid chromatography. Towards this end the known formula of membrane permeability (on the basis of Fick's diffusion equation) was modified so that membrane permeability may be estimated in terms of chromatographic characteristics. The two-factoral experiments on the basis of mathematical design of second order were carried out. The regression equations are derived which describe the dependence of membrane permeability on the concentration of polyoxyethylene (23) lauryl ether in the mobile phase and its flow-rate for compounds with biomedical significance. Some regularities were revealed, which characterize the permeability of compounds of the different nature through membranes. The extremal dependence (with passing through minimum) of permeability on the concentration of non-ionic surfactant was observed for anionic compounds. The increasing character of permeability in relation with flow-rate of mobile phase was recognized for cationic samples. Both dependences were basically fulfilled for zwitterionic compounds.

Comparison of the effect of fatty alcohols on the permeation of melatonin between porcine and human skin

Melatonin (MT) is a hormone secreted by the pineal gland that plays an important role in the regulation of the circadian sleep–wake cycle. It would be advantageous to administer MT using a transdermal delivery system for the treatment of sleep disorders such as delayed sleep syndrome, jet lag in travelers, cosmonauts and shift workers. The porcine skin has been found to have similar morphological and functional characteristics as human skin. The elastic fibres in the dermis, enzyme pattern of the epidermis, epidermal tissue turnover time, keratinous proteins and thickness of epidermis of porcine skin are similar to human skin. However, the fat deposition and vascularisation of the cutaneous glands of porcine skin are different from human skin. In addition, porcine skin has been found to have a close permeability character to human skin. However, the comparative effect of chemical penetration enhancers on the permeation of drugs between porcine and human skin has not been reported. The purpose of this study was to compare the effect of fatty alcohols on the permeability of porcine and human skin using MT as a model compound. The effect of saturated fatty alcohols (octanol, nonanol, decanol, undecanol, lauryl alcohol, tridecanol, myristyl alcohol) and unsaturated fatty alcohols (oleyl alcohol, linoleyl alcohol, linolenyl alcohol) at 5% concentration was tested across dermatomed porcine and human skin. Our studies showed a parabolic relationship between the carbon chain length of saturated fatty alcohols and permeation enhancement of MT with both porcine and human skin. Maximum permeation of MT was observed when fatty alcohol carbon chain length was 10. In general, as the level of unsaturation increased from one to two double bonds, there was an increase in the permeation of MT both in porcine and human skin. However, a decrease in the permeation was observed with three double bonds. Regression analysis using the steady state flux data showed a significant positive correlation between porcine and human skin for saturated fatty alcohols ( r 2=0.8868, P=0.0005). However, though a positive correlation was observed between the porcine and human skin ( r 2=0.8638), the correlation was statistically insignificant ( P=0.0706). The static diffusion cell system employed in this study has major artifact compared to a flow through system. In conclusion, the permeability of porcine skin to MT in the presence of saturated and unsaturated fatty alcohols was qualitatively similar to human skin but quantitatively different with some fatty alcohols.

Static and dynamic modeling of magnetoelastic dynamometers

Magnetoelastic transducers belong to the inductive transducers, in which the relative permeability of ferromagnetic materials changes on effect of mechanical loads. The change (of always anistropic character) of relative permeability results in a change of the impedance of the coil located in the transducer, or in a change of the transfer impedance in the case of several coils, too. The paper gives a newly developed description of the dynamic magnetoelastic interactions in dynamometers of magnetoelastic principle. The detailed description of calculation method of the electromagnetic field and impedance allows the design of the magnetoelastic dynamometers of anisotropic principle. The dynamic magnetomechanic interaction between the electric and mechanic variables means an additional information between the magnetostriction caused by ac current excitation and dynamic mechanic stress state inside of the ferromagnetic materials. According to the linearised mathematical model is ordered an equivalent electric circuit of the magnetomechanic interaction under the influence of the static mechanical load to be measured.

Dialysis membranes in convective treatments.

substitution fluid. No dialysis fluid is present. Thistechnique offers the advantage of excellent clearancesHaemodialysis is basically divided into two categories: for large molecules. The treatment, however, has onlylow-flux dialysis and high-flux dialysis. Low-flux dia- been applied in Europe because of the need for largelysis includes the standard haemodialysis technique in quantities of substitution fluid in commercially pre-which dialysers with low hydraulic permeability are pared bags. (ii) Haemodiafiltration is a form of therapyutilized. Blood and dialysate flow rates are at 250 and in which diffusion and convection are conveniently500 ml/min, respectively and the average duration is combined. Dialysate is circulated countercurrent to4 h. When the dialyser surface area is increased, and blood but the amount of ultrafiltration exceeds theflow rates of blood and dialysate are increased up to programmed patient weight loss and therefore the final400 and 800 ml/min, respectively, the treatment is fluid balance is achieved by the infusion in the venousdefined as high efficiency haemodialysis [1]. In this line of appropriate amounts of substitution fluid [4–6].treatment the clearance of small molecules is remark- Due to the high costs related to replacement solutions,ably increased and the treatment time generally can be new approaches have been proposed in Europe forshortened, but the clearance for middle to large molec- performing haemofiltration and haemodiafiltration [7].ules is still very low due to the permeability character- Part of the fresh dialysate is diverted from its line toistics of the membrane. the dialyser, it is filtered and it finally is used as aClassic cellulosic membranes such as cuprophan are replacement solution. These on-line treatments havetypically low-flux membranes i.e. permeability to water the advantage of reduced costs, unlimited productionis in the range of 5–6 ml/h/mmHg/m2, they are strongly of substitution fluid and no need for tons of commer-hydrophilic and remarkably thin to permit an optimal cially produced fluid in bags. On the other hand, theutilization in diffusive treatments such as microbiological and chemical purity of the on-linehaemodialysis. prepared fluid may represent a concern since no on-lineOn the other hand, classic high-flux synthetic mem- controls can be made. (iii) High-flux dialysis is abranes originally were fully hydrophobic, strongly technique in which highly permeable dialysers areasymmetric and with a thick wall. They were employed utilized in conjunction with an accurate ultrafiltrationprincipally in convective therapies such as haemofiltra- control of the dialysis machine. Because of the naturetion due to their high hydraulic permeability, i.e. of the hollow fibre dialyser, the correct water balance30–40 ml/h/mmHg/m2, and their high sieving coeffi- is achieved thanks to an internal filtration in thecients [2]. proximal part and a backfiltration in the distal part ofOnly recently has it been possible to design synthetic the filter [8]. As a consequence, some of the advantagesmembranes with reduced wall thickness and a mixed of removing larger molecules are maintained becausehydrophobic–hydrophilic structure. This has permitted of the internal convection, while the need for replace-their use in new techniques such as high-flux haemodia- ment solution is avoided by a significant amount oflysis and haemodiafiltration in which diffusion and backfiltration of fresh dialysate. In this way, someconvection are conveniently combined [3]. of the advantages of haemodiafiltration are maintainedWhen high-flux membranes are utilized, three differ- with a simpler and easier layout of the technique [8].ent approaches can be chosen: (i) haemofiltration is a Again, the dialysate purity is a key issue in thisfully convective treatment in which large amounts of treatment where bacterial products could be back-ultrafiltrate are produced and replaced by a sterile transported into the blood together with the reverseflux of water. This may affect the entire concept ofbiocompatibility of the system. Concerning this aspect,

Effect of AC driving current on magneto-impedance effect

Magneto-impedance (MI) ratio (Δ Z/ Z)= Z( H)− Z( H max)/ Z( H max) has been measured in different materials: amorphous (Fe 0.94Co 0.06) 72.5B 15Si 12.5 wires and Co 68.5Mn 6.5Si 10B 15 microwires and nanocrystalline Fe 73.5Si 13.5B 9Nb 3Cu 1 ribbons, with axial magnetic field H, intensity I, and frequency f, of the AC driving current as the parameters. The common feature of these samples is that they show a peculiar MI effect with a maximum of (Δ Z/ Z) at a certain axial magnetic field value, H m. Dependencies of (Δ Z/ Z) and H m on the AC driving current amplitude I have been observed: H m decreases with I. The MI ratio can be optimised by means of choosing an adequate value of I. Particularly, in the case of microwires, (Δ Z/ Z) has a maximum at I=2.8 mA. The observed effect is explained taking into account the tensor character of magnetic permeability and the circular magnetisation processes.

Cloning and Functional Expression of a New Aquaporin (AQP9) Abundantly Expressed in the Peripheral Leukocytes Permeable to Water and Urea, but Not to Glycerol

A new member (AQP9) of the aquaporin family was identified from human leukocytes by homology cloning using PCR. A full length clone was obtained by screening human liver cDNA library. AQP9 encodes a 295-amino-acid protein with the amino acid sequence identity with AQP3 (48%), AQP7 (45%), and other aquaporins (∼30%), suggesting that AQP3, AQP7, and AQP9 belong to a subfamily of the aquaporin family. Injection of AQP9-cRNA intoXenopusoocytes stimulated the osmotic water permeability 7- folds with a low activation energy (4.2 kcal/mol) which was inhibited by 0.3 mM mercury chloride by 48 %. AQP9 also facilitated urea transport 4-folds. However, in contrast to AQP3 and AQP7, AQP9 did not stimulate the glycerol permeability, suggesting a unique permeability character. Northern blot analysis revealed the high expression of 3.5-kb messages in peripheral leukocytes ⪢ liver > lung = spleen, but not in thymus. The possible role of AQP9 in the immunological function of leukocytes is intriguing and the identification of AQP9 with unique permeability profile may expand our understanding of water and small solute transport in the body.

Women's Movements and Political Parties

Comparing the orientation of the American and Canadian women's movements toward political parties and electoral politics between 1970 and 1993, the article concludes that the predisposition away from established parties posited by new social movement theorists is present in both movements, but is in tension with the substantive and symbolic benefits that engagement with partisan and electoral politics promises. Within the broad context of these contradictory impulses, opportunity structures have shaped specific movement strategies. The permeable character of American parties, coupled with a two-party system, have facilitated the American movement's engagement with political parties, particularly the Democrats. In contrast to this, the cohesive, impermeable character of Canadian parties and a three-party system have prevented the Canadian movement from developing an exclusive relationship with any one party, and have contributed to the movement's growing apartisan orientation since the mid-1980s.

Increase in fluidity of human placental syncytiotrophoblastic brush-border membrane with advancement of gestational age: A fluorescence polarization study

The syncytiotrophoblastic brush-border membrane (BBM) of human placenta plays a vital role in the exchange of metabolites between mother and developing fetus. The fluidity of this membrane renders its selective permeable character. To meet the changing needs of the growing fetus with the progress of gestational age changes in the composition and properties of BBM occur. In the present study, decrease in cholesterol/phospholipid ratio of BBM indicated an increase in fluidity with advancement of gestational age. Measurement of the steady state fluorescence anisotropy of labeled liposomes prepared from lipid extract of BBM as well as that of labeled BBM vesicles prepared from native BBM shows decrease in restriction of the bound dye molecule with increased gestational age. Decrease in transition temperature of BBM and enhanced glucose transport through it have been observed with advancement of pregnancy.

Stochastic Characterization of Gridblock Permeabilities

Summary Permeability is generally measured at the core scale and only at a few sites. By using geostatistical techniques, one can generate alternative high-resolution images of the reservoir at the measurement scale. These images will honor both the data values at the data sites and some prior structural information as modeled, for example, by a covariance function. However, these images must be averaged to the scale of the flow-simulation gridblocks. Two questions arise: (1) how should averaging be carried out? and (2) could the gridblock values be generated directly from the core or log without the intermediary step of small-scale imaging? This paper proposes avenues to answer both questions. First, we propose an averaging technique from point to block permeabilities, accounting for the tensorial character of permeability. Second, we propose a method to infer the covariances and cross-covariances among the different components of the block permeability tensor, and the cross-covariances between these block values and the point measurements. This set of covariances and cross-covariances is then used to generate directly multiple, equally likely spatial realizations of gridblock permeability tensors conditioned to the point measurements. The method is not constrained by small variability of the underlying point permeability distribution, nor does it require a multi-Gaussian-related hypothesis.

Anisotropic Permeability of Fiber Preforms: Constant Flow Rate Measurement

Fiber preform permeability has a strong influence on the resin impregna tion behavior during polymer composites fabrication. A straightforward procedure has been developed for determining the general anisotropic in-plane permeability character of fiber preforms from constant flow rate mold filling experiments. The procedure is based on the application of Darcy's law to a two-dimensional in-plane flow situation. From ex perimental data on changes in flow front position and inlet pressure with mold filling time, the components of the in-plane permeability tensor can be calculated directly using param eters obtained from two linear plots. Experimental data for a commercial fabric confirms the applicability of the procedure. The required equipment setup and the analytical proce dure are both uncomplicated in nature. The proposed method provides a simple solution to the measurement of permeability and comparison of different preforms for polymer composites application.

Deciphering hydrological systems by means of geochemical processes

ABSTRACT The distribution of permeability and chemical character of groundwater in carbonate aquifers is significantly influenced by the many diagenetic processes and reactions that occur in the early development of these rocks. Many of these diagenetic processes occur in the transition zone formed as the carbonate sediments emerge from the marine environment and become fresh-water aquifers. Analyses of trace elements and isotopes indicate that calcite cements and dolomites are formed in this groundwater mixing zone. Reverse reactions such as mineral dissolution and dedolomitization occur in carbonate aquifer systems. The geochemical reactivity of the fresh-water/salt-water mixing zone results from the nonlinearity of geochemical parameters as a function of ionic strength and causes extensive dissolution in coastal carbonate rocks. Interpretation of geochemical reactions and isotopic composition of groundwater provides a method to determine hydrological parameters such as porosity, hydraulic conductivity,...

Effect of anoxia and ATP depletion on the membrane potential and permeability of dog liver.

1. The mechanisms responsible for the depolarization of the hepatocytes secondary to anoxia have been studied in isolated perfused dog liver. It was attempted to elucidate the role of the inhibition of the sodium pump following exhaustion of the energy reserves and of the modifications of membrane permeability. Anoxia was compared to ouabain and to a reduction of the cellular ATP level. 2. Membrane potentials were measured with micro-electrodes. Potassium, sodium and chloride were determined in plasma samples and liver tissues. Extracellular space was measured with tritiated inulin or with an electrical impedance method. Adenine nucleotides were also measured in liver biopsies. 3. The fall in membrane potential produced by administration of ouabain (0-1 mM) is greater than the effect of the redistribution of sodium + potassium ions; this suggests that the sodium pump is functioning, at least partially, electrogenically. The administration of dinitrophenol (10 mM), which causes a 74% fall in the ATP level in 15 min, produces, as does ouabain, a depolarization which also corresponds to stopping an electrogenic pump. 4. A partial reduction in the level of ATP brought about by hypoxia, by an inhibitor of cellular respiration, antimycin (10 mM), or by fructose (20 mM) results in a hyperpolarization which may be attributed to an elevation of potassium permeability (PK) since it is concomitant to a loss of K from the liver. The change in membrane permeability could be related to a rise in the free calcium in the cells which has not been documented. Other possible hypothesis include a facilitated transport for potassium. 5. The administration of amobarbitone (10 mM) produces immediately a depolarization which is independent of the progressive reduction in the level of ATP. The depolarization has been attributed to a direct effect of amobarbitone on the membrane reducing the permeability for potassium ions. 6. The depolarization observed in ischaemic anoxia is greater than that produced by ouabain for the same variation in ions concentration. In addition to a likely inhibition of the electrogenic sodium pump, changes in membrane permeability inducing a rise in the PNa/PK ratio must also occur. 7. After ischaemic anoxia for 24 hr at 3 degrees C, the ratio of PNa/PK rises to 0-68 which indicates abolishment of the selective character of membrane permeability. The augmentation in cell volume produced by anoxia might result in an opening of membrane pores, which could entail the augmentation of sodium permeability; the latter would be responsible in part for the depolarization produced by anoxia. 8. According to the severity and length of oxygen deprivation an increase in PK, a cessation of the sodium pump activity and finally an increase in PNa will occur.

Optimal Permeability Character for Quasi-Static Countercurrent Dialysis

An important parameter in the design of countercurrent dialyzers is the permeability of the membrane which separates the blood and dialyzate. In this paper, methods of optimization theory are applied to specify membrane permeability along the length of a countercurrent dialyzer operating under quasi-static conditions. Two optimization problems are considered. In the first the performance functional is a quadratic measure of membrane complexity; in the second it includes also a quadratic measure of the deviation of the blood output concentration from a desired (low) level. For both situations it is shown that the optimal membrane is one of constant permeability along its length, a result which is intuitively appealing and has an obvious economic consequence. Formulas for computing the optimal permeabilities are given, and some problems for future research in this area are outlined. A generalization of the principal result is also included, and some deficiencies in the present analysis are discussed.

THE RELATIVE PERMEABILITY OF THE SURFACE AND INTERIOR PORTIONS OF THE CYTOPLASM OF ANIMAL AND PLANT CELLS

The permeability and osmotic properties of cells are explained on the assumption of the presence of surface and vacuolar plasmatic membranes which are of a semi-permeable or partially permeable character. It is generally held that the remainder of the protoplasm of a given cell plays a negligible r61e in both diosmosis and permeability. These assumptions are based on indirect evidence. The permeability of the internal cytoplasm of living animal and plant cells has not been investigated by direct methods.