Hydraulic Permeability Measurements Research Articles

Coupled measurements of hydraulic permeability and full stiffness tensor compaction trends in artificial shales

Understanding of compaction trends of elastic and hydraulic properties in anisotropic shales is crucial for exploration of energy resources, ecological disposal of nuclear waste, and hydrogeological applications. However, complexity of the natural shale mineralogy and lack of quality data available for analysis results in poor knowledge of these compaction trends. Careful control over the shale mineralogy, pore fluid composition and applied stresses allows us to simulate the natural environments and acquire quality data on the properties of artificial shales. Here for the first time we present methodology and describe a setup that allows simultaneous acquisition of all five independent elastic constants and extremely low hydraulic permeability values of transversely isotropic artificial shale samples during mechanical compaction experiments (porosity decrease from 40% to 10%). Hydraulic permeabilities of artificially compacted samples are comparable to the ones of natural shales. Permeability drops exponentially with compaction. Silt fraction and clay mineralogy are the two key parameters that are responsible for broad variations of permeability in shales with the same porosity. We provide analytical equations that allow calculating permeability if porosity and silt fraction are known. Elastic constants of clay matrix exhibit positive linear trends with the porosity decrease. Small variations in clay mineralogy have a minor effect on absolute values of elastic coefficients or anisotropy but lead to noticeable increase of the compressional (VP) to shear (VS) velocities ratio at the same porosity. Finally, strong correlations (R2 above 0.95) of the hydraulic permeability with acoustic impedance and VP/VS ratio are observed for all the prepared samples.

Elucidation of filtration performance of hollow-fiber membranes via a high-throughput screening platform

Hollow-fiber (HF) membranes are an ideal format for environmental applications and yet the fouling of HF membranes is a complex and ongoing challenge in the field of water and wastewater treatment. There is growing interest in the use of high-throughput (HT) techniques to accelerate the optimization of membrane-based separations. However, all of the previous works in this area have focused on employing HT techniques for flat sheet membranes. In this study, we have developed the first ever high-throughput hollow fiber (HT-HF) membrane device that can run multiple filtration tests in parallel with each test using a single HF membrane to minimize the hold-up volume. The effects of humic acid (HA) type, HA concentration, aqueous solution conditions, filtrate flux, and backwashing conditions on the constant flux filtration performance of polyvinylidene fluoride HF membranes were studied by comparing sieving coefficient results, transmembrane pressure profiles, and changes in hydraulic permeability. In total, over 60 individual filtration experiments and 190 hydraulic permeability measurements, were performed in this comprehensive study. The technique described in this work allows for an efficient way to screen the performance of HF membranes for various applications.

Unusually Stable Hysteresis in the pH-Response of Poly(Acrylic Acid) Brushes Confined within Nanoporous Block Polymer Thin Films

Stimuli-responsive soft materials are a highly studied field due to their wide-ranging applications; however, only a small group of these materials display hysteretic responses to stimuli. Moreover, previous reports of this behavior have typically shown it to be short-lived. In this work, poly(acrylic acid) (PAA) chains at extremely high grafting densities and confined in nanoscale pores displayed a unique long-lived hysteretic behavior caused by their ability to form a metastable hydrogen bond network. Hydraulic permeability measurements demonstrated that the conformation of the PAA chains exhibited a hysteretic dependence on pH, where different effective pore diameters arose in a pH range of 3 to 8, as determined by the pH of the previous environment. Further studies using Fourier transform infrared (FTIR) spectroscopy demonstrated that the fraction of ionized PAA moieties depended on the thin film history; this was corroborated by metal adsorption capacity, which demonstrated the same pH dependence. This hysteresis was shown to be persistent, enduring for days, in a manner unlike most other systems. The hypothesis that hydrogen bonding among PAA units contributed to the hysteretic behavior was supported by experiments with a urea solution, which disrupted the metastable hydrogen bonded state of PAA toward its ionized state. The ability of PAA to hydrogen bond within these confined pores results in a stable and tunable hysteresis not previously observed in homopolymer materials. An enhanced understanding of the polymer chemistry and physics governing this hysteresis gives insight into the design and manipulation of next-generation sensors and gating materials in nanoscale applications.

Hydraulic Performance Modifications of a Zeolite Membrane after an Alkaline Treatment: Contribution of Polar and Apolar Surface Tension Components

Hydraulic permeability measurements are performed on low cut-off Na-mordenite (MOR-type zeolites) membranes after a mild alkaline treatment. A decrease of the hydraulic permeability is systematically observed. Contact angle measurements are carried out (with three polar liquids) on Na-mordenite films seeded onto alumina plates (flat membranes). A decrease of the contact angles is observed after the alkaline treatment for the three liquids. According to the theory of Lifshitz-van der Waals interactions in condensated state, surface modifications are investigated and a variation of the polar component of the material surface tension is observed. After the alkaline treatment, the electron-donor contribution (mainly due to the two remaining lone electron pairs of the oxygen atoms present in the zeolite extra frameworks) decreases and an increase of the electron-receptor contribution is observed and quantified. The contribution of the polar component to the surface tension is attributed to the presence of surface defaults, which increase the surface hydrophilicity. The estimated modifications of the surface interaction energy between the solvent (water) and the Na-mordenite active layer are in good agreement with the decrease of the hydraulic permeability observed after a mild alkaline treatment.

Stirred well filtration (SWF) – A high-throughput technique for downstream bio-processing

A high-throughput technique for downstream processing studies was developed by integrating 96-well filter plates with a magnetic tumble stirrer that simultaneously mixes the solution above the membrane in each well akin to the conventional stirred-cell filtration module – thus we call this technique ‘stirred-well filtration’ (SWF). The performance of 30kDa Omega™ ultrafiltration membranes was assessed via hydraulic permeability measurements and protein sieving tests conducted in constant flux mode using a multi-rack syringe pump; individual pressure transducers were used to simultaneously monitor the transmembrane pressure (TMP) in eight wells on the filter plate. The stirring action was found to be critically important in controlling the effects of concentration polarization during protein sieving tests – for example, the maximum TMP in the unstirred wells were on average 7.5, 3.8, and 2.6 times higher than those in the stirred wells at fluxes of 12, 36, and 60LMH respectively. To demonstrate the usefulness of the SWF technique, we simultaneously ran the eight tests for a simple 22 factorial design-of-experiments (DOE) test with duplicates to evaluate the effect of solution pH and salt concentration on protein filtration. The results indicate that combining the SWF technique with statistical methods is a powerful approach for high-throughput testing of filtration processes.

Direct Measurement of the Permeability of Human Cervical Tissue

The mechanical integrity of the uterine cervix is critical for a pregnancy to successfully reach full term. It must be strong to retain the fetus throughout gestation and then undergo a remodeling and softening process before labor for delivery of the fetus. It is believed that cervical insufficiency (CI), a condition in pregnancy resulting in preterm birth (PTB), is related to a cervix with compromised mechanical strength which cannot resist deformation caused by external forces generated by the growing fetus. Such PTBs are responsible for infant developmental problems and in severe cases infant mortality. To understand the etiologies of CI, our overall research goal is to investigate the mechanical behavior of the cervix. Permeability is a mechanical property of hydrated collagenous tissues that dictates the time-dependent response of the tissue to mechanical loading. The goal of this study was to design a novel soft tissue permeability testing device and to present direct hydraulic permeability measurements of excised nonpregnant (NP) and pregnant (PG) human cervical tissue from women with different obstetric histories. Results of hydraulic permeability testing indicate repeatability for specimens from single patients, with an order of magnitude separating the NP and PG group means (2.1 ± 1.4×10(-14) and 3.2 ± 4.8×10(-13)m(4)/N[middle dot]s, respectively), and large variability within the NP and PG sample groups. Differences were found between samples with similar obstetric histories, supporting the view that medical history may not be a good predictor of permeability (and therefore mechanical behavior) and highlighting the need for patient-specific measurements of cervical mechanical properties. The permeability measurements from this study will be used in future work to model the constitutive material behavior of cervical tissue and to develop in vivo diagnostic tools to stage the progression of labor.

Flow-Induced Deformation of Poroelastic Tissues and Gels: A New Perspective on Equilibrium Pressure-Flow-Thickness Relations

Hydrostatic pressure-driven flows through soft tissues and gels cause deformations of the solid network to occur, due to drag from the flowing fluid. This phenomenon occurs in many contexts including physiological flows and infusions through soft tissues, in mechanically stimulated engineered tissues, and in direct permeation measurements of hydraulic permeability. Existing theoretical descriptions are satisfactory in particular cases, but none provide a description which is easy to generalize for the design and interpretation of permeation experiments involving a range of different boundary conditions and gel properties. Here a theoretical description of flow-induced permeation is developed using a relatively simple approximate constitutive law for strain-dependent permeability and an assumed constant elastic modulus, using dimensionless parameters which emerge naturally. Analytical solutions are obtained for relationships between fundamental variables, such as flow rate and pressure drop, which were not previously available. Guidelines are provided for assuring that direct measurements of hydraulic permeability are performed accurately, and suggestions emerge for alternative measurement protocols. Insights obtained may be applied to interpretation of flow-induced deformation and related phenomena in many contexts.

Improved characterization of cartilage mechanical properties using a combination of stress relaxation and creep

Mechanical characterization of cartilage, other soft tissues and gels has become a ubiquitous and essential aspect of biomechanics and biomaterials research. Current progress in theoretical modeling and tools for data analysis often exceed what is required for routine mechanical characterization assays in experimental studies, making selection of methodologies difficult for the nonspecialist. We have therefore developed an approach for measurement of confined compression modulus and hydraulic permeability based on simple poroelasticity theory and requiring only linear regression tools for data analysis. This technique involves a new application of an early-time solution for creep combined with stress relaxation measurements to characterize soft tissue mechanical parameters as a function of compressive strain or water content. This combined methodology allows measurement of hydraulic permeability by two different techniques with only a modest increase in experimental duration, providing a more precise assessment of permeability and associated measurement error.

Laser Scanning Confocal Microscopy Coupled with Hydraulic Permeability Measurements for Elucidating Fluid Flow across Porous Materials: Application to Human Dentine

Laser scanning confocal microscopy (LSCM) coupled to a constant volume flow-pressure measuring system is introduced as a new technique for the quantitative measurement of fluid flow across porous materials. Such processes are ubiquitous from the life sciences to materials science and the methodology herein could find widespread application. The methodology has been applied to the detection of fluid flow through human dentine, in-vitro, and in the assessment of occlusion actives. Dentine is a calcareous material sandwiched between the pulp and enamel in the tooth structure that contains tubules which traverse dentine in the pulp to enamel direction. The tubules become patent during enamel erosion or gum recession, leading to dentinal hypersensitivity. Understanding the nature of fluid flow is important, as a pressure gradient exists across dentine in-vivo and this has implications for the development of suitable treatments. The methodology described herein firstly allows a ready assessment of the general efficacy of treatments via hydraulic permeability measurements. Second, LSCM images allow the nature of the flow process and the mode of action of the treatments to be revealed at high spatial resolution. For the particular case of dentine, we demonstrate how the method allows candidate treatments to be compared and assessed.

Anisotropic hydraulic permeability in compressed articular cartilage

The extent to which articular cartilage hydraulic permeability is anisotropic is largely unknown, despite its importance for understanding mechanisms of joint lubrication, load bearing, transport phenomena, and mechanotransduction. We developed and applied new techniques for the direct measurement of hydraulic permeability within statically compressed adult bovine cartilage explant disks, dissected such that disk axes were perpendicular to the articular surface. Applied pressure gradients were kept small to minimize flow-induced matrix compaction, and fluid outflows were measured by observation of a meniscus in a glass capillary under a microscope. Explant disk geometry under radially unconfined axial compression was measured by direct microscopic observation. Pressure, flow, and geometry data were input to a finite element model where hydraulic permeabilities in the disk axial and radial directions were determined. At less than 10% static compression, near free-swelling conditions, hydraulic permeability was nearly isotropic, with values corresponding to those of previous studies. With increasing static compression, hydraulic permeability decreased, but the radially directed permeability decreased more dramatically than the axially directed permeability such that strong anisotropy (a 10-fold difference between axial and radial directions) in the hydraulic permeability tensor was evident for static compression of 20–40%. Results correspond well with predictions of a previous microstructurally-based model for effects of tissue mechanical deformations on glycosaminoglycan architecture and cartilage hydraulic permeability. Findings inform understanding of structure-function relationships in cartilage matrix, and suggest several biomechanical roles for compression-induced anisotropic hydraulic permeability in articular cartilage.

Fouling-resistant ceramic-supported polymer membranes for ultrafiltration of oil-in-water microemulsions

Fouling-resistant ultrafiltration ceramic-supported polymer (CSP) ultrafiltration membrane was developed for the treatment of oil-in-water (o/w) microemulsions. The CSP zirconia-based membrane was prepared via free-radical graft polymerization of vinylpyrrolidone onto the membrane surface. Pore reduction of about 25–28% was encountered upon modification as revealed by hydraulic permeability measurements. Oil rejection was higher for grafted membranes with smaller resultant pore size. Atomic force microscopy imaging of polymer-modified surfaces showed complete surface coverage by the polymer chains. The native zirconia membrane was irreversibly fouled after treating the o/w microemulsion for a brief period, while the CSP membranes maintained its pre-filtration hydraulic permeability even after many filtration runs. The present surface modification was found to be effective in preventing irreversible membrane fouling despite significant membrane surface roughness. Relative to the native membrane, oil rejection of the CSP membrane increased more than two-fold for the range of studied oil droplet size (18–66 nm), while surfactant rejection remained low for both the native and modified membranes.

Basal release of nitric oxide and its interaction with endothelin-1 on single vessel hydraulic permeability.

Both endothelin-1 (ET-1) and nitric oxide (NO) are released by the endothelium and are implicated in modulating the permeability of the endothelial barrier. The present study was designed to examine the interaction between ET-1 and NO and its influence on microvascular permeability as well as the role of NO in maintaining microvascular permeability. To isolate the direct effect of ET-1 and NO, experiments were conducted under conditions where hydraulic and oncotic pressures were controlled. Postcapillary venules in the rat mesentery were perfused in situ and paired measurements of hydraulic permeability (Lp) obtained using the modified Landis micro-occlusion method. The effect of basal endogenous NO was tested by measuring the effects of perfusion with the NO synthase inhibitor Nw-nitro-L-arginine-methyl-ester (L-NAME) (100 micromol/L) on Lp (n = 6). In addition, Lp measured after a 15-minute perfusion with L-NAME (100 micromol/L) was compared with measures of Lp obtained after perfusion with a combined mixture of L-NAME (100 micromol/L) and ET-1 (80 pmol/L) (n = 6). Units for Lp are mean +/- SE x 10(-8) cm x sec(-1) x cm H2O(-1). Under basal conditions, in the absence of exogenous ET-1, NO synthase inhibition led to a significant increase in Lp from 5.7 +/- 0.5 to 9.8 +/- 1.4 (p = 0.02). Compared with L-NAME alone, ET-1 + L-NAME significantly decreased Lp from 10.3 +/- 0.8 to 5.7 +/- 0.6 (p = 0.006). Constitutive release of NO from the microvascular endothelium plays a role in maintaining a basal level of microvascular permeability. Decreases in microvascular permeability seen with the administration of ET-1 are not mediated via the release of NO. These findings suggest important roles for ET-1 and NO in maintaining and modulating microvascular permeability.

Basal release of endothelin-1 and the influence of the ETB receptor on single vessel hydraulic permeability.

Endothelin-1 (ET-1) has a direct permeability decreasing effect on the microvasculature. The present study was designed to test the hypothesis that this effect is mediated via the endothelin B (ETB) receptor located on the microvascular endothelium and to determine whether basal microvascular permeability is dependent on constitutive release of ET-1. To isolate the direct effect of ET-1, experiments were conducted under conditions in which hydraulic and oncotic pressures were controlled. Postcapillary venules in the rat mesentery were perfused in situ, and paired measurements of hydraulic permeability (Lp) were obtained using the modified Landis micro-occlusion method. Lp measured after a 15-minute perfusion with the ETB receptor blocker BQ-788 (1 micromol/L) was compared with measures of Lp obtained after perfusion with a combined mixture of BQ-788 and ET-1 (80 pmol/L) (n = 6). In addition, the effect of basal endogenous ET-1 was tested by measuring the effects of BQ-788 perfusion on Lp (n = 6). Units for Lp are mean +/- SE x 10(-8) cm x s(-1) cm H2O(-1). ETB receptor blockade prevented any decrease in Lp induced by ET-1 (BQ-788 alone = 7.9 +/- 0.7; BQ-788 + ET-1 = 8.2 +/- 0.8;p = 0.5). Under basal conditions and in the absence of exogenous ET-1, ETB receptor blockade led to a significant increase in Lp from 6.8 +/- 0.9 to 9.7 +/- 1.2 (p = 0.001). Decreases in microvascular permeability in single postcapillary venules after the administration of ET-1 are mediated via the ETB receptor. Constitutive release of ET-1 from the microvascular endothelium also plays a role in maintaining basal levels of permeability. These findings suggest important roles for ET-1 in maintaining and modulating microvascular permeability.

Silica-suported polyvinylpyrrolidone filtration membranes

A hybrid ceramic-polymeric membrane was developed by the growth of covalently-bonded polyvinylpyrrolidone (PVP) chains from the surface of a porous silica support membrane via a graft polymerization process. These ceramic-supported polymeric (CSP) membranes can be produced with variable surface density and length of the terminally anchored polymer chains. Hydraulic permeability measurements demonstrated the effect of the grafted chain density and length on the water permeability of the CSP membranes. The potential application of these CSP membranes for the treatment of oil-in-water emulsions, was evaluated in cross-flow filtration experiments. This preliminary evaluation indicated improved performance of a CSP membrane, relative to an unmodified support, since the CSP membrane produced a lower permeate concentration at an equivalent permeability. The improved selectivity and reduced fouling tendency is attributed to the increased hydrophilicity of the membrane surface provided by the grafted PVP chains.

The permeability behavior of polyvinylpyrrolidone-modified porous silica membranes

The surface of 4100 Å-pore-size silica membranes was modified with a covalently bonded polyvinyl-pyrrolidone brush layer by a novel graft polymerization process. Hydraulic permeability measurements performed with six different solvents and both unmodified and modified membranes suggest that the permeability of the modified membrane is determined by the configuration of the terminally anchored polymer chains. In the modified ceramic-supported polymeric (CSP) membrane, the swelling of the polymer brush layer increases as the solvent power increases, resulting in a decrease in the pore radius and subsequently, the permeability.

Measurement of hydraulic permeability in human keratinocytes at subzero temperatures

Measurement of hydraulic permeability in human keratinocytes at subzero temperatures

Effect of concentration on the rejection coefficients of rigid macromolecules in track-etch membranes

To test theoretical predictions that the membrane rejection coefficient ( R) for rigid macromolecules should decrease with increasing bulk concentration, R was measured at volume fractions of 0.001 and 0.033–0.080 for Ficoll (a crosslinked polysaccharide) and bovine serum albumin (a globular protein) in track-etch polycarbonate membranes having uniform capillary pores. The membranes were characterized by scanning electron microscopy and hydraulic permeability measurements, yielding pore radii of 15–36 nm. R decreased with concentration for all membrane—solute combinations, in fair agreement with a hydrodynamic model of hindered transport in pores. For any given solute and pore size, however, R in either dilute or concentrated solutions was significantly larger than anticipated by the theory. This last finding can be interpreted in terms of a greater effect of macromolecule adsorption on rejection properties than on hydraulic permeability.

Influence of oxygen and glucose on the water and ion content of swine aorta.

The swelling properties of isolated swine arterial tissue have been studied to determine their effect on diffusion and hydraulic permeability measurements. Tissue potassium and sodium content were also measured to obtain an index of tissue metabolic activity. When oxygen and glucose were present in the incubation medium, a 5% decrease in tissue water content was observed over an incubation period of approximately 3.5 h. Under these conditions the tissue potassium content was higher and the sodium content was lower than when oxygen and/or glucose were omitted from the medium. When both oxygen and glucose were omitted, the potassium and sodium levels were significantly altered, suggesting a disturbance in the sodium-potassium transport system due to depletion of necessary metabolities.