A distributed two-pore model: theoretical implications and practical application to the glomerular sieving of Ficoll

2014 ◽  
Vol 306 (8) ◽  
pp. F844-F854 ◽  
Author(s):  
Carl M. Öberg ◽  
Bengt Rippe
Keyword(s):  
Pore Radius ◽  
Diffusion Length ◽  
Wide Distribution ◽  
Analytic Solutions ◽  
Length Ratio ◽  
Pore Sizes ◽  
Filtration Barrier ◽  
Large Pore ◽  
Small Pore ◽  
Pore Area

In the present study, an extended two-pore theory is presented where the porous pathways are continuously distributed according to small- and large-pore mean radii and SDs. Experimental glomerular sieving data for Ficoll were analyzed using the model. In addition, several theoretical findings are presented along with analytic solutions to many of the equations used in distributed pore modeling. The results of the data analysis revealed a small-pore population in the glomerular capillary wall with a mean radius of 36.6 Å having a wide arithmetic SD of ∼5 Å and a large-pore radius of 98.6 Å with an even wider SD of ∼44 Å. The small-pore radius obtained in the analysis was close to that of human serum albumin (35.5 Å). By reanalyzing the data and setting the distribution spread of the model constant, we discovered that a narrow distribution is compensated by an increased mean pore radius and a decreased pore area-to-diffusion length ratio. The wide distribution of pore sizes obtained in the present analysis, even when considering electrostatic hindrance due to the negatively charged barrier, is inconsistent with the high selectivity to proteins typically characterizing the glomerular filtration barrier. We therefore hypothesize that a large portion of the variance in the distribution of pore sizes obtained is due to the molecular “flexibility” of Ficoll, implying that the true variance of the pore system is lower than that obtained using flexible probes. This would also, in part, explain the commonly noted discrepancy between the pore area-to-diffusion length ratio and the filtration coefficient.

scholarly journals A distributed solute model: an extended two-pore model with application to the glomerular sieving of Ficoll

2018 ◽  
Vol 314 (6) ◽  
pp. F1108-F1116 ◽  
Author(s):  
Carl M. Öberg ◽  
Joseph J. Groszek ◽  
Shuvo Roy ◽  
William H. Fissell ◽  
Bengt Rippe
Keyword(s):  
Size Distribution ◽  
Pore Radius ◽  
Molecular Size ◽  
Geometric Standard Deviation ◽  
Pore Model ◽  
Filtration Barrier ◽  
Small Pore ◽  
The Difference ◽  
A Charge ◽  
Nanopore Membranes

One of the many unresolved questions regarding the permeability of the glomerular filtration barrier is the reason behind the marked difference in permeability between albumin and polysaccharide probe molecules such as Ficoll and dextran of the same molecular size. Although the differences in permeability have been mainly attributed to charge effects, we have previously shown that this would require a highly charged filtration barrier, having a charge density that is ~10 times more than that on the albumin molecule. In this article, the classic two-pore model was extended by introducing size distributions on the solute molecules, making them conformationally flexible. Experimental sieving data for Ficoll from the rat glomerulus and from precision-made silicon nanopore membranes were analyzed using the model. For the rat glomerulus a small-pore radius of 36.2 Å and a geometric standard deviation (gSD) for the Ficoll size-distribution of 1.16 were obtained. For the nanopore membranes, a gSD of 1.24 and a small-pore radius of 43 Å were found. Interestingly, a variation of only ~16% in the size of the polysaccharide molecule is sufficient to explain the difference in permeability between albumin and Ficoll. Also, in line with previous data, the effects of applying a size distribution on the solute molecule are only evident when the molecular size is close to the pore size. Surely there is at least some variation in the pore radii, and, likely, the gSD obtained in the current study is an overestimation of the “true” variation in the size of the Ficoll molecule.

scholarly journals Monitoring of the Variation in Pore Sizes of Woven Geotextiles with Uniaxial Tensile Strain

2021 ◽  
Vol 12 (1) ◽  
pp. 374
Author(s):  
Wenfang Zhao ◽  
Xiaowu Tang ◽  
Keyi Li ◽  
Jiaxin Liang ◽  
Weikang Lin ◽  
...  
Keyword(s):  
Pore Size ◽  
Tensile Strain ◽  
Pore Diameter ◽  
Filter Design ◽  
Uniaxial Tensile ◽  
Distribution Diagram ◽  
Pore Sizes ◽  
Large Pore ◽  
Small Pore ◽  
Pore Opening

Characteristic pore-opening size O95 or O90 has been widely used in the filter design of woven geotextiles. These manufactured products have different pore size proportions of large pore diameters, medium pore diameters, and small pore diameters, respectively. Therefore, uncertainties still exist regarding the prediction of geotextile pore diameter variations under the uniaxial tensile strain. This paper investigates the variations in five characteristic pore-opening sizes O95, O80, O50, O30, and O10, with uniaxial tensile strain by using the image analysis method. The large pore diameters, medium pore diameters, and small pore diameters show different variation behaviors as the uniaxial tensile strain increases. Fifteen specific pores are selected and then their pore diameter variations are monitored under each tensile strain of 1%. The colorful pore size distribution diagram is a visual way to identify the variation of pores arranged in the tension direction (warp direction) and the direction perpendicular to tensile loads (weft direction). The various pore diameters are proved to agree well with the bell-shaped Gaussian distribution. The results exhibit an accurate prediction of the variation in large pore sizes, medium pore sizes, and small pore sizes, respectively, for all tested woven geotextiles with uniaxial tensile strain.

Transport properties of alveolar epithelium measured by molecular hetastarch absorption in isolated rat lungs

2001 ◽  
Vol 91 (4) ◽  
pp. 1730-1740 ◽  
Author(s):  
Robert L. Conhaim ◽  
Kal E. Watson ◽  
Stephen J. Lai-Fook ◽  
Bruce A. Harms
Keyword(s):  
Molecular Weight ◽  
Transport Properties ◽  
High Molecular Weight ◽  
Pore Radius ◽  
Alveolar Epithelium ◽  
Low Molecular Weight ◽  
Pore System ◽  
Large Pore ◽  
Small Pore ◽  
Isolated Rat

To evaluate the transport properties of the alveolar epithelium, we instilled hetastarch (Het; 6%, 10 ml, 1 − 1 × 104kDa) into the trachea of isolated rat lungs and then measured the molecular distribution of Het that entered the lung perfusate from the air space over 6 h. Het transport was driven by either diffusion or an oncotic gradient. Perfusate Het had a unique, bimodal molecular weight distribution, consisting of a narrow low-molecular-weight peak at 10–15 kDa (range, 5–46 kDa) and a broad high-molecular-weight band (range 46–2,000 kDa; highest at 288 kDa). We modeled the low-molecular-weight transport as (passive) restricted diffusion or osmotic flow through a small-pore system and the high-molecular-weight transport as passive transport through a large-pore system. The equivalent small-pore radius was 5.0 nm, with a distribution of 150 pores per alveolus. The equivalent large-pore radius was 17.0 nm, with a distribution of one pore per seven alveoli. The small-pore fluid conductivity (2 × 10−5ml · h−1 · cm−2 · mmHg−1) was 10-fold larger than that of the large-pore conductivity.

Heteropore populations of bullfrog alveolar epithelium

1983 ◽  
Vol 54 (1) ◽  
pp. 140-146 ◽  
Author(s):  
K. J. Kim ◽  
E. D. Crandall
Keyword(s):  
Water Flow ◽  
Driving Forces ◽  
Alveolar Epithelium ◽  
Bulk Water ◽  
Rate Of Change ◽  
Flux Chamber ◽  
Pore Characteristics ◽  
Large Pore ◽  
Small Pore ◽  
Pore Area

Diffusional fluxes of a large number of hydrophilic solutes and water across bullfrog (Rana catesbeiana) alveolar epithelium were measured in the Ussing-type flux chamber. Lungs were isolated from double-pithed animals and studied as flat sheets. Radioactive solutes and water were added to the upstream reservoir, and the rate of change of downstream reservoir radioactivity was monitored. A permeability coefficient was estimated for each substance from a linear relationship between radiotracer concentration in the downstream reservoir and time. These permeability data were used to analyze the equivalent water-filled pore characteristics of the alveolar epithelial barrier. The data reveal that the alveolar epithelium is best characterized by two distinct pore populations rather than by a single homogeneous pore population. The large-pore population consists of pores with a radius of about 5 nm and occupies 4% of the available pore area. The small-pore population consists of pores with a radius of about 0.5 nm and occupies 96% of the available pore area. The number of small pores to large pores is 2.68 X 10(3). After the alveolar surface was damaged by acid, a large-pore population with a radius of about 27 nm was seen, allowing nearly free diffusion of solutes. A major implication of the presence of two populations of pores in the alveolar epithelium is that hydrostatically driven bulk water flow occurs predominantly through the large pores, while osmotically driven bulk water flow takes place predominantly through the small pores. As a result, in general, hydrostatic and osmotic gradients may not be equally effective driving forces for water flow across this tissue.

Functional characteristics of peritubular capillary membrane in rat kidney

1987 ◽  
Vol 253 (1) ◽  
pp. F180-F187 ◽  
Author(s):  
M. Larson ◽  
K. Nygren ◽  
M. Sjoquist ◽  
M. Wolgast
Keyword(s):  
Pore Radius ◽  
Rat Kidney ◽  
Molecular Probes ◽  
Peritubular Capillary ◽  
Equivalent Radius ◽  
Fluid Reabsorption ◽  
Pore Length ◽  
Capillary Membrane ◽  
Small Pore ◽  
Pore Area

The permeability characteristics of the peritubular capillary membrane in the rat kidney were investigated on the basis of the transport of hippuran, inulin, myoglobin, horseradish peroxidase, albumin, and gamma-globulin from peritubular capillary blood to renal hilar lymph. Data obtained in a previous investigation on single-nephron plasma flow, filtration fraction, net driving force, and fluid reabsorption along the peritubular capillary were also used. The data were analyzed in a computer-based model taking into account the transport both by diffusion and by convection. The results show that the membrane contains a few large pores through which the plasma proteins leak out into the renal interstitium and a system of several smaller pores responsible for the fluid reabsorption. The mean equivalent radius of the large pores was estimated from the larger molecular probes to be approximately 180 A (range 150-225 A), and the corresponding total pore area over pore length was estimated at 3 X 10(-4) cm (range 6 X 10(-4) to 1 X 10(-4) cm). The small-pore system was analyzed from the transport of hippuran, inulin, and myoglobin and from fluid reabsorption and showed a pore radius of somewhat below 20 A and pore areas over pore length of 50 cm. Here, the fluid reabsorption and the transport of hippuran turned out to be a sensitive marker of the pore area and the transport of inulin and myoglobin of the pore radius.

Tailoring the Pore Size of Hypercrosslinked Polymer Foams

1996 ◽  
Vol 431 ◽  
Author(s):  
W. P. Steckle ◽  
M. A. Mitchell ◽  
P. G. Apen
Keyword(s):  
Pore Size ◽  
Polyaromatic Hydrocarbons ◽  
Crosslinking Agent ◽  
Nitrogen Adsorption ◽  
Total Surface Area ◽  
Pore Sizes ◽  
Surface Areas ◽  
Small Pore ◽  
High Resolution Tem ◽  
Cure Time

AbstractOrganic analogues to inorganic zeolites would be a significant step forward in engineered porous materials and would provide advantages in range, selectivity, tailorability and processing. Rigid molecular foams or “organic zeolites” would not be crystalline materials and could be tailored over a broader range of pore sizes and volumes. A novel process for preparing hypercrosslinked polymeric foams has been developed via a Friedel-Crafts polycondensation reaction. A series of rigid hypercrosslinked foams have been prepared using simple rigid polyaromatic hydrocarbons including benzene, biphenyl, m-terphenyl, diphenylmethane, and polystyrene, with p-dichloroxylene (DCX) or divinylbenzene (DVB) as the crosslinking agent. Transparent gels are formed suggesting a very small pore size. After drying the foams are robust and rigid. Densities of the resulting foams can range from 0.15g/cc to 0.75g/cc. Nitrogen adsorption studies have shown that by judiciously selecting monomers and crosslinking agent along with the level of crosslinking and the cure time of the resulting gel, the pore size, pore size distribution, and the total surface area of the foam can be tailored. Surface areas range from 160 to 1,200 m2/g with pore sizes ranging from 6Å to 2,000Å. Further evidence of the uniformity of the foams and their pore sizes has been confirmed by high resolution TEM.

scholarly journals Electrospun Polyvinylidene Fluoride-Based Fibrous Scaffolds with Piezoelectric Characteristics for Bone and Neural Tissue Engineering

Nanomaterials ◽  
2019 ◽  
Vol 9 (7) ◽  
pp. 952 ◽  
Author(s):  
Li ◽  
Liao ◽  
Tjong
Keyword(s):  
Tissue Engineering ◽  
Polyvinylidene Fluoride ◽  
Neural Tissue ◽  
Electrospinning Process ◽  
Neural Cells ◽  
Neural Tissue Engineering ◽  
Engineering Applications ◽  
Pore Sizes ◽  
Β Phase ◽  
Small Pore

Polyvinylidene fluoride (PVDF) and polyvinylidene fluoride-trifluoroethylene (P(VDF-TrFE) with excellent piezoelectricity and good biocompatibility are attractive materials for making functional scaffolds for bone and neural tissue engineering applications. Electrospun PVDF and P(VDF-TrFE) scaffolds can produce electrical charges during mechanical deformation, which can provide necessary stimulation for repairing bone defects and damaged nerve cells. As such, these fibrous mats promote the adhesion, proliferation and differentiation of bone and neural cells on their surfaces. Furthermore, aligned PVDF and P(VDF-TrFE) fibrous mats can enhance neurite growth along the fiber orientation direction. These beneficial effects derive from the formation of electroactive, polar β-phase having piezoelectric properties. Polar β-phase can be induced in the PVDF fibers as a result of the polymer jet stretching and electrical poling during electrospinning. Moreover, the incorporation of TrFE monomer into PVDF can stabilize the β-phase without mechanical stretching or electrical poling. The main drawbacks of electrospinning process for making piezoelectric PVDF-based scaffolds are their small pore sizes and the use of highly toxic organic solvents. The small pore sizes prevent the infiltration of bone and neuronal cells into the scaffolds, leading to the formation of a single cell layer on the scaffold surfaces. Accordingly, modified electrospinning methods such as melt-electrospinning and near-field electrospinning have been explored by the researchers to tackle this issue. This article reviews recent development strategies, achievements and major challenges of electrospun PVDF and P(VDF-TrFE) scaffolds for tissue engineering applications.

Hydrophilic solute transport across rat alveolar epithelium

1989 ◽  
Vol 66 (5) ◽  
pp. 2320-2327 ◽  
Author(s):  
M. M. Berg ◽  
K. J. Kim ◽  
R. L. Lubman ◽  
E. D. Crandall
Keyword(s):  
Water Flow ◽  
Alveolar Epithelium ◽  
Lavage Fluid ◽  
Alveolar Space ◽  
Apparent Permeability ◽  
Diffusive Flow ◽  
Permeability Surface ◽  
Small Pore ◽  
Pore Area ◽  
Flow Through

Diffusional fluxes of a series of hydrophilic nonelectrolytes (molecular radii ranging from 0.15 to 0.57 nm) were measured across the alveolocapillary barrier in the isolated perfused fluid-filled rat lung. Radiolabeled solutes were lavaged into the distal air spaces of isolated Ringer-perfused lungs, and apparent permeability-surface area products were calculated from the rates of isotope appearance in the recirculating perfusate. These data were used to estimate theoretical equivalent pore radii in the alveolar epithelium, with the assumption of diffusive flow through water-filled cylindrical pores. The alveolar epithelium is best characterized by two pore populations, with small pores (radius 0.5 nm) occupying 98.7% of total pore area and larger pores (radius 3.4 nm) occupying 1.3% of total pore area. Net water flow out of the alveolar space was measured by including an impermeant solute (dextran) in the lavage fluid and measuring its concentration in the alveolar space as a function of time. Under control conditions, net water flow averaged 167 nl/s. When 24 microM terbutaline was added to the perfusate, net water flow increased significantly to 350 nl/s (P less than 0.001). Terbutaline had no effect on the fluxes of either glycerol (which traverses the small pore pathway) or sucrose (which traverses the large pore pathway). These findings indicate that the intact mammalian alveolar epithelium is complex and highly resistant to the flow of solutes and water.

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