Microporous Polycarbonate Filter Research Articles

Template‐Synthesized Nanotubes for Chemical Separations and Analysis.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Template-synthesized nanotubes for chemical separations and analysis.

We have developed a new class of synthetic membranes that consist of a porous polymeric support that contains an ensemble of gold nanotubes that span the thickness of the support membrane. The support is a commercially-available microporous polycarbonate filter with cylindrical nanoscopic pores. The gold nanotubes are prepared by electroless deposition of Au onto the pore walls, that is, the pores acts as templates for the nanotubes. We have shown that by controlling the Au deposition time, Au nanotubes that have effective inside diameters of molecular dimensions (<1 nm) can be prepared. These nanotube membranes can be used to cleanly separate small molecules on the basis of molecular size. Furthermore, use of these membranes as a novel electrochemical sensor is also discussed. This new sensing scheme involves applying a constant potential across the Au nanotube membrane and measuring the drop in the transmembrane current upon the addition of the analyte. This paper reviews our recent progress on size-based based transport selectivity and sensor applications in this new class of membranes.

Molecular sieving and sensing with gold nanotube membranes.

We have developed a new class of synthetic membranes that consist of a porous polymeric support that contains an ensemble of gold nanotubes that span the thickness of the support membrane. The support is a commercially available microporous polycarbonate filter with cylindrical nanoscopic pores. The gold nanotubes are prepared via electroless deposition of Au onto the pore walls; i.e., the pores act as templates for the nanotubes. We have shown that by controlling the Au deposition time, Au nanotubes that have effective inside diameters of molecular dimensions (<1 nm) can be prepared. These nanotube membranes can be used to cleanly separate small molecules on the basis of molecular size. Furthermore, use of these membranes as a novel electrochemical sensor is also discussed. This new sensing scheme involves applying a constant potential across the Au nanotube membrane and measuring the drop in the transmembrane current upon the addition of the analyte. This paper reviews our recent progress on size-based transport selectivity and sensor applications in this new class of membranes.

Template synthesized gold nanotube membranes for chemical separations and sensing.

We have developed a new class of synthetic membranes that consist of a porous polymeric support that contains an ensemble of gold nanotubes that span the thickness of the support membrane. The support is a commercially-available microporous polycarbonate filter with cylindrical nanoscopic pores. The gold nanotubes are prepared via electroless deposition of Au onto the pore walls; i.e., the pores acts as templates for the nanotubes. We have shown that by controlling the Au deposition time, Au nanotubes that have effective inside diameters of molecular dimensions (< 1 nm) can be prepared. These membranes are a new class of molecular sieves and can be used to separate both small molecules and proteins on the basis of molecular size. In addition, the use of these membranes in new approaches to electrochemical sensing is reviewed here. In this case, a current is forced through the nanotubes, and analyte molecules present in a contacting solution phase modulate the value of this transmembrane current.

Controlling Ion-Transport Selectivity in Gold Nanotubule Membranes

We have developed a new class of synthetic membranes that consist of a porous polymeric support. This support contains an ensemble of gold nanotubules that span the complete thickness of the support membrane. The support is a commercially available microporous polycarbonate filter with cylindrical nanoscopic pores. The gold nanotubules are prepared via electroless deposition of Au onto the pore walls, and tubules that have inside diameters of molecular dimensions (<1 nm) can be prepared. Hence, these membranes are a new class of molecular sieves. We review in this paper the ion-transport properties of these Au nanotubule membranes. We will show that these membranes can be cation-permselective or anion-permselective, and that the permselectivity can be reversibly switched between these two states. Ion permselectivity can be introduced by two different routes. The first entails chemisorption of an ionizable thiol, e.g., a carboxylated or ammonium-containing thiol to the Au tubule walls. If the thiol contains both of these functionalities (e.g., the amino acid cysteine), the permselectivity can be reversibly switched by varying the pH of the contacting solution phase. Ion permselectivity can also be introduced by potentiostatically charging the membrane in an electrolyte solution. By applying excess negative charge, cation permselective membranes are obtained, and excess positive charge yields anion permselective membranes. In this case the permselectivity can be reversibly switched by changing the potential applied to the membrane.

Controlling the Transport Properties of Gold Nanotubule Membranes Using Chemisorbed Thiols

We have developed a new class of synthetic membranes that consist of a porous polymeric support that contains an ensemble of gold nanotubules that span the complete thickness of the support membrane. The support is a commercially available microporous polycarbonate filter with cylindrical nanoscopic pores. The gold nanotubules are prepared via electroless deposition of Au onto the pore walls; that is, the pores act as templates for the nanotubules. We have shown that by controlling the Au deposition time, Au nanotubules that have effective inside diameters of molecular dimensions (<1 nm) can be prepared. Hence, these membranes are a new class of molecular sieves. In addition, because the tubules are composed of gold, well-known Au-thiol chemistry can be used to change the chemical environment within the tubules. This paper reviews recent research on using chemisorbed thiols to control the transport properties of Au nanotubule membranes. The use of both electrical neutral thiols to introduce chemical-transport selectivity and charged thiols to introduce ion-transport selectivity is reviewed.

Investigations of Potential-Dependent Fluxes of Ionic Permeates in Gold Nanotubule Membranes Prepared via the Template Method

We have been exploring the transport properties of gold nanotubule membranes prepared by electrolessly plating Au within the pores of a microporous polycarbonate filter. We have previously shown th...

Investigations of the Transport Properties of Gold Nanotubule Membranes

We have developed a new class of synthetic membranes that consist of a porous polymeric support that contains an ensemble of gold nanotubules that span the complete thickness of the support membrane. The support is a commercially available microporous polycarbonate filter with cylindrical nanoscopic pores. The gold nanotubules are prepared via electroless deposition of Au onto the pore walls; i.e., the pores acts as templates for the nanotubules. We have shown that by controlling the Au deposition time, Au nanotubules that have effective inside diameters of molecular dimensions (<1 nm) can be prepared. Hence, these membranes are a new class of molecular sieves. In addition, because these membranes are composed of an electronically conductive material, excess charge can be applied to the tubules by electrochemical charging in an electrolyte solution. We have shown that this allows for control of ion-transport selectivity in these membranes. Finally, because the tubules are composed of gold, well-known Au-t...

Electrokinetic separation of lysine and aspartic acid using polypyrrole-coated stacked membrane system

Abstract To reduce the electrical energy consumed in electrokinetic separation processes, a stacked membrane system composed of two polypyrrole (PPy)-coated porous membranes and a microporous polycarbonate filter (PCTE) has been suggested. In this PPy/PCTE/PPy membrane system, the outer two PPy membranes provide working electrodes for the migration of ions through the PCTE pores. Since the spacing between the two PPy membrane electrodes is only the thickness of the PCTE membrane, a strong electric field can be obtained by a small potential difference between the electrodes. Using this electrokinetic separation system, positively charged l -lysine (Lys) and negatively charged l -aspartic acid (Asp) are separated from their binary mixture at pH 4.7. For the efficient separation of both ions, the operation is carried out in a continuous and cyclic mode. The effects of potential difference on separation performance are investigated by varying the electric potential from ±1 to ±5 V. A higher potential difference results in a better separation. The key parameters determining the optimal experimental conditions are the electrokinetic migration and the pressure-driven convection rate of ions.

Development of a Cell Culture System To Study Antibody Convection in Tumors

The convective transport of fluid and of a binding antibody through a cultured tumor cell layer was investigated with a mouse melanoma cell line (B16F10) grown on a microporous polycarbonate filter (Snapwell inserts). The inserts were precoated with Matrigel or collagen, or were uncoated. The cell layers were exposed to nominal pressure gradients from 5 to 25 cm H2O, and the volume flux was measured by collecting the effluent volume over time. The rate of convective transport of a binding monoclonal antibody that recognizes the murina transferrin receptor (a-TfR) was investigated at a nominal pressure gradient of 15 cm H2O and compared with that of an isotype matched, nonbinding control. The resistance, R, of the cell layer to fluid flow was quantified as the hydraulic conductivity, Lp (= 1/R); the ability of the cell layer to retard antibody transport was quantified as the reflection coefficient, sigma. The resulting Lp values decreased with increasing cell density, in a manner consistent with Poiseuille flow. Collagen or Matrigel precoating also decreased Lp values, with cells grown on Matrigel providing the greatest resistance. The sigma values were 0.67 (+/-0.08) for the a-TfR antibody and 0.51 (+/-0.06) for the control, indicating that the cell layer acts as a semipermeable barrier to convective transport of antibody that is less permeable to the binding antibody.

Co-cultivation of rat pneumocytes and bovine endothelial cells on a liquid-air interface.

The blood-air barrier is a most important functional element of the lung but little information is available about the cells constituting this barrier in vivo. The aim of the present study was to create an in vitro model of the blood-air barrier that would allow investigation of cellular interactions and alveolar metabolism, and would be suitable for in vitro drug screening. Rat pneumocytes and bovine microvascular endothelial cells were grown on opposite sides of microporous polycarbonate filters, as immersion, perfusion and liquid-air interface (LAI) cultures. The effects of culture conditions on cell morphology were examined by light and transmission electron microscopy. For immersion and perfusion co-cultures, both compartments were supplied with culture medium. In contrast, for liquid-air interface studies, only the endothelial cell compartment was continuously supplied with serum-free medium, whilst the type II pneumocytes were ventilated with air. The pneumocytes lost their morphological characteristics when using immersion or perfusion co-cultures. Under liquid-air interface conditions, they retained most of their characteristic morphological features when compared to the intact blood-air barrier. A subset of primary type II pneumocytes retained its differentiated phenotype, with cuboidal morphology, lamellar bodies and apical microvilli. These type II pneumocytes appeared to be connected by tight junctions to cells expressing morphological characteristics of type I pneumocytes. As shown herein, the liquid-air interface co-culture possesses many morphological characteristics of the intact blood-air barrier. In summary, this article describes the design of an artificial blood-air barrier, in which rat pneumocytes were cultivated with bovine microvascular endothelial lung cells on opposing sides of a microporous polycarbonate filter. We conclude that it might be a promising in vitro model for studies of molecular transport via the blood-air barrier, the investigation of repair mechanisms after alveolar injury, or as an in vitro screening system.

Albumin and Ricinus communis agglutinin decrease endothelial permeability via interactions with matrix

We studied the effects of albumin and the lectin Ricinus communis agglutinin (RCA) on hydraulic conductivity (Lp) of bovine pulmonary microvascular endothelial cell monolayers (BPMVEC) because of the evidence that albumin and RCA can interfere with transendothelial albumin permeability (Siflinger-Birnboim, A., J. Schnitzer, H. Lum, F. Blumenstock, C. Shen, P. Del Vecchio, and A. Malik. J. Cell. Physiol. 149: 575-584, 1991). BPMVEC were seeded on microporous polycarbonate filters, and the liquid flux was measured by collecting effluent into a tubing of known inner diameter at transendothelial hydrostatic pressures (P) ranging from 5 to 20 cmH2O. Lp was calculated as the slope of the relationship of liquid flux per unit surface area (Jv) vs. P. Addition of RCA (50 micrograms/ml) or albumin (5 mg/ml) to the endothelial cell medium containing albumin-free Hanks' balanced saline solution (HBSS) decreased total Lp (expressed x 10(-6) cm.s-1 x cmH2O-1) from 17.2 +/- 3.6 during HBSS to 4.7 +/- 0.9 during albumin and 5.7 +/- 1.6 during RCA (P < 0.01 for both). The RCA effect, but not that of albumin, was prevented by the addition of D-galactose (0.1 M) (the cognate hapten monosaccharide of RCA). We determined the contribution of the extracellular matrix (ECM) in decreasing the Lp by obtaining ECM after treatment of the monolayers with 0.025 M NH4OH to detach endothelial cells from the ECM. Basal ECM Lp (expressed x 10(-6) cm.s-1 x cmH2O-1) was 57.0 +/- 15.3, and it decreased to 19.7 +/- 4.3 and 17.5 +/- 2.9 during RCA and albumin, respectively (P < 0.01 for both). In contrast, RCA and albumin did not alter the filter Lp values. Another lectin, Ulex europaeus agglutinin, and the protein immunoglobulin G had no effect on Lp values.(ABSTRACT TRUNCATED AT 250 WORDS)

Epithelial Transport of Drugs in Cell Culture. VII: Effects of Pharmaceutical Surfactant Excipients and Bile Acids on Transepithelial Permeability in Monolayers of Human Intestinal Epithelial (Caco‐2) Cells

The effects of anionic (sodium dodecyl sulfate and sodium dioctyl sufosuccinate) and nonionic (polysorbate 80 and polyoxyl 40 hydrogenated castor oil) synthetic surfactants and bile acids (sodium taurocholate, sodium taurodeoxycholate, and sodium taurodihydrofusidate) on epithelial integrity were studied in monolayers of human intestinal epithelial (Caco-2) cells grown on microporous polycarbonate filters. The effects of the surfactants on intracellular enzyme activity, cell monolayer permeability, and morphology were studied. The effects on permeability were studied by two methods: measurements of transport of marker molecules (mannitol and polyethylene glycol) and measurements of transepithelial electrical resistance. All surfactants demonstrated concentration-dependent effects on intracellular enzyme activities, permeability, and morphology. The effects of the anionic surfactants were more pronounced than those of the nonionic surfactants. The effects on transepithelial electrical resistance correlated with intracellular dehydrogenase activity. Fluxes of marker molecules were the most sensitive measure of epithelial integrity. The results indicate that the hydrophilic marker molecules permeate the epithelial monolayers through different pathways at different concentrations of the surfactants. The effects of the surfactants were reversible at intermediate concentrations, even though the morphology of the monolayers had changed. The results agree with published data obtained with experimental animals and indicate that Caco-2 cells can be used to study the concentration-dependent effects of surfactants and other pharmaceutical additives on intestinal epithelial permeability.

Effects of deoxycholate on the transepithelial transport of sucrose and horseradish peroxidase in filter-grown Madin-Darby canine kidney (MDCK) cells.

Madin-Darby canine kidney (MDCK) epithelial cells grown on microporous polycarbonate filters were used as a model system to investigate the mechanisms of enhancement by deoxycholate in the transepithelial transport of horseradish peroxidase (HRP) and 14C-sucrose. Deoxycholate at 0.025% had no effect on the transepithelial electrical resistance (TEER); a fivefold enhancement on the transepithelial transport of HRP, but not on that of 14C-sucrose, was observed. Deoxycholate at 0.05% induced a reversible decrease of TEER; a 2- and 50-fold enhancement on the transepithelial transport of 14C-sucrose and HRP, respectively, was observed. At 0.1%, deoxycholate induced an irreversible decrease in TEER and the epithelial barrier in the cell monolayer was completely eliminated. A 3.3-fold increase in cellular uptake in HRP, but not in 14C-sucrose, was also observed in the presence of 0.025% deoxycholate. The increase in cellular uptake was abolished when HRP was conjugated to polylysine. These results suggest that deoxycholate can increase the transepithelial transport by at least two different mechanisms, i.e., a transcellular pathway, possibly due to the enhancement of cellular uptake of selective molecules, and a nonselective paracellular pathway, due to the loosening of tight junctions by deoxycholate at higher concentrations.

Transcellular processing of disulfide‐and thioether‐linked peroxidase‐polylysine conjugates in cultured MDCK epithelial cells

Horseradish peroxidase (HRP) was conjugated to nondegradable polycationic poly(D-lysine) (PDL) through either a thioether (HRP-S-PDL) or a disulfide (HRP-SS-PDL) linkage. The binding and transcytosis of these conjugates was studied in Madin-Darby canine kidney (MDCK) cell monolayers grown on 3-microns microporous polycarbonate filters. Conjugation of HRP to PDL with both linkages markedly increased the binding of this protein onto the cell monolayers. However, an enhancement of the transcellular transport of HRP in both apical-to-basal and basal-to-apical directions was observed only in HRP-SS-PDL, but not in HRP-S-PDL. HRP-SS-PDL transport was inhibited by colchicine and by 4 degrees C incubation. The transport of 14C-sucrose was not affected by the presence of conjugates. These results indicate that the transport of the conjugate across the cell monolayers was due to a transcellular process rather than to any leakage of the cell junction caused by polycations. The disulfide linkage between HRP and PDL was cleaved rapidly at the basal and, to a lesser extent, at the apical surface of the cell. Neuraminidase treatment decreased the binding of the conjugates onto the cell surface, but did not decrease the transcellular transport, suggesting that not all surface-bound conjugates were available for transcytosis. These results demonstrate that disulfide linkages can be cleaved during transcytosis in MDCK cells. The cleavage, however, occurs mostly at the binding site on the cell surface, which may prevent the cellular uptake of the intact conjugate.