PA Membrane Research Articles

Biodegradation of phenol by immobilized Trichosporon cutaneum R57 on modified polymer membranes

Covalent immobilization of Trichosporon cutaneum R57 cells was conducted onto PA and PAN membranes with glutaraldehyde as a coupling agent. Amount of immobilized cells was determined: for polyamide—1.4 mg cm −2 and for polyacrylonitrile—1.8 mg cm −2 (dry weight). The efficiency of each immobilized system was evaluated by the extent of phenol biodegradation (1.0 g l −1). Polyacrylonitrile-immobilized system completed the process for 45 h, whereas polyamide-immobilized system for 51 h. During the six next cycles the complete biodegradation time for polyacrylonitrile-immobilized system was reduced at 24, 18 and 15 h for III, V, VII cycles, respectively. The biodegradation time at eighth cycle was prolonged (42 h) and this is probably due to substrate diffusion limitations to the local accumulation of microbial cells on the membrane surface and cause cell death. Comparing the SEM of immobilized microbial cells on polyacrylonitrile membrane before the first cycle and after the eight cycle could be seen that great amount of immobilized cells are accumulated on the membrane surface during the seven biodegradation cycles.

Pore diffusion studies with immobilized glucose oxidase plus catalase membranes

Glucose oxidase (GOD) and catalase (CAT) were chemically immobilized onto three types of ultrafiltration polyacrylonitrile membranes with increase pore sizes (PAN 1–PAN 3) and one microfiltration polyamide membrane. The initial membranes were modified to generate amino and amide groups on their surface, necessary for the covalent immobilization of the enzymes. The diffusivity parameter of glucose through the initial and modified membranes was determined. It was found out that the glucose diffusion, increased with the increase of the pore size. The slight increase of glucose diffusion parameters was observed for the modified membranes in comparison with the initial membranes. The diffusivity of glucose through the inactivated enzyme membranes was determined also. A minor decrease in the values of these parameters with respect to glucose was observed for the enzyme PAN 2 membrane, while for the PAN 3 and PA enzyme membrane there was two-fold decrease in the obtained parameter values (compared to the initial and modified membranes). There was no significant change in the values of the indicated parameters with respect to H 2O 2 for different modified and enzyme membranes. The mass transfer coefficients ( K L), thickness of boundary layer ( δ), Sherwood number (Sh) and Thiele modulus ( ϕ) as well as their influence on the efficiency of the enzyme couple GOD–CAT immobilized onto different pore size polymer membranes were also studied. The final results showed that the two immobilized systems with PAN 3 and PA membranes, as carriers were effective as compared to PAN 1 and PAN 2 membranes.

Biofouling potentials of microporous polysulfone membranes containing a sulfonated polyether-ethersulfone/polyethersulfone block copolymer: correlation of membrane surface properties with bacterial attachment

Multivariate methods were used to identify relationships between bacterial attachment (biofouling potential), water transport, and the surface properties of nine modified polysulfone (MPS) membranes comprising blends of polysulfone (PS) with a sulfonated polyether-ethersulfone/polyethersulfone block copolymer. The topology of the microporous MPS membranes, including surface roughness, surface height, pore size and pore geometry were determined by atomic force microscopy (AFM) and digital image analysis. Other measurements included relative surface hydrophobicity by captive bubble contact angle, surface charge (i.e., degree of sulfonation) by uranyl cation binding, wt% solids, porosity, membrane thickness, water flux, and the affinity of membranes for a hydrophilic Flavobacterium and hydrophobic Mycobacterium species. The mycobacteria attached best to the MPS membranes, but the attachment of both organisms was inversely correlated with the mean aspect ratio of pores, suggesting that irregular or elliptic pores discouraged attachment. Multivariate regression analyses identified the pore mean aspect ratio, mean surface height, PS content, and the n-methylpyrrolidone+propionic acid (NMP–PA) solvent concentration as influential factors in Mycobacterium attachment, whereas membrane thickness, surface roughness, pore mean aspect ratio, porosity, and the mean pore area/image area ratio influenced Flavobacterium attachment. Cluster analyses revealed that Mycobacterium attachment was associated with hydrophobic determinants of the MPS membranes, including PS content, wt% solids, and air bubble contact angle. In contrast, Flavobacterium attachment was primarily associated with membrane thickness and charge (i.e., uranyl cation binding or degree of sulfonation). Membrane flux was inversely correlated with surface hydrophobicity and PS content, but (in contrast to cell attachment) positively correlated with most pore geometry parameters including the mean aspect ratio, suggesting that pore geometry can be optimized to minimize cell attachment and maximize water transport. Other variables influencing water flux included the NMP–PA solvent concentration and membrane roughness. The results should facilitate the design of novel microporous PS membranes having reduced biofouling potentials and greater water fluxes.

HYDROPHOBIZING EFFECT OF CATIONS ON ACIDIC PHOSPHOLIPID MEMBRANES

ABSTRACT By means of contact angle measurements with water and aqueous salt solutions, it is shown that plurivalent cations increase the hydrophobicity of negatively charged phospholipid vesicle membranes (consisting of phosphatidic acid, PA, or of phosphatidylserine, PS), but does not influence the hydrophobicity of neutral phospholipid membranes, (e.g., phosphatidylcholine, PC, at up to 200 mM of CaCl2). The hydrophobizing action of cations on PA and PS membranes is concomitant with the reduction in (negative) zeta potential with increasing cation concentrations. Trivalent cations, La3+, showed more effective in hydrophobizing negatively charged phospholipid membranes than divalent and monovalent cations. Except for hydrogen ions, monovalent cations do not show any appreciable hydrophobizing effect on lipid vesicle membranes at concentrations less than 1 M. The hydrophobizing effect on phospholipid membranes can also be used to explain the induction of lateral phase separation into patches of different phospholipids as well as cell fusion.

Possible clinical effects of the interaction of hemodialysis membranes with adhesion proteins

In this study data obtained in an in vitro hemodialysis model are related to various parameters measured in patients' plasma during hemodialysis in a clinical crossover study. In vitro, blood from healthy volunteers was dialyzed under standardized conditions using the capillaries Fresenius MTS C (Cuprophane) and Hospal AN 69 (Polyacrylonitrile). Following dialysis, surface bound proteins were eluted with saline, 1 M Tris and 2% SDS, and analyzed by immunoblotting. Depending on the capillary, different protein patterns could be identified in the eluates. Intact forms of adhesion proteins were predominantly (fibrinogen) or exclusively (vitronectin) found in PA eluates. In contrast, low molecular weight products of fibrinogen as well as high molecular weight components containing antithrombin III (AT III) were present in CP eluates. Their presence may reflect fibrinolytic and procoagulatory activity during dialysis with CP capillaries. A microscopic investigation of CP membranes demonstrated fibrin lined platelet conglomerates. In the plasmas of patients dialyzed with CP capillaries high D-Dimer concentrations were found. We also noticed that during dialysis with PA membranes less heparin was consumed than during dialysis with CP membranes. Our study showed a good correlation of the observations in the vitro system and the measurements in patient samples.

Inhibition of capacitative Ca 2+ entry by a Cl − channel blocker in human endothelial cells

We have used the patch clamp technique in combination with intracellular calcium measurements to measure simultaneously Ca 2+ entry and ionic currents activated by emptying of intracellular Ca 2+ stores (capacitative Ca 2+ entry and Ca 2+ release-activated Ca 2+ currents, CRAC) in human endothelial cells from umbilical veins. Intracellular stores were depleted of Ca 2+ by preincubating endothelial cells for 20 minutes with 2 μM thapsigargin in Ca 2+-free solution. Reapplication of 10 mM [Ca 2+] e evoked an increase in [Ca 2+] i indicating Ca 2+ influx after the thapsigargin-induced store depletion (capacitative Ca 2+ entry), however no measurable CRAC could be detected. The increase in [Ca 2+] i after [Ca 2+] e resubmission was substantially reduced in the presence of 50 μM NPPB (5-nitro-2-(3-phenylpropylamino)-benzoic acid) from 0.77 ± 0.25 μM to 0.2 ± 0.06 μM (n = 6) at a holding potential of −40 mV. Estimates of the capacitative Ca 2+ entry at various membrane potentials from the first time derivative of the Ca 2+ transients showed a highly inwardly rectifying I–V curve with a Ca 2+ inward current amplitude of 1.0 ± 0.3 pA (membrane capacitance 59 ± 9 pF, n = 8) at −80 mV. This current amplitude was decreased to 0.32 ± 0.12 pA( n = 6) in the presence of 50 μM NPPB. This corresponds to a decrease in the Ca 2+ permeability of the endothelial cell membrane from 0.15·10 −8 cm/s (control) to 0.06·10 −8 cm/s (50 μM NPPB).

Multiple Applications of Hemodialysis in the Management of Acute Renal Failure

We studied the influence of different modes of hemodialysis (HD) on plasma levels of β2-microglobulin (P-β2-m) and its correlation to changes in leukocyte count, complement activation (C3a), and elastase generation. The influence of dialyzer membrane, membrane surface area, duration of treatment, and blood flow was analyzed with respect to post-HD levels of P-β2-m. Twenty patients underwent 12 modes of bicarbonate hemodialysis in random order (n = 252) using three different membranes (Cuprophan [CU], hemophan [HE], or polyamide [PA], two dialyzer areas, and fast (400 mL/min) or slow (200 mL/min) blood flow (Qb) for 2 or 4 hours, respectively. All dialysate was collected and β2m was analyzed (D-β2-m). After correction for hemoconcentration, P-,β2-m concentrations were found to have decreased significantly during treatment with all three membranes (CU, 0.9 ± 0.3 mg/L, P = 0.002; HE, 1.2 ± 0.3 mg/L, P < 0.001; and PA, 8.3 ± 0.3 mg/L, P < 0.001). Elimination of P-β2-m was influenced by type of membrane (P < 0.001) and ultrafiltration volume (P = 0.0019) but not by membrane area or Qb. The largest reduction in P-β2-m(-10.4 mg/L) was achieved by the following treatment combination: PA membrane, large dialyzer area, and low Qb for 4 hours. P-β2-m decreased more during PA dialysis at low Qb for 4 hours (-9.9 ± 0.5 mg/L) than during high Qb for 2 hours (-6.8 ± 0.5 mg/L, P < 0.001). D-β2-m was significantly higher after PA dialysis than after CU or HE dialyses (P < 0.001) and was influenced during PA dialyses by pre-HD P-β2-m (r = 0.57, P < 0.001). Changes in P-β2-m correlated to bioincompatibility markers, such as leukopenia (r = 0.20, P = 0.0014), Ma activation (r = 0.31, P < 0.001), and elastase production (r = 0.17, P = 0.012), but the statistical significance was due to covariation. This study shows that membrane type and ultrafiltration volume all have influence on β2-m removal and that dialysis time seems to be more important than membrane area and Qb. No factual correlation was seen between changes in β2-m and markers of bioincompatibility.