Small-pore Membranes Research Articles

Enhancing manganese removal through pre-deposition of powdered activated carbon-manganese oxide (PAC-MnOx) film on gravity-driven ceramic membrane: The impact of biofilm integrity and fluid dynamics

Manganese is widely distributed in the natural environment, and its presence in drinking water poses a risk to human health. In this study, an integrated pre-deposited powdered activated carbon (PAC) and manganese oxide (MnOx) bio-functional layer of inorganic origin was coupled with gravity-driven ceramic membrane (GDCM) reactor. The study aims to investigate the effects of the membrane pore size and functional layer integrity on the Mn2+ removal and flux. The results reveal that the average Mn2+ removal efficiency of the large pore size membranes (300 kDa and 0.45 μm) was lower (75 % – 78 %) compared to those with smaller pores (15 kDa and 50 kDa) (87 % – 88 %) during long-term operation. Such differences are attributed to a period of manganese leakage before the PAC-MnOx matured in large-pore membrane units and a longer residence time in small-pore membranes. The functional layer leaded to reversible fouling, which was more prominent in membranes with larger pores (contributing to 93 % of total resistance) than those with smaller ones (ranging from 51.7 % to 61.9 %). Although the damaged functional layer resulted in occasional high Mn2+ concentrations in the effluent, it did not significantly impact long-term flux development. Optical coherence tomography (OCT), in conjunction with COMSOL analysis, non-destructively evaluate biofilm formation process and indicate a homogeneous flow field and mass transfer in the “dual layers” (active film layer and ceramic membrane layer) of the GDCM. The presence of manganese-oxidizing bacteria (Hyphomicrobium, Reyranella, and Pseudomonas) in the GDCM reactor was verified using confocal laser scanning microscopy (CLSM) and high-throughput sequencing. Additional material characterization revealed that a portion of the PAC-MnOx exhibited characteristics of birnessite, with autocatalytic oxidation of Mn2+, and that Mn (III) and Mn (IV) were the primary species in MnOx, which exhibited excellent catalytic oxidation and adsorption capabilities for Mn (II), respectively. Overall, the developed PAC-MnOx GDCM system shows great promise in efficiently removing manganese and producing water of desired quality, thereby holding potential in applications across several sectors of advanced water treatment processes.

Optimization of a method for collecting infant and toddler urine for non-target analysis using cotton pads and commercially available disposable diapers.

Urine is an abundant and useful medium for measuring biomarkers related to chemical exposures in infants and children. Identification of novel biomarkers is greatly enhanced with non-targeted analysis (NTA), a powerful methodology for broad chemical analysis of environmental and biological specimens. However, collecting urine in non-toilet trained children presents many challenges, and contamination from specimen collection can impact NTA results. We optimized a caregiver-driven method for collecting urine from infants and children using cotton pads and commercially available disposable diapers for NTA and demonstrate its applicability to various children biomonitoring studies. Experiments were first performed to evaluate the effects of processing method (i.e., centrifuge vs. syringe), storage temperature, and diaper brand on recovery of urine absorbed to cotton pads. Caregivers of 11 children (<2 years) used and retained diapers (with cotton pads) to collect their child's urine for 24 h. Specimens were analyzed via a NTA method implementing an exclusion list of ions related to contamination from collection materials. Centrifuging cotton pads through a small-pore membrane, compared to a manual syringe method, and storing diapers at 4 °C, compared to room temperature, resulted in larger volumes of recovered sample. This method was successfully implemented to recover urine from cotton pads collected in the field; between 5-9 diapers were collected per child in 24 h, and the total mean volume of urine recovered was 44.7 (range 26.7-71.1) mL. NTA yielded a list of compounds present in urine and/or stool that may hold promise as biomarkers of chemical exposures from a variety of sources. Infant and children urine is a valuable matrix for studies of the early life exposome, in that numerous biological markers of exposure and outcome can be derived from a single analysis. Depending on the nature of the exposure study, it may be the case that a simple collection method that can be facilitated by caregivers of young children is desirable, especially when time-integrated samples or large volumes of urine are needed. We describe the process for development and results of an optimized method for urine collection and analysis using commercially available diapers and non-target analysis.

Experimental and theoretical retentions of sub-10 nm colloidal nanoparticles by large-pore ultrafiltration membranes in isopropanol and water

Effective removal of small colloidal nanoparticles (NPs, e.g., <20 nm), including rigid particles, macromolecules, organics, viruses, antibiotics, hormones, etc., by dead-end filtration, is very important in drinking water, chemical, biopharmaceutical, and semiconductor factories. Most existing operations focused on sieving mechanism-based filtration with small-pore membranes (e.g., <20 nm) to capture these tiny NPs, which unfortunately leads to high energy consumption. This study proposed an emerging method that is to use large pore membranes (i.e., ∼100 nm) to capture NPs down to 2.8 nm. The ultimate goal is to address the grand challenge presented in the United Nations Sustainable Development Goal 12 on energy saving. To capture (or adhere) small NPs by large-pore membranes, the surface electrostatic interactions between NP and membrane should be considered in addition to the sieving mechanism. To examine the feasibility of the proposed method, the retention efficiency of ∼100 nm rated polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), and polycarbonate track-etched (PCTE, as a model filter) membranes against 2.8 nm ZnS quantum dot (QD), 5 and 10 nm Au and 100 nm PSL in water and isopropanol (IPA, a representative organic solvent) were studied experimentally and theoretically. In the experiments, the electrospray-scanning mobility particle sizer (ES-SMPS) was used to measure the size distribution of these nanosized colloids before and after the membrane to determine the retention efficiency. In the theory, we combined the hydrodynamic particle transport, extended Derjaguin-Landau-Verwey-Overbeek (xDLVO), and Maxwell models to calculate the NP retention. Results showed that the data agreed with the theoretical model very well, and the NP retentions in IPA were higher than that in water due to a significant change of acid-base interaction from repulsion to attraction. The retention of the 10 nm Au NPs and the 2.8 nm NPs could be attained by ∼80 and 35%, respecively, in IPA by the PTFE. This study was the first to show the combined theoretical model can accurately predict the retention of sub-10 nm NPs by different membranes in an organic solvent and water. The model predicts the retention of 5 nm Au NPs can be increased to higher than 99% by increasing the zeta potential of the PTFE about 5 times, thus a sustainable UF cutting significant carbon footprint is foreseeable in near future.

Mass Transport of Lignin in Confined Pores.

A crucial step in the chemical delignification of wood is the transport of lignin fragments into free liquor; this step is believed to be the rate-limiting step. This study has investigated the diffusion of kraft lignin molecules through model cellulose membranes of various pore sizes (1–200 nm) by diffusion cells, where the lignin molecules diffuse from donor to acceptor cells through a membrane, where diffusion rate increases by pore size. UV–vis spectra of the donor solutions showed greater absorbance at higher wavelengths (~450 nm), which was probably induced by scattering due to presence of large molecules/clusters, while acceptor samples passed through small pore membranes did not. The UV–vis spectra of acceptor solutions show a characteristic peak at around 350 nm, which corresponds to ionized conjugated molecules: indicating that a chemical fractionation has occurred. Size exclusion chromatography (SEC) showed a difference in the molecular weight (Mw) distribution between lignin from the donor and acceptor chambers. The results show that small pore sizes enable the diffusion of small individual molecules and hinder the transport of large lignin molecules or possible lignin clusters. This study provides more detail in understanding the mass transfer events of pulping processes.

Farm-scale differentiation of active microbial colonizers

Microbial movement is important for replenishing lost soil microbial biodiversity and driving plant root colonization, particularly in managed agricultural soils, where microbial diversity and composition can be disrupted. Despite abundant survey-type microbiome data in soils, which are obscured by legacy DNA and microbial dormancy, we do not know how active microbial pools are shaped by local soil properties, agricultural management, and at differing spatial scales. To determine how active microbial colonizers are shaped by spatial scale and environmental conditions, we deployed microbial traps (i.e. sterile soil enclosed by small pore membranes) containing two distinct soil types (forest; agricultural), in three neighboring locations, assessing colonization through 16S rRNA gene and fungal ITS amplicon sequencing. Location had a greater impact on fungal colonizers (R2 = 0.31 vs. 0.26), while the soil type within the microbial traps influenced bacterial colonizers more (R2 = 0.09 vs. 0.02). Bacterial colonizers showed greater colonization consistency (within-group similarity) among replicate communities. Relative to bacterial colonizers, fungal colonizers shared a greater compositional overlap to sequences from the surrounding local bulk soil (R2 = 0.08 vs. 0.29), suggesting that these groups respond to distinct environmental constraints and that their in-field management may differ. Understanding how environmental constraints and spatial scales impact microbial recolonization dynamics and community assembly are essential for identifying how soil management can be used to shape agricultural microbiomes.

Self-sorted Compartmentalization by Simultaneous Use of Natural and Synthetic Amphiphiles.

Exploiting the orthogonal molecular interactions of natural (phospholipids) and synthetic (mono-allyloxylated cucurbit[7]uril) amphiphiles to form their own vesicles, the formation of two different types of compartments in a self-sorted manner mimicking cellular compartments is demonstrated. Even after simultaneous extrusion of both vesicles through small pore membranes, which transformed them into smaller vesicles, both vesicles were not fused but still appeared as independent compartments in sucrose solution. The simultaneous use of natural and synthetic amphiphiles, forming independent compartments, holds great potential for in-depth investigation of self-sorted multi-compartments and their structures as prototype cells.

A small copper carrier in blood plasma: purification, characterization, and metabolism

In mammals, concentrations of copper in tissues and fluids are kept very constant. The main mechanism underlying this constancy is the ability of the liver to modulate excretion of copper by varying the amounts entering the bile – which end up in the feces. When biliary excretion of copper is hindered, as occurs when one of the proteins involved is defective, copper accumulates in the liver and later in other organs, with fatal consequences if untreated. Major examples are the copper “pump”, ATP7B, defective in Wilson Disease, and COMMD1, which also aids biliary excretion. With copper overload, there is increased copper in the urine, which normally is very low. Studies by Gray et al.[1] with the mouse Atp7b knockout model of Wilson disease determined that the increase in urine is due to a small copper carrier (SCC) of about 2 kDa, which our laboratory then determined was also in the blood plasma of these mice. Moreover, canines with defective ATP7B also had large increases in SCC-Cu in their blood and urine. We have been researching ways of purifying significant amounts of SCC, using commercially available porcine plasma, so it can be further characterized. Based on size exclusion chromatography (SEC) of 3 kDa ultrafiltrates in small pore gels, we know that usually most of the Cu is in a single component (SCC), which by ESI-MS appears to have a mass/charge ratio of 845, one atom of Cu(II) – detected in EPR as bound to N and O ligands, and a pI in the range of 3-4. New ways of purifying SCC beyond the ultrafiltration stage have been developed, involving concentration by lyophilization and special forms of dialysis using very small pore membranes. Hydrophilic interaction chromatography and additional SEC are providing much purer SCC, with more reasonable yields. Meanwhile, we have also been investigating the secretion and uptake of SCC-Cu, using cultured cells. SCC is secreted by hepatic cells as well as those modeling intestinal and kidney epithelium, particularly when preloading with Cu(II)-diHis. Intestinal (Caco2) cell monolayers with tight junctions secreted SCC mainly across the apical membrane (representing the gut lumen), but this was dramatically reversed when albumin was present in the basal medium (which is more physiological). Kidney epithelial cells also secreted SCC-Cu and some additional copper components mainly into the apical fluid. Other studies, with 67Cu-labeled SCC from hepatic secretions, confirmed not only that SCC was secreted, but showed that it was also taken up by all cell types examined. These findings suggest that metabolism of SCC and its copper is very active, and that SCC may play an important role in mammalian copper homeostasis. [1]Gray et al. PLoS ONE 7(6): e38327.

The removal of phospholipid from crude rapeseed oil by enzyme-membrane binding

Membrane technology has unique advantages over centrifugal equipment and has been widely applied. In this work, the hydrophobic ceramic membranes were used to remove phospholipid micelles from crude rapeseed oil, and their fouling mechanism, control, cleaning and influence on oil quality were investigated. The results of four different treatments showed that enzyme-membrane binding was the most effective degumming method. The flux performance can meet the needs of small-scale oil production. Concentration experimental results showed that the fouling mechanism was a combination of intermediate blockage and cake. Although increasing pressure, temperature, concentration, flow rate, and pore size could all reduce available area and increase resistance, the effects of TMP and pore size are the most significant in these factors. Non-cleaning resistance was very small under all conditions, and increasing transmembrane pressure and pore size promoted non-cleaning resistance. Increasing temperature and cross-flow velocity significantly reduced the resistance of cleanable pollution. In terms of membrane fouling control, the critical and threshold transmembrane pressures of the large-pore membrane were lower than those of the small-pore membrane and decreased with increasing concentration. Fouled membranes can be cleaned and restored by oil without phospholipid micelles, and the flux recovery rate of the membranes can exceed 85% after 10 reuses. The membranes removed phospholipids and water and were beneficial for decreasing free fatty acids and peroxide values. Therefore, the enzyme-membrane binding can be considered for gradual use in the production of small-scale oil.

Silicone rubber membrane with specific pore size enhances wound regeneration.

A porous structure is critically important for wound dressing or tissue engineering scaffolds. However, the influence of the pore sizes on cell proliferation, tissue regeneration and the underlying mechanism remains unclear. In this study, silicone rubber membranes with different pore sizes were prepared using certain constituents of liquid silicone rubber precursor/liquid paraffin/hexane based on our previous studies. It was found that pore size had a significant impact on cell proliferation and wound healing. The CCK8 analysis revealed that the membrane with a certain pore size (110.47μm, middle pore membrane, MPM) was suitable for cell proliferation compared with the membranes with other pore sizes (218.03μm, large pore membrane, LPM; 5.27μm, small pore membrane, SPM; non-porous membrane, NPM). Further studies demonstrated that the MPM promoted cell proliferation via activating the Wnt/β-catenin signalling pathway. More importantly, wound healing experiments showed that 7days post-wounding, the rate of wound healing was 89.25% with the MPM, which was significantly higher than with LPM, SPM or NPM. The in vivo data indicated that wound healing was accelerated by treatment with a silicone rubber membrane with a pore size of 110.47μm. Our results strongly suggest that different pore structures might affect cell proliferation and wound healing and that a silicone rubber membrane with a specific pore size could potentially be used as a promising wound dressing. Copyright © 2017 John Wiley & Sons, Ltd.

Cell-to-Cell Contact and Nectin-4 Govern Spread of Measles Virus from Primary Human Myeloid Cells to Primary Human Airway Epithelial Cells.

Measles is a highly contagious, acute viral illness. Immune cells within the airways are likely first targets of infection, and these cells traffic measles virus (MeV) to lymph nodes for amplification and subsequent systemic dissemination. Infected immune cells are thought to return MeV to the airways; however, the mechanisms responsible for virus transfer to pulmonary epithelial cells are poorly understood. To investigate this process, we collected blood from human donors and generated primary myeloid cells, specifically, monocyte-derived macrophages (MDMs) and dendritic cells (DCs). MDMs and DCs were infected with MeV and then applied to primary cultures of well-differentiated airway epithelial cells from human donors (HAE). Consistent with previous results obtained with free virus, infected MDMs or DCs were incapable of transferring MeV to HAE when applied to the apical surface. Likewise, infected MDMs or DCs applied to the basolateral surface of HAE grown on small-pore (0.4-μm) support membranes did not transfer virus. In contrast, infected MDMs and DCs applied to the basolateral surface of HAE grown on large-pore (3.0-μm) membranes successfully transferred MeV. Confocal microscopy demonstrated that MDMs and DCs are capable of penetrating large-pore membranes but not small-pore membranes. Further, by using a nectin-4 blocking antibody or recombinant MeV unable to enter cells through nectin-4, we demonstrated formally that transfer from immune cells to HAE occurs in a nectin-4-dependent manner. Thus, both infected MDMs and DCs rely on cell-to-cell contacts and nectin-4 to efficiently deliver MeV to the basolateral surface of HAE. Measles virus spreads rapidly and efficiently in human airway epithelial cells. This rapid spread is based on cell-to-cell contact rather than on particle release and reentry. Here we posit that MeV transfer from infected immune cells to epithelial cells also occurs by cell-to-cell contact rather than through cell-free particles. In addition, we sought to determine which immune cells transfer MeV infectivity to the human airway epithelium. Our studies are based on two types of human primary cells: (i) myeloid cells generated from donated blood and (ii) well-differentiated airway epithelial cells derived from donor lungs. We show that different types of myeloid cells, i.e., monocyte-derived macrophages and dendritic cells, transfer infection to airway epithelial cells. Furthermore, cell-to-cell contact is an important component of successful MeV transfer. Our studies elucidate a mechanism by which the most contagious human respiratory virus is delivered to the airway epithelium.

INVESTIGATION ON THE MORPHOLOGY AND PROPERTIES OF AGGREGATE STRUCTURES OF NATURAL PHOSPHOLIPIDS IN AQUEOUS SYSTEM USING CRYO-TEM

Cryogenic transmission electron microscopy (Cryo-TEM) was used to investigate the aggregates morphology and properties of candle tree (Aleurites moluccana) endosperm, sesame (Sesamum indicum L. syn.) seeds, and coconut (Cocos nucifera) endosperm phospholipids in dilute aqueous system. The micrographs showed that candle tree phospholipids formed planar bilayer and cluster of vesicles with lipid droplets, while coconut and sesame phospholipids formed well-defined unilamellar vesicles. The vesicles size could be as small as 50 nm in diameter. Coconut phospholipids also showed a good bending ability. Formation of clusters of vesicles was also found in coconut phospholipids dispersion, but this cluster was easily broken by extrusion through a small pore membrane.

The electrokinetic sonic amplitude effect in filtration membranes: Part I. Experimental

The term Electrokinetic Sonic Amplitude, or ESA refers to the generation of ultrasound by the application of MHz electric fields. ESA measurements are frequently used in colloid science to determine the zeta potential and particle size in concentrated sols, and commercial devices have been developed for this purpose (R.W. O’Brien, D.W. Cannon, W.N. Rowlands, J. Colloid Interface Sci. 173 (1995) 406). The aim of these two papers is to explore the possibility of using ESA measurements to determine membrane properties such as zeta potential and pore size. In this paper we describe a procedure for using the ZetaProbe11Manufactured by Colloidal Dynamics LLC, 5150 Palm Valley Road, Suite 303, Ponte Vedra Beach, FL 32082, USA, www.colloidal-dynamics.com. to measure the ESA of a filtration membrane, and we present measurements for some small-pore membranes. By using the theory for membrane ESA, which is presented in part II of this paper, we have been able to extract precise zeta potentials, but we could not get information about pore size. This is not a limitation of the ESA method but is a limitation due to our frequency range, for to get pore size distributions for these membranes from the ESA it is necessary to work at frequencies ω for which the ratio ωa2/ν is not small, where a is the pore radius and ν is the kinematic viscosity of the solvent; such frequencies lie above the range of our current device.

Removal versus fragmentation of amyloid‐forming precursors via membrane filtration

The presence of even minute amounts of protein aggregates in solution can significantly alter the kinetics of amyloid formation. Removal of such pre-existing aggregates is critical for reproducible analysis of amyloid formation. Here we examine the effects of membrane filtration on insulin fibrillization. We find that filtration of insulin with large pore membranes (≥ 100 nm) generally slows fibril formation relative to unfiltered solutions by removing pre-aggregated protein. Unexpectedly, filtration with small pore membranes (< 100 nm) showed no beneficial effect and, in some cases, accelerated insulin fibril formation. This effect may be due to fragmentation of pre-existing aggregates during filtration through small pore membranes, which can increase the number of amyloid-forming precursors. These findings reveal the complexity of removing protein aggregates via filtration and suggest optimal filtration protocols for conducting fibril formation analysis of insulin and similar amyloidogenic proteins.

Virus filtration of high‐concentration monoclonal antibody solutions

The ability to process high-concentration monoclonal antibody solutions (> 10 g/L) through small-pore membranes typically used for virus removal can improve current antibody purification processes by eliminating the need for feed stream dilution, and by reducing filter area, cycle-time, and costs. In this work, we present the screening of virus filters of varying configurations and materials of construction using MAb solutions with a concentration range of 4-20 g/L. For our MAbs of interest-two different humanized IgG1s-flux decay was not observed up to a filter loading of 200 L/m(2) with a regenerated cellulose hollow fiber virus removal filter. In contrast, PVDF and PES flat sheet disc membranes were plugged by solutions of these same MAbs with concentrations >4 g/L well before 50 L/m(2). These results were obtained with purified feed streams containing <2% aggregates, as measured by size exclusion chromatography, where the majority of the aggregate likely was composed of dimers. Differences in filtration flux performance between the two MAbs under similar operating conditions indicate the sensitivity of the system to small differences in protein structure, presumably due to the impact of these differences on nonspecific interactions between the protein and the membrane; these differences cannot be anticipated based on protein pI alone. Virus clearance data with two model viruses (XMuLV and MMV) confirm the ability of hollow fiber membranes with 19 +/- 2 nm pore size to achieve at least 3-4 LRV, independent of MAb concentration, over the range examined.

Annual Meeting of the Society for Cutaneous Ultrastructure Research (33rd Annual Meeting of SCUR) 8–10 June 2006 WARSZAWA, POLAND

Unsupported keratinocyte grafts, while fragile, provide excellent clinical benefits and wound coverage. We aim to overcome the fragile nature of these grafts by using keratinocytes and fibroblast grafts grown on biocompatible, biodegradable, hexagonalpacked porous poly-calprolactone membranes. To confirm the feasibility of this proposal, human epidermal keratinocytes and dermal fibroblasts were cultured on membranes with controlled-sized pores (ranging from 3–20 microns). We examined the effects of growing monocultures on these porous membranes and on flat (pore less) polymer films. Cell adhesion, growth and migration rates and basic morphology were examined using confocal laser scanning microscopy. Cell ultrastructure was subsequently examined using scanning and transmission electron microscopy. Human keratinocytes and fibroblasts attached to all porous membranes. Furthermore, small pore (3 and 5 micron) membranes provided the best surfaces, on which fibroblasts could attach, adhere, divide and grow. However, keratinocytes, the most discerning of the two cell types adhered and grew best on 3 micron pore membranes. In addition, cells were prevented from undergoing transmembrane migration (to the opposing membrane surface) by the 3 micron porous membrane. Larger pores (45microns) allowed migration of both fibroblasts (and to a lesser extent keratinocytes) on to the opposite side of the membrane. Our data show that keratinocytes and fibroblasts attached and grew optimally on small pore membranes due to greater pores numbers and a larger surface area over which cells adhere. The small pore size also inhibits cells from traversing the membrane while, at the same time allowing cell adhesion, matrix communication and diffusion of soluble nutrients/factors from the environment. These characteristics are important in development of graft technology, in the treatment of human skin wounds and in the study of cell-substrate adhesion on novel patterned structures

Thermal conductivity of periodic microporous silicon films

This letter reports the experimental in-plane thermal conductivity of microfabricated, free-standing, single-crystal silicon thin films with periodically arranged through-film micropores. The experimental data suggest that strong size effects exist even in micro-sized porous silicon structures, particularly at low temperatures. Even at room temperature, all porous membranes show thermal conductivity values lower than expected by porosity and bulk phonon mean free path of silicon, and small-pore membranes have smaller thermal conductivity compared to the large-pore ones despite that they have close porosity values.

Survival of hemodialysis patients and uremic toxin removal.

Uremic toxin removal based on diffusion and/or convection allows eliminating solutes with negative metabolic impact. Uremic solutes can be classified as small and water-soluble compounds, larger "middle" molecules, or protein bound solutes. The question arises whether more removal of each of these solute classes affects patient survival. Kt/V of urea is currently used as a surrogate for small water-soluble solute removal. There is ample evidence that Kt/V and survival are correlated, but the threshold Kt/V remains a matter of debate. Probably, the actually proposed threshold of 1.2 is too low. This impact of Kt/V is in contradiction with the low toxicity of urea and points to a role for other water-soluble solutes, e.g., potassium. More removal of middle molecules results in a lower morbidity and also in a lower mortality. In addition, a relationship has been demonstrated between the use of membranes with large pore size and a decrease of inflammatory status, by itself an important factor related to mortality. One of the problems is that large pore membranes are at the same time more biocompatible and reflect more dialysate impurities, compared to many small pore membranes, whereas they also reflect more dialysate impurities. It remains uncertain which one of these factors, if any, has a predominant effect. Recent studies point to a separate effect of pore size but await confirmation. Protein bound toxins inhibit several biochemical functions. Their removal pattern is totally different from that of classical markers such as urea. In analogy with drugs, it is essentially the free unbound fraction that exerts biological action; this free fraction is inversely related to serum albumin, another inflammatory marker related to survival. In a final section of this presentation, attention will be drawn to the relationship in uremic patients between inflammation, malnutrition, cardiovascular disease, and mortality, and some of the potential culprits are discussed. Virtually all of these molecules have a high molecular weight or are protein bound. It is concluded that both small and middle molecule removal have an impact on survival, so that more than urea removal alone should be pursued.

Chemical and electrical characterization of virgin and protein-fouled polycarbonate track-etched membranes by FTIR and streaming-potential measurements

Electrical properties for a range of virgin and protein-fouled polycarbonate track-etched (PCTE) membranes have been determined by streaming-potential measurements at pH 4–7 and 10 −3 M KCl at 25°C. The apparent zeta potentials generally increased with increasing pore size above pH 5 and decreased with pore size below pH 5. For membranes with smaller pores (PCTE 0.01, 0.03 and 0.05 μm) the zeta potentials became constant (the surface is fully charged) at about −6 mV at pH ≥ 5, whereas those of larger pores (PCTE 0.1 and 0.2 μm) showed constant zeta potentials of ca. −10 to −13 mV at pH > 6. In contrast, the protein-fouled membranes showed very similar apparent zeta potential vs. pH profiles for all pore sizes. This suggests that the measured zeta potentials are determined by the protein properties. The loss of strong pore-size dependence on zeta potentials upon protein fouling of membranes implies that membrane zeta potentials could be controlled by the conditions at pore entry. This ‘model’ requires protein deposition around the pore openings for all pore sizes; this was in agreement with electron microscope observations. While the isoelectric points (IEP) of the virgin membranes determined from the pH dependence of streaming-potential measurements were between pH 3.7 – 4.4 with a trend to higher IEP for the larger pore membrane, all protein-fouled membranes showed IEP values at pH 4.6 – 4.8, which is close to the IEP of the BSA protein used. The chemical properties of the PCTE membranes investigated had FTIR spectra similar to those of polycarbonate from bis(4-hydroxyphenyl)-2-propane, bisphenol A polycarbonate. No BSA peak was revealed in the FTIR spectra of the small-pore membranes fouled with protein, possibly due to the insufficient instrument detection limit. For the membranes with larger pores, however, the BSA peaks increased with increasing pore size. The depth profiling of the fouled membranes indicated a predominant BSA adsorption on the surface or near the pore entries rather than throughout the membrane thickness, confirming the zeta potential ‘model’ and electron microscope observations.

Gas Permeation Characteristics of Zirconia-Silica Composite Membranes at High Temperature.

Permeabilities for pure gases of H2, He, CH4, NH3, H2O, N2, N2, O2 and CO2 were measured at trans-membrane pressures up to 0.2 MPa and 303, 423, 523 and 773 K for two types (with small pores and large pores) of composite zirconia-silica membranes coated on the surface of porous ceramic tubes (0.5μm). The composition of the metal-alkoxides solution used successfully in the coating process was Zr (OC3H7) 4 : 3.09, Si (OC2H5) 4 : 7.20, Y (CH3COO) 3.4H2O : 0.21, i-PrOH : 89.50 in molar %.At low temperatures, with large-and small-pore membranes, the permeation mechanism for H2O, NH3 and CO2 is surface diffusion, and for other gases it is Knudsen flow.At higher temperature, with a large-pore membrane, the permeation mechanism for H2O, NH3, CO, and CH4 is Knudsen flow, and for other gases it is a combination of Knudsen flow and activated diffusion. With a small-pore membrane, for H2O it is Knudsen flow, and for all other gases it is activated diffusion.

BONE-GRAFTING MATERIALS IN IMPLANT DENTISTRY

There are three classes of bone-grafting materials based upon the mode of action. Autogenous bone is an organic material and forms bone by osteogenesis, osteoinduction, and osteoconduction. Allografts such as demineralized freeze-dried bone are osteoinductive and osteoconductive and may be cortical and/or trabecular in nature. Alloplasts such as hydroxyapatite and tricalcium phosphate may be synthetic or natural, vary in size, and are only osteoconductive. They can be divided into three types based upon the porosity of the product and include dense, macroporous, and microporous materials. In addition, alloplastic materials may be crystalline or amorphous. These materials have different properties and therefore indications. The use of the three classes of materials in diverse combinations depends upon the size and topography of the bony defect. Small defects or defects with four walls of host bone can be repaired with alloplasts alone or allografts in combination with alloplasts. The loss of three or more bony walls mandates the addition of autogenous bone to the graft or the use of a small pore membrane. The larger the defect, the more autogenous bone is required. The different indications of bone substitutes are discussed as to their specific applications in implant dentistry.