Protein fouling during microfiltration has been investigated for mixtures of bovine serum albumin (BSA) and lysozyme and of BSA and pepsin. Flux decay curves were analyzed using a recently developed model that accounts for simultaneous pore blockage and cake formation. The model is in good agreement with the data and can be used to evaluate the effect of mixture composition on the concentration of protein aggregates and the properties of the protein deposit. For pepsin–BSA mixtures, the initial fouling appears to be dominated by the BSA, whereas the rate of cake growth occurs primarily by the pepsin. This behavior is consistent with the large concentration of pepsin aggregates and the electrostatic repulsive interactions between the negatively-charged BSA and pepsin. The behavior is more complex for mixtures of BSA and lysozyme. In this case, the fouling is dominated by the lysozyme, although mixtures with small amounts of added BSA foul more slowly than observed with either of the pure proteins.
Ochoa, N. A.
Mixed matrix-composite membranes (MMCM) for gas separation are prepared and characterized in this work. Acrylonitrile-butadiene-styrene (ABS) copolymer was used for the continuum phase of the membrane filled with two different activated carbons (AC). The so-obtained membranes have been characterized by gas permeability, optical microscopy, electronic microscopy and atomic force microscopy. The membranes have different roughness on both their surfaces but are always recovered by the polymeric material. Better ABS-AC adhesion has been always reached giving high selectivity and permeability for CO2/CH4. Such intimate contact can be attributed to the rubber proper-ties of the butadiene-styrene chains in ABS. The morphological characteristics and the increase in both permeability and selectivity with the volume fraction of the filler are explained in terms of the properties of pure activated carbons. (c) 2006 Elsevier Ltd. All rights reserved.
Le, N. L. O.
Sharpless, N. E.
Beausejour, C. M.
Exposure of murine and human tissues to ionizing radiation (IR) induces the expression of p16(INK4a), a tumor suppressor gene and senescence/aging biomarker. Increased p16(INK4a) expression is often delayed several weeks post exposure to IR. In this context, it remains unclear if it occurs to suppress aberrant cellular growth of potentially transformed cells or is simply a result of IR-induced loss of tissue homeostasis. To address this question, we used a conditional p16(INK4a) null mouse model and determined the impact of p16(INK4a) inactivation long-term post exposure to IR. We found that, in vitro, bone marrow stromal cells exposed to IR enter DNA replication following p16(INK4a) inactivation. However, these cells did not resume growth; instead, they mostly underwent cell cycle arrest in G2. Similarly, delayed inactivation of p16(INK4a) in mice several weeks post exposure to IR resulted in increased BrdU incorporation and cancer incidence. In fact, we found that the onset of tumorigenesis was similar whether p16(INK4a) was inactivated before or after exposure to IR. Overall, our results suggest that IR-induced p16(INK4a) dependent growth arrest is reversible in mice and that sustained p16(INK4a) expression is necessary to protect against tumorigenesis.
Otero, J. A.
Calvo, J. I.
Dilute Pb(II) aqueous solutions were nanofiltered through a tubular membrane with good rejections. Retention was modeled using the Modified Spiegler-Kedem theory. The true retention, evaluated from concentration-polarization measurements, was similar to the observed value. The three characteristic parameters of the model: reflection coefficient , solute permeability , and mass transfer coefficient were evaluated simultaneously. The reflection coefficient decreased with an increase in concentration until a plateau was reached at a concentration of 30 ppm. At low concentrations, the solute permeability increased with an increase in concentration, reaching a maximum at a concentration of 30 ppm. Subsequently, the permeability decreased with further increase in concentration, until at concentrations ae 100 ppm, it reached values close to those observed for very dilute solutions (< 10 ppm). Industrial scale nanofiltration of dilute solutions of Pb(II) is viable with high retentions. High pressures and tangential speeds and low temperatures increase retention. Moreover, moderately high concentrations of aqueous Pb(II) solutions can be reduced to totally sure levels in less than four nanofiltration steps. This makes nanofiltration a suitable tool to decrease Pb(II) levels below those recommended by the world health organization.
Lugo, C. Aguilar
Lozano, A. E.
Mixed matrix membranes, MMMs, consisting of variable loads of a porous polymer network, PPN, within an o-hydroxipolyamide, HPA (6FCl-APAF, made from the reaction between 2,2-bis [4-chlorocarbonylphenyl)hexafluoropropane, 6FCl, and 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane, APAF), have been thermally treated to induce the rearrangement of HPA to a polybenzoxazole (beta-TR-PBO). HPA is 6FCl-APAF was loaded with a PPN synthesized, by us, by combining triptycene (TRP) and trifluoroacetophenone (TFAP). Mechanical, thermal and morphological properties of the membranes have been determined. CO2/CH4 selectivity of MMMs decreased slightly both when the PPN load was augmented and when thermal rearrangement took place. The changes in selectivity can be attributed mostly to solubility effects for beta-TR-MMMs and to diffusive effects for the MMM from neat HPA. CO2 and CH4 permeabilities increased to the 2008 Robesoris upper bond for an optimal 30% PPN load both before and after thermal rearrangement. These relatively good permselectivities are explained in terms of compaction, rigidity, fractional free volumes and filling-matrix interactions.
Alves, A. M. Brites
This work presents experimental observations on the permeation of multi-ionic solutions through a commercial DESAL-HL nanofiltration membrane. Two types of mixed-salt solutions have been analysed with a common co-ion (NaCl + Na(2)SO(4)) and with a common counter-ion ((NaCl + MgCl(2))). The NaCl concentrations have been similar to those of seawater with divalent ions with lower concentrations up to a tenth of that of the monovalent salt. In this study. SEDE-VCh model that includes the variation of the charge inside the membrane pores has been used to model the system and structural, electrical and dielectrical membrane parameters for such systems have been obtained. We show that accurate enough predictions can be achieved for the retention of monovalent ions in the presence of counter or co-ion divalent ions from the single NaCl salt results. While correct predictions for the retention of the divalent ions require membrane charges and dielectric constants dependent of the ionic composition of the solutions filtered. (C) 2011 Elsevier B.V. All rights reserved.