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This study investigated the impact of membrane pore morphology on repeated fouling and physical cleaning behavior during > 1000 h operation of a membrane bioreactor process. Four microfiltration membranes with different backbone polymers (PVDF and PTFE) and varied hydrophobicity, operated in parallel, were compared. The PVDF membranes presented a porous particulate-packing morphology, while the PTFE/PVDF blend membranes (PTFE accounting for > 80% of monomer proportion) resembled a nonwoven network of thin fibrous material. These membranes had similar short-term apparent fouling rates in a single fouling-and-cleaning cycle, but different long-term fouling development due to their physical cleaning efficiencies differing in the order: hydrophobic PVDF << hydrophobic blend < hydrophilic (PVDF and blend) membranes, as revealed by statistical analyses. The physically irreversible fouling was likely attributed to hydrophobic adsorption onto the membranes, with the adsorbed polysaccharides and proteins detected using confocal laser scanning microscopy. The irreversibility of fouling on the blend membranes was much less sensitive to membrane hydrophobicity than that on the PVDF membranes, probably because the blend membranes had smaller adsorption propensity. For further evidence, the adsorption properties of the membranes were explored via batch tests of dynamic adsorption using model compounds, with the adsorption rate and equilibrium constants quantified using the Thomas model. The thin thread-like pore walls (which characterized the morphology of the blend membranes) may provide limited contact area for foulant adsorption, and/or weaken the interfacial membrane–foulant interaction via shape effect. Therefore, it is suggested that membranes with thin fibrous network-like pore morphology may perform more robustly and be less troubled by adsorptive irreversible fouling for long-term operation of MBR. [ABSTRACT FROM AUTHOR]

Virus filters provide size-based removal of >99.9% of viruses and virus-like particles during biopharmaceutical processing. Here, we quantitatively evaluate the 3D pore space and virus capture behavior in two commercial virus removal filters with very different morphologies: the highly asymmetric Viresolve® Pro and the relatively homogeneous Pegasus™ SV4 virus filters. Focused ion beam (FIB) – SEM was used to reconstruct the 3D pore morphology of both virus filters. The Pegasus™ SV4 filter had pores that were, on average, significantly larger than 20 nm, which is the size of small parvovirus (as well as the average size of the pore throats near the exit of the Viresolve® Pro filter). Virus retention within each membrane was simulated using GeoDict®, which evaluates the detailed particle trajectories and capture locations through the filter. The Pegasus™ SV4 filter showed virus capture throughout a significant fraction of the filter depth, in contrast to virus capture in the Viresolve® Pro filter that occurred only in the very small pores in the 2 μm region near the filter exit. In both cases, viruses were captured in highly restrictive regions within the pore space. These results provide new insights into the impact of pore morphology on virus capture during virus removal filtration. [Display omitted] • 3D pore morphology of two virus filters evaluated by focused ion beam – SEM. • Quantitative comparison of pore space performed using a pore-network model. • Model simulations of particle trajectories confirm high level of virus removal. • Virus capture profiles depend on detailed morphology of pore space. [ABSTRACT FROM AUTHOR]

Abstract: To develop the large-scale production of alkali-resistant Shirasu porous glass (SPG) membranes based on phase separation and subsequent acid leaching, the crystallization and phase separation in mother glasses in the NaO–CaO–Al2O3–B2O3–SiO2 system containing ZrO2 were investigated. A crystalline phase of wollastonite (CaSiO3) was formed in the ZrO2-free mother glass heat-treated at approximately 900°C, corresponding to the glass-shaping temperature. This crystallization was induced by the phase separation in the mother glass. The crystallization tendency was reduced by adding ZrO2 to the mother glass due to an increase in the glass viscosity, and there was no crystallization in the mother glass with 3.5mol.% ZrO2. SPG membranes containing 3mol.% ZrO2 were successfully prepared from the mother glass with 3.5mol.% ZrO2 by the phase separation of the mother glass at 700–760°C and subsequent acid leaching with a 0.5moldm−3 hydrochloric acid. The membranes had an interconnected pore structure over a wide pore diameter range of 0.1–10μm. The membrane pore diameter increased with increasing heat-treatment temperature and holding time during the phase-separation process for the mother glass. The alkali resistance of the membranes was about 3.5 times higher than that of conventional SPG membranes. [Copyright &y& Elsevier]

The control of membrane pore size is critical for the separation efficiency of the isotopic separation of 235/238U in the conventional uranium enrichment process by gaseous diffusion. Theoretical evaluations generally assume that the pores are cylindrical, however the actual pore morphology could be completely different. Here, we consider the case of pores with rectangular slit morphology (‘groove-like’ pores) of width l and length D (when D≫l). We evaluate the separation factor α for membranes consisting of a mixture of ‘cylindrical’ and ‘rectangular’ pores. These two shapes may be considered as two extreme cases of pore morphology, and it is possible to represent any arbitrary actual morphology approximately as a mixture of such pores. In addition, the existence of defects on membranes, such cracks, crevices, grooves, etc. may severely affect membrane performance; and this will be more critical the smaller the pores. Here, we also use this ‘rectangular’ model to study the influence of such cracks on the separation efficiency of membranes. [Copyright &y& Elsevier]

Virus removal filters are designed to ensure very high levels of removal of viruses and virus-like particles during bioprocessing, but the performance of some virus removal filters can be compromised at high-throughputs, after process disruptions, or during operation at low pressures. Several studies have hypothesized that the different behavior is due to differences in underlying pore morphology, but current techniques are limited to examining the 2D pore structure. Here, we use the combination of a focused ion beam and scanning electron microscopy (FIB-SEM) to obtain 3D reconstructions of the pore structure of the asymmetric Viresolve® Pro virus removal filter. Images were obtained through a 3 μm section into the membrane starting at the size-selective skin. The membrane porosity decreases from 41 to 17% as one approaches the filter exit. Model simulations based on flow through the full 3D pore reconstruction show 100% virus retention, with all virus particles captured at least 400 nm from the filter exit. A pore-network model was developed from the reconstructions and used to evaluate the body and throat size distribution and pore interconnectivity. The number of throats is approximately twice the number of bodies, with an average throat size of 21 nm within the selective skin. The pore interconnectivity remains relatively constant at a value of 4 throats per body. These results provide insights into the underlying pore structure of the Viresolve® Pro virus removal filter as well as a general framework for characterizing the 3D pore space in nanoporous membranes. [Display omitted] • FIB-SEM tomography reveals 3D morphology of virus removal filters. • Open and closed porosity reported throughout depth of virus retentive region. • Model simulations show 100% virus retention near previously reported capture region. • Pore-network models generated from 3D structures. • Network model enabled calculation of virus retentive pore diameter and connectivity. [ABSTRACT FROM AUTHOR]

Nitrocellulose membrane (NC), as a paper-like matrix with microscale porous structures, has found widespread applications in biomedical fields due to its excellent biological features and physiochemical properties. In these biomedical applications, diffusion, convection, and binding reaction of biomolecules (e.g., acids and proteins) in NC through wicking flow is the fundamental physical process. However, the optimization of NC based biomedical devices has been limited by the lack of the understanding on the wicking flow behavior of NC membranes from the microstructural point of view. To address this, we experimentally and theoretically investigated the microstructural effects on the wicking flow behaviors (e.g., permeability, effective pore radius) of NC membrane and found that the wicking flow is highly dependent on the pore-morphology characterizing parameters (e.g., porosity and pore size). We further developed a theoretical model yielding a closed-form solution to predict the microstructure-permeability relation, which was validated by our experimental results. Our theoretical model would be a powerful tool for tailoring the wicking flow behavior of NC membranes through controlling the microstructural parameters, and thus for optimizing NC membrane-based biomedical devices from the view point of material design in the future. • The pore microstructure of NC membranes was characterized based on SEM images. • The permeability and effective pore radius was measured by rate-of-rise experiment. • A geometrical model was proposed to represent the pore morphology of NC membranes. • The particle-cubic model was verified by pore-morphology characterizing data. • Given the particle size constant, the denser stacking leads to a lower permeability. [ABSTRACT FROM AUTHOR]