Nominal Molecular Weight Cutoff Research Articles

UF fractionation of fish protein hydrolysate

A commercial fish protein hydrolysate was fractionated using polymeric spiral wound ultrafiltration (UF) membranes. As protein hydrolysates are electrolytes, the effects of pH and ionic strength were investigated. Three different polyethersulfones (PES) membranes with different nominal molecular weight cut-offs (10, 5, and 3 kDa) and a polyamide-thin film composite (PA) membrane with a nominal molecular weight cut-off of 3 kDa were used. The membrane flux and retention profile, and the selectivity for <4 kDa peptides were analyzed and discussed. The PES membranes were suitable for fractionation of the hydrolysate, while the PA membrane showed high retention for all components because of the adsorption of solutes to the membrane surface. The results showed that with charged solutes, the nominal molecular weight cut-off as supplied by manufacturers was not the decisive parameter for choosing a membrane. The permeate flux at pH 8 was higher than that at pH 5 for all PES membranes. The presence of salt in the hydrolysate significantly improved the flux and selectivity. The overall retention mainly was dependent on the retention of small peptides (<4 kDa). The mass transfer mechanism of charged peptides within the concentration polarization during UF separation was simplified and presented regarding size and charge exclusions.

New approach to recycle and valorize the first filtrate of the LignoForce system™: Lignin extraction and its use in rigid lignin-based polyurethane foams

In this work, we report on the fractionation, recovery and characterization of softwood kraft lignin from the first filtrate of the LignoForce™ process. It is estimated that the lignin content in this stream could be >20–30 % of the lignin present initially in the black liquor. The use of a membrane filtration system was experimentally validated as an effective method for fractionating the first filtrate. Two membranes with different nominal molecular weight cut-offs (4000 and 250 Da) were tested. Higher lignin retention and recovery was obtained using the 250-Da membrane. This lignin (lignin_250) was found also to have a lower molecular weight and a tighter molecular weight distribution compared to the lignin obtained using the 4000-Da membrane (lignin_4000). The lignin_250 was characterized for it's hydroxyl group content and used to produce polyurethane (PU) foams. Up to 30 wt% petroleum-based polyol replacement by lignin_250, the resulting lignin-based PU (LBPU) foams presented the same thermal conductivity as the control (0.0303 W/m.K (control) vs 0.029 W/m.K (30 wt%)), as well as comparable mechanical (max stress: 145.8 kPa (control) vs 222.7 KPa (30 wt%), modulus 64.3 kPa (control) vs 75.1 (30 wt%)) and morphological properties to the petroleum polyol-based PU foams.

Single-Pass Tangential Flow Filtration (SPTFF) of Nanoparticles: Achieving Sustainable Operation with Dilute Colloidal Suspensions for Gene Therapy Applications.

Recent approval of several viral-vector-based therapeutics has led to renewed interest in the development of more efficient bioprocessing strategies for gene therapy products. Single-Pass Tangential Flow Filtration (SPTFF) can potentially provide inline concentration and final formulation of viral vectors with enhanced product quality due. In this study, SPTFF performance was evaluated using a suspension of 100 nm nanoparticles that mimics a typical lentivirus system. Data were obtained with flat-sheet cassettes having 300 kDa nominal molecular weight cutoff, either in full recirculation or single-pass mode. Flux-stepping experiments identified two critical fluxes, one based on boundary-layer particle accumulation (Jbl) and one based on membrane fouling (Jfoul). The critical fluxes were well-described using a modified concentration polarization model that captures the observed dependence on feed flow rate and feed concentration. Long-duration filtration experiments were conducted under stable SPTFF conditions, with the results suggesting that sustainable performance could potentially be achieved for as much as 6 weeks of continuous operation. These results provide important insights into the potential application of SPTFF for the concentration of viral vectors in the downstream processing of gene therapy agents.

Bitter substances recovery from hot trub: A study of polymeric membranes performance in a sequential mode with fouling investigation

Crossflow membrane technologies were used to clarify and concentrate the raw extract of bitter substances from hot trub, a brewing by-product, seeking to produce an alternative route for hop products via a study performance and fouling investigation. Microfiltration was performed in concentration (MF/CO) and diafiltration (MF/DF) operation modes, feeding with extract composed of lupulone/analogs (∼6 mg/g), iso-α-acid (∼4 mg/g), and humulones/analogs (∼2 mg/g). The MF/CO had ∼69 % bitter substances permeation, while the MF/DF exhibited an increase of about 22 % in relation to MF/CO only (achieving 81–92 % the bitter substances permeation), being colupulone and n-+adlupulone presenting minor retention (<16 %). Adding the diafiltration step had not modified the profile of permeate fluxes curves, which was close to the exhibited by MF/CO. Concerning the sequential nanofiltration approach, six commercial membranes with different thin-film features and nominal molecular weight cut-offs ranging from 1000 to 150 g/mol (NP010 ≥ UA60 > NP030 > XN45 > NF9 > HL) were tested, operating with a clarified extract from MF/DF. XN45 and HL membranes presented higher bitter substance retention with less flux decay (∼42 %) than others. Membrane surfaces were altered after filtrations in relation to chemical profiles, morphology, and hydrophobicity, indicating a foulant layer formation. Different compositions and morphology of foulant layer were observed, being proteins the principal fouling agent for microfiltration while bitter substances were the main agent for nanofiltrations.

SEPARATION OF HEMICELLULOSES FROM AN INDUSTRIAL STREAM BY NANOFILTRATION AND ULTRAFILTRATION PROCESSES

The performance of nanofiltration (NF) and ultrafiltration (UF) membranes was studied for separating hemicelluloses from a highly alkaline industrial stream, containing 17-18 wt% sodium hydroxide, resulting from the viscose process. Initially, screening experiments were performed to select suitable membranes, which were then investigated on a pilot scale spiral module. Screening experiments showed that the UF membrane, with a nominal molecular weight cut-off (MWCO) value of 3 kDa, and the NF one, with a nominal MWCO value of 0.5 kDa, showed a similar range of filtration performance and a flux of 4.2 L/m2.h. Further, a retention efficiency of 50% was observed for the 5 kDa and the 10 kDa membranes, indicating absence of any significant proportion of hemicelluloses in this range of molecular weights. The effects of process conditions were studied to understand their correlation with membrane performance with respect to hemicelluloses retention and permeate flux. UF membranes were found to be more prone to performance deterioration over time and with the number of cycles of usage during the pilot scale study, whereas the NF membrane showed consistent performance. It was seen that feed dilution can improve the membrane performance with respect to sodium hydroxide recovery. Significant reduction in feed viscosity with dilution resulted in a 50% increase in flux after normalizing for concentration.

Effect of Polysaccharide Conformation on Ultrafiltration Separation Performance

The manifold array of saccharide linkages leads to a great variety of polysaccharide architectures, comprising three conformations in aqueous solution: compact sphere, random coil, and rigid rod. This conformational variation limits the suitability of the commonly applied molecular weight cut-off (MWCO) as selection criteria for polysaccharide ultrafiltration membranes, as it is based on globular marker proteins with narrow Mw and hydrodynamic volume relation. Here we show the effect of conformation on ultrafiltration performance using randomly coiled pullulan and rigid rod-like scleroglucan as model polysaccharides for membrane rejection and molecular weight distribution. Ultrafiltration with a 10 kDa polyethersulfone membrane yielded significant different recoveries for pullulan and scleroglucan showing 1% and 71%, respectively. We found deviations greater than 77-fold between nominal MWCO and apparent Mw of pullulan and scleroglucan, while recovering over 90% polysaccharide with unchanged Mw. We anticipate our work as starting point towards an optimized membrane selection for polysaccharide applications.

Influence of fish protein hydrolysate-pistachio green hull extract interactions on antioxidant activity and inhibition of α-glucosidase, α-amylase, and DPP-IV enzymes

This study investigated the effects of protease type (Alcalase, papain and pepsin), fractionation (2 and 10 kDa nominal molecular weight cutoff) and pistachio green hull (PGH) extract addition on antioxidant activity (DPPH radical scavenging and metal chelating activity), α-glucosidase, α-amylase, and dipeptidyl peptidase IV (DPP-IV) inhibitory activity of Sind sardine hydrolysates. Papain led to the highest degree of hydrolysis and antioxidant activity and the addition of PGH enhanced the bioactivity. Hydrolysates and fractions had stronger inhibition of α-amylase than α-glucosidase, and hydrolysates from papain and Alcalase were more active than those from pepsin against α-amylase. Interaction of PGH and the hydrolysates/peptidic fractions resulted in a decrease in α-glucosidase and α-amylase inhibition. The kinetics of α-amylase inhibition with papain hydrolysates and papain-PGH showed competitive inhibition. Hydrolysates and fractions also significantly inhibited DPP-IV, but PGH did not inhibit the enzyme or change the inhibitory effect of the hydrolysates and fractions (P ≥ 0.05). Furthermore, the highest surface hydrophobicity was observed for the >10 kDa fractions and the values increased by the addition of PGH to the hydrolysates. Therefore, PGH–hydrolysate interaction improved only the antioxidant capacity of the protein hydrolysates with nil or negative effects on the enzyme inhibition.

Characterization of dextran transport and molecular weight cutoff (MWCO) of large pore size hollow fiber ultrafiltration membranes

The development of vaccines, gene therapy agents, and virus-like particles has created exciting opportunities for the use of large pore size ultrafiltration membranes in downstream processing. One of the challenges facing both membrane producers and end-users is the difficulty in evaluating the membrane pore size or nominal molecular weight cutoff (MWCO) for the selection of appropriate membranes for targeted separations. We have used a combination of experimental measurements and theoretical modeling to develop an improved methodology for evaluating the MWCO of these large pore size ultrafiltration membranes based on dextran retention measurements. The model accounts for both concentration polarization effects and the intrinsic dextran retention behavior. The results not only provide fundamental insights into the factors controlling dextran retention, but they can also guide membrane manufacturers and end-users to the most appropriate conditions (i.e. feed flow rate and permeate flux) for evaluating the MWCO for hollow fibers with different geometry, pore size, and permeability.

Colloidal toxic trace metals in urban riverine and estuarine waters of Yantai City, southern coast of North Yellow Sea

The environmental characteristics of colloidal toxic trace metals Cd, Cu and Pb in riverine and estuarine waters collected from two urban rivers of Yantai City in eastern China, the Guangdang and Xin'an Rivers, were investigated using a modified centrifugal ultrafiltration (CUF) method in conjunction with acid extraction and inductively coupled plasma mass spectrometry. The target metals in dissolved pool were divided into four CUF fractions, i.e. <1 kDa, 1–3 kDa, 3–10 kDa and 10 kDa–0.2 μm, and the results showed that colloidal Cd, Cu and Pb were dominated by 1–10 kDa (1–3 and 3–10 kDa), 1–3 kDa and 10 kDa–0.2 μm fractions, respectively. The coagulation/flocculation of low-molecular-weight (1–10 kDa) colloidal Cd and Cu in the estuaries was obvious and strong, while the enrichment of dissolved Pb in the 10 kDa–0.2 μm fraction may be mainly related to its biogeochemical interactions with Fe-oxides, which is easy to occur in macromolecular colloids. In addition, the actual molecular weight cutoffs (MWCOs) of the three used CUF units with nominal MWCOs of 1, 3 and 10 kDa were determined to be 4.9, 8.5 and 33.9 kDa, respectively, indicating that membrane calibration is essential for explaining the actual fraction of dissolved trace metals and verifying the integrity of ultrafiltration membrane. Overall, the results in this study provide a further understanding of the heterogeneity in biogeochemical features, migration and fate of toxic trace metals in aquatic ecosystems, especially that of the river-sea mixing zone.

Recovery, overloading, and protein interactions in asymmetrical flow field-flow fractionation

In asymmetrical flow field-flow fractionation (AF4), similar to other separation techniques, mass recovery and overloading require special attention in order to obtain quantitative results. We conducted a systematic study with five globular proteins of different molecular weight (36.7–669 kDa) and isoelectric point (4.0–6.5), and ultrafiltration membranes that are commonly used in aqueous AF4, regenerated cellulose (RC) and polyethersulfone (PES). Phosphate-buffered saline (PBS) with ionic strength 0.15 M and pH 7.2 was used as the carrier liquid in this study. The actual molecular weight cutoff (MWCO) was found to be higher than the nominal value and varied between membranes of different chemistry but the same nominal MWCO. Adsorption on the membrane was found to be dependent on the membrane chemistry (RC had lower adsorption compared to PES), and independent of the protein standard for the examined proteins. On the other hand, the mass overloading effects (i.e., higher retention times, peak broadening, and fronting peaks) were significantly more pronounced for γ-globulin than for the other proteins. The overloading effects could be rationalized with the increase of the local viscosity close to the membrane, depending on the properties of the proteins, and we derived theoretical equations that related the dependency of the migration velocity on the protein concentration through this non-ideal viscosity effect.

Recovery of bruteridin and melitidin from clarified bergamot juice by membrane operations

AbstractFour commercial spiral‐wound membranes with nominal molecular weight cut‐off (NMWCO) from 150–300 to 3,500 Da were tested in order to evaluate their performance in the recovery of brutieridin and melitidin from clarified bergamot juice. Filtration experiments in batch concentration mode were performed on a laboratory filtration membrane equipment in selected operating conditions up to a weight reduction factor (WRF) of 5. The performance of selected membranes was evaluated in terms of permeate flux and rejection coefficients for melitidin, brutieridin, glucose, fructose, and sucrose. Experimental results indicated that the rejection of selected membranes toward melitidin and brutieridin was strictly correlated to their NMWCO. Among the selected membranes, the Desal GE membrane (NMWCO 1,000 Da) offered the best performance in terms of separation between sugars and brutieridin/melitidin in the clarified juice with high retentions toward flavonoids (&gt;67% for melitidin and &gt;82% for brutieridin) and lower retention toward glucose (21.9%) and fructose (10.6%).Practical applicationsBergamot (Citrus bergamia) juice has not found a real use in the food industry due to its bitter taste and it is considered a waste of the essential oil production. On the other hand, flavonoid diglycosides of the juice, such as brutieridin and melitidin, have been recently recognized for their hypocholesterolemic action. The proposed membrane‐based technology offers a valid alternative to the use of conventional purification methodologies for the recovery of this phenolic fraction from the clarified juice and its reuse for the production of fortified juices and functional foods.

Evaluation of ultrafiltration membranes for treating poultry processing wastewater

The US poultry industry produces over 60 billion gallons of poultry processing wastewater (PPW) per year which requires treatment prior to discharge. In this work, nine different commercially available ultrafiltration membranes, having different nominal molecular weight cut-offs (10–300 kDa) and made of different polymeric materials (polyethersulfone and regenerated cellulose), were screened for treating PPW streams obtained from bird washer and chiller operations. Wastewater samples were treated for recycling and reuse purposes. Bird washer wastewater was found to cause more fouling as it contained higher biochemical oxygen demand (BOD), chemical oxygen demand (COD), fat, oil and grease (FOG) and total suspended solid (TSS) compared to the chiller wastewater.The presence of suspended particles can lead to plugging of the membrane pores. Thus, it is important to select the most appropriate membrane (pore size, polymeric material, flux, etc.) that minimizes fouling and maximizes contaminate rejection. For the feed streams considered here, membranes with 30 kDa nominal molecular weight cut-off provided the most stable performance in laboratory scale tangential flow filtration. Larger pore size membranes displayed rapid flux decline most likely due to entrapment of smaller particulate matter within the membrane structure. These particles were excluded from the smaller pore size membrane by size exclusion. The particle size distribution of the feed stream affected the level of contaminate rejection. Significant removal of BOD (up to 93%), COD (up to 94%), TSS (up to 100%) and FOG (up to 100%) was obtained for both wastewater streams.

Evaluation of graphene oxide-coated ultrafiltration membranes for humic acid removal at different pH and conductivity conditions

Abstract Graphene oxides (GO) were coated on three different commercially available polyethersulfone (PES) ultrafiltration membranes (nominal molecular weight cutoffs; 5, 10, and 30 kDa) via a simple vacuum filtration process in our laboratory. The physicochemical properties of resultant membranes were analyzed by Fourier-transform infrared spectroscopy, Raman spectroscopy, field-emission scanning electron microscopy, confocal laser scanning microscopy, and water contact angle measurements. The GO-coated membranes appeared to be more hydrophilic, resulting in approximately 20% higher pure water flux than pristine PES membranes. It was also found that GO nanosheets were not easily damaged or detached from the PES membrane support by filtration or water rinsing due to strong hydrogen bonding interactions between the sulfone and carboxylic groups. Moreover, the humic acid rejection of GO-coated membranes (85.3–93.9%) was significantly higher by approximately 3.4 times depending on various pH and conductivity conditions than that of the pristine PES membranes (25.2–34.8%). Along with the increase in pH and conductivity, HA rejection was slightly increased for both pristine PES and GO-coated membranes: nevertheless, GO-coated membranes (5.3%) were less affected by high pH/conductivity conditions for the humic acid rejection than the pristine PES membranes (19.0%). In particular, it was relatively easier to remove foulant from the GO-coated membrane surface by water rinsing than from the pristine membranes, resulting in high membrane recovery and antifouling capabilities at various pH and conductivity conditions.

Assessment of the efficacy of membrane filtration processes to remove human enteric viruses and the suitability of bacteriophages and a plant virus as surrogates for those viruses

Here, we evaluated the efficacy of direct microfiltration (MF) and ultrafiltration (UF) to remove three representative human enteric viruses (i.e., adenovirus [AdV] type 40, coxsackievirus [CV] B5, and hepatitis A virus [HAV] IB), and one surrogate of human caliciviruses (i.e., murine norovirus [MNV] type 1). Eight different MF membranes and three different UF membranes were used. We also examined the ability of coagulation pretreatment with high-basicity polyaluminum chloride (PACl) to enhance virus removal by MF. The removal ratios of two bacteriophages (MS2 and φX174) and a plant virus (pepper mild mottle virus; PMMoV) were compared with the removal ratios of the human enteric viruses to assess the suitability of these viruses to be used as surrogates for human enteric viruses. The virus removal ratios obtained with direct MF with membranes with nominal pore sizes of 0.1–0.22 μm differed, depending on the membrane used; adsorptive interactions, particularly hydrophobic interactions between virus particles and the membrane surface, were dominant factors for virus removal. In contrast, direct UF with membranes with nominal molecular weight cutoffs of 1–100 kDa effectively removed viruses through size exclusion, and >4-log10 removal was achieved when a membrane with a nominal molecular weight cutoff of 1 kDa was used. At pH 7 and 8, in-line coagulation–MF with nonsulfated high-basicity PACls containing Al30 species had generally a better virus removal (i.e., >4-log10 virus removal) than the other aluminum-based coagulants, except for φX174. For all of the filtration processes, the removal ratios of AdV, CV, HAV, and MNV were comparable and strongly correlated with each other. The removal ratios of MS2 and PMMoV were comparable or smaller than those of the three human enteric viruses and MNV, and were strongly correlated with those of the three human enteric viruses and MNV. The removal ratios obtained with coagulation–MF for φX174 were markedly smaller than those obtained for the three human enteric viruses and MNV. However, because MS2 was inactivated after contact with PACl during coagulation pretreatment, unlike AdV, CV, MNV, and PMMoV, the removal ratios of infectious MS2 were probably an overestimation of the ability of coagulation–MF to remove infectious AdV, CV, and caliciviruses. Thus, PMMoV appears to be a suitable surrogate for human enteric viruses, whereas MS2 and φX174 do not, for the assessment of the efficacy of membrane filtration processes to remove viruses.

Effect of ionic strength on membrane fouling during ultrafiltration of plasmid DNA

Abstract Recent studies have demonstrated that the selectivity of membrane systems for DNA purification can be enhanced by proper selection of solution ionic strength, but these data were all obtained in dilute solutions where fouling is negligible. The objective of this work was to evaluate the effect of solution conditions on the fouling characteristics of both supercoiled and linear plasmid DNA isoforms with different length. Data were obtained using Biomax polyethersulfone ultrafiltration membranes with 300 and 1000 kDa nominal molecular weight cutoffs. Sieving coefficient and filtrate flux data were analyzed using a model based on the partial blockage of the membrane pores by trapped plasmids. Fouling increased dramatically at low ionic strength, with the flux decline parameter for the 3.0 kbp plasmid in a 1 mM NaCl solution being an order of magnitude greater than that in a 10 mM solution. Fouling was also most pronounced for the larger 16.8 kbp plasmid, consistent with the greater probability of plasmid trapping at the pore entrance. These results provide important insights into the development of membrane systems for plasmid DNA filtration in different solution conditions.

Effect of electrostatic interactions on the ultrafiltration behavior of charged bacterial capsular polysaccharides.

Charged polysaccharides are used in the food industry, as cosmetics, and as vaccines. The viscosity, thermodynamics, and hydrodynamic properties of these charged polysaccharides are known to be strongly dependent on the solution ionic strength because of both inter- and intramolecular electrostatic interactions. The goal of this work was to quantitatively describe the effect of these electrostatic interactions on the ultrafiltration behavior of several charged capsular polysaccharides obtained from Streptococcus pneumoniae and used in the production of Pneumococcus vaccines. Ultrafiltration data were obtained using various Biomax™ polyethersulfone membranes with different nominal molecular weight cutoffs. Polysaccharide transmission decreased with decreasing ionic strength primarily because of the expansion of the charged polysaccharide associated with intramolecular electrostatic repulsion. Data were in good agreement with a simple theoretical model based on solute partitioning in porous membranes, with the effective size of the different polysaccharide serotypes evaluated using size exclusion chromatography at the same ionic conditions. These results provide fundamental insights and practical guidelines for exploiting the effects of electrostatic interactions during the ultrafiltration of charged polysaccharides. © 2016 American Institute of Chemical Engineers Biotechnol. Prog., 32:1531-1538, 2016.

Evaluation of Humic Acid and Tannic Acid Fouling in Graphene Oxide-Coated Ultrafiltration Membranes

Three commercially available ultrafiltration (UF) membranes (poly(ether sulfone), PES) that have nominal molecular weight cut-offs (5, 10, and 30 kDa) were coated with graphene oxide (GO) nanosheets. Field-emission scanning electron microscopy, Fourier-transform infrared spectroscopy, confocal laser scanning microscopy, water contact angle measurements, and X-ray photoelectron spectroscopy were employed to determine the changed physicochemical properties of the membranes after GO coating. The water permeability and single-solute rejection of GO-coated (GOC) membranes for humic acid (HA) molecules were significantly higher by approximately 15% and 55%, respectively, compared to those of pristine UF membranes. However, the GOc membranes for single-solute tannic acid (TA) rejection showed similar trends of higher flux decline versus pristine PES membranes, because the relatively smaller TA molecules were readily adsorbed onto the membrane pores. When the mixed-solute of HA and TA rejection tests were performed, in particular, the adsorbed small TA molecules resulted in irreversible membrane fouling due to cake formation and membrane pore blocking on the membrane surface for the HA molecules. Although both membranes showed significantly higher flux declines for small molecules rejection, the GOc membranes showed better performance than the pristine UF membranes in terms of the rejection of various mixed-solute molecules, due to higher membrane recovery and antifouling capabilities.

Betalain rich functional extract with reduced salts and nitrate content from red beetroot (Beta vulgaris L.) using membrane separation technology

An initial laboratory-scale evaluation of separation characteristics of membranes with nominal molecular weight cut-offs (NMWCO) ranging from 30kD down to 0.5kD indicated effective separation of betalains in the 0.5kD region. Subsequent pilot-level trials using 1kD, loose reverse osmosis (LRO) and reverse osmosis (RO) spiral-wound membranes showed LRO membrane to be very efficient with up to 96% salt and 47% other dissolved solids removed while retaining majority of the pigment (∼98%) in the betalain rich extract (BRE). The total betalain content in the BRE increased up to 46%, the highest recovery reported so far at pilot scale level. Interestingly, more than 95% of the nitrates were removed from the BRE after the three diafiltrations. These studies indicate that membrane technology is the most efficient technique to produce BRE with highly reduced amounts of salts and nitrate content.

Size-based separation of supercoiled plasmid DNA using ultrafiltration

HypothesisMost previous studies of membrane-based separations have shown no effect of DNA size on plasmid transmission through small pore size ultrafiltration membranes, consistent with the predicted behavior for flexible polymer chains. However, supercoiled plasmids are known to have a highly “branched” structure with the number of branches dependent on the DNA length. This difference in branching could lead to a significant dependence of the transmission on the plasmid size, providing opportunities for size-based separations using ultrafiltration. ExperimentsData were obtained with 3.0, 9.8, and 16.8kbp plasmids using both cellulosic and polyethersulfone ultrafiltration membranes with different nominal molecular weight cutoffs. Initial experiments were performed with purified samples of the supercoiled and linear isoforms, with the results used to identify appropriate conditions for plasmid separation. FindingsPlasmid transmission increased with increasing filtrate flux due to elongation of the plasmids in the converging flow field. However, the flux dependence was different for each plasmid due to differences in the extent of branching of the twisted supercoiled DNA. This behavior provided a significant selectivity that could be used to separate the 3.0 and 16.8kbp supercoiled plasmids using small pore size ultrafiltration membranes.

Membrane-based purification of proteins from nanoparticle dispersions: Influences of membrane type and ultrafiltration conditions

Abstract The combination of nanoparticles with proteins to form functional hybrid systems is receiving undiminished attention because of its many biotechnological and medical applications. The separation of these hybrid materials from unbound free biomolecules has posed difficult challenges to fractionation and purification. Here, a model study has been carried out by removing proteins (bovine serum albumin (BSA) or lysozyme (LYS)) from the dispersion mixtures with silica nanoparticles (nominal size 20 nm) using ultrafiltration (UF) membranes. Regenerated cellulose (RC) and polyethersulfone (PES) membranes with nominal molecular weight cut-off (NMWCO) of 100 kDa, and a PES UF membrane (NMWCO 300 kDa) functionalized with UV-grafted amphoteric polymer hydrogel layer consisting of N -[3-(dimethylamino)propyl]-acrylamide (DMAPAA) and 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS) and having an experimentally determined cut-off of 180 kDa (identical with the experimental data for PES 100 kDa) were studied. Membrane properties and filtration conditions, in particular pH value and flux, were selected or adapted based on data for single component feeds to achieve maximum protein transmission, complete silica retention and, hence, maximum silica/protein selectivity. Batch dead-end and continuous diafiltration processes were used for fractionation and purification. Overall, the performance of PES UF membranes was inferior compared to the other membranes because of too strong fouling. With membrane RC 100, the transmission data of LYS and BSA from the mixture with silica were 80% and 30%, respectively. With the hydrogel-functionalized PES membrane, the respective transmissions from the mixture were ∼35% and ∼15% for LYS and BSA, respectively. In both cases, quantitative rejection of silica could be achieved. Using continuous diafiltration, membrane RC 100 had better purification efficiency, removing a total of 91% of LYS using 6 diavolumes (DV) in 2.4 h and 84% of BSA using 10 DV in 5.5 h. With the hydrogel-functionalized PES membrane, 82% of LYS and 74% of BSA were removed using 6 and 10 DV within larger time, i.e. 4.0 and 6.8 h, respectively. Importantly, the retained silica nanoparticles remained stable in the dispersion, without any indication of aggregation. Overall, this study will add valuable knowledge to the most efficient use of ultrafiltration sieving properties for the removal or purification of proteins from systems comprising other colloidal particles having a size which is larger by a factor of only 3–10.