Filtration Of Protein Solution Research Articles

Hybrid Star-Shaped Block Copolymers for Fabricating Fouling-Resistant Membranes

Star-shaped block copolymers (SPs), comprising a hydrophobic cross-linked polystyrene (PS) core with extended hydrophilic polyethylene glycol (PEG) arms, showed high promise as a class of branched amphiphilic coating material, since the coatability and antifouling properties of the SPs could be tailored simply by tuning the core and/or arm compositions. However, the complex reaction sequences required for synthesizing SPs have been an obstacle for scale-up and, therefore, their practical applications. Herein, we have developed an SP architecture from an inorganic silica nanoparticle (SiO2NP) core, significantly simplifying the synthesis and enabling scale-up at much lower costs. The pressure-assisted coatability of three SiSPs with three different PEG lengths (i.e., SiSP1, SiSP2, and SiSP3 with 28, 54, and 129 PEGMA repeating units) on polysulfone ultrafiltration membranes was evaluated by scanning electron microscopy (SEM) and contact angle measurement. The SiSPs with medium PEG arm length (i.e., SiSP2 with 54 PEGMA repeating units) demonstrated superior thin-layer coatability and UV-induced stabilization. The protein solution filtration exhibited very low fouling, ca. 3% flux decline ratio (FDR) and ca. 97% flux recovery ratio (FRR), for UV-SiSP2 coated PSF UF membrane compared to significant fouling for pristine membrane (ca. 41% FDR and ca. 71% FRR). The three times enhancement in oleophobicity of the SiSP2 coated membrane has endowed almost seven times improvement in the permeation flux during oil emulsion filtration and 100% FRR contrary to zero flux recovery for pristine membrane. This study offers insights regarding the cost-efficient and facile synthesis of block copolymer nanoarchitecture SiSPs, which has the potential for water purification, lubrication, emulsification, and biomedical applications.

Impact of MWCO and Dopamine/Polyethyleneimine Concentrations on Surface Properties and Filtration Performance of Modified Membranes.

The mussel-inspired method has been investigated to modify commercial ultrafiltration membranes to induce antifouling characteristics. Such features are essential to improve the feasibility of using membrane processes in protein recovery from waste streams, wastewater treatment, and reuse. However, some issues still need to be clarified, such as the influence of membrane pore size and the polymer concentration used in modifying the solution. The aim of the present work is to study a one-step deposition of dopamine (DA) and polyethyleneimine (PEI) on ultrafiltration membrane surfaces. The effects of different membrane molecular weight cut-offs (MWCO, 20, 30, and 50 kDa) and DA/PEI concentrations on membrane performance were assessed by surface characterization (FTIR, AFM, zeta potential, contact angle, protein adsorption) and permeation of protein solution. Results indicate that larger MWCO membranes (50 kDa) are most benefited by modification using DA and PEI. Moreover, PEI is primarily responsible for improving membrane performance in protein solution filtration. The membrane modified with 0.5:4.0 mg mL−1 (DA: PEI) presented a better performance in protein solution filtration, with only 15% of permeate flux drop after 2 h of filtration. The modified membrane can thus be potentially applied to the recovery of proteins from waste streams.

MEMBRANES MODIFIED BY NANOCOMPOSITES OF HYDRATED ZIRCONIUM DIOXIDE AND OXIDIZED GRAPHENE

Organo-inorganic membranes were obtained by impregnating ultrafiltration membranes with a composite modifier - zirconium (IV) hydroxide, containing oxidized graphene (0.5 wt.%). The modifier was precipitated in the active layer of the membrane, thus forming a "secondary active layer". The layer thickness calculated according to the Kozeny-Carman equation is 0.66-1.38 μm. A thinner layer is formed in the membrane with smaller pore size. The diffusion coefficients of Li+ and Na+ ions were found. The effect of the modifier on the retention ability relative to hardness ions (10-14%) and to protein compounds (95-98%) during filtration is determined. Mathematical modeling of the dependence of the permeate flux via time showed that the presence of ion exchanger particles in the polymer active layer prevents the accumulation of organic substances in the pores. Therefore, only the outer surface of the membrane is contaminated, and the precipitate can be easily removed mechanically. It was shown that insertion of a carbon component into pores of the membranes, in addition to the inorganic ion-exchangers, is advisable only in the case of a finely porous active layer. In particular, the performance of the initial polymer membrane (20 dm3/m3.h)) and the selectivity to the calibration substance with a molecular weight of 40 kDa (99%) serve as expediency criteria. In comparison with a membrane modified only with inorganic ion exchanger, selectivity is increased, the rate of filtration of protein solutions is higher, and resistance to contamination by organic substances is achieved. The results are discussed from the view of the hydrophobic-hydrophilic properties of oxidized graphene.

Filtration of Uncharged Solutes: An Assessment of Steric Effect by Transport and Adsorption Modelling

The major aim of this work was to understand and estimate the evolution of the membrane selectivity of neutral solutes after the filtration of protein or amino acid solutions. Classical methodologies led to the estimation of the mean pore radius, different for each filtrated neutral solute. The use of pore size distribution from nitrogen adsorption/desorption experiments enabled a good description of hydraulic and selectivity performances. The modification of the membrane hydraulic properties after the successive filtration of protein solutions revealed that the decrease is quasi linear, the same for all the studied membranes and independent of prior tests. According to the experimental observations, an adsorption model was developed, considering a layer by layer adsorption in the larger pores of the membrane. The predictive obtained results are in good agreement with the experimental rejection rates, validating the assumptions.

Microscopic visualization of virus removal by dedicated filters used in biopharmaceutical processing: Impact of membrane structure and localization of captured virus particles.

Virus filtration with nanometer size exclusion membranes (“nanofiltration”) is effective for removing infectious agents from biopharmaceuticals. While the virus removal capability of virus removal filters is typically evaluated based on calculation of logarithmic reduction value (LRV) of virus infectivity, knowledge of the exact mechanism(s) of virus retention remains limited. Here, human parvovirus B19 (B19V), a small virus (18–26 nm), was spiked into therapeutic plasma protein solutions and filtered through Planova™ 15N and 20N filters in scaled‐down manufacturing processes. Observation of the gross structure of the Planova hollow fiber membranes by transmission electron microscopy (TEM) revealed Planova filter microporous membranes to have a rough inner, a dense middle and a rough outer layer. Of these three layers, the dense middle layer was clearly identified as the most functionally critical for effective capture of B19V. Planova filtration of protein solution containing B19V resulted in a distribution peak in the dense middle layer with an LRV >4, demonstrating effectiveness of the filtration step. This is the first report to simultaneously analyze the gross structure of a virus removal filter and visualize virus entrapment during a filtration process conducted under actual manufacturing conditions. The methodologies developed in this study demonstrate that the virus removal capability of the filtration process can be linked to the gross physical filter structure, contributing to better understanding of virus trapping mechanisms and helping the development of more reliable and robust virus filtration processes in the manufacture of biologicals.

Investigation of fouling mechanisms of virus filters during the filtration of protein solutions using a high throughput filtration screening device.

The downstream process development of novel antibodies (Abs) is often challenged by virus filter fouling making a better understanding of the underlying mechanisms highly desirable. The present study combines the protein characterization of different feedstreams with their virus filtration performance using a novel high throughput filtration screening system. Filtration experiments with Ab concentrations of up to 20 g/L using either low interacting or hydrophobically interacting pre-filters indicate the existence of two different fouling mechanisms, an irreversible and a reversible one. At the molecular level, size exclusion chromatography revealed that the presence of large amount of high molecular weight species-considered as irreversible aggregates-correlates with irreversible fouling that caused reduced Ab throughput. Results using dynamic light scattering show that a concentration dependent increase of the mean hydrodynamic diameter to the range of dimers (17 nm at 20 g/L) together with a negative DLS interaction parameter kD (-18 mL/g) correlate with the propensity to form reversible aggregates and to cause reversible fouling, probably by a decelerated Ab transport velocity within the virus filter. The two fouling mechanisms are further supported by buffer flush experiments. Finally, concepts for reversible and irreversible fouling mechanisms are discussed together with strategies for respective fouling mitigation. © 2019 American Institute of Chemical Engineers Biotechnol. Prog., 35: e2776, 2019.

Analysis of Membrane Fouling Reduction by Natural Convection Instability Flow in Membrane Filtration of Protein Solution Using Blocking Filtration Model

Analysis of Membrane Fouling Reduction by Natural Convection Instability Flow in Membrane Filtration of Protein Solution Using Blocking Filtration Model

Temporal evolution of the selectivity-permeability relationship during porous membrane filtration of protein solutions

Currently, there is no clear understanding on the effects of membrane properties on temporal evolution of membrane selectivity-permeability relationships during microfiltration or ultrafiltration-based water treatment. In this study, porous polyvinylidene fluoride (PVDF) membrane, polyvinyl chloride membrane, and glass-fiber membrane with distinctive physical and chemical properties were employed to filter bovine serum albumin (BSA) at different pH, coupled with model simulation approaches. Both the experimental results and model prediction showed that, due to the existence of different filtration mechanisms, selectivity of the PVDF membrane and the PVC membrane increase with decreasing permeability, whereas an opposite trend was observed for the glass-fiber membrane. Also, pH strongly affected permeability by changing the zeta potentials of the solutes and the membrane surfaces. Moreover, membrane selectivity was less significantly affected by pH for the polymeric membranes than for the glass-fiber membrane. Practically, high selectivity and permeability may be simultaneously achieved during water treatment by: (1) selection of membranes with suitable pore structure (such as control of solute diameter >1/5 pore diameter); (2) control of feed water condition (such as pH) to suppress intermolecular interactions or solute-membrane interactions, further influence the deposition/adsorption of solute on membrane.

Biocatalytic Self-Cleaning Polymer Membranes

Polymer membrane surfaces have been equipped with the digestive enzyme trypsin. Enzyme immobilization was performed by electron beam irradiation in aqueous media within a one-step method. Using this method, trypsin was covalently and side-unspecific attached to the membrane surface. Thus, the use of preceding polymer functionalization and the use of toxic solvents or reagents can be avoided. The resulting membranes showed significantly improved antifouling properties as demonstrated by repeated filtration of protein solutions. Furthermore, the biocatalytic membrane can be simply “switched on” to actively degrade a fouling layer on the membrane surface and regain the initial permeability. The membrane pore structure (pore size and porosity) was neither damaged by the electron beam treatment nor blocked by the enzyme loading, ensuring a stable membrane performance.

Zwitterionic copolymer self-assembly for fouling resistant, high flux membranes with size-based small molecule selectivity

Membranes that exhibit size-based rejection between small molecules (<1500g/mol) independent of solute charge would be valuable for many separations, but commercial membranes show poor and unpredictable selectivity at this size range. This arises from high pore size polydispersity and charged membrane surfaces that lead to separations affected by solute charge. Furthermore, these membranes are susceptible to fouling. Self-assembly is a promising technique for making polymeric membranes with fouling resistance, high permeability and selectivity along with opportunity for easy fabrication and scalability. We report the first examples of a new class of membrane materials that derive their permeability, size-based selectivity and fouling resistance from the self-assembly of zwitterion-containing amphiphilic random copolymers. Zwitterionic groups strongly resist biomacromolecular fouling due to their high affinity with water, and self-assemble into channel-type clusters of 0.6–2nm in size. We show that these copolymers self-assemble into bicontinuous nanodomains. Thin film composite membranes formed by coating these copolymers onto porous supports exhibit permeances as high as 8.4Lm−2h−1bar−1, over three times that of a commercial membrane with similar MWCO. They show size-based selectivity, with a cut-off around 1nm. This closely matches the size of zwitterionic domains measured by transmission electron microscopy, indicating permeation occurs through these self-assembled “nanochannels.” These membranes show excellent fouling resistance during filtration of protein solutions and oil emulsions, completely resisting irreversible fouling and retaining over 96% of their permeance during filtration. These membranes have potential uses in biomolecule separations, purification of pharmaceuticals, and wastewater treatment.

A novel membrane showing both hydrophilic and oleophobic surface properties and its non-fouling performances for potential water treatment applications

Membrane organic and biological fouling has been one of the major problems for membrane technology applications in water and wastewater treatment. In this study, a novel membrane showing both hydrophilic and oleophobic surface properties was developed and evaluated for its resistance against organic and biological fouling. The membranes in flat sheet configuration were prepared from PVDF as the base matrix polymer, blended with an additive polymer that was synthesized to contain both hydrophilic and oleophobic segments. The prepared novel membranes displayed high affinity to water but low affinity to oil. Experimental results from the filtration of protein solution, humic acid solution and oil/water emulsion confirmed that the developed membranes had greatly enhanced water flux and reduced organic fouling performance (shown as slow flux decay and high flux recovery after membrane cleaning). In the biofouling tests with the developed membranes being immersed in bacteria suspension or used for the filtration of bacteria suspension, it was found that the novel membranes effectively prevented bacteria adhesion on the membrane and the flux decay incurred during the filtration can be fully recovered after a simple cleaning with water under the experimental conditions. This study also demonstrated that a membrane surface showing both hydrophilic and oleophobic surface properties provided an effective and better way to reduce the effect of membrane fouling by organic as well as biological foulants than a membrane surface showing the hydrophilic property only. The developed membrane has a great potential for water and wastewater treatment applications.

Hydrophilic modification of poly(vinylidene fluoride) membrane with poly(vinyl pyrrolidone) via a cross‐linking reaction

AbstractA highly hydrophilic hollow fiber poly(vinylidene fluoride) (PVDF) membrane [PVDF‐cl‐poly(vinyl pyrrolidone) (PVP) membrane] was prepared by a cross‐linking reaction with the hydrophilic PVP, which was immobilized firmly on the outer surface and cross‐section of the PVDF hollow fiber membrane via a simple immersion process. The cross‐linking between PVDF and PVP was firstly verified via nuclear magnetic resonance measurement on PVP solution after cross‐linking. The hydrophilic stability of the modified PVDF membrane was evaluated by measuring the pure water flux after different times of immersion and drying. The anti‐fouling properties were estimated by cyclic filtration of protein solution. When the cross‐linking time was as long as 6 hr and the PVP content reached 5 wt %, the pure water flux (Jv) was constant as ∼ 600 L m−2 hr−1. The hydrophilicity of the PVDF‐cl‐PVP membrane was significantly enhanced and exhibited a good stability. The PVDF‐cl‐PVP membrane showed an excellent anti‐protein‐fouling performance during the cyclic filtration of bovine serum albumin solution. Therefore, a highly hydrophilic and anti‐protein‐fouling PVDF hollow fiber membrane with a long‐term stability can be prepared by a simple and economical cross‐linking process with PVP. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

Hydrophilic modification of P(VDF- co-CTFE) porous membranes

This paper describes fabrication of a poly(vinylidene difluoride- co-chlorotrifluoroethylene) (P(VDF- co-CTFE)) porous membrane via non-solvent induced phase inversion and subsequent hydrophilic modification using high efficient surface initiated atom transfer radical polymerization (ATRP). The effect of viscosities of casting solutions on microstructures of the P(VDF- co-CTFE) membrane was investigated. The surface chemistry, thermal stability, morphological structure, and hydrophilicity of the modified membranes were evaluated by Fourier Transform Infrared Attenuated Total Reflection (FTIR-ATR), Differential Scanning Calorimeter (DSC), Scanning Electron Microscope (SEM), and contact angle measurements, respectively. The degree of grafting and the degree of swelling were measured to analyze the effect of polymerization time on the wettability. The mechanical strength of the membranes after modification was also investigated. The permeability and fouling resistance were evaluated according to pure water flux and protein solution filtration measurements. The results demonstrate that the hydrophobic P(VDF- co-CTFE) membrane can be feasibly modified by immobilization of hydrophilic poly(ethylene glycol) methyl ether methacrylate (PEGMA) brushes via surface initiated ATRP.

Fabrication of non-woven composite membrane by chitosan coating for resisting the adsorption of proteins and the adhesion of bacteria

A facile and effective method, chitosan coating and glutaraldehyde crosslink combined with pretreatment by ozone was developed for endowing non-woven membrane with an antifouling and antibacterial surface. Characteristics of these composite membranes were monitored by Fourier transform infrared-attenuated total reflectance, X-ray photoelectron spectroscopy, water contact angle, and environment scanning electron microscopy. The carbonyl and carboxyl functional groups were generated on the membrane surface after ozone pretreatment. The hydrophilicity of the composite membrane surface was improved. No obvious influence was observed on the structure of the membrane bulk while the membrane surface became smoother after coating. The static adsorption of protein on the composite membrane significantly decreased comparing with the original membrane. The relatively higher flux recovery ratio of permeation flux for protein solution filtration was obtained for the composite membrane. Furthermore, antibacterial properties of the composite membranes were investigated by staining and growth inhibition. The results indicated that there were less bacteria attached onto the composite membranes. The composite membrane was thus demonstrated to be very effective in preventing the formation of biofilm, especially for the membrane with glutaraldehyde crosslink.

Highly hydrophilic and low-protein-fouling polypropylene membrane prepared by surface modification with sulfobetaine-based zwitterionic polymer through a combined surface polymerization method

Poly(sulfobetaine methacrylate) [poly(SBMA)], a zwitterionic polymer, was successfully tethered in high density onto polypropylene (PP) membrane surface through a combined method consisting of UV-induced surface graft polymerization followed by surface-initiated atom transfer radical polymerization (ATRP). 2-Hydroxyethyl methacrylate (HEMA) was first immobilized onto PP membrane surface by UV-induced graft polymerization, and then each of the grafted poly(HEMA) chains, after coupled with 2-bromopropionyl groups, provided multiple initiation sites for subsequent ATRP of SBMA. Images from scanning electron microscope (SEM) showed that the membrane surface was fully covered with small dot-like surface structures of poly(SBMA) after 6 h of ATRP. Both attenuated total reflectance Fourier transform infrared spectroscopy (FTIR/ATR) and X-ray photoelectron spectroscopy (XPS) confirmed the grafted poly(HEMA) and poly(SBMA) on the membrane surface. Water contact angle measurements showed that the surface hydrophilicity of the PP membrane was improved significantly with the increase of the grafted poly(SBMA) content, and a water contact angle of as low as 17.4° was obtained in this study. Experimental results for protein solution filtration demonstrated that the extent of fouling was significantly reduced and most of the fouling on the modified PP membrane surface was reversible, suggesting good anti-protein-fouling performance.

Fouling Reduction by Graft‐Modification with Hydrophilic Polymers

Flat sheet polypropylene microfiltration membranes were successfully graft‐modified with acrylic acid using the macroinitiator method. The surface modification induced a change in the course of fouling. Unmodified membranes showed the strong form of critical flux during filtration of protein solution, while for the surface modified membranes the weak form of critical flux was determined. Although the critical flux could be shifted towards higher values (from ca. 20 l/m2h to>40 l/h2m) by the surface modification, the permeability decreased by a factor of 6.

Biomimetic surface modification on polyacrylonitrile-based asymmetric membranes via direct formation of phospholipid moieties

To improve the antifouling property and biocompatibility for polyacrylonitrile-based asymmetric membranes, phospholipid moieties were directly anchored on the poly(acrylonitrile- co-2-hydroxyethyl methacrylate) (PANCHEMA) membrane surface through the reaction of hydroxyl groups and 2-chloro-2-oxo-1,3,2-dioxaphospholane (COP) followed by the ring-opening of COP with trimethylamine. Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy and water contact angle measurement were employed to confirm the conducted surface modification. Water and protein solution filtration tests plus cell adhesion measurement were used to evaluate the antifouling property and the biocompatibility of the membranes. It was found that the content of the phospholipid moieties on the membrane surface, which can be mainly modulated by the content of reactive hydroxyl groups in PANCHEMA, has a great influence on the performances of the studied membranes. With the increase in the phospholipid moieties content at the modified membrane surface, the hydrophilicity and biocompatibility on the basis of water contact angle and macrophage adhesion can be improved significantly. Furthermore, the modified membranes show higher water and protein solution fluxes, and better flux recovery after cleaning than those of the original PANCHEMA membranes. All these results reveal that the antifouling property and biocompatibility of PANCHEMA membrane could be enhanced obviously by the introduction of phospholipid moieties on the membrane surface.

Flux stabilization of silicon nitride microsieves by backpulsing and surface modification with PEG moieties

The influence of the surface properties of chemically modified silicon nitride microsieves on the filtration of protein solutions and defatted milk is described in this research. Prior to membrane filtrations, an antifouling polymer based on poly(ethylene glycol), poly(TMSMA-r-PEGMA) was synthesized and applied on silicon-based surfaces like silicon, silicon nitride, and glass. The ability of such coating to repel proteins like bovine serum albumin (BSA) was confirmed by ellipsometry and confocal fluorescence microscopy. In BSA and skimmed milk filtrations no differences could be seen between unmodified and PEG-coated membranes (decreasing permeability in time). On the other hand, reduced fouling was observed with PEG-modified microsieves in combination with backpulsing and air sparging.

An approach to membrane fouling characterization by confocal scanning laser microscopy

Confocal scanning laser microscopy (CSLM) is an optical microscopic technique that, among other advantages, can provide high-resolution images from different depths of a three-dimensional object, therefore rendering invasive techniques unnecessary for sample preparation. CSLM in fluorescence mode is a powerful technique in biological applications and in the microscopy of food materials. The main goal of the present study is to develop the appropriate strategies so that CSLM can be used for membrane fouling characterization during the filtration of protein solutions. Single and binary solutions of BSA–fluorescein and ovalbumin–Texas red conjugates were filtered using 0.8 μm polycarbonate membranes. Samples of the membranes at the end of the filtration runs were analyzed by CSLM. A standardized protocol for sample analysis by CSLM was developed and applied in this study. The most significant results show that CSLM can be used to visualize BSA–fluorescein and ovalbumin–Texas red conjugates on top of and inside the membranes, and that they can be distinguished when they jointly foul the membrane. Finally, if the appropriate sectioning is applied a 3D reconstruction of the membrane and the adsorbed/deposited protein can be obtained which give information on the fouling morphology.

Membrane filtration.

The filtration of protein solutions, especially in the manufacture of biologically derived proteins, is a large and increasingly important step in the production of protein pharmaceuticals. The focus of this chapter is on the use of membrane filters for purification and sterilization of protein pharmaceuticals. However, we also review other important uses of membranes and nonmembrane filters in the production of protein pharmaceuticals. The reader is directed to several useful reference books that describe in more detail both the theory and the practice of filtration in the biopharmaceutical industry (Cheryan, 1986; Ho and Sirkar, 1992; Johnston, 1992a; Meltzer, 1987; Meltzer and Jornitz, 1998). Additional discussion of interactions between filters and protein formulations can be found in Chapters 2 and 3. The appendix to this chapter contains definitions of terms for those readers unfamiliar with terminology of membrane filtration.KeywordsCleaning AgentFinal FilterProtein PharmaceuticalBiopharmaceutical IndustryRejection CoefficientThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.