Preparation of high-capacity, weak anion-exchange membranes for protein separations using surface-initiated atom transfer radical polymerization

Preparation of Protein A Membranes Using Propargyl Methacrylate-Based Copolymers and Copper-Catalyzed Alkyne-Azide Click Chemistry

The development of convective technologies for antibody purification is of interest to the bioprocessing industries. This study developed a Protein A membrane using a combination of graft polymerization and copper(I)-catalyzed alkyne-azide click chemistry. Regenerated cellulose supports were functionalized via surface-initiated copolymerization of propargyl methacrylate (PgMA) and poly(ethylene glycol) methyl ether methacrylate (PEGMEMA300), followed by a reaction with azide-functionalized Protein A ligand. The polymer-modified membranes were characterized using attenuated total reflectance Fourier-transform infrared spectroscopy (ATR-FTIR), gravimetric analysis, and permeability measurements. Copolymer composition was determined using the Mayo-Lewis equation. Membranes clicked with azide-conjugated Protein A were evaluated by measuring static and dynamic binding (DBC10) capacities for human immunoglobulin G (hIgG). Copolymer composition and degree of grafting were found to affect maximum static binding capacities, with values ranging from 5 to 16 mg/mL. DBC10 values did not vary with flow rate, as expected of membrane adsorbers.

Recent development and application of membrane chromatography

Membrane chromatography is mainly used for the separation and purification of proteins and biological macromolecules in the downstream processing process, also applications in sewage disposal. Membrane chromatography is recognized as an effective alternative to column chromatography because it significantly improves chromatography from affinity, hydrophobicity, and ion exchange; the development status of membrane chromatography in membrane matrix and membrane equipment is thoroughly discussed, and the applications of protein capture and intermediate purification, virus, monoclonal antibody purification, water treatment, and others are summarized. This review will provide value for the exploration and potential application of membrane chromatography.

Preparation of polyvinyl chloride (PVC) membrane blended with acrylamide grafted bentonite for oily water treatment

The current work aims to advance the hydrophilicity, morphology, and antifouling characteristics of polyvinyl chloride (PVC) membranes for oily wastewater separation by incorporating modified bentonite. The surface of bentonite nanoparticles is altered by adopting the "grafting from" method using the surface-initiated atom transfer radical polymerization (SI-ATRP) approach. The PVC-based membrane is first prepared by blending acrylamide grafted bentonite (AAm-g-bentonite). AAm is grafted on bentonite in the presence of 2,2'-Bipyridyl and copper (I) bromide as a catalyst. The modified bentonite nanoparticles are studied using multiple techniques, such as fourier transform infrared spectroscopy (FTIR), thermal gravimetric analysis (TGA), sedimentation tests, field emission scanning electron microscope (FE-SEM), etc. Flat-sheet PVC-based membrane is prepared by blending AAm-g-bentonite using the nonsolvent induced phase separation (NIPS) technique. Different methods, including FE-SEM, FTIR, sedimentation test, contact angle, porosity, antifouling property, and filtration studies of pure and oily water, are used to characterize and determine the performance of mixed-matrix membranes. Membrane performance is improved in the presence of modified bentonite (i.e., AAm-g-bentonite), with the best result achieved at PVC/AAm-g-ben-8 (i.e., 8 wt % of AAm-g-bentonite). Enhanced pure water flux (293.14 Lm^-2h^-1), permeate flux (123.96 Lm^-2h^-1), and oil rejection >93.2% are obtained by the reduced contact angle (49.1°) and improved porosity (71.22%).

Purification of Adeno-Associated Virus (AAV) Serotype 2 from Spodoptera frugiperda (Sf9) Lysate by Chromatographic Nonwoven Membranes

The success of adeno-associated virus (AAV)-based therapeutics in gene therapy poses the need for rapid and efficient processes that can support the growing clinical demand. Nonwoven membranes represent an ideal tool for the future of virus purification: owing to their small fiber diameters and high porosity, they can operate at high flowrates while allowing full access to target viral particles without diffusional limitations. This study describes the development of nonwoven ion-exchange membrane adsorbents for the purification of AAV2 from an Sf9 cell lysate. A strong anion-exchange (AEX) membrane was developed by UV grafting glycidyl methacrylate on a polybutylene terephthalate nonwoven followed by functionalization with triethylamine (TEA), resulting in a quaternary amine ligand (AEX-TEA membrane). When operated in bind-and-elute mode at a pH higher than the pI of the capsids, this membrane exhibited a high AAV2 binding capacity (9.6 × 10¹³ vp·mL^-1) at the residence time of 1 min, and outperformed commercial cast membranes by isolating AAV2 from an Sf9 lysate with high productivity (2.4 × 10¹³ capsids·mL^-1·min^-1) and logarithmic reduction value of host cell proteins (HCP LRV ~ 1.8). An iminodiacetic acid cation-exchange nonwoven (CEX-IDA membrane) was also prepared and utilized at a pH lower than the pI of capsids to purify AAV2 in a bind-and-elute mode, affording high capsid recovery and impurity removal by eluting with a salt gradient. To further increase purity, the CEX-IDA and AEX-TEA membranes were utilized in series to purify the AAV2 from the Sf9 cell lysate. This membrane-based chromatography process also achieved excellent DNA clearance and a recovery of infectivity higher that that reported using ion-exchange resin chromatography.

Iminodiacetic Acid (IDA) Cation-Exchange Nonwoven Membranes for Efficient Capture of Antibodies and Antibody Fragments

There is strong need to reduce the manufacturing costs and increase the downstream purification efficiency of high-value therapeutic monoclonal antibodies (mAbs). This paper explores the performance of a weak cation-exchange membrane based on the coupling of IDA to poly(butylene terephthalate) (PBT) nonwoven fabrics. Uniform and conformal layers of poly(glycidyl methacrylate) (GMA) were first grafted to the surface of the nonwovens. Then IDA was coupled to the polyGMA layers under optimized conditions, resulting in membranes with very high permeability and binding capacity. This resulted in IgG dynamic binding capacities at very short residence times (0.1–2.0 min) that are much higher than those achieved by the best cation-exchange resins. Similar results were obtained in the purification of a single-chain (scFv) antibody fragment. As is customary with membrane systems, the dynamic binding capacities did not change significantly over a wide range of residence times. Finally, the excellent separation efficiency and potential reusability of the membrane were confirmed by five consecutive cycles of mAb capture from its cell culture harvest. The present work provides significant evidence that this weak cation-exchange nonwoven fabric platform might be a suitable alternative to packed resin chromatography for low-cost, higher productivity manufacturing of therapeutic mAbs and antibody fragments.

Synthesis of Cellulose-graft-Polypropionic Acid Nanofiber Cation-Exchange Membrane Adsorbers for High-Efficiency Separations

Fabrication of membrane adsorbers with elevated binding capacity and high throughput is highly desired for simplifying and improving purification efficiencies of bioproducts (biotherapeutics, vaccines, etc.) in the biotechnological and biopharmaceutical industries. Here we demonstrate the preparation of a novel class of self-supported, cellulose-graft-polypropionic acid (CL-g-PPA) cation-exchange nanofiber membrane adsorbers under mild reaction conditions for the purification of positively charged therapeutic proteins. In our fabrication method, acrylonitrile was first polymerized and surface grafted onto cellulose nanofibers using cerium ammonium nitrate as a redox initiator to form cellulose-g-polyacrylonitrile (CL-g-PAN). CL-g-PAN was then submitted to a hydrolyzation reaction to form CL-g-PPA cationic membrane adsorbers. Morphology and structural characterization illustrated the formation of CL-g-PPA membranes with uniform coating of polyacid nanolayers along the individual nanofibers without disturbing the nanofiber structure. Benefiting from these numerous cationic polyacid binding sites and inherent large surface area and open porous structure, CL-g-PPA nanofiber membrane adsorbers showed a lysozyme static adsorption capacity of 1664 mg/g of nanofibers. These membranes showed a lysozyme dynamic binding capacity of 508 mg/g of nanofibers at 10% breakthrough (equivalent to 206 g/L capacity), with a residence time of less than 6 s. Moreover, CL-g-PPA self-supported nanofibers displayed excellent structural stability and reversibility after several cycles of protein binding studies. This dynamic binding capacity of the CL-g-PPA nanofiber membranes was 3.2 times higher than that of macroporous cellulose membranes and 8.5 times higher than that of the Sartobind S commercial membrane adsorber. Considering the simple fabrication method employed, excellent protein adsorption capacity, remarkable structural stability, and reusability, CL-g-PPA nanofiber membranes provided a versatile platform for the chromatographic separations of biomolecules (e.g., proteins, nucleic acids, and viral vaccines) as well as water purification and similar ion-exchange applications.

Electrospun Regenerated Cellulose Nanofiber Membranes Surface-Grafted with Water-Insoluble Poly(HEMA) or Water-Soluble Poly(AAS) Chains via the ATRP Method for Ultrafiltration of Water

Electrospun nanofiber membranes (ENMs) have demonstrated promising applications for water purification primarily due to high water flux and low degree of fouling. However, the equivalent/apparent pore sizes of as-electrospun ENMs are in microns/submicrons; therefore, the ENMs can only be directly utilized for microfiltration applications. To make regenerated cellulose (RC) ENMs for ultrafiltration applications, atom transfer radical polymerization (ATRP) was studied to graft polymer chains onto the surface of RC nanofibers; specifically, monomers of 2-hydroxyethyl methacrylate (HEMA) and sodium acrylate (AAS) were selected for surface-grafting water-insoluble and water-soluble polymer chains onto RC nanofibers, respectively. With prolonging of the ATRP reaction time, the resulting surface-modified RC ENMs had reduced pore sizes. The water-insoluble poly(HEMA) chains coated the surface of RC nanofibers to make the fibers thicker, thus decreasing the membrane pore size and reducing permeability. On the other hand, the water-soluble poly(AAS) chains did not coat the surface of RC nanofibers; instead, they partially filled the pores to form gel-like structures, which served to decrease the effective pore size, while still providing elevated permeability. The surface-modified RC ENMs were subsequently explored for ultrafiltration of ∼40 nm nanoparticles and ∼10 nm bovine serum albumin (BSA) molecules from water. The results indicated that the HEMA-modified RC membranes could reject/remove more than 95% of the nanoparticles while they could not reject any BSA molecules; in comparison, the AAS-modified RC membranes had complete rejection of the nanoparticles and could even reject ∼58% of the BSA molecules.

Preparation of polyamine grafted bentonite by surface-initiated atom transfer radical polymerization for efficient adsorption of Orange I from aqueous solution

A poly(glycidyl methacrylate) grafted bentonite was modified with tetraethylenepentamine to form Bent–PGMA–TEPA which is a good novel adsorbent for OI.

Affinity membrane adsorbers for binding arginine-rich proteins

Delivering protein chemotherapeutics into cancer cells is a challenge. Fusing the protein to an arginine-rich cell-penetrating peptide offers a possible solution. The goal of this work was to develop an affinity membrane for purification of Arg-rich fusion proteins via capture chromatography. Membranes were prepared by grafting polymers bearing diethyl-4-aminobenzyl phosphonate (D4ABP) ligands from macroporous membrane supports. Incorporation of D4ABP was studied by infrared spectroscopy and energy dispersive spectroscopy. Protein binding capacities of 3 mg lysozyme/mL were measured. While further studies are required to evaluate binding kinetics and Arg-selectivity, achieving higher protein binding capacity is needed before investment in such studies.

Layer-by-Layer Deposition with Polymers Containing Nitrilotriacetate, A Convenient Route to Fabricate Metal- and Protein-Binding Films

This paper describes a convenient synthesis of nitrilotriacetate (NTA)-containing polymers and subsequent layer-by-layer adsorption of these polymers on flat surfaces and in membrane pores. The resulting films form NTA-metal-ion complexes and capture 2-3 mmol of metal ions per mL of film. Moreover, these coatings bind multilayers of polyhistidine-tagged proteins through association with NTA-metal-ion complexes. Inclusion of acrylic acid repeat units in NTA-containing copolymers promotes swelling to increase protein binding in films on Au-coated wafers. Adsorption of NTA-containing films in porous nylon membranes gives materials that capture ∼46 mg of His-tagged ubiquitin per mL. However, the binding capacity decreases with the protein molecular weight. Due to the high affinity of NTA for metal ions, the modified membranes show modest leaching of Ni(2+) in binding and rinsing buffers. Adsorption of NTA-containing polymers is a simple method to create metal- and protein-binding films and may, with future enhancement of stability, facilitate development of disposable membranes that rapidly purify tagged proteins.

Protein adsorption by a high-capacity cation-exchange membrane prepared via surface-initiated atom transfer radical polymerization

A weak cation-exchange membrane was prepared via surface-initiated atom transfer radical polymerization of glycidyl methacrylate and subsequent two-step derivation, and then two new parameters were used to explain the protein adsorption behavior.

Functionalizing Microporous Membranes for Protein Purification and Protein Digestion

This review examines advances in the functionalization of microporous membranes for protein purification and the development of protease-containing membranes for controlled protein digestion prior to mass spectrometry analysis. Recent studies confirm that membranes are superior to bead-based columns for rapid protein capture, presumably because convective mass transport in membrane pores rapidly brings proteins to binding sites. Modification of porous membranes with functional polymeric films or TiO₂ nanoparticles yields materials that selectively capture species ranging from phosphopeptides to His-tagged proteins, and protein-binding capacities often exceed those of commercial beads. Thin membranes also provide a convenient framework for creating enzyme-containing reactors that afford control over residence times. With millisecond residence times, reactors with immobilized proteases limit protein digestion to increase sequence coverage in mass spectrometry analysis and facilitate elucidation of protein structures. This review emphasizes the advantages of membrane-based techniques and concludes with some challenges for their practical application.

Immobilization of carboxymethylated polyethylenimine-metal-ion complexes in porous membranes to selectively capture his-tagged protein

Membrane adsorbers rapidly capture tagged proteins because flow through membrane pores efficiently conveys proteins to binding sites. Effective adsorbers, however, require membrane pores coated with thin films that bind multilayers of proteins. This work employs adsorption of polyelectrolytes that chelate metal ions to create functionalized membranes that selectively capture polyhistidine-tagged (His-tagged) proteins with binding capacities equal to those of high-binding commercial beads. Adsorption of functional polyelectrolytes is simpler than previous membrane-modification strategies such as growth of polymer brushes or derivatization of adsorbed layers with chelating moieties. Sequential adsorption of protonated poly(allylamine) (PAH) and carboxymethylated branched polyethylenimine (CMPEI) leads to membranes that bind Ni(2+) and capture ∼60 mg of His-tagged ubiquitin per mL of membrane. Moreover, these membranes enable isolation of His-tagged protein from cell lysates in <15 min. The backbone amine groups in CMPEI likely increase swelling in water to double protein binding compared to films composed of PAH and the chelating polymer poly[(N,N-dicarboxymethyl)allylamine] (PDCMAA), which has a hydrocarbon backbone. Metal leaching from PAH/CMPEI- and PAH/PDCMAA-modified membranes is similar to that from GE Hitrap FF columns. Eluates with 0.5 M imidazole contain <10 ppm of Ni(2+).

Electrospun regenerated cellulose nanofibrous membranes surface-grafted with polymer chains/brushes via the atom transfer radical polymerization method for catalase immobilization

In this study, an electrospun regenerated cellulose (RC) nanofibrous membrane with fiber diameters of ∼200-400 nm was prepared first; subsequently, 2-hydroxyethyl methacrylate (HEMA), 2-dimethylaminoethyl methacrylate (DMAEMA), and acrylic acid (AA) were selected as the monomers for surface grafting of polymer chains/brushes via the atom transfer radical polymerization (ATRP) method. Thereafter, four nanofibrous membranes (i.e., RC, RC-poly(HEMA), RC-poly(DMAEMA), and RC-poly(AA)) were explored as innovative supports for immobilization of an enzyme of bovine liver catalase (CAT). The amount/capacity, activity, stability, and reusability of immobilized catalase were evaluated, and the kinetic parameters (Vmax and Km) for immobilized and free catalase were determined. The results indicated that the respective amounts/capacities of immobilized catalase on RC-poly(HEMA) and RC-poly(DMAEMA) nanofibrous membranes reached 78 ± 3.5 and 67 ± 2.7 mg g(-1), which were considerably higher than the previously reported values. Meanwhile, compared to that of free CAT (i.e., 18 days), the half-life periods of RC-CAT, RC-poly(HEMA)-CAT, RC-poly(DMAEMA)-CAT, and RC-poly(AA)-CAT were 49, 58, 56, and 60 days, respectively, indicating that the storage stability of immobilized catalase was also significantly improved. Furthermore, the immobilized catalase exhibited substantially higher resistance to temperature variation (tested from 5 to 70 °C) and lower degree of sensitivity to pH value (tested from 4.0 and 10.0) than the free catalase. In particular, according to the kinetic parameters of Vmax and Km, the nanofibrous membranes of RC-poly(HEMA) (i.e., 5102 μmol mg(-1) min(-1) and 44.89 mM) and RC-poly(DMAEMA) (i.e., 4651 μmol mg(-1) min(-1) and 46.98 mM) had the most satisfactory biocompatibility with immobilized catalase. It was therefore concluded that the electrospun RC nanofibrous membranes surface-grafted with 3-dimensional nanolayers of polymer chains/brushes would be suitable/ideal as efficient supports for high-density and reusable enzyme immobilization.

Cationic polymer brush-modified cellulose nanocrystals for high-affinity virus binding

Surfaces capable of high-affinity binding of biomolecules are required in several biotechnological applications, such as purification, transfection, and sensing. Therein, the rod-shaped, colloidal cellulose nanocrystals (CNCs) are appealing due to their large surface area available for functionalization. In order to exploit electrostatic binding, their intrinsically anionic surfaces have to be cationized as biological supramolecules are predominantly anionic. Here we present a facile way to prepare cationic CNCs by surface-initiated atom-transfer radical polymerization of poly(N,N-dimethylaminoethyl methacrylate) and subsequent quaternization of the polymer pendant amino groups. The cationic polymer brush-modified CNCs maintained excellent dispersibility and colloidal stability in water and showed a ζ-potential of +38 mV. Dynamic light scattering and electron microscopy showed that the modified CNCs electrostatically bind cowpea chlorotic mottle virus and norovirus-like particles with high affinity. Addition of only a few weight percent of the modified CNCs in water dispersions sufficed to fully bind the virus capsids to form micrometer-sized assemblies. This enabled the concentration and extraction of the virus particles from solution by low-speed centrifugation. These results show the feasibility of the modified CNCs in virus binding and concentrating, and pave the way for their use as transduction enhancers for viral delivery applications.

Membrane adsorbers comprising grafted glycopolymers for targeted lectin binding

This work details the design and testing of affinity membrane adsorbers for lectin purifications that incorporate glucose-containing glycopolymers. It is the selective interaction between the sugar residues of the glycopolymer and the complementary carbohydrate-binding domain of the lectin that provides the basis for the isolation and purification of lectins from complex biological media. The design approach used in these studies was to graft glycopolymer 'tentacles' from macroporous regenerated cellulose membranes by atom transfer radical polymerization. As shown in earlier studies, this design approach can be used to prepare high-productivity membrane adsorbers. The model lectin, concanavalin A (conA), was used to evaluate membrane performance in bind-and-elute purification, using a low molecular weight sugar for elution. The membrane capacity for binding conA was measured at equilibrium and under dynamic conditions using flow rates of 0.1 and 1.0 mL/min. The first Damkohler number was estimated to relate the adsorption rate to the convective mass transport rate through the membrane bed. It was used to assess whether adsorption kinetics or mass transport contributed the primary limitation to conA binding. Analyses indicate that this system is not limited by the accessibility of the binding sites, but by the inherent rate of adsorption of conA onto the glycopolymer.