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

Bioseparation using membrane chromatography: Innovations, and challenges

The resin-based column continues to be the dominant incumbent in bioprocess chromatography. While alternative formats such as membrane-, monolith- and fiber-based chromatography are more visible than before, each still plays minor roles. The reasons for this are complex and some of these are explained in this paper. However, the fact remains that membrane chromatography has come a long way since its early days of development. The main advantage of membrane chromatography continues to be its convection dominant transport mechanism, the resultant benefit being fast and scalable separation. Also, resolution obtained with properly designed devices could be comparable or even better than resin-based chromatography. Significant progress has been made in new membrane development, membrane characterization, device design and novel applications development. A wider range of new membrane matrices, ligands, and ligand-matrix linking chemistries are now available. New membrane modules, formats, and process configurations have also helped improve membrane performance. However, some significant challenges still exist, and these need to be addressed if membrane chromatography is to become more mainstream in the field of bioprocessing. Also, membrane chromatography has significant potential for application in analytical separations and this space has hardly been explored. In this paper, the advances in the areas of membrane preparation, device design and process development are reviewed. A high-level cost analysis is presented and the role of process design in membrane chromatography is discussed.

Quaternized Nanofiber-Based Anion-Exchange Chromatography Membrane with Periodic Diagonal Surface Structure for Efficient Protein Separation

Constructing a nanofibrous membrane with high flow rate surface pore structure and high-density ligand chemical structure is a promising strategy to balance the trade-off between high flow rates and high adsorption capacity for protein separation and purification. Herein, a nanofiber-based ion-exchange chromatography membrane with a periodic diagonal surface structure and high ionic strength ligands was fabricated using dispersion in situ cross-linking, wet coating, and template printing with a three-wire diagonal woven mesh. For this membrane, EVOH nanofibers were used as skeleton, glutaraldehyde (GA) as cross-linking agent, and quaternized chitosan (QCS) as binder and functional ligand. The results show that when QCS content was 35%, the morphology, pore size, and comprehensive performance of NFM-QCS were optimized. NFM-QCS demonstrated high flow rates under low pressure, a high static adsorption capacity of 1285.16 mg/g, and a high dynamic adsorption capacity of 135.63 mg/mL (1 mm/min) for bovine serum albumin (BSA), which is superior to reported state-of-the-art and commercial ion-exchange chromatography columns. Based on the excellent adsorption performance, NFM-QCS can efficiently separate and purify IgG from the mixed solution of BSA and IgG. Our work provides a facile approach for the preparation of a high-performance ion-exchange chromatography membrane for protein separation.

Advances in high-throughput, high-capacity nonwoven membranes for chromatography in downstream processing: A review

Nonwoven membranes are highly engineered fibrous materials that can be manufactured on a large scale from a wide range of different polymers, and their surfaces can be modified using a large variety of different chemistries and ligands. The fiber diameters, surface areas, pore sizes, total porosities, and thicknesses of the nonwoven mats can be carefully controlled, providing many opportunities for creative approaches for the development of novel membranes with unique properties to meet the needs of the future of downstream processing. Fibrous membranes are already finding use in ultrafiltration, microfiltration, depth filtration, and, more recently, in membrane chromatography for product capture and impurity removal. This article summarizes the various methods of manufacturing nonwoven fabrics, and the many methods available for the modification of the fiber surfaces. It also reviews recent studies focused on the use of nonwoven fabric devices in membrane chromatography and provides some perspectives on the challenges that need to be overcome to increase binding capacities, decrease residence times, and reduce pressure drops so that eventually they can replace resin column chromatography in downstream process operations.

Organic-Solvent-Resistant Polyimide/Hydroxyapatite Mixed Matrix Membranes for Lysozyme Adsorption

This work reports new mixed matrix membranes (MMMs) for the adsorption of enzymes from organic solvents. In this work, polyimide/hydroxyapatite (PI/HAP) MMMs were prepared via phase inversion method and further crosslinked with 3-aminopropyl triethoxysilane (APTES). The chemical and structural stability of the crosslinked PI/HAP MMMs were improved and applied for lysozyme (LZ) adsorption in organic solvent. PI/HAP MMMs were crosslinked by changing the 3-aminopropyltriethoxysilane (APTES) concentration and crosslinking time. The optimal APTES crosslinking condition for PI/HAP MMMs is 6% of concentration for 8 h. The LZ adsorption performance was studied by changing solvent types. PI/HAP MMMs possessed a high LZ adsorption in organic-solvent-aqueous solutions, and the LZ adsorption capacity reached 34.1 mg/g. The MMMs had a high desorption capacity and recovery ability. The MMMs maintained 60% of their adsorption capacity and 58% of their desorption at the fourth cycle of adsorption and desorption. The MMMs provided a new technology for the purification and separation of enzymes or proteins by MMMs in organic solvents.

Application of cellulose to chromatographic media: Cellulose dissolution, and media fabrication and derivatization

As the cornerstone of chromatographic technology, the development of high-performance chromatographic media is a crucial means to enhance the purification efficiency of biological macromolecules. Cellulose is a popular biological separation medium due to its abundant hydroxyl group on the surface, easy modification and, weak non-specific adsorption. In this paper, the development of cellulosic solvent systems, typical preparation methods of cellulosic chromatographic media, and the enhancement of chromatographic properties of cellulosic chromatographic media by polymeric ligand grafting strategies and their mechanism of action are reviewed. Ultimately, based on the current research status, a promising outlook for the preparation of high-performance cellulose-based chromatographic media was presented.

On the Performance of a Ready-to-Use Electrospun Sulfonated Poly(Ether Ether Ketone) Membrane Adsorber

Motivated by the need for efficient purification methods for the recovery of valuable resources, we developed a wire-electrospun membrane adsorber without the need for post-modification. The relationship between the fiber structure, functional-group density, and performance of electrospun sulfonated poly(ether ether ketone) (sPEEK) membrane adsorbers was explored. The sulfonate groups enable selective binding of lysozyme at neutral pH through electrostatic interactions. Our results show a dynamic lysozyme adsorption capacity of 59.3 mg/g at 10% breakthrough, which is independent of the flow velocity confirming dominant convective mass transport. Membrane adsorbers with three different fiber diameters (measured by SEM) were fabricated by altering the concentration of the polymer solution. The specific surface area as measured with BET and the dynamic adsorption capacity were minimally affected by variations in fiber diameter, offering membrane adsorbers with consistent performance. To study the effect of functional-group density, membrane adsorbers from sPEEK with different sulfonation degrees (52%, 62%, and 72%) were fabricated. Despite the increased functional-group density, the dynamic adsorption capacity did not increase accordingly. However, in all presented cases, at least a monolayer coverage was obtained, demonstrating ample functional groups available within the area occupied by a lysozyme molecule. Our study showcases a ready-to-use membrane adsorber for the recovery of positively charged molecules, using lysozyme as a model protein, with potential applications in removing heavy metals, dyes, and pharmaceutical components from process streams. Furthermore, this study highlights factors, such as fiber diameter and functional-group density, for optimizing the membrane adsorber's performance.

Negatively Charged Composite Nanofibrous Hydrogel Membranes for High-Performance Protein Adsorption

Nanofibrous materials are considered as promising candidates for fabricating high-efficiency chromatography media, which are urgently needed in protein pharmaceuticals purification and biological research, yet still face several bottlenecks. Herein, novel negatively charged composite nanofibrous hydrogel membranes (NHMs) are obtained by a facile combination of electrospinning and surface coating modification. The resulting NHMs exhibit controllable morphologies and chemical structures. Benefitting from the combined effect of the stable framework of silicon dioxide (SiO₂) nanofiber and the function layer of negatively charged hydrogel, as well as good pore connectivity among nanofibers, NHMs exhibit a high protein adsorption capacity of around 1000 mg g^-1, and are superior to the commercial cellulose fibrous adsorbent (Sartobind^®) and the reported nanofibrous membranous adsorbents. Moreover, due to their relatively stable physicochemical and mechanical properties, NHMs possess comprehensive adsorption performance, favorable resistance to acid and solvents, good selectivity, and excellent regenerability. The designed NHMs composite adsorbents are expected to supply a new protein chromatography platform for effective protein purification in biopharmaceuticals and biochemical reagents.

Cationic microcrystalline cellulose - Montmorillonite composite aerogel for preconcentration of inorganic anions from dairy wastewater

Development of efficient adsorbents to inorganic anions as a solid phase extraction (SPE) material is highly desirable for chromatographic analysis and pollution control. In this work we developed a new hybrid cationic microcrystalline cellulose aerogel composite. Cationic cetylpyridinium imbedded montmorillonite (CPC-MT) was uniformly entrapped in microcrystalline cellulose (MCC) to enhance anionic adsorption efficiency and mechanical stability. The developed CPC-MT@MCC aerogel was used as an SPE adsorbent for anions from dairy wastewater by coupling with ion-column chromatography. Further quaternized CPC-MT@MCC aerogel (CPC-MT@QMCC) showed unique low density (10.6 mg cm^-3), large specific surface area (320 m² g^-1), porosity 70%, 800 mg g^-1 nitrate adsorption capacity within 60 min and ease of elution in alkaline solutions. The CPC-MT@QMCC aerogel showed efficient regeneration and reuse performances for up to 10 cycles. More importantly, a dynamic binding efficiency of 710 mg g^-1 highlights its excellent performance for practical applications. 96% of nitrate anion from environmental manure wastewater samples were adsorbed with 98.7% recovery. A good linear relationship was obtained in the range of 0.01-10 mg L^-1 and the limits of detection was 0.5 mg L^-1 using CPC-MT@QMCC aerogel as a preconcentration column. The successful synthesis of such intriguing and economic CPC-MT@QMCC aerogel may provide a promising matrix for high-performance and high efficiency chromatographic media.

Bisphosphonated-immobilized porous cellulose monolith with tentacle grafting by atom transfer radical polymerization for selective adsorption of lysozyme

Here, a m-xylene bisphosphonate immobilized tentacle-type cellulose monolith (BP-PCM) is prepared by atom transfer radical polymerization for lysozyme purification. In the preparation, the m-xylene bisphosphonate was anchored glycidyl methacrylate and then polymerized to enhance the flexibility of the ligands to improve lysozyme adsorption capacity, and glycerol monomethacrylate serves as spacer to further optimize the layers structure and ligands density of the grafted tentacles for satisfactory adsorption capacity. The maximum static and dynamic adsorption capacity (10% breakthrough) of BP-PCM reach to 169.6 and 102.6 mg mL-1, respectively. Moreover, BP-PCM displays weak nonspecific adsorption and is able to successfully enrich lysozyme from diluted chicken egg white, indicating the excellent selectivity. The results demonstrated that BP-PCM is promising for use as high-capacity protein 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.

Preparation and Protein Separation Properties of the Porous Polystyrene/Ethylene-Vinyl Acetate Copolymer Blend Nanofibers Membranes

To date, the preparation of a novel ultrafiltration membrane and the efficient separation and purification of protein solutions have gradually attracted widespread attention of many researchers. In this study, a hollow porous polystyrene/ethylene-vinyl acetate copolymer blend nanofibrous membrane (PS/EVA-BNM) was generated by electrospinning and chemical modification and then used to separate and purify proteins in solution. The BNM was characterized by scanning electron microscopy and specific surface area and pore size analyses. The membrane separation system was assembled using the BNM, which was overlaid to form the reaction layer. The optimal conditions for protein separation were determined by adjusting the operating pressure, filtration time, and pH. The results showed that the rejection rate of serum albumin and the membrane flux could reach 94.35% and 2.04 L/(m2 min), respectively, under the following conditions: the operating pressure was 0.10 MPa and the processing time was 1.5 h. By comparing the parameters of the polyethersulfone commercial ultrafiltration membrane with the PS/EVA-BNM system, it could be inferred that the rejection rate of the latter decreased slightly, whereas its transport flux improved several times. At the same time, the experimental results indicated that the PS/EVA-BNM possessed excellent reusability and mechanical properties. Additionally, the BNM could retain its nanofibrous morphological structure after the separation of serum albumin several times in an aqueous environment.