Surface-functionalized electrospun carbon nanofiber mats as an innovative type of protein adsorption/purification medium with high capacity and high throughput

Cation-exchange performance of a citric-acid esterified cellulose nanofibrous membrane for highly-selective proteins' permeability and adsorption capacity

The usage of low-cost, readily available, or even disposable, single-use membranes in macromolecules' purification and separation is still in the development phase. In this research, highly porous (>95 %), water- and compression stable cation-exchange membranes were prepared by freeze-casting using cellulose nanofibrils (CNF) and citric acid (CA) acting as a crosslinker and source of weak anionic (carboxylic) surface groups arising from the mono-esterified CA. The membranes were characterized by different analytical techniques, and evaluated for the ionic adsorption efficacy of different proteins in dead-end filtration mode using a Tri-buffer of pH 8. The membrane's internal microstructure (porosity and density) with the available (quantity and access) carboxylic groups was confirmed, to determine not only the proteins' specific (related to the net charged and molecular weight) adsorption dynamic (>52 % of positive Lysozyme/Cytochrome, <8 % of negative BSA/Myoglobin; ≤0.5 g/L) at extremely high flow rates (>3.000 hL/h*MPa*m2), but also their desorption (>97 %) and re-equilibration (using NaCl) with flux recovery (>80 %). Such efficiency was achieved with up to 5 consecutive filtering cycles. The high permeability (>87 %) of the spherical and negatively surface charged microparticles (used as models) also suggests the likelihood of removing larger microbial species, which, while retaining relatively smaller and positively charged proteins, further increases their potential in biopharma applications.

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.

Aggregation States and Segmental Dynamics of Poly(methyl methacrylate) in Nanofiber Mats

Nanofiber mats composed of polymers, having a large surface-to-volume ratio and high porosity, have been widely applied in the environmental and biomedical fields but fundamental knowledge on the polymer chains in the mats seems to be limited. We here report the aggregation states and segmental dynamics of poly(methyl methacrylate)s (PMMAs) with different stereoregularities in electrospun nanofiber mats. Attenuated total reflectance Fourier transform infrared (ATR/FTIR) spectroscopy revealed that, in the case of atactic PMMA (at-PMMA), the population of the trans-trans conformation of the main chain part, which allows carbonyl groups of the side group to interact affirmatively with each other, increased in the electrospun nanofiber mat. On the other hand, in the case of isotactic PMMA (it-PMMA), the skeletal conformation was unchanged even in the nanofiber mat. As a result of the aggregation states of PMMA chains, the glass-transition temperature (T_g) of the electrospun nanofiber mats increased and remained unchanged from the corresponding bulk value for at- and it-PMMA, respectively. These findings should be useful for designing materials and devices composed of electrospun nanofibers.

Surface Functionalization of Nanofibers: The Multifaceted Approach for Advanced Biomedical Applications

Nanocarriers are gaining significant importance in the modern era of drug delivery. Nanofiber technology is one of the prime paradigms in nanotechnology for various biomedical and theranostic applications. Nanofibers obtained after successful electrospinning subjected to surface functionalized for drug delivery, biomedical, tissue engineering, biosensing, cell imaging and wound dressing application. Surface functionalization entirely changes physicochemical and biological properties of nanofibers. In physicochemical properties, wettability, melting point, glass transition temperature, and initial decomposition temperature significantly change offer several advantageous for nanofibers. Similarly, biological properties include cell adhesion, biocompatibility, and proliferation, also changes by functionalization of nanofibers. Various natural and synthetic materials polymers, metals, carbon materials, functional groups, proteins, and peptides, are currently used for surface modification of nanofibers. Various research studies across the globe demonstrated the usefulness of surface functionalized nanofibers in tissue engineering, wound healing, skin cancers, melanoma, and disease diagnosis. The delivery of drug through surface functionalized nanofibers results in improved permeation and bioavailability of drug which is important for better targeting of disease and therapeutic efficacy. This review provides a comprehensive insight about various techniques of surface functionalization of nanofibers along with its biomedical applications, toxicity assessment and global patent scenario.

Electrospun Hydrophobic Interaction Chromatography (HIC) Membranes for Protein Purification

Responsive membranes for hydrophobic interaction chromatography have been fabricated by functionalizing poly(N-vinylcaprolactam) (PVCL) ligands on the substrate of electrospun regenerated cellulose nanofibers. Both static and dynamic binding capacities and product recovery were investigated using bovine serum albumin (BSA) and Immunoglobulin G (IgG) as model proteins. The effects of ligand chain length and chain density on static binding capacity were also studied. A static binding capacity of ~25 mg/mL of membrane volume (MV) can be achieved in optimal ligand grafting conditions. For dynamic binding studies, protein binding capacity increased with protein concentration from 0.1 to 1.0 g/L. Dynamic binding capacity increased from ~8 mg/mL MV at 0.1 g/L BSA to over 30 mg/mL at 1.0 g/L BSA. However, BSA recovery decreased as protein concentration increased from ~98% at 0.1 g/L BSA to 51% at 1 g/L BSA loading concentration. There is a clear trade-off between binding capacity and recovery rate. The electrospun substrate with thicker fibers and more open pore structures is superior to thinner fibrous membrane substrates.

Electrospinning of Quaternized Chitosan-Poly(vinyl alcohol) Composite Nanofiber Membrane: Processing Optimization and Antibacterial Efficacy

N-(2-hydroxy) propyl-3-trimethylammonium chitosan chloride (HTCC) is a type of quaternary ammonium chitosan derivative with an antibacterial activity superior to the pristine chitosan, but its electrospinnability is limited. In this study, polyvinyl alcohol (PVA) was blended with HTCC to improve the electrospinnability of nanofibers. The electrospinning of PVA–HTCC nanofiber membranes was optimized in terms of structural stability and antimicrobial performance. Based on scanning electron microscopic analysis, the morphology and diameter of the produced nanofibers were influenced by the applied voltage, flow rate of the feed solution, and weight ratio of the polymer blend. An increase in the HTCC content decreased the average nanofiber diameter. The maximum water solubility of the PVA–HTCC nanofibers reached the maximum value of 70.92% at 12 h and 25 °C. The antibacterial activity of PVA–HTCC nanofiber membranes against Escherichia coli was ~90%, which is significantly higher than that of PVA–chitosan nanofiber membrane. Moreover, the antibacterial efficiency of PVA–HTCC nanofiber membranes remained unaffected after 5 cycles of antibacterial treatment. The good antibacterial performance and biocompatibility of PVA–HTCC nanofiber membrane makes them attractive for biomedical and biochemical applications that necessitate sterile conditions.

Self-Enriching Electrospun Biosensors for Impedimetric Sensing of Zika Virus

Zika virus (ZIKV) infection is associated with the Guillain-Barré syndrome, and when non-vector congenital transmission occurs, fetal brain abnormalities are expected. After ZIKV infection, the blood, breast milk, and other body fluids contain low viral loads. Their detection is challenging as it requires the processing of larger input volumes of the clinical samples. Pre-enrichment is a valuable strategy to increase the analyte concentration. Therefore, the authors propose the use of a hierarchal composite polyaniline-(electrospun nanofiber) hydrogel mat (ENM) for the simultaneous enrichment and impedimetric sensing of ZIKV viral particles. The electrospinning conditions of polyvinyl alcohol and alginate, including blend formulation, were optimized through a factorial design. Disintegration and gelatinization were controlled via cross-linking to improve the hydrogel properties. Hierarchization was achieved by in situ chemical deposition of conductive polyaniline. The carboxyl groups of the ENM were used for the covalent immobilization of anti-ZIKV polyclonal antibodies used in the specific recognition of ZIKV within the medium of Vero cell culture. The specific capture and desorption of virions were studied at different pHs. ENMs were characterized by scanning electron microscopy and FTIR. Atomic force microscopy along with UV-vis and electrochemical impedance spectroscopies was used to monitor the antibody immobilization, ZIKV capture, and elution processes. Our results show that 14.2 mg (0.25 cm³) of ENM can capture 38.7 ± 2.5 μg of ZIKV with a desorption rate of 99.97% (38.29 ± 2.7 μg ZIKV), which is reusable for at least three times. Therefore, the capture capacity (micrograms of ZIKV captured per milligram of ENM) of polyaniline-hierarchized mats was 2.72 μg ZIKV/mg. The impedance LOD value was determined to be 2.76 μg of ZIKV particles (approximately 6.6 × 103 PFU/mL). As a result, we present a fast small-scale purification system that can simultaneously monitor ZIKV electrochemically and optically.

Antibacterial efficacy of quaternized chitosan/poly (vinyl alcohol) nanofiber membrane crosslinked with blocked diisocyanate

N-[(2-hydroxyl-3-trimethylammonium) propyl] chitosan chloride (HTCC), which is a type of chitosan derivative with quaternary ammonium groups, possesses a higher antibacterial activity as compared to the pristine chitosan. The nanofiber membranes made of HTCC are attractive for applications demanding for antibacterial function. However, the hydrophilic nature of HTCC makes it unsuitable for electrospinning of nanofibers. Hence, biodegradable polyvinyl alcohol (PVA) was proposed as an additive to improve the electrospinnability of HTCC. In this work, PVA/HTCC nanofiber membrane was crosslinked with the blocked diisocyanate (BI) to enhance the stability of nanofiber membrane in water. Microbiological assessments showed that the PVA/HTCC/BI nanofiber membranes possessed a good antibacterial efficacy (∼100 %) against E. coli. Moreover, the biocompatibility of PVA/HTCC/BI nanofiber membrane was proven by the cytotoxicity test on mouse fibroblasts. These promising results indicated that the PVA/HTCC/BI nanofiber membrane can be a promising material for food packaging and as a potential wound dressing for skin regeneration.

Electrospun Nanofibers for Chemical Separation

The separation and purification of specific chemicals from a mixture have become necessities for many environments, including agriculture, food science, and pharmaceutical and biomedical industries. Electrospun nanofiber membranes are promising materials for the separation of various species such as particles, biomolecules, dyes, and metals from liquids because of the combined properties of a large specific surface, light weight, high porosity, good connectivity, and tunable wettability. This paper reviews the recent progress in the design and fabrication of electrospun nanofibers for chemical separation. Different capture mechanisms including electrostatic, affinity, covalent bonding, chelation, and magnetic adsorption are explained and their distinct characteristics are highlighted. Finally, the challenges and future aspects of nanofibers for membrane applications are discussed.

Electrospun Weak Anion-exchange Fibrous Membranes for Protein Purification

Membrane based ion-exchange (IEX) and hydrophobic interaction chromatography (HIC) for protein purification is often used to remove impurities and aggregates operated under the flow-through mode. IEX and HIC are also limited by capacity and recovery when operated under bind-and-elute mode for the fractionation of proteins. Electrospun nanofibrous membrane is characterized by its high surface area to volume ratio and high permeability. Here tertiary amine ligands are grafted onto the electrospun polysulfone (PSf) and polyacrylonitrile (PAN) membrane substrates using UV-initiated polymerization. Static and dynamic binding capacities for model protein bovine serum albumin (BSA) were determined under appropriate bind and elute buffer conditions. Static and dynamic binding capacities in the order of ~100 mg/mL were obtained for the functionalized electrospun PAN membranes whereas these values reached ~200 mg/mL for the functionalized electrospun PSf membranes. Protein recovery of over 96% was obtained for PAN-based membranes. However, it is only 56% for PSf-based membranes. Our work indicates that surface modification of electrospun membranes by grafting polymeric ligands can enhance protein adsorption due to increased surface area-to-volume ratio.

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.

Functionalized Electrospun Poly(Vinyl Alcohol) Nanofibrous Membranes with Poly(Methyl Vinyl Ether-Alt-Maleic Anhydride) for Protein Adsorption

In this work, electrospun poly(vinyl alcohol) (PVA) nanofiber membranes were functionalized by incorporating poly(methyl vinyl ether-alt-maleic anhydride) (poly(MVE/MA), PMA) for the selective adsorption of proteins. The capture performance was regulated by an optimizing buffer pH, PMA content, and protein concentration. Lysozyme was used as the model protein and a high adsorption capacity of 476.53 ± 19.48 was obtained at pH 6, owing to the electrostatic attraction between the negatively charged nanofibers and positively charged proteins. The large specific surface area, highly open porous structure, and abundant available carboxyl groups contributed to such high adsorption performance. Moreover, the nanofiber membranes exhibited good reusability and good selectivity for positively charged proteins. The obtained results can provide a promising method for the purification of proteins in small analytic devices.

Raman studies of the interactions of fibrous carbon nanomaterials with albumin

Adsorption or immobilization of proteins on synthetic surfaces is a key issue in the context of the biocompatibility of implant materials, especially those intended for the needs of cardiac surgery but also for the construction of biosensors or nanomaterials used as drug carriers. The subject of research was the analysis of Raman spectra of two types of fibrous carbon nanomaterials, of great potential for biomedical applications, incubated with human serum albumin (HSA). The first nanomaterial has been created on the layer of MWCNTs deposited by electrophoretic method (EPD) and then covered by thin film of pyrolytic carbon introduced by chemical vapor deposition process (CVD). The second material was formed from carbonized nanofibers prepared via electrospinning (ESCNFs) of polyacrylonitrile (PAN) precursor and then covered with pyrolytic carbon (CVD). The G-band blue-shift towards the position of about 1600cm^-1, observed for both studied surfaces, clearly indicates the albumin (HSA) adhesion to the surface. The G and G' (2D) peak shift was employed to assess the stress build up on the carbon nanomaterials. The surface nano- and micro-topography as well as the method of ordering the carbon nanomaterial has a significant influence on the mode of surface-protein interaction.

Scalable Fabrication of Electrospun Nanofibrous Membranes Functionalized with Citric Acid for High-Performance Protein Adsorption

Fabricating protein adsorbents with high adsorption capacity and appreciable throughput is extremely important and highly desired for the separation and purification of protein products in the biomedical and pharmaceutical industries, yet still remains a great challenge. Herein, we demonstrate the synthesis of a novel protein adsorbent by in situ functionalizing eletrospun ethylene-vinyl alcohol (EVOH) nanofibrous membranes (NFM) with critic acid (CCA). Taking advantage of the merits of large specific surface area, highly tortuous open-porous structure, abundant active carboxyl groups introduced by CCA, superior chemical stability, and robust mechanical strength, the obtained CCA-grafted EVOH NFM (EVOH-CCA NFM) present an excellent integrated protein (take lysozyme as the model protein) adsorption performance with a high capacity of 284 mg g(-1), short equilibrium time of 6 h, ease of elution, and good reusability. Meanwhile, the adsorption performance of EVOH-CCA NFM can be optimized by regulating buffer pH, ionic strength, and initial concentration of protein solutions. More importantly, a dynamic binding efficiency of 250 mg g(-1) can be achieved driven solely by the gravity of protein solution, which matches well with the demands of the high yield and energy conservation in the actual protein purification process. Furthermore, the resultant EVOH-CCA NFM also possess unique selectivity for positively charged proteins which was confirmed by the method of sodium dodecyl sulfate polyacrylamide gel electrophoresis. Significantly, the successful synthesis of such intriguing and economic EVOH-CCA NFM may provide a promising candidate for the next generation of protein adsorbents for rapid, massive, and cost-effective separation and purification of proteins.

ZrO2 Nanofiber as a Versatile Tool for Protein Analysis

Phosphorylation is one of the most important post-translational modifications in proteins. Their essential roles in the regulation of cellular processes and alteration of protein-protein interaction networks have been actively studied. However, phosphorylated proteins are present at low abundance in cells, and ionization of the modified peptides is often suppressed by the more abundant species in mass spectrometry. Effective enrichment techniques are needed to remove the unmodified peptides and concentrate the phosphorylated ones before their identification and quantification. Herein, we prepared ZrO2 nanofibers by electrospinning, a straightforward and easy fabrication technique, and applied them to enrich phosphorylated peptides and proteins. The fibers showed good size homogeneity and porosity and could specifically bind to the phosphorylated peptides and proteins, allowing their separation from the unmodified analogues when present in either simple protein digests or highly complex cell lysates. The enrichment performance was superior to that of the commercially available nanoparticles. Moreover, modifying the solution pH could lead to selective adsorption of proteins with different pI values, suggesting the fibers' potential applicability in charge-based protein fractionation. Our results support that the electrospun ZrO2 nanofibers can serve as a versatile tool for protein analysis with great ease in preparation and handling.

Highly carbonylated cellulose nanofibrous membranes utilizing maleic anhydride grafting for efficient lysozyme adsorption

Construction of adsorptive materials for simple, efficient, and high-throughput adsorption of proteins is critical to meet the great demands of highly purified proteins in biotechnological and biopharmaceutical industry; however, it has proven extremely challenging. Here, we report a cost-effective strategy to create carbonyl groups surface-functionalized nanofibrous membranes under mild conditions for positively charged protein adsorption. Our approach allows maleic anhydride to in situ graft on cellulose nanofibrous membranes (CMA) to construct adsorptive membranes with large surface area and tortuous porous structure. Thereby, the resultant CMA membranes exhibited high adsorption capacity of 160 mg g(-1), fast equilibrium within 12 h, and good reversibility to lysozyme. Moreover, the dynamic adsorption was performed under low pressure-drops (750 Pa), with a relatively high saturation adsorption amount of 118 mg g(-1), which matched well with the requirements for proteins purification. Considering the excellent adsorption performance of the as-prepared adsorptive membranes, this simple and intriguing approach may pave a way for the design and development of robust and cost-effective adsorption membranes to meet the great demands for fast and efficient adsorption of positively charged proteins.

Flexible hollow CeO2/Al2O3 fibers: preparation, characterization and dye adsorption efficiency

Flexible hollow CeO₂/Al₂O₃ fibers were prepared by a coaxial electro-blowing spinning technique and exhibited strong adsorption capacity for MO molecules.

In situ cross-linked and highly carboxylated poly(vinyl alcohol) nanofibrous membranes for efficient adsorption of proteins

In situ cross-linked and highly carboxylated poly(vinyl alcohol) nanofibrous membranes for lysozyme adsorption were fabricated by a combination of electrospinning and graft polymerization of poly(vinyl alcohol) and maleic anhydride.

Hierarchical porous carbon nanofibrous membranes with an enhanced shape memory property for effective adsorption of proteins

A hierarchical porous CNF membrane with robust mechanical properties, exhibiting intriguing shape memory properties and efficient protein adsorption performance.