Characterization of the adsorption-fouling layer using globular proteins on ultrafiltration membranes

Process monitoring of virus-like particle reassembly by diafiltration with UV/Vis spectroscopy and light scattering

Virus-like particles (VLPs) have shown great potential as biopharmaceuticals in the market and in clinics. Nonenveloped, in vivo assembled VLPs are typically disassembled and reassembled in vitro to improve particle stability, homogeneity, and immunogenicity. At the industrial scale, cross-flow filtration (CFF) is the method of choice for performing reassembly by diafiltration. Here, we developed an experimental CFF setup with an on-line measurement loop for the implementation of process analytical technology (PAT). The measurement loop included an ultraviolet and visible (UV/Vis) spectrometer as well as a light scattering photometer. These sensors allowed for monitoring protein concentration, protein tertiary structure, and protein quaternary structure. The experimental setup was tested with three Hepatitis B core Antigen (HBcAg) variants. With each variant, three reassembly processes were performed at different transmembrane pressures (TMPs). While light scattering provided information on the assembly progress, UV/Vis allowed for monitoring the protein concentration and the rate of VLP assembly based on the microenvironment of Tyrosine-132. VLP formation was verified by off-line dynamic light scattering (DLS) and transmission electron microscopy (TEM). Furthermore, the experimental results provided evidence of aggregate-related assembly inhibition and showed that off-line size-exclusion chromatography does not provide a complete picture of the particle content. Finally, a Partial-Least Squares (PLS) model was calibrated to predict VLP concentrations in the process solution. Q 2 values of 0.947-0.984 were reached for the three HBcAg variants. In summary, the proposed experimental setup provides a powerful platform for developing and monitoring VLP reassembly steps by CFF.

A comparative study of dissolving hyaluronic acid microneedles with trehalose and poly(vinyl pyrrolidone) for efficient peptide drug delivery

We studied the role of the additives trehalose and poly(vinyl pyrrolidone) in the physical and pharmacokinetic properties of peptide drug incorporated microneedles.

Nano Spray Drying Technique as a Novel Approach To Formulate Stable Econazole Nitrate Nanosuspension Formulations for Ocular Use

The effect of using methyl-β-cyclodextrin and hydroxypropyl-β-cyclodextrin as carriers for econazole nitrate nanoparticles prepared by nano spray dryer was explored in this work. Stabilizers, namely, poly(ethylene oxide), polyvinylpyrrolidone k30, poloxamer 407, Tween 80, and Cremophor EL, were used. The nano spray dried formulations revealed almost spherical particles with an average particle size values ranging from 121 to 1565 nm and zeta potential values ranging from -0.8 to -2.5 mV. The yield values for the obtained formulations reached 80%. The presence of the drug in the amorphous state within the nanosuspension matrix system significantly improved drug release compared to that for pure drug. Combination of hydroxypropyl-β-cyclodextrin with Tween 80 achieved an important role for preserving the econazole nanosuspension from aggregation during storage for one year at room temperature as well as improving drug release from the nanosuspension. This selected formulation was suspended in chitosan HCl to increase drug release and bioavailability. The in vivo evaluation on albino rabbit's eyes demonstrated distinctly superior bioavailability of the selected formulation suspended in chitosan compared to its counterpart formulation suspended in buffer and crude drug suspension due to its mucoadhesive properties and nanosize. The nano spray dryer could serve as a one step technique toward formulating stable and effective nanosuspensions.

Ammonia recovery from agricultural wastes by membrane distillation: fouling characterization and mechanism

One of the main obstacles impeding implementation of membrane distillation for the recovery and concentration of ammonia from swine manure is wetting caused by fouling. Due to the different types of fouling which can occur in a membrane system, foulants characterization is a complex problem. To elucidate the fouling mechanism, deposit morphology and composition of foulants have been determined using Scanning Electron Microscopy, X-ray Energy Dispersive Spectrometry, Attenuated Total Reflectance Infrared Spectrometry, Ion chromatography and Inductively coupled plasma-optical emission spectroscopy. Based on the analysis of fouled membranes, it is concluded that membrane fouling is dominated by organic fouling in combination with deposits of inorganic elements and microorganisms. After a week of running the membrane process without cleaning, the average fouling layer thickness was estimated to 10-15 μm. The fouling layer further results in a loss of membrane hydrophobicity. This indicates that fouling could be a severe problem for membrane distillation performance.

Assembly and degradation of low-fouling click-functionalized poly(ethylene glycol)-based multilayer films and capsules

Nano-/micrometer-scaled films and capsules made of low-fouling materials such as poly(ethylene glycol) (PEG) are of interest for drug delivery and tissue engineering applications. Herein, the assembly and degradation of low-fouling, alkyne-functionalized PEG (PEG(Alk) ) multilayer films and capsules, which are prepared by combining layer-by-layer (LbL) assembly and click chemistry, are reported. A nonlinear, temperature-responsive PEG(Alk) is synthesized, and is then used to form hydrogen-bonded multilayers with poly(methacrylic acid) (PMA) at pH 5. The thermoresponsive behavior of PEG(Alk) is exploited to tailor film buildup by adjusting the assembly conditions. Using alkyne-azide click chemistry, PEG(Alk)/PMA multilayers are crosslinked with a bisazide linker that contains a disulfide bond, rendering these films and capsules redox-responsive. At pH 7, by disrupting the hydrogen bonding between the polymers, PEG(Alk) LbL films and PEG(Alk) -based capsules are obtained. These films exhibit specific deconstruction properties under simulated intracellular reducing conditions, but remain stable at physiological pH, suggesting potential applications in controlled drug release. The low-fouling properties of the PEG films are confirmed by incubation with human serum and a blood clot. Additionally, these capsules showed negligible toxicity to human cells.

Surface modification of chromatography adsorbents by low temperature low pressure plasma

In this study we show how low temperature glow discharge plasma can be used to prepare bi-layered chromatography adsorbents with non-adsorptive exteriors. The commercial strong anion exchange expanded bed chromatography matrix, Q HyperZ, was treated with plasmas in one of two general ways. Using a purpose-designed rotating reactor, plasmas were employed to either: (i) remove anion exchange ligands at or close to the exterior surface of Q HyperZ, and replace them with polar oxygen containing functions ('plasma etching and oxidation'); or (ii) bury the same surface exposed ligands beneath thin polymer coatings ('plasma polymerization coating') using appropriate monomers (vinyl acetate, vinyl pyrrolidone, safrole) and argon as the carrier gas. X-ray photoelectron spectroscopy analysis (first ∼10 nm depth) of Q HyperZ before and after the various plasma treatments confirmed that substantial changes to the elemental composition of Q HyperZ's exterior had been inflicted in all cases. The atomic percent changes in carbon, nitrogen, oxygen, yttrium and zirconium observed after being exposed to air plasma etching were entirely consistent with: the removal of pendant Q (trimethylammonium) functions; increased exposure of the underlying yttrium-stabilised zirconia shell; and introduction of hydroxyl and carbonyl functions. Following plasma polymerization treatments (with all three monomers tested), the increased atomic percent levels of carbon and parallel drops in nitrogen, yttrium and zirconium provided clear evidence that thin polymer coats had been created at the exteriors of Q HyperZ adsorbent particles. No changes in adsorbent size and surface morphology, nor any evidence of plasma-induced damage could be discerned from scanning electron micrographs, light micrographs and measurements of particle size distributions following 3 h exposure to air (220 V; 35.8 W L(-1)) or 'vinyl acetate/argon' (170 V; 16.5 W L(-1)) plasmas. Losses in bulk chloride exchange capacity before and after exposure to plasmas enabled effective modification depths within hydrated Q HyperZ adsorbent particles to be calculated as 0.2-1.2 μm, depending on the conditions applied. The depth of plasma induced alteration was strongly influenced by the power input and size of the treated batch, i.e. dropping the power or increasing the batch size resulted in reduced plasma penetration and therefore shallower modification. The selectivity of 'surface vs. core' modification imparted to Q HyperZ by the various plasma treatments was evaluated in static and dynamic binding studies employing appropriate probes, i.e. plasmid DNA, sonicated calf thymus DNA and bovine serum albumin. In static binding studies performed with adsorbents that had been exposed to plasmas at the 5 g scale (25 g L(-1) of plasma reactor), the highest 'surface/core' modification selectivity was observed for Q HyperZ that had been subjected to 3 h of air plasma etching at 220 V (35.8 W L(-1)). This treatment removed ∼53% of 'surface' DNA binding at the expense of a 9.3% loss in 'core' protein binding. Even more impressive results were obtained in dynamic expanded bed adsorption studies conducted with Q HyperZ adsorbents that had been treated with air (220 V, 3 h) and 'vinyl acetate/argon' (170 V, 3 h) plasmas at 10.5 g scale (52.5 g L(-1) of plasma reactor). Following both plasma treatments: the 10% breakthrough capacities of the modified Q HyperZ adsorbents towards 'surface' binding DNA probes dropped very significantly (30-85%); the DNA induced inter-particle cross-linking and contraction of expanded beds observed during application of sonicated DNA on native Q HyperZ was completely eradicated; but the 'core' protein binding performance remained unchanged cf. that of the native Q HyperZ starting material.

Protein adsorption on poly(N-vinylpyrrolidone)-modified silicon surfaces prepared by surface-initiated atom transfer radical polymerization

Well-controlled poly(N-vinylpyrrolidone) (PVP)-grafted silicon surfaces were prepared by surface-initiated atom transfer radical polymerization (SI-ATRP) with 1,4-dioxane/water mixtures as solvents and CuCl/5,7,7,12,14,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane (Me6TATD) as a catalyst. The thickness of the PVP layer on the surface increased with reaction time, suggesting that the ATRP grafting of N-vinylpyrrolidone (NVP) from the silicon surfaces was a well-controlled process. The water contact angle and X-ray photoelectron spectroscopy (XPS) were used to characterize the modified surfaces. The protein adsorption property of the PVP-grafted surfaces was evaluated using a radiolabeling method. Compared with unmodified silicon surfaces, a Si-PVP60 surface with a PVP thickness of 15.06 nm reduced the level of adsorption of fibrinogen, human serum albumin (HSA), and lysozyme by 75, 93, and 81%, respectively. Moreover, the level of fibrinogen adsorption decreases gradually with an increase in PVP thickness. However, no significant difference in fibrinogen adsorption was found when the PVP layer was thicker than the critical thickness of 13.45 nm.

High-performance thin-layer hydrogel composite membranes for ultrafiltration of natural organic matter

Thin-layer hydrogel composite (TLHC) ultrafiltration (UF) membranes were synthesized by photo-grafting of either poly(ethylene glycol) methacrylate (PEGMA) or N,N-dimethyl-N-(2-methacryloyloxyethyl-N-(3-sulfopropyl) ammonium betaine (SPE) onto commercial polyethersulfone (PES) UF membranes. The performance of TLHC UF membranes was evaluated for natural organic matter (NOM) filtration and compared to commercial PES UF membranes. The fouling evaluation was done by investigation of membrane-solute interactions (adsorptive fouling) and membrane-solute-solute interactions (UF). The results suggest that the TLHC membranes convincingly displayed a higher adsorptive fouling resistance than unmodified PES UF membranes. In long-term stirred dead-end UF, a much lower fouling was observed for TLHC membranes than for commercial membranes with the same flux and rejection. Further, water flux recovery was also much higher. An analysis using an existing blocking model was performed in order to elucidate the effect of a polymer hydrogel layer on fouling mechanism as well as cake layer characteristics. The TLHC membranes synthesized by photo-grafting of PEGMA (40 g/L) and PEGMA with a low concentration of cross-linker monomer in the reaction mixture (ratio: 40/0.4 (g/L)/(g/L)) showed a much better performance than the other composite membranes. Those membranes could reduce the cake resistance on the membrane surface. This work has relevance for the design of high-performance UF membranes for applications in water treatment.

Separation and purification of benzylpenicillin produced by fermentation using coupled ultrafiltration and nanofiltration technologies

The purpose of this study was to evaluate the capacity of using coupled ultrafiltration-nanofiltration technologies for separation and purification of benzylpenicillin (BP). More specifically, we verified the efficiency of three ultrafiltration (UF) membranes (cut-off of 5000, 30,000 and 100,000 Da) to remove impurities that cause stable emulsion during the chemical extraction of the antibiotic. We also tested the effectiveness of a nanofiltration (NF) membrane (cut-off of 300 Da) to concentrate the benzylpenicillin recovered from permeates and to decrease the osmotic pressure by reducing the ionic charge of the broth. Results have shown that high recovery (89.0-91.0%) can be obtained in permeate generated by the 30,000 and 100,000 UF membranes, but a slight emulsion will be formed during phase separation. With the 5000 UF membrane, lower recovery is obtained (81.0%) but no emulsion is produced, leading to a high solvent extraction yield (94.6%). The nanofiltration of 30,000 and 100,000 UF permeates leads to very high recovery (98.0%), but stable emulsions are formed, reducing the chemical extraction yield (80.0-82.6%). For the nanofiltration of 5000 UF permeate, excellent recovery of the antibiotic is noted (97.4%) leading to high extraction yield (92.4%) with no emulsion formed. Diafiltration step should be applied during UF procedure in order to increase the antibiotic recovery in the generated permeates.

Quantitative analysis of membrane fouling by protein mixtures using MALDI-MS

Binary aqueous solutions of bovine serum albumin (BSA) and beta-lactoglobulin (bLG) were subject to flux-stepping and constant flux ultrafiltration to identify the apparent critical flux and to study the mechanisms and factors affecting fouling when the membrane is permeable to one protein component. Membranes from these filtration experiments were analyzed using matrix-assisted laser desorption ionization mass spectrometry (MALDI-MS) to locate and quantify levels of fouling below and above the apparent critical flux. Hydrophilic (PLTK) regenerated cellulose and hydrophobic (PBTK) polysulfone asymmetric membranes were used, both of 30 kDa nominal molecular weight cut-off. For the hydrophilic PLTK membrane, protein deposition was shown to depend on electrostatic forces, exhibiting little or no fouling when the proteins had the same charge sign as that of the membrane. This was found to apply for both dilute equal mass-per-unit-volume and equimolar binary mixtures. For the PBTK membrane, hydrophobic protein-membrane attractive forces were sufficiently strong to cause deposition of bLG even in the presence of repulsive electrostatic forces. For the PBTK membrane deposition exceeded monolayer coverage below and above apparent critical flux conditions but for the PLTK membrane this generally occurred when the apparent critical flux was exceeded. MALDI-MS was shown to be a facile direct analytical technique for individually quantifying adsorbed proteins on membrane surfaces at levels as low as 50 fmol/mm(2). The high levels of compound specificity inherent to mass spectrometry make this approach especially suited to the quantification of individual components in mixed deposits. In this study, MALDI-MS was found to be successful in identifying and quantifying the protein species responsible for fouling.

Modified capillary electrophoresis system for peptide, protein and double-stranded DNA analysis

The results of high-performance capillary electrophoresis (HPCE) studies of peptide, protein and double-stranded DNA separations on a laboratory-made HPCE system are presented. Parameters of the HPCE system are given. The new method of capillary surface modification by grafting poly(glycidyl methacrylate) is described. The problems of HPCE biopolymer analysis connected with the sample-wall interactions are discussed.

Phospholipid coatings for the prevention of membrane fouling

The aim of the present work was the development of phosphorylcholine-based treatments for biofiltration membranes and the demonstration that such treatments prevent or inhibit protein fouling. Microfiltration membranes of cellulose triacetate, polyether sulphone and polyvinylidene fluoride were etched with oxygen in a plasma chamber to generate surface hydroxyl groups and were then treated with the monomer 2-methacryloyloxyethyl phosphorylcholine. These membranes were evaluated with water, buffer, bovine serum albumin (BSA), yeast fermentation broth, beer and orange juice. The treatment of cellulose triacetate membranes reduced both the initial flux and the extent of water fouling. In terms of the integrated flux, these factors tended to cancel each other out. For protein, the membranes gave similar or higher fluxes but worse fouling. The cellular feed (yeast) reacted more favourably to the coating than the BSA. The polyether sulphone was scarcely affected by the coating; fouling remaining high with most 'real' feeds. There was lower initial flux but less flux decline with water and beer. Washing with water and cleaning with Tergazyme did not restore the initial flux. Polyvinylidene fluoride membranes gave the most positive results. In most cases, the coating both increased initial flux and decreased the rate of fouling. The coating was particularly effective for BSA and for beer and orange juice, where fouling is probably caused by a polysaccharide rather than by a protein. Electron microscopy showed, nonetheless, that fouling by proteins was accompanied by protein adsorption primarily on the upper surface of the membrane and that coated membranes showed less deposition and in different places than did untreated membranes.