Filtration Of Protein Solution Research Articles

CROSS-FLOW FILTRATION OF β-LACTOGLOBULIN SOLUTIONS LOADED WITH ADSORBENT PARTICLES

The influence of adsorbent particles on the characteristics of protein solution filtration was studied. Three media, activated carbon suspensions, β-lactoglobulin solutions, and a mixture of both, were filtered on a 0.2-μm pore alumina membrane. Moreover, the adsorption of protein on microparticles was studied and 1 isotherm was determined. Comparison of permeate fluxes, apparent retention coefficients, and hydraulic resistance values at steady state conditions highlights the existence of adsorbent-protein interactions. Permeability and retention seems to depend on cross-flow velocity. Correlations are proposed to express steady state fluxes versus operating parameters: cross-flow velocity, transmembrane pressure, and adsorbent and protein concentrations.

Intermolecular Forces between Proteins and Polymer Films with Relevance to Filtration

In order to understand the effects of protein fouling during ultrafiltration of biological fluids, we have investigated the molecular interactions between a thin polysulfone film and hen egg lysozyme with the surface forces apparatus (SFA). The normalized forces between the adsorbed protein layers and polymer films were measured below, at and above the pI of lysozyme, and compared with four different permeation fluxes obtained from ultrafiltration experiments. The intermolecular forces between two protein layers were also measured at the different pH values. Adsorption kinetics of lysozyme onto mica were also obtained. Buffer and lysozyme solutions at similar pH values and concentrations were filtered with 6 kD polysulfone membranes to obtain flux decline and hence fouling measurements. Hydrophobic membranes, such as polysulfone, exhibit extremely long-range attractive interactions (on the order of 1500−2000 Å) with proteins such as lysozyme. Even in the presence of electrostatic repulsion at pH values above the isoelectric point of lysozyme (when both lysozyme and polysulfone were negatively charged), a long-range attractive interaction of around 210 μN/m was observed. Such interactions were absent with measurements between adsorbed lysozyme−lysozyme layers. From these measurements, simple linear correlations were found relating the normalized forces to the fluxes from the ultrafiltration experiments. With respect to fouling, protein−protein and protein−polymer interactions are about equally important during ultrafiltration. This suggests that both the surface chemistry of the membrane and the solution conditions could be chosen to minimize fouling for specific protein solutions. Hence, as a result of this study, fouling of polysulfone membranes with lysozyme solutions can be reduced if (i) filtration is conducted at pH values above the pI of lysozyme (approximately 10.8) and (ii) the membranes are modified such that the long-range attractive interactions are reduced. These results support those from previous phenomenological studies on membrane filtration of protein solutions and are the first evidence relating intermolecular force interactions with macroscopic events in membrane fouling.

Membrane fouling in sterile filtration of recombinant human growth hormone

The most troublesome problem encountered during the sterile filtration of protein solutions is membrane fouling. This article presents our study on sterile filtration of a model protein, recombinant human growth hormone (rhGH). Scanning electron microscopy (SEM) analysis shows that 0.22-mum membranes, when used to filter the mannitol-formulated protein solution under a 0.35-bar transmembrane pressure, were plugged to a great extent. When zinc ions were added to induce aggregates, the fouling tendency of rhGH solutions increased with increasing amount and size of the aggregates, indicating that the aggregates present before filtration might be responsible for membrane fouling. However, repeated filtration of the same solution using a fresh filter each time cannot reduce membrane fouling, and all filtrates contain the same trace amount of hGH particulates as the prefiltered solution. Particulate size was determined to be between 0.03 and 0.15 mum by dynamic light scattering. Also, in view of the fact that protein formulations significantly affected the tendency of fouling with the same preexisting aggregates, it is likely that fouling was more attributed to the aggregation taking place in the filter pores during filtration (secondary aggregation) than to the aggregates present before filtration. Adding a surfactant to or increasing the pH of the protein solution improves the filtration, whereas increasing ionic strength slows down the filtration. This result suggests that the balance of the protein's interaction and electrostatic repulsion plays an important role in the protein's fouling tendency. Many factors might change the microenvironment in the pores and disturb this balance. Those considerations and the aggregation tendency of rhGH in the filter pores will be discussed in detail separately.

Membrane fouling in sterile filtration of recombinant human growth hormone

The most troublesome problem encountered during the sterile filtration of protein solutions is membrane fouling. This article presents our study on sterile filtration of a model protein, recombinant human growth hormone (rhGH). Scanning electron microscopy (SEM) analysis shows that 0.22-μm membranes, when used to filter the mannitol-formulated protein solution under a 0.35-bar transmembrane pressure, were plugged to a great extent. When zinc ions were added to induce aggregates, the fouling tendency of rhGH solutions increased with increasing amount and size of the aggregates, indicating that the aggregates present before filtration might be responsible for membrane fouling. However, repeated filtration of the same solution using a fresh filter each time cannot reduce membrane fouling, and all filtrates contain the same trace amount of hGH particulates as the prefiltered solution. Particulate size was determined to be between 0.03 and 0.15 μm by dynamic light scattering. Also, in view of the fact that protein formulations significantly affected the tendency of fouling with the same preexisting aggregates, it is likely that fouling was more attributed to the aggregation taking place in the filter pores during filtration (secondary aggregation) than to the aggregates present before filtration. Adding a surfactant to or increasing the pH of the protein solution improves the filtration, whereas increasing ionic strength slows down the filtration. This result suggests that the balance of the protein's interaction and electrostatic repulsion plays an important role in the protein's fouling tendency. Many factors might change the microenvironment in the pores and disturb this balance. Those considerations and the aggregation tendency of rhGH in the filter pores will be discussed in detail separately. © 1996 John Wiley & Sons, Inc.

Coatings reduce the fouling of microfiltration membranes

The effect of polymeric phospholipid analogue coatings on the performance of microfiltration membranes in the filtration of protein solutions was assessed by cross-flow filtration. Affinity gold stains and transmission electron microscopy were used to investigate protein adsorption to the membranes. Polyvinylidene difluoride (PVDF) and cellulose acetate (CA) microfiltration membranes were coated with the phospholipid analogue by a grafting reaction. Phospholipid coating improved the flux of both PVDF and cellulose acetate membranes, but was more effective on the former. Electron microscopy confirmed the reduction in fouling of the coated membranes.

Molecular Interactions between Proteins and Synthetic Membrane Polymer Films

To help understand the effects of protein adsorption on membrane filtration performance, we have measured the molecular interactions between cellulose acetate films and two proteins with different properties (ribonuclease A and human serum albumin) with a surface force apparatus. Comparison of forces between two protein layers with those between a protein layer and a cellulose acetate (CA) film shows that, at high pH, both proteins retained their native conformation on interacting with the CA film while at the isoelectric point (pI) or below the tertiary structure of proteins was disturbed. These measurements provide the first molecular evidence that disruption of protein tertiary structure could be responsible for the reduced permeation flows observed during membrane filtration of protein solutions and suggest that operating at high pH values away from the pI of proteins will reduce such fouling. 60 refs., 9 figs., 5 tabs.

The Filtration of Protein Solutions across Films of Renal Basement Membrane in vitro

The Filtration of Protein Solutions across Films of Renal Basement Membrane <i>in vitro</i>