Zandrie Borneman

Preparation of mixed matrix adsorber membranes for protein recovery

This paper presents a generic technology allowing the incorporation of functional entities into a porous substrate. Various ion exchange particles were incorporated into an ethylene vinyl alcohol (EVAL) copolymer porous matrix by an immersion phase separation process and a heterogeneous matrix, composed of solid particles surrounded by a polymeric film, was formed. The developed concept is flexible and offers the possibility to easily adjust the geometry, the adsorption capacity, as well as the functionality of the structure. A series of fibers as well as flat membranes bearing an adsorptive function and high protein binding capacities were prepared. The membranes were characterized with respect to their morphology, porosity, permeability and adsorption capacity. High values of the protein adsorption capacity (40?45 mg bovine serum albumin (BSA)/ml membrane) were obtained by static adsorption experiments. In a sequential desorption step by changing the pH and/or the ionic strength of the eluent, up to 90% protein recovery can be obtained. Dynamic capacity experiments were performed by flowing the protein solution through a stack of 10 membranes. The protein mass adsorbed per unit of membrane bed was calculated at a breakthrough concentration 10% of the feed concentration. The adsorber membranes can be reused in multiple adsorption/desorption cycles without significant loss of performance.

Mixed-matrix membrane adsorbers for protein separation.

The separation of two similarly sized proteins, bovine serum albumin (BSA) and bovine hemoglobin (Hb) was carried out using a new type of ion-exchange mixed-matrix adsorber membranes. The adsorber membranes were prepared by incorporation of various types of Lewatit ion-exchange resins into an ethylene-vinyl alcohol copolymer porous structure. The obtained heterogeneous matrices, composed of solid particles surrounded by the polymeric film, display high static and dynamic protein adsorption capacities. The effect of operational parameters such as filtration flow-rate, pH, and ionic strength on the protein separation performances was investigated for cation- as well as anion-exchange adsorber membranes. An average separation factor was calculated by numerical integration of the protein concentration in the permeate curve during the filtration run. High average separation factor values were obtained for BSA-Hb separation at physiological ionic strength with a filtration flow-rate up to 20 1/h per m2, until the protein breakthrough point at 10% of the feed concentration.

Mixed matrix hollow fiber membranes for removal of protein-bound toxins from human plasma

In end stage renal disease (ESRD) waste solutes accumulate in body fluid. Removal of protein bound solutes using conventional renal replacement therapies is currently very poor while their accumulation is associated with adverse outcomes in ESRD. Here we investigate the application of a hollow fiber mixed matrix membrane (MMM) for removal of these toxins. The MMM hollow fiber consists of porous macro-void free polymeric inner membrane layer well attached to the activated carbon containing outer MMM layer. The new membranes have permeation properties in the ultrafiltration range. Under static conditions, they adsorb 57% p-cresylsulfate, 82% indoxyl sulfate and 94% of hippuric acid from spiked human plasma in 4 h. Under dynamic conditions, they adsorb on average 2.27 mg PCS/g membrane and 3.58 mg IS/g membrane in 4 h in diffusion experiments and 2.68 mg/g membrane PCS and 12.85 mg/g membrane IS in convection experiments. Based on the dynamic experiments we estimate that our membranes would suffice to remove the daily production of these protein bound solutes.

A novel approach for blood purification: Mixed-matrix membranes combining diffusion and adsorption in one step

Hemodialysis is a commonly used blood purification technique in patients requiring kidney replacement therapy. Sorbents could increase uremic retention solute removal efficiency but, because of poor biocompatibility, their use is often limited to the treatment of patients with acute poisoning. This paper proposes a novel membrane concept for combining diffusion and adsorption of uremic retention solutes in one step: the so-called mixed-matrix membrane (MMM). In this concept, adsorptive particles are incorporated in a macro-porous membrane layer whereas an extra particle-free membrane layer is introduced on the blood-contacting side of the membrane to improve hemocompatibility and prevent particle release. These dual-layer mixed-matrix membranes have high clean-water permeance and high creatinine adsorption from creatinine model solutions. In human plasma, the removal of creatinine and of the protein-bound solute para-aminohippuric acid (PAH) by single and dual-layer membranes is in agreement with the removal achieved by the activated carbon particles alone, showing that under these experimental conditions the accessibility of the particles in the MMM is excellent. This study proves that the combination of diffusion and adsorption in a single step is possible and paves the way for the development of more efficient blood purification devices, excellently combining the advantages of both techniques.

Selective removal of polyphenols and brown colour in apple juices using PES/PVP membranes in a single ultrafiltration process

Abstract Polyphenols that are responsible for haze formation and browning during storage of clear apple juice and concentrates could be selectively removed by an ultrafiltration process using tailor-made membranes out of polyethersulfone (PES) and polyvinylpyrrolidone (PVP). The results were compared with commercial regenerated cellulose acetate membranes. The PES/PVP-membranes were prepared with different pore sizes by varying the polymer composition. This study has shown that, due to the adsorption capacity of PVP, the tailor-made membranes were more effective than the commercial regenerated cellulose membranes for the reduction of both polyphenols and yellowish brown pigments in apple juices. The flux was also significantly higher. Polyphenol removal rates from the model solution were up to 40% for a membrane prepared from a 22.5 wt.% polymer solution with a PES/PVP ratio of 3.5. Initial adsorption and flux values could be restored easily by regenerating the membranes in 0.1 M NaOH.

Selective removal of polyphenols and brown colour in apple juices using PES/PVP membranes in a single-ultrafiltration process

Home-made membranes made of polyethersulfone (PES) and polyvinylpyrrolidone (PVP) were studied and compared with commercial cellulose membranes to reduce the amount of polyphenols and yellowish brown pigment in model solutions and apple juice. PES/PVP membranes were prepared with different pore sizes by varying the PES/PVP composition. At a pressure of 1 bar, no water flux was obtained through the membrane without PVP. In comparison with regenerated cellulose membranes, the PES/PVP membranes were found more effective for the reduction of polyphenols, as well as discoloration. The flux was also remarkably higher. Polyphenol removal rates from the model solution were up to 40% for a membrane prepared out of a solution with 22.5 wt% polymer in which the PES/PVP ratio is 3.5. Initial adsorption and flux values could be restored easily by regenerating the membranes in 0.1 M NaOH solution for 30 min.

Characterization of polyacrylonitrile ultrafiltration membranes

Various methods have been used to characterize ultrafiltration membranes, such as gas flux measurements, (field emission) scanning electron microscopy, permporometry and liquid-liquid displacement. Significant differences in the pore size distributions determined from permporometry and liquid-liquid displacement were found.

Mixed Matrix Membranes: A New Asset for Blood Purification Therapies

a Institute for Biomedical Technology and Technical Medicine MIRA, Biomaterials Science and Technology, and b Membrane Technology Group, Faculty of Science and Technology, University of Twente, Enschede , c Department of Internal Medicine, University Hospital Maastricht, Maastricht , and d Department of Nephrology and Hypertension, University Medical Center Utrecht, Utrecht , The Netherlands; e State Key Laboratory for Modification of Chemical Fibers and Polymer Materials, College of Material Science and Engineering, Donghua University, Shanghai , PR China

Anisotropic Dye Adsorption and Anhydrous Proton Conductivity in Smectic Liquid Crystal Networks: The Role of Cross-Link Density, Order, and Orientation

In this work, the decisive role of rigidity, orientation, and order in the smectic liquid crystalline network on the anisotropic proton and adsorbent properties is reported. The rigidity in the hydrogen-bonded polymer network has been altered by changing the cross-link density, the order by using different mesophases (smectic, nematic, and isotropic phases), whereas the orientation of the mesogens was controlled by alignment layers. Adding more cross-linkers improved the integrity of the polymer films. For the proton conduction, an optimum was found in the amount of cross-linker and the smectic organization results in the highest anhydrous proton conduction. The polymer films show anisotropic proton conductivity with a 54 times higher conductivity in the direction perpendicular to the molecular director. After a base treatment of the smectic liquid crystalline network, a nanoporous polymer film is obtained that also shows anisotropic adsorption of dye molecules and again straight smectic pores are favored over disordered pores in nematic and isotropic networks. The highly cross-linked films show size-selective adsorption of dyes. Low cross-linked materials do not show this difference due to swelling, which decreases the order and creates openings in the two-dimensional polymer layers. The latter is, however, beneficial for fast adsorption kinetics.

Semi-continuous protein fractionating using Affinity Cross-Flow Filtration

Protein purification by means of downstream processing is increasingly important. At the University of Twente a semi-continuous process is developed for the isolation of BSA out of crude protein mixtures. For this purpose an automated Affinity Cross-Flow Filtration, ACFF, process is developed. This process combines the advantages of both affinity adsorption, having high resolution, and microfiltration, for rapid and large continuous processing capacity. The overall process contains 4 sequential steps: affinity binding; purification; dissociation; regeneration. In the first step binding of the desired protein to a tailor-made ligand-immobilized particle is established. This temporary fixation of target proteins on a large entity allows us to wash out the unbound components in the purification step using high flux microfiltration membranes. After washing out the unbound proteins the target protein-ligand immobilized particle complex is dissociated by adding an appropriate salt. In a second filtration cycle the purified protein can be collected as the permeate. In the last step the ligand-immobilized particle is regenerated for the next cycle with buffer. Using this process it was possible to obtain the target protein BSA with a purity of more than 95%.