M.E. Avramescu

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.

Preparation of ethylene vinylalcohol copolymer membranes suitable for ligand coupling in affinity separation

Hydrophilic microfiltration membranes with functional groups that can be used as coupling sites for ligands are of central interest in affinity separation, especially in view of biomedical applications. In this study, we employed ethylene vinyl alcohol copolymer (EVAL) to prepare macrovoid-free open cellular-type membranes with a high internal surface area and interconnectivity that can chemically be modified in aqueous and organic media. To tailor the required membrane morphology, we investigated the ternary water/DMSO/EVAL system and quaternary systems using a series of n-alcohols (n=2?12) as non-solvent additives in the casting solution. Addition of solvent (DMSO) to the coagulation bath (water) performed in the ternary system to delay the onset of liquid?liquid demixing, resulted in structures dominated by solid?liquid demixing before macrovoid formation was completely suppressed. The symmetric particulate membranes obtained did not display the necessary mechanical strength. Addition of medium chain alcohols (n=7?8) in the casting solution yielded macrovoid-free cellular membranes with a significantly higher pore interconnectivity and structural integrity upon drying. A model is proposed to understand the influence of the alcohol chain length and concentration on the membrane morphology.

Functionalised ethylene vinyl alcohol copolymer (EVAL) membranes for affinity protein separation

Hydrophilic microfiltration membranes with functional groups that can be used as coupling sites for ligands are of central interest in affinity separation, especially in view of biomedical applications. In this study we investigate covalent coupling of bovine serum albumin (BSA) as model ligand onto cellular-type poly(ethylene vinyl alcohol) (EVAL) microfiltration membranes. EVAL membranes prepared from the ternary water/DMSO/EVAL system are only suitable for activation and coupling reactions in aqueous media. Employing glutaraldehyde (GA) or oxiran to activate the secondary alcohol groups of the vinyl alcohol segments yielded a BSA-immobilization per internal area of 0.1–0.2 μg/cm2 (4–8 mg/g per membrane mass). Preparing microfiltration membranes from the quaternary water/1-octanol/DMSO/EVAL system, using 1-octanol as nonsolvent-additive in the casting solution, enabled to perform surface functionalization reactions in organic media as well as surface activation by a low-pressure glow discharge treatment. 0.3–0.45 μg/cm2 BSA per internal area (16–18 mg/g per membrane mass) was covalently coupled onto the porous membranes by applying trichloro-s-triazine (sTT) or sulfonyl chloride activation reactions, while a BSA-immobilization of 0.5–0.55 μg/cm2 (20–22 mg/g per membrane mass) was reached via plasma activation. To determine the degree of BSA-immobilization, the internal surface area of the membranes prepared was measured by BET. The formation of a BSA-monolayer is assumed on the pore surface as maximum immobilization. Such membranes can function as adsorptive devices for endotoxin removal from blood or blood plasma.