Charged porous membrane structures for separation of biomolecules

Thesis presents various membrane techniques for biomolecules separation. New charged membranes and new methods to introduce charge into the membranes are demonstrated. All chapters present characterization of the hollow fiber membranes produced via the immersion precipitation dry-wet spinning. Apart from the spinning technique, the phase separation in-situ and polymer foaming are explored, too. A model protein or a model protein mixture is investigated in each chapter to give a proof of concept of the new method. Bovine serum albumin is used, as this protein is known of its stability, lack of effect in many biochemical reactions and low cost. First, a new in-line method of introduction charge onto the bore surface of the hollow fiber membrane in a one-step spinning process is described. A negatively charged polyelectrolyte sulphonated poly(ether ether ketone) (SPEEK) is dissolved in the bore liquid and during the membrane formation deposited on the bore surface. Secondly, a crosslinking agent for the membrane forming polymer, the polyethyleneimine (PEI) is dissolved in the bore liquid. This is a new method of simultaneous membrane formation and chemical modification in a one-step spinning process. It is shown that two types of membranes: either a completely crosslinked and porous fiber (for ultrafiltration), or a porous fiber with crosslinked dense inner layer (for gas separation), can be produced via the same spinning procedure, only by changing the composition of the bore liquid and/or shell liquid and dope solution. Third method explores application of mixed matrix membranes for adsorption of biomolecules. These membranes are produced by dispersion of negatively charged particles in the matrix polymer. The novelty of this work is that the membranes are crosslinked and for the first time applied for the adsorption of biomolecules (lysozyme and cholesterol) from organic solvents, rather than from aqueous solutions. The last part introduces membrane technology in a completely new field, capillary elelectrochromatography (CEC) – a hybrid analytical separation technique. Here, membrane fabrication methods described previously, together with new methods, are applied for preparation of novel stationary phases for CEC columns, which are tested in a laboratorydesigned and laboratory-built CEC unit.