Synthesis of Stimuli-Responsive Polymer Brushes on Cellulose Membranes for the Reduction of Protein Fouling on Membranes Used for Field-Flow Fractionation

Synthesis of Stimuli-Responsive Polymer Brushes on Cellulose Membranes for the Reduction of Protein Fouling on Membranes used for Field-Flow Fractionation

                Field-Flow Fractionation (FFF) is an analytical technique used to separate macromolecules such as polymers, nanoparticles, and proteins. The technique employs a flowing fluid with a laminar velocity profile inside a small, ribbon-like channel. The analyte is separated in the channel via two competing forces. The first is applied by the user (electric, thermal, hydraulic, etc.) and causes the analyte injected into the channel to sink to the bottom. This defines the type of FFF, as well as the kind of samples the technique can separate. The opposing force is molecular diffusion, which causes the analyte to rise from the bottom according to a physical parameter such as size. Each particle diffuses away from the channel wall towards the center of the flowing fluid, reaching faster layers of liquid in the channel. Thus, the particles are separated by reaching different fluid velocity layers.

                In Cross-Flow Field-Flow Fractionation (AF4), the applied force is another fluid crossing the laminar separation stream. To allow the crossing of fluids, a membrane must be present at the bottom of the channel which allows the crossing liquid to exit, but not the analyte. The addition of a membrane into AF4 also introduces a challenge associated with membranes used in other separations. This problem is called membrane fouling, which is simply the adsorption of matter to the surface of a membrane. The cellulose membranes used in AF4 are prone to fouling by proteins; a problem my research addresses.

                Polymer brushes are end-attached polymer chains which are covalently linked to a surface. The grafting of polymer brushes from or to a surface allows the tuning of surface properties without altering the overall bulk properties of the material. Thus, in order to reduce membrane fouling by proteins in AF4, poly(N-isopropylacrylamide) (PNIPAM), a temperature-responsive polymer shown to reversibly adsorb and desorb to proteins, was grafted from the cellulose membranes used in the separation technique.

Using Atom-Transfer Radical Polymerization (ATRP) and a novel scale-up procedure which can be completed in-lab, a method for the synthesis of PNIPAM brushes on cellulose membranes used in AF4 has been developed. The effects of these brushes on membrane fouling are currently under investigation.  If successful, this study may lead to a solution to membrane fouling in AF4 which can be applied to other separations.