Responsive membranes for hydrophobic interaction chromatography

Poly N-vinylcaprolactam (PVCL) chains were grown from the surface of regenerated cellulose membranes using atom transfer radical polymerization (ATRP). Modified membranes were characterized using scanning electron microscopy, infrared spectroscopy, X-ray photoelectron spectroscopy and by measuring surface contact angles. The grafting degree of PVCL increases with increasing ATRP initiator immobilization time. PVCL is a thermo-responsive polymer with a lower critical solution temperature (LCST) that depends on the concentration of salt ions present in solution. The LCST decreases below room temperature in buffer containing 1.8 M (NH3)2SO4 where the polymer adopts a more hydrophobic/collapsed conformation. At low ionic strength, the LCST remains above room temperature. Contact angles for PVCL in 20 mM phosphate buffer with and without 1.8 M (NH3)2SO4 were determined. Contact angles in the buffer with high ionic strength were higher than those in low ionic strength. Adsorption and desorption of bovine serum albumin (BSA) and immunoglobulin G (IgG) have been investigated. Loading was conducted in high ionic strength buffer. Elution was conducted in low ionic strength buffer. By using a responsive ligand that changes its conformation during loading and elution, high protein recoveries were obtained. Ligands that respond to solution ionic strength show promise for high performance hydrophobic interaction chromatography.