Morphology Control of Thermosensitive Membranes and Fundamental Investigation of Its Protein Purification

Abstract

A novel separation system was demonstrated for protein purification. The pore surface of the porous substrate is covered with thermosensitive grafted polymer, and hydrophobicity of the pore surface can be drastically varied by small temperature change. A feed solution containing hydrophobic and hydrophilic proteins is continuously supplied to the feed side, and the membrane temperature is changed stepwise below and above a lower-critical solution temperature for the thermosensitive polymer. Hydrophobic proteins adsorb on the hydrophobic pore surface above the critical temperature, and only the hydrophilic protein can pass to the permeate side. When the temperature is changed to below the critical point, the pore surface becomes hydrophilic and the adsorbed proteins will be desorbed from the membrane, the the hydrophobic proteins might be condensed in permeate side. N-isopropyl acrylamide (NIPAM) was employed as the thermosensitive polymer, and the NIPAM grafted polymer was fixed in the pores of the porous base membranes by plasma-graft filling polymerization technique. The grafted polymer formation profile was controlled by changing plasma treatment and graft polymerization conditions. Above 32°C, the membrane adsorbed the globulin due to its hydrophobic interaction, and the solutes were desorbed from the pore surface below 32°C due to its hydrophilic nature. Solute adsorption and desorption took place each cycle, and the protein was concentrated in the permeate at the desorption step. The results show the potential of this separation system for protein purification.