Polishing monoclonal antibody using pH-responsive TiO₂/polysulfone membrane in dual size-exclusion strategy

Membrane with pH-responsiveness offers an alternative to simplify the multiple steps in purification using dual size-exclusion strategy regulated by pH switch. In this work, a pH-responsive polysulfone (PSf) membrane was synthesized to control the permeation of a monoclonal anti-ubiquitin single chain fragment variable (scFv) antibody. The change of solution pH allowed the switch of membrane's exclusion limits, retaining scFv at high pH and releasing scFv at low pH in a single unit. The small impurities could be removed from scFv at high pH while the larger impurities could be separated from scFv at low pH. The PSf membrane was incorporated with TiO₂ nanoparticles grafted with the pH-responsive polymer, poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA). FTIR confirmed that PDAMEMA was successfully grafted on TiO₂ nanoparticles. The higher ratio of DMAEMA to TiO₂ in grafting could result in the more significant protonation, improving the dispersion of TiO₂ nanoparticles. Energy dispersive X-ray analysis proved that PDMAEMA-TiO₂ nanoparticles were successfully incorporated into PSf membrane with finger-like structure as shown in scanning electron microscopic images. The molecular cut-off of membrane was improved for the pH-controlled filtration of scFv. PDMAEMA-TiO₂/PSf membrane in tangential filtration rejected scFv at pH 8 but allowed the permeation of scFv at pH 6 as proven by the sodium dodecyl sulfate polyacrylamide gel electrophoresis. By changing the buffer solution from pH 8 to pH 6, pH-responsive membrane with dual size-exclusion property could be used to purify monoclonal antibody sustainably without chromatography polishing steps.