Polydopamine Anchored Poly(2-methyl-2-oxazoline)/Poly(4-vinyl pyridine) Mixed Brushes with Switchable Properties for Pepsin Adsorption

Mixed polymer brushes coating based on poly (2-methyl-2-oxazoline)/poly(4-vinyl pyridine) (PMOXA/P4VP) was prepared by simultaneously grafting amine-terminated PMOXA and thiol-terminated P4VP onto poly(dopamine) (PDA)-modified substrates in this work. The coatings were characterized by X-ray photoelectron spectroscopy, ellipsometry, zeta potential measurements, and the static water contact angle tests. The results indicated that it is feasible to control the components of the coating by adjusting the feed ratio of PMOXA to P4VP. Moreover, the zeta potential and the water contact angle of mixed brushes modified surfaces could be tuned by changing the environmental pH value and surface compositions. Finally, fluorescein isothiocyanate-labelled pepsin assay and surface plasmon resonance were performed to investigate the responsive adsorption/desorption of pepsin by PMOXA/P4VP mixed brushes. The results showed that by adjusting the fraction of PMOXA or P4VP, the PMOXA/P4VP mixed brushes coated surfaces could adsorb a high amount of pepsin at pH=3, and achieve a desorption efficiency of over 92% at pH=7.