Influence Of Poly(Acrylic Acid)Grafting Density On The Performance Of Poly(2-methyl-2-oxazoline)/poly(Acrylic Acid)mixed Brushes

Poly(2-methyl-2-oxazoline(PMOXA)based polymers have drawn considerable attention recently because of their similar or better properties to poly(ethylene glycol)(PEG),i.e.low toxicity,good hydrophilicity,biocompatibility,excellent antifouling ability,and high stability in oxidizing media because of their peptidomimetic structure.Poly(acrylic acid)(PAA)is a typical weak polyacid bearing carboxylic group on each repeating unit,with a pKa situated around 5.It is widely used in the study of protein adsorption/release systems.In this paper,the PMOXA/PAA binary mixed brush was prepared by grafting-to method.The effect of the grafting density of PAA on the performance of the mixed brush was studied.The specific work is as follows:Firstly,we employed poly(dopamine)(PDA)as an anchor to obtain a series of PMOXA/PAA mixed brush coatings by sequential grafting-to methods with PAA chains longer than PMOXA chains.Then the prepared mixed brush coatings were rigorously characterized in terms of the fraction of surface roughness,surface coverage,surface chemical composition,and thickness using atomic force microscope(AFM),cyclic voltammetry(CV),X-ray photoelectron spectroscopy(XPS),and ellipsometry.The results showed that the grafting density of PAA in mixed brushes could be well adjusted by changing the concentration of PAA solution used for the preparation of mixed brush coatings.The switchable properties of PMOXA/PAA mixed brush coatings toward hydrophilicity and lysozyme adsorption/desorption were monitored with static water contact angle(WCA)and surface plasmon resonance(SPR)upon pH and ionic strength(I)change.The results indicated that the amounts of lysozyme adsorbed on PMOXA/PAA mixed brushes increased with increasing the grafting density of PAA chains while the desorption percentage decreased with increasing grafting density of PAA chains.When the grafting density of PAA is about one-half of PMOXA chains,the mixed brush could absorb high amounts of lysozyme(898.4 ng cm-2)at pH 7(I=10-5 M)and then more than 90%of adsorbed proteins could be released sharply by changing pH and I to pH 3(I=10-1 M).