PH responsive switchable protein adsorption properties of poly(2-methyl-2-oxazoline)/ poly(4-vinyl pyridine) based coatings: Influence of poly(4-vinyl pyridine) chain length and ionic strength

Abstract

Protein adsorption at interfaces is a key for many applications especially in the biomedical field, biotechnologies, biocatalysis, food industry, etc. The development of surface layers that allow to control and manipulate protein adsorption is thus highly desired. To achieve this desired goal, we designed a smart thin stimuli responsive coating based on poly[(2-methyl-2-oxazoline)-random-glycidyl methacrylate)] (PMOXA-r-GMA) comb copolymer and poly(4-vinyl pyridine)-block-poly(glycidyl methacrylate) (P4VP-b-PGMA) block copolymer and scrutinized its ability to control protein adsorption properties by unraveling the effect of ionic strength (I) along with the pH of the surrounding medium and variation of chain length of P4VP. Firstly, PMOXA/P4VP based coatings were prepared by spin coating the mixture of PMOXA-r-GMA and P4VP-b-PGMA copolymer solutions onto silicon substrates followed by annealing at 110 °C. The surface composition and morphology of the PMOXA/P4VP based coatings were evaluated through X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). The switchable ability of the coating with the variation of chain length of P4VP upon pH and ionic strength trigger was characterized by water contact angle (WCA) and variable angle spectroscopic ellipsometry (VASE). The experimental observations illustrated that the change in the water contact angle (ΔWCA) and thickness (Δh) were found to be maximum when the chain length of P4VP was almost three times that of PMOXA while turning the environmental condition from pH 3, with low ionic strength (I = 10−3 M) to pH 9 with high ionic strength (I = 10-1 M). Finally, the adsorption and desorption behavior of mixed polymer coating against bovine serum albumin (BSA) protein was analyzed qualitatively and quantitatively using the fluorescein isothiocyanate-labelled BSA (FITC-BSA) assay and quartz crystal microbalance with dissipation monitoring (QCM-D), respectively. The low ionic strength (I = 10-3 M) at pH 3, caused to increase the adsorption of BSA and this increment was enhanced by increasing the chain length of P4VP in PMOX/P4VP based coatings. Subsequently, the adsorbed protein was then efficiently desorbed by changing the conditions to pH 9, I = 10-1 M, as well as the maximum desorption percentage (> 92 %) could be obtained at these optimized conditions in PMOXA/P4VP based polymer coatings.