Temperature and pH dual-responsive coatings of oligoperoxide-graft-poly(N-isopropylacrylamide): Wettability, morphology, and protein adsorption

Poly(N-isopropylacrylamide) (PNIPAM) coatings attached to glass with novel approach involving polymerization from oligoperoxide grafted to surface with (3-aminopropyl)triethoxysilane exhibit not only temperature- but also pH-dependence of wettability and protein adsorption. Wettability and composition of coatings, fabricated with different polymerization times, were determined using contact angle measurements and Time Of Flight-Secondary Ion Mass Spectrometry (TOF-SIMS), respectively. Thermal response of wettability, measured between 20 and 40 °C, was prominent at pH 9 and 7 and diminished or absent at pH 5 and 3. This indicates a transition between hydrated loose coils and hydrophobic collapsed chains that is blocked at low pH. Higher surface roughness and dramatically increased adsorption of model protein (lentil lectin labeled with fluorescein isothiocyanate) were observed with AFM and fluorescence microscopy to occur in hydrophobic phases (at pH 3, for pH varied at constant temperature of 22 °C and at ∼33 °C, for temperature varied at constant pH 9). Protein adsorption response to pH was confirmed by TOF-SIMS and Principal Component Analysis.

Graphical abstractFluorescence and multivariate TOF-SIMS analysis of pH- and temperature-controlled protein adsorption to the coatings.Figure optionsDownload full-size imageDownload high-quality image (125 K)Download as PowerPoint slideHighlights► Poly(N-isopropylacrylamide) brushes were polymerized from oligoperoxide on glass. ► Thermal but also pH-response is observed (as for mixed and copolymer brushes). ► Thermal sensitivity, observed in wettability, diminishes with decreasing pH. ► Increased temperature (at pH 9) and reduced pH (at 22 °C) lead to hydrophobic phase. ► Such transitions induce changes in coating morphology and protein adsorption.