Thermosensitive Copolymer Coatings with Enhanced Wettability Switching

Abstract

Expanded cross-linked copolymers of poly(N-isopropylacrylamide) (PNiPAAm) and poly(acrylic acid) (PAAc) of varying monomer ratios were grafted from a crystalline silicon surface. Surface-tethered polymerization was performed at a slightly basic pH, where electrostatic repulsion among acrylic acid monomer units forces the network into an expanded polymer conformation. The influence of this expanded conformation on switchability between a hydrophilic and a hydrophobic state was investigated. Characterization of the copolymer coating was carried out by means of X-ray photoelectron spectroscopy (XPS) ellipsometry, and diffuse reflectance IR. Lower critical solution temperatures (LCSTs) of the copolymer grafts on the silicon surfaces were determined by spectrophotometry. Temperature-induced wettability changes were studied using sessile drop contact angle measurements. The surface topography was investigated by atomic force microscopy (AFM) in Milli-Q water at 25 and 40 degrees C. The reversible attachment of a fluorescently labeled model protein was studied as a function of temperature using a fluorescence microscope and a fluorescence spectrometer. Maximum switching in terms of the contact angle change around the LCST was observed at a ratio of 36:1 PNiPAAm to PAAc. The enhanced control of biointerfaces achieved by these coatings may find applications in biomaterials, biochips, drug delivery, and microfluidics.

In Situ Characterization of Thermo‐Responsive Poly(N‐Isopropylacrylamide) Films with Sum‐Frequency Generation Spectroscopy

“…The polymer chains exhibit temperature-dependent solvation behaviour in which they become less solvated with increasing temperature. This results in a thermo-responsive behaviour leading to applications in the areas of biointerfaces, [1][2][3][4][5][6] drug delivery systems, [7][8][9][10][11] permeation-controlled filters, [12] and functional composite surfaces. [13][14][15] In addition to bulk applications, pNIPAM films can be attached to a solid support by methods including atom transfer radical polymerization (ATRP), [16][17][18] initiated either by UV light [19] or by electron beam radiation.…”

Time-Resolved Polymer Propagation for Acrylic Acid-Mediated Nanolatexes Containing Magnetic Fe<SUB>3</SUB>O<SUB>4</SUB> Cores

“…For the sample prepared at 1 h reaction time the latex particles were larger than those produced at 0.5 h and the gel shrank due to a phase transition above the LCST. The particle diameter decreased from 190 to 160 nm as the temperature increased from 30 to 40 C. At a reaction time of 2 h, a typical volume shrinkage within a smaller temperature window (34)(35)(36) NIP-(AAc2.6-Fe)-2 sample. The diameter decreased from 250 to 170 nm.…”

Tissue Engineering of the Corneal Endothelium: A Review of Carrier Materials

“…Atomic force microscopy (AFM) was used to study the surface morphology of thermo-responsive coatings in the dry state, as well as in the swollen state [139,181,188]. Furthermore, AFM can provide a simple proof of the temperature-dependent swelling and, also, allows for estimating the degree of swelling [176].…”