Poly(N-isopropylacrylamide) Grafted on Plasma-Activated Poly(ethylene oxide): Thermal Response and Interaction With Proteins

Abstract

Thermoresponsive polymer layers offer the possibility of preparing smart surfaces with properties that are switchable through a phase transition, usually close to the lower critical solution temperature of the polymer. In particular, poly( N-isopropylacrylamide) (pNIPAM) has gained a great deal of attention because it has such a phase transition in a physiologically interesting temperature range. We have prepared ultrathin thermoresponsive coatings by grafting pNIPAM on a plasma-CVD-deposited, poly(ethylene oxide)-like polymer substrate that was activated in an Ar plasma discharge to initiate the grafting. The presence and integrity of pNIPAM was verified by XPS and ToF-SIMS, and a dramatic change in the wettability during the phase transition was identified by temperature-dependent contact angle measurements. The transition from the hydrated to the collapsed conformation was analyzed by temperature-dependent QCM measurements and by AFM. An unusual, reversible behavior of the viscoelastic properties was seen directly at the phase transition from the swollen to the collapsed state. The phase transition leads to a switching from protein repulsion to a state that allows the adsorption of proteins.

Thermoresponsive surfaces prepared using adsorption of a cationic graft copolymer: A versatile method for triggered particle capture

“…Even though PNIPAm gradually desorbed from the surface it was possible to measure h c values of 50°and 85°at 20 and 50°C, respectively, prior to significant adsorption occurring. Those values are similar to those reported by Heinz et al [37] for surfaces containing covalently bonded PNIPAm.…”

“…It has been reported that for surfaces containing covalently grafted PNIPAm chains [37] that the contact angle, h c , increases when the temperature increases above the LCST. The effect of linear PNIPAm70k adsorbed onto laponite/quartz on h c is first considered.…”

Quartz crystal microbalance electrode modified with thermoresponsive crosslinked and non-crosslinked N-isopropylacrylamide polymers. Response to changes in temperature

“…The literature reports on EQCM response on the phase transition are somewhat confusing. On some curves there is no minima, on others the minima are not so spectacular [26,28,29]. In our investigations, the differences in the behavior of both materials (crosslinked and non-crosslinked) can be related to the difference in the process of changing the volume of thin gel layers attached to the electrode surface.…”

“…However, in the literature, for a crosslinked pNIPA l a y e r o b t a i n e d v i a c h r o n o a m p e r o m e t r i c electropolymerization, that behavior was not observed [26]. The minima were shown in two other papers [28,29]. They were explained in terms of changing the polymer structure and coupling of the layer to the surrounding fluid.…”

“…However, in that paper, frequency change at the EQCM electrode was not examined under the conditions of the volume phase transition [27]. There are a few literature reports on EQCM response to layers of pNIPA [26,28,29]. These reports are somewhat contradictive; the presented EQCM responses differed much regarding the appearance of sharp, unexpected minima in the recorded output.…”