PH- and thermoresponsive aggregation behavior of polymer-grafted magnetic nanoparticles

Abstract

Commercially available Resovist is a superparamagnetic iron oxide used as a magnetic resonance imaging contrast agent. In this study, pH- and thermoresponsive poly(N,N-dimethylaminoethyl methacrylate) (PDMAEMA) was grafted onto the surface of Resovist (PDMA@Rv) via atom transfer radical polymerization. The zeta potential of PDMA@Rv was positive at pH values lower than the acid dissociation constant (pKa = 6.2) of the grafted PDMAEMA because of the protonation of the pendant tertiary amino groups. At pH 5.4, PDMAEMA became hydrophilic, and the size of PDMA@Rv remained constant, irrespective of temperature. Above pH 7, the zeta potential showed a negative value because of the deprotonation of the pendant tertiary amino groups in the grafted PDMAEMA chains. PDMA@Rv formed aggregates and showed lower critical solution temperature behavior above pH 7. The phase transition temperature (Tp), which is defined as the temperature at which the particle size began to increase during the heating process, was 61.5 °C for PDMA@Rv at pH 7.4. PDMA@Rv contained a larger number of core particles of iron oxide than Resovist, which reduced the initial magnetic susceptibility due to the interaction of the core magnetic particles inside PDMA@Rv. pH- and thermoresponsive polymer bearing pendant tertiary amino groups was grafted onto the surface of Resovist (PDMA@Rv). At pH 5.4, the grafted-polymer became hydrophilic, and the size of PDMA@Rv remained constant, irrespective of temperature. PDMA@Rv formed aggregates and showed lower critical solution temperature behavior above pH 7. PDMA@Rv contained a larger number of core particles of iron oxide than Resovist, which reduced the initial magnetic susceptibility due to the interaction of the core magnetic particles inside PDMA@Rv.