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

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 (pK(a) = 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 (T-p), which is defined as the temperature at which the particle size began to increase during the heating process, was 61.5 degrees 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.

Automated summary

In this study, pH- and thermoresponsive poly(N,N-dimethylaminoethyl methacrylate) was grafted onto the surface of superparamagnetic iron oxide Resovist via atom transfer radical polymerization, resulting in different zeta potential and physical properties of PDMA@Rv under different acidic conditions. Moreover, PDMA@Rv was observed to form aggregates above pH 7, indicating a lower critical solution temperature behavior.