Magnetic nanoparticles for magnetic resonance imaging: modulation of macrophage uptake by controlled PEGylation of the surface coating

Magnetic nanoparticles (MNPs) have great potential as a contrast agent in magnetic resonance imaging (MRI). They can be used to label macrophages which then function as cellular probes to study inflammatory disorders such as atherosclerosis. Alternatively, they can be made to evade the reticuloendothelical system (RES) and attain a long blood circulation time to reach other target organs. The purpose of this work is to develop a polymer coating for MNPs which can be readily tuned to modulate the interaction of the MNPs with macrophages. The coating developed is based on poly(DL-lactic acid-co-malic acid) (PLMA) with adjustable polyethylene glycol (PEG) content. The physical, surface and magnetic properties, cytotoxicity and macrophage uptake of the polymer-coated MNPs were evaluated. The results indicated that a wide range of cellular iron concentration in macrophages can be achieved by changing the PEG content of the coating, the incubation time and the concentration of nanoparticles. No significant cytotoxicity was observed and the nanoparticles exhibited high magnetic resonance enhancement effects. Hence, these nanoparticles can be expected to be suitable for a wide range of MRI applications.