Characterization of MRI contrast agent-loaded polymeric nanocapsules as versatile vehicle for targeted imaging

Various contrast agents (Magnevist, Gadovist and Multihance) loaded into polymeric nanocapsules were synthesized by the inverse miniemulsion technique. The relaxivity of the resultant contrast agents was assessed at 1.5 T magnetic field strength. The ionic relaxivity of the contrast agents could at least be maintained after their encapsulation in different polymer capsules. The chemical composition of the nanocapsules was characterized by Fourier transform infrared spectroscopy. The distribution of the contrast agent in the nanocapsules could be identified by energy filtered transmission electron microscopy and energy dispersive X-ray spectroscopy. The results indicate entrapment of the gadolinium complex into the inner shell of the polymeric nanocapsules. The payload of contrast agent per nanocapsule resulted in some 2.5 x 10(6) Gd(3+) complexes yielding a particle-based relaxivity of 10.75 x 10(6) mM(-1) s(-1). Maintained or even slightly increased ionic relaxivity of the different contrast agents after encapsulation in combination with high payloads and the possibility of functionalization of the capsules' surface facilitate the application of the nanocapsules as promising targeted contrast agents for MRI.