New biomimetic contructs for improved in vivo circulation of superparamagnetic nanoparticles.

Superparamagnetic iron oxide nanoparticles (SPIOs) have been produced and used as a potent and versatile contrast media for magnetic resonance imaging (MRI). Despite a number of efforts to improve their surface chemistry and biocompatibility, the SPIOs half life in blood circulation is very short and they are rapidly taken up by the reticuloendothelial system (RES). In this paper we describe a new method that permits to avoid the rapid clearance of SPIOs. Nanoparticles are made biocompatible by encapsulation into autologous red blood cells. These biomimetic constructs preserve the main properties of the cells that escape RES clearance as well as the properties of the nanoparticles that perform even better than in blood suspension with reduced T 2*. These SPIO-loaded RBCs are promising intravascular imaging contrast agents and could also be addressed to selected body compartments by an external magnetic field