“…The absorption of such systems by cells can be realized through specific endocytosis. Another possible trend in the use of fullerenes is the creation of bioactive [203,204,206,208] or contrast materials for nuclear magnetic resonance imaging (MRI) through internal functionalization by contrast agents, including Gd 3+ , Sc 3+ , Ho 3+ , Tm 2+ , Ga 3+ and Tc 2+ ions, with isolation of unstable and potentially toxic contrast materials from the internal medium of the body [209][210][211][212]. A similar solution for creating contrast materials is proposed in [213] for Keplerates, the non-carbon analogs of fullerenes which form ionic associates with cations of the above-mentioned metals.…”