Current Gd-based MRI contrast agents suffer from toxicity spurring a resurgence of interest in Gd-free MRI agents. Towards this goal, we have developed a new class of efficient and biocompatible MRI contrast agents based on micellar nanoparticles formed from amphiphilic poly(Fe<sup>III</sup>-catecholate)-based copolymers. Compared with recently reported natural or synthetic melanin-based T<sub>1</sub> agents, our approach utilizes well-defined tri-block copolymers prepared via a controlled living polymerization method. This synthetic route gives access to a tunable polymer system and hence, differently shaped self-assembled nanoparticles with controlled physical parameters. These nanoparticles have the potential to be used for various applications in diagnostic radiology and imaging, due to their enhanced relaxivity, and long-term stability in biological media. Moreover, we further demonstrate that the resulting nanoparticles provide enhanced positive contrast for MR imaging in HeLa cells. Notably, we observed shape-dependent behavior in terms of cellular uptake with cylindrical micelles exhibiting brighter contrast and shorter relaxation times than the analogous spherical micelles. We present this study with the goal that it stimulates further investigation of polycatechol nanoparticles in terms of their potential as Gd-free MRI contrast agents. Work in our laboratory on shape-dependent behavior in vivo is underway with respect to both intraperitoneal and intravenous delivery of polycatechol nanoparticle-based contrast agents.

Polycatechol nanoparticle MRI contrast agents

251st National Meeting (2016)

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