Relaxivity Enhancement of Hybrid Micelles via Modulation of Water Coordination Numbers for Magnetic Resonance Lymphography

Considerable efforts have been made to develop nanoparticle-based magnetic resonance contrast agents (CAs) with high relaxivity. The prolonged rotational correlation time (t(R)) induced relaxivity enhancement is commonly recognized, while the effect of the water coordination numbers (q) on the relaxivity of nanoparticle-based CAs gets less attention. Herein, we first investigated the relationship between T-1 relaxivity (r (1)) and q in manganese-based hybrid micellar CAs and proposed a strategy to enhance the relaxivity by increasing q. Hybrid micelles with different ratios of amphiphilic manganese complex (MnL) and DSPE-PEG2000 were prepared, whose q values were evaluated by Oxygen-17-NMR spectroscopy. Micelles with lower manganese doping density exhibit increased q and enhanced relaxivity, corroborating the conception. In vivo sentinel lymph node (SLN) imaging demonstrates that DSPE-PEG/MnL micelles could differentiate metastatic SLN from inflammatory LN. Our strategy makes it feasible for relaxivity enhancement by modulating q, providing new approaches for the structural design of high-performance hybrid micellar CAs.

Automated summary

This study investigates the effect of water coordination numbers on the relaxivity of manganese-based hybrid micellar contrast agents and proposes a strategy to enhance relaxivity by increasing the water coordination numbers. The results demonstrate the feasibility of the strategy and show the potential of the hybrid micelles for in vivo imaging.