Effect of PEG molecular weight on stability, T2 contrast, cytotoxicity, and cellular uptake of superparamagnetic iron oxide nanoparticles (SPIONs)

•SPIONs with various PEG MWs coating for potential atherosclerosis MRI contrast agents.•Optimal condition determined for stability, T2 contrast, cytotoxicity, and cellular uptake.•100ppm Fe SPION with PEG 2K showed the optimal condition for the application.•Cell viability increased when SPIONs were washed (simulating circulation). Superparamagnetic iron oxide nanoparticles (SPIONs) are currently unavailable as MRI contrast agents for detecting atherosclerosis in the clinical setting because of either low signal enhancement or safety concerns. Therefore, a new generation of SPIONs with increased circulation time, enhanced image contrast, and less cytotoxicity is essential. In this study, monodisperse SPIONs were synthesized and coated with polyethylene glycol (PEG) of varying molecular weights. The resulting PEGylated SPIONs were characterized, and their interactions with vascular smooth muscle cells (VSMCs) were examined. SPIONs were tested at different concentrations (100 and 500ppm Fe) for stability, T2 contrast, cytotoxicity, and cellular uptake to determine an optimal formulation for in vivo use. We found that at 100ppm Fe, the PEG 2K SPIONs showed adequate stability and magnetic contrast, and exhibited the least cytotoxicity and nonspecific cellular uptake. An increase in cell viability was observed when the SPION-treated cells were washed with PBS after 1h incubation compared to 5 and 24h incubation without washing. Our investigation provides insight into the potential safe application of SPIONs in the clinic.