For the sake of simplifying the processes of synthesizing polymer modified gadolinium-based MRI contrast agents

and preparing gadolinium-containing and temperature-sensitive polymeric microsphere in a facile way

we choose soap-free emulsion polymerization as a synthetic method.Temperature-sensitive polymeric microspheres are prepared by soap-free emulsion polymerization in the presence of temperature-sensitive monomer N-isopropylacrylamide and polymerizable gadolinium monomer.Transmission electron microscope tests show the monodispersity of the polymeric microspheres.The dynamic light scattering tests indicate that the hydrodynamic diameters of the polymeric microspheres are about 260 nm with narrow size distribution

the hydrodynamic diameters of the polymeric microspheres decrease by about 60 nm when temperature increases from 25 ℃ to 45 ℃

and the swelling ratio (defined as (Dh

25 ℃/Dh

45 ℃)3) is 2.06

indicating the good temperature-sensitive property of the polymeric microsphere.The contents of gadolinium in polymeric microsphere emulsion (solid content 1%) are 1 mg/L. In vitro T1-weighted ralaxivity (r1) at 3.0 T is 8.01 (mmol/L)-1 S-1

which is much higher than that of clinical gadolinium chelate (Gd-DTPA).The polymeric microspheres show great prospects in pre-clinical MR imaging.