Dispersion of super paramagnetic iron oxide nanoparticles in poly(d,l-lactide-co-glycolide) microparticles

Superparamagnetic iron oxide nanoparticles (SPIONs) coated with oleic acid were encapsulated into poly(d,l-lactide-co-glycolide) (PLGA) particles using an oil-in-water-in-oil emulsion technique. The use of the oleic acid-coated SPIONs, and their suspension in the first oil phase led to well-dispersed nanoparticles in the PLGA matrix. Relative amounts of SPIONs encapsulated in PLGA could be varied by increasing the concentration of SPIONs in the first oil phase: doubling the amount in that phase doubled the amount of SPIONs in the PLGA. The saturation magnetization scaled proportionally with the amount of SPIONs in the PLGA and was significantly larger than other efforts to encapsulate magnetic nanoparticles in PLGA. Size of the composite particles, as determined by dynamic light scattering (DLS), could be varied from 280 to 160 nm by varying either power or time of sonication while the zeta potential remained near −20 mV for the composite, independent of SPION content. Transmission electron microscopy images showed SPIONs ranging in diameter from 5 to 15 nm embedded inside the polymer and indicated that they were uniformly dispersed within the PLGA particles. Small angle X-ray scattering (SAXS) showed that only the particles containing the largest amount of encapsulated SPIONs displayed a peak indicative of aggregation.