Magnetic thermosensitive core/shell microspheres: synthesis, characterization and performance in hyperthermia and drug delivery

Abstract

In order to explore a stable and biocompatible material for encapsulating magnetic nanoparticles and supporting thermosensitive polymers, the present study describes a facile route for preparing monodisperse hybrid microspheres with superparamagnetic cores, in which Fe₃O₄ nanocrystals are encapsulated in carbon microsphere matrices (Fe₃O₄/carbon). Magnetic thermosensitive core/shell structure microspheres were prepared using Fe₃O₄/carbon microspheres as cores, N-isopropylacrylamide as a thermosensitive monomer, potassium persulfate as initiator and N,N-methylene bisacrylamide as crosslinker. A series of investigations using field emission scanning electron microscopy, transmission electron microscopy, Fourier transformation infrared spectroscopy, thermogravimetry and dynamic light scattering was carried out to characterize the hybrid microspheres. The as-synthesized microspheres have a hydrodynamic diameter of 280 nm with a lower critical solution temperature at around 45 °C. They are superparamagnetic with a saturation magnetization of 13.75 emu g⁻¹ at 20 kOe. They generate heat when an inductive magnetic field is applied to them and have a specific absorption rate of 77.0 W g⁻¹ at 230 kHz and 290 Oe, showing good potential for hyperthermia. The controlled release experiments demonstrate that the microspheres have excellent drug-loading and temperature-triggered drug-release ability for 5-fluorouracil.