Fe3O4/poly(N-Isopropylacrylamide)/Chitosan Composite Microspheres with Multiresponsive Properties

Multiresponsive composite microspheres were fabricated via emulsion polymerization in two steps. Fe 3 O 4 nanoparticles modified by oleic acid (about 13 nm in diameter) were first prepared, and then they were embedded in biocompatible chitosan (CS) and N -isopropylacrylamide (NIPAm). Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and thermogravimetric analysis (TGA) examined the structure and morphology of the composite microspheres. Scanning electron microscopy (SEM) and transmission electronic microscopy (TEM) indicate the diameter of the composite microspheres to be about 400 nm. The magnetic, thermo, and pH-sensitive properties of the composite microspheres were investigated. Magnetic measurements with magnet and superconducting quantum interference device (SQUID) reveal that the composite microspheres are superparamagnetic. The electromagnetically induced heating shows that the composite microspheres could be heated up to 45 °C in an alternating electromagnetic field. The dynamic light scattering (DLS) results confirm the thermoresponsive and pH-responsive properties. It was found that the lower critical solution temperature (LCST) of the composite microspheres is 29 °C in water, and the LCST changed from 28 to 32 °C in the pH range from 4.7 to 7.4. These composite microspheres with the multiresponsive properties show great promise in biomedical applications.