BACKGROUND: Thermoresponsive hybrid Ni0.5Zn0.5Fe2O4 magnetic hydrogel particles based on PEG-g-poly(NIPAM-co-AMPS) were synthesized by soap-free emulsion polymerization of N-isopropylacrylamide (NIPAM) and 2-acrylamido-2-methylpropane sulphonic acid (AMPS) via a free radical mechanism using polyethylene glycol (PEG) as macro-initiator in the presence of N,N'-Methylenebisacrylamide (MBA) as crosslinking agent. The thermoresponsive pure copolymers and hybrid particles were characterized by Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), vibrating sample magnetometer (VSM) and dynamic light scattering (DLS). Furthermore, the hybrid magnetic particles were used to study the drug release characteristics of theophylline (TPH) as model drug at pH 7.4 and temperature 37 degrees C. RESULTS: The sizes of the particles were found to be 121 nm to 245 nm at 50 degrees C and 580 nm to 694 nm at 25 degrees C depending on the amount of AMPS present in the hybrid particles. The volume phase transition temperature (VPTT) of the hybrid particles was tuned above body temperature from 33 degrees C to 41 degrees C. The hybrid magnetic particles with incorporation of AMPS in polymer chains showed high TPH loading capacity compared with that of PEG-g-PNIPAM. The entrapment efficiency of TPH was increasing with increase of AMPS concentration. The releasing capacity of TPH was decreased with increase in AMPS concentration and observed to have sustained drug release profile without initial burst release. CONCLUSIONS: The prepared hybrid particles were both temperature sensitive as well as superparamagnetic, and thus found to be a suitable candidate for applications in targeted drug delivery system. (C) 2016 Society of Chemical Industry