Magnetic nanoparticles continue to garner widespread interest in biomedical applications, such as visualization agents in MRI, therapeutic vehicles for drug delivery and heat mediators in hyperthermia. Recent advances in colloidal synthesis and surface-functionalization techniques have greatly contributed to the design of functionalized magnetic nanoparticles with controlled properties and multifunctional capabilities, which are harnessed for dual diagnostic and therapeutic purposes. The surface-functionalization methods in particular have aided in obtaining magnetic nanoparticles coated with molecules, with tailored functionalities that enhance their applications. In this article, the methods of synthesis and functionalization are examined, with emphasis on how these impact their biomedical applications.

Core magnetite (Fe(3)O(4)) nanoparticles have been functionalized with a model intelligent hydrogel system based on the temperature responsive polymer poly(n-isopropyl acrylamide) (PNIPAAm) to obtain magnetically responsive core-shell nanocomposites. Fe(3)O(4) nanoparticles were obtained from a one-pot co-precipitation method which provided either oleic acid (hydrophobic) or citric acid (hydrophilic) coated nanoparticles. Subsequent ligand exchange of these coatings with various bromine alkyl halides and a bromo silane provided initiating sites for functionalization with NIPAAm using atom transfer radical polymerization (ATRP). The bromine alkyl halides that were used were 2-bromo-2-methyl propionic acid (BMPA) and 2-bromopropionyl bromide (BPB). The bromo silane that was used was 3-bromopropyl trimethoxysilane (BPTS). The intelligent polymeric shell consists of NIPAAm crosslinked with poly(ethylene glycol) 400 dimethacrylate (PEG400DMA). Fourier transform infrared (FTIR) spectroscopy, thermogravimetric analysis (TGA), and transmission electron microscopy (TEM) were used to confirm the presence of the polymeric shell. Dynamic light scattering (DLS) was used to characterize the nanocomposites for particle size changes with temperature. Their magnetic and temperature responsiveness show great promise for further biomedical applications. This platform for functionalizing magnetic nanoparticles with intelligent hydrogels promises to impact a wide range of medical and biological applications of magnetic nanoparticles.

Magnetically responsive hydrogel networks based on composites of magnetic nanoparticles and temperature responsive hydrogels were developed. These systems show great promise as active components of microscale and nanoscale devices and are expected to have a wide applicability in various biomedical applications. Specifically, nanocomposite hydrogel systems based on the temperature sensitive N-isopropylacrylamide hydrogels crosslinked with ethylene glycol dimethacrylate, tetraethylene glycol dimethacrylate, and poly(ethylene glycol) 400 dimethacrylate (PEG400DMA) were synthesized and characterized. The composite systems were synthesized by UV free-radical polymerization. Iron oxide magnetic nanoparticles were incorporated into the hydrogel systems by polymerizing mixtures of the nanoparticles and monomer solutions. The swelling response of these composite systems to different crosslinking molecular weights, temperature, and the effect of the presence of the magnetic nanoparticles were examined.

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