Thermal behavior of magnetically modalized poly(N-isopropylacrylamide)-chitosan based nanohydrogel

Poly(NIPAAm)-CS based nanohydrogels (NHGs) and iron oxide (Fe3O4) magnetic nanoparticles encapsulated magnetic nanohydrogels (MNHGs) were synthesized by free radical polymerization of N-isopropylacrylamide (NIPAAm) at 60 degrees C in presence of chitosan (CS) in different feed ratios. The polymerization of NIPAAm and the presence of CS as well as Fe3O4 in hydrogels were confirmed from Fourier transform infrared (FTIR) spectra and X-ray diffraction (XRD), respectively. C-13 solid state nuclear magnetic resonance (NMR) spectra clearly revealed the grafting of CS into poly(NIPAAm). The scanning electron microscopy (SEM) and atomic force microscopy (AFM) images showed the formation of spherical shaped NHGs of different sizes ranging from 50 nm to 200 nm depending upon the feed ratios of CS and NIPAAm, which was further supported by mean hydrodynamic diameter measured by dynamic light scattering (DLS). It has been observed that CS not only served as a cross linker during polymerization but also plays a critical role in controlling the growth of NHG and enhancement in lower critical solution temperature (LCST). The encapsulation of Fe3O4 nanoparticles (10-12 nm) into NHGs (similar to 200 nm) was confirmed by transmission electron microscopy (TEM) and further corroborated with magnetic force microscopy (MFM) image. The LCST of poly(NIPAAm) was found to increase with increasing weight ratio of CS to NIPAAm. Furthermore, the encapsulation of iron oxide nanoparticles into hydrogels also caused an increment in LCST. Specifically, temperature optimized NHG and MNHG were fabricated having LCST close to 42 degrees C (hyperthermia temperature). The MNHG shows optimal magnetization, good specific absorption rate (under external AC magnetic field) and excellent cytocompatibility with L929 cell lines, which may find potential applications in hyperthermia treatment of cancer and targeted drug delivery. (C) 2010 Elsevier B.V. All rights reserved.