Magnetic hyperthermic response of nanocomposites based on PEG2000-gallol-coated iron oxide nanoparticles dispersed in poly(N-isopropylacrylamide-co-acrylamide) hydrogels

Nanoparticles can be incorporated into hydrogel matrices by various means. Non-covalent methods such as blending and in situ co-precipitation are straightforward, but can result in uncontrolled diffusion of the nanoparticles... [ view full abstract ]

Nanoparticles can be incorporated into hydrogel matrices by various means. Non-covalent methods such as blending and in situ co-precipitation are straightforward, but can result in uncontrolled diffusion of the nanoparticles out of the gel. Covalent methods graft reactive groups onto the nanoparticle surface, which can then act as nano-crosslinkers, forming stable networks. [1]
Superparamagnetic iron oxide nanoparticles were synthesised step-wise from 6 nm seeds, according to the method by Sun. The hydrophobic oleic acid and oleylamine ligands were exchanged with the cathecol-bearing methoxy-PEG2000-gallol. These modified iron oxide nanoparticles could be transferred almost quantitatively into ethanol.
Subsequently, the methoxy-PEG2000-gallol coated nanoparticles were mixed with a solution containing various amounts of N-isopropyacrylamide, acrylamide, PEG700-diacrylate, ammonium persulfate, and TEMED. The solutions underwent thermal radical polymerisation to obtain the magnetic hydrogel nanocomposite. After purification, the gels were exposed to an AC magnetic field (475 kHz, 12.44 mT). Deswelling with respect to nanoparticle loading and acrylamide concentration was investigated. The methoxy-PEG chains on the nanoparticle surface ensure facile dispersion, a stable nanocomposite, with reproducible heating profile and deswelling behaviour.
Dhyd of the iron oxide nanoparticles was 44 nm and DTEM was 12 nm. For gels containing 200 µL of nanoparticle suspension (22.6 mM Fe, Tf=24.3°C), the deswelling ratio in the AC field was 8.6, 7.3, and 5.1%, respective of increasing acrylamide content. For gels containing 400 µL of nanoparticle suspension (45.1 mM Fe, Tf=32.1°C), the deswelling ratio was 39.7, 26.3, and 19.0%, respectively. For gels containing 800 µL of nanoparticle suspension (90.3 mM Fe, Tf=35.4°C), the deswelling ratio was 45.4, 43.1, and 26.4%, respectively.
The amount of acrylamide influences both the rates of swelling and deswelling in the hydrogel. Increasing iron oxide nanoparticle loading increases the temperature of the gels and accelerates the deswelling further. Both swelling and deswelling are reproducible for a given gel. It is planned to investigate deswelling of the gels at a baseline temperature of 37 °C.

[1] Li, Y., Huang, G., Zhang, X., Li, B., Chen, Y., Lu, T., Lu, T. J. and Xu, F. (2013), Magnetic Hydrogels and Their Potential Biomedical Applications. Adv. Funct. Mater., 23: 660–672. doi:10.1002/adfm.201201708