(292c) Award Submission: Radiofrequency Actuation of Iron Oxide-Hydrogel Nanocomposites: Experimental Analysis and Modeling

Hydrogels and hydrogel nanocomposites are attractive materials for a variety of biomedical/pharmaceutical applications. In recent studies, magnetic hydrogel composites of N-isopropylacrylamide (NIPAAm) hydrogels have been demonstrated as pulsatile drug delivery systems with radiofrequency(RF) at 293 kHz as a trigger.1 In another study, magnetic nanocomposites were demonstrated as actuators in microfluidic device, with ability to control the flow by application of RF.2 Some of the other applications being pursued with these systems is use of RF induced heating for hyperthermia cancer treatment. All these applications rely heavily on design of the nanocomposite systems. In order to achieve desired response from hydrogel nanocomposite system, it is very important to understand the heating induced by application of RF and resultant change in the hydrogel properties.

Goal of this study was to analyze and predict nanocomposite response based on hydrogel composition, nanoparticle loading, RF strength, and nanocomposite dimensions. Magnetic nanocomposites of poly (ethylene glycol) hydrogels were synthesized with iron oxide (Fe3O4) nanoparticles. Different nanocomposite systems were obtained by variation of nanoparticle loadings and hydrogel composition. 293 kHz RF was applied to nanocomposite discs and surface temperatures were analyzed using infrared (IR) thermography. The strength of RF was varied to further analyze the heating effect.

A heat transfer model was developed to account heat generation due to RF as well as heat loss to surroundings. By fitting the temperature data, a correlation was obtained for dependence of heat generation on nanoparticle loadings, and RF strength. It was demonstrated that the model could successfully predict the resultant temperatures by using a hydrogel system with different swelling properties. The heating analysis was further extended for potential hyperthermia cancer treatment applications. The bioheat equation was used to account the heat transport in vivo, and resultant nanocomposite temperatures were predicted.

In the case of NIPAAm nanocomposites, RF heating is accompanied by collapse, which forces the fluids out of hydrogel network. Magnetic NIPAAm nanocomposites of different dimensions (thickness) were synthesized and subjected to RF heating. The resultant collapse and recovery process was quantified by weight measurements at different time points. The heat transfer model was modified to account change in the mass as hydrogel collapsed. Furthermore, a mass transfer model was developed for transport of liquid as the nanocomposite collapsed and recovered.

1. Satarkar, N. S.; Hilt, J. Z. J. Control. Rel. 2008, 130, 246-251.

2. Satarkar, N. S.; Zhang, W.; Eitel, R. E.; Hilt, J. Z. Lab Chip 2009, In Press.