The Heating Effects of Dextran Coated Iron Oxides
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0962-P10-16
The Heating Effects of Dextran Coated Iron Oxides Qi Zeng1, Ian Baker1, and Jack Hoopes2 1 Thayer School of Engineering, Dartmouth College, Hanover, NH, 03755 2 Department of Surgery, Dartmouth College, Lebanon, NH, 03756
ABSTRACT The structural and quasi-static magnetic behaviors and the temperature rises of three Dextran-coated maghemite nanoparticles subjected to alternating magnetic field (AMF) were investigated for potential use in magnetic hyperthermia treatments. In order to elucidate the effect of the hydrodynamic particle size on the specific absorption rate, the temperature rises for various hydrodynamic particle sizes were investigated in AMFs of various strengths and frequencies. Structural characterization was performed using a TEM and a SEM as well as by dynamic light scattering, and the quasi-static magnetic hysteresis loops were measured using a VSM. The heating behavior is discussed in relation to the magnetic behavior and particle size. While it was found that the heating mechanism for the ferromagnetic particles was mainly magnetic hysteresis losses, Brownian relaxation losses also contributed to the heating. INTRODUCTION The first use of magnetic hyperthermia for the treatment of tumors dates back to only 1957 when Gilchrist et al. demonstrated through in vitro experiments that 20-100 nm dia. Fe2O3 o particles in lymph nodes could produce a temperature rise of 14 C in an AMF of 200-240 Oe at 1.2 MHz [1]. In selecting nanoparticles for magnetic hyperthermia, using those with the highest specific absorption rate (SAR) value is key. Having a large SAR not only minimizes the dose of nanoparticles required for hyperthermia treatment, thereby minimizing toxicity, but also allows smaller tumors to be treated [2]. Having a high SAR is also important because there is presumably a limit to the concentration of nanoparticles that a cell can uptake [2]. There is no ideal magnetic particle for all heating applications. Iron oxide particles, often coated with Dextran, seem to be the most commonly used in magnetic hyperthermia studies. This is for two reasons: they have excellent biocompatibility with almost zero toxicity [3], while also having a very high SAR, resulting in good heating [4]. Heating of ferromagnetic particles is largely due to hysteresis losses and Brownian relaxation losses. For the former, the heat per unit volume, PH = f ∫ HdB , where B is the magnetic induction, H is the applied field strength, and f is the frequency of the applied field. The hysteresis loop area, and hence PH, generally increase non-linearly with increasing H until the materials is magnetically saturated. The ideal response of a magnetic material to an applied AMF for clinical applications is to develop sufficient heat at the lowest possible f and H, a constraint arising from both field-induced eddy-current heating, and nerve-muscle actuation. It has been suggested [5] that for human use the product H⋅f should be ≤ 6×106Oe⋅Hz.
Our previous study showed that the heating effect depends strongly on the size, s
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