Published by the American Institute of Physics. Related ArticlesFe3O4-citrate-curcumin: Promising conjugates for superoxide scavenging, tumor suppression and cancer hyperthermia J. Appl. Phys. 111, 064702 (2012) Integrated intravital microscopy and mathematical modeling to optimize nanotherapeutics delivery to tumors AIP Advances 2, 011208 (2012) In vitro cytotoxicity of Selol-loaded magnetic nanocapsules against neoplastic cell lines under AC magnetic field activation J. Appl. Phys. 111, 07B335 (2012) Magnetically driven spinning nanowires as effective materials for eradicating living cells J. Appl. Phys. 111, 07B329 (2012) Experimental characterization of electrochemical synthesized Fe nanowires for biomedical applications J. Appl. Phys. 111, 056103 (2012) Additional information on J. Appl. Phys. We show both experimental evidences and Monte Carlo modeling of the effects of interparticle dipolar interactions on the hysteresis losses. Results indicate that an increase in the intensity of dipolar interactions produce a decrease in the magnetic susceptibility and hysteresis losses, thus diminishing the hyperthermia output. These findings may have important clinical implications for cancer treatment.

The specific absorption rate (SAR) of a maghemite-based ferrofluid, measured at 315 K, 3 kA/m, and 109 kHz, was found to double as the ferrofluid concentration was decreased by a factor of 4. The ferrofluid contained nonagglomerated, highly crystalline, and monodisperse nanoparticles with an average size of 11.6 nm and an initial concentration of 8.14 mg/mL. The magnetic characterization of three different concentrations of this ferrofluid revealed several effects typical of the presence of magnetic interactions, such as the decrease of initial susceptibility values (liquid ferrofluid) and Néel relaxation times, τN (frozen ferrofluid), with increasing concentration. The accurate SAR determination in adiabatic conditions allowed estimating the τN values of the liquid ferrofluid, which displayed the same trend against concentration as those obtained in the frozen state. Such a trend allowed explaining qualitatively the degradation of the heating performance of the ferrofluid upon increasing concentration. Eventually, correlation between τN values in both states was discussed in terms of several theoretical models described in the literature and developed to explain the properties of an assembly of nanoparticles with dipolar interactions.

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Accurate measurements of the specific absorption rate ͑SAR͒ of solids and fluids were obtained by a calorimetric method, using a special-purpose setup working under adiabatic conditions. Unlike in current nonadiabatic setups, the weak heat exchange with the surroundings allowed a straightforward determination of temperature increments, avoiding the usual initial-time approximations. The measurements performed on a commercial magnetite aqueous ferrofluid revealed a good reproducibility ͑4%͒. Also, the measurements on a copper sample allowed comparison between experimental and theoretical values: adiabatic conditions gave SAR values only 3% higher than the theoretical ones, while the typical nonadiabatic method underestimated SAR by 21%. © 2008 American Institute of Physics. ͓DOI: 10.1063/1.2891084͔ Magnetic-fluid hyperthermia ͑MFH͒ for cancer treatment is currently attracting considerable scientific and technical work. 1-3 The use of nanoscale heaters to destroy cancerous tissue allows overcoming certain problems arising from other hyperthermia therapies, 4 such as damage of healthy tissue, temperature miscontrol, and use of hazardous alternating magnetic fields out of the biological range.The heating efficiency of the fluids is quantified by the specific absorption rate ͑SAR͒, defined as the thermal power per unit mass dissipated by the active material in the presence of an alternating magnetic field. SAR highly depends on field parameters and on material properties, since different heating mechanisms can be involved. 5,6 So accurate measurements are necessary for the studies on correlation between the SAR and material properties, 7-11 simulations of temperature distributions in tissues or phantoms, 12,13 and the optimization of hyperthermia therapies. 1,2 SAR can be estimated by calorimetric methods as SAR = ͑1 / m͒C͑⌬T / ⌬t͒, where m is the mass of the dissipating material, C the heat capacity of the whole sample, and ⌬T the sample temperature increase during the ac-field application interval ⌬t. Current SAR installations reported in literature 8,10,14-16 consist of an ac magnetic field generator, a sample space delimited by an isolating material, temperature sensors, and a data acquisition system. These setups do not provide adiabatic conditions, since heat losses ͑conduction, radiation, and convection͒ are not minimized. SAR must be estimated from the temperature-versus-time exponential curve, 16 according to the expression SAR= C␤ / m, where ␤ = ͉͑dT / dt͉͒ t→0 is the initial slope. This procedure can lead to unknown errors in the determination of ␤ and, therefore, to incorrect SAR values, if the initial thermal losses are not negligible, or if there is not a homogeneous temperature distribution across the sample, facts that are not easy to infer in practice.In this letter, we report accurate SAR measurements using an adiabatic magnetothermal setup, 17 in which the sample undergoes only a weak net heat exchange with the surroundings, overcoming the previous limitations. In such conditions, the generated hea...