This implies deposition of a relatively thin lipid layer around the Fe3O4 core that did not dramatically impact oscillation and relaxation of these superparamagnetic nanocomposites. This conclusion is further supported by the absence of significant change in temperature profile around the anticipated melting temperature of 41°C. Review
of hyperthermia kinetics, however, suggests that the design of the magnetic field generator significantly impacts conversion of electromagnetic energy into heat. Most notably, heating profiles generated in the MFG-1000 begin at room temperature and appear to plateau after 30 min around 50°C. In contrast, temperature profiles measured in MHS, which was maintained Selleck Nutlin3 at 37°C prior to initiation of the alternating magnetic field, revealed a maximum temperature of only 43°C despite a two-fold stronger magnetic field. It is hypothesized that the large space in the experimental device designed to accommodate test samples up to small animals
acts as an effective heat sink preventing temperature increases above 43°C. It remains to be explored whether the apparent steady-state temperature of 43°C can be maintained in preclinical animals without the adjustment of the magnetic field. If required, a feedback loop could be engineered into this device that facilitates real-time field adjustments using a coupled sensor circuit. However, the results from this study demonstrate the feasibility of effectively raising the temperature of this magnetic fluid to the clinically relevant hyperthermia range of 40°C to 45°C within 10 min using selleck chemical alternating magnetic fields between 7 and 17 mT. Figure 2 Heating behavior of uncoated and lipid-coated SPIONs within an alternating magnetic field. Uncoated (open symbols) and lipid-coated (closed symbols) Fe3O4 nanoparticles suspended at 0.02 mg/mL in citrate buffer, pH 7.4, were exposed in the MGS-1000 to an alternating magnetic field of 7.0 mT at 1.0 MHz (circles) and in the MHS to 16.6 mT at 13.6 Methocarbamol MHz (squares). Temperature of suspension vehicle was recorded using an optical fiber probe. Data
are shown as mean ± SD (n = 3). Heat production by SPIONs following exposure to an alternating magnetic field are consequences of several types of loss processes, including hysteresis as well as Néel and Brownian relaxations [26, 27]. Brownian relaxation loss is due to the physical rotation of the particles within the fluid whereas Néel relaxation loss occurs when magnetic moments of individual nanoparticles overcome the energy barrier between easy axis orientations. The time delay between the alignment time and effective relaxation time results in an energy transfer from the SPIONs to the surrounding environment [26, 28]. Initial heating rates represent inherent thermal properties of the material tested without system-associated limitations (e.g.