A scanning system for specific absorption rate of ferrofluids with superparamagnetic nanoparticles is presented in this study. The system contains an induction heating device designed and built with a resonant inverter in order to generate magnetic field amplitudes up to 38 mT, over the frequency band 180-525 kHz. Its resonant circuit involves a variable capacitor with 1 nF of capacitance steps to easily select the desired frequency, reaching from 0.3 kHz/nF up to 5 kHz/nF of resolution. The device performance is characterized in order to compare with the theoretical predictions of frequency and amplitude, showing a good agreement with the resonant inverters theory. Additionally, the setup is tested using a synthetic iron oxide with 10 ± 1 nm diameter suspended in liquid glycerol, with concentrations at 1%. Meanwhile, the temperature rise is measured to determine the specific absorption rate and calculate the dissipated power density for each f. This device is a suitable alternative to studying ferrofluids and analyzes the dependence of the power absorption density with the magnetic field intensity and frequency.

In this study, a frequency tuner system is developed for generating variable frequency magnetic fields for magnetic hyperthermia applications. The tuning device contains three specially designed phase lock loop devices that drive a resonant inverter working in the frequency band of 180–525 kHz. This tuner system can be adapted for other resonant inverters employed in the studies of ferrofluids with superparamagnetic nanoparticles. The performance of the whole system is also examined. Our findings were in agreement with the theoretical expectations of phase locking and frequency tuning. The system is tested for samples of a solid magnetic material of cylindrical shape and ferrofluids with differing concentrations of powdered magnetite. The observations indicate significant frequency changes of the magnetic field due to heating of the samples. These frequency variations can be a source of errors, which should not be neglected in experiments determining the specific absorption rate or power dissipated density.

Theranostic strategies are advancing personalized medicine, with particularly impactful applications in cancer treatment. Among these, magnetic hyperthermia (MH) stands out, employing high-frequency magnetic field (MF) and magnetic nanoparticles (MNPs) to selectively target and heat cancerous cells. Real-time temperature monitoring and MNP localization, however, remain significant challenges in clinical translation. Previous studies have shown that magnetomotive ultrasound (MMUS) effectively addresses these challenges. Developing an automated and synchronized transition between MMUS and MH within an integrated platform is, however, challenging due to incompatible frequency requirements, with MH operating in the 0.1–1 MHz range and MMUS requiring lower frequency MF below 100 Hz. This study aimed to develop an automated platform enabling interleaved MF applications using a single excitation coil for both MH and MMUS. We propose using a high-frequency ferrite transformer to couple both generators for automated electronic switching. The platform used a multipurpose air-core inductor capable of producing MF pulses up to 205 kA/m (with currents reaching 2.16 kA) for MMUS, interleaved with MH stimulation at 170 kHz and 28 kA/m. The MH framework induced an $8~^{\circ }$ C temperature increase in 1 cm3 ferrofluid samples at an MF strength of 15 kA/m. Preliminary phantom experiments demonstrated the system’s capability to localize MNPs noninvasively, monitor thermal variations up to $1~^{\circ }$ C, and visualize tissue property changes during MH, showcasing promising integration of MMUS and MH.

Magnetomotive ultrasound (MMUS) stands out as a promising and effective ultrasound-based method for detecting magnetic nanoparticles (MNPs) within tissues. This innovative technique relies on the precise estimation of micrometric displacements induced by the interaction of an external magnetic field with MNPs. Pulsed MMUS has emerged as a strategic alternative to address limitations associated with harmonic excitation, such as heat generation in amplifiers and coils, frequency-dependent tissue mechanical responses, and prolonged magnetic field rise times. Despite the growing interest in MMUS, the devices conventionally employed to excite the coil are not specifically tailored to generate intense magnetic fields while minimizing interference with the transient behavior of induced displacements. To bridge this gap, our work introduces the design and fabrication of two pulse generators: one based on a capacitor-discharge circuit and the other on a resonant-inverter circuit. We evaluated the performance of these pulse generators by considering parameters such as the magnetic field generated, rise and fall times, and their ability to supply sustained current for varied pulse widths across different pulse repetition frequencies. Furthermore, we carried out a practical MMUS implementation using tissue-mimicking phantoms, demonstrating the capability of both devices to achieve magnetic fields of up to 1 T and average displacements of 25 µm within the phantom. In addition, we estimated the shear wave velocity, effective shear modulus, and their temperature-dependent variations. Our findings highlight the versatility and efficacy of the proposed pulse generators and emphasize their potential as low-cost platforms for theranostic applications, enabling the assessment of targeted entities within biological tissues.

Magnetic hyperthermia (MHT) is a therapy that uses the heat generated by a magnetic material for cancer treatment. Magnetite nanoparticles are the most used materials in MHT. However, magnetite has a high Curie temperature (Tc~580 °C), and its use may generate local superheating. To overcome this problem, strontium-doped lanthanum manganite could replace magnetite because it shows a Tc near the ideal range (42–45 °C). In this study, we developed a smart composite formed by an F18 bioactive glass matrix with different amounts of Lanthanum-Strontium Manganite (LSM) powder (5, 10, 20, and 30 wt.% LSM). The effect of LSM addition was analyzed in terms of sinterability, magnetic properties, heating ability under a magnetic field, and in vitro bioactivity. The saturation magnetization (M_s) and remanent magnetization (M_r) increased by the LSM content, the confinement of LSM particles within the bioactive glass matrix also caused an increase in Tc. Calorimetry evaluation revealed a temperature increase from 5 °C (composition LSM5) to 15 °C (LSM30). The specific absorption rates were also calculated. Bioactivity measurements demonstrated HCA formation on the surface of all the composites in up to 15 days. The best material reached 40 °C, demonstrating the proof of concept sought in this research. Therefore, these composites have great potential for bone cancer therapy and should be further explored.

An AC magnetometer system is developed to determine the specific absorption rate (SAR) of ferrofluids designed to work in the range of interest for magnetic hyperthermia. The experimental setup contains a set of configurable RL coil sensors (resistance plus inductance) to obtain the inner area of the dynamic hysteresis loops of colloidal dispersions, which are stimulated using a multi-range alternating magnetic field generator. This magnetometer is suitable for covering the frequency band of 100–450 kHz, and special considerations concerning sample size and placement inside the magnetic field region are taken into account. The performance of the system is tested using a ferrofluid of water-dispersed iron oxide nanoparticles. The SAR determined with the developed system is compared with that obtained using the typical calorimetric procedure. The observations are consistent with both kinds of measurement, and also coincide with the results for other previously reported experimental systems.