On the Evaluation of the Hyperthermic Efficiency of Magnetic Scaffolds

Abstract

Goal: Deep-seated tumors (DST) can be treated using thermoseeds exposed to a radiofrequency magnetic field for performing local interstitial hyperthermia treatment (HT). Several research efforts were oriented to the manufacturing of novel biocompatible magnetic nanostructured thermo-seeds, called magnetic scaffolds (MagS). Several iron-doped bioceramics or magnetic polymers in various formulations are available. However, the crucial evaluation of their heating potential has been carried out with significantly different, lab specific, variable experimental conditions and protocols often ignoring the several error sources and inaccuracies estimation. Methods: This work comments and provides a perspective analysis of an experimental protocol for the estimation methodology of the specific absorption rate (SAR) of MagS for DST HT. Numerical multiphysics simultions have been performed to outline the theoretical framework. After the in silico analysis, an experimental case is considered and tested. Results: From the simulations, we found that large overestimation in the SAR values can be found, due to the axial misplacement in the radiofrequency coil, while the radial misplacement has a lower impact on the estimated SAR value. Conclusions: The averaging of multiple temperature records is needed to reliably and effectively estimate the SAR of MagS for DST HT.

Keywords: Heating evaluation protocol; hyperthermia; magnetic biomaterials; specific absorption rate.

Fig. 1.

Graphical representation of the proposed experimental protocol for assessing the specific absorption rate (SAR) of biocompatible magnetic scaffolds (MagS) to be used as implants for local, interstitial hyperthermia treatment (HT) of deep-seated tumors (DST).

Fig. 2.

(a) System geometry for the numerical simulations of the different experimental setup for the calorimetric characterization of magnetic scaffolds (MagS). The heating system has conductors mad of copper, whilst the light grey cylinder represent the agarose matrix and the dark grey cylinder is the MagS. (b) Representation of the possible misplacement of the scaffold in the agar phantom. (c) Screenshot of the system geometry in Comsol Multiphysics v5.5 (Comsol Inc., Burlinghton, MA USA).

Fig. 3.

(a) Magnetic flux density distribution, in mT, for different position of the sample in the coil (0 cm, 1 cm, 2 cm). (b) Field homogeneity () for different sample placement. (c) Temperature distribution ()), at 600 s, for different position of the sample in the coil (0 cm, 1 cm, 2 cm). (d) Average magnetic scaffold (MagS) temperature versus time. (e) Peak temperatures, and relative differences between the initial condition for different coil axial positions. (f) Relative SAR variation, with respect to the initial condition, for different sample placement in the coil.

Fig. 4.

(a) Simulated average temperature of the magnetic thermossed as a function of time. There is a partial overlap of the curves. (b) Percentual variation of the SAR with respect to the values estimated for the scaffolds placed in .

Fig. 5.

Preparation of (a) 3D printed magnetic scaffold (MagS) sample for magnetic hyperthermia experiment. (b) 3 symmetrical holes are opened to place the temperature probe-optical fiber in (c) three positions within the MagS and one background measurement. Control samples in agarose gel from (d) top and (e) side view. Heating evaluation experimental setup with (f) control and (g) MagS samples placed at the center of the induction heating coil with optical fiber (green).

Fig. 6.

Measured magnetization (Am kg) of the ferromagentic poly-lactic acid (PLA) as a function of the applied magnetic flux density (T).

Fig. 7.

Expeirmental temperature curves acquired in four different position (T = Top, C = Center, R = Right, L = Left) in the magnetic scaffold (MagS) and in the agarose phantom (O = Out). The simulated counterparts are reported in lighter colors. The shaded red area represents the typical temperature range for hyperthremia treatment.