Modeling the Complex Susceptibility of Magnetic Nanocomposites for Deep-Seated Tumor Hyperthermia

Goal: Magnetic scaffolds (MagS), obtained by loading polymers with magnetic nanoparticles (MNPs) or by chemical doping of bio-ceramics, can be implanted and used as thermo-seeds for interstitial cancer therapy if exposed to radiofrequency (RF) magnetic fields. MagS have the potential to pave new therapeutic routes for the treatment of deep-seated tumors, such as bone cancers or biliary tumors. However, the studies of their fundamental RF magnetic properties and the understanding of the heat dissipation mechanism are underdeveloped. Therefore, in this work an in-depth analysis of the magnetic susceptibility spectra of several representative nanocomposites thermoseeds found in the literature is performed. Methods: A Cole-Cole model, instead of the Debye formulation, is proposed and analyzed to interpret the experimentally observed different power dissipation, due to hindered Brownian relaxation and large dipole-dipole and particle-particle interactions. To this aim, a fitting procedure based on genetic algorithm is used to derive the Cole-Cole model parameters. Results: The proposed Cole-Cole model can interpret the MNPs response when dispersed in solution and when embedded in the biomaterial. Significant differences in the equilibrium susceptibility, relaxation times and, especially, the broadening parameter are observed between the ferrofluid and MagS systems. The fitting errors are below 3%, on average. Non-linear relationships between the dipole-dipole interaction dimensionless number and the Cole-Cole parameters are found. Conclusions: The findings can foster MagS design and help planning their use for RF hyperthermia treatment, ensuring a high-quality therapy.