Hollow spherical Mn _0.5 Zn _0.5 Fe ₂ O ₄ nanoparticles with a magnetic vortex configuration for enhanced magnetic hyperthermia efficacy

Conventional magnetic nanoagents in cancer hyperthermia therapy suffer from a low magnetic heating efficiency. To address this issue, researchers have pursued magnetic nanoparticles with topological magnetic domain structures, such as the vortex-domain structure, to enhance the magnetic heating performance of conventional nanoparticles while maintaining excellent biocompatibility. In this study, we synthesized hollow spherical Mn_0.5Zn_0.5Fe₂O₄ (MZF-HS) nanoparticles using a straightforward solvothermal method, yielding samples with an average outer diameter of approximately 350 nm and an average inner diameter of about 220 nm. The heating efficiency of the nanoparticles was experimentally verified, and the specific absorption rate (SAR) value of the hollow MZF was found to be approximately 1.5 times that of solid MZF. The enhanced heating performance is attributed to the vortex states in the hollow MZF structure as validated with micromagnetic simulation studies. In vitro studies demonstrated the lower cell viability of breast cancer cells (MCF-7, BT549, and 4T1) after MHT in the presence of MZF-HS. The synthesized MZF caused 51% cell death after MHT, while samples of MZF-HS resulted in 77% cell death. Our findings reveal that magnetic particles with a vortex state demonstrate superior heating efficiency, highlighting the potential of hollow spherical particles as effective heat generators for MHT applications.