Smart single hollow magnetothermal nanorings with phase change materials for controlled drug release and negative MRI guided cancer therapy.

Magnetic hyperthermia therapy (MHT) for tumors is alocalized, minimally invasive, and deeply penetrating treatment, but it faces limitations such as low magnetothermal conversion efficiency, strict safety thresholds for magnetic field intensity, and the inability of single-mode magnetic hyperthermia to completely eradicate tumors. In this work, we develop an innovative, thermoresponsive drug-delivery platform composed of single hollow magnetic vortex iron oxide nanorings (MVIONs) coated with phase-change materials (PCM), designated MVIONs@PCM. Under an alternating magnetic field (AMF), MVIONs efficiently generate heat, triggering the melting of the PCM shell and releasing co-encapsulated anticancer drugs in a controlled, "on/off" manner. In vitro experiments confirm the exceptional thermal induction capacity of MVIONs@PCM, yielding a specific absorption rate of 1058.68 W·g-1 at 600 Oe, sufficient to produce robust hyperthermia effects. Additionally, this nano platform exhibits very low basal release without AMF activation. MVIONs@PCM also achieves strong negative magnetic resonance imaging (MRI) contrast, with a high transverse relaxivity (R2 = 45.986 mM-1·s-1) even at 0.5 T, supporting real-time treatment guidance and monitoring. Combining magnetic hyperthermia and AMF-induced chemotherapy significantly enhances tumor growth inhibition. This multifunctional platform represents a promising strategy for MRI-guided magnetothermal chemotherapy.