High SAR values for OD15 and MF66 MNP dispersed in water, agarose and polyvinylalcohol. The two latest reproduce immobilization conditions in vivo. (a) SAR values of both used MNP depending on the viscosity of the media (water, 1% (w/v) agar in water, 10% PVA in DMSO: water (80: 20% (v/v))). Intrinsic loss power (ILP) of OD15 and MF66 dispersed in water, agarose, and PVA. (b) Prussian Blue staining of MDA-MB-231 cells after incubation with 125 pg Fe/cell of OD15 and MF66 for 24 h at 37°C. Bars: 50 μm. (c) Hematoxylin stained tumor tissue of MF66 treated MDA-MB-231 xenografts 3 days after intratumoral application. Nuclei stained blue, MNP stained brown. Bar: 20 μm. Error bars indicate standard deviations. MNP magnetic nanoparticles, PVA polyvinylalcohol hydrogel, SAR specific absorption rate.