Magnetic SiO₂ gel microspheres for arterial embolization hyperthermia

We have prepared magnetic SiO₂ microspheres with a diameter of 20-30 μm as thermoseeds for hyperthermia of cancer. These were prepared by directly introducing preformed magnetic iron oxide nanoparticles (IONPs) into microspheres of a SiO₂ gel matrix derived from the hydrolysis of tetramethoxysilane (TMOS) in a water-in-oil (W/O) emulsion. Dimethylformamide (DMF) was used as a stabilizer, methanol (CH₃OH) as a dispersant and ammonia (NH₄OH) as the catalyst for the formation of the spherical particles in the aqueous phase of the W/O emulsion. The magnetic IONPs were synthesized hydrochemically in an aqueous system composed of ferrous chloride, sodium nitrate and sodium hydroxide. Mono-dispersed magnetic SiO₂ gel microspheres with a diameter of approximately 20 μm were successfully obtained by adding a determined amount of solution with a molar ratio of TMOS/DMF/CH₃OH/H₂O/NH₄OH = 1:1.4:9:20:0.03 to kerosene with a surfactant (sorbitan monooleate/sorbitan monostearate = 3:1 by weight ratio) that was 30 wt% of the total amount of the oil phase. These were estimated to contain up to 60 wt% of IONPs that consisted mainly of Fe ₃O₄ and showed a higher specific absorption rate (SAR = 27.9-43.8 W g^-1) than that of the starting IONPs (SAR = 25.3 W g ^-1) under an alternating current magnetic field of 300 Oe and 100 kHz.