Structural Control of Magnetite Nanoparticles for Hyperthermia by Modification with Organic Polymers: Effect of Molecular Weight

Hyperthermia treatment using appropriate magnetic materials in an alternating magnetic field to generate heat has been recently proposed as a low-invasive cancer treatment method. Magnetite (FeO) nanoparticles are expected to be an appropriate type of magnetic thermal seed for this purpose, and the addition of organic substances during the synthesis process has been studied for controlling particle size and improving biological functions. However, the role of the properties of the organic polymer chosen as the modifier in the physical properties of the thermal seed has not yet been comprehensively revealed. Therefore, this study clarifies these points in terms of the molecular weight and the charge of the functional groups of the added polymers. Excepting polyethyleneimine, the FeO crystallite size decreased with increasing polymer molecular weight. Neutral polymers did not suppress the FeO formation regardless of the difference in molecular weight, while suppression of the FeO formation was observed for low molecular weight anionic polymers and high molecular weight cationic polymers. Samples with a small amount of FeO or with crystallite size less than 10 nm induced low heat generation under an alternating magnetic field.