In situ synthesis of magnetic iron oxide nanoparticles in chitosan hydrogels as a reaction field: Effect of cross-linking density.

Magnetic iron oxides such as magnetite and γ-hematite have attracted considerable attention as thermoseeds for hyperthermia treatment because of their ability to generate heat under an alternating magnetic field. Control of the particle size and their combination with biocompatible polymers are expected to be beneficial for optimization of the nanoparticles. These processes can be accomplished through the synthesis of magnetite in gels, as the network structure of the polymer gel can control the grain growth of the magnetite. However, the effect of the cross-linking density of the gels remains unclear. In this study, we synthesized magnetic iron oxides in situ in chitosan hydrogels with different cross-linking densities and examined the crystalline structure and heat generation under alternating magnetic field. The crystalline phase and amount of magnetite were observed to be dependent on the cross-linking density of the gel, and the heat generation of the nanoparticles was governed by their crystalline structure and particle size rather than solely the amount of formed iron oxide.