Heating efficiency of magnetic nanoparticles decreases with gradual immobilization in hydrogels.

Highlights • Hydrogels of tunable mesh size enable gradual immobilization of magnetic particles. • Brownian rotation is gradually inhibited with particle immobilization states. • Particle heating in alternating magnetic field decreases with immobilization state. • Brownian relaxation contributes at least one third to the overall particle heating. Abstract Magnetic nanoparticles (MNP) applied in magnetic fluid hyperthermia cancer treatment interact with cancerous tissue in various ways. The impact of these interactions on MNP heating efficiency is hard to quantify and strongly depends on the MNP mobility inside the cancerous environment. There, this MNP mobility is inhibited by cell attachment and internalization. In this study, we model this impact and analyze the MNP heating under gradual immobilization of MNP in acrylamide hydrogels with tailored mesh size. Our results confirm a clear particle heating dependency on the state of immobilization of MNP. This state is related to the mean mesh size of the respective hydrogel. From this, the contributions of Brownian and Néel relaxation mechanisms to the overall particle heating are estimated. In fact, the heating efficiency decreases by up to 35% for the highest immobilization state of MNP. This result is discussed in the context of the field-dependent Brownian and Néel relaxation time, showing that the former significantly contributes to the heating efficiency even for small particles under the field parameters employed in this study. [ABSTRACT FROM AUTHOR]