A review on an effect of dispersant type and medium viscosity on magnetic hyperthermia of nanoparticles

Recently localized magnetic hyperthermia therapy is zell researched to treat cancer tumor as an independent therapy or an adjunct therapy to increase efficiency of the established radiation-, chemo-, and immuno-therapies. At the heart of the therapy is the generation of controlled heat by superparamagnetic nanoparticles (SPNPs) and their biocompatibility to human tissue and blood. Colloidal SPNPs produce heat under alternate magnetic field by electron magnetic spin relaxation mechanism. Magnetic spins relax through either Neel or Brown or both the mechanism in a nanocolloid. Neel relaxation is predominant in magnetic isotropic SPNPs, and Brown relaxation is predominant in magnetic anisotropic samples. Brown relaxation leads to rotation of whole magnetic nanoparticles under magnetic field to produce heat. Brown relaxation time (tau(B)) strongly depends on hydrodynamic volume of nanoparticles (NPs) and dispersion medium viscosity. As the generation of magnetic hyperthermia power strongly depends on relaxation time, the recent literature is reviewed to understand the effect of dispersant type on hydrodynamic volume of SPNPs and relaxation time, and medium viscosity on relaxation time in nanocolloids. It is observed that dispersants on individual SPNPs increase both colloidal stability and spin relaxation time of NPs resulting in higher specific heat power generation compared to NPs without dispersants. Different amino acids, long-chain steric dispersants, and small-chain zwitterionic surfactants anchored on similar NPs show varied magnetic hyperthermia values due to varied hydrodynamic volume. Medium viscosity also played a significant role on hyperthermia values of NPs. The above characteristics are prominent in anisotropic magnetic materials, including core-shell bimagnetic nanoparticles. This review may help researchers in the field to design and synthesize new hyperthermia materials in future.