Controlled localization of ultrasound heating using magnetic nanoparticle assemblies

Localized ultrasound hyperthermia is a therapeutic approach that enables precise energy delivery to targeted tissues, which can be combined with diagnostics. In this study, we explored the use of iron oxide nanoparticles (IONPs) and magnetic Pickering emulsions as innovative biomaterial assemblies incorporated into agar-based tissue phantoms to enhance local ultrasound-induced heating without using focusing transducers. Three phantom configurations were evaluated: uniformly distributed IONPs, spherical inclusions containing IONPs, and injections of oil-in-oil Pickering emulsions stabilized by IONPs. Temperature measurements were performed at various distances from the ultrasound transducer using thermocouples or infrared imaging. Results revealed that the addition of IONPs significantly increased heating efficiency. Localized configurations, such as phantoms with spherical inclusions and those injected with emulsions, exhibited greater temperature rise at their centers compared to uniformly doped phantoms. IONPs enabled locally focused ultrasound heating without focusing transducers. Emulsion-injected phantoms achieved the highest heating rates, as they efficiently enhanced ultrasound absorption and scattering while limiting deeper penetration. The simultaneous improvement of thermal effects in regions of interest and reduced heating of non-targeted areas highlights their potential for future theranostic strategies aimed at protecting non-targeted tissues.