(268a) Response of Magnetic Nanoparticles to Time Varying Magnetic Fields: Ferrohydrodynamics, Nanoscale Thermal Therapy, and Magnetic Particle Imaging

Colloidal suspensions of magnetic nanoparticles are fascinating from an intellectual and practical perspective because of their behavior in externally applied static and dynamic magnetic fields. This includes particle translation in magnetic field gradients, internal dipole or whole-particle rotation when the local magnetic field changes direction, and dissipation of magnetic field energy in the form of heat, among others. Suspensions of magnetic nanoparticles in Newtonian fluids, commonly known as ferrofluids, have been of interest since the 1960’s due to their practical applications and unique fluid mechanics. More recently, biomedical applications of magnetic nanoparticles have been of great interest. Magnetic nanoparticles have been clinically translated for use as magnetic resonance imaging contrast agents, in sentinel lymph node detection, and in nanoscale thermal therapy for cancer. Furthermore, the nonlinear magnetization response of superparamagnetic iron oxide nanoparticle tracers is critical for magnetic particle imaging, a new molecular imaging modality that allows for non-invasive, tomographic, unambiguous, and quantitative imaging of tracer distribution. This talk will focus on the response of magnetic nanoparticles to applied time varying magnetic fields. First, the phenomenological description of ferrofluid flows in rotating magnetic fields will be presented, along with theoretical and experimental work suggesting the existence of antisymmetric and couple stresses, features of structured fluid continua. Second, experimental evidence will be presented in support of nanoscale thermal phenomena in the vicinity of magnetic nanoparticles, resulting in lysosomal permeabilization and death in cancer cells without a macroscopic temperature rise. Third, magnetic particle imaging guided nanoscale thermal therapy will be presented, along with recent results demonstrating unprecedented spatial resolution imaging using strongly interacting magnetic particle imaging tracers.