UC San Diego

Nanoparticles (NPs) are promising candidates to penetrate the blood brain barrier for delivering therapeutics to treat diseases affecting the central nervous system. However, obtaining effective doses of therapeutic NPs in diseased locations is challenging due to rapid sequestering by phagocytic organs. A potential solution is to use magnetic nanoparticles (MNPs) and guide them away from undesired organs through blood vessel networks. This can come to fruition if MNPs have large magnetic moments that enable high guiding efficiencies in technologically feasible magnetic field gradients (∇B ⃑). To this end, we designed nanobowls composed of a silica core embedded with magnetic iron oxide-NPs. These nanobowls are nanoparticles featuring a bowl-like pit for drug encapsulation. Nanobowls have a large magnetic moment of 2x〖10〗^(-17) Am^2. Guiding efficiency for nanobowls was determined in vitro using particle trajectories. The mathematical framework for particle trajectories involves the force balance between magnetic (F_M) and Stokes drag force. Magnetic drift velocity was measured as concentration flux toward a magnet to quantify F_M. This framework can be used to predict particle trajectories. Their validity was confirmed by imaging nanobowl cluster trajectories in different convective fluid flow and magnetic conditions. ∇B ⃑ used was larger than the average in commercial MRI machines. As expected, in 15 μm/s fluid velocity, clusters of nanobowls deviate 15° due to magnetic force. In case of physiological convection velocities often >1mm/s, framework calculations predict negligible deviation of nanobowls to the same ∇B ⃑ , insufficient for high guiding efficiency. Further work is thus required to develop larger magnetic moment nanocarriers.