Magnetic Injection of Nanoparticles Into Rat Inner Ears at a Human Head Working Distance

Due to the physics of magnetic fields and forces, any single magnet will always attract or pull-in magnetically-responsive particles. However, there are a variety of clinical needs where it is advantageous to be able to push away or `magnetically inject' therapeutic particles. Here we focus on magnetic injection to treat inner-ear diseases. The inner ear is behind the blood-ear barrier, meaning, blood vessels that supply blood to the inner ear have vessel walls that are impermeable and prevent drugs from exiting the vessels and reaching inner ear tissues. In our prior work, we showed that a simple four-magnet system could successfully push nanoparticles from the middle into the inner ear, thus circumventing the blood-ear barrier. That first-generation system could only push at a 2 cm distance: a range sufficient for rat experiments but not appropriate for adult human patients whose face-to-middle-ear distance varies from 3 to 5 cm. Here we demonstrate an optimal two-magnet system that can push at 3 to 5 cm distances. The system is designed using semi-definite quadratic programming which guarantees a globally optimal magnet configuration, is fabricated, characterized in detail, compared to theory, and then tested in rat experiments but now at a human 4 cm working distance.