Abstract
Recently, Magnetoelectric nanoparticles (MENPs) have been introduced as a potential enabler of a wireless brain-machine interface (BMI). MENPs convert externally applied magnetic fields into electric dipole fields, which can stimulate neurons without the need for invasive electrodes. So far, the main challenge with this approach is in providing sufficiently high magnetic-to-electric field coupling to locally depolarize the resting membrane potential of neurons and evoke action potentials. In this dissertation, we addressed this challenge and successfully demonstrated wireless neuron stimulation in vitro via MENPs with a high magnetoelectric coefficient. Herein, ~30 nm polyethylene glycol coated MENPs consisting of a magnetostrictive core (CoFe2O4) and piezoelectric shell (BaTiO3) with a coercivity field of ~300 Oe have been used in rat hippocampal cell cultures. Neuronal cultures were loaded with Cal‑520 to do an optical read-out of action potentials. When stimulated, MENPs were shown to wirelessly induce calcium spikes which were synchronized with the application of 2-seconds-long trains of ~1200 Oe bipolar magnetic pulses from an electromagnet. The observed calcium spikes were compared with the traditional electrical stimulation with a 50 μA current applied by two silver electrodes placed in the cell culture and showed similar spikes in terms of shape and magnitude. Also, a very common control study was made with sodium channel blocker tetrodotoxin and no neural activity was observed. Furthermore, expected on/off operation MENPs operated below their coercivity value of 300 Oe failed to induce synchronized calcium spikes. Furthermore, localization and channelization were demonstrated with a special two-headed electromagnet design in vitro as well as in vivo (rats) with sub-50-ms temporal resolution. Moreover, the physics of recording neural activity with MENPs is explained, and preliminary in vitro experiments successfully proved the theory. Overall, this dissertation provides evidence for MENPs-induced non-invasive and wireless 2-way communication of brain.