Doctor of Philosophy (PhD)
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MagnetoElectric Nanoparticles (MENPs) are known to be a powerful tool for a broad range of applications spanning from medicine to energy-efficient electronics. MENPs allow to couple intrinsic electric fields in the nervous system with externally controlled magnetic fields. This thesis exploited MENPs to achieve contactless brain-machine interface (BMIs). Special electromagnetic devices were engineered for controlling the MENPs’ magnetoelectric effect to enable stimulation and recording. The most important engineering breakthroughs of the study are summarized below.
(I) Metastable Physics to Localize Nanoparticles: One of the main challenges is to localize the nanoparticles at any selected site(s) in the brain. The fundamental problem is due to the fact that according to the Maxwell’s equations, magnetic fields could not be used to localize ferromagnetic nanoparticles under stable equilibrium conditions. Metastable physics was used to overcome this challenge theoretically and preliminary results show the potential of single neuron localization in neural cell culture. 3D electromagnetic sources generated a time varying magnetic field pattern which effectively kept the nanoparticles in a metastable diamagnetic state.
(II) Electromagnetic Systems to Locally Stimulate Neurons: Assuming a magnetoelectric coefficient of 1 V/cm/Oe, application of a 1000 Oe field can lead to a local electric field of 1000 V/cm, which can be sufficient to induce stimulation. Two approaches for achieving local stimulation relied on localization of nanoparticles and field profiles, respectively. The nanoparticles were localized via the aforementioned metastable physics. As for the field profiles, they were controlled by specially designed electromagnetic sources. Both approaches were used to achieve sub-mm firing in hippocampal cell cultures. This controllably induced neural firing was confirmed via standard calcium ion imaging and electroencephalography.
(III) Engineering Electromagnetic Systems to Record Neural Activity with MENPs: A theoretical model was developed to use MENPs for contactless recording of local neural activity. With MENPs, neural firing from a 1 mm3 depth could generate a magnetic field of 100 pT a few millimeters above the skull. For comparison, this value is approximately 3 orders of magnitude higher than the field generated by the same brain volume without using MENPs, i.e., on the order of 100 fT. Such amplification of the magnetic field generated by MENPs has the potential to enable cost-effective magnetoencephalography (MEG) based brain imaging systems which could operate at room temperature in a shield-free environment.
Navarrete, Brayan Ricardo, "Engineering Electromagnetic Systems for Next-Generation Brain-Machine Interface" (2020). FIU Electronic Theses and Dissertations. 4698.
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