Cellular-level neuron stimulation has attracted much attention in the areas of prevention, diagnosis, and treatment of neurological disorders. Herein, we propose a spintronic neurostimulator based on the domain wall movement inside stationary magnetic nanostructures driven by the spin transfer torques. The electromotive forces generated by the domain wall motion can serve as highly localized stimulation signals for neuron cells. Our simulation results show that the induced electric field from the domain wall motion in permalloy nanostructures can reach up to 14 V / m, which is well above the reported threshold stimulation signal for clinical applications. The proposed device operates on a current range of several microamperes that is 103 times lower than the current needed for the magnetic stimulation by microcoils. The duration and amplitude of the stimulating signal can be controlled by adjusting the applied current density, the geometry of the nanostructure, and the magnetic properties of the material.
Bibliographical noteFunding Information:
In 2013, the National Institutes of Health (NIH), the Defense Advanced Research Projects Agency (DARPA), and the National Science Foundation (NSF) launched a project named the BRAIN Initiative1,2 to accomplish the prevention, diagnosis, and treatment of brain disorders such as Alzheimer’s disease, attention deficit hyperactivity disorder (ADHD), Parkinson’s disease, migraines, and traumatic brain injury (TBI). The primary challenge in this process is the lack of understanding of the pathogenesis, which makes it necessary to investigate the interactions within the brain from the cellular level to the complex neural circuits through brain stimulation. Since the early work of Wise et al.,3 research studies in neuroscience and neural engineering have experienced rapid growth, especially in exploring new probe materials and new fabrication technologies to produce miniaturized, customized, and high-density electrode arrays for the stimulation of neurons. Despite their great potential, the electrode arrays employed in most of the current brain stimulation technologies are constantly affected by the migration of cells (such as astrocytes) around the devices, which leads to increased impedance and alterations of the electric field in the stimulation processes. One way to avoid the influence of surrounding neuron cells on the stimulation signal is magnetic stimulation, where a magnetic field is generated and is not affected by the encapsulation of astrocytes or any other cells. Transcranial magnetic stimulation (TMS) is a commonly used noninvasive brain stimulation technique that utilizes a strong alternating magnetic field (1.5 T to 3 T) to modulate the neuron activities.4–6 However, due to the bulky and noninvasive nature of this setup, it is impossible to generate a highly focused magnetic field. Moreover, as the magnetic field decays exponentially over distance, this technique cannot stimulate neurons located deep inside the brain. As a complementation of TMS, deep brain stimulation (DBS) implants electrodes in certain regions of the brain permanently to activate deeply located neurons.7–9 Nevertheless, heating effects and large power consumption due to the constant application of relatively large-amplitude current are major drawbacks of DBS. Consequently, the development of an implantable magnetic neurostimulator with the ability of generating a highly localized magnetic field through a low power input is essential for both the study of neuron activities and the treatment of neuron disorders.
This study was financially supported by the Institute of Engineering in Medicine of the University of Minnesota through FY18 IEM Seed Grant Funding Program, the National Science Foundation MRSEC Facility Program, the Centennial Chair Professorship, and Robert F. Hartmann Endowed Chair from the University of Minnesota. The authors declare no conflict of interest.