Magnetostrictive nanoparticles in piezoelectric environments for spatially-confined electric brain and nerve stimulation

Magnetoelectric nanomaterials are investigated in view of their application in noninvasive electrical stimulation of brain cells and nerves for the treatment of neural diseases and pain. The interplay of physical properties in nanoparticles comprised of a magnetostrictive core and a piezoelectric shell is described by modeling the core as a magnetic double-well system with uniaxial anisotropy and the shell as an array of randomly oriented piezoelectric nanocrystals. A careful analysis exploiting the symmetry of magnetic anisotropy allows to calculate the magnetostrictive deformation induced by an ac magnetic field, the resulting electric polarization and the stray electric field of the core-shell structure. An appropriate choice of the core is demonstrated to be crucial in eliciting a strong magnetoelectric response. Dispersing core-shell nanoparticles in a target tissue induces a time-dependent electric field which is always parallel to the magnetic field, permitting the directional stimulation of brain cells. Further, the properties of a magnetoelectric nanocomposite obtained dispersing bare magnetostrictive nanoparticles in a piezoelectric polymer film are investigated. It is shown that the nanocomposite submitted to an ac magnetic field generates an electric field of proper amplitude and can be used as a single flexible electrode for electrical stimulation of nerves in local analgesia.