Magnetoelectric nonlinear metamaterials are 120 times faster at stimulating neural activity compared to previously used magnetic materials. One of the challenges they faced was finding fabrication techniques compatible with the materials. The researchers layered platinum, hafnium oxide and zinc oxide and added the stacked materials on top of the original magnetoelectric film. “We had to think about the kinds of materials we could deposit on this film that would create that nonlinear response.” “For all other magnetoelectric materials, the relationship between the electric field and the magnetic field is linear, and what we needed was a material where that relationship was nonlinear,” Robinson said. The challenge was to engineer a new material that could generate an electric signal that would actually get cells to respond. However, the electric signals magnetoelectrics generate are too fast and uniform for neurons to detect. So when those two are combined, the conversion that you’re getting is that the magnetic field you’re applying from the outside of the body turns into an electric field.” “The piezoelectric material is something that, when it changes its shape, creates electricity. “This vibration means it basically changes its shape,” Bhave said. (Image courtesy of Josh Chen/Rice University) Schematic of neural response for linear magnetic-to-electric conversion (top two conversions) versus nonlinear (bottom third). Gauri Bhave, a former researcher in the Robinson lab who now works in technology transfer for Baylor College of Medicine, explained that the magnetorestrictive element vibrates with the application of a magnetic field. The researchers started with a magnetoelectric material made up of a piezoelectric layer of lead zirconium titanate sandwiched between two magnetorestrictive layers of metallic glass alloys, or Metglas, which can be rapidly magnetized and demagnetized. They respond to magnetic fields, which easily penetrate into the body, and convert them into electric fields ⎯ a language our nervous system already uses to relay information.” “With that question in mind, we thought that magnetoelectric materials were ideal candidates for use in neurostimulation. “We asked, ‘Can we create a material that can be like dust or is so small that by placing just a sprinkle of it inside the body you’d be able to stimulate the brain or nervous system?’” said Joshua Chen, a Rice doctoral alumnus who is a lead author on the study. Gauri Bhave, a former research scientist in the Robinson lab, is a lead co-author on a study published in Nature Materials. Moreover, given magnetoelectrics’ range of application in computing, sensing, electronics and other fields, the research provides a framework for advanced materials design that could drive innovation more broadly. Instead of implanting a neurostimulation device, tiny amounts of the material could simply be injected at the desired site.

The material’s qualities and performance could have a profound impact on neurostimulation treatments, making for significantly less invasive procedures, Robinson said. According to a study published in Nature Materials, the researchers showed the material can be used to precisely stimulate neurons remotely and to bridge the gap in a broken sciatic nerve in a rat model. Rice University neuroengineer Jacob Robinson and his team designed the first magnetoelectric material that not only solves this issue but performs the magnetic-to-electric conversion 120 times faster than similar materials.

(Photo by Gustavo Raskosky/Rice University) Rice University doctoral alum Joshua Chen is lead author on a study published in Nature Materials. The problem, however, is that neurons have a hard time responding to the shape and frequency of the electric signal resulting from this conversion. Researchers have long recognized the therapeutic potential of using magnetoelectrics ⎯ materials that can turn magnetic fields into electric fields ⎯ to stimulate neural tissue in a minimally invasive way and help treat neurological disorders or nerve damage.

Piezoelectric film