Researchers have long recognized the therapeutic potential of using magnetoelectric materials, materials that convert magnetic fields into electric fields, to stimulate neural tissue in a minimally invasive way to help treat neurological disease or nerve damage. The problem, however, is that neurons have difficulty responding to the shape and frequency of the electrical signals produced by this conversion.
Rice University researcher and doctoral student Joshua Chen is the lead author of a study published in the journal Nature Materials. (Photo by Gustavo Laskoski/Rice University)
Rice University neuroengineer Jacob Robinson and his team designed the first magnetoelectric material that not only solves this problem, but also converts magnetoelectricity 120 times faster than similar materials. According to a study published in Nature Materials, researchers show that the material can be used to precisely stimulate neurons remotely and bridge gaps in severed sciatic nerves in a rat model.
Robinson said the material's quality and properties could have a profound impact on neurostimulation treatments, significantly reducing invasive procedures. There is no need to implant a neurostimulation device; just a small amount of material is injected into the desired area. Furthermore, given the range of applications of magnetoelectronics in computing, sensing, electronics and other fields, this research provides a framework for advanced materials design that could drive innovation more broadly.
Researcher Gauri Bhave, a former research scientist in the Robinson Laboratory, is the lead co-author of a study published in Nature Materials. (Photo courtesy of Gauri Bhave)
"We asked, 'Could we create a material that's like dust, or so small that it could stimulate the brain or nervous system just by spreading it around the body?' With that question in mind, we thought magnetoelectric materials would be ideal candidates for neurostimulation. They respond to magnetic fields that easily penetrate the body and convert them into electric fields—the language our nervous systems already use to communicate information."
The researchers first used a magnetoelectric material consisting of a lead-zirconium titanate piezoelectric layer sandwiched between two magnetostrictive layers of a metallic glass alloy (Metglas) that can be rapidly magnetized and demagnetized.
Gauri Bhave, a former researcher in Robinson's lab who now works in technology transfer at Baylor College of Medicine, explains that magnetostrictive elements vibrate in response to the application of a magnetic field.
Study illustration Schematic representation of neural responses to linear magnetoelectric transitions (top two transitions) versus nonlinear (bottom third). (Photo courtesy of Josh Chen/Rice University)
"This vibration means it basically changes its shape," Bhave said. "A piezoelectric material is a material that generates electricity when it changes shape. So when those two are combined, the conversion you get is the magnetic field you apply from outside the body becomes an electric field."
However, the electrical signals generated by magnetoelectricity are too fast and uniform for neurons to detect. The challenge is to design a new material that can generate electrical signals so that cells actually respond.
"For all other magnetoelectric materials, the relationship between the electric and magnetic fields is linear, and we need materials where that relationship is nonlinear," Robinson said. "We have to consider what materials can be deposited on the film to produce a nonlinear response."
The researchers layered platinum, hafnium oxide and zinc oxide and added the stacked material on top of the original magnetoelectric film. One of the challenges they face is finding manufacturing techniques that are compatible with the materials.
Research illustration: Magneto-electrically nonlinear metamaterials stimulate neural activity 120 times faster than previously used magnetic materials. (Image courtesy of Robinson Laboratory/Rice University)
"A lot of effort went into making this very thin layer, less than 200 nanometers, which gives us really special properties," Robinson said. "This shrinks the size of the entire device so that it can be injected in the future."
As a proof of concept, the researchers used the material to stimulate peripheral nerves in rats and demonstrated the material's potential for use in nerve prosthetics by demonstrating that it could restore function to severed nerves.
"We can use this metamaterial to bridge the gap in severed nerves and restore fast electrical signal speeds," Chen said. "Overall, we were able to rationally design a new metamaterial that overcomes many challenges in neurotechnology. More importantly, this advanced materials design framework can be applied to other applications such as sensing and storage in electronic devices."
Researcher Jacob Robinson is a professor of electrical and computer engineering and bioengineering at Rice University. (Photo courtesy of Robinson Laboratory/Rice University)
Robinson, who uses his PhD research in photonics to design new materials, said he finds it "really exciting that we can now design devices or systems using materials that have never existed before, rather than being limited to materials found in nature."
"Once a new material or class of materials is discovered, I think it's very difficult to predict all of their potential uses," said Robinson, a professor of electrical and computer engineering and bioengineering. "We are focused on bioelectronics, but I anticipate there may be many applications outside of that field."
Antonios Mikos, Rice's Louis Calder Professor of Chemical Engineering, professor of bioengineering, materials science and nanoengineering and director of the Biomaterials Laboratory in the Center of Excellence for Tissue Engineering and the J.W. Cox Laboratory of Biomedical Engineering, is also an author on the study.
This research was supported by the National Science Foundation (2023849) and the National Institutes of Health (U18EB029353).