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Developmental Biology - Brain Stimulation
A Tiny, Magnet Powers Neural Stimulation
Tests show a magnetoelectric implant is an option for clinical treatment of epilepsy, Parkinson's disease and chronic pain...
Rice University neuroengineers have created a tiny surgical implant that can electrically stimulate the brain and nervous system without using a battery or wired power supply.
The neural stimulator draws its power from magnetic energy and is about the size of a grain of rice. It is the first magnetically powered neural stimulator that produces the same kind of high-frequency signals as clinically approved, battery-powered implants that are used to treat epilepsy, Parkinson's disease, chronic pain and other conditions.
The research is available online today in the journal Neuron.
The implant's key ingredient is a thin film of "magnetoelectric material" that converts magnetic energy directly into an electrical voltage.
This method avoids the drawbacks of radio waves, ultrasound, light and even magnetic coils. All of these have shown interference with living tissue or produce harmful amounts of heat.
To demonstrate the viability of the magnetoelectric technology, researchers demonstrated implants working in rodents fully awake and free to roam about their enclosures.
"Doing a proof-of-principle demonstration is really important, as it is a huge technological leap to go from a benchtop demonstration to something that might actually be useful for treating people. Our results suggest using magnetoelectric materials for wireless power delivery is more than a novel idea. These materials are excellent candidates for clinical-grade, wireless bioelectronics."
Jacob T. Robinson BS, PhD, Associate Professor, Electrical and Computer Engineering, Assistant Professor, Bioengineering Department of Electrical and Computer Engineering, Rice University, Houston, Texas, USA and study author.
While battery-powered implants are frequently used to treat epilepsy and reduce tremors in patients with Parkinson's disease, research has shown that neural stimulation could be useful for treating depression, obsessive-compulsive disorders and for those who suffer from chronic, intractable pain that often leads to anxiety, depression and opioid addiction.
Robinson explains how miniaturization, designed by study lead author and graduate student Amanda Singer, is key to making neural stimulation therapy more widely available. It is battery-free, wireless and small enough to be implanted without major surgery. About the size of a grain of rice, these devices can be implanted almost anywhere in the body in a minimally invasive procedure similar to placing stents in blocked arteries.
"When you have to develop something to be implanted subcutaneously on the skull of small animals, your design constraints change significantly. Getting this to work on a rodent in a constraint-free environment forced Amanda to push the size and volume to the minimum possible scale."
Caleb Kemere BA, MS, PhD, Associate Professor, ECE Department of Electrical and Computer Engineering, Rice University University, Study co-author and Neuroengineering initiative member.
For the rodent tests, devices were placed beneath the skin of rodents that were free to roam throughout their enclosures. The rodents preferred to be in portions of the enclosures where a magnetic field activated the stimulator and provided a small voltage to the reward center of their brains.
Amanda Singer is an applied physics student in Robinson's lab. She solved the wireless power problem by joining layers of two very different materials in a single film. The first layer, a magnetostrictive foil of iron, boron, silicon and carbon, vibrates at a molecular level when it's placed in a magnetic field. The second, a piezoelectric crystal, converts mechanical stress directly into an electric voltage.
"The magnetic field generates stress in the magnetostrictive material. It doesn't make the material get visibly bigger and smaller, but generates acoustic waves - some of those are at a resonant frequency that creates a particular mode we use called - 'an acoustic resonant mode," explains Singer.
Acoustic resonance in magnetostrictive materials is what causes large electrical transformers to audibly hum. With Singer's implants, acoustic reverberations activate the piezoelectric half of the film. Robinson explained that these magnetoelectric films harvest plenty of power but operate at a frequency that's too high to affect brain cells.
"A major piece of engineering that Amanda solved was creating circuitry to modulate that signal at a lower frequency that cells could respond to," explains Robinson. Singer found creating a modulated biphasic signal that could stimulate neurons without harming them was a challenge, along with miniaturization.
"When we first submitted this paper, we didn't have the miniature implanted version. Up to that point, the biggest thing was figuring out how to get a biphasic signal and what circuit elements we needed to do that. We spent another a year or so making it small and showing that it really works. That was probably the biggest hurdle."
Amanda Singer, Applied Physics Program; Department of Electrical and Computer Engineering, Rice University, Houston, Texas, USA.
The study took more than five years, largely because Singer had to make virtually everything for the project from scratch, according to Robinson.
"Amanda [Singer] had to build the entire system, from the device that generates the magnetic field to the layered films that convert the magnetic field into voltage, the circuit elements that they modulate, and turn it into something that's clinically useful. She had to fabricate it, package it, put it in an animal, create the test environments and fixtures for the in vivo experiments — and perform those experiments. Aside from the magnetostrictive foil and the piezoelectric crystals, there wasn't anything in this project that could be purchased from a vendor."
Jacob T. Robinson
Highlights
• Magnetoelectric materials enable millimeter-sized wireless stimulators
• Wireless neural stimulators reach therapeutic frequencies in freely moving rodents
• Miniature bioelectronic devices treat Parkinson's disease in a rat model
Summary
A major challenge for miniature bioelectronics is wireless power delivery deep inside the body. Electromagnetic or ultrasound waves suffer from absorption and impedance mismatches at biological interfaces. On the other hand, magnetic fields do not suffer these losses, which has led to magnetically powered bioelectronic implants based on induction or magnetothermal effects. However, these approaches have yet to produce a miniature stimulator that operates at clinically relevant high frequencies. Here, we show that an alternative wireless power method based on magnetoelectric (ME) materials enables miniature magnetically powered neural stimulators that operate up to clinically relevant frequencies in excess of 100 Hz. We demonstrate that wireless ME stimulators provide therapeutic deep brain stimulation in a freely moving rodent model for Parkinson's disease and that these devices can be miniaturized to millimeter-scale and fully implanted. These results suggest that ME materials are an excellent candidate to enable miniature bioelectronics for clinical and research applications.
Authors
Amanda Singer, Shayok Dutta, Eric Lewis, Ziying Chen, Joshua C. Chen, Nishant Verma, Benjamin Avants, Ariel K. Feldman, John O’Malley, Michael Beierlein, Caleb Kemere and Jacob T. Robinson.
Acknowledgements
The research was supported by the National Science Foundation (1250104, 1351692) and the National Institutes of Health (1U18EB029353-01, R21EY028397A).
Located on a 300-acre forested campus in Houston, Rice University is consistently ranked among the nation's top 20 universities by U.S. News & World Report. Rice has highly respected schools of Architecture, Business, Continuing Studies, Engineering, Humanities, Music, Natural Sciences and Social Sciences and is home to the Baker Institute for Public Policy. With 3,962 undergraduates and 3,027 graduate students, Rice's undergraduate student-to-faculty ratio is just under 6-to-1. Its residential college system builds close-knit communities and lifelong friendships, just one reason why Rice is ranked No. 1 for lots of race/class interaction and No. 4 for quality of life by the Princeton Review. Rice is also rated as a best value among private universities by Kiplinger's Personal Finance.
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Jun 12 2020 Fetal Timeline Maternal Timeline News
 To demonstrate the viability of miniature, magnetoelectric-powered neural stimulating technology, Rice University neuroengineers created tiny devices they placed beneath the skin of rodents. The rats were then free to roam throughout their enclosures, but preferred to be where a magnetic field activated their stimulator, providing a small voltage to the reward center of their brains. Image Courtesy of J. Robinson/Rice University.
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