Tiny, magnetically powered neural stimulator
Tests show 'magnetoelectric' power is viable option for clinical-grade implants

Date:
June 8, 2020
Source:
Rice University
Summary:
Neuroengineers have created a tiny surgical implant that can
electrically stimulate the brain and nervous system without using
a battery or wired power supply.



FULL STORY ==========================================================================
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. The method avoids the drawbacks of radio waves, ultrasound,
light and even magnetic coils, all of which have been proposed for
powering tiny wireless implants and have been shown to suffer from
interference with living tissue or produce harmful amounts of heat.

To demonstrate the viability of the magnetoelectric technology, the
researchers showed the implants worked in rodents that were fully awake
and free to roam about their enclosures.

"Doing that proof-of-principle demonstration is really important, because
it's a huge technological leap to go from a benchtop demonstration to
something that might be actually useful for treating people," said
Jacob Robinson, corresponding author of the study and a member of
the Rice Neuroengineering Initiative. "Our results suggest that using magnetoelectric materials for wireless power delivery is more than a
novel idea. These materials are excellent candidates for clinical-grade, wireless bioelectronics." Tiny implants capable of modulating activity of
the brain and nervous system could have wide-ranging implications. 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 more than a third of those who suffer
from chronic, intractable pain that often leads to anxiety, depression
and opioid addiction.



========================================================================== Robinson said the miniaturization by study lead author and graduate
student Amanda Singer is important because the key to making neural
stimulation therapy more widely available is creating battery-free,
wireless devices that are small enough to be implanted without major
surgery. Devices about the size of a grain of rice could be implanted
almost anywhere in the body with a minimally invasive procedure similar
to the one used to place stents in blocked arteries, he said.

Study co-author and neuroengineering initiative member Caleb Kemere said,
"When you have to develop something that can 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 really forced Amanda to push down the size and volume to
the minimum possible scale." 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.

Singer, an applied physics student in Robinson's lab, 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,"
Singer said. "It doesn't make the material get visibly bigger and smaller,
but it generates acoustic waves and some of those are at a resonant
frequency that creates a particular mode we use called an acoustic
resonant mode." Acoustic resonance in magnetostrictive materials is what causes large electrical transformers to audibly hum. In Singer's implants,
the acoustic reverberations activate the piezoelectric half of the film.



========================================================================== Robinson said the 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 the
circuitry to modulate that activity at a lower frequency that the cells
would respond to," Robinson said. "It's similar to the way AM radio
works. You have these very high-frequency waves, but they're modulated
at a low frequency that you can hear." Singer said creating a modulated biphasic signal that could stimulate neurons without harming them was
a challenge, as was miniaturization.

"When we first submitted this paper, we didn't have the miniature
implanted version," she said. "Up to that point, the biggest thing was
figuring out how to actually get that biphasic signal that we stimulate
with, what circuit elements we needed to do that.

"When we got the reviews back after that first submission, the comments
were like, 'OK, you say you can make it small. So, make it small,'"
Singer said.

"So, we spent another a year or so making it small and showing that it
really works. That was probably the biggest hurdle. Making small devices
that worked was difficult, at first." All told, the study took more than
five years, largely because Singer had to make virtually everything from scratch, Robinson said.

"There is no infrastructure for this power-transfer technology," he
said. "If you're using radio frequency (RF), you can buy RF antennas and
RF signal generators. If you're using ultrasound, it's not like somebody
says, 'Oh, by the way, first you have to build the ultrasound machine.'
"Amanda 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 and the circuit elements that modulate that and turn it
into something that's clinically useful. She had to fabricate all of 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."

========================================================================== Story Source: Materials provided by Rice_University. Note: Content may
be edited for style and length.


========================================================================== Journal Reference:
1. 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, Jacob T. Robinson. Magnetoelectric
Materials for Miniature, Wireless Neural Stimulation at Therapeutic
Frequencies.

Neuron, 2020; DOI: 10.1016/j.neuron.2020.05.019 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/06/200608132537.htm

--- up 19 weeks, 6 days, 2 hours, 34 minutes
* Origin: -=> Castle Rock BBS <=- Now Husky HPT Powered! (1337:3/111)