Improved Control of Prosthetics via Fused Nerves

Researchers are investigating new ways to improve amputees’ control
over prosthetics with the aid of their own nervous systems by creating
biocompatible interface scaffolds.

Through a collaborative effort with Sandia National Laboratories, the
University of New Mexico and the University of Texas MD Anderson Cancer Center,
researchers are working to improve prosthetics with flexible nerve-to-nerve or
nerve-to-muscle interfaces by which transected nerves can grow, putting small
groups of nerve fibers in close contact to electrode sites connected to
separate, implanted electronics.

“The overarching long-term goal of our research is to develop an
improved neural interface between peripheral nerves and a prosthetic
device,” said researcher Shawn M. Dirk, PhD, principal member of
technical staff in the Organic Materials Department at the Center for Materials
Science and Engineering at Sandia.

While this research is in the very early stages of development, if
successful it “could eventually lead to improved prosthetic devices that
should be easier for the user to control,” according to Dirk.

  A porous, biocompatible scaffold provides the foundation for nerve growth.
  A porous, biocompatible scaffold
provides the foundation for nerve growth.
  Image: Randy Montoya, Sandia
National Labratories.

“We are very optimistic that the new materials developed at Sandia
and the University of New Mexico combined with the novel surgical procedures
being developed at the University of Texas MD Anderson Cancer Center will
eventually lead to improved neural interfaces,” he said.

Researcher Patrick Lin, MD, associate professor of Orthopaedic
Oncology at the University of Texas MD Anderson Cancer Center, believes that in
the future prosthetic limbs will be controlled by the patient’s nervous

“This research is part of an effort to develop the next generation
of smart prosthetics,” he told O&PBusiness News .

Improved neural control

Neural interfaces operate where the nervous system and an artificial
device intersect. Interfaces can potentially detect and monitor nerve signals
or provide inputs to the nerve that let amputees control prosthetic devices by
direct neural signals, the same way they would control parts of their own

Dirk and colleagues are evaluating flexible conducting electrode
materials using thin evaporated metal or patterned multiwalled carbon

Dirk explained that the neural interfaces must be physically structured
and biocompatible to allow nerve fibers to grow through them, either by being
porous or by including specific channels for the axons. In addition, they must
exhibit selective and structured conductivity and must be capable of being
physically connected to external circuitry.

  Shawn M. Dirk, PhD
  Shawn M. Dirk

The most recent research conducted by the team is focused on matching
the materials properties of peripheral nerves in order to create a healthy
environment for nerve growth while creating a porous scaffold, according to
Dirk. In addition, they evaluated two techniques to create this scaffold:
electrospinning and projection microstereolithography.

“We are developing materials that will enable future prosthetic
devices that should improve patient quality of life,” said Dirk.
“Much work still needs to be accomplished before a neural
interface/prosthetic device can be fielded commercially.”

Dustin J. Tyler, PhD, who is not affiliated with this research,
believes achieving a highly functional, stable interface to the nervous system
will help enable the next revolution in prosthetic function.

“This technology is one of several approaches that are being
investigated to achieve this goal. One of the most significant and unsolved
challenges, however, is how to control the complex capabilities of advanced
devices without interrupting the patient’s normal daily function,”
said Tyler, associate professor in the Department of Biomedical Engineering at
Case Western Reserve University, and associate director of Advanced Platform
Technology Center at Louis-Stokes Cleveland Department of Veteran’s
Affairs Medical Center.

“The cutting edge research into this problem is to tap into the
residual nerves to extract the natural signals that controlled the muscle that
were present before amputation,” Tyler said.

Challenges ahead

According to Lin, some of the research challenges lie in the areas of
component miniaturization, biocompatibility, power supply and the need for
long-term performance studies.

Interfaces must be structured so nerve fibers can grow through. In
addition, they must be mechanically compatible so they don’t harm the
nervous system or surrounding tissues, and biocompatible to integrate with
tissue and promote nerve fiber growth, according to a press release. They must
also incorporate conductivity to allow electrode sites to connect with external
circuitry, and electrical properties must be tuned to transmit neural signals.

“Improving neural interface lifetime is a major challenge,”
Dirk said. “We believe that our materials should overcome many of the
limitations that are present with high modulus electrode materials.”

Electrodes fabricated from high modulus materials tend to be walled-off
by the body as the implants are considered a foreign body. This, in turn, tends
to increase the impedance of the device, according to Dirk.

“Improving conductivity of our materials at high switching
frequencies will be critical in order to create an improved implant,” he

Tyler believes another challenges to neural interfaces is that it is
more invasive in nature and will require surgery. That said, additional
practitioner training would be required for the care and maintenance of the
more complex systems available with these new technologies.

“In general, as the mechanisms and capabilities of these prostheses
continue to get more sophisticated, the practitioner will be required to have a
more intimate knowledge of the mechanics and engineering of the devices,”
he said.

Although this research is in its early stages, and it might be years
before these materials reach the market, the researchers believe the need for
such a product is there.

  Dustin J. Tyler, PhD
  Dustin J.

“At this time, this is early research and direct benefit to the
patient is negligible. Tangible results from this approach are still a few
years away,” Tyler said. “Over time, this research might demonstrate
a technology that can provide a more intimate and functional interface than is
currently available in clinical studies.” – by Tara Grassia

Disclosures: Dirk, Lin and Tyler did not report any relevant
financial disclosures.

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