Inflatable robotic hand gives amputees real-time tactile control
Prosthetic enables a wide range of daily activities, such as zipping a suitcase, shaking hands, and petting a cat.

Date:
August 16, 2021
Source:
Massachusetts Institute of Technology
Summary:
An MIT-developed inflatable robotic hand gives amputees real-time
tactile control. The smart hand is soft and elastic, weighs about
half a pound, and costs a fraction of comparable prosthetics.



FULL STORY ==========================================================================
For the more than 5 million people in the world who have undergone
an upper- limb amputation, prosthetics have come a long way. Beyond
traditional mannequin-like appendages, there is a growing number
of commercial neuroprosthetics -- highly articulated bionic limbs,
engineered to sense a user's residual muscle signals and robotically
mimic their intended motions.


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But this high-tech dexterity comes at a price. Neuroprosthetics can
cost tens of thousands of dollars and are built around metal skeletons,
with electrical motors that can be heavy and rigid.

Now engineers at MIT and Shanghai Jiao Tong University have designed a
soft, lightweight, and potentially low-cost neuroprosthetic hand. Amputees
who tested the artificial limb performed daily activities, such as
zipping a suitcase, pouring a carton of juice, and petting a cat, just
as well as -- and in some cases better than -- those with more rigid neuroprosthetics.

The researchers found the prosthetic, designed with a system for tactile feedback, restored some primitive sensation in a volunteer's residual
limb. The new design is also surprisingly durable, quickly recovering
after being struck with a hammer or run over with a car.

The smart hand is soft and elastic, and weighs about half a pound. Its components total around $500 -- a fraction of the weight and material
cost associated with more rigid smart limbs.

"This is not a product yet, but the performance is already similar
or superior to existing neuroprosthetics, which we're excited about,"
says Xuanhe Zhao, professor of mechanical engineering and of civil and environmental engineering at MIT. "There's huge potential to make this
soft prosthetic very low cost, for low-income families who have suffered
from amputation." Zhao and his colleagues have published their work
today in Nature Biomedical Engineering. Co-authors include MIT postdoc
Shaoting Lin, along with Guoying Gu, Xiangyang Zhu, and collaborators
at Shanghai Jiao Tong University in China.



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Big Hero hand The team's pliable new design bears an uncanny resemblance
to a certain inflatable robot in the animated film "Big Hero 6." Like the squishy android, the team's artificial hand is made from soft, stretchy material -- in this case, the commercial elastomer EcoFlex. The prosthetic comprises five balloon- like fingers, each embedded with segments of
fiber, similar to articulated bones in actual fingers. The bendy digits
are connected to a 3-D-printed "palm," shaped like a human hand.

Rather than controlling each finger using mounted electrical motors, as
most neuroprosthetics do, the researchers used a simple pneumatic system
to precisely inflate fingers and bend them in specific positions. This
system, including a small pump and valves, can be worn at the waist, significantly reducing the prosthetic's weight.

Lin developed a computer model to relate a finger's desired position
to the corresponding pressure a pump would have to apply to achieve
that position.

Using this model, the team developed a controller that directs the
pneumatic system to inflate the fingers, in positions that mimic five
common grasps, including pinching two and three fingers together, making
a balled-up fist, and cupping the palm.

The pneumatic system receives signals from EMG sensors -- electromyography sensors that measure electrical signals generated by motor neurons to
control muscles. The sensors are fitted at the prosthetic's opening,
where it attaches to a user's limb. In this arrangement, the sensors can
pick up signals from a residual limb, such as when an amputee imagines
making a fist.



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The team then used an existing algorithm that "decodes" muscle signals and relates them to common grasp types. They used this algorithm to program
the controller for their pneumatic system. When an amputee imagines,
for instance, holding a wine glass, the sensors pick up the residual
muscle signals, which the controller then translates into corresponding pressures. The pump then applies those pressures to inflate each finger
and produce the amputee's intended grasp.

Going a step further in their design, the researchers looked to enable
tactile feedback -- a feature that is not incorporated in most commercial neuroprosthetics. To do this, they stitched to each fingertip a pressure sensor, which when touched or squeezed produces an electrical signal proportional to the sensed pressure. Each sensor is wired to a specific location on an amputee's residual limb, so the user can "feel" when the prosthetic's thumb is pressed, for example, versus the forefinger.

Good grip To test the inflatable hand, the researchers enlisted two
volunteers, each with upper-limb amputations. Once outfitted with
the neuroprosthetic, the volunteers learned to use it by repeatedly
contracting the muscles in their arm while imagining making five common
grasps.

After completing this 15-minute training, the volunteers were asked to
perform a number of standardized tests to demonstrate manual strength
and dexterity.

These tasks included stacking checkers, turning pages, writing with a pen, lifting heavy balls, and picking up fragile objects like strawberries
and bread. They repeated the same tests using a more rigid, commercially available bionic hand and found that the inflatable prosthetic was as
good, or even better, at most tasks, compared to its rigid counterpart.

One volunteer was also able to intuitively use the soft prosthetic
in daily activities, for instance to eat food like crackers, cake,
and apples, and to handle objects and tools, such as laptops, bottles,
hammers, and pliers. This volunteer could also safely manipulate the
squishy prosthetic, for instance to shake someone's hand, touch a flower,
and pet a cat.

In a particularly exciting exercise, the researchers blindfolded the
volunteer and found he could discern which prosthetic finger they poked
and brushed. He was also able to "feel" bottles of different sizes that
were placed in the prosthetic hand, and lifted them in response. The
team sees these experiments as a promising sign that amputees can regain
a form of sensation and real-time control with the inflatable hand.

The team has filed a patent on the design, through MIT, and is working
to improve its sensing and range of motion.

"We now have four grasp types. There can be more," Zhao says. "This
design can be improved, with better decoding technology, higher-density myoelectric arrays, and a more compact pump that could be worn
on the wrist. We also want to customize the design for mass
production, so we can translate soft robotic technology to benefit
society." Viideo: https://www.youtube.com/watch?v=p1d8i2lwuFw&t=20s ========================================================================== Story Source: Materials provided by
Massachusetts_Institute_of_Technology. Original written by Jennifer
Chu. Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Guoying Gu, Ningbin Zhang, Haipeng Xu, Shaoting Lin, Yang Yu,
Guohong
Chai, Lisen Ge, Houle Yang, Qiwen Shao, Xinjun Sheng, Xiangyang Zhu,
Xuanhe Zhao. A soft neuroprosthetic hand providing simultaneous
myoelectric control and tactile feedback. Nature Biomedical
Engineering, 2021; DOI: 10.1038/s41551-021-00767-0 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/08/210816125700.htm

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