Bionics  

A Danish man is the first amputee in the world to feel sensory rich information – in real-time – with a bionic hand wired to nerves in his upper arm. Using the Lifehand 2, Dennis Aabo Sørensen can grasp objects intuitively and identify what he is touching while blindfolded.

Nine years after an accident caused the loss of his left hand, Dennis Aabo Sørensen from Denmark became the first amputee in the world to feel – in real-time – with a sensory-enhanced bionic hand that was surgically wired to nerves in his upper arm.

Silvestro Micera and his team at EPFL (Switzerland) and SSSA (Italy) developed the revolutionary sensory feedback that allowed Sørensen to feel again while handling objects. A prototype of this bionic technology was tested in February 2013 during a clinical trial in Rome under the supervision of Paolo Maria Rossini at Gemelli Hospital (Italy). The study is published in Science Translational Medicine, and represents a collaboration called Lifehand 2 between several European universities and hospitals.

“The sensory feedback was incredible,” reports the 36 year-old amputee from Denmark. “I could feel things that I hadn’t been able to feel in over nine years.” In a laboratory setting wearing a blindfold and earplugs, Sørensen was able to detect how strongly he was grasping, as well as the shape and consistency of different objects he picked up with his prosthetic. “When I held an object, I could feel if it was soft or hard, round or square.”

Micera and his team enhanced the artificial hand with sensors that detect information about touch. This was done by measuring the tension in artificial tendons that control finger movement and turning this measurement into an electrical current. But this electrical signal is too coarse to be understood by the nervous system. Using computer algorithms, the scientists transformed the electrical signal into an impulse that sensory nerves can interpret. The sense of touch was achieved by sending the digitally refined signal through wires into four electrodes that were surgically implanted into what remains of Sørensen’s upper arm nerves.

“This is the first time in neuroprosthetics that sensory feedback has been restored and used by an amputee in real-time to control an artificial limb,” says Micera.

“We were worried about reduced sensitivity in Dennis’ nerves since they hadn’t been used in over nine years,” says Stanisa Raspopovic, first author and scientist at EPFL and SSSA. These concerns faded away as the scientists successfully reactivated Sørensen’s sense of touch.

Image Source - © LifeHand 2 / Patrizia Tocci

A year ago, Sørensen underwent surgery in Rome at Gemelli Hospital. A specialized group of surgeons and neurologists, led by Paolo Maria Rossini, implanted transneural electrodes into the ulnar and median nerves of Sørensen’s left arm. After 19 days of preliminary tests, Micera and his team connected their prosthetic to the electrodes – and to Sørensen – every day for an entire week.

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The ultra-thin, ultra-precise electrodes, developed by Thomas Stieglitz’s research group at Freiburg University  in Germany, made it possible to relay extremely weak electrical signals directly into the nervous system. A tremendous amount of preliminary research was done to ensure that the electrodes would continue to work even after the formation of post-surgery scar tissue. It is also the first time that such electrodes have been transversally implanted into the peripheral nervous system of an amputee.

The clinical study provides the first step towards a bionic hand, although a sensory-enhanced prosthetic is years away from being commercially available and the bionic hand of science fiction movies is even further away.

The next step involves miniaturizing the sensory feedback electronics for a portable prosthetic. In addition, the scientists will fine-tune the sensory technology for better touch resolution and increased awareness about the angular movement of fingers.

The electrodes were removed from Sørensen’s arm after one month due to safety restrictions imposed on clinical trials, although the scientists are optimistic that they could remain implanted and functional without damage to the nervous system for many years.

Image Source - © LifeHand 2 / Patrizia Tocci

Sørensen’s psychological strength was an asset for the clinical study. He says, “I was more than happy to volunteer for the clinical trial, not only for myself, but to help other amputees as well.” Now he faces the challenge of having experienced touch again for only a short period of time.

Sørensen lost his left hand while handling fireworks during a family holiday. He was rushed to the hospital where his hand was immediately amputated. Since then, he has been wearing a commercial prosthetic that detects muscle movement in his stump, allowing him to open and close his hand, and hold onto objects.




SOURCE  EPFL

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 Nanotechnology  

Researchers have developed a sensor device using nanowires that glow under mechanical pressure. The sensor device could provide an artificial sense of touch, offering sensitivity comparable our skin. It could be used for collecting signatures and fingerprints and in biological imaging and a new approach for human-machine interfaces.

Researchers at the Georgia Institute of Technology want to put your signature up in lights – tiny lights, that is. Using thousands of nanometer-scale wires, the researchers have developed a sensor device that converts mechanical pressure – from a signature or a fingerprint – directly into light signals that can be captured and processed optically.

The sensor device could provide an artificial sense of touch, offering sensitivity comparable to that of the human skin. Beyond collecting signatures and fingerprints, the technique could also be used in biological imaging and micro-electromechanical (MEMS) systems. Ultimately, it could provide a new approach for man-machine interfaces.

“You can write with your pen and the sensor will optically detect what you write at high resolution and with a very fast response rate,” said Zhong Lin Wang, Regents’ professor and Hightower Chair in the School of Materials Science and Engineering at Georgia Tech. “This is a new principle for imaging force that uses parallel detection and avoids many of the complications of existing pressure sensors.”

Individual zinc oxide (ZnO) nanowires that are part of the device operate as tiny light emitting diodes (LEDs) when placed under strain from the mechanical pressure, allowing the device to provide detailed information about the amount of pressure being applied. Known as piezo-phototronics, the technology – first described by Wang in 2009 – provides a new way to capture information about pressure applied at very high resolution: up to 6,300 dots per inch.

The research was reported in the journal Nature Photonics. It was sponsored by the U.S. Department of Energy’s Office of Basic Energy Sciences, the National Science Foundation, and the Knowledge Innovation Program of the Chinese Academy of Sciences.

Piezoelectric materials generate a charge polarization when they are placed under strain. The piezo-phototronic devices rely on that physical principle to tune and control the charge transport and recombination by the polarization charges present at the ends of individual nanowires. Grown atop a gallium nitride (GaN) film, the nanowires create pixeled light emitters whose output varies with the pressure, creating an electroluminescent signal that can be integrated with on-chip photonics for data transmission, processing and recording.

“When you have a zinc oxide nanowire under strain, you create a piezoelectric charge at both ends which forms a piezoelectric potential,” Wang explained. “The presence of the potential distorts the band structure in the wire, causing electrons to remain in the p-n junction longer and enhancing the efficiency of the LED.”

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The efficiency increase in the LED is proportional to the strain created. Differences in the amount of strain applied translate to differences in light emitted from the root where the nanowires contact the gallium nitride film.

To fabricate the devices, a low-temperature chemical growth technique is used to create a patterned array of zinc oxide nanowires on a gallium nitride thin film substrate with the c-axis pointing upward. The interfaces between the nanowires and the gallium nitride film form the bottom surfaces of the nanowires. After infiltrating the space between nanowires with a PMMA thermoplastic, oxygen plasma is used to etch away the PMMA enough to expose the tops of the zinc oxide nanowires.

A nickel-gold electrode is then used to form ohmic contact with the bottom gallium-nitride film, and a transparent indium-tin oxide (ITO) film is deposited on the top of the array to serve as a common electrode.

When pressure is applied to the device through handwriting or other source of pressure, nanowires are compressed along their axial directions, creating a negative piezo-potential, while uncompressed nanowires have no potential.

The researchers have pressed letters into the top of the device, which produces a corresponding light output from the bottom of the device. This output – which can all be read at the same time – can be processed and transmitted.

The ability to see all of the emitters simultaneously allows the device to provide a quick response. “The response time is fast, and you can read a million pixels in a microsecond,” said Wang. “When the light emission is created, it can be detected immediately with the optical fiber.”

The nanowires stop emitting light when the pressure is relieved. Switching from one mode to the other takes 90 milliseconds or less, Wang said.

The researchers studied the stability and reproducibility of the sensor array by examining the light emitting intensity of the individual pixels under strain for 25 repetitive on-off cycles. They found that the output fluctuation was approximately five percent, much smaller than the overall level of the signal. The robustness of more than 20,000 pixels was studied.

A spatial resolution of 2.7 microns was recorded from the device samples tested so far. Wang believes the resolution could be improved by reducing the diameter of the nanowires – allowing more nanowires to be grown in a given space – and by using a high-temperature fabrication process.



SOURCE  Georgia Tech

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