Prosthetic hands endowed with a sense of touch (2) Ortiz Catalan - TopicsExpress



          

Prosthetic hands endowed with a sense of touch (2) Ortiz Catalan and his colleagues developed a way to secure these wires by taking advantage of “osseointegration,” a technique for anchoring the prosthesis directly to the bone. The prosthesis screws into a titanium post surgically implanted in the bone, much as in a dental implant. And the electrical connections are made within that coupling through connectors that go to the nerves themselves. An amputee has used this connection scheme successfully since January 2013 to go about his daily life as a truck driver and a father, the researchers report today in Science Translational Medicine. - Prosthetic hands endowed with a sense of touch news.sciencemag.org/brain-behavior/2014/10/prosthetic-hands-endowed-sense-touch Four years ago, Igor Spetic lost his right arm in an industrial accident. Doctors outfitted him with a prosthetic arm that restored some function, but they couldnt restore his sense of touch. Without it, simple tasks like picking up a glass or shaking hands became hit-or-miss propositions. The lack of touch also robs Spetic of basic pleasures. “I would love to feel my wife’s hand,” he says. In time, he may regain that pleasure: Two independent research teams have now equipped artificial hands with sensors that send signals to the wearer’s nerves to recreate this missing sense. The sensing technologies work only in the lab, but they have proved durable, and amputees who have tried them, including Spetic, say that they are effective. One technology advances the range of touch sensations available, while the other promises to enable touch through a better way to attach the prosthesis. “All of these results are very positive,” says Mandayam Srinivasan, a neuroengineer at the Massachusetts Institute of Technology in Cambridge, who was not involved in either project. “Each of them fills a piece of the puzzle in terms of [prosthesis] development.” Almost 40 years ago, researchers tried to provide sensory feedback by adding pressure sensors to prostheses that relayed the sensation through electrodes attached to nerves. But for the most part, they just made it seem like the hand was tingling. And durability has been an issue in such efforts, too. In February, Silvestro Micera, a neuroengineer at the SantAnna School of Advanced Studies in Pisa, Italy, and the Swiss Federal Institute of Technology in Lausanne and his team showed that it was possible for sensor-equipped prosthetic arms to gently or powerfully grab objects and even to distinguish a round from a square object (1). But the study lasted just 4 weeks, in part because of the delicate interface with the body. Dustin Tyler thought he could do better. The biomedical engineer at Case Western Reserve University in Cleveland, Ohio, and his colleagues outfitted prostheses worn by Spetic and a second amputee with more than a dozen pressure sensors, the outputs of which were conveyed by wires to a computer. The computer processes all incoming signals to create specific patterns of electrical impulses that vary in duration and intensity. For Spetic, more wires relay those electrical impulses to nerves in the arm via three electrodes built into cuffs implanted under the skin. Each electrode goes to a different nerve and from there branches for a total of 20 potential points of connection. The other amputee was similarly fitted but with fewer points of connection. Depending on which point gets the signal, the brain “feels” something on a different place on the hand, say the thumb or pinkie. Tyler thinks the signals are not exactly the same as would come from a real hand, but must be close enough to trigger the particular sensation. That ability to “feel” greatly sharpened the amputees’ ability to pull a stem off a cherry without squashing it or put toothpaste on a toothbrush, Tyler and his colleagues report today in Science Translational Medicine (2). And the sensor connections have lasted more than 2 years in Spetic and 18 months in the other amputee. Spetic is working on distinguishing sandpaper from smooth and ridged textures and even to tell what finger is sensing which texture. And as the researchers refine the computer processing and put more “points” on the nerves, the diversity of sensations conveyed should improve (Watch a related video: Prosthetic hands endowed with a sense of touch (1) - bcove.me/hpsjqaig) (*). “They managed to move from that tingling sensation to a more natural sensation,” says Max Ortiz-Catalan, a research scientist at Chalmers University of Technology in Gothenburg, Sweden, who was not involved with the work. Besides restoring some touch, the sensor-equipped hand also gave the amputees the sense that it was part of their body. Spetic told researchers that it eliminated the phantom pain lingering from his lost hand—which he likened to the closed fist being crushed in a vice. Ortiz-Catalan has taken a different tack in improving prosthetic arms. Most artificial limbs are challenging to attach securely and comfortably to the body. And the wires that control the limbs movement typically enter the upper arm through the skin and are implanted directly into the nerves. This setup can be jostled out of connection and prone to infection, so that sometimes amputees just give up wearing their prostheses. Ortiz-Catalan and his colleagues developed a way to secure these wires by taking advantage of “osseointegration,” a technique for anchoring the prosthesis directly to the bone. The prosthesis screws into a titanium post surgically implanted in the bone, much as in a dental implant. And the electrical connections are made within that coupling through connectors that go to the nerves themselves. An amputee has used this connection scheme successfully since January 2013 to go about his daily life as a truck driver and a father (3), the researchers report today in Science Translational Medicine (Click here for a related video: Prosthetic hands endowed with a sense of touch (2) - bcove.me/hrrpzu4k) (**). In the lab, Ortiz-Catalan’s team has shown that these connections can transmit touch sensations as well. This long-term success bodes well for amputees, Tyler says. “By having this direct connection [into] the bone, that’s going to be a major advance, he says. Ultimately, Tylers and Ortiz-Catalans approaches might be combined. “Now we can borrow their findings to improve our sensory part,” Ortiz-Catalan says. “We want to make [the sensing technology] reliable and small enough that the patient can use it at home.” But don’t expect a touch-sensitive artificial arm to hit the market any time soon, Micera says. “If you look at both papers, there’s no evidence that they can use their approach to do sophisticated tasks in real time.” he says. But the work “is going in the right direction in improving the quality of life of these people, he says, which is the most important thing.” Video (*) Prosthetic hands endowed with a sense of touch (1) bcove.me/hpsjqaig That ability to “feel” greatly sharpened the amputees’ ability to pull a stem off a cherry without squashing it or put toothpaste on a toothbrush, Tyler and his colleagues report today in Science Translational Medicine. And the sensor connections have lasted more than 2 years in Spetic and 18 months in the other amputee. Spetic is working on distinguishing sandpaper from smooth and ridged textures and even to tell what finger is sensing which texture. And as the researchers refine the computer processing and put more “points” on the nerves, the diversity of sensations conveyed should improve. (**) Prosthetic hands endowed with a sense of touch (2) bcove.me/hrrpzu4k Ortiz Catalan and his colleagues developed a way to secure these wires by taking advantage of “osseointegration,” a technique for anchoring the prosthesis directly to the bone. The prosthesis screws into a titanium post surgically implanted in the bone, much as in a dental implant. And the electrical connections are made within that coupling through connectors that go to the nerves themselves. An amputee has used this connection scheme successfully since January 2013 to go about his daily life as a truck driver and a father, the researchers report today in Science Translational Medicine. References 1. Restoring Natural Sensory Feedback in Real-Time Bidirectional Hand Prostheses Sci Transl Med 5 February 2014: Vol. 6, Issue 222, p. 222ra19 Sci. Transl. Med. DOI: 10.1126/scitranslmed.3006820 stm.sciencemag.org/content/6/222/222ra19 Abstract Hand loss is a highly disabling event that markedly affects the quality of life. To achieve a close to natural replacement for the lost hand, the user should be provided with the rich sensations that we naturally perceive when grasping or manipulating an object. Ideal bidirectional hand prostheses should involve both a reliable decoding of the user’s intentions and the delivery of nearly “natural” sensory feedback through remnant afferent pathways, simultaneously and in real time. However, current hand prostheses fail to achieve these requirements, particularly because they lack any sensory feedback. We show that by stimulating the median and ulnar nerve fascicles using transversal multichannel intrafascicular electrodes, according to the information provided by the artificial sensors from a hand prosthesis, physiologically appropriate (near-natural) sensory information can be provided to an amputee during the real-time decoding of different grasping tasks to control a dexterous hand prosthesis. This feedback enabled the participant to effectively modulate the grasping force of the prosthesis with no visual or auditory feedback. Three different force levels were distinguished and consistently used by the subject. The results also demonstrate that a high complexity of perception can be obtained, allowing the subject to identify the stiffness and shape of three different objects by exploiting different characteristics of the elicited sensations. This approach could improve the efficacy and “life-like” quality of hand prostheses, resulting in a keystone strategy for the near-natural replacement of missing hands. 2. A neural interface provides long-term stable natural touch perception Sci Transl Med 8 October 2014: Vol. 6, Issue 257, p. 257ra138 Sci. Transl. Med. DOI: 10.1126/scitranslmed.3008669 stm.sciencemag.org/content/6/257/257ra138 Abstract Touch perception on the fingers and hand is essential for fine motor control, contributes to our sense of self, allows for effective communication, and aids in our fundamental perception of the world. Despite increasingly sophisticated mechatronics, prosthetic devices still do not directly convey sensation back to their wearers. We show that implanted peripheral nerve interfaces in two human subjects with upper limb amputation provided stable, natural touch sensation in their hands for more than 1 year. Electrical stimulation using implanted peripheral nerve cuff electrodes that did not penetrate the nerve produced touch perceptions at many locations on the phantom hand with repeatable, stable responses in the two subjects for 16 and 24 months. Patterned stimulation intensity produced a sensation that the subjects described as natural and without “tingling,” or paresthesia. Different patterns produced different types of sensory perception at the same location on the phantom hand. The two subjects reported tactile perceptions they described as natural tapping, constant pressure, light moving touch, and vibration. Changing average stimulation intensity controlled the size of the percept area; changing stimulation frequency controlled sensation strength. Artificial touch sensation improved the subjects’ ability to control grasping strength of the prosthesis and enabled them to better manipulate delicate objects. Thus, electrical stimulation through peripheral nerve electrodes produced long-term sensory restoration after limb loss. 3. An osseointegrated human-machine gateway for long-term sensory feedback and motor control of artificial limbs Sci Transl Med 8 October 2014: Vol. 6, Issue 257, p. 257re6 Sci. Transl. Med. DOI: 10.1126/scitranslmed.3008933 stm.sciencemag.org/content/6/257/257re6 Abstract A major challenge since the invention of implantable devices has been a reliable and long-term stable transcutaneous communication. In the case of prosthetic limbs, existing neuromuscular interfaces have been unable to address this challenge and provide direct and intuitive neural control. Although prosthetic hardware and decoding algorithms are readily available, there is still a lack of appropriate and stable physiological signals for controlling the devices. We developed a percutaneous osseointegrated (bone-anchored) interface that allows for permanent and unlimited bidirectional communication with the human body. With this interface, an artificial limb can be chronically driven by implanted electrodes in the peripheral nerves and muscles of an amputee, outside of controlled environments and during activities of daily living, thus reducing disability and improving quality of life. We demonstrate in one subject, for more than 1 year, that implanted electrodes provide a more precise and reliable control than surface electrodes, regardless of limb position and environmental conditions, and with less effort. Furthermore, long-term stable myoelectric pattern recognition and appropriate sensory feedback elicited via neurostimulation was demonstrated. The opportunity to chronically record and stimulate the neuromuscular system allows for the implementation of intuitive control and naturally perceived sensory feedback, as well as opportunities for the prediction of complex limb motions and better understanding of sensory perception. The permanent bidirectional interface presented here is a critical step toward more natural limb replacement, by combining stable attachment with permanent and reliable human-machine communication.
Posted on: Sun, 19 Oct 2014 18:17:24 +0000

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