DARPA is developing a high-tech interface system that would provide a sense of touch and better coordination to artificial limb users

Nerve-connected prosthetics to make artificial limbs feel real

DARPA is developing a neural interface microsystem for prosthetics that would improve amputees’ experience by giving them sense of touch and better control over artificial limbs.

The Hand Proprioception and Touch Interfaces (HAPTIX) programme, run by the Biological Technologies Office of the US Defense Advanced Research Projects Agency (DARPA) aims to add the sense of touch and better mind-body coordination to existing prosthetics.

Proprioception – the sense of the relative position of various body parts – is something that has so far been completely missing in the prosthetics technology. As a result, amputees usually perceive their artificial limbs as something alien, rather a tool than an integral part of the body. Therefore, many of them don’t feel comfortable wearing the fake limbs and put them aside as soon they complete the needed task.

The HAPTIX project wants to change the situation by developing a sensory interface, connecting the prosthesis to the peripheral nerves and muscles of the amputees’ stumps. This interface will measure and decode signals transmitted through the nerves for better coordination, as well as deliver tactile and positioning feedback from the artificial limb to the user.

One of the key challenges will be to identify stimulation patterning strategies that elicit naturalistic sensations of touch and movement. The ultimate goal is to create a fully-implantable device that is safe, reliable, effective, and approved for human use.

“Peripheral nerves are information-rich and readily accessible targets for interfacing with the human nervous system,” said DAPRA programme manager Doug Weber.

“Research performed under DARPA’s RE-NET (Revolutionizing Prosthetics and Reliable Neural-Interface Technology) programme and elsewhere showed that these nerves maintain motor and sensory fibres that previously innervated the amputated limb, and that these fibres remain functional for decades after limb loss. HAPTIX will try to tap into these biological communication pathways so that users can control and sense the prosthesis via the same neural signalling pathways used for intact hands and arms.”

The researchers believe gaining better physical control and sense of the prostheses will have a positive psychological effect and may possibly help reduce the phantom limb pain – a feeling of pain in the non-existent limb which is perceived by up to 80 per cent of all amputees.

DARPA will assemble a multi-disciplinary team including psychologists, engineers and clinicians to help develop electrodes, algorithms and electronic technology components for the HAPTIX system.

“We have the opportunity to not only significantly improve an amputee’s ability to control a prosthetic limb, but to make a profound, positive psychological impact,” Weber said. “Amputees view existing prostheses as if they were tools, like a wrench, used only to perform a specific job, so many people abandon their prostheses unless absolutely needed. We believe that HAPTIX will create a sensory experience so rich and vibrant that the user will want to wear his or her prosthesis full-time and accept it as a natural extension of the body.”

At the end of the development, DARPA will run a 12-month take-home trial of the complete HAPTIX prosthesis system. The agency believes the HAPTIX technology could find wider use in medicine and plans to fund teams interested in developing science and technology for next-generation HAPTIX capabilities.

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