The robotic device's electrodes are fused directly to the bones and nerves of amputees
A postdoctoral student has developed a technique for implanting thought-controlled robotic arms
and their electrodes directly to the bones and nerves of amputees, a move which he is calling “the future of artificial limbs”. The first volunteers will receive their new limbs early in 2013.
“The benefits have no precedent,” Max Ortiz Catalan, who carries out research in biomedicine and artificial intelligence at the Chalmers University of Technology in Sweden, told Wired.co.uk. “They will be able to simultaneously control several joints and motions, as well as to receive direct neural feedback on their actions. These features are today not available for patients outside research labs. Our aim is to change that.”
Ordinary myoelectric prostheses work by placing electrodes over the skin to pick up nerve signals that would ordinarily be sent by the brain to the limb. An algorithm then translates these signals, and sends instructions to motors within the electronic limb. Since the electrodes are applied to the skin surface, however, they will undoubtedly encounter countless issues in maintaining the fluid transfer of information back and forth between the brain and the limb. By implanting those electrodes directly to the patient’s nerves, Catalan is hoping to get one step closer than anyone else to replicating natural movement.
“Our technology helps amputees to control an artificial limb, in much the same way as their own biological hand or arm, via the person’s own nerves and remaining muscles,” he said.
Using the Osseointegrated Prosthesis for the Rehabilitation of Amputees (OPRA) method developed by Rickard Brånemark at Sahlgrenska University Hospital in Gothenburg, Catalan and his team plan to forgo traditional sockets in place of bone-anchored prostheses attached via titanium screws. It was a method inspired by Brånemark’s father, who was the first to discover that titanium can fuse with bone tissue.
“The operation will consist of placing neural and muscular electrodes on the patient’s stumps, as well as placing the bidirectional interfaces into the human body.”
A titanium implant acts as the bidirectional interface, transmitting signals from the electrodes, placed on nerves and muscles, to the limb. It is a truer replication of how the arm was designed to work, with information from existing nerves being transferred to the limb and to the implant, where algorithms can translate thought-controlled instructions into movement. It is, Catalan told Wired.co.uk, a “closed loop control” that moves us “one step further to providing natural control of the artificial limb”. Add to this the fact that every finger is motorised and can be individually controlled, and Catalan’s bold statement might just be accurate.
The first surgeries, due to be carried out by Brånemark in January or February 2013, will all be on patients that had limbs amputated several years prior. Asked whether or not this will make success harder, Catalan said it was one question they are looking to answer.
“The possibilities are higher in recent amputation. Our first patients however, have been amputated for several years. This project aims to answer several very interesting scientific questions in neurorehabilitation.”
In preparation, for both the amputees’ learning and the algorithm’s, Catalan has been training his subjects in the lab using virtual reality simulations. “It provides real-time feedback to the patients on their performance executing different motions. It is definitely very important for them to re-learn some motions, and for us to quantitatively qualify our algorithms’ performance.”
The work echoes that of the Centre for Bionic Medicine in Chicago. In October Zac Vawter highlighted the centre’s work by climbing 103 flights of stairs using his bionic leg, attached following an amputation technique called targeted muscle reinnervation (TMR). This involves transferring amputated nerves to remaining muscle and skin so that they can provide additional signals the limb’s inbuilt microprocessor can process — it dramatically improves the reactivity of a robotic prosthetic. Catalan is in touch with the Centre and plans to collaborate and combine the two technologies to help create an “osseointegrated human-machine gateway”.
“We definitely see the combination of these technologies as the future of artificial limbs,” he told Wired.co.uk. “They have done excellent work, a lot of very useful scientific research has come from Todd Kuiken’sgroup. We have complementing technologies, while targeted muscle TMR is useful to provide additional control signals in the muscles, it still needs surface electrodes.”
Ultimately, Catalan hopes the surgical trials will prove the potential for dramatic progress in prosthetics and secure the university more funding to take that progress from a clinical setting, to a real world one on a far larger scale.
“This technology can then become a reality for lots of people. We want to leave the lab and become part of the patients’ everyday life. If the first operations this winter are successful, we will be the first research group in the world to make ‘thought-controlled prostheses’ a reality for patients to use in their daily activities, and not only inside research labs.”