Brain controlled prosthetic arm

A Swedish truck driver has become the first person to receive a new design of prosthetic arm that is mounted directly onto the bone in his upper arm and is controlled by electrical signals picked up from nearby nerves and muscles.

Touch sensations from the artificial arm itself can also be sent back into the nerves that would have picked up sensations from the patient's missing fingers, restoring a sense of touch. All of this information is carried inside - and through - the metal arm implant, so there are no external wires or holes in the skin, which minimises the risk of infection.

Chalmers University of Technology researcher Max Ortiz Catalan is leading the project.

Max -  There are basically two main problems when it comes to prosthetic devices today.  One of them is how do you attach the artificial limb to the body.  The second one is how you get the patient to control their prosthetic device.  We solved the problem of the mechanical attachment with putting a titanium implant inside the bone and the bone cells will grow very tight around it and anchor it.  And that gives you mechanical stability.  So, the prosthesis is fixated to the bone.

Chris -  I see.  So, you've effectively got a very strong anchor point which comes out at the end of wherever the bone has been severed or cut-off and this then provides you with a firm attachment that's rigid.  It's not going to move, so you've got strength there.  What about the other problem which is, if you're using one of these prosthetics, you need to be able to control it in all these degrees of freedom, given how many different directions of movement a functional arm has?

Max -  For a long time, people has been thinking about implanting electrodes.  So, you go directly to the nerves and muscles and get the signals from there.  That also could leave with a possibility that if you're connected to a nerve for instance, you can send electrical pulses.  So, the patient can perceive sensory feedback that's coming from the missing limb.  So, we used this anchoring point as a feedthrough mechanism.  So, we embed connectors inside the implant.  So, these signals can go and come between the prosthesis and the person using this anchoring point.  So, we have mechanical attachment but also, communication between the control system of the prosthesis and nerves and muscles.

Chris -  So, what?  There are little wires which run through the anchor point so they could carry signals out of the prosthesis and feed them into nerves in the stump so the person could feel what's going on and you can also pick up signals from the muscles around where the implant is, enabling the person to control the prosthesis downstream.

Max -  So, it's a little bit more tricky than wires running inside the implant, but it's a series of mechanisms because we have sealing compartments to avoid bacteria to go in and so on.

Chris -  What about controlling the prosthesis and also, giving the person who's wearing the prosthesis feedback about what they're doing, what they're touching, and how hard they're pressing on something for instance.

Max -  What we can do now because we have electrodes in the muscles and around the nerves is record signals that are travelling from the brain and that will normally go to the missing hand and use those to tell the prosthesis what to do.  In a similar way, because those wires that are the nerves that are going to the brain are sealed there, we can still send electrical impulses and the person can perceive different sensations depending on how you're stimulating or which fibres you're stimulating.

Chris -  How do you collect the electrical signals which are going down those nerves or present in the muscles in order to then transmit them into the prosthesis?

Max -  So, we have electronics that amplify the signals from the nerves and the muscles and then we take that information and reduce that information with algorithms to predict what is the person trying to do because we know what the person is trying to do because the person is telling us.  So, in that way, we can correlate how those signals look like and then translate that into the motion the patient is intending to do.

Chris -  And then you feed those signals into the arm itself.  How long does it take for a patient who receives one of your implants to actually get used to using it?

Max -  It's very straightforward.  The patient basically needs to remember how he was using the hand before.  So, how to contract the muscles in a way that it used to be when he had an arm and then the system will work.

Chris -  With Max is the patient who has received this implant.  Hello, Magnus.

Magnus -  Hello.

Chris -  Tell us a bit about you.  What do you do for a living?

Magnus -  I'm a truck driver for mining.

Chris -  How did you come to meet Max?

Magnus -  I got a tumour in my arm, so they asked to cut it.

Chris -  What did you then do?  Did you just get a prosthetic arm straightaway?

Magnus -  I was one year without arm.

Chris -  When you did get a prosthetic arm, what was it like?  How did you cope?

Magnus -  It was really bad.  It was not so comfortable.

Chris -  What was the problem?  What did you find was difficult?

Magnus -  The arm was heavy and when it's warm outside, you get sweaty and it was difficult to work.

Chris -  What sorts of tasks did you find tricky with it?

Magnus -  I couldn't lift heavy things.  I couldn't lift the arm in every positions.

Chris -  Could you do your job?

Magnus -  No.  I couldn't work.

Chris -  You then get fitted with this new device.  How did that make a difference?

Magnus -  I can work 100% and it's more like a real arm, not like a tool.

Chris -  Max, in this device, you must be delighted.

Max -  This is why I'm in this business really.  Technically and scientifically, it's very interesting and appealing, but it's also very rewarding.  And something that has to be said about this is that it was a close collaboration between the technical side that's Chalmers University of Technology, but also the hospital.  Without the medical and the technical working together as well as an industrial partner because you need to have the regulatory system in place to be able to produce an implant that you're going to put inside a person.  If you take one of those three components out of the equation, this will not happen.  Engineers cannot do it alone.  Doctors cannot do it alone.  So, it's been a very nice collaboration.

Kat -  That was Max Ortiz Catalan and before him, Magnus Niska and their work appeared in the journal Science Translational Medicine.