Name: 本物のように感じることができる義肢。バイオニック医療の実態と導入 | WIRED Japan
Uploaded: 2025-02-18T08:56:02.000Z
Duration: 9 min 34 s
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you're looking at a game-changer in prosthetics.

The only one today using electrodes implanted in the nerves and to have sensation.

The developer of this bionic system is speaking to us from Ukraine, where war has led to a crisis.

There is more than 15,000 people with amputations in the country.

Let's walk through every step needed to implant his bionic arm into a patient.

Bionic basically means that it's a combination between biology and electronics.

But traditionally, prosthetic arms are pretty lo-fi.

Some are purely aesthetic, made in silicone, but not functional.

Then there are functional mechanical ones, powered by a wire and a patient's own movements.

You can think about a claw or a hook that can open and close, and it has a system of gears like brakes for your bicycle.

Then you have fancy electric prostheses, where a patient can control the fingers independently via electrodes placed on the surface of the skin.

This is normally done with a socket, something that is on your skin, putting a lot of pressure.

It's uncomfortable and heavy, so that's why the first step in installing Dr. Ortiz-Catalan's bionic arm is osseointegration, or implanting a titanium structure directly to the skeleton.

Osseointegration made a big splash in the medical field.

The first application were dental implants.

Eventually, scientists applied this to prosthetics after discovering in the 50s that if you attach titanium inside bone, the bone cells can grow directly on the titanium, making a very strong attachment to the residual limb.

Say you have a transhumeral amputation above the elbow.

The surgeon will place a titanium implant that looks like a screw inside the center of the bone, and you leave it there for a few months.

In that period, the bone cells grow around the titanium implant, and then you place a portion of the implant that comes out through the skin, and that's where you're gonna connect your prosthesis.

Implanting into a residual limb that has been amputated below the elbow has its own challenges because there are two smaller bones, the radius and the ulna, and they move independently from each other.

So they will move like this, they will move like this, and they will also move in their own axis.

So we develop an artificial joint that allows for those movements to take place while preserving a natural orbit for the movement.

Now, the next step is to surgically implant the electrodes inside the body.

We will place electrodes in the muscles and the nerves around the residual limb.

Electrodes on the surface of the skin are susceptible to electromagnetic interference.

Stuff all around us, like tools or computers, can create noise interference, radiating to the electrodes if they're merely sitting on the surface of the skin.

This will cause the prosthetic to become uncontrollable.

Even just moving your arm around can throw off a conventional sensor.

If it lifts a little bit, it generates this, what's called a motion artifact.

If you move too fast, if you sweat, the prosthesis becomes less controllable.

With electrodes implanted directly inside muscles on nerves, you don't have any of those problems.

If you have an amputation where the hand is gone, you have many muscles here that help you to control the fingers of the hand.

So there's a lot of sources that you can use to drive the prosthesis.

But in the case of an amputation above the elbow, you don't have as much to work with.

So the team has to get creative and rejigger the body's original biological wiring.

You have the biceps and the biceps has two heads.

So it's not enough information that we can extract from the muscles to drive all the missing joints.

So a solution for that is you can take a nerve that used to go to the hand and then you transfer it into one head of the biceps.

So then when the patient thinks about closing the hand, this part of the muscle will contract, the short head.

There are three big nerves in the arm, the radial, the ulnar, and the median, which allows you to control these three fingers.

Basically, a nerve is a collection of axons which are bundled into fascicles.

So if you think about my fingers as the bundles of the nerve, what you can do is split them.

You take one of those bundles to connect with that muscle that is available there.

And then for the other ones, we can borrow a piece of muscle from the legs.

And then we transfer that to the arm to connect to one of these fascicles.

Next, you insert a metal electrode into the muscle and connect that to the connector inside the titanium implants.

And that wire is covered by materials that are biocompatible, meaning that they're well taken by the body.

The signals that come from your brain to control your limbs travel through nerves, but these organic signals are relatively weak, about 10,000 times smaller than the strength of the signals generated by these new electric plugs.

So in a way, the implanted electrodes use the muscle like a loudspeaker, amplifying the signals from the brain to the muscles and to the prosthesis.

You can think about it as a USB port into the nervous system.

The next step involves training the AI in the bionic hand's CPU to understand what the signals from the brain mean.

The way we control our limbs is by electric signals coming down through the nerves to the muscles, and these come in the form of electric impulses.

Those signals are captured by the electronics of the prosthesis, so they travel down to the prosthesis where there is the brain of the prosthesis, understands what those signals are.

But that CPU in the prosthesis doesn't automatically know what those patterns of activation mean.

What we do is we tell the patient, try to close your hand, and then we record signals.

And then we say, try to open your hand, and we record the signals.

And then the team labels that action for the AI, translating neural signals from the brain into code that is now understood by the tiny computer in the prosthetic arm, which then engages its robotic motors to move in specific ways.

The next step involves training the patient using software.

This was actually the first time we saw the patient after the surgery.

We connected it to a virtual reality system.

Those two cables coming out of the implants are sending signals wirelessly to the computer where they are interpreted and used to control a virtual limb.

This trains the muscles and makes the signals more distinct and reliable in preparation for when the patient gets their bionic limb.

But this training also addresses another challenge that arises from amputation.

After you have an amputation, there's pain that remains from something called phantom limb pain.

Which is caused by the brain getting confused and imagining that the missing limb is frozen or twisting in awkward ways.

So I developed some technologies to treat phantom limb pain.

We coupled those with a virtual augmented reality so the patient can engage the same neural resources that were used to control the hand.

This training is useful in fine-tuning the algorithms that will drive the robotic motors.

But working in the virtual world is one thing.

Without their bionic arm attached, patients will do relatively well because there's no load.

So the final step involves fitting the prosthesis and testing in the real world.

Patients come into the lab, put on their bionic arm, and perform daily tasks like packing a suitcase or picking up small objects.

These are tasks that can tell you a little bit about the function the patient has with the prosthesis.

The team then makes adjustments and runs further tests that evaluate and help improve one of the most jaw-dropping features of the prosthetic, its ability to feel objects in its grasp.

When the prosthesis makes contact with the object, there are sensors in the fingertips.

And then the brain of the prosthesis has also a neurostimulator, which delivers electrical pulses to the nerves.

And because the brain receives this data from a nerve that used to be connected to the biological limb, it will interpret it as coming from the bionic hand.

If I have a biological receptor in my index finger, that has a nerve that goes all the way up to my brain.

If I put an electrode along that nerve, it doesn't matter where I stimulate, the brain will create a sensation that's coming from the fingertip.

It's an automatic sensation that rises in consciousness.

The bionic hand uses sensors in its thumb and index finger to send an electrical signal through the prosthetic and then along the original severed nerves straight to the brain.

But the information from the fingertips is not as nuanced as what a biological fingertip feels.

For us, we have hundreds of sensors that travel in hundreds of neurons.

Today, we don't have that resolution at the neural interface.

We're still a long way off from the type of sensation seen in the artificial limbs in Star Wars.

This hand only provides rough sensations, but they're still useful because now a patient can feel when there's an object in their hand and if that object is slipping away.

They have to power the CPU and the motors that drive the prosthesis, right?

You can have interchangeable batteries and whenever the prosthesis run out of battery, they just switch it.

So the days of patients carrying heavy backpacks full of computers or bulky batteries are gone.