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To help the body and brain accept bionic limbs and implants

Bionic implants can bring many benefits to humans, but the question arises of how the human body and brain adapt to these devices (photo: CC0 Public Domain)

by Gareth Wilmer

Not so long ago, the concept of a bionic human being seemed unrealistic, but robotic suits, brain-controlled extra limbs and mind-powered wheelchairs are already in development. This brings us much closer to the dream of human-machine integration.

“This is an extremely exciting time for robotics and the advancement of science,” says Professor Tamar Meikin, who works in the field of cognitive neuroscience at the University of Cambridge, UK. “We’ve seen bionic limbs from the realm of science fiction, as well as unconventionally designed prosthetic limbs that don’t look like body parts.”

For some, this idea may seem slightly disturbing. Clearly, robotic suits and bionic implants can bring many benefits as medical devices, such as improving prosthetics. But beyond all that, bionics and robotic assistance systems can potentially empower people in the workplace and increase productivity.

Given such rapid progress, according to Prof. Meikin, the question arises of how the human body and brain adapt and assimilate these devices. “I felt that an important element that was often left out of the discussion was how the user’s brain and cognitive skills would relate to an artificial body part,” she says.

Prof Meikin leads the Horizon-supported EmbodiedTech project, which investigates such questions as how effectively the human brain can support artificial body parts. Also, to what extent does the brain begin to recognize the artificial limb as part of one’s body? In this case, how much reliance is placed on the resemblance to a real limb? And how does the brain apply the feedback received from the limb?

Robotic assistance systems

Finding answers to these questions is central to making robotic assistance systems as user-friendly as possible and helping to ensure that our brains can handle them. There is room for improvement, some estimates suggest, as nearly half of amputees do not regularly use their prostheses.

A study led by Prof. Meikin’s team used functional magnetic resonance imaging (fMRI) on both ambidextrous and ambidextrous individuals. They found that the more regularly the prosthesis was used, the stronger the part of the brain associated with hand recognition responded to images of the prosthesis.

Prosthetic users also have stronger neural connections between the areas that enable people to recognize and control their hands, suggesting that the brain itself has adapted to perceive the prosthesis.

Another study found that the brains of people who regularly use prostheses seem to imagine prostheses as a separate category to a hand or tool. The reason for this is that it responds more similarly between different prosthetics that look like real hands and ones that don’t—such as the mechanical hook—than between them and hands or tools.

“Different types of prostheses perform similarly to each other, so they’ve been lumped together as one category,” says Prof Meikin. “There is no way the brain can be tricked into associating these prostheses with biological hands.”

Hands tentacles

Prof Meakin says this fact means there may be less need for full ‘switching on’ of prostheses than previously thought, potentially expanding the possibilities for robotic aids.

“We don’t need to blindly follow the solutions we already know,” she says. “We can think of entirely new materials like tentacle hands, as this means the brain must be able to recognize and accept them just like the bionic prostheses that have been the focus of prosthetic design for the past decade.”

Evidence also suggests that there is greater potential for augmenting the human body with additional limbs. An example of this is the robotic ‘third toe’, designed by her Cambridge University colleague and designer Danny Claude to be attached to the hand below the little finger, controlled by sensors attached to the wearer’s toes.

“We’re not supposed to have six fingers, but this seems like an acceptable solution as far as the brain is concerned,” says Prof Meakin. “You can use it to hold another instrument ready while you’re welding, or if you’re playing guitar and need to play an impossible chord.”

Indeed, participants in good health who are trained with the extra finger become more adept at using it and develop a stronger sense of its belonging to the body over time. However, a slight change in the brain’s representation of hand motor function after prolonged use suggests the need for caution.

“We shouldn’t be exploring these technologies in isolation from the body,” says Prof Meakin. “We need to be very aware of the side effects or limitations of increased brain use.”

Human-Machine Interaction

Another Horizon-funded study, the Living Bionics project, is exploring ways to better integrate medical devices that interact directly with the nervous system. Such devices include deep brain stimulation for Parkinson’s disease, as well as cochlear implants and bionic eyes used to treat hearing and vision disorders.

“When you implant a device, it’s essentially very different from the surrounding tissue,” said Dr Roberto Portillo-Lara, a bioengineer at Imperial College London who worked on the project. “We are trying to develop the interface between these implantable devices and physiological tissues.”

He explains that the problem with many of the current implants is that they use metals that the nervous system recognizes as foreign. This can cause scarring and isolate the implant, compromising it for a long time and creating potential safety issues.

The solution may lie in combining electronic devices with cell-encased polymers that aim to mimic the composition of biological tissues. They are carried inside a soft hydrogel that can act as a shell for existing devices or be used to create new ones.

Implant covers

“We’re bringing together different technologies from biomaterials science and we’re also working with neural stem cells, bringing them together to create living coatings for implants,” says Dr. Portillo-Lara.

He explains that finding the right balance between synthetic and natural polymers is critical. “Synthetic polymers offer many advantages because they are reliable and predictable,” says Dr. Portillo-Lara. “Natural polymers are more difficult to work with, but they are more similar to what cells are used to.”

After starting with more synthetic mixtures in laboratory tests, they found that they were not very conducive to successful cell development. However, the incorporation of more natural polymers over time contributes to the ultimate performance of the coatings.

“The answer is simple: when we make it more like natural tissues, the cells behave better,” he says. “Now we combine the best of both worlds.” Dr. Portillo-Lara believes that more advanced testing could begin early next year.

As with EmbodiedTech, the scientific research has implications for future technology beyond the clinical setting—including controlling machines, such as electric wheelchairs, with the mind. “Better interaction with the nervous system has implications for brain-computer interaction,” says Dr. Portillo-Lara.

Effects on the brain

This means that it is particularly important to understand what the possible effects are on the brain. “We have to think about what will happen once these technologies become affordable enough that not only patients will want to get one of these implants, but also ordinary consumers.”

Dr Portillo-Lara believes such technologies could be ready within a decade, although it is far more difficult to predict when they will become available, given the ethical and regulatory issues.

“The applications would be virtually limitless,” he says. “There are a large number of emerging applications that we can’t even predict right now because the technology for them doesn’t exist.”

The research in this article was funded through the European Research Council (ERC) of the EU. It was first published inHorizonthe EU research and innovation journal.

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