The surgeon leans over the operating table. In one hand are her forceps, in the other a clamp. With a third hand, fixed to the end of a robotic arm attached to her shoulder, she deftly maneuvers a tiny camera…
This is the potential future world of the “supernumerary robotic limb”—a form of mechanical augmentation that could upgrade human abilities by giving us extra arms, legs, or fingers. It may sound a little far-fetched, but not to Dani Clode. She already has one.
Clode is Head Designer & Senior Technical Specialist at the Plasticity Lab, University of Cambridge, and she has a flexible, 3D-printed “Third Thumb”. It can be strapped to the side of her hand next to her little finger, and is powered by two wrist-based motors wirelessly connected to pressure sensors under her toes and microcontrollers in the soles of her shoes.
“There are tasks that would normally require both hands, but the extra thumb means I can do them with just one,” she says. “Like gripping a jar and opening the lid at the same time. It’s no problem.”
By pressing her big toes, she can move her extra digit with considerable precision—almost like a real thumb, in fact. Clode envisages that one day such an appendage could be designed for the specific needs of craftspeople such as jewelers, watchmakers or carpenters.
Developing supernumerary body parts is a relatively new facet to the world of wearable robotics and is not without challenges. A significant issue is the fact that they need to be controlled by another part of the body, which potentially compromises existing capabilities. In the case of Clode’s Third Thumb, for example, is the agency of her big toes diminished because she’s using them part of the time to control her extra digit? She acknowledges the problem. “In the long term, it’s something we’re going to have to look at,” she says. “If we’re going to augment ourselves, will we have to make a trade-off to get the functionality we’re looking for?” Perhaps developments in brain-computer interfaces, which allow machines to be controlled by thought alone, could prove a fruitful solution.
Clode’s journey to designing her Third Thumb began while she was studying for a Master’s at the Royal College of Art and became interested in prosthetics, in particular how users interact with them. “It’s very unusual to have a product where a person has such a feeling of embodiment towards it,” she says. “I wanted to focus on the thumb, because that’s the most challenging part of prosthetic hand design, but I also wanted to investigate how it would make me feel when I had full control of something that was responding to my movements.”
The question of embodiment and how our brains adapt to having an extra limb or finger was recently studied by scientists in Japan, led by Ken Arai at the Research Center for Advanced Science and Technology at the University of Tokyo. In their research they gave subjects a virtual reality extra limb that was controlled by the motion of their feet, and set a task that involved touching a VR ball. They were then questioned to establish how much they felt the extra arm really belonged to them. The results showed that participants did indeed feel as if they had acquired a new, although different, body part.
Clode’s experience has been similar. She first wore her Third Thumb for a prolonged period of time during her week-long Master’s show, and immediately started to notice a kind of mental attachment. Taking it off in the evening, she had a feeling of missing something. On the stand at her show, she had an automated, moving thumb on display, and if she caught sight of it moving in the corner of her eye, her toe would press down as a reflex. “It was clear that I’d generated some kind of connection with the technology,” she says.
Clode also began to have an awareness of where the end of her Third Thumb was without looking at it. This is something that’s known as proprioception, often referred to as a sixth sense, which is the body’s ability to perceive its own position in space. “Embodiment is a complex thing,” she says. “I don’t feel like the thumb is another human digit, but I do feel agency over it when I wear it.”
Clode believes that sensors and AI will one day play a role in extending the performance and functionality of supernumerary robotic limbs, as this is something that is already starting to happen in a more traditional area of mechanical human augmentation: Motorized exoskeletons.
These wearable devices are widely used both in medical rehabilitation and in logistics and manufacturing. However, they are generally heavy, stiff, and not easily adapted to individual users, often making them uncomfortable to operate.
But things are changing. At London Tech Week in 2023, researchers from Canterbury Christ Church University presented a lower limb exoskeleton designed to help children with cerebral palsy and other neurological conditions to stand and walk as part of their rehabilitation therapy. The pioneering use of AI in the device is a pointer to a new wave of more user-friendly exoskeletons.
“It’s very exciting,” says Professor Konstantinos Sirlantzis, who leads the university’s Artificial Intelligence and Assistive Robotics team. “What we have developed is algorithm-based, personalized, predictive control for an exoskeleton.”
The researchers’ AI was trained using gait data collected over 15 years, including data from children with neuro disabilities. Sensors on the exoskeleton measure the user’s gait at intervals of milliseconds, and the AI can then, based on its own learnings, predict movement, powering six separate motors on the device to sync precisely with movement. The next stage of development will be to undergo clinical trials.
Sirlantzis believes it’s only a matter of time before AI and the development of lighter materials make exoskeletons much more generally accessible. Perhaps this, and other forms of wearable robotics such as supernumerary limbs, will lead to a future where humans can be mechanically augmented in a multitude of ways for different purposes, whether industrial or personal. In Japan, where nearly a third of the population is over 65, exoskeletons are already being used to allow the elderly to continue to do manual jobs well into their 70s. As the global “demographic time-bomb” of falling birth rates and increased life expectancy ticks ever louder in the rest of the world, mechanical augmentation could one day prove essential for maintaining the global workforce, bringing new powers to those who might otherwise be disqualified from specific tasks because of their age or physical strength.
Key to that would be computational power that allows processing to take place within the machinery itself—Sirlantzis’ device is tethered to a laptop. “The algorithms are quite computationally intensive,” he says. “But recent developments in microprocessor technology and embedded applications on printed circuit boards is making it possible to run them on the devices themselves.”
Dr. Helen Dudfield | Chief Scientist for Training & Human Performance and Dean of Fellows at QinetiQ
The defense and security sector often operates in harsh, high-stakes environments, and it is within these that “mechanical human augmentation” could be a game-changer. Imagine an explosive ordnance disposal operator being able to dispose of a bomb faster and more securely thanks to the use of additional digits. Or a drone pilot, in hostile territory, able to control multiple devices through a personalized immersive interface that enhances their situational awareness and decision-making through information received by body- and head-worn devices controlled by augmented digits.
Implementing such an innovative technology will not be without risk. There may be unintended consequences, such as a user’s neural pathways adapting, and the impact of this needs to be understood. What is required is an approach that evaluates the operational benefits and risks continuously through evidence-based experimentation while integrating this technology with other equipment assemblies. We should also gather evidence about the potential ethical, medical, and legal implications. Scientists can support this by designing from the start with the user and use-case in mind, and by monitoring the technology’s impact via psychological and physiological performance data.
- Power beaming. Sending power wirelessly over long distances could transform everything from electric vehicles to offshore wind farms.
- Biohybrid robots. Combining artificial and organic parts, biohybrid robots offer advantages such as self-repair and agility.
- Neuromorphic computing. Inspired by the brain, neuromorphic chips aim to equal the speed, efficiency, and intelligence of the human mind.
- Gene-editing and enhancement. Advances in biotech are spurring scientists to explore how genomes can be tweaked to make ecosystems more sustainable.
- Hyperspectral imaging. Hyperspectral cameras don’t merely record what something looks like, they can tell you what that thing is made from and help you see what the human eye cannot.
To find out more about QinetiQ, click here
To find out more about WIRED Consulting, click here
