When someone loses a hand, today’s prosthetic options force painful compromises. Rigid prosthetics offer strength but can’t handle delicate objects gently. Soft robotic alternatives provide gentleness but lack gripping power. And neither option lets users actually feel what they’re touching.
A breakthrough from Johns Hopkins University researchers aims to finally solve these problems. In a newly published study in Science Advances, the research team has developed what they’re calling a “natural biomimetic prosthetic hand” that blends rigid and soft materials while adding touch-sensing abilities based on human skin.
“The goal from the beginning has been to create a prosthetic hand that we model based on the human hand’s physical and sensing capabilities—a more natural prosthetic that functions and feels like a lost limb,” says lead study author Sriramana Sankar, a Johns Hopkins biomedical engineer, in a statement. “We want to give people with upper-limb loss the ability to safely and freely interact with their environment, to feel and hold their loved ones without concern of hurting them.”
Best of Both Worlds
Instead of choosing between rigid or soft designs, the research team took inspiration from human anatomy. Our hands combine rigid bone structures with soft tissues and joints, so why not do the same with prosthetics?
The Johns Hopkins team built a hand with a hard 3D-printed internal skeleton surrounded by soft, independently controlled joints made of silicone. But their biggest innovation might be the touch-sensing system built into the fingertips.
The researchers embedded three different types of sensors within the prosthetic fingertips to mimic how human skin works. Our skin contains specialized cells called mechanoreceptors that detect different aspects of touch, from light pressure to vibrations to skin stretching. The artificial version includes layers of sensors that work together to create a rich picture of whatever the hand is touching. The system converts touch data into patterns similar to the electrical signals our nerves would normally send to our brains.
Putting It to the Test
In lab tests, the hybrid hand showed remarkable abilities. When asked to identify 26 different textured surfaces, from smooth plates to various ridged patterns, it achieved 98.38% accuracy, far outperforming both purely soft robotic fingers (82.31%) and rigid prosthetic fingers (83.02%) tested with the same surfaces.
The hand was also tested with 15 everyday objects including stuffed toys, fruit, dishes, and water bottles. It correctly identified these items with 99.69% accuracy while handling them appropriately; gentle with delicate items, firm with heavier ones.
Perhaps most impressive was when the hand picked up a thin plastic cup filled with water using just three fingers without crushing or denting it, a task that would be nearly impossible for conventional prosthetics.
“We’re combining the strengths of both rigid and soft robotics to mimic the human hand,” says Sankar. “The human hand isn’t completely rigid or purely soft—it’s a hybrid system, with bones, soft joints, and tissue working together. That’s what we want our prosthetic hand to achieve. This is new territory for robotics and prosthetics.”
How It Works
The prosthetic uses electromyography (EMG), the same control method used in many modern prosthetic hands. EMG sensors detect electrical signals from remaining muscles in the user’s arm, allowing them to control the hand’s movements by intentionally flexing those muscles.
“This hybrid dexterity isn’t just essential for next-generation prostheses,” says study author Nitish Thakor, a Johns Hopkins biomedical engineering professor. “It’s what the robotic hands of the future need because they won’t just be handling large, heavy objects. They’ll need to work with delicate materials such as glass, fabric, or soft toys.”
A key benefit of the hybrid design is efficiency. It generates three times more gripping force than a purely soft robotic hand while needing only a quarter of the air pressure to operate. The hybrid hand produced 1.8 Newtons of force at just 7 psi (pounds per square inch), compared to 0.55 Newtons at 28 psi for a soft robotic hand.
Restoring the Sense of Touch
Beyond just improving grasping abilities, this technology might eventually restore the sensation of touch to prosthetic users. While the current study focused on demonstrating the hand’s physical capabilities, the researchers designed the system with sensory feedback in mind.
“If you’re holding a cup of coffee, how do you know you’re about to drop it? Your palm and fingertips send signals to your brain that the cup is slipping,” says Thakor. “Our system is neurally inspired—it models the hand’s touch receptors to produce nerve-like messages so the prosthetics’ ‘brain,’ or its computer, understands if something is hot or cold, soft or hard, or slipping from the grip.”
This technology builds on the lab’s previous work, which included creating the world’s first electronic “skin” with human-like pain sensing in 2018. While the system is designed to provide sensory feedback, it has not yet been tested on amputees to determine how effectively users perceive and respond to the touch signals.
Looking Forward
The current prototype’s 1.8 Newtons of gripping force, while an improvement over soft robotic hands, falls well short of a human finger’s capability (around 32 Newtons) or traditional rigid prosthetics (about 34 Newtons). It also relies on an air compressor to function, which would be impractical for everyday portable use.
For people who’ve lost hands, this research offers a glimpse of prosthetics that might one day feel like a genuine replacement that is able to handle both fragile and heavy objects, sense textures and shapes, and respond naturally to the user’s intentions. Prosthetic technology has long focused on looks and basic functionality, but this approach aims to restore what matters most: the hand’s remarkable ability to both act and feel.
Source : https://studyfinds.org/new-bionic-hand-mimicking-human-touch/
