Future of prosthetics: Bionic hand 'knows' what it’s touching

A team of engineers has recently created a breakthrough prosthetic hand that can deftly handle everyday objects, from plush toys to water bottles, adjusting its grip to avoid damaging them. 

In doing so, the experts have introduced a novel hybrid approach to robotic hands, merging rigid and soft elements in a way that mimics the human hand’s unique design.

The innovative research was conducted in the Neuroengineering and Biomedical Instrumentations Lab at Johns Hopkins University. The team previously developed an electronic “skin” with a humanlike sense of pain in 2018. 

Prosthetic hand with sensing capabilities 

The new hand features a multi-finger setup made of rubberlike polymers over a rigid, 3D-printed skeleton.

Its three layers of tactile sensors, modeled after the layers of human skin, go beyond simple contact detection to identify textures, shapes, and the precise force needed to pick up various items.

“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,” said Sriramana Sankar, a Johns Hopkins biomedical engineer who led the work. 

“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.”

Bridging soft and rigid elements

In prosthetic technology, robotic hands have often been either too stiff to safely handle fragile objects or too soft to manage heavier ones. This new device tackles that issue by combining a pliable exterior with an internal frame. 

The soft, air-filled finger joints can accommodate delicate items without crushing them, while the solid core provides the stability needed to lift or grip sturdier materials.

“We’re combining the strengths of both rigid and soft robotics to mimic the human hand,” Sankar explained. “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.” 

Sankar noted that this is new territory for robotics and prosthetics, which haven’t fully embraced this hybrid technology before. “It’s being able to give a firm handshake or pick up a soft object without fear of crushing it.”

Restoring the sensation of touch 

Another central focus is restoring a sensation of touch to individuals with upper-limb loss. The device employs machine learning algorithms to process signals from the artificial receptors embedded in its fingertips. 

These signals merge with muscle activity from the forearm to guide grip strength, finger positioning, and overall dexterity.

“The sensory information from its fingers is translated into the language of nerves to provide naturalistic sensory feedback through electrical nerve stimulation,” Sankar said. “Each of its soft air-filled finger joints can be controlled with the forearm’s muscles.”

For many prosthesis users, regaining the ability to “feel” objects is equally as important as being able to hold them. 

Lifelike prosthetic hands 

According to Nitish Thakor, a Johns Hopkins biomedical engineering professor who directed the work, any lifelike prosthetic hand must incorporate three major components. 

First, sensors need to detect what the hand is touching; second, the system must convert that data into nerve-like signals; and third, the user’s nerves have to receive those signals as if they come from a natural limb.

“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,” Thakor said. 

“Our system is neurally inspired – it models the hand’s touch receptors to produce nervelike messages so the prosthetics’ ‘brain,’ or its computer, understands if something is hot or cold, soft or hard, or slipping from the grip.”

Successful tests on everyday objects

In controlled lab experiments, the researchers tested the new hand’s performance on 15 ordinary items, ranging from stuffed animals and dish sponges to pineapples and sturdy cardboard boxes.

These trials showed the hand deftly recognized each object’s characteristics and adjusted its grip accordingly.

The team reported a success rate of 99.69% in handling these items without error, a marked improvement over existing prosthetic hands. 

One notable demonstration involved the hand lifting a fragile plastic cup filled with water using only three fingers – without denting the cup or spilling the liquid.

Although the prototype represents a major step toward prostheses that blend humanlike sensitivity and adaptability, the researchers emphasize that the system is still in early development. 

Stronger grip forces, additional sensors, and more durable materials are among the enhancements they envision.

What’s next for prosthetics?

Thakor also sees this hybrid approach to dexterity benefiting not just amputees but the broader robotics field.

Robots that can handle delicate objects, such as glassware or soft materials, while still possessing the strength for more demanding tasks will be vital in settings ranging from warehouses to healthcare facilities.

“This hybrid dexterity isn’t just essential for next-generation prostheses,” Thakor said. “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.” 

“That’s why a hybrid robot, designed like the human hand, is so valuable – it combines soft and rigid structures, just like our skin, tissue, and bones.”

As this technology matures, it could lead to more natural prosthetics that let users regain a full range of motion and sensation. 

The engineers hope that the progress made here will spur further refinements, ultimately resulting in prosthetic hands that can handle everything from a gentle handshake to a firm grasp of heavier objects – all while preserving a truly humanlike sense of touch.

The study is published in the journal Science Advances. 

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