New material allows amputees to adjust fit of prosthetic limbs throughout day

The latest advance in wearable robotic technology promises to solve a 200-year-old problem by revolutionising the fit of prosthetic limbs.

The new material, ‘Roliner,’ offers amputees the power to change the shape, volume, and stiffness of the liner that is used to attach a prosthetic limb’s socket to a residual leg. Amputees could make these tweaks using their smartphone in real-time, providing a more comfortable and personalised fit. 

After eight years of prototype development and clinical investigation, researchers at the Department of Bioengineering at Imperial College London have published the details of their patented new material in Nature Communications.

"Badly fitting prosthetic limbs are a constant struggle for amputees. They increase the risk of blisters and sores that can become infected, and the situation can become so painful that there is no choice but to go back to using a wheelchair." Dr Uğur Tanriverdi Co-founder of Unhindr

Principal Investigator Dr Firat Guder, from the Department of Bioengineering at Imperial College London, said: “Prosthetic limbs are often uncomfortable because they have a fixed rigid shape. Even though this shape can be moulded to fit the individual’s body as it is at the time of fitting, it cannot adapt responsively to how our bodies change. Ultimately, no matter how sophisticated the limb itself is, if it cannot connect closely and comfortably with the human body, it becomes unwearable.”

Dr Guder added: “Up until now, researchers have tried and failed to solve this problem by trying to improve the limbs and sockets themselves. But we took a different approach by developing a dynamically adaptive interface for the liners used between the body and the rigid prosthetic socket.”

Dr Uğur Tanriverdi, an Imperial graduate and co-founder of the wearable robotics company Unhindr that produces Roliner, said: “Badly fitting prosthetic limbs are a constant struggle for amputees. They increase the risk of blisters and sores that can become infected, and the situation can become so painful that there is no choice but to go back to using a wheelchair.

“Alongside causing extreme physical pain, problems with prosthetics not fitting can also impact on a person’s mental health as they are unable to live as independently and freely as they deserve.”

The researchers hope that Roliner will be available for use in the UK by the end of 2025.

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Roliner can incorporate artificial intelligence so each liner can ‘learn’ the personal preferences of their amputee. It can automatically adjust its properties according to how the human body changes in response to variables such as the time of day, weight loss or gain, and hormonal fluctuations. An amputee’s desired fit may also change due to the type of activity being undertaken. For example, they may prefer a looser fit while sitting and a tighter, more controlled fit when walking.

"Ultimately, no matter how sophisticated the limb itself is, if it cannot connect closely and comfortably with the human body, it becomes unwearable." Dr Firat Guder Department of Bioengineering

Roliner is made from silicone elastomers with channels that can be pressurised to change the material’s properties, meaning its volume and shape can change. “Just like a basketball, it becomes bigger and more rigid when it is inflated, and smaller and softer when it is deflated,” Dr Tanriverdi said.

Guglielmo Senesi, the Imperial engineer building Roliner’s electronics and clinical data architecture, and the Chief Technology Officer at Unhindr, said: "Currently, most prosthetists still rely on plaster casting and moulding techniques that have been used for centuries to determine what socket shape and size will give the most personalised fit. Roliner’s data-driven approach standardises the quality of prosthetic fittings.”

Tarek Asfour, an Imperial master’s graduate and Chief Operating Officer of Unhindr, said: “Roliner marks the shift from rigid mechanics to soft, adaptive robotics, proving that the future of prosthetics isn’t just about movement – it's about seamless human integration.”

The researchers also believe that the technology could have applications beyond prosthetics, because it could be used in any situation where rigid materials must touch the human body.

For example, Roliner could be used to increase the flexibility of exoskeletons used in rehabilitation, to modulate the pressure points of hospital beds, or to improve the personalised fit and safety potential of protective gear such as ski boots and even wearables used by astronauts in space.

“Dynamically adaptive soft metamaterial for wearable human–machine interfaces” by Ugur Tanriverdi, Guglielmo Senesi, Tarek Asfour, Hasan Kurt, Sabrina L. Smith, Diana Toderita, Joseph Shalhoub, Laura Burgess, Anthony Bull, Firat Güder is published in Nature Communications.