A recent study published in Nature Communications introduces a new metamaterial, called Roliner, designed as a soft, adaptive human-machine interface for wearable devices.
Roliner is made from silicone elastomers embedded with millifluidic channels that can be inflated with air. The researchers demonstrated its use in improving the fit of prosthetic limbs, marking the first application of this technology.
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Background
Limb loss due to chronic illness or injury is a growing healthcare issue. Most people with amputations rely on prosthetics to regain movement or perform daily tasks. While robotic limbs have made significant progress, getting a comfortable and secure fit remains a challenge.
Today’s prosthetic limbs are typically attached using a hard polymer socket with a soft inner sleeve. These sockets are often custom-made using time-consuming plaster casting methods. But even with customization, the shape of the residual limb can change over time, leading to poor fit and discomfort.
This study proposes a more adaptable, reconfigurable liner called Roliner that can be worn with standard prosthetic sockets. The goal is to provide a better fit, reduce discomfort, and eliminate the need for frequent socket replacements.
How Roliner Was Made and Tested
The team designed a hexagonal fluidic pattern in Adobe Illustrator and printed it onto wax paper, which acted as a placeholder during fabrication. Silicone was poured into a mold and partially cured, allowing the wax paper to create fluidic channels within the final cured material.
To evaluate the material’s mechanical properties, the researchers fabricated two sets of 12 dog bone–shaped samples, each backed with fabric. The samples were 45 mm in diameter and included wax paper channels of either 3 cm2 or 6 cm2, positioned at the center and 1 mm above the fabric layer.
All samples were conditioned for 24 hours in a room maintained at 20.9 °C and 55 % relative humidity. Before testing, the samples were pre-conditioned and subjected to 10 minutes of cyclic compression under lubrication.
The team measured tensile elasticity (TE), compressive elasticity (CE), and volumetric elasticity (VE) using a material testing machine. These metrics helped assess the material’s stretchability, compressibility, and ability to adapt to shape changes.
To measure actuation force (FA)—the force applied inward when the fluidic channels were pressurized—they used a flexible silicone sheet with embedded channels, placed flat between two aluminum plates. By analyzing how pressure curves changed as the channels expanded, the team could estimate the gap between the residual limb and the prosthetic socket. This could be useful for remote volume mapping and automated fitting feedback.
Finally, the researchers ran preclinical trials with participants aged 18 to 60. These trials assessed how the Roliner performed under everyday conditions, focusing on comfort, usability, and pressure control.
What They Found
The Roliner’s mechanical properties—TE, CE, and VE—allowed the material to stretch, support comfort and control, and adapt to different shapes. In testing, it met or exceeded the performance of polyurethane (PU), a material commonly used in prosthetic liners.
One of Roliner’s key features is its ability to adjust stiffness based on activity. For example, the material could be softer while sitting and stiffer while walking. These changes were controlled by varying the air pressure or fluid channel size.
When inflated, Roliner functioned like an array of soft actuators. It applied an inward force that increased friction between the liner, the socket, and the residual limb. This helped secure the limb in place during movement, reducing unwanted motion and improving attachment.
In preclinical studies, participants used a mobile app to control inflation in two ways: by pressing and holding a button or by pressing multiple times. The liner responded well to both input methods, and users reported better comfort and pressure control.
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Conclusion and Next Steps
The study successfully demonstrated a soft, reconfigurable metamaterial that can be a prosthetic liner. Roliner is compatible with existing sockets made from carbon fiber composites, thermoplastics, and other common materials. Though made entirely from silicone, the material’s mechanical properties can be adjusted to behave like other elastomers, such as PU.
While the initial cost of Roliner may be higher than that of traditional passive liners, the long-term savings could be significant. Reducing the need for new socket fittings and clinic visits may lower overall healthcare costs. More importantly, Roliner has the potential to greatly improve daily comfort and mobility for amputees.
Looking ahead, the researchers plan to integrate flexible electrodes into the Roliner design. This could enable continuous, non-invasive monitoring of physical and biochemical signals—opening the door for broader wearable health applications.
Journal Reference
Tanriverdi, U., et al. (2025). Dynamically adaptive soft metamaterial for wearable human–machine interfaces. Nature Communications. DOI: 10.1038/s41467-025-57634-8, https://www.nature.com/articles/s41467-025-57634-8
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