Researchers at Purdue University, working with collaborators from the University of Notre Dame, have developed an embroidered textile sensing system that can measure both pressure and shear forces inside a prosthetic socket in real time — potentially giving prosthetists a much clearer picture of what is happening between the residual limb and socket during everyday movement.
The technology, reported in Science Advances, uses flexible embroidered sensors integrated into a textile sheath worn inside the prosthetic socket. Unlike many existing pressure-monitoring systems, it is designed to detect not only forces pushing directly against the residual limb but also the sideways, or shear, forces generated as the user stands, walks and changes posture.
For prosthetists, that distinction is significant.
Socket comfort and skin health are influenced by a complex combination of loading patterns, and some of the forces most relevant to tissue irritation and breakdown can be difficult to identify during a conventional clinical fitting.
Looking beyond pressure alone
Assessing socket fit has traditionally depended heavily on clinical experience, patient feedback, visual inspection of the residual limb and modifications made during static and dynamic alignment.
Pressure measurement systems can provide additional objective information, but existing approaches come with limitations.
According to the Purdue researchers, optical systems can require signal-processing hardware and electronic components to be incorporated into the already restricted space inside a socket. Strain-gauge technologies may require modification of the socket itself, while other sensing systems measure pressure without providing information about shear.
The new textile platform was designed to address several of these issues simultaneously.
Researchers sought a system that would be flexible, washable, capable of detecting forces in multiple directions and compatible with wireless electronics.
The resulting technology resembles wearable clothing more than a conventional laboratory sensor array.
An embroidered sensor inside the prosthetic socket
The sensing system is incorporated into a textile sheath positioned between the residual limb and prosthetic socket.
The researchers used machine embroidery to produce the sensors, combining polyester thread with silver-plated conductive thread. A multilayer capacitive structure allows the system to distinguish between normal compression and combined pressure-and-shear loading.
Under direct compression, the sensor’s four measurement quadrants respond in a broadly similar way.
When shear is introduced, the signals become asymmetric, allowing the system to estimate both the magnitude and direction of the sideways force.
That ability to map multidirectional loading could be particularly useful in areas of the socket where users experience repeated rubbing, discomfort or skin problems despite apparently acceptable static pressure.
Real-time data during walking and daily activity
The researchers demonstrated the system with a transtibial prosthesis user, monitoring pressure and shear forces during functional activities.
Sensor data is transmitted through a Bluetooth-enabled acquisition module to a portable device, where pressure information can be mapped digitally.
The technology also has an unusual visual component.
The sensing system is connected to an embroidered electroluminescent textile display that can communicate pressure information through illuminated pixels, creating a real-time visual representation of what the sensors are detecting.
The modular system uses snap-button connections between the textile sensors and electronics, which the researchers describe as allowing plug-and-play functionality.
For clinical prosthetics, however, the most interesting aspect may be less the light-emitting display itself and more the possibility of collecting objective socket-interface data while the patient performs real activities.
Why shear matters to prosthetists
Pressure inside a prosthetic socket is only part of the interface problem.
As the residual limb moves relative to the socket, tissues can also experience shear forces parallel to the skin surface.
These forces are particularly relevant when combined with repeated loading, heat and moisture.
A patient may therefore report pain or irritation even when pressure readings alone do not immediately explain the problem.
A system capable of identifying both types of loading could potentially help clinicians answer more precise questions:
- Is excessive force concentrated at one part of the socket?
- Does the problem appear only during a particular phase of gait?
- Is shear occurring even when overall pressure remains acceptable?
- Does a socket modification actually reduce the problematic load?
- How does a change in alignment alter loading at the residual limb?
- What happens to interface forces during stairs, slopes or prolonged activity?
Instead of relying entirely on what happens during a short appointment, future systems could potentially provide a more complete picture of how the socket behaves in the real world.
Sensors that survive the washing machine
Wearability is one of the important practical considerations in any textile sensor system.
The Purdue team tested the embroidered sensors through more than 30 complete washing-machine cycles, including washing, rinsing, spinning and drying, while using ordinary household detergent.
That does not yet mean the technology is ready for routine clinical use, but durability under repeated washing is important if textile sensors are eventually expected to become part of everyday prosthetic wear.
The researchers also say the architecture can be adapted in size, sensor positioning and electrode configuration to accommodate different socket shapes and user requirements. Sensitivity and measurement range can similarly be tuned for different loading conditions.
Could this change socket fitting?
For CPOs, one of the most interesting possibilities is the move towards objective, data-assisted socket fitting.
Digital technologies have already transformed several parts of prosthetics.
Residual limbs can be scanned digitally. Sockets can be modified using CAD software. Components can be aligned with increasingly sophisticated measurement systems, and patient activity can be monitored with wearable sensors.
Yet the socket interface itself remains difficult to measure continuously.
A thin textile system capable of generating usable pressure and shear data could potentially become another layer in the digital prosthetic workflow.
A clinician might one day be able to compare interface maps before and after a socket modification rather than depending only on subjective feedback.
The data could also help in difficult cases where patients experience recurrent discomfort or skin breakdown without an immediately obvious cause.
Potential value across IMEA
The technology could have particular relevance across the IMEA region, although cost and simplicity will ultimately determine how widely such systems can be adopted.
Many clinics across the region treat high volumes of lower-limb amputees, including people with diabetes, vascular disease and traumatic limb loss.
For users with compromised skin integrity, understanding how forces are distributed inside the socket may be particularly valuable.
There is also potential for use in education.
P&O students could see in real time how changes in socket design, suspension and alignment alter loading at the residual limb, potentially turning concepts that are normally taught theoretically into measurable clinical information.
High-performance and sports prosthetics could represent another application, where repeated high loads and very small fitting differences can have significant consequences for comfort and performance.
Still a research technology
The system remains a research development rather than a commercially available clinical product.
The study reported testing with a transtibial prosthesis user, and substantially more work would be required before a sensor platform of this type could be validated across large numbers of amputees, different socket designs and long-term everyday use.
There are also practical questions that would matter enormously to clinicians.
How much would such a system cost?
Would wearing the sensor textile itself alter socket fit?
How easily could data be interpreted during a normal appointment?
Could the system identify clinically meaningful thresholds rather than simply generating more measurements?
And could it withstand months of sweat, movement and repeated use in addition to washing?
Those questions will determine whether the technology ultimately moves from an engineering laboratory into routine prosthetic practice.
Purdue University has disclosed the invention through its technology commercialisation office, which intends to seek patent protection.
Moving towards the measurable socket
Despite those uncertainties, the research points towards an important direction for prosthetics.
Socket fitting has always combined science with considerable clinical skill and experience.
The next generation of technologies may not replace that expertise, but they could give CPOs more information with which to apply it.
Being able to see where, when and in which direction forces are acting inside a prosthetic socket could make assessment more objective and potentially allow problems to be identified earlier.
For prosthetists across IMEA, the most significant aspect of the Purdue research is therefore not simply that a textile can light up.
It is that the socket — traditionally one of the most difficult parts of a prosthesis to measure dynamically — may gradually become much more visible to the clinician.
- Tech Xplore – Light-emitting textile sensors could optimize prosthetic fit and comfort
- Science Advances – Embroidered textile sensors for real-time multiaxial force mapping in prosthetics
- Purdue University
- Purdue Weldon School of Biomedical Engineering
- University of Notre Dame
- IMEA CPO