AsianScientist (Oct.28, 2024) – Every day, before heading out of her house, Singaporean Tan Ter Cheah puts on her shoes, one at a time—just like most other 53-year-old women. Except, the right one goes on her prosthetic foot.
When Tan was seven years old, her leg had to be amputated at mid-calf due to synovial sarcoma, a rare soft-tissue cancer that usually develops in arms, legs and feet. Over the last four and a half decades, Tan has witnessed first-hand the progression of everyday prosthetics technology. As a child, her first prosthetic leg was crafted by a deaf-mute technician, lovingly known to her as Uncle Ah Ju. The upper part of the prosthetic consisted of a hard socket, in which Tan inserted her sock-covered stump. Tan also had a leather collar that wrapped around the base of her thigh. The collar had two leather straps that attached to either side of the prosthetic leg to keep it firmly in place.
“I hated it. It was like a dog collar with two things hanging down to hook to my prosthetic leg,” Tan told Asian Scientist Magazine.
But today, Tan’s prosthetic leg is much more comfortable and functional. She covers her stump with a silicon sock that goes into a soft plastic socket. The soft socket slides into a hard socket, which is attached to a metal rod that ends in a sturdy foot—shaped like a foot with toes. Unlike her childhood prosthetic, her current one closely imitates muscle and flesh. It also has an inconspicuous knob on the ankle that helps her adjust the ankle joint so she can wear shoes with different heel heights.
While Tan experienced these advancements over the course of several decades, technological improvements in the industry have been taking place particularly rapidly in recent years. Such technological improvements have offered variety and accessibility to support the unique needs of amputees like Tan. In the Asia Pacific region, as spending on healthcare increases, robotic prosthetics are of particular interest. Their market is expected to be the fastest growing with a compound annual growth rate of over 9.9 percent from 2023 to 2030, according to Coherent MI, a market research firm based in India.
How it works
At the Foot Care and Limb Design Centre located at Singapore’s Tan Tock Seng Hospital, prosthetists like Trevor Binedell work closely with patients to craft and fit prosthetic limbs. The center’s patients consist mostly of older individuals who have had leg or foot amputations as a result of diabetes. In fact, in 2021, according to the Ministry of Health, Singapore, close to nine out of 10 individuals who had lower limb amputations in the country were diabetic.
After determining that a patient needs a prosthetic attachment and understanding their goals, Binedell moves on to crafting one. He uses plaster of Paris to create a cast of an individual’s stump. The cast is then used to fabricate a socket at the center’s workshop using either plastic or composite fibers.
While this method remains tried-and-tested, Binedell has also recently begun to use digital processes to scan a patient’s stump. Digital scans allow Binedell to make necessary adjustments easily before crafting a socket. To make sure the prosthetics fit well, Binedell pays a lot of attention to the patient’s comfort. Each patient’s biomechanics—from the way they shift their weight to the pressure distribution in their stump—are different and must be catered to.
Similarly, many patients today take the fit and look of their prosthetics seriously. For example, Tan takes her prosthetic for a test drive around the neighborhood. “After a while it became a little bit like fitting for a pair of perfectly comfortable shoes,” shared Tan. “I walk around. I go up and down a few steps. I try walking on a slope, then I come back and tell Trevor what hurts.”
This process is repeated a few times with Binedell making minute changes at each visit until patients like Tan are happy and comfortable with the fit of their prosthetic.
In comparison to designing legs, creating prosthetic hands is far more complicated, said Rafael Masters, CEO and co-founder at Vietnam-based prosthetic developer Vulcan Augmetics. Hands must be made to interact with the environment in more complex ways, Masters told Asian Scientist Magazine.
Over the years, prosthetic hands technology has also advanced. Today, prosthetic arms are typically fitted with sensors that control the hand using muscle signals from the stump. They can be programmed to accomplish several different grip patterns compared to the simple open and close function of earlier prosthetic hands.
Recent advancements
Now, Binedell offers a variety of specialized and advanced prosthetics at the Foot Care and Limb Design Centre. One example is a robotic leg with a microprocessor that controls the knee joint. Unlike spring-loaded prosthetic legs that can result in an awkward gait for the user, microprocessor-controlled prosthetics collect real-time data to adjust stance and movements in the leg. A patient’s data can be saved and managed with an app that patients and clinicians can access. The data can also be transferred to a new prosthetic leg when a replacement is needed.
Prosthetic researchers in Asia and abroad are also exploring neuroprosthetics for more seamless prosthetic use. “When we think about moving our fingers, the brain sends control signals through peripheral nerves to our hand muscles, telling them what to do,” explained Anh Tuan Jules Nguyen, a researcher at the Department of Biomedical Engineering, University of Minnesota, the US. “For a robotic hand to work similarly, we have to tap into these signals and decode the neural information.”
To do so, Nguyen and his collaborator from the same department, associate professor Zhi Yang, harnessed artificial intelligence (AI). The team implants microelectrodes in nerve fibers to capture the relevant signals. These signals must then be matched to specific body movements. Yang and the team train their AI model to recognize these signals by feeding it multiple examples of what a signal would look like if someone wanted to move in a specific way. The model then learns to recognize the signals and operate the robotic limb.
“The key advantage of this system is that it’s intuitive for the user. The amputee can control the prosthetic hand simply by thinking about making the corresponding hand gesture—just like they would with their real hand,” shared Nguyen.
However, Vulcan Augmetics CEO Masters suggested that the industry move away from overselling complicated bionic hands. He said that the companies should prioritize usability of prosthetics over complexity and avoid setting impractical consumer expectations that can lead to high product abandonment. He added that Vulcan’s multi-grip myoelectric hand offers six main grips in the fingers, which contract when the sensors in the upper arm are activated by the muscles in a patient’s stump.
The myoelectric arm is capable of several grip options— from holding a card to grasping handles. “Users just need something that they can use to grab a thing quickly,” said Masters. “That’s the number one functionality that you want to give them.”
While Masters would like the industry to make more functional prosthetics—like a hook prosthetic that is split down the middle to open and close for better grip— instead of focusing on how to make the prosthetics look like real limbs, some patients seem to prefer the latter.
As materials like silicone become more readily available, it is possible to design prosthetics that look and feel almost like skin. Michael Leow, chief prosthetist at the Department of Hand and Reconstructive Microsurgery in the National University of Singapore, crafts such hyperrealistic prosthetics. These prosthetics bring comfort to patients who have lost fingers or parts of their hands.
“Finger and partial hand loss with retention of acceptable hand function is the most common type of upper-limb amputations,” Leow told Asian Scientist Magazine. “While the functional disability may be relatively minimal, the loss of aesthetic appearance frequently causes a lot of distress to patients.”
In Asia, a majority of such amputations occur as a result of industrial accidents. While many of these patients opt to go without a prosthetic, those who choose to have one can have a lifelike finger molded by Leow. He takes an impression mold of an uninjured digit and makes its replica by following its exact measurements and colors.
Other than using the molding machine that creates the molds used to fabricate the prosthetic, Leow has also explored 3D printing for the same purposes. Although they may be less costly to produce, 3D-printed prostheses may not be as realistic or aesthetically appealing to the patients compared with the prostheses that are crafted by a trained prosthetist,” said Leow.
The printing problem
A prosthetic leg can cost anywhere between US$1,500 and US$100,000—with bionic legs typically costing the most. Although 3D printing technology has been touted as a possible boon to make prosthetics more affordable, not everyone agrees. In 2020, Binedell and collaborators from the Singapore University of Technology and Design (SUTD) developed a 3D printed non-metallic self-locking prosthetic arm that is 20 percent cheaper than a conventional prosthetic. The team used a digital scanner to capture the geometries of a patient’s arm before designing and printing an arm for fit, comfort and function.
“3D printing freed us from the manufacturing constraints and enabled us to optimize the design to suit the patient’s needs. More importantly, this work sets the groundwork for future patient-specific end-use 3D printed parts for prosthetic needs,” said principal investigator Subburaj Karupppasamy from SUTD’s Engineering Product Development pillar in an SUTD article.
Despite the cheaper printing costs and positive outcomes in this particular project, Binedell finds that 3D printing has a long way to go before becoming a scalable option in his daily practice at Tan Tock Seng Hospital. His team at the hospital has done 3D printing trials with sockets and ankle braces. But they have not noticed a significant difference in cost. “People are demonstrating that 3D printing can be a comparative manufacturing process to current processes, but as far as I can see, they haven’t shown that it’s superior,” said Binedell.
According to Binedell, one specific challenge with 3D printing comes with fitting and refining a leg socket. For the most part, it can be easier to adjust and reprint a socket for a decent fit—but the important last step of refining the socket for a perfect fit becomes more difficult with the less pliable printing material.
“That last 5 to 10 percent is so important for a patient’s acceptance and making sure that the leg is usable and useful in their lives,” Binedell added. For now, the best approach may be a mix of traditional artisan methods and advanced techniques.
“Patients come in and want the best—but they don’t always need the best in terms of cutting-edge technology,” shared Binedell. “What they need is the best leg for them and it’s our job to work out what that is and how to make it.”
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This article was first published in the print version of Asian Scientist Magazine, January 2024.Click here to subscribe to Asian Scientist Magazine in print.
Design: Ajun Chuah/ Asian Scientist Magazine
Copyright: Asian Scientist Magazine.
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