When most people walk, they do so in a symmetrical fashion: They take even steps and place equal pressure on each foot as it touches the ground, with the heel striking first, the arch second, the toe last. It’s so intuitive, they don’t even have to think about it.
Sensor module, as worn by amputee subject
But for people with lower-limb sensory loss — due to either amputation of the leg or to peripheral neuropathy (a nervous system condition) — this ability to feel contact with the ground is missing or impaired. For these individuals, many neural signals from the legs and feet that normally provide sensory information to the brain no longer exist, making it hard to coordinate movement.
This loss of sensory perception often makes it difficult for people to trust their prosthetic or impaired limbs, causing them to develop various gait abnormalities, such as uneven steps or slower speeds.
Biomedical engineering graduate student Zach McKinney
The work of UCLA researchers in the Henry Samueli School of Engineering and Applied Science could soon help remedy that problem, however. In the Center for Advanced Surgical and Interventional Technology (CASIT), biomedical engineering graduate student Zach McKinney and postdoctoral fellow Bryan Nowroozi have been working on a tactile feedback device that could help people improve sensory awareness of their prosthetic and sensory-impaired limbs.
Postdoctoral fellow Bryan Nowroozi
McKinney and Nowroozi have been making improvements to the device under the direction of Dr. Warren Grundfest, UCLA professor of bioengineering, electrical engineering and surgery. Their latest version of the tactile feedback system, in development since 2007, consists of three functional blocks: a sensing module, a control module and a tactile feedback module. It resembles three athletic braces that the patient wears around his torso, thigh and foot.
"The sensing module is basically a sensorized shoe insole that measures the distribution of forces on the bottom of the foot," McKinney explained. "That module transmits wirelessly [via a Bluetooth connection] to a central control module — a little microcomputer that the patient wears like a fanny pack. The microcomputer receives this data, processes it, executes a control algorithm and then controls output."
That output, or tactile feedback module, takes the form of a cuff housing a set of pneumatically inflating silicon balloons that the patient wears on his thigh. The inflating balloons press against the patient's skin, McKinney explained, providing tactile feedback, "so you could almost think of it as dynamic Braille for the leg."
McKinney and Nowroozi have been collaborating with the Naval Medical Center San Diego (NMCSD), whose staff has been testing the device on military service members who have lost lower limbs. NMCSD’s Marilynn Wyatt explained that when their test patients wear the sensorized shoe insole, the foot-sensor mechanism communicates with the cuff, letting the patient know exactly what part of the foot is hitting the ground.
"At heel strike, they get a sensation on one part of their leg; at toe strike, they get sensation on another part of their leg," Wyatt said. "So it is giving them feedback about their walking. ... This device tells their brain, basically, that their foot has hit the ground. It’s another kind of sensation, substituting for the missing sensory input."
Interior view of the tactile feedback cuff, including four silicon balloon actuator blocks
UCLA’s CASIT lab and NMCSD are still in the basic-science stage of their experiment, so testing of the device thus far has been restricted to the lab. But while the data is still preliminary, patients have been giving the researchers positive feedback about the device, Wyatt said.
McKinney and Nowroozi have also been testing the prototype device on one of their neuropathy patients at UCLA, which produced some encouraging data: The patient walked faster and took longer, more frequent steps. His steps were also narrower, which is a good indicator of stability, McKinney said.
One of the most promising things Nowroozi noted when he first came on the project last March was that changes seemed to occur with little training time, in some cases, only 20 minutes. They weren’t huge, across-the-board changes, but they were nonetheless significant, he said.
"One of the next steps we’re interested in taking is a longitudinal therapy study, where somebody will be wearing the device throughout the course of his physical therapy," Nowroozi said. "As Zach said, they become accustomed to it over time and, using the system over a course of weeks, their brains become accustomed to the additional feedback. We’ll see what happens."
Full tactile feedback system, worn by peripheral neuropathy subject
"Zach and Bryan have made considerable progress making the device more robust, more user-friendly and more appropriate for clinical trials," said Grundfest of his young researchers. "Translation of prototype devices requires time, effort and interaction with patients and clinicians. Bryan and Zach have worked closely with our partners to successfully improve the performance of the system."
McKinney hopes that some version of the technology will be commercially available in two years, but he realizes that research demonstrating the value of the technology as a rehabilitation device and as a sensory prosthetic device that will be used in the home could go on for years.
"For quality-of-life improvements, you have to have people wearing it in the community, in the clinic, in the home environment, and to be able to monitor improvements in their activity levels and their stability and so forth," McKinney said. "And that’s something we’re working toward."