A STEP IN THE RIGHT DIRECTION
The way a person walks can reveal a lot about their health—a new smart insole looks to take advantage of that by gathering important health information straight from the sole.
Written by Cassandra Kelly
A PERSON’S GAIT is almost as individualized as their fingerprints or their irises. Researchers at The Ohio State University (OSU) have found a way to unlock these unique insights with smart insoles that are showing promise in the prevention, diagnosis, and treatment of conditions such as lumbar degenerative disease, Parkinson’s disease, and diabetic foot ulcers.
The interdisciplinary nature of this work involved materials sciences, electrical engineering, and signal processing and resulted in an insole that is both comfortable and durable, while also being wireless and self powered. The design has the ability to monitor both static and dynamic movements, including standing, sitting, walking, and running, to identify potential health indicators.
“The design includes an array of pressure sensors to map out the distribution of the pressure on the foot,” said Jinghua Li, co-author of the study and an assistant professor of materials science and engineering at OSU. “If someone has a neurodegenerative disease, for example, it can often change their gait. So, we measured those patterns and combined it with a machine learning algorithm to provide accurate and personalized health information.”
But making sure the insole was durable and comfortable was the biggest challenge, Li explained. To do this, they needed the insole to withstand repetitive deformation cycles and maintain a high fidelity.
A researcher holds an insole with the pressure sensors attached. Photo: Meggie Biss/The Ohio State University
ENGINEERED FOR DURABILITY AND COMFORT
On average, a person walks anywhere from 60 to 135 miles each month (up to 300,000 steps). To create an insole that could withstand this amount of use, the team looked for a highly porous, carbon-based material that would allow the insole to maintain its shape and function through countless cycles. Qi Wang, lead author of the study and a current doctoral student in materials science and engineering, explained that they used a low-cost material as a template: sugar cubes.
“You can imagine a sugar cube is a highly porous structure,” Wang said. “We used a polymer material to infiltrate the sugar cube, allowing the material to adopt the original porous structure of the sugar cube. Then the sugar cube was dissolved, leaving behind a highly conductive material and a template that we could use.”
Unlike traditional solid materials that might experience permanent deformation, the insole’s highly porous carbon-based framework, derived from the sugar cube template, maintains its original shape even after repeated compressions. Initial testing revealed that the insoles withstood 180,000 compression and decompression cycles.
This unique architecture is crucial to ensuring the sensor’s ability to accurately detect subtle changes in pressure. As pressure is applied, the pores within the material subtly deform, creating new conductive pathways that the insole immediately registers. To optimize the insole's sensitivity, the team developed a synergistic material blend, combining the porous carbon aerogel with carbon nanotubes. The two-dimensional conductive network acts like tiny bridges, connecting the porous material and ensuring stable conductivity even at low initial pressures.
The insole features 22 pressure sensors, so the next challenge was developing and training a machine learning model (MLM) that could interpret the vast amount of data being collected.
This precise porosity was not just about durability, but about unlocking the delicate yet vital pressure distribution data that can revolutionize health monitoring, Li explained.
Jinghua Li (right) works with doctoral student Qi Wang in her lab. Photo: Meggie Biss/The Ohio State University
“You can imagine a sugar cube is a highly porous structure. We used a polymer material to infiltrate the sugar cube, allowing the material to adopt the original porous structure of the sugar cube. Then the sugar cube was dissolved, leaving behind a highly conductive material and a template that we could use.”
— Qi Wang, lead author of the study and doctoral student in materials science and engineering at The Ohio State University
BRAINS BEHIND THE SOLE
To build the MLM, the research team used real-world data from people performing a range of specific motions. That data was then used to create a visual map of a person’s foot, which they were able to plug into a smartphone app so that insole users can get real-time feedback as they are moving.
“Many products currently on the market and being developed can give important health data, but insole devices are really underrepresented in wearable devices,” Li explained. “And shoes specifically can provide a higher level of data to the user.”
Another consideration is that people don’t want to have to charge their shoes before they leave the house. So, the team’s final challenge was creating a product with self-powering capability in a stride toward truly integrated and maintenance-free wearable electronics.
The team incorporated high-efficiency perovskite solar cells directly onto the top of the shoes, allowing them to effectively harvest ambient light, whether from bright sunlight during an outdoor run or even moderate indoor lighting. The harvested solar energy isn’t used immediately but instead efficiently stored in small, integrated lithium batteries located in the insole’s arch area, a region that typically experiences minimal pressure during movement.
The beauty of this design is that even if the insole can’t fully self-power in dim light, its battery can rapidly charge when exposed to strong light—just a quick six-minute charge under bright 50,000 lux illumination can power the system for a full hour in a typical indoor setting.
In the next stage of development, the team is interested in collaborating with industry leaders to move toward a final product, which will take further improvements in reliability, scaling fabrication, and power efficiency.
“We hope this system can revolutionize the future of wearable devices, integrating fundamental research and also clinical practices,” Li said.
Cassandra Kelly is a technology writer in Columbus, Ohio.
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