A group of engineering students at the University of Delaware has designed an orthopedic walking boot that provides weight-bearing data on its wearer, which will help to improve compliance with physical therapy recommendations and may advance research in this area.
As part of their senior design project, five students in biomedical, mechanical and electrical engineering designed the SmartBoot based on a proposal from Jill Higginson, PhD, associate professor of mechanical engineering at the University of Delaware, and Brian Knarr, PhD, associate scientist for the Delaware Rehabilitation Institute.
Demystifying loading and recovery
According to Knarr, the idea for the SmartBoot was inspired by a conversation he had with a physical therapy colleague. The colleague “wanted a better way to understand the interaction between loading and recovery after injury and how it affects patients with lower limb injuries,” Knarr said. “But he had a lack of tools to understand both what the loading was for an individual as they are walking around after an injury and how physical therapists could train patients more effectively to load their limbs appropriately. It seemed like a fantastic starting point for a senior design class.”
Creating a treatment plan for patients with ankle sprains to increase their weight-bearing abilities can be difficult, according to Tim West, a biomedical engineering student at the time of the project who graduated in the spring of 2015.
“It has been guesswork based on pain thresholds — how long do you stay off the foot? If you are on the foot, how much weight do you put on it?” West said. “There are instances where an injury will get exacerbated or worsened if a patient is bearing too much weight or too little weight, and then that muscle will atrophy.”
West and the rest of the design team, which included two mechanical engineering students (Michael Schenk and Megan O’Brien), another biomedical engineering student (David Schnall) and an electrical engineering student (Melissa Groome), set out to enhance the orthopedic walking boot and equip it with instrumentation that could provide the patient and clinician with usable information.
“The three pillars of the SmartBoot are load sensing, biofeedback and data storage and management,” Knarr said.
The SmartBoot senses the load a patient is applying and provides real-time feedback on whether the patient is applying the appropriate amount of force. It also logs the patient’s daily-life activity so the physical therapist can determine compliance. Finally, the data provided by the SmartBoot can better inform researchers.
“Having these data available can drive some innovation and improvements in rehabilitation moving forward,” Knarr said.
The main features required for the SmartBoot as part of the senior design project included a force sensor to measure force traveling through the bottom of the boot; the ability to store data to nonvolatile memory such as a flash drive or SD card; sensory feedback to the patient such as a noise, vibration or small light in real time so the patient can monitor their own compliance; and real-time wireless data transmission such as Bluetooth or Zigbee technology.
“Researchers could view a real-time graph [using the wireless data transmission] and get an idea for how well the patient is partially weight-bearing,” West said. “That would go a long way toward speeding up the process of teaching the patient.”
The students mocked up several different solutions, used metrics to determine the best option and then fabricated the device. “We started with just a basic orthopedic walking boot and then the students had to modify it, put all the components in, do the electrical-mechanical side of things, write the code to make everything work better and then create the final device,” Knarr said.
Engineering specialties collaborate
In this collaborative design project, the mechanical engineering students integrated the force sensors into the boot and designed the protective casing mounted on the side of the boot with the remaining electronics. In addition to choosing a force sensor that would comply with the forces and space constraints in the boot, the students also custom-manufactured a pair of aluminum plates and placed them in the sole of the boot so the force sensor was resting on top of the hard sole inside the boot but was underneath the cushion. “That design allowed us to capture as much of the force through the bottom of the boot as possible,” West said.
The mechanical engineering students also created a 3-D design of the casing for the electronics that could be looped with Velcro straps on the boot and secured on the side.
West and Schnall led the interactions with physical therapists and clients to ensure they were meeting their needs and giving them useful biomechanical information. West also created the real-time graph program and did the microprocessor programming.
The electrical engineering student managed all of the wiring for the force sensors and LEDs, a system of lights that notify the patient if they are bearing the appropriate amount of weight. This student also ensured that the SmartBoot contained the appropriate resistors, capacitors and switches needed for the microprocessors.
Images: University of Delaware Media Services
who is currently a senior biomedical engineering student, continued the project over the summer and completed work on the second prototype. According to West, the second prototype included a change in the force sensors from a slim piezoelectric-based force sensor to strain-gauge force sensors, as found in a bathroom scale. “Although the original force sensor had a great form factor, it could not handle the dynamic loads at the large force that we needed to accommodate,” West said. “The response time on those sensors was a bit too slow to actually grab the gait-based data.”
With the new force sensors came the need to manufacture new aluminum force plates, realign the data processing and redo some of the circuitry. In addition, the students migrated to a smaller processor to lower the form factor and put in a high-capacity rechargeable battery. In addition, “in our second prototype, the LEDs are removable because they incorporate USB technology so the LED wire can unplug from the microprocessor with the USB port,” West said.
“As of mid-August, the boot is fully operational and has a battery lifetime of about 8-plus hours,” Patterson said.
He hopes to optimize the size of the circuitry and make it smaller. “All the circuitry on the outside of the boot has been reduced in size over the last couple of months and the current design is pretty small, but there are many steps ahead as far as making everything more efficient and smaller,” he said.
In addition, he hopes that the layout of the boot design can be applied to other devices for which clinicians are measuring force sensors, such as running shoes or ice skates. “I hope that even after the SmartBoot is completed, we can use the concept to build other cost-effective devices to measure force readings in other clinical studies,” he said. – by Tina DiMarcantonio
Disclosure: Groome, Higginson, Knarr, O’Brien, Patterson, Schenk, Schnall and West report no relevant financial disclosures.