University of Michigan has developed world's first Open Source Bionic-Leg Platform

Bionic limbs are artificial limbs that use signals from an individual's muscles to effortlessly move, much like human limbs. For instance, while walking, legs send a variety of sensory information to the brain, where it is used to adjust motion to avoid obstacles, climb stairs, or change direction. This sensory information includes touch and pressure on the foot and leg, vibration, and the stretch of muscles. Most bionic limbs have built-in computers that detect the muscle signals. Some bionic limbs require sensors to be implanted into the remaining muscles of the limb stump. This type of bionic limb is much more advanced and can allow users to control the limb with their minds. However, developing control systems of bionic limbs has proven difficult.

Elliott Rouse, a biomedical engineer, and Director of the neurobionics lab at the University of Michigan, Ann Arbor, explains that the challenge arises from the fact that these limbs support a person's body weight. So, in case it makes a mistake, a person can fall and get seriously injured. 'That's a really high burden on a control system, in addition to trying to have it help people with activities in their daily life," says Rouse. This is why we see many open-source prosthetics for the upper body, such as hands; there is no platform for the lower extremities. Another issue is that the researchers working on these systems often are limited to testing in simulation or spending the time and money to build their own prosthetics for testing. This often lowers the barriers to entry for researchers.

Therefore to solve these problems, Rouse and colleagues created the Open Source Leg. They report that the Open Source Leg costs $10,000 to $30,000 to build, compared to $100,000 for similar commercial products. Additionally, the design uses high-torque, lightweight motors developed for drones that make it easier to walk with less fatigue, and the batteries onboard the prosthetic could be smaller.

The team mentioned its research findings online in the journal Nature Biomedical Engineering. Along with the artificial limb, there are free-to-copy step-by-step guides to assist researchers in assembling it or order parts. The researchers also released videos illustrating the hardware's assembly and testing and developed code to program the prosthesis to walk using a pre-control system. The bionic leg, which is designed, weighs just 4 kg. Though comparatively, it is much lighter than a biological leg, it still seems heavier for patients because they do not attach closely to the skeleton but to the prosthetic device.

While designing the leg, Rouse focused on keeping it simple, low cost and portable, yet high-performance. The result incorporates relatively inexpensive parts from just a few suppliers, a modular design that can act as a knee, ankle, or both; and an onboard power supply and control electronics that allows it to be tested anywhere. The knee and ankle joints can operate independently, allowing research in patients with above-knee and below-knee amputations. Moreover, each joint has onboard batteries and its own set of sensing and control systems, enabling test outside the laboratory. Most of the Open Source Leg's design and control features can be customized to fit specific research needs, such as the foot type and the knee elasticity.

The team also experimented with the device through a clinical trial of Open Source Leg with three volunteers. These volunteers wore the new device in a hospital setting and found that they were able to meet the goals set by the physical therapists, i.e. they walked up and down and found that the device gave them a feeling of support, responsiveness, and fluidity. One volunteer informed that he didn't feel like he was riding it, as he did with other prostheses. He said it did what he wanted it to do. "He got a feeling of embodiment, which he didn't get with conventional prostheses," says Rouse

The team previously presented progress on the leg at the 2018 IEEE International Conference on Biomedical Robotics and Biomechatronics. This paper included first author Alejandro Azocar, a Ph.D. student in mechanical engineering at U-M, and Luke Mooney, Co-founder of Dephy Inc. Currently, they have teamed up with various national and international groups to develop and test the leg, including Carnegie Mellon University, the University of Texas at Dallas, Georgia Tech, VA Puget Sound and the University of Washington, and the University of Sydney. The project is supported by the National Science Foundation's National Robotics Initiative and the MSL Renewed Hope Foundation.

Rouse says, instead of beginning from scratch, healthcare researchers can take this common platform and, after some assembly, start working on better solutions to help people with mobility impairments. The common platform also enables direct comparisons of new algorithms used to control the bionic leg, which researchers can then iterate and build upon. He also hopes that this open-source bionic leg will unite researchers with a common hardware platform and enable new investigators from related fields to develop innovative control strategies.