Bio-Inspired Bionic Limbs

I am pretty lucky to work on some cool projects. I am currently working on a project to improve the function of a remarkable Bionic limb (BiOM), developed by MIT’s Hugh Herr lab group. If you want to see what science is capable of today, watch this video.

Dr. Herr’s Biomechatronics lab does a lot of really fascinating stuff….enjoy spending hours looking it over here.

40489_4704_f6Qv23FtX0OFbnWjH8mJNF9agAs of right now, our lab’s main bread and butter is working with the muscle protein titin. Turns out this little protein’s role in muscle function has been overlooked for decades and our lab is uncovering its role. In recent work, we have observed that titin has two identities: by day (relaxed muscle) the protein works as a passive elastic element that helps with the structural integrity of the muscle cells. By night (active muscle) it plays a much larger role in muscle properties (check the literature of the “winding filament hypothesis” or go here). Anyhow, we have used our new understanding of muscles to develop a computer model of muscles that can successfully predict muscle force from almost any situation a muscle can be in.

What about foot prostheses?

Advances in prosthesis development have been driven largely by technology (e.g., light-weight materials, long-life lithium batteries, programmable electronics, and wireless communication), rather than by advances in our understanding of the underlying biological principles of movement. For a person with a trans-tibial amputation, the iWalk BiOM is a commercially available powered ankle-foot prosthesis that utilizes a motor to assist the user through the gait cycle. Provision of motor power permits faster walking than can be produced using only the spring-like behavior provided by passive devices. The BiOM can adapt to changes in walking speed on level ground, but the use of active motor power raises the issue of control. The main problem is that the control approach exhibits no inherent adaptation to varying environmental conditions. Instead, algorithms are required to generate particular torque control for all intended activities and variations of terrain, along with an appropriate means to select among them. Although the current BiOM performs well across a range of level walking speeds, improvements in the range of conditions in which it can reproduce normal ankle torques would significantly increase the quality of life for users. The muscles in our body are able to adapt instantaneously to changes in load without requiring sensory feedback, a property that has remain unexplained for decades. We have developed control algorithms for the BiOM based on the novel winding filament hypothesis (WFH) , which builds on the sliding filament theory by incorporating a role for titin. The WFH explains muscle properties including force enhancement force depression, which are unexplained by the sliding filament theory. We implemented a control algorithm based on the WFH into the BiOM and tested subjects under a variety of conditions including level walking, stair ascent/descent, ramps, backwards walking and uneven terrain.

PROGRESS: Our results indicate that the WFH-based control algorithm for the BiOM is capable of producing ankle torque profiles during level walking that are similar to the BiOM stock controller. Unlike the BiOM, the WFH-based control algorithm is also capable of reproducing ankle torque profiles that match those of able-bodied individuals during stair ascent. By implementing a control algorithm that, like muscle, can adapt instantaneously to changes in load, we hope achieve more robust prosthesis control. Future studies include metabolic cost of transport, backwards walking, ramp ascent and descent, and walking on uneven terrain, such as astroturf.

Below is a video of a test subject trying out the BiOM with the WF controller installed.


 SICB 2015 ALH Poster


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