The incorporation of actual muscles or neurons into a robotic system may appear to be science fiction, but researchers at Carnegie Mellon University’s Department of Mechanical Engineering are working to make it a reality. The Biohybrid and Organic Robotics Group (B.O.R.G.) is led by Victoria Webster-Wood, an assistant professor of mechanical engineering, and focuses on biohybrid robotics.
“Our ultimate goal is to be able to use biological materials as engineering materials in robotics to create renewable, biodegradable robots,” she says.
Ph.D. student Wenhuan Sun sought to better understand how to fabricate material threads for use in these specialized robots in a paper published in The Journal of Biomedical Engineering. Collagen, a naturally occurring protein found in structural tissues such as skin, ligaments, and tendons, is used to make the threads.
The idea of incorporating actual muscles or neurons into a robotic system might sound like science fiction, but researchers in Carnegie Mellon University’s Department of Mechanical Engineering are taking steps to make it a reality.
In essence, the goal of this study was to learn more about how to create an artificial tendon for use on a robot. Tendons are very strong and work to connect muscle to bone in our bodies. This means that these collagen threads could be used in a robot to connect living muscle actuators to the robot, allowing it to walk, jump, or swim. The mechanical properties of the robot’s materials, on the other hand, can have a significant impact on how living muscle actuators grow and perform.
This means that Sun would have to investigate not only how to best create these collagen threads, but also how to tune their mechanical properties. Depending on what you want your robot to do, a material that is more muscle-like or tendon-like may be required.
Sun’s threads were created using an electrocompaction technique. It was initially developed for use in tissue engineering and is now being fine-tuned by organizations such as the B.O.R.G. Because of the charge that collagen fibers naturally carry, they are moved through a special type of cell called an electrocompaction cell to create the threads. The fibers will eventually get compacted together in the process, creating electrochemically aligned collagen (ELAC) threads.
Sun wanted to see how much this compaction process could be tweaked to produce different threads, in order to diversify the fabrication process as a whole. Previous tissue engineering research has primarily focused on creating the strongest, most tendon-like threads possible. Biohybrid robotics necessitates a higher level of nuance and finesse.
When first compacted, the threads are surprisingly brittle and difficult to work with—they are not yet as strong as natural tendons. Sun described how difficult it was to get the compacted threads into a container. “Because there is static around the plastic container, the thread clings or sticks to either side of the walls.” That makes things very difficult,” he explained.
Despite the fact that the threads can be quite long—Sun created one that was up to 40 centimeters (around 15 inches) long—they are extremely thin. The widths ranged from 50 to 100 microns, or about the width of a human hair.
He was able to carry out a series of experiments determining how a set of fabrication parameters affect the resulting thread with time and practice. He also investigated the interactions between these parameters and was able to achieve a diverse set of tunable properties.
Even though the results were somewhat predictable—for example, more time spent allowing the threads to compact resulted in stronger, larger threads—this study provided the first, verifiable evidence of the team’s hypotheses and will aid future researchers in designing and selecting electrocompacted collagen materials for their own work. Sun was also able to train a deep neural network to recommend specific fabrication parameters based on the mechanical properties desired by a specific researcher.
Sun intends to feed the threads into a 3D printer so that they can be used to create various shapes and structures in the future. He is currently collaborating with Adam Feinberg, professor of biomedical engineering and materials science and engineering, to accomplish this goal. Because of the strength of the compacted collagen threads, they could be used for a broader range of applications than soft, squishy, muscle-based prints, and they will most likely help a new generation of biohybrid robots get off to a flying start.
