Biohybrid robots work by combining organic components such as muscles, plant material and even fungi with non-biological materials. Although we are pretty good at making the non-biological parts work, we have always had a problem to keep the organic components alive and good. This is why machines powered by organic muscles have always been fairly small and simple – up to a few centimeters long and usually with only one activation joint.
“Scaling up biohybrid robots has been difficult because of the weak contractile power of laboratory-grown muscles, the risk of necrosis in thick muscle tissues and the challenge to integrate biological actuators with artificial structures,” says Shoji Takeuchi, a professor at Tokyo University, Japan. Takeuchi led a research team that built a full-size, 18-centimeter long biohybrid human-like hand with all five fingers driven by lab-grown human muscles.
Keep the muscles alive
Of all the roadblocks that prevent us from building large -scale biohybrid robots, necrosis is probably the most difficult to overcome. Growing muscles in a laboratory usually means a liquid medium to supply nutrients and oxygen to muscle cells sown on petri dishes or applied to gel scaffolding. Because these cultivated muscles are small and ideally flat, nutrients and oxygen from the medium can easily reach any cell in the growing culture.
When we try to make the muscles thicker and therefore more powerful, cells are buried deeper in those thicker structures cut off from nutrients and oxygen, so that they die and undergo necrosis. In living organisms this problem is solved by the vascular network. But building artificial vascular networks in laboratory-welded muscles is still something that we cannot do so well. So Takeuchi and his team had to find their way to the necrose problem. Their solution was sushi rolling.
The team started growing thin, flat muscle fibers that were arranged on a petri dish next to each other. This gave all cells access to nutrients and oxygen, so the muscles turned out to be robust and healthy. As soon as all fibers were grown, Takeuchi and his colleagues rolled them in tubes called Mumutas (multiple muscle tissue factuators) as if they were preparing sushi buns. “Mumutas are made by growing thin muscle plates and rolling them in cylindrical bundles to optimize contractility while retaining oxygen diffusion,” Takeuchi explains.
