How could you build an artificial joint that can do work on its own, but doesn't require a tethered power source? Researchers have found a potential answer by 3D printing a skeleton that they later grew mouse muscle on. The muscle actually moves, and is powered by electrical impulses, just like the muscles inside you and me.
The biologically powered robot—known as bio-bot—has a hydrogel skeleton composed of a flexible connecting beam and two protruding poles. Cells are grown in between these two poles, as demonstrated in a new study published in PNAS.
The bio-bot - in the last image, it's released from the holder. All scale bars 1 mm. Image: PNAS/Cvetkovic et al.
The researchers used skeletal muscle cells for an extra robust muscle strip. They also optimized the flexibility of the 3D printed skeleton's beam by changing its porousness.
To stimulate the muscles to contract, the bio-bot was placed in a liquid dish with a bi-polar electrical field. When electricity is pulsed, it's sufficiently similar to our motor neurons' signaling to cause protein expression and muscle contraction.
To make it move, they had to print a new skeleton. They found the pillars needed to be different heights to generate momentum. When this skeleton was placed in the bi-polar electrical field dish, it created the same crawling movement you see with an inchworm.
This isn't the first demonstration of biological building blocks generating force or work. Researchers have demonstrated that cardiac muscle tissue can be manipulated into a contracting actuator, and that sperm can power robots to move towards magnetic targets.
A major difference with this study, however, is that the method to 3D print the skeleton could be scaled to different-sized joints and could accommodate various types of cells. Furthermore, 3D printing is well suited to integrate more surfaces for cells to grow on.
The researchers believe it would be possible to integrate motor neurons into a similar 3D printed skeletal design to replace the electrical field that tells the muscle cells to contract, that we could incorporate an endothelium to deliver food and oxygen in a closed system, and maybe wrap the whole system in an epithelial layer. Then you have something that's starting to resemble a living biological creature.
The researchers think their bio-bot will help us to better understand how organisms are constructed, and hopefully with this knowledge in hand, lead us to develop new ways to test clinically relevant drugs or design mdeical implants that wouldn't be rejected be the body.