I ran into a truly fascinating research paper recently that described “xenobots”. Briefly, a xenobot is a tiny (about 4 one-hundredths of an inch in diameter — about the size of a grain of sand) programmable bio-robot made from frog skin and heart cells. This image illustrates the key ideas:
The green objects are frog skin cells that provide the xenobot structure. The red objects are frog heart muscle cells that contract and expand, and provide the xenobot motion. The first step in creating a xenobot is to design a model using evolutionary algorithm machine learning. The design target is for the xenobot to perform a specific task, such as walking, pushing pellets, carrying payloads, and working together in a swarm to aggregate debris.
Once the abstract model has been created, the physical xenobot is manufactured using frog cells. Xenobots can survive for weeks without food and can heal themselves after damage.