A walking biological machine made from hydrogels and rat heart cells is described in Scientific Reports this week. The ‘bio-bot’ has two legs, one that propels it forward, and the other that acts as a stabilizer. Complex biological machines have potential applications that include organ mimics for drug testing, as well as other health, security, and environment applications.

Combinations of different cell types in a suitable material can produce complex biological materials with interesting functions. Rashid Bashir and colleagues made their biological machine using a 3D printer, which provides flexibility in the design and fabrication of 3D structures. The bio-bot has a cantilever structure seeded with heart muscle cells, and it is the contraction of these cells allows the bio-bot to self-propagate. Another factor that enables the bio-bot to hop forward is the difference in friction between the two legs; greater friction in the propagating leg than the stabilizing leg results in forward motion. The bio-bots measure just under a centimetre long, and move at speeds of around 236 micrometres per second in fluid.