Though C-3PO and R2D2 in Star Wars are fictional, these personable machines match our traditional view of robots as rigid, often metallic devices.

The latest real-world robots might not be able to save the galaxy, but they do have an advantage over their on-screen counterparts: recent advances in tissue engineering have allowed the construction of biologically inspired robots from soft tissues instead of hard materials, creating highly responsive machines that more closely mimic actual biological functions like locomotion.

In the latest example of this technology, a team of researchers from the University of Illinois at Urbana-Champaign (UIUC) and the Massachusetts Institute of Technology (MIT) has created a three-dimensional (3D) printed biological robot powered by skeletal muscle tissue that can move across a surface like an inchworm. Their results, published on July 15 in Proceedings of the National Academy of Sciences (DOI: 10.1073/pnas.1401577111; p. 10125), demonstrate the potential of forward engineered machines to enhance our understanding of biological systems.

Previous biological machines have used cardiac muscles to power locomotion. However, “cardiac muscle cells self-pace—they move on their own. If you want to actually control the motion, you want to use skeletal muscle cells,” said Rashid Bashir, a bioengineer from UIUC and the leader of the research team.

Using 3D printing technology, the team of researchers created a scaffold—two rigid pillars connected by a pliant beam. An extracellular matrix made of collagen and fibrin proteins placed over the scaffold provided structure for the embryonic muscle cells, which self-assembled into a muscle strip over a period of a week to create a bio-bot.

An external electrical pulse mimicking a neural signal caused the muscle to contract and the robot to move—when the device was lopsided. “To get a directional movement, you somehow have to break symmetry. Either the force that’s generated has to be asymmetric, or the structure has to be asymmetric,” Bashir said. To create asymmetry that would drive the robot forward, the researchers shortened one of the scaffold’s pillars, causing the crossbeam to bend slightly and the muscle cells to exert differential force on the pillars.

This bio-bot is no cheetah: it moves at a relatively slow pace of around 1.5 body lengths per minute. However, Bashir hopes that the concept could ultimately be incorporated into a more complex machine with neural connections regulating the muscle cells. “Our next step is working to integrate neurons into the structure, so you could provide a signal to the neuron and the neuron would control the movement,” he said.

“It’s clear that there’s an opportunity to take technological advances and combine them with what nature has developed to come up with ways of making things that are even better,” said Ali Khademhosseini, a bioengineer at Harvard-MIT's Division of Health Sciences and Technology who was not involved in the research. “I think [this experiment] opens up a lot of new possibilities.”