Over the next few years, Saif plans to train the swimming biobot’s neurons to develop primitive memories and eventually decide which direction to move. Training will be based on punishment and reward. “For example, if the swimmer moves to the right, we’ll punish him with chemicals, but if he moves to the left, we’ll give him sugar,” Saif says. “The hope is that if we give him this choice enough times, the neurons will automatically move to the left. Just like in our own lives, the biobot will progress: we make decisions based on experience.”
But back to Saif’s dream: Future biobots, he says, could be used not only to detect and treat cancer in humans, but also to detect and remove toxins from the environment and test the efficacy of drugs. In his words, “We are paving the way for intelligent machines.”
Towards a world of soft and sustainable robots
Saif’s biobots are tiny for a reason: if the tissues grew beyond the size of a lentil seed, it would have difficulty providing them with the nutrients and oxygen they needed, and they would die.
But researchers at ETH Zurich are exploring ways to create larger-scale biohybrid robots that are powered by living muscles. Researchers in the university’s Soft Robotics Lab have found a way to 3D print muscle cells and slowly stretch them into muscle tissue that incorporates built-in channels that can distribute (or “perfuse”) nutrients internally, mimicking the vascular structure of human muscles.
The largest muscles made so far are about two centimetres long and one centimetre thick. According to Robert Kutchman, PhD, assistant professor of robotics at the university, the barriers to making even bigger muscles are mainly logistical: just a two-centimeter muscle would require about 50 million cells, and manufacturing enough cells to make an even bigger muscle would require a factory-scale facility. “But in theory, there’s no limit,” Kutchman says. “If you have the cells and the perfusion capacity, you can make a bigger muscle.”
The lab currently uses so-called “immortalized” cell lines from rats and mice – cells that have been artificially engineered to keep growing indefinitely. This alleviates the ethical concerns associated with using “primary cells” extracted directly from an animal. Katzman says that in theory, it’s possible to make new muscle tissue from cells from any species. “You could basically make it from grasshoppers,” he says. “You just need to be able to grow them in large quantities when you grow them in the lab.”
Katzman’s ultimate goal is to create living muscle and tendon structures that can be integrated with artificial parts to create large-scale biohybrid robots. These muscles are actuated by electrical pulses. But like our own bodies, they are driven by chemical nutrients. Common nutrients include amino acids and proteins, which are usually supplied in the form of bovine serum from fetal cows, which is widely used in cell culture. Perhaps, and more ethically, in the future, this will be replaced by those obtained from non-animal sources. “This is a question that remains to be answered, but eventually we will find a way to generate a mixture of glucose and other nutrients from plant sources so that cells can function,” says Katzman. In addition, these bioactuators can serve as functional models for fundamental research into the pathophysiology of locomotion, which is currently mainly conducted through laboratory animals.
