Tiny medical robots made of polymers derived from cellulose could one day travel through your body, delivering drugs, transporting cells, and taking biopsies. That’s the ultimate goal of Hamed Shahsavan, a chemical engineer at the University of Waterloo.

So-called “soft robots” made of polymers have revolutionized the field of robotics over the past 20 years, says Shahsavan. “Soft robots are based on a very wide application of soft materials like polymers, which play a role as building blocks as well as actuators, sensors, and even computing units,” he says.

He and his team are developing new kinds of polymers for soft robots that could open up new applications that traditional hard-bodied robots with their bulky components like motors are not suited for – including ones small enough to perform tasks inside the human body. “There is significant need for new smart materials for the creation of simple but effective microrobots that can go into the body to target a specific location or even a diseased organ for release of drugs,” says Eric Diller, who leads the microrobotics lab at the University of Toronto and was not involved in Shahsavan’s research.

Shahsavan and his team are developing new “smart” materials that can do just that, serving not only as the structural building blocks of the robot, but also providing the intelligence of the robot itself. “In the field of microrobotics we are searching for materials that can do it all,” he says. “They can sense, they activate, they can make decisions, basically molecules that become robots.”

The team embedded liquid crystal cellulose nanoparticles derived from plants in advanced hydrogels to create tiny robots no more than one centimetre long that are bio-compatible and non-toxic. The hydrogels are also self-healing, allowing the researchers to cut the robots and paste them back together without glue to form different shapes for different procedures.

The cellulose nanoparticles are anisotropic, meaning they have physical properties that have different values when measured in different directions. This is what can give the material something resembling intelligence, reacting in different ways to different stimuli. The robots can alter their shape when exposed to changes in pH or temperature, giving them the ability to grip and release cargo or overcome obstacles. Adding magnetic particles allows them to steer the robots through mazes using magnetic fields – suggesting that they could be guided through the body and tracked using MRI.

Diller says the work is an important advance towards the use of soft robots in medicine. “The combination of both pH-responsiveness and self-healing capability is unique and will enable the creation of much more sophisticated devices,” he says.

Changing shape in response to pH could be used as a way to move the robot or even change its behaviour on-the-fly, says Diller, while self-healing will enable drug delivery microrobots to be robust to damage, and may enable new abilities such as microrobots that can reconfigure into new designs as needed in response to environmental conditions. “Such behaviour is important to design microrobots that are simple yet highly functional,” he says.

It will be some time before tiny robots are swimming through your bloodstream to deliver drugs, however. As small as Shahsavan’s robots are, they need to be made much smaller to be used inside the body. Scaling them down to sub-millimetre scale will be the next step in the research, but for that Shahsavan will need help from his colleagues around the world. Even though Canada is a world leader in developing cellulose nanoparticles, the technology to take the next step is not available here. “We don’t have the means to do this miniaturization in Canada like they do in the US, Europe, and Asia,” he says.