Optical waveguide enables self-healing soft robotic system

LAURA LEAY: Welcome to MRS Bulletin’s Materials News Podcast, providing breakthrough news & interviews with researchers on the hot topics in materials research. My name is Laura Leay. There are some things that nature is great at, and other things that we can draw inspiration from and improve. Some robotic devices are made from soft, bendable materials so that they can move a bit like creatures from the natural world but their soft structure can easily be damaged. Biological structures can heal themselves and now soft robots can do it, too. This advance in soft robotics has been pioneered by Rob Shepherd from Cornell University, which could help develop agile, adaptive robotic systems.

 ROB SHEPHERD: What we would like to do is have maneuverability and agility more like a monkey. It’s more likely to accumulate damage and have a lifetime be governed by its ability to fix itself.

 LAURA LEAY: To produce an agile robot that is able to explore space, seas and other extreme environments and be able to adapt to it means that you’re likely to need a complex robotic system much like a monkey or a fish.

 ROB SHEPHERD: Any organism at that level is pretty complicated: multiple organ systems communicating with each other, each organ system is multifunctional in itself and the amount of communication between everything is really sophisticated. Nature has done a good job: something evolved something for a purpose and then the situation changed and then adapted that for the new situation so it’s not optimal. We can do better. 

 LAURA LEAY: Rob’s team has developed waveguides made of self-healing polyurethane urea crosslinked with aromatic sulfide bonds. When this material is cut, relatively weak hydrogen bonds quickly form. Disulfide exchange then occurs and, although this takes longer than the formation of hydrogen bonds, results in much stronger bonding and so recovering much of the mechanical strength of the polymer. Light is transmitted down the waveguide and, when the material is cut or punctured, the signal is attenuated. The loss of signal can be acted on by the robot and it can change its pattern of movement until the strong disulfide bonds are formed. This self-healing material absorbs more light than previous versions of the polymer that couldn’t effect a chemical repair. This level of light absorption is actually useful as it makes the robot more sensitive to damage or deformation. Soft sensors are pretty handy for understanding an environment. Think about the skin on your fingertips.

 ROB SHEPHERD: My finger can envelop corners and just sample more information with larger density of sensors. One example is on rocky terrain which appears to be stable but as you stand on it, it can move. Even the slightest amount of movement you can detect with touch.

 LAURA LEAY: The newly developed polymer has a lower viscoelasticity than previous iterations which means that it took longer for the material to go back to its original shape after being deformed. To overcome this, the waveguides were given a particular architecture so that they would have to strain less while still being able to sense change in the physical surroundings. So it seems that robots will become ever more complex and reach a level of complexity akin to mammals. A robotic system that is not only inspired by nature but goes beyond what evolution can achieve is a step toward a complex system that can adapt to damage, spontaneously repair, and be able to interact with its environment in a way that other types of robots cannot. These self-healing optical sensors are a step towards a complex robotic system that can look after itself. Although robotics is traditionally the realm of mechanical and electronic engineers, it’s clear that materials science has a role to play.

 ROB SHEPHERD: Materials scientists can really create new boundary conditions that these disciplines can exploit to make these robots better.

 LAURA LEAY: This work was published in a recent issue of Science Advances. My name is Laura Leay from the Materials Research Society. For more news, log onto the MRS Bulletin website at mrsbulletin.org and follow us on twitter, @MRSBulletin. Don’t miss the next episode of MRS Bulletin Materials News – subscribe now. Thank you for listening.