New self-healing soft robot material

Engineers at Carnegie Mellon University have developed a soft polymer impregnated with gallium-indium liquid metal and silver micro-flakes to create a conductive material with self-healing properties. This marks a big step in the advancement of new materials for robotics, electronics, medicine, and the lesser-known field of "softbotics."

This study, published in Nature Electronics, showcases the first material of its kind to maintain enough electrical adhesion to support digital electronics and motors.

Soft robots are the next generation of machines designed along the lines of biomimicry – the process of studying and applying nature's evolved engineering solutions to modern design challenges.

Softbotics on its own or in combination with more traditional mechanics allows for finely integrated sensing, smooth actuation, and more organic feedback and responsiveness for improved machine intelligence.

Soft robot engineering provident delicate touch, nimble movement, flexibility and optimal adaptability in applications across a broad collection of fields such as surgery, specimen collection, and even space exploration.

The breakthrough

The research engineers formulated an electrically conductive polymer composite by starting with an organogel-based on polyvinyl alcohol and sodium borate matrix-then carefully mixing in gallium-indium liquid metal microdroplets and tiny flakes of silver, producing a stretchy gel with enough conductivity to run small electronic devices.

If the composite is crushed, cut, or torn, the edges can be lightly touched together like bubble gum, re-forming the pliable molecular bond and reconnecting the circuit.

Future applications of this type of material include more intricate 3D-printed circuitry that heals itself, flexible biological monitors for measuring muscle activity, and eventually, robotic nervous systems and better human prosthetics.

To integrate softbots more seamlessly into our everyday lives, they need to be able to flex with us, stand up to wear and tear and be easily reconfigured without being bulky or uncomfortable.

Today's robots and wearable electronics minimally possess partial rigidity in the form of metallic hardware and silicon components. In contrast, living tissue has evolved multitasking capabilities, efficiently controlling our physical movement, and manipulating the environment, all while conveying constant electrical feedback and complex internal and external perceptions to our brains.

The possibilities

One of the experimental designs from the Carnegie Mellon project is a soft-bodied snail analog, which "illustrates one possibility of using these materials as, basically, an artificial nervous tissue for soft robots," said Carmel Majidi, the study's senior author and professor of mechanical engineering.

The snail robot utilizes the composite on its exterior, connecting a battery and electric motor to control an inch worm-type of motion. During one demonstration, the team partially severed and then reconnected the conductive material by lightly pressing the severed edges back together.

"This is the first soft material that can maintain a high-enough electrical conductivity to support digital electronics and power-hungry devices," said Majidi. "We have demonstrated you can actually power motors with it."

Flexible and self-healing materials would also allow future robots to deform and adapt to changing environments like an octopus or other invertebrate.

The composite can also be reconfigured, acting as modular circuit components. In another demonstration, the research team used it to connect a toy car to a motor. The team then split a third of the composite off to a roof-mounted LED and restored a connection to the motor using the remaining material.

"In practice, we would want to have digital printing capabilities so we can make much more complex circuits that could interface with microelectronic chips, as well as other types of components that we could actually use in more sophisticated robotics and electronics applications," Majidi said. "There are so many possibilities that arise when you take machines and robots out of the hard case and engineer them out of materials that are soft and squishy."

Lastly, the research team tested the composite's ability to register readings of the subtle electrical activity of human musculature from multiple locations on the body, demonstrating the success of this material as a reusable biofeedback interface.

Helping humans

Majidi intends to continue his research on artificial muscle and nervous systems to build robots made entirely of soft, gel-like materials.

"It would be interesting to see soft-bodied robots used for monitoring hard to reach places. Whether that be a snail that could monitor water quality, or a slug that could crawl around our houses looking for mold," he said.

"Softbotics is about seamlessly integrating robotics into everyday life, putting humans at the center," Majidi added. "Instead of being wired up with biomonitoring electrodes connecting patients to bio measurement hardware mounted on a cart, our gel can be used as a bioelectrode that directly interfaces with body-mounted electronics that can collect information and transmit it wirelessly."

These properties could lead to highly accurate free-form medical monitors as well as fully flexible robots and machines that could navigate the human body, from tiny devices capable of intricate repair functions like blood clot removal to mechanized fleshlike appendages working to gently shift or stabilize organs during surgery, reducing the number of specialists crowded into an OR.

As the field advances, practical and algorithmic autonomy is developing in tandem with new materials tech.

From machine learning to motion control software and renewable energy use, these latest discoveries promise increasingly capable, hardy tools to improve the quality of human life.