Nanoengineers at UC San Diego printed a self-healing circuit on the sleeve of a T-shirt and connected it to an LED light and a coin battery. They then cut the circuit and the fabric it was printed on, causing the LED to turn off. But then within a few seconds, it turned back on as the two sides of the circuit came together again and healed themselves, restoring conductivity. Photo: Jacobs School of Engineering/UC San Diego.A team of engineers at the University of California San Diego has developed a magnetic ink that can be used to make self-healing batteries, electrochemical sensors and wearable, textile-based electrical circuits.
The key ingredient for the ink is microparticles oriented in a certain configuration by a magnetic field. Because of the way they're oriented, particles on both sides of a tear are magnetically attracted to one another, causing a device printed with the ink to heal itself. The devices can repair tears as wide as 3mm – a record in the field of self-healing systems. The engineers detail their findings in a paper in Science Advances.
"Our work holds considerable promise for widespread practical applications for long-lasting printed electronic devices," said Joseph Wang, director of the Center for Wearable Sensors and chair of the nanoengineering department at UC San Diego.
Existing self-healing materials require an external trigger to kick-start the healing process, and can also take anywhere between a few minutes to several days to work. By contrast, the system developed by Wang and colleagues doesn't require any outside catalyst to work, and the damage is repaired within about 50 milliseconds (0.05 seconds).
The engineers used the magnetic ink to print batteries, electrochemical sensors and wearable, textile-based electrical circuits. They then set about damaging these devices by cutting them and pulling them apart to create increasingly wide gaps. This included damaging the devices nine times at the same location and inflicting damage in four different places on the same device. In each case, the devices healed themselves and recovered their function while losing a minimum amount of conductivity.
For example, nanoengineers printed a self-healing circuit on the sleeve of a T-shirt and connected it to an LED light and a coin battery (see photo). They then cut the circuit and the fabric it was printed on, causing the LED to turn off. But then within a few seconds, it turned back on as the two sides of the circuit came together again and healed themselves, restoring conductivity.
"We wanted to develop a smart system with impressive self-healing abilities with easy-to-find, inexpensive materials," said Amay Bandodkar, one of the papers' first authors, who earned his PhD in Wang's lab and is now a postdoctoral researcher at Northwestern University.
Wang's research group is a leader in the field of printed, wearable sensors, so his team of nanoengineers naturally turned to ink as a starting point for their self-healing system. The nanoengineers loaded the ink with microparticles of a soft, silvery, magnetic metal known as neodymium, which is commonly used in research. The magnetic field of these particles is much larger than their individual size, which is key to the ink's self-healing properties because the attraction between the particles causes them to close tears that are millimeters wide.
The particles also conduct electricity and are inexpensive. But they have poor electrochemical properties, making them difficult to use in electrochemical devices such as sensors. To remedy this problem, the researchers added carbon black to the ink, a material commonly used to make batteries and sensors.
The researchers also realized that the microparticles' magnetic fields canceled each other out when in their natural configuration, robbing them of their healing properties. They solved this by printing the ink in the presence of an external magnetic field, which ensured that the particles oriented themselves so that they behaved as a permanent magnet with two opposite poles at the end of each printed device. When the device is cut in two, the two damaged pieces act as different magnets that attract each other and self-heal.
In the future, engineers envision making different inks with different ingredients for a wide range of applications. In addition, they plan to develop computer simulations to test different self-healing ink recipes in silico before trying them out in the lab.
This story is adapted from material from the University of California San Diego, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.