University of California San Diego engineers have developed a magnetic ink that can be used to make self-healing batteries, electrochemical sensors, and wearable 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 repair tears as wide as 3 millimeters - a new record in the field of self-healing systems. Current self-healing materials require an external trigger to kick start the healing process and can take anywhere between a few minutes to several days to work. The new system requires no outside catalyst to work and damage is repaired within about 50 milliseconds (0.05 seconds).