Artificial nerve fibers
Flexible and stretchable electronics are being used more and more frequently these days, e.g. in artificial skin or robots made of highly flexible materials (soft robotics), as this flexibility is very similar to biological systems. As flexible as these structures are, they are susceptible to mechanical damage such as scratches or cracks. This is often the main reason for device failures.
The development of self-healing materials can counteract these consequences, which in turn can significantly increase the service life of the devices and their safety in use.
To date, many of these self-healing materials have been developed based on very different modes of action and have been successfully used in flexible touchscreens or portable energy generators. However, these materials have always had one major problem: cold ambient temperatures, such as in winter or when used at high latitudes, are detrimental to this process. It slows down or is simply no longer possible under these conditions.
If you now build a polymer scaffold from a polyvinyl alcohol with many -OH groups and a polyethyleneimine rich in amino groups, this is held together via hydrogen bonds and electrostatic interactions. If lithium ions, e.g. from lithium chloride, are then added, they are strongly hydrated by a large amount of bound water and thus form the “flesh and blood” of this framework.
If the temperature goes below 0 degrees Celsius, the previously strongly directed arrangement of the hydrogen bonds breaks down and makes way for a reconstruction of the interactions and diffusion of polymer segments during the self-healing process. This ionic hydrogel has a constant self-healing performance, consistent conductivity and ultra-stretchability even at sub-zero temperatures, making it an excellent starting material for electronic devices.
To illustrate this, Chinese researchers have developed an artificial nerve fiber by replicating both the structure and properties of the potential-controlled signal transmission of an axon. This structure was then integrated into a robot and continued to show an amazingly high information throughput under cold conditions and strong deformations, even at temperatures as low as -80 degrees Celsius.
The nanostructure of this hydrogel was then further optimized and even achieved self-healing within 10 minutes, a deformation tolerance of over 7,000 percent, excellent conductivity and freeze protection, which is otherwise impossible to achieve in combination of all properties. This hydrogel thus opens up completely new possibilities for the use of electronic devices at sub-zero temperatures, e.g. robots on unmanned missions under extreme conditions.
Very exciting, in my opinion – we’ll stay tuned.
Dr Ronald Hinz, Market Intelligence Senior Expert
Sources:
„Ultra-Stretchable and Fast Self-Healing Ionic Hydrogel in Cryogenic Environments for Artificial Nerve Fiber“ Adv. Mater. 2022, 2105416; DOI: 10.1002/adma.202105416
