Degradation of the inflator propellant
means metal fragments could shoot out in an accident, putting occupants at serious risk of injury, even death...
To understand how they work, we can take a look at nature itself: while natural elements acquire their physical properties from the atoms that form them and the way in which they are ordered, metamaterials use natural
means, like small
metal fragments that fit together like parts of a Meccano model to artificially synthesise properties that are impossible to find otherwise.