Self-healing polymers mend themselves by reforming broken cross-linking bonds. Yet this cross-linking healing mechanism usually requires an external stimulus, which means that these materials aren’t necessarily practical. These stimuli can include energy inputs or specific environmental conditions, such as pH. The researchers came close before to making such a self-healing material. In Spain, scientists created self-healing silicone elastomers using silver nanoparticles. Unfortunately, an applied external pressure was needed to make them work.