Self-healing polymers took a big step forward today with the publication in Science of research from the University of Illinois (White in Aerospace, and Moore and Sottos, both in MatSci) showing a technology for self-repair of impact craters as large as 3.5 cm within hours.
The chemistry is more complicated than you might imagine. Each of the two fluids has two components with in it - a gelling component and a reactive monomer. The gelling components react first (within seconds or a few minutes) providing a scaffolding for the polymerization of the monomers that occurs over hours. The gelation is needed as surface tension could otherwise prevent the coverage of such large areas. The final product has 62% of the initial impact strength - not bad for an initial result.
I've written about self-healing polymers many times in the past and have generally not had nice things to say about them (such as here, here or here). While 62% recovery is not great, the innovative and flexible approach demonstrated here is what I find exciting. There are plenty of chemistries that can be used in this setup and that versatility is what is so exciting.