French scientists have developed a new rubber that heals itself after being cut. As seen in the above video if the two broken ends are pushed together and left for an hour, they join and retain its original characteristics as they remain stretchy as before.
'Regular rubber gets its strength from the fact that long chains of polymer molecules are coupled, or "crosslinked," in three different ways: through covalent, ionic, and hydrogen bonding between molecules. Of these three bond types, only the hydrogen bonds can be remade once a material is fractured, although normally there are not enough hydrogen bonds for the rubber to re-couple in this way. The solution devised by Leibler and colleagues is to simply get rid of the ionic and covalent bonds. They developed a transparent, yellowy-brown rubber in which crosslinking is performed only by hydrogen bonds.'"

Source via Slashdot