German researchers have copied the caoutchouc tree's modus operandi to create a self-sealing elastic polymer. When the caoutchouc tree is damaged, liquid latex containing capsules of the protein hevein escapes from inside it. Those capsules rupture, releasing the hevein, which links the latex particles together and ultimately closes up the wound. The bursting/sealing-microcapsules process has been put to use in human technology such as self healing concrete, electronics, paint and aircraft epoxy resin. Scientists from the Fraunhofer Institute for Environmental, Safety and Energy Technology loaded microcapsules with the adhesive polyisobutylene, then put those capsules into synthetic caoutchouc sap elastomers. The idea was that when pressure was put on the elastomers to the point of cracking, the capsules would rupture and mix with the elastomers' polymer chains, thus sealing the cracks. However, the capsules did not cooperate. However, when the polyisobutylene was added in an uncapsulized form, a self-healing effect did occur – the elastomers' tension expansion was restored by 40% after a 24-hour healing period. The scientists further copied the caoutchouc tree, by charging the elastomer with ions. In the case of the tree, the hevein proteins link up with one another (and in the process, with the latex) via ionic bonding. By charging the synthetic elastomer, a similar effect could be achieved with the polyisobutylene.