The material, developed by Zhenan Bao and coworkers at Stanford University, is made of a randomly branched, hydrogen-bonding polymeric network embedded with nickel microparticles that have nanostructured surfaces (Nat. Nanotechnol., DOI: 10.1038/nnano.2012.192).
Bao and coworkers started with a mixture of polyurethanes. To the polymer mixture, they added as much as 30% by volume nickel microparticles. The optimum amount of nickel is a trade-off between the materialís conductivity and flexibility.
The polymer network forms hydrogen bonds with itself and with oxides on the surface of the nickel particles. The hydrogen bonds are the weakest bonds in the system, and they preferentially break when the composite is damaged. When cut pieces of the material are brought together, the hydrogen bonds quickly re-form.