Pulickel Ajayan and co-workers, Rice University, Houston, USA, have shown the potential of stiffening polymer-based nanocomposites with carbon nanotube fillers. The team created the composite by including vertically aligned, multiwalled nanotubes in polydimethylsiloxane.

The composite displayed the unusual property of strengthening upon repeated mechanical stress. Dynamic mechanical analysis showed a 12 % increase in stiffness after 3.5 million compressions. Metals and bones are known to strain-harden in this way, but polymers and other synthetic materials generally undergo irreversible microstructral damage under these conditions, leading to weakening of the material.

This material could be used to develop adaptive materials for building in earthquake-prone areas or for medical applications where active, load-bearing artificial connective tissues are required.

• Observation of Dynamic Strain Hardening in Polymer Nanocomposites
  B. J. Carey, P. K. Patra, L. Ci, G. G. Silva, P. M. Ajayan,
  ACS Nano 2011.
  DOI: 10.1021/nn103104g