Credit: © 2009 AAAS

Materials that are able to mend themselves when damaged would make particularly good coatings in a variety of fields, including transportation, packaging and biomedicine. Investigations in this direction have been guided by the self-healing abilities of materials in nature — such as some plants, or the human skin.

In a departure from these methods, Biswajit Ghosh and Marek Urban at the University of Southern Mississippi have now prepared1 a heterogeneous material that can repair itself at ambient temperature under ultraviolet (UV) irradiation. The researchers have incorporated UV-sensitive chitosan units, which are covalently bonded with constrained four-member oxetane rings, into heterogeneous polyurethane networks. These polymer networks are in turn crosslinked to form solid films. Characterization by infrared and optical imaging revealed that an area damaged by scratching could be repaired in less than 1 h under UV irradiation from a lamp or the Sun.

The repair mechanism is a recombination of the free radicals formed when the mechanical damage is inflicted (opening the oxetane rings) and those formed by exposure to UV light (upon cleavage of the chitosan chains) to crosslink the networks. Despite a limited ability of an area to heal itself if it is damaged a second time, these materials do not require other components to be repaired and so offer great promise for various applications.