From the archive, originally posted by: [ spectre ]
Plastic That Heals Itself
Researchers have developed a new material that can fill in its own surface cracks.
By Prachi Patel-Predd / June 11, 2007
Self-healer: Modeled on human skin, a new material that heals itself
multiple times is made of two layers. The polymer coating on top
contains tiny catalyst pieces scattered throughout. The substrate
contains a network of microchannels carrying a liquid healing agent.
When the coating cracks, the cracks spread downward and reach the
underlying channels, which ooze out healing agent. The agent mixes
with the catalyst and forms a polymer, filling in the cracks.
Researchers at the University of Illinois at Urbana-Champaign (UIUC)
have made a polymer material that can heal itself repeatedly when it
cracks. It’s a significant advance toward self-healing medical
implants and self-repairing materials for use in airplanes and
spacecraft. It could also be used for cooling microprocessors and
electronic circuits, and it could pave the way toward plastic coatings
that regenerate themselves.
The first self-healing material was reported by the UIUC researchers
six years ago, and other research groups have created different
versions of such materials since then, including polymers that mend
themselves repeatedly when subject to heat or pressure. But this is
the first time anyone has made a material that can repair itself
multiple times without any external intervention, says Nancy Sottos,
materials-science and engineering professor at UIUC and one of the
researchers who led the work.
“It’s essentially like giving life to a plastic,” says Chris
Bielawski, a chemistry professor at the University of Texas at Austin.
The ultimate goal would be to create materials that mend themselves,
he says, and “this is an amazing proof of concept.”
Sottos and her colleagues have designed the new material, reported in
this week’s Nature Materials, to mimic human skin. If the skin’s outer
protective layer is cut, the inner layer, which is infused with a
dense network of tiny blood vessels, rushes nutrients to the cut to
help with healing. The self-healing material consists of an epoxy
polymer layer deposited on a substrate that contains a three-
dimensional network of microchannels. The epoxy coating contains tiny
catalyst particles, while the channels in the substrate are filled
with a liquid healing agent.
To test the material, the researchers bend it and crack the polymer
coating. The crack spreads down through the coating and reaches the
underlying microchannel. This prompts the healing agent to “whip
through the channels and into the crack,” Sottos says. There, it comes
into contact with the catalyst and, in about 10 hours, becomes a
polymer and fills in the crack. The system does not need any external
pressure to push the healing agent into the crack. Instead, the liquid
moves through the narrow channels just as water moves up a straw.
The researchers are able to crack and reheal the surface as many as
seven times before the catalyst wears out and stops working. The next
generation of the self-healing material should be able to heal itself
many more times, according to the researchers. Sottos and her
colleagues are designing it so that it will have a two-part system
that injects both a healing agent and a catalyst into the crack.
The researchers could also increase the rehealing capacity of the
material by hooking up the microchannel network to a little reservoir,
Sottos says. If the material runs out of healing agent or catalyst,
the reservoir could pump in more.
The material’s microchannel design could be a solution to the
increasing problem of heat buildup in microelectronics chips.
Typically, microelectronic circuit chips sit on substrates that are
designed to conduct heat away from the circuit. These heat regulators
have their limits. Instead, Sottos says, “you could put a cooling
fluid through a [microchannel] network like a little mini-heat
Sottos says that researchers could use the same design with other
resin and catalyst combinations that can form different polymers. This
opens the door for many other applications. While practical self-
healing materials might be years away, it’s easy to imagine their
applications in prosthetics and medical implants made from
biocompatible self-healing materials. The cost of the materials might
keep them limited, at least initially, to certain high-value, high-
performance applications such as use in air- and spacecraft, says Ian
Bond, aerospace engineering professor at the University of Bristol, in
the United Kingdom.
In the future, different chemistries could lead to cheaper self-
healing materials, according to Bielawski. “You could use cheap
epoxies … that you can buy at Home Depot … as a healing agent,” he
White, S. R., N. R. Sottos, P. H. Geubelle, J. S. Moore, M. R.
Kessler, S. R. Sriram, E. N. Brown, and S. Viswanathan. 2001.
Autonomic healing of polymer composites. Nature 409, 794-797.
Sottos research group page
Nancy R. Sottos
Department of Materials Science and Engineering
Donald B. Willett Professor of Engineering
Professor of Materials Science and Engineering
216 Talbot Laboratory
Department of Materials Science and Engineering
1304 W. Green St.
Urbana, IL 61801
Telephone: : 217-333-1041
E-mail: n-sottos [at] uiuc [dot] edu
“Professor Sottos received her B.S. in Mechanical Engineering at the
University of Delaware in 1986 and her Ph.D. in Mechanical Engineering
at the University of Delaware in 1991. Sottos is co-chair of the
Molecular and Electronic Nanostructures Research Initiative and a part
time faculty member at the Beckman Institute for Advanced Science and
Technology. Her research group studies the mechanics of complex,
heterogeneous materials such as advanced composites, thin film
devices, and microelectronic packaging, specializing in micro and
nanoscale characterization of deformation and failure in these
material systems. Current research focuses on the development of
autonomic materials systems that have the ability to achieve
adaptation and response in an independent and autonomic fashion (e.g.,
recent work on autonomic healing in polymers). Research and teaching
awards include the Office of Naval Research Young Investigator Award
(1992), Outstanding Engineering Advisor Award (1992, 1998, 1999 and
2002), the Robert E. Miller award for Excellence in Teaching (1999),
the University of Delaware Presidential Citation for Outstanding
Achievement (2002), University Scholar (2002) and the Hetényi Award
from the Society for Experimental Mechanics (2004). Her research group
was awarded the American Society for Composites Best Paper Award in
2002 and 2003, and the Tech Museum of Innovation Award for Technology
Benefiting Humanity in 2001 for work on self-healing polymers. She is
a member-at-large of the U.S. National Committee on Theoretical and
Applied Mechanics, on the editorial board for Composites Science and
Technology and Experimental Mechanics, and is the faculty advisor for
the student chapter of the Society of Women Engineers.”