Researchers at the University of Rochester have developed a shape-memory
rubber that may enable applications as diverse as biomedical implants,
conformal face-masks, self-sealing sutures, and "smart" labels.
The material, described in the journal Advanced Materials, forms a new
class of shape-memory polymers, which are materials that can be
stretched to a new shape and will stay in that form until heated, at
which time they revert to their initial shape.
Unlike conventional shape-memory polymers, however, the new material
is transparent, rubbery, and most importantly, engineers will be able
to control the speed at which it returns to its original shape. Other
shape memory polymers use crystallization to hold a temporary shape,
which often makes them opaque, hard, and brittle in their frozen
states, and this can limit their use.
Professor Mitchell Anthamatten, and graduate
student Jiahui Li, of the Department of Chemical Engineering.
Credit: University of Rochester
"At higher temperatures the material stretches
like a rubber band, but, at lower temperatures, it stiffens up," says
Mitchell Anthamatten, assistant professor of chemical engineering and
inventor of the material. "This property can be used to temporarily
hold the material in a deformed shape; and its original shape can be
recalled by heating. Imagine an optical lens that can be triggered to
change shape, a face-mask that can fit any user, or a biomedical
implant that changes shape slow enough for a surgical procedure."
The new rubber functions differently than conventional shape-memory
materials by using "sticker groups" - hydrogen
bonding groups that form temporary bonds. These sticker groups break
and reform constantly. It's akin to tearing a net apart only to find
that new knots have formed between different strands. When the
material is stretched, new bonds form that hold the material,
temporarily, in its deformed shape. Creating the rubber with different
amounts of sticker groups controls the rate at which the rubber
returns to its original shape. With this control, Anthamatten
envisions applications that today's shape-memory polymers simply can't
fulfill.
"The pressure at which you hold together a sutured wound determines a
lot about how it will heal," says Anthamatten. "This polymer could be
made into a thread that responds precisely to body temperature,
tightening the sutures to the perfect pressure."
Anthamatten is currently investigating how dyes diffuse through his
networks. "We expect the rate of dye diffusion to increase with
temperatures," says Anthamatten. This property may enable "smart"
labels that account for time and temperature and can inform customers
when products are about to expire. "We may not always have to rely on
the expiration date. What if our milk was not refrigerated properly?
What if the air conditioner failed for some time at the pharmacy?
People want to know that their products are fresh."
One aspect of the clear rubber that surprised Anthamatten was how easy
it is to make. "It's ridiculously simple," he says, "and we're
fascinated by how small modifications lead to major changes in how the
material behaves."
Further Information and Source:
-
J. Li, J. A. Viveros, M. H. Wrue, M. Anthamatten: Shape-Memory Effects in Polymer Networks Containing Reversibly
Associating Side-Groups.
In: Advanced Materials; Volume 19, Issue 19 , Pages 2851 -
2855;
DOI
10.1002/adma.200602260.
-
Source: The
University of
Rochester is one of the nation's leading private universities.
Located in Rochester, N.Y., the University gives students
exceptional opportunities for interdisciplinary study and close
collaboration with faculty through its unique cluster-based
curriculum. Its College of Arts, Sciences, and Engineering is
complemented by the Eastman School of Music, Simon School of
Business, Warner School of Education, Laboratory for Laser
Energetics, Schools of Medicine and Nursing, and the Memorial Art
Gallery.
