|
The silk card above shows diffractive optics entirely constituted by pure silk obtained by pouring silk solution on nanopatterned molds and letting the solution dry and crystallize. The resulting film retains the pattern and is a free-standing optical component so flexible it can be rolled up.
(Fiorenzo Omenetto/Tufts University)
|
Tougher
than a bullet-proof vest yet synonymous with beauty and luxury, silk
fibers are a masterpiece of nature whose remarkable properties have yet
to be fully replicated in the laboratory.
Thanks
to their amazing mechanical properties as well as their looks, silk
fibers have been important materials in textiles, medical sutures, and
even armor for 5,000 years.
Silk
spun by spiders and silk worms combines high strength and
extensibility. This one-two punch is unmatched by synthetics, even
though silk is made from a relatively simple protein processed from
water.
But in recent years scientists have begun to unravel the secrets of silk.
In the July 30, 2010, issue of the journal Science,
Tufts biomedical engineering researchers Fiorenzo Omenetto, Ph.D., and
David Kaplan, Ph.D., report that "Silk-based materials have been
transformed in just the past decade from the commodity textile world to a
growing web of applications in more high technology directions."
Fundamental
discoveries into how silk fibers are made have shown that chemistry,
molecular biology and biophysics all play a role in the process. These
discoveries have provided the basis for a new generation of applications
for silk materials, from medical devices and drug delivery to
electronics.
Edible Optics, Implantable Electronics
The Science
paper notes that the development of silk hydrogels, films, fibers and
sponges is making possible advances in photonics and optics,
nanotechnology, electronics, adhesives and microfluidics, as well as
engineering of bone and ligaments. Because silk fiber formation does not
rely on complex or toxic chemistries, such materials are biologically
and environmentally friendly, even able to integrate with living
systems.
Down
the silk road of the future, Kaplan and Omenetto believe applications
could include degradable and flexible electronic displays for sensors
that are biologically and environmentally compatible and implantable
optical systems for diagnosis and treatment. Progress in "edible optics"
and implantable electronics has already been demonstrated by Kaplan and
Omenetto, John Rogers at the University of Illinois at
Urbana-Champaign, and others.
|
Using biocompatible green processing, silk cocoons can yield a pure silk protein with numerous applications in fields such as medicine and electronics. (Fiorenzo Omenetto/Tufts University)
|
Many
challenges remain. Kaplan and Omenetto say that key questions include
how to fully replicate native silk assembly in the lab, how best to
mimic silk protein sequences via genetic engineering to scale-up
materials production, and how to use silk as a model polymer to spur new
synthetic polymer designs that mimic natural silk's green chemistry.
Techniques
for reprocessing natural silk protein in the lab continue to advance.
Silks are also being cloned and expressed in a variety of hosts,
including E. coli bacteria, fungi, plants and mammals, and through transgenic silkworms.
One
day, efficient transgenic plants could be used to crop silk in much the
same way that cotton is harvested today, the Tufts researchers note in
their paper. In some regions, silk production might create a new
microeconomy, as demand grows and production techniques improve.
"Based
on the recent and rapid progression of silk materials from the ancient
textile use into a host of new high-technology applications, we
anticipate growth in the use of silks in a wide platform of applications
will continue as answers to these remaining questions are obtained,"
say Omenetto and Kaplan.
Kaplan
is chair of the Biomedical Engineering Department at Tufts School of
Engineering and the Stern Family Professor in Engineering. He also
directs the NIH Tissue Engineering Resource Center that involves Tufts
and Columbia University. His work lies at the interface between biology
and materials science and engineering, and he has been studying novel
biomaterials, many of them silk-based, for 30 years. Professor of
Biomedical Engineering Fiorenzo Omenetto is a frequent collaborator with
Kaplan who has pioneered silk optics and use of silk as a green
material for photonics and other high tech applications.
Support
for this research on silk comes from the National Institutes of Health,
National Science Foundation, Air Force Office of Science Research and
the Defense Advanced Research Projects Agency.
Study abstract
Original article
