In
nature, some organisms create their own mineralized body parts--such as bone,
teeth and shells--from sources they find readily available in their
environment. Certain sea creatures, for example, construct their shells from
calcium carbonate crystals they build from ions found in the ocean.
"The
organism takes brittle carbonate and turns it into a structural shape that
protects it from predators, and from being bashed against the rocks," says
Lara Estroff, an associate professor of materials science and engineering at
Cornell University. "There is much scientific interest in how the organism
controls the crystal growth, and what mechanisms are involved in strengthening
and toughening the shells, especially in comparison to their components, which
are brittle."
Researchers
such as Estroff are very interested in synthesizing this kind of biology in the
lab, and creating new organic and inorganic materials that mimic the
"biomineralization" that occurs in nature, so they can gain a better
understanding of how these natural processes work.
"We
are trying to learn the techniques from the organisms, and apply them in the
laboratory," says the National Science Foundation (NSF)-funded scientist,
a synthetic chemist by training. "Part of it is creating simplified
systems so that we can tease apart the more complicated mechanisms that are
going on in biology. I am not recreating biology in the lab. I am learning from
biology to create new materials."
Estroff's
primary research
focus is to discover the role of gels in crystal formation. Hydrogels, which
are gels made in water, similar to Jell-O®, are involved in a number of natural
biological systems, including the mother-of-pearl in mollusk shells, tooth
enamel in mammals, even otoconia, which are tiny particles found in human ears.
These substances are composed of both organic and inorganic materials; often the
organic components form a gel. Estroff wants to know their purpose.
"Is
there something special about a hydrogel in directing crystal growth?" she
asks. "Does it change properties? Is it somehow responsible for giving
rise to organic-inorganic composites?"
Understanding
and controlling crystal growth is very important in many industrial fields,
chief among them the manufacture of pharmaceuticals, since many drugs are in
crystalline form, and "it's of vast importance to know how to modulate the
solubility of crystals and how they pack into tablets," she says.
There
also may be potential applications in producing biomaterials for bone and tooth
repair, and in creating more functional inorganic materials, such as substances
structured at the nanoscale that could enhance energy storage, for example in
batteries. "Being able to manipulate these crystal structures down to the
nanoscale opens up a lot of opportunities," she says.
Estroff
is conducting her research
under an NSF Faculty Early Career Development (CAREER) award, which she
received in 2009. The award supports junior faculty who exemplify the role of
teacher-scholars through outstanding research, excellent education and the
integration of education and research within the context of the mission of
their organization. NSF is funding her work with $472,773 over five years.
The
project focuses on observations, both in nature and in the laboratory, of
macroscopic, single crystals with incorporated polymer fibers and other
macromolecules. The project aims to understand the mechanisms by which these
polymer networks become incorporated into macroscopic, single crystals.
Her lab,
in studying crystal growth mechanisms in gels and their relationship to
biomineralization, is trying to answer at least three questions. "First,
what is the internal structure of these crystals, and where does the gel
material become trapped?" she asks. "Second, can we understand the
mechanism of how it is trapped to control how much is trapped? And, third, what
effect does this material have on the mechanical properties of the
crystals?"
To find
the answers, her team developed a synthetic analog to the biological system.
Using agarose, a more purified form of the gel agar-agar, they grew their own
crystals in the lab, then compared them to crystals grown without gel in an
ordinary water-based solution, and later to natural biological crystals.
During
the process, they ran a high resolution electron tomography scan of their
samples, creating a three-dimensional image of the gel-grown crystal, which
"was the first time that people had actually seen how the organic phase
can be incorporated in the crystal," she says. "A crystal is an order
array of ions, and a polymer is a floppy, poorly-defined blob. How do you
accommodate this floppy blob into this ordered array?"
In
comparing their synthetic crystals to natural ones, "there were
similarities and differences," she says. "We now have the best image
of how these objects are incorporated and now can start asking questions about
the structure-property relationships, including how this internal structure
translates into changes in the mechanical properties. We've been poking at the
crystals and looking at the response."
As it
turns out, "these organic inclusions mechanically strengthen and toughen
the material in both biological crystals and synthetic crystals," she
says. "The organic material that is trapped within the crystals makes them
stronger and harder--more resistant to fracture--than their geologic
counterparts with no organic material."
The
researchers' next step is to synthesize other materials. "We'd like to
find out if we can grow different types of crystals in different types of
gels," she says. "We're now pursuing that route."
As part
of the grant's educational component, Estroff teaches a course on
biomineralization for both graduate students and undergraduates. "One of
my goals is to get them reading primary literature and analyzing it," she
says. "They also go out and look for biomineralizing organisms on campus.
They go to local streams and bring them back to the lab."
She also
is trying to recruit more female students to her department. She is the faculty
advisor to a group known as WIMSE, which stands for Women in Materials Science
and Engineering, and has organized a mentoring program where freshmen and
sophomores are paired with juniors and seniors who, in turn, are paired with
graduate students. The enrollment of women in the materials science and
engineering major has grown from 10 percent to 30 percent during the last five
years.
"Having
a group creates a critical mass," she says. "It's really had a
positive impact."
-- Marlene Cimons, National Science
Foundation
Investigators
Lara
Estroff
Related Institutions/Organizations
Cornell
University
Related Awards
#0845212
CAREER: Synthesis, Characterization, and Application of Gel-Grown,
Polymer-Reinforced Single Crystals
Total Grants
$472,773
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