[Editors] MIT probes bones' tiny building blocks

[Elizabeth Thomson]

MIT News Office
Massachusetts Institute of Technology
Room 11-400
77 Massachusetts Avenue
Cambridge, MA  02139-4307
Phone: 617-253-2700
http://web.mit.edu/newsoffice/www

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MIT probes bones' tiny building blocks
--Work could lead to more effective diagnoses of bone disease
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For Immediate Release
THURSDAY, MAY 24, 2007
Contact: Elizabeth A. Thomson, MIT News Office
Phone: 617-258-5402
Email: thomson at mit.edu

GRAPHIC, PHOTO AVAILABLE

CAMBRIDGE, Mass.-In work that could lead to more effective diagnoses 
and treatments of bone diseases using only a pinhead-sized sample of 
a patient's bone, MIT researchers report a first-of-its-kind analysis 
of bone's mechanical properties.

The work, reported in the May 21 advance online edition of Nature 
Materials, sheds new light on how bone absorbs energy.

The researchers' up-close-and-personal look at bone probes its 
fundamental building block-a corkscrew-shaped protein called collagen 
embedded with tiny nanoparticles of mineral-at the level of tens of 
nanometers, or billionths of a meter. A human hair, by comparison, is 
80,000 nanometers in diameter.

"If you want to investigate the origins of the strength and toughness 
of a material, you probe it at smaller and smaller length scales," 
said co-author Subra Suresh, Ford Professor of Engineering, with 
appointments in materials science and engineering, biological 
engineering, mechanical engineering and the Harvard-MIT Division of 
Health Sciences and Technology. "The methodologies used in this 
research can be employed to assess the quality of bone with extremely 
high precision by providing new and detailed structural and 
mechanical information on the nature of its fundamental constituents."

The insights gained from the work could also lead to the creation of 
new, tougher materials, he said.

The study was led by Christine Ortiz, associate professor of 
materials science and engineering. "The structure, quality and 
integrity of bone change dramatically with age and disease, hence 
understanding the origins of the mechanical properties of this major 
load-bearing, structural tissue in our body is extremely important 
from a medical standpoint," Ortiz said.

Using a table-top instrument called a molecular force probe, which 
uses an extremely small probe tip to poke out a tiny fragment of 
bone, Ortiz and colleagues mapped the stiffness of bovine shin bone 
into complex, colorful, two-dimensional contour maps similar to those 
used by geographers.

The team found that the mechanical properties of bone vary greatly 
within a single region only two micrometers (thousandths of a meter) 
wide. Because a variety of disorders tied to disease or aging lead to 
changes in bone structure, the researchers' discovery of the 
non-uniformity of bone's mechanical properties at very small length 
scales could lead to improved diagnoses of diseases. For example, if 
specific nanoscale patterns of stiffness within bone structure are 
tied to disease or aging, these could potentially be identified 
earlier or provide more conclusive evidence of a disorder.

The researchers also formulated a computer model to study the effects 
of their experimental results on larger-scale biomechanical 
properties. For example, using the model they found that the 
non-uniform stiffness patterns were advantageous to bone's ability to 
absorb energy.

"We tend to think that if a material is non-uniform, it is not as 
tough," Suresh said. "This work shows otherwise. Our thesis is that 
nature, by making bones non-uniform at extremely small length scales 
over the course of millions of years of evolution, has designed bone 
to be able to absorb much more energy than a uniform material with 
the same properties."

"I was surprised that we observed such beautiful and complex 
patterns," Ortiz said. "Cells sense and respond to stresses in their 
environment. Since different local mechanical properties in bone 
change the magnitude of stresses around the cell, the cells' behavior 
can be altered in response, thereby affecting the health of the 
tissue."

In addition, the team's results could lead to new ways of producing 
improved structural composites that mimic nature's clever design that 
allows bones to resist sudden fractures; to "fail gracefully," as 
Suresh put it. For example, certain kinds of a new class of materials 
called nanocomposites are composed of a polymer or metallic matrix 
filled with nanoscale particles randomly distributed or periodically 
spaced. "There may be ways to disperse particles non-uniformly that 
may lead to improved material toughness," Suresh said.

Ortiz' and Suresh's colleagues on the work are Kuangshin Tai, a 
recent MIT Ph.D. graduate; research scientist Ming Dao of the 
Department of Materials Science and Engineering; and Ahmet Palazoglu 
of the University of California at Davis.

Ortiz is currently looking at stem-cell-based, tissue-engineered bone 
in collaboration with Dan Gazit at the Hebrew University of Jerusalem 
to see how similar it is to native bone. She is also applying the new 
analysis and related imaging and simulation techniques to different 
types of mineralized biological materials such as armored scales from 
ancient fish and seashells.

This work was supported by the Whitaker Foundation, the U.S. Army 
Research Office, the MIT Institute for Soldier Nanotechnologies and 
the National Institutes of Health.

--MIT--

Written By Deborah Halber, MIT News Office