R&D DIGEST

More-complete diagnoses and
treatments for bone diseases
could be achieved by analyzing a sample
of bone that is only 2 μm wide. Researchers
from the Harvard-MIT
Division of Health Sciences and Technology
(HST; Cambridge, MA) were
able to assess the mechanical properties
of bones and draw conclusions on
bone health from such samples.

The bone probe used by the MIT
team enabled the researchers to examine
collagen embedded within the
bone minerals at the nanoscale. This
helped them to understand energy absorption
and could lead to tougher materials
for implants.

“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,” explains
Christine Ortiz. Ortiz is the
study's leader and an associate professor
of materials science and engineering
at HST.

The team found that the mechanical
properties of bone vary greatly within
small regions. Because a variety of disorders
tied to disease or aging lead to
changes in bone structure, the researchers'
discovery of the nonuniformity
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 used a molecular
force probe to extract a bovine bone
fragment and then mapped the stiffness
into 2-D contour maps. Then,
using a formulated computer model,
the team applied the experimental results
to large-scale biomechanical
properties. For example, using the
model, they found that nonuniform
stiffness patterns were beneficial to
bone's ability to absorb energy.

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

The 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.