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.

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