The imaging involved special preparation of sheep bone samples led by graduate student and first author Garry Brock. First they cut 2 mm square matchstick-like samples.
The matchsticks were "damaged" in the lab at various levels: Some received 20,000 cycles of "loading" in bending; others received a single dose of loading; and others were notched before loading. All samples were treated with a lead-uranyl acetate X-ray negative stain that seeps into porosity caused by damage in the bone tissue. Then sections from the loaded segment were polished to 50-micron thicknesses.
A greater amount of stain was seen in sections subjected to repetitive stress. But instead of seeing new surfaces formed by damage, or cracks, as was expected, the researchers observed damage in the cellular structures. The X-rays picked up the dye within existing, intact structures, like the lacunae where the cells sit, and in the caniliculi.
"The tissue is not breaking, but rather, there is staining within the cells," Brock said.
Added van der Meulen: "We were surprised by how cell-based the staining was, as opposed to forming lots of new surfaces in the material."
In osteoporotic individuals, including many postmenopausal women, fractures usually occur in the forearm, spine and hip. van der Meulen's team is trying to understand why these fractures occur by studying nano- and microscale changes in bone tissue.
They are also exploring the possibility of studying whether a class of osteoporosis drugs called bisphosphonates, which reduce the overall rate of hip fractures but can lead to "atypical femoral fractures," affect nanoscale damage processes. These unusual fractures occur at sites that normally do not fracture with osteoporosis such as in the middle of the bone shaft. The new damage visualization method could lend new insights in future studies.
|Contact: Syl Kacapyr|