A microscopic slide showing a region of cancellous bone (blue). The brighter blue regions are more brittle regions where we found cracks more likely to grow. (Credit: Cornell)
The combination of softer surfaces and brittle interior allows cancellous bone to direct cracks to locations where they are less detrimental, allowing the structure to recover its shape, bouncing back, after it breaks.
An image of cancellous bone with regions of microscopic tissue damage shown in green and orange. (Credit: Cornell)
Ashley Torres, a graduate student in biomedical engineering, who was one of two individuals to lead the study, says:
“That’s totally not what we expected from an engineering standpoint. But it allows the material to continue to function after failure.”
Function After Failure
The discovery provides a compelling answer to the long-standing question as to why bones have foam-like regions.
“We used to think that we had cancellous bone for the same reasons that we use foams in engineering, to absorb energy or make the structure more lightweight, but it turns out that cancellous bone does something different, the way cancellous bone breaks actually makes it heal better,” says Hernandez.
An image of a high-resolution finite element model of cancellous bone is shown. The color map indicates the distribution of mechanical stress (red means a highly stressed location). (Credit: Cornell)
Jonathan Matheny the other graduate student leading the project, adds:
“In the future, this could help in the design of new materials that can take advantage of this ‘function after failure.’”
Material heterogeneity in structures, the group proposes, could help mitigate the effects of small structural flaws that are inevitable in manufacturing. Additionally, Matheny says these findings have implications for medicine, to help us identify people at risk for an osteoporosis-related fracture and prescribe drug treatment.
Top Image: Paul R. Odgren, Ph.D., University of Massachusetts Medical School. Image of cartilage (purple and white) from a young mouse femur, osteoclasts (red) surrounding a blood vessel filled with red blood cells (yellow).