Conventional AFM, which generates high-resolution images by "feeling" the surface of a sample with a tiny probe tip, can also be used to subject samples to cyclic loading to measure their nanomechanical properties. But conventional AFM can apply only up to about 300 hertz (cycles per second). Hadi Tavakoli Nia, the lead author of the paper, and Iman Soltani Bozchalooi, both graduate students in mechanical engineering, developed a modified system that can apply much higher frequencies up to 10 kilohertz, frequencies relevant to impact loading of joints.
'A very floppy sponge'
Using this system, the researchers compared normal cartilage and cartilage treated with an enzyme that destroys GAG chains, mimicking the initial stages of osteoarthritis. In this early phase, collagen, which gives cartilage its structure, is usually still intact.
The researchers found that when exposed to very high loading rates similar to what would be seen during running or jumping normal cartilage was able to absorb fluid and stiffen normally. However, in the GAG-depleted tissue, fluid leaked out rapidly.
"That's what puts the collagen in trouble, because now this becomes a very floppy sponge, and if you load it at higher rates the collagen network can be damaged," Grodzinsky says. "At that point you begin an irreversible series of activities that can result in damage to the collagen and eventually osteoarthritis."
There is currently no good way to diagnose arthritis during those early stages, which are usually painfree. Many researchers ar
|Contact: Sarah McDonnell|
Massachusetts Institute of Technology