Many of us have suffered from broken bones, but it's rare, outside of the most serious accidents, for bones to ever shatter. Now, researchers have worked out why: because our bones, it turns out, are filled with goo.
Researchers at the University of Cambridge have discovered that much of the mineral content from which bones are made is actually in the form of a goo, which sits trapped between tiny crystals, lubricating them—and, crucially, allowing for small movements. It's that flexibility that stops our bones from shattering, according the work they've published in the Proceedings of the National Academy of Sciences.
The goo is made from citrate—a by-product of cell metabolism—mixed with water. It's a viscous fluid, and a thin layer of it sits between the nanocrystals—made of calcium phosphate—which make up the solid aspect of our bones. There's enough of it, though, to provide slip between the crystals, which absorbs the energy of impact that would otherwise shatter a solid piece of the crystal bone structure. Dr Melinda Duer, one of the researchers, explains:
"Bone mineral was thought to be closely related to this substance called hydroxyapatite. But what we've shown is that a large part of bone mineral – possibly as much as half of it in fact – is made up of this goo, where citrate is binding like a gel between mineral crystals. This nano-scopic layering of citrate fluid and mineral crystals in bone means that the crystals stay in flat, plate-like shapes that have the facility to slide with respect to each other. Without citrate, all crystals in bone mineral would collapse together, become one big crystal and shatter. It's this layered structure that's been missing from our knowledge, and we can now see that without it you're stuffed."
In fact, the researchers have observed that when the goo escapes, leaving just crystals, they fuse together, forming large brittle clumps that can shatter. They reckon that this could be what causes osteoporosis. The new finding, then, isn't just interesting; it could change the way we think about brittle bones diseases and, with any luck, inspire new treatments, too. [PNAS via Cambridge University]
Image by Moody Man Chang under Creative Commons license