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Chemical citrate - a by-product of natural cell metabolism - is mixed with water to create a viscous fluid that is trapped between the nano-scale crystal leading to formation of bones, according to a new research. 

The fluid enables appropriate movement between these crystals making bones flexible enough so that they don't shatter under pressure. The shock absorber in the bone was unknown before until now.

Researchers also noted that if the citrate leaks out the crystals which are made of calcium phosphate fuse together into bigger and bigger clumps that become inflexible. The same could be the root cause of osteoporosis. 

"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," said Dr Melinda Duer, who led the study in a press release.

"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."

Researchers compared it to two panes of glass with water in the middle sticking together but are able to slide. 

"It's the same thing in these flat bone crystals. But you've got to have something that keeps the water there, stops it from drying out and stops the plates from either flying apart or sticking fast together. We now know that thing is citrate," added Duer.

The study is published in the journal Proceedings of the National Academy of Sciences.