A somewhat technical question for all Anatomy experts

Bone is a mixture of mineral crystals that are suspended in an organic collagen matrix. The crystals provide 'stiffness', or skeletal rigidity, explains Professor John Currey from the University of York in an accompanying article.

These crystals are very rigid, but cannot dissipate much energy. The collagen matrix is what makes bones 'tough' — that is, able to absorb impacts and resist the weakening effects of small scratches and holes. Until now not much has been known about this mechanism.

The researchers used a diamond to manipulate the collagen from bone while they observed it under an atomic force microscope. They stretched the collagen to measure how much force was needed to stretch it, and how far it would go.

They also pushed the diamond into the surface of the bone and measured how long it took to move back into shape.

What they found was that the collagen kept stretching. And each time they went back to the collagen, it would stretch more easily. This indicated that some of the bonds in the collagen were being broken. It seems, too, that some of these bonds reform after the pressure comes off, meaning the bone is able to repair itself to some extent.

This mechanism is very similar to something the same group had already observed in abalone.

“Bone, like abalone nacre, contains polymers with sacrificial bonds,” they write in the paper.

Nacre is the substance that forms over a piece of grit to create pearls. The researchers describe abalone nacre as a biocomposite material with 'remarkable toughness'.

In order to find out more about how the bonds work, the group 'marinated' the collagen in different substances and tried the experiments again. The collagen became harder to stretch after it has been soaked in divalent calcium ions than when it had been soaked in monovalent sodium ions.

Divalent ions can link molecules together. “This suggests that some kind of ionic bond between charged residues in collagen might be responsible for reconnecting the individual collagen molecules to each other,” explained Professor Currey.

Having read that earlier today, I have been doing a lot of thinking about factors that might have an impact on the ability to deform collagenous tissues. I know there are 5 primary types (classifications) of collagen. I am unsure if the collagen in bones (like the collagen used in the cited study) and the collagen in connective tissue are of the same type, but I would assume if anything that the collagen in bones would be tougher and more resistant to deformation even if it were a different type. These divalent ions which are spoken of, are these just naturally occuring free radicals in calcium? Is it plausible that calcium sources would cause more of these ions to be available to the body and become trapped within the collagen matrix of other collagenous tissues (thus making them tougher to stretch and more resistant to change)? Go easy on me if these are dumb questions as Biology/Anatomy is not a branch of science I have studied extensively … I’m more of a Chemistry and Physics kind of guy.

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