The combined strength, flexibility and lightness of our bones outdoes all our synthetic building materials. A shin bone can bear thirty times the weight of the person standing on it. A piece of iron is no stronger, but has the disadvantage of being far too heavy and rigid to take the stresses of the body in motion.
It’s only recently that we have found some clues as to why our bones are so resilient. Bones are composite materials. They are made of a combination of mineral crystals, a form of calcium phosphate and collagen. The natural polymer, collagen, forms a toughening network of fibres which holds the bone together.
New findings indicate that bone’s resilience comes largely from the way the chemical bonds, in the collagen molecules, break easily on impact and quickly dissipate energy. This occurs before forces can build up enough to break the carbon backbone of the collagen molecule. The collagen bonds really sacrifice themselves to preserve the polymer network.
As we age, our bones become brittle. A clumsy, young child has bones that are still soft enough to absorb considerable jolting without breaking. As children grow, their bones harden as the rubbery cartilage is slowly replaced by rigid material of bone tissue.
So next time you take a tumble, be thankful for those collagen bonds, which take the worst of your fall.
