Professor Markus Buehler of MIT`s Department of Civil and Environmental Engineering has revealed for the first time the role of bone`s atomistic structure in a toughening mechanism that incorporates two theories previously proposed by researchers eager to understand the secret behind the material`s lightweight strength. He studied the molecular structure of the mineralized collagen fibrils that make up level 2 bone, hoping to find the mechanism behind bone`s strength, which is considerable for such a lightweight, porous material. When pressure is applied to the fabric-like fibrils, some of the weak bonds between the collagen molecules and crystals break, creating small gaps or stretched areas in the fibrils. This stretching spreads the pressure over a broader area, and in effect, protects other, stronger bonds within the collagen molecule itself, which might break outright if all the pressure were focused on them. The stretching also lets the tiny crystals shift position in response to the force, rather than shatter, which would be the likely response of a larger crystal.