Understanding biomineralization at the nanoscale: the mechanism of collagen mineralization

Abstract
The often astonishing materials properties of crystalline biominerals such as bone, teeth and sea shells are generally related to the hierarchical assembly of specifically interacting soft organic and hard inorganic components. The mineralized collagen fibril is the basic building block of our bones and as such lies at the basis of the remarkable mechanical properties of bone. Due to its complex organization, its nanoscopic dimensions and the fact that it consists of both hard and soft components, the detailed analysis of the structure of the mineralized collagen fibril has proven difficult. It is an even more challenging task to unravel the mechanism by which collagen is mineralized, as this occurs on the nanometer scale, through a multistep process and in a complex aqueous multicomponent environment. Understanding the process of collagen mineralization is not only will open the way to the development of new treatments for bone defects and mineralization-related diseases, but will also offer new opportunities for the design of new bio-inspired materials.[1]
The in situ study of the development of mineral formation can make an important contribution to the understanding of the processes involved in biomineralization.[2] Cryogenic transmission electron microscopy (cryoTEM) has been demonstrated as a method to investigate the early stages of mineral formation without removing the developing materials from their aqueous environment. [3] CryoTEM investigations towards the mechanism of bone formation revealed that the mineralization of calcium phosphate confined within the collagen matrix leads to the formation of apatite platelets which are geometrically and crystallographically oriented along the long axis of the collagen. [4] CryoTEM shows that these platelets are preceded by a disordered precursor phases that eventually transform in to the final crystalline material.[5,6] We demonstrate the role of collagen in directing different stages off this process.
Furthermore, we demonstrate that the ability of collagen to direct the shape and orientation of crystals in not restricted to apatite. Crystals of other minerals formed within confinement of the collagen matrix have similar sizes, shapes and orientations and reveal exiting details about the mechanism by which collagen directs the mineralization in bone.