Molecular mechanics of mineralized collagen fibrils in bone

TLDR

Bone is a composite of collagen and hydroxyapatite, and its load‑bearing properties depend on a molecular‑scale structure that is not yet fully understood. The study uses full‑atomistic simulations of mineralized collagen to elucidate its tensile mechanics across different mineral densities. The authors model the mineralized collagen matrix at atomic resolution and simulate tensile deformation at multiple mineral densities. The simulations show that increasing mineral density raises the tensile modulus beyond that of pure collagen, with mineral crystals bearing up to four times the stress of collagen fibrils, explaining bone’s enhanced energy dissipation and fracture resistance.

Abstract

Bone is a natural composite of collagen protein and the mineral hydroxyapatite. The structure of bone is known to be important to its load-bearing characteristics, but relatively little is known about this structure or the mechanism that govern deformation at the molecular scale. Here we perform full-atomistic calculations of the three-dimensional molecular structure of a mineralized collagen protein matrix to try to better understand its mechanical characteristics under tensile loading at various mineral densities. We find that as the mineral density increases, the tensile modulus of the network increases monotonically and well beyond that of pure collagen fibrils. Our results suggest that the mineral crystals within this network bears up to four times the stress of the collagen fibrils, whereas the collagen is predominantly responsible for the material's deformation response. These findings reveal the mechanism by which bone is able to achieve superior energy dissipation and fracture resistance characteristics beyond its individual constituents.