Mechanics of collagen–hydroxyapatite model nanocomposites

• Bone, a hierarchical biological composite, shows many interesting mechanical properties.
• This study focuses on identifying small-scale deformation phenomena.
• We report a molecular study of bone model composite.
• We assess how the geometry of the composite increases the strength and stiffness.
• We find a crucial role of H-bonds in enhancing the toughness.

Bone is a hierarchical biological composite made of a mineral component (hydroxyapatite crystals) and an organic part (collagen molecules). Small-scale deformation phenomena that occur in bone are thought to have a significant influence on the large scale behavior of this material. However, the nanoscale behavior of collagen–hydroxyapatite composites is still relatively poorly understood. Here we present a molecular dynamics study of a bone model nanocomposite that consist of a simple sandwich structure of collagen and hydroxyapatite, exposed to shear-dominated loading. We assess how the geometry of the composite enhances the strength, stiffness and capacity to dissipate mechanical energy. We find that H-bonds between collagen and hydroxyapatite play an important role in increasing the resistance against catastrophic failure by increasing the fracture energy through a stick-slip mechanism.