Effects of hydration and mineralization on the deformation mechanisms of collagen fibrils in bone at the nanoscale.

Bone is a biomaterial with a structural load-bearing function. Investigating the biomechanics of bone at the nanoscale is important in application to tissue engineering, the development of bioinspired materials, and for characterizing factors such as age, trauma, or disease. At the nanoscale, bone is composed of fibrils that are primarily a composite of collagen, apatite crystals (mineral), and water. Though several studies have been done characterizing the mechanics of fibrils, the effects of variation and distribution of water and mineral content in fibril gap and overlap regions are unexplored. We investigate how the deformation mechanisms of collagen fibrils change as a function of mineral and water content. We use molecular dynamics to study the mechanics of collagen fibrils of 0 wt%, 20 wt%, and 40 wt% mineralization and 0 wt%, 2 wt%, and 4 wt% hydration under applied tensile stresses. We observe that the stress-strain behavior becomes more nonlinear with an increase in hydration, and an increase in mineral content for hydrated fibrils under tensile stress reduces the nonlinear stress versus strain behavior caused by hydration. The Young's modulus of both non-mineralized and mineralized fibrils decreases as the water content increases. As the water content increases, the gap/overlap ratio increases by approximately 40% for the non-mineralized cases and 16% for the highly mineralized cases. Our results indicate that variations in mineral and water content change the distribution of water in collagen fibrils and that the water distribution changes the deformation of gap and overlap regions under tensile loading.