Multiscale Modeling of Collagen Fibril in Bone at Various Crosslink Densities: An Insight into Its Deformation Mechanisms

Multiscale modeling of collagen fibril is carried out by incorporating the material properties of collagen obtained from steered molecular dynamics into the finite element model of collagen fibril with inclusion of crosslinks. The results indicate that the nonbonded interactions between collagen and mineral contribute to the significant enhancement of the elastic modulus of collagen fibril at all the crosslink densities in both the low strain and high strain regimes. The crosslinks are found to play an important role in the mechanical response of collagen fibril, the enhancement in elastic modulus ranging from 5-11% for various crosslink densities compared to the collagen fibril with no crosslinks. Further, two different mechanisms of fibril deformation are described based on the characteristic length of collagen fibril. The deformation mechanism is governed by the pullout between the ends of collagen molecules in the overlap zone, following the breaking of crosslinks, if the effective length is greater than the characteristic length. However, if the effective length is less than the characteristic length the deformation mechanism is influenced by the shearing between the staggered collagen molecules which are adjacent to each other.