Large Deformation Mechanisms, Plasticity, and Failure of an Individual Collagen Fibril With Different Mineral Content

Abstract

Mineralized collagen fibrils are composed of tropocollagen molecules and mineral crystals derived from hydroxyapatite to form a composite material that combines optimal properties of both constituents and exhibits incredible strength and toughness. Their complex hierarchical structure allows collagen fibrils to sustain large deformation without breaking. In this study, we report a mesoscale model of a single mineralized collagen fibril using a bottom‐up approach. By conserving the three‐dimensional structure and the entanglement of the molecules, we were able to construct finite‐size fibril models that allowed us to explore the deformation mechanisms which govern their mechanical behavior under large deformation. We investigated the tensile behavior of a single collagen fibril with various intrafibrillar mineral content and found that a mineralized collagen fibril can present up to five different deformation mechanisms to dissipate energy. These mechanisms include molecular uncoiling, molecular stretching, mineral/collagen sliding, molecular slippage, and crystal dissociation. By multiplying its sources of energy dissipation and deformation mechanisms, a collagen fibril can reach impressive strength and toughness. Adding mineral into the collagen fibril can increase its strength up to 10 times and its toughness up to 35 times. Combining crosslinks with mineral makes the fibril stiffer but more brittle. We also found that a mineralized fibril reaches its maximum toughness to density and strength to density ratios for a mineral density of around 30%. This result, in good agreement with experimental observations, attests that bone tissue is optimized mechanically to remain lightweight but maintain strength and toughness. © 2015 The Authors. Journal of Bone and Mineral Research published by Wiley Periodicals, Inc. on behalf of American Society for Bone and Mineral Research (ASBMR).

A generalized inelastic modeling concept for soft fibrous tissues

“…During the preconditioning phase, the baseline test, and during the holding phase less than 13 % intermolecular bonds failed. This behavior is in line with results of previous studies suggesting that intermolecular bond rupture and molecular failure are prevalent mainly under large deformations . Accordingly, the amount of damaged molecules during the baseline test is negligible (see Figure A).…”

Multiscale characterization of cortical bone composition, microstructure, and nanomechanical properties in experimentally induced osteoporosis

“…Incorporation of mineral into the collagen fibril increases its strength up to 10 times and its toughness up to 35 times, and the mineralized fibril reaches its maximum toughness‐to‐density and strength‐to‐density ratios at a mineral density of ∼30%. The addition of crosslinks makes the mineralized fibril stiffer but more brittle . Furthermore, without extreme alterations in the stoichiometry of the mineral phase, high mineral content is not only associated with large increases in stiffness and hardness, but also contributes to a loss of strength and toughness .…”

“…The addition of crosslinks makes the mineralized fibril stiffer but more brittle. 4 Furthermore, without extreme alterations in the stoichiometry of the mineral phase, high mineral content is not only associated with large increases in stiffness and hardness, but also contributes to a loss of strength and toughness. 5 Indeed, bone mechanics exhibit different behavior at different length scales.…”

Osseointegration of 3D printed microalloyed CoCr implants—Addition of 0.04% Zr to CoCr does not alter bone material properties

“…The mechanical properties of bone are determined by the overall phosphate content, that is, the apatite‐to‐collagen ratio. At a mineral density around 30%, the mineralized collagen fibril reaches its maximum toughness‐to‐density and strength‐to‐density ratios . The dimensions of bone apatite crystallites are constrained to the nanometer scale by the high carbonate content, but despite increased carbonate‐to‐phosphate ratios, the mineral crystallinity of bone mineral may remain unaffected .…”