Bone is a composite material that is mainly made of proteins and minerals. Osteogenesis gives rise to the unique hierarchical structures of the bone with the basic constituents of collagen, minerals, noncollagenous proteins (NCP), and water. NCPs, with \~1% of the bone weight, mostly exist in the interfibrillar interface and function as “natural glue” to bond the microfibrils together. Given the significant challenges in experimentally measuring the mechanical properties of the collagen and interfibrillar interface, there is a continuing interest in developing computational modeling approaches to study the mechanics of collagen. At the nanoscale, the interfibrillar interfaces are primarily made of noncollagenous proteins such as OPN and OC, which are known to be closely linked to biomineralization and bone remodeling. Although these interfaces occupy very small volume by percentage (\~3%) in bone, there are growing evidences suggesting that the noncollagenous OC/OPN protein complexes in the collagen interfibrillar interface contribute significantly to the bone toughness and provides an important mechanism for energy dissipation when bone is subjected to deformation and fracture. Motivated by the current developments, we established a computational model to quantify the role of noncollagenous OC/OPN protein complex in collagen interfibrillar interface \[1, 2\].  Molecular model of the collagen interfibrillar interface was constructed in the form of composite of OC/OPN sandwiched between two HAP mineral platelets. Mechanical response and deformation mechanisms were subsequently investigated by applying two types of loading conditions, i.e., simple shear and uniaxial tension to the interface. Simulation results revealed synergistic effects of OC and OPN that enable the interface to dissipate large amount of energy before complete failure. More specifically, OC facilitates the load transfer between the OPN chain and the HAP mineral platelets, while OPN is mainly responsible for the unusually high ductility of the interface. This finding provided a key molecular mechanism that is responsible for bone toughness. The established computational model also provided a great deal of details on the mechanical responses at the sub-nanometer scale that were employed to test several hypotheses that have been proposed based on experimental evidence.

 

Reference:

\[1\]       Y. Wang, R. Morsali, Z. Dai, M. Minary-Jolandan, and D. Qian, "Computational Nanomechanics of Noncollagenous Interfibrillar Interface in Bone," *ACS Applied Materials & Interfaces,* vol. 12, pp. 25363-25373, 2020/06/03 2020.

\[2\]       R. Morsali, Z. Dai, Y. Wang, D. Qian, and M. Minary-Jolandan, "Deformation Mechanisms of “Two-Part” Natural Adhesive in Bone Interfibrillar Nano-Interfaces," *ACS Biomaterials Science & Engineering,* vol. 5, pp. 5916-5924, 2019/11/11 2019.


Multiscale Mechanics of Noncollagenous Interfibrillar Interface in Bone

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Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2020/volume/84478

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