Bone and Bone Surrogate Fragmentation Under Dynamic Compression

Abstract

The rate-dependent compressive response and resulting fragmentation characteristics of dry ox cortical bone and cyanoacrylate-based cortical bone surrogate material was investigated in two material orientations. Tests were conducted under quasi-static (10−3 s−1) and dynamic (103 s−1) loading in the longitudinal and transverse direction with respect to the osteon and die-press orientation. The fragments resulting from dynamic loading were analyzed by fitting 2D ellipses of representative distributions using post-mortem optical microscopy, and are related to existing flaws in the microstructure and the energetics of dynamic fracture evolution. The compressive strength of the bone surrogate increases 20–27 % (±7 %) from quasi-static to dynamic when loaded in either the longitudinal or transverse orientation, while the compressive strength of the ox bone increased 43–66 % (±9 %). Resulting bone fragments had a mean size of 266 ± 28 μm for longitudinal and 410 ± 19 μm for transverse loading, while the bone surrogate produced larger fragments with mean sizes of 431 ± 14 μm for longitudinal and 694 ± 25 μm for transverse. Fragment size distributions exhibit a power-law dependence on length, as the onset of fracture asymptotes to a range of length scales where the fragmentation is self-similar and fractal. Pre- and post-mortem scanning electron microscopy reveals that the bone surrogate has pre-existing flaws of pores and microcracks in a nominally homogeneous microstructure which resulted in a larger characteristic fragmentation length, whereas the ox bone has an inherently anisotropic composition that resulted in fragments linked to microstructural features of the internal canal system.