Measurement of lacunar bone strains and crack formation during tensile loading by digital volume correlation of second harmonic generation images

Abstract

The maintenance of healthy bone tissue depends upon the ability of osteocytes to respond to mechanical cues on the cellular level. The combination of digital volume correlation and second harmonic generation microscopy offers the opportunity to investigate the mechanical microenvironment of intact bone on the scale of individual osteocytes. Adult human femurs were imaged under tensile loads of 5 and 15MPa and volumes of approximately 492×429×31μm(3) were analyzed, along with an image of a bone microcrack under the same loading conditions. Principal strains were significantly higher in three-dimensional digital volume correlation when compared to two-dimensional digital image correlation. The average maximum principal strain magnitude was 5.06-fold greater than the applied global strain, with peak strains of up to 23.14-fold over global strains measured at the borders of osteocyte lacunae. Finally, a microcrack that initiated at an osteocyte lacunae had its greatest tensile strain magnitudes at the crack expansion front in the direction of a second lacunae, but strain at the crack border was reduced to background strain magnitudes upon breaching the second lacunae. This serveed to demonstrate the role of lacunae in initiating, mediating and terminating microcrack growth.

Digital volume correlation for the characterization of musculoskeletal tissues: Current challenges and future developments

“…One of the main aspects is in relation to how imaging setup and sample preparation could resolve the texture needed to run DVC. This can be done by employing imaging techniques that are historically developed and refined for soft biomaterials (e.g., confocal microscopy, second/third harmonic generation) where DVC has been used, for example, in strain measurements of the extracellular matrix ( Roeder et al, 2004 ), tendons ( Khodabakhshi et al, 2013 ), tendon cell-induced extracellular matrix deformations ( Fung et al, 2018 ), a variety of other soft materials ( Mac Donald and Ravichandran, 2019 ) and even thin sections of bone ( Wentzell et al, 2016 ). Optical coherence tomography (OCT) combined with DVC is also a promising technique to investigate soft tissues.…”