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Instruments / Technical Area	Publication Details	Published
I13-2-Diamond Manchester Imaging	Low-cycle full-field residual strains in cortical bone and their influence on tissue fracture evaluated via in situ stepwise and continuous X-ray computed tomography Marta Pena Fernandez , Alexander P. Kao , Frank Witte , Hari Arora , Gianluca Tozzi Journal Of Biomechanics DOI: 10.1016/j.jbiomech.2020.110105 Diamond Proposal Number(s): [22575] Open Access Show Abstract ▼ Abstract: As a composite material, the mechanical properties of bone are highly dependent on its hierarchical organisation, thus, macroscopic mechanical properties are dictated by local phenomena, such as microdamage resulting from repetitive cyclic loading of daily activities. Such microdamage is associated with plastic deformation and appears as a gradual accumulation of residual strains. The aim of this study is to investigate local residual strains in cortical bone tissue following compressive cyclic loading, using in situ X-ray computed tomography (XCT) and digital volume correlation (DVC) to provide a deeper insight on the three-dimensional (3D) relationship between residual strain accumulation, cortical bone microstructure and failure patterns. Through a progressive in situ XCT loading-unloading scheme, localisation of local residual strains was observed in highly compressed regions. In addition, a multi-scale in situ XCT cyclic test highlighted the differences on residual strain distribution at the microscale and tissue level, where high strains were observed in regions with the thinnest vascular canals and predicted the failure location following overloading. Finally, through a continuous in situ XCT compression test of cycled specimens, the full-field strain evolution and failure pattern indicated the reduced ability of bone to plastically deform after damage accumulation due to high number of cyclic loads. Altogether, the novel experimental methods employed in this study, combining high-resolution in situ XCT mechanics and DVC, showed a great potential to investigate 3D full-field residual strain development under repetitive loading and its complex interaction with bone microstructure, microdamage and fracture.	Oct 2020
I13-2-Diamond Manchester Imaging	Uncertainties of Synchrotron microCT-based Digital Volume Correlation bone strain measurements under simulated deformation F. Comini , M. Palanca , L. Cristofolini , E. Dall'Ara Journal Of Biomechanics DOI: 10.1016/j.jbiomech.2019.01.041 Diamond Proposal Number(s): [10315] Show Abstract ▼ Abstract: Digital Volume Correlation (DVC) is used to measure internal displacements and strains in bone. Recent studies have shown that synchrotron radiation micro-computed tomography (SR-microCT) can improve the accuracy and precision of DVC. However, only zero-strain or virtually-moved test have been used to quantify the DVC uncertainties, leading to potential underestimation of the measurement errors. In this study, for the first time, the uncertainties of a global DVC approach have been evaluated on repeated SR-microCT scans of bovine cortical bone (voxel size: 1.6μm), which were virtually deformed for different magnitudes and along different directions. The results showed that systematic and random errors of the normal strain components along the deformation direction were higher than the errors along unstrained directions. The systematic percentage errors were smaller for larger virtual deformations. The random percentage error was in the order of 10% of the virtual deformation. However, higher errors were localized at the boundary of the volumes of interest, perpendicular to the deformation direction. When only the central region of the samples was considered (100 micrometers layers removed from the borders where the deformation was applied), the errors in the direction of virtual deformation were comparable to the errors in the unstrained directions. In conclusion, the method presented to estimate the uncertainties of DVC is suitable for testing anisotropic specimens as cortical bone. The good agreement between the uncertainties in measurements of strain components obtained with this approach and with the simpler zero-strain-test suggests that the latter is adequate in the tested deformation scenarios.	Jan 2019
I13-2-Diamond Manchester Imaging	Local displacement and strain uncertainties in different bone types by digital volume correlation of synchrotron microtomograms Marco Palanca , Andrew J. Bodey , Mario Giorgi , Marco Viceconti , Damien Lacroix , Luca Cristofolini , Enrico Dall'Ara Journal Of Biomechanics DOI: 10.1016/j.jbiomech.2017.04.007 Diamond Proposal Number(s): [10315] Open Access Show Abstract ▼ Abstract: Understanding bone mechanics at different hierarchical levels is fundamental to improve preclinical and clinical assessments of bone strength. Digital Volume Correlation (DVC) is the only experimental measurement technique used for measuring local displacements and calculating local strains within bones. To date, its combination with laboratory source micro-computed tomography (LS-microCT) data typically leads to high uncertainties, which limit its application. Here, the benefits of synchrotron radiation micro-computed tomography (SR-microCT) for DVC are reported. Specimens of cortical and trabecular bovine bone and murine tibiae, were each scanned under zero-strain conditions with an effective voxel size of 1.6 micrometers. In order to consider the effect of the voxel size, analyses were also performed on downsampled images with voxel size of 8 micrometers. To evaluate displacement and strain uncertainties, each pair of tomograms was correlated using a global DVC algorithm (ShIRT-FE). Displacement random errors for original SR-microCT ranged from 0.024 to 0.226 micrometers, depending on DVC nodal spacing. Standard deviation of strain errors was below 200 microstrain (ca. 1/10 of the strain associated with physiological loads) for correlations performed with a measurement spatial resolution better than 40 micrometers for cortical bovine bone (240 micrometers for downsampled images), 80 micrometers for trabecular bovine bone (320 micrometers for downsampled images) and murine tibiae (120 micrometers for downsampled images). This study shows that the uncertainties of SR-microCT-based DVC, estimated from repeated scans, are lower than those obtained from LS-microCT-based DVC on similar specimens and low enough to measure accurately the local deformation at the tissue level.	Apr 2017

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