Optimization of digital volume correlation computation in SR‐microCT images of trabecular bone and bone‐biomaterial systems

Abstract

A micromechanical characterization of biomaterials for bone tissue engineering is essential to understand the quality of the newly regenerated bone, enabling the improvement of tissue regeneration strategies. A combination of microcomputed tomography in conjunction with in situ mechanical testing and digital volume correlation (DVC) has become a powerful technique to investigate the internal deformation of bone structure at a range of dimensional scales. However, in order to obtain accurate three-dimensional strain measurement at tissue level, high-resolution images must be acquired, and displacement/strain measurement uncertainties evaluated. The aim of this study was to optimize imaging parameters, image postprocessing and DVC settings to enhance computation based on 'zero-strain' repeated high-resolution synchrotron microCT scans of trabecular bone and bone-biomaterial systems. Low exposures to SR X-ray radiation were required to minimize irradiation-induced tissue damage, resulting in the need of advanced three-dimensional filters on the reconstructed images to reduce DVC-measured strain errors. Furthermore, the computation of strain values only in the hard phase (i.e. bone, biomaterial) allowed the exclusion of large artefacts localized in the bone marrow. This study demonstrated the suitability of a local DVC approach based on synchrotron microCT images to investigate the micromechanics of trabecular bone and bone-biomaterial composites at tissue level with a standard deviation of the errors in the region of 100 microstrain after a thorough optimization of DVC computation. LAY DESCRIPTION: Understanding the quality of newly regenerated bone after implantation of novel biomaterials is essential to improve bone tissue engineering strategies and formulation of biomaterials. The relationship between microstructure and mechanics of bone has been previously addressed combining microcomputed tomography with in situ mechanical testing. The addition of an image-based experimental technique such as digital volume correlation (DVC) allows to characterize the deformation of materials in a three-dimensional manner. However, in order to obtain accurate information at the micro-scale, high-resolution images, obtained for example by using synchrotron radiation microcomputed tomography, as well as optimization of the DVC computation are needed. This study presents the effect of different imaging parameters, image postprocessing and DVC settings for as accurate investigation of trabecular bone structure and bone-biomaterial interfaces. The results showed that when appropriate image postprocessing and DVC settings are used DVC computation results in very low strain errors. This is of vital importance for a correct understanding of the deformation in bone-biomaterial systems and the ability of such biomaterials in producing new bone comparable with the native tissue they are meant to replace.

Full-Field Strain Analysis of Bone–Biomaterial Systems Produced by the Implantation of Osteoregenerative Biomaterials in an Ovine Model

“…The exposure time was set to 64 ms per projection in order to minimise irradiationinduced damage during image acquisition 62 . The propagation distance (sample to detector) was set to 150 mm to provide sufficient in-line phase contrast and better visualise the microstructure 55 . The projection images were flat-field and dark-field corrected prior to reconstruction.…”

“…This problem can be overcome using synchrotron radiation (SR) based microCT, to access fast imaging with high spatial resolution and SNR [49][50][51] . Additionally, DVC based on SR-microCT images has recently been proven to provide reliable strain measurements at the tissue level [52][53][54] , suggesting that an accurate 3D full-field strain evaluation can be obtained at bone-biomaterial interfaces 55 .…”

Anisotropic Crack Propagation and Deformation in Dentin Observed by Four-Dimensional X-ray Nano-Computed Tomography

“…DaVis software is based on a local approach operating on the intensity values (grey-scale) of 3D images, which has been extensively used in hard tissue biomechanics [52,57,58]. Details of the operating principles and algorithm are detailed elsewhere [59]. The volumes were correlated using a multi-pass scheme with a final sub-volume of 48 voxels ($3 mm), reached via predictor passes using sub-volumes of 144, 72, 64 and 56 voxels with a 0% overlap.…”

Preface to ToScA 2017 special issue

“…Advances on the use of in situ XCT mechanics and DVC were reported for bone and bone‐biomaterial systems at tissue level as shown in Fig. (Peña Fernández et al., ).…”

“…3D strain error distribution (ezz) ranging from ‐300 (blue) to 300 (red) microstrain in a bone‐biomaterial system produced in vivo (ovine model) after the implantation of an osteoregenerative biomaterial. Lower strain values are observed in regions of bone‐biomaterial integration (bottom) compared to regions of greater remodelled trabecular bone (top) (Peña Fernández et al., ).…”