In situ characterization of nanoscale strains in loaded whole joints via synchrotron X-ray tomography

Abstract

Imaging techniques for quantifying how the hierarchical structure of deforming joints changes are constrained by destructive sample treatments, sample-size restrictions and lengthy scan times. Here, we report the use of fast, low-dose pink-beam synchrotron X-ray tomography combined with mechanical loading at nanometric precision for the in situ imaging, at resolutions lower than 100 nm, of mechanical strain in intact untreated joints under physiologically realistic conditions. We show that, in young, aged, and osteoarthritic mice, hierarchical changes in tissue structure and mechanical behaviour can be simultaneously visualized, and that tissue structure at the cellular level correlates with whole-joint mechanical performance. We also used the tomographic approach to study the co-localization of tissue strains to specific chondrocyte lacunar organizations within Users may view, print, copy, and download text and data-mine the content in such documents, for the purposes of academic research, subject always to the full Conditions of use:

Exploratory Full-Field Mechanical Analysis across the Osteochondral Tissue—Biomaterial Interface in an Ovine Model

“…In comparison at the same subvolume size we calculated cartilage strain MAER of 0.12% strain (1200 µε), bone MAER of under 0.04% strain (400 µε), cartilage SDER of under 0.08% (800 µε) and bone SDER of under 0.04% (400 µε). The cartilage MAER we calculated was over twice as large as in the previous study, though well within the allowable range [ 15 ]. Bone MAER was comparable between both studies whilst SDER for both components was considerable higher in our study.…”

“…Despite imperfect scaffold placement, the technique developed in this preliminary study provided valuable insights into relative micromotion of the system components. We present a sample preparation and micro-CT scanning protocol ( Figure 7 ) using only laboratory equipment and avoiding the need to access synchrotrons which has been noted as a limitation [ 15 ]. Visualisation of displacement and strain within the system was possible including quantification of local strain concentrations ( Figure 4 ) and micromotion ( Figure 5 ).…”

“…This could ultimately increase efficacy of regenerative medicine solutions by enabling optimisation of strain-matching, fixation methods to limit micromotion, and ensuring local implant behaviour is compatible with the surrounding tissue. Quantified displacement and strain errors within all tissue and biomaterial components of the system were within acceptable limits ( Figure 6 ) [ 15 , 20 ]. It is possible that the magnitude of errors could be further reduced by further optimising the DVC steps [ 20 ] or image filtering [ 29 ].…”

“…Following optimisation of the DVC calculation technique and subvolume size using the error quantification, the loading scenario image stacks (unloaded-load1-load2) were processed in accordance with the maximum acceptable error set as 10% of the nominal strain [ 15 ]. For this osteochondral system, the highest nominal strain applied to a component of interest was approximately 2.5%; therefore, the maximum acceptable error was set as 0.25% strain (2500 µS).…”

“…The technique enabled non-destructive mechanical evaluation of the tissue and ultimately provided 3D strain maps for the first time [ 14 ]. In the last 20 years, DVC has provided the opportunity to characterise mechanics such as: strain across the osteochondral interface [ 15 , 16 ] examining ex vivo explants to quantify bone-implant micromotion [ 17 ], bone cement implantation [ 18 ] and cementless implant press-fitting [ 19 ]. Following sample retrieval, ex vivo analysis has taken place on bone-biomaterial systems for tissue regeneration [ 20 ], the stability of bone-screw systems [ 21 ] and newly formed bone tissue [ 22 ].…”