Abstract
A deeper understanding of the cartilage-bone mechanics is fundamental to unravel onset and progression of osteoarthritis, enabling better diagnosis and treatment. The aim of this study is therefore to explore the capability of X-ray computed (XCT) phase-contrast imaging in a lab-based system to enable digital volume correlation (DVC) measurements of unstained cartilage-bone plugs from healthy adult bovines. DVC strain uncertainties were computed for both articular cartilage and mineralized tissue (calcified cartilage and subchondral bone) in the specimens at increasing propagation distances, ranging from absorption up to four times (4× such effective distance. In addition, a process of dehydration and rehydration was proposed to improve feature recognition in XCT of articular cartilage and mechanical properties of this tissue during the process were assessed via micromechanical probing (indentation), which was also used to determine the effect of long X-ray exposure. Finally, full-field strain from DVC was computed to quantify residual strain distribution at the cartilage-bone interface following unconfined compression test (ex situ). It was found that enhanced gray-scale feature recognition at the cartilage-bone interface was achieved using phase-contrast, resulting in reduced DVC strain uncertainties compared to absorption. Residual strains up to ~7000 µε in the articular cartilage were transferred to subchondral bone via the calcified cartilage and micromechanics revealed the predominant effect of long phase-contrast X-ray exposure in reducing both stiffness and hardness of the articular cartilage. The results of this study will pave the way for further development and refinement of the techniques, improving XCT-based strain measurements in cartilage-bone and other soft-hard tissue interfaces.
Highlights
Osteoarthritis (OA) is one of the most prevalent and disabling chronic degenerative diseases with a7-fold increase in its incidence predicted by 2030 [1]
REVIEWosteocyte and hypertrophic chondrocyte lacunae was observed mineralized tissue for all specimens, enhancement of chondrocyte organization mineralized tissue for all specimens, enhancement of chondrocyte organization in in articular cartilage was mostly detected with specimen kept moist throughout the duration of the articular cartilage was mostly detected with specimen kept moist throughout the duration of the experiment (Figure 2a–c)
Typical(median trend observed inof the threemineralized specimens) of the articular cartilage (Figure followed the same typical trend observed in tissue (Figure 3b,d), in which strain errors decreased with the Digital volume correlation (DVC) sub‐volume size
Summary
Osteoarthritis (OA) is one of the most prevalent and disabling chronic degenerative diseases with a7-fold increase in its incidence predicted by 2030 [1]. Experimental strains in articular cartilage were mainly limited to two-dimensional (2D) image analysis (i.e., via digital image correlation (DIC) [4,5]) of local regions of the tissue, where their full interplay and extent in the cartilage-bone unit could not be interrogated. Digital volume correlation (DVC) using contrast-enhanced high-resolution X-ray computed tomography (XCT), where both the soft and calcified tissues can be visualized, would be able to capture the three-dimensional (3D) full-field strain distribution at the cartilage-bone interface over applied loads. XCT-based DVC has been previously used to assess strain evolution in bone [6,7] and bone-biomaterial systems [8,9] under different loading conditions, including residual strains [10,11].
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