Davis Sarah, Karali Aikaterina, Zekonyte Jurgita, Roldo Marta, Blunn Gordon
School of Pharmacy and Biomedical Science, University of Portsmouth, Portsmouth, PO1 2DT, UK; School of Mechanical and Design Engineering, University of Portsmouth, PO1 3DJ, UK.
School of Mechanical and Design Engineering, University of Portsmouth, PO1 3DJ, UK.
J Mech Behav Biomed Mater. 2023 Aug;144:105999. doi: 10.1016/j.jmbbm.2023.105999. Epub 2023 Jun 29.
Strain changes at the cartilage-bone interface play a crucial role in osteoarthritis (OA) development. Contrast-Enhanced X-ray Computed Tomography (CECT) and Digital Volume Correlation (DVC) can measure 3D strain changes at the osteochondral interface. Using lab-based CT systems it is often difficult to visualise soft tissues such as articular cartilage without staining to enhance contrast. Contrast-Enhancing Staining Agents (CESAs), such as Phosphotungstic Acid (PTA) in 70% ethanol, can cause tissue shrinkage and alter tissue mechanics. The aims of this study were, firstly, to assess changes to the mechanical properties of osteochondral tissue after staining with a PTA/PBS solution, and secondly, to visualise articular cartilage during loading and with CECT imaging in order to compare strain across the interface in both healthy and OA joints using DVC.
Nanoindentation was used to assess changes to mechanical properties in articular cartilage and subchondral bone before and after staining. Hindlimbs from Dunkin-Hartley guinea pigs were stained with 1% PTA/PBS at room temperature for 6 days. Two consecutive CECT datasets were acquired for DVC error analysis. In-situ compression with a load corresponding to 2x body weight was applied, the specimen was re-imaged, and DVC was performed between the pre- and post-load tomograms.
Nanoindentation before and after PTA/PBS staining showed similar cartilage stiffness (p < 0.05), however, staining significantly decreased the stiffness of subchondral bone (∼9-fold; p = 0.0012). In severe OA specimens, third principal/compressive (ε) strain was 141.7% higher and shear strain (γ) was 98.2% higher in tibial articular cartilage compared to non-OA (2 - month) specimens. A 23.1% increase in third principal stain strain and a 54.5% significant increase in the shear (γ) strain (p = 0.0027) was transferred into the mineralised regions of calcified cartilage and subchondral bone in severe OA specimens.
These results indicate the suitability of PTA in PBS as a contrast agent for the visualisation of cartilage during CECT imaging and allowed DVC computation of strain across the cartilage-bone interface. However, further research is needed to address the reduction in stiffness of subchondral bone after incubation in PBS.
软骨 - 骨界面的应变变化在骨关节炎（OA）发展中起关键作用。对比增强X射线计算机断层扫描（CECT）和数字体积相关（DVC）可测量骨软骨界面的三维应变变化。使用基于实验室的CT系统时，通常很难在不染色以增强对比度的情况下可视化诸如关节软骨之类的软组织。对比增强染色剂（CESA），如70％乙醇中的磷钨酸（PTA），可导致组织收缩并改变组织力学性能。本研究的目的，首先是评估用PTA / PBS溶液染色后骨软骨组织力学性能的变化，其次是在加载过程中以及通过CECT成像可视化关节软骨，以便使用DVC比较健康和OA关节界面处的应变。
使用纳米压痕评估染色前后关节软骨和软骨下骨力学性能的变化。将来自Dunkin - Hartley豚鼠的后肢在室温下用1％PTA / PBS染色6天。获取两个连续的CECT数据集用于DVC误差分析。施加相当于2倍体重的载荷进行原位压缩，对标本重新成像，并在加载前和加载后的断层图像之间进行DVC分析。
PTA / PBS染色前后的纳米压痕显示软骨硬度相似（p <0.05），然而，染色显著降低了软骨下骨的硬度（约9倍；p = 0.0012）。在严重OA标本中，与非OA（2个月）标本相比，胫骨关节软骨中的第三主应变/压缩应变（ε）高141.7％，剪切应变（γ）高98.2％。在严重OA标本中，第三主应变增加23.1％，剪切应变（γ）显著增加54.5％（p = 0.0027），并传递到钙化软骨和软骨下骨的矿化区域。
这些结果表明PTA在PBS中作为CECT成像期间软骨可视化的造影剂是合适的，并允许通过DVC计算软骨 - 骨界面的应变。然而，需要进一步研究以解决在PBS中孵育后软骨下骨硬度降低的问题。
