Department of Biomedical Engineering, University of California, Irvine, Irvine, California, USA.
Tissue Eng Part C Methods. 2021 Apr;27(4):276-286. doi: 10.1089/ten.TEC.2020.0367.
The surface of articular cartilage is integral to smooth, low-friction joint articulation. However, the majority of cartilage literature rarely includes measurements of surface characteristics and function. This may, in part, be due to a shortage of or unfamiliarity with fast, nondestructive, and, preferably, noncontact methods that can be applied to large cartilage surfaces for evaluating cartilage surface characteristics. A comprehensive methodology for characterizing cartilage surfaces is useful in determining changes in tissue function, as for example, in cases where the quality of cartilage grafts needs to be assessed. With cartilage storage conditions being an area of ongoing and active research, this study used interferometry and tribology methods as efficient and nondestructive ways of evaluating changes in cartilage surface topography, roughness, and coefficient of friction (CoF) resulting from various storage temperatures and durations. Standard, destructive testing for bulk mechanical and biochemical properties, as well as immunohistochemistry, were also performed. For the first time, interferometry was used to show cartilage topographical anisotropy through an anterior-posterior striated pattern in the same direction as joint articulation. Another novel observation enabled by tribology was frictional anisotropy, illustrated by a 53% increase in CoF in the medial-lateral direction compared to the anterior-posterior direction. Of the storage conditions examined, 37°C, 4°C, -20°C, and -80°C for 1 day, 1 week, and 1 month, a 49% decrease in CoF was observed at 1 week in -80°C. Interestingly, prolonged storage at 37°C resulted in up to an 83% increase in the compressive aggregate modulus by 1 month, with a corresponding increase in the glycosaminoglycan (GAG) bulk content. This study illustrates the differential effects of storage conditions on cartilage: freezing tends to target surface properties, while nonfreezing storage impacts the tissue bulk. These data show that a bulk-only analysis of cartilage function is not sufficient or representative. The nondestructive surface characterization assays described here enable improvement in cartilage functionality assessment by considering both surface and bulk cartilage properties; this methodology may thus provide a new angle to explore in future cartilage research and tissue engineering endeavors.
关节软骨的表面对于关节的平滑低摩擦运动至关重要。然而，大多数关于软骨的文献很少包括对表面特征和功能的测量。部分原因可能是缺乏或不熟悉快速、非破坏性且最好是非接触的方法，这些方法可用于评估软骨表面特征的大表面积软骨。全面的软骨表面特征分析方法有助于确定组织功能的变化，例如在需要评估软骨移植物质量的情况下。由于软骨储存条件是一个正在进行和活跃研究的领域，本研究使用干涉测量法和摩擦学方法作为评估不同储存温度和时间下软骨表面形貌、粗糙度和摩擦系数（CoF）变化的有效且非破坏性的方法。还进行了标准的、用于评估整体机械和生物化学特性的破坏性测试，以及免疫组织化学测试。这是首次使用干涉测量法显示软骨形貌各向异性，表现为与关节运动方向一致的前后条纹图案。摩擦学方法还能观察到另一个新颖的现象，即摩擦各向异性，与前后方向相比，中-外侧方向的 CoF 增加了 53%。在所检查的储存条件中，37°C、4°C、-20°C 和-80°C 分别储存 1 天、1 周和 1 个月，在-80°C 下，CoF 在 1 周时下降了 49%。有趣的是，在 37°C 下长时间储存会导致 1 个月时压缩聚集体模量增加高达 83%，同时糖胺聚糖（GAG）的整体含量也相应增加。本研究说明了储存条件对软骨的不同影响：冷冻倾向于靶向表面特性，而非冷冻储存则影响组织整体。这些数据表明，仅对软骨功能进行整体分析是不够的或不具有代表性。这里描述的非破坏性表面特征分析方法通过同时考虑软骨的表面和整体特性，提高了对软骨功能的评估；因此，该方法可能为未来的软骨研究和组织工程努力提供一个新的角度。
