The conventional mechanical properties of articular cartilage, such as compressive stiffness, have been shown to have limited capacity to distinguish visually normal from degraded cartilage samples. In this study, a new mechanical indentation framework for assessing functional properties of articular cartilage during loading/unloading, i.e. deformation and recovery, was established. The capacity of a ring-shaped indenter integrated with an ultrasound transducer to distinguish mechanically intact from proteoglycan-depleted tissue was investigated. To achieve this, normal and enzymatically degraded bovine osteochondral samples were subjected to loading/unloading while the response of the tissue at the middle was captured by ultrasound at the same time. The enzymatic degradation model was characterized by amount of proteoglycan content, glycosaminoglycan release and proteomic analysis. The mechanical response of a wider continuum of articular cartilage in the loaded area and its surrounding region was captured in this framework leading to investigate two parameters, L and TS, related to the surrounding tissue of the loaded area for functional assessment of cartilage. L is the distance between the ultrasound transducer and articular cartilage surface and TS is the transient strain of articular cartilage during loading and unloading. Classification Analysis based on Principal Component Analysis was used to investigate the capacity of the new parameters to assess the functionality of the tissue. Multivariate statistics based on Partial Least Squares regression was employed to identify the correlation between the response of the tissue in the indented area and its surrounding cartilage. The results of this study indicate that L during loading (deformation) can differentiate normal and mildly proteoglycan-depleted samples from severely depleted samples and L during unloading (recovery) can distinguish between normal and proteoglycan-depleted tissue. However, TS during deformation and recovery is unable to discriminate normal cartilage samples from proteoglycan-depleted tissue. The results also demonstrate a strong correlation between mechanical properties of the loaded area with the response of its surrounding cartilage during recovery. It is therefore concluded that L in this newly established framework can discriminate between normal and proteoglycan-depleted cartilage samples. However, more samples will be needed to verify the demarcation between samples degraded for varying amount of time.

关节软骨的常规机械性能（例如抗压刚度）已显示出有限的能力，无法从视觉上区分正常的软骨样品和退化的软骨样品。在这项研究中，建立了一种新的机械压痕框架，以评估关节软骨在加载/卸载过程中的功能特性，即变形和恢复。研究了与超声换能器集成在一起的环形压头的能力，以区分机械完好无损和蛋白聚糖耗尽的组织。为此，对正常和酶降解的牛骨软骨样品进行加载/卸载，同时通过超声捕获中间组织的响应。酶促降解模型的特征是蛋白聚糖含量高，糖胺聚糖的释放和蛋白质组学分析。在此框架中捕获了负载区域及其周围区域中较宽的连续软骨连续区的机械响应，从而研究了与负载区域周围组织相关的两个参数L和TS，以评估软骨的功能。L是超声换能器与关节软骨表面之间的距离，TS是加载和卸载过程中关节软骨的瞬态应变。基于主成分分析的分类分析用于研究新参数评估组织功能的能力。采用基于偏最小二乘回归的多元统计量来确定凹陷区域的组织反应与其周围软骨之间的相关性。这项研究的结果表明，加载（变形）过程中的L可以区分正常和轻度蛋白聚糖耗尽的样品与严重耗尽的样品，而卸载（恢复）过程中的L可以区分正常组织和蛋白聚糖耗尽的组织。但是，在变形和恢复过程中，TS无法从蛋白聚糖贫化的组织中区分出正常的软骨样品。结果还表明，在恢复过程中，加载区域的机械性能与其周围软骨的响应之间具有很强的相关性。因此得出的结论是，在这个新建立的框架中，L可以区分正常和蛋白聚糖耗尽的软骨样品。但是，将需要更多的样本来验证在不同时间退化的样本之间的分界。