Boettcher K, Kienle S, Nachtsheim J, Burgkart R, Hugel T, Lieleg O
Institute of Medical Engineering IMETUM and Department of Mechanical Engineering, Technische Universität München, Boltzmannstraße 11, 85748 Garching, Germany.
Institute of Medical Engineering IMETUM and Physics Department, Technische Universität München, Boltzmannstraße 11, 85748 Garching, Germany.
Acta Biomater. 2016 Jan;29:180-187. doi: 10.1016/j.actbio.2015.09.034. Epub 2015 Sep 30.
Articular cartilage is a mechanically highly challenged material with very limited regenerative ability. In contrast to elastic cartilage, articular cartilage is exposed to recurring partial dehydration owing to ongoing compression but maintains its functionality over decades. To extend our current understanding of the material properties of articular cartilage, specifically the interaction between the fluid and solid phase, we here analyze the reversibility of tissue dehydration. We perform an artificial dehydration that extends beyond naturally occurring levels and quantify material recovery as a function of the ionic strength of the rehydration buffer. Mechanical (indentation, compression, shear, and friction) measurements are used to evaluate the influence of de- and rehydration on the viscoelastic properties of cartilage. The structure and composition of native and de/rehydrated cartilage are analyzed using histology, scanning electron microscopy, and atomic force microscopy along with a 1,9-dimethylmethylene blue (DMMB) assay. A broad range of mechanical and structural properties of cartilage can be restored after de- and rehydration provided that a physiological salt solution is used for rehydration. We detect only minor alterations in the microarchitecture of rehydrated cartilage in the superficial zone and find that these alterations do not interfere with the viscoelastic and tribological properties of the tissue.
We here demonstrate the sturdiness of articular cartilage towards changes in fluid content and show that articular cartilage recovers a broad range of its material properties after dehydration. We analyze the reversibility of tissue dehydration to extend our current understanding of how the material properties of cartilage are established, focusing on the interaction between the fluid and solid phase. Our findings suggest that the high resilience of the tissue minimizes the risk of irreversible material failure and thus compensates, at least in part, its poor regenerative abilities. Tissue engineering approaches should thus not only reproduce the correct tissue mechanics but also its pronounced sturdiness to guarantee a similar longevity.
关节软骨是一种机械性能面临高度挑战且再生能力非常有限的材料。与弹性软骨不同，关节软骨由于持续受压而反复经历部分脱水，但能在数十年间维持其功能。为拓展我们目前对关节软骨材料特性的理解，特别是流体相和固相之间的相互作用，我们在此分析组织脱水的可逆性。我们进行了超出自然发生水平的人工脱水，并将材料恢复情况量化为再水化缓冲液离子强度的函数。通过机械（压痕、压缩、剪切和摩擦）测量来评估脱水和再水化对软骨粘弹性特性的影响。使用组织学、扫描电子显微镜、原子力显微镜以及1,9 - 二甲基亚甲基蓝（DMMB）测定法分析天然和脱水/再水化软骨的结构与组成。如果使用生理盐溶液进行再水化，软骨的广泛机械和结构特性在脱水和再水化后均可恢复。我们仅检测到再水化软骨表层区域微观结构的微小变化，并且发现这些变化不会干扰组织的粘弹性和摩擦学特性。
我们在此证明了关节软骨对流体含量变化的坚固性，并表明关节软骨在脱水后能恢复其广泛的材料特性。我们分析组织脱水的可逆性，以拓展我们目前对软骨材料特性如何形成的理解，重点关注流体相和固相之间的相互作用。我们的研究结果表明，组织的高弹性将不可逆材料失效的风险降至最低，从而至少部分补偿了其较差的再生能力。因此，组织工程方法不仅应再现正确的组织力学性能，还应再现其显著的坚固性，以确保类似的使用寿命。
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