Baaijens Frank P T, Trickey Wendy R, Laursen Tod A, Guilak Farshid
Department of Biomedical Engineering, Eindhoven University of Technology, Eindhoven, The Netherlands.
Ann Biomed Eng. 2005 Apr;33(4):494-501. doi: 10.1007/s10439-005-2506-3.
Chondrocytes, the cells in articular cartilage, exhibit solid-like viscoelastic behavior in response to mechanical stress. In modeling the creep response of these cells during micropipette aspiration, previous studies have attributed the viscoelastic behavior of chondrocytes to either intrinsic viscoelasticity of the cytoplasm or to biphasic effects arising from fluid-solid interactions within the cell. However, the mechanisms responsible for the viscoelastic behavior of chondrocytes are not fully understood and may involve one or both of these phenomena. In this study, the micropipette aspiration experiment was modeled using a large strain finite element simulation that incorporated contact boundary conditions. The cell was modeled using finite strain incompressible and compressible elastic models, a two-mode compressible viscoelastic model, or a biphasic elastic or viscoelastic model. Comparison of the model to the experimentally measured response of chondrocytes to a step increase in aspiration pressure showed that a two-mode compressible viscoelastic formulation accurately captured the creep response of chondrocytes during micropipette aspiration. Similarly, a biphasic two-mode viscoelastic analysis could predict all aspects of the cell's creep response to a step aspiration. In contrast, a biphasic elastic formulation was not capable of predicting the complete creep response, suggesting that the creep response of the chondrocytes under micropipette aspiration is predominantly due to intrinsic viscoelastic phenomena and is not due to the biphasic behavior.
软骨细胞是关节软骨中的细胞，在受到机械应力时表现出类似固体的粘弹性行为。在模拟这些细胞在微吸管抽吸过程中的蠕变反应时，以往的研究将软骨细胞的粘弹性行为归因于细胞质的固有粘弹性或细胞内流固相互作用产生的双相效应。然而，软骨细胞粘弹性行为的机制尚未完全了解，可能涉及这两种现象中的一种或两种。在本研究中，使用包含接触边界条件的大应变有限元模拟对微吸管抽吸实验进行建模。细胞使用有限应变不可压缩和可压缩弹性模型、双模式可压缩粘弹性模型或双相弹性或粘弹性模型进行建模。将模型与软骨细胞对抽吸压力阶跃增加的实验测量反应进行比较，结果表明双模式可压缩粘弹性公式准确地捕捉了软骨细胞在微吸管抽吸过程中的蠕变反应。同样，双相双模式粘弹性分析可以预测细胞对阶跃抽吸的蠕变反应的所有方面。相比之下，双相弹性公式无法预测完整的蠕变反应，这表明微吸管抽吸下软骨细胞的蠕变反应主要是由于固有粘弹性现象，而不是由于双相行为。
