Department of Biomedical Sciences, University of Padova, Padova, Italy.
Centre for Mechanics of Biological Materials, University of Padova, Padova, Italy.
PLoS One. 2019 Nov 5;14(11):e0224232. doi: 10.1371/journal.pone.0224232. eCollection 2019.
The forces that allow body movement can be divided into active (generated by sarcomeric contractile proteins) and passive (sustained by intra-sarcomeric proteins, fibre cytoskeleton and extracellular matrix (ECM)). These are needed to transmit the active forces to the tendon and the skeleton. However, the relative contribution of the intra- and extra- sarcomeric components in transmitting the passive forces is still under debate. There is limited data in the literature about human muscle and so it is difficult to make predictions using multiscale models, imposing a purely phenomenological description for passive forces. In this paper, we apply a method for the experimental characterization of the passive properties of fibres and ECM to human biopsy and propose their clear separation in a Finite Element Model. Experimental data were collected on human single muscle fibres and bundles, taken from vastus lateralis muscle of elderly subjects. Both were progressively elongated to obtain two stress-strain curves which were fitted to exponential equations. The mechanical properties of the extracellular passive components in a bundle of fibres were deduced by the subtraction of the passive tension observed in single fibres from the passive tension observed in the bundle itself. Our results showed that modulus and tensile load bearing capability of ECM are higher than those of fibres and defined their quantitative characterization that can be used in macroscopic models to study their role in the transmission of forces in physiological and pathophysiological conditions.
使身体运动的力可以分为主动力（由肌节收缩蛋白产生）和被动力（由肌节内蛋白、纤维细胞骨架和细胞外基质 (ECM) 维持）。这些力需要传递到肌腱和骨骼。然而，在传递被动力方面，肌节内和肌节外成分的相对贡献仍存在争议。由于文献中关于人类肌肉的数据有限，因此使用多尺度模型进行预测非常困难，这就需要对被动力进行纯粹的唯象描述。在本文中，我们应用一种用于纤维和 ECM 被动特性实验表征的方法对人体活检进行了研究，并在有限元模型中对其进行了清晰的分离。实验数据取自老年受试者的股外侧肌，取自单个肌肉纤维和束。对这两者都进行了逐渐的拉伸，以获得两条应力-应变曲线，并将其拟合到指数方程中。通过从纤维束中观察到的被动张力中减去单个纤维中观察到的被动张力，得出纤维束中细胞外被动成分的力学性能。我们的研究结果表明，细胞外基质的模量和拉伸承载能力高于纤维，确定了其定量特征，可用于宏观模型研究其在生理和病理生理条件下传递力的作用。
