Substrate deformation affects the behavior of many cell types, as for example bone, skeletal muscle and endothelial cells. Nowadays, in vitro tests are widely employed to study the mechanotransduction induced by substrate deformation. The aim of in vitro systems is to properly reproduce the mechanical stimuli sensed by the tissue in the cellular microenvironment. An accurate strain measurement and control is therefore necessary to ensure the cell sensing the proper strain for the entire treatment. Different types of in vitro systems are commercially available or custom made designed; however, none of these devices performs a real-time measurement of the induced strains. In this study, we proposed a uniaxial strain device for in vitro cell stimulation with an innovative real-time strain control. The system was designed to induce sinusoidal waveform stimulation in a huge range of amplitude and frequency, to three silicone chambers stretched by a linear actuator. The real-time strain measurement and control algorithm is based on an optical tracking method implemented in LabView 2015, and it is able adapting the input amplitude to the linear motor, if necessary, hanging the stimulation signal for about 120 ms. A validation of the strain values measured during the real-time tracking algorithm was carried out through a comparison with digital image correlation (DIC) technique. We investigated the influence of number of reference points and image size on the algorithm accuracy. Experimental results showed that the tracking algorithm allowed for a real-time measurement of the membrane longitudinal strains with a relative error of 0.3%, on average, in comparison to the strains measured with DIC in post-processing analysis. We showed a high homogeneity of the strain pattern on the entire chamber base for different stimulation conditions. Finally, as proof of concept, we employed the uniaxial strain device to induce substrate deformation on human Osteosarcoma cell line (SaOS-2). Experimental results showed a consistent cells' change in shape in response to the mechanical strain.

中文翻译：

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具有实时应变控制的体外单轴细胞基底变形装置的开发和验证

底物变形会影响许多细胞类型的行为，例如骨骼、骨骼肌和内皮细胞。如今，体外试验被广泛用于研究由基底变形引起的机械传导。体外系统的目的是在细胞微环境中正确地再现组织感知的机械刺激。因此，必须进行准确的应变测量和控制，以确保细胞在整个治疗过程中感应到适当的应变。不同类型的体外系统可商购或定制设计；然而，这些设备都没有对诱导应变进行实时测量。在这项研究中，我们提出了一种具有创新实时应变控制的用于体外细胞刺激的单轴应变装置。该系统被设计成在一个巨大的幅度和频率范围内诱导正弦波形刺激到由线性致动器拉伸的三个硅胶室。实时应变测控算法基于LabView 2015中实现的一种光学跟踪方法，它能够适应线性电机的输入幅度，如果需要，将刺激信号悬挂约120 ms。通过与数字图像相关 (DIC) 技术的比较，对实时跟踪算法期间测量的应变值进行了验证。我们研究了参考点数量和图像大小对算法精度的影响。实验结果表明，跟踪算法允许实时测量膜纵向应变，相对误差为 0.3%，平均而言，与后处理分析中用 DIC 测量的应变相比。对于不同的刺激条件，我们在整个腔室底座上显示了应变模式的高度均匀性。最后，作为概念证明，我们采用单轴应变装置在人骨肉瘤细胞系 (SaOS-2) 上诱导基底变形。实验结果表明，响应于机械应变，细胞的形状发生了一致的变化。