Soft tissue mechanical characterisation is important in many areas of medical research. Examples span from surgery training, device design and testing, sudden injury and disease diagnosis. The liver is of particular interest, as it is the most commonly injured organ in frontal and side motor vehicle crashes, and also assessed for inflammation and fibrosis in chronic liver diseases. Hence, an extensive rheological characterisation of liver tissue would contribute to advancements in these areas, which are dependent upon underlying biomechanical models. The aim of this paper is to define a liver constitutive equation that is able to characterise the nonlinear viscoelastic behaviour of liver tissue under a range of deformations and frequencies. The tissue response to large amplitude oscillatory shear (1-50%) under varying preloads (1-20%) and frequencies (0.5-2 Hz) is modelled using viscoelastic-adapted forms of the Mooney-Rivlin, Ogden and exponential models. These models are fit to the data using classical or modified objective norms. The results show that all three models are suitable for capturing the initial nonlinear regime, with the latter two being capable of capturing, simultaneously, the whole deformation range tested. The work presented here provides a comprehensive analysis across several material models and norms, leading to an identifiable constitutive equation that describes the nonlinear viscoelastic behaviour of the liver.

中文翻译：

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牛肝组织的非线性粘弹性本构模型。

软组织力学表征在医学研究的许多领域都很重要。示例包括手术培训、设备设计和测试、突发性损伤和疾病诊断。肝脏是特别令人感兴趣的，因为它是正面和侧面机动车碰撞中最常受伤的器官，并且还在慢性肝病中评估炎症和纤维化。因此，肝脏组织的广泛流变学表征将有助于这些领域的进步，这取决于潜在的生物力学模型。本文的目的是定义一个肝脏本构方程，该方程能够表征肝脏组织在一系列变形和频率下的非线性粘弹性行为。在不同的预载荷 (1-20%) 和频率 (0.5-2 Hz) 下，组织对大振幅振荡剪切 (1-50%) 的响应使用 Mooney-Rivlin、Ogden 和指数模型的粘弹性适应形式进行建模。这些模型使用经典或修改后的客观规范来拟合数据。结果表明，所有三种模型都适合捕获初始非线性状态，后两种模型能够同时捕获测试的整个变形范围。此处介绍的工作提供了对多种材料模型和规范的综合分析，从而产生了一个可识别的本构方程，该方程描述了肝脏的非线性粘弹性行为。这些模型使用经典或修改后的客观规范来拟合数据。结果表明，所有三种模型都适合捕获初始非线性状态，后两种模型能够同时捕获测试的整个变形范围。此处介绍的工作提供了对多种材料模型和规范的综合分析，从而产生了一个可识别的本构方程，该方程描述了肝脏的非线性粘弹性行为。这些模型使用经典或修改后的客观规范来拟合数据。结果表明，所有三种模型都适合捕获初始非线性状态，后两种模型能够同时捕获测试的整个变形范围。此处介绍的工作提供了对多种材料模型和规范的综合分析，从而产生了一个可识别的本构方程，该方程描述了肝脏的非线性粘弹性行为。