Department of Biomedical Engineering, University of Wisconsin-Madison, 1550 Engineering Drive, ECB 2139, Madison, WI 53706.
J Biomech Eng. 2024 Dec 1;146(12). doi: 10.1115/1.4066434.
Soft biological tissues often function as highly deformable membranes in vivo and exhibit impressive mechanical behavior effectively characterized by planar biaxial testing. The Generalized Anisotropic Inverse Mechanics (GAIM) method links full-field deformations and boundary forces from mechanical testing to quantify material properties of soft, anisotropic, heterogeneous tissues. In this study, we introduced an orthotropic constraint to GAIM to improve the quality and physical significance of its mechanical characterizations. We evaluated the updated GAIM method using simulated and experimental biaxial testing datasets obtained from soft tissue analogs (PDMS and TissueMend) with well-defined mechanical properties. GAIM produced stiffnesses (first Kelvin moduli, K1) that agreed well with previously published Young's moduli of PDMS samples. It also matched the stiffness moduli determined via uniaxial testing for TissueMend, a collagen-rich patch intended for tendon repair. We then conducted the first biaxial testing of TissueMend and confirmed that the sample was mechanically anisotropic via a relative anisotropy metric produced by GAIM. Next, we demonstrated the benefits of full-field laser micrometry in distinguishing between spatial variations in thickness and stiffness. Finally, we conducted an analysis to verify that results were independent of partitioning scheme. The success of the newly implemented constraints on GAIM suggests notable potential for applying this tool to soft tissues, particularly following the onset of pathologies that induce mechanical and structural heterogeneities.
软生物组织在体内通常作为高度可变形的膜发挥功能，并表现出令人印象深刻的机械行为，这些行为可通过平面双向测试有效地进行特征描述。广义各向异性逆力学（GAIM）方法将全场变形和边界力从力学测试联系起来，以量化软的、各向异性的、不均匀的组织的材料特性。在这项研究中，我们在 GAIM 中引入了各向异性约束，以提高其力学特性的质量和物理意义。我们使用具有明确力学性能的软组织类似物（PDMS 和 TissueMend）的模拟和实验双向测试数据集来评估更新的 GAIM 方法。GAIM 产生的刚度（第一凯氏模量，K1）与之前发表的 PDMS 样品的杨氏模量吻合良好。它还与用于肌腱修复的富含胶原蛋白的 TissueMend 的单向测试确定的刚度模量相匹配。然后，我们对 TissueMend 进行了首次双向测试，并通过 GAIM 生成的相对各向异性度量证实了该样本的力学各向异性。接下来，我们展示了全场激光微测在区分厚度和刚度空间变化方面的优势。最后，我们进行了一项分析，以验证结果与分区方案无关。GAIM 上新实施的约束的成功表明，该工具在软组织中的应用具有很大的潜力，特别是在引发引起机械和结构异质性的病理之后。
