Optimization of Material Coefficients in the Holzapfel-Gasser-Ogden Material Model for the Main Four Ligaments of the Knee Joint-A Finite Element Study

Accurate representation of soft tissue material properties plays a crucial role in computational biomechanics. Several material models have been used for knee ligaments in finite element (FE) studies, including the neo-Hookean model (widely used) and the Holzapfel-Gasser-Ogden (HGO) model (seldom used). While the coefficients of neo-Hookean models for the knee ligaments are available in the literature, limited data exists for the HGO model. Furthermore, no peer-reviewed comparison of these two material models for the knee ligaments while including the 3D representation of the ligaments for both material models is present in the literature. We used mechanical properties from the tensile test experiments in the literature for each ligament to obtain the HGO material coefficients while accounting for the ligaments’ viscoelastic behavior. Resultant coefficients were then used in an Abaqus/explicit knee model to simulate bipedal landing from a jump. The simulations were repeated with neo-Hookean values from the literature. Knee kinematics plus ACL and MCL strains were evaluated and compared for these two material models. The outputs from the simulations with HGO properties were predominantly within 1.5 standard deviations from the mean in-vitro data. When the material properties changed to Neo-Hookean, the outputs for kinematics and strain values were higher than the HGO case, and in most instances, they were outside the experimental range for ACL and MCL strains (by up to 11.35 SD) as well as some ITR angles (by up to 2.86 SD). Reported HGO material model with optimized coefficients produces a more realistic representation of the ligaments’ material properties, and will help improve the outcomes of FE models for more accurate predictions of knee behavior.

猪降主动脉腹侧与背侧组织力学性能的实验研究

动脉组织的力学性能对于维持心血管健康具有重要意义,并与心血管相关疾病的发生发展密切相关。主动脉腹侧和背侧组织力学性能之间存在显著差异,但缺乏量化的力学性能参数,且其成因尚不清楚。本文以猪降主动脉腹侧与背侧组织为研究对象,通过双轴拉伸方法获取应力-应变曲线,分析组织正交各向异性,采用Gasser-Ogden-Holzapfel型应变能函数描述动脉组织力学性能参数,采用Elastic Van Gieson(EVG)法和天狼星红染色法观测动脉组织弹性纤维和胶原纤维显微结构。结果表明,与降主动脉腹侧组织相比,降主动脉背侧组织表现出更明显的正交各向异性,且在周向上的弹性模量明显大于降主动脉腹侧组织。降主动脉腹侧和背侧组织的超弹本构参数之间差异均无统计学意义,但几乎所有降主动脉组织的纤维角度都小于0.785 rad(45°),胶原纤维的排列更趋于周向。EVG和天狼星红染色显示降主动脉腹侧外-中膜弹性纤维层密度明显高于背侧组织,外-中膜胶原纤维背侧多于腹侧。结果提示,猪降主动脉背侧组织与腹侧组织之间的力学性能差异与外-中膜组织中的微观结构有关。在相对较小的应变范围内,可忽略降主动脉腹侧与背侧组织力学性能的差异;当应变较高时,则需区别对待。本研究结果可为动脉疾病(如动脉夹层)的成因以及人工血管设计等提供数据参考。