Towards predicting shear-banding instabilities in lipid monolayers
Towards predicting shear-banding instabilities in lipid monolayers
复制标题
预测脂质单层中的剪切带不稳定性
DOI：
10.1016/j.jmbbm.2023.105743
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发表时间：
2023
影响因子：
3.9
通讯作者：
Deseri, L.
中科院分区：
文献类型：
--
作者：
Carotenuto, A.R.;Gaffney, A.;Nguyen, N.;Lee, K.Y.C.;Pocivavsek, L.;Fraldi, M.;Deseri, L.
朗缪尔单分子膜是用于研究脂膜如何参与许多活体结构的生理过程的有利系统，例如肺泡结构中的塌陷现象。很多工作集中在表征朗缪尔薄膜的承压能力，用等温线曲线的形式表示。这表明，单层在压缩过程中经历了不同的阶段，其力学响应也发生了相应的变化，当超过临界应力阈值时，会引发不稳定事件。虽然建立在表面压力和面积变化之间的逆关系的众所周知的状态方程能够正确地描述液体膨胀相期间的单层行为，但它们在随后的凝聚区的非线性行为的模拟仍然是一个开放的问题。在这方面，主要是借助线弹性板理论来模拟屈曲和起皱来解释平面外坍塌。然而，在朗缪尔单分子膜上的一些实验也显示了导致所谓剪切带形成的面内不稳定性现象，并且到目前为止，还没有提供关于单分子膜中剪切带分叉开始的理论描述。为此，我们采用宏观描述的方法，研究了脂单分子膜的材料稳定性，并采用增量式方法找到了激发剪切带的条件。特别是，从广泛假设的单层在类固体区域弹性行为的假设出发，本工作引入了超泡沫超弹性势作为一种新的本构策略来跟踪致密化过程中单层响应的非线性响应。通过这种方法，所获得的力学性能和所采用的应变能被成功地用于再现某些脂质体系在不同化学和热条件下所表现出的剪切带的起始。
Langmuir monolayers are advantageous systems used to investigate how lipid membranes get involved in the physiology of many living structures, such as collapse phenomena in alveolar structures. Much work focuses on characterizing the pressure-bearing capacity of Langmuir films, expressed in the form of isotherm curves. These show that monolayers experience different phases during compression with an according evolution of their mechanical response, incurring into instability events when a critical stress threshold is overcome. Although well-known state equations, which establish an inverse relationship between surface pressure and area change, are able to properly describe monolayer behaviour during liquid expanded phase, the modelling of their nonlinear behaviour in the subsequent condensed region is still an open issue. In this regard, most efforts are addressed to explain out-of-plane collapse by modelling buckling and wrinkling mainly resorting to linearly elastic plate theory. However, some experiments on Langmuir monolayers also show in-plane instability phenomena leading to the formation of the so-called shear bands and, to date, no theoretical description of the onset of shear banding bifurcation in monolayers has been yet provided. For this reason, by adopting a macroscopic description, we here study material stability of the lipid monolayers and exploit an incremental approach to find the conditions that kindle shear bands. In particular, by starting from the widely assumed hypothesis that monolayers behave elastically in the solid-like region, in this work a hyperfoam hyperelastic potential is introduced as a new constitutive strategy to trace back the nonlinear response of monolayer response during densification. In this way, the obtained mechanical properties together with the adopted strain energy are successfully employed to reproduce the onset of shear banding exhibited by some lipid systems under different chemical and thermal conditions.