Lytra A, Sboros V, Giannakopoulos A, Pelekasis N
Department of Mechanical Engineering, University of Thessaly, Volos, 38334, Greece.
Institute of Biological Chemistry, Biophysics and Bioengineering, Heriot-Watt University, Edinburgh EH14 4AS, UK.
Soft Matter. 2020 May 21;16(19):4661-4681. doi: 10.1039/d0sm00300j. Epub 2020 May 11.
We present an extensive comparison with experimental data of our theoretical/numerical model for the static response of coated microbubbles (MBs) subject to compression from an atomic force microscope (afm). The mechanics of the MB's coating is described in the context of elastic thin shell theory. The encapsulated fluid is treated as compressible/incompressible pertaining to a gas/liquid, while the thinning of the liquid film between the MB and the afm cantilever is modeled via introduction of an interaction potential and the resulting disjoining pressure. As the external force increases, the experimental force-deformation (f-d) curves of MBs covered with polymer have an initial linear response (Reissner regime), followed by a non-linear curved downwards response (Pogorelov regime) where buckling takes place. On the other hand, the f-d curve for MBs covered with lipid monolayers initially follows the Reissner regime, but buckling is bypassed to a curved upwards regime where internal gas pressure dominates. The elastic properties, namely Young's modulus and shell thickness, for MB's covered with polymer can be estimated by combining the buckling point and the slope of the Reissner regime or the slopes of Reissner and Pogorelov regimes. Comparison of the present model with afm f-d curves for polymer shows satisfactory agreement. The area dilatation and bending moduli are shown to be the appropriate independent elastic parameters of MBs covered with phospholipid monolayers and are estimated by combination of the transition from Reissner to pressure dominated regime. Simulations and experiments in this case are in excellent agreement.
我们对涂覆微泡（MBs）在原子力显微镜（afm）压缩下的静态响应的理论/数值模型与实验数据进行了广泛比较。MBs涂层的力学特性在弹性薄壳理论的背景下进行描述。封装的流体根据其为气体/液体而被视为可压缩/不可压缩，而MB与afm悬臂之间液膜的变薄通过引入相互作用势和由此产生的分离压力进行建模。随着外力增加，覆盖聚合物的MBs的实验力-变形（f-d）曲线具有初始线性响应（Reissner区域），随后是发生屈曲的非线性向下弯曲响应（Pogorelov区域）。另一方面，覆盖脂质单层的MBs的f-d曲线最初遵循Reissner区域，但屈曲被绕过，进入内部气体压力占主导的向上弯曲区域。对于覆盖聚合物的MBs，其弹性特性，即杨氏模量和壳厚度，可以通过结合屈曲点和Reissner区域的斜率或Reissner和Pogorelov区域的斜率来估计。本模型与聚合物的afm f-d曲线的比较显示出令人满意的一致性。面积膨胀模量和弯曲模量被证明是覆盖磷脂单层的MBs合适的独立弹性参数，并通过结合从Reissner区域到压力主导区域的转变来估计。在这种情况下，模拟和实验结果非常吻合。
