Wetting of bio-inspired, stimulus-responsive polymer surfaces by lipid vesicles

与液滴类似，囊泡的形状由其封闭的体积、膜-基物相互作用(界面电势)以及内外界面(膜)的性质决定。囊泡润湿的独特之处在于膜的固有弯曲刚性和封闭液体的浮力的重要性。实验田中团队建立了一种受生物启发的聚合物刷子平台，能够切换囊泡的粘连，并通过3D共聚焦显微镜监测了大规模囊泡的形状。这一设置将得到显微干涉技术的补充，提供有关刷泡接触区边缘的局部几何信息。理论Müler团队在并行的GPU加速MD程序中实现了可切换聚合物刷子的高度粗粒粒子模型和薄脂膜的三角化Helfrich-Hamilton量，并推广了Helfrich描述以包括有限范围的界面电势和浮力。在新的时期，他们将明确包括考虑粘性耗散的溶剂。两个团队将通过对囊泡几何形状的随时间变化的测量，共同研究囊泡形状的动态变化，以响应粘附力的变化以及刷子与囊泡接触的适应性。热力(弯曲能、粘附力和浮力)和耗散机制(例如，接触区和周围液体的耗散)对囊泡大小表现出不同的依赖关系，它们的系统变化将使我们能够区分不同的耗散机制，并有助于实验和模拟之间的比较。此外，我们将考虑膜物种(例如，带正电荷的脂类，与刷子的-COOH基团结合)向接触区的运输如何影响囊泡的动力学。这条研究路线将扩展到不同种类的衬底，其中润湿性梯度可能导致接触区的收缩，或者逐渐变化可能导致囊泡的平移和扩散。我们还将研究在衬底上移动的润湿性和润湿性梯度的时间周期开关。小泡的横向运动将引起额外的动力学，例如小泡的滑动或滚动运动/坦克踩踏。

Analog to liquid drops, the shape of a vesicle is dictated by its enclosed volume, the membrane-substrate interaction (interface potential), and the properties of the interface (membrane) between the interior and exterior. Unique to wetting by vesicles is the importance of the membrane’s intrinsic bending rigidity and the buoyancy of the enclosed liquid.The experimental Tanaka team has established a bio-inspired polymer brush platform, capable of switching the adhesion of vesicles, and has monitored the large-scale vesicle shape by 3D confocal microscopy. This setup will be complemented by a micro-interferometry technique, providing information about the local geometry of the edge of the brush-vesicle contact zone. The theoretical Müller team has implemented a highly coarse-grained particle model of the switchable polymer brush and a triangulated Helfrich-Hamiltonian of the thin lipid membrane in a parallel, GPU-accelerated MD program and has generalized the Helfrich description to include a finite-ranged interface potential and buoyancy. In the new period, they will explicitly include solvents to account for viscous dissipation.Both teams will jointly investigate the dynamic change of vesicle shapes in response to a switch in adhesion and the adaptation of the brush to the contact with a vesicle by time-dependent measurements of the vesicle geometry. Thermodynamic forces (bending energy, adhesion, and buoyancy) and dissipation mechanisms (e.g., dissipation at the contact zone and of the surrounding liquids) exhibit different dependencies on the vesicle size, whose systematic variation will allow us to distinguish between different dissipation mechanisms and aid the comparison between experiment and simulation. Additionally, we will consider how transport of membrane species (e.g., positively charged lipids, binding to -COOH groups of the brush) toward the contact zone influences the dynamics of the vesicle. This line of study will be extended to heterogeneous substrates, where a wettability gradient may result in a pining of the contact zone or a gradual variation may induce a translation and spreading of the vesicle. We will also study time-periodic switches of the wettability and wettability gradients that move over the substrate. The lateral motion of vesicles will give rise to additional dynamics such as e.g. sliding or rolling motion/tank-treading of the vesicle.