Approach and penetration of cell membranes by microswimmers and self-propelled particles

在这个项目中，我们的目标是在理论上和数值上获得自推进活性粒子对细胞膜的方法和渗透的完整表征。该项目分为两个主要部分，如下所述。在物理接触发生之前，了解膜附近活性颗粒的行为和动力学，是了解它们渗透到细胞内部的关键因素。因此，这个项目的第一部分将致力于活性粒子和微游泳者的近膜动力学。为此，我们将使用流体的连续统描述，分析地解决由于在细胞膜附近的表面发生化学反应而导致的催化活性颗粒移动的扩散电泳自推进机制。以前的工作只集中在刚性壁附近的自推进和可变形膜附近的定向运动，到目前为止还没有解决。化学活性和膜弹性之间的物理相互作用有望导致一个非常丰富和可行的现象学。我们的计算将使用各种不同的模型进行，包括蠕动模型和远场流的高阶表示。然后，我们的理论预测将通过边界积分模拟进行测试和验证。在项目的第二部分，我们将研究自走粒子在建立物理接触后进入细胞膜的渗透过程。为此，我们将利用基于耗散粒子动力学方法的介观模拟来研究不同大小和形状的自扩散活性粒子进入脂质双层膜的物理进入。此外，我们将探索活性颗粒之间的流体和膜介导的相互作用。然后，我们的模拟将通过使用渐近分析和缩放参数的理论计算来补充和补充，以便检查活性物质与细胞膜结合时的包裹机制。我们的合作者将在活细胞膜附近和穿过活细胞膜进行相应的生物相容性自推进实验。

Our goal in this project is to obtain a full characterization of the approach and penetration of cell membranes by self-propelled active particles both theoretically and numerically. The project is structured into two main parts as outlined below. The understanding of the behavior and dynamics of active particles near membranes, before physical contact takes place, is a crucial ingredient to understand their penetration into the cell interior. The first part of this project will therefore be devoted to the near-membrane dynamics of active particles and microswimmers. For this purpose, we will address analytically, using a continuum description of the fluid, the diffusiophoretic self-propulsion mechanism of a catalytically active particle moving due to a chemical reaction on its surface in the vicinity of a cell membrane. Previous works have only focused on self-propulsion near stiff walls and directed motion near deformable membranes has not been addressed so far. The physical interplay between the chemical activity and membrane elasticity is expected to lead to a very rich and viable phenomenology. Our calculations will be carried out using a variety of different model swimmers including the squirmer model and the higher order representation of the far-field flow. Our theoretical predictions will then be tested and validated by boundary integral simulations. In the second part of the project, we will investigate the penetration process of a self-propelled particle into a cell membrane after physical contact is established. For that aim, we will make use of mesoscopic simulations based on the dissipative particle dynamics method to investigate the physical entry of a self-diffusiophoretic active particle with different sizes and shapes into the lipid bilayer membrane. Additionally, we will explore the fluid- and membrane-mediated interactions between active particles. Our simulations will then be complemented and supplemented by theoretical calculations using asymptotic analysis and scaling arguments in order to examine the wrapping mechanism upon binding of an active article to the cell membrane. Corresponding experiments of biocompatible self-propulsion near and through living cell membranes will be performed by our collaborators.