Energetic investigations of induced particle uptake in functionalized, synthetic membrane systems.

如果机械化学信号和所需的能量都能被召集起来，活细胞通常通过吞噬作用将细菌吸收到它们的内部。特别是巨噬细胞，作为我们免疫系统的一部分，不仅吸收细菌，也吸收未被包裹的颗粒，这只有在不同生物物理力量的相互作用下才有可能。为了更好地分析相关力并更好地评估吞噬过程中已知因素的作用，一种可能的方法是使用仿生系统，它相对于细胞显着降低了复杂性。最简单的细胞仿生变体是一个巨大的单层囊泡（GUV），其中球形脂质双分子层的化学和机械特性可以通过许多不同的方式进行操纵。为了吞没和吸收粒子，GUV的膜必须发生明显的变形。最近的一项研究表明，在颗粒结合和包裹过程中释放的粘附能可以补偿膜变形的能量成本，而细胞骨架力是可替代性的。工作组Rohrbach和Römer的合作建议的目标是更好地理解颗粒摄取的物理机制，特别是膜变形的作用。在这种情况下，我们希望建立两种互补的测量技术，以确定颗粒摄取到人工细胞（GUV）期间的能量学。利用光子力显微镜观察中、小的吸收力，用原子力显微镜观察中、大的吸收力，将粒子以可控的方式接近膜，同时精确测量粒子的位移，以确定力和能量的变化。在自下而上的方法中，我们将逐步增加仿生系统的复杂性，这样在粒子摄取过程中，力和能量分布总是用完全相同的实验方案来测量。一方面，通过在GUV膜中加入不同的脂质和受体可以增加系统的复杂性，另一方面，颗粒的大小、形状/取向和表面功能化将以良好的控制方式改变。数学建模将有助于提高对颗粒吸收过程的机理理解，并更好地解释实验数据。

Living cells take up bacteria into their interior typically by phagocytosis, if both mechano-chemical signals and the required energy can be summoned up. In particular, macrophages, as part of our immune system, take up bacteria, but also uncoated particles, which is only possible by the interplay of different biophysical forces. For a better analysis of the relevant forces and to better assess the role of known factors during phagocytosis, a possible approach is to use biomimetic systems, which show a significantly reduced complexity relative to a cell. The simplest biomimetic variant of the cell is a giant unilamellar vesicle (GUV), where the chemical and mechanical properties of the spherical lipid bilayer can be manipulated in many different ways. In order to engulf and uptake a particle, the membrane of the GUV has to be deformed significantly. In a recent study it could be shown that the adhesion energy released during particle binding and wrapping can compensate the energy costs for membrane deformation and that cytoskeleton forces were dispensable. The goal of the collaborative proposal of the working groups Rohrbach and Römer is to better understand the physical mechanisms of particle uptake, in particular the role of the membrane deformation. In this context, we want to establish two complementary measurement techniques allowing to determine the energetics during particle uptake into an artificial cell (GUV). By using a photonic force microscope for small and medium uptake forces and an atomic force microscope for medium and larger forces, a particle will be approached in a controlled manner to the membrane, while the particle displacements are measured precisely to determine the changes in force and energy. In a bottom-up approach we will add stepwise more complexity to the biomimetic system, such that the force and energy profiles during particle uptake are measured always with exactly the same experimental scheme. On the one hand the complexity of the system can be increased by adding different lipids and receptors into the GUV membrane, on the other hand the size, the shape / orientation and the surface functionalization of the particle will be changed in a well-controlled manner. Mathematical modelling will help to improve the mechanistic understanding during particle uptake and to better interpret the experimental data.