Artificial Model Systems
Biological membranes are mechanically challenged in various ways: during adhesion of cells, migration, growth, and cell division, among others. Membrane mechanics essentially determine the resistance to bending, stretching, and compression. Using atomic force microscopy, pivotal membrane properties such as pre-tension, area compressibility, breakthrough distance or force, can be determined under a variety of external influences.
To better understand the mechanical features of the membrane surroundings, such as the actin cortex, we create experimental models that allow us to investigate the viscoelastic response of membranes and artificial cortices to external stimuli. The membrane models used range from solid-supported lipid bilayers over giant liposomes to hybrids such as pore spanning bilayers and cortex models of epithelial cells. In collaboration with Prof. B. Geil, we are working on analyzing the actin structures in these models via artificial retina analysis and neuronal network analysis.
A step to further approach the creation of a life-like system lies in the encapsulation of networks consisting of biopolymers such as actin or DNA nanotubes within giant unilamellar vesicles. Apart from studying the influence of the composition of the membrane lipids on the emerging internal structures, we are also interested in quantifying the network properties. In that vein, we compare properties such as the network stiffness of encapsulated biopolymer networks with non-confined reference systems. Of special interest is the function two isoforms of cytoplasmic actin, which have been shown to have specific interactions with certain actin-binding proteins as well as distinct localizations within living cells.
Addtitionally, our group uses micropipette aspiration to study membrane properties of small biological objects like cells or cell mimetic systems (such as giant unilamellar vesicles) by sucking up the membrane by a micro-sized glass pipette opening upon application of suction pressure. Membrane tension can be determined from the observed geometry based on Young-Laplace’s law by monitoring the aspiration and the applied suction pressure. From the obtained logarithmic plot of the membrane tension against the relative apparent area expansion we can readily infer mechanical membrane quantities such as the bending modulus and the area compressibility modulus.
Membrane-membrane interactions play a pivotal role in processes such as self-recognition between cells and the fusion of membranes, for example, during neurotransmission. We have devised various colloidal probe architectures to address different membrane-membrane interacting scenarios with different levels of complexity. Among other things, we are studying biological adhesion and membrane-membrane interactions in various model systems to study small forces in carbohydrate-carbohydrate interactions during cell adhesion events.
Understanding living matter either requires to take living systems apart in a top-down fashion or to build model systems in a bottom-up approach mirroring the essential aspects of life. While the top-down strategy has to cope with the massive biochemical redundancy and structural complexity of living organisms, the beauty of the bottom-up approach lies in controlled, rational design enabling researchers to move from self-organization over the formation of active matter to interconnected living systems step by step. In this context, our central goal is the microfluidic production and assembly of interconnected multifunctional minimal cell compartments (MCCs) based on giant liposomes/polymersomes to form a functional syncytium (living foams) that allows to relay chemical and mechanical information/signals/properties with the ultimate aim to substitute and mimic cellular assemblies in specific organs.
