Mechanical interactions between cells and their environment play an important role in many biological processes. These interactions are often anisotropic in nature, but most mathematical models in... Show moreMechanical interactions between cells and their environment play an important role in many biological processes. These interactions are often anisotropic in nature, but most mathematical models in the field of cell mechanics describe cells as isotropic entities. In this thesis we theoretically study the role of anisotropic forces in cell mechanics, and compare our predictions to experimental data. Show less
Shape and biological function are tightly connected. Physical descriptions are used to connect the shape of a biological system with its function. One system investigated here is the dendritic... Show moreShape and biological function are tightly connected. Physical descriptions are used to connect the shape of a biological system with its function. One system investigated here is the dendritic spine, which is the connection between neurons. The dendritic spine is mimicked in an artificial system. In this way, I was able to show that the shape of the dendritic spine is important in memory and learning. The shape of a cell itself is governed by its actin cytoskeleton. I showed that a simple model can be used to describe the shape of adherent cells. An adherent cell attaches itself at discrete points to the substrate. The edge of the cell in between these points can be described as a part of an ellipse. I show that all edges of a single cell can all be described with a single ellipse. On a small scale, the shape of the membrane of a cell changes with changing lipid content. I used light to change the lipid content, triggering phase unmixing in an artificial lipid membrane. I show that various important parameters change significantly. Show less
In this thesis we present a new method to simulate realistic three-dimensional networks of biopolymers under shear. These biopolymer networks are important for the structural functions of cells and... Show moreIn this thesis we present a new method to simulate realistic three-dimensional networks of biopolymers under shear. These biopolymer networks are important for the structural functions of cells and tissues. We use the method to analyze these networks under shear, and consider the elastic modulus, the non-affinity during deformation, the normal modes and the density of states. We expand our analysis to composite networks consisting of stiff and floppy filaments. In the final chapter of the thesis we incorporate the thermal and viscous interactions of the surrounding medium in the calculations, and present the results of the simulations of the shear frequency dependence of the network response. We find that non-affine reorientations are important for understanding the network response. These non-affine reorientations make the networks relatively soft under shear and delay the onset of stiffnening. In composite networks non-affine reorientations allow for an intricate interplay between the stiff and floppy filaments. The frequency-dependent response shows a transition from a soft, non-affine regime at low frequencies to a stiff, close-to-affine response at high frequencies. Show less
