You can download my PhD thesis
It is written in English (apart from the acknowledgment page).
It is also available on this thesis repository.
My PhD research dealt with the theoretical physics of complex biological membranes, which surround each of our cells. Lipid bilayers, which form the basis of biological membranes, feature very rich physical properties. They are self-assembled structures that belong to the field of soft matter. While each of the two monolayers of the membrane is a two-dimensional fluid, the membrane resists bending and stretching: it is elastic.
Biological membranes contain various inclusions, in particular membrane proteins, which play crucial biological roles. In addition, it is through the membrane that a cell interacts with its environment.
My thesis focused on some generic effects of the presence of one or two membrane inclusions, or of a local chemical change of the environment of the membrane.
Casimir-like interactions between two membrane inclusions
Inclusions impose constraints on the thermal fluctuations of the shape of the membrane. These constraints generate a force between inclusions that is analogous to the Casimir force in quantum electrodynamics. In my thesis, we show the importance of the fluctuations of the Casimir-like force between two point-like membrane inclusions, such as proteins, and we study their dependence on the distance between the inclusions. We then clarify a definition necessary to study the Casimir-like force beyond its thermal equilibrium value. Finally, we study Casimir-like interactions between rod-shaped membrane inclusions, such as polymers.
This work was carried out with Prof. Jean-Baptiste Fournier.
Inclusions and membrane thickness deformations
Membrane proteins can also be coupled to membrane thickness. Indeed, many intrinsic membrane proteins have a hydrophobic mismatch with the membrane: their hydrophobic thickness is slightly different from that of the unperturbed membrane. This induces local membrane thickness deformations in the vicinity of proteins. In order to study them, it is necessary to describe membrane elasticity at the nanoscale, which is tricky. In my thesis, we put forward the importance of an energetic term that is neglected in existing models. We reanalyze numerical and experimental data, obtaining some evidence for the presence of this term.
This work was carried out with Prof. Jean-Baptiste Fournier and Dr. Doru Constantin.
Dynamics of a membrane submitted to a local chemical modification
Biological membranes are affected by inclusions, but also by the environment of the membrane, which is heterogeneous and constantly changing. In my thesis, we present a theoretical description of the dynamics of a membrane submitted to a local chemical perturbation of its environment, starting from first principles. We compare our theoretical predictions to new experimental results regarding the dynamical deformation of a biomimetic membrane submitted to a local pH increase. Finally, we show that investigations of dynamical local perturbations provide original information on the response of the membrane.
This work was carried out with Prof. Jean-Baptiste Fournier (theory), in close collaboration with Prof. Miglena I. Angelova, Prof. Nicolas Puff and Dr. Yuka Sakuma (experiments).