ED Sciences Chimiques
Assembly and dynamics of cell-mimetic active systems
by Vivien WILLEMS (Centre de Recherche Paul Pascal)
The defense will take place at 10h00 - Amphitheatre CRPP Centre de Recherche Paul Pascal 115 Avenue du Dr Albert Schweitzer 33600 Pessac
in front of the jury composed of
- Jean-Christophe BARET - Professeur - Université de Bordeaux - Directeur de these
- Laura ALVAREZ FRANCES - Maîtresse de conférences - Université de Bordeaux - CoDirecteur de these
- Anke LINDNER - Professeure - ESPCI Paris PSL - Rapporteur
- Christophe YBERT - Directeur de recherche - Université Claude Bernard Lyon 1 - Rapporteur
- Laura RODRIGUEZ ARRIAGA - Professeure - Universidad Autonoma de Madrid - Examinateur
- Cécile ZAKRI - Professeure - Université de Bordeaux - Examinateur
This thesis explores the behaviour of phase-separated giant unilamellar vesicles (GUVs) under the influence of AC electric fields and how they can be utilised as a novel type of biomimetic compartmentalised microswimmer with reconfigurable dynamics. Inspired by biological microswimmers, artificial microswimmers aim to mimic the dynamical behaviour and functionality of their biological counterparts. Typically, active colloidal Janus particles act as model systems capable of self-propulsion when driven out of equilibrium by energy input such as fuel or an actuation mechanism due to their asymmetry in composition. However, the use of solid colloidal particles limits the versatility and functionality of these colloidal microswimmers despite the inclusion of responsive and adaptive materials. Mimicking the dynamics and behavior of the membrane architecture of cells is, therefore, a logical next step towards the development of functional soft artificial microswimmers. For this we use giant unilamellar vesicles (GUVs) as a model system of cell membranes as new active system. Ternary lipid systems combining high and low melting temperature lipids with cholesterol (e.g. DOPC/DPPC/chol) form GUVs exhibiting spontaneous phase separation at room temperature, leading to a lateral asymmetry of the vesicle membrane reminiscent of Janus particles. This allows the actuation of the GUVs under an AC field between parallel electrodes and the observation of their self-propulsion via induced charge electroosmosis (ICEO). The characterisation of the phase-separated GUVs behaviour over a range of AC field conditions allows the identification of ideal field conditions to study the active motion of these Janus GUVs. Thus, under certain field conditions, the asymmetric GUVs exhibit active motion similar to their colloidal analogues. Interestingly, in this case, the fluidity of the GUV membranes enables the emergence of reconfigurable dynamics at room temperature, leading to run and tumble motion due to the emergence of transient asymmetry-symmetry states, not observed in solid colloidal particles. Measurements of the membrane fluidity show a distinct dependence on the cholesterol concentration, thus indicating the dependence of GUV dynamics on the cholesterol content. Furthermore, the dependence of the phase separation on temperature provides a trigger to access different regimes of GUV motion actuated by AC-fields: rolling, run and tumble, and subdiffusive. Finally, this work shows perspectives on improving this system towards increasing control over or adding functionality to these novel cell-inspired soft microswimmers. It tackles current challenges at the interface between active matter and synthetic cells design. Overall, this thesis shows how simple cell-inspired architectures actuated by external fields can exhibit a variety of behaviours and replicate intricate dynamics similar to cellular motility. Thus, these vesicular systems provide an exciting alternate route towards the development of next-generation functional microswimmers for future applications relating to motile artificial cells or soft microdevices.