Description du sujet de thèse

Interfacial gelation of polymers for encapsulation

Contexte de travail

The GENNIAL ANR project, which involves ESPCI, Mines Paris Tech and Sao Paulo State University, aims at understanding the mechanisms at play during during an encapsulation process called the dripping method. This method widely used to encapsulate drugs or cells in biomedical applications consists in dripping a drop of negatively charged polymer solution (typically alginate) onto a liquid bath filled with a divalent cation (for example calcium ions) . When the droplets impact the bath, the divalent ions diffuse through the drops containing the polymer solution and bind together the negatively charged polymer molecules through electrostatic interactions. Consequently an elastic gelled shell which grows over time. In an attempt to better control the shape and mechanical properties of the gel beads we have studied experimentally using a high speed camera the shape of the drops as they hit the bath and then become spherical over time. We have shown that the shape relaxation is controlled by the elasticity of the gelling shell forming around the drops.
During the thesis we will study this gelation process in a model geometry in a capillary tube. We will put in contact the polymer and calcium solutions and observe to how the gelled shell forms over time using fluorescence imaging. Furthermore we will explore different formulations to control the mechanical properties of the gel. We will for example replace the calcium ions by a cationic polymer to obtain an interfacial complexation of the two oppositely charged polymers or explore other interactions such as hydrogen bonds. We will measure the bulk mechanical properties of the gels as well as the interfacial rheology of the gelling membrane.
Techniques used : high speed camera, fluorescent microscopy, bulk and interfacial rheology, mechanical measurements