Development of a method of encapsulation of bacteria in polysaccharide nanotubes

Bacteria evolving on the skin like S. epidermidis are currently considered as potential components for skin-care products because of the beneficial effects they provide. However, considering the risks associated with their proliferation, it is crucial to think of solutions, such as encapsulation, to enjoy the full clinical potential of these bacteria while controlling their development and limiting the risks of adverse outcomes. The encapsulation method used in this thesis was based on the use of bicompartmentalized microtubes having a sacrificial outer compartment erasable in order to liberate the inner microtube compartment. Such bicompartimentalized microtubes were fabricated by LBL deposition, on the pores of a porous track-etched membrane, of synthetic polyelectrolytes PVCL/PMAA for the outer compartment and a pair of oppositely charged polysaccharides ALG/CHI for the inner compartment. The ALG/CHI microtubes were then released by filtering NaCl aqueous solution at pH 6.5 through the membrane, causing the desintegration of the PVCL/PMAA sacrificial compartments. Finally, microtubes were collected by filtering the filtrate containing released microtubes on a porous support. The first part of this thesis consisted in the optimization of the encapsulation method of fluorescent latex microparticles modelling bacterial cells. Different parameters were studied in order to increase the fraction of encapsulated microparticles. Results showed a larger fraction of encapsulated microparticles when using membranes with larger pore size. However, this parameter decreased the encapsulation efficiency of microtubes by making difficult or even impossible to close microtubes at their extremities. The deposition of a negatively charged ALG layer as last layer in the inner wall of microtubes allowed microparticles to penetrate deeper in the pores, increasing the amount of microparticles encapsulated. Despite the formation of a cake and aggregates of microparticles, the forced filtration process is easier, more rapid and more efficient to load the microparticles inside the pores of the membrane compared to the passive diffusion. The filtration conditions leading to the best results in terms of fraction of encapsulated microparticles were obtained for the filtration of 50mL of a microparticle suspension at the concentration of 3×10^6 microparticles/mL in 5 steps (5×10mL). After establishing the optimal parameters for the encapsulation of microparticles, the second part of this thesis consisted in transposing and adapting this method on bacterial cells. The bacterial cells chosen for this study were S. epidermidis bacteria because of the large range of beneficial effects they provide to their hosts. Results of the first conducted assays showed very few microtubes containing bacteria, with many bacteria outside the microtubes. Few experiments could unfortunately be carried out for this part because of the health crisis (COVID-19). This part will therefore be the subject of a further study.