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The shape and permeability of polymersomes
Polymer vesicles, also named polymersomes, are valuable candidates for drug delivery and micro- or nanoreactor applications. As far as drug delivery is concerned, the shape of the carrier is believed to have a strong influence on the biodistribution and cell internalization. Polymersomes can be submitted to an osmotic imbalance when injected in physiological media leading to morphological changes. To understand these osmotic stress-induced variations in membrane properties and shapes, several nanovesicles made of the graft polymer poly(dimethylsiloxane)-g-poly(ethylene oxide) (PDMS-g-PEO) or the triblock copolymer PEO-b-PDMS-b-PEO were osmotically stressed and observed by light scattering, neutron scattering (SANS), and cryo-transmission electron microscopy (cryo-TEM). Hypotonic shock leads to a swelling of the vesicles, comparable to optically observable giant polymersomes, and hypertonic shock leads to collapsed structures such as stomatocytes and original nested vesicles, the latter being only observed for bilayers formed by amphiphilic copolymers. The vesicle radius and membrane curvature are also shown to be critical parameters for such transformations : the shape evolution trajectory agrees with theoretical models only for large enough vesicle radii above a threshold value around 4 times the thickness.
I will also describe how such polymersomes of giant size (GUVs) can be used as mineralization reactors thanks to their impermeability to ions. GUVs are initially formed in a carbonate-rich medium and trapped in a microfluidic device. When the external medium is exchanged by a calcium solution, the membranes can be made permeable to the calcium ions by a specific carrier molecule. Calcium carbonate mineralization is then observed in the confined medium of the GUVs in view of testing some scenarios of biomineralization.