Influence of surface charge on the formulation of elongated PEG-b-PDLLA nanoparticles

Polymeric vesicles (polymersomes) are an important class of nanoparticles for various biomedical applications. Their interaction with biological systems is strongly dependent on their topological features such as size, shape and surface charge. We have recently developed a versatile method that enables the formation of tubes or bowl-shaped vesicles (stomatocytes) out of spherical vesicles composed of the biodegradable block copolymer poly(ethylene glycol)-poly(D,L-lactic acid) (PEG-b-PDLLA), via a dialysis process. Applying this method for particles with different surface charge is however a far from trivial task, as the shape change process is affected by spontaneous membrane curvature, which is strongly influenced by the presence of charged polymer end groups. Here we describe an optimized procedure to attain an effective shape transformation toward tubes of PEG-b-PDLLA polymersomes containing PEG blocks with amine (A) or carboxylic acid (CA) end groups. The salt concentration employed during the dialysis process turns out to be key, with the CA-polymersomes requiring substantially lower concentrations than unmodified or A-ones. The ability to control now reliably shape and surface charge in these polymer vesicles, allows a future systematic analysis of the effect of these topological parameters on the biological response of the nanoparticles.