Stability of polymersomes prepared by size exclusion chromatography and extrusion

摘要

In this work, stability of poly(butadiene)-poly(ethylene oxide) (PBD-PEO) polymersomes, self-assembled from two polymers with different molecular weights (PBD32-PEO21 and PBD125-PEO80) in either pure H2O or phosphate buffered saline (PBS), is studied. Polymersome dispersions usually show large polydispersity, and it is thus desirable to separate different-sized vesicles if a narrow size distribution is required, e.g. for model systems in certain applications. This is typically achieved by extrusion through a membrane with a designated pore size or, less commonly, by size exclusion chromatography (SEC). Here, we find that both extrusion and SEC of polymersome dispersions with vesicle sizes ranging from 100–5000 nm and polydispersity index (PDI) = 1, can yield smaller vesicles with PDIs 0.35. With SEC, it is possible to separate fractions of polymersomes with different sizes. However, the SEC polymersome size and particularly the spread in the size increase significantly over time, whereas the extruded polymersomes are shown to be more stable. We attribute this to possible dilution of the polymersome dispersion during the SEC elusion process. The effects of temperature and the PBD-PEO molecular weight on the stability of the extruded polymersomes against dilution in pure water and phosphate buffer are further studied. It is found that the polymersomes show higher stability when stored at lower temperature, undiluted, and prepared in phosphate buffer, whereas the polymer molecular weight does not have a large influence on the stability.