Polymersomes  have been a popular subject of investigation during the last decade. Possible applications of these vesicles are foreseen and proven in the area of drug delivery and in vivo imaging. For in vivo applications polymersomes need to circulate in the blood stream. In the case of liposomes this is achieved by covering the phospholipid periphery with up to ten percent PEG to obtain so called stealth liposomes. Polymersomes are assembled from amphiphilic block copolymers. Because of the good biocompatibility PEG is a popular water soluble block, leading to inherently hundred percent PEGylated polymersomes.In a recent study we designed a biocompatible block copolymer of polybutadiene-b-polyethylene glycol. The two blocks were coupled via an hydrazone bond, which is susceptible to hydrolysis below physiological pH. First we showed how the long term stability of polymersomes formed from this block copolymer is strongly dependent on the pH of its environment. At physiological pH the particles were stable for at least three days, but at pH 5.4 the colloidal stability was lost within hours. Upon changing the length of the peripheral PEG chains we were able to tune the colloidal stability of these polymersomes at a fixed pH.In a second experiment we examined what the minimum amount of surface PEG is to keep polymersomes in solution. We synthesized a acid stable analogue and mixed it in at different concentrations. Upon lowering the pH we showed that only about five percent of the PEG chains is required to obtain a stable polymersome solution.

Dynamic polymersome surfaces

242nd National Meeting (2011)

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