Polymersomes: smart vesicles of tunable rigidity and permeability

We report an experimental study on the mechanical and permeability properties of giant polymersomes made of diblock (PBD-PEO) and triblock (PEO-PPO-PEO) copolymers. These polymer amphiphiles bear the architecture and macromolecular dimensions adequate for assembling stable flat bilayers with a different hydrophobicity. In the highly hydrophobic case (PBD-PEO) an extremely compact membrane is formed, resulting in rigid polymersomes which represent a permeability barrier against solute transport across. In the case of water soluble PEO-PPO-PEO triblock copolymers, the bilayer structure is less stable in favour of the micellar state; therefore giant vesicles can be solely formed at large PPO contents. These cases (Pluronics (R) L121 and its mixtures with P85 and P105) are characterised by a much lower chain entangling than highly hydrophobic membranes, their polymersomes being softer than those based on PBD-PEO. Pluronic-based polymersomes are also found to be highly permeable to hydrophilic solutes, even remaining undamaged in the case of an extreme osmotic shock. This high permeability together with their high flexibility endows Pluronics polymersomes smart core/shell properties ideal to catch large biomolecules inside and able to resist under osmotic and mechanical stresses.