Box 1: Slow dynamics or demonstration of tough behavior?
Polymersomes exhibit slow dynamics. This vesicle was aspirated in a micropipette and after being releazed it keeps memory of its form for a long time. To the right you see the modified "tough" version of the vesicle.
Hyperviscous vesicles made of diblock copolymers (polymersomes)
We studied vesicles prepared from the diblock copolymer polybutadien-b-polyethylene glycol (PB-PEG). They exhibit a shear surface viscosity, which is about 500 times higher than those found in common phospholipid bilayers. Our result constitutes the first direct measurement of the shear surface viscosity of such polymersomes. At the same time, we measured the bending and stretching elastic constants, which fall in the range of values typical for lipid membranes.
Pulling out a tether from an immobilized polymersome and following its relaxation back to the vesicle body provides an estimate of the viscous coupling between the two monolayers composing the polymer membrane: the detected intermonolayer friction is about an order of magnitude higher than the characteristic one for phospholipid membranes. These polymersomes exhibit very slow dynamics (see Box 1). The dissipation in relaxation processes occurs mainly within the membrane rather than in the surrounding media (which is the case for lipid membranes). For details click here.