  Lipid vesicles are known to undergo complex conformational transitions, but
it remains challenging to systematically characterize non-equilibrium membrane
shape dynamics. Here, we report the direct observation of lipid vesicle
relaxation from highly deformed shapes using a Stokes trap. Vesicle shape
relaxation is described by two distinct characteristic time scales governed by
the bending modulus and membrane tension. Interestingly, experimental results
are consistent with a viscoelastic model of a deformed membrane. Overall, these
results show that vesicle relaxation is governed by an interplay between
membrane elastic moduli, surface tension, and vesicle deflation.
