Mechanics of Irradiation-Induced Structural Changes in a Lipid Vesicle

Irradiation-induced oxidation of lipid membranes is implicated in diseases and has been harnessed in medical treatments. Irradiation induces the formation of oxidative free radicals, which attack double bonds in the hydrocarbon chains of lipids. Studies of the kinetics of this reaction suggest that the result of the first stage of oxidation is a structural change in the lipid that causes an increase in the area per molecule in a vesicle. Since area changes are directly connected to membrane tension, irradiation-induced oxidation affects the mechanical behavior of a vesicle. Here, we analyze shape changes of axisymmetric vesicles that are under simultaneous influence of adhesion, micropipette aspiration, and irradiation. We study both the equilibrium and kinetics of shape changes and compare our results with experiments. The tension-area relation of a membrane, which is derived by accounting for thermal fluctuations, and the time variation of the mechanical properties due to oxidation play important roles in our analysis. Our model is an example of the coupling of mechanics and chemistry, which is ubiquitous in biology.