Cyclic micropipette aspiration reveals viscoelastic change of a gelatin microgel prepared inside a lipid droplet.

Gelatin microgels prepared inside lipid droplets have a much higher elasticity than that of bulk gels due to their differences in nanostructure. This nanostructural difference in gelatin microgels is expected to provide the microgels with unique viscoelastic properties that differ from the bulk gels. To clarify this hypothesis, here we evaluated the frequency dependent viscoelasticity of gelatin gels by developing a cyclic micropipette aspiration. The frequency dependent relationship between storage modulus E' (reflecting elasticity) and loss modulus E'' (reflecting viscosity) was compared between the microgels and the bulk gels. The microgels have a smaller ratio between elasticity and viscosity E''/E' than that of the bulk gels. Because the E''/E' of the bulk gels is constant regardless of the concentration, the microgel viscoelasticity cannot be achieved for the bulk gels with a different concentration. Theses findings mean that preparing biopolymer gels in droplets is useful to change the viscoelasticity via nanostructural transition through the interaction with the droplet interface.