Abstract
Liposomes are closed lipid bilayer membranes that have attracted attention as drug delivery carriers and cellular molecular robots. Since their mechanical properties are essential for their functionalization for such purposes, a method to evaluate their mechanical properties is desirable. Here we applied the micropipette aspiration method for liposomes prepared with two different compositions (POPC/DOPG/Cholesterol = 9/1/1 (molar ratio); Condition 1, POPC/DOPG/Cholesterol = 5/5/1; Condition 2) and numerically calculated the mechanical properties of these liposomes held at the tip of the micropipette. The mechanical properties of the aspirated liposomes, such as instantaneous elastic modulus E0, equilibrium modulus of elasticity E∞, and viscosity μ, were estimated by the standard linear viscoelastic model: E0 = 239.0 ± 106.6 Pa, E∞ = 157.0 ± 67.2 Pa, and μ = 49.7 ± 46.8 Pa･s for liposomes of Condition 1, and E0 = 100.1 ± 84.0 Pa, E∞ = 53.2 ± 45.3 Pa and μ = 57.1 ± 48.1 Pa･s for those of Condition 2. There was no statistically significant difference in the results between Condition 1 and Condition 2. We discussed these results along the references regarding lipid composition and solvent incorporating in the liposome membrane. The finite element method on liposome aspiration showed that the diameter of a micropipette tip holding the liposome has little effect on the liposome aspiration length. In the future, we will clarify the effect that membrane compositions and solvent on the mechanical properties of liposomes.
