Development of a Microchannel with Tapered Funnels for Evaluating Liposome Membrane Tension

Amoeba-type molecular robots, which are deformed by internal actuator molecules, use micrometer-sized liposomes as their flexibly deformable housings. To design amoeba-type molecular robots, it is crucial to evaluate the liposome membrane tension because the deformation of these robots is influenced by the membrane tension of the housing liposomes. In this study, we proposed a microchannel that enabled the evaluation of liposome membrane tension by observing the radii of liposomes trapped in tapered funnels integrated into the microchannel. Because the funnels were connected in series, the liposome membrane tension could be evaluated in a single experiment without requiring advanced experimental techniques or considerable experimental time. In addition, the evaluated liposomes were trapped in the funnels while adhering to the funnel walls, which may prevent damage due to stress concentrations and reduce the influence of dispersion leakage and fabrication inaccuracy of the microchannel. The membrane tension was derived by substituting the radii of the trapped liposomes and the pressure difference between the inlet and outlet of the funnel into the Young–Laplace equation. We evaluated the membrane tension under two conditions: (1) single-liposome trapping condition (0.57 and 0.34 mN/m) and (2) multiple-liposome trapping condition (0.41 mN/m). The difference in membrane tension between these conditions was not significant. However, we observed variability in the contact angle between the liposome and funnel wall, as well as in the membrane curvature, under the multiple-trapping condition. Therefore, we deduced that the single-liposome trapping condition was more suitable for membrane tension evaluation using the proposed microchannel.