Sculpting vesicles with active particles:Less is more

Biological cells are able to generate intricate structures and respond to external stimuli, sculpting their membrane from within. In this talk, we present a simplified biomimetic experimental model system in order to address the question how the lipid/cell membrane responds to highly localized point forces from inside, such as those exerted by the cytoskeleton. In our experimental model system, the cell membrane is mimicked by giant unilamellar vesicles of lipid bilayers, and the local internal forces are generated by enclosing self-propelled particles [1]. We demonstrate that the propulsion forces of individual self-propelled particles, as small as ~ 0.1 pN, are sufficient to induce dramatic vesicle shapes and lead to active membrane fluctuations. Microscopic visualization is revealing, strikingly, the formation of tethered, dendric-like structures at low volume fractions and low tensions, whereas more global deformations of the vesicle shape are observed for increasing particle loadings. Moreover, the analysis of the mechanical properties of the membrane by shape fluctuation spectra shows a strong deviation from the Helfrich model elucidating the specific role of active non-equilibrium processes. Our state diagram predicts the conditions under which local internal forces generate various membrane morphologies. Strikingly-Less is more!  Our study shows how the interplay of local active forces, membrane elasticity and viscosity can give rise to a plethora of novel vesicle shapes, which do not exist in equilibrium systems. 

References.

 

[1]   H. R. Vutukuri, et al.  Active particles induce large shape deformations in giant lipid vesicles, Nature, 586, 52-56 (2020)