Vesicle Geometries Enabled by Dynamically Trapped States

Abstract

Understanding and controlling vesicle shapes is a fundamental challenge in biophysics and materials design. In this paper, we design dynamic protocols for enlarging the shape space of both fluid and crystalline vesicles beyond the equilibrium zone. By removing water from within the vesicle at different rates, we numerically produced a series of dynamically trapped stable vesicle shapes for both fluid and crystalline vesicles in a highly controllable fashion. In crystalline vesicles that are continuously dehydrated, simulations show the initial appearance of small flat areas over the surface of the vesicles that ultimately merge to form fewer flat faces. In this way, the vesicles transform from a fullerene-like shape into various faceted polyhedrons. We perform analytical elasticity analysis to show that these salient features are attributable to the crystalline nature of the vesicle. The potential to use dynamic protocols, such as those used in this study, to engineer vesicle shape transformations is helpful for exploiting the richness of vesicle geometries for desired applications.

Asymmetric osmotic water permeation through a vesicle membrane

“…Furthermore, it will be more insightful if we can connect the water osmotic transport to the vesicle shape transformation. In our recent work, 19 we directly remove some parts of the water volume inside the vesicle so as to speed up the osmotic process and change the vesicle volume. Although 1 µs is a long time simulation even for the current coarse-grained MD method, the amount of water flux is still very limited, e.g., for R = 28 nm, T = 350 K, and c = 2M, the salt-out flux is 1253/µs, while the total number of water molecules inside is 38 748.…”

“…Our previous simulation work demonstrated rich morphology evolutions of both fluid and crystalline vesicles composed of ionic amphiphiles, i.e., 1 palmitic acid (C 15 -COOH) and +3 trilysine (C 16 -K 3 ), 19 where some faceted polyhedron shapes can be an analogy to experiments. 26 It deserves to note that in that work and other related simulations, the water volume inside vesicles is always removed partially in order to speed up the osmotic process that takes time beyond the simulation ability.…”

“…Similar to previous work, 19,26 we use 1 palmitic acid (C 15 -COOH) and +3 trilysine (C 16 -K 3 ) as the building blocks to construct electroneutral vesicles with an average ionization of 30% in the palmitic acid molecules, corresponding to a 4.0 pH value in experiments. 26 The elementary ionic amphiphiles can spontaneously form bilayer, spherical vesicles filled with water, where the melting temperature for such bilayer membrane is around 328 K, determined by experiments.…”

“…Vesicles are versatile since they are synthesized for various purposes. Vesicle shape transformation can greatly help us to recognize the complex shapes of cells 19 triggered by the membrane permeation of water molecules. Meanwhile, recent experimental work inspires some biological and medical applications for vesicles by inserting protein channels such as Aquaporin Z (AQP) and Gramicidin A (GA), where the water permeability can be significantly enhanced by several hundreds of times.…”

Polymersomes as protocellular constructs

“…32 The additional order found in the membrane counteracts membrane tension, resulting in faceted tetrahedral vesicles. It is in theory possible to control the final morphology of a polymersome system by combining both the crystallinity of a smectic phase and the rate of organic solvent removal, as demonstrated in a computational study by Su et al 33 While these strategies result in an assortment of non-spherical morphologies, they are all essentially non-dynamic, unlike nature. One of the next big challenges in this area is the development of metastable, out of equilibrium shape changes reminiscent of nature.…”