Evaporation-Induced Pattern Formation of Decanol Droplets

Pattern formation in far-from-equilibrium systems is observed in several disciplines including biology, geophysics, and reaction-diffusion chemistry, comprising both living and nonliving systems. We aim to study such nonequilibrium dynamics on the laboratory scale with materials of simple composition. We present a novel system based on a 1-decanol droplet placed in a solution of alkaline decanoate. Previously, we showed the short time scale behavior of this system, which included chemotaxis and maze solving. Here we explore long time scale dynamics of the system (several hours) when open to the environment. We observe dramatic morphological changes in the droplet including long tentacular structures, and we analyze the morphology of these structures at both the macroscopic and microscopic scales across a large range of initial conditions. Such reproducible morphological changes in simple droplets open a path to the exploration of shape-based effects in larger-scale pattern-formation studies

Dynamics of Chemotactic Droplets in Salt Concentration Gradients

The chemotactic movement of decanol droplets in aqueous solutions of sodium decanoate in response to concentration gradients of NaCl has been investigated. Key parameters of the chemotactic response, namely the induction time and the migration velocity, have been evaluated as a function of the sodium decanoate concentration and the NaCl concentration gradient. The ability of the decanol droplets to migrate in concentration gradients has been demonstrated not only in a linear chemotactic assay but also in a topologically complex environment. Additionally, the ability to reverse the direction of movement repeatedly, to carry and release a chemically reactive cargo, to select a stronger concentration gradient from two options, and to initiate chemotaxis by an external temperature stimulus have been demonstrated

Predictions of the minimal and maximal number of encapsulated giant unilamellar vesicles (GUVs).

<p>The minimal number (dashed lines) of encapsulated GUVs needed to induce sedimentation of an intact hierarchical unilamellar vesicle (HUV) of a given size is different for the sedimentation induced by centrifugation (squares) and induced by spontaneous sedimentation (circles). The maximal number (solid line) of encapsulated GUVs that can be packed into an intact HUV of a given size (diamonds) solely depends on the volume available.</p

Fluorescence intensity of giant unilamellar vesicles (GUVs) and intact hierarchical unilamellar vesicles (HUVs).

<p>The fluorescence intensity of the lumen of immobilized released GUVs is shown in light gray. The fluorescence intensity of the membrane of intact HUVs is shown in dark gray. Lines represent log-logistic fits with mean 0.42 and standard deviation 0.16 (solid line) and mean 0.13 and standard deviation 0.13 (dashed line).</p

Size distribution of giant unilamellar vesicles (GUVs) and intact hierarchical unilamellar vesicles (HUVs).

<p>The size distribution of the GUVs is shown in light gray. The size distribution of the HUVs is shown in dark gray. Lines represent normal fits with mean 2.3 μm and standard deviation 0.7 μm (solid line) and mean 9.9 μm and standard deviation 2.6 μm (dashed line).</p

Transmission and fluorescence micrographs of a representative intact hierarchical unilamellar vesicle.

<p>A) The unilamellar fluorescently labeled phospholipid membrane confining the densely packed encapsulated giant unilamellar vesicles (GUVs) is only visible in the fluorescence micrographs B and C. B) Image overlay of C) indicating the envelope membrane labeled green and D) indicating the encapsulated GUVs, the lumen of which is labeled red. Scale bar: 10 μm.</p

Schematic illustration of the preparation and isolation of intact hierarchical unilamellar vesicles (HUVs).

<p>A–C) Preparation of intermediate giant unilamellar vesicles (GUVs) employing the water-in-oil (w/o) emulsion transfer method. Black solid circles indicate biotinylated phospholipids. B, right) Imperfections in either of the two monolayers induce a release of the internal cargo into the hosting solution. C) When passing the water-oil interface the two phospholipid monolayers combine and form a bilayer confining the fluorescently active internal cargo (red circles). D) Repeated extrusion to homogenize the size distribution of the intermediate GUVs. E,F) Preparation of HUVs employing the vesicle-in-water-in-oil emulsion (v/w/o) transfer method. Green solid diamonds indicate fluorescently labeled phospholipids. G, H) Isolation of HUVs from released GUVs using a specially prepared isolation chamber. For details see text.</p

Fluorescence micrographs of intact hierarchical unilamellar vesicles (HUVs) and released giant unilamellar vesicles (GUVs).

<p>Intact HUVs and released GUVs before (A–C) and after separation (D–J). A, D, G) Image overlays of the green and red channel micrographs. B, E, H) Separate green channel and C, F, J) separate red channel micrographs. A) The intact HUVs are indicated by the confining membrane fluorescently labeled green and the encapsulated GUVs loaded with a fluorescent cargo (red). In addition, solitary released GUVs not confined by a green labeled membrane are visible. After separation, released GUVs (D) became spatially separated from intact HUVs (G). Scale bar: 25 μm.</p

Programmed Vesicle Fusion Triggers Gene Expression

The membrane properties of phospholipid vesicles can be manipulated to both regulate and initiate encapsulated biochemical reactions and networks. We present evidence for the inhibition and activation of reactions encapsulated in vesicles by the exogenous addition of charged amphiphiles. While the incorporation of cationic amphiphile exerts an inhibitory effect, complementation of additional anionic amphiphiles revitalize the reaction. We demonstrated both the simple hydrolysis reaction of β-glucuronidase and the <i>in vitro</i> gene expression of this enzyme from a DNA template. Furthermore, we show that two vesicle populations decorated separately with positive and negative amphiphiles can fuse selectively to supply feeding components to initiate encapsulated reactions. This mechanism could be one of the rudimentary but effective means to regulate and maintain metabolism in dynamic artificial cell models

Representation of a 3-dimensional section of experimental space.

<p>For each PG-type lipid, shown in bold, the horizontal section lists the lipids from the group with a net negative charge and the vertical section lists the reagents in the aqueous phase and their corresponding pH values. Response levels (the UV/Vis absorbance of Amphotericin B associated with the formulation): dark grey, >0.20; medium grey, 0.15–0.20; light grey, 0.10–0.15; white, <0.10; Blank cells, not determined. For abbreviations, see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0008546#s4" target="_blank">Materials and Methods</a>.</p