Fluid Mixing in Growing Microscale Vesicles Conjugated by Surfactant Nanotubes

Abstract

This work addresses novel means for controlled mixing and reaction initiation in biomimetic confined compartments having volume elements in the range of 10(-12) to 10(-15) L. The method is based on mixing fluids using a two-site injection scheme into growing surfactant vesicles. A solid-state injection needle is inserted into a micrometer-sized vesicle (radius 5-25 microm), and by pulling on the needle, we create a nanoscale surfactant channel connecting injection needle and the vesicle. Injection of a solvent A from the needle into the nanotube results in the formation of a growing daughter vesicle at the tip of the needle in which mixing takes place. The growth of the daughter vesicle requires a flow of surfactants in the nanotube that generates a flow of solvent B inside the nanotube which is counterdirectional to the pressure-injected solvent. The volume ratio psi between solvent A and B inside the mixing vesicle was analyzed and found to depend only on geometrical quantities. The majority of fluid injected to the growing daughter vesicle comes from the pressure-based injection, and for a micrometer-sized vesicle it dominates. For the formation of one daughter vesicle (conjugated with a 100-nm radius tube) expanded from 1 to 200 microm in radius, the mixing ratios cover almost 3 orders of magnitude. We show that the system can be expanded to linear strings of nanotube-conjugated vesicles that display exponential dilution. Mixing ratios spanning 6 orders of magnitude were obtained in strings of three nanotube-conjugated micrometer-sized daughter vesicles.

Generation of phospholipid vesicle-nanotube networks and transport of molecules therein

“…Membrane protein integration was demonstrated 64 , as was the interconnection and interaction with biological cells and active surfaces 17,43,44 . Vesicle content control and differentiation 30 , as well as external control of the outside solution composition, provide a large variety of possible chemical environments, and dynamic sub-compartmentalization has opened pathways to more advanced artificial cell models 65 .…”

“…If a new needle with different internal solution is used for the generation of each new vesicle, a network with differentiated contents can be created. The composition of the internal volume of each newly created vesicle is determined by the size ratio of mother and daughter vesicles 30 .…”

Zipper Dynamics of Surfactant NanotubeYJunctions

“…However, we first assume that the variations in the nanotube radius are sufficiently small to be neglected. The tension driven surface flow of surfactants induces a Marangoni plug flow of the solvent inside the nanotube [17]. Membrane tension variations also cause variations in Laplace pressure inside the vesicles, which induce a Poiseuille flow through the nanotubes.…”

“…Membrane tension variations also cause variations in Laplace pressure inside the vesicles, which induce a Poiseuille flow through the nanotubes. However, the Poiseuille flow is always small compared to the plug flow provided that the tube length is much larger than the tube diameter [17]. We therefore model the nanotubes as strings under tension with the capability to merge two strings into one at the junction point.…”

Chemical Analysis in Nanoscale Surfactant Networks

“…When several vesicles are formed sequentially, controlled mixing that spans several orders of magnitude in concentration can occur (47 ). Thus, with knowledge of R, r, and the concentration of solutes in the pipette, the solute concentration in all vesicles in a network can be calculated.…”