Large-Scale Preparation of Giant Vesicles by Squeezing a Lipid-Coated Marshmallow-like Silicone Gel in a Buffer

Menthyl acetate powered self-propelled Janus sponge Marangoni motors with self-maintaining surface tension gradients and active mixing

HYPOTHESIS

Small scale Marangoni motors, which self-generate motion by inducing surface tension gradients on water interfaces through release of surface-active "fuels", have recently been proposed as self-powered mixing devices for low volume fluids. Such devices however, often show self-limiting lifespans due to the rapid saturation of surface-active agents. A potential solution to this is the use volatile surface-active agents which do not persist in their environment. Here we investigate menthyl acetate (MA) as a safe, inexpensive and non-persistent fuel for Marangoni motors.

EXPERIMENTS

MA was loaded asymmetrically into millimeter scale silicone sponges. Menthyl acetate reacts slowly with water to produce the volatile surface-active menthol, which induces surface tension gradients across the sponge to drive motion by the Marangoni effect. Videos were taken and trajectories determined by custom software. Mixing was assessed by the ability of Marangoni motors to homogenize milliliter scale aqueous solutions containing colloidal sediments.

FINDINGS

Marangoni motors, loaded with asymmetric "Janus" distributions of menthyl acetate show velocities and rotational speeds up to 30 mm s-1 and 500 RPM respectively, with their functional lifetimes scaling linearly with fuel volume. We show these devices are capable of enhanced mixing of solutions at orders of magnitude greater rates than diffusion alone.

Scalable Synthesis of Planar Macroscopic Lipid-Based Multi-Compartment Structures

As life evolved, the path from simple single cell organisms to multicellular enabled increasingly complex functionalities. The spatial separation of reactions at the micron scale achieved by cellular structures allowed diverse and scalable implementation in biomolecular systems. Mimicking such spatially separated domains in a scalable approach could open a route to creating synthetic cell-like structured systems. Here, we report a facile and scalable method to create multicellular-like, multi-compartment (MC) structures. Aqueous droplet-based compartments ranging from 50 to 400 μm were stabilized and connected together by hydrophobic layers composed of phospholipids and an emulsifier. Planar centimeter-scale MC structures were formed by droplet deposition on a water interface. Further, the resulting macroscopic shapes were shown to be achieved by spatially controlled deposition. To demonstrate configurability and potential versatility, MC assemblies of both homogeneous and mixed compartment types were shown. Notably, magnetically heterogeneous systems were achieved by the inclusion of magnetic nanoparticles in defined sections. Such structures demonstrated actuated motion with structurally imparted directionality. These novel and functionalized structures exemplify a route toward future applications including compartmentally assembled "multicellular" molecular robots.