Oscillatory Reversible Osmotic Growth of Sessile Saline Droplets on a Floating Polydimethylsiloxane Membrane

Spontaneous Emulsification: Elucidation of the Local Processes

While various attempts have been made to understand the mechanism of spontaneous emulsification within the scopes of equilibrium and nonequilibrium thermodynamics, the local processes underlying spontaneous emulsification still remain elusive. In this research, we investigate the local processes that involve the transfer of surfactants as well as water from an aqueous phase to oil, which results in the formation of a water-in-oil emulsion in the organic phase. Subsequently, these emulsions invert into the oil-in-water emulsion rather abruptly as they cross the phase boundary. Studies based on ultraviolet (UV) spectroscopy and nonequilibrium molecular dynamics simulations indicate that the crossing of the phase boundary may involve catastrophic explosions and subsequent assembly of the resulting fragments to other organized structures. These processes lead to the fluctuation of the component concentrations below the interface that also becomes evident in the fast (athermal) diffusion of the emulsion droplets from the interfacial region farther into bulk water. Spontaneous emulsification is found to be amplified in mixed solvents, but it can be arrested with additives that reduce solubility or inhibit the transfer of water and surfactants in the organic phase.

One-Step Fabrication of Porous Membrane-Based Scaffolds by Air-Water Interfacial Phase Separation: Opportunities for Engineered Tissues

Common methods for fabricating membrane-based scaffolds for tissue engineering with (hydrophobic) polymers include thermal or liquid-phase inversion, sintering, particle leaching, electrospinning and stereolithography. However, these methods have limitations, such as low resolution and pore interconnectivity and may often require the application of high temperatures and/or toxic porogens, additives or solvents. In this work, we aim to overcome some of these limitations and propose a one-step method to produce large porous membrane-based scaffolds formed by air-water interfacial phase separation using water as a pore-forming agent and casting substrate. Here, we provide proof of concept using poly (trimethylene carbonate), a flexible and biocompatible hydrophobic polymer. Membrane-based scaffolds were prepared by dropwise addition of the polymer solution to water. Upon contact, rapid solvent-non-solvent phase separation took place on the air-water interface, after which the scaffold was cured by UV irradiation. We can tune and control the morphology of these scaffolds, including pore size and porosity, by changing various parameters, including polymer concentration, solvent type and temperature. Importantly, human hepatic stellate cells cultured on these membrane-based scaffolds remained viable and showed no signs of pro-inflammatory stress. These results indicate that the proposed air-water interfacial phase separation represents a versatile method for creating porous membrane-based scaffolds for tissue engineering applications.