Microfluidic Formation of Honeycomb-Patterned Droplets Bounded by Interface Bilayers via Bimodal Molecular Adsorption

Abstract

Assembled water-in-oil droplets bounded by lipid bilayers are used in synthetic biology as minimal models of cell tissue. Microfluidic devices successfully generate monodispersed droplets and assemble them via droplet interface bilayesr (DIB) formation. However, a honeycomb pattern of DIB-bounded droplets, similar to epithelial tissues, remains unrealized because the rapid DIB formation between the droplets hinders their ability to form the honeycomb pattern. In this paper, we demonstrate the microfluidic formation of a honeycomb pattern of DIB-bounded droplets using two surfactants with different adsorption rates on the droplet surface. A non-DIB forming surfactant (sorbitan monooleate, Span 80) was mixed with a lipid (1,2-dioleoyl-sn-glycero-3-phosphocholine, PC), whose adsorption rate on the droplet surface and saturated interfacial tension were lower than those of Span 80. By changing the surfactant composition, we established the conditions under which the droplets initially form a honeycomb pattern and subsequently adhere to each other via DIB formation to minimize the interfacial energy. In addition, the reconstituted membrane protein nanopores at the DIBs were able to transport molecules. This new method, using the difference in the adsorption rates of two surfactants, allows the formation of a honeycomb pattern of DIB-bounded droplets in a single step, and thus facilitates research using DIB-bounded droplet assemblies.

Microfluidic formation of crystal-like structures

“…surfactants with two different adsorption rates were limited by low flow rate values (same range as Seo et al 27,36 ); furthermore, the honeycomb structure in Fujiwara et al 37 was not perfectly uniform and changed over time because of the absorption of the second surfactant on the droplet surface. Very recently, the morphology of microfluidic crystals observed by Raven and Marmottant 38 were numerically reproduced 39 using a multicomponent Lattice Boltzmann method augmented by a forcing term representing the near-contact forces at the interface between two droplets.…”

“…However, shapes different from the circular one in 2D crystals have been generated only for very small flow rate values, which somehow limits the applications to low throughput ones. Even more recent attempts 37 to form honeycomb microfluidic crystals using…”

Competitive membrane wetting of polymer blends in artificial cells initiates phase separation and promotes fractionation

“…This is because such millimeter-sized droplets require a much longer time to reach the equilibrium value upon slow lipid adsorption to the W/O surface as compared with the micron-sized droplets. 29 However, we could not analyze the γ for the micron-sized droplets containing PEG/dextran blends because the blends caused phase separation, and their viscoelasticity increased with time. To evaluate the possible artifacts arising from the slow relaxation at the droplet surface upon lipid adsorption, we performed similar experiments using the nonionic Span 80, which showed a much faster relaxation and a smaller γ of ~3 mN/m, 29 as shown in Figure S3.…”

Efficient Lipid Bilayer Formation by Dipping Lipid-Loaded Microperforated Sheet in Aqueous Solution

“…Over the years, the "painting method" [10] and "monolayer-folding method" [11] have been frequently used and regarded as simple methods for obtaining BLMs. In recent years, the "droplet contact method" [12][13][14] has received significant attention for BLM production as an easier technique that generates a droplet interface bilayer (DIB) in organic solvents containing lipid molecules.…”