We describe the formation of water in oil droplets, which are commonly used in lab-on-a-chip systems for sample generation and dosing, at microfluidic Tshaped nozzles from elastic feed lines. A narrow nozzle forms a barrier for a liquid-liquid interface, such that pressure can build up behind the nozzle up to a critical pressure. Above this critical pressure, the liquid bursts into the main channel. Build-up of pressure is possible when the fluid before the nozzle is compressible or when the channel that leads to the nozzle is elastic. We explore the value of the critical pressure and the time required to achieve it. We describe the fluid flow of the sudden burst, globally in terms of flow rate into the channel and spatially resolved in terms of flow fields measured using micro-PIV. A total of three different stages-the lag phase, a spill out phase, and a linear growth phase-can be clearly discriminated during droplet formation. The lag time linearly scales with the curvature of the interface inside the nozzle and is inversly proportional to the flow rate of the dispersed phase. A complete overview of the evolution of the growth of droplets and the internal flow structure is provided in the digital supplement.
Label-free and gentle separation of cell stages with desired target properties from mixed stage populations are a major research task in modern biotechnological cultivation process and optimization of micro algae. The reported microfluidic sorter system (MSS) allows the subsequent investigation of separated subpopulations. The implementation of a viability preserving MSS is shown for separation of late stage 1 Haematococcus pluvialis (HP) cells form a mixed stage population. The MSS combines a three-step flow focusing unit for aligning the cells in single file transportation mode at the center of the microfluidic channel with a pure hydrodynamic sorter structure for cell sorting. Lateral displacement of the cells into one of the two outlet channels is generated by piezo-actuated pump chambers. In-line decision making for sorting is based on a user-definable set of image features and properties. The reported MSS significantly increased the purity of target cells in the sorted population (94%) in comparison to the initial mixed stage population (19%).
Droplet-based microfluidics provide a powerful platform for high-throughput operations applied in micro analytics, micro reaction technology and live sciences. Todays research interests focus on the development of highly integrated fluidic networks for sample processing according to a microchemical or microanalytical protocol. Normally, fluidic networks with integrated fluidic loops and bypasses are very complicated systems that require a huge effort for external control and integration of actor components. In contrast, in droplet-based microfluidics interface generated forces can be used to temporarily seal bypasses or to generate well defined pressure gradients at strictures. This potential can be used to implement self-control and self-synchronization at functional nodes in order to minimize the effort for external control and actors integration. Here we report on progress in development of functional nodes for self-synchronized 1:1 coalescence of two independently generated droplet sequences at a Y-shaped junction and on approaches for droplet aliquotation at a Y-shaped bifurcation. The droplet connector automatically balances the time delay between two droplets arriving at the junction. On this account, strictures are integrated into the Y-junction and an additional bypass connects the arriving channels. The first arriving droplet stops at the stricture until its fusion partner arrives. The droplet splitter performs an 1:1 aliqoutation of all elements of a droplet sequence. The main challenges are the balancing of pressure differences at the outlets and the correct aliquotation of droplets independent of their volume at a wide range of flow rates. The splitter design is based on the rule that forces required for splitting are always lower than the forces required for complete droplet inflow into only one of the outlet channels without splitting.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.