A virtual valve for smooth contamination-free flow switching

Abstract

We present a channel geometry that allows for clean switching between different inlets of a microchip without any contamination of the inlets or the downstream flow. We drive this virtual valve with a pneumatic pressure setup that minimizes disturbance of the downstream flow during the switching procedure by simultaneous variation of the pressures applied to the different inlets. We assess the efficiency of the setup by spectroscopic measurement of downstream dye concentrations, and demonstrate its practical utility by sequentially constructing multiple layers of alginate hydrogel. The method is potentially useful for a whole series of further applications, such as changing perfusion liquids for cell culture and cell analysis, metering, chemical-reaction initiation and multi-sample chromatography, to name a few.

Fluidic microstructuring of alginate hydrogels for the single cell niche

“…The virtual valves use bypass channels in combination with the flow pattern illustrated exemplarily for the calcium side to keep all inlets clean while allowing to select an arbitrary sequence among them. 16 (B) Micrograph of the fluidic device for gel formation. Immobilized cells are stationary, while the liquid alginate precursor solution is still flowing.…”

“…By changing the alginate precursor solution during the gel growth using the virtual valve, 16 we get successive distinct layers. If the alginate is chemically modified, successive layers of chemically distinct alginate are obtained.…”

“…We propose on-chip layer-by-layer deposition of chemically modified alginates to achieve three-dimensional environments on the single cell scale. In the past, we have demonstrated layer-by-layer deposition of alginates with different particle loads, 15,16 here we extend the technique to chemically modified alginates, enabling structuring of the environment around single cells. We provide a proof of principle of this concept by depositing alternatively fluorescently labeled and non-fluorescent alginate under biocompatible conditions; we investigate the maximum resolution achievable and show that is well below the typical size of mammalian cells when the necessary experimental precautions are taken.…”

A miniaturized continuous dielectrophoretic cell sorter and its applications

“…3 DEP has been previously used in continuously operating microfluidic applications, such as flow cytometry 4 and cell dipping. 5 Furthermore, DEP-based separation methods require a standard technology of inexpensive and well-established microfabrication processes; they are easily interfaced to fluidic control 6,7 to inject the sample and to standard electronics for the electrical signals generation. DEP probes both the cell interior and the cell membrane 3 and can therefore discriminate between cells on the basis of physical or biochemical phenomena occurring inside the cells or at the cell surfaces in a noninvasive manner.…”

Microfluidics: A New Layer of Control for Extrusion-Based 3D Printing

“…To further overcome this limitation, extrusion-based 3D printing can benefit from more complex microfluidic systems, which can implement a number of fluidic manipulation functions at the micro-scale. Microfluidics has seen major developments in recent years, and has contributed to the emergence of the concept of “Lab on a chip” by allowing the implementation of many fluidic functions such as micro-mixers [ 39 , 40 , 41 ], switching valve [ 42 , 43 , 44 ], flow focusing [ 45 ], particles focusing [ 46 , 47 , 48 ], in-channel detection [ 49 ] or particles and cell sorting [ 49 , 50 , 51 , 52 ] in compact, microfabricated devices.…”