Controllable Active Micro Droplets Merging Device Using Horizontal Pneumatic Micro Valves

Abstract

Abstract:We present an active droplet merging device, which can merge various sizes of micro droplets in different numbers by using pneumatically controlled horizontal PDMS microvalves. The merging part consists of a main and side channels separated by a pillar array. The pillar array structure is contained within a microfuidic channel. The function of the pillar array provides a bypass path to the continuous flow (oil) inside the merging chamber. Droplets are successfully generated within the channel and achieve merging by controlling the selective different numbers and diameters of droplets through varying the flow resistance of main and side channel. In the merging chamber, a droplet will enter and slow down its movement. It will wait and then merge with the sequential droplets. These experiments demonstrate that such a merging device can controllably select and adjust the distance between the different adjacent micro droplets without any generation of sister droplets in the side channel. The device has no desynchronization problems. Thus, it can be applied for efficiently mixing the droplets in various diameters and numbers without changing the structure of the merging chamber. Hence, this device can be a more effective choice when applying microfluidics to chemical and biological applications.

Actuation Mechanism of Microvalves: A Review

“…The marking LC stands for liquid channel, P is for pressure, indicating the volume where the pressure for opening or closing is applied, cross-hatch is a PDMS layer, diagonal-hatch glass or thermoplastic layers [74]. Because of the simple structure and low cost, the pneumatic microvalve is applied to many applications including microfluidic circuits design [75], fuel cell systems [78], mix and sort droplets [79,80], rapid hydrodynamic sample injection [81] and so on. What is more, due to the ease of fabrication and robust operation, microfluidic systems have been developed with the multiple pneumatic microvalves to improve throughput and expand applications [73,80], which are shown in Figure 10.…”

“…The device has numerous advantages like high precision and flexible manipulation. A pneumatic horizontal PDMS microvalve was proposed for the droplet merging system [79]. Changing flow resistances of main and side channels could adjust the number and diameter of droplets.…”

Technological Development – Droplet as a Tool

“…This accordingly affects the droplet trapping time within the micropillar array which subsequently controls the number of droplets merged in the process. Without pneumatic actuation, passive merging is still attainable, when the bypass channel is blocked by the accumulated droplets 134 . The number of droplets to be merged however would not be controllable.…”

Selective droplet splitting using single layer microfluidic valves

“…Once pressurised, the valve actuation chamber causes the membrane to deform into the main channel, hence changing the channels physical geometry. Based on shapes of the deformation that extracted from previous studies on single-layer valves 74,75 , we hypothesised that if the head of single layer valve is curved, more actuation would be observed especially in the splitting zone. After running and analysing a series of experiments, a mushroom-shaped valve (with 1000 length of the head) with membrane thickness 30 was selected with a PDMS mix ratio of 20:1.…”