Towards combinatorial mixing devices without any pumps by open-capillary channels: fundamentals and applications.

Marie Tani,Koki Kamiya,Ko Okumura,Ryuji Kawano

doi:10.1038/srep10263

Abstract

In chemistry, biology, medical sciences and pharmaceutical industries, many reactions have to be checked by transporting and mixing expensive liquids. For such purposes, microfluidics systems consisting of closed channels with external pumps have been useful. However, the usage has been limited because of high fabrication cost and need for a fixed setup. Here, we show that open-capillary channels, which can be fabricated outside a clean room on durable substrates and are washable and reusable, are considerably promising for micro-devices that function without pumps, as a result of detailed studies on the imbibition of open micro-channels. We find that the statics and dynamics of the imbibition follow simple scaling laws in a wide and practical range; although a precursor film obeying a universal dynamics appears in the vertical imbibition, it disappears in the horizontal mode to make the design of complex micro-channel geometry feasible. We fabricate micro open-channel devices without any pumps to express the green florescent protein (GFP) by transporting highly viscous solutions and to accomplish simultaneous chemical reactions for the Bromothymol blue (BTB) solution. We envision that open-capillary devices will become a simple and low-cost option to achieve microfluidic devices that are usable in small clinics and field studies.

Highlights

Two different fronts of the liquid become distinguishable. This is because a thin precursor film (PF) develops gradually ahead of the front of the bulky liquid column (LC), below which the rectangular channel is almost completely filled
While the length of the liquid column saturates to a fixed value as in the usual capillary rise, the precursor film keeps proceeding to the top of the plate
Our study resolves the following problems that have limited practical application of the previous studies on mixing solutions by capillary force[46]: (1) Only conventional closed micro-channels have been discussed for mixing, which are less attractive than open channels because of various advantages of open channels as discussed in the paragraph and because of the readiness for use with pumps at the cost of expensive facilities for fabrication

Summary

Introduction

14,33,34,41), and z ~ t (see Fig. 1f and Ref. 5) Since such scaling laws are highly useful for the development of the device for the transport of a small amount of liquid, studies on the imbibition of open capillary is indispensable from a fundamental viewpoint and from a practical viewpoint. This film, which potentially limits practical applications, is, suppressed when the imbibition proceeds in the horizontal direction Together with this disappearance of the precursor film, the simple quantitative laws for the final height and the dynamics established for the liquid column allow the design of complex micro-devices for transporting small amounts of liquids without any flow systems, such as electronic pumps. Rectangular open channels function well compared with closed ones, even though rectangular open channels are much more easy to make, durable, and much less expensive

Methods

Results

Conclusion