Flow control in a laminate capillary-driven microfluidic device

Abstract

Capillary-driven microfluidic devices are of significant interest for on-site analysis because they do not require external pumps and can be made from inexpensive materials. Among capillary-driven devices, those made from paper and polyester film are among the most common and have been used in a wide array of applications. However, since capillary forces are the only driving force, flow is difficult to control, and passive flow control methods such as changing the geometry must be used to accomplish various analytical applications. This study presents several new flow control methods that can be utilized in a laminate capillary-driven microfluidic device to increase available functionality. First, we introduce push and burst valve systems that can stop and start flow. These valves can stop flow for >30 min and be opened by either pressing the channel or inflowing other fluids to the valve region. Next, we propose flow control methods for Y-shaped channels that enable more functions. In one example, we demonstrate the ability to accurately control concentration to create laminar, gradient, and fully mixed flows. In a second example, flow velocity in the main channel is controlled by adjusting the length of the inlet channel. In addition, the flow velocity is constant as the inlet length increases. Finally, the flow velocity in the Y-shaped device as a function of channel height and fluid properties such as viscosity and surface tension was examined. As in previous studies on capillary-driven channels, the flow rate was affected by each parameter. The fluidic control tools presented here will enable new designs and functions for low cost point of need assays across a variety of fields.

Figure 1

Schematics of the y-shape and valve device. (a) The y-shape device consisted of two inlet channels placed in the different vertical positions, as shown in the cross-sectional view of [1–1’] and [2–2’], and the main channel with a larger height than inlet channels. (b) Channel geometries of the y-shape device defined on each layer. (c) The valve device with the cross-sectional views for three different locations along the channel. (d) Channel geometries of the valve device defined on each layer.

Figure 2

Sequential images and side-sectional schematics of the simultaneous inflow system at the moments of (a) pipetting the solutions, (b) arriving the junction, (c) making a combined meniscus, and (d) entering into the main channel.

Figure 3

Side-sectional schematics when (a) the flow stop, (b) burst valve system forming a single meniscus, and (c) push valve system. Sequential images of the valve device showing the moments of (d) flow stop, (e) push valve open, (f) push valve release, (g) form a single meniscus, and (h) burst valve release.

Figure 4

(a) Three types of the Y-shaped device generating (i) non-mixing, (ii) a concentration gradient, (iii) fully mixing concentration profile. (b) Different geometries of the middle transparency layers. (c) Blue fraction distributions with respect to the channel width. Each value indicated in the plot calculated by averaging an enlarged image shown in Figure 4a. Error bars represent the standard deviation between experiments for each value.

Figure 5

(a) Y-shape devices with three different inlet length channels. All images show 2 s after blue and yellow dyes begin to flow through the main channel. (b) Flow distance in the main channel and (c) velocity variations over time for three different inlet channel devices. All data were calculated every 0.5 s and indicate the average (symbol) with the standard deviation (error bar) for three repeated experiments.

Figure 6

(a) Cross-sectional view of the y-shape device with three different channel height. (b) Flow distance in the main channel and (c) velocity variations over time for three devices. Distance variations over time for different concentrations of (d) glycerin and (e) SDS solutions in the y-shape device with 200 μm of the main channel height. All data were calculated every 0.5 s and indicate the average (symbol) with the standard deviation (error bar) for three repeated experiments.