Latex micro-balloon pumping in centrifugal microfluidic platforms

Abstract

Centrifugal microfluidic platforms have emerged as point-of-care diagnostic tools. However, the unidirectional nature of the centrifugal force limits the available space for multi-step processes on a single microfluidic disc. To overcome this limitation, a passive pneumatic pumping method actuated at high rotational speeds has been previously proposed to pump liquid against the centrifugal force. In this paper, a novel micro-balloon pumping method that relies on elastic energy stored in a latex membrane is introduced. It operates at low rotational speeds and pumps a larger volume of liquid towards the centre of the disc. Two different micro-balloon pumping mechanisms have been designed to study the pump performance at a range of rotational frequencies from 0 to 1500 rpm. The behaviour of the micro-balloon pump on the centrifugal microfluidic platforms has been theoretically analysed and compared with the experimental data. The experimental data show that the developed pumping method dramatically decreases the required rotational speed to pump liquid compared to the previously developed pneumatic pumping methods. It also shows that within a range of rotational speed, a desirable volume of liquid can be stored and pumped by adjusting the size of the micro-balloon.

Fig. 1

Schematic of conventional pneumatic pumping and latex micro-balloon pumping. a Static pneumatic pumping before liquid enters the compression chamber, and b after liquid enters the compression chamber and it compresses the air. c latex micro-balloon before liquid enters the air chamber, and d after liquid enters the air chamber, it pushes against the trapped air inside the chamber and expands the micro-balloon.

Fig. 2

Schematics showing assemblies of CD-like microfluidic platforms consisting of PMMA, PSA layers and latex film; a Fabricating arrays of micro-balloon by a single fabrication process (seven layer design). b Fabricating a single micro-balloon (three layer design).

Fig. 3

Microfluidic platform designs. Design A (on the left) contains a U-shaped destination chamber connected to the source chamber via a vertical micro-channel. The destination chamber comprises of an intake compartment and an air chamber attached with a micro-balloon. Design B (in the middle) consists of an air chamber attached with a micro-balloon. The air chamber is connected to the source chamber through an intake compartment. Design C (on the right) demonstrates the assisted siphon of liquid using design A.

Fig. 4

Figure showing parameters regarding to micro-balloon expansion volume and hydrostatic pressure when the disc is stopped and rotational. R_i0, R_c0, R_i, R_c are liquid plug distances from the disc centre in the intake compartment and air chamber when the disc is stopped and rotated, x and y are liquid level heights in the intake compartment and air chamber respectively. Micro-balloon expansion height (bulge height) is defined by z and r_b is the Micro-balloon radius

Fig. 5

Schematic of micro-balloon micro-pumping analysis design. a liquid is loaded. b rotational the platform causes filling through the intake compartment. c continued filling traps air in the air chamber. d high centrifugal force causes continued of liquid transfer and expansion of the micro-balloon which allows near equalization of the liquid levels. e slowing the rotational speed reduces the centrifugal pressure, constricts the micro-balloon and liquid inside the intake compartment is pumped back towards the centre of the disc. f when rotational speed is reduced to zero the micro-balloon is flattened (returned to its initial state) and liquid is pumped to the closest position to centre of the disc.

Fig. 6

Schematic of micro-balloon micro-pumping analysis design. a the rotational frequency versus the liquid level in the intake compartment for three sizes of micro-balloons. b rotational the platform causes filling through the intake compartment. c continued filling traps air in the air chamber. d high centrifugal force causes continued of liquid transfer and expansion of the micro-balloon which allows near equalization of the liquid levels. e slowing the rotational speed reduces the centrifugal pressure, constricts the micro-balloon and liquid inside the intake compartment is pumped back towards centre of the disc. f when rotational speed is reduced to zero the micro-balloon is flattened (returned to its initial state) and liquid is pumped to the closest position to centre of the disc.

Fig. 7

Schematic of micro-balloon micro-pumping. a Sample liquid is initially loaded into the source chamber. b The platform is then spun to burst the liquid from the source chamber into the air chamber. The absence of any vent hole in the air chamber forces the displaced air into the micro-balloon. c Increasing rotational speed results in higher centrifugal force and more volume of liquid is transferred to the air chamber. d All the liquid is transferred into the air chamber. e Reducing the rotational speed to lower levels result in micro-balloon contraction, this in return pumps the sample liquid back to the disc centre. f All the liquid is pumped back towards the disc centre to the source chamber.

Fig. 8

The rotational frequency versus the amount of stored liquid using design B (see Fig. 3b) for three different sizes of micro-balloons.

Fig. 9

schematic of siphon valve. a loading source chamber. b transferring liquid to the destination chamber by centrifugal force and trapping the air in the air chamber. c equalization of liquid levels at intake compartment and air chamber, and micro-balloon expansion. d decreasing the rotational speed cause micro-balloon contraction and pumps liquid in intake toward the disc centre. e when liquid level is higher than the siphon crest siphon activates and liquid sample transfers to ultimate destination. f slightly increasing the rotational frequency transfers whole liquid samples.