Push pull microfluidics on a multi-level 3D CD

Abstract

A technique known as thermo-pneumatic (TP) pumping is used to pump fluids on a microfluidic compact disc (CD) back towards the CD center against the centrifugal force that pushes liquids from the center to the perimeter of the disc. Trapped air expands in a TP air chamber during heating, and this creates positive pressure on liquids located in chambers connected to that chamber. While the TP air chamber and connecting channels are easy to fabricate in a one-level CD manufacturing technique, this approach provides only one way pumping between two chambers, is real-estate hungry and leads to unnecessary heating of liquids in close proximity to the TP chamber. In this paper, we present a novel TP push and pull pumping method which allows for pumping of liquid in any direction between two connected liquid chambers. To ensure that implementation of TP push and pull pumping also addresses the issue of space and heating challenges, a multi-level 3D CD design is developed, and localized forced convection heating, rather than infra-red (IR) is applied. On a multi-level 3D CD, the TP features are placed on a top level separate from the rest of the microfluidic processes that are implemented on a lower separate level. This approach allows for heat shielding of the microfluidic process level, and efficient usage of space on the CD for centrifugal handling of liquids. The use of localized forced convection heating, rather than infra-red (IR) or laser heating in earlier implementations allows not only for TP pumping of liquids while the CD is spinning but also makes heat insulation for TP pumping and other fluidic functions easier. To aid in future implementations of TP push and pull pumping on a multi-level 3D CD, study on CD surface heating is also presented. In this contribution, we also demonstrate an advanced application of pull pumping through the implementation of valve-less switch pumping.

Fig. 1

(a) TP pumping by Abi-Samra el al. Ventless chamber A prevents incorporation of of TP pumping in centrifugal driven microfluidic processes. (b) Push and Pull pumping principles. Design of “U” bent, location of channel opening at bottom of chambers, and vented chamber A allows incorporation of TP pumping as part of centrifugal driven microfluidic processes.

Fig. 2

Layered fabrication of the multi-level microfluidic CDs.

Fig. 3

Experimental setup: custom made CD spin test system consisting of a motorized spinning module, digital rpm meter, and high speed camera all controlled and monitored with a computer configured with LabVIEW. Forced convection heating and CD surface temperature measurement are performed using a modified industrial grade hot-air gun and infrared (IR) thermometer.

Fig. 4

(a) A design to evaluating CD surface heating. CD shown contains TP air chambers placed along various CD radii, and at 40% density (calculated by the percentage of area taken by TP air chambers on a radial path, denoted by (A/B) × 100%). (b) CD designs to evaluated single-level TP pumping (SL TP), multi-level TP pumping (ML TP 1), and multi-level TP pumping with double volumed TP air chamber (ML TP 2).

Fig. 5

(a) A design to demonstrate push-pull pumping. Liquid will be pushed from chamber A to B, and then pulled from chamber B to A (b) A design to demonstrate valve-less switch pumping. Liquid will burst from chamber A1 to B, then pulled into C1, followed by liquid bursting from chamber A2 to B, then pulled into C2.

Fig. 6

(a) Heating pattern of CD surface with TP air chambers placed along various radi on the CD, at 40% density, 300rpm, and 190°C heating. (b) Heating pattern of CD surface with TP air chambers of various density, placed along 60mm radius, at 300rpm, and 190°C heating. (c) Achievable CD surface temperature with stepped increments of heat source setting.

Fig. 7

(a) Liquid is loaded into chamber A. The heat source is then powered ON. (b) Heating activates push pumping of liquid out of chamber A. (c) Push pumping of liquid from chamber A to B in progress. (d) Push pumping of liquid into chamber B is complete. The Heat source is then powered OFF. (e) Cooling of CD activates pull pumping of liquid from chamber B to A. (f) Pull pumping of liquid from chamber B back into chamber A is complete. Note: circle indicates heating / cooling zones.

Fig. 8

(a) Coloured liquids are individually loaded into chambers A1 and A2. The heat source is then powered ON over TP air chamber T1. (b) Blue liquid bursts from chamber A1 into chamber B. The heat source is then repositioned over TP air chamber T2. (c) Pull pumping of blue liquid from chamber B into chamber C1 in progress. (d) Pull pumping of blue liquid into chamber C1 is completed. (e) Red liquid bursts from chamber A2 into chamber B. The heat source setting is then lowered, and repositioned over TP air chamber T1. (f) Pull pumping of red liquid from chamber B into chamber C2 is in progress. (g) Pull pumping of red liquid into chamber C2 is completed. The heat source is then powered OFF. Note: circles indicate heating and cooling areas where the surface temperature is measured.