Pumping fluids in microfluidic systems using the elastic deformation of poly(dimethylsiloxane)

Abstract

This paper demonstrates a methodology for storing and pumping fluids that provide a useful capability for microfluidic devices. It uses microfluidic screw valves to isolate fluids in poly(dimethylsiloxane) (PDMS) microcompartments, in which the pressure of the liquid is stored in the elastic deformation of the walls and ceiling of the compartments. Fluids can be stored under pressure in these structures for months. When the valves are opened, the walls and ceiling push the fluid out of the compartments into microfluidic channels. The system has five useful characteristics: (i) it is made using soft lithographic techniques; (ii) it allows multiple reagents to be preloaded in devices and stored under pressure without any additional user intervention; (iii) it makes it possible to meter out fluids in devices, and to control rates of flow of fluids; (iv) it prevents the user from exposure to potentially toxic reagents; and (v) it is hand-operated and does not require additional equipment or resources.

Microvalves and Micropumps for BioMEMS

“…Another form of pinch microvalve is the TWIST valve developed by Weibel et al [2], which incorporates stainless steel screws with photocurable polyurethane threads directly on PDMS replicas (Figure 12). This represents a highly manual option, but offers advantages in simple, disposable microfluidic systems.…”

“…Electrokinetic valving is now only used in a very specific set of applications (mainly, capillary electrophoresis, for which electroosmotic flow is well suited) due to serious drawbacks: (1) As with all electrokinetic transport, it is strongly influenced by the surface properties of the channel (in practice, it only works reliably with glass surfaces, which happen to be difficult and expensive to micromachine); (2) It is strongly influenced by the ionic composition of the buffer: at pH > 3, the hydroxyl groups on the walls dissociate, creating negatively charged walls (with pH-dependent charge)-it is the loosely bound positive ions next to the wall that the voltages move; (3) It requires high-voltage sources and switches that are cumbersome, expensive, and unsafe; (4) Valving requires continuous flow to work: what "closes" the "valve" is the flow of buffer. …”

“…The valves can be actuated mechanically [1][2][3][4], pneumatically [5][6][7][8][9][10][11][12][13], electrokinetically [14][15][16][17], by phase changes [10,11,[18][19][20][21][22], or by introduction of external force [23,24]. Using the method of actuation as the differentiating parameter, five major classes of active microvalves can be identified in the literature: electrokinetic, pneumatic, pinch, phase change, and burst.…”

“…Pneumatic valves typically rely on a flexible membrane to control the flow pattern in the flow channel. Pinch microvalves [1][2][3] operate by physically deforming PDMS using mechanical pressure. Phase-change microvalves alternate between different phases of materials such as paraffin [10,11,22], hydrogels [20,21], or aqueous solutions [18] to modulate flow.…”

Polydimethylsiloxane-based conducting composites and their applications in microfluidic chip fabrication

“…For example, Weibel et al fabricated a screw-valve-actuated PDMS-based pump that offers the advantages not only of storing multiple reagents in chips but also of controlling the rates of reagent flow. 44 Liu et al 45 designed and fabricated a GER fluid-driven pump actuated by electric signals and applied to eight PDMS-based conducting electrodes ͓shown, respectively, from A to H in Fig. 4͑a͔͒.…”