Micropumps & Micro Throttle Pumps (MTPs) - Microfluidics & Microengineering Group @ STRI @ University of Hertfordshire

Micropumps, Microthrottles and Microvalves

The ability to accurately transport fluids within integrated microfluidic systems is essential if microfluidic instruments are to become reliable and more commonplace.

Many variations of microvalve and micropump associated topologies and actuation principles have been reported in the literature. However pumping of 'real-world' fluids (for instance biological cell suspensions) continues to prove problematic.

We have developed piezoelectrically actuated elastomer-glass valves and pumps which minimize the problems of blockage and sticking often encountered with microvalves when applied in such real-world conditions.

Micro Throttles

Micro throttles take advantage of the elastic properties of elastomer-glass composite substrates. Microstructures are fabricated within polydimethylesiloxane (PDMS) layers using standard soft lithographic techniques. Thin borosilicate glass is then bonded to the PDMS to form a composite structure. Piezoelectric actuation of a bimorph bonded to the top surface of the thin glass allows the flow resistance of the PDMS throttles to be increased or decreased significantly via deformation of the PDMS microstructures. These piezoelectrically actuated elastomer-glass throttles have been incorporated in throttle-style micropumps. The non-closing design of the micro throttles minimizes the typical microvalve problems of blockage and sticking.


Piezoelectrically actuated pdms-glass throttle test chip containing six throttle designs.	3D map of the surface profile of a PDMS throttle structure - image supplied by Lambda Photometrics.	2D ANSYS model of a channel in an elastomeric substrate compressed from the top surface. Click to play.

Single Piezo Actuated Solid Phase Compatible Micro Throttle Pumps

Single piezo actuated Micro Throttle Pumps (MTPs) have been developed which facilitate smaller internal volumes and significantly simplified assembly processes. Microfluidic structures are positioned in the elastomeric substrate to exploit regions which concurrently flex in opposing directions due to stresses induced in the elastomer/glass composite by flexure of the PZT.

Schematic cross section demonstrating the bi-directional deformation generated by the flexure of the offset PZT on a elastomer/glass composite substrate.

The first-generation single piezo actuated MTPs have been tested with both water and a suspensions of 5μm diameter polystyrene beads (at 4.5x10⁷ beads ml^-1). Maximum pumping rates of 132μl min^-1 for water and 108μl min^-1 for beads were achieved at a drive frequency of 800Hz. The pumping rate is easily controlled by changing the drive voltage (and hence power). A maximum back pressure of 6 kPa was achieved with zero flow. The internal volume of the pump from input to output connection is just 1.4ml.


Single piezo actuated MTP (first-generation).	SEM of microstructured PDMS layer of single piezo actuated MTP. Displaying the simply fabricated single depth structure.	3D vibrometric map of the top surface of the single piezo MTP measured @ 800Hz - image supplied by Lambda Photometrics. Click to play.


Pump rate v's drive frequency for a single piezo actuated MTP for water and 5μm bead suspension.	Pump rate v's Backpressure for a single piezo actuated MTP for water and 5μm bead suspension.

It is anticipated that modification of the single piezo actuated MTP design, to further exploit the regions of opposing flexure, will result in both increased pumping rates and backpressure capabilities and the possibility of pumping cellular matter without damage or contamination.

We believe that MTPs have significant potential in areas requiring non-destructive transport of both particulate and cellular suspensions. In addition the simple planar fabrication technique presented represents a practical step towards implementation of low-cost integrated polymer based Microfluidic systems.

Bi-Directional 3 Piezo Actuated Micro Throttle Pumps

Bi-directional MTPs have been fabricated by combining two separate PZT actuated micro throttles with a PZT operated PDMS-glass pumping chamber. Patterned deformable PDMS layers contain the microfluidic channels, micro-throttles and pump chamber features. Glass layers provide multi layer manifolding, seal the features and provide diaphragms for the piezoelectric bimorph actuators.

Tests have demonstrated that our first-generation bi-directional MTPs can successfully pump water at up to 300μl min^-1 in either direction. The pumping rate is again simply controlled by changing the applied voltage.


PCB mounted 3 piezo actuated Bi-directional MTP.	Pump rate v's drive frequency of a 3 piezo actuated Bi-directional MTP in both directions.

Sealing Valves and Micropumps

Piezoelectrically actuated elastomer-glass sealing valves have been fabricated using the same technologies as the throttles. These devices utilize the compliance of the elastomer substrate to form internal valve seats which should be tolerant of suspended phases whilst also creating a more effective seal and being able to pump against greater pressures.


PDMS seal valve structure.	Pump rate v's backpressure of a PDMS-glass Seal valve micropump in the forward direction.