Colloidal Micro-Pumps

Colloidal Micro-Pumps

Manipulating micro-particles is very important in microfluidic applications, such as biomedical flows and self-assembled structures. Here, flows generated by the forced motion of colloidal micro-particles in a microchannel are investigated. The force coupling method combined with the spectral/hp element method is used to numerically simulate the dynamics of the flow, while a penalty method is used to determine the required forces on the particles. The pumping motion is investigated for two specific systems: a peristaltic micro-pump and a gear micro-pump. We verify the accuracy of the simulations and then for each system, we investigate the net flow rate as a function of pump frequency and channel dimension, and present optimization results. The results for the net flow rate are comparable to and within the range of the experimental data.

This work was motivated by the experiments of Terray et al (Science 296 1841-4, 2002), where they designed and operated colloidal micro-devices (pumps and valves) for microfluidic control. Pump designs that employ inertial, centrifugal action, e.g. impeller-based pumps, are inappropriate for microfluidic applications due to the very small Reynolds number. However, designs based on positive-displacement methods can be quite effective. To this end, Terray et al developed two positive-displacement micro-pumps by using colloidal microspheres as the active flow-control element. Small microspheres, at colloidal scales, can be manipulated remotely using electric or magnetic fields or optical trapping; the latter was employed by Terray et al in their experiments. Remote activation techniques are particularly attractive in controlling micro-devices as there is no need to interface directly the microfluidic application with the macroscopic environment-a major drawback in many recent designs of micro-devices.

The animations show the streamwise velocity as color-coded contours for a peristaltic pump and for a rotary gear pump. Both operate at low Reynolds number Stokes flow. The peristaltic pump operates by creating a wave traveling down the line of spherical particles. The references provide details of the flow rates achieved.

For further details see D. Liu, M.R. Maxey and G.E. Karniadakis, 2004. Modeling and optimization of colloidal micro-pumps. J. Micromech. Microeng., 14, 567-575.