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Stanford University

Stanford Microfluidics Laboratory

Electroosmotic Pumps for Drug Delivery

Principal Investigators: J.G. Santiago, Shawn Litster, Elia Junco, and Matthew Suss


There is a substantial and rapidly growing market for drug delivery technology. The US market for drug delivery has been estimated at $43.7 billion in 2003 (advanced sales) and projected to $74.5 billion in 2008.1 Some challenges associated with drug delivery device development include miniaturization, ease of use, reliability, and dosage consistency. We are developing EO pumps in an effort to meet the needs of this market and address the associated technical hurdles.

Electroosmotic (EO) pumps have no moving parts, require low parasitic power, and can be realized from readily available materials.2-6 Glass (and other oxide surfaces) in contact with DI water2,3 spontaneously deprotonate, resulting in a charge separation effect known as an electric double layer (EDL). Application of an external field causes ions to migrate from anode to cathode, resulting in pumping via ion drag of the bulk liquid. Three key figures of merit are flow rate per power (Q/P), self-pumping frequency (fsp, maximum flow rate normalized by package size), and flow rate stability to pressure fluctuations, k.


EO pumps compare very favorably with other micropumps, as they can achieve Q/P up to several mL/min/mW,7 fsp of 2 min-1,8 and designed for k up to hundreds of Pa/ml/min. Therefore, EO pumps are ideal for drug delivery applications; they require low parasitic power, can pump highly stable flow rates at required pressure loads and require small package volume (typically 0.1cm3). 

Key design aspects of our novel EO pump for drug delivery include9:

  • Two-liquid system, allowing for drug independent pumping (Fig 1a)

  • Sodium borate as working fluid, allowing for high buffering capacity for long-term operation at stable pH levels, and maximization of Q/P. As well, the low reversible potential of sodium borate electrolysis allows for low voltage and power operation.

  • Bubble-less performance through operation at high flow rate per current (H2 and O2 concentration remain under the solubility limit of the electrolyte).

Figure 1: Adapted from Litster et al9 (a) Schematic of the two-liquid EO pump. Two collapsible membranes actuate the drug delivery. Working electrolyte is pumped from reservoir 1 to reservoir 2 by electroosmosis. Membrane B displacement drives the liquid in reservoir 3 through the outlet. (b) The flow rate of the liquid pumped from reservoir 3 as a function of applied voltage. Flow rate is plotted at times when the fully charged device has pumped 0.2, 0.4, 0.6, 0.8, and 1.0 ml from reservoir 3.



(1)        [1] G. Orive, R. M. H., A.R. Gascon, A. Dominguez-Gil, J.L. Pedraz, Curr. Opin. Biotechnol. 2003, 14, 659-664.
(2)        Yao, S. H.;Santiago, J. G. Porous glass electroosmotic pumps: theory, Journal of Colloid and Interface Science 2003, 268, 133-142.
(3)        Yao, S. H.;Hertzog, D. E.;Zeng, S. L.;Mikkelsen, J. C.;Santiago, J. G. Porous glass electroosmotic pumps: design and experiments, Journal of Colloid and Interface Science 2003, 268, 143-153.
(4)        Yao, S. H.;Myers, A. M.;Posner, J. D.;Rose, K. A.;Santiago, J. G. Electroosmotic pumps fabricated from porous silicon membranes, Journal of Microelectromechanical Systems 2006, 15, 717-728.
(5)        Chen, C. H.;Santiago, J. G. A planar electroosmotic micropump, Journal of Microelectromechanical Systems 2002, 11, 672-683.
(6)        Zeng, S. L.;Chen, C. H.;Santiago, J. G.;Chen, J. R.;Zare, R. N.;Tripp, J. A.;Svec, F.;Frechet, J. M. J. Electroosmotic flow pumps with polymer frits, Sensors and Actuators B-Chemical 2002, 82, 209-212.
(7)        Kim, D.;Posner, J. D.;Santiago, J. G. High flow rate per power electroosmotic pumping using low ion density solvents, Sensors and Actuators a-Physical 2008, 141, 201-212.
(8)        Laser, D. J.;Santiago, J. G. A review of micropumps, Journal of Micromechanics and Microengineering 2004, 14, R35-R64.
(9)        Litster, S. H., B.; Kim, D.; Santiago, J.G. A two-liquid electroosmotic pump for portable drug delivery systems, Proceedings of IMECE 2007, November 11-15, Seattle, USA 2007.



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