A Miniature, Nongassing Electroosmotic Pump Operating at 0.5 V

Abstract

Electroosmotic pumps are arguably the simplest of all pumps, consisting merely of two flow-through electrodes separated by a porous membrane. Most use platinum electrodes and operate at high voltages, electrolyzing water. Because evolved gas bubbles adhere and block parts of the electrodes and the membrane, steady pumping rates are difficult to sustain. Here we show that when the platinum electrodes are replaced by consumed Ag/Ag(2)O electrodes, the pumps operate well below 1.23 V, the thermodynamic threshold for electrolysis of water at 25 °C, where neither H(2) nor O(2) is produced. The pumping of water is efficient: 13 000 water molecules are pumped per reacted electron and 4.8 mL of water are pumped per joule at a flow rate of 0.13 mL min(-1) V(-1) cm(-2), and a flow rate per unit of power is 290 mL min(-1) W(-1). The water is driven by protons produced in the anode reaction 2Ag(s) + H(2)O → Ag(2)O(s) + 2H(+) + 2e(-), traveling through the porous membrane, consumed by hydroxide ions generated in the cathode reaction Ag(2)O(s) + 2 H(2)O + 2e(-) → 2Ag(s) + 2 OH(-). A pump of 2 mm thickness and 0.3 cm(2) cross-sectional area produces flow of 5-30 μL min(-1) when operating at 0.2-0.8 V and 0.04-0.2 mA. Its flow rate can be either voltage or current controlled. The flow rate suffices for the delivery of drugs, such as a meal-associated boli of insulin.

A miniature, single use, skin-adhered, low-voltage, electroosmotic pumping-based subcutaneous infusion system

“…Application of a current (or a voltage) across the electrodes of pump drives protons, produced in the anodic reaction 2Ag(s)+H 2 O→Ag 2 O(s)+2H + +2e − , to the cathode, where they are consumed by the cathodic reaction Ag 2 O(s)+2H 2 O+2e − →2Ag(s)+2OH − . The protons propagate rapidly at the polyanionic surface of the ceramic membrane dragging the proximal water sheet, which transfer momentum to the water bulk causing its flow [11]. Because the electroosmotic flow is driven by a fast proton flux at the surface of the sandwiched porous membrane and because adsorption of an impurity on the membrane perturbs the flux, only pure protic liquids like water are permitted in the pump.…”

“…Figure 1 shows photographs of a skin-adhered 36×30×8 mm system designed to subcutaneously infuse 1.2 mL of a drug solution. Its electroosmotic pump is 8 mm OD and 3 mm thick [11]. In addition to the drug solution (1.2 mL, dyed red), the system contains pure water (1.1 mL, transparent) for pumping the drug, a non-allergenic adhesive patch for attachment to the skin, a needle (6 mm long, 27 gauge), and a re-usable electronic module (20×14×8 mm).…”

“…The flow, i.e., dose rate, is set by either the applied current or by the applied voltage, and the delivered dose is set by setting the starting time and the ending time of each constant current or constant voltage pulse and by counting the pulses. The membrane and the electrodes have been described earlier [11]. Briefly, the membrane (1.3 mm thick and 8 mm diameter) was made by pelletizing and firing phosphosilicic acid coated 1 μm diameter monodisperse silica microspheres at 700°C for 4 h. A similar membrane can be formed of polydisperse silica microparticles with 80% of the particles in the 1 to 5 μm range (Aldrich S5631).…”

Electroosmotic Flow Pump

“…Other noncontact microelectrodes, such as fused silica capillary microelectrodes [31,44], polyaniline-wrapped aminated graphene microelectrodes [45], and Ag/Ag2O microelectrodes [46], have been successfully fabricated to work as noncontact electrodes for bubble-free EOF pumps. In fabrication, three noncontact microelectrodes can be made from the chemical synthesis or assembly method in the laboratory.…”

Induced charge electroosmosis micropumps using arrays of Janus micropillars

“…56,58,63 Recently, new designs of electroosmotic pumps have continued to optimize designs for high flow rate or pressure 64 or low voltage. 59,65 Nonlinear electrokinetic flows represent an alternative solution; the capacitive AC current used to drive such flows alleviates Faradaic reactions. However, the pressures achieved in ICEO pumps are typically orders of magnitude smaller than those achieved with DC electroosmosis through porous structures, largely due to the limited 'pore size' s in typical ACEO systems (ΔP max~1 /s 2 ) compared with the small s possible in DCEO through porous frits.…”