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Part Ⅰ. A Miniature, Nongassing Electroosmotic Pump Operating at 0.5 V and Its Application in Drug Delivery. Part Ⅱ. Miniaturization of Zn Anode for Power Source in a Neutral pH.

초록/요약

Electroosmotic pumps (EOP) 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. By using 50 mM ascorbic acid as pumping solution, gas bubbles generated from anode could be avoided, and the flow rate of 11 μL/min at 1.2 V and 500 μA was obtained for EOP consisted of Pt/Polyaniline coated carbon paper and SiO2 membrane. The inactivation of Pt and the adsorption of ascorbic acid and its oxidized form onto SiO2 membrane caused unstable flow and led to the failure of the pump. Another EOP consisted of Ag/AgCl electrodes was tested in low concentration of HCl pumping solution. The pump produced no gas bubbles with the efficient flow of ~14 μL/min at ~1 V and 100 μA at initial stage, , but it was difficult to maintain a steady flow and the flow rate decreased as increasing Cl- concentration. It led the idea of the Ag/Ag2O might be the main redox components, not Ag/AgCl. The newlyprepared Ag/Ag2O EOP operates well below 1.23 V, the thermodynamic threshold for electrolysis of water at 25 °C, where neither H2 nor O2 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) + H2O  Ag2O(s) + 2H+ + 2e-, traveling through the porous membrane, consumed by hydroxide ions generated in the cathode reaction Ag2O(s) + 2 H2O + 2e-  2Ag(s) + 2OH-. A pump of 2 mm thickness and 0.3 cm2 cross-sectional area produces flow of 5 ~ 30 μL /min 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. With the Ag/Ag2O EOP, a programmable, skin-attached, 36 x 30 x 8 mm system for subcutaneous infusion of 1.0 mL of a drug solution is described. The system is intended to be replaced daily. It comprises a 20 x 14 x 8 mm electronic controller and power source, a 8 mm diameter and 2 mm thick electroosmotic pump, a two compartment reservoir for a pumped water and a drug solution, an adhesive tape for attachment to the skin, and a 6 mm long 27 gauge needle. Its removable electronic controller programs the dose rate and dose and is re-used. The flow rate can be adjusted between 4 µL and 30 µL min-1 by setting either by the voltage (0.2 - 0.8 V) or the current (30 - 200 µA). For average flow rates below 4 µL min-1 the pump is turned on and off intermittently. For example, a flow rate of 160 μL day-1 i.e. 0.13 µL min-1 for basal insulin infusion in Type 1 diabetes management is obtained when 10 s pulses of 75 µA are applied every 15 min. High flow rates, of 10 - 30 µL min-1, required for prandial insulin administration, are obtained when the pump operates at 50 - 200 µA. To prevent fouling by the drug, only pure water passes the pump; the water pushes a drop of oil, which, in turn, pushes the drug solution.

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초록/요약

Zn anode which can be operated at -1.0 V vs Ag/AgCl in physiological saline buffer and serum with nafion coating for 3 weeks was already developed [1]. In this study, Zn anode was miniaturized to micrometer scale, and discharge properties were characterized to develop micro sized-battery. To prepare anode, Zn was deposited on gold electrodes of 4 mm and 10 μm diameter and platinum electrode of 127 μm diameter followed by spin coating with nafion for homogeneous discharge. In case of 10 and 127 μm diameter electrode, the diameters were increased to 45 and 152 μm after Zn deposition, so Zn anodes used to discharge were 45 μm, 152 μm and 4 mm in diameter. In physiological saline buffer solution (pH 7.4, 0.15 M NaCl, 20 mM phosphate), the 4 mm diameter Zn anode had showed more than 80 % discharge efficiency with current density of 100 μA cm-2 at -1.0 V vs Ag/AgCl in physiological saline buffer. The 152 μm Zn anode had showed 61 % discharge efficiency with current density of 115 μA cm-2 and the 45 diameter Zn anodes had showed 50 % discharge efficiency with current density of 270 μA cm-2. After increase of nafion thickness twice, it was observed a stable discharge curve for 4~5 hour with the discharge efficiency of 77 %. To compose a full cell in micro scale, the 45 μm diameter Zn anodes in combination with micro scaled Ag/AgCl cathode and 5mm diameter MnO2 cathode were tested. Both cases showed a steady discharge curve with at least 60 % of discharge efficiency.

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