Valve for controlling flow of a fluid

Abstract

A valve for controlling flow of a primary fluid in a primary flow channel comprises a valve fluid channel, and a membrane of a porous dielectric material located in the channel so as to divide the channel into an inlet part and an outlet part and so that valve fluid flowing between the inlet and outlet parts flows through the said membrane. First and second electrodes are located for electrical communication with valve fluid in the inlet and outlet parts respectively of the valve fluid channel for application of an electric potential across the membrane in order to promote electro-osmotic flow of valve fluid through the membrane. A valve member can be displaced between open and closed positions as a result of valve fluid moving in the valve fluid channel through the membrane, into or out of the outlet part of the valve fluid channel, in which the valve member causes a reduction in the capacity for flow of the primary fluid in the primary flow channel when it is in the closed position compared with when it is in the open position.

Description

CROSS-REFERENCED RELATED APPLICATIONS [0001] This application is a continuation of prior application Ser. No. 10 / 651,835, filed Aug. 29, 2003. This invention relates to a valve for controlling flow of a fluid in a flow channel, and to a pump for controlling flow of a fluid in a flow channel.BACKGROUND OF THE INVENTION [0002] The flow of fluids through conduits can be controlled using components such as pumps and valves. Pumps and valves can operate to control parameters such as flow rate; adjustment of relative flow rates of constituents in a mixture can be used to vary the composition of the mixture. [0003] Accurate control of flow of a fluid can be important in many medical applications, for example in drug delivery and in the modulation of body fluid drainage. Devices in which flow control is important include pumps for dispensing drugs such as insulin and opiates, and hydrocephalus shunts for drainage of spinal fluids. [0004] Accurate control over the flow of drugs and fluids in...

AI Technical Summary

Benefits of technology

[0015] Electro-osmotic flow may be generated using a wide variety of fluids and dielectric materials. Indeed, it is an advantage of the present invention that the valve fluid can be isolated from the primary fluid so that an optimum fluid can be selected for operating the valve without reference to the particular requirements or nature of the primary fluid. The valve fluid should provide conditions that yield a high zeta potential with respect to the porous dielectric material. The fluid might be a pure fluid or a mixture of pure fluids. The fluid might have added to it a conducting species, especially a material which dissolves in the fluid to form ions. Preferably, the or each pure fluid should have a high dielectric constant (for example, between about 5 and 100 relative units), low dynamic viscosity (for example, between about 0.1 and 2 centipoise) and low conductivity (for example, between about 10.sup.-4 and 10.sup.-14 mho.multidot.m.sup.-1).

[0016] The valve fluid can include at least one additive to control the pH of the fluid. The valve fluid can include at least one additive to control the ionic strength of the fluid. Additives should preferably dissolve completely in the fluid. The kind and concentration of additives should preferably be such as to enhance or to optimise the zeta potential under the conditions imposed by the size of the pores in the porous dielectric medium.

[0017] The degree of ionization of the surface sites depends on the pH of the fluid. In most cases there is a pH at which the surface is net neutral and hence the zeta potential is zero. The zeta potential reaches a maximum value for pH values significantly above (for acidic surface sites) or pH values significantly below (for basic surface sites) the pH value at which the surface is net neutral. Ionisable surface sites can be added to a material by chemical reaction or grafting, or induced by creation of reactive surface chemistry or creation of defects via plasma or radiation treatment.

[0018] Examples of fluids which can be used in the valve fluid include water, cyclic carbonates, methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 1-pentanol, 1-hexanol, 1-heptanol, benzyl alcohol, nitromethane, nitrobenzene, butanone, dimethoxymethane, dimethylacetamide, dioxane, p-dioxane, acetonitrile, formamide, tetrahydrofuran, dimethyl formamide, acetone, acetic acid, triethylamine, dichloromethane, ethylene glycol, dimethylsulphoxide, ammonium acetate.

[0019] The valve fluid can include additives which can affect the zeta potential. Ionic species can have the opposite charge sign to the zeta potential. Ionic species can have the same charge sign as the zeta potential. Preferably, ionic species which are included in the valve fluid are monovalent. Species which ionise fully can be used to adjust the ionic strength of the fluid. Species which ionise partially can be used to adjust the pH of the fluid. Examples of useful ionic and buffering additives include alkali-halide salts, mineral acids and bases, organic acids and bases, phosphates, borates, acetates, citrates, malates, formates, carbonates, chlorates, nitrates, sulphates and sulphites, nitrates and nitrites, ammonium-, methylammonium-, ethylammonium-, propylammonium-salts, BIS, MES, TRIS, TES, HEPES, and TEA.

[0020] Preferably, the materials of the valve fluid and the porous dielectric material are such that the zeta potential is at least about 1 mV, especially at least about 30 mV. Generally, the zeta potential will be not more than about 150 mV, for example not more than about 120 mV. The zeta potential may be either positive or negative in sign. Factors affecting the sign and magnitude of the zeta potential include the dielectric constant of the fluid, the pH of the fluid, the ionic strength of the fluid, and the type of ions in the fluid.

Problems solved by technology

However, once implanted, the rate of flow of drug through the membrane cannot readily be adjusted.

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