Dispensing device

Details Dispensing device Dispensing device

2000-04-11

2003-07-22

Lo, Weilun (Department: 3761)

Surgery

Respiratory method or device

Means for mixing treating agent with respiratory gas

C128S200140, C239S690000

Reexamination Certificate

active

06595208

ABSTRACT:

This invention relates to a dispensing device and a method of dispensing comminuted material to, particularly but not exclusively, the respiratory system of an animal such as a mammal or a bird.
As described in for example BG-A-1569707, dispensing devices are known which produce a monodispersed spray or cloud of liquid droplets by a process in which a liquid emerging from an outlet is subjected to an electric field such that the net electric charge in the liquid as the liquid emerges into free space counteracts the surface tension forces of the liquid and the repulsive forces generated by the like electrical charges result in an electrohydrodynamic cone or jet which breaks up to form liquid droplets. This process is generally referred to as electrohydrodynamic comminution. The particular device described in GB-A-156707 is intended primarily for crop spraying and is an inherently bulky, though portable, device. The droplets produced by this device are charged close to their Rayleigh Limit and thus in use migrate quickly toward wet conductive surfaces. Accordingly, such a device would not be suitable for delivery of liquid droplets to an animal respiratory system because the charge on the droplets would cause them to migrate quickly toward the wet conductive surfaces in the mouth rather than to pass to the upper respiratory tract.
GB-A-2018627 describes an electrohydrodynamic spray device wherein a charged droplet spray produced at a comminution site is fully or partially electrically discharged by means of a discharge electrode in the form of a sharp or pointed edge which is located downstream of the comminution site. Thus, in operation of this device, an electrical potential applied to the discharge electrode causes the discharge electrode to generate gaseous ions by corona discharge. The gaseous ions are then attracted to the oppositely charged droplets of the spray produced by the comminution site and fully or at least partially discharge the liquid droplets. GB-A-2018627 thus effects at least partial discharging of the liquid droplets by ion bombardment.
Unfortunately, ion bombardment discharging may interfere with the comminution process and may reduce the quality and reliability of the liquid droplet spray. Indeed, the detrimental affect on ion bombardment on the comminution spray has been observed in laboratory experiments. In order to counteract these detrimental effects, EP-A-0234842 proposes the use of an annular shield electrode which is positioned between the comminution site and the discharge electrode and aims to maintain a steady electrical field at the comminution site and to shield the comminution site and resulting liquid droplet spray from ions crated at the discharge electrode downstream of the comminution jet or spray. The central aperture of the shield electrode needs, of course, to be sufficiently large to allow free passage of the charged droplets but also small enough to hinder ions from travelling around the spray cloud and interfering with the electrohydrodynamic cone or jet. Experiments have, however, shown that using liquid formulations compatible with human physiology such as water, ethanol and polyethylene glycol, for example, the aperture in the shield electrode must be so large that it is not capable efficiently of hindering the passage of ions as required.
An electrohydrodynamic liquid droplet dispensing device of the kind described in EP-A-0234842 is discussed in a paper entitled “Generation of Micron Sized Droplets from the Taylor Cone” by Meesters et al published in the Journal of Aerosol Science 23 (1992) at pages 37 to 49. The device described in that paper is relatively large being of the order of approximately 150 mm high and 50 mm in diameter. Experiments have shown that if the dimensions of this device are reduced serious stability problems arise. For example, if the current from the discharge electrode is of the same order as the current produced by the charged liquid droplet spray, droplets inevitably impact on the tip of the discharge electrode so seriously reducing the ion current, leading to further droplet impaction and rapid reduction in the overall efficiency of this device. Although such problems could be overcome by increasing the ion current with respect to the electronic current produced by the electrohydrodynamic spray, the ionic wind resulting from air entrainment by the rapidly moving ions produced by the discharge electrode would either cause excessive air turbulence within the device resulting in an unacceptably large proportion of droplets impacting on the interior surfaces of the device or interfere with the electrohydrodynamic cone or jet of the liquid droplet spray causing it to become unstable as well as reducing the monodispersed nature of the spray.
According to one aspect of the present invention, there is provided a dispensing device particularly suitable for use for delivering comminuted material such as liquid droplets to the respiratory system of an animal such as human being, having comminution means for generating an electric field sufficient to produce charged comminuted material from liquid supplied to the comminution means and electrical discharge means for at least partially discharging the comminuted material wherein an ion migration path is provided which does not include the comminution means so that ions produced by the electrical discharge means do not travel to the comminution means until there is a space charge built up by the production of a charged comminuted material spray by the comminution means.
In another aspect, the present invention provides a dispensing device having a geometry such that when a charged spray of comminuted material is produced by electrohydrodynamic comminution means, the resulting space charge diverts ions of opposite charge to the comminuted material away from a path away from the comminution means back towards the comminution means so that the ions may at least partially discharge the spray.
In another aspect, the present invention provides a dispensing device having air-permeable electrically conductive or semi-conductive internal walls through which air is drawn into a comminution area when comminuted material is sucked from the device, so reducing impact of comminuted material within the device and enabling the amount of comminuted material which may be inhaled by a user to be increased.
In another aspect, the present invention provides an electrohydrodynamic dispensing device comprising a flexible or collapsible liquid reservoir which inhibits contact of air with the liquid to be dispensed and acts to retard evaporation of, for example, solvents during storage, thereby increasing the useful lifetime of the device.
In another aspect, the present invention provides a dispensing device which uses a piezoelectric diaphragm pump coupled to an electrical control circuit to provide a steady flow of liquid to electrohydrodynamic comminution means.
In another aspect, the present invention provides a dispensing device wherein valve means are provided at an electrohydrodynamic comminution site to inhibit liquid evaporation when the device is not in use. The valve means may be actuable by, for example, a piezoelectric element and/or by a mechanically, magnetically or electrostatically coupled lever system.
In another aspect, the present invention provides a dispensing device having means for pumping liquid to electrohydrodynamic comminution means. The pumping means may be in the form of a hydraulic syringe having a user-operable piston which may be acted upon by a steady mechanical force provided by, for example, spring biasing means, or may be in the form of, for example, an electrohydrodynamic pump as described in EP-A-0029301 or an electroosmotic pump such as described in WO94/12285.
In an embodiment where the reservoir is collapsible or has a movable wall the pumping action may be provided by means of a pressure system. The pressure system may be, for example, a spring-loaded pressure system wherein a spring applies a substantially constant pressure onto the reservoir

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