Surgery – Liquid medicament atomizer or sprayer
Reexamination Certificate
1999-08-19
2002-05-14
Weiss, John G. (Department: 3761)
Surgery
Liquid medicament atomizer or sprayer
C128S200230, C128S203120, C239S690000
Reexamination Certificate
active
06386195
ABSTRACT:
The invention relates to a dispensing device for comminuting a liquid and the uses of such a device, especially in medicine.
BACKGROUND
Dispensing devices are known which produce a finely divided spray of liquid droplets by electrostatic (more properly referred to as ‘electrohydrodynamic’) means. The droplet spray in such devices is generated by the application of an electric field to a liquid at a spray head or spray edge. The potential of the applied electric field is sufficiently high to provide comminution of the liquid from the spray head. The droplets produced are electrically charged and thus are prevented from coagulating by mutual repulsion.
Electrohydrodynamic sprayers have potential uses in many areas, including agriculture and the automotive industry and also for dispensing cosmetics and medicines.
United Kingdom patent number 1569707 describes such an electrohydrodynamic spray device principally for use in crop spraying.
United Kingdom patent number 2018627B discloses an electrohydrodynamic spray device wherein the charged droplet spray is fully or partially electrically discharged by means of an earthed electrode having a sharp or pointed edge and located downstream of the spray head. European Patent number 0234842 also uses this technology and relates to an inhaler in which charged droplet spray is discharged prior to inhalation by means of a sharp or pointed discharge electrode carrying an opposite charge to the droplet spray and located downstream of the spray head. The droplets are discharged to facilitate droplet deposition into the respiratory tract by preventing deposition of charged droplets onto the mouth and throat of the user.
A common feature of all known electrohydrodynamic spray devices is that the electric charge used to generate the spray is applied directly to the spray head. It has now surprisingly been found that the direct application of the field is not essential and that the electrohydrodynanic comminution of a liquid may be accomplished by inducing the required electric charge at the spray head. In addition and advantageously, it has been found that the comminution produced can be partially or fully discharged prior to use.
This method of induced charging has been found to provide better comminution of liquids having lower electrical resistivity.
SUMMARY OF THE INVENTION
Accordingly, it is one aspect of the invention that there is provided an electrohydrodynamic dispensing device for comminuting a liquid, wherein the liquid is comminuted by an induced electrical charge.
In yet a further aspect, the means for fully or partially discharging the liquid comminution is provided by an electrode arranged to have a first surface capable of producing an electric field sufficient to induce the required charge for liquid comminution in the comminution means and also to impart sufficient inertia to the liquid comminution so that it substantially bypasses the first surface, the electrode also having a second surface capable of producing an ionic discharge to fully or partially discharge the liquid comminution.
The dispensing device normally comprises a comminution site, a means for supplying liquid to the comminution site and a means for inducing an electrical charge at the comminution site sufficient to comminute the liquid.
The comminution site may be any conventional electrohydrodynamic comminution site such as a surface or edge generally provided by a thin capillary tube, a nozzle or a slot defined by two parallel plates.
Appropriate means for supplying liquid to the comminution site include mechanical or electrically powered pumps which are capable of providing the required flow rate of liquid to the comminution site such as a syringe pump or the electrically powered pump described in EP 0029301.
The comminution means of the invention can be used with a large range of flow rates; but generally operates with flow rates in the range of between 0.1 to 500 &mgr;L per second, such as 0.5 to 5 &mgr;L per second, especially for inhaled administration, or 10 to 200 &mgr;L per second, especially for agricultural use.
The means for inducing the electrical charge at the comminution site may be any conventional source of electrical charge which in use is capable of inducing a charge sufficient to comminute the liquid from the comminution means including a high voltage generator or a piezo-electric generator. The charge required is usually of the order of 1-20 kilovolts for example 10 kilovolts.
After formation of the liquid comminution, the electrically charged liquid droplets are attracted towards and will impact the means for inducing the electrical charge at the comminution site. In a preferred aspect of the present device, there is therefore provided a means for partially or fully electrically neutralizing the liquid comminution before it impacts the induced charging means.
One suitable means for partially or fully electrically discharging the liquid comminution is a sharp or pointed discharge electrode located downstream of the comminuted liquid.
The sharp or pointed discharge electrode may be earthed or it may be maintained at a polarity opposite to that of the induced charging means by connection to a suitable charging means. In either case the comminuted liquid is partially or fully discharged by a cloud of charged ions produced from the surrounding air having an opposite electrical charge to that on the comminuted liquid spray. The ion cloud is attracted towards, collides with and thereby partially or fully discharges the liquid spray.
In one particularly advantageous form of the device, the means for fully or partially discharging the liquid comminution is provided by a combination of the sharp or pointed discharge electrode and at least one capacitor, the capacitor acting to absorb the charge from the gaseous ions from the sharp or pointed discharge electrode until the induced comminution of the liquid is established, the capacitor is arranged to absorb the ions until it reaches a predetermined potential at which potential it ceases to absorb the ions thereby allowing them to partially or fully discharge the liquid comminution.
Generally, the capacitor is chosen to have a time constant having the same order as the time required to establish the liquid comminution spray cloud. Thus the time constant will have a value, in seconds, which is the product of the capacitance, C and the resistance, R, of the capacitor.
The value of C×R for the capacitor is chosen so that the capacitor will charge until it reaches a prearranged potential sufficient to modify the electric field, the capacitor then discharges towards the established spray cloud. Generally, the time-constant required will be of the order of seconds or a number of milliseconds. For example, a capacitor of 0.1 microfarad with a resistance of 10 megohms will produce a time constant of one second.
In yet a further aspect, the means for fully or partially discharging the liquid comminution is provided by an electrode arranged to have a first surface capable of producing an electric field sufficient to induce the required charge for liquid comminution in the comminution means and also to impart sufficient inertia to the liquid comminution so that it substantially bypasses the first surface, the electrode also having a second surface capable of producing an ionic discharge to fully or partially discharge the liquid comminution.
Generally, the second surface is shaped to have a sharp edge or a point which in use produces the ionic discharge.
Suitably, the electrode is an annular electrode coaxially located with respect to the intended flight path of the liquid comminution, in use the upper surface of the annular electrode induces the required charge in the comminution means, the lower surface being shaped so as to produce the ionic discharge.
In operation the field pattern of the upper surface of the annular electrode is such that the comminution is directed onto an axial flight path with respect to the annular electrode and is provided with sufficient inertial force to substantially bypass the
Cobrin & Gittes
Electrosols Ltd.
Patel Mital
Weiss John G.
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