Aerosol generator and methods of making and using an aerosol generator

[0002] The present invention relates generally to aerosol generators and, more particularly, to aerosol generators able to generate aerosols without compressed gas propellants and methods of making and using such aerosol generators.

[0003] Aerosols are useful in a wide variety of applications. For example, it is often desirable to treat respiratory ailments with, or deliver drugs by means of, aerosol sprays of finely divided particles of liquid and/or solid, e.g., powder, medicaments, etc., which are inhaled into a patient's lungs. Aerosols are also used for purposes such as providing desired scents to rooms, applying scents on the skin, and delivering paint and lubricant.

[0004] Various techniques are known for generating aerosols. For example, U.S. Pat. Nos. 4,811,731 and 4,627,432 both disclose devices for administering medicaments to patients in which a capsule is pierced by a pin to release a medicament in powder form. A user then inhales the released medicament through an opening in the device. While such devices may be acceptable for use in delivering medicaments in powder form, they are not suited to delivering medicaments in liquid form. The devices are also, of course, not well-suited to delivery of medicaments to persons who might have difficulty in generating a sufficient flow of air through the device to properly inhale the medicaments, such as asthma sufferers. The devices are also not suited for delivery of materials in applications other than medicament delivery.

[0005] Another well-known technique for generating an aerosol involves the use of a manually operated pump which draws liquid from a reservoir and forces it through a small nozzle opening to form a fine spray. A disadvantage of such aerosol generators, at least in medicament delivery applications, is the difficulty of properly synchronizing inhalation with pumping. More importantly, however, because such aerosol generators tend to produce particles of large size, their use as inhalers is compromised because large particles tend to not penetrate deep into the lungs.

[0006] One of the more popular techniques for generating an aerosol including liquid or powder particles involves the use of a compressed propellant, often containing a chloro-fluoro-carbon (CFC) or methylchloroform, to entrain a material, usually by the Venturi principle. For example, inhalers containing compressed propellants such as compressed oxygen for entraining a medicament are often operated by depressing a button to release a short charge of the compressed propellant. The propellant entrains the medicament as the propellant flows over a reservoir of the medicament so that the propellant and the medicament can be inhaled by the user. Since the medicament is propelled by the propellant, such propellant-based arrangements are well-suited for those who might have difficulty inhaling. Nonetheless, aerosols generated by propellant-based arrangements have particles that are too large to ensure deep lung penetration.

[0007] In propellant-based arrangements, however, a medicament may not be properly delivered to the patient's lungs when it is necessary for the user to time the depression of an actuator such as a button with inhalation. Moreover, such arrangements tend to be poorly suited for delivery of materials in large quantities. Although propellant-based aerosol generators have wide application for uses such as antiperspirant and deodorant sprays and spray paint, their use is often limited because of the well-known adverse environmental effects of CFC's and methylchloroform, which are among the most popular propellants used in aerosol generators of this type.

[0008] In drug delivery applications, it is typically desirable to provide an aerosol having average mass median particle diameters of less than 2 microns to facilitate deep lung penetration. Most known aerosol generators are incapable of generating aerosols having average mass median particle diameters less than 2 to 4 microns. It is also desirable, in certain drug delivery applications, to deliver medicaments at high flow rates, e.g., above 1 milligram per second. Most known aerosol generators suited for drug delivery are incapable of delivering such high flow rates in the 0.2 to 2.0 micron size range.

[0009] U.S. Pat. No. 5,743,251, which is hereby incorporated by reference in its entirety, discloses an aerosol generator, along with certain principles of operation and materials used in an aerosol generator, as well as a method of producing an aerosol, and an aerosol. The aerosol generator disclosed according to the '251 patent is a significant improvement over earlier aerosol generators, such as those used as inhaler devices. It is desirable to produce an aerosol generator that is portable and easy to use.

[0010] According to one aspect of the present invention, an aerosol generator includes a tube having a first and a second end, a heater arranged relative to the tube for heating at least a portion of the tube, a source of material to be volatilized, the second end of the tube being in communication with the source of material, and a valve operatively located between the source of material and the tube, the valve being openable and closeable to open and close communication between the source and the first end of the tube. A pressurization arrangement is provided for causing material in the source of material to be introduced into the tube from the source of material when the valve is in an open position. A source of power is provided for operating the heater and for the valve, and a control device is provided for controlling supply of power from the source of power to the heater and the valve.

[0011] According to a further aspect of the present invention, a method of making an aerosol generator is disclosed. According to the method, a heater is arranged relative to a tube for heating of the tube, the tube having first and second ends. The second end of the tube is connected to a source of material to be volatilized. An openable and closeable valve is provided between the source of material and the tube. A pressurization arrangement is provided for causing material in the source of material to be introduced into the tube from the source of material when the valve is in an open position. The valve is connected to a source of power for opening and closing the valve. The heater is connected to the source of power. The source of power is connected to a control device for controlling a supply of power from the source of power to the heater and the valve.

[0012] According to yet another aspect of the present invention, a method of using an aerosol generator is disclosed. According to the method, a first signal, indicative of a user's intention to use the aerosol generator, is provided to a control device. With the control device and in response to the first signal, a second signal is sent to a source of power to cause the source of power to open an openable and closeable valve, the valve being disposed between a source of material to be volatilized and a tube, opening of the valve permitting material from the source of material to flow from the source of material and into the tube. Material from the source of material is caused to flow from the source of material and into the tube. With the control device and in response to the first signal, a third signal is sent to the source of power to supply power to a heater disposed relative to the tube to heat the tube. Material from the source of material is heated in the tube with the heater to a vaporization temperature such that the material volatilizes and expands out of an open end of the tube.

[0013] The features and advantages of the present invention are well understood by reading the following detailed description in conjunction with the drawings in which like numerals indicate similar elements and in which:

[0014] FIG. 1 is a schematic, partially broken, side view of an aerosol generator according to an embodiment of the present invention;

[0015] FIG. 2 is a logic diagram of powered components of an aerosol generator according to an embodiment of the present invention;

[0016] FIG. 3 is a schematic, partially broken, side view of an aerosol generator according to a second embodiment of the present invention;

[0017] FIG. 4 is a schematic, partially broken, side view of an aerosol generator according to a third embodiment of the present invention;

[0018] FIG. 5 is a schematic, partially broken, side view of an aerosol generator according to a fourth embodiment of the present invention;

[0019] FIGS. 6A-6C show steps according to a method, according to a further aspect of the present invention, of manufacturing an aerosol generator according to the fifth embodiment of the present invention.

[0020] An aerosol generator 21 according to the present invention is shown in FIG. 1. The principles of operation of the aerosol generator 21 and, where applicable, materials used in the aerosol generator are preferably similar to the principles of operation and materials used in the aerosol generator disclosed in U.S. Pat. No. 5,743,251, which is hereby incorporated by reference in its entirety.

[0021] A preferred application for the aerosol generator 21 is as an inhaler device, such as an inhaler for medicaments, such as asthma medication and pain killers. The aerosol generator 21 preferably includes a first component 23, which preferably includes, for example, the material to be turned into an aerosol and which is preferably disposable after one or a predetermined plurality of uses, removably attached to a second component 25, which preferably includes, for example, power source and logic circuitry structures and which is preferably permanent in the sense that it is reusable with successive ones of the first components. The first and second components 23 and 25 can be attachable to one another in end to end or side by side relationships. If desired or necessary, however, the aerosol generator can be a one-piece device.

[0022] The first component 23 preferably includes a tube 27 having a first and a second end 29, 31, and a heater 33 arranged relative to the tube for heating the tube. A valve 35 is provided either on the tube 27 or between the second end 31 of the tube and a source 37 of material, the valve preferably being openable and closeable to open and close communication between the first end 29 of the tube and the source of material. The valve 35 may define the second end 31 of the tube. The valve 35 is preferably electronically openable and closeable, preferably a solenoid-type valve. The first component 23 preferably further includes the source 37 of material to be volatilized. The first component 23 preferably also includes a pressurization arrangement 39 for causing material in the source 37 of material to be introduced into the tube 27 from the source of material when the valve 35 is in an open position.

[0023] The second component 25 is preferably attachable and detachable to the first component 23 and includes a source 41 of power for the heater 33 and for the valve 35, and a control device 43, such as a microchip, for controlling supply of power from the source of power to the heater and the valve. The source 41 of power is preferably a battery, more preferably a rechargeable battery, however, the source of power may, if desired or necessary, be a non-depleting source of power, such as a conventional power line. International Publication No. WO 98/17131 discloses a power controller and a method of operating an electrical smoking system that discloses a power source and a control device, particularly for heaters, the principles of operation and features of which are transferrable to the present invention, and is hereby incorporated by reference.

[0024] General operation of the aerosol generator 21 involves a user providing a signal, such as by compressing a button or performing some other action such as inhaling near the first end 29 of the tube 27 to actuate a flow sensing detector or a pressure drop sensing detector, which is received by the control device 43. In response to the signal, the control device 43 preferably controls the supply of power from the power source 41 such that the valve 35 is opened and power is supplied to the heater 33 to cause it to heat up to its desired operating temperature. It may be desired or necessary, depending upon the application and the equipment employed, to open the valve 35 before or after supplying power to the heater 33.

[0025] Upon opening the valve 35, the pressurization arrangement 39 causes material in the source 37 of material to be introduced into the tube 27. The material in the tube 27 is heated to a vaporization temperature in the tube, volatilizes, and expands out of the free first end 29 of the tube. Upon exiting the tube 27, the volatilized material contacts cooler air and condenses to form an aerosol. Preferably, after a predetermined period of time, the control device 43 automatically closes the valve 35 and shuts off the supply of power to the heater 33. After one or a plurality of uses, the first component 23 is preferably separated from the second component 25 and is disposed of, and a new first component is attached to the second component for further use.

[0026] Because presently preferred applications for the aerosol generator 21 include use as an inhaler, the aerosol generator is preferably as small as possible. The valve 35 is preferably a microvalve. More preferably, the valve 35, the heater 33, and the tube 27 are a single micoelectronic machine formed on a single chip. To the extent that other components of the aerosol generator 21 disclosed in the present application are subject to production as microelectronic devices, they may also be formed on a single chip with the valve 35, the heater 33, and the tube 27, or on another chip.

[0027] According to the preferred embodiment, the source 37 of material includes a flexible container 45, and the pressurization arrangement 39 includes a chamber 47 in which the flexible container is disposed. A pressurized gas G is preferably sealed in the chamber 47 and surrounds the flexible container 45. The pressurization arrangement 39 is preferably a so-called sepra container of the type used for dispensing, for example, gel shaving creams, caulking compounds, and depilatories, although other pressurization arrangements for delivering the material, such as propellants and manual or automatic pumps, may be used if desired or necessary. The sepra container pressurization system is particularly preferred, however, particularly due to its capacity for resistance to surrounding temperature variations, as well as to variations in pressure of the gas G because the gas is not depleted. When it is desired to dispense material from the source 37 of material, and the valve 35 is opened, the pressure of the gas G, which is preferably about two atmospheres (about 30 psi) greater than ambient pressure, compresses the flexible container 45, causing material to enter the tube 27 through the second end 31 of the tube in communication with the source of material. A preferred gas G is nitrogen because of its ready availability and comparatively low cost, although various other gases are also suitable and may be preferred for particular applications.

[0028] Displacement of material from the flexible container 45 means that there is more room in the chamber 47, which means that the gas G enclosed in the chamber occupies a greater volume. Preferably, the size of the flexible container 45 relative to the size of the chamber 47 is selected such that pressure of the gas G is about ten percent lower when the flexible container is empty than when the flexible container is full.

[0029] A pressure sensor 48 may be provided to sense the pressure of the gas G in the chamber 47. As seen in FIG. 2, the pressure sensor 48 is preferably arranged to send a signal representative of the pressure in the chamber 47 to the control device 43. The control device 43, in turn, is preferably arranged to control the power source 41 to adjust a length of time that power is supplied to the valve 35, and if desired or necessary, to the heater 33, in response to the signal from the pressure sensor. In this way, pressure drops in the chamber 47, which may result in a decrease in the rate at which material in the flexible container 45 is dispensed, can be compensated for by dispensing material for somewhat longer periods of time, i.e., by keeping the valve 35 open longer and, if desired or necessary, maintaining a supply of power to the heater 33.

[0030] A signal to the control device 43 to supply power to the valve 35 and the heater 33 and, where provided, other features of the aerosol generator 21, is preferably provided by a user of the aerosol generator. While the signal may be provided by, for example, pressing a button, turning a knob, or switching a switch, a preferred arrangement for providing a signal is based on a user causing some manner of air flow in the proximity of the free first end 29 of the tube 27, such as by inhaling on a mouthpiece section 49 of the aerosol generator. The aerosol generator 21 preferably includes an air flow detecting device 51 for determining when a predetermined air flow rate exists proximate the first end 29 of the tube 27. The air flow detecting device 51 is preferably arranged to send a signal to the control device 43 to indicate that the predetermined air flow rate exists, which may be indicative that a user is drawing on the open end 53 of the mouthpiece 49 section, and the controller is preferably arranged to control the power source to supply power to the valve 35 and the heater 33, and any other components, in response to the signal from the air flow detecting device. As seen in FIG. 1, the air flow detecting device 51 is preferably disposed transversely to and upstream of the first end 29 of the tube 27 so that the air flow detecting device will assist in ensuring that an adequate supply of air flow exists to produce and effectively deliver an aerosol from the volatilized material as it expands out of the first end of the tube.

[0031] Where the aerosol generator 21 is a multi-piece device, the air flow detecting device 51 is preferably permanently attached to the second component 25 and is, thus, preferably a permanent component, i.e., it is not disposed of. If desired or necessary, however, the air flow detecting device 51 can be a disposable component forming part of the first component 23 and can be removably connected, such as through an electrical connection, to the control device 43.

[0032] The mouthpiece section 49 preferably has an open end 53. The tube 27 is preferably disposed in the mouthpiece section 49 and the first end 29 of the tube is preferably disposed inside of the mouthpiece section at a distance from the open end 53 to permit complete mixing of volatilized material expanding out of the first end of the tube with surrounding air to form an aerosol. To ensure an adequate supply of air for mixing with the volatilized material, as well as to ensure an adequate supply of air for permitting a user to draw on the mouthpiece section and actuate the air flow detecting device 51, the mouthpiece section 49 preferably has a plurality of vent holes 55. To facilitate the flow of air past the first end 29 of the tube 27 and thereby facilitate formation of an aerosol, the first end of the tube is preferably disposed in the mouthpiece section 49 between the vent holes 55 and the open end 53 of the mouthpiece section. The vent holes 55 are preferably located relative to the tube 27, preferably close to the end 29, such that air passing through the vent holes has no or minimal cooling effect on the tube. The tube 27 may, of course, be insulated from air flowing through the vent holes 55, such as by providing insulation material or a concentric tube 56 (shown in phantom) or the like around the tube to channel air away from the tube.

[0033] As an alternative to, or in addition to, using an air flow detecting device 51 to send a signal to the control device 43, as seen in FIG. 2 in phantom, a pressure drop detecting device 57 for determining when a predetermined pressure drop occurs proximate the first end 29 of the tube 27 may be used. The pressure drop detecting device 57 is preferably arranged to send a signal to the control device 43 to indicate that the predetermined pressure drop is occurring, which may be indicative of a user drawing on the open end 53 of the mouthpiece section 49, and the control device is arranged to control the power source 41 to supply power to the valve 35 and the heater 33, and any other electrically powered components, in response to the signal from the pressure drop detecting device.

[0034] A suitable pressure drop detecting device is a puff-actuated sensor in the form of a Model 163PC01D35 silicon sensor, manufactured by MicroSwitch division of Honeywell, Inc., Freeport, Ill., or an SLP004D 0-4″ H₂O Basic Sensor Element, manufactured by SenSym, Inc., Milpitas, Calif. Other known flow-sensing devices, such as those using hot-wire anemometry principles, are also believed to be suited for use with the aerosol generator 21. The use of an air flow detecting device 51, as compared to a pressure drop detecting device, is presently preferred for inhaler-type applications because it is anticipated that an air flow detecting device will be easier for users to actuate as compared to a pressure drop detecting device.

[0035] Presently anticipated applications for the aerosol generating device 21 include drug delivery applications. For such applications, as well as in other applications to which the aerosol generating device 21 might be applied, the control device 43 may include a timer 59 for controlling a frequency with which the control device controls the power supply 41 to supply power to the valve 35 and the heater 33 and other components. In this way, the aerosol generating device 21 can automatically limit the frequency with which a user can operate the aerosol generating device, thereby facilitating in preventing accidental misuse and overdosages. Moreover, to assist caregivers in treating their patients, the aerosol generator 21 can be associated with a remote control device 61 remote from the control device 43. The remote control device 61 is preferably capable of adjusting the timer 59 to adjust the frequency with which the control device 43 controls the power supply 41 to supply power to the valve 35 and the heater 33, and other components. In this way, when a caregiver desires to increase or decrease the frequency with which the user is able to operate the aerosol generator, the caregiver can do so in situations where the caregiver and the user are separated by some distance. In this way, users who might otherwise be required to personally see their caregivers to have their treatment schedules adjusted have greater mobility.

[0036] The control device 43 and, if provided, the remote control device 61, may also be configured to permit adjustment or remote adjustment of other powered components of the aerosol generator 21, such as the length of time that the valve 35 is open, and the length of time that power is supplied to the heater from the power source 41. In this manner, it is possible to adjust dosages up or down, as well as to adjust operating conditions of the aerosol generator 21 to maintain the same operation where, for example, pressure of the gas G in the chamber 47 drops or the rate at which power is supplied from the power source 41 reduces, such as where the aerosol generator is used in different temperatures, material in the flexible container 45 is used up, or the charge of a battery forming the power source diminishes.

[0037] The timer 59 of the control device preferably is associated with an indicator 63, such as a beeper or light forming part of the timer or, for example, electrically connected to the timer, for indicating that the control device 43 is available to control the power supply 41 to supply power to the valve 35 and the heater 33 and other components. Where, for example, the aerosol generator 21 is used to dispense medication, the indicator 63 serves to remind the user that it is time for the medication. The indicator 63 may also, if desired or necessary, be operable by the remote control device 61. The indicator 63 may also be used to indicate to a user a length of time since the aerosol generator 21 was actuated, such as where the aerosol generator is used as an inhaler, and the user is supposed to hold his or her breath for a length of time after inhaling, with the indicator 63 indicating when a period of time has elapsed.

[0038] The aerosol generator 21 may also include a display device 65, such as an LCD display, for displaying information such as a number of times that the control device 43 controls the power supply 41 to supply power to the valve and the heater. The display device 65 may display, for example, a number of times that the aerosol generator 21 has been operated, e.g., 1 or 2 or 3, or a number of operations remaining, which may be based on, for example, the size of the source 37 of material and the amount of material dispensed each time that the valve 35 is opened and closed, or the life of the power supply 41, such as the remaining life of a battery. The same or additional display devices can be provided to display other information, such as pressure in the pressure chamber 47 and power level of the power source 41. Further, the aerosol generator 21 may be equipped with various sensors and displays to provide feedback to be displayed in a display device 65 to, for example, assist a user in learning how to use the aerosol generator properly as an inhaler, such as sensors to measure the volume and duration of an inhalation after completion of an inhalation, and even to provide feedback during an inhalation to assist the user in employing an optimum inhalation profile. The display device 65 is preferably controlled by the control device 43 and powered by the power supply 41.

[0039] The control device 43 may be individually programmable, such as by a pharmacist, to control the aerosol generator 21 to dispense medications according to a prescription, i.e., quantity of medication, frequency, etc., as well as programming in the information that would prevent improper use of the aerosol generator. In this manner, fewer types of aerosol generators 21 may be useful for a wide range of medications. The particular aerosol generator 21 would preferably be optimized for different classes of medications and then “fine tuned” by, for example, the pharmacist, for a specific drug or prescription.

[0040] The aerosol generator 21 may also be programmed to permanently prevent use after a set period of time. In this way, it would be possible to prevent the use of expired medications. This may be accomplished by, for example, having a battery power source 41 be non-replaceable, or by incorporating a battery and/or control device that keeps track of date and time and prevents operation past a particular date and time.

[0041] While not wishing to be bound by theory, depending upon selection of factors presently understood to primarily include a rate of power supplied from the source of power 41 to the heater 33, a diameter of the tube 27, and the material to be volatilized and delivered as an aerosol, the aerosol generator 21 is preferably specifically designed to generate an aerosol having certain desired characteristics. For many applications, particularly for medication delivery applications, the aerosol generator 21 according to the present invention is preferably designed to produce an aerosol having a mass median particle diameter of less than 3 microns, more preferably less than 2 microns, still more preferably between 0.2 and 2 microns, and still more preferably between 0.5 and 1 microns. While not wishing to be bound by theory, depending upon selection of factors presently understood to primarily include a length of the tube 27, a pressure with which the pressurization arrangement 39 supplies the material from the source 37 of material, and a rate at which power is supplied from the source 41 of power, the rate at which the material is supplied and volatilized in the tube is established. The aerosol generator 21 is preferably designed to supply and volatilize material at a rate greater than 1 milligram per second.

[0042] It may be desirable to produce an aerosol formed from different liquid components that, for a variety of reasons, may be best kept separated until the moment that it is desired to form the aerosol. As seen in FIG. 3, another embodiment of the aerosol generator 121 may, in addition to the features described with respect to the aerosol generator 21, include, preferably as part of a modified first component 123, a source 137 of a second material in liquid form that is supplied to the tube 27 together with the material from the first source of material 37. The source 137 of second material preferably communicates with the tube 27 at a point 171 before the heater 33. A separate valve 135 is preferably powered by the power source 41 and controlled by the control device 43 to permit the pressurization arrangement 39 to cause material in the source 137 of second material to be introduced into tube 27 from the source of second material when the valve 35 is in an open position. If desired or necessary, the valve 35 and the valve 135 can be opened and closed at different times.

[0043] The source 137 of second material preferably includes a second flexible container 145. The pressurization arrangement 39 preferably includes a second chamber 147 in which the second flexible container 145 is disposed, and a second pressurized gas G₂sealed in the second chamber and surrounding the second flexible container. The pressurized gas G and the second pressurized gas G₂may be pressurized to different pressures to facilitate delivery of the material and the second material to the tube 27 at different rates. If desired or necessary, the flexible container 45 and the second flexible container 145 may be disposed in the same pressurized chamber. Additional sources of material and other components may be provided to produce an aerosol having still further components.

[0044] As seen with respect to FIG. 4, a third embodiment of the aerosol generator 221 may include, preferably as part of a modified first component 223, a structure, or several structures, that is substantially entirely parallel to the structure of the first component to permit generation of an aerosol formed from two or more components. The aerosol generator 221 preferably includes a second tube 227 having a first and a second end 229, 231. A second heater 233 is preferably arranged relative to the second tube 227 for heating the second tube. A second valve 235 is preferably provided on the second tube 227 and is openable and closeable to open and close communication between the first and the second ends 229 and 231 of the second tube. A source 237 of second material to be volatilized is provided and the second end 231 of the second tube 227 communicates with the source of second material. A second pressurization arrangement 239 is provided for causing material in the source 237 of second material to be introduced into the second tube 227 from the source of second material when the second valve 235 is in an open position. If desired or necessary, the pressurization arrangement 39 can be used to cause material in the source 237 of second material to be introduced into the second tube 227. Preferably, the source 41 of power supplies power for the second heater 233 and for the second valve 235, as well as to any other electrically powered components of the aerosol generator, and the control device 43 controls supply of power from the source of power to the second heater and the second valve.

[0045] The aerosol generator 221 preferably includes a chamber 249, such as a mouthpiece section. The first ends 29 and 229 of the tube 27 and the second tube 227 are preferably disposed in the chamber 249 proximate each other. The chamber 249 is preferably of sufficient size and configuration to permit mixture of volatilized material and volatilized second material that expands out of the tube 27 and the second tube 227 together with ambient air such that the volatilized material and the volatilized second material form first and second aerosols, respectively, the first and second aerosols being mixed with each other to form a combination aerosol including the first and second aerosols.

[0046] In the embodiment described with reference to FIG. 1, a combination aerosol can be formed by providing material in the source 37 of material that includes two or more components mixed together before the material is volatilized. While the components in the source 37 of material may be two or more liquids, it is also possible to suspend solid particles in solution in a liquid material, or to dissolve solid particles in a liquid material. If desired or necessary, the solid particles, when suspended in solution, may be of a larger average diameter than particles of the material in aerosol form. The solid particles, when they form a part of the aerosol, may be of a larger average diameter than particles of the material in aerosol form. Solid particles can, of course, also be suspended in solution in liquid materials in the embodiments described with reference to FIGS. 3 and 4.

[0047] As noted, a preferred pressurization arrangement 39 for the aerosol generator 21 includes a sepra container type of arrangement. An aerosol generator 321 having an alternative pressurization arrangement 339 is shown in FIG. 5. In this embodiment, the source 337 of material preferably includes a second tube 345 having first and second ends 345a,345b.The first end 345aof the second tube 345 is connected to the second end 31 of the tube 27. The pressurization arrangement 339 includes a chamber 347 filled with a pressurized gas G. The second end 345bof the second tube 345 is disposed in the chamber 347 and is open to the chamber. The source 337 of material, the second tube 345, and the tube 27 preferably form part of a modified first component 323.

[0048] As seen in FIGS. 6A-6C, the source 337 of material is preferably filled with material by first opening the valve 35 in the tube 27, then immersing the open second end 345bof the second tube 345 in liquid material L (FIG. 6A). After the liquid material in which the second tube 345 is immersed fills the second tube, the valve 35 is then shut. The second tube 345 is withdrawn from the liquid material, with the liquid material that filled the second tube remaining in the second tube due to closure of the valve (FIG. 6B), i.e., air is unable to get behind the liquid material in the second tube. The second tube 345 is then positioned in the chamber 347 and the chamber is pressurized (FIG. 6C). When the valve 35 is opened, the pressure in the chamber forces the liquid material in the second tube 345 to enter the tube 27 where it can be volatilized by the heater 27.

[0049] In a method of making the aerosol generator 21 described with reference to the embodiment shown in FIG. 1, the heater 33 is arranged relative to the tube 27 to permit heating of the tube. The second end 31 of the tube 27 is connected to the source 37 of material to be volatilized. The openable and closeable valve 35 is provided to allow and stop communication between the source 37 of material and the tube 27.

[0050] The pressurization arrangement 39 for causing material in the source 37 of material to be introduced into the tube 27 from the source of material when the valve 35 is in an open position is provided. The valve 35 is connected to the source 41 of power for opening and closing the valve. The heater 35 is connected to the source 41 of power. The source 41 of power is connected to the control device 43 for controlling the supply of power from the source of power to the heater 33 and the valve 35, as well as to any other components of the aerosol generator.

[0051] The step of providing the pressurization arrangement 39 preferably includes positioning the source 37 of material in a chamber 47 and pressurizing the chamber, preferably to about two atmospheres. The source 37 of material preferably includes a flexible container 45. However, other embodiments are also possible. For example, as described with reference to FIGS. 5 and 6A-6B, the source 337 of material may include a second tube 345 having first and second ends 345a,345b,the first end of the second tube being connected to the second end 31 of the tube 27 and the second end 345bof the second tube being positioned in the chamber 345.

[0052] In making the aerosol generator 21 according to the present invention, it is particularly preferred that the heater 33, the tube 27, the valve 35, the source 37 of material, and the pressurization arrangement 39 are arranged relative to each other to form a first component 23, and that the source 41 of power and the control device 43 are arranged relative to each other to form a second component 25, and that the second component is attachable to and detachable from the first component. In this way, the second component 25 can be made as a permanent device, with most or all of the more expensive features of the aerosol generator being associated with the second component, and the first component 23, which preferably includes the depletable or less expensive components of the aerosol generator, can be disposable. The different features of the aerosol generator 21 can be provided on whichever one of the components 23 and 25 seems appropriate for a particular application. However, according to the presently envisioned preferred application of the aerosol generator as a medical inhaler device, it is believed that the arrangement of features on the components 23 and 25 properly distributes the more and less disposable features.

[0053] The aerosol generator 21 is preferably used by a user providing a first signal, indicative of a user's intention to use the aerosol generator, to the control device 43. The first signal may be provided by the user pressing a button 58 (FIG. 2, in phantom) but, particularly where the aerosol generator 21 is intended to be used as an inhaler device, it is preferred that the first signal be provided by some form of draw-actuated device, such as a pressure drop detecting sensor 53 or, more preferably, an air flow detecting sensor 51.

[0054] The control device 43, in response to the first signal, sends a second signal to the source of power 41 to cause the source of power to open the openable and closeable valve 35. The valve 35 is preferably disposed between the tube 27 and the source 37 of material. Opening of the valve 35 permits material from the source 37 of material to flow from the source of material and into the tube 27.

[0055] Material from the source 37 of material is caused to flow from the source of material and into the tube 27, preferably by means of the pressurization arrangement. The source 37 of material preferably includes the flexible container 45, and material in container is caused to flow from the source of material by a pressurization arrangement 39. The pressurization arrangement 39 preferably includes the chamber 47 filled with gas G under pressure and in which the flexible container 45 is disposed. In an alternative embodiment, as described with reference to FIGS. 5 and 6A-6C, the source 337 of material includes the second tube 345 having first and second ends 345a,345b.The first end 345aof the second tube 345 is connected to the second end 31 of the tube 27, and material in the source 337 of material is caused to flow from the source of material by the pressurization arrangement 339. The pressurization arrangement 339 includes a chamber 347 filled with gas G under pressure and in which the second end 345bof the second tube 345 is disposed.

[0056] A third signal is sent by the control device 43 and in response to the first signal to the source 41 of power to supply power to the heater 33 disposed relative to the tube 27 to heat the tube. Material from the source 37 of material is heated in the tube 27 with the heater 35 to a vaporization temperature such that the material volatilizes and expands out of the first end 29 of the tube.

[0057] The aerosol generator according to the present invention is preferably constructed in accordance with certain design principles that the inventors have recognized. These design relationships permit design of the aerosol generator with a certain robustness, particularly with respect to ambient temperature and container pressure variations, such that it is possible to ensure that the rate of aerosol delivery is substantially constant. While not wishing to be bound by theory, one relationship involves the rate at which aerosol is delivered (D), which is understood to be substantially linearly related to the power delivered to the liquid to be volatilized, i.e., the power (P), according to the relationship: D=k₁P, where k₁is substantially constant and depends upon design factors peculiar to the particular aerosol generator.

[0058] While not wishing to be bound by theory, the amount of aerosol delivered (d), or the aerosol delivery rate D multiplied by the time that the aerosol is delivered, is understood to be substantially linearly related to the pressure drop (p) of the liquid material through the tube 27, which is usually the difference between whatever pressure at which the liquid is maintained in the source 37 of material (e.g., container pressure) and atmospheric pressure, and substantially linearly related to the inverse of the length (L) of the tube from the beginning of the tube to the point PV along the tube where the liquid material has completely volatilized, according to the relationship: D=k₂p/L, where k₂is substantially constant and, like k₁, depends upon factors peculiar to the particular aerosol generator.

[0059] Further to the foregoing relationships, and while not wishing to be bound by theory, the value L will tend to increase with increasing pressure drop p or, conversely, decreases with decreasing pressure drop p. Accordingly, the capillary aerosol generator tends to maintain delivery rate D despite changes in p, which might result from, for example, changes in ambient temperature or pressure or container pressure or other causes, at least over a usable range.

[0060] The aerosol generator 21 according to the present invention is preferably designed according to the relationships discovered by the inventors. For example, while not wishing to be bound by theory, when a desired delivery amount and a delivery rate are known beforehand, such as where the aerosol generator 21 is to be used as an inhaler for predetermined dosages of medication, a designer can provide an appropriately sized battery as the power source 41 and can allow for a certain pressure drop of the gas G in the chamber 47 as material is depleted from the container 45 and still be certain that the desired delivery amount is achieved. If the pressure is too low, the consequence will be too low a delivery rate. If the pressure is too high, the consequence is that material emerges from the tube 27 as a liquid.

[0061] According to one potential sequence of events in a design process, and while not wishing to be bound by theory, the pressure drop p of the material prior to complete volatilization is a function of factors such as the diameter of the tube 27, and the nature of the material to be volatilized. Changing tube diameter can affect where the point P_voccurs, i.e., affect the the length L. If it is desired to have a tube with a certain length, and to accommodate changes in battery power, e.g., due to the battery losing its charge, and changes in pressure of the gas G, the length of the tube 27 can be designed with certain factors of safety in view of calculations for the length L involving different tube diameters that affect the pressure drop p. Similarly, if it is known that a particular battery loses a charge at a certain predetermined rate, the length of the tube 27 can be selected to ensure that volatilization of the material occurs in the tube at all intended operating levels of the battery.

[0062] According to another potential sequence of events in a design process, and while not wishing to be bound by theory, for a given delivery rate D, tube diameter d should be chosen taking into account the effect of tube diameter upon particle size. Tube length and the pressure in the container should then be adjusted to ensure that P_voccurs prior to the first end 29 of the tube 27, particularly in view of the likelihood of some variation in container pressure p.

[0063] Moreover, the control device 43 can be programmed to ensure that, as the pressure of the gas G drops, or the power level of the source 41 of power drops, certain changes in operation to accommodate these changes will take place. For example, as power levels drop, delivery of the same amount of material will take a longer time. Accordingly, the control device 43 can be programmed to, for example, keep the valve 35 open for a longer time as drops in power levels are detected.

[0064] While this invention has been illustrated and described in accordance with a preferred embodiment, it is recognized that variations and changes may be made therein without departing from the invention as set forth in the claims. For instance, the aerosol generator could include arrangements for manually operating the valve 35, i.e., instead of actuation by detection of air flow or pressure drop, with the controller 43 being configured to execute a scheduled heating cycle upon receipt of a signal indicating actuation of the valve. Such arrangements might further include devices (electrical or mechanical) to maintain the valve 35 in an opened position for a predetermined amount of time once it is mechanically actuated.