Micropump having a polyolefin sealing element

Abstract

A micropump 100 comprising a delivery body 102 comprising a metering chamber 104 having a first end and an opposed second end, where fluid in the metering chamber can be delivered through the second e

Description

TECHNICAL FIELD The present invention relates to micropumps for delivery of fluids that use a polyolefin seal. More particularly, the present invention relates to sealing elements for the micropumps. BACKGROUND Micro liquid dispensing systems (‘micropumps’) have long been utilised as economical and convenient devices for dispensing of diverse fluids. These systems are capable of dispensing small quantities of fluids within flow rates that are typically micro / millilitres per minute. Such systems are of special interest as a robust fluid delivery method in a host of important applications such as controlled and accurate drug delivery, dispensing paint, chemicals delivery, and so forth. The openings of the micropumps are sealed using sealing arrangements for efficient administration of flow of fluid therein. However, micropumps typically have very small components, making designing and constructing the sealing arrangements complicated. Seals within the pump are typically seated in sealing grooves or similar, and correctly locating the seal in the groove makes construction of the micropump tedious and challenging. The sealing groove may have restricted and precise tolerances owing to its small size, and precise deployment of the sealing arrangement may necessitate cavity sorting of components in order to achieve the precision and match of the sealing arrangement in the sealing groove. Additionally, operation of the micropump under high pressure can cause deformation of the seal, which can cause extrusion of the seal out of the sealing groove. In addition to this, any slight deviation with respect to tolerances for accommodation of the seal in the sealing groove increases the risk of extrusion of the seal. High contact pressure in a micropump can also contribute to the wearing of the sealing arrangement. The seal arrangement can also be subjected to high friction owing to the pressurised operation of the micropump. This can cause shredding resulting in a reduced lifespan for the seal. Furthermore, filtering systems may need to be used to prevent debris generated from the shredding blocking the micropump and / or being dispensed from the micropump. Such filtering systems add to the cost of the system. US7,284,474 describes and shows a sealing material having a high gas permeation coefficient for nitrogen, a radial compression of <30%, and this filling the sealing groove to >90%. However, such filling of the sealing groove may lead to high tolerance sensitivity both on the sealing component and the groove, potentially requiring further in-process steps to achieve the required precision. Therefore, in light of the foregoing discussion, there exists a need to overcome the aforementioned drawbacks associated with prior sealing arrangements in micropumps. SUMMARY It is an object of the present invention to provide a micropump for delivery of a fluid which goes some way to overcoming the abovementioned disadvantages or which at least provides the public or industry with a useful choice. It is a further object of the present invention to provide an inhaler device for delivery of a fluid which goes some way to overcoming the abovementioned disadvantages or which at least provides the public or industry with a useful choice. It is a yet still further object of the invention to provide a seal for a micropump which goes some way to overcoming the abovementioned disadvantages or which at least provides the public or industry with a useful choice. Accordingly, in a first aspect the present invention may broadly be said to consist in a micropump for delivery of a fluid, comprising: a delivery body comprising a metering chamber having a first end and an opposed second end, the second end configured so that fluid in the metering chamber can be delivered therethrough; a capillary configured to deliver fluid into the metering chamber; a piston comprising a body portion and a head portion, the piston and delivery body mutually configured so that the axial movement of the piston causes fluid to be delivered into the metering chamber from the capillary, the head portion and metering chamber configured so that in use the head portion moves axially within the metering chamber along a path between the first and second ends; the delivery body further comprising a groove, the groove radially surrounding the piston body portion and having a common axis with the piston and; a sealing ring, the sealing ring and groove mutually configured so the sealing ring locates in use within the groove; the sealing ring having a seal main body that extends radially around the piston body portion, and a lip that extends from the seal main body both radially around and axially along the piston with the sealing ring in contact with the piston and the delivery body to seal therebetween. In an embodiment, the sealing ring and delivery body are configured so that in use the lip extends from the seal main body towards the metering chamber. In an embodiment, the sealing ring and groove are configured so that in use only the lip is in contact with the piston, the lip providing a radial and axial seal against the piston body portion. In an embodiment, the sealing ring is at least partly formed from a polyolefin. In an embodiment, the capillary is implemented as a capillary bore running through the piston. In an embodiment, the capillary runs axially through the piston. In an embodiment, the capillary and piston head portion are mutually configured to comprise a valve arrangement configured to restrict backward flow of the fluid from the metering chamber into the capillary. In an embodiment, the delivery body, piston, capillary and sealing ring are configured for delivery of a pharmaceutical compound fluid. In a second aspect the present invention may broadly be said to consist in an inhaler device comprising the micropump of any one of the preceding claims. In an embodiment, the inhaler device is configured as a soft mist inhaler. In a third aspect the present invention may broadly be said to consist in a seal for a micropump, comprising a main body and a lip potion, the lip portion configured to extend from the main body substantially axially. With respect to the above description then, it is to be realised that the optimum dimensional relationships for the parts of the invention, to include variations in size, materials, shape, form, function and manner of operation, assembly and use, are deemed readily apparent and obvious to one skilled in the art, and all equivalent relationships to those illustrated in the drawings and described in the specification are intended to be encompassed by the present invention. This invention may also be said broadly to consist in the parts, elements and features referred to or indicated in the specification of the application, individually or collectively, and any or all combinations of any two or more said parts, elements or features, and where specific integers are mentioned herein which have known equivalents in the art to which this invention relates, such known equivalents are deemed to be incorporated herein as if individually set forth. Therefore, the foregoing is considered as illustrative only of the principles of the invention. Further, since numerous modifications and changes will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and operation shown and described, and accordingly, all suitable modifications and equivalents may be resorted to, falling within the scope of the invention. BRIEF DESCRIPTION OF THE DRAWINGS Further aspects of the invention will become apparent from the following description which is given by way of example only and with reference to the accompanying drawings which show an embodiment of the device by way of example, and in which: Figure 1 shows a simplified or stylised cross-sectional view of an inhaler device according to an embodiment of the invention, a micropump forming part of the inhaler, the micropump having a cylinder body with a metering chamber for delivering fluid, a capillary configured to deliver fluid into the metering chamber, a piston configured so that axial movement of the piston causes fluid to be delivered into the metering chamber from the capillary, and a sealing ring that locates into a groove in the delivery body, the sealing ring having a main body that extends radially around the body of the piston and a lip that extends from the seal main body both radially around and axially along the piston, the lip in contact with the piston and the delivery body to seal therebetween. DETAILED DESCRIPTION Embodiments of the invention, and variations thereof, will now be described in detail with reference to the figures. As used in this specification, the term "micropump" refers to micro liquid dispensing systems employed to dispense a fluid in small quantities with increased accuracy, and which can control and manipulate small volumes of fluid (generally in micrometric volumes). The term "fluid" refers to a substance, typically a liquid, that undergoes a deformation in shape and / or volume when subjected to an external force. Examples of fluids include, but are not limited to, inhalation aerosol drug formulations. It will be appreciated that the micropump is required to deliver fluids such as these in small quantities, with accurate volume, and to precise locations. Inhalation drug formulations frequently need to be provided as a spray with a droplet size small enough to penetrate to the lungs. A typical method for producing such a spray is to force fluid through nozzles at high pressure, e.g. 10 to 80MPa. The fluid may be a pharmaceutical compound, dissolved in a suitable solvent (such as for example water or another acceptable low volatility substance). In the preferred embodiment, the fluid delivered by the micropump is a substance used as a medication, i.e. the fluid is chemical compound that has a physiological effect on the patient when administered, such as for example tiotropium bromide. However, it should be noted that the pharmaceutical compound could be for example a cannabinoid or cannabinoid mix, or a homeopathic formulation, or any similar type of compound. Micropump and Inhaler Figure 1 shows a stylised cross section of a micropump 100 for delivery of a fluid according to an embodiment of the invention, the micropump 100 forming part of a larger assembly that forms an inhaler device 1. The micropump 100 comprises three main parts: an elongate hollow body 102; a piston 108, and; a seal 110. These are described in detail below. Elongate Hollow Body The preferred embodiment of body 102 forms a main hollow cylindrical structure that retains the internal components of the micropump 100 (as described below). The body 102 is designed to withstand high pressure and minimise leakage, and is further potentially adapted for the connection of additional components such as a nozzle holder and / or a nozzle piece, screw-on end caps at each end that retain the components of the micropump within the body, and sealing elements between such components. The body 102 is elongate and hollow, having a substantially central piston passage running from one end to the other. One end of the hollow body 102 is adapted for connection to a delivery nozzle 106. Fluid is delivered in use through an aperture in the body 102 to the nozzle 106. The word ‘cylinder’ is used in this specification - i.e. ‘cylinder body’ - in reference to body 102, as this terminology is the terminology that is used for conventional pistons, and using this terminology therefore aligns the description with standard terminology. However, this should not be taken as indicating that the body 102 is, and has to be, cylindrical. The body 102 can be any suitable shape as required - e.g. oval, hexagonal, or similar. The piston passage contains an internal metering chamber 104 at or towards the end which is adapted for connection to the nozzle 106. ‘Metering chamber’ as used in this specification in relation to the preferred embodiment refers to a hollow volume provided in the piston passage of the body 102 that in use holds a metered or predefined volume of fluid prior to the delivery of the fluid (via the nozzle). The metering chamber 104 has a first end and a second end, the second end being the end adapted for connection to the delivery nozzle 106. ‘Nozzle’ as used in this specification generally refers to either an outlet for the fluid on the body 102 of the micropump, or an attachment to the body 102 to allow the delivery of fluid therethrough. The nozzle 106 is intended to enable an efficient delivery of the fluid to a user, and the nozzle 106 can be configured as required to deliver the fluid in the manner required - for example a jet stream, a spray, a sprinkle, a diffusion - based on the particular application of the micropump. For example, the nozzle may be fabricated in a cylindrical shape, and may include a plurality of miniscule openings that allow the fluid to pass through to deliver the fluid as a spray. The body 102 of the micropump 100 further comprises a groove 112 at or towards that end of the body 102 opposite the end connected to or forming the nozzle 106. The groove 112 runs radially around the piston passage and has a common central axis with the piston passage (and piston 108 in the piston passage). The groove 112 is configured to contain a seal 110 (described in detail below), which in use seals between the piston 108 and the body 102. Piston The piston 108 comprises a body portion 108a and a head portion 108b, the head portion 108b located at that end of the piston 108 adjacent to the metering chamber 104. The other end of the piston 108 is a ‘free’ end that in use is in fluid communication with a fluid reservoir. The piston 108 and piston passage are mutually configured so that the piston 108 fits snugly within the passage, and in use moves axially / linearly within the passage. A capillary passage 120 runs axially through the centre of the piston 108, from the free end to the head portion 108b. The head portion 108b and capillary passage 120 are configured so that in use fluid is delivered from the capillary passage 120 to the metering chamber 104, with axial movement of the piston 108 within the cylinder body 102 causing fluid to be delivered into the metering chamber 104 from the capillary 120 by moving that end of the head portion 108b closest to the nozzle 106 - the piston face 114 - between the first end and the second end of the metering chamber 104. That is, the head portion 108b and metering chamber 104 are configured so that in use the head portion 108b moves axially within the metering chamber 104 along a path between the first and second ends. It will be appreciated that the metered volume delivered corresponds to the volume of the metering chamber 104 swept by the piston 108 in its stroke, which may be calculated from the cross-sectional area of the piston 108 and the stroke length. For example, the cross-sectional area may be about 2mm, and the stroke about 8mm, resulting in a metered volume of about 16pl. Accordingly, the micropump 100 may be constructed to deliver a metered dose in the range 3 to 25 pl. It is preferred that delivery of fluid through the nozzle is driven by an axial force on the piston that causes a peak pressure to develop in the metering chamber in the range between 10-80MPa. However, typically the peak pressure will be approximately 28 MPa. In order to create a peak pressure inside the capillary, a force is applied on the piston , at the outer end of the piston (the reservoir end) to deliver the fluid through the nozzle. A typical arrangement is for the force to be applied to a reservoir receptacle to which the piston is rigidly attached. Alternatively, post-delivery of the fluid through the nozzle, when the piston 108 is pulled back towards the second end of the metering chamber 104, the piston 108 may generate a suction force inside the metering chamber 104, and cause fluid to travel from the reservoir through the capillary 120 to the metering chamber 104. In an embodiment, the capillary has a valve arrangement to provide a one-way path of travel for fluid inside the capillary, and to restrict backward flow of fluid from the metering chamber. The valve arrangement can use valves such as a ball valve, gate valve, plug valve, etc. Seal The seal 110 has a general overall form similar to that of a lip seal, with a main body 110a and a lip 110b. The main body 110a locates into and fits snugly within the groove 112, and extends radially around the delivery body 102 to seal against the delivery body 102. The lip 110b extends from the seal main body 110a to extend both radially around and axially along the piston 108. The inner surface of the outer end of the lip 110b is in contact with the piston 108 radially around the piston, to seal against the piston 108. By sealing both against the delivery body 102 and the piston 108, a seal is created between these items to prevent the passage of fluids. As shown in figure 1, the groove 112 and seal 110 are configured so that when the seal 110 is located in the groove 112, the seal main body 110a is located at or towards the end of the body 102, with the lip 110b extending towards the metering chamber 104. The lip 110b tapers as it extends away from the seal main body 110a. The seal 110 is in this embodiment a unitary item, formed from a soft plastic material. In the most preferred embodiment, the material is a polyolefin. However, any suitable soft plastic material or soft polymer could be used, such as for example TPEs, TPVs, rubber, silicone rubber, or similar could be used. Only the inner surface of the lip 110b is in contact with the piston 108, and only for part of the inner surface of the lip 110b - substantially around one-third of the length of the lip 110b, at that end or part closest to the metering chamber 104. The seal 110 and piston 108 are configured so that there is an interference fit between the seal 110 (that is, the upper third of the lip 110b as outlined above) and the surface of the piston 108. That is, the lip 110b is put in tension as it is pushed radially outwards away from the piston 108 as it is slid onto the shaft of the piston 108. It should be understood by a person skilled in the art that figure 1 depicts a simplified or stylised illustration of the micropump 100 for the sake of clarity only, which should not unduly limit the scope of the claims herein. The person skilled in the art will recognize many variations, alternatives, and modifications of embodiments of the present disclosure.

Claims

23 05 251. A micropump (100) for delivery of a fluid, comprising:a delivery body (102) comprising a metering chamber (104) having a first end and an opposed second end, the second end configured so that fluid in the metering chamber (104) can be delivered therethrough;a capillary (120) configured to deliver fluid into the metering chamber (104);a piston (108) comprising a body portion (108a) and a head portion (108b), the piston (108) and delivery body (102) mutually configured so that the axial movement of the piston (108) causes fluid to be delivered into the metering chamber (104) from the capillary (120), the head portion (108b) and metering chamber (104) configured so that in use the head portion (108b) moves axially within the metering chamber (104) along a path between the first and second ends;the delivery body (102) further comprising a groove (112), the groove (112) radially surrounding the piston body portion (108a) and having a common axis with the piston (108) and;a sealing ring (110), the sealing ring (110) and groove (112) mutually configured so the sealing ring (110) locates in use within the groove (112);the sealing ring (110) having a seal main body (110a) that extends radially around the piston body portion (108a), and a lip (110b) that extends from the seal main body (110a) both radially around and axially along the piston (108) with the sealing ring (110) in contact with the delivery body (102), and only the lip (110b) in contact with the piston (108), the lip (110b) providing a radial and axial seal against the piston (108).

2. A micropump as claimed in claim 1 wherein the sealing ring and delivery body are configured so that in use the lip extends from the seal main body towards the metering chamber.

3. A micropump as claimed in claim 1 or claim 2 wherein the sealing ring is at least partly formed from a polyolefin.

4. A micropump as claimed in any one of claims 1 to 3 wherein the capillary is implemented as a capillary bore running through the piston.

5. A micropump as claimed in claim 5 wherein the capillary runs axially through the piston.

6. A micropump as claimed in any one of claims 1 to 5, wherein the capillary and piston head portion are mutually configured to comprise a valve arrangement configured to restrict backward flow of the fluid from the metering chamber into the capillary.

7. A micropump as claimed in any one of claims 1 to 6, wherein the delivery body, piston, capillary and sealing ring are configured for delivery of a pharmaceutical compound fluid.

8. An inhaler device comprising the micropump of any one of the preceding claims.

9. An inhaler device as claimed in claim 9 wherein the inhaler device is configured as a soft mist inhaler.23 05 25

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