A nozzle for use in micropumps, and a method of creating a nozzle for use in micropumps

Abstract

A nozzle (101) for use in micropumps comprises a first plate (102a) having a first substantially planar surface (103a); a second plate (102b) having a second substantially planar surface (103b); the first (102a) and second (102b) plates positioned so that the first and second planar surfaces are directly adjacent to one another, the substantially planar surfaces (103a, 103b) of each of the first (102a) and second (102b) plates etched to form open-topped channels (104a, 104b); the first (102a) and second (102b) plates etched and aligned so that at least part of the open-topped channels (104a) on one plate associate with the channels (104b) on the other plate so as to form a plurality of enclosed passages that run at least partly through the nozzle (101); at least some of the channels on one of the plates formed with a greater width than the associated narrower channels on the other plate.

Description

[0001] A NOZZLE FOR USE IN MICROPUMPS, AND A METHOD OF CREATING A NOZZLE FOR USE IN MICROPUMPS

[0002] TECHNICAL FIELD

[0003] The present invention relates to a nozzle for use in micropumps for delivery of fluids. More particularly, the present invention relates to a nozzle for use in micropumps for delivery of fluids where the nozzle comprises two connected plates, each one of the plates having channels formed in / on the inner face, the channels on one plate associated with the channels on the other.

[0004] The present invention also relates to an inhaler device that comprises a nozzle.

[0005] The present invention also relates to a method of creating a nozzle for use in micropumps for delivery of fluids. More particularly, the present invention relates to a method of creating a nozzle for use in micropumps for delivery of fluids where the nozzle comprises two connected plates, each one of the plates having channels formed in / on the inner face, the channels on one plate associated with the channels on the other, the method ensuring that the nozzle has a substantially consistent hydraulic diameter even if the mutual alignment of the two plates is not perfect.

[0006] The present invention also relates to an inhaler device that comprises a nozzle for use in micropumps formed using this method.

[0007] BACKGROUND

[0008] Micro liquid dispensing systems (‘micropumps’) are a type of device that is used for dispensing small quantities of fluids within a range of flow rates that is typically in the micro / millilitres per minute range. Such systems are of special interest for use as fluid delivery systems in applications such as drug delivery, where control and accuracy are important.

[0009] In inhalation drug delivery systems, micropumps are used to generate a spray of fine droplets, also known as an aerosol, for delivery to the lungs of a user. Atypical known type of inhalation drug delivery system includes a nozzle (also known as a chip or filter) that contains a pattern of microchannels therethrough. In use, fluids pass into and out of the nozzle through the microchannels. Nozzles of this type are typically formed by sandwiching two large substrate sheets together - typically a glass substrate and a silicon substrate - so as to form a two-layer wafer, with the microchannels formed and located on one of the directly adjacent inner faces of the two substrates. This larger wafer is then cut into pieces so as to form a number of individual nozzles. Within the nozzle, parts of the microchannels form part of an impingement surface that helps to dictate the aerosol's characteristics. The microchannels are therefore formed as precisely as possible in order to accurately manage fluids inside the microchannels and achieve the desired dispensing accuracy (e.g. in terms of volume of fluid delivered and in terms of its aerosol particle size distribution).

[0010] Atypical channel layout or channel pattern for a typical chip / filter 1001 is shown in figure 5, which shows a side view of one plate of a typical chip / filter, with the other plate that makes up the chip / filter not shown so that detail of the internal structure of the chip / filter can be seen. The pattern of microchannels is etched into the inner face of one of the two layers of plates that make up the chip / filter. In use, fluids flow through the moulded or engraved pattern of microchannels, the microchannels forming part of an impingement surface that helps to dictate the aerosol's characteristics. The figure is intended to be exemplary - to show the general layout and form only.

[0011] The plate of the chip / filter as shown in figure 5 has a series of pillars 1020 spaced across one side or edge, the pillars forming inlet channels 1021 therebetween through which the formulation to be dispensed enters the nozzle. Filtering region 1022 is represented by a zigzag line in figure 5, but in the actual product this region is created by having a plurality of microchannels formed in the surface of the plate. The filtering region 1022 filters out small particles from the formulation, and contamination from the assembly process, and prevents these particles and contamination from reaching and blocking the nozzle jet 1023 (the passages that form the filter of the filtering region 1022 are finer than the width / height of the nozzle jet 1023).

[0012] Columns 1024 between the filtering region 1022 and the nozzle jet 1023 are spaced and configured to even out the flow and increase the bond strength between the upper and lower plates. In a real physical product, the columns 1024 will each be smaller than shown in this schematic view, and more densely packed.

[0013] The cross-sectional shape and size of a channel (microchannel) has a significant effect on the flow characteristics of a fluid within the channel, due to the distribution of shear stress and velocity profiles within the channel. Microchannels with a well-formed cross sectional aspect ratio (depth:width) help to generate the controlled liquid jets required, so as to cause disintegration of the liquid stream into small droplets. In soft mist inhaler nozzles of the known type, it is normal to etch the nozzle jets into one of the substrates (leaving the other unetched), and the etch depth, wetted perimeter and the cross-sectional shape and area of the etched channel dictates how much of the fluid flow will impinge, or the shape and velocity of the emerging liquid jet, or both. Channels having a square cross-section can be relatively easily formed in a silicon substrate by using an anisotropic etching process such as for example Deep Reactive Ion Etching (DRIE). Anisotropic etching of this type when used on a silicon substrate can produce channels having a square cross-section and sharp corners within the channel. However, channels with sharp corners have complex flow patterns near the corners. The flow velocity is highest at the centre of the channel, and decreases towards the walls. The presence of corners can lead to secondary flows (that is, minor flows superimposed on the primary flow direction). This potentially affects mixing, and also particle distribution in the channel in the case of fluids that comprise suspensions of solid particles in the liquid, for example solid medicament particles.

[0014] DRIE is generally less suitable for etching glass. In glass, rounded channels with semicircular cross-sections can also be formed more easily and with generally less cost than square channels, by using isotropic etching processes to etch the glass substrates rather than using an anisotropic process such as the anisotropic processes described above that are used to etch silicon. Isotropic / wet etching is preferred for glass because it can offer better control over the etching rate and can achieve smoother surfaces, and isotropic / wet etching processes can be carried out at a batch level (whereas DRIE processes need to be conducted on individual wafers). The application of a light-sensitive photoresist and its exposure using photolithography via a lithographic mask are typically used when patterning wafers by wet etching. These techniques are well-known to those skilled in the art.

[0015] Rounded channels (e.g. channels with circular or semi-circular cross-sections, or with very rounded corners / sides) offer a more uniform velocity profile and lower resistance to flow compared to channels with a square cross-section, due to the absence of sharp corners. Rounded channels offer a parabolic velocity profile across the channel for flow within the channel, with the maximum velocity at the centre. Rounded channels also typically have a higher hydraulic diameter compared to square channels with the same cross-sectional area. This can lead to more efficient flow characteristics within rounded channels as compared to square channels, such as for example a lower pressure drop over the length of the channel, and potentially higher flow rates for the same pressure difference between the ends of the channel.

[0016] A disadvantage of isotropic etching is that it results in shallow and wide channels due to width restrictions on the lithographic masks used to pattern the wafer with the desired layout of microchannels, pillars and columns, and it results in the etching spreading outwards as much as downwards / into the depth of the glass. Wet etching or isotropic etching also usually results in etched channels with curved or radiused sidewalls and lower aspect ratios than when etching is carried out using anisotropic techniques such as DRIE techniques. US7,896,264 describes and shows a microstructured nozzle used with an atomiser which produces an aerosol from a fluid containing a medicament. The nozzle consists of a number of channels produced by microstructuring a plate-shaped member or substrate. In the nozzle the channels are located between projections which are arranged side by side in rows and project from a base plate / substrate. This microstructured base plate / substrate is covered with a cover plate / substrate. The channels are narrowly defined in terms of shape, cross sectional area and length. The nozzle contains a filter as the primary structure and a secondary structure downstream of the filter.

[0017] As noted above, nozzles of this type are typically formed by sandwiching two large substrate sheets together to form a nozzle wafer (a nozzle wafer being a single large wafer from which smaller individual nozzles can be cut for multiple individual micropumps or inhaler devices). The nozzle wafer is formed from a base plate / first substrate and a cover plate / second substrate.

[0018] Typically, nozzle wafers formed from two substrate sheets as outlined above will only have channels on one of the substrates, with the other substrate being ‘blank’ or un-etched.

[0019] It is possible to etch channels on both substrates and then bring the substrates together so as to align the channels to form single channels from the associated, aligned channels on each substrate. Ideally, the alignment would create a single channel having a smooth or uniform profile with no corners, as shown schematically in figure 6a. However, there are significant difficulties with correctly bringing the two etched substrates together with enough precision so that the channels align correctly. For some applications, the alignment needs to be carried out to within tolerances of down to one (1) micron or less in order to create channels having an effective cross-sectional shape and size. If the two substrate sheets are misaligned (such as for example as shown schematically in figure 6b), then this causes significant changes in the hydraulic diameter of the channels, and therefore significant changes in the flow characteristics, which has an impact on the final spray delivered to a user in use - See Appendix A. The cross-sectional area is unchanged if the mutual alignment of the two substrate sheets varies between wafers, but the cross-sectional profile is different and has a different wetted perimeter..

[0020] SUMMARY

[0021] It is an object of the present invention to provide a nozzle for use in micropumps for delivery of fluids which goes some way to overcoming the abovementioned disadvantages or which at least provides the public or industry with a useful choice.

[0022] It is a further object of the present invention to provide a method of creating a nozzle for use in micropumps for delivery of fluids which goes some way to overcoming the abovementioned disadvantages or which at least provides the public or industry with a useful choice.

[0023] It is a yet still further object of the present invention to provide an inhaler device that comprises a nozzle for use in micropumps which goes some way to overcoming the abovementioned disadvantages or which at least provides the public or industry with a useful choice.

[0024] Accordingly, in a first aspect the present invention may broadly be said to consist in a nozzle, comprising: a first plate having a first substantially planar surface; a second plate having a second substantially planar surface; the first and second plates positioned so that the first and second planar surfaces are directly adjacent to one another, the substantially planar surfaces of each of the first and second plates etched to form open-topped channels; the first and second plates etched and aligned so that at least part of the open-topped channels on one plate associate with the channels on the other plate so as to form a plurality of enclosed passages that run at least partly through the nozzle, the passages extending along the substantially planar surfaces at least some of the channels on one of the plates formed with a greater width than the associated narrower channels on the other plate.

[0025] In an embodiment, the width difference between the greater and narrower widths is the same as or greater than the manufacturing alignment tolerance / control between the two plates.

[0026] In an embodiment, the width difference between the greater and narrower widths is the same as the manufacturing alignment tolerance / control between the two plates.

[0027] In an embodiment, the width difference between the greater and narrower widths is one micron.

[0028] In an embodiment, the first and second plates comprise glass plates.

[0029] In an embodiment, the open-topped channels are formed with a rounded profile.

[0030] In an embodiment, the first and second plates comprise silicon plates.

[0031] In an embodiment, the open-topped channels are formed with a square or rectangular profile.

[0032] In an embodiment, the first plate comprises a glass plate and the second plate comprises a silicon plate.

[0033] In an embodiment, the open-topped channels in the glass plate are formed with a rounded profile and the open-topped channels In the silicon plate are formed with a substantially square or rectangular profile. In a second aspect the present invention may broadly be said to consist in a method of forming a nozzle that comprises a first plate having a first planar inner surface, and a second plate having a second planar inner surface, characterised in that the method comprises the steps of: i) Etching open-topped channels on two plates, at least some of the channels on one of the plates formed with a greater width than the narrower channels on the other plate; ii) Sandwiching the two plates together so as to form a two-layer wafer, with the microchannels formed and located on the directly adjacent inner faces of the two plates, the sheets etched and aligned so that at least part of the open-topped channels on one sheet associate with the channels on the other sheet so as to form a plurality of enclosed passages; iii) Cutting the wafer into a number of individual nozzles with enclosed passages that run at least partly through the nozzle;

[0034] In an embodiment, in the step of sandwiching the two plates together, the alignment is carried out to within tolerances of substantially one micron.

[0035] In an embodiment, in the step of etching the open-topped channels, the channels are formed so that the width difference between the channels on one plate and the channels on the other plate is substantially the same as or greater than the manufacturing alignment tolerance / control between the two plates.

[0036] In an embodiment, in the step of etching the open-topped channels, the channels are formed so that the width difference between the channels on one plate and the channels on the other plate is substantially the same as the manufacturing alignment tolerance / control between the two plates.

[0037] In an embodiment, in the step of etching the open-topped channels, the channels are formed so that the width difference between the channels on one plate and the channels on the other plate is substantially one micron.

[0038] In an embodiment, in the step of etching the open-topped channels on two plates, the plates are glass and the open-topped channels are etched with a rounded profile.

[0039] In an embodiment, in the step of etching the open-topped channels on two plates, the plates are silicon and the open-topped channels are etched with a substantially square or rectangular profile.

[0040] In an embodiment, in the step of etching the open-topped channels on two plates, one of the plates is a glass plates and one of the plates is a silicon plates, the open-topped channels in the glass plate etched with a rounded profile and the open-topped channels in the silicon plate etched with a substantially square or rectangular profile..

[0041] 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.

[0042] 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.

[0043] 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.

[0044] BRIEF DESCRIPTION OF THE DRAWINGS

[0045] 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 embodiments of the device by way of example, and in which:

[0046] Figure 1 shows a side view of a known type of manually-operated nebuliser / Soft Mist Inhaler that has an upper housing part and a lower housing part, the two housing parts rotated relative to one another in use to pump or prime the device for use, the upper housing part having a lid that can be opened and closed to allow a user to access a mouthpiece, the lid shown in a fully open position.

[0047] Figure 2 shows a perspective view from one side and slightly above of the nebuliser / Soft Mist Inhaler of figure 1 , the lid shown slightly open.

[0048] Figure 3 shows a perspective cutaway side view of the nebuliser / Soft Mist Inhaler of figures 1 and 2, the lid shown in the closed position, the upper housing part comprising a mouthpiece and nozzle assembly, the nozzle assembly located within the mouthpiece. Figure 4 shows a cutaway schematic side view of the nozzle assembly of figure 3, the nozzle assembly comprising a nozzle retainer, upper and lower seals, a nozzle chip / filter, a pre-filter and pre-filter holder, and a top nut that screws onto the upper end of an upper tube housing located within the upper housing so as to enclose these items.

[0049] Figure 5 shows a schematic side view of one plate of a known type of chip / filter of the type that is formed from two sandwiched plates, with the other plate not shown so that the internal structure of the chip / filter can be shown, this figure showing the general form of the structure of the channels inside the chip / filter.

[0050] Figure 6a shows a schematic end view of part of a chip / filter formed from two sandwiched plates, the chip / filter having a passage running therethrough, the passage formed by associating etched channels in the two sandwiched plates as these are brought together, the etched channels of substantially the same width, the plates formed from glass, the etched channels formed by using an isotropic / wet etching process, the channels fully aligned.

[0051] Figure 6b shows a schematic end view of part of a chip / filter formed from two sandwiched plates in a similar manner to that shown in figure 6a, the passage formed by associating etched channels of substantially the same width in the two sandwiched plates as these are brought together, the channels mis-aligned or not fully aligned.

[0052] Figure 7a shows a schematic end view of part of a chip / filter formed from two sandwiched glass plates, the chip / filter having a passage running therethrough, the passage formed by associating etched channels in the two sandwiched plates as these are brought together, the etched channel in one plate being of greater width than the etched channel in the other plate, the increase in the etch width being substantially the same as the alignment tolerance / control between the two substrates used to form the plates during assembly, the channels shown aligned centrally.

[0053] Figure 7b shows a schematic end view of part of a chip / filter similar to that shown in figure 7a, with the channels shown offset from one another.

[0054] Figure 7c shows an exploded view of the chip / filter of figure 7a.

[0055] Figure 8a shows a schematic end view of part of a chip / filter formed from two sandwiched silicon plates, the chip / filter having a passage running therethrough, the passage formed by associating etched channels in the two sandwiched plates as these are brought together, the etched channel in one plate of greater width than the etched channel in the other plate, the increase in the etch width being substantially the same as the alignment tolerance / control between the two substrates used to form the plates during assembly, the channels shown aligned centrally. Figure 8b shows a schematic end view of a chip / filter similar to that shown in figure 8a, with the channels shown offset from one another.

[0056] Figure 8c shows an exploded view of the chip / filter of figure 8a.

[0057] DETAILED DESCRIPTION

[0058] General

[0059] Embodiments of the invention, and variations thereof, will now be described in detail with reference to the figures.

[0060] As used in this specification, the term "micropump" refers to micro liquid dispensing systems employed to dispense a fluid in small quantities with accuracy, and which can control and manipulate small volumes of fluid (generally in volumes of a few microlitres). 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 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.

[0061] Terms such as ‘upper’, ‘lower’, ‘base’, and ‘cove / as used in this specification are context- dependent, and not absolute. For example, where ‘upper’ is used in the description of figure 1 above and in the detailed description below, this is within the context of the figure as shown. The nebuliser / Soft Mist Inhaler as shown in the figure can be used in any orientation, and does not have to be used in the upright orientation shown.

[0062] As used in this specification, ‘substrate’ refers to a single piece of glass or silicon either etched or unetched, and (depending on the context as outlined in the relevant portion of the description) will usually refer to a single large sheet of glass or silicon that will be etched and then cut into smaller units.

[0063] ‘Wafer’ refers to a sandwich of two substrates formed as a result of a bonding process, a wafer containing multiple ones of the final product but not yet cut out from the wafer, and ‘nozzle’ or ‘chip / filter’ refers to an example of the final, finished product, following the final manufacturing step of dicing the wafer into separate items - that is, separate chips / filters or nozzles (‘nozzle’ and ‘chip / filter’ are used interchangeably, and ‘chip’, and ‘filter1may also be used separately from one another and in isolation).

[0064] ‘Layer’ or ‘plate’ as used in this specification refers in general to one of the two main pieces of the finished product (e.g. one of the two layers of the chip / filter). As used in this specification, the final finished product - the ‘chips / filters’ and / or ‘nozzles’ - are used to indicate items through which fluids flow, through a moulded or engraved pattern of microchannels in the item. More specifically, the fluids flow through moulded or engraved microchannels that are formed in one or both of the directly adjacent or adjoining faces of two plates that are sandwiched together to comprise part or all of the chip / filter, with fluid flowing in use generally / substantially along the axis of the passage or passages thus formed.

[0065] 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 chips / filters at high pressure, e.g. substantially between 10 to 59MPa. 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 embodiments as described and shown herein, the micropump is designed for use as part of an apparatus (a liquid delivery device) for delivering one or more substances used as a medication, i.e. the fluid comprises at least one chemical compound that has a physiological effect on the patient when administered.

[0066] For all of the embodiments described below, the invention is described as forming part of a liquid delivery device (the invention may also be considered as the liquid delivery device itself). Specifically for the embodiments described, the liquid delivery device is a nebuliser or inhaler (more specifically, a Soft Mist Inhaler).

[0067] A typical known type of nebuliser or inhaler in or with which the chip / filter of the present invention can be used is shown in figures 1 to 3. In the nebuliser shown in these figures, a chip / filter forms part of the nebuliser / inhaler.

[0068] The chip / filter of the present invention, and the chips / filters formed using the method of the present invention, can be used in the typical known types of nebulisers or inhalers such as those shown in figures 1 to 3, in place of the already-known chips / filters.

[0069] The known type of chip / filter is referred to generally as chip / filter 1001 , with the specific embodiments of the chips / filters of the present invention described separately and numbered appropriately as detailed below.

[0070] As noted above, a nebuliser 1 of a known type is shown in figures 1 to 3. The nebuliser 1 comprises an upper housing part 2 and a lower housing part 3. The upper housing part 2 contains a retaining structure / nozzle assembly (described in detail below) and a mouthpiece 5 within the lid. The lower housing part 3 contains a liquid reservoir (not shown), which typically comprises a cartridge that can be removed and replaced as required. A riser tube or capillary tube 6 extends between the reservoir and the nozzle assembly. A lid 4 is hingedly connected to the upper housing part, the lid configured so that when closed, the lid encloses the nozzle retaining structure / nozzle assembly.

[0071] In use, a user rotates the upper and lower housing parts 2, 3 relative to one another to pump or prime the device 1 for use. Liquid from the reservoir is sucked up the tube 6 towards the upper end of the tube. When a user then triggers the nebuliser (e.g. by pressing button 7), the tube 6 is forced rapidly upwards with the head of the tube 6 forcing liquid through the nozzle assembly, and then through the mouthpiece 5, for delivery to a user as a spray or aerosol of fine droplets.

[0072] For the purposes of this specification, references to orientations such as ‘upper, ‘lower’, ‘top’, ‘bottom’, ‘vertical’, ‘horizontal’ and similar or related references should be taken as meaning with respect to an orientation with the nebuliser stood upright with the mouthpiece at the upper end, even if in use the orientation would differ from this. These references to orientation should not be taken as absolute.

[0073] Nozzle Retaining Structure I Nozzle Assembly

[0074] A known type of nozzle retaining structure I nozzle assembly is shown in figure 4.

[0075] The typical known type of nozzle assembly comprises the following main parts: a filter holder 9; a pre-filter 10; an upper seal or nozzle seal 11 ; a lower seal 12; a chip / filter 1001 ; a top nut 14, and; a nozzle retainer 13.

[0076] The filter holder 9, pre-filter 10, upper and lower seals 11 , 12, nozzle retainer 13 and chip / filter 1001 are contained within the top nut 14. The top nut 14 is screwed to the top of an upper tube housing 8 (that contains the tube 6, with tube 6 moving axially / vertically within the tube housing 8), the top nut 14 and upper tube housing 8 mutually threaded to allow them to be screwed together.

[0077] As outlined above, the tube 6 moves along a passage within the upper tube housing 8, the passage aligned axially within the upper tube housing 8. The head of the tube 6 fits snugly within the passage. In use, fluid from the reservoir (not shown) travels through the hollow centre of the tube 6 (which forms a capillary tube), and during use is forced under pressure through the pre-filter 10, which is located directly above the top end of the passage. The pre-filter 10 is held in place by the filter holder 9, with the filter holder 9 located above and directly adjacent to the top end of the tube housing 8. The lower seal 12 is located between the filter holder 9 and tube housing 8 so as to seal between the two and prevent fluid from leaking out through the seam or gap between the two.

[0078] The chip / filter (e.g. chip / filter 1001 in the known type of inhaler, or chip / filter 101 , 201 of the embodiments of the invention described below) is located above the top end of the pre-filter 10, the chip / filter located within and held in place by the upper seal 11 . The upper seal 11 locates into a recess within the nozzle retainer 13, which extends around the sides and top of the chip / filter and upper seal 11 .

[0079] In use, fluids flow through a moulded or engraved pattern of microchannels in the chip / filter to the outlet end, the outlet end of the chip / filter comprising one or more spray jets.

[0080] The top nut 14 and tube housing 8 are mutually threaded as already described, so that the top nut 14 can be screwed onto the tube housing 8, so as to hold the lower seal 12, filter holder 9, filter 10, upper seal 11 , chip / filter and nozzle retainer 13 in place within the top nut 14, the top nut 14 substantially surrounding and enclosing the other elements of the nozzle retaining structure I nozzle assembly.

[0081] Chip / Filter - General

[0082] ‘Chip / filter’ as used in this specification in relation to the specific embodiments of the invention indicates an item that has been formed by sandwiching two plates together, both or each of the plates having microchannels on their inner faces. The microchannels / channels are formed so that the channels on one plate are matched or associated with the channels on the other plate. That is, channels on the inner face of one plate are at least partly matched / associated with channels on the inner face of the other plate, so that when the two plates are brought together and joined, associated channels at least partly overlap to form a single passage. In use, fluid flows generally / substantially along the axis of the passage or passages thus formed - that is, substantially parallel to the plane of the inner faces of the plates.

[0083] The significant advantage of forming a single passage from associated channels formed in both or each of the two plates is that the passage can have a larger cross-sectional area and / or hydraulic diameter, and hence can allow greater fluid flow at a given pressure drop across its ends than could a channel of the same width formed in the surface of just one of the two substrate plates. This is important, because the widths of the channels and other features (e.g. pillars and columns) in the chip / filter are constrained for example by reasons of space, the need for strong bonding between each plate (e.g. to resist high internal fluid pressures during operation) and the depth:width aspect ratios that can be achieved in etched channels, particularly in wet etched channels. Other factors and constraints may also be applicable. The present invention allows the formation of passages of greater size closer together than would be possible with channels formed in just one plate, whilst allowing their fluid handling performance and characteristics to be substantially unaffected by small alignment errors between the two channelled plate surfaces, such errors being an intrinsic feature of the plates alignment and joining process. The present invention thus provides for chip / filter structures of better performance and better consistency than has been possible before with chip / filter structures of the prior art.

[0084] In the embodiments of the present invention, similar numbering is used for similar elements - e.g. the chip / filter is referred to as chip / filter 101 , 201 , for different embodiments. Similarly, the two layers or plates of the two halves that form the chip / filter are generally referred to as 102a, 102b, 202a, 202b, the inner faces of the two layers are generally referred to as 103a, 103b, 203a, 203b, etc.

[0085] In the plates of the embodiments of the present invention, one or both of the inner faces 103a, 103b, 203a, 203b is / are etched to form channels (microchannels) 104, 204. These channels are open-topped or opening towards the inner face.

[0086] The channels 104, 204 as shown in the figures and as described for each of the embodiments below are not intended to be exactly representative of the shape and configuration of the channels and plates - these are intended to be stylised representations to show the general relationships between the channels and plates, and to exemplify the relative positions and shapes of the channels and plates that can be achieved.

[0087] In the embodiments described below, a single set of associated channels is shown and described. In an actual chip / filter, multiple channels will be formed through the filter in a similar manner to that shown in figure 5 for the prior art.

[0088] Chip / Filter - Glass-glass

[0089] In a first set of embodiments, the chip / filter 101 is formed from two glass plates - an upper glass plate 102a and a lower glass plate 102b. The two glass plates 102a, 102b are sandwiched together to form a nozzle or chip / filter 101 , the individual chips / filters formed by cutting these out from a wafer. The wafer is formed from two glass substrates that have been etched to form channels 104a, 104b on what will be the inner surfaces of the chip / filter 101 when the substrates are sandwiched together to form the wafer.

[0090] The etching to form the channels is carried out using an isotropic / wet etching process (that is, using an acid solution or chemical etchant, as outlined above).

[0091] The use of two glass sheets means that inspection of the sheets can be carried out more easily and quickly before these are joined / bonded, and the use of two sheets formed from the same material (glass) ensures that there is a stronger bond between them than for two parts made of different materials.

[0092] Each of the two glass plates 102a, 102b has an inner surface (surfaces 103a, 103b) that is configured to in use contact the equivalent surface on the other plate, so that the inner surfaces 103a, 103b on the plates form adjoining or directly adjacent inner faces. This arrangement is shown schematically in figure 7.

[0093] In order to compensate for misalignment of the substrates when these are brought together for assembly into a wafer, the etching process is carried out so that the width of the channels that are formed in one of the substrates is a greater width than the width of the channels that are formed in the other substrate. The end result in the nozzle 101 is that the channel or channels in one of the plates is / are wider than the channels or channels in the other half / part of the nozzle 101.

[0094] In figure 7, this is shown by having the channel 104a in the upper glass plate 102a be wider than the channel 104b in the lower glass plate 102b. As shown in the end or cross-sectional view of figure 7, flow is along the passage - that is, in a direction that would be into or out of the page.

[0095] The increased width is achieved during the etching process (which takes place on the larger substrates before these are brought together to form the wafer, the wafer then cut into individual nozzles). A deliberate increase in the etch width by an amount the same as or similar to the alignment tolerance / control between the two substrates during assembly (sandwiching together) means that any misalignment during assembly will not affect the overall hydraulic diameter of the flow channels (upper and lower channels 104a, 104b) when these are associated to form a passage.

[0096] In manufacturing, tolerances are usually quoted as [main dimension] ± [X], so the channel width / etch width is deliberately increased by an amount the same as or similar to the alignment tolerance / control between the two substrates. That is, the wider channel has a width that is the same as that of the narrower channel, plus 2X (where ‘X’ is the alignment tolerance / control between the two substrates). So, for example, if the alignment can be carried out to within tolerances of + / - one (1 ) micron, the wider channel will be formed so that it is two microns wider than the narrower channel. The width difference between the greater and narrower widths is substantially the same as the manufacturing alignment tolerance / control between the two substrates used to form the plates.

[0097] It can be seen that having two channels of different sizes means that the larger channel will either overlap on both sides (as shown in figure 7a), or on one side (as shown in figure 7b). It should be noted that the offset could also be anywhere between the positions shown in figures 7a and 7b, or to either side. Figures 7a and 7b should be taken only as exemplary.

[0098] If the increase or difference in the channel widths is substantially the same as or greater than the alignment tolerance / control between the two substrates during manufacture, then any misalignment of the substrates does not affect the hydraulic diameter of the passage thus formed (see Appendix A for a full discussion of hydraulic diameter). The cross-sectional area remains the same, as does the dimension of the wetted perimeter. This is in contrast to the construction for example shown in figures 6a and 6b, where misalignment causes a change in the dimension of the wetted perimeter, and therefore a change in the hydraulic diameter Dh.

[0099] In this embodiment, it can be seen that corners are an inherent part of the passage - corners will inevitably be formed when one channel is wider than the other. As outlined in the appendix, corners within a passage can cause flow separation (when the fluid flow detaches from the boundary), which can lead to the creation of recirculation zones or vortices downstream. Flow separation and the subsequent reattachment of the flow can lead to increased pressure losses and affect the overall efficiency of fluid transport within the microfluidic system.

[0100] In nozzles where the channels are of substantially equal size, there are significant difficulties with correctly bringing the two etched substrates together with enough precision so that the channels align correctly, as outlined in the prior art section. So it is possible for a nozzle of this type to have passages that are substantially aligned (and which therefore have no or minimal internal corners), or which are misaligned in a similar manner to that shown in figure 6a, with internal corners created by the misalignment. Misaligned channels therefore cause significant changes in the hydraulic diameter of the passage thus formed, and therefore significant changes in the flow characteristics as compared to a passage formed from aligned channels. This therefore has an impact on the final spray as delivered - for a particular design or production run of e.g. inhalers using the nozzle, the spray as delivered by any one of the inhalers produced according to the design or the production run can or will vary from another one of the inhalers - there will be a range of flow / spray characteristics rather than a consistent flow / spray.

[0101] In a nozzle created according to the present invention, corners are an inherent part of the design - it is known that there will be corners in the passage. However, due to the known size differences in the channels, the impact on hydraulic diameter is consistent (the wetted perimeter is consistent as this is independent of the alignment), and therefore the impact on flow characteristics is consistent - a nozzle can be designed / manufactured that will have consistent flow / spray characteristics.

[0102] Chip / Filter - Silicon-silicon

[0103] In a second set of embodiments, the chip / filter 201 is formed from two silicon plates - an upper silicon plate 202a and a lower silicon plate 202b. The two silicon plates 202a, 202b are sandwiched together to form a nozzle or chip / filter, the individual chips / filters formed by cutting these out from a wafer. The wafer is formed from two silicon substrates that have been etched to form channels 204a, 204b on what will be the inner surfaces of the chip / filter when the substrates are sandwiched together to form the wafer.

[0104] The etching to form the channels is carried out using an anisotropic DRIE etching process. This process provides accurate results as outlined above, with deep narrow channels (channels with a high aspect ratio), these channels having vertical side walls, and formed within tight tolerances.

[0105] Each of the two silicon plates 202a, 202b has an inner surface (surfaces 203a, 203b) that is configured to in use contact the equivalent surface on the other plate, so that the inner surfaces 203a, 203b on the plates form adjoining or directly adjacent inner faces. This arrangement is shown schematically in figure 8.

[0106] In order to compensate for misalignment of the substrates when these are brought together for assembly into a wafer, the etching process is carried out so that the width of the channels that are formed in one of the substrates is a greater width than the width of the channels that are formed in the other substrate. The end result in the nozzle 201 is that the channel or channels in one of the plates is / are wider than the channels or channels in the other half / part of the nozzle 201.

[0107] In figure 8, this is shown by having the channel 204a in the upper silicon plate 202a be wider than the channel 204b in the lower silicon plate 202b. As shown in the end or cross- sectional view of figure 8, flow is along the passage - that is, in a direction that would be into or out of the page.

[0108] The increased width is achieved during the etching process (which takes place on the larger substrates before these are brought together to form the wafer, the wafer then cut into individual nozzles). A deliberate increase in the etch width by an amount the same as or similar to the alignment tolerance / control between the two substrates during assembly (sandwiching together) means that any misalignment during assembly will not affect the overall hydraulic diameter of the flow channels (upper and lower channels 204a, 204b) when these are associated to form a passage. It can be seen that having two channels of different sizes means that the larger channel will either overlap on both sides (as shown in figure 8a), or on one side (as shown in figure 8b). It should be noted that the offset could also be anywhere between the positions shown in figures 8a and 8b, or to either side. Figures 8a and 8b should be taken only as exemplary.

[0109] If the increase or difference in the channel widths is substantially the same as or greater than the alignment tolerance / control between the two substrates during manufacture, then any misalignment of the substrates does not affect the hydraulic diameter of the passage thus formed (see Appendix A for a full discussion of hydraulic diameter). The cross-sectional area remains the same, as does the dimension of the wetted perimeter. This is in contrast to the construction for example shown in figures 6a and 6b, where misalignment causes a change in the dimension of the wetted perimeter, and therefore a change in the hydraulic diameter Dh.

[0110] As noted in the background section, channels having a square cross-section can be formed in a silicon substrate by using an anisotropic etching process such as Deep Reactive Ion Etching (DRIE). Anisotropic etching of this type when used on a silicon substrate will produce channels having a square cross-section and sharp corners within the channel.

[0111] Nozzles with square channels are formed by sandwiching two large substrate sheets together to form a nozzle wafer. Silicon is used for the substrate sheets because the anisotropic DRIE etching process can be used to form channels in / on the silicon, and this process provides accurate results as outlined above - the DRIE process provides deep narrow channels (channels with a high aspect ratio) on the silicon substrate, these channels having vertical side walls, and formed within tight tolerances.

[0112] Misalignment of the substrates used to form the wafers is possible in the same manner as described above for the isotropically-etched substrates, and it is possible to compensate for this misalignment in the same manner, as outlined above. Alignment of the channels on one substrate with the channels of the other substrate is important, so as to create channels having a known or calculable hydraulic diameter, or one within a certain range, so that the chip / filter has the required properties for fluid delivery. That is, the use of the present invention makes it possible to allow for a less tight alignment between the substrates by changing the relative shapes and sizes of the channels at the design stage. For example, if the etch width of the channels in one side of the nozzle is increased so that these channels are wider than the channels in the other half / part of the nozzle, and if the increase or difference in the channel widths is substantially the same as or greater than the alignment tolerance / control between the two substrates during manufacture, then any misalignment of the substrates does not affect the hydraulic diameter of the combined flow channels when these are brought together to form a single passage (see Appendix A for a full discussion of hydraulic diameter).

[0113] The advantage with this embodiment is substantially the same as that outlined above for the glass-glass embodiment - that is, that corners are an inherent part of the design and it is known that there will be corners in the passage. However, due to the known size differences in the channels, the impact on hydraulic diameter is consistent, and therefore the impact on flow characteristics is consistent - a nozzle can be designed / manufactured that will have consistent flow / spray characteristics.

[0114] Chip / Filter - Silicon-Glass

[0115] The chip / filter can also be formed from a silicon plate and a glass plate - e.g. an upper silicon plate and a lower glass plate (or the other way around).

[0116] As for the previous embodiments described above, the two plates are sandwiched together to form a nozzle or chip / filter, the individual chips / filters formed by cutting these out from a wafer. The wafer is formed from two substrates (one glass, one silicon) that have been etched to form channels on what will be the inner surfaces of the chip / filter when the substrates are sandwiched together to form the wafer, with each of the two plates having an inner surface that is configured to in use contact the equivalent surface on the other plate, so that the inner surfaces on the plates form adjoining or directly adjacent inner faces.

[0117] As for the previous embodiments, in order to compensate for misalignment of the substrates when these are brought together for assembly into a wafer, the etching process is carried out so that the width of the channels that are formed in one of the substrates is a greater width than the width of the channels that are formed in the other substrate. The end result in the nozzle is that the channel or channels in one of the plates is / are wider than the channels or channels in the other half / part of the nozzle.

[0118] A nozzle formed in this manner could for example have a lower glass plate the same as or similar to the lower glass plate 102b as shown in figure 7, and an upper silicon plate the same as or similar to the upper silicon plate 202a shown in figure 8 (or a lower silicon plate the same as or similar to lower silicon plate 202b, and a an upper glass plate the same as or similar to glass plate 102a). As for the previous embodiments, flow is along the passage.

[0119] The advantages of a nozzle formed in this manner are substantially the same as outlined for the two embodiments above - that is, that corners are an inherent part of the design and it is known that there will be corners in the passage. However, due to the known size differences in the channels, the impact on hydraulic diameter is consistent, and therefore the impact on flow characteristics is consistent - a nozzle can be designed / manufactured that will have consistent flow / spray characteristics. APPENDIX A - MICROFLUIDIC CHANNEL DYNAMICS

[0120] When considering a microfluidic channel that has a fluid flowing through the channel, the flow characteristics of the fluid (e.g. flow velocity, pressure distribution, and fluid dynamics within the channel) are affected by the dimensions (cross-sectional area) of the channel, the particular properties of the fluid, and the boundary conditions. The cross-sectional shape of the channel also has a significant impact on the flow characteristics.

[0121] The effect of the cross-sectional shape and area are discussed in detail below, using the example of a channel that is nine microns wide, six microns deep, and fifty microns long, with channels with rounded cross-sectional shapes (circular, semi-circular, or with highly rounded corners) compared to channels having a square or rectangular cross-section.

[0122] Cross-Sectional Area

[0123] The cross-sectional area directly affects the flow rate through the channel according to the Hagen-Poiseuille equation for laminar flow, which is applicable in many microfluidic applications due to the small dimensions and resulting low Reynolds numbers. The flow rate (Q) is proportional to the square of the cross-sectional area (A):

[0124] Where AR is the pressure difference across the length (L) of the channel, and is the dynamic viscosity of the fluid. Therefore, for a channel that is nine microns wide and six deep, the cross-sectional area for a square channel is 54 pm2. However, the area varies slightly for a channel with a rounded cross-section, depending on the exact shape of the channel.

[0125] Cross-Sectional Shape

[0126] The shape of the cross-section significantly impacts the flow characteristics due to the distribution of shear stress and velocity profiles within the channel. For example:

[0127] Square Cross-Section: In channels with a square cross-section, the flow velocity is highest at the centre and decreases towards the walls. Square cross-section channels have sharp corners and this can lead to secondary flows (minor flows superimposed on the primary flow direction, potentially affecting mixing and particle distribution (in situations where the fluid comprises a suspension of particles) in the channel). Therefore, sharp corners can cause a complex flow pattern near the corners. Rounded Cross-Section: In channels with a rounded cross-section (that is, a channel having a circular or semi-circular cross-sectional profile, or a profile that has highly rounded corners) there is a more uniform velocity profile, and the absence of sharp corners means that there is a lower resistance to flow. This results in a parabolic velocity profile across the channel, with maximum flow velocity at the centre. Rounded channels typically have a higher hydraulic diameter as compared to square channels that have the same cross-sectional area. This can lead to more efficient flow characteristics, such as lower pressure drops and potentially higher flow rates for the same pressure difference between the ends of the channel.

[0128] Specific Channel Dimensions

[0129] For a channel that is nine (9) microns wide, six (6) microns deep, and fifty (50) microns long:

[0130] Flow Characteristics: The flow in such small dimensions is likely to be laminar for both rounded and square / rectangular cross-sectional shapes, with the flow characterised by smooth, orderly flow layers that slide past one another.

[0131] Shape Comparison: A rounded cross-section in general facilitates a smoother flow with less resistance, compared to a square cross-section. This is due to the smaller surface area of the channel wall that is in contact with the fluid, which assists with minimising friction and allows for a more streamlined flow. Moreover, the rounded shape helps in avoiding the formation of vortices or dead zones of the type that can occur in the corners of a square channel.

[0132] Practical Implications: The choice between a rounded or square cross-section might depend on the specific application requirements, such as the need for efficient mixing, precise control of the flow rate, or minimizing the pressure drop across the channel.

[0133] It can be seen that both the cross-sectional shape and area are important for determining the flow characteristics in microfluidic channels. Rounded cross-sections generally offer advantages in terms of flow efficiency and uniformity. This can be particularly beneficial in applications requiring precise fluid handling and manipulation at the microscale.

[0134] To address how boundary conditions and shape affect flow at a high pressure of 250 bar, and to estimate the Reynolds number for the flow in microfluidic channels with the given dimensions, several factors need to be considered. The impact of boundary conditions and shape on flow involves understanding the pressure-driven flow characteristics and the resulting Reynolds number, which indicates the flow regime (laminar vs. turbulent). Calculating The Hydraulic Diameter

[0135] Calculating the hydraulic diameter of complex microfluidic channel cross-sections is required in order to understand flow characteristics and so as to optimise a design for a specific application.

[0136] The hydraulic diameter (Dh), is a commonly used parameter in fluid mechanics to characterise non-circular conduits, allowing equations used for pipes / channels that have a circular cross-section to be applied to pipes / channels having a non-circular cross-section.

[0137] The hydraulic diameter (Dh) is defined as Dh = 4A / P, where A is the cross-sectional area and P is the wetted perimeter.

[0138] The hydraulic diameter of complex microfluidic channel cross-sections can be calculated as follows:

[0139] 1. Identify the Cross-Section Shape: As a first step, the geometry of the microfluidic channel needs to be clearly defined. If the cross-section is complex, it can be broken down into different sub-shapes that can for example include rectangles with rounded corners, trapezoids, etc.

[0140] 2. Calculate the Cross-Sectional Flow Area (A): The area through which fluid flows needs to be calculated. This calculation will depend on the shape of the crosssection. For standard shapes (e.g., circles, rectangles), the area can be calculated using well-known formulae. For irregular shapes, numerical methods can be used, or the cross-sectional shape can be divided into simpler sub-shapes whose areas can be individually calculated, and then added up.

[0141] 3. Calculate the Wetted Perimeter (P): The wetted perimeter is the boundary length of the cross-section, that is in contact with the fluid. This is easily calculated for standard shapes using well-known geometric formulae. Approximation methods such as breaking the perimeter into segments can be used for more complex shapes, or CAD software can provide precise measurements.

[0142] 4. Apply the Hydraulic Diameter Formula: With the values of (A) and (P), use the hydraulic diameter formula (above) to find the hydraulic diameter. Sharp Corners In A Microfluidic Structure

[0143] Sharp corners in a microfluidic structure such as a microchannel can significantly affect the hydraulic diameter and therefore the flow characteristics within the channel. The key factors when assessing the impact of sharp corners on hydraulic diameter and fluid flow are as follows:

[0144] 1. Increased Wetted Perimeter: Sharp corners can increase the wetted perimeter of the channel without also providing a proportional increase in the cross-sectional area through which fluid flows. Since hydraulic diameter is inversely proportional to the wetted perimeter, an increased wetted perimeter leads to a decreased hydraulic diameter. This can make the channel seem 'narrower' from a fluid dynamics perspective, even if the cross-sectional area remains constant.

[0145] 2. Flow Separation and Reattachment: Sharp corners can cause flow separation (when the fluid flow detaches from the boundary), which can lead to the creation of recirculation zones or vortices downstream. Flow separation and the subsequent reattachment of the flow can lead to increased pressure losses and affect the overall efficiency of fluid transport within the microfluidic system.

[0146] 3. Local Changes in Velocity Profiles: The presence of sharp corners can lead to non-uniform velocity profiles across the channel. In the vicinity of the corners, fluid velocity may decrease significantly, affecting the average flow velocity and potentially leading to areas of stagnation or significantly slowed flow.

[0147] 4. Increased Pressure Drop: Sharp corners can contribute to an increased pressure drop along the microfluidic channel due to the effects mentioned above, particularly flow separation and the formation of recirculation zones. The increase in pressure drop means that more energy is required in order to maintain a given flow rate, and this affects the efficiency of the system.

[0148] 5. Impact on Mass and Heat Transfer: The hydraulic diameter is a critical parameter in determining the Reynolds number, which in turn affects the flow regime (laminar or turbulent) and the associated mass and heat transfer coefficients. A reduced hydraulic diameter due to sharp corners can lead to changes in the flow regime and altered mass and heat transfer characteristics, which might be beneficial or detrimental, depending on the application.

[0149] Impact of Boundary Conditions and Shape

[0150] At a high pressure of 250 bar (where 1 bar is 100 kPa or around 1 atmosphere pressure) applied to the inlet of microfluidic channels, the driving force for the flow is significantly high. The boundary conditions (inlet pressure, outlet pressure / atmospheric pressure, no-slip at the walls) and the channel shape will have the following impacts:

[0151] 1 . Pressure-driven Flow: A higher inlet pressure leads to an increase in the flow velocity. The flow behaviour, and the efficiency in delivering the fluid through the channel, are influenced by the channel shape due to differences in hydraulic diameter and the total channel surface area in contact with the fluid.

[0152] 2. Shape Impact: At high pressures such as 250 bar, the differences in flow resistance between different cross-sectional shapes becomes more pronounced. Rounded channels still exhibit lower resistance compared to square channels, potentially leading to higher flow rates for the same pressure difference (this assumes that the material can withstand such pressures without deforming).

[0153] Estimating the Reynolds Number

[0154] The Reynolds number (Re) for a channel can be calculated using the formula:

[0155] Where:

[0156] • p is the density of the fluid (e.g. water, having a density of 1000 kg / m3)

[0157] • v is the mean velocity of the fluid (calculated based on the flow rate)

[0158] • Dh is the hydraulic diameter of the channel

[0159] • p is the dynamic viscosity of the fluid (approximately 1 x 10’3Pa . s for water at room temperature)

[0160] The hydraulic diameter (Dh) is defined as Dh = 4A / P, where A is the cross-sectional area and P is the wetted perimeter.

[0161] Therefore, for a rectangular cross-section:

[0162] A = width x depth = 9 pm x 6 pm

[0163] P = 2 x (width + depth) = 2 x (9 pm + 6 pm)

[0164] If the flow rate is known, then the average velocity can be determined from the flow rate. The hydraulic diameter can be calculated, and the Reynolds number can be estimated.

[0165] If the flow rate is not known, then the Reynolds number can be estimated by using some assumptions. The calculated hydraulic diameter (Dh) of the aforementioned microfluidic channel is 7.2 m, and the estimated Reynolds number (Re) for an assumed mean velocity of 1 m / s is approximately 7.2. This Reynolds number indicates laminar flow, as it is well below the critical threshold for turbulence in conventional channels, that threshold being typically approximately Re = 2000.

[0166] Impact On Flow

[0167] Given the high inlet pressure of 250 bar, the actual mean velocity is likely to be significantly higher than the assumed mean velocity of 1 m / s, depending on the exact flow conditions and channel resistance.

[0168] However, even at higher velocities, the small dimensions of microfluidic channels tend to favour laminar flow, due to their significantly high surface area-to-volume ratio, which enhances viscous forces relative to inertial forces.

[0169] The shape of the channel (rounded vs. square) under these conditions will influence flow primarily through its effect on resistance to flow and flow profile distribution. Rounded channels may promote more uniform flow profiles and potentially higher flow rates for a given pressure difference due to lower hydraulic resistance.

[0170] Conclusion

[0171] The high pressure of 250 bar will certainly enhance flow rates through these microfluidic channels, but the fundamentally laminar nature of the flow should remain unchanged due to the low Reynolds numbers typical of microfluidic systems. The channel shape plays a critical role in determining the efficiency and characteristics of the flow, with rounded channels potentially offering advantages in flow uniformity and resistance. However, the actual flow rate and velocity depend on more specific details of the fluid properties and the response of the material that forms the channel to the high-pressure conditions.

Claims

Claims1. A nozzle, comprising: a first plate having a first substantially planar surface; a second plate having a second substantially planar surface; the first and second plates positioned so that the first and second planar surfaces are directly adjacent to one another, the substantially planar surfaces of each of the first and second plates etched to form open-topped channels; the first and second plates etched and aligned so that at least part of the open-topped channels on one plate associate with the channels on the other plate so as to form a plurality of enclosed passages that run at least partly through the nozzle, the passages extending along the substantially planar surfaces, ; characterised in that at least some of the channels on one of the plates are formed with a greater width than the associated narrower channels on the other plate.

2. A nozzle as claimed in claim 1 wherein the width difference between the greater and narrower widths is the same as or greater than the manufacturing alignment tolerance / control between the two plates.

3. A nozzle as claimed in claim 2 wherein the width difference between the greater and narrower widths is the same as the manufacturing alignment tolerance / control between the two plates.

4. A nozzle as claimed in any one of claims 1 to 3 wherein the width difference between the greater and narrower widths is one micron.

5. A nozzle as claimed in any one of claims 1 to 4 wherein the first and second plates comprise glass plates.

6. A nozzle as claimed in claim 5 wherein the open-topped channels are formed with a rounded profile.

7. A nozzle as claimed in any one of claims 1 to 4 wherein the first and second plates comprise silicon plates.

8. A nozzle as claimed in claim 7 wherein the open-topped channels are formed with a square or rectangular profile.

9. A nozzle as claimed in any one of claims 1 to 4 wherein the first plate comprises a glass plate and the second plate comprises a silicon plate.

10. A nozzle as claimed in claim 9 wherein the open-topped channels in the glass plate are formed with a rounded profile and the open-topped channels In the silicon plate are formed with a substantially square or rectangular profile.

11. A method of forming a nozzle that comprises a first plate having a first planar inner surface, and a second plate having a second planar inner surface, characterised in that the method comprises the steps of: i) Etching open-topped channels on two plates, at least some of the channels on one of the plates formed with a greater width than the narrower channels on the other plate; ii) Sandwiching the two plates together so as to form a two-layer wafer, with the microchannels formed and located on the directly adjacent inner faces of the two plates, the sheets etched and aligned so that at least part of the open-topped channels on one sheet associate with the channels on the other sheet so as to form a plurality of enclosed passages; ill) Cutting the wafer into a number of individual nozzles with enclosed passages that run at least partly through the nozzle;12. A method of forming a nozzle as claimed in claim 11 wherein in the step of sandwiching the two plates together, the alignment is carried out to within tolerances of substantially one micron.

13. A method of forming a nozzle as claimed in claim 11 or claim 12 wherein in the step of etching the open-topped channels, the channels are formed so that the width difference between the channels on one plate and the channels on the other plate is substantially the same as or greater than the manufacturing alignment tolerance / control between the two plates.

14. A method of forming a nozzle as claimed in claim 11 or claim 12 wherein in the step of etching the open-topped channels, the channels are formed so that the width difference between the channels on one plate and the channels on the other plate is substantially the same as the manufacturing alignment tolerance / control between the two plates.

15. A method of forming a nozzle as claimed in claim 11 or claim 12 wherein in the step of etching the open-topped channels, the channels are formed so that the width difference between the channels on one plate and the channels on the other plate is substantially one micron.

16. A method of forming a nozzle as claimed in any one of claims 11 to 15 wherein in the step of etching the open-topped channels on two plates, the plates are glass and the opentopped channels are etched with a rounded profile.

17. A method of forming a nozzle as claimed in any one of claims 11 to 15 wherein in the step of etching the open-topped channels on two plates, the plates are silicon and the opentopped channels are etched with a substantially square or rectangular profile.

18. A method of forming a nozzle as claimed in any one of claims 11 to 15 wherein in the step of etching the open-topped channels on two plates, one of the plates is a glass plates and one of the plates is a silicon plates, the open-topped channels in the glass plate etched with a rounded profile and the open-topped channels in the silicon plate etched with a substantially square or rectangular profile. 1

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