Particle Coating Method

Abstract

A method of producing a particle coating on one or more items is provided. The method comprises mixing a supercritical fluid with a solution comprising dissolved material for forming particles. The method further comprises spraying the mixture into a precipitation chamber (316) to precipitate particles, wherein the chamber is at a pressure below a supercritical pressure of the supercritical fluid. The method comprises conveying items to be coated from an inlet of the chamber to an outlet of the chamber. The method also comprises capturing the precipitated particles on items within the chamber.

Claims

1. A method of producing a particle coating on one or more items, the method comprising: mixing a supercritical fluid with a solution comprising dissolved material for forming particles; spraying the mixture into a precipitation chamber to precipitate particles, wherein the chamber is at a pressure below a supercritical pressure of the supercritical fluid: conveying items to be coated from an inlet of the chamber to an outlet of the chamber; and capturing the precipitated particles on items within the chamber.

2. The method of claim 1, comprising introducing the items substantially from a top portion of the chamber.

3. The method of claim 1, comprising gravity feeding items to be coated into the chamber.

4. The method of claim 2, comprising controlling a feed rate of items introduced to the chamber.

5. The method of claim 1, comprising capturing the precipitated particles on carrier particles, and optionally wherein the carrier particles comprise microcrystalline cellulose.

6. (canceled)

7. The method of claim 1, comprising: mixing the supercritical fluid with a first solution comprising a first dissolved material for forming particles to form a first mixture, and spraying the first mixture into the chamber to precipitate particles of a first material; and mixing the supercritical fluid with a second solution comprising a second dissolved material for forming particles to form a second mixture, and spraying the second mixture into the chamber to precipitate particles of a second material.

8. The method of claim 1, comprising introducing a flow of drying gas into the chamber, and optionally, i) introducing a flow of drying gas substantially from a top portion of the chamber; and/or ii) introducing a flow of drying gas substantially from a side portion of the chamber.

9. (canceled)

10. (canceled)

11. The method of claim 1, comprising collecting items coated with precipitated particles, and optionally using a cyclone separator.

12. The method of claim 1, comprising spraying the mixture substantially from a side portion of the chamber.

13. The method of claim 1, comprising i) spraying the mixture through at least one nozzle into the chamber to precipitate particles, and optionally wherein a nozzle orifice size of the nozzle is substantially 50 μm or smaller; and/or ii) mixing the supercritical fluid with the solution in at least one nozzle, and/or wherein the at least one nozzle comprises a coaxial nozzle.

14. The method of claim 1, wherein the solution comprises an active pharmaceutical ingredient dissolved in an organic solvent, and optionally wherein: i) the active pharmaceutical ingredient comprises one of carbamazepine, risperidone, ketoprofen and hydrochlorothiazide; and/or ii) the organic solvent comprises an alcohol, and optionally wherein the alcohol is methanol.

15. The method of claim 1, wherein the solution comprises a saturated solution.

16. (canceled)

17. An apparatus for producing a particle coating on one or more items, the apparatus comprising: a chamber: at least one nozzle configured to spray a mixture of supercritical fluid and a solution comprising dissolved material for forming particles into the chamber; wherein the chamber is configured to be held at a pressure below a supercritical pressure of the supercritical fluid; and a hopper configured to feed items to be coated into the chamber.

18. The apparatus of claim 17, further comprising an outlet through which items coated with precipitated particles are removable from the apparatus.

19. The apparatus of claim 17, wherein the hopper is disposed substantially on a top portion of the chamber.

20. The apparatus of claim 17, further comprising a cyclone separator for collecting items coated with precipitated particles.

21. The apparatus of claim 17, wherein the at least one nozzle is located substantially on a side portion of the chamber.

22. The apparatus of claim 17, wherein the chamber further comprises at least one inlet for receiving a flow of drying gas, and optionally, wherein the at least one inlet is located on at least one of substantially a top portion of the chamber and substantially a side portion of the chamber.

23. (canceled)

24. The apparatus of claim 17, comprising: at least one first nozzle configured to spray a first mixture into the chamber, the first mixture comprising the supercritical fluid and a solution comprising a first dissolved material for forming particles; and at least one second nozzle configured to spray a second mixture into the chamber, the second mixture comprising supercritical fluid and a solution comprising a second dissolved material for forming particles.

25. The apparatus of claim 17, further comprising a pump for maintaining an operating pressure in the chamber.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0069] The invention will now be described by way of example with reference to the accompanying drawings in which:

[0070] FIG. 1 shows an embodiment of a method for producing a nanoparticle coating on one or more items in accordance with the invention;

[0071] FIG. 2 shows an embodiment of a method for producing an API nanoparticle coating on carrier particles in accordance with the invention;

[0072] FIG. 3 shows an embodiment of an apparatus for use in the method of FIG. 1 or FIG. 2 in accordance with the invention;

[0073] FIG. 4 shows an embodiment of an apparatus for use in the method of FIG. 1 or FIG. 2 in accordance with the invention; and

[0074] FIG. 5 shows an embodiment of an apparatus for use in the method of FIG. 1 or FIG. 2 in accordance with the invention.

[0075] Like reference numbers and designations in the various drawings may indicate like elements.

DETAILED DESCRIPTION

[0076] FIG. 1 shows an embodiment of a method 100 for producing a particle coating on one or more items.

[0077] The method 100 comprises mixing supercritical carbon dioxide with a solution comprising dissolved material for forming particles at step 102 (although other supercritical fluids may be used instead). The method 100 further comprises spraying the mixture into a precipitation chamber held at a pressure below a supercritical pressure of the supercritical fluid (for example atmospheric pressure) to precipitate particles at step 104. The method 100 also comprises conveying items from an inlet of the chamber to an outlet of the chamber at step 106. The method 100 comprises capturing precipitated particles on items travelling through the chamber at step 108.

[0078] FIG. 2 shows an embodiment of a method 200 for producing a nanoparticle coating on one or more items, in line with the method 100 as set out above. The method 200 may carried out using, and is described with respect to, an apparatus 300 shown in FIG. 3.

[0079] Step 202 of the method 200 comprises compressing carbon dioxide gas to a liquid state. In the embodiment shown, carbon dioxide from a cylinder 302 is compressed using a pump 304. In the embodiment shown, the pump 302 is a SFE Process Dose HPP 400-C pump, but any suitable pump may be used.

[0080] Step 204 of the method 200 comprises temporarily storing the compressed carbon dioxide in a temperature controlled vessel 306. The temperature controlled vessel 306 is stored in a temperature controlled air chamber 308. The temperature of the vessel 306 is controlled by virtue of the vessel 306 being located in the temperature controlled air chamber 308. In the embodiment shown, the temperature controlled air chamber 308 is held at 60° C., but any suitable temperature may be used. A controller 310 is used to control the temperature in the air chamber 308. A pressure indicator 312 is used to monitor a pressure of the supercritical carbon dioxide. Any suitable pressure indicator may be used.

[0081] Step 206 of the method 200 comprises delivering the compressed carbon dioxide to a first nozzle 314a, second nozzle 314b and third nozzle 314c of the apparatus 300 respectively. Alternatively, the compressed carbon dioxide may be delivered directly to the nozzles 314a, 314b, 314c of the apparatus 300 without any intervening steps, such as temporary storage in a temperature controlled vessel 306. In the embodiment shown, three nozzles 314a, 314b, 314c are used, but any suitable number of nozzles may be used. Alternatively, the apparatus 300 may comprise only one nozzle 314 to which compressed carbon dioxide is delivered.

[0082] Step 208 of the method 200 comprises delivering a solution comprising dissolved material for forming nanoparticles from a storage vessel 315 to the nozzles 314a, 314b, 314c of the apparatus 300. In the embodiment shown, the solution comprises carbamazepine dissolved in methanol. The solution may alternatively comprise any active pharmaceutical ingredient (API), from any of classes I, II, III or IV (according to the biopharmaceutical classification system (BCS)), dissolved in an organic solvent. For example, the API may be or comprise one of carbamazepine, risperidone, ketoprofen and hydrochlorothiazide. The organic solvent may be or comprise an alcohol, for example methanol. Alternatively, the solution may comprise any suitable solvent in which any suitable material for forming nanoparticles is dissolved, depending on the desired properties of the nanoparticle coating to be formed. A plurality of different solutions may be delivered separately to separate nozzles 314, 314b, 314c. That may allow multiple different types of nanoparticle to be coated onto one or more items simultaneously in a single process. In the embodiment shown, the solution is delivered to the nozzles 314a, 314b, 314c using an Agilent Technologies 1260 Infinity II pump, but any suitable pump may be used. In the embodiment shown, the flow rate of solution delivered to the nozzles 314a, 314b, 314c is maintained between substantially 0.1 mL.Math.min.sup.−1 and substantially 2.0 mL.Math.min.sup.−1, but any suitable flow rate may be used depending, for example, on characteristics of the apparatus 300.

[0083] Step 210 of the method 200 comprises mixing supercritical carbon dioxide with the solution comprising dissolved material for forming nanoparticles in the nozzles 314a, 314b, 314c of the apparatus 300. In the embodiment shown, the nozzles 314a, 314b, 314c are coaxial nozzles having a mixing volume of approximately 0.1 cm.sup.3. The solution and the compressed carbon dioxide are delivered to the nozzle 314 separately (for example, via separate fluid lines). In the embodiment shown, the nozzles 314a, 314b, 314c are maintained at a temperature of substantially 50° C. in order to heat the compressed carbon dioxide delivered to the nozzles 314a, 314b, 314c to a supercritical state, but any suitable temperature may be used. For example, the temperature may be dependent on the particular solvent used to dissolve the material for forming nanoparticles. In the embodiment shown, the solvent used is methanol which has a boiling point of 65° C. In the embodiment shown, supercritical carbon dioxide pressure is maintained between substantially 9 MPa and substantially 17 MPa, but any suitable pressure of supercritical carbon dioxide may be used. The nozzles 314a, 314b, 314c are heated using heating resistors (not shown) in close proximity to the nozzles 314a, 314b, 314c. The heating resistors may be controlled by a controller. However, any suitable heating means may alternatively be used. The supercritical carbon dioxide mixes with the solution in the mixing volume of the nozzles 314a, 314b, 314c.

[0084] The compressed carbon dioxide may alternatively be heated to supercritical conditions prior to being delivered to the nozzles 314a, 314b, 314c, for example using a heating coil enveloping a pipe containing compressed carbon dioxide. Additionally or alternatively, the solution may be mixed with supercritical carbon dioxide prior to being delivered to the nozzles 314a, 314b, 314c. The method 200 may therefore alternatively comprise delivering a pre-formed mixture of supercritical carbon dioxide and solution to the nozzles 314a, 314b, 314c, rather than separately delivering compressed or supercritical carbon dioxide and solution to the nozzles 314a, 314b, 314c. The nozzles 314a, 314b, 314c may therefore not be coaxial nozzles.

[0085] Steps 202 to 210 of the method 200 may be replaced by any suitable technique(s) for forming a mixture of supercritical carbon dioxide and solution comprising dissolved material for forming nanoparticles. Exactly how either or both i) the supercritical carbon dioxide, or ii) the mixture of supercritical carbon dioxide and solution are formed is not critical to the invention, as long as the mixture is formed before being introduced into a precipitation chamber 316.

[0086] Step 212 of the method 200 comprises spraying the mixture through the nozzles 314a, 314b, 314c into a precipitation chamber 316 to precipitate nanoparticles. It will be appreciated that means other than the nozzles 314a, 314b, 314c may be used to introduce the mixture into the chamber 316. The chamber 316 is held at atmospheric pressure. The mixture experiences a rapid pressure drop as the mixture passes through the nozzles 314a, 314b, 314c into the chamber 316. In the embodiment shown, the nozzles 314a, 314b, 314c comprise substantially circular nozzle orifices having a diameter of substantially 40 μm. Nozzles having nozzle orifices of any shape, for example square, rectangular, polygonal or other shapes may be used. Any nozzle orifice having a size so as to form nanoparticles on spraying the mixture into the chamber 316 may alternatively be used, for example a nozzle orifice size of substantially 150 μm or smaller. As the supercritical carbon dioxide depressurizes to form carbon dioxide gas due to the chamber 316 being at atmospheric pressure, nanodroplets (nanosized droplets) of the solution are formed. The supercritical carbon dioxide may therefore act to enhance atomisation of the solution as the mixture passes through the nozzles 314a, 314b, 314c into the chamber 316. The rapid pressure drop may work in conjunction with the anti-solvent effect of the supercritical carbon dioxide to form the nanodroplets. The chamber 316 being held at atmospheric pressure may also enable the nanodroplets to dry rapidly in order to precipitate nanoparticles. It will be appreciated that the same could be achieved by using a chamber 316 held at a pressure below a supercritical pressure of the supercritical fluid, enabling the supercritical fluid to depressurize on introduction to the chamber 316. The chamber 316 being held at atmospheric pressure may avoid the need for specialist equipment to pressurize or provide a vacuum in the chamber 316, further reducing cost and complexity.

[0087] Additionally or alternatively, process parameters other than nozzle orifice size may be selected or controlled to obtain particles of a desired size. For example, one or more of a flow rate of solution delivered to the nozzle 314, a flow rate of compressed carbon dioxide delivered to the nozzle 314, a density of supercritical carbon dioxide formed in the nozzle 314, a flow rate of drying gas introduced to the chamber 316 (discussed below), and a temperature inside the chamber 316 may influence a size of droplets formed by spraying the mixture through the nozzle 314. A size of the droplets in turn influences a size of particles produced by the method 200. Nanoparticles having a size of substantially 10 nm (or greater) may be produced by controlling one or more of the operating parameters accordingly.

[0088] Step 214 of the method 200 comprises introducing a flow of drying gas into the chamber 316. In the embodiment shown, the drying gas comprises nitrogen gas, although it will be appreciated any suitable gas or mixture of gases may be used as a drying gas (for example, carbon dioxide and/or nitrogen gas may be used). In the embodiment shown, the drying gas is introduced into the chamber 316 through an inlet 317b from a storage vessel 317a. In the embodiment shown, the flow rate of the nitrogen gas is substantially 0.4 mL.Math.min.sup.−1, but any suitable flow rate may be used. In the embodiment shown, the drying gas is introduced from a top portion of the chamber 316. Additionally or alternatively, the drying gas may be introduced from a side portion of the chamber 316 (discussed further below). Using a drying gas in conjunction with a rapid pressure drop may further increase a rate of solvent evaporation from the nanodroplets, leading to faster precipitation of nanoparticles. Alternatively, a flow of drying gas may not be introduced into the chamber 316, and nanoparticles may be precipitated using only the rapid pressure drop after spray of the mixture from the nozzles 314a, 314b, 314c, and ambient pressure of the chamber 316.

[0089] Step 216 of the method 200 comprises conveying carrier particles to be coated from an inlet of the chamber 316 to an outlet of the chamber 316. In the embodiment shown, the chamber 316 comprises a cylindrical shape, but the chamber 316 may comprise any suitable shape. The carrier particles are shown schematically in FIG. 3 and are not to scale. In the embodiment shown, the carrier particles comprise microcrystalline cellulose particles, but any suitable excipient or mixture of excipients may alternatively be used. The carrier particles are continuously introduced to the chamber 316 from a hopper 318. In the embodiment shown, the hopper 318 is disposed on a top portion of the chamber 316. That allows the carrier particles to be gravity fed into the chamber 316. Alternatively, the hopper 318 may be located elsewhere on the chamber 316, for example a side portion of the chamber 316. The carrier particles capture precipitated nanoparticles whilst passing through the spray from the nozzles 314a, 314b, 314c. The carrier particles may be fluidized within the chamber 316 due to momentum of depressurized carbon dioxide and a flow of drying gas within the chamber 316. Fluidized carrier particles may more effectively capture precipitated nanoparticles whilst travelling through the chamber 316. Capturing the precipitated nanoparticles on the carrier particles within the chamber 316 may mean that the precipitated nanoparticles are captured on the carrier particles substantially immediately or shortly after precipitation, before having a chance to agglomerate or coalesce. Nanoparticles can be difficult to process or manipulate after agglomeration. Capturing the nanoparticles shortly after precipitation may avoid the need to manipulate the nanoparticles to overcome interactions between nanoparticles.

[0090] Conveying the carrier particles from an inlet of the chamber 316 to an outlet of the chamber 316 may enable carrier particles to be continuously introduced to the chamber. That means that the apparatus 300 may run continuously, without the apparatus 300 needing to be placed in a non-operational state (for example, in between introducing different carrier particles to be coated to the chamber 316, or to remove coated items from the apparatus 300).

[0091] A size of an opening of the hopper 318 through which carrier particles are introduced into the chamber 316 may be controlled to control a feed rate of carrier particles into the chamber 316.

[0092] For example, the opening of the hopper 318 may be occluded (for example, partially) or expanded to decrease or increase a feed rate of the carrier particles respectively. The size of the opening of the hopper 318 may be controlled manually or automatically (for example using a controller).

[0093] In the embodiment shown, the nozzles 314a, 314b, 314c are disposed on a side portion of the chamber 316 and distributed uniformly over a length or height of the chamber 316. That may mean that the carrier particles are coated with progressively more and more nanoparticles whilst travelling through the chamber 316 (for example falling under gravity from a top portion of the chamber 316), enhancing the continuous nature of the process. It may also improve homogeneity of the nanoparticle coating by increasing opportunity for the carrier particles to capture precipitated nanoparticles. The nozzles 314a, 314b, 314c may alternatively be distributed non-uniformly over the height of the chamber 316, but may provide substantially the same benefit. In the embodiment shown, the nozzles 314, 314b, 314c are shown disposed on the same side of the chamber 316. Alternatively, the nozzles 314b, 314b, 314c may be disposed on different sides of the chamber 316. For example, the nozzles 314a, 314b, 314c may be distributed around a perimeter of the chamber 316 (in addition to being distributed over a height of the chamber 316). One or more nozzles may alternatively be disposed or located on a top portion of the chamber 316.

[0094] Alternatively, the method 200 may comprise capturing precipitated nanoparticles on one or more items as the items pass through the chamber 316. The one or more items may be or comprise a medical implant, for example a joint replacement implant or a stent. Alternatively, the one or more items may be or comprise other non-medical or non-medicinal items for which a nanoparticle coating is required. Larger items (for example, joint replacement implants) may not travel through the chamber 316 by falling under gravity, but may instead be supported and conveyed through the chamber 316 (for example, may be supported on a structure such as a belt which passes through the chamber 316). A speed of the support structure through the chamber 316 may be altered analogously to altering a feed rate of carrier particles through the hopper 318.

[0095] Step 220 of the method 200 comprises collecting the coated carrier particles. In the embodiment shown, the coated carrier particles are collected using a cyclone separator 320. In the embodiment shown, the coated carrier particles are conveyed from an outlet of the chamber 316 to the cyclone separator 320 for collection. The cyclone separator 320 separates the coated carrier particles from residual carbon dioxide, residual solvent and drying gas. The coated carrier particles settle at the bottom of the cyclone separator ready for collection, whilst the residual gases are removed using a pump (not shown), for example a vacuum pump, and expelled through an outlet in the cyclone separator. The pump may therefore maintain atmospheric pressure in the chamber 316. In the embodiment shown, the cyclone separator 320 is spatially separated from the chamber 316.

[0096] Alternatively, the cyclone separator 320 may be disposed within the chamber 316. The coated carrier particles may alternatively be collected in a different manner. For example, the coated carrier particles may simply collect on a floor of the chamber 316 ready to be removed from the apparatus 300. Residual gases (and optionally residual solvent) may be removed using a pump, for example a vacuum pump, to maintain atmospheric pressure in the chamber 316.

[0097] In the embodiment shown, a concentration of the carbamazepine solution may be varied between substantially 20 mg.Math.L.sup.−1 and substantially 60 mg.Math.L.sup.−1. Those concentrations are near to but not above a saturation limit of the solution (at the operating parameters set out as described above), and are referred to herein as saturated solutions. It has been found that undersaturated solution results in the production of amorphous nanoparticles using the method 200. In contrast, supersaturated solution (having a concentration above a saturation limit) results in precipitation of crystalline nanoparticles in the nozzles 314a, 314b, 314c, which may lead to blockage of the nozzles 314a, 314b, 314c. Saturated solution results in liquid-like cluster formation (nucleation) of the nanoparticles in the nozzles 314a, 314b, 314c. The clusters convert to crystals upon passing through the nozzles 314a, 314b, 314c due to formation of nanodroplets which dry rapidly under atmospheric pressure in the chamber 316. In addition, as the mixture of supercritical carbon dioxide and solution is formed in the nozzles 314a, 314b, 314c in the embodiment shown, there is not sufficient time for nanoparticles to crystallise in the nozzles 314a, 314b, 314c, as residence time of the mixture in the nozzles 314a, 314b, 314c is of the order of milliseconds. Alternatively, any suitable concentration of solution may be used. For example, if crystalline nanoparticles are not required and amorphous nanoparticles will be satisfactory, an undersaturated solution may be used. A saturated solution may comprise different concentrations for different nanoparticle materials and/or different solvents. A saturated solution may also comprise different concentrations depending on operating parameters such as temperature and pressure (which may determine a saturation limit of the solution).

[0098] Varying a concentration of the solution may enable nanoparticle loading onto the carrier particles to be altered or controlled. In the embodiment shown, nanoparticle loading onto the carrier particles is substantially 5% for a solution concentration of substantially 20 mg.Math.L.sup.−1, whereas nanoparticle loading onto the carrier particles is substantially 25% for a solution concentration of substantially 60 mg.Math.L.sup.−1. A lower concentration of the solution may alternatively be used, which may further reduce nanoparticle loading but may result in an undersaturated solution being used, producing amorphous nanoparticles. As above, a range of concentrations forming a saturated solution may be different for different nanoparticles and/or different solvents. Alternatively, nanoparticle loading onto the carrier particles can be altered or controlled by varying a mass of material for forming nanoparticles introduced into the chamber 316 without changing a concentration of the solution. For example, the solution may be sprayed into the chamber 316 for a greater length of time, which will result in a greater mass of material for forming nanoparticles being introduced to the chamber 316. A greater mass of material for forming nanoparticles introduced into the chamber 316 may result in an increased nanoparticle loading onto the carrier particles, and vice versa. Introducing a greater mass of material for forming nanoparticles into the chamber 316 may increase the possible amount of nanoparticle material that may be captured by the carrier particles (or other items). Controlling loading of nanoparticles onto the carrier particles, particularly in the case of API or anti-bacterial drug nanoparticles, may enable the dose of API or anti-bacterial drug to be accurately controlled.

[0099] The method 200 described above relates to production of a nanoparticle coating on one or more items. However, the methods 100, 200 described above are not limited to producing nanoparticles or nanoparticle coatings. Different particle sizes may be produced using the methods 100, 200, for example by altering a nozzle orifice size of the nozzles 314a, 314b, 314c through which the mixture is sprayed into the chamber 316. A larger nozzle orifice size may produce larger droplets of solution as the mixture enters the precipitation chamber 316. Conversely, smaller nozzle orifices may produce smaller droplets of solution as the mixture enters the precipitation chamber 316. The rapid pressure drop as the mixture is sprayed into the chamber 316 through the nozzles 314a, 314b, 314c may result in rapid evaporation of the solvent in the droplets, irrespective of the droplet size. The rate of solvent evaporation may be further increased by a flow of drying gas. The particle size produced may therefore be substantially dictated by a size of solution droplets formed by spraying the mixture through the nozzles 314a, 314b, 314c.

[0100] FIG. 4 shows an embodiment of an apparatus 400 for producing a nanoparticle coating on one or more items, for example using the methods 100, 200 described above. The apparatus 400 comprises a chamber 416, a hopper 418 and a plurality of nozzles 414. In the embodiment shown, the chamber 416 comprises a cylindrical shape, but the chamber 416 may comprise any suitable shape. The nozzles 414 are substantially uniformly distributed both over a height or length of the chamber 416, and around a perimeter of the chamber 316. The nozzles 414 are arranged in a substantially helical pattern across a side portion of the chamber 416, as indicated by the dashed lines between the nozzles 414. That arrangement may provide a volume or region within the chamber 416 in which the precipitated particles are concentrated. The region may prevent contact of the items and precipitated particles with internal walls of the chamber 416. The region may be symmetrical as a result of the substantially uniform distribution of the nozzles 414 around the chamber 416. Carrier particles or other items may be introduced to the chamber 416 via the hopper 418. The hopper 418 is disposed on a top portion of the chamber 416, enabling the items to be gravity fed into the chamber 416. The items travel through the concentrated region of precipitated particles and become coated.

[0101] In the embodiment shown, the nozzles 414 are arranged in three nozzle layers 414a, 414b, 414c. In the embodiment shown, the nozzles in the top or first nozzle layer 414a are oriented at an angle of substantially 130° (where 0° is a vertical direction, for example parallel to a side wall or side portion of the chamber 416). The nozzles in the second nozzle layer 414b are oriented at an angle of substantially 125°. The nozzles in the third layer 414c are oriented at an angle of substantially 120°. The angles for each nozzle layer have been optimised using computational fluid modelling to optimise a helical travel path of precipitated particles and items through the chamber 416 having the specific cylindrical shape shown in FIG. 4. A chamber 416 having or comprising a different shape may require nozzles oriented at different angles to those shown in order to promote a helical path through the chamber 416. Alternatively, the nozzles in each nozzle layer 414a, 414b, 414c may be oriented at substantially the same angle. One or more of the nozzles may be oriented at a different angle to the other nozzles. The nozzles may be oriented at an angle of substantially 90° (substantially perpendicular to a vertical direction of 0°) or greater. That may prevent a mixture spray from the nozzles 414 from opposing a direction of travel of the items through the chamber 416.

[0102] The apparatus 400 also comprises inlets 417 for providing a flow of drying gas into the chamber 416. In the embodiment shown, the inlets 417 are disposed on a top portion of the chamber 416. Alternatively, the drying gas inlets 417 may be located on a side portion of the chamber 416. The drying gas inlets 417 may be arranged similarly to the nozzles 414 (for example, arranged promote a helical travel path of items and precipitated particles through the chamber 416, such as in a substantially helical pattern). For example, a drying gas inlet 417 may be located adjacent to each nozzle 414 on a side portion of the chamber 416.

[0103] In the embodiment shown, the chamber 416 is supported on a platform 422. A cyclone separator 420 is located below the platform. The cyclone separator 420 is in fluid communication with the chamber 416. Once the items (for example, carrier particles) have travelled through the chamber 416 and been coated with precipitated particles, the items enter the cyclone separator 420 and collect at a bottom of the cyclone separator 420. Supporting the chamber 416 on a platform 422 above the cyclone separator 420 allows for the apparatus 400 to have an inline arrangement. The height of the platform 422 may depend on a height of the cyclone separator 420. Of course, it is not essential that the chamber 416 be supported on a platform 422. The chamber 416 may be supported by the cyclone separator 420 itself (for example, in an inline arrangement), or both the chamber 416 and the cyclone separator may be located on the same surface (for example, the floor).

[0104] FIG. 4 shows an embodiment of an apparatus 500 for producing a nanoparticle coating on one or more items, for example using the methods 100, 200 described above. The apparatus 500 is substantially similar to the apparatus 400 described above, and like reference numerals have been used to indicate like features.

[0105] The apparatus 500 comprises a chamber 516. The chamber 516 comprises a first chamber segment 516a and a second chamber segment 516b. A plurality of nozzles 514 are located on a side portion of the first chamber segment 516a. As described above with respect to FIG. 4, the nozzles are arranged in three nozzle layers 514a, 514b, 514c. A plurality of nozzles 514 are also located on a side portion of the second chamber segment 516b. The second chamber segment 516b is substantially identical in construction to the first chamber segment 516a. In the embodiment shown, each of the chamber segments 516a, 516b has a substantially cylindrical shape. Alternatively, each chamber segment 516a, 516b may have or comprise a substantially prismatic construction (for example, having a circular, triangular, square, rectangular or higher polygon cross-sectional shape or profile).

[0106] In the embodiment shown, the chamber 516 therefore has a modular construction. One or more additional chamber segments may be added to the chamber 516 in order to increase a size of the chamber 516. For example, a third chamber segment may be attached in between the first chamber segment 516a and the second chamber segment 516b. In the embodiment shown, adjacent chamber segments 516a, 516b are attached to one another end to end. The third chamber segment may have or comprise a substantially identical construction to the first and second chamber segments 516a, 516b. That may increase a length or height of the chamber 516. Increasing a length of the chamber 516 may increase a travel path length (and therefore travel time) of items travelling through the chamber 516. In the embodiment shown, each chamber segment 516a, 516b comprises nozzles 514 located on a side portion of the chamber segment 516a, 516b. Increasing a length of the chamber 516 may therefore increase particle loading onto the items passing through the chamber 516, as the items may interact with the mixture sprays from a greater number of nozzles 514 (from a plurality of chamber segments 516a, 516b) whilst travelling through the chamber 516. One or more chamber segments 516a, 516b may be removed from the chamber 516 to reduce a size of the chamber 516, if required.

[0107] In the embodiment shown, the chamber 516 is supported on a platform 522. The apparatus 500 also comprises a cyclone separator 520. The chamber 516 is held at a greater height than the cyclone separator 520. However, unlike the apparatus 400 described above, the chamber 516 and cyclone separator 520 are not arranged in line with one another in the embodiment shown. Rather, the cyclone separator 520 is laterally displaced from the chamber 516. The chamber 516 is in fluid communication with the cyclone separator 520 via a conduit 519. The conduit 519 is configured to convey coated items from the chamber 516 to the cyclone separator 520. The conduit 519 is connected at a first end to a bottom of the chamber 516, and at a second end to a side of the cyclone separator 520. An outlet for residual gases and solvent is provided in a top of the cyclone separator 520.

[0108] From reading the present disclosure, other variations and modifications will be apparent to the skilled person. Such variations and modifications may involve equivalent and other features which are already known in the art of particle coating, and which may be used instead of, or in addition to, features already described herein.

[0109] Although the appended claims are directed to particular combinations of features, it should be understood that the scope of the disclosure of the present invention also includes any novel feature or any novel combination of features disclosed herein either explicitly or implicitly or any generalisation thereof, whether or not it relates to the same invention as presently claimed in any claim and whether or not it mitigates any or all of the same technical problems as does the present invention.

[0110] Features which are described in the context of separate embodiments may also be provided in combination in a single embodiment. Conversely, various features which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable sub-combination. The applicant hereby gives notice that new claims may be formulated to such features and/or combinations of such features during the prosecution of the present application or of any further application derived therefrom. Features of the devices and systems described may be incorporated into/used in corresponding methods. Where features are disclosed in connection with one embodiment of a particle coating method, it should be appreciated that any one or more or all of the same features may be incorporated in other embodiments of particle coating methods, instead of or in addition to the features described for the particular embodiment. That is, any and all combinations of features are envisaged, and are envisaged to be interchangeable, replaceable, added or removed.

[0111] For the sake of completeness, it is also stated that the term “comprising” does not exclude other elements or steps, the term “a” or “an” does not exclude a plurality, a single processor or other unit may fulfil the functions of several means recited in the claims and any reference signs in the claims shall not be construed as limiting the scope of the claims.