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A method and apparatus for producing particles, the apparatus includes a solution source that supplies a solution, and a fluid source that supplies a fluid. The solution includes a solvent and a solute. A mixer receives the solution and the fluid from the sources, and mixes the solution and the flui

A method and apparatus for producing particles, the apparatus includes a solution source that supplies a solution, and a fluid source that supplies a fluid. The solution includes a solvent and a solute. A mixer receives the solution and the fluid from the sources, and mixes the solution and the fluid together to form a mixture. The mixture is supplied from the mixer to an expansion assembly at first pressure. The expansion assembly sprays and expands the mixture substantially simultaneously to form frozen droplets, and preferably to form a low-density powder of frozen droplets. A freeze-dry apparatus sublimes the solvent from the particles. A high mass-transfer rate and a uniform open-structure of the powder bed enhances the freeze-drying process. Solid particles having a controlled size distribution are obtained. The particles preferably have a hollow or porous morphology suitable for differing drug delivery applications to include aerosol formulations.

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What is claimed is: 1. A method of producing particles comprising the steps of: providing a solution comprising a solute dissolved in a solvent; mixing the solution with a supercritical fluid at a first pressure sufficient to maintain the supercritical fluid in a supercritical state and thereby for

What is claimed is: 1. A method of producing particles comprising the steps of: providing a solution comprising a solute dissolved in a solvent; mixing the solution with a supercritical fluid at a first pressure sufficient to maintain the supercritical fluid in a supercritical state and thereby form a mixture; flowing the mixture across a pressure drop into an expansion chamber that is controlled to be below the solution freezing temperature, wherein the mixture nebulizes into droplets, at least a first portion of the supercritical fluid expands and decompresses and the droplets freeze to form frozen solution droplets; and freeze-drying the frozen solution droplets to sublime the solvent and produce substantially solvent-free solid solute particles. 2. The method according to claim 1 wherein the supercritical fluid has a freezing point that is less than or equal to the freezing point of the solution when the mixture is flowed across the pressure drop into the expansion chamber, and wherein a second portion of the supercritical fluid freezes is frozen in solution droplets, and wherein the freeze-drying step further comprises subliming the frozen supercritical fluid from the frozen solution droplets. 3. The method according to claim 1 further comprising the step of controlling the temperature in the expansion chamber to a temperature that is below the freezing point of the solvent but above the freezing point the supercritical fluid so that the solvent freezes but no portion of the supercritical fluid freezes. 4. The method according to claim 1 further comprising the step of adjusting the pressure drop differential to control the size and/or morphology of the solid solute particles. 5. The method according to claim 4 wherein the pressure in the expansion chamber is adjusted to be less than atmospheric pressure. 6. The method according to claim 1 further comprising the steps of metering the solution into a mixer, and metering the supercritical fluid into the mixer, and thereby controlling a ratio of solution to supercritical fluid in the mixture prior to the step of flowing the mixture across the pressure drop. 7. The method according to claim 1 further comprising the steps of pumping the solution from a first tank to a mixer, and pumping the supercritical fluid from a second tank to the mixer, and thereby continuously supplying solution and supercritical fluid to the mixer, the mixer continuously mixing the solution and the supercritical fluid to form the mixture, and the step of flowing the mixture across a pressure drop into an expansion chamber is a continuous process. 8. A method for producing particles comprising: providing a solution comprising a solvent and a solute; providing a supercritical fluid; mixing the solution and the supercritical fluid together to form a mixture at a first pressure and temperature that sufficient to maintain the supercritical fluid in a supercritical state; providing an expansion chamber maintained at a temperature below the freezing point of the solution; flowing the mixture across a pressure drop into the expansion chamber to form frozen droplets that comprise the solute and frozen solvent; and freeze-drying the frozen droplets to sublime the frozen solvent from the frozen droplets and thereby produce solid solute particles that are substantially free of solvent. 9. The method according to claim 8 wherein the expansion assembly receives the mixture from the mixer at the first pressure, and sprays the mixture at a second, lower pressure such that a portion of the fluid expands in response to a change from the first pressure to the second lower pressure, the expansion of the fluid portion reducing a temperature of the mixture so as to be below a freezing point of the solution. 10. The method according to claim 8 wherein the solvent is selected from the group consisting of water, alcohol, toluene, ethyl acetate, methyl chloride, methylene chloride, dimethyl sulfoxide (DMSO), dimethyl formamide (DMF), or other organic or inorganic solvents. 11. The method according to claim 8 wherein the solute is selected from the group consisting of a polymer, filler, disintegrant, binder, solubilizer, excipient, surfactant, and combinations thereof. 12. The method according to claim 11 wherein the solute is a polymer selected from the group consisting of polysaccharide, polyester, polyether, polyanhydride, polyglycolide (PLGA), polylactic acid (PLA), polycaprolactone (PCL), polyethylene glycol (PEG), or polypeptide. 13. The method according to claim 8 wherein the solute is selected from the group consisting of a biologically active material, drug, pharmaceutical, pharmaceutical excipient, therapeutic agent, medicinal agent, sugar, pigment, toxin, insecticide, viral material, diagnostic aid, agricultural chemical, nutritional material, protein, alkyloid, alkaloid, peptide, animal extract, plant extract, dye, explosive, paint, cosmetic, antigen, enzyme, catalyst, nucleic acid, zeolite, polymer precursor, and combinations thereof. 14. The method according to claim 13 wherein the solute further comprises a polymer, filler, disintegrant, binder, solubilizer, stabilizer, buffer or combinations thereof. 15. The method according to claim 13 wherein the solution further comprises a surfactant or a processing aid. 16. The method according to claim 8 wherein the supercritical fluid comprises carbon dioxide, nitrous oxide, propane and/or ethane. 17. A method for producing particles comprising: providing a solution comprising a solvent and a solute; providing a first supercritical fluid and a second supercritical fluid, the first supercritical fluid having a higher freezing point than the second supercritical fluid; mixing the solution, the first supercritical fluid and the second supercritical fluid together to form a mixture; providing an expansion chamber that is maintained at a temperature below the freezing point of the solution; flowing the mixture across a pressure drop through a nozzle having a contra-current, co-axial, single or multiple opening configuration into the expansion chamber to form a spray of frozen droplets that comprise the solute and frozen solvent, wherein the first supercritical fluid component operates as a blowing or expanding agent and the second supercritical fluid component operates as a freezing agent; and freeze-drying the frozen droplets to sublime the frozen solvent from the frozen droplets and thereby produce solid solute particles that are substantially free of solvent.