WO2004006893A1

WO2004006893A1 - Method for particle precipitation using near-critical and supercritical antisolvents

Info

Publication number: WO2004006893A1
Application number: PCT/NL2003/000516
Authority: WO
Inventors: Hubert Clemens Pellikaan; Gerrit Borchard
Original assignee: Feyecon Development & Implementation B.V.; Universiteit Leiden
Priority date: 2002-07-15
Filing date: 2003-07-15
Publication date: 2004-01-22
Also published as: AU2003253508A1; AU2003253508A8

Abstract

The present invention is concerned with a continuous or semi-continuous process for the preparation of small particles through precipitation, which process employs (i) a fluid solution comprising a solvent and a solute to be precipitated and (ii) a non-gaseous antisolvent, said solvent being soluble in or miscible with the antisolvent and said solute being substantially insoluble in the antisolvent, said process comprising the successive steps of: a. combining the fluid solution and the antisolvent so as to achieve a condition of super saturation; b. allowing nucleation to commence and the nuclei formed to grow to particles with a volume weighted average diameter of between 5 nm and 50,000 nm, c. collecting the resulting particles and separating them from the antisolvent; wherein the solvent contains an organic solvent and less than 20 wt.% water and the solute comprises a charged carbohydrate polymer in combination with a second biopolymer component selected from the group consisting of polynucleotides, amino acid polymers and mixtures thereof; and wherein step a. and b. are carried out under a substantially constant pressure. Suitable examples of the charged carbohydrate polymer include chitosan polymers, heparin, hyaluronic acid polymers and derivatives thereof. The particles obtained from the above process may suitably be used for intracellular delivery of a polynucleotide and/or a polyamino acid in animals and humans.

Description

METHOD FOR PARTICLE PRECIPITATION USING NEAR-CRITICAL AND SUPERCRITICAL

ANTISOLVENTS

TECHNICAL FIELD OF THE INVENTION

The present invention relates to a continuous or semi-continuous process for the manufacture of very small particles, commonly referred to as nanoparticles or microparticles, which particles can suitably be used as a drug delivery system for a polynucleotide or polyamino acid; especially a gene or a vaccine. The nanoparticles obtained by the present method are particularly suited for enhancing transmucosal admimstration, e.g. pulmonary administration, and subsequent uptake of the polynucleotide or polyamino acid by an organism. The nano- or microparticles can be used for both in vitro and in vivo transfections and delivery.

The nanoparticles according to the invention are prepared through a precipitation process. The precipitation process, carried out under substantial constant pressure, employs a fluid solution comprising a solvent and solute to be precipitated and a non- gaseous antisolvent, said solvent being soluble in or miscible with the antisolvent and said solute being substantially insoluble in the antisolvent. The process comprises the successive steps of combining a stream of the fluid solution with a stream of the antisolvent to achieve a condition of super saturation that triggers the nucleation of the solute; allowing the nuclei formed to grow to particles; collecting the particles and separating them from the antisolvent.

The solute employed in the present process comprises a charged carbohydrate polymer in combination with the aforementioned polynucleotide or polyamino acid and yields nanoparticles containing these two components. Examples of charged carbohydrate polymers that may suitably be employed in the present process include chitosan polymers, heparin, hyaluronic acid polymers and derivatives of these carbohydrate polymers.

BACKGROUND OF THE INVENTION

WO 00/56361 describes a composition which is suitable for the delivery of medicaments and in particular vaccines to mucosal surfaces, which composition comprises (i) a biologically active agent that is capable of generating a protective immune response in an animal to which it is administered, (ii) an adjuvant chemical which increases the effect of the biologically active agent and (iii) a pharmaceutically acceptable carrier or diluent. It is mentioned that the composition may comprise an immunostimulant in the form of a chitin derivative. Furthermore it is observed that microencapsulated compositions may be prepared using a double emulsion solvent evaporation method, hi such a method the biologically active agent, suitably in a lyophilised state, is suspended in an aqueous solution of the polymer such as polyvinyl alcohol and the adjuvant chemical. A solution of further polymer, in particular high molecular weight polymer in an organic solvent such as dichloromethane, is added by vigorous mixing. The resultant emulsion is then dropped into a secondary aqueous phase, also containing polymer (PNA or the like) and optionally also the adjuvant material by vigorous stirring. After addition, the organic solvent is allowed to evaporate off and the resultant microspheres are separated.

WO 98/01160 describes a composition comprising a particulate complex of chitosan and nucleic acid wherein the complex is between 10 nm and 1 μm in size and carries a surface charge. The compositions described are particularly suitable for delivery of genes to epithelial cells, notably epithelial cell of the gastrointestinal tract. It is observed that it is possible to obtain enhanced levels of expression in the epithelial tissues of a model animal (the rabbit) by the complexation of DΝA with the material chitosan (polyglucosamine). The particulate complex according to WO 98/01160 is obtained by a method of mixing nucleic acid and chitosan together, without the need of further treatment. It is observed that it is believed that the chitosan compacts the plasmid DΝA into a nanoparticle to confer upon the compacted material suitable surface characteristics that will lead to good adherence of the particle to the surface of the target cell followed by intemahsation that will to expression of the encoded material. Example 7 describes the preparation of a chitosan complex by admixture of 1 ml chitosan solution (4 mg/ml) to 10 ml a DΝA solution (40 μg/ml), followed by the addition of 0.4 ml mannitol solution (1%) and freeze drying.

WO 98/01662 is concerned with a gene delivery system based on nanospheres of less than 3 μm, which nanospheres comprise a polymeric cation such as chitosan and a polyanion consisting of nucleic acids. It is observed in the application that nucleic acid molecules of various chain lengths can complex with polymeric cations in aqueous conditions to form solid nanospheres which nucleic acid-loaded nanospheres can efficiently transfect cells. The method of preparation of the nanospheres involves coacervation of polymeric cations and nucleic acids. Figure 7 depicts the preparation of DNA-chitosan nanospheres by complex coacervation. Nanospheres formed as a result of Na SO₄ induced desolvation of the polyelectrolyte complexes. WO 97/42975 discloses a method of making a drug delivery composition comprising a chitosan-based compound and a nucleic acid or oligonucleotide, which method comprises the steps of: (a) exposing said chitosan-based compound to an acid; (b) filtering the acid treated product of step (a); adding the acid treated and filtered product of step (b) to said nucleic acid or said oligonucleotide in an acceptable pharmaceutical carrier. According to WO 97/42975, the administration includes but is not limited to intravenous, intramuscular, systemic, subcutaneous, subdermal, topical or oral methods of delivery. In example 3 the complexation of chitosan and chitosan oligomers with DNA is described. The chitosan or chitosan oligomers were dissolved in dilute acetic acid and sterile filtered. The resulting filtered higher molecular weight chitosans were dissolved in 1% acetic acid and sonicated with heat to promote dissolution. The lower filtered molecular weight chitosan and chitosan oligomers were dissolved in 0.2% acetic acid without sonication. Chitosan or chitosan oligomers (4 mg/ml in either 0.2% or 1% acetic acid) were added to 100-400 μg DNA in water or lactose, so that the final charge ratio (-/+) of the compositions ranged from 1:0.8 (-/+) to 1 : 12 (-/+) in per 1 ml of carrier solutions for compositions made in lactose. The final lactose concentration was 10%.

WO 96/29998 describes microspheres as carriers for the preparation of pharmaceutical compositions for human gene therapy, which microspheres have a dimension between 0.1 and 1 micron comprising a biocompatible polymer and optionally an active ingredient such as a pharmaceutically active polypeptide. Biocompatible polymers disclosed therein are ester of a polysaccharide acid such as hyaluronic acid ester, cross-linked ester of hyaluronic acid, ester of chitin, ester of pectin, ester of gellan, or ester of alginic acid. Specifically, the microspheres are obtained by a discontinuous process involving the precipitation of the biocompatible polymer by means of a supercritical antisolvent (SAS) whereby the pressure is varied throughout the process. The above mentioned publications have in common that they describe methods for the preparation of a drug delivery system in the form of nanoparticles containing a combination of chitosan or ester of chitin or ester of hyaluronic acid and a polynucleotide or an amino acid polymer. An important drawback of these prior art methods is associated with the difficulty to manufacture nanoparticles of a predefined and uniform particle size. Since the pharmaceutical impact of the nanoparticles is dependent on the particle size (distribution) of the nanoparticles, it will be evident that there is a need for a method that enables the manufacture of the aforementioned nanoparticles in a predefined and uniform particle size and in a reproducible fashion.

SUMMARY OF THE INVENTION

The inventors have discovered a method that overcomes the drawbacks of the prior art methods. It was found that nanoparticles comprising a charged carbohydrate polymer in combination with a second biopolymer component selected from the group consisting of polynucleotides, amino acid polymers and mixtures thereof, may be obtained in a predetermined and uniform particle size from a precipitation process that employs (i) a fluid solution comprising a solvent and a solute to be precipitated and (ii) a non-gaseous antisolvent, said solvent being soluble in or miscible with the antisolvent and said solute being substantially insoluble in the antisolvent. In the present method, the solute comprises the charged carbohydrate polymer in combination with a second biopolymer component and the solvent contains an organic solvent and a relatively small amount of water. The process of the invention is a continuous or semi-continuous process and comprises the successive steps of: a. combining the fluid solution and the antisolvent so as to achieve a condition of super saturation; b. allowing nucleation to commence and the nuclei formed to grow to particles with a volume weighted average diameter of between 5 nm and 50,000 nm; and c. collecting the resulting particles and separating them from the antisolvent; and wherein step a. and b. are carried out under a substantially constant pressure.

The process according to the invention offers the advantage that the particle formation process, i.e. nucleation and subsequent particle growth, can be controlled very effectively. Thus particles can be obtained with little variation in diameter and without significant agglomeration. Also the method makes it possible to obtain extremely small particles in high yields without significant contamination with larger particles.

The present method enables the effective control of particle size by varying the degree of supersaturation. The degree of supersaturation can be manipulated by changing the percentages of solvent, antisolvent and solute that are admixed in the mixing zone. Another possibility to influence particle size in the present method is to manipulate the nucleation and growth time by varying flow rates and/or by changing the volume of the mixing and/or nucleation zones. Precipitation processes as described above are known in the art. WO 99/59710 describes a method for forming particles, said method involving (a) preparing a solution of the target substance in a vehicle which is or includes either a near-critical fluid or a first supercritical fluid; (b) introducing the solution into a particle formation vessel; and (c) contacting the solution, in the particle formation vessel, with a second supercritical fluid, under conditions which allow the second supercritical fluid to cause precipitation of particles of the target substance, wherein the second supercritical fluid is miscible with the vehicle and is a fluid in which the target substance is insoluble. WO 99/59710 does not contain any observations regarding the suitability of the method disclosed therein for the manufacture of nanoparticles containing a charged carbohydrate polymer in combination with a second biopolymer component selected from the group consisting of polynucleotides, amino acid polymers and mixtures thereof.

The present process enables the condensation of DNA by using the electrostatic interaction between the DNA and the charged carbohydrate polymer. The present method can advantageously be used to produce nanoparticles with bio- and mucoadhesive properties Consequently, the nanoparticles of the invention are particularly suitable for delivering a polynucleotide or an polyamino acid to a mucosal surface as it enables effective uptake of the polynucleotide or polyamino acid. The invention offers the additional advantage that it enables the manufacture of nanoparticles that are biodegradable, biocompatible and non-toxic. DETAILED DESCRIPTION OF THE INVENTION

Accordingly, one aspect of the invention relates to a continuous or semi- continuous process for the preparation of small particles through precipitation, which process employs (i) a fluid solution comprising a solvent and a solute to be precipitated and (ii) a non-gaseous antisolvent, said solvent being soluble in or miscible with the antisolvent and said solute being substantially insoluble in the antisolvent, said process comprising the successive steps of: a. combining the fluid solution and the antisolvent so as to achieve a condition of super saturation; b. allowing nucleation to commence and the nuclei formed to grow to particles with a volume weighted average diameter of between 5 nm and 50,000 nm, c. collecting the resulting particles and separating them from the antisolvent; . wherein the solvent contains an organic solvent and less than 20 wt.% water and the solute comprises a charged carbohydrate polymer in combination with a second biopolymer component selected from the group consisting of polynucleotides, amino acid polymers and mixtures thereof; and wherein step a. and b. are carried out under a substantially constant pressure.

The terms "polymer" and "biopolymer" relate to molecules that contain at least 2 covalently bound monomeric units. In the case of the carbohydrate polymer, the monomeric unit is a monosaccharide. In the case of polynucleotide, the monomeric unit is a nucleic acid and in the case of the polyamino acid, the monomeric unit is an amino acid. It should be understood that the term polymer also encompasses copolymers, e.g. a copolymer of a polyamino acid and a carbohydrate polymer such as glycoprotein. In order to facilitate the co-precipitation of the charged carbohydrate polymer and the second biopolymer, it was found to be highly advantageous to employ a solvent which contains a completely miscible combination of organic solvent and water. Preferably, said organic solvent is selected from DMSO, ethylacetate, n-propanol, n- butanol, propylene glycol, ethylene glycol, ethanol, methanol, glycerol, and acetone. Particularly good results can be obtained with the present process if the solvent contains water and dimethyl sulfoxide. hi a particularly preferred embodiment, the solvent comprises dimethyl sulfoxide and water in a weight ratio between 800:200 and 995:5. Even more preferably the solvent comprises dimethyl sulfoxide and water in a weight ratio between 900:100 and 990:10. The application of such a solvent-mixture offers the advantage that it enables the preparation of a stable solution of the two polymer components. In addition, it was found that such a solvent-mixture is ideally suited for achieving controlled co-precipitation of the carbohydrate polymer and the second biopolymer in the present process.

In a preferred embodiment of the invention, not only the carbohydrate polymer, but also the second biopolymer component is charged and the respective charges of the charged carbohydrate polymer and the second biopolymer are opposite. As a result of the opposite charges, the two polymer components are bound together electrostatically in the fluid solution when said solution is combined with the antisolvent. As a result, the co-precipitation of the 2 components can be realised very efficiently and in high yield. Best results in terms of efficiency and/or yield are achieved if the net charge of the combination of the charged carbohydrate polymer and the second biopolymer has the same sign as the charge of the charged carbohydrate polymer. The charged carbohydrate polymer, as present in the fluid solution, preferably has an absolute surface charge of at least 5 mV, more preferably of at least 20 mV. The carbohydrate polymer serves as a carrier for the second biopolymer. In addition, the carbohydrate polymer may enhance the absorption of the said second biopolymer. Both these functionalities are most pronounced if the carbohydrate polymer, as present in the fluid solution, is cationically charged. hi the present process the solute suitably contains 50-99.5 wt.% of the charged carbohydrate polymer and 0.5-50 wt.% of the second biopolymer component. More preferably the solute contains 70-99 wt.% of the charged carbohydrate polymer and 1- 30 wt.% of the second biopolymer. Best results are obtained with the present method if the average number of monomers in charged carbohydrate polymer is within the range of 2-3000, more preferably within the range of 10-300. The charged carbohydrate polymer is preferably selected from the group consisting of chitosan polymers, heparin, hyaluronic acid polymers and derivatives thereof, more preferably selected from the group consisting of chitosan derivatives and heparin. Examples of suitable derivatives of the aforementioned biopolymers include: trimethylchitosan (TMC); DMC (dimethylchitosan) , triethylchitosan (TEC); 6-O-carboxymethyl-TMC (CM-TMC); CM-TEC; peptide conjugates of CM-TMC and CM-TEC; glucosylated or galactosylated chitosan; low molecular weight heparins (LMWH). Chitosan and chitosan derivatives, in particular chitosan derivatives, offer the important advantage that they are capable of enhancing the absorption of the second biopolymer by opening the tight junctions in mucosal tissues. Preferred chitosan derivatives are selected from TMC, TEC, CM-TMC, CM- TEC, and mixtures thereof. TMC is the most preferred chitosan derivative for use as charged carbohydrate. This compound can be used in pure form or in combination with TEC and DMC whereby TMC is the predominant compound and represent 10 to 100wt.% of the mixture.

The present method is particularly suitable for the manufacture of nanoparticles that can be used for delivering DNA or RNA to cells, e.g. in the context of (non- viral) gene therapy. Gene therapy refers to a method of medical treatment that employs the insertion of gene material into living cells, either in vitro or in vivo. Gene therapy may be beneficial in the treatment of genetic diseases and can also be used as a means to produce a biologically active agent in the body. In a particularly preferred embodiment, the polynucleotide is capable of being expressed and encodes an antigenic material intended as a vaccine, an anti-inflammatory agent, an anti-infective agent, a drug, an antisense agent or a mammalian, viral, bacterial or parasite protein. Unlike viral vectors, which cannot deliver genes larger than 10 kb, the present nanospheres do not have such size limitations. Polynucleotides of greater than 2 kb can be used and may be as large as 50 kb.

The method of the invention may also advantageously be used in for delivering a biologically active agent that acts as a vaccine. Examples of such biologically active agents include mammalian, viral, bacterial or parasite proteins. As used herein the expression "protein" encompasses proteins as well as epitopic fragments thereof. The term "fragment" refers to a portion of the basic sequence which includes at least one antigenic determinant.

The present process is advantageously operated as a continuous or semi- continuous process, hi case of a semi-continous process, steps a. & b. may be operated in an essentially continuous fashion, whereas step c. is carried out batch-wise. It is preferred to mix the stream of fluid solution and antisolvent in an essentially constant ratio throughout the process in order to obtain a reproducible product quality. For the purpose of the present invention, it is important that the process steps a. and b. are carried out under a substantially constant pressure. By such constant pressure, a continuous particle formation process is achieved, so the batch size is determined by the process duration. Processes wherein the pressure is gradually increased produce predetermined batch sizes depending from equipment parameters. By "substantially", it is meant that the pressure is not varied by more than 0,5 bar. Tyically a pressure of 80 to 200 bar is applied.

In a preferred embodiment of the invention, the process employs an antisolvent that is selected from the group consisting of carbon dioxide, nitrogen, argon, oxygen, methane, ethane, propane, butane, n-pentane, nitrous oxide, sulfur hexafluoride, a chlorofluorocarbon, a fluorocarbon, an ether comprising two alkyl radicals which may be the same or different and which contain no more than 3 carbon atoms, carbon monoxide, helium, hydrogen, xenon, ethanol, water and mixtures thereof. Particularly preferred is an antisolvent selected from the group consisting of carbon dioxide, nitrogen, argon, ethane, nitrous oxide, xenon and mixtures thereof. Most preferably the antisolvent is carbon dioxide.

The solvent employed in the present process may suitably contain minor amounts of cosolvents. Examples of suitable cosolvents include methanol, ethanol, dichloromethane, acetone, acetonitril, acetic acid, carbon dioxide, dimethyl ether, diethyl ether and mixtures thereof. In step a. of the present process the fluid solution and the antisolvent are suitably mixed in a weight ratio of between 0.1:99.9 and 90:10. This ratio may vary widely because the proper weight ratio is very much dependent on the nature of the solvent, antisolvent and solute used.

In a particularly preferred embodiment of the invention, the antisolvent is a supercritical or nearcritical fluid. The use of such an antisolvent offers the important advantage that essentially solvent-free particles are obtained from the process. In order to ensure that the antisolvent is in a suitable supercritical or nearcritical state, it is preferred that during step a. conditions are maintained at 0.7xT_c to 1.4xT_c and 0.2xP_cto 7xP_c of the antisolvent, more preferably at T_c to 1.2xT_c and 0.9xP_cto 3xP_c. Here T_c and P_c refer to the critical temperature and critical pressure respectively.

It is feasible to operate the present process with a fluid solution containing widely varying levels of solute as the rate of precipitation is very much dependent on the nature of the antisolvent employed. Generally, the solution comprises between 0.0001 and 30 wt.% solute. Preferably the solution comprises between 0.01 and 10 wt.%, more preferably between 0.1 and 5 wt.% of the solute.

In the present process usually at least 10 wt.%, preferably at least 50 wt.% of the solute present in the stream of the fluid solution is recovered in the particles obtained from step c. The particles obtained generally contain between 0.1% and 50% of the second biopolymeric component, calculated on dry weight. More preferably the recovered particles contain between 0.2% and 30% of the second biopolymeric component.

Another aspect of the invention concerns the particles obtainable from the present process. These particles are characterised by a very uniform particle size. In a particularly preferred embodiment, the particles obtained from the present process have a particle size distribution with a standard deviation of less than 50% of the volume weighted average particle size, more preferably of less than 30%, most preferably of less than 20% of the volume weighted average particle size. Yet another aspect of the invention relates to the use of the particles obtainable from the present process in a method of delivering a polynucleotide and/or an polyamino acid into the cell of an animal or human, said method comprising administering an effective amount the nanoparticles to the animal or human, wherein the charged carbohydrate are selected from the group consisting of chitosan derivatives and heparin, preferably chitosan derivatives selected from TMC, TEC, DMC; CM- TMC; CM-TEC; peptide conjugates of CM-TMC and CM-TEC; glucosylated chitosan, galactosylated chitosan, and mixtures thereof.

The aforementioned method is particularly advantageous if it comprises the administration of the particles to mucosal surfaces, e.g. those found within the nose, lungs, vagina, eyes and gasto-intestinal tract. Administration to mucosal surfaces may be effected by oral application, by pulmonary application, for example by intra-tracheal admimstration, or by intra-nasal application. Most preferably the present method employs pulmonary administration of the nanoparticles.

The invention is further illustrated by means of the following examples. EXAMPLES

Example 1

A vessel of 1 liter was filled with carbon dioxide to a pressure of 120 bar at 40°C. At the bottom of this vessel a filter was mounted to harvest the produced particles, as illustrated in figure 1. In addition, a solution of 0.5 wt.% TMC, 4 wt.% water and 95.5 wt.% dimethyl sulfoxide (DMSO) was prepared. During 15 minutes this solution was sprayed into the vessel through a nozzle of 0.1 mm diameter at a 10 ml/min rate. Simultaneously an additional amount of HOg/min carbon dioxide was pumped into the vessel. A thermostatic bath was used to maintain the temperature of 40°C, while the pressure was maintained at 120 bar by means of a backpressure valve. After 15 minutes the introduction of the solution and the carbon dioxide was stopped and the vessel was flushed with 10kg of CO2 to remove all DMSO and water. Then the pressure was reduced to atmospheric condition. The vessel was opened and the tTMC particles were recovered in the form of a dry powder. The size of the particles so obtained was in the range of 0.5-10 μm.

Example 2

Example 1 was repeated, with the exception that the rate of introducing the TMC solution into the vessel was decreased to 2ml/min.As a result of the lower introduction rate the effective mixing energy was decreased. A dry powder was obtained with particle sizes varying between 1 and 50 μm.

Example 3 Example 1 was repeated using a mixture of 0.5 wt.% TMC, 0.05 wt.% Bovine

Serum Albumin (BSA), 4 wt.% water and 95.45 wt.% DMSO. A dry powder was obtained with particle sizes varying between 0.2 and 70 μm.

The powder was analyzed and it was found that the BSA was co-precipitated with the TMC.

Example 4

Example 3 was repeated with the exception that the mixing energy was increased so as to decrease the particle size. The increase in applied mixing energy was achieved by introducing the carbon dioxide as an opposed stream towards the solution stream. This double impingement construction is shown in figure 2. A dry powder was obtained with particle sizes varying between 0.5 and 8μm.

Example 5

Example 4 was repeated with the exception that the mixing energy was further increased so as to decrease the particle size. The increase in applied mixing energy was achieved by introducing the carbon dioxide as an opposed stream towards the solution stream and performing this in a V" T-piece. This double impingement construction is shown in figure 3. A mixture of 0.25 wt.% chitosan, 2 wt.% water and 97.75 wt.% DMSO was used. A dry powder was obtained with particle sizes varying between 0.2 and 5μm.

Example 6

Example 5 was repeated using a mixture of 0.25 wt.% TMC, 0,012wt.% FITC Albumin, 2 wt.% water and 97.738 wt.% DMSO. A dry powder was obtained with particle sizes varying between 0.2 and 5μm. The powder was also analysed by CLSM confocal laser scanning microscopy and it was found that the FITC albumin was co- precipitated together with the TMC

Example 7

Example 6 was repeated using a mixture of 0.25 wt.% TMC, 0,012wt.% buserelin acetate (a peptide), 2 wt.% water and 97.738 wt.% DMSO. A dry powder was obtained with particle sizes varying between 0.2 and 5μm. The produced powder was compared to buserelin acetate alone in an in vitro model using human CALU-3 cells (human alveolar epithelium cells) to determine the trans epithelial transportation of the peptide. It was shown that after three hours 6% of the buserelin alone was transported across the CALU-3 cell membrane. The TMC/buserelin acetate particles achieved a 36% transportation of buserelin acetate across the CALU-3 cell membrane. This experiment shows that the formed nanoparticles enhance transmucosal admimstration.

Claims

1. A continuous or semi-continuous process for the preparation of small particles through precipitation, which process employs (i) a fluid solution comprising a solvent and a solute to be precipitated and (ii) a non-gaseous antisolvent, said solvent being soluble in or miscible with the antisolvent and said solute being substantially insoluble in the antisolvent, said process comprising the successive steps of: a. combining the fluid solution and the antisolvent so as to achieve a condition of super saturation; b. allowing nucleation to commence and the nuclei formed to grow to particles with a volume weighted average diameter of between 5 nm and 50,000 nm, c. collecting the resulting particles and separating them from the antisolvent; . wherein the solvents contains an organic solvent and less than 20 wt.% water and the solute comprises a charged carbohydrate polymer in combination with a second biopolymer component selected from the group consisting of polynucleotides, polyamino acids and mixtures thereof; and wherein step a. and b. are carried out under a substantially constant pressure.

2. The process according to claim 1, wherein the solvent comprises dimethyl sulfoxide and water in a weight ratio between 800:200 and 995:5.

3. The process according to claim 1 or 2, wherein the second biopolymer component is charged and wherein the respective charges of the charged carbohydrate polymer and the second biopolymer are opposite.

4. The process according to any one of claims 1-3, wherein the carbohydrate polymer, as present in the fluid solution, is cationically charged.

5. The process according to any one of claims 1-4, wherein the solute contains 50-99.5 wt.% of the charged carbohydrate polymer and 0.5-50 wt.% of the second biopolymer component.

6. The process according to any one of claims 1-5, wherein the charged carbohydrate polymer is selected from the group consisting of chitosan polymers, heparin, hyaluronic acid polymers and derivatives thereof, preferably selected from the group consisting of chitosan derivatives and heparin, more preferably chitosan derivatives selected from the group consisting of trimethylchitosan (TMC); dimethylchitosan (DMC); triethylchitosan (TEC); 6-O-carboxymethyl-TMC (CM- TMC); CM-TEC; peptide conjugates of CM-TMC and CM-TEC; glucosylated chitosan, galactosylated chitosan and mixtures thereof.

7. The process according to any one of claims 1-6, wherein the polynucleotide is capable of being expressed and encodes an antigenic material intended as a vaccine, an anti-inflammatory agent, an anti-infective agent, a drug, an antisense agent or a mammalian, viral, bacterial or parasite protein.

8. The process according to any one of claims 1-7, wherein the poly amino acid is a mammalian, viral, bacterial or parasite protein.

9. The process according to any one of claims 1-8, wherein the antisolvent is a supercritical or nearcritical fluid.

10. Particles obtainable from a process according to any one of claims 1-9; wherem the charged carbohydrate is selected from the group consisting of chitosan derivatives and heparin, preferably chitosan derivatives selected from the group consisting of trimethylchitosan (TMC); dimethylchitosan (DMC); triethylchitosan (TEC); 6-0- carboxymethyl-TMC (CM-TMC); CM-TEC; peptide conjugates of CM-TMC and

CM-TEC; glucosylated chitosan, galactosylated chitosan and mixtures thereof. .

11. The particles according to claim 10 for use in a method of delivering a polynucleotide and/or an polyamino acid into the cells of an animal or human, said method comprising administering an effective amount the nanoparticles to the animal or human.