AU2836599A

AU2836599A - Microcapsules having delayed release

Info

Publication number: AU2836599A
Application number: AU28365/99A
Authority: AU
Inventors: Uwe Bayer; Bernd Hahn; Anna Majeres
Original assignee: Aventis Research and Technologies GmbH and Co KG
Current assignee: Aventis Research and Technologies GmbH and Co KG
Priority date: 1998-03-25
Filing date: 1999-03-12
Publication date: 1999-10-18
Anticipated expiration: 2019-03-12
Also published as: EP1063970A1; CA2325554A1; JP2002507472A; DE19813010A1; WO1999048479A1; AU736941B2

Description

WO 99/48479 PCT/EP99/01625 Microcapsules having delayed release Description 5 The present invention relates to microcapsules having a greatly delayed release of the active compounds. The term microcapsules is understood as meaning capsules of from 50 nm to 3 mm in size, which have an outer shell of polymer and an inner, mostly 10 liquid phase. Microcapsules are customarily produced by encapsulation of finely dispersed liquid phases by enveloping with film-forming polymers. Such microcapsules are especially used in the area of depot preparations, accordingly the active compound found in the inner phase of the microcapsules is protected by the shell of the microcapsule and is not 15 released immediately, but only with a delayed release (release of active compound). It is known to produce microcapsules by atomization of an organic polymer solution, the liquid droplets produced in this way being sprayed into a 20 precipitation bath. Thus US-A-4 352 883 describes a 2-stage process for the production of microcapsules, in which living cells, such as, for example, islet of Langerhans cells, are encapsulated. For this, the living cells are 25 suspended in sodium alginate and this suspension is sprayed into a precipitation bath which contains polyvalent cations (for example Ca 2 ). The physical crosslinking of the alginate on the surface occurs here due to the polyvalent cation. In the second step, the capsules produced in this way are mixed with a cationic polymer, which brings about further physical 30 crosslinking. Polycations mentioned in this publication are polyethylene imine and polylysine. These capsules are completely permeable to proteins having a molecular weight of less than 100,000 g/mol. Consequently, there is no delayed release of these substances. US-A-5 389 379 discloses a process for the production of microcapsules in which the liquid droplets produced by means of an ultrasonic nozzle are first introduced into a liquid in which the liquid droplets are not soluble (for WO 99/48479 PCT/EP99/01625 2 example into ethanol). This liquid is then replaced by water in order to crosslink the microcapsules. This process has the disadvantage that the active compound to be encapsulated has to be dissolved in an organic solvent together with the 5 film-forming polymer. This considerably restricts the choice of active compounds on account of their solubility and possible denaturation by the solvent. It is furthermore known to use chitosan for the production of 10 microcapsules. Chitosan is the general term for a polymer which is obtainable by deacetylation of chitin, an unbranched 0(1 -4)-linked polysaccharide of 2-acetamido-2-deoxy-D-glucose (N-acetyl D-glucosamine). 15 Chitosan can be described by the following formula H3 0 NH C0 20 CH2H NH 2 y x 25 where the ratio of deacetylated to acetylated segments is greater than 1 and the number-average molecular weight is between 50,000 and several million g/mol. This chitosan is insoluble in water and can be obtained, for example, from Fluka. Thus, in Journal of Bioactive and Compatible Polymers, Vol. 3, 1988, 30 pp. 334 to 355, C.A. McKnight et al. describe a three-stage process for the production of microcapsules based on alginate and chitosan. According to this process, the alginate solution containing the active compound is first introduced into a calcium chloride solution, where an initial hardening of the outer capsule surface takes place. The hardened capsules are then 3 coated with a chitosan solution, which leads to crosslinking of the outer shell. Finally, the microcapsules obtained in this way are washed with alginate. The chitosan used in this publication has a number-average molecular weight of 160,000 to 330,000. Permeability investigations of WO 99/48479 PCT/EP99/01625 3 these chitosan/alginate membranes have shown that the molecular weight of the chitosan used has no significant effect on the permeation behavior of various proteins. Even after two hours, 20% of the active compound BSA has already diffused into the chitosan-containing microcapsules. 5 The release of these microcapsules is very high even after a short time. In "Controlled Release of Albumin from Chitosan-Alginate Microcapsules" in Journal of Pharmaceutical Sciences,,1994, pp. 178 to 185, A. Polk et al. report on the influence of the molecular weight of chitosan in 10 microcapsules. The chitosan used in these experiments has a molecular weight of 250,000 to 1,250,000. These investigations show that an increase in the molecular weight of the chitosan used is accompanied by a decrease in the release of the active compound albumin. The authors come to the conclusion that a higher molecular weight of the chitosan 15 leads to the best results witli respect to delayed release of the active compound. The release of these micr6eapsules after 24 hours is already 50% of the encapsulated active compound. 20 A disadvantage of th4 known process for the production of chitosan containing microcapsules is that the production is carried out in two or more different wo king steps. Above all, the transportation of the microcapsules from one reaction container to the other necessitates complicated devices, especially when small microcapsules are to be 25 produced. The object of the present invention consists in the provision of microcapsules which, compared to the prior art, exhibit delayed release of the active compounds. Moreover, these microcapsules should be simple to 30 produce. This object is achieved according to the invention by a process for the production of microcapsules, which comprises a) in one process step introdu44Wg liquid droplets of an aqueous 35 solution 1, which contains at least one water-soluble polyanion, into an aqueous solution 2, comprising * 0.1 to 5% by weight of calcium cations; and WO 99/48479 PCT/EP99/01625 4 0.1 to 5% by weight of hydrolyzed chitosan having a number average molecular weight of between 2200 and 40,000 g/mol, obtainable by partial hydrolysis of a chitosan having a number average molecular weight of more than 50,000 g/mol in an 5 aqueous, 0.1 to 4 N HCI-containing solution at a temperature between 50 and 95 0 C for a period of between 0.5 and 8 hours, the weight ratio of HCI-containing solution to commercially available chitosan being between 1 and 50 and the product of normality of the HCI solution and of the hydrolysis period in 10 hours being between 0.1 and 7; and b) after completion of the addition of the solution 1 the microcapsules thus obtained remaining in the solution 2 for a period of 15 to 360 minutes, in particular for a period of 60 to 180 minutes. 15 Compared to the chitosan-containing microcapsules of the prior art, the microcapsules produced according to the invention have a markedly decreased permeability. After 10 days' measurement, the release of the microcapsules produced according to the invention is still below 50% (active compound: bovine serum albumin). 20 Moreover, the process according to the invention has the advantage that the production of the microcapsules can be carried out in a single process step. The complicated devices which were previously necessary for the transport of the microcapsules in the multistage processes of the prior art are thus not required. 25 The aqueous solution 1 can be converted into liquid droplets by processes known per se. In particular, commercially available atomizers can be used for this. 30 It has proven advantageous if the water-soluble polyanion is an alginate, in particular an alginate having a high guluronic acid content. The water-soluble polyanion, however, can also be selected from the group 'P P- consisting of carrageenan, sulfated polysaccharides, gelatin and agar-agar. 35 According to a particularly preferred embodiment of the present invention, the solution 1 additionally contains at least one polyacid or its alkali metal salt, selected from the group consisting of polyamino acids, poly phosphates and polysulfates of polysaccharides.

WO 99/48479 PCT/EP99/01625 5 Preferred examples of a polyphosphate are sodium polyphosphate and a polyphosphate of a polysaccharide. The polysaccharide can be selected from the group consisting of starch hydrolyzates, inulin, hydroxyethyl starch, xylan and dextrans. 5 As a polyamino acid, it is preferred to use polyaspartic acid or polyglutamic acid. According to a further advantageous embodiment of the invention, the solution 2 additionally contains a polycation selected from the group 10 consisting of polylysine, polyvinylamine, poly-ap-(2-2dimethylaminoethyl) D,L-aspartamide, aminated polysaccharides, such as, for example, aminated dextrans, cyclodextrins, cellulose ethers, starches, pectins, and their hydrophobically substituted derivatives. 15 The release can moreover be reduced by reacting the microcapsules, after preparation of the particles, in an additional process step with a crosslinker selected from the group consisting of glyoxal, glutaraldehyde, succinaldehyde, or dicarboxylic acids, such as, for example, oxalic acid, succinic acid, fumaric acid, maleic acid, malic acid, glutaric acid, adipic 20 acid, 2,3-0-isopropylidenetartaric acid, diacid chlorides, such as, for example, succinyl chloride, fumaryl chloride, glutaryl chloride, adipoyl chloride, or tricarboxylic acids, such as, for example, citric acid, 1,2,3-propanetricarboxylic acid, hemimellitic acid, trimellitic acid, trimesic acid. 25 The size of the microcapsules produced according to the invention is between 1 and 3000 pm, in particular between 10 and 1000 pm. The microcapsules according to the invention are preferably used as 30 carriers for active compounds, in particular for pharmaceuticals, foodstuff additives, flavorings, fragrances, colorants, herbicides, fungicides, bactericides, pesticides and insecticides. The following examples serve to illustrate the invention.

WO 99/48479 PCT/EP99/01625 6 Example 1: Preparation of the solution 1: 9 mg of sodium alginate from Sigma (catalog No.: A-7128) together with 5 6 mg of BSA-FITC (from Sigma, catalog No.: A-9771) are dissolved in 3 ml of 0.9% NaCl solution. Preparation of the solution 2: 1500 ml of 1.0 M hydrochloric acid are heated to 90 0 C in a 4 I two-necked 10 flask, equipped with a condenser. 60 g of chitosan (obtainable under the name chitosan from Fluka, catalog No.: 22743) are then slowly added with stirring. After addition has taken place, the reaction mixture is stirred at 900C for 4 hours and then filtered through a G2 frit. The filtrate obtained is allowed to stand overnight in a refrigerator at 2-8*C. The precipitate 15 obtained in this way is isolated by centrifugation (Lobofuge GL from Heraeus; at 4500 rpm, 25 min). The residue is dissolved in water and freeze-dried with the aid of a freeze-drying device (LDC-1 m from Christ). 300 mg of the chitosan prepared in this way is dissolved in 15 ml of water together with 450 mg of CaCl2 (from Riedel deHaen, catalog No.: 12018). 20 Production of the microcapsules: The solution 1 is dripped into the solution 2 by means of a nozzle which consists of a cannula having an internal diameter of 0.2 mm and an external diameter of 0.4 mm. The nozzle is concentrically admitted into a 25 hollow cylinder, such that, through the resulting annular gap, a tangential air stream can be generated which sweeps along the drops emerging from the cannula. The drops generated in this way fall into the solution 2. After 1 ml of the solution 1 has been introduced into 15 ml of the solution 2, the resulting microcapsules is allowed to sediment and the solution is 30 decanted off. The microcapsules obtained are then suspended three times using 0.9% strength NaCl solution. The most widespread size of the microcapsules produced in this way was determined by Frauenhofer diffraction and was 90 pm. 35 Determination of the release of active compound: For the determination of the release properties of the capsules produced, BSA-FITC from Sigma (catalog No.: A-9771) is used as a model protein. Further materials are: sodium alginate from Sigma (A-7128), chitosan from WO 99/48479 PCT/EP99/01625 7 Fluka (22743), CaCl 2 from Riedel de Haen (12018), NaCl from Merck (6404). The release measurements are carried out in PBS buffer (Sigma, P4417), additionally using 0.005% timerosol (from Fluka, catalog No.: 71230). 5 After production, the PEC capsules are transferred to 10 ml of PBS buffer solution, in 15 ml rolled-rim vials, and the microcapsules are incubated at 370C. The BSA-FITC concentration is measured Qy means of a UVNIS 10 spectrophotometer from Beckmann (DU 70). First, the proportion of included BSA-FITC is determined by determining the BSA-FITC concentration in the combined supernatants. The concentration is determined by measurement of the absorption at 494 nm using a calibration curve. Falsification of the measurement by the intrinsic 15 coloration of the chitosan is circumvented by subtracting the absorption of the chitosan. From the amount of BSA-FITC employed, it can be calculated how much of the BSA-FITC has been included. The release measurement is carried out by removing 3 ml from the 20 incubation solution and determining the BSA-FITC concentration in this supernatant. After completion of the measurement, the sample solution is combined again with the release sample. After 11 days, the release of the microcapsules obtained in this way is only 20% of the encapsulated active compound. 25 Example 2 The procedure is carried out analogously to Example 1. After the production of the microparticles, the particles are crosslinked using glyoxal. For this, the microparticles are introduced into 10 ml of a 2% strength by 30 weight glyoxal solution for 30 minutes and allowed to stand. They are then washed with 0.9% NaCl solution. After 45 days, the release of the microcapsules obtained in this way is less than 10% of the encapsulated active compound. )ST ' s

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Claims

1.) A process for the production of microcapsules, which comprises a) in one process step introducing liquid droplets of an aqueous 5 solution 1, which contains at least one water-soluble polyanion, into an aqueous solution 2, comprising * 0.1 to 5% by weight of calcium cations; and * 0.1 to 5% by weight of hydrolyzed chitosan having a number-average molecular weight of between 2200 and 10 40,000 g/mol, obtainable by partial hydrolysis of a chitosan having a number-average molecular weight of more than 50,000 g/mol in an aqueous, 0.1 to 4 N HCl containing solLtiort at a temperature between 50 and 950C for a period of between 0.5 and 8 hours, the weight 15 ratio of HCI-containing solution to commercially available chitosan being between 1 and 50 and the product of normality of the HCI solution and of the hydrolysis period in hours being between 0.1 and 7; and b) after completion of the addition of the solution 1 the 20 microcapsules thus obtained remaining in the solution 2 for a period of 15. to 360 minutes, in particular for a period of 60 to 180 minutes.

2.), The process as claimed in claim 1, wherein the water-soluble 25 polyanion is an alginate, in particular an alginate having a high guluronic acid content.

3.) The process as claimed in claim 1 or 2, wherein the water-soluble polyanion is selected from the group consisting of carrageenan, 30 sulfated pojysaccharides, gelatin and agar-agar.

4.) The process as claimed in one of the preceding claims, wherein the solution 1 additionally contains at least one polyacid or its alkali metal salt, selected from the group consisting of polyamino acids, 35 polyphosphates and polysulfates of polysaccharides.

5.) The process as claimed in claim 4, wherein the polyphosphate is sodium polyphosphate or a polyphosphate of a polysaccharide. WO 99/48479 PCT/EP99/01625 9

6.) The process as claimed in claim 4 or 5, wherein the polysaccharide is selected from the group consisting of starch hydrolyzates, inulin, hydroxyethyl starch, xylan and dextrans. 5

7.) The process as claimed in claim 4, wherein the polyamino acid is polyaspartic acid or polyglutamic acid.

8.) The process as claimed in one of the preceding claims, wherein the 10 solution 2 additionally contains a polycation selected from the group consisting of polylysine, polyvinylamine, poly-a,p-(2-2dimethyl aminoethyl)-D,L-aspartamide, aminated polysaccharides, such as, for example, aminated dextrans, cyclodextrins, cellulose ethers, starches, pectins, and their hydrophobically substituted derivatives. 15

9.) The process according to one of the preceding claims, wherein the microcapsules are reacted in an additional process step with a crosslinker selected from the group consisting of glyoxal, glutaraldehyde, succinaldehyde, or dicarboxylic acids, such as, for 20 example, oxalic acid, succinic acid, fumaric acid, maleic acid, malic acid, glutaric acid, adipic acid, 2,3-0-isopropylidenetartaric acid, diacid chlorides, such as, for example, succinyl chloride, fumaryl chloride, glutaryl chloride, adipoyl chloride or tricarboxylic acids, such as, for example, citric acid, 1,2,3-propanetricarboxylic acid, 25 hemimellitic acid, trimellitic acid, trimesic acid.

10.) The process as claimed in one of the preceding claims, wherein the size of the microcapsules is between 1 and 3000 pm, in particular between 10 and 1000 pm. 30

11.) The use of the microcapsules produced by a process of the prior claims as carriers for active compounds, in particular for pharmaceuticals, foodstuff additives, flavorings, fragrances, colorants, herbicides, fungicides, bactericides, pesticides and insecticides. P