GB2192171A - Production of polymetric beads having alginate shells - Google Patents

Description

1 GB 2 192 171 A 1

SPECIFICATION

Production of polymeric beads The invention relates to a device forthe production of alginate beads which can be produced in an essentially 5 uniform size. The beads comprise an outer alginateshel land a core which can consist of a liquid or gel or water-in-oil emulsion, said gel or liquid containing entrapped cells in suspension, biologically active part icles in suspension. The core can also consist of an oil or oily substance which may also contain a biologically active materia L If desired the alginate shell can be subsequently removed. The beads can be produced in the millimeter size range, and there can be produced beads within a desired predetermined essentially uniform size range. 10 The device of the invention comprises 3 conduits through which there flow an alginate solution, a solution orsuspension subsequentlyforming the core of the bead and a gaseous stream. The resulting beads are dropped into a solution adapted to solidifythe alginate shell of the beads, which are subsequently washed.

The active material can be present in a prepolymer, and in such case the bead can be contacted after harden ing of the alginate shell with a medium adapted to polymerize the prepolymer. Although mainly intended for 15 the entrapment of cells and other biologically active material in millimeter-size beads, the same alginate shell can also be produced to contain an oil, such as vegetable oil, paraffin oil, or suspensions or emulsions based on a hydrophobic water-insoluble medium.

The immobilization of whole cells has gained much attention in recentyears. Several methodsforwhole cell immobilization were developed (for reviewsee J. Klein and F. Wagner, App. Biochem. Bioeng. 4,12-51, 1983). The advantages inherent in immobilized cell systems, such as reuse of biocatalyst, flexibility in reactor 20 design and significantly improved operational stability, led to the development and use of immobilized cell systems on bench, pilot and industrial scale (for review see P. Linko &Y. Linko, CRC Critical Reviews in Biotech nology,'I, 289-338,1984).

The most popular approach to cell immobilization is by gel entrapment. Cells are suspended in an aqueous 2. solution of a monomer or prepolymer; by physical or chemical change (e. g. cooling, pH change, introduction 25 of polymerization initiator) the solution is gelified, physically entrapping the cells.

In recent years, gel entrapment of cells by crosslinking of synthetic prepolymers gained much attention (S.

Fukui &A. Tanaka, Ad. Biochem. Eng. 29, 2-33,1984). A novel gel entrapment technique, based on chemical crosslinking of linear, water soluble polyacrylamide, partially substituted with acy1hydrazide groups,was developed in our laboratory.

The method is based on suspending cells, organelles or enzymes in a solution of polyacrylamide- 30 hydrazide (PAAH) and crosslinking by the addition of controlled amounts of dialdehyde (e.g. glyoxal).

Following hardening, the resulting gel block is mechanically fragmented. This technique was found useful forthe immobilization of bacteria, yeast, plant cells, liver microsomes and enzymes (for review see A. Free man, AnnaL N.Y. Acad: Sci. 434,418-426 1984). The advantages of this technique include retention of activity (90% and more of input activity), high porosity, good chemical, biological and mechanical stability and stabil35 ization of entrapped cells towards organic solvents, There is provided a device forthe production of beads of essentially uniform size, in the millimeter diameter range, comprising an outer alginate shell and containing a cell suspension, or cells entrapped in a gel, or a biologically active material, such as enzyme, antibodies, immobilized on a suitable carrier, within such shell.

The device provided also enablesthe preparation of macrocapsules comprising an alginate outershell 40 retaining droplets of hydrophobic moietysuch asvegetable oil, paraffin oil, or solutions, emulsions orsus pensions based on hydrophobic, water immiscible medium.

There is further provided a process forthe production of such alginate beads. Other and further objects of invention will become apparent hereinafter.

The invention is described by way of illustration with reference to the Drawings, in which: 45 Figure I is a longitudinal sectional schernatical view, not according to size, of a device according tothe invention; Figure2 is a comparison of size distribution of PAAH-entrapped yeast preparations: top right: previous procedure, one fragmentation; top left: previous procedure, two fragmentations; bottom: bead preparate; Figure 3 is a graph illustrating the conversion of glucose to ethanol byfreely suspended, and by PAAH bead-entrappedSaccharomycescerevisiae; 50 Figure 4 is a graph illustrating the A'-dehydrogenation of hydrocortisones by free and PAAH bead entrapped Arthobactersimplex; and Figure5illustrates the amount of Cyolane release from Ca-alginate beads of the invention over a period of a number of days and the rate of release.

Essentially the device according to the invention comprises 3 conduits terminating at a common exit port, 55 one of these supplying a cell suspension or a suspension of small particles with attached biologically active material, in a liquid medium which can be a polymerizable prepolymer; the second conduit supplying an aqueous alginate solution, and the third a stream of a gaseous medium, the flow of each of these being adjustable at will. Preferably an inner conduit supplies the cell or particle suspension. According to a prefer- red embodiment of the invention, the three conduits are in the form of three concentric tubular members,the 60 65 2 GB 2 192 171 A 2 inner supplying the suspension, the second the alginate, and the third the gaseous medium.

The exact distance of the outlets respective each other can be adjusted, thus permitting, togetherwith the adjustment of the flow of each of the three media, to obtain beads of predetermined size, shell thickness and production rate.

The injector device according to the invention is illustrated bywayof examplewith reference to the en- 5 closed schematical drawing in Figure 1.

As shown in Figure 1, the injector comprises three coaxial tubular members 11, 12 and 13, termed hereinaf ter as 'needles", where 14 designates the inlet of the cell suspension, 15the inlet of the alginate solution and 16the inlet of the gas stream. Each of these can be adjusted atwill as regards flowvelocity and volume. The distance of the needle tips defining the outlets can be adjusted at will by varying the distances h, and h2. The 10 experimental unit illustrated has an overall length of about 5 em and the exact dimensions of the components is indicated hereinafter.

It is clear that this is byway of illustration only, and various modifications in the arrangement and size of parts can be resorted to.

The PAAH bead entrapped cells maybe readily prepared in large quantity, under sterile and anaerobic 15 conditions, in a continuous process. The head entrapped cells have the advantages inherent in the PAAH technique: retention of high activity, high porosity and good stability. The beads are quite uniform and can be adjusted to be within the range of 1 - 5 mm in diameter; the alginate layer occupies - 5 - 10 % of thetotal volume. The inner needle is supplied with a controlled feed of a cell suspension in PAAH (or othersolution) through entry port 14. This needle is positioned in a needle of large diameter, which is supplied with a 20 sodium alginate solution through entry port 15. The two needles are held in the center of a third coaxial needle, which is supplied with a controllable stream of air or other gas via entry port 16. The exact distances between the needles maybe adjusted by varying the distanced h, and h2. The unit described is about 5 - 10 em in length and is held mechanically in an upright position.

By adjusting the flow rate of the cell suspension, alginate solution and gas, droplets comprising an inner 25 core, originating from 14, encapsulated in an outer shell coming from 15, are formed; these are detached and spun down by the gas stream from 16, these are of quite uniform size. When an alginate solution is supplied via 15, the shell is gelified by contact with a CaC12 solution. The beads drop from the injector into a CaC12 solution and are left for hardening; and the medium is changed to a glyoxal containing buffer. The glyoxal penetrates the alginate layer and thus the inner PAAH solution is crosslinked. Following washings, the beads 30 are ready for use. The process allows immobilization of a wide variety of cells in uniform size, chemically stable, crosslinked polymeric beads.

In a similar way, by feeding oils, oil-based solutions, emulsion or suspension in oils through 14, mac rocapsules comprised of caalg inate outer shell and f il led with oil- based internal droplet are formed.

35 Example 1

Glucose conversion into alcoholby immobilized saccaromyses cerevisiae in PAAH- beads a. Preparation ofsolutions:

1. Cel/suspension: 40 Into a 5% (w/v) aqueous solution of polyacrylamide-hydrazide (mean average molecular weight of 100,000 containing 0.8 meq. acrylhydrazide groups), a preweighed amount of yeasts, as obtained from the producer "Paka" Industries Ltd., Bat-Yam, Israel, in a ratio of 0.5 g (wlv) of yeaststo 20 mi of gel forming reaction mixture, was added, and the suspension was homogenized by magnetic stirring for 15 minutes at room temperature. 45 2. Sodium alginate solution:

3% (w/v) solution was prepared by dissolving sodium alginate (BDH) in water by magnetic stirring over night at room temperature. Priorto use this solution was deaerated undervacuum.

b. Injection system: Specifications (see Figure 1) 50

Dimensions andflowrates:

1. Innertube:

innerdiameter -(A)-0.35mm-2.Omm 1r flow rate -0.7-0.9m]/min 55 2. Median tube -(B): inner diameter 1.2mm-3.Omm flow rate -0.5-0.7m]lmin 3. External tube (C): inner diameter 2.Omm-5.Omm flow rate 2.5-4.Omi/min 60 Distances between tube outlets:

h, 2.0 - 2.2 em h2 2.2 - 2.5 em 65 3 GB 2 192 171 A 3 c. The flowing-through tubesA,8 and Q 1. Via tube A: cells suspended in an aqueous solution of polyacrylamide- hydrazide (3 - 5% (w/v)) or in an appropriate buffer solution.

2. Via tube B: sodium alginate solution (BDH, 2-4% MM).

3. Via tube C: nitrogen or air. 5 d. Immobilization of yeasts in PWIAHbeads The homogenized yeast suspension was passed through the innertube (A) of the system at the flow rate indicated above. Alg inate solution and air were supplied atthe rates given. The formed drops were collected in a 1 % (w/v) aqueous CaC12 solution and after 1 h incubation this solution was replaced by 50 mi of 10 phosphate buffer (50 mM, pH = 7) containing 2 mi of 5% glyoxal solution (in 50 mM phosphate, pH = 7). The PAAH core was allowed to undergo gelation by incubation overnight at 4C. The beads were then washed with cold 0.3% (w/v) citrate buffer, pH=5.

e. Assay: 15 Gel beads (1.5 - 2.0 mm in diameter) containing 0.5 g (w/v) of entrapped yeasts were washed three times with 50 mi of cold medium containing 160/6 (w/v) glucose; 0.15 (w/v) yeast extract; 0.25% (w/v) NH4C1; 0.55% (wlv) KH2P04; 0.025 (wlv) M9S04.71-120; 0.01% (w/v) NaCi; 0.001% (wlv) CaC12 and 0.3% (w/v) citric acid, pH 5.

Finally, the same medium was added to a final volume of 50 mi. This last reaction mixture was then 20 transferred into a 125 mi baffled Erlenmeyer flask that was shaken in a reciprocal shaker at 100 strokes/min. at WC allowing the formed C02to escape through a pinhole outlet.

Samplesofl m 1 were withdrawn for ethanol and glucose determinations up to 20 h. Under these con ditionsfull conversion of glucose into ethanol was observed within 20 h of incubation.

25 Ethanol determination:

The concentration of ethanol in samples was determined by G.C.

Glucose determination:

The concentration of glucose was assayed by the "Glucostat" kit of Sigma. 30 Underthe conditions employed, 9 lucose conversion by the PAM bead entrapped yeast was the same as that of the f reely suspended yeast control (see Figure 2).

Example2

A'-Dehydrogenation of hydrocortisone by PWIAH- bead entrappedA rthrobactersimplex cells 35 a. Cellgrowth and harvest 1. Arthrobacter simplex colony (ATCC 6946) was scraped from slant agar into 30 m[ of 8 g/1 nutrient broth (Oxoid CM 15) sterilized solution in a 250 m[ closed universal bottle and incubated fora period of 48 h atWC on a gyratoryshaker (150 rpm). Into a 2.51 baffled Erlenmeyerflast2.5 g yeast extract, 0.75 9 (NH4)2S04,0.66 g K2HP04:3H20 were added, dissolved in 225 mi water, 0.25 mi of trace element stock solution consisting of: 40 ZnS04.71-120 1.44 g/1 MMS04.4H20 1.12g/1 H3B03 0.319/1 CUS04.5H20 0.63 g/1 45 Na2M0)4.21-120 0.259/1 COC12.6H20 0.24 g/1 KI 0.42 g/1 FeS04.7H20 2.78 g/[ H2S04 1-2mi 50 were added and the final solution sterilized (121%, 15).

In parallel, 3.75 9 91 ucose and 25mg M9C12 were dissolved in 25 m 1 H20 sterilized and added to the above solution.

One mi of the cell suspension was transferred into the flask and the flask was incubated for a period of 24 h 55 at 300C on a gyratory shaker (210 rpm). Five mi of this was used to innoculate in a 2.5 1 baffled Erlenmeyer, in the same medium fol lowing incubation for 16.5 h at 30C on a gyratory shaker. After this incu bation, 0.25 9 of hydrocortisone, finely suspended (magnetic stirring overnight) in 5 mi of 2.5% (w/v) Tween 80 in waterwere added. Induction was al lowed to proceed for 6.5 h.

Cells were collected by centrifugation, f rozen i n liquid nitrogen and stored at -20'C. 60 2. Cel/suspension Prior to use, a weighed quantity of frozen cells was tranferred to ice cold 0.05 M tris, pH = 7.8 (0.1 g WW (20 mg dcw) cells per m]) and magnetically stirred over ice for 30 minutes. The suspension was then horno genized by a glass-Teflon homogenizerto ensure the formation of a uniform suspension.

65 4 GB 2 192 171 A 4 b. Immobilization of cells in PAAH-beads Into 10 m] of 5% prepolymer (100,000 MW) solution, equipped with a magnetic stirrer and cooled over ice, 0.4 mi of cell suspension was added, following homogenization of the cell suspension by magnetic stirring.

The fine prepolymer cell suspension was then processed to make PAAH-beads as in Example 1. After over night gelation in 0.05 M phosphate buffer (pH = 7.8, containing 2 m[ 5% glyoxal solution), the PAAH-beads 5 entrapped cells were washed three times with cold 0.05 M tris buffer (pH = 7.8) and brought to a final volume of 40 mi withthe same buffer.

c. Assay 40 g of hydrocortisone was dissolved in 4 m] ethylene glycol followed by the gradual addition of 4 m] water 10 and 2 mi of 0.25 M tris pH = 7.8. The substrate was then transferred into a 250 mi baffled Erienmeyerflask containing the abovementioned PAAH-bead entrapped cells. 0.05 M tris buffer, pH = 7.8was added to bring the final volume to 50 m]. The flask was then incubated in a gyratory shaker (30'C, 150 rpm).

The substrate and product were extracted with CH2C12 and analyzed by HPLC. Under these conditions, 50% conversion of hydrocortisone to prednisolone was observed within 3 hours; (see Figure 4). 15 Example 3

Beads containing oil droplets:

(1) By applying liquid paraffin oil (Cat. No. 29437, BIDH, Poole, England) at a flow rate of 4.5 mi/min through tubeA and 3% (wlv) sodium aiginate solution (BDH) ata flow rate of 12 mi/min through tube B, and 20 nitrogen at a flow rate of 6 1/min through tube C, and 2% (wlv) CaC12 in tap water, paraffin oil droplets en capsulated in a Ca-alginate shell were obtained ' (2) In a similarway, by applying corn oil through A (0.4 milmin) 3% sodium alginate through B (2.0 mi/min) and nitrogen through C (10 Ilmin), corn oil droplets encapsulated within Ca-alginated shell were obtained. In a similar way, p-carotene solution in corn oil was encapsulated within Caaiginate shell. 25 Example 4

Preparation of controlledrelease formulation forsystemic insecticides By applying "Cyolan" (2-(Diethoxyphosphinylimino)-1,3-dithiolane). (American Cyanamid Co., USA) 10 mglml solution in corn oil-l-clodecyl alcohol (Cat. No. 28276, BDH) 40:60 (v/v) solution (at40'C) at a flow rate 30 of 0.4 milmin through A, and 3% sodium alginate solution through B (2.0 milmin) and nitrogen through C (10 1/min), solid Cyolan solution in corn-oil-dodecanol, encapsulated within an alginate shell could be obtained (in 3% CaC12 solution in tap water).

Following 1 hour incubation for hardening in CaC12 solution the beads were transferred into methanol for 5 min and then into hexane for 1 min. The beads were separated by filtration and 8 gr of beads (WW) were 35 placed in 50 mi distilled water in a glass beaker. Samples were withdrawn daily, followed by washing of the beads with 20 mi of water and reincubation in fresh 50 m] distilled water. Cyolan content in waterwas determined by HPLC. Samples (5 0) were assayed on a 12.5 X 0.4cm Lichrochart RP-8 (4 L) column (Merck, Darmstadt, FRG) employing methanol-water (60:40) as mobile phase at a rate of 0.6 mi/min (retention time: 4 min). Standards and samples were detected at 245 nm. Cyolan release profile underthese conditions is 40 shown in Figure 5.

Claims (11)

1. A process for the production of millimeter-size alginate beads comprising an alginate shell and a core 45 of a biologically active material or of an oily substance, which comprises simultaneously supplying to a common coaxial outlet port an inner stream of core material, a median stream of an alginate solution and an outer gas stream to form drops, and dropping the said drops into a solution adapted to coagulate the alginate and leaving the beads in said solution to harden the shell.

2. A process according to Claim 1, wherein the core material is a suspension of cells, organelles orbio- 50 logically active particulate material in a solution of a prepolymer which is subsequently polymerized.

3. A process according to Claim 2, wherein the prepolymer is polyacrylamide-hydrazide (PAAH), which is subsequently cross-linked by means of glyoxal.

4. A process according to anyone of the preceding claims wherein the biologically active material is selected from bacteriajungi, yeast cells, plant cells, enzymes and antibodies. 55

5. A process according to anyone of the preceding claims wherein the active material is entrapped in a polymer matrix and the alginate shell is subsequently removed.

6. A process for the production of beads of millimeter size-range of essentially uniform size, comprising a core of biologically active material in a suspension medium or in a polymer matrix confined in an alginate shell, substantially as hereinbefore described. 60

7. Beads of essentially uniform size in the millimeter range, containing a core of biologically active mat erial and an outer alginate shell, whenever obtained by a process as claimed in any one of the preceding claims.

8. Millimeter-size alginate shell beads containing a core of a suspension of a biologically active protein or cells or of such material entrapped in a polymer matrix which does not impair the biological activity of such 65 GB 2 192 171 A 5 materials, substantially as hereinbefore described.

9. A device forthe production of millimeter-size beads comprising an alginate shell and a liquid or gel form core of biologically active material or of an oily substance, which device comprises three fluid conduits with individually adjustable flow rates means for adjusting the distance of these respective each other at a common coaxial outlet port, the inner conduit serving as conduit forthe material forming the core content, 5 the second conduit being that of the alginate solution and the third being a gas conduit.

10. A device according to Claim 9, wherein the conduits are in the form of three coaxial tubular members having a downwardly pointing common outlet.

11. A device for the production of alginate beads defined in Claim 10, substantially as hereinbefore des- cribed with reference to Figure 1. 10 Printed for Her Majesty's Stationery Office byCroydon Printing Company (U K) Ltd, 11187, D8991685. Published byThe Patent Office, 25 Southampton Buildings, LondonWC2AlAY, from which copies maybe obtained.