Per
`
`WORLD INTELLECTUAL PROPERTY ORGANIZATION
`International Bureau
`
`INTERNATIONAL APPLICATION PUBLISHED UNDER THE PATENT COOPERATION TREATY (PC1)
`wo 90/13780
`(51) International Patent Oassification 5 :
`F26B 5/06, A61K 9/16
`15 November.I990 (15.11.90)
`
`Al
`
`(11) International Publication Number:
`
`(43) International Publication Date:
`
`(21) International Application Number:
`
`PCT/US90/02425
`
`(22) International Filing Date:
`
`I May 1990 (01.05.90)
`
`(30) Priority data:
`346,143
`
`I May 1989 (01.05.89)
`
`us
`
`.. (71)Applicant: ENZYTECH, INC. [US/US]; 763D Concord
`Avenue, Cambridge, MA 02138 (US).
`
`(72) Inventors: GOMBOTZ, Wayne, R. ; 492 Marrett Road,
`Lexington, MA 02173 (US). HEALY, Michael, S. ; 185
`Walnut Street, East Bridgwater, MA 02333
`(US).
`BROWN, Larry, R.; 38 Cummings Road, Newton, MA
`02159-1753 (US).
`(74)Agents: PABST, Patrea, L. et al.; Kilpatrick & Cody, 100
`Peachtree Street, Suite 3100, Atlanta, GA 30303 (US).
`
`(81) Designated States: AT (European patent), AU, BE (Euro-
`+ pean patent), CA, CH (European patent), DE (Euro-
`pean patent), DK (European patent), ES (European pa-
`tent), FR (European patent), GB (European patent), IT
`(European patent), JP, LU (European patent), NL (Eu-
`ropean patent), SE (European patent).
`
`Published
`With international search report .
`Before the expiration of the time limit for amending the
`claims and to be republished in the event of the receipt of
`amendments.
`
`(54) Title: VERY LOW TEMPERATURE CASTING OF CONTROLLED RELEASE MICROSPHERES
`
`(57) Abstract
`
`A process for preparing microspheres using very cold temperatures to freeze polymer-biologically active agent mixtures in-
`to polymeric microspheres with very high retention of biological activity and material. Polymer is dissolved in a solvent together
`with an active agent that can be either dissolved in the solvent or dispersed in the solvent in the form of microparticles. The po-
`lymer/active agent mixture is atomized into a vessel containing a liquid non-solvent, alone or frozen and overlayered with a liqui-
`fied gas, at a temperature below the freezing point of the polymer/ active agent solution. The cold liquified gas or liquid immedi-
`ately freezes the polymer droplets. As the droplets and non-solvent for the polymer is warmed, the solvent in the droplets thaws
`and is extracted into the non-solvent, resulting in hardened microspheres .
`
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`

`DESIGNATIONS OF "DE"
`
`Until further notice, any designation of "DE" in any international application
`whose international filing date is prior to October 3, 1990, shall have effect in the
`territory of the Federal Republic of Germany with the exception of the territory of the
`former German Democratic Republic.
`
`/
`
`FOR THE PURPOSES OF INFORMATION ONLY
`
`Codes used to identify States party to the Per on the front pages of pamphlets publishing international
`application!\ under the PCr.
`
`AT
`AU
`88
`BE
`BF
`8G
`8J
`8R
`CA
`CF
`CG
`CH
`CM
`DE
`DK
`
`Austria
`Australia
`Barbados
`Belgium
`Burkina Fasso
`Bulgaria
`Benin
`BrwJI
`Canada
`Central African Republic
`Congo
`Switzerland
`Cameroon
`Germany, Federal Republic of
`Denmark
`
`Spain
`ES
`Finland
`Fl
`France
`FR
`GA Gabon
`G8 United Kingdom
`GR Greece
`HU
`Hungary
`Italy
`IT
`Japan
`JP
`KP
`Democratic People's Republic
`of Koreif
`Republic of Korea
`Liechtenstein
`Sri Lanka
`Luxembourg
`
`KR
`Ll
`LK
`LU
`
`MC Monaco
`MG Madagascar
`ML Mali
`MR Mauritania
`MW Malawi
`NL
`Netherlands
`Norway
`NO
`RO
`Romania
`Sudan
`SD
`Sweden
`SE
`Senegal
`SN
`su
`Soviet Union
`TD
`Chad
`TG
`Togo
`us
`United States of America
`
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`PCf /US90/02425
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`VERY LOW TEMPERATURE CASTING OF
`CONTROLLED RELEASE MICROSPHERES
`
`Background of the Invention
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`This invention generally relates to processes for making
`polymeric microspheres for controlled release of substances.
`A variety of techniques are known by which active agents
`can be incorporated into polymeric microspheres. An example is
`spray drying. In spray drying, the polymer and active agent are mixed
`together in a solvent for the polymer, then the solvent is evaporated
`by spraying the solution, leaving polymeric droplets containing the
`active agent. Spray drying is reviewed in detail by K. Masters in
`"Spray Drying Handbook" (John Wiley & Sons, New York 1984); and
`Patrick B. Deasy in "Microencapsulation and Related Drug Processes"
`(Marcel Dekker, Inc., New York 1984). Spray drying works well for
`15 many agents but may inactivate some materials, particularly
`biologically active proteins, due to the heat generated during the
`process. In addition, considerable amounts of the material can be lost
`during the spray drying process due to sticking of the polymer to the
`large surface area on the sides of the chamber.
`Solvent evaporation techniques have also been used to
`form microspheres. These techniques involve dissolving the polymer
`in an organic solvent which contains either dissolved or dispersed
`active agent. The polymer/active agent solution is then added to an
`agitated continuous phase which is usually aqueous and immiscible
`with the polymer/active agent. Emulsifiers can be included in the
`aqueous phase to stabilize the oil~in~water emulsion. The organic
`solvent is then evaporated over a period of several hours or more,
`ther~by depositing the polymer around the core material. Solvent can
`be removed from the microspheres in a single step, as described in
`U.S. Pat. No. 3,737,337 and U.S. Pat. No. 3,523,906, or in U.S. Pat.
`No. 3,691,090 (under reduced pressure), or by the application of heat,
`as shown in U.S. Pat. No. 3,891,570. A two-step technique is
`described in U.S. Pat. No. 4,389,330. ~reeze drying has also been
`
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`used to remove the solvent from microspheres, as reported by Sato, et
`al, in "Porous Biodegradable Microspheres for Controlled Drug
`Delivery. I. Assessment of Processing Conditions and Solvent
`Removal Techniques," Pharmaceutical Research 5, 21-30 (1988).
`Solvent evaporation works reasonably well for hydrophobic
`drugs but the amount of incorporated material is usually lower than
`the theoretical values due to loss of drug to the aqueous phase, as
`reported by Benita, et al., in "Characterization of Drug Loaded
`Poly(d,l-lactide) Microspheres," J. Pharm. Sci. 73, 1721-1724 (1984). If
`10 water soluble active agents are used, such as proteins, a much more
`significant loss of material can occur.
`Phase separation techniques have also been used to form
`microspheres. These techniques involve the formation of a water-in-
`oil or an oil-in-water emulsion. The polymer is precipitated from the
`continuous phase onto the active agent by a change in temperature,
`pH, ionic strength or the addition of precipitants. For example, U.S.
`Pat. No. 4,675,189 describes the formation of poly(lactic-co-glycolic
`acid) microspheres containing hormonally active polypeptides. The
`polypeptide is first dissolved in the aqueous phase of a water-in-oil
`emulsion. Polymer is then precipitated around the aqueous droplets
`by addition of a non-solvent for the polymer such as silicon oil. The
`final product, as with most phase separation techniques, is in the form
`of a microcapsule. Microcapsules contain a core material surrounded
`by a polymer membrane capsule. The release kinetics of active agents
`from these devices can be difficult to control.
`Although these phase separation techniques result in the
`formation of microspheres containing active agents, active agent is
`often lost during the solvent extraction process. In addition, as with
`spray drying, biologically active proteins may be denatured during the
`process.
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`Cold temperatures have also been employed in certain
`steps of the microsphere formation process. For example, U.S. Pat.
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`No. 4,166,800 describes the use of temperatures between -40"C and-
`100"C along with a phase separation agent to stabilize the polymeric
`microspheres during phase separation.
`A method using low temperature to form microspheres
`from an ethylene-vinyl acetate co-polymer, but not other polymers
`such as poly(lactic acid), is reported by Sefton, et al., in "Ethylene-
`Vinyl Acetate Copolymer Microspheres for Controlled Release of
`Macromolecules," J. Pharm. Sci. 73, 1859-1861 (1984). Polymer is
`dissolved in a dispersion of albumin in methylene chloride, added
`dropwise through a syringe into ethanol in a dry ice-ethanol bath (-
`78oC), where, upon hitting the cold ethanol, the drops gel and sink to
`the bottom of the container. After five to ten minutes the container is
`removed from the dry ice bath and allowed to warm to room
`temperature to extract the solvent from the microspheres. This
`system, however, does not work with other polymers such as
`poly(lactic acid).
`Most of these methods result in the loss of some of the
`material being incorporated, and/or its activity. Many are very
`specific for a particular type of polymer, in part because the majority
`of these techniques rely on the use of a two phase system to form the
`microspheres, which are also very specific for each polymer type.
`It is therefore an object of the present invention to provide
`a method for making microspheres containing biologically active
`materials with very little loss of activity and material.
`It is a further object of the present invention to provide a
`method for making microspheres which can be used with a broad
`, range of polymers.
`It is a still further object of the present invention to
`provide such a process which is relatively quick, simple, and
`inexpensive.
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`Summary of the Invention
`
`A process for preparing microspheres using very cold
`temperatures to freeze polymer-biologically active agent mixtures into
`polymeric microspheres with very high retention of biological activity
`and material.
`Polymer is dissolved in a solvent together with an active
`agent that can be either dissolved in the solvent or dispersed in the
`solvent in the form of microparticles. The polymer I active agent
`mixture is atomized into a vessel containing a liquid non-solvent,
`alone or frozen and overlayed with a liquified gas, at a temperature
`below the freezing point of the polymer I active agent solution. When
`the combination with the liquified gas is used, the atomized droplets
`freeze into microspheres upon contacting the cold liquified gas, then
`sink onto the frozen non-solvent layer. The frozen non-solvent is then
`thawed. As the non-solvent thaws, the microspheres which are still
`frozen sink into the liquid non-solvent. The solvent in the
`microspheres then thaws and is slowly extracted into the non-solvent,
`resulting in hardened microspheres containing active agent either as a
`homogeneous mixture of the polymer and the active agent or as a
`heterogeneous two phase system of discrete zones of polymer and
`active agent.
`If a cold solvent is used alone, the atomized droplets freeze
`upon contacting the solvent, and sink to the bottom of the vessel. As
`the non-solvent for the polymer is warmed, the solvent in the
`microspheres thaws and is extracted into the non-solvent, resulting in
`hardened microspheres.
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`Brief Description of the Drawings
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`Figure 1 is a schematic of the process of the present
`invention for making microspheres containing an agent to be
`incorporated using a liquified gas, frozen non-solvent system.
`Figure 2 a schematic of the freezing and solvent extraction
`steps of Figure 1 in detail.
`Figure 3 is a graph of temperature of the ethanol in the
`process of the present invention as described in example 1 versus time
`in minutes: (a) as the liquified nitrogen is evaporated; (b) as the
`ethanol melts; (c) as the ethanol warms and the solvent in the
`microspheres begins to melt; and (d) as the temperature of the
`ethanol and microspheres begins to stabilize.
`Figure 4 is a graph of the release of active superoxide
`dismutase (SOD) from poly(L-lactide) microspheres (p.g SOD
`released/mg SOD loaded microspheres) over time (days) at three
`loadings: 5% SOD, 10% SOD, and 20% SOD.
`Figure 5 is a schematic comparing the microspheres
`produced by varying the process of Figure 1: (a) using cold ethanol (-
`78oC) as the non-solvent without first freezing the polymer-agent
`solution; (b) using room temperature ethanol as the non-solvent
`without first freezing the polymer-agent solution; (c) using cold hexane
`as the non-solvent without first freezing the polymer-agent solution;
`and (d) using the method of Figure 1.
`
`Detailed Description of the Invention
`
`Microspheres made according to the method described
`below can be formed in a size suitable for injection through a 26-
`gauge needle (less than 50 micrometers in diameter) and can contain
`from less than 0.01% by weight up to approximately 50% by weight
`active agent. Active agents_which can be incorporated into the
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`microspheres include peptides, proteins, carbohydrates,
`polysaccharides, nucleic acids, lipids, steroids, and organic and
`inorganic drugs which are either hydrophobic or hydrophilic. Other
`excipients can also be entrapped in the microspheres, including, for
`example, dextran, poly( ethylene glycol), glucose and various salts.
`Polymers that can be used to form the microspheres
`include bioerodible polymers such as poly(lactic acid), poly(lactic-co-
`glycolic acid), poly( caprolactone ), polycarbonates, polyamides,
`polyanhydrides, polyamino acids, polyortho esters, polyacetals,
`polycyanoacrylates and degradable polyurethanes, and non-erodible
`polym~rs such as polyacrylates, ethylene-vinyl acetate copolymers and
`other acyl substituted cellulose acetates and derivatives thereof, non-
`erodible polyurethanes, polystyrenes, polyvinyl chloride, polyvinyl
`fluoride, poly(vinyl imidazole), chlorosulphonated polyolefins, and
`polyethylene oxide. Almost any type of polymer can be used provided
`the appropriate solvent and non-solvent are found which have the
`desired melting points. In general, a polymer solution is prepared
`containing between 1% polymer and 20% polymer, preferably 5-10%
`polymer.
`
`There are two principal embodiments of the system for
`making microspheres: a combination cold liquified gas - frozen non-
`solvent system and a cold non-solvent system, wherein "cold" is
`defined as a temperature which will immediately freeze the polymer
`and "non-solvent" is a liquid in which the polymer is not soluble.
`The process is shown schematically in Figure 1 for a
`liquified gas-frozen solvent system. Polymer 10 and agent to be
`incorporated 12 in solution 14 are atomized 16 using an ultrasonic
`device 18 into a cold liquified gas 20. The microspheres 22 are
`immediately frozen by the liquified gas 20. The non-solvent 24 thaws
`and the frozen spheres 22 sink into the very cold non-solvent 24. The
`non-solvent 24 extracts the solvent 14 from the spheres 22 as they
`thaw, leaving microspheres 26 containing the incorporated agent.
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`The liquified gas 20 can be liquid argon (-185.6°C), liquid
`nitrogen (-195.8°C), liquid oxygen (-182.9oC) or any other gas that
`results in the immediate freezing of the atomized droplets into frozen
`spheres 22.
`Alternatively, a cold non-solvent for the polymer can be
`substituted for the combination of liquified gas-frozen non-solvent,
`provided the temperature of the non-solvent is below the freezing
`temperature of the polymer/ active agent solution.
`In both embodiments, it is important that the solution or
`suspension of polymer and active agent freeze immediately upon
`contacting the cold liquid, and then be slowly thawed and the polymer
`solvent extracted from the microspheres, leaving behind the polymer
`and active agent.
`Figure 2 is a schematic of the freezing and solvent
`extraction steps of the process depicted in Figure 1. In Figure 2a, the
`atomized droplets 16 freeze when they contact the liquified gas 20
`(liquid nitrogen), forming frozen spheres 22. In Figure 2b, these sink
`to the surface 28 of the frozen non-solvent (ethanol) 24. In Figure 2c,
`the liquid gas 20 is evaporated and, in Figure 2d, the spheres 22 begin
`to sink into the non-solvent 24 as the non-solvent thaws. In Figure 2e,
`the solvent 14 in the spheres 22 is extracted into the non-solvent 24 to
`form microspheres 26 containing the polymer and the active agent. In
`Figure 2f, other non-solvents such as hexane are added to the non-
`solvent (ethanol) to increase the rate of solvent extraction from
`certain polymers, where appropriate, for example, when spheres are
`formed of poly(lactic-co-glycolic acid) polymers.
`The thawing rate is dependent on the choice of solvents
`and non-solvents, and the ambient temperature at which the system is
`thawed. It is important to select a solvent for the polymer having a
`higher melting point than the non-solvent for the polymer so that the
`non-solvent melts first, allowing the frozen microspheres to sink into
`the liquid where they later-thaw. If a cold liquid non-solvent system
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`for making the polymeric microspheres is used, the microspheres will
`sink immediately into the non-solvent. As the solvent in the
`microsphere thaws, it is extracted into the non-solvent. The solvent
`for the polymer and the non-solvent for the polymer must be miscible
`to allow extraction of the solvent from the microspheres. Table 1
`shows some exemplary polymer/solvent/non-solvent systems that can
`be used in this process along with their melting points.
`An advantage of this method is that surface active agents
`are not required in most cases, as in most processes for making
`10 microspheres involving formation of an emulsion, such as phase
`separation. There are many drug delivery applications where surface
`active agents, or emulsifiers, interfere with release or cause an
`undesirable reaction. However, when desired, other materials can be
`incorporated into the microspheres with the biologically active agents.
`Examples of these materials are salts, metals, sugars, surface active
`agents, acids, bases, stabilizers, and release enhancing agents. Surface
`active agents may also be added to the non-solvent during extraction
`of the solvent to reduce the possibility of aggregation of the
`microspheres.
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`Table 1: Polymers and Appropriate Solvents and Non-Solvents
`Systems, with Solvent and Non-Solvent Melting Points (in
`oc)
`POLYMER
`Poly(lactic
`acid)
`
`SOLVENT
`Methylene
`Chloride (-95.1)
`Chloroform ( -63.5)
`
`NON-SOLVENT
`Ethanol (-114.5)
`
`Methanol ( -97 .5)
`
`Poly(lactic-
`co-glycolic
`acid)
`
`Poly( capro-
`lactone)
`
`Poly (vinyl
`alcohol)
`
`Ethylene-
`vinyl
`acetate
`
`Ethyl
`1\cetate (-83.6)
`1\cetone (-95.4)
`
`Methylene
`Chloride (-95.1)
`
`Methylene
`Chloride (-95.1)
`
`Ethanol (-114.5)
`
`Ethyl ether
`(-116.3)
`Pentane (-130)
`Isopentane (-160)
`
`Ethanol (-114.5)
`
`Water (0)
`
`Acetone (-95.4)
`
`Methylene
`Chloride ( -95 .0)
`
`Ethanol (-114.5)
`
`The polymer/ active agent/ solvent mixture can be sprayed
`into the cold liquid, either the liquified gas or the cold non-solvent,
`using a variety of devices which can be used to form small droplets,
`including sonic nozzles, pressure nozzles, pneumatic nozzles and rotary
`atomizers.
`
`1\ wide range of sizes of microspheres can be made by
`varying the droplet size, for example, by changing the nozzle diameter.
`If very large spheres are desired, the spheres can be extruded through
`a syringe directly into the cold liquid. Increasing the inherent viscosity
`of the polymer solution can also result in an increasing microspheres
`size. The size of the spheres produced by this process can range from
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`greater than 1000 down to 5 micrometers in diameter. A preferred
`size range for injectable microspheres is from 30 to 50 micrometers in
`diameter. The microspheres made by this technique are spherical in
`shape, without irregularities.
`The microspheres made by this process can be either
`homogeneous or heterogeneous mixtures of the polymer and the
`active agent. Homogeneous mixtures are produced when the active
`agent and the polymer are both soluble in the solvent, as in the case
`of certain hydrophobic drugs such as steroids. Heterogeneous two
`phase systems having discrete zones of polymer and active agent are
`prod11:ced when the active agent is not soluble in the polymer/solvent,
`and is introduced as a suspension in the polymer I solvent solution, as
`with hydrophilic compounds such as proteins in methylene chloride.
`The present invention is further described by the following
`non-limiting examples which. demonstrate that the process is
`applicable to a wide range of polymers, solvents, and substances to be
`incorporated within the microspheres.
`Preparation of poly(L-Iactic acid) microspheres
`Example 1:
`containing SOD.
`0.7 g of poly(L-lactic acid) (Polysciences, Inc., Warrington,
`PA, mw 2000) was dissolved in 14.0 m1 of methylene chloride to
`produce a 5% (w /v) polymer solution. 3.36 m1 of this polymer
`solution was added to 42 mg of the enzyme superoxide dismutase
`(SOD) (American International Chemicals, Inc., Natick MA), to yield
`a 20% by weight superoxide dismutase (SOD) in 5% polymer solution.
`Similar preparations were made containing 10% and 5% SOD. The
`mixture was sonicated using a VirSonic 300 Ultrasonic Probe, Virtis
`Company, Inc., Gardiner, NY, to decrease the size of the protein
`particles, using the method of co-pending U.S. Serial No. 07/345,684
`entitled "Process for Producing Small Particles of Biologically Active
`Molecules" filed May 1, 1989 by Wayne R. Gombotz, MichaelS.
`Healy, Larry R. Brown, and Henry E. Auer, and then placed in a 5 m1
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`gas tight syringe. A 150 ml amount of 100% ethanol was added to a 8
`x 6 x 1.5 in poly(propylene) tray. To this was added 300 ml of liquid
`nitrogen ( -195.8oC) which resulted in a frozen layer of ethanol
`covered by a layer of liquid nitrogen. The polymer /protein mixture
`5 was extruded from the syringe via a syringe pump at a rate of 6.75
`ml/min, into an ultrasonic nozzle (Model 8700-60MS Microspray
`Atomic Nozzle, SonoTek Corp., Poughkeepsie, NY) that was placed
`over the liquid nitrogen/frozen ethanol solution. The nozzle atomized
`the mixture into droplets which froze upon contacting the liquid
`nitrogen and formed microspheres which then sank onto the frozen
`ethanol.
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`The container was placed in a -800C freezer where the
`liquid nitrogen evaporated and the ethanol slowly melted over time.
`At (a), the ethanol is still frozen. At (b), the microspheres are
`beginning to sink into the ethanol as it melts. Once the temperature
`reaches -95.1oC, the methylene chloride is extracted from the
`polymer /protein spheres into the ethanol ( c and d). After three days
`the container was removed from the freezer and the microspheres
`were filtered from the solvent. They were then dried in a vacuum
`desiccator for 24 hrs.
`Under light microscopy, the microspheres were round and
`had diameters ranging from 30 to 50 micrometers. Scanning electron
`microscopy of microsphere cross sections showed the spheres to be
`porous.
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`The dried microspheres were suspended in a phosphate
`buffered solution, pH 7.4, and the release of the superoxide dismutase
`, was ~onitored. Active protein was released over a time period of 38
`days, as shown in Figure 4. The specific activity of the SOD released
`was 90% of the starting specific activity. Release was compared for
`three different loadings: 5%, 10% and 20%. The 5% loaded
`microspheres released the least amount of enzyme, with a greater
`amount being released from the 10% and 20% loaded microspheres,
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`approximately 5-6 micrograms SOD /mg of microsphere for both
`loadings.
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`The microspheres containing 20% SOD (60 mg) were
`suspended in a 1.5 m1 aqueous solution containing 5.5 mg of
`carboxymethylcellulose, 75 mg of D-mannitol and 1.5 mg of
`polysorbate 80. The microspheres were then injected into a rat
`through a 26-gauge needle at a concentration of 40 mg/ml. No
`clogging of the needle occurred demonstrating that these microspheres
`can be used for injection through a narrow gauge needle.
`Example 2:
`Preparation of poly(DL-Iactide-co-glycolide) (50:50)
`microspheres containing SOD.
`The procedure in Example 1 was repeated using poly(DL-
`lactide-co-glycolide) (50:50) Resomer L-104, (Boehringer Ingelhiem,
`W.Germany) to form the microspheres. After the microspheres were
`extracted for three days in the cold ethanol at -800C, 100 m1 of
`hexane was added and the extraction was continued for another 24
`hrs. The microspheres were then filtered and dried in a vacuum
`desiccator. Results of the size analysis and SEM observations were
`similar to those in example 1.
`Example 3:
`Preparation of Poly(DL-Iactide-co-glycolide) (50:50)
`microspheres containing HRP.
`The procedure of example 1 was repeated using Poly(DL-
`lactide-co-glycolide) (50:50) in methylene chloride to form
`microspheres containing horse radish peroxidase (HRP) (Sigma
`Chemical Co.) extracted into ethanol and hexane. Results were
`similar to those in example 1.
`Example 4:
`Preparation of Poly(L-Iactic acid) 2000
`microspheres containing mitomycin C.
`Poly(L-lactic acid) 2000 in methylene chloride with 5% by
`30 weight mitomycin C was sprayed into ethanol. Mitomycin C is a 334
`dalton chemotherapeutic agent. Results of the size analysis and SEM
`were similar to those in ex~ple 1. This example demonstrates that
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`molecules other than proteins can be incorporated into the
`microspheres.
`Example 5:
`
`Preparation of Poly(L-lactic acid) 2000
`microspheres containing etoposide.
`Etoposide is an antineoplastic agent that is soluble in
`organic solvents. Poly(L-lactic acid) 2000 was dissolved in methylene
`chloride with 40% by weight etoposide and sprayed into ethanol. The
`resulting microspheres were 30 to 50 micrometer in diameter.
`Continuous release of etopodsid was measured over a one week
`period. The results demonstrate that microspheres can be made from
`solutions containing both dissolved polymer and dissolved active agent.
`Example 6:
`Preparation of microspheres from a blend of poly(L-
`lactic acid) and poly(DL-lactic-co-glycolic acid)
`containing hemoglobin.
`A (1:1) blend of 5% poly(L-lactic acid) and 5% poly(DL-
`lactic-co-glycolic acid) with bovine hemoglobin (Sigma Chemical Co.)
`suspended in methylene chloride was sprayed into ethyl ether. Results
`of size analysis and SEM were similar to those in example 1,
`demonstrating that the process is applicable to microspheres formed
`from polymer blends. Release of the hemoglobin from the
`microsphere into physiological buffer was achieved over a two month
`period.
`Example 7:
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`Preparation of microspheres from Poly(L-lactic
`acid) 2000 containing hemoglobin using liquid
`Argon.
`Hemoglobin suspended in a solution of poly(L-lactic acid)
`1 2000. in methylene chloride was sprayed into liquid argon and frozen
`ethanol. Under the light microscope, the resulting dried spheres were
`seen to contain a heterogeneous dispersion of small hemoglobin
`particles distributed throughout the polymer matrix. This example
`demonstrates the applicability of other gases in the process.
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`Examples 8 through 12 describe the preparation of
`microspheres from different polymer solutions, demonstrating the
`variety of different polymers, solvents and non-solvents that can be
`used in the process of the present invention.
`Example 8;
`Preparation of polyvinyl alcohol microspheres.
`A 5% by weight solution of polyvinyl alcohol (Elvanol, du
`Pont de Nemour & Co., Wilmington, DE) was dissolved in water.
`This was atomized through an ultrasonic nozzle into liquid nitrogen
`covering a layer of frozen acetone. After thawing for three days the
`30 to 50 micrometer diameter microspheres were filtered and dried.
`Example 9:
`Preparation of Poly(caprolactone) microspheres.
`A 5% by weight solution of poly(caprolactone) (Sigma
`Chemical Co.) was dissolved in methylene chloride. This was
`atomized through an ultrasonic nozzle into liquid nitrogen covering a
`layer of frozen ethanol. After thawing for three days the microspheres
`were filtered and dried.
`Example 10:
`Preparation of ethylene vinyl acetate copolymer
`micro spheres.
`A 5% by weight solution of ethylene-vinyl acetate
`copolymer (Vynathene, USI Chemicals, Cincinnati, OH) was dissolved
`in methylene chloride. This was atomized through an ultrasonic
`nozzle into liquid nitrogen covering a layer of frozen ethanol. After
`thawing for three days the microspheres were filtered and dried.
`Example 11;
`Preparation of poly(lactic acid) 2000 microsplteres
`in a cold liquid solvent.
`A 5% by weight solution of poly(l-lactic acid) was dissolved
`in m~thylene chloride. This was atomized through an ultrasonic
`nozzle into cold isopentane (-141.2°C). The droplets froze into
`spheres upon contact with the cold liquid and sank to the bottom of
`the container. The microspheres were placed in an -800C freezer for
`three days to extract the solvent. They were then filtered and dried.
`This example illustrates tha~ a cold non-solvent for the polymer can be
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`used, if its temperature is below the melting point of the
`polymer /solvent solution.
`Example 12:
`Demonstration of Criticality of the temperature.
`Experiments were conducted to determine the necessity of
`using a liquid that has a temperature below the freezing point of the
`polymer/solvent solution. A 5% solution of poly(L-lactic acid) was
`prepared in methylene chloride. This solution was atomized into six
`different systems (a) cold ethanol (-80"C); (b) room temperature
`ethanol (23°C); (c) cold hexane (-80"C); (d) liquid nitrogen layered
`over frozen ethanol (-195.8oC); (e) room temperature hexane (23oC);
`and (f) cold isopentane (-80oC). The results of systems (a) through
`(e) are shown in Figure 5. (In (a), atomized droplets of polymer were
`sprayed into cold ethanol ( -80"C). Only teardrop shaped polymer
`particles and polymer fibers were produced. In (b), atomized polymer
`droplets were sprayed onto room temperature ethanol. Although
`spheres formed initially, these spheres gradually took on amorphous
`shapes and some of them fused. In (c), atomized droplets were
`sprayed onto cold hexane ( -80°C). Room temperature hexane was
`also used (e). In both cases, although spheres formed initially, these
`fused to form a polymer film. Similar results were obtained spraying
`into isopentane ( -80"C) (f).
`In (d), the atomized dro