WO2005025543A2

WO2005025543A2 - Polymer-based sustained release device and method for preparation

Info

Publication number: WO2005025543A2
Application number: PCT/US2004/029645
Authority: WO
Inventors: Gregory C. Troiano; Tina Paszyc; Warren E. Jaworowicz; Josiah Brown
Original assignee: Alkermes Controlled Therapeutics, Inc.
Priority date: 2003-09-08
Filing date: 2004-09-08
Publication date: 2005-03-24
Also published as: WO2005025543A3

Abstract

Methods for preparing a polymer-based sustained release device including a biocompatible polymer having incorporated therein a biologically active agent are described. In one embodiment, the method of preparing a polymer-based sustained release device comprises the steps of (a) exchanging a continuous medium component of a disperse system, the disperse system including a biologically active agent as a dispersed entity, with an organic liquid, thereby forming a first mixture that includes the biologically active agent and the organic liquid; (b) combining a biocompatible polymer with the first mixture, thereby forming a second mixture that includes the biologically active agent, the organic liquid, and the biocompatible polymer; and (c) separating the organic liquid from the second mixture, thereby forming the polymer-based sustained release device. In one embodiment, the continuous medium component of the disperse system is exchanged with the organic liquid using diafiltration, for example, diafiltration using tangential flow filtration.

Description

POLYMER-BASED SUSTAINED RELEASE DEVICE AND METHOD FOR PREPARATION

RELATED APPLICATION This application claims the benefit of U.S. Provisional Application No. 60/501,051, filed September 8, 2003, the entire teachings of which are incoφorated herein by reference.

BACKGROUND OF THE INVENTION Many illnesses or conditions require administration of a constant or sustained level of a medicament or biologically active agent to provide the desired prophylactic or therapeutic effect. This can be accomplished through a multiple dosing regimen or by employing a system that releases the medicament in a sustained fashion. Attempts to sustain medication levels include the use of biodegradable materials, such as polymeric matrices, containing the medicament. The use of these matrices, for example, in the form of microparticles or microcarriers, provides sustained release of medicaments by utilizing the inherent biodegradability ofthe polymer. The ability to provide a sustained level of medicament can result in improved patient compliance and therapeutic effects. Certain methods of fabricating polymer-based sustained release devices include the steps of dissolving a polymer in a solvent, adding to the polymer solution the active agent to be incorporated and removing the solvent from the mixture, thereby forming a matrix ofthe polymer with the active agent distributed throughout the matrix. Many of these methods often include a step wherein the active agent is formulated, prior to mixing with the polymer solution (i.e., preformulated), in order to maximize process efficiency and/or product characteristics. For example, the active agent can be formulated prior to mixing with the polymer solution to achieve a desired particle size, to form a stabilized complex with a suitable stabilizing agent and or to remove excipients not desired in the resulting sustained release device. Formulating ofthe active agent prior to mixing with the polymer solution often requires that the active agent be isolated in a form that is compatible with the remaining processing steps. For example, formulation ofthe active agent can result in the active agent being present in a solvent which is not suitable for use in the processing ofthe sustained release device. When this is the case, the preformulated active agent must be isolated (e.g., the solvent removed) prior to formation ofthe sustained release device which can result in a significantly more complex production process, thereby increasing manufacturing time and cost. In view ofthe above, improved methods for the preparation of polymer- based sustained release devices are needed.

SUMMARY OF THE INVENTION The present invention relates to methods and apparatus for preparing a polymer-based sustained release device including a biocompatible polymer having incoφorated therein a biologically active agent. The polymer-based sustained release device is also referred to herein as a "polymer/biologically active agent matrix." The biologically active agent can be a therapeutic, prophylactic or diagnostic agent, also referred to herein as a "drug" or an "agent." The polymer- based sustained release device can be used to deliver a biologically active agent to a subject in need thereof in a sustained manner. The present invention is directed to a method of forming a polymer-based sustained release device, comprising the steps of (a) exchanging a continuous medium component of a disperse system, the disperse system including a biologically active agent as a dispersed entity, with an organic liquid, thereby forming a first mixture that includes the biologically active agent and the organic liquid; (b) combining a biocompatible polymer with the first mixture, thereby forming a second mixture that includes the biologically active agent, the organic liquid, and the biocompatible polymer; and (c) separating the organic liquid from the second mixture, thereby forming the polymer-based sustained release device. In one embodiment, the continuous medium component ofthe disperse system is exchanged with the organic liquid using diafiltration, for example, diafiltration using tangential flow filtration. In a particular embodiment, the method further includes the step of forming droplets, e.g., microdroplets, ofthe second mixture prior to separating the organic liquid from the second mixture. Further, the method can include freezing the droplets prior to separating the organic liquid from the second mixture. In a specific embodiment, wherein droplets are formed and frozen, the organic liquid can be separated from the second mixture by an evaporation and/or extraction process. For example, in one embodiment the organic liquid is extracted from frozen droplets into a non-solvent of the biocompatible polymer. Phase separation and/or emulsion formation are also suitable methods for removing the organic liquid. For example, the method for forming a polymer-based sustained release device can further include the step of forming an emulsion that includes the second mixture prior to separating the organic liquid from the second mixture. In one embodiment, the method further includes the step of combining the second mixture with an oil phase, thereby forming an emulsion, e.g., a solid-oil-oil emulsion (S/O/O), prior to separating the organic liquid from the second mixture. In another embodiment, the method further includes the step of combining the second mixture with an aqueous phase, thereby forming an emulsion, e.g., a solid-oil-water emulsion (S/O/W), prior to separating the organic liquid from the second mixture. Following formation ofthe emulsion, the organic liquid ofthe second mixture can be extracted into a non-solvent ofthe biocompatible polymer. The present invention also relates to a method for exchanging a continuous medium component of a disperse system, the disperse system including a biologically active agent, with an organic liquid. The method comprises the steps of (a) displacing the continuous medium component ofthe disperse system, the disperse system including a biologically active agent, with an intermediate organic liquid to thereby form an intermediate mixture that includes the biologically active agent; and (b) displacing the intermediate organic liquid ofthe intermediate mixture with an organic liquid to thereby form a mixture that includes the biologically active agent and the organic liquid. The present invention further relates to a polymer-based sustained release device (e.g., microparticles) formed according to the methods described herein. The sustained release device includes a biocompatible polymer such as, for example, poly(lactic acid) or a poly(lactic acid-co-glycolic acid) copolymer, and a biologically active agent, for example, a therapeutic, prophylactic or diagnostic agent such as a protein, peptide, nucleic acid or small organic molecule. In one embodiment, the sustained release device further includes one or more excipients and/or release modifiers. The present invention also relates to apparatus for forming a polymer-based sustained release device. For example, a system for production of a sustained release device, wherein the initial feed stream is a disperse system including a biologically active agent and a continuous medium component is described. The production system comprises (a) at least one tangential flow filter including a feed stream inlet, a retentate stream outlet, and a permeate stream outlet for producing a permeate and a retentate from a feed stream; (b) means for adding an organic liquid to the retentate; (c) means for adding a biocompatible polymer to the retentate and thereby forming a mixture of biologically active agent, biocompatible polymer, and organic liquid; and (d) means for removing the organic liquid from the mixture of biologically active agent, biocompatible polymer, and organic liquid to form a polymer-based sustained release device. In a particular embodiment, the biologically active agent is a protein. In a preferred embodiment, the system is capable of providing diafiltration ofthe feed stream. The methods and apparatus described herein provide for efficient, facile and cost effective preparation of polymer-based sustained release devices having desirable physical and chemical properties. For example, practice ofthe present invention provides for simplified manufacture of sustained release formulations of therapeutic, prophylactic or diagnostic agents. Advantageously, practice of the present invention allows simplified transfer of a biologically active agent from a disperse system which includes a continuous medium component, e.g., an aqueous continuous medium component and/or an organic continuous medium component, to an organic liquid. For example, isolation ofthe agent from the continuous medium component, e.g., via drying or lyophilization, and subsequent suspension or dissolution in the organic liquid is avoided. In addition, transfer ofthe biologically active agent from the continuous medium component to an organic liquid advantageously can be made under closed and/or sterile conditions, under various temperature conditions, and using various miscible organic liquids. Also advantageously, active agents as both solutions and suspensions in continuous medium components can be transferred to organic liquids in accordance with the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic representation of an embodiment ofthe present invention. FIG. 2 is schematic representation of another embodiment ofthe present invention wherein the apparatus includes a permeate recycle stream. FIG. 3 is schematic representation of yet another embodiment ofthe present invention wherein the apparatus includes at least two tangential flow filters.

DETAILED DESCRIPTION OF THE INVENTION The foregoing and other objects, features and advantages ofthe invention will be apparent from the following more particular description of preferred embodiments ofthe invention, as illustrated in the accompanying drawings. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles ofthe invention. The present invention relates to methods and apparatus for preparing a polymer-based sustained release device including a biocompatible polymer having incoφorated therein a biologically active agent. The polymer-based sustained release device is also referred to herein as a "polymer/biologically active agent matrix." The biologically active agent can be a therapeutic, prophylactic or diagnostic agent. The polymer-based sustained release device can be used to deliver a biologically active agent to a subject in need thereof in a sustained manner. The present invention is directed to a method of preparing a polymer-based sustained release device comprising the steps of (a) exchanging a continuous medium component of a disperse system, the disperse system including a biologically active agent as a dispersed entity, with an organic liquid, thereby forming a first mixture that includes the biologically active agent and the organic liquid; (b) combining a biocompatible polymer with the first mixture, thereby forming a second mixture that includes the biologically active agent, the organic liquid, and the biocompatible polymer; and (c) separating the organic liquid from the second mixture, thereby forming the polymer-based sustained release device. In one embodiment, the continuous medium component ofthe disperse system is exchanged with the organic liquid using diafiltration, for example, diafiltration using tangential flow filtration. In a particular embodiment, the method further comprises the step of forming droplets ofthe second mixture prior to separating the organic liquid from the second mixture. Further, the method can include freezing the droplets prior to separating the organic liquid from the second mixture. According to the method ofthe invention, the droplets can be microdroplets. In a specific embodiment, wherein droplets are formed and frozen, the organic liquid can be separated from the second mixture by an evaporation and/or extraction process. For example, in one embodiment, the organic liquid is extracted from frozen droplets into a non-solvent ofthe biocompatible polymer. Phase separation and/or emulsion formation, described infra, are also suitable methods for removing the organic liquid. The present invention also relates to a method for exchanging a continuous medium component of a disperse system, the disperse system including a biologically active agent, with an organic liquid. The method comprises the steps of (a) displacing the continuous medium component ofthe disperse system with an intermediate organic liquid to thereby form an intermediate mixture that includes the biologically active agent; and (b) displacing the intermediate organic liquid ofthe intermediate mixture with an organic liquid to thereby form a mixture that includes the biologically active agent and the organic liquid. As used herein, the term "disperse system" refers to a suspension, a dispersion, a colloidal system or a solution of biologically active agent as a dispersed entity in a continuous medium component. The biologically active agent can be a stabilized biologically active agent as described infra. In addition, stabilizing agents and excipients can also be present in the disperse system. As used herein, the terms "continuous medium," "continuous medium component" and "continuous medium component ofthe disperse system" refer to the major phasic component ofthe disperse system. The continuous medium component includes a member selected from the group consisting of an aqueous liquid and an organic liquid. For example, the continuous medium can include water, a mixture of water and alcohol, or one or more alcohols. In one embodiment, the organic liquid component ofthe continuous medium is at least partially miscible with the aqueous liquid ofthe continuous medium and can be at least partially miscible or immiscible with the organic liquid which is exchanged for the continuous medium. In one embodiment, the organic liquid ofthe continuous medium is immiscible with the organic liquid which is exchanged for the continuous medium component and solvent exchange for one or more intermediate organic liquids can be used to promote miscibility with the organic liquid (i.e., the organic liquid which is exchanged for the continuous medium) prior to solvent exchange. The continuous medium component ofthe disperse system can act to dissolve the biologically active agent at least partially or, alternatively, essentially none ofthe agent is dissolved by the continuous medium. In one embodiment, the organic liquid which is exchanged for the continuous medium is used to dissolve, partially or completely, the polymer in the processing ofthe polymer-based sustained release device. An "intermediate organic liquid" refers to an organic liquid that is at least partially miscible with the continuous medium component of a disperse system and the organic liquid for which the continuous medium is exchanged or a second intermediate organic liquid. For example, in one embodiment, the continuous medium is at least partially miscible with an intermediate organic liquid, the intermediate organic liquid is at least partially miscible with a second intermediate organic liquid and the second intermediate organic liquid is at least partially miscible with the organic liquid for which the continuous medium component is exchanged. Any aqueous liquid is suitable for use as the continuous medium component ofthe disperse system. For example, water and aqueous buffers are suitable aqueous liquids for use in the disperse system. The selection of a suitable aqueous liquid for the continuous medium component can be made based on the particular biologically active agent used and the type of disperse system desired. A preferred aqueous liquid is a buffer. Suitable buffers include those containing, for example, ammonium salts such as, for example, ammonium bicarbonate and sodium salts such as, for example, sodium bicarbonate. Organic liquids which are at least partially miscible with the continuous medium component (e.g., aqueous liquid, organic liquid, and mixtures thereof) and/or with other organic liquids can be readily determined. Suitable examples include, but are not limited to, ethanol, methanol, acetonitrile, DMF, DMSO, acetone, acetic acid, isopropyl alcohol (also partial miscibihty with methyl or ethyl acetate, methyl ethyl ketone, or ether) and combinations thereof. However, one skilled in the art will recognize that whether a particular organic liquid is miscible depends on the continuous medium component, the organic liquid for which the continuous medium is exchanged, and/or the intermediate organic liquid(s) of choice. When the process is directed to preparation of a polymer-based sustained release device, the organic liquid for which the continuous medium is exchanged is suitable for the formation of a polymer-based sustained release device, e.g., the organic liquid at least partially dissolves the polymer. Suitable organic liquids for which the continuous medium is exchanged include, but are not limited to, methylene chloride, chloroform, ethyl acetate, methyl acetate, and toluene. In one embodiment, the biologically active agent is a dispersed entity of a disperse system including a continuous medium component that is at least partially incompatible with formation of a polymer-based sustained release device. The continuous medium can be considered incompatible with the formation of a polymer-based sustained release device because, for example, the polymer is at least -im¬

partially insoluble in the continuous medium component ofthe disperse system. In another example, the continuous medium component ofthe disperse system can be considered incompatible with the formation of a polymer-based sustained release device because the continuous medium component degrades the polymer employed to form the sustained release device. In one particular embodiment, the biologically active agent is transformed into a desired chemical or physical form in a continuous medium that is at least partially incompatible with formation of a polymer-based sustained release device. For example, the biologically active agent is complexed or chemically bonded to another species in a continuous medium component that is at least partially incompatible with formation of a polymer-based sustained release device. The concentration ofthe agent in the continuous medium that is at least partially incompatible with formation of a sustained release device is, for example, at least about 0.1 g/L, e.g., from about 0.5 g/L to about 20 g/L, to about 100 g/L. For example, in one embodiment the disperse system includes about 1 to about 30 milligrams of biologically active agent per milliliter of disperse system, for instance, about 1 to about 20 milligrams of agent per milliliter of disperse system. Advantageously, the present invention includes a method for transferring a biologically active agent from a continuous medium component that is at least partially incompatible with formation of a polymer-based sustained release device to a more suitable liquid medium such as an organic liquid, e.g., a polymer solvent. The biologically active agent can be stabilized against degradation, loss of potency and/or loss of biological activity, all of which can occur during formation of a pharmaceutical composition having the biologically active agent dispersed therein and/or prior to or during in vivo release of the biologically active agent from the sustained release device. In one embodiment, a complexed biologically active agent is formed to stabilize the agent. For example, a stabilized biologically active agent (e.g., a complexed biologically active agent) can formed in a continuous medium that is at least partially incompatible with formation of a polymer-based sustained release device. By practicing the present invention, the continuous medium that is at least partially incompatible with formation of a sustained release device is then exchanged for an organic liquid that is compatible with formation of a polymer- based sustained release device. As used herein, a "solution" is a mixture of one or more substances, referred to as the solute(s), dissolved in one or more other substances, referred to as the solvent(s). As used herein, the term "non-solvent" refers to a material that essentially does not dissolve a second or reference material. As used herein, the terms "a" and "an" refer to one or more. The term "polymer-based sustained release device" as used herein includes a biocompatible polymer having a biologically active agent incoφorated therein. The terms "polymer-based sustained release device," "polymer/biologically active agent matrix," "polymer/drug matrix," and "polymer/agent matrix" are used interchangeably herein. The polymer-based sustained release device can be of any size and shape. For example, the sustained release device can be a film, pellet, cylinder, disc, particle or microparticle (e.g., spherical, non-spherical or irregularly shaped). The sustained release device can be homogeneous or heterogeneous, for example, the sustained release device can have a homogeneous distribution of drug in the device or the distribution of drug in the device can be heterogeneous. The sustained release device can further include other components such as, for example, surfactants, carbohydrates (e.g., monosaccharides and polysaccharides), release modifying agents, stabilizers, other excipients, one or more additional biologically active agents and any combination thereof. As used herein, the term "microparticles" refers to particles having a volume median particle size from about 1 to about 1000 microns. The term "biologically active agent," as used herein, is an agent or its pharmaceutically acceptable salt which, when released in vivo, possesses the desired biological activity, for example, therapeutic, diagnostic and/or prophylactic properties. It is understood that the term includes stabilized biologically active agents as described infra. The terms "biologically active agent," "therapeutic, prophylactic or diagnostic agent," "drug," "active agent," and "agent" are used interchangeably herein. Examples of suitable biologically active agents include, but are not limited to, proteins, muteins and active fragments thereof, such as immunoglobulins, antibodies, cytokines (e.g., lymphokines, monokines, chemokines), interleukins, interferons (β-EFN, α-IFN and γ-IFN), erythropoietin, nucleases, tumor necrosis factor, colony stimulating factors, insulin, enzymes (e.g., superoxide dismutase, tissue plasminogen activator), tumor suppressors, blood proteins, hormones and hormone analogs (e.g., growth hormone (e.g., human growth hormone), follicle stimulating hormone, adrenocorticotropic hormone, luteinizing hormone releasing hormone (LHRH), GLP-1 and exendin), vaccines (e.g., tumoral, bacterial and viral antigens), antigens, blood coagulation factors; growth factors; peptides such as protein inhibitors, protein antagonists, and protein agonists; nucleic acids, such as antisense molecules; oligonucleotides; ribozymes and derivatives (e.g., pegylated derivatives) thereof. Both naturally occurring and synthetic biologically active agents are suitable for use in the present invention. Additional biologically active agents suitable for use in the invention include, but are not limited to, antipsychotic agents such as aripiprazole, risperidone, and olanzapine; antitumor agents such as bleomycin hydrochloride, carboplatin, methotrexate and adriamycin; antibiotics such as gentamicin, tetracycline hydrochloride and ampicillin; antipyretic, analgesic and anti-inflammatory agents; antitussives and expectorants such as ephedrine hydrochloride, methylephedrine hydrochloride, noscapine hydrochloride and codeine phosphate; sedatives such as chloφromazine hydrochloride, prochloφerazine hydrochloride and atropine sulfate; muscle relaxants such as tubocurarine chloride; antiepileptics such as sodium phenytoin and ethosuximide; antiulcer agents such as metoclopramide; antidepressants such as clomipramine; antiallergic agents such as diphenhydramine; cardiotonics such as theophillol; antiarrhythmic agents such as propranolol hydrochloride; vasodilators such as diltiazem hydrochloride and bamethan sulfate; hypotensive diuretics such as pentolinium and ecarazine hydrochloride; antidiuretic agents such as metformin; anticoagulants such as sodium citrate and sodium heparin; hemostatic agents such as thrombin, menadione sodium bisulfite and acetomenaphthone; antituberculous agents such as isoniazide and ethanbutol; hormones such as prednisolone sodium phosphate and methimazole; and narcotic antagonists such as naloφhine hydrochloride. In one embodiment, the biologically active agent is stabilized. The biologically active agent can be stabilized against degradation, loss of potency and/or loss of biological activity, all of which can occur during formation ofthe sustained release composition having the biologically active agent dispersed therein, and/or prior to and during in vivo release ofthe biologically active agent. In one embodiment, stabilization can result in a decrease in the solubility ofthe biologically active agent, the consequence of which is a reduction in the initial release of biologically active agent, in particular, when release is from a sustained release composition. In addition, the period of release ofthe biologically active agent can be prolonged. Stabilization ofthe biologically active agent can be accomplished, for example, by the use of a stabilizing agent or a specific combination of stabilizing agents. The stabilizing agent can be present in the disperse system. "Stabilizing agent," as that term is used herein, is any agent which binds or interacts in a covalent or non-covalent manner or is included with the biologically active agent. Stabilizing agents suitable for use in the invention are described in U.S. Patent Nos. 5,716,644 and 5,674,534 to Zale, et al; U.S. Patent Nos. 5,654,010 and 5,667,808 to Johnson, et al; U.S. Patent Nos. 5,711,968 to Tracy, et al, and 6,265,389 to Burke, et al; and U.S. Patent No. 6,514,533 to Burke, et al., the entire teachings of each of which are incoφorated herein by reference. For example, a metal cation can be complexed with the biologically active agent, or the biologically active agent can be complexed with a polycationic complexing agent such as protamine, albumin, spermidine and spermine, or associated with a "salting-out" salt. In addition, a specific combination of stabilizing agents and/or excipients may be needed to optimize stabilization ofthe biologically active agent. For example, when the biologically active agent in the mixture is an acid-stable or free sulfhydryl-containing protein such as β-IFN, a particular combination of stabilizing agents which includes a disaccharide and an acidic excipient can be added to the mixture. This type of stabilizing formulation is described in detail in U.S. Patent No. 6,465,425 issued to Tracy, et al, on October 15, 2002, the entire contents of which is incoφorated herein by reference. Suitable metal cations include any metal cation capable of complexing with the biologically active agent. A metal cation-stabilized biologically active agent, as defined herein, includes a biologically active agent and at least one type of metal cation wherein the cation is not significantly oxidizing to the biologically active agent. In a particular embodiment, the metal cation is multivalent, for example, having a valency of +2 or more. If the agent is metal cation-stabilized, it is preferred that the metal cation is complexed to the biologically active agent. Suitable stabilizing metal cations include biocompatible metal cations. A metal cation is biocompatible if the cation is non-toxic to the recipient in therapeutic dosage and also presents essentially no deleterious or untoward effects on the recipient's body, such as a significant immunological reaction at the injection site. The suitability of metal cations for stabilizing biologically active agents and the ratio of metal cation to biologically active agent needed can be determined by one of ordinary skill in the art by performing a variety of stability-indicating techniques such as polyacrylamide gel electrophoresis, isoelectric focusing, reverse phase chromatography, and High Performance Liquid Chromatography (HPLC) analysis on particles of metal cation-stabilized biologically active agents prior to and following particle size reduction and/or encapsulation. The molar ratio of metal cation to biologically active agent is typically between about 1 :2 and about 100:1 , preferably between about 2:1 and about 50:1. Examples of stabilizing metal cations include, but are not limited to, K⁺,

Zn⁺², Mg⁺² and Ca⁺². Stabilizing metal cations also include cations of transition metals such as Cu⁺². Combinations of metal cations can also be employed. For example, in one embodiment, Zn⁺² is used as a stabilizing metal cation for growth hormone (e.g. , human growth hormone (hGH)) at a zinc cation component to hGH molar ratio of about 4: 1 to about 100: 1. In a preferred embodiment, the zinc cation component to hGH molar ratio is about 4:1 to about 12:1, and most preferably 10:1. In another embodiment, Zn⁺² is used as a stabilizing metal cation for bovine serum albumin (herein "BSA") at a zinc cation component to BSA molar ratio of about 25:1 to about 100:1. In a preferred embodiment, the zinc cation component to BSA molar ratio is about 50:1. The biologically active agent can also be stabilized with at least one polycationic complexing agent. Suitable polycationic complexing agents include, but are not limited to, protamine, spermine, spermidine and albumin. The suitability of polycationic complexing agents for stabilizing biologically active agents can be determined by one of ordinary skill in the art in the manner described above for stabilization with a metal cation. An equal weight ratio of polycationic complexing agent to biologically active agent is suitable. Further excipients can be added to the polymer-based sustained release devices ofthe present invention, for example, to maintain the potency ofthe biologically active agent over the duration of release or to modify polymer degradation and agent release. One or more excipients can be added to the mixture which is then used to form the sustained release device. For example, an excipient may be suspended or dissolved along with polymer and biologically active agent prior to formation ofthe sustained release device. In addition, excipients can be mixed with the sustained release device from which the organic liquid has been removed. Suitable excipients include, for example, carbohydrates, amino acids, fatty acids, surfactants, and bulking agents. Such excipients are known to those of ordinary skill in the art. An acidic or a basic excipient is also suitable. The amount of excipient used is based on its ratio to the biologically active agent, on a weight basis. For amino acids, fatty acids and carbohydrates, such as sucrose, trehalose, lactose, marmitol, dextran and heparin, the ratio of carbohydrate to biologically active agent, is typically between about 1 :10 and about 20:1. For surfactants, the ratio of surfactant to biologically active agent is typically between about 1 : 1000 and about 2:1. Bulking agents typically include inert materials. Suitable bulking agents are known to those of ordinary skill in the art. The excipient can include a metal cation component which is separately dispersed within the sustained release device. This metal cation component acts to modulate the release ofthe biologically active agent and is not complexed with the biologically active agent. The metal cation component can optionally contain the same species of metal cation, as is contained in the metal cation stabilized biologically active agent, if present, and/or can contain one or more different species of metal cation. The metal cation component acts to modulate the release ofthe biologically active agent from the sustained release device and can enhance the stability of the biologically active agent in the composition. A metal cation component used in modulating release typically includes at least one type of multivalent metal cation. Examples of metal cation components suitable to modulate release include or contain, for example, Mg(OH)₂, MgCO₃ (such as 4MgCO₃ ^«Mg(OH)₂ ^»5H₂O), MgSO₄, Zn(OAc)₂, Mg(OAc)₂, ZnCO₃ (such as 3Zn(OH)₂ ^»2ZnCO₃)ZnSO₄, ZnCl₂, MgCl₂, CaCO₃, Zn₃(C₆H₅O₇)₂ and Mg₃(C₆H₅O₇)₂. A suitable ratio of metal cation component to polymer is between about 1 :500 to about 1 :2 by weight. The optimum ratio depends upon the polymer and the metal cation component utilized and can be determined by one of ordinary skill in the art without undue experimentation. A polymer matrix containing a dispersed metal cation component to modulate the release of a biologically active agent from the polymer matrix is further described in U.S. Patent Nos. 5,656,297 issued to Bernstein, et al, on August 12, 1997, and 5,912,015 issued to Bernstein, et al., on June 15, 1999, the entire contents of both of which are incoφorated herein by reference. In yet another embodiment, at least one pore forming agent, such as a water soluble salt, sugar or amino acid, is included in the sustained release composition to modify the micro structure ofthe particles. The proportion of pore forming agent added to the mixture, e.g., a dispersion or solution, including a biologically active agent, a biocompatible polymer, and an organic liquid (e.g. , a polymer solvent) is about 0.1% (w/w) to about 30% (w/w). The polymer-based sustained release devices prepared according to the invention can contain from about 0.01% (w/w) to about 90% (w/w) ofthe biologically active agent (dry weight of composition). The amount of agent can vary depending upon the desired effect ofthe agent, the planned release levels, and the time span over which the agent is to be released. A preferred range of agent loading is about 0.1% (w/w) to about 75% (w/w), for example, about 0.1 % (w/w) to about 60% (w/w) or about 0.5% (w/w) to about 40% (w/w). In one embodiment, the present invention includes the use of tangential flow filtration ("TFF"), also known by those skilled in the art as "cross-flow filtration," to transfer a biologically active agent from a disperse system which includes a continuous medium component that is at least partially incompatible with formation of a polymer-based sustained release device to a more suitable liquid medium such as an organic liquid, e.g. , a polymer solvent. The present invention includes the use of continuous, batch, and semi-batch tangential flow filtration and closed loop and open loop tangential flow filtration. Tangential flow filtration typically includes the separation of a process stream into a permeate stream and a retentate stream through use of a selectively permeable barrier, e.g., a membrane or filter. The permeate stream includes the portion ofthe process stream that passes through the selectively permeable barrier. The terms "permeate" and "filtrate" are used interchangeably herein. The retentate stream includes the portion ofthe process stream that does not pass through the selectively permeable barrier. The terms "retentate" and "concentrate" are used interchangeably herein. In a preferred embodiment, the retentate includes the biologically active agent. For example, the TFF selectively permeable barriers are sized such that the pores ofthe barrier are smaller than the drug or drug complex, whereby the drug particles are retained in the retentate stream. For example, the pores ofthe barrier are smaller than the drug particles in the case of filtering a suspension or are smaller than the drug molecules in the case of filtering a solution. The pores ofthe selectively permeable barrier are sized to prevent a selected species, e.g., the drug particles, from passing into the permeate stream while allowing a liquid medium such as the continuous medium component, an organic liquid, an intermediate organic liquid, and/or mixtures thereof, e.g., water, alcohol and/or polymer solvent, to pass through the barrier. The selectively permeable barrier is typically rated by pore size or by a molecular weight limit. For example, microfiltration using TFF typically involves pore sizes of about 0.05 to about 0.8 microns and ulfrafiltration using TFF typically involves pores for a molecular weight cut-off of about 1 to 500 kilodaltons (kD). In one embodiment, the mixture to be filtered is modified to enlarge the effective drug particle size and thus permit the use of selectively permeable barriers having larger pore sizes. For example, the drug in the mixture, e.g., a solution, is salted out; the pH of the mixture is changed; or the mixture is diluted using an organic solvent, e.g., an organic liquid, in order to enlarge the effective drug particle size. The selectively permeable barrier ofthe TFF is preferably constructed of a material that is compatible with the substances and the process temperatures employed. For example, in one embodiment the selectively permeable barrier is a ceramic membrane. In a preferred embodiment, diafiltration is used to transfer the agent from a disperse system which includes a continuous medium component to a organic liquid. For example, an agent-containing mixture is diafiltered, e.g., via constant volume diafiltration, using a tangential flow filter. The concentration ofthe continuous medium component in the disperse system, e.g., an aqueous continuous medium component in the disperse system, is thus reduced, for example, to less than about 5 % (v/v), less than about 1 % (v/v), or less than about 0.01 % (v/v). In one embodiment, the resulting disperse system is in the substantial absence of an aqueous continuous medium component. In various embodiments, at least about 1, 2, 3, 4, or about 5 or more diavolumes are used for the diafiltration. The present invention also includes the step of transferring the agent from a disperse system which includes a continuous medium component such as, for example, alcohol or an alcohol/water mixture to an organic liquid, e.g., a polymer solvent, using tangential flow filtration. In one embodiment, this continuous medium component, e.g., alcohol or a alcohol/water mixture, is at least partially miscible in the organic liquid for which the continuous medium is exchanged. For example, the method includes transferring an agent from a disperse system including an aqueous continuous medium component to an ethanol or ethanol water continuous medium and then transferring the agent from the ethanol or ethanol/water continuous medium to methylene chloride. The concentration ofthe water and/or alcohol in the system including agent and organic liquid is thus reduced, for example, to less than about 5 % (v/v), less than about 1 % (v/v), or less than about 0.01 % (v/v). In one embodiment, the resulting agent/organic liquid mixture is in the substantial absence of water and/or alcohol. In various embodiments, at least about 1, 2, 3, 4, or about 5 or more diavolumes are used for the diafiltration. Suitable organic liquids, e.g., polymer solvents, suitable for subsequent production of a polymer-based sustained release device can be determined via routine experimentation using techniques well known to those of ordinary skill in the art. Suitable organic liquids for which the continuous medium are exchanged (e.g., polymer solvents) include, but are not limited to, methylene chloride, acetone, ethyl acetate, methyl acetate, tetrahydrofuran, dimethylsulfoxide (DMSO), acetonitrile, and chloroform. The concentration of agent in the resulting agent/organic liquid mixture is, for example, about 0.01 to about 100 g/L. The amount of agent can be determined based on the desired dosage of agent from the sustained release device, the desired period of agent release, and the condition being treated. For example, in one embodiment, the agent is hGH and the concentration of agent in the resulting agent/organic liquid mixture can be from about 10 to about 50 g/L, e.g., about 20 to about 40 g/L. In another embodiment, the agent is follicle stimulating hormone (FSH) and the concentration of agent in the resulting agent/organic liquid mixture can be about 0.1 to about 10 g/L, for example, from about 1 to about 5 g/L. In a preferred embodiment, a polymer is subsequently added to the mixture including the agent and organic liquid. Polymers used in the formulation of the polymer-based sustained release devices described herein include any polymer which is biocompatible. Biocompatible polymers suitable for use in the present invention include biodegradable and non-biodegradable polymers and blends and copolymers thereof, as described herein. A polymer is biocompatible if the polymer and any degradation products ofthe polymer are non-toxic to the recipient and also do not cause significant deleterious or untoward effects on the recipient's body, such as a significant immunological reaction at the injection site. "Biodegradable," as defined herein, means the composition will degrade or erode in vivo to form smaller chemical species. Degradation can result, for example, by enzymatic, chemical and physical processes. Suitable biocompatible, biodegradable polymers include, for example, poly(lactides), poly(glycolides), poly(lactide-co-glycolides), polyøactic acid)s, poly(glycolic acid)s, polycarbonates, polyesteramides, polyanydrides, poly(amino acids), polyorthoesters, poly(dioxanone)s, poly(alkylene alkylate)s, copolymers or polyethylene glycol and polyorthoester, biodegradable polyurethane, blends thereof, and copolymers thereof. Suitable biocompatible, non-biodegradable polymers include non- biodegradable polymers such as, for example, polyacrylates, polymers of ethylene- vinyl acetates and other acyl substituted cellulose acetates, non-degradable polyurethanes, polystyrenes, polyvinylchloride, polyvinyl flouride, poly( vinyl imidazole), chlorosulphonate polyolefins, polyethylene oxide, blends thereof, and copolymers thereof, such as PLG-co-EMPO described in U.S. Patent Application No. 09/886,394 entitled "Functionalized Degradable Polymer" and filed on June 22, 2001, now U.S. Patent No. 6,730,772, issued on May 4, 2004, the entire contents of which is hereby incoφorated by reference. Further, the terminal functionalities or pendant groups ofthe polymers can be modified, for example, to modify hydrophobicity, hydrophilicity and/or to provide, remove or block moieties which can interact with the active agent via, for example, ionic or hydrogen bonding. In a preferred embodiment ofthe present invention, the polymer used is a polyøactic acid-co-glycolic acid) ("PLG") copolymer. The polyøactic acid-co-glycolic acid) polymer includes d, I, or racemic forms ofthe polymer, for example, in some embodiments the polymer used is poly /-lactic acid-co-glycolic acid). In some embodiments, the polyøactic acid-co-glycolic acid) contains free carboxyl end groups. In other embodiments, the polyøactic acid-co-glycolic acid) contains alkyl ester end groups such as methyl ester end groups. Acceptable molecular weights for polymers used in this invention can be determined by a person of ordinary skill in the art taking into consideration factors such as the desired polymer degradation rate, physical properties such as mechanical strength, and rate of dissolution of polymer in solvent. Typically, an acceptable range of molecular weight is of about 2,000 Daltons to about 2,000,000 Daltons. In a preferred embodiment, the polymer is a biodegradable polymer or copolymer. In a more preferred embodiment, the polymer is a poly(lactide-co-glycolide) which can have lactide:glycolide ratios of about 25:75 to about 85:15 such as about 25:75, 50:50, 75:25 and 85:15, and a molecular weight of about 5,000 Daltons to about 150,000 Daltons. In one embodiment, the molecular weight ofthe PLG has a molecular weight of about 5,000 Daltons to about 42,000 Daltons. The present invention includes the step of forming a polymer-based sustained release device, e.g. , microparticles, from a mixture including a biologically active agent, a biocompatible polymer, and an organic liquid (e.g., a solvent for the polymer ofthe device) formed as described above. The polymer-based sustained release device is formed from this mixture using any ofthe techniques known in the art. In one embodiment, the polymer-based sustained release device is formed by removing the polymer solvent from the mixture including a biologically active agent, a biocompatible polymer and an organic liquid (e.g., a polymer solvent), thereby forming the polymer-based sustained release device. The biologically active agent is in solution and/or suspended in the mixture. A number of methods are known and suitable for forming the polymer-based sustained release device by removing the organic liquid from the mixture. For example, methods for forming a composition for the sustained release of biologically active agent are described in U.S. Patent No. 5,019,400, issued to Gombotz, et αl, on May 28, 1991; U.S. Patent No. 5,922,253 issued to Herbert, et α , on July 13, 1999; and U.S. Patent No. 6,455,074 issued to Tracy, et αl., on September 24, 2002, the entire contents of each of which are incoφorated herein by reference. In one embodiment, a mixture including a biologically active agent, a biocompatible polymer and a organic liquid is processed to create droplets, wherein at least a significant portion ofthe droplets contains polymer, organic liquid and the active agent. These droplets are then frozen by a suitable means. Examples of means for processing the mixture to form droplets include directing the dispersion through an ultrasonic nozzle, pressure nozzle, Rayleigh jet, or by other known means for creating droplets from a solution. In one embodiment, means for processing the mixture to form droplets includes a two-fluid nozzle. In some embodiments using two-fluid nozzles, the two-fluid nozzle includes an air cap containing one or more orifices, in addition to one or more orifices through which droplets are formed, to provide for flow of gas from the nozzle. The presence of one or more additional orifices in the air cap can increase the flow of gas through the nozzle. Means suitable for freezing droplets include directing the droplets into or near a liquified gas such as liquid argon or liquid nitrogen to form frozen microdroplets which are then separated from the liquified gas. The frozen microdroplets are then exposed to a liquid or solid non-solvent ofthe biocompatible polymer such as ethanol, hexane, ethanol mixed with hexane, heptane, ethanol mixed with heptane, pentane or oil. The organic liquid in the frozen microdroplets is extracted as a solid and/or liquid into the polymer non-solvent to form a sustained release device including a biocompatible polymer and a biologically active agent. Mixing ethanol with other polymer non-solvents, such as hexane, heptane or pentane, can increase the rate of organic liquid extraction above that achieved by ethanol alone from certain polymers ■ such as, for example, poly(lactide-co-glycolide) polymers. Organic liquid/non- solvent systems suitable for production of a polymer-based sustained release device can be determined via routine experimentation using techniques well known to those of ordinary skill in the art. A wide range of sizes of polymer-based sustained release devices can be made by varying the droplet size, for example, by changing the ultrasonic nozzle diameter. If the polymer-based sustained release device is in the form of particles and very large particles are desired, the particles can be extruded, for example, through a syringe directly into a cold liquid. Increasing the viscosity ofthe polymer/organic liquid mixture can also increase the size ofthe sustained release device (e.g., particle size). The size ofthe sustained release devices (e.g., particles) which can be produced by this process ranges, for example, from about 1 micron to greater than about 1000 microns in diameter. Yet another method of forming a polymer-based sustained release device from a suspension or solution including a biocompatible polymer and a biologically active agent includes film casting, such as in a mold, to form a film or a shape. For instance, after putting the suspension or solution into a mold, the organic liquid is removed (e.g., via evaporation or sublimation) or the temperature ofthe polymer mixture is reduced (e.g., the polymer mixture is frozen) until a film or shape is obtained. Means for removing the organic liquid (e.g., polymer solvent) from a cast film are known in the art and include vacuum drying, lyophilization, flash drying, and sublimation, among others. The organic liquid is removed until the residual organic liquid levels are brought to concentrations that are suitable for administration to a patient. One of ordinary skill in the art can determine the concentrations of residual organic liquid in particles administered to a patient that are acceptable or tolerated without undue experimentation. Another method of forming a polymer-based sustained release device, e.g., microparticles, includes forming an emulsion that includes the second mixture and subsequently separating the organic liquid from the second mixture. For example, a mixture of polymer, agent, and organic liquid can be mixed with an organic medium, e.g., polyvinyl alcohol (PVA), and the sustained release device can be subsequently formed by evaporating and/or extracting the liquids and then drying the sustained release device. In another example, a mixture of polymer, agent, and organic liquid is coacervated into microparticles by slowly adding a polymer non-solvent, e.g., silicone oil such as polydimethylsiloxane (PDMS), the coacervate is quenched in another non-solvent, e.g. , heptane, and the sustained release device is collected in a filter dryer. In one embodiment, the method for forming the polymer-based sustained release device further comprises the step of combining the second mixture with an oil phase, thereby forming an emulsion, e.g. , a solid-oil-oil (S/O/O) emulsion, prior to separating the organic liquid from the second mixture. The oil phase, e.g., a phase including silicone oil, can be combined with the second mixture to induce phase separation, thereby forming embryonic microparticles. Typically, the organic liquid is then separated from the second mixture. For example, the embryonic microparticles can be contacted with a non-solvent ofthe biocompatible polymer that removes the organic liquid from the second mixture, thereby forming microparticles. In one embodiment, the organic liquid is extracted into a non- solvent ofthe biocompatible polymer such as, for example, ethanol, heptane, or a combination thereof. In one embodiment, the embryonic microparticles are added to a solvent (e.g. , an ethanol/heptane mixture) and the mixture is gently agitated, for example, for about 1 hour at about 3°C; the solvent is decanted, and another solvent (e.g., heptane) is added and the mixture gently agitated, for example, for about 1 hour at about 3°C. In another embodiment, the method for forming the polymer-based sustained release device further comprises the step of combining the second mixture with an aqueous phase, thereby forming an emulsion, e.g., a so lid-oil- water (S/O/W) emulsion, prior to separating the organic liquid from the second mixture. The aqueous phase can be combined with the second mixture to induce phase separation, thereby forming embryonic microparticles. In one embodiment, the aqueous phase includes a surfactant such as PVA. In some embodiments, the aqueous phase also includes an organic compound such as, for example, ethyl acetate or methyl acetate. In one embodiment, the aqueous phase contains about 1 to about 5 wt% surfactant (e.g., PVA) such as about 1 to about 3 wt% or about 1 wt% surfactant and about 1 to about 10 wt% organic compound (e.g., ethyl acetate) such as about 3 to about 7 wt% or about 6 to about 7 wt% or about 6.5 wt% organic compound. In one specific embodiment, the aqueous phase contains about 1 wt% PVA) and 6.5 wt% ethyl acetate. Typically, the organic liquid is subsequently separated from the second mixture. As described above, the embryonic microparticles can be contacted with a non-solvent ofthe biocompatible polymer that removes the organic liquid from the second mixture, thereby forming the sustained release device. In one embodiment, the organic liquid is extracted into a non-solvent ofthe biocompatible polymer such as, for example, an aqueous liquid. In another embodiment, the emulsion is combined with a non-solvent ofthe biocompatible polymer (e.g., an aqueous liquid) and the organic liquid is separated from the second mixture through evaporation. The aqueous liquid can include, for example, an organic compound such as ethyl acetate, methyl acetate, and/or an alcohol such as ethanol. In some embodiments, the aqueous liquid includes about 1 to about 30 wt% organic compound, such as about 1 to about 25 wt% organic compound. In one embodiment, the aqueous liquid includes about 1 to about 5 wt% ethyl acetate, such as about 2 to about 3 wt% or about 2.5 wt% ethyl acetate. In one embodiment, the aqueous liquid includes about 1 to about 30 wt% alcohol (e.g., ethanol) such as about 5 to about 25 wt%, about 10 to about 25 wt%, about 20 to 25 wt%, or about 25 wt% alcohol. In one embodiment, the embryonic microparticles are contacted with a first non-solvent ofthe biocompatible polymer and then contacted with a second non-solvent ofthe biocompatible polymer, to thereby form the sustained release device. For example, the embryonic microparticles can be contacted with a first aqueous liquid (e.g., aqueous ethyl acetate) and then contacted with a second aqueous liquid (e.g., aqueous ethanol), to thereby form microparticles. In one embodiment, the embryonic microparticles are contacted with 2.5 wt% aqueous ethyl acetate and then contacted with 25 wt% aqueous ethanol. The sustained release device, e.g., microparticles, is typically collected after separation ofthe organic liquid form the second mixture, for example, by centrifugation, filtration and or drying. In one embodiment, the sustained release device is collected from the polymer non-solvent(s) and rinsed. In some embodiments, the sustained release device is dried under nitrogen gas, for example, over a four day period with temperature ramping from about 3°C to about 38°C. In one embodiment, a filter dryer is used to collect the sustained release device. Sources for suitable filter dryers or dryer components include Martin Kurz & Co., Inc. (Mineola, NY), Pope Scientific Inc. (Saukville, WI), and National Filter Media Coφoration (Salt Lake City, UT). Alternatively, a freeze/filter dryer similar to that described in U.S. Patent Application No. 10/304,058, filed on November 26, 2002, entitled "Method and Apparatus for Filtering and Drying a Product," incoφorated in its entirety herein by reference, can be used to collect the sustained release device. In some embodiments, additional separation (e.g., extraction), washing, dewatering, filtration, drying, and/or lyophihzation steps can also be performed on the collected sustained release device. In one embodiment, the sustained release device is in the form of injectable microparticles. In another embodiment, the sustained release device is processed, e.g., fragmented, to produce injectable microparticles. An "injectable microparticle," as defined herein, includes a biocompatible polymer component having a volume median particle size from about 1 to about 1000 microns and having a biologically active agent dispersed therein. For example, the particle size can be about 500 microns or less, such as about 400, 300, 200 or about 100 microns or less. The microparticles can be of any shape, for example, spherical, non- spherical or irregular shape, and are suitable for administration by any means (e.g. , by needle, needle-free delivery, or inhalation). It is understood that injectable refers to a size range ofthe microparticle rather than the mode of administration employed to deliver the microparticles to a patient. As used herein, the term "particle size" refers to the volume median particle size as determined by conventional particle size measuring techniques known to those skilled in the art such as, for example, laser diffraction, photon correlation spectroscopy, sedimentation field flow fractionation, disk centrifugation or electrical sensing zone method. Laser diffraction is prefened. The volume median diameter is the median diameter ofthe volume weighted size distribution, also referred to as D_{v 50}. The volume median diameter reflects the distribution of volume as a function of particle diameter. Another designation of particle size often used in the art is the "number median diameter" which reflects the distribution of particles (by number) as a function of particle diameter. Descriptions of various apparatuses used to practice the present invention follow. In one embodiment, an apparatus as illustrated in FIG. 1 is used. Biologically active agent 10 can be fed to vessel 12, e.g., a tank. In one embodiment, biologically active agent 10 is a protein, e.g., insulin, growth hormone, or follicle stimulating hormone. In some embodiments, biologically active agent 10 is added as apart of a liquid composition such as a disperse system, e.g., as an suspension or solution, which contains a continuous medium component, e.g., water and/or organic liquid. In other instances, biologically active agent 10 can be added as a solid composition, e.g., as a powder. In one embodiment, the biologically active agent is provided as a solution and the present invention further includes the step of filtering, e.g., sterile filtering, the provided solution. Thus, in one embodiment, the present invention advantageously provides a simplified method for purifying a biologically active agent and subsequently providing the agent in a desired organic liquid. Vessel 12 can be stirred or unstirred, jacketed or unjacketed. In one preferred embodiment, vessel 12 is both stirced and jacketed. Also encompassed within the present invention is the use of a homogenizer, e.g. , an impeller, to provide particles of a desired size distribution. Also included in the present invention is precipitation ofthe active agent to produce particles of a desired size distribution. For example, an organic liquid, e.g., ethanol, is added to a solution or suspension of biologically active agent, e.g., a protein, to precipitate agent particles. In one embodiment, excipients 14 are added to vessel 12 as necessary to produce a desired form ofthe active agent, e.g., a complexed protein form. Excipients 14 can include, but are not limited to, pH modifiers such as acids, bases, or salts thereof, complex forming metal salts, one or more solvents, e.g., water and/or an alcohol, polymers, and sugars. Alternatively, biologically active agent 10 can be fed to vessel 12 in a desired form without the need to add excipients 14. In some embodiments, a quantity of additional continuous medium component such as an organic liquid, e.g. , ethanol, is added to vessel 12. Once a desired form ofthe active agent is produced, the feed mixture contained in vessel 12, e.g., a disperse system containing a continuous medium component and a biologically active agent, is directed as stream 16 through valve 18, and then as stream 20 to tangential flow filter 22. Tangential flow filter 22 separates stream 20 into retentate stream 24 and permeate stream 26. Preferably, retentate stream 24 contains substantially all ofthe active agent in the desired form, e.g., as a complex. Permeate stream 26 includes mostly liquid, e.g., water and/or organic liquid, and can be directed to disposal. In one embodiment, permeate stream 26 is directed for use in another tangential flow filtration process, e.g., for use in a earlier stage of a multistage tangential flow filtration process. Tangential flow filter 22 includes a membrane filter medium selected using techniques known to those skilled in the art. Preferably, the membrane filter medium is selected for compatibility with the continuous medium component(s) and or organic liquid(s) used and has a pore size for selectively separating the active agent from the continuous medium component, e.g., water and/or organic liquid. Advantageously, tangential flow filter 22 can be selected to separate active agents from both solutions and suspensions ofthe agent. In a preferred embodiment, the membrane filter medium is a ceramic membrane. Ceramic membranes are particularly appropriate when organic liquid(s) such as, for example, methylene chloride are used. Retentate stream 24 can then be directed to vessel 12 where it can be combined with any residual feed mixture and cycled again through tangential flow filter 22. In one embodiment, the above cycle is repeated to concentrate the active agent in the desired form by removing the continuous medium component, e.g., water and/or organic liquid, via permeate stream 26. In another embodiment, an intermediate mixture is formed by adding an intermediate organic liquid, e.g., an organic liquid such as an alcohol, via stream 28 to vessel 12. The intermediate organic liquid can be added via stream 28 at various timepoints in the filtration cycle described above. For example, the intermediate organic liquid is added after the formation ofthe desired active agent form but before the feed mixture is filtered. In other embodiments, the intermediate organic liquid is added to vessel 12 during filtration ofthe feed mixture, for example, as in diafiltration, or after concentration ofthe feed mixture. In a preferred embodiment, the feed mixture is diafiltered using the above described system, e.g., the continuous medium component filtered out of the feed mixture can be continuously replaced by an organic liquid added to the filtered feed mixture. For example, in one embodiment, an aqueous continuous medium component of a disperse system containing a biologically active agent is exchanged for an organic liquid, e.g., alcohol, using diafiltration, thereby forming a disperse system including the biologically active agent and an organic liquid continuous medium component. Subsequently, one or more liquid phases, e.g. , organic liquids and/or intermediate organic liquids, are used to displace the continuous medium component then present in the feed mixture. The organic liquid for which the continuous medium is exchanged is used to displace the continuous medium component then present in the feed mixture. An organic liquid, e.g., the organic liquid for which the continuous medium is exchanged or a intermediate organic liquid, is added via stream 28 to vessel 12 to displace the continuous medium component contained in the feed mixture. In other embodiments, additional one or more organic liquids are used to subsequently displace the continuous medium component then present in the feed mixture. Advantageously, the organic liquids can be selected such that the continuous medium component then present in the feed mixture is at least partially miscible in a subsequently added organic liquid. For example, a feed mixture, e.g., a disperse system, originally containing an aqueous continuous medium component is diafiltered using an alcohol, such as ethanol, until the new feed mixture contains a predominantly alcohol continuous medium component. The new feed mixture, now containing a predominantly alcohol continuous medium component, is then diafiltered using an organic liquid, such as methylene chloride, until the resulting system contains a continuous medium component that is predominantly organic liquid. In one embodiment, the alcohol and the organic liquid for which the continuous medium component is exchanged are at least partially miscible. For example, in one embodiment the method comprises the steps of (a) displacing the continuous medium component ofthe disperse system, the disperse system including a biologically active agent, with an intermediate organic liquid to thereby form an intermediate mixture that includes the biologically active agent; and (b) displacing the intermediate organic liquid ofthe intermediate mixture with an organic liquid to thereby form a mixture that includes the biologically active agent and the organic liquid. Once the active agent in the desired form has been transferred, using one of the above described methods, from the original continuous medium component (e.g., water and/or organic liquid) to an organic liquid, a polymer can be added (e.g. , as a solution of biocompatible polymer). Preferably, the organic liquid includes a polymer solvent. For example, the active agent contained in the organic liquid including a polymer solvent is collected in vessel 12 and polymer can be added via stream 30 thus forming a second mixture containing the biologically active agent, the organic liquid, and the biocompatible polymer. Then, the second mixture can be transferred from vessel 12 as stream 16, passed through valve 18 as stream 32, and directed to sustained release device production process 34. The polymer can also be added to stream 32 to form a second mixture containing the biologically active agent, the organic liquid, and the biocompatible polymer just prior to being directed to sustained release device production process 34. Sustained release device production process 34 includes means for separating the organic liquid from the second mixture. Sustained release device production process 34 includes any ofthe processes known in the art for separating a organic liquid from a mixture containing a biologically active agent, an organic liquid, and a biocompatible polymer. For example, sustained release device production process 34 includes a spray freezing process wherein a sustained release device, e.g., microparticles, is prepared. As another example, sustained release device production process 34 includes a film casting process. In a preferred embodiment, residual organic liquid is separated from the sustained release device, for example, by extraction or sublimation. In one embodiment, sustained release device production process 34 includes means for forming droplets ofthe second mixture, means for freezing the droplets, and/or means for extracting the organic liquid into a polymer non-solvent thereby forming microparticles. For example, in one embodiment, the method comprises the steps of (a) exchanging a continuous medium component of a disperse system, the disperse system including a biologically active agent as a dispersed entity, with an organic liquid, thereby forming a first mixture that includes the biologically active agent and the organic liquid; (b) combining a biocompatible polymer with the first mixture, thereby forming a second mixture that includes the biologically active agent, the organic liquid, and the biocompatible polymer; and (c) separating the organic liquid from the second mixture, thereby forming the polymer-based sustained release device. In another embodiment, an apparatus as illustrated in FIG. 2 is used to practice the present invention. The illustrated embodiment includes additional apparatus for directing a mixture including an active agent, e.g., a disperse system, through tangential flow filter 22. Retentate stream 24 is directed through valve 36 to form recycle stream 38. Recycle stream 38 is combined with stream 20 and directed to tangential flow filter 22. In one embodiment, an organic liquid, e.g., an intermediate organic liquid or a organic liquid for which the continuous medium component is exchanged, is added to stream 38 via stream 40. Alternatively, no liquid is added to stream 38 via stream 40 with the effect that retentate stream 24 is concentrated as the agent/liquid mixture is circulated through tangential flow filter 22. Once stream 24 has become sufficiently concentrated or once the organic liquid has displaced the continuous medium component present in the agent/liquid mixture (e.g., the disperse system), stream 24 can be diverted through valve 36 as stream 42. Stream 42 can be directed to vessel 12. One or more liquid phases, e.g., organic liquids and/or intermediate organic liquids, are used to displace the continuous medium component then present in the feed mixture. The organic liquid for which the continuous medium is exchanged is added via stream 28 and is used to displace the continuous medium component then present in the feed mixture. The active agent in the desired form has been transferred using the above method from the original continuous medium component, e.g., water and or organic liquid, to an organic liquid for which the continuous liquid medium has been exchanged, e.g., a polymer solvent, and a polymer is added, e.g., as a solution of a biocompatible polymer, via stream 30. For example, the active agent contained in the organic liquid is collected in vessel 12 and polymer is added via stream 30 thus forming a second mixture containing the biologically active agent, the organic liquid, and the biocompatible polymer. As described above, the second mixture then can be transferred from vessel 12 as stream 16, passed through valve 18 as stream 32, and directed to sustained release device production process 34. FIG. 3 shows apparatus for use in yet another embodiment ofthe present invention. Feed mixture 50, e.g., a disperse system containing an active agent in a desired form and a continuous medium component, is combined with first recycle stream 66 and combined stream 52 is directed to first tangential flow filter 54. First tangential flow filter 54 separates combined stream 52 into retentate stream 56 and permeate stream 58. Retentate stream 56 contains substantially all ofthe active agent in the desired form, e.g., as a complex. Permeate stream 58 includes mostly continuous medium component, e.g., water and/or organic liquid, and can be directed to disposal. Retentate stream 56 is combined with liquid stream 60 containing, for example, an organic liquid such as an alcohol. In one embodiment, combined stream 62 is directed through valve 64 as recycle stream 66 to combine with feed stream 50. The combined stream can then again be directed into first tangential flow filter 54. For example, the active agent contained in the liquid streams can be repeatedly circulated through first tangential flow filter 54. In another embodiment, combined stream 62 is directed through valve 64 as second feed stream 68. For example, combined stream 62 is directed through valve 64 as second feed stream 68 after the active agent contained therein has made only one pass through first tangential flow filter 54 or, alternatively, after the active agent contained therein has made repeated passes through first tangential flow filter 54. Second feed stream 68 can be combined with second recycle stream 84 and resulting combined stream 70 is directed to second tangential flow filter 72. Second tangential flow filter 72 separates combined stream 70 into retentate stream 74 and permeate stream 76. Retentate stream 76 contains substantially all ofthe active agent in the desired form, e.g., as a complex. Permeate stream 76 includes mostly a liquid phase, e.g., water and/or organic liquid, and is directed to disposal. Retentate stream 74 is combined with liquid phase stream 78 containing, for example, an organic liquid such as an alcohol or a polymer solvent. One or more liquid phases, e.g., organic liquids and/or intermediate organic liquids, are used to displace the continuous medium component then present in the feed mixture. The organic liquid for which the continuous medium is exchanged is added, for example, via stream 78 and is used to displace the continuous medium component then present in the feed mixture. In one embodiment, combined stream 80 is directed through valve 82 as second recycle stream 84 to combine with second feed stream 68. The combined stream can be then again directed into second tangential flow filter 72. For example, the active agent contained in the liquid streams can be repeatedly circulated through second tangential flow filter 72. In another embodiment, combined stream 80 is directed through valve 82 as stream 86. For example, combined stream 80 is directed through valve 82 as stream 86 after the active agent contained therein has made only one pass through second tangential flow filter 72 or, alternatively, after the active agent contained therein has made repeated passes through second tangential flow filter 72. Stream 86 can then be combined with polymer, e.g., biocompatible polymer, added via stream 88 thus forming a second mixture, stream 32, containing the biologically active agent, the organic liquid, and the biocompatible polymer. As described above, the second mixture can then be directed to sustained release device production process 34. In some embodiments not illustrated in FIG. 3, one or more additional tangential flow filters are arranged with recycle schemes similar to those shown for first tangential flow filter 54 and second tangential flow filter 72 wherein stream 86 provides a feed stream to those filters. The product stream, emerging from the filter processes and containing the active agent in the desired form and the desired organic liquid, e.g. , a polymer solvent, can be combined with a polymer and directed to a sustained release device production process as described above. Each ofthe processes described above can be temperature controlled, e.g., the temperature of the various mixtures can be kept at or near a set temperature, and/or blanketed with an inert gas such as, for example, nitrogen as necessary to protect the integrity ofthe active agent. One of ordinary skill in the art can select conditions appropriate to protect the integrity ofthe active agent without undue experimentation. For example, diafiltration can be performed at a temperature such that the integrity ofthe biologically active agent is essentially preserved. In one embodiment, diafiltration is performed at a temperature of about -25°C to about 10°C. The above processes can be operated in batch, semi-batch, or continuous modes with only slight modifications. The above descriptions do not explicitly include storage tanks, holding tanks, pumps, utilities, or instrumentation but these elements are understood to be included as necessary for the practice ofthe invention. The present invention further relates to a polymer-based sustained release device (e.g., microparticles) formed according to the methods described herein. The sustained release device includes a biocompatible polymer such as, for example, polyøactic acid) or a polyøactic acid-co-glycolic acid) copolymer, and a biologically active agent, for example, a therapeutic, prophylactic or diagnostic agent such as a protein, peptide, nucleic acid or small organic molecule. In one embodiment, the sustained release device further includes one or more excipients and/or release modifiers. The present invention also relates to use ofthe polymer-based sustained release device prepared according to the described method for the manufacture of a medicament for use in therapy. The invention includes polymer-based sustained release devices, produced according to the methods described herein, and pharmaceutical compositions including the polymer-based sustained release devices. Pharmaceutical compositions including the polymer-based sustained release devices are suitable for administration to a patient. The pharmaceutical compositions described herein may also include pharmaceutically acceptable excipients such as, for example, diluents, stabilizers, and delivery vehicles. Pharmaceutically acceptable excipients can be selected by one of ordinary skill in the art without undue experimentation. Compositions for the delivery of polymer-based sustained release devices are described, for example, in U.S. Patent No, 6,495,164 issued to Ramstack, et al. , on December 17, 2002. The polymer-based sustained release devices described herein can be administered in vivo, for example, to a human or to an animal, orally, or parenterally such as by injection, implantation (e.g., subcutaneously, intramuscularly, intraperitoneally, intracranially, and intradermally), administration to mucosal membranes (e.g., intranasally, intravaginally, intrapulmonary, buccally or by means of a suppository), or in situ delivery (e.g., by enema or aerosol spray) to provide the desired dosage of biologically active agent based on the known parameters for treatment with the particular agent of various medical conditions. "Sustained release," as that term is used herein, is release of biologically active agent from the polymer-based sustained release devices which occurs over a period which is longer than the period during which a biologically significant amount of agent would be available following direct administration of an agent, e.g., a solution or suspension of agent. In one embodiment, a sustained release is a release of agent which occurs over a period of at least about one day such as, for example, at least about 2, 4, 6, 8, 10, 15, 20, 30, 60, or at least about 90 days. A sustained release of agent can be a continuous or a discontinuous release, with relatively constant or varying rates of release. The continuity of release and level of release can be affected by the type of polymer composition used (e.g., monomer ratios, molecular weight, block composition, and varying combinations of polymers), protein loading, and/or selection of excipients to produce the desired effect. "Sustained release" is also referred to in the art as "modified release," "prolonged release," "long acting release ('LAR')," or "extended release." "Sustained release," as used herein, also encompasses "sustained action" or "sustained effect." "Sustained action" and "sustained effect," as those terms are used herein, refer to an increase in the time period over which an agent performs its therapeutic, prophylactic or diagnostic activity as compared to an appropriate control. "Sustained action" is also known to those experienced in the art as "prolonged action" or "extended action." The sustained release compositions can be administered using any dosing schedule which achieves the desired therapeutic levels for the desired period of time. For example, the sustained release composition can be administered and the patient monitored until levels ofthe drug being delivered return to baseline. Following a return to baseline, the sustained release composition can be administered again. Alternatively, the subsequent administration ofthe sustained release composition can occur prior to achieving baseline levels in the patient. The polymer-based sustained release devices described herein can be used in a method for providing a therapeutically, prophylactically, or diagnostically effective amount of a biologically active agent to a subject for a sustained period. The polymer-based sustained release devices formed by the method ofthe present invention can provide increased therapeutic benefits by reducing fluctuations in active agent concentration in blood, by providing a more desirable release profile and by potentially lowering the total amount of biologically active agent needed to provide a therapeutic benefit without the need for additional components in the composition. As used herein, a "therapeutically effective amount," "prophylactically effective amount" or "diagnostically effective amount" is the amount ofthe biologically active agent or ofthe sustained release composition of biologically active agent needed to elicit the desired biological, prophylactic or diagnostic response following administration.

EXEMPLIFICATION The invention will now be further and specifically described by the following examples which are not intended to be limiting.

MATERIALS Materials used in the Exemplification were acquired from the following sources: Ethanol: 200 proof, Aaper Alcohol (Shelbyville, KY) Methylene Chloride: Catalog No. DX0837-1, EMD Chemicals, Inc. (Gibbstown, NJ) Sodium Bicarbonate: Catalog No. SO125, Spectrum Chemicals & Laboratory Products, Inc. (Gardena, CA) Zinc Acetate: Catalog No. ZI200, Spectrum Chemicals & Laboratory Products, Inc. (Gardena, CA)

EXAMPLE 1 - BSA PROCESSING EXAMPLE 1A The following example describes solvent exchange of a disperse system including zinc-complexed bovine serum albumin (BSA) and aqueous sodium ^■' bicarbonate. Ten grams BSA (Catalog No. EM-2930, EMD Chemicals, hie. (Gibbstown, NJ)) was dissolved in 250 milliliters (mL) of 25 millimolar (mM) sodium bicarbonate (0.5 grams sodium bicarbonate in 250 mL of water ). The BSA was then complexed with zinc (50:1 molar complex) by adding 1.7 grams zinc acetate in 250 mL of water. The resulting disperse system had a volume of 500 mL with a concentration of zinc-complexed BSA of 20 milligrams/milliliter (mg/mL). A sample ofthe disperse system was taken and stored for later analysis (Sample #1A). The remainder ofthe disperse system was then directed through a ceramic TFF system, similar to that shown in FIG. 1, including a ceramic tangential flow filter having a MEMBRALOX^® 10 inch membrane housing (Model No. TI-70, Pall Exekia, Deland, FL) and a 0.2 micron ceramic membrane (CeRam inside, single channel, 6 mm diameter membrane; Tami North America, St. Laurent, Quebec); a 1 L jacketed tank (ITT Sherotec, Simi Valley, CA); and a JABSCO^® Vτ inch rotary lobe pump (Model #JE55210-120078, ITT Industries, Inc., White Plains, NY) in fluid communication between the jacketed tank and the tangential flow filter. The TFF system was brought into temperature equilibrium using water at about 2°C. The disperse system (zinc-complexed BSA in sodium bicarbonate buffer) was then added to the jacketed tank. The disperse system was circulated through the tangential flow filter and the retentate was directed into the jacketed mixing tank from which the feed stream to the filter was drawn. The disperse system was cycled through the TFF until the volume ofthe disperse system was concentrated to about 267 mL. During the concentration, the transmembrane pressure (TMP) was about 20 to 30 psi, the permeate flow rate varied up to about 3.5 mL/min, and the temperature of the retentate was about 7 to 12°C. A sample was taken from the concentrated disperse system and stored for later analysis (Sample #1B). The concentrated disperse system was then diafiltered using a constant volume diafiltration method. The disperse system in the tank was once again circulated through the tangential flow filter and cold ethanol (about -80°C), at the same volumetric flow rate as that of the permeate, was combined with the retentate in a tee and added back to the jacketed tank. TMP was maintained at about 30 psi, the permeate flow rate varied from about 0.5 to 1 mL/min, and the temperature of the retentate was about 1 to 4°C. About 125 mL of retentate was collected before the process was halted and the membrane cleaned using 0.1 M sodium hydroxide and then water. The process was then resumed. TMP was maintained at about 25 to 30 psi, the permeate flow rate varied from about 6 to 8 mL/min, and the temperature ofthe retentate/ethanol stream was about -4 to 7°C. The liquid phase ofthe final disperse system was approximately 95% ethanol and 5% water (v/v). A sample ofthe final disperse system was taken and stored for testing (Sample #1C). The volume ofthe final disperse system was about the same as the starting volume (e.g., 261 L). As described above, the trans-membrane flow (permeate) was much higher using ethanol/water mixtures that were processed after cleaning the membrane. Particle size analysis of Samples #1A, #1B, and #1C taken as described above, was conducted using a Coulter LS Particle Size Analyzer (Model 130) (Beckman Coulter, Inc.) equipped with a Small Volume Module. The data were deconvoluted to obtain the particle size distribution using water as the circulating fluid and the analysis software supplied with the unit. Sample #1 A had a volume median particle size of about 3.1 microns. The volume median particle size of Sample #1B was about 1.1 microns. The volume median particle size of Sample #1C was about 0.47 microns. EXAMPLE IB The following example describes solvent exchange of a disperse system including zinc-complexed bovine serum albumin (BSA) complexed in an aqueous medium including aqueous sodium bicarbonate and ethanol. The resulting solution was suitable for formation of a polymer/BSA sustained release device. 10 grams BSA (Catalog No. EM-2930, EMD Chemicals, Inc.) was dissolved in 100 mL of 25 mM sodium bicarbonate and complexed at a 50:1 zinc to BSA ratio by adding 50 mL of 155 mM zinc acetate solution (containing about 1.7 grams of zinc acetate). The total volume ofthe zinc-complexed BSA mixture was about 150 mL. Cold ethanol (-80°C, 117 mL) was added to produce a disperse system having zinc-complexed BSA present at a concentration of 37.5 mg/mL in an aqueous based system including aqueous sodium bicarbonate and ethanol (44% (v/v) ethanol). The temperature of the resulting mixture was about 0°C from which Sample #1D was taken. Sample #1D had a volume median particle size of about 3.7 microns. The mixture was then directed through a ceramic TFF system, similar to that shown in FIG. 1, including a ceramic tangential flow filter having a MEMBRALOX^® 10 inch membrane housing (Model No. TI-70, Pall Exekia) and a 0.1 micron ceramic membrane (Part #S700-00111 ; Pall Exekia); a 1 L jacketed tank (ITT Sherotec); and a JABSCO^® Vi inch rotary lobe pump (Model #JE55210- 120078, ITT Industries, Inc.) in fluid communication between the jacketed tank and the tangential flow filter. A Promass 63 flowmeter with totalizer (Erdress-t-Hauser, Inc., Greenwood, IN) and a ball valve metering valve were used to control the rate of solvent (e.g., ethanol or methylene chloride) addition to the system. The TFF system was brought into equilibrium using ethanol and the jacketed tank set to -40°C. The system was then drained of ethanol. The disperse system, including zinc-complexed BSA in an aqueous liquid medium containing sodium bicarbonate solution and ethanol, was then added to the jacketed tank. The disperse system was circulated through the tangential flow filter and the retentate was directed into the jacketed mixing tank from which the feed stream to the filter was drawn. The disperse system was diafiltered using a constant volume diafiltration method. Cold ethanol (about -80°C) at the same volumetric flow rate as that of the permeate was mixed with the retentate in a tee and added to the jacketed tank. TMP was maintained at about 20 to 25 psi, the permeate flow rate varied from about 10 to 13 mL/min, and the temperature ofthe retentate/ethanol stream was about -2 to -9°C. A total of 1743 mL of permeate was collected. Sample #1E was taken from the ethanol/zinc-complexed BSA disperse system. Sample #1E had a volume median particle size of about 3.8 microns. The ethanol zinc-complexed BSA disperse system was then diafiltered using methylene chloride. Methylene chloride, at the same volumetric flow rate as that of the permeate, was mixed with the retentate in a tee and added to the jacketed tank. TMP was maintained at about 25 psi, the permeate flow rate varied from about 12 to 28 mL/min, and the temperature ofthe retentate/methylene chloride stream was about -6 to 2°C. A total of 1350 mL of permeate was collected. Sample #1F was taken from the methylene chloride/zinc-complexed BSA disperse system. The final methylene chloride/zinc-complexed BSA mixture had characteristics suitable for subsequent addition of biocompatible polymer and formation of microparticles. Characteristics which can be assessed include, for example, the amount of polymer non-solvent in the polymer solvent/active agent mixture (e.g., methylene chloride/zinc-complexed BSA), which is preferably about 2% or less; the particle size ofthe active agent, which is preferably less than about 20 microns; and the stability ofthe active agent.

SIZE EXCLUSION CHROMATOGRAPHY Size Exclusion Chromatography (SEC) was then used to assess protein degradation. SEC was performed using an isocratic high performance liquid chromatography (HPLC) system with DBPS (Dulbeco's Phosphate Buffer Solution) at 0.5 mL/minute using a TosoHaas Model No. G3000SWXL column (Tosoh

Bioscience LLC, Montgomeryville, PA) containing 5 micron silica beads with 250 Angstrom pores. SAMPLE PREPARATION The samples obtained in Examples 1A and IB above, which contained organic solvents (Samples #1C, #1D, #1E and #1F) were individually filtered through 0.2 micron polytetrafluoroethylene (PTFE) membrane filter paper (Pall Gelman Laboratory, Ann Arbor, MI), allowed to dry, and reconstituted in 4°C, 150 mM phosphate buffer (75 mM monobasic, 75 mM dibasic) to a concentration of about 1 mg/mL. Aqueous samples in Examples 1A and IB above (Samples #1A and #1B) were diluted using 4°C, 150 mM phosphate buffer (75 mM monobasic, 75 mM dibasic) to a concentration of 1 mg/mL. Table 1 summarizes the contents ofthe above prepared samples.

SAMPLE ANALYSIS The data of Table 2 show that the produced mixtures exhibit about 0 to 5% BSA aggregation and suggests that the methods ofthe present invention do not cause substantial chemical degradation ofthe BSA protein. Table 2: Size Exclusion Chromatography results

Control = starting BSA, not diafiltered

EXAMPLE 1C The following example describes solvent exchange of a disperse system including uncomplexed bovine serum albumin (BSA) and water. 10 grams of OmniPur^® BSA, Fraction V, Heat Shock Isolation (Catalog No. EM-2930

(purchased from VWR International), Lot #1252B54, EMD Chemicals, Inc.) was dissolved in 500 mL water to foπn a 20 mg BS A/mL disperse system. 210 mL ofthe above prepared aqueous BSA disperse system was mixed with 50 mL ethanol at about -80°C. The resulting disperse system was then directed through a ceramic TFF system, similar to that shown in FIG. 1, including a ceramic tangential flow filter including a membrane housing (Model No. CLC0251O0100, Tami North America) and a ceramic membrane having a 8 kilodalton (kD) molecular weight cut-off, a 1 L jacketed tank (ITT Sherotec) and a JABSCO^{® l}A inch rotary lobe pump (Model No. JE55210-120078, ITT Industries, Inc.) in fluid communication between the jacketed tank and the tangential flow filter. During initial processing using the TFF system, the transmembrane pressure (TMP) ranged from about 35-36.5 pounds per square inch (psi), the permeate stream had a temperature of approximately 12 to 20°C, and the permeate flow rate was about 2 to 3 mL /min. After about 38 minutes, 112 mL of peπneate had been collected. 100 mL of ethanol at -80°C was then added to the jacketed tank. Diafiltration was continued for 67 more minutes. The penneate rate was about 1 mL/min and the permeate temperature was about 21°C near the end of this time period. Another 100 mL of ethanol at -80°C was added to the jacketed tank.

Diafiltration was continued for another 3 hours and 48 minutes. The total penneate collected was 267 mL. The disperse system was then removed from the TFF system and stored overnight in a freezer. The TFF system was cleaned by circulating CIP-100 (a commercial cleaning solution containing KOH and surfactants) through the system. The TFF system was drained ofthe cleaning solution, rinsed with water, and the disperse system was returned to the jacketed tank. The disperse system was once again circulated through the tangential flow filter under conditions similar to those initially employed. The permeate was cloudy, indicating the presence of protein. The cloudy permeate had a flow rate of about 34 mL/min. The cloudy permeate and/or high flux were likely due to a leak around or through the membrane. A sample was taken and particle size was determined using a Coulter LS Particle Size Analyzer (Model 130) (Beckman Coulter, Inc.) equipped with a Small Volume Module. The data were deconvoluted to obtain the particle size distribution using acetone as the circulating fluid and the analysis software supplied with the unit. The sample had a volume median particle size of about 17 microns at the volume-weighted median. The 8 kD molecular weight cut-off ceramic membrane ofthe tangential flow filter was replaced with a MEMBRALOX^® 10 inch membrane housing (Model No. TI-70, Pall Exekia) and a 0.2 micron ceramic membrane (Part #S700-00108; Pall Exekia). The diafiltration was continued but due to extremely low permeate flux, the experiment was stopped and subsequent experiments incoφorating pre- precipitation ofthe BSA in the disperse system prior to diafiltration (Example ID) were conducted. EXAMPLE ID This example describes a study performed in furtherance ofthe experiment described in Example 1 C. The particle sizes of uncomplexed BSA in various ethanol/water mixtures were measured to demonstrate pre-precipitation of BSA in preparation for subsequent solvent exchange using a TFF apparatus. Aqueous solutions containing 60 mg BSA/mL and 20 mg BSA/mL were prepared (OmniPur^® BSA, Fraction V, Heat Shock Isolation, Catalog No. EM-2930 (purchased from VWR International), Lot #1252B54, EMD Chemicals, Inc.). These BSA solutions were mixed with ethanol under various conditions including at various temperatures and order of mixing. Table 3 shows several combinations of ethanol and BSA solution that produced sub-micron precipitates. Samples 1G, 1H, and IM to IQ were prepared by adding ethanol to BSA solutions. Samples IN and IQ were prepared using cold (< -60°C) ethanol. Samples II to IL were prepared by adding BSA solution to ethanol. BSA particle size (volume median diameter) was determined using a Coulter LS Particle Size Analyzer (Model 130) (Beckman

Coulter, Inc.) equipped with a Small Volume Module as described in Example 1A.

Table 3: Pre-precipitation of BSA particles

The experiment showed that appropriate conditions for forming sub-micron BSA precipitates are achievable. For example, specific conditions include mixing about 30 to about 70% ethanol with 20 mg/mL aqueous BSA solution at room temperature or adding 70% cold ethanol to an aqueous BSA solution. The resulting precipitates were stable with respect to temperature, time, and mixing.

EXAMPLE 2 -INSULIN PROCESSING The following example describes the production of polymer/insulin microparticles. The production method included forming a composition of zinc- complexed insulin in aqueous sodium bicarbonate, exchanging the aqueous medium for an organic liquid using diafiltration with a tangential flow filtration (TFF) system, and directly forming the polymer/insulin microparticles. Four grams of recombinant human insulin (Catalog No. 64819-0002-0, Batch Lot No. SIHR024, Akzo Nobel, Arnhem, the Netherlands) was dissolved and decomplex ed from zinc in 100 mL of 0.1% hydrochloric acid (HCl). Concentrated hydrochloric acid was then added (about 200 micro liters total) to fully dissolve the insulin (resulting in an HCl concentration of about 0.3% (v/v)). The insulin was then recomplexed at a 10:1 zinc:insulin molar ratio by adding 1.6 grams of zinc acetate in 15 mL water to the insulin solution. The pH ofthe resulting mixture was about 4.9. The pH ofthe mixture was then adjusted to about 7 using 10 mL of 1 M sodium hydroxide. The mixture was then chilled to about 2 to 8°C. 375 mL of ethanol chilled to -80°C was then added to the complexed insulin mixture, thus producing a total volume of 500 mL of a disperse system including zinc-complexed insulin, an aqueous medium, and ethanol having an insulin concentration of about 8 mg zinc-complexed insulin/mL. The disperse system was then directed through a ceramic TFF system, similar to that shown in FIG. 1, including a ceramic tangential flow filter having a MEMBRALOX^® 10 inch membrane housing (Model No. TI-70, Pall Exekia) and a 0.1 micron ceramic membrane (Part #S700-00111; Pall Exekia); a 1 L jacketed tank (ITT Sherotec); and a JABSCO^® Vi inch rotary lobe pump (Model No. JE55210- 120078, ITT Industries, Inc.) in fluid communication leading from the jacketed tank to the tangential flow filter. The disperse system was circulated through the tangential flow filter and the retentate was directed into the jacketed mixing tank from which the feed stream to the filter was drawn. The filter permeate, with a volumetric flow rate of between about 2 and 10 mL/min, was discarded. A sample ofthe disperse system (Sample #2A) was taken after approximately 50 mL had been collected as penneate and the sample was stored for later analysis. The temperature of the jacketed tank was kept between about -46 and -55°C. The disperse system was concentrated to a total volume of about 200 L. The concentrated disperse system was then diafiltered using 1 liter (5 diavolumes, i.e., 5 volumes per feed volume assuming constant feed volume) of ethanol. As the disperse system was circulated through the tangential flow filter and back into a mixing tank, ethanol chilled to -80°C was gradually added to the mixing tank to combine with the tangential flow filter penneate. The ethanol was added at a volumetric flow rate to maintain a constant 200 mL volume ofthe disperse system (i.e., at a flow rate approximately equal to the permeate flow rate). The permeate flow rate varied between about 3 and 4 mL/min. During diafiltration, the temperature of the jacketed mixing tank was maintained between -40°C and -60°C. The final volume of disperse system, now containing a mostly ethanol continuous medium component, was about 350 mL having a concentration of about 1 1 mg insulin mL ofthe disperse system. A sample of the disperse system (Sample #2B) was then taken and stored for later analysis. The disperse system was then concentrated to a volume of about 200 mL using the TFF system as described above. The filter permeate, with a volumetric rate of between about 10 and 25 mL/minute, was discarded. The temperature ofthe jacketed tank was kept at about -40°C. The concentrated disperse system was then diafiltered using 1 liter (5 diavolumes) of methylene chloride. As the disperse system was circulated through the tangential flow filter and back into the mixing tank, the methylene chloride (at -80°C) was gradually added to the mixing tank to combine with the tangential flow filter permeate. The methylene chloride was added at a volumetric flow rate to maintain a constant 200 mL volume of insulin mixture. The permeate flow rate varied between about 6.5 and 10 mL/min. During diafiltration, the temperature of the jacketed mixing tank was maintained between -40 and -45°C. About 260 mL of the insulin containing mixture, now including mostly methylene chloride liquid phase, was collected. Following diafiltration with methylene chloride, a sample of the disperse system (Sample #2C) was taken and stored for later analysis. Seventy-five grams of a poly(cfJ-lactide-co-glycolide) polymer having 50 mol% J-lactide, 50 mol% glycolide, and an acid end group (Medisorb^® 5050 DL PLG 2A polymer; Alkermes, Inc., Cincinnati, OH) was dissolved using 120 mL of methylene chloride. This solution was then mixed with the insulin mixture giving a total volume of about 380 mL with a concentration of about 19.7% (w/v) polymer. Sample #2D was taken from this mixture. The resulting mixture was then spray frozen to produce microparticles. The mixture was spray frozen by atomizing the mixture at about 120 mL/minute in a 2-fluid nozzle with a 35 psi nitrogen gas stream (about 160 standard liters per minute) into a liquid nitrogen stream (through 4 nozzles at 30 psi). The nozzles used were as follows: 2-fluid nozzle: fluid cap 2050, air cap 70m (modified for microparticle production by drilling 8 holes tlirough the air cap to provide for flow of nitrogen gas through the air cap) (Spraying Systems Co., Wheaton, IL); and liquid nitrogen nozzles: Model No. 110015 (Spraying Systems Co.). The microparticles were collected and placed into a container of frozen ethanol. The container was stored in a freezer at -80°C for several days, after which the microparticles were filtered from the ethanol. The microparticles were then placed overnight in a lyophilizer (Model No. E1NB352EBCB, Kinetics FTS Systems, Stone Ridge, NY). A total of 57.9 grams of microparticles were subsequently collected for a yield of 73.3%. PARTICLE SIZE ANALYSIS Particle size analysis of Samples #2A, #2B, #2C, and #2D, taken as described above, was conducted as described earlier but using acetone as the circulating fluid. Sample #2A (zinc-complexed insulin in a liquid medium of about 25%o (v/v) aqueous, 75% (v/v) ethanol) had a volume median particle size of about 5.5 microns. The volume median particle size of Sample #2B (liquid phase about 100% (v/v) ethanol) was about 1.9 microns. The median particle size of Sample #2C (liquid phase about 100% (v/v) methylene chloride) was about 2.8 microns. The median particle size of Sample #2D (mixture of zinc-complexed insulin in methylene chloride with poly( ,/-lactide-co-glycolide) polymer solution) was about 2.4 microns. For particle size comparison, a control aqueous mixture was prepared similar to that described above. Briefly, 0.4 grams of recombinant human insulin (Batch Lot No. SJHR024) was mixed with 12.5 mL 0.3% HCl. The insulin was then recomplexed at a 10:1 zinc:insulin molar ratio by adding 0.2 grams of zinc acetate in 2 mL water. The pH of the mixture was then adjusted to about 7 using 1.25 mL of 1 M sodium hydroxide and the mixture chilled to about 2 to 8°C. The volume median particle size of this mixture was about 28 microns.

PROTEIN INTEGRITY ANALYSIS Insulin complex samples were prepared for reverse phase high performance liquid chromatography (φHPLC) as follows. The control aqueous mixture sample was diluted to about 40 micrograms insulin/mL using HPLC buffer (99.95% of (98% water, 2% acetonitrile), and 0.05% trifluoroacetic acid (TFA)). Samples #2A, 2B, and 2C were filtered through 0.2 micron polytetrafluoroethylene (PTFE) membrane filter paper, dried and reconstituted with HPLC buffer to about 40 micrograms insulin/mL. Sample #2D was filtered through 0.2 micron polytetrafluoroethylene (PTFE) membrane filter paper, rinsed with DCM, dried and reconstituted with HPLC buffer to about 40 micrograms insulin/mL. A sample of microparticles, produced as described above, were dissolved in methylene chloride, filtered through 0.2 micron PTFE membrane filter paper, rinsed with DCM, dried, and reconstituted with HPLC buffer to about 40 micrograms insulin mL. A control sample was also prepared using recombinant human insulin (Batch Lot No. SIHR024) dissolved in HPLC buffer to make a mixture having 25 micrograms insulin/mL. Standards having concentrations of 40 and 15 micrograms insulin/mL were also prepared using HPLC buffer. Table 4 summarizes the results of φHPLC measurements. The data of Table 4 suggest that the methods ofthe present invention do not cause chemical degradation ofthe complexed insulin.

Table 4: Reverse Phase High Performance Liquid Chromatography Results

Example 3 - hGH PROCESSING The following example describes the production of polymer/human growth hormone (hGH) microparticles. The production method included forming a composition of zinc-complexed hGH in aqueous sodium bicarbonate, exchanging the aqueous medium for an organic liquid using diafiltration with a tangential flow filtration (TFF) system, and forming the polymer/hGH microparticles. Recombinant human growth hormone was originally obtained from Genentech, Inc. (South San Francisco, CA) and subsequently recovered from various microparticles produced using processes similar to those described herein. 18.3 L of aqueous solution containing hGH and sodium bicarbonate was prepared. The hGH concentration was 19.15 mg/mL and the sodium bicarbonate concentration was 25 mM. The hGH was then complexed with zinc (10: 1 molar complex) by adding 34.96 g zinc acetate dissolved in 2922.8 mL water to the 18.3 L of hGH solution. The resulting disperse system had a concentration of zinc-complexed hGH of 19.15 mg/mL. A sample ofthe disperse system was taken (Sample #3 A) and stored for later analysis. 2423 mL of the dispersed system was retained for production of control microparticles, described infra. About 18.18 L ofthe disperse system was then mixed with 18 L of cold ethanol. A sample of this resulting disperse system was taken (Sample #3B) and stored for later analysis. The disperse system was then directed through a ceramic TFF system, similar to that shown in FIG. 1 , including a ceramic tangential flow filter having a MEMBRALOX^® membrane housing with a 3 mm pore size (Model No. P373OGL, Pall Exekia) and a 0.1 micron ceramic membrane (Part #IP37- 306LE05; Pall Exekia); a 50 L jacketed tank (Precision Stainless Steel, Springfield, MO); and a Waukesha Cherry-Burrell Pump (Model 045/02; SPX Process Equipment, Delavan, WI) in fluid communication leadmg from the jacketed tank to the tangential flow filter. The disperse system was then concentrated to a volume of about 8 L (about 37.5 mg/mL) using the TFF system described above. The filter permeate (about 28 L) was discarded. The temperature of the jacketed tank was kept at about -40°C. The pump was run at about 30 hertz (Hz) to produce a TMP of about 1-2 psi. A sample ofthe concentrated disperse system was taken (Sample #3C) and stored for later analysis. The concentrated disperse system was then diafiltered using 40 L (5 diavolumes, i.e., 5 volumes per feed volume assuming constant feed volume) of ethanol. As the disperse system was circulated through the tangential flow filter and back into the 50 L tank, ethanol chilled to -80°C was added at about 1 L/min to the tank to combine with the tangential flow filter penneate. During diafiltration, the temperature of the jacketed tank was maintained at about -40°C. A sample ofthe disperse system (Sample #3D) was then taken and stored for later analysis. The resulting disperse system was then diafiltered using 40 L (5 diavolumes) of methylene chloride. As the disperse system was circulated through the tangential flow filter and back into the 50 L tank, methylene chloride chilled to -80°C was added at about 1 L/min to the tank to combine with the tangential flow filter permeate. During diafiltration, the temperature of the jacketed tank was maintained at about -40°C. A sample of the resulting mixture (Sample #3E) was then taken and stored for later analysis. During the above-described diafiltration steps, the following operating parameters were used: bulk solution temperature: -17 to +2°C; retentate temperature: -12 to +10°C; TMP: less than 3 psi; pump speed: 30 to 50 Hz; and permeate flux: 500 to 1200 mL/min. The resulting mixture was then concentrated to a volume of about 4 to 6 L using the TFF system. The filter pemieate was discarded. A sample ofthe concentrated mixture was taken (Sample #3F) and stored for later analysis. The concentrated mixture was removed from the TFF system and methylene chloride was added to produce a 4200 mL protein/solvent mixture. 840 grams of a poly(dJ-lactide-co-glycolide) polymer having 50 mol% d, /-lactide, 50 mol% glycolide, and an acid end group (Medisorb^® 5050 DL PLG 2 A polymer; Alkermes, Inc.) was dissolved into the protein mixture. Then, a sample ofthe protein mixture was taken (Sample #3G) and stored for later analysis. 10 grams of zinc carbonate was added to the protein mixture with mixing. Another sample ofthe protein mixture was taken (Sample #3H) and stored for later analysis. The final mixture had about 20%) (w/v) polymer in methylene chloride with 1% zinc carbonate and 15% hGH (both by weight, excluding methylene chloride). The mixture was then homogenized using an IKA rotor/stator homogenizer (IKA Works USA, Wilmington, NC) for 2 minutes at 24,000 rotations per minute (rpm). The resulting mixture was then spray frozen to produce microparticles. The mixture was spray frozen by atomizing the mixture at about 120 mL/minute in a 2-fluid nozzle with a 35 psi nitrogen gas stream (about 160 standard liters per minute) into a liquid nitrogen stream (througli 4 nozzles at 30 psi). The nozzles used were as follows: 2-fluid nozzle: fluid cap 2050, air cap 70m (modified for microparticle production by drilling 8 holes through the air cap to provide for flow of nitrogen gas through the air cap) (Spraying Systems Co.); and liquid nitrogen nozzles: Model No. 110015 (Spraying Systems Co.). The microparticles were directed into an extraction vessel containing cold ethanol at about -104°C. The temperature ofthe ethanol was raised to about -40°C over about 2-3 hours. The microparticles were then dried in a filter dryer made by ITT Sherotec. A total of 849 grains of microparticles were subsequently collected for a yield of 84.9%. The microparticles were sieved using a 106 micron sieve.

CONTROL MICROPARTICLE PRODUCTION 2423 mL ofthe dispersed system, retained as described supra, was spray _t frozen by atomizing the mixture at about 400 mL/minute in a 2-fluid nozzle with a 35 psi nitrogen gas stream (about 62 standard liters per minute) into a liquid nitrogen stream (through 4 nozzles at 30 psi). The nozzles used were as follows: 2-fluid nozzle: fluid cap 2850, 70 air cap (Spraying Systems Co.); and liquid nitrogen nozzles: Model No. 3004 (Spraying Systems Co.). The frozen particles were placed overnight in a lyophilizer (Model No. E1NB352EBCB, Kinetics FTS Systems) to produce a lyophilized drug substance (LDS). 152.4 grams of Medisorb^® 5050 DL PLG 2A polymer (Alkermes, Inc.) was dissolved in 762 mL of methylene chloride. Then, 35.6 grams ofthe LDS was added followed by 1.90 grains of zinc carbonate. The resulting mixture was then spray frozen to produce microparticles using the microparticle production apparatus described supra. The microparticles were directed into an extraction vessel containing cold ethanol at about -104°C. The temperature ofthe ethanol was raised to about -40°C over about 2-3 hours. The microparticles were then dried in a filter dryer made by ITT Sherotec. A total of 148.5 grams of control microparticles were subsequently collected for a yield of 78.2%. The microparticles were sieved using a 106 micron sieve. ANALYSIS OF MICROPARTICLES The microparticles produced as described supra were subjected to various performance tests, the results of which are summarized in Table 5.

Table 5 : Microparticle Performance

Protein integrity ofthe hGH microparticles and the control were comparable, with the control showing slightly more deamidation and bioactivity. hGH loading was lower for the hGH micropaiticles and was likely due to an assumption of 100% yield for the diafiltration process and the subsequent use of this as a basis for microparticle production weights. The data indicate that hGH micropaiticles have a slower release of hGH than the control microparticles.

PARTICLE SIZE ANALYSIS Particle size analysis of Samples #3A to #3H, taken as described above, was conducted as described in Example 1. Table 6 shows the measured median particle sizes. Sample #3F was stored in a -80°C freezer overnight prior to particle size determination. Table 6: Median Particle Size

While this invention has been particularly shown and described with references to prefeπed embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope of the invention encompassed by the appended claims.

Claims

CLAΓMSWe claim:

1. A method for forming a polymer-based sustained release device, comprising the steps of: (a) exchanging a continuous medium component of a disperse system, the disperse system including a biologically active agent as a dispersed entity, with an organic liquid, thereby forming a first mixture that includes the biologically active agent and the organic liquid; (b) combining a biocompatible polymer with the first mixture, thereby forming a second mixture that includes the biologically active agent, the organic liquid, and the biocompatible polymer; and (c) separating the organic liquid from the second mixture, thereby forming the polymer-based sustained release device.

2. The method of Claim 1 wherein the biologically active agent includes a protein.

3. The method of Claim 2 wherein the protein is selected from the group consisting of insulin, follicle stimulating hormone, and human growth hormone.

4. The method of Claim 1 wherein the biologically active agent includes a peptide.

5. The method of Claim 1 wherein the biologically active agent includes a complexed protein.

6. The method of Claim 5 wherein the complexed protein is selected from the group consisting of zinc-complexed insulin and zinc-complexed human growth hormone.

7. The method of Claim 1 wherein the biologically active agent includes at least one member selected from the group consisting of an immunoglobulin, an antibody, a cytokine, an interleukin, an interferon, erythropoietin, a nuclease, a tumor necrosis factor, a colony stimulating factor, insulin, an enzyme, a tumor suppressor, a blood protein, a hoπnone or a hoπnone analog, a vaccine, an antigen, a blood coagulation factor, and a growth factor.

8. The method of Claim 1 wherein the disperse system includes from about 1 to about 30 milligrams of biologically active agent per milliliter of disperse system.

9. The method of Claim 8 wherein the disperse system includes from about 5 to about 20 milligrams of biologically active agent per milliliter of disperse system.

10. The method of Claim 1 wherein the continuous medium component includes an aqueous liquid.

11. The method of Claim 1 wherein the continuous medium component includes a mixture of an aqueous liquid and an organic liquid, the organic liquid being distinct from the organic liquid for which the continuous medium component is exchanged.

12. The method of Claim 1 wherein the continuous medium component includes an organic liquid, the organic liquid being distinct from the organic liquid for which the continuous medium component is exchanged.

13. The method of Claim 1 wherein the continuous medium component includes an alcohol.

14. The method of Claim 1 wherein the continuous medium component includes a buffer.

15. The method of Claim 1 wherein the continuous medium component is essentially hnmiscible with the organic liquid.

16. The method of Claim 1 wherein the organic liquid includes at least one member selected from the group consisting of methylene chloride, chlorofonn, ethyl acetate and methyl acetate.

17. The method of Claim 1 wherein the step of exchanging the continuous medium component ofthe disperse system with the organic liquid includes the steps of: (a) exchanging the continuous medium component ofthe disperse system with an inteπnediate organic liquid, thereby forming an intermediate mixture; and (b) exchanging the intermediate organic liquid ofthe intermediate mixture with the organic liquid, thereby forming the first mixture that includes the biologically active agent and the organic liquid.

18. The method of Claim 17 wherein the continuous medium component of the disperse system is at least partially miscible with the organic liquid.

19. The method of Claim 17 wherein the continuous medium component of the disperse system is essentially immiscible with the organic liquid.

20. The method of Claim 17 wherein the intermediate organic liquid is at least partially miscible with the continuous medium component ofthe disperse system and at least partially miscible with the organic liquid.

21. The method of Claim 17 wherein the intermediate organic liquid includes an alcohol.

22. The method of Claim 1 wherein the biocompatible polymer includes at least one member selected from the group consisting of a poly(lactide), a poly(glycolide), a poly(lactide-co-glycolide), a polyøactic acid), and a poly(glycolic acid).

23. The method of Claim 1 further comprising the step of forming droplets of the second mixture prior to separating the organic liquid from the second mixture.

24. The method of Claim 23 further comprising the step of freezing the droplets prior to separating the organic liquid from the second mixture.

25. The method of Claim 1 wherein the organic liquid is separated from the second mixture by extraction into a non-solvent ofthe biocompatible polymer.

26. The method of Claim 1 further comprising the step of combining the second mixture with an oil phase, thereby forming an emulsion, prior to separating the organic liquid from the second mixture.

27. The method of Claim 1 further comprising the step of combining the second mixture with an aqueous phase, thereby foπning an emulsion, prior to separating the organic liquid from the second mixture.

28. The method of Claim 1 wherein the disperse system is a suspension.

29. The method of Claim 1 wherein the disperse system is a solution.

30. The method of Claim 1 wherein exchanging the continuous medium component ofthe disperse system with the organic liquid includes diafiltering the disperse system.

31. The method of Claim 30 wherein the diafiltration is continuous.

32. The method of Claim 30 wherein the diafiltration includes tangential flow filtration.

33. The method of Claim 32 wherein tangential flow filtration includes using a ceramic membrane.

34. The method of Claim 30 wherein at least about three diavolumes of organic liquid are used for the diafiltration.

35. The method of Claim 1 wherein the step of exchanging the continuous medium component ofthe disperse system with the organic liquid is performed at a temperature in a range of from about -25°C to about 10°C.

36. The method of Claim 1 wherein continuous medium component is exchanged for the organic liquid under an inert gas atmosphere.

37. A polymer-based sustained release device produced by the method of Claim 1.

38. A method for fonning a polymer-based sustained release device, comprising the steps of: (a) exchanging a continuous medium component of a disperse system, the disperse system including a biologically active agent as a dispersed entity, with an organic liquid thereby forming a first mixture that includes the biologically active agent and the organic liquid; (b) combining a biocompatible polymer with the first mixture, thereby forming a second mixture that includes the biologically active agent, the organic liquid, and the biocompatible polymer; (c) forming droplets ofthe second mixture; (d) freezing the droplets; and (e) extracting the organic liquid into a non-solvent of the biocompatible polymer, thereby forming the polymer-based sustained release device.

39. The method of Claim 38 wherein the step of exchanging the continuous medium component ofthe disperse system with the organic liquid includes the steps of: (a) exchanging the continuous medium component ofthe disperse system with an intennediate organic liquid, thereby forming an intermediate mixture; and (b) exchanging the intermediate organic liquid ofthe intermediate mixture with the organic liquid, thereby forming the first mixture that includes the biologically active agent and the organic liquid.

40. The method of Claim 38 wherein the biologically active agent includes a protein.

41. The method of Claim 38 wherein the biologically active agent includes a complexed protein.

42. The method of Claim 38 wherein the biologically active agent includes a peptide.

43. The method of Claim 38 wherein the biocompatible polymer includes at least one member selected from the group consisting of a polyøactide), a poly(glycolide), a polyøactide-co-glycolide), a polyøactic acid), and a poly(glycolic acid).

44. The method of Claim 38 wherein the biocompatible polymer includes a polyøactide-co-glycolide).

45. The method of Claim 38 wherein the organic liquid is a solvent ofthe biocompatible polymer.

46. The method of Claim 38 wherein the step of exchanging the continuous medium component ofthe disperse system with the organic liquid is performed at a temperature in a range of from about -25°C to about 10°C.

47. The method of Claim 38 wherein exchanging the continuous medium component of the disperse system with the organic liquid includes diafiltering the disperse system.

48. The method of Claim 47 wherein the diafiltration is continuous.

49. The method of Claim 47 wherein the diafiltration includes tangential flow filtration.

50. The method of Claim 47 wherein at least about three diavolumes are used for the diafiltration.

51. The method of Claim 38 wherein the droplets of the second mixture are formed by atomization ofthe second mixture and the resulting droplets are frozen by exposing the droplets to a liquified gas.

52. The method of Claim 38 wherein the continuous medium component is exchanged for the organic liquid under an inert gas atmosphere.

53. A polymer-based sustained release device produced by the method of Claim 38.

54. A method for exchanging a continuous medium component of a disperse system with an organic liquid, comprising the steps of: (a) displacing the continuous medium component ofthe disperse system, the disperse system including a biologically active agent, with an intermediate organic liquid to thereby form an intermediate mixture that includes the biologically active agent; and (b) displacing the intermediate organic liquid ofthe intermediate mixture with an organic liquid to thereby foπn a mixture that includes the biologically active agent and the organic liquid.

55. The method of Claim 54 wherein the intermediate organic liquid is at least partially miscible with the continuous medium component and is at least partially miscible with the organic liquid.

56. The method of Claim 54 wherein the organic liquid includes an alcohol.

57. The method of Claim 56 wherein the alcohol includes ethanol.

58. The method of Claim 54 wherein the organic liquid includes at least one member selected from the group consisting of methylene chloride, chloroform, ethyl acetate and methyl acetate.

59. The method of Claim 58 wherein the organic liquid includes methylene chloride or ethyl acetate.

60. The method of Claim 54 wherein the biologically active agent includes a protein.

61. The method of Claim 60 wherein the protein includes at least one member selected from the group consisting of insulin, follicle stimulating hormone, and human growth hormone.

62. The method of Claim 54 wherein the biologically active agent includes at least one member selected from the group consisting of a peptide, an immunoglobulin, an antibody, a cytokine, an interleukin, an interferon, erythropoietin, a nuclease, a tumor necrosis factor, a colony stimulating factor, insulin, an enzyme, a tumor suppressor, a blood protein, a hormone or a hormone analog, a vaccine, an antigen, a blood coagulation factor, and a growth factor.

63. The method of Claim 54 wherein displacing the continuous medium component of the disperse system with the intermediate organic liquid includes using a tangential flow filter.

64. The method of Claim 54 wherein displacing the intermediate organic liquid with the organic liquid includes using a tangential flow filter.

65. A method for fonning a polymer-based sustained release device, comprising the steps of: (a) exchanging a continuous medium component of a disperse system, the disperse system including a biologically active agent as a dispersed entity, with an organic liquid thereby forming a first mixture that includes the biologically active agent and the organic liquid; (b) combining a biocompatible polymer with the first mixture, thereby forming a second mixture that includes the biologically active agent, the organic liquid, and the biocompatible polymer; (c) forming an emulsion that includes the second mixture; and (d) extracting the organic liquid into a non-solvent ofthe biocompatible polymer, thereby forming the polymer-based sustained release device.

66. The method of Claim 65 wherein the step of exchanging the continuous medium component ofthe disperse system with the organic liquid includes the steps of: (a) exchanging the continuous medium component ofthe disperse system with an intermediate organic liquid, thereby forming an intermediate mixture; and (b) exchanging the inteπnediate organic liquid ofthe intermediate mixture with the organic liquid, thereby forming the first mixture that includes the biologically active agent and the organic liquid.

67. The method of Claim 65 wherein exchanging the continuous medium component ofthe disperse system with the organic liquid includes diafiltering the disperse system.

68. The method of Claim 65 wherein forming an emulsion that includes the second mixture includes combining the second mixture with an oil phase.

69. The method of Claim 68 wherein the oil phase includes silicone oil.

70. The method of Claim 65 wherein forming an emulsion that includes the second mixture includes combining the second mixture with an aqueous phase.

71. The method of Claim 70 wherein the aqueous phase includes a surfactant.

72. The method of Claim 71 wherein the aqueous phase includes polyvinyl alcohol.

73. The method of Claim 70 wherein the aqueous phase includes ethyl acetate.

74. The method of Claim 65 wherein the non-solvent ofthe biocompatible polymer includes an aqueous liquid.

75. The method of Claim 74 wherein the aqueous liquid includes ethyl acetate.

76. The method of Claim 65 wherein the non-solvent ofthe biocompatible polymer includes an organic solvent.

77. The method of Claim 76 wherein the organic solvent includes heptane.

78. A polymer-based sustained release device produced by the method of Claim 65.