Block Copolymer Particles

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of, and claims priority under 35 U.S. C. § 120 to, U.S. Patent Application Serial No. 11/314,056, filed on December 21, 2005 and entitled "Block Copolymer Particles", and U.S. Patent Application Serial No. 11/314,557, filed on December 21 , 2005 and entitled "Block Copolymer Particles", both of which are incorporated herein by reference in their entirety.

TECHNICAL FIELD

The disclosure relates to block copolymer particles, and to related compositions and methods.

BACKGROUND

Agents, such as therapeutic agents, can be delivered systemically, for example, by injection through the vascular system or oral ingestion, or they can be applied directly to a site where treatment is desired. In some cases, particles are used to deliver a therapeutic agent to a target site.

SUMMARY

In one aspect, the invention features a particle including a block copolymer and having at least one pore. The particle has a diameter of about 3,000 microns or less.

In another aspect, the invention features a method of making a particle including a block copolymer and having at least one pore. The method includes generating a drop including the block copolymer and at least one salt, water-soluble polymer, base, or combination thereof, and forming the drop into the particle.

In an additional aspect, the invention features a method of making a particle including a block copolymer and having at least one pore. The method includes forming a drop including the block copolymer and a solvent, and removing some or all of the solvent from the drop to form the particle.

Embodiments can also include one or more of the following.

The particle can include a therapeutic agent, such as one or more proteins, genes, or cells, DNA, RNA, insulin, or a combination thereof.

The block copolymer can include at least one first block having a glass transition temperature of at most 37°C and at least one second block having a glass transition temperature of greater than 37°C. The first block can include at least one polyolefin block. In some embodiments, the first block can include at least one isobutylene monomer. The second block can include at least one vinyl aromatic block, methacrylate block, or a combination thereof. In certain embodiments, the first block (e.g., the polyolefin block) can include at least one isobutylene monomer, and the second block (e.g., the vinyl aromatic block) can include at least one monomer selected from styrene, α-methylstyrene, and combinations thereof.

The block copolymer can have the formula X-(AB) _n , in which A is a polyolefin block, B is a vinyl aromatic block or a methacrylate block, n is a positive whole number, and X is an initiator. In some embodiments, A can have the formula — (CRR' — CH2) _n — , in which R and R are linear or branched aliphatic groups or cyclic aliphatic groups, and B is a methacrylate block or a vinyl aromatic block. In certain embodiments, B includes at least one monomer selected from methylmethacrylate, ethylmethacrylate, hydroxyethyl methacrylate, and combinations thereof.

The block copolymer can have the formula BAB or ABA, in which A is a first block and B is a second block.

The block copolymer can have the formula B(AB) _n or A(BA) _n , in which A is a first block, B is a second block, and n is a positive whole number.

The block copolymer can include from about 45 mol percent to about 95 mol percent of polyolefin blocks. The block copolymer can have a molecular weight of more than about 40,000 Daltons. In some embodiments, the block copolymer can include polyolefin blocks having a combined molecular weight of from about 60,000 Daltons to about 200,000 Daltons and vinyl aromatic blocks having a combined molecular weight of from about 20,000 Daltons to about 100,000 Daltons.

The block copolymer can be styrene-isobutylene-styrene. The block copolymer can be biocompatible.

The block copolymer can form a coating on the particle.

The particle can include a bioabsorbable material. In some embodiments, the particle can include a hydrogel. In certain embodiments, the particle can include a second polymer (e.g., that is blended with the block copolymer). In some embodiments, the second polymer can be a block copolymer. In certain embodiments, the second polymer can be selected from polyvinyl alcohols, polyacrylic acids, polymethacrylic acids, poly vinyl sulfonates, carboxymethyl celluloses, hydroxyethyl celluloses, substituted celluloses, polyacrylamides, polyethylene glycols, polyamides, polyureas, polyurethanes, polyesters, polyethers, polystyrenes, polysaccharides, polylactic acids, poly ethylenes, polymethylmethacrylates, polycaprolactones, polyglycolic acids, poly(lactic-co-glycolic) acids, and styrene maleic anhydride copolymers. The particle can have a diameter of about 3,000 microns or less. The pore can have a maximum dimension of at least 0.01 micron (e.g., at least about 0.1 micron, at least about 35 microns) and/or at most about 300 microns (e.g., at most about 35 microns, at most about 0.1 micron). The particle can have a plurality of pores. Some or all of the pores can have a maximum dimension of from 0.01 micron to about one micron, and/or some or all of the pores can have a maximum dimension of from about 10 microns to about 300 microns.

Forming the drop into the first particle can include contacting the drop with a solution including water. The solution can have a temperature of at least about 20 ⁰ C (e.g., at least about 25°C, at least about 30 ⁰ C, at least about 50 ⁰ C, at least about 75°C) and/or at most about 100 ⁰ C (e.g., at most about 75°C, at most about 50 ⁰ C, at most about 30 ⁰ C, at most about 25°C).

The method can include generating the drop including the block copolymer and a salt, and forming the drop into the first particle can include dissolving the salt. The salt can include at least one of sodium chloride, calcium chloride, and sodium bicarbonate. Generating the drop including the block copolymer and a salt can include combining the block copolymer with at least one particle including the salt. The particle including the salt can have a maximum dimension of at least 0.01 micron and/or at most about 300 microns. In some embodiments, generating the drop including the block copolymer and a salt can include combining the block copolymer with a plurality of particles including the salt. Some or all of the particles including the salt can have a maximum dimension of

from 0.01 micron to about one micron, and/or some or all of the particles including the salt can have a maximum dimension of from about 10 microns to about 300 microns.

The method can include generating the drop including the block copolymer and a water-soluble polymer. The water-soluble polymer can include at least one of polyethylene glycol, polyvinylpyrrolidone, carboxymethylcellulose, and hydroxyethylcellulose.

The method can include generating the drop including the block copolymer and a base. The base can include at least one of sodium bicarbonate, ammonium bicarbonate, and potassium bicarbonate. Generating the drop including the block copolymer and a base can include combining the block copolymer with at least one particle including the base. The particle including the base can have a maximum dimension of at least 0.01 micron and/or at most about 300 microns. In some embodiments, generating the drop including the block copolymer and a base can include combining the block copolymer with a plurality of particles including the base. Some or all of the particles including the base can have a maximum dimension of from 0.01 micron to about one micron, and/or some or all of the particles including the base can have a maximum dimension of from about 10 microns to about 300 microns.

Forming the drop into the first particle can include contacting the drop with an acid. The acid can include at least one of citric acid, acetic acid, and hydrochloric acid. Contacting the drop with an acid can include generating a gas. The gas can include at least one of carbon dioxide, ammonia, and combinations thereof.

Forming the drop into the particle can include exposing the drop to a temperature of at least about 40 ⁰ C, and/or exposing the drop to an atmosphere having a pressure of less than 30 inches Hg (e.g., at most about 25 inches Hg, at most about 20 inches Hg, at most about 15 inches Hg, at most about 10 inches Hg, at most about five inches Hg). In some embodiments, removing some or all of the solvent from the drop can include exposing the drop to an atmosphere having a pressure of less than 30 inches Hg (e.g., at most about 25 inches Hg, at most about 20 inches Hg, at most about 15 inches Hg, at most about 10 inches Hg, at most about five inches Hg). In certain embodiments, removing some or all of the solvent from the drop can include exposing the drop to a

temperature of at least about 40 ⁰ C (e.g., at least about 70 ⁰ C) and/or at most about 120 ⁰ C (e.g., at most about 70 ⁰ C).

Embodiments can include one or more of the following advantages. The particles can be used to deliver one or more therapeutic agents to a target site effectively and efficiently, and/or to occlude the target site. In certain embodiments, the particles can absorb, retain, and/or deliver a relatively high volume of therapeutic agent. In some embodiments, the particles can be loaded with a relatively high volume of therapeutic agent using a passive loading technique (e.g., absorption). In certain embodiments, the particles can be used to deliver one or more therapeutic agents (e.g., proteins, DNA, RNA, genes, cells, growth hormone, insulin) that can be fragile and/or thermally sensitive, and/or that can break down when loaded into particles using active loading techniques.

The particles can be used to release a therapeutic agent at a specific time and/or over a period of time. In some embodiments, the particles can be used to deliver a metered dose of a therapeutic agent to a target site over a period of time. In certain embodiments, the release of a therapeutic agent from the particles can be delayed until the particles have reached a target site. For example, the particles can include a bioerodible coating that erodes during delivery, such that when the particles reach the target site, they can begin to release the therapeutic agent. The particles can be relatively durable and/or flexible, and thus can be unlikely to be damaged during storage, delivery, or use. In some embodiments (e.g., embodiments in which the particles are formed of styrene-isobutylene-styrene), the particles can have a relatively high mechanical integrity (e.g., such that contact with the walls of a catheter will not harm the particles). In certain embodiments (e.g., embodiments in which the particles are formed of styrene-isobutylene-styrene), the particles can be relatively flexible, and thus can be adapted for use in many different environments.

The particles can be used to deliver multiple therapeutic agents, either to the same target site, or to different target sites. For example, the particles can deliver one type of therapeutic agent (e.g., an anti-inflammatory) as the particles are being delivered to a target site, and another type of therapeutic agent (e.g., a chemotherapeutic agent) once the particles have reached the target site.

Features and advantages are in the description, drawings, and claims.

DESCRIPTION OF DRAWINGS

FIG. IA is a side view of an embodiment of a particle.

FIG. IB is a cross-sectional view of the particle of FIG. IA, taken along line IB- IB.

FIG. 2 is a cross-sectional view of an embodiment of a particle. FIG. 3 A is a schematic illustrating an embodiment of injection of a composition including particles into a vessel.

FIG. 3B is a greatly enlarged view of region 3B in FIG. 3 A. FIG. 4 is a cross-sectional view of an embodiment of a particle.

FIG. 5 is a cross-sectional view of an embodiment of a particle. FIG. 6 is a cross-sectional view of an embodiment of a particle. FIGS. 7A-7C are an illustration of an embodiment of a system and method for producing particles. FIG. 8 is an illustration of an embodiment of a drop generator.

FIGS. 9A and 9B are an illustration of an embodiment of a system and method for producing particles.

FIGS. 10A- 1OF are an illustration of an embodiment of a system for producing particles. FIG. 11 is a cross-sectional view of an embodiment of a particle.

FIG. 12 is a cross-sectional view of an embodiment of a particle.

DETAILED DESCRIPTION

FIGS. IA and IB show a particle 100 that can be used, for example, to deliver one or more therapeutic agents to a target site within the body. Particle 100 includes a matrix 102 and pores 104. The therapeutic agent(s) can be included on particle and/or within particle 100 (e.g., within matrix 102 and/or pores 104). In some embodiments, the therapeutic agents can be dispersed throughout particle 100. Matrix 102 of particle 100 is formed of a block copolymer that includes a first block having a glass transition

temperature (T _g ) of at most 37°C and a second block having a glass transition temperature of greater than 37°C.

Block copolymers are copolymers that contain two or more differing polymer blocks selected, for example, from homopolymer blocks, copolymer blocks (e.g., random copolymer blocks, statistical copolymer blocks, gradient copolymer blocks, periodic copolymer blocks), and combinations of homopolymer and copolymer blocks. A polymer "block" refers to a grouping of multiple copies of a single type (homopolymer block) or multiple types (copolymer block) of constitutional units. A "chain" is an unbranched polymer block. In some embodiments, a polymer block can be a grouping of at least two (e.g., at least five, at least 10, at least 20, at least 50, at least 100, at least 250, at least 500, at least 750) and/or at most 1000 (e.g., at most 750, at most 500, at most 250, at most 100, at most 50, at most 20, at most 10, at most five) copies of a single type or multiple types of constitutional units. A polymer block may take on any of a number of different architectures. In some embodiments, the block copolymer in particle 100 can include a central block having a glass transition temperature of at most 37°C and end blocks each having a glass transition temperature of greater than 37°C. In certain embodiments, the block copolymer can have one of the following general structures: (a) BAB or ABA (linear triblock), (b) B(AB) _n or A(BA) _n (linear alternating block), or

(c) X — (AB) _n or X — (BA) _n (includes diblock, triblock and other radial block copolymers), where A is a block having a glass transition temperature of at most 37°C, B is a block having a glass transition temperature of greater than 37°C, n is a positive whole number and X is an initiator (e.g., a monofunctional initiator, a multifunctional initiator).

The X — (AB) _n structures are frequently referred to as diblock copolymers (when n=l) or triblock copolymers (when n=2). (This terminology disregards the presence of the initiator, for example, treating A — X — A as a single A block with the triblock therefore denoted as BAB.) Where n=3 or more, these structures are commonly referred to as star-shaped block copolymers.

As described above, the A blocks have a glass transition temperature of at most 37°C. In some embodiments, the A blocks can have a glass transition temperature of at most about 30 ⁰ C (e.g., at most about 25°C, at most about 20 ⁰ C, at most about 10 ⁰ C, at most about 0 ⁰ C, at most about -10 ⁰ C, at most about -20 ⁰ C, at most about -30 ⁰ C, at most about -50 ⁰ C, at most about -70 ⁰ C, at most about -90 ⁰ C). As referred to herein, the glass transition temperature of a material (e.g., a polymer block) is determined according to ASTM E1356. Examples of blocks having a glass transition temperature of at most 37°C when the blocks are in the dry state (e.g., in powder form) include blocks including at least one of the following monomers: (1) acrylic monomers including:

(a) alkyl acrylates, such as methyl acrylate, ethyl acrylate, propyl acrylate, isopropyl acrylate (e.g., isotactic isopropyl acrylate), butyl acrylate, sec-butyl acrylate, isobutyl acrylate, cyclohexyl acrylate, 2-ethylhexyl acrylate, dodecyl acrylate and hexadecyl acrylate,

(b) arylalkyl acrylates, such as benzyl acrylate,

(c) alkoxyalkyl acrylates, such as 2-ethoxyethyl acrylate and 2- methoxy ethyl acrylate,

(d) halo-alkyl acrylates, such as 2,2,2-trifluoroethyl acrylate, and (e) cyano-alkyl acrylates, such as 2-cyanoethyl acrylate;

(2) methacrylic monomers including:

(a) alkyl methacrylates, such as butyl methacrylate, hexyl methacrylate, 2-ethylhexyl methacrylate, octyl methacrylate, dodecyl methacrylate, hexadecyl methacrylate and octadecyl methacrylate, and

(b) aminoalkyl methacrylates, such as diethylaminoethyl methacrylate and 2-tert-butyl-aminoethyl methacrylate;

(3) vinyl ether monomers including:

(a) alkyl vinyl ethers, such as methyl vinyl ether, ethyl vinyl ether, propyl vinyl ether, butyl vinyl ether, isobutyl vinyl ether, 2- ethylhexyl vinyl ether and dodecyl vinyl ether;

(4) cyclic ether monomers, such as tetrahydrofuran, trimethylene oxide, ethylene oxide, propylene oxide, methyl glycidyl ether, butyl glycidyl ether, allyl glycidyl ether, epibromohydrin, epichlorohydrin, 1 ,2- epoxybutane, 1 ,2-epoxyoctane, and 1 ,2-epoxydecane; (5) ester monomers (other than acrylates and methacrylates), such as ethylene malonate, vinyl acetate, and vinyl propionate;

(6) alkene monomers, such as ethylene, propylene, isobutylene, 1-butene, trans-butadiene, 4-methyl pentene, 1-octene and other α-olefins, cis- isoprene, and trans-isoprene; (7) halogenated alkene monomers, such as vinylidene chloride, vinylidene fluoride, cis-chlorobutadiene, and trans-chlorobutadiene;

(8) siloxane monomers, such as dimethylsiloxane, diethylsiloxane, methylethylsiloxane, methylphenylsiloxane, and diphenylsiloxane; and

(9) maleic monomers, such as maleic anhydride. In certain embodiments, the A blocks can include one or more derivatives of the above monomers.

In some embodiments, the A blocks can be based upon one or more polyolefϊns. In certain embodiments, the A blocks can be polyolefϊnic blocks having alternating quaternary and secondary carbons of the general formulation: — (CRR' — CH ₂ ) _n — , where R and R' are linear or branched aliphatic groups (e.g., methyl, ethyl, propyl, isopropyl, butyl, isobutyl) or cyclic aliphatic groups (e.g., cyclohexane, cyclopentane), with and without pendant groups. For example, the A blocks can be polyolefinic blocks having the above formula, in which R and R' are the same. As an example, the A blocks can be based on isobutylene:

(i.e., in which R and R' are both methyl groups).

In some embodiments, the block copolymer can include at least about 40 mol percent (e.g., from about 45 mol percent to about 95 mol percent) of polyolefϊn blocks.

As described above, the B blocks have a glass transition temperature of greater than 37°C. In some embodiments, the B blocks can have a glass transition temperature of

at least about 40 ⁰ C (e.g., at least about 50 ⁰ C, at least about 70 ⁰ C, at least about 90 ⁰ C, at least about 100 ⁰ C, at least about 120 ⁰ C). Examples of blocks having a glass transition temperature of greater than 37°C when the blocks are in the dry state (e.g., in powder form) include blocks including at least one of the following monomers: (1) vinyl aromatic monomers including:

(a) unsubstituted vinyl aromatics, such as atactic styrene, isotactic styrene and 2 -vinyl naphthalene,

(b) vinyl-substituted aromatics, such as α-methyl styrene, and

(c) ring-substituted vinyl aromatics including ring-alkylated vinyl aromatics (e.g., 3-methylstyrene, 4-methylstyrene, 2,4- dimethylstyrene, 2,5-dimethylstyrene, 3,5-dimethylstyrene, 2,4,6- trimethylstyrene, 4-tert-butylstyrene), ring-alkoxylated vinyl aromatics (e.g., 4-methoxystyrene, 4- ethoxy styrene), ring- halogenated vinyl aromatics (e.g., 2-chlorostyrene, 3- chlorostyrene, 4-chlorostyrene, 2,6-dichlorostyrene, 4- bromostyrene,

4-fluorostyrene), ring-ester-substituted vinyl aromatics (e.g., 4-acetoxystyrene), and hydroxyl styrene;

(2) other vinyl monomers including: (a) vinyl esters such as vinyl benzoate, vinyl 4-tert-butyl benzoate, vinyl cyclohexanoate, vinyl pivalate, vinyl trifiuoroacetate, vinyl butyral,

(b) vinyl amines such as 2-vinyl pyridine, 4-vinyl pyridine, and vinyl carbazole, (c) vinyl halides such as vinyl chloride and vinyl fluoride,

(d) alkyl vinyl ethers such as tert-butyl vinyl ether and cyclohexyl vinyl ether, and

(e) other vinyl compounds such as vinyl ferrocene;

(3) other aromatic monomers including acenaphthalene and indene; (4) methacrylic monomers including:

(a) methacrylic acid anhydride,

(b) methacrylic acid esters (methacrylates) including

(i) alkyl methacrylates such as atactic methyl methacrylate, syndiotactic methyl methacrylate, ethyl methacrylate, isopropyl methacrylate, isobutyl methacrylate, t-butyl methacrylate and cyclohexyl methacrylate,

(ii) aromatic methacrylates such as phenyl methacrylate and including aromatic alkyl methacrylates such as benzyl methacrylate,

(iii) hydroxyalkyl methacrylates such as 2-hydroxyethyl methacrylate and 2-hydroxypropyl methacrylate,

(iv) additional methacrylates including isobornyl methacrylate and trimethylsilyl methacrylate, and

(c) other methacrylic-acid derivatives including methacrylonitrile;

(5) acrylic monomers including: (a) certain acrylic acid esters such as tert-butyl acrylate, hexyl acrylate and isobornyl acrylate, (b) other acrylic-acid derivatives including acrylonitrile; and

(6) silicate monomers including polyhedral oligomeric silsesquioxane (POSS) monomers. In some embodiments, the B blocks can include one or more derivatives of the above monomers.

In certain embodiments, the B blocks can be polymers of methacrylates or polymers of vinyl aromatics. In some embodiments, the B blocks can be either: (a) made from monomers of styrene:

or styrene derivatives (e.g., α-methylstyrene, ring-alkylated styrenes or ring-halogenated styrenes) or mixtures thereof, or (b) made from monomers of methylmethacrylate, ethylmethacrylate, hydroxyethyl methacrylate, or mixtures thereof.

In some embodiments, the block copolymer can include at least about five mol percent (e.g., at least about 30 mol percent, about 60 mol percent) of styrene blocks.

An example of one of the above copolymers is styrene-isobutylene-styrene ("SIBS"), in which the A blocks are based on isobutylene, and the B blocks are based on styrene. Another example of one of the above copolymers is styrene maleic anhydride ("SMA"), in which the A blocks are based on maleic anhydride and the B blocks are based on styrene.

Typically, the combined molecular weight of the block copolymer can be more than about 40,000 Daltons (e.g., more than about 60,000 Daltons). For example, the combined molecular weight of the block copolymer can be from about 80,000 Daltons to about 300,000 Daltons (e.g., from about 90,000 Daltons to about 300,000 Daltons). In some embodiments (e.g., embodiments in which the A blocks are polyolefin blocks), the combined molecular weight of the A blocks can be from about 60,000 Daltons to about 200,000 Daltons. In certain embodiments (e.g., embodiments in which the B blocks are vinyl aromatic blocks), the combined molecular weight of the B blocks can be from about 20,000 Daltons to about 100,000 Daltons.

Generally, the properties of the block copolymer used in particle 100 can depend upon the lengths of the A block chains and B block chains in the block copolymer, and/or on the relative amounts of A block and B blocks in the block copolymer. As an example, in some embodiments, blocks with a glass transition temperature of at most 37°C may be elastomeric. In such embodiments, the elastomeric properties of the block copolymer can depend on the length of the A block chains. In certain embodiments, the A block chains can have a weight average molecular weight of from about 2,000 Daltons to about 30,000 Daltons. In such embodiments, the block copolymer and/or particle 100 may be relatively inelastic. In some embodiments, the A block chains can have a weight average molecular weight of at least about 40,000 Daltons. In such embodiments, the block copolymer and/or particle 100 may be relatively soft and/or rubbery.

As another example, in certain embodiments, blocks with a glass transition temperature of greater than 37°C may be relatively hard at 37°C. In such embodiments, the hardness of the block copolymer at 37°C can depend on the relative amount of B

blocks in the block copolymer. In some embodiments, the block copolymer can have a hardness of from about Shore 2OA to about Shore 75D (e.g., from about Shore 4OA to about Shore 90A). In certain embodiments, a copolymer with a desired degree of hardness may be formed by varying the proportions of the A and B blocks in the copolymer, with a lower relative proportion of B blocks resulting in a copolymer of lower hardness, and a higher relative proportion of B blocks resulting in a copolymer of higher hardness. As a specific example, high molecular weight (i.e., greater than 100,000 Daltons) polyisobutylene is a relatively soft and gummy material with a Shore hardness of approximately 1 OA. By comparison, polystyrene is much harder, typically having a Shore hardness on the order of 10OD. As a result, when blocks of polyisobutylene and styrene are combined, the resulting copolymer can have a range of hardnesses from as soft as Shore 1OA to as hard as Shore 10OD, depending upon the relative amounts of polystyrene and polyisobutylene in the copolymer. In some embodiments, from about two mol percent to about 25 mol percent (e.g., from about five mol percent to about 20 mol percent) of polystyrene can be used to form a block copolymer with a hardness of from about Shore 30A to about Shore 9OA (e.g., from about Shore 35A to about Shore 70A).

Polydispersity (the ratio of weight average molecular weight to number average molecular weight) gives an indication of the molecular weight distribution of the copolymer, with values significantly greater than four indicating a broad molecular weight distribution. When all molecules within a sample are the same size, the polydispersity has a value of one. Typically, copolymers used in particle 100 can have a relatively tight molecular weight distribution, with a polydispersity of from about 1.1 to about 1.7. In some embodiments, one or more of the above-described copolymers can have a relatively high tensile strength. For example, triblock copolymers of polystyrene- polyisobutylene -polystyrene can have a tensile strength of at least about 2,000 psi (e.g., from about 2,000 psi to about 4,000 psi).

In certain embodiments, one or more of the above-described copolymers can be relatively resistant to cracking and/or other forms of degradation under in vivo conditions. Additionally or alternatively, one or more of the above-described polymers can exhibit

excellent biocompatibility, including vascular compatibility. For example, the polymers can provoke minimal adverse tissue reactions, resulting in reduced polymorphonuclear leukocyte and reduced macrophage activity. In some embodiments, one or more of the above-described polymers can generally be hemocompatible, and can thereby minimize thrombotic occlusion of, for example, small vessels.

The above-described block copolymers can be made using any appropriate method known in the art. In some embodiments, the block copolymers can be made by a carbocationic polymerization process that includes an initial polymerization of a monomer or mixtures of monomers to form the A blocks, followed by the subsequent addition of a monomer or a mixture of monomers capable of forming the B blocks. Such polymerization reactions are described, for example, in Kennedy et al., U.S. Patent No. 4,276,394; Kennedy, U.S. Patent No. 4,316,973; Kennedy, 4,342,849; Kennedy et al., U.S. Patent No. 4,910,321; Kennedy et al., U.S. Patent No. 4,929,683; Kennedy et al., U.S. Patent No. 4,946,899; Kennedy et al., U.S. Patent No. 5,066,730; Kennedy et al., U.S. Patent No. 5,122,572; and Kennedy et al., U.S. Patent No. Re. 34,640. Each of these patents is incorporated herein by reference.

The techniques disclosed in these patents generally involve an "initiator", which can be used to create X — (AB) _n structures, where X is the initiator, and n can be 1 , 2, 3 or more. The initiator can be monofunctional or multifunctional. As noted above, the resulting molecules are referred to as diblock copolymers where n is 1 , triblock copolymers (disregarding the presence of the initiator) where n is 2, and star-shaped block copolymers where n is 3 or more.

In general, the polymerization reaction can be conducted under conditions that minimize or avoid chain transfer and termination of the growing polymer chains. Steps can be taken to keep active hydrogen atoms (water, alcohol and the like) to a minimum. The temperature for the polymerization is usually from about -10 ⁰ C to about -90 ⁰ C (e.g., from about -60 ⁰ C to about -80 ⁰ C), although lower temperatures can be used.

Typically, one or more A blocks (e.g., polyisobutylene blocks) can be formed in a first step, followed by the addition of B blocks (e.g., polystyrene blocks) at the ends of the A blocks. More particularly, the first polymerization step is generally carried out in an appropriate solvent system, such as a mixture of polar and non-polar solvents (e.g.,

methyl chloride and hexanes). The reaction bath can contain the aforementioned solvent system, olefin monomer (e.g., isobutylene), an initiator (e.g., a tert-ester, tert-ether, tert- hydroxyl or tert-halogen containing compound, a cumyl ester of a hydrocarbon acid, an alkyl cumyl ether, a cumyl halide, a cumyl hydroxyl compound, or a hindered version of the above), and a coinitiator (e.g., a Lewis acid, such as boron trichloride or titanium tetrachloride). In some embodiments, electron pair donors (e.g., dimethyl acetamide, dimethyl sulfoxide, dimethyl phthalate) can be added to the solvent system. Additionally, proton-scavengers that scavenge water, such as 2,6-di-tert-butylpyridine, 4- methyl-2,6-di-tert-butylpyridine, 1 ,8-bis(dimethylamino)-naphthalene, or diisopropylethyl amine can be added.

The reaction is commenced by removing the tert-ester, tert-ether, tert-hydroxyl or tert-halogen (herein called the "tert-leaving groups") from the initiator by reacting the initiator with the Lewis acid. In place of the tert-leaving groups is a quasi-stable or "living" cation which is stabilized by the surrounding tertiary carbons, as well as the polar solvent system and electron pair donors. After obtaining the cation, the A block monomer (e.g., isobutylene) is introduced, and cationically propagates or polymerizes from each cation on the initiator. When the A block is polymerized, the propagated cations remain on the ends of the A blocks. The B block monomer (e.g., styrene) is then introduced, and polymerizes and propagates from the ends of the A block. Once the B blocks are polymerized, the reaction is terminated by adding a termination molecule such as methanol, water and the like.

Product molecular weights are generally determined by reaction time, reaction temperature, the nature and concentration of the reactants, and so forth. Consequently, different reaction conditions may produce different products. In general, synthesis of the desired reaction product is achieved by an iterative process in which the course of the reaction is monitored by the examination of samples taken periodically during the reaction — a technique widely employed in the art. To achieve the desired product, an additional reaction may be required in which reaction time and temperature, reactant concentration, and so forth are changed. Additional details regarding cationic processes for making copolymers are found, for example, in Kennedy et al, U.S. Patent No. 4,276,394; Kennedy, U.S. Patent No.

4,316,973; Kennedy, 4,342,849; Kennedy et al., U.S. Patent No. 4,910,321; Kennedy et al, U.S. Patent No. 4,929,683; Kennedy et al., U.S. Patent No. 4,946,899; Kennedy et al., U.S. Patent No. 5,066,730; Kennedy et al., U.S. Patent No. 5,122,572; and Kennedy et al., U.S. Patent No. Re. 34,640, incorporated supra. The block copolymer may be recovered from the reaction mixture by any of the usual techniques including evaporation of solvent, precipitation with a non-solvent such as an alcohol or alcohol/acetone mixture, followed by drying, and so forth. In addition, purification of the copolymer can be performed by sequential extraction in aqueous media, both with and without the presence of various alcohols, ethers and ketones. In some embodiments, matrix 102 can be formed of a block copolymer that includes one or more functional groups. The functional groups can be negatively charged or positively charged, and/or can be ionically bonded to the polymer. In some embodiments, the functional groups can enhance the biocompatibility of the polymer. Alternatively or additionally, the functional groups can enhance the clot-forming capabilities of the polymer. Examples of functional groups include phosphate groups, carboxylate groups, sulfonate groups, sulfate groups, phosphonate groups, and phenolate groups. For example, a polymer can be a sulfonated styrenic polymer, such as sulfonated SIBS. Sulfonation of styrene block copolymers is disclosed, for example, in Ehrenberg, et al., U.S. Patent No. 5,468,574; Vachon et al., U.S. Patent No. 6,306,419; and Berlowitz-Tarrant, et al., U.S. Patent No. 5,840,387, all of which are incorporated herein by reference. Examples of other functionalized polymers include phosphated SIBS and carboxylated SIBS. In certain embodiments, a polymer can include more than one different type of functional group. For example, a polymer can include both a sulfonate group and a phosphate group. In some embodiments, a polymer that includes a functional group can be reacted with a cross-linking and/or gelling agent during particle formation. For example, a particle that includes a sulfonates group, such as sulfonated SIBS, may be reacted with a cross-linking and/or gelling agent such as calcium chloride. Functionalized polymers and cross-linking and/or gelling agents are described, for example, in Richard et al., U.S. Patent Application Serial No. 10/927,868, filed on August 27, 2004, and entitled "Embolization", which is incorporated herein by reference.

The presence of pores 104 in particle 100 can enhance the ability of particle 100 to retain a relatively high volume of therapeutic agent. In some embodiments, as the sizes of pores 104 increase, the volume of therapeutic agent retained by particle 100 can increase. In certain embodiments, one or more of pores 104 can have a maximum dimension of at least 0.01 micron (e.g., at least 0.05 micron, at least about 0.1 micron, at least about 0.5 micron, at least about one micron, at least about five microns, at least about 10 microns, at least about 15 microns, at least about 20 microns, at least about 25 microns, at least about 30 microns, at least about 35 microns, at least about 50 microns, at least about 100 microns, at least about 150 microns, at least about 200 microns, at least about 250 microns), and/or at most about 300 microns (e.g., at most about 250 microns, at most about 200 microns, at most about 150 microns, at most about 100 microns, at most about 50 microns, at most about 35 microns, at most about 30 microns, at most about 25 microns, at most about 20 microns, at most about 15 microns, at most about 10 microns, at most about five microns, at most about one micron, at most about 0.5 micron, at most about 0.1 micron, at most about 0.05 micron). In some embodiments, some or all of pores 104 can have a maximum dimension of from 0.01 micron to about one micron, and/or some or all of pores 104 can have a maximum dimension of from about 10 microns to about 300 microns (e.g., from about 100 microns to about 300 microns).

In certain embodiments, the pores in a particle can form a porosity gradient. The porosity gradient can be used, for example, the regulate the delivery of therapeutic agent from a particle.

As an example, FIG. 2 shows a particle 150 formed of a block copolymer matrix 151. Particle 150 includes a center region, C, from the center c' of particle 150 to a radius of about r/3, a body region, B, from about r/3 to about 2r/3, and a surface region, S, from about 2r/3 to r. In general, the mean size of the pores in region C of particle 150 is greater than the mean size of the pores at region S of particle 150. In certain embodiments, the mean size of the pores in region C of particle 150 is greater than the mean size of the pores in region B particle 150, and/or the mean size of the pores in region B of particle 150 is greater than the mean size of the pores at region S of particle 150.

For example, region C of particle 150 includes relatively large pores 152. In some embodiments, relatively large pores 152 can have a mean diameter of about 20 microns or more (e.g., about 30 microns or more, from about 20 microns to about 35 microns). Region B of particle 150 includes intermediate-sized pores 154. In certain embodiments, intermediate-sized pores 154 can have a mean diameter of about 18 microns or less (e.g. about 15 microns or less, from about two microns to about 18 microns). Region S of particle 150 includes relatively small pores 156. In some embodiments, relatively small pores 156 can have a mean diameter of one micron or less (e.g. from 0.01 micron to about 0.1 micron). In certain embodiments, the density of pores (the number of pores per unit volume) at region S of particle 150 can be greater than the density of pores in region C of particle 150. In some embodiments, the density of pores at region S of particle 150 can be greater than the density of pores in region B of particle 150, and/or the density of pores in region B of particle 150 can be greater than the density of pores in region C of particle 150.

While FIGS. IB and 2 show particles with pores having different sizes, in some embodiments, a particle can include pores that have the same size (e.g., that have the same diameter).

As described above, particle 100 can be used to deliver one or more therapeutic agents (e.g., a combination of therapeutic agents) to a target site. In some embodiments, a therapeutic agent can be hydrophilic. In certain embodiments, a therapeutic agent can be lipophilic. Therapeutic agents include genetic therapeutic agents, non-genetic therapeutic agents, and cells, and can be negatively charged, positively charged, amphoteric, or neutral. Therapeutic agents can be, for example, materials that are biologically active to treat physiological conditions; pharmaceutically active compounds; proteins; gene therapies; nucleic acids with and without carrier vectors (e.g., recombinant nucleic acids, DNA (e.g., naked DNA), cDNA, RNA, genomic DNA, cDNA or RNA in a non-infectious vector or in a viral vector which may have attached peptide targeting sequences, antisense nucleic acids (RNA, DNA)); oligonucleotides; gene/vector systems (e.g., anything that allows for the uptake and expression of nucleic acids); DNA chimeras (e.g., DNA chimeras which include gene sequences and encoding for ferry proteins such

as membrane translocating sequences ("MTS") and herpes simplex virus- 1 ("VP22")); compacting agents (e.g., DNA compacting agents); viruses; polymers; hyaluronic acid; proteins (e.g., enzymes such as ribozymes, asparaginase); immunologic species; nonsteroidal anti-inflammatory medications; oral contraceptives; progestins; gonadotrophin-releasing hormone agonists; chemotherapeutic agents; and radioactive species (e.g., radioisotopes, radioactive molecules). Non-limiting examples of therapeutic agents include anti-thrombogenic agents; antioxidants; angiogenic and anti- angiogenic agents and factors; anti-pro liferative agents (e.g., agents capable of blocking smooth muscle cell proliferation, such as rapamycin); calcium entry blockers (e.g., verapamil, diltiazem, nifedipine); and survival genes which protect against cell death (e.g., anti-apoptotic Bcl-2 family factors and Akt kinase).

Exemplary non-genetic therapeutic agents include: anti-thrombotic agents such as heparin, heparin derivatives, urokinase, and PPack (dextrophenylalanine proline arginine chloromethylketone); anti- inflammatory agents such as dexamethasone, prednisolone, corticosterone, budesonide, estrogen, acetyl salicylic acid, sulfasalazine and mesalamine; antineoplastic/antiproliferative/anti-mitotic agents such as paclitaxel, 5- fluorouracil, cisplatin, methotrexate, doxorubicin, vinblastine, vincristine, epothilones, endostatin, angiostatin, angiopeptin, monoclonal antibodies capable of blocking smooth muscle cell proliferation, and thymidine kinase inhibitors; anesthetic agents such as lidocaine, bupivacaine and ropivacaine; anti-coagulants such as D-Phe-Pro-Arg chloromethyl ketone, an RGD peptide-containing compound, heparin, hirudin, antithrombin compounds, platelet receptor antagonists, anti-thrombin antibodies, antiplatelet receptor antibodies, aspirin, prostaglandin inhibitors, platelet inhibitors and tick antiplatelet factors or peptides; vascular cell growth promoters such as growth factors, transcriptional activators, and translational promoters; vascular cell growth inhibitors such as growth factor inhibitors (e.g., PDGF inhibitor- Trapidil), growth factor receptor antagonists, transcriptional repressors, translational repressors, replication inhibitors, inhibitory antibodies, antibodies directed against growth factors, bifunctional molecules consisting of a growth factor and a cytotoxin, bifunctional molecules consisting of an antibody and a cytotoxin; protein kinase and tyrosine kinase inhibitors (e.g., tyrphostins, genistein, quinoxalines); prostacyclin analogs; cholesterol-lowering agents;

angiopoietins; antimicrobial agents such as triclosan, cephalosporins, aminoglycosides and nitrofurantoin; cytotoxic agents, cytostatic agents and cell proliferation affectors; vasodilating agents; and agents that interfere with endogenous vasoactive mechanisms. Exemplary genetic therapeutic agents include: anti-sense DNA and RNA; DNA coding for anti-sense RNA, tRNA or rRNA to replace defective or deficient endogenous molecules, angiogenic factors including growth factors such as acidic and basic fibroblast growth factors, vascular endothelial growth factor, epidermal growth factor, transforming growth factor α and β, platelet-derived endothelial growth factor, platelet-derived growth factor, tumor necrosis factor a, hepatocyte growth factor, and insulin like growth factor, cell cycle inhibitors including CD inhibitors, thymidine kinase ("TK") and other agents useful for interfering with cell proliferation, and the family of bone morphogenic proteins ("BMP's"), including BMP2, BMP3, BMP4, BMP5, BMP6 (Vgrl), BMP7 (OPl), BMP8, BMP9, BMPlO, BMl 1 , BMP12, BMP13, BMP14, BMP15, and BMP16. Currently preferred BMP's are any of BMP2, BMP3, BMP4, BMP5, BMP6 and BMP7. These dimeric proteins can be provided as homodimers, heterodimers, or combinations thereof, alone or together with other molecules. Alternatively or additionally, molecules capable of inducing an upstream or downstream effect of a BMP can be provided. Such molecules include any of the "hedgehog" proteins, or the DNA's encoding them. Vectors of interest for delivery of genetic therapeutic agents include: plasmids; viral vectors such as adenovirus (AV), adenoassociated virus (AAV) and lentivirus; and non- viral vectors such as lipids, liposomes and cationic lipids.

Cells include cells of human origin (autologous or allogeneic), including stem cells, or from an animal source (xenogeneic), which can be genetically engineered if desired to deliver proteins of interest. Several of the above and numerous additional therapeutic agents appropriate for the practice of the present invention are disclosed in Kunz et al., U.S. Patent No. 5,733,925, assigned to NeoRx Corporation, which is incorporated herein by reference. Therapeutic agents disclosed in this patent include the following:

"Cytostatic agents" (i.e., agents that prevent or delay cell division in proliferating cells, for example, by inhibiting replication of DNA or by inhibiting spindle fiber formation). Representative examples of cytostatic agents include modified toxins,

methotrexate, adriamycin, radionuclides (e.g., such as disclosed in Fritzberg et al., U.S. Patent No. 4,897,255), protein kinase inhibitors, including staurosporin, a protein kinase C inhibitor of the following formula:

as well as diindoloalkaloids having one of the following general structures:

as well as stimulators of the production or activation of TGF -beta, including Tamoxifen and derivatives of functional equivalents (e.g., plasmin, heparin, compounds capable of reducing the level or inactivating the lipoprotein Lp(a) or the glycoprotein apolipoprotein(a)) thereof, TGF-beta or functional equivalents, derivatives or analogs thereof, suramin, nitric oxide releasing compounds (e.g., nitroglycerin) or analogs or functional equivalents thereof, paclitaxel or analogs thereof (e.g., taxotere), inhibitors of specific enzymes (such as the nuclear enzyme DNA topoisomerase II and DNA polymerase, RNA polymerase, adenyl guanyl cyclase), superoxide dismutase inhibitors, terminal deoxynucleotidyl-transferase, reverse transcriptase, antisense oligonucleotides that suppress smooth muscle cell proliferation and the like. Other examples of "cytostatic agents" include peptidic or mimetic inhibitors (i.e., antagonists, agonists, or competitive or non-competitive inhibitors) of cellular factors that may (e.g., in the presence of extracellular matrix) trigger proliferation of smooth muscle cells or pericytes: e.g., cytokines (e.g., interleukins such as IL-I), growth factors (e.g., PDGF, TGF-alpha or - beta, tumor necrosis factor, smooth muscle- and endothelial-derived growth factors, i.e., endothelin, FGF), homing receptors (e.g., for platelets or leukocytes), and extracellular matrix receptors (e.g., integrins). Representative examples of useful therapeutic agents in this category of cytostatic agents addressing smooth muscle proliferation include: subfragments of heparin, triazolopyrimidine (trapidil; a PDGF antagonist), lovastatin, and prostaglandins El or 12.

Agents that inhibit the intracellular increase in cell volume (i.e., the tissue volume occupied by a cell), such as cytoskeletal inhibitors or metabolic inhibitors.

Representative examples of cytoskeletal inhibitors include colchicine, vinblastin, cytochalasins, paclitaxel and the like, which act on microtubule and microfilament networks within a cell. Representative examples of metabolic inhibitors include staurosporin, trichothecenes, and modified diphtheria and ricin toxins, Pseudomonas exotoxin and the like. Trichothecenes include simple trichothecenes (i.e., those that have only a central sesquiterpenoid structure) and macrocyclic trichothecenes (i.e., those that have an additional macrocyclic ring), e.g., a verrucarins or roridins, including Verrucarin A, Verrucarin B, Verrucarin J (Satratoxin C), Roridin A, Roridin C, Roridin D, Roridin E (Satratoxin D), Roridin H. Agents acting as an inhibitor that blocks cellular protein synthesis and/or secretion or organization of extracellular matrix (i.e., an "anti-matrix agent"). Representative examples of "anti-matrix agents" include inhibitors (i.e., agonists and antagonists and competitive and non- competitive inhibitors) of matrix synthesis, secretion and assembly, organizational cross-linking (e.g., transglutaminases cross- linking collagen), and matrix remodeling (e.g., following wound healing). A representative example of a useful therapeutic agent in this category of anti-matrix agents is colchicine, an inhibitor of secretion of extracellular matrix. Another example is tamoxifen for which evidence exists regarding its capability to organize and/or stabilize as well as diminish smooth muscle cell proliferation following angioplasty. The organization or stabilization may stem from the blockage of vascular smooth muscle cell maturation in to a pathologically proliferating form.

Agents that are cytotoxic to cells, particularly cancer cells. Preferred agents are Roridin A, Pseudomonas exotoxin and the like or analogs or functional equivalents thereof. A plethora of such therapeutic agents, including radioisotopes and the like, have been identified and are known in the art. In addition, protocols for the identification of cytotoxic moieties are known and employed routinely in the art.

A number of the above therapeutic agents and several others have also been identified as candidates for vascular treatment regimens, for example, as agents targeting restenosis. Such agents include one or more of the following: calcium-channel blockers, including benzothiazapines (e.g., diltiazem, clentiazem); dihydropyridines (e.g., nifedipine, amlodipine, nicardapine); phenylalkylamines (e.g., verapamil); serotonin

pathway modulators, including 5-HT antagonists (e.g., ketanserin, naftidrofuryl) and 5- HT uptake inhibitors (e.g., fluoxetine); cyclic nucleotide pathway agents, including phosphodiesterase inhibitors (e.g., cilostazole, dipyridamole), adenylate/guanylate cyclase stimulants (e.g., forskolin), and adenosine analogs; catecholamine modulators, including α-antagonists (e.g., prazosin, bunazosine), β-antagonists (e.g., propranolol), and α/β-antagonists (e.g., labetalol, carvedilol); endothelin receptor antagonists; nitric oxide donors/releasing molecules, including organic nitrates/nitrites (e.g., nitroglycerin, isosorbide dinitrate, amyl nitrite), inorganic nitroso compounds (e.g., sodium nitroprusside), sydnonimines (e.g., molsidomine, linsidomine), nonoates (e.g., diazenium diolates, NO adducts of alkanediamines), S-nitroso compounds, including low molecular weight compounds (e.g., S-nitroso derivatives of captopril, glutathione andN-acetyl penicillamine) and high molecular weight compounds (e.g., S-nitroso derivatives of proteins, peptides, oligosaccharides, polysaccharides, synthetic polymers/oligomers and natural polymers/oligomers), C-nitroso-, O-nitroso- and N-nitroso-compounds, and L- arginine; ACE inhibitors (e.g., cilazapril, fosinopril, enalapril); ATII -receptor antagonists (e.g., saralasin, losartin); platelet adhesion inhibitors (e.g., albumin, polyethylene oxide); platelet aggregation inhibitors, including aspirin and thienopyridine (ticlopidine, clopidogrel) and GP Ilb/IIIa inhibitors (e.g., abciximab, epitifibatide, tirofiban, intergrilin); coagulation pathway modulators, including heparinoids (e.g., heparin, low molecular weight heparin, dextran sulfate, β-cyclodextrin tetradecasulfate), thrombin inhibitors (e.g., hirudin, hirulog, PPACK (D-phe-L-propyl-L-arg-chloromethylketone), argatroban), FXa inhibitors (e.g., antistatin, TAP (tick anticoagulant peptide)), vitamin K inhibitors (e.g., warfarin), and activated protein C; cyclooxygenase pathway inhibitors (e.g., aspirin, ibuprofen, flurbiprofen, indomethacin, sulfinpyrazone); natural and synthetic corticosteroids (e.g., dexamethasone, prednisolone, methprednisolone, hydrocortisone); lipoxygenase pathway inhibitors (e.g., nordihydroguairetic acid, caffeic acid; leukotriene receptor antagonists; antagonists of E- and P-selectins; inhibitors of VCAM-I and ICAM-I interactions; prostaglandins and analogs thereof, including prostaglandins such as PGEl and PGI2; prostacyclins and prostacyclin analogs (e.g., ciprostene, epoprostenol, carbacyclin, iloprost, beraprost); macrophage activation preventers (e.g., bisphosphonates); HMG-CoA reductase inhibitors (e.g., lovastatin,

pravastatin, fluvastatin, simvastatin, cerivastatin); fish oils and omega-3 -fatty acids; free- radical scavengers/antioxidants (e.g., probucol, vitamins C and E, ebselen, retinoic acid (e.g., trans-retinoic acid), SOD mimics); agents affecting various growth factors including FGF pathway agents (e.g., bFGF antibodies, chimeric fusion proteins), PDGF receptor antagonists (e.g., trapidil), IGF pathway agents (e.g., somatostatin analogs such as angiopeptin and ocreotide), TGF-β pathway agents such as polyanionic agents (heparin, fucoidin), decorin, and TGF-β antibodies, EGF pathway agents (e.g., EGF antibodies, receptor antagonists, chimeric fusion proteins), TNF-α pathway agents (e.g., thalidomide and analogs thereof), thromboxane A2 (TXA2) pathway modulators (e.g., sulotroban, vapiprost, dazoxiben, ridogrel), protein tyrosine kinase inhibitors (e.g., tyrphostin, genistein, and quinoxaline derivatives); MMP pathway inhibitors (e.g., marimastat, ilomastat, metastat), and cell motility inhibitors (e.g., cytochalasin B); antiproliferative/antineoplastic agents including antimetabolites such as purine analogs (e.g., 6-mercaptopurine), pyrimidine analogs (e.g., cytarabine and 5-fluorouracil) and methotrexate, nitrogen mustards, alkyl sulfonates, ethylenimines, antibiotics (e.g., daunorubicin, doxorubicin, daunomycin, bleomycin, mitomycin, penicillins, cephalosporins, ciprofalxin, vancomycins, aminoglycosides, quinolones, polymyxins, erythromycins, tertacyclines, chloramphenicols, clindamycins, linomycins, sulfonamides, and their homologs, analogs, fragments, derivatives, and pharmaceutical salts), nitrosoureas (e.g., carmustine, lomustine) and cisplatin, agents affecting microtubule dynamics (e.g., vinblastine, vincristine, colchicine, paclitaxel, epothilone), caspase activators, proteasome inhibitors, angiogenesis inhibitors (e.g., endostatin, angiostatin and squalamine), and rapamycin, cerivastatin, flavopiridol and suramin; matrix deposition/organization pathway inhibitors (e.g., halofuginone or other quinazolinone derivatives, tranilast); endothelialization facilitators (e.g., VEGF and RGD peptide); and blood rheology modulators (e.g., pentoxifylline).

Other examples of therapeutic agents include anti-tumor agents, such as docetaxel, alkylating agents (e.g., mechlorethamine, chlorambucil, cyclophosphamide, melphalan, ifosfamide), plant alkaloids (e.g., etoposide), inorganic ions (e.g., cisplatin), biological response modifiers (e.g., interferon), and hormones (e.g., tamoxifen,

flutamide), as well as their homologs, analogs, fragments, derivatives, and pharmaceutical salts.

Additional examples of therapeutic agents include organic-soluble therapeutic agents, such as mithramycin, cyclosporine, and plicamycin. Further examples of therapeutic agents include pharmaceutically active compounds, anti-sense genes, viral, liposomes and cationic polymers (e.g., selected based on the application), biologically active solutes (e.g., heparin), prostaglandins, prostcyclins, L-arginine, nitric oxide (NO) donors (e.g., lisidomine, molsidomine, NO-protein adducts, NO-polysaccharide adducts, polymeric or oligomeric NO adducts or chemical complexes), enoxaparin, Warafin sodium, dicumarol, interferons, interleukins, chymase inhibitors (e.g., Tranilast), ACE inhibitors (e.g., Enalapril), serotonin antagonists, 5-HT uptake inhibitors, and beta blockers, and other antitumor and/or chemotherapy drugs, such as BiCNU, busulfan, carboplatinum, cisplatinum, Cytoxan, DTIC, fludarabine, mitoxantrone, velban, VP- 16, herceptin, leustatin, navelbine, rituxan, and taxotere. Therapeutic agents are described, for example, in DiMatteo et al., U.S. Patent

Application Publication No. US 2004/0076582 Al , published on April 22, 2004, and entitled "Agent Delivery Particle", and in Schwarz et al., U.S. Patent No. 6,368,658, both of which are incorporated herein by reference.

In certain embodiments, in addition to or as an alternative to including therapeutic agents, particle 100 can include one or more radiopaque materials, materials that are visible by magnetic resonance imaging (MRI-visible materials), ferromagnetic materials, and/or contrast agents (e.g., ultrasound contrast agents). Radiopaque materials, MRI- visible materials, ferromagnetic materials, and contrast agents are described, for example, in Rioux et al., U.S. Patent Application Publication No. US 2004/0101564 Al, published on May 27, 2004, and entitled "Embolization", which is incorporated herein by reference.

In general, particle 100 can have a diameter of about 3,000 microns or less (e.g., from about two microns to about 3,000 microns, from about 10 microns to about 3,000 microns, from about 40 microns to about 2,000 microns; from about 100 microns to about 700 microns; from about 500 microns to about 700 microns; from about 100 microns to about 500 microns; from about 100 microns to about 300 microns; from about 300 microns to about 500 microns; from about 500 microns to about 1 ,200 microns; from

about 500 microns to about 700 microns; from about 700 microns to about 900 microns; from about 900 microns to about 1,200 microns, from about 1,000 microns to about 1,200 microns). In some embodiments, particle 100 can have a diameter of about 3,000 microns or less (e.g., about 2,500 microns or less; about 2,000 microns or less; about 1,500 microns or less; about 1,200 microns or less; about 1,150 microns or less; about 1,100 microns or less; about 1,090 microns or less; about 1,080 microns or less; about 1,070 microns or less; about 1,060 microns or less; about 1,050 microns or less; about 1,040 microns or less; about 1,030 microns or less; about 1,020 microns or less; about 1,010 microns or less; about 1,000 microns or less; about 900 microns or less; about 700 microns or less; about 500 microns or less; about 400 microns or less; about 300 microns or less; about 100 microns or less; about 50 microns or less; about 10 microns or less; about five microns or less) and/or about one micron or more (e.g., about five microns or more; about 10 microns or more; about 50 microns or more; about 100 microns or more; about 300 microns or more; about 400 microns or more; about 500 microns or more; about 700 microns or more; about 900 microns or more; about 1,000 microns or more; about 1,010 microns or more; about 1,020 microns or more; about 1,030 microns or more; about 1,040 microns or more; about 1,050 microns or more; about 1,060 microns or more; about 1,070 microns or more; about 1,080 microns or more; about 1,090 microns or more; about 1,100 microns or more; about 1,150 microns or more; about 1,200 microns or more; about 1,500 microns or more; about 2,000 microns or more; about 2,500 microns or more). In some embodiments, particle 100 can have a diameter of less than about 100 microns (e.g., less than about 50 microns).

In some embodiments, particle 100 can be substantially spherical. In certain embodiments, particle 100 can have a sphericity of about 0.8 or more (e.g., about 0.85 or more, about 0.9 or more, about 0.95 or more, about 0.97 or more). Particle 100 can be, for example, manually compressed, essentially flattened, while wet to about 50 percent or less of its original diameter and then, upon exposure to fluid, regain a sphericity of about 0.8 or more (e.g., about 0.85 or more, about 0.9 or more, about 0.95 or more, about 0.97 or more). The sphericity of a particle can be determined using a Beckman Coulter RapidVUE Image Analyzer version 2.06 (Beckman Coulter, Miami, FL). Briefly, the RapidVUE takes an image of continuous-tone (gray-scale) form and converts it to a

digital form through the process of sampling and quantization. The system software identifies and measures particles in an image in the form of a fiber, rod or sphere. The sphericity of a particle, which is computed as Da/Dp (where Da = V(4A/π); Dp = P/π ; A = pixel area; P = pixel perimeter), is a value from zero to one, with one representing a perfect circle.

Matrix 102 can include one or more of the block copolymers described above. In some embodiments, matrix 102 can include multiple (e.g., two, three, four, five, six, seven, eight, nine, 10) different block copolymers. For example, in some embodiments, a particle can include a blend of at least two different block copolymers. Alternatively or additionally, matrix 102 can include other types of materials, such as other polymers that are not block copolymers. Examples of polymers include polyvinyl alcohols ("PVA"), polyacrylic acids, polymethacrylic acids, poly vinyl sulfonates, carboxymethyl celluloses, hydroxyethyl celluloses, substituted celluloses, polyacrylamides, polyethylene glycols, polyamides, polyureas, polyurethanes, polyesters, polyethers, polystyrenes, polysaccharides, polylactic acids, polyethylenes, polyolefins, polypropylenes, polymethylmethacrylates, polycaprolactones, polyglycolic acids, poly(lactic-co-glycolic) acids (e.g., poly(d-lactic-co-glycolic) acids), polysulfones, polyethersulfones, polycarbonates, nylons, silicones, linear or crosslinked polysilicones, and copolymers or mixtures thereof. In certain embodiments, matrix 102 can include a highly water insoluble, high molecular weight polymer. An example of such a polymer is a high molecular weight PVA that has been acetalized. Matrix 102 can include substantially pure intrachain 1,3 -acetalized PVA, and can be substantially free of animal derived residue such as collagen. In some embodiments, matrix 102 can include a minor amount (e.g., about 2.5 weight percent or less, about one weight percent or less, about 0.2 weight percent or less) of a gelling material (e.g., a polysaccharide, such as alginate). In certain embodiments, matrix 102 can include a bioabsorbable (e.g., resorbable) polymer (e.g., alginate, gelatin, albumin, resorbable polyvinyl alcohol, albumin, dextran, starch, ethyl cellulose, polyglycolic acid, polylactic acid, polylactic acid/polyglycolic acid copolymers, poly(lactic-co-glycolic) acid). Matrix 102 can include, for example, polyvinyl alcohol, alginate, or both polyvinyl alcohol and alginate.

In some embodiments, in addition to or as an alternative to being used to deliver a therapeutic agent to a target site, particle 100 can be used to embolize a target site (e.g., a lumen of a subject). For example, multiple particles can be combined with a carrier fluid (e.g., a pharmaceutically acceptable carrier, such as a saline solution, a contrast agent, or both) to form a composition, which can then be delivered to a site and used to embolize the site. FIGS. 3A and 3B illustrate the use of a composition including particles to embolize a lumen of a subject. As shown, a composition, including particles 100 and a carrier fluid, is injected into a vessel through an instrument such as a catheter 1150. Catheter 1150 is connected to a syringe barrel 1110 with a plunger 1160. Catheter 1150 is inserted, for example, into a femoral artery 1120 of a subject. Catheter 1150 delivers the composition to, for example, occlude a uterine artery 1130 leading to a fibroid 1140. Fibroid 1140 is located in the uterus of a female subject. The composition is initially loaded into syringe 1110. Plunger 1160 of syringe 1110 is then compressed to deliver the composition through catheter 1150 into a lumen 1165 of uterine artery 1130. FIG. 3B, which is an enlarged view of section 3B of FIG. 3 A, shows a uterine artery 1130 that is subdivided into smaller uterine vessels 1170 (e.g., having a diameter of about two millimeters or less) which feed fibroid 1140. The particles 100 in the composition partially or totally fill the lumen of uterine artery 1130, either partially or completely occluding the lumen of the uterine artery 1130 that feeds uterine fibroid 1140. Compositions that include particles such as particles 100 can be delivered to various sites in the body, including, for example, sites having cancerous lesions, such as the breast, prostate, lung, thyroid, or ovaries. The compositions can be used in, for example, neural, pulmonary, and/or AAA (abdominal aortic aneurysm) applications. The compositions can be used in the treatment of, for example, fibroids, tumors, internal bleeding, arteriovenous malformations (AVMs), and/or hypervascular tumors. The compositions can be used as, for example, fillers for aneurysm sacs, AAA sac (Type II endoleaks), endoleak sealants, arterial sealants, and/or puncture sealants, and/or can be used to provide occlusion of other lumens such as fallopian tubes. Fibroids can include uterine fibroids which grow within the uterine wall (intramural type), on the outside of the uterus (subserosal type), inside the uterine cavity (submucosal type), between the layers of broad ligament supporting the uterus (interligamentous type), attached to

another organ (parasitic type), or on a mushroom-like stalk (pedunculated type). Internal bleeding includes gastrointestinal, urinary, renal and varicose bleeding. AVMs are for example, abnormal collections of blood vessels, e.g. in the brain, which shunt blood from a high pressure artery to a low pressure vein, resulting in hypoxia and malnutrition of those regions from which the blood is diverted. In some embodiments, a composition containing the particles can be used to prophylactically treat a condition.

The magnitude of a dose of a composition can vary based on the nature, location and severity of the condition to be treated, as well as the route of administration. A physician treating the condition, disease or disorder can determine an effective amount of composition. An effective amount of embolic composition refers to the amount sufficient to result in amelioration of symptoms and/or a prolongation of survival of the subject, or the amount sufficient to prophylactically treat a subject. The compositions can be administered as pharmaceutically acceptable compositions to a subject in any therapeutically acceptable dosage, including those administered to a subject intravenously, subcutaneously, percutaneously, intratrachealy, intramuscularly, intramucosaly, intracutaneously, intra-articularly, orally or parenterally.

A composition can include a mixture of particles (e.g., particles that include different types of block copolymers, particles that include different types of therapeutic agents), or can include particles that are all of the same type. In some embodiments, a composition can be prepared with a calibrated concentration of particles for ease of delivery by a physician. A physician can select a composition of a particular concentration based on, for example, the type of procedure to be performed. In certain embodiments, a physician can use a composition with a relatively high concentration of particles during one part of an embolization procedure, and a composition with a relatively low concentration of particles during another part of the embolization procedure.

Suspensions of particles in saline solution can be prepared to remain stable (e.g., to remain suspended in solution and not settle and/or float) over a desired period of time. A suspension of particles can be stable, for example, for from about one minute to about 20 minutes (e.g. from about one minute to about 10 minutes, from about two minutes to about seven minutes, from about three minutes to about six minutes).

In some embodiments, particles can be suspended in a physiological solution by matching the density of the solution to the density of the particles. In certain embodiments, the particles and/or the physiological solution can have a density of from about one gram per cubic centimeter to about 1.5 grams per cubic centimeter (e.g., from about 1.2 grams per cubic centimeter to about 1.4 grams per cubic centimeter, from about 1.2 grams per cubic centimeter to about 1.3 grams per cubic centimeter).

In some embodiments, the carrier fluid of a composition can include a surfactant. The surfactant can help the particles to mix evenly in the carrier fluid and/or can decrease the likelihood of the occlusion of a delivery device (e.g., a catheter) by the particles. In certain embodiments, the surfactant can enhance delivery of the composition (e.g., by enhancing the wetting properties of the particles and facilitating the passage of the particles through a delivery device). In some embodiments, the surfactant can decrease the occurrence of air entrapment by the particles in a composition (e.g., by porous particles in a composition). Examples of liquid surfactants include Tween ^® 80 (available from Sigma- Aldrich) and Cremophor EL ^® (available from Sigma-Aldrich). An example of a powder surfactant is Pluronic ^® F127 NF (available from BASF). In certain embodiments, a composition can include from about 0.05 percent by weight to about one percent by weight (e.g., about 0.1 percent by weight, about 0.5 percent by weight) of a surfactant. A surfactant can be added to the carrier fluid prior to mixing with the particles and/or can be added to the particles prior to mixing with the carrier fluid. In some embodiments, among the particles delivered to a subject (e.g., in a composition), the majority (e.g., about 50 percent or more, about 60 percent or more, about 70 percent or more, about 80 percent or more, about 90 percent or more) of the particles can have a diameter of about 3,000 microns or less (e.g., about 2,500 microns or less; about 2,000 microns or less; about 1,500 microns or less; about 1,200 microns or less; about 1,150 microns or less; about 1,100 microns or less; about 1,090 microns or less; about 1,080 microns or less; about 1,070 microns or less; about 1,060 microns or less; about 1,050 microns or less; about 1,040 microns or less; about 1,030 microns or less; about 1,020 microns or less; about 1,010 microns or less; about 1,000 microns or less; about 900 microns or less; about 700 microns or less; about 500 microns or less; about 400 microns or less; about 300 microns or less; about 100 microns or less; about 50

microns or less; about 10 microns or less; about five microns or less) and/or about one micron or more (e.g., about five microns or more; about 10 microns or more; about 50 microns or more; about 100 microns or more; about 300 microns or more; about 400 microns or more; about 500 microns or more; about 700 microns or more; about 900 microns or more; about 1,000 microns or more; about 1,010 microns or more; about 1,020 microns or more; about 1,030 microns or more; about 1,040 microns or more; about 1,050 microns or more; about 1,060 microns or more; about 1,070 microns or more; about 1,080 microns or more; about 1,090 microns or more; about 1,100 microns or more; about 1,150 microns or more; about 1,200 microns or more; about 1,500 microns or more; about 2,000 microns or more; about 2,500 microns or more). In some embodiments, among the particles delivered to a subject, the majority of the particles can have a diameter of less than about 100 microns (e.g., less than about 50 microns).

In certain embodiments, the particles delivered to a subject (e.g., in a composition) can have an arithmetic mean diameter of about 3,000 microns or less (e.g., about 2,500 microns or less; about 2,000 microns or less; about 1,500 microns or less; about 1,200 microns or less; about 1,150 microns or less; about 1,100 microns or less; about 1,090 microns or less; about 1,080 microns or less; about 1,070 microns or less; about 1,060 microns or less; about 1,050 microns or less; about 1,040 microns or less; about 1,030 microns or less; about 1,020 microns or less; about 1,010 microns or less; about 1,000 microns or less; about 900 microns or less; about 700 microns or less; about 500 microns or less; about 400 microns or less; about 300 microns or less; about 100 microns or less; about 50 microns or less; about 10 microns or less; about five microns or less) and/or about one micron or more (e.g., about five microns or more; about 10 microns or more; about 50 microns or more; about 100 microns or more; about 300 microns or more; about 400 microns or more; about 500 microns or more; about 700 microns or more; about 900 microns or more; about 1,000 microns or more; about 1,010 microns or more; about 1,020 microns or more; about 1,030 microns or more; about 1,040 microns or more; about 1,050 microns or more; about 1,060 microns or more; about 1,070 microns or more; about 1,080 microns or more; about 1,090 microns or more; about 1,100 microns or more; about 1,150 microns or more; about 1,200 microns or more; about 1,500 microns or more; about 2,000 microns or more; about 2,500

microns or more). In some embodiments, the particles delivered to a subject can have an arithmetic mean diameter of less than about 100 microns (e.g., less than about 50 microns).

Exemplary ranges for the arithmetic mean diameter of particles delivered to a subject include from about 100 microns to about 500 microns; from about 100 microns to about 300 microns; from about 300 microns to about 500 microns; from about 500 microns to about 700 microns; from about 700 microns to about 900 microns; from about 900 microns to about 1,200 microns; and from about 1,000 microns to about 1,200 microns. In general, the particles delivered to a subject (e.g., in a composition) can have an arithmetic mean diameter in approximately the middle of the range of the diameters of the individual particles, and a variance of about 20 percent or less (e.g. about 15 percent or less, about 10 percent or less).

In some embodiments, the arithmetic mean diameter of the particles delivered to a subject (e.g., in a composition) can vary depending upon the particular condition to be treated. As an example, in embodiments in which the particles are used to embolize a liver tumor, the particles delivered to the subject can have an arithmetic mean diameter of about 500 microns or less (e.g., from about 100 microns to about 300 microns; from about 300 microns to about 500 microns). As another example, in embodiments in which the particles are used to embolize a uterine fibroid, the particles delivered to the subject can have an arithmetic mean diameter of about 1,200 microns or less (e.g., from about 500 microns to about 700 microns; from about 700 microns to about 900 microns; from about 900 microns to about 1,200 microns). As an additional example, in embodiments in which the particles are used to treat a neural condition (e.g., a brain tumor) and/or head trauma (e.g., bleeding in the head), the particles delivered to the subject can have an arithmetic mean diameter of less than about 100 microns (e.g., less than about 50 microns). As a further example, in embodiments in which the particles are used to treat a lung condition, the particles delivered to the subject can have an arithmetic mean diameter of less than about 100 microns (e.g., less than about 50 microns). As another example, in embodiments in which the particles are used to treat thyroid cancer, the particles can have a diameter of about 1,200 microns or less (e.g., from about 1,000 microns to about 1,200 microns).

The arithmetic mean diameter of a group of particles can be determined using a Beckman Coulter RapidVUE Image Analyzer version 2.06 (Beckman Coulter, Miami, FL), described above. The arithmetic mean diameter of a group of particles (e.g., in a composition) can be determined by dividing the sum of the diameters of all of the particles in the group by the number of particles in the group.

In certain embodiments, a particle that includes one of the above-described block copolymers can also include a coating. For example, FIG. 4 shows a particle 200 with an interior region 202 including a block copolymer matrix 203 and pores 204, and a coating 205 formed of a polymer (e.g., polyvinyl alcohol) that is different from the block copolymer in matrix 203. Coating 205 can, for example, regulate the release of therapeutic agent from particle 200, and/or can provide protection to interior region 202 of particle 200 (e.g., during delivery of particle 200 to a target site). In certain embodiments, coating 205 can be formed of a bioerodible and/or bioabsorbable material that can erode and/or be absorbed as particle 200 is delivered to a target site. This can, for example, allow interior region 202 to deliver a therapeutic agent to the target site once particle 200 has reached the target site. A bioerodible material can be, for example, a polysaccharide (e.g., alginate); a polysaccharide derivative; an inorganic, ionic salt; a water soluble polymer (e.g., polyvinyl alcohol, such as polyvinyl alcohol that has not been cross-linked); biodegradable poly DL-lactide-poly ethylene glycol (PELA); a hydrogel (e.g., polyacrylic acid, hyaluronic acid, gelatin, carboxymethyl cellulose); a polyethylene glycol (PEG); chitosan; a polyester (e.g., a polycapro lactone); a poly(ortho ester); a polyanhydride; a poly(lactic-co-glycolic) acid (e.g., a poly(d-lactic-co-glycolic) acid); a poly(lactic acid) (PLA); a poly(glycolic acid) (PGA); or a combination thereof. In some embodiments, coating 205 can be formed of a swellable material, such as a hydrogel (e.g., polyacrylamide co-acrylic acid). The swellable material can be made to swell by, for example, changes in pH, temperature, and/or salt. In certain embodiments in which particle 200 is used in an embolization procedure, coating 205 can swell at a target site, thereby enhancing occlusion of the target site by particle 200.

In some embodiments, a particle can include a porous coating that is formed of a block copolymer. For example, FIG. 5 shows a particle 300 including an interior region 302 formed of a polymer (e.g., polyvinyl alcohol) and a coating 304 formed of a block

copolymer (e.g., SIBS) matrix 306. Coating 304 includes pores 308. In certain embodiments, interior region 302 can be formed of a swellable material. Pores 308 in coating 304 can expose interior region 302 to changes in, for example, pH, temperature, and/or salt. When interior region 302 is exposed to these changes, the swellable material in interior region 302 can swell, thereby causing particle 300 to become enlarged. In certain embodiments, coating 304 can be made of a relatively flexible material (e.g., SIBS) that can accommodate the swelling of interior region 302. The enlargement of particle 300 can, for example, enhance occlusion during an embolization procedure. Examples of swellable materials include hydrogels, such as polyacrylic acid, polyacrylamide co-acrylic acid, hyaluronic acid, gelatin, carboxymethyl cellulose, poly( ethylene oxide)-based polyurethane, polyaspartahydrazide, ethyleneglycoldiglycidylether (EGDGE), and polyvinyl alcohol (PVA) hydrogels. In some embodiments in which a particle includes a hydrogel, the hydrogel can be crosslinked, such that it may not dissolve when it swells. In other embodiments, the hydrogel may not be crosslinked, such that the hydrogel may dissolve when it swells.

In certain embodiments, a particle can include a coating that includes one or more therapeutic agents. In some embodiments, a particle can have a coating that includes a high concentration of one or more therapeutic agents. One or more of the therapeutic agents can also be loaded into the interior region of the particle. Thus, the surface of the particle can release an initial dosage of therapeutic agent, after which the body of the particle can provide a burst release of therapeutic agent. The therapeutic agent on the surface of the particle can be the same as or different from the therapeutic agent in the body of the particle. The therapeutic agent on the surface can be applied by exposing the particle to a high concentration solution of the therapeutic agent. In some embodiments, a therapeutic agent coated particle can include another coating over the surface the therapeutic agent (e.g., a bioerodible polymer which erodes when the particle is administered). The coating can assist in controlling the rate at which therapeutic agent is released from the particle. For example, the coating can be in the form of a porous membrane. The coating can delay an initial burst of therapeutic agent release. The coating can be applied by dipping or spraying the particle. The bioerodible polymer can be a polysaccharide (such as an alginate). In some embodiments, the

coating can be an inorganic, ionic salt. Other bioerodible coatings include polysaccharide derivatives, water-soluble polymers (such as polyvinyl alcohol, e.g., that has not been cross-linked), biodegradable poly DL-lactide-poly ethylene glycol (PELA), hydrogels (e.g., polyacrylic acid, hyaluronic acid, gelatin, carboxymethyl cellulose), polyethylene glycols (PEG), chitosan, polyesters (e.g., polycaprolactones), poly(ortho esters), polyanhydrides, poly(lactic acids) (PLA), polyglycolic acids (PGA), poly(lactic-co- glycolic) acids (e.g., poly(d-lactic-co-glycolic) acids), and combinations thereof. The coating can include therapeutic agent or can be substantially free of therapeutic agent. The therapeutic agent in the coating can be the same as or different from an agent on a surface layer of the particle and/or within the particle. A polymer coating (e.g., a bioerodible coating) can be applied to the particle surface in embodiments in which a high concentration of therapeutic agent has not been applied to the particle surface. Coatings are described, for example, in DiMatteo et al., U.S. Patent Application Publication No. US 2004/0076582 Al , published on April 22, 2004, and entitled "Agent Delivery Particle", which is incorporated herein by reference.

In some embodiments, a particle can include one or more smaller sub-particles. For example, FIG. 6 shows a particle 400 that includes a matrix 402 and pores 406 within matrix 402. Particle 400 also includes sub-particles 404 that are embedded within matrix 402. Matrix 402 can be formed of, for example, one or more polymers (e.g., block copolymers such as SIBS). Alternatively or additionally, sub-particles 404 can be formed of one or more polymers (e.g., block copolymers such as SIBS). In some embodiments, both matrix 402 and sub-particles 404 can be formed of one or more block copolymers. Block copolymer(s) in matrix 402 can be the same as, or different from, block copolymer(s) in sub-particles 404. In certain embodiments, particle 400 can include one or more therapeutic agents, such as water-soluble therapeutic agents and/or organic- soluble therapeutic agents. This can allow particle 400 to be used, for example, to deliver multiple therapeutic agents to a target site in one procedure. The therapeutic agents can be included in (e.g., dispersed throughout) matrix 402 and/or sub-particles 404. In some embodiments, matrix 402 can include one type of therapeutic agent (e.g., an organic- soluble therapeutic agent), while sub-particles 404 include another type of therapeutic agent (e.g., a water-soluble therapeutic agent). In certain embodiments, matrix 402 can

be made out of a porous material (e.g., SIBS), which can help in the release of therapeutic agent from sub-particles 404. Examples of water-soluble therapeutic agents include DNA, oligonucleotides, heparin, urokinase, halofuginone, and protein. Examples of organic-soluble therapeutic agents include paclitaxel, trans-retinoic acid, mithramycin, probucol, rapamycin, dexamethason, 5-fiuorouracil, methotrexate, doxorubicin, daunorubicin, cyclosporine, cisplatin, vinblastine, vincristine, colchicine, epothilones, endostatin, angiostatin, and plicamycin.

Particles can be formed by any of a number of different methods. As an example, FIGS. 7A-7C show a single-emulsion process that can be used, for example, to make particle 100 (FIGS. IA and IB). As shown in FIGS. 7A-7C, a drop generator 500 (e.g., a pipette) forms drops 510 of a solution including a block copolymer (e.g., SIBS) and an organic solvent (e.g., methylene chloride, chloroform, tetrahydrofuran (THF), toluene). In some embodiments, the solution can include at least about one percent weight/volume (w/v) (e.g., from about one percent w/v to about 20 percent w/v) of the block copolymer. Drops 510 fall from drop generator 500 into a vessel 520 that contains an aqueous solution including a surfactant. In some embodiments, the surfactant can be water- soluble. Examples of surfactants include polyvinyl alcohols, poly(vinyl pyrrolidone) (PVP), and polysorbates (e.g., Tween ^® 20, Tween ^® 80). In certain embodiments, the aqueous solution can be mixed (e.g., homogenized) while drops 510 are being added to it. In some embodiments, the aqueous solution can be mixed at a speed of at most about

10,000 revolutions per minute (e.g., at most about 5,000 revolutions per minute, at most about 1,500 revolutions per minute). The concentration of the surfactant in the aqueous solution can be at least 0.05 percent w/v (e.g., from 0.05 percent w/v to about 10 percent w/v). In general, as the concentration of surfactant in the aqueous solution increases, particle size can decrease.

As FIG. 7B shows, after drops 510 have fallen into vessel 520, the solution is mixed using a stirrer 530. In some embodiments, the solution can be mixed (e.g., homogenized) at a speed of at least about 1,000 revolutions per minute (e.g., at least about 2,500 revolutions per minute, at least about 5,000 revolutions per minute, at least about 6,000 revolutions per minute, at least about 7,500 revolutions per minute) and/or at most about 10,000 revolutions per minute (e.g., at most about 7,500 revolutions per

minute, at most about 6,000 revolutions per minute, at most about 5,000 revolutions per minute, at most about 2,500 revolutions per minute). For example, the solution can be mixed at a speed of from about 1000 revolutions per minute to about 6000 revolutions per minute. In certain embodiments, as mixing (e.g., homogenization) speed increases, particle size can decrease. In some embodiments, the solution can be mixed for a period of at least about 0.5 hour (e.g., at least about one hour, at least about two hours, at least about three hours, at least about four hours) and/or at most about five hours (e.g., at most about four hours, at most about three hours, at most about two hours, at most about one hour). In certain embodiments, the solution can be mixed for a period of from about one hour to about three hours (e.g., for about one hour). In some embodiments, mixing can occur at a temperature of at least about 25°C (e.g., at least about 30 ⁰ C, at least about 35°C). In general, as mixing (e.g., homogenization) temperature increases, particle size can increase. The mixing results in a suspension 540 that includes particles 100 suspended in the solvent (FIG. 7C). Particles 100 are then separated from the solvent by, for example, filtration, or centrifuging followed by removal of the supernatant.

Thereafter, particles 100 are dried (e.g., by evaporation, by lyophilization, by vacuum drying).

In some embodiments, certain materials and/or methods can be used during a particle formation process, such as the above-described single-emulsion process, to promote the formation of pores 104.

As an example, in certain embodiments, pores 104 can be formed by adding at least one salt into the solution that is used to form drops 510. Examples of salts include sodium chloride, calcium chloride, and sodium bicarbonate. In some embodiments, the salt can be kosher salt and/or sea salt. In certain embodiments, the salt can be in the form of particles. One or more of the salt particles can have a maximum dimension of at least 0.01 micron (e.g., at least 0.05 micron, at least about 0.1 micron, at least about 0.5 micron, at least about one micron, at least about five microns, at least about 10 microns, at least about 15 microns, at least about 20 microns, at least about 25 microns, at least about 30 microns, at least about 35 microns, at least about 50 microns, at least about 100 microns, at least about 150 microns, at least about 200 microns, at least about 250 microns), and/or at most about 300 microns (e.g., at most about 250 microns, at most

about 200 microns, at most about 150 microns, at most about 100 microns, at most about 50 microns, at most about 35 microns, at most about 30 microns, at most about 25 microns, at most about 20 microns, at most about 15 microns, at most about 10 microns, at most about five microns, at most about one micron, at most about 0.5 micron, at most about 0.1 micron, at most about 0.05 micron).

Particles formed from drops 510 when drops 510 include one or more salts can include the salts incorporated into a block copolymer matrix. To remove the salts from the particles, the particles can be contacted with water. For example, the particles can be placed in a water bath. In some embodiments, the water bath can have a temperature of at least about 20 ⁰ C (e.g., at least about 25°C, at least about 30 ⁰ C). The water in the water bath can dissolve the salt within the particles, thereby forming pores 104. In certain embodiments, after the particles have been formed, they can remain in vessel 520 for a period of time, thereby allowing the aqueous solution in vessel 520 to dissolve the salt in the particles and form pores 104. In some embodiments, salt particles of different sizes can be used to form pores of different sizes. For example, in certain embodiments, some of the salt particles can have a maximum dimension of from 0.01 micron to about one micron, and some of the salt particles can have a maximum dimension of from about 10 microns to about 300 microns. In some embodiments, the dimensions of the salt particles can be selected to account for a predicted extent of premature salt dissolution (e.g., during the single- emulsion process). For example, in some embodiments, a salt particle that is used to form a pore can have a maximum dimension that is at least about two times larger, and/or at most about 10 times larger, than a corresponding maximum dimension of the pore.

As another example, in certain embodiments, pores 104 can be formed by adding at least one water-soluble polymer into the solution that is used to form drops 510.

Examples of water-soluble polymers include polyethylene glycol, polyvinylpyrrolidone, carboxymethylcellulose, and hydroxy ethylcellulose. Particles formed from drops 510 when drops 510 include one or more water-soluble polymers can include the water- soluble polymers incorporated into a block copolymer matrix. To remove the water- soluble polymers from the particles, the particles can be contacted with water (e.g., as described above). The water can dissolve the water-soluble polymers within the

particles, thereby forming pores 104. In some embodiments, the amount of water-soluble polymer included in the solution that is used to form drops 510 can be selected to account for premature dissolution of some of the water-soluble polymer (e.g., during the single- emulsion process). As an additional example, in some embodiments, pores 104 can be formed by adding at least one base into the solution that is used to form drops 510. Examples of bases include sodium bicarbonate, ammonium bicarbonate, and potassium bicarbonate. In certain embodiments, the base can be in the form of particles. One or more of the particles can have a maximum dimension of at least 0.01 micron (e.g., at least about 0.05 micron, at least about 0.1 micron, at least about 0.5 micron, at least about one micron, at least about five microns, at least about 10 microns, at least about 15 microns, at least about 20 microns, at least about 25 microns, at least about 30 microns, at least about 35 microns, at least about 50 microns, at least about 100 microns, at least about 150 microns, at least about 200 microns, at least about 250 microns), and/or at most about 300 microns (e.g., at most about 250 microns, at most about 200 microns, at most about 150 microns, at most about 100 microns, at most about 50 microns, at most about 35 microns, at most about 30 microns, at most about 25 microns, at most about 20 microns, at most about 15 microns, at most about 10 microns, at most about five microns, at most about one micron, at most about 0.5 micron, at most about 0.1 micron, at most about 0.05 micron). In some embodiments, pores 104 can be formed by reacting the base with an acid.

For example, in certain embodiments, the aqueous solution in vessel 520 can include at least one acid. Examples of acids include citric acid, acetic acid, and hydrochloric acid. When drops 510 contact the acid in the aqueous solution in vessel 520, the base in drops 510 can react with the acid, generating at least one gas (e.g., carbon dioxide and/or ammonia). For example, in some embodiments, drops 510 can include sodium bicarbonate and the aqueous solution in vessel 520 can include citric acid. When drops 510 contact the aqueous solution in vessel 520, the sodium bicarbonate in drops 510 can react with the citric acid in the aqueous solution, thereby generating carbon dioxide gas. The generation of the gas during the formation of particles 100 can result in the generation of pores 104.

In certain embodiments, vessel 520 can be heated and/or can be maintained in an atmosphere having a relatively low pressure. This can, for example, cause the salt (e.g., ammonium bicarbonate) in drops 510 to sublimate, thereby producing a gas that can result in the formation of pores 104. In some embodiments, vessel 520 can be heated to a temperature of at least about 70 ⁰ C (e.g., at least about 80 ⁰ C, at least about 90 ⁰ C). The temperature of vessel 520 can be increased by, for example, placing vessel 520 in a hot water bath, placing a water jacket around vessel 520 and flowing hot water through the water jacket, and/or heating vessel 520 on a hot plate. In certain embodiments, vessel 520 can be maintained in an atmosphere having a pressure of less than 30 inches Hg (e.g., at most about 25 inches Hg, at most about 20 inches Hg, at most about 15 inches Hg, at most about 10 inches Hg, at most about five inches Hg). For example, vessel 520 can be situated in a sealed chamber that is connected to a vacuum pump. The vacuum pump can be used to maintain a relatively low pressure within the chamber. An example of a vacuum pump is the Adixen ACP 15 series dry roughing pump (from Alcatel Vacuum Products, Hingham, MA).

As a further example, in some embodiments, pores 104 can be formed using a solvent evaporation process. For example, during the single-emulsion process described with reference to FIGS. 7A-7C, the solvent in drops 510 can be evaporated at an accelerated rate. In certain embodiments, this accelerated evaporation of the solvent can result in the formation of pores 104. Without wishing to be bound by theory, it is believed that accelerating the solvent evaporation rate during the particle formation process can result in incomplete annealing and ordering of the block copolymer. The result can be the formation of a block copolymer matrix including pores.

In certain embodiments, the evaporation rate of the solvent can be increased by increasing the temperature of the single-emulsion process. For example, in some embodiments, the single-emulsion process can take place at a temperature of at least about 40 ⁰ C. In certain embodiments (e.g., in certain embodiments in which the solvent in vessel 520 is toluene), the single-emulsion process can take place at a temperature of about 70 ⁰ C. In some embodiments (e.g., some embodiments in which the solvent in vessel 520 is chloroform), the single-emulsion process can take place at a temperature of about 60 ⁰ C.

In certain embodiments, the single-emulsion process can take place at a temperature of at most about 90 ⁰ C. In some embodiments, maintaining the single- emulsion process at a temperature of at most about 90 ⁰ C can increase the likelihood of particle formation. In certain embodiments, the evaporation rate of the solvent can be increased by decreasing the pressure of the atmosphere in which the single-emulsion process takes place. The atmosphere of the single-emulsion process can be maintained at a relatively low pressure by, for example, conducting the single-emulsion process in a sealed chamber that is connected to a vacuum pump. In some embodiments, the single - emulsion process can take place in at atmosphere having a pressure of less than 30 inches Hg (e.g., at most about 25 inches Hg, at most about 20 inches Hg, at most about 15 inches Hg, at most about 10 inches Hg, at most about five inches Hg).

In certain embodiments, one or more combinations of the above-described methods can be used to form pores 104. In certain embodiments, after particle 100 has been formed, one or more therapeutic agents can be incorporated into particle 100. The therapeutic agents can be incorporated into particle 100 by, for example, immersing particle 100 in the therapeutic agents (e.g., in a solution including the therapeutic agents), and/or spraying particle 100 with the therapeutic agents (e.g., with a solution including the therapeutic agents). The porosity of particle 100 can, for example, help the therapeutic agents to diffuse into particle 100 and/or can help particle 100 to retain a relatively high volume of the therapeutic agents.

In certain embodiments, after one or more therapeutic agents have been added to particle 100, particle 100 can be dried (e.g., lyophilized). This drying of particle 100 can, for example, result in drying of the therapeutic agent in particle 100 as well. In some embodiments, particle 100 may be able to retain a dried therapeutic agent relatively easily (e.g., prior to use, such as during storage).

In some embodiments, one or more therapeutic agents can be included in the process described with reference to FIGS. 7A-7C. In certain embodiments, this can result in the formation of particles that include the therapeutic agents. For example, in some embodiments, drops 510 can be formed of a solution including a block copolymer, an

organic solvent, and a therapeutic agent. In certain embodiments, particle 100 can include the therapeutic agent when particle 100 is formed.

In some embodiments, particles that are formed using the above-described process can be coated (e.g., with a polymer). The coating can be added to the particles by, for example, spraying and/or dip-coating. These coating processes can be used, for example, to make particles like particle 200 (FIG. 4).

While a pipette has been described as an example of a drop generator that can be used in a particle formation process, in some embodiments, other types of drop generators or drop generator systems can be used in a particle formation process. For example, FIG. 8 shows a drop generator system 601 that includes a flow controller 600, a viscosity controller 605, a drop generator 610, and a vessel 620. Flow controller 600 delivers a solution (e.g., a solution that contains a block copolymer such as SIBS, a therapeutic agent, and an organic solvent) to a viscosity controller 605, which heats the solution to reduce viscosity prior to delivery to drop generator 610. The solution passes through an orifice in a nozzle in drop generator 610, forming drops of the solution. The drops are then directed into vessel 620 (e.g., containing an aqueous solution that includes a surfactant such as PVA). Drop generators are described, for example, in Lanphere et al, U.S. Patent Application Publication No. US 2004/0096662 Al, published on May 20, 2004, and entitled "Embolization", and in DiCarlo et al., U.S. Patent Application Serial No. 11/111,511, filed on April 21, 2005, and entitled "Particles", both of which are incorporated herein by reference.

FIGS. 9 A and 9B show an embodiment of a system 602 that includes drop generator system 601 , and that can be used to make particles like particle 200 (FIG. 4) and particle 300 (FIG. 5). System 602 includes a drop generator system 601 , a reactor vessel 630, a gel dissolution chamber 640 and a filter 650. As shown in FIG. 9B, flow controller 600 delivers a solution that contains one or more polymers (e.g., a block copolymer) and a gelling precursor (e.g., alginate) to viscosity controller 605, which heats the solution to reduce viscosity prior to delivery to drop generator 610. The solution passes through an orifice in a nozzle in drop generator 610, forming drops of the solution. The drops are then directed into vessel 620 (in this process, used as a gelling vessel), where the drops contact a gelling agent (e.g., calcium chloride) that converts the

gelling precursor from a solution form into a gel form, stabilizing the drops and forming particles. In some embodiments, the particles may be transferred from vessel 620 to reactor vessel 630, where one or more polymers in the gel-stabilized particles may be reacted (e.g., cross-linked). In certain embodiments, the particles may be transferred to gel dissolution chamber 640, where the gelling precursor (which was converted to a gel) can be removed from the particles. In some embodiments, the removal of the gel from the particles can result in the formation of pores in the particles. After they have been formed, the particles can be filtered in filter 650 to remove debris. In some embodiments, the particles may thereafter be coated with, for example, a polymer (e.g., a polyvinyl alcohol). Finally, the particles can be sterilized and packaged as, for example, an embolic composition including the particles.

While alginate has been described as a gelling precursor, other types of gelling precursors can be used. Gelling precursors include, for example, alginate salts, xanthan gums, natural gum, agar, agarose, chitosan, carrageenan, fucoidan, furcellaran, laminaran, hypnea, eucheuma, gum arabic, gum ghatti, gum karaya, gum tragacanth, hyaluronic acid, locust beam gum, arabinogalactan, pectin, amylopectin, other water soluble polysaccharides and other ionically cross-linkable polymers. A particular gelling precursor is sodium alginate, such as high guluronic acid, stem-derived alginate (e.g., about 50 percent or more, about 60 percent or more guluronic acid) with a low viscosity (e.g., from about 20 centipoise to about 80 centipoise at 20 ⁰ C), which can produce a high tensile, robust gel.

As described above, in some embodiments (e.g., embodiments in which alginate is used as a gelling precursor), vessel 620 can include a gelling agent such as calcium chloride. The calcium cations in the calcium chloride have an affinity for carboxylic groups in the gelling precursor. In some embodiments, the cations complex with carboxylic groups in the gelling precursor. Without wishing to be bound by theory, it is believed that the complexing of the cations with carboxylic groups in the gelling precursor can cause different regions of the gelling precursor to be pulled closer together, causing the gelling precursor to gel. In certain embodiments, the complexing of the cations with carboxylic groups in the gelling precursor can result in encapsulation of one or more other polymers (e.g., a block copolymer) in a matrix of gelling precursor.

While calcium chloride has been described as a gelling agent, other types of gelling agents can be used. Examples of gelling agents include divalent cations such as alkali metal salts, alkaline earth metal salts, or transition metal salts that can ionically cross-link with the gelling precursor. In some embodiments, an inorganic salt, such as a calcium, barium, zinc or magnesium salt, can be used as a gelling agent.

Examples of cross-linking agents that may be used to react one or more of the polymers (e.g., polyvinyl alcohol) in reactor vessel 630 include one or more aldehydes (e.g., formaldehyde, glyoxal, benzaldehyde, aterephthalaldehyde, succinaldehyde, glutaraldehyde) in combination with one or more acids, such as relatively strong acids (e.g., sulfuric acid, hydrochloric acid, nitric acid) and/or relatively weak acids (e.g., acetic acid, formic acid, phosphoric acid).

In certain embodiments, it can be desirable to reduce the surface tension of the mixture contained in vessel 620 (e.g., when forming particles having a diameter of about 500 microns or less). This can be achieved, for example, by heating the mixture in vessel 620 (e.g., to a temperature greater than room temperature, such as a temperature of about 30 ⁰ C or more), by bubbling a gas (e.g., air, nitrogen, argon, krypton, helium, neon) through the mixture contained in vessel 620, by stirring (e.g., via a magnetic stirrer) the mixture contained in vessel 620, by including a surfactant in the mixture containing the gelling agent, and/or by forming a mist containing the gelling agent above the mixture contained in vessel 620 (e.g., to reduce the formation of tails and/or enhance the sphericity of the particles).

In certain embodiments, particles can be formed by omitting one or more of the steps from the process described with reference to FIGS. 9 A and 9B. For example, one or more of the polymers may not be crosslinked, and/or the gelling precursor may not be removed.

In some embodiments, particles can be formed using a double-emulsion process. For example, FIGS. 10A- 1OF show a double-emulsion process that can be used to make particles that, like particle 400 (FIG. 6), include sub-particles.

First, drop generator 800 (e.g., a pipette) forms drops 810 of an aqueous solution containing a water-soluble therapeutic agent (e.g., DNA) and a surfactant. In some embodiments, the surfactant can be water-soluble. Examples of surfactants include

polyvinyl alcohols, poly(vinyl pyrrolidone) (PVP), and polysorbates (e.g., Tween ^® 20, Tween ^® 80). Drops 810 fall into a vessel 820 that includes a solution of a block copolymer (e.g., SIBS) and an organic-soluble therapeutic agent (e.g., paclitaxel) dissolved in an organic solvent, forming a mixture 830. As shown in FIG. 1OB, mixture 830 is then mixed (e.g., homogenized) using a stirrer 835, to produce a suspension 832 that includes sub-particles 404 suspended in solvent (FIG. 10C). Mixing of mixture 830 can occur at a speed of, for example, at least about 5,000 revolutions per minute (e.g., at least about 7,500 revolutions per minute) and/or at most about 10,000 revolutions per minute (e.g., at most about 7,500 revolutions per minute). In some embodiments, mixture 830 can be mixed for a period of at least about one minute (e.g., at least about two minutes, at least about five minutes, at least about seven minutes) and/or at most about 10 minutes (e.g., at most about seven minutes, at most about five minutes, at most about two minutes). For example, mixture 830 may be mixed for a period of from about one minute to about five minutes. After suspension 832 has been formed, suspension 832 is added to a drop generator 840 (FIG. 10D) to produce drops 850. Drops 850 fall into a vessel 870 that includes an aqueous solution, forming a mixture 880. In some embodiments, the aqueous solution in vessel 870 includes a surfactant (e.g., PVA). As FIG. 1OE shows, mixture 880 is mixed (e.g., homogenized) using a stirrer 885, at a mixing speed that is lower than the speed of the first mixing. In certain embodiments, mixture 880 can be mixed at a speed of at most about 2,000 revolutions per minute (e.g., at most about 1,500 revolutions per minute, at most about 1 ,000 revolutions per minute, at most about 500 revolutions per minute) and/or at least about 100 revolutions per minute (e.g., at least about 500 revolutions per minute, at least about 1,000 revolutions per minute, at least about 1,500 revolutions per minute). This second mixing can last for a period of, for example, at least about one minute (e.g., at least about two minutes, at least about four minutes, at least about six minutes, at least about eight minutes, at least about 10 minutes, at least about 20 minutes, at least about 30 minutes, at least about 40 minutes, at least about 50 minutes, at least about one hour, at least about two hours, at least about four hours, at least about six hours, at least about eight hours, at least about 10 hours) and/or at most about 12 hours (e.g., at most about 10 hours, at most about 8 hours, at most about 6 hours, at most about

four hours, at most about two hours, at most about one hour, at most about 50 minutes, at most about 40 minutes, at most about 30 minutes, at most about 20 minutes, at most about 10 minutes, at most about eight minutes, at most about six minutes, at most about four minutes, at most about two minutes). Mixing (e.g., homogenization) of mixture 880 produces a suspension 890 including particles 400 in solvent (FIG. 10F). Particles 400 are then separated from the solvent (e.g., by filtration) and dried (e.g., by evaporation). In some embodiments, particles 400 are separated from the solvent by evaporating the solvent.

In certain embodiments, one or more of the therapeutic agents can be omitted from the above-described process. In some embodiments, all of the therapeutic agents can be omitted from the above-described process, such that the particles that are produced do not include any therapeutic agent. Alternatively or additionally, one or more therapeutic agents can be added to the particles (e.g., by absorption) after the particles have been formed. In some embodiments, certain materials and/or methods can be used during the double-emulsion process to promote the formation of pores in particles formed by the double-emulsion process. For example, in certain embodiments, the double-emulsion process can take place at a temperature of at least about 40 ⁰ C (e.g., at least about 50 ⁰ C, at least about 60 ⁰ C), and/or in an atmosphere having a pressure of less than 30 inches Hg (e.g., at most about 25 inches Hg, at most about 20 inches Hg, at most about 15 inches Hg, at most about 10 inches Hg, at most about five inches Hg) (e.g., as described above with respect to the single-emulsion process). In some embodiments, one or more salts, bases, and/or water-soluble polymers can be combined with the organic solvent and used to form porous particles (e.g., as described above with respect to the single-emulsion process).

Methods of forming particles are described in, for example, Song et al., U.S. Patent Application Serial No. 11/314,056, filed on December 21, 2005 and entitled "Block Copolymer Particles"; Song et al., U.S. Patent Application Serial No. 11/314,557, filed on December 21, 2005 and entitled "Block Copolymer Particles"; Buiser et al., U.S. Patent Application Publication No. US 2003/0185896 Al, published on October 2, 2003, and entitled "Embolization"; Lanphere et al., U.S. Patent Application Publication No. US

2004/0096662 Al, published on May 20, 2004, and entitled "Embolization"; Lanphere et al, U.S. Patent Application Publication No. US 2005/0263916 Al, published on December 1, 2005, and entitled "Embolization"; and DiCarlo et al., U.S. Patent Application Serial No. 11/111,511, filed on April 21, 2005, and entitled "Particles", all of which are herein incorporated by reference.

Other Embodiments

While certain embodiments have been described, other embodiments are possible. As an example, in some embodiments, a particle can include one or more channels, either in addition to pores, or as an alternative to pores. For example, FIG. 11 shows a particle 900 that is formed of a block copolymer matrix 902. Particle 900 includes pores 904 and channels 906. The presence of channels 906 in particle 900 can, for example, help particle 900 to absorb and/or retain therapeutic agent, and/or to release therapeutic agent (e.g., at a target site). In some embodiments, a particle such as particle 900 can be formed using a single-emulsion process, such as the single-emulsion process described with reference to FIGS. 7A-7C. In certain embodiments, during a single- emulsion process, the drops that are contacted with an aqueous solution can be formed of a solution including a block copolymer, an organic solvent, and one or more water- soluble polymers. As the drops are formed into particles, some or all of the water-soluble polymers can leach through the hardening block copolymer, thereby forming channels 906.

As another example, in some embodiments, a particle can encapsulate one or more therapeutic agents. For example, FIG. 12 shows a particle 950 having a shell 952 formed of a block copolymer matrix 953 and including pores 954. Shell 952 encapsulates a therapeutic agent 956. Particle 950 can be formed, for example, by forming a particle out of a bioerodible and/or bioabsorbable material, forming a porous block copolymer coating over the particle, eroding and/or absorbing the bioerodible and/or bioabsorbable material, and soaking the resulting shell 952 in a solution including therapeutic agent 956. As a further example, in some embodiments, multiple salt particles and/or base particles can agglomerate during a porous particle formation process. This agglomeration

can result in the formation of a porous particle including one or more relatively large pores having dimensions that are larger than those of the individual salt particles and/or base particles.

As an additional example, in certain embodiments a particle can include a block copolymer and a bioabsorbable and/or bioerodible material dispersed uniformly or non- uniformly throughout the block copolymer. The bioabsorbable and/or bioerodible material can, for example, help to delay and/or moderate therapeutic agent release from the particle.

As a further example, while particles including sub-particles embedded within a porous matrix have been described, in some embodiments, a particle can include sub- particles (e.g., porous sub-particles, non-porous sub-particles) embedded within a non- porous matrix. In certain embodiments, a particle can include porous sub-particles embedded within a porous matrix.

As another example, in some embodiments in which a particle that includes a block copolymer is used for embolization, the particle can also include one or more other embolic agents, such as a sclerosing agent (e.g., ethanol), a liquid embolic agent (e.g., n- butyl-cyanoacrylate), and/or a fibrin agent. The other embolic agent(s) can enhance the restriction of blood flow at a target site.

As a further example, in some embodiments a particle does not include any therapeutic agents.

As another example, in some embodiments a porous particle can have a substantially uniform pore structure. Alternatively, a porous particle can have a nonuniform pore structure. For example, the particle can have a substantially non-porous interior region (e.g., formed of a polyvinyl alcohol) and a porous exterior region (e.g., formed of a mixture of a polyvinyl alcohol and alginate). Porous particles are described, for example, in Lanphere et al., U.S. Patent Application Publication No. US 2004/0096662 Al, published on May 20, 2004, and entitled "Embolization", which is incorporated herein by reference.

As an additional example, in some embodiments, a particle that includes a block copolymer can also include a shape memory material, which is capable of being configured to remember (e.g., to change to) a predetermined configuration or shape. In

certain embodiments, particles that include a shape memory material can be selectively transitioned from a first state to a second state. For example, a heating device provided in the interior of a delivery catheter can be used to cause a particle including a shape memory material to transition from a first state to a second state. Shape memory materials and particles that include shape memory materials are described in, for example, Bell et al, U.S. Patent Application Publication No. US 2004/0091543 Al , published on May 13, 2004, and entitled "Embolic Compositions", and DiCarlo et al., U.S. Patent Application Publication No. US 2005/0095428 Al, published on May 5, 2005, and entitled "Embolic Compositions", both of which are incorporated herein by reference.

As another example, in some embodiments, a particle that includes a block copolymer can also include a surface preferential material. Surface preferential materials are described, for example, in DiCarlo et al., U.S. Patent Application Publication No. US 2005/0196449 Al, published on September 8, 2005, and entitled "Embolization", which is incorporated herein by reference.

As a further example, while homogenization has been described in the single- emulsion and double-emulsion processes that can be used to form particles (e.g. particles including SIBS), in some embodiments, vortexing or sonication can be used as an alternative to, or in addition to, homogenization. As another example, in certain embodiments, particles can be linked together to form particle chains. For example, the particles can be connected to each other by links that are formed of one or more of the same material(s) as the particles, or of one or more different material(s) from the particles. Particle chains and methods of making particle chains are described, for example, in Buiser et al., U.S. Patent Application Publication No. US 2005/0238870 Al , published on October 27, 2005, and entitled "Embolization", which is incorporated herein by reference.

As an additional example, in some embodiments one or more particles is/are substantially nonspherical. In some embodiments, particles can be mechanically shaped during or after the particle formation process to be nonspherical (e.g., ellipsoidal). In certain embodiments, particles can be shaped (e.g., molded, compressed, punched, and/or agglomerated with other particles) at different points in the particle manufacturing

process. As an example, in some embodiments in which particles include SIBS, the particles can be sufficiently flexible and/or moldable to be shaped. As another example, in certain embodiments in which particles are formed using a gelling agent, the particles can be physically deformed into a specific shape and/or size after the particles have been contacted with the gelling agent, but before the polymer(s) in the particles have been cross-linked. After shaping, the polymer(s) (e.g., polyvinyl alcohol) in the particles can be cross-linked, optionally followed by substantial removal of gelling precursor (e.g., alginate). While substantially spherical particles have been described, in some embodiments, nonspherical particles can be manufactured and formed by controlling, for example, drop formation conditions. In some embodiments, nonspherical particles can be formed by post-processing the particles (e.g., by cutting or dicing into other shapes). Particle shaping is described, for example, in Baldwin et al., U.S. Patent Application Publication No. US 2003/0203985 Al, published on October 30, 2003, and entitled "Forming a Chemically Cross-Linked Particle of a Desired Shape and Diameter", which is incorporated herein by reference.

As a further example, in some embodiments, particles can be used for tissue bulking. As an example, the particles can be placed (e.g., injected) into tissue adjacent to a body passageway. The particles can narrow the passageway, thereby providing bulk and allowing the tissue to constrict the passageway more easily. The particles can be placed in the tissue according to a number of different methods, for example, percutaneously, laparoscopically, and/or through a catheter. In certain embodiments, a cavity can be formed in the tissue, and the particles can be placed in the cavity. Particle tissue bulking can be used to treat, for example, intrinsic sphincteric deficiency (ISD), vesicoureteral reflux, gastroesophageal reflux disease (GERD), and/or vocal cord paralysis (e.g., to restore glottic competence in cases of paralytic dysphonia). In some embodiments, particle tissue bulking can be used to treat urinary incontinence and/or fecal incontinence. The particles can be used as a graft material or a filler to fill and/or to smooth out soft tissue defects, such as for reconstructive or cosmetic applications (e.g., surgery). Examples of soft tissue defect applications include cleft lips, scars (e.g., depressed scars from chicken pox or acne scars), indentations resulting from liposuction, wrinkles (e.g., glabella frown wrinkles), and soft tissue augmentation of thin lips. Tissue

bulking is described, for example, in Bourne et al., U.S. Patent Application Publication No. US 2003/0233150 Al, published on December 18, 2003, and entitled "Tissue Treatment", which is incorporated herein by reference.

As an additional example, in some embodiments, particles can be used in an ablation procedure. For example, the particles may include one or more ferromagnetic materials and may be used to enhance ablation at a target site. Ablation is described, for example, in Rioux et al., U.S. Patent Application Publication No. US 2004/0101564 Al, published on May 27, 2004, and entitled "Embolization"; Lanphere et al. U.S. Patent Application Publication No. US 2005/0129775 Al, published on June 16, 2005, and entitled "Ferromagnetic Particles and Methods"; and Lanphere et al., U.S. Patent Application Serial No. 11/117,156, filed on April 28, 2005, and entitled "Tissue- Treatment Methods", all of which are incorporated herein by reference.

As another example, in some embodiments a solution can be added to the nozzle of a drop generator to enhance the porosity of particles produced by the drop generator. Examples of porosity-enhancing solutions include starch, sodium chloride at a relatively high concentration (e.g., more than about 0.9 percent, from about one percent to about five percent, from about one percent to about two percent), and calcium chloride (e.g., at a concentration of at least about 50 mM). For example, calcium chloride can be added to a sodium alginate gelling precursor solution to increase the porosity of the particles produced from the solution.

As a further example, while certain methods of making particles have been described, in some embodiments, other methods can be used to make particles. For example, in some embodiments (e.g., in some embodiments in which particles having a diameter of less than about one micron are being formed), particles can be formed using rotor/stator technology (e.g., Polytron rotor/stator technology from Kinmatica Inc.), high-pressure homogenization (e.g., using an APV-Gaulin micro fluidizer or Gaulin homogenizer), mechanical shear (e.g., using a Gifford Wood colloid mill), and/or ultrasonification (e.g., using either a probe or a flow-through cell).

As an additional example, in some embodiments, particles having different shapes, sizes, physical properties, and/or chemical properties, can be used together in an embolization procedure. The different particles can be delivered into the body of a

subject in a predetermined sequence or simultaneously. In certain embodiments, mixtures of different particles can be delivered using a multi-lumen catheter and/or syringe. In some embodiments, particles having different shapes and/or sizes can be capable of interacting synergistically (e.g., by engaging or interlocking) to form a well- packed occlusion, thereby enhancing embolization. Particles with different shapes, sizes, physical properties, and/or chemical properties, and methods of embolization using such particles are described, for example, in Bell et al., U.S. Patent Application Publication No. US 2004/0091543 Al, published on May 13, 2004, and entitled "Embolic Compositions", and in DiCarlo et al., U.S. Patent Application Publication No. US 2005/0095428 Al, published on May 5, 2005, and entitled "Embolic Compositions", both of which are incorporated herein by reference. Other embodiments are in the claims.