Freeze Thaw Methods For Making Polymer Particles

RELATED APPLICATIONS

This application claims priority under 35 U. S. C. § 119(e) to U.S. Patent Application Serial No. 60/870,238, filed on December 15, 2006, the entire contents of which are hereby incorporated by reference.

5 TECHNICAL FIELD

The disclosure relates to freeze thaw methods for making polymer particles, as well as related particles, compositions and methods.

BACKGROUND

Agents, such as therapeutic agents, can be delivered systemically, for example, by 10 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. Additionally or alternatively, particles may be used to perform embolization procedures and/or to perform radiotherapy procedures.

SUMMARY

15 In one aspect, the invention features a method of forming a particle. The method includes forming a polymer into a particle and subsequently at least partially crystallizing the polymer without increasing a temperature of the polymer to more than 25°C to provide a particle that includes an at least partially crystalline polymer, where the particle has a maximum dimension of 5,000 microns or less

-0 In another aspect, the invention features a method that includes: forming a polymer into a particle, and then reducing the temperature of the polymer to less than -25°C for at least one hour. The method further includes subsequently increasing the temperature of the polymer to at least 10 ⁰ C for at least one hour. The polymer includes at least 25 weight percent vinyl alcohol monomer units, and the particle has a maximum

!5 dimension of 5,000 microns or less. i

In a further aspect, the invention features a method that includes forming a polymer into a particle, and then reducing the temperature of the polymer to less than -5O ⁰ C for at least 15 hours. The method also includes subsequently increasing the temperature of the polymer to at least 20 ⁰ C for at least five hours, and then repeating the steps of reducing the temperature and increasing the temperature in sequence at least two times. The polymer comprising at least 25 weight percent vinyl alcohol monomer units, and the particle has a maximum dimension of 5,000 microns or less.

In an additional aspect, the invention features a method that includes of forming a polymer into a particle. The method includes forming a particle that includes a polymer that is at least partially crystalline. The polymer includes at least 25 weight percent vinyl alcohol monomer units. Forming the particle is performed without using chemical crosslinking, and the particle has a maximum dimension of 5,000 microns or less.

In a further aspect, the invention features a particle having a maximum dimension of 5,000 microns or less, where the partially crystalline polymer is at least 2% crystalline. Embodiments can include one or more of the following features.

The method can include reducing the temperature of the polymer to less than 0 ⁰ C (e.g., less than -25°C, less than -50 ⁰ C) after forming the particle.

The method can include reducing the temperature of the polymer to less than 0 ⁰ C for at least one hour (e.g., at least 10 hours) after forming the particle. The method can include, after forming the particle, reducing the temperature of the polymer to less than 0 ⁰ C, and subsequently increasing the temperature of the polymer to at least 10 ⁰ C (e.g., at least 25 ⁰ C).

The polymer can include at least about 10 (e.g.,. at least about 25) weight percent vinyl alcohol monomer units. The at least partially crystalline polymer can be at least 2% crystalline.

The particle can include a therapeutic agent. The therapeutic agent can be formed before, during or after at least partially crystalline the polymer.

The polymer can be at least partially crystallized which can stabilize the microspheres without the use, for example, of an acid or an aldehyde to crosslink them. Conceptually, the at least partially crystallized polymer can be considered to be "pseudo- cosslinked" in that, without chemical cross-linking, the at least partially crystallized

polymer can exhibit mechanical properties (e.g., compressability) similar to that observed for the chemically crosslinked polymer.

The method can include repeating the following at least two times (e.g., at least three times, at least four times, at least five times): reducing the temperature of the polymer to less than -25°C for at least one hour; and then increasing the temperature of the polymer to at least 1O ⁰ C for at least one hour

The polymer can be formed into a particle using a droplet generator.

Embodiments can include one or more of the following advantages.

The at least partially crystalline polymer can render the particle(s) relatively stable (e.g., insoluble) in vivo.

The methods can provide particles appropriate for use in, for example, embolization and/or therapeutic agent delivery within a body lumen (e.g., a blood vessel of a human or an animal).

The methods can be relatively gentle so that an additive, such as therapeutic agents, can be provided in the particle before and/or during the crystallizing of the polymer with little or no undesirable chemical reaction involving the additive occurring during the crystallizing process.

The methods can provide particles having certain desirable physical properties for delivery in a body lumen (e.g., a blood vessel), such as, for example, hardness. Features and advantages are in the description, drawings, and claims.

DESCRIPTION OF DRAWINGS

FIGs IA and IB are side view of an embodiment of a particle.

FIGS. 2A, 2 B and 3 are an illustration of an embodiment of a system and method for producing particles. FIG 4A is a schematic illustrating an embodiment of a method of injecting a composition including particles into a vessel.

FIG 4B is a greatly enlarged view of region 4B in FIG 4A.

FIG 5 is a cross-sectional view of an embodiment of a particle.

DETAILED DESCRIPTION

FIGS. IA and IB show a particle 10 that can be used, for example, in an embolization procedure. Particle 10 includes a cavity 12 surrounded by a matrix 14 including pores 16. The matrix 14 is formed of a polymer, such as polyvinyl alcohol (PVA).

Generally, the polymer from which matrix 14 is formed is at least partially crystalline. For example, the polymer can be at least 2% (e.g., at least 3%, at least 4%, at least 5%, at least 10%) crystalline. As used herein, the degree that a polymer is crystalline is measured using differential scanning calorimetry, X-ray diffraction or density measurements.

FIGS. 2A, 2B, and 3 show a system 100 for producing particles. System 100 includes a flow controller 1 10, a drop generator 120 including a nozzle 130, a gelling vessel 140, a cooling vessel 150, an optional gel dissolution chamber 160, and a filter 170. An example of a commercially available drop generator is the model NISCO Encapsulation unit VAR D (NISCO Engineering, Zurich, Switzerland).

Flow controller 1 10 includes a high pressure pumping apparatus, such as a syringe pump (e.g., model PHD4400, Harvard Apparatus, Holliston, MA). Flow controller 1 10 delivers a stream 190 of a solution including a polymer and a gelling precursor to a viscosity controller 180, which heats the solution to reduce its viscosity prior to delivery to drop generator 120. Viscosity controller 180 is connected to nozzle 130 of drop generator 120 via tubing 121. After stream 190 has traveled from flow controller 180 through tubing 121, stream 190 flows around a corner having an angle a, and enters nozzle 130. As shown, angle αis about 90 degrees. However, in some embodiments, angle α?can be less than 90 degrees (e.g., less than about 70 degrees, less than about 50 degrees, less than about 30 degrees).

As stream 190 enters nozzle 130, a membrane 131 in nozzle 130 is subjected to a periodic disturbance (a vibration). The vibration causes membrane 131 to pulse upward (to the position shown in phantom in FIG. 3) and then return back to its original position. Membrane 131 is connected to a rod 133 that transmits the vibration of membrane 131, thereby periodically disrupting the flow of stream 190 as stream 190 enters nozzle 130. This periodic disruption of stream 190 causes stream 190 to form drops 195. Drops 195

fall into gelling vessel 140, where drops 195 are stabilized by gel formation. During gel formation, the gelling precursor in drops 195 is converted from a solution to a gel form by a gelling agent contained in gelling vessel 140. The gel-stabilized drops are then transferred from gelling vessel 140 to cooling vessel 150, where the polymer in the gel- stabilized drops are cooled and maintained at a reduced temperature to allow at least partial crystallization of the polymer to form particles. The particles are subsequently thawed. The cooling/thawing cycle can be repeated as desired to obtain, for example, a desired degree of crystallinity of the polymer.

In some embodiments, when in cooling vessel 150, the particles are reduced to a temperature less than 15 ⁰ C (e.g., less than 10 ⁰ C, less than 0 ⁰ C, less than -15°C, less than - 25 ⁰ C, less than -35 ⁰ C, less than -50 ⁰ C, less than -60 ⁰ C). For example, when in cooling vessel 150, the particles are reduced to a temperature of from -80 ⁰ C to -50 ⁰ C (e.g., from -75 ⁰ C to -60 ⁰ C, from -75 ⁰ C to -65 ⁰ C). In certain embodiments, when in cooling vessel 150, the particles are at a temperature of -70 ⁰ C. In certain embodiments, the particles are held in cooling vessel 150 at reduced temperature for at least 10 minutes (e.g., at least 30 minutes, at least one hour, at least two hours, at least five hours, at least 10 hours, at least 20 hours, at least one day) and/or at most one week (e.g., at most three days, at most two days, at most one day). For example, the particles can be held in cooling vessel 150 at reduced temperature for from one hour to two days (e.g., from five hours to two days, from 10 hours to two days). In some embodiments, the particles are held in cooling vessel 150 at reduced temperature for one day.

In some embodiments, when thawing the particles, the temperature of the particles is increased to particles are reduced to at least 10 ⁰ C (e.g., at least 2O ⁰ C, at least 25°C). For example, when thawing the particles, the temperature of the particles can be increased to a temperature of particles are of from 10 ⁰ C to 3O ⁰ C (e.g., from 15°C to 3O ⁰ C, from 20 ⁰ C to 30 ⁰ C). In certain embodiments, when thawing the particles, the particles are at a temperature of 25°C.

In certain embodiments, the particles are held at the relatively high (e.g., from 10 ⁰ C to 30 ⁰ C) temperature for at least 10 minutes (e.g., at least 30 minutes, at least one hour, at least two hours, at least three hours, at least four hours, at least five hours, at least

six hours) and/or at most one week (e.g., at most three days, at most one day, at most 15 hours, at most 10 hours). For example, the particles are held at the relatively high (e.g., from 10 ⁰ C to 30 ⁰ C) temperature for from one hour to one day (e.g., from two hours to 10 hours, from four hours to 10 hours). In some embodiments, the particles are held at the relatively high (e.g., from 10 ⁰ C to 3O ⁰ C) temperature for six hours.

In some embodiments, the cooling/thawing cycle is repeated at least two times (e.g., at least three times, at least four times, at least five times, at least six times) and/or at most 100 times (e.g., at most 50 times, at most 25 times, at most 10 times). For example, the cooling/thawing cycle can be repeated from two times to 25 times (e.g., from four times to 10 times, from five times to 10 times). In certain embodiments, the cooling/thawing cycle is repeated six times.

In some embodiments, the cooling/thawing process is as follows: the particles are held in cooling vessel 150 at a temperature of less than -50 ⁰ C (e.g., from -8O ⁰ C to -6O ⁰ C) for at least 10 hours (e.g., from 10 hours to two day); the particles are then held at a temperature of at least 15°C (e.g., from 20 ⁰ C to 30 ⁰ C) for at least two hours (e.g., from four hours to 10 hours); and the cooling/thawing cycle is repeated at least two times (e.g., from three times to six times).

Optionally, in addition to being disposed in cooling vessel 150 at the temperatures noted above, the particles can be disposed in a coolant (e.g., liquid nitrogen, liquid carbon dioxide) for a period of time (e.g., one minute to one hour, two minutes to 30 minutes, three minutes to 10 minutes, five minutes).

After the cooling/thawing cycle(s), the particles can optionally be transferred to gel dissolution chamber 160. In gel dissolution chamber 160, the gelling precursor (which was converted to a gel) in the particles is dissolved. After the particle formation process has been completed, the particles can be filtered in filter 170 to remove debris, and sterilized and packaged as a composition including particles.

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. 1 1/1 1 1,51 1, filed on April 21, 2005, and entitled "Particles", both of which are incorporated herein by reference.

In general, the maximum dimension of particle 10 is 5,000 microns or less (e.g., from two microns to 5,000 microns; from 10 microns to 5,000 microns; from 40 microns to 2,000 microns; from 100 microns to 700 microns; from 500 microns to 700 microns; from 100 microns to 500 microns; from 100 microns to 300 microns; from 300 microns to 500 microns; from 500 microns to 1 ,200 microns; from 500 microns to 700 microns; from 700 microns to 900 microns; from 900 microns to 1 ,200 microns; from 1 ,000 microns to 1 ,200 microns). In some embodiments, the maximum dimension of particle 10 is 5,000 microns or less (e.g., 4,500 microns or less, 4,000 microns or less, 3,500 microns or less, 3,000 microns or less, 2,500 microns or less; 2,000 microns or less; 1 ,500 microns or less; 1,200 microns or less; 1 ,150 microns or less; 1 ,100 microns or less; 1,050 microns or less; 1 ,000 microns or less; 900 microns or less; 700 microns or less; 500 microns or less; 400 microns or less; 300 microns or less; 100 microns or less; 50 microns or less; 10 microns or less; five microns or less) and/or one micron or more (e.g., five microns or more; 10 microns or more; 50 microns or more; 100 microns or more; 300 microns or more; 400 microns or more; 500 microns or more; 700 microns or more; 900 microns or more; 1 ,000 microns or more; 1 ,050 microns or more; 1 ,100 microns or more; 1 ,150 microns or more; 1 ,200 microns or more; 1 ,500 microns or more; 2,000 microns or more; 2,500 microns or more). In some embodiments, the maximum dimension of particle 10 is less than 100 microns (e.g., less than 50 microns). In some embodiments, particle 10 can be substantially spherical. In certain embodiments, particle 10 can have a sphericity of 0.8 or more (e.g., 0.85 or more, 0.9 or more, 0.95 or more, 0.97 or more). Particle 10 can be, for example, manually compressed, essentially flattened, while wet to 50 percent or less of its original diameter and then, upon exposure to fluid, regain a sphericity of 0.8 or more (e.g., 0.85 or more, 0.9 or more, 0.95 or more, 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 =

^4A/7τ); Dp = P/7T ; A = pixel area; P = pixel perimeter), is a value from zero to one, with one representing a perfect circle.

Examples of polymers include polymers that include vinyl alcohol monomers, vinyl formal monomers and/or vinyl acetate monomers. As referred to herein, a vinyl formal monomer unit has the following structure:

As referred to herein, a vinyl alcohol monomer unit has the following structure:

s referred to herein, a vinyl acetate monomer unit has the following structure:

In general, the monomer units can be arranged in a variety of different ways. As an example, in some embodiments, the polymer can include different monomer units that alternate with each other. For example, the polymer can include repeating blocks, each block including a vinyl formal monomer unit, a vinyl alcohol monomer unit, and a vinyl acetate monomer unit. As another example, in certain embodiments, the polymer can include blocks including multiple monomer units of the same type. Generally, however, there should be sufficient PVA present in the polymer to allow the polymer to crystallize.

In some embodiments, the polymer can have the formula that is schematically represented below, in which x, y and z each are integers that are greater than zero. In certain embodiments, x is zero. The individual monomer units that are shown can be directly attached to each other, and/or can include one or more other monomer units (e.g., vinyl formal monomer units, vinyl alcohol monomer units, vinyl acetate monomer units) between them:

vinyl formal monomer unit vinyl alcohol monomer unit vinyl acetate monomer unit

Optionally, formal linkages can occur between PVA molecules giving crosslinks. In some embodiments, the polymer can include at least five percent by weight

(e.g., at least 15 percent by weight, at least 25 percent by weight, at least 35 percent by weight) vinyl alcohol monomer units, and/or at most 80 percent by weight (e.g., at most 50 percent by weight, at most 25 percent by weight, at most 10 percent by weight) vinyl alcohol monomer units. The weight percent of a monomer unit in a polymer can be measured using solid-state NMR spectroscopy.

Generally, the polymer will contain little or no vinyl formal monomer units. In some embodiments, the polymer can include at most 10 percent by weight (e.g., at most 5 percent by weight, at most 2 percent by percent by weight) vinyl formal monomer units

and/or at least 0.1 percent by weight (e.g., at least 0.5 percent by weight, at least 1 percent by weight) vinyl formal monomer units. As used herein, the weight percent of a monomer unit in a polymer is measured using solid-state NMR spectroscopy as described above. In some embodiments, the polymer can include at least one percent by weight

(e.g., at least two percent by weight, at least five percent by weight, at least 10 percent by weight, at least 15 percent by weight) vinyl acetate monomer units, and/or at most 20 percent by weight (e.g., at most 15 percent by weight, at most 10 percent by weight, at most five percent by weight) vinyl acetate monomer units. As used herein, the weight percent of a monomer unit in a polymer is measured using solid-state NMR spectroscopy as described above.

Other polymers may also be used as a matrix polymer in particle 10. Examples of polymers include 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, polymethylmethacrylates, polycaprolactones, polyglycolic acids, poly(lactic-co-glycolic) acids (e.g., poly(d-lactic-co-glycolic) acids) and copolymers or mixtures thereof. Polymers 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"; Song et al., U.S. Patent Application Serial No. 1 1/314,056, filed on December 21, 2005, and entitled "Block Copolymer Particles"; and Song et al., U.S. Patent Application Serial No. 1 1/314,557, filed on December 21, 2005, and entitled "Block Copolymer Particles", all of which are incorporated herein by reference. 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. 4A and 4B 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 250. Catheter 250 is connected to a syringe barrel 210 with a plunger 260. Catheter 250 is inserted, for example, into a

femoral artery 220 of a subject. Catheter 250 delivers the composition to, for example, occlude a uterine artery 230 leading to a fibroid 240 located in the uterus of a female subject. The composition is initially loaded into syringe 210. Plunger 260 of syringe 210 is then compressed to deliver the composition through catheter 250 into a lumen 265 of uterine artery 230.

FIG. 4B, which is an enlarged view of section 2B of FIG. 4A, shows uterine artery 230, which is subdivided into smaller uterine vessels 270 (e.g., having a diameter of two millimeters or less) that feed fibroid 240. The particles 100 in the composition partially or totally fill the lumen of uterine artery 230, either partially or completely occluding the lumen of the uterine artery 230 that feeds uterine fibroid 240.

Compositions including 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 formed of polymers including different weight percents of vinyl alcohol monomer units, particles including 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 one minute to 20 minutes (e.g. from one minute to 10 minutes, from two minutes to seven minutes, from three minutes to 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 one gram per cubic centimeter to 1.5 grams per cubic centimeter (e.g., from 1.2 grams per cubic centimeter to 1.4 grams per cubic centimeter, from 1.2 grams per cubic centimeter to 1.3 grams per cubic centimeter).

In certain 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 ^® F 127 NF (available from BASF). In certain embodiments, a composition can include from 0.05 percent by weight to one percent by weight (e.g., 0.1 percent by weight, 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., 50 percent or more, 60 percent or more, 70 percent or more, 80 percent or more, 90 percent or more) of the particles can have a maximum dimension of 5,000 microns or less (e.g., 4,500 microns or less, 4,000 microns or less, 3,500 microns or less, 3,000 microns or less, 2,500 microns or less; 2,000 microns or less; 1,500 microns or less; 1 ,200 microns or less; 1,150 microns or less; 1,100 microns or less; 1,050 microns or less; 1,000 microns or less; 900 microns or less; 700 microns or less; 500 microns or less; 400 microns or less; 300 microns or less; 100 microns or less; 50 microns or less; 10 microns or less; five microns or less) and/or one micron or more (e.g., five microns or more; 10 microns or more; 50 microns or more; 100 microns or more; 300 microns or more; 400 microns or more; 500 microns or more; 700 microns or more; 900 microns or more; 1,000 microns or more; 1,050 microns or more; 1,100 microns or more; 1,150 microns or more; 1,200 microns or more; 1,500 microns or more; 2,000 microns or more; 2,500 microns or more). In some embodiments, among the particles delivered to a subject, the majority of the particles can have a maximum dimension of less than 100 microns (e.g., less than 50 microns).

In certain embodiments, the particles delivered to a subject (e.g., in a composition) can have an arithmetic mean maximum dimension of 5,000 microns or less (e.g., 4,500 microns or less, 4,000 microns or less, 3,500 microns or less, 3,000 microns or less, 2,500 microns or less; 2,000 microns or less; 1,500 microns or less; 1,200

microns or less; 1 ,150 microns or less; 1 ,100 microns or less; 1 ,050 microns or less; 1 ,000 microns or less; 900 microns or less; 700 microns or less; 500 microns or less; 400 microns or less; 300 microns or less; 100 microns or less; 50 microns or less; 10 microns or less; five microns or less) and/or one micron or more (e.g., five microns or more; 10 microns or more; 50 microns or more; 100 microns or more; 300 microns or more; 400 microns or more; 500 microns or more; 700 microns or more; 900 microns or more; 1 ,000 microns or more; 1 ,050 microns or more; 1 , 100 microns or more; 1 ,150 microns or more; 1 ,200 microns or more; 1,500 microns or more; 2,000 microns or more; 2,500 microns or more). In some embodiments, the particles delivered to a subject can have an arithmetic mean maximum dimension of less than 100 microns (e.g., less than 50 microns).

Exemplary ranges for the arithmetic mean maximum dimension of particles delivered to a subject include from 100 microns to 500 microns; from 100 microns to 300 microns; from 300 microns to 500 microns; from 500 microns to 700 microns; from 700 microns to 900 microns; from 900 microns to 1 ,200 microns; and from 1,000 microns to 1 ,200 microns. In general, the particles delivered to a subject (e.g., in a composition) can have an arithmetic mean maximum dimension in approximately the middle of the range of the diameters of the individual particles, and a variance of 20 percent or less (e.g. 15 percent or less, 10 percent or less). In some embodiments, the arithmetic mean maximum dimension 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 certain embodiments in which the particles are used to embolize a liver tumor, the particles delivered to the subject can have an arithmetic mean maximum dimension of 500 microns or less (e.g., from 100 microns to 300 microns; from 300 microns to 500 microns). As another example, in some embodiments in which the particles are used to embolize a uterine fibroid, the particles delivered to the subject can have an arithmetic mean maximum dimension of 1,200 microns or less (e.g., from 500 microns to 700 microns; from 700 microns to 900 microns; from 900 microns to 1 ,200 microns). As an additional example, in certain 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 maximum dimension of less than 100 microns (e.g., less than 50 microns). As a further example, in some embodiments in which the particles are used to treat a lung condition, the particles delivered to the subject can have an arithmetic mean maximum dimension of less than 100 microns (e.g., less than 50 microns). As another example, in certain embodiments in which the particles are used to treat thyroid cancer, the particles can have an arithmetic maximum dimension of 1,200 microns or less (e.g., from 1,000 microns to 1,200 microns). As an additional example, in some embodiments in which the particles are used only for therapeutic agent delivery, the particles can have an arithmetic mean maximum dimension of less than 100 microns (e.g., less than 50 microns, less than 10 microns, less than five microns).

The arithmetic mean maximum dimension 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 maximum dimension 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. Additionally or alternatively to having pores, a particle can have one or more cavities. For example, a particle can be formed so that the polymer surrounds one or more cavities.

A pore has a maximum dimension of at least 0.01 micron (e.g., at least 0.05 micron, at least 0.1 micron, at least 0.5 micron, at least one micron, at least five microns, at least 10 microns, at least 15 microns, at least 20 microns, at least 25 microns, at least 30 microns, at least 35 microns, at least 50 microns, at least 100 microns, at least 150 microns, at least 200 microns, at least 250 microns), and/or at most 300 microns (e.g., at most 250 microns, at most 200 microns, at most 150 microns, at most 100 microns, at most 50 microns, at most 35 microns, at most 30 microns, at most 25 microns, at most 20 microns, at most 15 microns, at most 10 microns, at most five microns, at most one micron, at most 0.5 micron, at most 0.1 micron, at most 0.05 micron).

A cavity has a maximum dimension of at least one micron (e.g., a least five microns, at least 10 microns, at least 25 microns, at least 50 microns, at least 100 microns, at least 250 microns, at least 500 microns, at least 750 microns) and/or at most

1 ,000 microns (e.g., at most 750 microns, at most 500 microns, at most 250 microns, at most 100 microns, at most 50 microns, at most 25 microns, at most 10 microns, at most five microns). In some embodiments (e.g., when the particle is used to deliver a therapeutic agent within a body lumen, independent of whether embolization is desired), the particle can also include a therapeutic agent (e.g., in one or more pores, in one or more cavities, on the surface of the particle).

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 noninfectious 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). Examples of radioactive species include yttrium ( ⁹⁰ Y), holmium ( ¹⁶⁶ Ho), phosphorus ( ³² P), lutetium ( ¹⁷⁷ Lu), actinium ( ²²⁵ Ac), praseodymium, astatine ( ^{21 1} At), rhenium ( ¹⁸⁶ Re), bismuth ( ²¹² Bi or ²¹³ Bi),), samarium ( ¹⁵³ Sm), iridium ( ¹⁹² Ir), rhodium ( ¹⁰⁵ Rh), iodine ( ¹³¹ I or ¹²⁵ I), indium ( ^{1 1 1} In), technetium ( ⁹⁹ Tc), phosphorus ( ³² P), sulfur ( ³⁵ S), carbon ( ¹⁴ C), tritium ( ³ H), chromium ( ⁵¹ Cr), chlorine ( ³⁶ Cl), cobalt ( ⁵⁷ Co or ⁵⁸ Co), iron ( ⁵⁹ Fe), selenium ( ⁷⁵ Se), and/or gallium ( ⁶⁷ Ga). In some embodiments, yttrium ( ⁹⁰ Y), lutetium ( ¹⁷⁷ Lu), actinium ( ²²⁵ Ac), praseodymium, astatine ( ²¹¹ At), rhenium ( ¹⁸⁶ Re), bismuth ( ²¹² Bi or ²¹³ Bi), holmium ( ¹⁶⁶ Ho), samarium ( ¹⁵³ Sm), iridium ( ¹⁹² Ir), and/or rhodium ( ¹⁰⁵ Rh) can be used as therapeutic agents. In certain embodiments, yttrium ( ⁹⁰ Y), lutetium ( ¹⁷⁷ Lu), actinium

( ²²⁵ Ac), praseodymium, astatine ( ^{21 1} At), rhenium ( ¹⁸⁶ Re), bismuth ( ²¹² Bi or ²¹³ Bi), holmium ( ¹⁶⁶ Ho), samarium ( ¹⁵³ Sm), indium ( ¹⁹² Ir), rhodium ( ¹⁰⁵ Rh), iodine ( ¹³¹ I or ¹²⁵ I), indium ( ^{11 1} In), technetium ( ⁹⁹ Tc), phosphorus ( ³² P), carbon ( ¹⁴ C), and/or tritium ( ³ H) can be used as a radioactive label (e.g., for use in diagnostics). In some embodiments, a radioactive species can be a radioactive molecule that includes antibodies containing one or more radioisotopes, for example, a radiolabeled antibody. Radioisotopes that can be bound to antibodies include, for example, iodine ( ¹³¹ I or ¹²⁵ I), yttrium ( ⁹⁰ Y), lutetium ( ¹⁷⁷ Lu), actinium ( ²²⁵ Ac), praseodymium, astatine ( ²¹¹ At), rhenium ( ¹⁸⁶ Re), bismuth ( ²¹² Bi or ²¹³ Bi), indium ( ^{1 1 1} In), technetium ( ⁹⁹ Tc), phosphorus ( ³² P), rhodium ( ¹⁰⁵ Rh), sulfur ( ³⁵ S), carbon ( ¹⁴ C), tritium ( ³ H), chromium ( ⁵¹ Cr), chlorine ( ³⁶ Cl), cobalt ( ⁵⁷ Co or ⁵⁸ Co), iron ( ⁵⁹ Fe), selenium ( ⁷⁵ Se), and/or gallium ( ⁶⁷ Ga). Examples of antibodies include monoclonal and polyclonal antibodies including RS7, Movl8, MN- 14 IgG, CC49, COL- 1, mAB A33, NP-4 F(ab')2 anti-CEA, anti-PSMA, ChL6, m-170, or antibodies to CD20, CD74 or CD52 antigens. Examples of radioisotope/antibody pairs include m-170 MAB with ⁹⁰ Y. Examples of commercially available radioisotope/antibody pairs include

Zevalin™ (IDEC pharmaceuticals, San Diego, CA) and Bexxar™ (Corixa corporation, Seattle, WA). Further examples of radioisotope/antibody pairs can be found in J. Nucl. Med. 2003, Apr: 44(4): 632-40.

Non-limiting examples of therapeutic agents include anti-thrombogenic agents; thrombogenic agents; agents that promote clotting; agents that inhibit clotting; antioxidants; angiogenic and anti-angiogenic agents and factors; anti-proliferative agents (e.g., agents capable of blocking smooth muscle cell proliferation, such as rapamycin); calcium entry blockers (e.g., verapamil, diltiazem, nifedipine); targeting factors (e.g., polysaccharides, carbohydrates); agents that can stick to the vasculature (e.g., charged moieties) (e.g., gelatin, chitosn, collagen, polymers containg bioactive groups like RGD peptides); and survival genes which protect against cell death (e.g., anti-apoptotic Bcl-2 family factors and Akt kinase).

Examples of 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. Examples of 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 a 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, BMP 12, BMP 13, BMP 14, BMP 15, and BMP 16. 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 are disclosed in Kunz et al., U.S. Patent No. 5,733,925, 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: sub fragments 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 a- antagonists (e.g., prazosin, bunazosine), /3-antagonists (e.g., propranolol), and o/jS-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 and N-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 Iib/IIIa inhibitors (e.g., abciximab, epitifibatide, tirofϊban, intergrilin); coagulation pathway modulators, including heparinoids (e.g., heparin, low molecular weight heparin, dextran sulfate, /3-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-/3 pathway agents such as polyanionic agents

(heparin, fucoidin), decorin, and TGF-/3 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.

In some embodiments, a therapeutic agent can be hydrophilic. An example of a hydrophilic therapeutic agent is doxorubicin hydrochloride. In certain embodiments, a therapeutic agent can be hydrophobic. Examples of hydrophobic therapeutic agents include paclitaxel, cisplatin, tamoxifen, and doxorubicin base. In some embodiments, a therapeutic agent can be lipophilic. Examples of lipophilic therapeutic agents include paclitaxel, other taxane derivative, dexamethasone, other steroid based therapeutics. 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"; Schwarz et al., U.S. Patent No. 6,368,658; Buiser et al., U.S. Patent Application Serial No. 11/311,617, filed on December 19, 2005, and entitled "Coils"; and Song, U.S. Patent Application Serial No. 11/355,301, filed on February 15, 2006, and entitled "Block Copolymer Particles", all 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). These materials can, for example, be bonded to the chemical species (monomer(s), oligomers(s), polymer(s)). 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 certain embodiments, a particle can also include a coating. For example, FIG. 5 shows a particle 300 having a matrix 104, pores 106 and, and a coating 310. Coating 310 can, for example, be formed of a polymer (e.g., alginate) that is different from the polymer in matrix 304. Coating 310 can, for example, regulate release of therapeutic agent from particle 300, and/or provide protection to the interior region of particle 300 (e.g., during delivery of particle 300 to a target site). In certain embodiments, coating 310 can be formed of a bioerodible and/or bioabsorbable material that can erode and/or be absorbed as particle 300 is delivered to a target site. This can, for example, allow the

interior region of particle 300 to deliver a therapeutic agent to the target site once particle 300 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 polycaprolactone); 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 310 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 300 is used in an embolization procedure, coating 310 can swell at a target site, thereby enhancing occlusion of the target site by particle 300. In some embodiments, the coating can be porous. The coating can, for example, be formed of one or more of the above-disclosed polymers.

In certain embodiments, a particle can include a coating that includes one or more therapeutic agents (e.g., a relatively 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 interior region 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 interior region of the particle. The therapeutic agent on the surface of the particle can be applied to the particle by, for example, 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 of 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. In certain embodiments, the coating can be applied by dipping and/or

spraying the particle. The bioerodible polymer can be a polysaccharide (e.g., alginate). In some embodiments, the coating can be an inorganic, ionic salt. Other examples of bioerodible coating materials 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. Examples

The following examples are illustrative only and not intended as limiting. PVA-containing particles were prepared as follows. 10.5 grams of PVA and 0.65 gram of sodium alginate were mixed in a 200 milliliter bottle to break up clumps. 100 milliliters of deionized water was added to the bottle, the top of the bottle was closed, and the bottle was then shaken. The bottle was put in a microwave oven and heated at the highest power for one minute. This was repeated (1.5 to two total minutes) until the mixture was clear. The mixture was then homogenized with a homogenizer at high speed for three minutes, and the mixture was filtered using a vacuum filter.

A 300 tip was put on a drop generator (NISCO Encapsulation unit VAR D), and the drop generator was flushed with one liter of 80 ⁰ C deionized water. The mixture from the preceding paragraph was then input to the drop generator at 65°. The pressure was increased to one bar to get a flow of 1 ,875. The waveform was set to 500kHz and the electrostatic ring was set to 2.24keV. This caused a stream of the mixture to pass through the nozzle. The stream was collected in a container containing 150 milliliter of calcium

chloride solution (two weight percent calcium chloride in water. This formed particles in the calcium chloride solution, which were allowed to sit in the calcium chloride solution for two minutes and 41 seconds.

The resulting particles were subjected to one or more freeze/thaw cycles, where each cycle was composed of: freezing the particles to -70 ⁰ C for 20 hours and thawing the particles at room temperature for four hours.

A portion of the resulting particles were then submerged in deionized water. Particles that had been through only one, two, three or four freeze/thaw cycles did not dissolve in the deionized water. Another portion of the resulting particles were then submerged in a sodium hexametaphosphate solution (5% w/v in water) to see if the particles would dissolve. Particles that had been through only one freeze/thaw cycle did dissolve in the sodium hexametaphosphate solution, whereas particles that had been through two, three or four freeze/thaw cycles did not dissolve in the sodium hexametaphosphate solution. However, after about 45 minutes of being submerged in the sodium hexametaphosphate solution, particles that had been through two, three or four freeze/thaw cycles became jelly-like. Other Embodiments

While certain embodiments have been described, other embodiments are possible. As an 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 certain embodiments, particles can be used to treat trauma and/or to fill wounds. In some embodiments, the particles can include one or more bactericidal agents and/or bacteriostatic agents. As a further example, while compositions including particles suspended in at least one carrier fluid have been described, in certain embodiments, particles may not be suspended in any carrier fluid. For example, particles alone can be contained within a syringe, and can be injected from the syringe into tissue during a tissue ablation procedure and/or a tissue bulking procedure. As an additional example, in some embodiments, particles having different shapes, sizes, physical properties, and/or chemical properties can be used together in a procedure (e.g., 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.

As a further example, in some embodiments in which a particle including a polymer is used for embolization, the particle can also include (e.g., encapsulate) one or more 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 another example, in some embodiments, a treatment site can be occluded by using particles in conjunction with other occlusive devices. For example, particles can be used in conjunction with coils. Coils are described, for example, in Elliott et al., U.S. Patent Application Serial No. 1 1/000,741, filed on December 1 , 2004, and entitled "Embolic Coils", and in Buiser et al., U.S. Patent Application Serial No. 1 1/311,617, filed on December 19, 2005, and entitled "Coils", both of which are incorporated herein by reference. In certain embodiments, particles can be used in conjunction with one or more gels. Gels are described, for example, in Richard et al., U.S. Patent Application Publication No. US 2006/0045900 Al, published on March 2, 2006, and entitled "Embolization", which is incorporated herein by reference. Additional examples of materials that can be used in conjunction with particles to treat a target site in a body of a subject include gel foams, glues, oils, and alcohol. As a further example, while particles including a polymer have been described, in some embodiments, other types of medical devices and/or therapeutic agent delivery devices can include such a polymer. For example, in some embodiments, a coil can include a polymer as described above. In certain embodiments, the coil can be formed by flowing a stream of the polymer into an aqueous solution, and stopping the flow of the polymer stream once a coil of the desired length has been formed. Coils are described, for example, in Elliott et al., U.S. Patent Application Serial No. 11/000,741, filed on December 1, 2004, and entitled "Embolic Coils", and in Buiser et al., U.S. Patent Application Serial No. 1 1/311,617, filed on December 19, 2005, and entitled "Coils", both of which are incorporated herein by reference. In certain embodiments, sponges (e.g., for use as a hemostatic agent and/or in reducing trauma) can include a polymer as described above. In some embodiments, coils and/or sponges can be used as bulking agents and/or tissue support agents in reconstructive surgeries (e.g., to treat trauma and/or congenital defects).

Other embodiments are in the claims.