Embolization

1. A method of making particles, the method comprising:

flowing a first material through a first orifice defined by a nozzle to form a first stream comprising the first fluid;

flowing a second material comprising a gelling precursor through a second orifice defined by the nozzle to form a second stream comprising the second fluid;

combining the first and second streams;

exposing the combined first and second streams to a periodic disturbance to form drops comprising the first and second materials; and

forming particles from the drops, the particles comprising the first and second materials,

wherein forming the particles includes converting the gelling precursor from a solution into a gel, and the method further comprises removing at least some of the gel from the particles.

2. The method of claim 1 , wherein the particles have an arithmetic mean diameter of from about ten microns to about 3,000 microns.

3. The method of claim 1 , wherein the first orifice has a diameter of from about 50 microns to about 1,000 microns.

4. The method of claim 1 , wherein the first orifice has a diameter of from about 50 microns to about 300 microns.

5. The method of claim 1 , wherein the second orifice has a diameter of from about 50 microns to about 1,000 microns.

6. The method of claim 1 , wherein the first orifice has a first diameter, the second orifice has a second diameter, and the difference between the first and second diameters is at least about 50 microns.

7. The method of claim 1 , wherein the first orifice is disposed within the second orifice.

8. The method of claim 7 , wherein the first orifice and the second orifice are concentric.

9. The method of claim 8 , wherein the first orifice is disposed at a vertical distance of about one millimeter from the second orifice.

10. The method of claim 1 , wherein the first material flows through the first orifice at a rate of from about two milliliters per minute to about ten milliliters per minute.

11. The method of claim 10 , wherein the second material flows through the second orifice at a rate of from about two milliliters per minute to about 20 milliliters per minute.

12. The method of claim 1 , wherein the first material comprises a polymer.

13. The method of claim 1 , wherein the first material and the second material are immiscible.

14. The method of claim 1 , wherein the first stream and the second stream are concentric.

15. The method of claim 1 , wherein the first material forms an interior region of the drops and the second material forms a surface region of the drops.

16. The method of claim 1 , wherein a viscosity of the first material is greater than a viscosity of the second material.

17. The method of claim 1 , wherein a viscosity of the second material is greater than a viscosity of the first material.

18. The method of claim 1 , wherein the particles contain pores.

19. The method of claim 18 , wherein the particles have a first density of pores in an interior region and a second density of pores at a surface region, the first density being different from the second density.

20. The method of claim 19 , wherein the first density is greater than the second density.

21. The method of claim 18 , wherein the particles have a first average pore size in an interior region and a second average pore size at a surface region, the first average pore size being different from the second average pore size.

22. The method of claim 21 , wherein the first average pore size is greater than the second average pore size.

23. The method of claim 1 , wherein the periodic disturbance is provided by vibrating the plurality of streams.

24. The method of claim 1 , wherein forming the drops includes establishing an electrostatic potential between the first and second streams and a vessel configured to receive the drops.

25. A method of making particles, the method comprising:

flowing a polymer through a first orifice defined by a nozzle to form a first stream comprising the first fluid;

flowing a gelling precursor through a second orifice defined by the nozzle to form a second stream comprising the second fluid;

combining the first and second streams;

exposing the combined first and second streams to a periodic disturbance to form drops comprising the polymer and the gelling precursor; and

contacting the drops with a gelling agent to convert the gelling precursor to a gel, thereby providing particles comprising the polymer and the gel.

26. The method of claim 25 , wherein the particles have an arithmetic mean diameter of from about ten microns to about 3,000 microns.

27. The method of claim 25 , wherein the polymer comprises polyvinyl alcohol.

28. The method of claim 25 , further comprising cross-linking the polymer contained in the particles.

29. The method of claim 28 , further comprising, after cross-linking the polymer contained in the particles, removing the gel from the particles.

30. The method of claim 29 , wherein the polymer comprises polyvinyl alcohol.

31. A method of making particles, the method comprising:

flowing polyvinyl alcohol through a first orifice defined by a nozzle to form a first stream comprising the first fluid;

flowing a gelling precursor through a second orifice defined by the nozzle to form a second stream comprising the second fluid;

combining the first and second streams;

exposing the combined first and second streams to a periodic disturbance to form drops comprising the polyvinyl alcohol and the gelling precursor;

contacting the drops with a gelling agent to convert the gelling precursor to a gel and form particles comprising the polyvinyl alcohol and the gel;

cross-linking the polyvinyl alcohol in the particles;

removing the gel from the particles to provide particles having pores,

wherein the particles having pores have an arithmetic mean diameter of from about ten microns to about 3,000 microns.