Eluting medical devices

1. A medical device comprising:

a. an expandable member;

b. a hydrophilic coating comprising a therapeutic agent disposed around said expandable member;

c. a sheath disposed around said coating, wherein said sheath comprises an ePTFE material having a variably permeable microstructure comprised of nodes interconnected by fibrils, and wherein the microstructure is configured to be substantially closed when the sheath is not under a strain so as to limit unintended transfer of therapeutic agent through said sheath;

d. wherein said sheath includes a wetting agent; and

e. wherein the microstructure is further configured such that when said expandable member and sheath are expanded, said sheath has an open microstructure sufficient to allow fluid external to said sheath to flow through said sheath and contact said therapeutic agent.

2. The medical device of claim 1 , wherein upon expansion, said sheath allows for transfer of said therapeutic agent to an area external to the sheath.

3. The medical device of claim 1 , wherein the wetting agent is selected from the group consisting of heparin coatings polyvinyl alcohol, polyethylene glycol, polypropylene glycol, dextran, agarose, alginate, polyacrylamide, polyglycidol, poly(vinyl alcohol-co-ethylene), poly(ethyleneglycolco-propyleneglycol), poly(vinyl acetate-co-vinyl alcohol), poly(tetrafluoroethylene-co-vinyl alcohol), poly(acrylonitrile-co-acrylamide), poly(acrylonitrile-co-acrylic acid-co-acrylamidine), polyacrylic acid, poly-lysine, polyethyleneimine, polyvinyl pyrrolidone, polyhydroxyethylmethacrylate, and polysulfone, and their copolymers, either alone or in combination.

4. The medical device of claim 1 , wherein said sheath undergoes wetting as a result of a preinsertion preparatory procedure.

5. The medical device of claim 1 , wherein said medical device comprises a catheter.

6. The medical device of claim 1 , wherein said sheath limits the transfer of particles out of said sheath greater than about 25 microns in size.

7. The medical device of claim 1 , wherein said expandable member is a medical balloon.

8. The medical device of claim 1 , wherein said sheath is configured such that it undergoes microscopic wetting in a vessel while said expandable member and sheath are in the unexpanded state.

9. The medical device of claim 1 , wherein said medical device is configured such that bodily fluids substantially wet-out the sheath as said sheath is expanded.

10. The medical device of claim 1 , wherein said medical device is configured such that said wetting of the sheath is facilitated when said sheath is in contact with the vessel wall.

11. The medical device of claim 1 , wherein said sheath further comprises at least one material from the group consisting of a fluoropolymer, polyamides, polyurethane, polyolefins, polyesters, polyglycolic acid, poly lactic acid, and trimethylene carbonate.

12. The medical device of claim 1 , wherein said nodes are aligned substantially longitudinally to the longitudinal axis of said balloon catheter and said fibrils are aligned substantially circumferentially to said axis.

13. The medical device of claim 12 , wherein the sheath is configured such that a distance between said nodes increases as said outer sheath expands.

14. The medical device of claim 1 , wherein said medical device is configured such that hydrophilic component in said coating raises the solubility point of a hydrophobic therapeutic agent.

15. The medical device of claim 1 , wherein said coating comprises at least one compound selected from the group consisting of benzethonium chloride, PEG, poloxamer, sodium salicylate, and hydroxypropyl-β-cyclodextrin.

16. The medical device of claim 1 , wherein said therapeutic agent is a hydrophilic agent.

17. The medical device of claim 1 , wherein said therapeutic agent is a hydrophobic agent.

18. The medical device of claim 17 , wherein hydrophobic agent is selected from the group consisting of taxane domain-binding drugs, such as paclitaxel, and rapamycin.

19. The medical device of claim 1 , wherein said coating comprises benzethonium chloride and said therapeutic agent is a hydrophobic agent, wherein said hydrophobic agent is less than 40 wt % of the dry coating.

20. The medical device of claim 1 , wherein said coating comprises poloxamer-188 and said therapeutic agent is a hydrophobic agent, wherein said hydrophobic agent is less than 60 wt % of the dry coating.

21. The medical device of claim 1 , wherein said coating comprises poloxamer-188 and PEG and said therapeutic agent is a hydrophobic agent, wherein said hydrophobic agent is less than 50 wt % of the dry coating.

22. The medical device of claim 1 , said coating comprises benzethonium chloride, and PEG and said therapeutic agent is a hydrophobic agent, wherein said PEG is less than 30 wt % of the dry coating and wherein said hydrophobic agent is less than 50 wt % of the dry coating.

23. The medical device of claim 1 , wherein said coating comprises benzethonium chloride, poloxamer-188 and said therapeutic agent is a hydrophobic agent, wherein poloxamer-188 is less than 30 wt % and wherein said hydrophobic agent is less than 50 wt % of the dry coating.

24. The medical device of claim 1 , wherein said coating comprises hydroxypropyl-3-cyclodextrin and said therapeutic agent is a hydrophobic agent, wherein said hydroxypropyl-3-cyclodextrin is equal to or less than 98 wt % of the dry coating.

25. The medical device of claim 1 , wherein said coating comprises sodium salicylate and said therapeutic agent is a hydrophobic agent, wherein said sodium salicylate is equal to or less than 80 wt % of the dry coating.

26. The medical device of claim 1 , wherein said expandable member further comprises a structural layer disposed around an outer surface of the expandable member.

27. The medical device of claim 26 , wherein said coating and said therapeutic agent are disposed on said structural layer.