System and method for treating biological vessels

1. A system for performing angioplasty comprising:

(a) a balloon mounted on a catheter shaft and having a longitudinal axis; and

(b) an expandable constraining structure including a plurality of axial struts crossing a plurality of radially-expandable rings configured for constraining said balloon such that isolated balloon regions protrude through openings in said constraining structure when said balloon is inflated,

said expandable constraining structure being configured such that radial expansion of said radially-expandable rings does not substantially alter a distance between adjacent radially-expandable rings along said longitudinal axis,

wherein said expandable constraining structure is configured such that radial expansion of said radially-expandable rings axially moves adjacent axial struts attached to said adjacent radially-expandable rings in opposite directions wherein said expandable constraining structure further includes first and second end rings for fixedly attaching said expandable constraining structure to the catheter shaft.

2. The system of claim 1 , wherein said radially-expandable rings are configured with peaks and valleys forming an undulating omega loop path.

3. The system of claim 2 , wherein said plurality of axial struts interconnect said plurality of radially-expandable rings at said peaks and said valleys.

4. The system of claim 2 , wherein said undulating omega loop path comprises a plurality of contiguous omega loops.

5. The system of claim 1 , comprising at least 4 axial struts crossing at least 4 radially-expandable rings, forming at least 16 of said openings.

6. The system of claim 1 , wherein said first and second end rings are connected to terminal radially-expandable rings via N end struts, N being half of a number of said plurality of axial struts.

7. The system of claim 6 , wherein said N end struts of said first end ring are connected to peaks of a first terminal radially-expandable ring, and said N end struts of said second end ring are connected to valleys of a second terminal radially-expandable ring.

8. The system of claim 6 , wherein said N end struts of said first end ring are connected to peaks of a first terminal radially-expandable ring, and said N end struts of said second end ring are connected to peaks of a second terminal radially-expandable ring.

9. The system of claim 6 , wherein N equals 2.

10. The system of claim 1 , wherein said plurality of axial struts are fabricated from a super-elastic alloy having a thickness within the range of from about 0.04 to about 0.12 mm.

11. The system of claim 1 , wherein said plurality of radially-expandable rings are fabricated from a super-elastic alloy having a thickness within the range of from about 0.05 to about 0.12 mm.

12. The system of claim 1 , wherein said plurality of radially-expandable rings are capable of radially expanding from a compressed state of 1 mm in diameter to an expanded state of 6 mm in diameter.

13. The system of claim 1 , wherein said plurality of radially-expandable rings form an undulating radial path when compressed and a substantially linear radial path when expanded.

14. The system of claim 1 , wherein a length of said expandable constraining structure from said first end ring to said second end ring is within the range of from about 5 mm to about 300 mm.

15. The system of claim 1 , wherein said isolated balloon regions protrude about 0.1-0.5 mm from an outer surface of said expandable constraining structure.

16. The system of claim 1 , wherein said balloon is coated with a drug.

17. The system of claim 16 , wherein said drug coating contains a drug or a drug and one or more excipients.

18. The system of claim 17 , wherein said drug is an antiproliferative drug.

19. The system of claim 16 , wherein said drug coating is coated on said isolated balloon regions that protrude through said openings.

20. The system of claim 19 , wherein said isolated balloon regions protruding through said openings are about 1-5 mm in length and about 1-3.5 mm in width.

21. A method of treating a body vessel comprising:

(a) positioning, in the vessel, a balloon disposed within an expandable constraining structure including a plurality of axial struts crossing a plurality of radially-expandable rings configured for constraining said balloon such that isolated balloon regions protrude through openings in said expandable constraining structure when said balloon is inflated;

said expandable constraining structure being configured such that radial expansion of said radially-expandable rings:

(i) does not substantially alter an axial distance between adjacent radially-expandable rings; and

(ii) axially moves adjacent axial struts attached to said adjacent radially-expandable rings in opposite directions; and

(b) inflating said balloon so as to enable said isolated balloon regions to protrude through said openings and contact a wall of the vessel while said plurality of axial struts and said plurality of radially-expandable rings are displaced from the vessel, thereby treating the body vessel.

22. The method of claim 21 , wherein (b) is effected by inflating said balloon to at least 3 atm.

23. The method of claim 21 , wherein the vessel is an artery and the treatment is angioplasty.