System and method for treating biological vessels

1. A medical prosthesis comprising:

a plurality of undulating rings, each of the plurality of undulating rings being radially expandable, each of the plurality of undulating rings comprising one or more valleys extending towards a proximal end of the medical prosthesis and one or more peaks extending towards a distal end of the medical prosthesis, the plurality of undulating rings comprising a proximal undulating ring and a distal undulating ring;

a plurality of undulating struts in an unexpanded configuration, the plurality of undulating struts configured to transition from the unexpanded configuration to an expanded configuration, wherein as the plurality of undulating rings expand radially, each of the plurality of undulating struts becomes less undulating compared to the unexpanded configuration, the plurality of undulating struts crossing the plurality of undulating rings, undulating portions of the plurality of undulating struts in the unexpanded configuration are positioned between the plurality of undulating rings; and

a proximal end ring and a distal end ring, each of the plurality of undulating rings positioned between the proximal end ring and the distal end ring;

wherein a first subset of the plurality of undulating struts extend from the proximal end ring and terminate at the distal undulating ring and a second subset of the plurality of undulating struts extend from the distal end ring and terminate at the proximal undulating ring; wherein radial expansion of the plurality of undulating rings does not substantially alter a distance between adjacent rings of the plurality of undulating rings.

2. The medical prosthesis of claim 1 , wherein the first subset of the plurality of undulating struts is a first half of the plurality of undulating struts, and wherein the second subset of undulating struts is a second half of the plurality of undulating struts.

3. The medical prosthesis of claim 1 , wherein a shape of the proximal and distal end rings is different from a shape of each the plurality of undulating rings.

4. The medical prosthesis of claim 1 , wherein each of the first subset of the plurality of undulating struts crosses one of the valleys of each of the plurality of undulating rings, and wherein each of the second subset of the plurality of struts crosses one of the peaks of each of the plurality of undulating rings.

5. The medical prosthesis of claim 4 ,

wherein of the first subset of the plurality of undulating struts is adjacent a second strut of the second subset of the plurality of struts a first strut.

6. The medical prosthesis of claim 4 , wherein upon radial expansion of the plurality of undulating rings, the first subset of the plurality of undulating struts moves in a distal direction and the second subset of the plurality of undulating struts moves in a proximal direction.

7. The medical prosthesis of claim 1 , wherein radial expansion of the plurality of undulating rings axially moves adjacent struts of the plurality of undulating struts in opposite directions.

8. A system comprising:

a balloon mounted on a catheter shaft; and

the medical prosthesis of claim 1 , the medical prosthesis mounted over the balloon, the proximal end ring and the distal end ring fixedly attached to the catheter shaft.

9. An expandable constraining structure comprising:

a distal end ring and a proximal end ring;

a plurality of expandable rings between the distal end ring and the proximal end ring, the plurality of expandable rings comprising a first expandable ring adjacent a second expandable ring;

a plurality of struts crossing the plurality of expandable rings, wherein each of the plurality of struts is an undulating strut in an unexpanded configuration, the plurality of struts configured to transition from the unexpanded configuration to an expanded configuration, wherein in the expanded configuration, each of the plurality of struts is less undulating compared to the unexpanded configuration, undulating portions of the plurality of struts in the unexpanded configuration are positioned between the plurality of expandable rings;

wherein each of the plurality of expandable rings undulates forming peaks oriented towards a distal end of the expandable constraining structure and valleys oriented towards a proximal end of the expandable constraining structure; and

wherein a strut portion of at least one of the plurality of struts extends from a peak of the first expandable ring and to a peak of the second expandable ring,

wherein radial expansion of the plurality of expandable rings does not substantially alter a distance between adjacent expandable rings.

10. The expandable constraining structure of claim 9 , wherein each of a first subset of the plurality of struts extends between valleys of the plurality of expandable rings.

11. The expandable constraining structure of claim 10 , wherein each of a second subset of the plurality of struts extends between peaks of the plurality of expandable rings.

12. The expandable constraining structure of claim 11 , wherein during expansion of the plurality of expandable rings, each strut of the first subset of struts moves in a first direction and each strut of the second subset of struts moves in a second direction opposite the first direction.

13. The expandable constraining structure of claim 12 , wherein the first direction is a distal direction and the second direction is a proximal direction.

14. The expandable constraining structure of claim 9 , wherein each of the plurality of struts is attached to only one of the distal end ring and the proximal end ring.

15. The expandable constraining structure of claim 9 , wherein each of the plurality of struts is directly attached to only one of the distal end ring and the proximal end ring.

16. The expandable constraining structure of claim 9 , wherein each of the plurality of struts is attached to only one of the distal end ring and the proximal end ring by a flexible coupler.

17. The expandable constraining structure of claim 9 , wherein each of the plurality of expandable rings has an undulating configuration and each of the proximal and distal end rings has a zig-zag configuration.

18. The expandable constraining structure of claim 9 , wherein each of the plurality of expandable rings is expandable to a greater diameter than the distal end ring and the proximal end ring.

19. The expandable constraining structure of claim 9 , wherein each of the plurality of expandable rings is configured to expand from an unexpanded configuration to an expanded configuration, wherein the peaks and the valleys of each of the plurality of expandable rings are less undulating in the expanded configuration compared to the unexpanded configuration.

20. The expandable constraining structure of claim 9 , wherein each of the plurality of expandable rings has a different shape from the distal end ring and the proximal end ring.

21. A system comprising:

a balloon mounted on a catheter shaft; and

the expandable constraining structure of claim 9 , the expandable constraining structure mounted over the balloon, the proximal end ring and the distal end ring fixedly attached to the catheter shaft.