Crush recoverable polymer scaffolds
A medical device includes a polymer scaffold crimped to a catheter having an expansion balloon. The scaffold, after being deployed by the balloon, provides a crush recovery of about 90% after the diameter of the scaffold has been pinched or crushed by 50%. The scaffold has a pattern including an asymmetric closed cell connecting links connecting the closed cells.
1. A balloon-expandable medical device for being implanted in a peripheral vessel of the body, comprising:
a scaffold formed from a polymer tube
configured for being crimped to a balloon,
the scaffold having a pattern of interconnected elements and
the scaffold having an expanded diameter when plastically deformed from a crimped state by the balloon,
wherein the scaffold attains greater than 90% of the expanded diameter after being crushed by an amount equal to at least 33% of the expanded diameter; and
wherein the scaffold has a radial stiffness greater than 0.3 N/mm.
2. The medical device of claim 1 , wherein the interconnected elements comprise struts and links, and wherein an aspect ratio (AR) of the width to wall thickness of a strut or link is between 0.4 and 1.4.
3. The medical device of claim 2 , wherein the AR is between 0.4 to 0.9, a scaffold wall thickness is between 0.008 inches and 0.014 inches and the scaffold expanded diameter is between 5 mm and 8 mm.
4. The medical device of claim 2 , wherein the AR is between 0.8 to 1.4, a scaffold wall thickness is between 0.008 inches and 0.014 inches and the scaffold expanded diameter is between 5 mm and 8 mm.
5. The medical device of claim 2 , wherein the struts form rings having crowns and the rings are interconnected by the links, wherein the crowns have a maximum crown angle between about 90 degrees and 115 degrees when the scaffold has the expanded diameter.
6. The medical device of claim 2 , wherein the interconnected elements include a plurality of rings and the links connect a ring to another ring, wherein the interconnected elements form an asymmetric closed cell, wherein the closed cell is asymmetric both with respect to a bending axis and the longitudinal axis of the scaffold, which is perpendicular to the bending axis, and wherein the asymmetry of the closed cell is with respect to a portion of the links connecting the closed cell to adjacent closed cells.
7. The medical device of claim 1 , wherein the interconnected elements include rings formed by struts, links, crown angles of rings, and there are no more than 9 crowns in a ring and 3 links connecting any ring to an adjacent ring, and
wherein prior to crimping the scaffold to the balloon the scaffold has an outer diameter of 8 to 10 mm, the crown angles for rings of the scaffold are between 90 and 115 degrees, and
the scaffold has a wall thickness of at least 0.008 in.
8. The medical device of claim 7 ,
wherein a network of struts and links form a plurality of closed cells, each closed cell having a first end circumferentially spaced from an opposing second end and a pair of bending elements extending between the circumferentially spaced ends, each bending element forming at least two crowns,
wherein the first and second ends of a closed cell are shared with an adjacent cell, and
wherein adjacent rings are connected to each other by links such that the links connecting a ring to its two, adjacent rings are not co-linear with each other.
9. The medical device of claim 1 , wherein the interconnected elements include a plurality of asymmetric closed cells having bending elements comprising struts forming crowns, unconnected crowns, Y-crowns and W-crowns,
wherein each of the asymmetric closed cells includes more than one unconnected crown disposed between a Y-crown and a W-crown, and the asymmetry of the closed cell is with respect to a plurality of links connecting the closed cell to adjacent closed cells.
10. The medical device of claim 1 , wherein the scaffold has a ratio of pinching stiffness to wall thickness times tube diameter of 0.08:1 to 0.18:1.
11. The medical device of claim 10 , wherein the scaffold has a ratio of pre-crimp diameter of 7 mm and 10 mm,
the scaffold is fabricated to have a pair of adjacent rings, wherein the ring pair forms no more than three closed cells, and
the scaffold is fabricated from a PLLA tube.
12. The medical device of claim 11 , wherein the scaffold has a wall thickness of at least 0.008 inches.
13. The medical device of claim 1 , wherein the polymer is PLLA, or a blend of PLLA with a polymer having a lower T g than PLLA, or a block co-polymer, or a multi-layered structure having different T g values for the material of different layers.
14. The medical device of claim 13 , wherein the block co-polymer or blend is PLLA with PEG (poly-ethylene glycol).
15. A balloon-expandable medical device, comprising:
a scaffold crimped to a balloon, the crimped scaffold adapted for being plastically deformed by the balloon such that the plastically deformed scaffold has a diameter 300-400% greater than a diameter of the crimped scaffold; and
wherein the plastically deformed scaffold is capable of regaining more than 90% of the plastically deformed scaffold diameter after being crushed to at least 75% of the plastically deformed scaffold diameter.
16. The medical device of claim 15 , wherein the plastically deformed scaffold diameter is an expanded diameter.
17. The medical device of claim 16 , wherein the scaffold is made from a radially expanded tube, and wherein a tube diameter is greater than the expanded diameter.
18. The medical device of claim 15 ,
wherein the scaffold is formed from a tube,
the scaffold has a pre-crimp outer diameter of 7 to 10 mm,
the scaffold has a wall thickness of at least 0.008″, and
the interconnected elements include a plurality of closed cells having bending elements comprising struts forming crowns, unconnected crowns, Y-crowns and W-crowns, wherein each closed cell includes more than one unconnected crown disposed between a Y-crown and a W-crown.
19. The medical device of claim 15 , wherein the scaffold includes interconnected elements comprising struts and links, and wherein an aspect ratio (AR) of the width to wall thickness of a strut or link is between 0.4 to 1.4, a scaffold wall thickness is between 0.008 inches and 0.014 inches and the plastically deformed scaffold diameter is between 5 mm and 8 mm.
20. The medical device of claim 19 , wherein the scaffold is made from a radially expanded tube.
21. The medical device of claim 15 , wherein the plastically deformed scaffold is capable of regaining more than 80% of the plastically deformed scaffold diameter after being crushed by an amount equal to 50% of the plastically deformed scaffold diameter, the scaffold has a wall thickness of between 0.008 inches and 0.014 inches, and the plastically deformed scaffold diameter is between 5 mm and 8 mm.
22. A peripherally implantable medical device, comprising:
a crimped scaffold that when plastically deformed by a balloon forms a scaffold having an expanded diameter, wherein,
the scaffold regains more than 90% of the expanded diameter after being crushed to at least 67% of the expanded diameter,
the scaffold is formed from PLLA,
the scaffold has a pre-crimp diameter of 7 to 10 mm,
the scaffold has struts and links, wherein a strut and/or link has a width to thickness ratio of between about 0.8 and 1.4, and
the scaffold has a radial stiffness greater than or equal to 0.3 N/mm.
23. The medical device of claim 22 , wherein the scaffold expanded diameter is between 5 mm and 8 mm.
24. The medical device of claim 22 , wherein the scaffold is capable of regaining more than 80% of the expanded diameter after being crushed by an amount equal to 50% of the expanded diameter.