Balloon expanded polymer stent
A medical device includes a polymer stent (or scaffold) crimped to a catheter balloon. The stent, after being expanded from a crimped state by the balloon, provides a crush recovery of about 90% of its expanded diameter after being pinched or crushed by an amount equal to about 50% of the expanded diameter. The stent has a pattern including a W-shaped or W-V shaped closed cell and links connecting the closed cells.
1. A medical device, comprising:
a stent made from a polymer composition comprising poly (L-lactide),
the stent has a pre-crimp diameter and a wall thickness such that a ratio of the pre-crimp diameter to the wall thickness is between 30 and 60,
the stent is configured for being crimped to a balloon by plastic deformation of the stent, and
the stent has a pattern of interconnected elements, the interconnected elements including a plurality of undulating rings connected by links, wherein each ring includes struts and crowns, and the struts are configured to fold at the crowns when the stent is crimped to the balloon.
2. The medical device of claim 1 , wherein the pre-crimp diameter is between 6 mm and 12 mm.
3. The medical device of claim 1 , wherein the wall thickness is between 0.2 mm and 0.4 mm.
4. The medical device of claim 1 , wherein the pre-crimp diameter is between 7 mm and 10 mm and the wall thickness is 0.2 mm.
5. The medical device of claim 1 , wherein the pre-crimp diameter is between 9 mm and 10 mm and the wall thickness is 0.3 mm.
6. The medical device of claim 1 , wherein the struts and the links each have a width and a thickness, and wherein an aspect ratio (AR) of the width to thickness of at least some of the struts or at least some of the links is between 0.8 and 1.4.
7. The medical device of claim 1 , wherein the links each have a width and a thickness, and wherein an aspect ratio (AR) of the width to thickness of at least some of the links is between 0.4 and 0.9.
8. The medical device of claim 1 , wherein each of the rings includes U crowns, and the links connected to their respective rings forms, with the respective rings, either a W crown or a Y crown.
9. The medical device of claim 8 , wherein the rings comprise a first ring and a second ring and the links comprise a first link and a second link,
the first ring and the second ring are connected to each other by the first link and the second link,
the first link forms a first W crown with the first ring and a first Y crown with the second ring, and
the second link forms a second W crown with the first ring and a second Y crown with the second ring.
10. The medical device of claim 9 , wherein the links comprise a third link and a fourth link,
the first ring forms with the third link a third Y crown located between the first W crown and the second W crown, and
the second ring forms with the fourth link a third W crown located between the first Y crown and the second Y crown.
11. The medical device of claim 10 , wherein a first number of U crowns are between the first W crown and the third Y crown and a second number of U crowns are between the third Y crown and the second W crown.
12. The medical device of claim 11 , wherein the pattern of interconnected elements further comprise:
a W shaped closed cell or a W-V shaped closed cell, either of which are formed by a first ring portion extending from the first W crown to the second W crown, a second ring portion extending from the first Y crown to the second Y crown, the first link and the second link, wherein
the first number of U crowns are equal to the second number of U crowns when the cell is a W shaped closed cell, and
the first number of U crowns are not equal to the second number of U crowns when the cell is a W-V shaped closed cell.
13. The medical device of claim 11 , wherein the first number is 1 or 3.
14. A medical device, comprising:
a stent made from a polymer composition comprising poly (L-lactide),
the stent has a pre-crimp diameter, an expanded diameter, and a wall thickness such that a ratio of the pre-crimp diameter to the wall thickness is between 25 and 45,
the stent is configured for being crimped to a balloon by plastic deformation of the stent, and
the stent has a pattern of interconnected elements, the interconnected elements including a plurality of undulating rings connected by links, wherein
each ring includes struts and crowns, and the struts are configured to fold at the crowns when the stent is crimped to the balloon, and
each of the struts and each of the links has a width and a thickness, and wherein an aspect ratio (AR) of the width to thickness of at least some of the struts or at least some of the links is between 0.4 and 1.4,
wherein when the stent has the expanded diameter the stent has a radial stiffness greater than 0.3 N/mm 2 .
15. A medical device, comprising:
a balloon,
a stent crimped to the balloon so that the stent is configured in a crimped state,
the stent is made from a polymer composition comprising poly (L-lactide),
the stent has a pattern of interconnected elements, the interconnected elements including a plurality of undulating rings connected by links, wherein each ring includes struts and crowns,
the struts are configured to unfold at the crowns when the balloon inflates, thereby causing the stent to expand from the crimped state to an expanded state, wherein there is an inelastic deformation at the crowns when the stent expands from the crimped state to the expanded state, and
the stent has an expanded diameter and a wall thickness when in the expanded state, and a ratio of the expanded diameter to the wall thickness is between 25 and 50,
wherein when the stent has the expanded diameter the stent has a radial stiffness greater than 0.3 N/mm 2 .
16. The medical device of claim 15 , wherein the pattern of interconnected elements is characterized by a minimum crimped diameter (Dmin), which is defined by equation 1 or equation 2:
D min=(Σ Swi+ΣCrj+ΣLwk )*(1/π)+2*WT (equation 1)
D min=(Σ Swi+ΣCrj+ΣLwk )*(1/π) (equation 2), wherein
ΣSwi (i=1 . . . n) is the sum of n ring struts having width Swi;
ΣCrj (j=1 . . . m) is the sum of m crown inner radii each having radius Crj (times 2);
ΣLwk (k=1 . . . p) is the sum of p links having width Lwk; and
WT is the scaffold wall thickness.
17. The medical device of claim 16 , wherein the stent has a crimped diameter less than Dmin.
18. The medical device of claim 15 , wherein the struts and the links each have a width and a thickness, and wherein an aspect ratio (AR) of the width to thickness of the struts or the links is between 0.8 and 1.4.
19. The medical device of claim 15 , wherein the stent has a pinching stiffness to a wall thickness ratio of between 0.6 to 1.8 N/mm 3 .
20. The medical device of claim 15 , wherein the stent is made from a radially expanded tube.