Self-curving stent-graft

Abstract

An endovascular self-curving stent-graft ( 20 ) includes a self-curving longitudinal portion ( 22 ), which is curved so as to define an innermost curve ( 26 ) and an outermost curve ( 28 ), when the stent-graft ( 20 ) is unconstrained in a radially-expanded state. The stent-graft ( 20 ) includes a plurality of circumferential strut members ( 30 ); a compression-generation spring ( 40 ), which (a) is in an elongated configuration when the stent-graft ( 20 ) is in a radially-compressed state, and (b) overlaps respective first portions ( 44 ) of at least two of the circumferential strut members ( 30 ); and an anti-buckling spring ( 50 ), which overlaps respective second portions ( 54 ) of at least two of the circumferential strut members ( 30 ). The anti-buckling spring ( 50 ) and the compression-generation spring ( 40 ) are together configured to curve the self-curving longitudinal portion ( 22 ) when the stent-graft ( 20 ) is unconstrained in the radially-expanded state, such that a lesser length of the self-curving longitudinal portion ( 22 ), measured along the innermost curve ( 26 ), is less than 80% of a greater length of the self-curving longitudinal portion ( 22 ), measured along the outermost curve ( 28 ).

1 . Apparatus comprising a generally tubular endovascular self-curving stent-graft, which (a) comprises a self-curving longitudinal portion having proximal and distal ends, (b) is configured to transition from a radially-compressed delivery state to a radially-expanded state, wherein, when the stent-graft is unconstrained in the radially-expanded state, the self-curving longitudinal portion of the stent-graft is curved so as to define an innermost curve and an outermost curve, and (c) comprises:
 a plurality of circumferential strut members, disposed at respective axial positions along the self-curving longitudinal portion of the stent-graft, surrounding a central longitudinal axis of the self-curving longitudinal portion of the stent-graft;   a graft member, which comprises one or more substantially blood-impervious flexible sheets, and which is fixed to the circumferential strut members;   a compression-generation spring, which (a) is in an elongated configuration when the stent-graft is in the radially-compressed state, and (b) overlaps respective first portions of at least two of the circumferential strut members; and   an anti-buckling spring, which (a) overlaps respective second portions of at least two of the circumferential strut members, (b) is shaped so as to define a plurality of curves, and (c) is in fixed orientation with respect to the graft member such that the curves reside substantially in a plane that is substantially parallel to the surface of the graft member,   wherein the anti-buckling spring and the compression-generation spring are together configured to curve the self-curving longitudinal portion of the stent-graft when the stent-graft is unconstrained in the radially-expanded state, such that a lesser length of the self-curving longitudinal portion of the stent-graft, measured along the innermost curve, is less than 80% of a greater length of the self-curving longitudinal portion of the stent-graft, measured along the outermost curve.   
     
     
         2 - 3 . (canceled) 
     
     
         4 . The apparatus according to  claim 1 , wherein if the stent-graft were to be placed in a right circular cylinder while in the radially-expanded state, each of the compression-generation spring and the anti-buckling spring would be substantially longitudinally-disposed. 
     
     
         5 . The apparatus according to  claim 1 , wherein the anti-buckling spring and the compression-generation spring are together configured such that, when the stent-graft is unconstrained in the radially-expanded state, the lesser length of the self-curving longitudinal portion of the stent-graft is less than 75% of the greater length of the self-curving longitudinal portion of the stent-graft. 
     
     
         6 . The apparatus according to  claim 1 , wherein a length of the compression-generation spring is at least 15% greater when the stent-graft is in the radially-compressed delivery state than when the stent-graft is unconstrained in the radially-expanded state. 
     
     
         7 . The apparatus according to  claim 6 , wherein the length of the compression-generation spring is at least 20% greater when the stent-graft is in the radially-compressed delivery state than when the stent-graft is unconstrained in the radially-expanded state. 
     
     
         8 - 10 . (canceled) 
     
     
         11 . The apparatus according to  claim 1 , wherein a height of each of the circumferential strut members of the self-curving longitudinal portion of the stent-graft, measured along the stent-graft, is greater at the outermost curve than at the innermost curve, when the stent-graft is unconstrained in the radially-expanded state. 
     
     
         12 - 13 . (canceled) 
     
     
         14 . The apparatus according to  claim 1 , wherein the anti-buckling spring is in a substantially relaxed configuration when the stent-graft is unconstrained in the radially-expanded state. 
     
     
         15 . The apparatus according to  claim 1 , wherein the anti-buckling spring is in a longitudinally-compressed configuration when the stent-graft is unconstrained in the radially-expanded state. 
     
     
         16 - 23 . (canceled) 
     
     
         24 . The apparatus according to  claim 1 , wherein a longitudinal spring constant of the compression-generation spring is 70 N/m to 300 N/m. 
     
     
         25 . The apparatus according to  claim 1 , wherein a longitudinal spring constant of the anti-buckling spring is 70 N/m to 300 N/m. 
     
     
         26 . The apparatus according to  claim 1 , wherein, if the stent-graft were to be placed in a right circular cylinder while in the radially-expanded state, an axial compression force exerted by the compression-generation spring against an inner surface of the cylinder would be 3 to 10 N. 
     
     
         27 - 31 . (canceled) 
     
     
         32 . The apparatus according to  claim 1 ,
 wherein each of the circumferential strut members of the self-curving longitudinal portion is shaped so as to define a plurality of proximal peaks, and   wherein, when the stent-graft is unconstrained in the radially-expanded state, for at least one of the circumferential strut members of the self-curving longitudinal portion:
 a first set of the proximal peaks of the circumferential strut member, which includes at least a circumferentially-closest one of the proximal peaks to the outermost curve of the self-curving longitudinal portion, and no more than half of the proximal peaks of the circumferential strut member, are bent radially inward at least an average angle of 20 degrees toward the central longitudinal axis of the self-curving longitudinal portion, and 
 a second set of the proximal peaks of the circumferential strut member, which includes all of the proximal peaks of the circumferential strut member not in the first set, are not bent radially inward by at least an average angle of 20 degrees toward the central longitudinal axis of the self-curving longitudinal portion. 
   
     
     
         33 - 46 . (canceled) 
     
     
         47 . The apparatus according to  claim 1 , wherein an angle about the central longitudinal axis of the self-curving longitudinal portion of the stent-graft between the anti-buckling spring and the compression-generation spring, averaged along the self-curving longitudinal portion of the stent-graft, is between 140 and 220 degrees, when the stent-graft is unconstrained in the radially-expanded state. 
     
     
         48 - 71 . (canceled) 
     
     
         72 . The apparatus according to  claim 1 , wherein the anti-buckling spring is sinusoidal or serpentine in the plane that is substantially parallel to the surface of the graft member. 
     
     
         73 . The apparatus according to  claim 32 , wherein the first set includes no more than 40% of the proximal peaks of the circumferential strut member. 
     
     
         74 . A method for treating a subject, comprising:
 transvascularly introducing a generally tubular endovascular self-curving stent-graft into a blood vessel of the subject while the stent-graft is in a radially-compressed delivery state, which stent-graft (1) includes a self-curving longitudinal portion having proximal and distal ends, (2) is configured to transition from the radially-compressed delivery state to a radially-expanded state, wherein, when the stent-graft is unconstrained in the radially-expanded state, the self-curving longitudinal portion of the stent-graft is curved so as to define an innermost curve and an outermost curve, and (3) includes:
 (i) a plurality of circumferential strut members, disposed at respective axial positions along the self-curving longitudinal portion of the stent-graft, surrounding a central longitudinal axis of the self-curving longitudinal portion of the stent-graft; 
 (ii) a graft member, which includes one or more substantially blood-impervious flexible sheets, and which is fixed to the circumferential strut members; 
 (iii) a compression-generation spring, which (a) is in an elongated configuration when the stent-graft is in the radially-compressed state, and (b) overlaps respective first portions of at least two of the circumferential strut members; and 
 (iv) an anti-buckling spring, which (a) overlaps respective second portions of at least two of the circumferential strut members, (b) is shaped so as to define a plurality of curves, and (c) is in fixed orientation with respect to the graft member such that the curves reside substantially in a plane that is substantially parallel to the surface of the graft member, 
 wherein the anti-buckling spring and the compression-generation spring are together configured to curve the self-curving longitudinal portion of the stent-graft when the stent-graft is unconstrained in the radially-expanded state, such that (A) a lesser length of the self-curving longitudinal portion of the stent-graft, measured along the innermost curve, is less than 80% of a greater length of the self-curving longitudinal portion of the stent-graft, measured along the outermost curve; and 
   creating a tight seal between the graft member at the proximal end of the self-curving longitudinal portion of the stent-graft and a wall of the curved blood vessel, by transitioning the stent-graft to the radially-expanded state in the curved blood vessel.   
     
     
         75 . The method according to  claim 74 , wherein the anti-buckling spring is sinusoidal or serpentine in the plane that is substantially parallel to the surface of the graft member. 
     
     
         76 . The method according to  claim 74 ,
 wherein each of the circumferential strut members of the self-curving longitudinal portion is shaped so as to define a plurality of proximal peaks, and   wherein, when the stent-graft is unconstrained in the radially-expanded state, for at least one of the circumferential strut members of the self-curving longitudinal portion:
 a first set of the proximal peaks of the circumferential strut member, which includes at least a circumferentially-closest one of the proximal peaks to the outermost curve of the self-curving longitudinal portion, and no more than half of the proximal peaks of the circumferential strut member, are bent radially inward at least an average angle of 20 degrees toward the central longitudinal axis of the self-curving longitudinal portion, and 
 a second set of the proximal peaks of the circumferential strut member, which includes all of the proximal peaks of the circumferential strut member not in the first set, are not bent radially inward by at least an average angle of 20 degrees toward the central longitudinal axis of the self-curving longitudinal portion. 
   
     
     
         77 . The method according to  claim 76 , wherein the first set includes no more than 40% of the proximal peaks of the circumferential strut member.