Patent Publication Number: US-2019175325-A1

Title: High packing density pre-folding of side branch end rings

Description:
BACKGROUND 
     The present application generally relates to medical devices. More particularly, the present application relates to a stent graft and a method of making the stent graft involving a compact architecture for loading and delivery of the stent graft. 
     Treatment of aneurysms has included the use of stent grafts that are implanted within the vascular networks and that include one or more stents affixed to graft material. The stent grafts may be secured at a treatment site by endovascular insertion utilizing introducers and catheters, after which they are enlarged radially and remain in place by attachment to the vessel wall. In particular, stent grafts are known for use in treating descending thoracic and abdominal aortic aneurysms where the stent graft at one end defines a single lumen for placement within the aorta and at the other end is branched to form a plurality of lumens, for extending into the branch arteries. 
     During implantation, which is typically conducted through the vasculature of the patient rather than by open surgery, the progress of the procedure may be monitored by a practitioner using a visualization method, such as fluoroscopy. Visualization methods increase the success of an implantation procedure as they ensure that the correct portions of the device are aligned with, or placed in, the appropriate anatomical features to be treated. However, because the stent graft is introduced in a crimped or compressed format, there may be ambiguity as to which components are truly being viewed by the practitioner. 
     It has been a challenge to develop a stent graft architecture which has a predictable crimped or collapsed configuration which can be easily recognized and comprehended when viewed by a visualization method, such as fluoroscopy. 
     SUMMARY 
     In one aspect, the present disclosure provides a stent graft for placement in a body vessel of a patient. The stent graft has an expanded configuration and a collapsed configuration. The stent graft may include a main tubular portion having a sidewall and defining a main lumen. The stent graft may include at least one aperture being formed through the sidewall. The stent graft may include at least one side branch which may be a tubular body extending from a first end to a second end. At least one of the side branches may include a graft material and defines a side lumen therethrough. The side branch may be attached to the main tubular portion at an aperture formed in the main branch such that each side lumen is in fluid communication with the main lumen. The side branch may include a ringed structure enclosed within the graft material. The ringed structure may include a first ring disposed along a length of the side branch, and may include a second ring; and may include at least one rib extending from the first ring to the second ring. The first ring includes four contact points spaced approximately equally about the circumference thereof. In the expanded configuration, a first contact point and third contact point define a diameter of the first ring therebetween, and a second contact point and fourth contact point define a diameter of the first ring therebetween. In the collapsed configuration, the first contact point is disposed adjacent the third contact point, and the second contact point is disposed adjacent the fourth contact point. 
     In another aspect, the present disclosure provides a method of making a stent graft having an expanded configuration and a collapsed configuration. The method includes folding a first end of a tubular body to form a folded end, the tubular body extending from the first end to a second end, the tubular body comprising a graft material and defining a lumen therethrough and including a ringed structure enclosed within the graft material. The ringed structure may includes a first ring disposed along a length of the side branch, and may include a second ring disposed along a length of the side branch, and may include at least one rib extending from the first ring to the second ring. The first ring includes four contact points spaced equally about the circumference thereof. In the expanded configuration, a first contact point and third contact point define a diameter of the first ring therebetween, and a second contact point and fourth contact point define a diameter of the first ring therebetween. Folding the first end may include a step of inserting a superelastic wire in the lumen and through the graft material proximate the first contact point. The method may include a step of threading the superelastic wire through the graft material proximate the third contact point. The method may include a step of pulling the superelastic wire such that the first contact point is disposed adjacent the third contact point. The method may include a step of threading the superelastic wire through the graft material proximate the second contact point. The method may include a step of threading the superelastic wire through the graft material proximate the fourth contact point. The method may include a step of pulling the superelastic wire such that the second contact point is disposed adjacent the fourth contact point to yield the folded end. 
     In another aspect, the present disclosure provides a method of making a stent graft having an expanded configuration and a collapsed configuration. The method includes folding a first end of a tubular body to form a folded end, the tubular body extending from the first end to a second end, the tubular body comprising a graft material and defining a lumen therethrough and including a ringed structure enclosed within the graft material. The ringed structure may includes a first ring disposed along a length of the side branch, and may include a second ring disposed along a length of the side branch, and may include at least one rib extending from the first ring to the second ring. The first ring includes four contact points spaced equally about the circumference thereof. In the expanded configuration, a first contact point and third contact point define a diameter of the first ring therebetween, and a second contact point and fourth contact point define a diameter of the first ring therebetween. Folding the first end may include a step of moving the first contact point such that it is disposed adjacent the third contact point, and applying an adhesive to secure the first contact point to the third contact point. The method may include a step of bringing the second contact point adjacent the fourth contact point to yield the folded end. 
     Further objects, features and advantages of this system will become readily apparent to persons skilled in the art after a review of the following description, with reference to the drawings and claims that are appended to and form a part of this specification. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic side view of a stent graft constructed in accordance with the principles of the present invention; 
         FIG. 2A  is a side view of a stent graft and folding method resulting in a less-orderly folding scheme; 
         FIG. 2B  is a view of the end rings of the device of  FIG. 2A  when in a crimped condition; 
         FIG. 3A  is a schematic end view of an end ring of a side branch of a stent graft when being folded in accordance with an aspect of the present disclosure; 
         FIG. 3B  is a perspective view of an end ring of a side branch of a stent graft when being folded in accordance with an aspect of the present disclosure; 
         FIG. 4A  is a of a stent graft and folding method resulting in a less-orderly folding scheme; 
         FIG. 4B  is a radiograph displaying a side view of a stent graft folded in accordance with an embodiment of the present disclosure; 
         FIG. 5  is an illustration of the steps of a method for prefolding a side branch of a stent graft in accordance with an embodiment of the present disclosure; 
         FIG. 6A  is a perspective view of a ringed structure being set over a mandrel in accordance with an embodiment of the present disclosure; 
         FIG. 6B  is an end view of the ringed structure and mandrel of  FIG. 6A ; 
         FIG. 7  is a view of the ringed structure as disclosed in  FIG. 6 ; 
         FIG. 8  is a series of side views of method steps for folding an end of a side branch in accordance with an embodiment of the present disclosure; 
         FIGS. 9A-9C  are views of a side branch having a ringed structure as in  FIG. 7  in an open configuration; 
         FIGS. 9D-9E  are views of the side branch of  FIGS. 9A-9C  in a closed configuration; and 
         FIG. 10  is a view of a partially-folded end of a side branch the folding of which is aided by an adhesive, in accordance with another embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     The drawings are purely schematic illustrations of various aspects of the invention and are not necessarily to scale, unless expressly stated. 
     The terms “substantially” or “about” used herein with reference to a quantity includes variations in the recited quantity that are equivalent to the quantity recited, such as an amount that is equivalent to the quantity recited for an intended purpose or function. “Substantially” or derivatives thereof will be understood to mean significantly or in large part. When used in the context of a numerical value or range set forth, “about” or “substantially” means a variation of ±15%, or less, of the numerical value. For example, a value differing by ±15%, ±14%, ±10%, or ±5%, among others, would satisfy the definition of “about.” 
     In the first embodiment, a stent graft  10  is illustrated. The stent graft  10  extends from a first end  14  to a second end  16  and defines a lumen  12  therethrough. As shown in  FIG. 1 , the stent graft  10  is shown in an expanded configuration  18 . The stent graft  10  may be made up of a series of stent rings  20 , which, on the main branch  21 , are concentric and disposed at longitudinal intervals along the length of stent graft  10 . The stent rings  20  surround and support at least one piece of graft material  22 , which may be in sheet or tubular form, and which forms an inner surface of the stent graft  10  and defines a lumen  12  running therethrough. The stent graft  10  may optionally include at least one radiopaque marker  60 , which in some cases may be located at an end of the stent graft  10 , such as at first end  14 , or at second end  16 , or at both ends. 
     The stent rings  20  may be self-expanding or balloon-expandable elements. As illustrated, the stent rings  20  are defined by a plurality of struts arranged in a zigzag shape. In one embodiment, the rings  20 , and struts of the stent ring, can be laser cut from a metallic tube or cannula. The metal may be suitably heat treated to make it deformable and resilient. Alternatively, the rings  20  may be made from both a shape memory alloy (such as a nickel-titanium alloy) and the rib or connector  32  made from stainless steel wire, these two components being joined by crimping with a small tube. 
     The stent rings  20  may be manufactured in diameters of from about 3 millimeters (mm) to about 100 mm, or from about 3 mm to about 40 mm, and lengths of from about 3 mm to about 40 mm. The wire from which the stent ring may be formed may have a diameter or thickness of from approximately 35 microns to approximately 1000 microns, or about 35 microns to about 500 microns. Where the stent is formed by laser cutting from a metal tube, the diameter of the metal tube may have a diameter of from 3 mm to 40 mm and have a wall thickness of from about 35 microns to about 1000 microns. Each stent ring may be formed from a single piece of wire. 
     The graft material  22  may be a tubular graft material, and may be non-porous so that it does not leak or sweat under physiologic forces. The graft material may be made of a biocompatible material, including but not limited to a DACRON® polyester, another polyester fabric, polytetrafluoroethylene (PTFE), expanded PTFE, THORALON®, a polyamide, and other synthetic materials known to those of skill in the art. Naturally occurring biomaterials, such as collagen, particularly a derived collagen material known as extracellular matrix (ECM), such as small intestinal submucosa (SIS), may also be employed. In some embodiments, the graft material  22  may be constructed as a preshaped tube. In some embodiments, the graft material  22  may be a woven material. 
     As illustrated in  FIG. 1 , in one embodiment the stent graft  10  may include a number of side branches  31  extending from the main body of the stent graft  10 . Multi-branched stent grafts are known in the field of thoracoabdominal aortic artery (TAAA) repair, with the smaller side branches  31  being used for placement adjacent or in smaller branching vessels running from the aorta. Each side branch  31  may be connected to the main branch  21  at a fenestration formed through the graft material of the main branch  21 , and may extend to a free end  38 , defining a side branch lumen  34  therebetween and in fluid communication with the lumen of the main branch. Each side branch  31  may be connected at a different point along its length to the main branch  21 . In some embodiments, the side branch  31  may be connected to the main branch  21  by a connected end  36 . In other embodiments, the side branch may be connected to the main branch  21  at a different point along its length between the ends. 
     In the embodiment illustrated, the side branch  31  is supported by a ringed structure  30 . Each ringed structure includes a first ring  50 , and may include a second ring  40 . In some embodiments, the ringed structure  30  may also include a connector  32  which is attached to and joins first ring  50  to second ring  40 , and provides axial spacing therebetween. 
     In some embodiments, the ringed structure  30  may be rendered radiopaque in order to provide for better visualization during delivery and implantation of the stent graft  10 . In one embodiment, this may be achieved by wrapping the ringed structure in a radiopaque material, such as a platinum wire. In other embodiments, the ringed structure  30  may be provided with a radiopaque coating, or a material other than platinum, including but not limited to gold, palladium, tungsten, and tantalum, or a mixture of any of these materials, may be employed. 
     The stent graft  10  of  FIG. 1  is illustrated in a compressed or crimped condition  19  in  FIG. 2A . In this figure, the crimping or radial compression has been achieved using a method of crimping which lacks the pre-folding step. As can be seen in  FIG. 2A , the first rings  50  and second rings  40  of the ringed structures  30  take on a variety of haphazard shapes after crimping, as exemplified by misfolded rings  70 ,  71 ,  72 ,  73 ,  74 , and  75 . The shapes of misfolded rings  70 - 75  are shown independent of the structure of the device in  FIG. 2B  for increased clarity. When visualized during a procedure, the misfolded rings  70 - 75  may be difficult or impossible to deconvolute, leading to potential errors in placement of the implant. 
       FIG. 3A  illustrates a method of pre-folding an end ring of a side branch, or of a stent graft, in accordance with an embodiment of the present disclosure. Pre-folding can yield well-defined folded structures that are readily visible and distinguishable during visualization procedures (as can be seen in  FIG. 4B , contrasted with the difficult-to-discern structures of  FIG. 4A  from the method lacking pre-folding.) In the embodiment of  FIG. 3A , the first ring  50  defines four different contact points  52 / 54 / 56 / 58  about its circumference. 
     In one embodiment, these four contact points may simply be geographical markers, which may not define additional components of the ring  50 . In other embodiments, the ring  50  may be constructed such that some or all of the contact points  52 / 54 / 56 / 58  have properties differing from the remainder of the ring  50  such that folding is facilitated by these differences. In one embodiment, the ring  50  may be bent at some or all of the contact points  52 / 54 / 56 / 58 . In another embodiment, some or all of the contact points  52 / 54 / 56 / 58  may be constructed to be thinner than the thickness of the remainder of the ring  50 , thereby predisposing the thinner contact points to bending first when the ring  50  is compressed. 
     First contact point  52  is disposed approximately 90 degrees counterclockwise of second contact point  54 , which is likewise disposed about 90 degrees counterclockwise of third contact point  56 , which is likewise disposed about 90 degrees counterclockwise of fourth contact point  58 . Put another way, the four contact points  52 ,  54 ,  56 , and  58  may be considered substantially equivalent to the  12 : 00 ,  3 : 00 ,  6 : 00 , and  9 : 00  positions of a standard clock face. 
     A folding scheme for a ring  50  of such construction is now described, and depicted in  FIGS. 3A and 3B . The end ring  50  starts in first configuration  101 . In first folding step, the ring is moved to configuration  102 , wherein the ring  50  is folded such that second contact point  54  is brought into proximity with fourth contact point  58 . In folding step  103 , the ring  50  is then compressed such that the first contact point  52  is brought into proximity of third contact point  56 . In the next step, the ring is folded into configuration  103 , in which the ring  50  takes on a U-shape, or a C-shape. In configuration  104 , the first contact point  52  is brought adjacent third contact point  56 , and in configuration  105 , the second contact point  54  is brought adjacent the fourth contact point  58 . After the final step, the compressed configuration of the end ring  50  is defined. This configuration  105  can be easily distinguished from other components of the device  10  under visualization during an implantation procedure. The configurations of the ring  101 ,  102 ,  103 ,  104 , and  105  are shown in the context of the side branch  31  of a stent graft  10  in  FIG. 3B , which demonstrates how the free end  38  compresses after such a folding regimen. 
       FIG. 5  illustrates one particular method of achieving the folding of an end of a stent graft, or the end of a side branch of a stent graft. The side branch  31  is shown in its expanded configuration  18  in step  401  of  FIG. 5 . The ringed structure  30  is encompassed by graft material  22 , and so is not directly visible in the illustration. The graft material surrounds first ring  50  and second ring  40 , and may be attached to the ring structures buy a plurality of blanket stitches  82 . 
     In step  402 , a superelastic wire  80  is run through the lumen  34  of the side branch  31  and threaded through the graft material  22  which lies proximate and surrounding the first ring  50  at first contact point  52 . In one embodiment, the superelastic wire  80  may be made of a shape memory alloy, such as a nickel titanium alloy. Additionally, the superelastic wire  80  may be coated with a low-friction material, such as polytetrafluoroethylene (PTFE) in order to facilitate easy threading and removal of the wire. 
     In step  403 , the superelastic thread  80  is threaded through a portion  86  of the graft material  22  which is proximate third contact point  56  of the end ring  50 . In step  404 , the superelastic wire is pulled taut, optionally in both the directions of first end  36 , and free end  38 , to bring first contact point  52  and second contact point  56  into proximity of one another. In step  405 , the superelastic wire  80  is threaded through a portion  90  of the graft material  22  which is proximate fourth contact point  58 . In step  406 , the superelastic thread is then threaded through the graft material  22  at a position  92  proximate second contact point  54 . In the finally illustrated step  407 , the superelastic wire  80  may be pulled in direction  94  and may be pulled free of the side branch  31  in order to yield closed end  96 . 
     As shown in  FIG. 4B , the use of such a folding scheme results in a stent graft  110  that has a compressed configuration  119  that gives rise to predictably folded end rings  176  of ringed structures  130 . This is in contrast to the structure seen in  FIG. 4A , which is the result of crimping without pre-folding. 
     In order to prepare the end rings to be folded, the ringed structure may be made by setting over a mandrel, as shown in  FIG. 6A , in order to bias it to a partially-folded state. 
     As shown in  FIG. 6A , the mandrel  200  includes four rounded protrusions  237  on its outer surface  235 . These protrusions  237  can be formed of separate elements attached to the cylindrical body of the mandrel, such as screws, or can be formed from the outer surface  235  of the mandrel  200  itself. The ringed structure  230  is formed by placement of a wire  236  over the outer surface  235  of the mandrel, and winding the wire to form end ring  240 . The mandrel  200  has a first diameter D 1 , which may define the diameter of the side branch or of the stent graft in which the ringed structure  230  is to be employed. Each protrusion  237  has a diameter D 2  in order to define a radius of curvature for the partially collapsed form of the end ring  240 . 
     The mandrel made further and optionally include locking screws, such as screw  233  and screw  239 , in order to keep the wire  236  in place on the outer surface  235  of the mandrel  200 . Further anchoring elements such as anchor  244  and anchor  208  as shown in  FIG. 6A  may also be employed to further stabilize the wire  236 . 
     In one embodiment, the ringed structure  230  may be shaped by heat setting the wire  236  over the mandrel  200 . The wire  236 , which may be made of a shape memory material, such as nickel titanium alloy, can be pre-coiled with a radiopaque wire thereabout, such as a wire made of platinum, prior to engagement with the mandrel  200 . In one embodiment, the wire  236  may be heat set, for example at about 400 degrees Celsius for about five minutes, and then cooled, such as by quenching in water. In one embodiment, when the wire  236  is shaped into the ringed structure  230 , it may include two rings  250  and  240 , on opposing sides of, and connected to, a connector  232 . 
     As shown in  FIG. 7 , the finished ringed structure  230  including rib or connector  232  may attain its final shape by cutting of excess wire at the positions indicated by dashed lines. As shown in  FIG. 7 , the final structure includes a fish mouth shape  253  of ring  230 . As can further be seen in  FIG. 7 , the wire  201  and ring structure  230  may be formed to include a pair of hoops  243  and  245 , which are formed by winding the wire  236  around anchors  233  and  239  of mandrel  200 . These hoops  243 / 245  may be used as a junction point to assist proper fixation to a graft material during blanket suture sewing when the graft material is disposed over the ringed structure  230 . 
       FIG. 8  illustrates a compression scheme for a stent graft or a side branch  210  including a ringed structure  230  which has been preset to a fishmouth shape  253 . The fishmouth shape assists in bringing first contact point  252  into proximity with third contact point  256  as a crimping force  276  is applied to the side branch  210 . The crimping force may be a substantially radially-directed force, which also brings second contact point  254  into proximity of fourth contact point  258 . 
       FIGS. 9A-9E  illustrate a side branch or a stent graft in accordance with the embodiments described herein. As can be best seen in  FIGS. 9B and 9C , both the first ring  240  and the second ring  250  of the ringed structure  230  are shown in a fishmouth configuration  253 . Blanket stitching  282  holds the graft material  231  on to the ring structure  230 . Each fishmouth in  FIGS. 9B and 9C  are illustrated in an open configuration  277 . Side and perspective views, respectively, are displayed in  FIGS. 9D and 9E . As shown, the end of the side branch  210  is instead in a closed position  279 . As can be seen in  FIG. 9D , first contact point  252  has been brought into proximity with third contact point  256 . Second contact point  254  is also in proximity of and adjacent to fourth contact point  258 . 
     In another embodiment, and as illustrated in  FIG. 10 , the stent graft  331  according to the principles of the present disclosure may be constructed by a method that strategically employs an adhesive to aid in achieving the collapsed or closed configuration. The unfolded side branch  331  (or stent graft) is illustrated in a first step  301 . In second step  302 , the first contact point  352  has been folded and is in proximity of third contact point  356 . 
     In step  303 , an adhesive  397  may be applied to junction  369 , which is formed by the contact between the graft material  322  covering first contact point  352  and third contact point  356 . Optionally, a crimping tool  395  or a clamp may be used to hold the first contact point  352  to third contact point  356  in order to allow the adhesive to set at the junction  369 . 
     The adhesive  397  may be a biocompatible, and in some instances a bioresorbable material. Because the adhesive will be exposed to the bloodstream of the patient in whom the device will be deployed, the adhesive should break down into digestible components that may safely circulate in the vascular system. In one example the adhesive may include a molten sugar, such as glucose. Sugar constantly circulates in the bloodstream as an energy source for the body, so its introduction on an implant such as a stent graft will not provoke a negative response in the patient. In one embodiment, the sugar is applied as a molten sugar, which is viscous and adheres readily to many materials. Additionally, molten sugar will harden as it cools, and the crimping procedure will pulverize the hardened sugar on the device. This solidified, pulverized sugar allows for easy dissolution in the bloodstream during and after the deployment procedure. Other examples biocompatible and/or bioresorbable adhesives include, but are not limited to, polymers including low molecular weight polyethylene glycol, fibrin glue, hydrogels including those generated by mixing aldehyded dextran and c-poly(L-lysine), and other carbohydrates. 
     In step  304 , the adhesive has set to form interface  399 . Finally, in step  305 , second contact point  354  can be brought into proximity with and adjacent to fourth contact point  358  in order to achieve closed structure  377  of ring  350 . Adhesive  399  can be seen at the interface at which the folded halves of the ring  350  meet. 
     As a person skilled in the art will readily appreciate, the above description is only meant as an illustration of implementation of the principles this application. This description is not intended to limit the scope of this application in that the system is susceptible to modification, variation and change, without departing from the spirit of this application, as defined in the following claims.