Patent Publication Number: US-2023146006-A1

Title: Conduit vascular implant sealing device for reducing endoleaks

Description:
PRIORITY 
     This application is a continuation of U.S. patent application Ser. No. 16/128,047, filed Sep. 11, 2018, which claims priority to U.S. Provisional Application No. 62/556,612 filed on Sep. 11, 2017, the disclosures of which are incorporated herein by reference in their entireties. 
    
    
     BACKGROUND 
     This patent document is directed to medical implants, and, more specifically, to conduit vascular implants and related methods. 
     Aneurysms of the aorta and principal arteries of the chest, abdomen and pelvis can progress, by expansion, to life-threatening rupture. Thrombus may develop within the aneurysm and cause embolic occlusion of arteries and ischemic organ injury. Clinical approach to treatment generally involves the insertion of a tubular graft that spans the extent of the aneurysmal portion of the vessel to exclude the aneurysm from the circulation by either surgical or transcatheter means, termed “endovascular aneurysm repair”, or “EVAR”. In either case, the success of the technique depends on effective sealing between the ends of the graft and the non-aneurysmal segments of the vessel proximal to and distal to the aneurysm to prevent leaking of blood flow into the aneurysm. The open surgical approach allows for complete suturing of the graft ends to the vessel and even excision of the aneurysm. However, transcatheter device insertion has supplanted the surgical approach for most aneurysms, owing to the clinical advantages of a minimally-invasive procedure with less morbidity and rapid recovery. 
     Devices for transcatheter insertion through the femoral artery and into the abdominal aorta for exclusion of an aneurysm are typically constructed, for example, of polymer fabric configured as a tube, with a metal alloy wire form or lattice attached at the ends or throughout the length of the resulting tube graft to provide axial and radial support and for fixation of the ends of the tube graft to the vessel. Such devices must be radially compressible to a profile that is capable of being inserted into the femoral artery and then expanded within the aorta to a size that matches that of the aorta and engages its inner wall for fixation and exclusion of the aneurysm. Shape memory alloy is widely utilized in these components. 
     Despite engagement and fixation of the ends of the transcatheter tube graft, leakage of blood into the aneurysm sac is relatively common and is termed “endoleak.” Endoleak involves blood flow under normal hemodynamic pressure being conducted around the terminal edges of the conduit implant and into the aneurysm, thereby continuing to pressurize the aneurysm chamber and allowing possible progression to clinical aneurysm rupture. EVAR devices incorporate a number of features directed to limiting endoleak, including circumferential cuffs of additional graft material and stents for fixation and enhanced expansion of the graft ends against the inner wall of the vessel. Often, the vessel is susceptible to endoleak because of a short extent of mating inner surface of the vessel between the aneurysm and the origins of visceral arteries, such as the renal arteries, that cannot be covered and obstructed by the graft. 
     Existing methods and devices have shown variable effectiveness in limiting and/or preventing endoleak. Some of these devices are complex to manufacture or bulky in profile, which limits the ease of percutaneous delivery. Additionally, fabric or polymer layers have not been shown to promote biological integration of the prosthetic surface into the tissue environment of the vessel as well as do tissue membrane layers. Therefore, endoleak is a persistent problem for endovascular exclusion devices. 
     Accordingly, there is a need for a simple, reliable, low-profile device for minimizing endoleak associated with EVAR implants that is biocompatible with the native vascular intimal surface and promotes integration with the native tissue. In addition, other intravascular applications such as transcatheter heart valve implants may also benefit from devices that provide effective circumferential sealing between the implant and the native vascular site. 
     This patent document describes devices and methods that are intended to address issues discussed above and/or other issues. 
     SUMMARY 
     The summary of the disclosure is given to aid understanding of medical devices (such as vascular implants), and not with an intent to limit the disclosure or the invention. The present disclosure is directed to a person of ordinary skill in the art. It should be understood that various aspects and features of the disclosure may advantageously be used separately in some instances, or in combination with other aspects and features of the disclosure in other instances. Accordingly, variations and modifications may be made to the medical devices, the architectural structure, and their method of operation to achieve different effects. 
     In one aspect, a sealing device for use as a vascular implant comprises a frame having an inflow edge and an outflow edge relative to axial blood flow within a vessel, and a membrane layer coupled to the at least partial axial extent of the frame between the inflow edge and the outflow edge of the frame. At least a partial axial extent of the frame is configured to decrease in axial length when expanded from a radially compressed configuration to a radially expanded configuration. The membrane layer is coupled to the at least partial axial extent of the frame at one or more axially spaced connection points such that at least a portion of the membrane layer projects radially outward relative to the frame when the at least partial axial extent of the frame is in the radially-expanded configuration. 
     In some embodiments, the at least partial axial extent of the frame may be formed as a lattice structure. Optionally, the membrane layer may be coupled to the lattice structure at a plurality of axially-spaced and circumferentially-distributed connection points. Additionally and/or alternatively, the membrane layer may be coupled to the lattice structure by a plurality of sutures. 
     In one or more embodiments, the one or more connection points of the frame may include a plurality of circumferentially-distributed connection points proximate to the inflow edge of the at least partial axial extent of the frame. 
     In one or more embodiments, the one or more connection points of the frame may include a plurality of circumferentially-distributed connection points proximate to the outflow edge of the at least partial axial extent of the frame. 
     In certain other embodiments, the connection points of the frame may include one or more circumferentially-distributed connection points proximate to the outflow edge of the at least partial axial extent of the frame, one or more circumferentially-distributed connection points proximate to the inflow edge of the at least partial axial extent of the frame, and/or one or more intermediate connection points located axially between the connection points proximate the outflow edge and the connections points proximate the inflow edge. Optionally, the one or more intermediate connection points may be configured to enforce an inflow-angled fold in the membrane layer. Additionally, the one or more intermediate connection points may enforce an outflow-angled fold in the membrane layer. Furthermore, the one or more intermediate connection points may be configured to enforce both an inflow-angled and an outflow-angled fold in the membrane layer. 
     In some embodiments, the membrane layer may be formed of at least one of processed mammalian pericardium tissue, a biocompatible fabric, or a polymer material. The membrane layer may be formed of porcine and/or bovine pericardium tissue. Optionally, the membrane layer may be formed of a substantially dry tissue. In at least one embodiment, the sealing device may be in a radially-compressed condition and associated to a delivery system, and the delivery system associated with the sealing device may be provided in a sterile condition within an internally sterile package. 
     In certain embodiments, a circumferential extent of the membrane layer may exceed a circumferential extent of the frame. Alternatively, the circumferential extent of the membrane layer may not exceed a circumferential extent of the frame. 
     In at least one embodiment, the membrane layer may extend over an entire axial length of the frame. Alternatively, the membrane layer may extend over only a portion of an axial length of the frame. In yet another embodiment, the membrane layer may axially extend beyond at least one of the inflow edge or the outflow edge of the frame. 
     In some scenarios, the radially projecting portion of the membrane layer may be configured to contact an inner wall of the vessel to cause an impeding of blood flow over an outer surface of the sealing device. 
     In another aspect, a sealing device for use as a vascular implant is disclosed. The sealing device comprises a frame and a membrane layer. The frame is configured to have an at least partial expandable axial extent including a plurality of circumferentially distributed members configured to circumferentially separate from each other when expanded from a radially compressed configuration to a radially expanded configuration coupled to the at least partial expandable axial extent of the frame at a plurality of connection points. The membrane layer is configured to have at least a transverse curvilinear extent exceeding an underlying circumferential extent of the frame between connection points at an axial level of at least some of the connection points upon the frame. 
     In various embodiments, the connection points between the frame and the membrane layer may be circumferentially regularly spaced or circumferentially irregularly spaced. 
     In certain embodiments, the at least partial expandable axial extent of the frame may be formed as a lattice structure. Optionally, the membrane layer may be coupled to the lattice structure at a plurality of axially-spaced and circumferentially-distributed connection points by, for example, a plurality of sutures. 
     In some embodiments, the connection points of the frame may include a plurality of circumferentially-distributed connection points proximate to the inflow edge of the at least partial expandable axial extent of the frame. Additionally and/or alternatively, the one or more connection points of the frame may include a plurality of circumferentially-distributed connection points proximate to the outflow edge of the at least partial expandable axial extent of the frame. Optionally, the connection points of the frame may include one or more circumferentially-distributed connection points proximate to the outflow edge of the axial extent of the frame, one or more circumferentially-distributed connection points proximate to the inflow edge of the axial extent of the frame, and/or one or more intermediate connection points located axially between the connection points proximate the outflow edge and the connection points proximate the inflow edge. 
     In at least one embodiment, wherein the membrane layer may be formed of processed mammalian pericardium tissue (e.g., bovine or porcine), a biocompatible fabric, and/or a polymer material. 
     Optionally, the membrane layer may be formed of a substantially dry tissue. In at least one embodiment, the sealing device may be in a radially-compressed condition and associated to a delivery system, and the delivery system associated with the sealing device may be provided in a sterile condition within an internally sterile package. 
     In at least one embodiment, the membrane layer may extend over an entire axial length of the frame. Alternatively, the membrane layer may extend over only a portion of an axial length of the frame. In yet another embodiment, the membrane layer may axially extend beyond at least one of the inflow edge or the outflow edge of the frame. In some embodiments, the membrane layer may extend over an entire circumferential length of the frame and/or over only a portion of a circumferential length of the frame. 
     In some scenarios, the radially projecting portion of the membrane layer may be configured to contact an inner wall of the vessel to cause an impeding of blood flow over an outer surface of the sealing device. 
     Additionally and/or alternatively, the radially projecting portion of the membrane layer may be configured to contact an inner wall of the vessel to cause an impeding of blood flow over an outer surface of the sealing device. 
     In some other scenarios, one or more of the connections at the connection points may enforce a radially outwardly angled direction upon the membrane layer adjacent the connection points. 
     In various embodiments, two or more portions of the membrane layer may be connected at connection points independent of the connections to the frame and/or may form one of a linear or curvilinear seam of at least two points. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    illustrates a radially-compressed cylindrical lattice frame for a vascular implant, according to an embodiment. 
         FIG.  2    illustrates an expanded cylindrical lattice frame for a vascular implant, according to an embodiment. 
         FIG.  3    illustrates a membrane layer for a vascular implant in an axially-shortened state, according to an embodiment. 
         FIG.  4    illustrates a longitudinal cross-sectional view of suture attachment of a membrane layer to a lattice frame for a vascular implant in both a radially-compressed configuration and a radially-expanded configuration, according to an embodiment. 
         FIG.  5    illustrates a side elevation view of an axially-shortened membrane layer on a radially-expanded lattice frame for a vascular implant, according to an embodiment. 
         FIG.  6    illustrates a side elevation view of an axially-shortened membrane layer coupled to a radially-expanded lattice frame, according to an embodiment. 
         FIG.  7    illustrates a side elevation view of an axially-shortened membrane layer coupled to a radially-expanded lattice frame, according to another embodiment. 
         FIG.  8    illustrates a side elevation view of an axially-shortened membrane layer coupled to a radially expanded lattice frame and deployed within a vessel, according to an embodiment. 
         FIG.  9    illustrates a plurality of side elevation views of variations in axial position of attachment points along a radially compressed lattice frame, according to various embodiments. 
         FIG.  10    illustrates a plurality of side elevation views of variations in axial position of membranes along a radially compressed lattice frame, according to various embodiments. 
         FIG.  11    illustrates a plurality of side elevation views of variations in axial position of membranes along a radially compressed lattice frame, according to various embodiments. 
         FIG.  12    illustrates a plurality of side elevation views of variations in axial position of membranes along a radially compressed lattice frame showing variations of attachments of the membrane to the frame, according to various embodiments. 
         FIG.  13    illustrates a transverse cross section of a vascular implant, according to another embodiment. 
         FIG.  14    illustrates a transverse cross section of the vascular implant of  FIG.  13    expanded within a vessel. 
     
    
    
     DETAILED DESCRIPTION 
     The following description is made for the purpose of illustrating the general principles of the present system and method and is not meant to limit the inventive concepts claimed in this document. Further, particular features described in this document can be used in combination with other described features in each of the various possible combinations and permutations. 
     Unless otherwise specifically defined in this document, all terms are to be given their broadest possible interpretation including meanings implied from the specification as well as meanings understood by those skilled in the art and/or as defined in dictionaries, treatises, etc. 
     It must also be noted that, as used in the specification and the appended claims, the singular forms “a,” “an” and “the” include plural referents unless otherwise specified. Unless defined otherwise, all technical and scientific terms used herein have the same meanings as commonly understood by one of ordinary skill in the art. All publications mentioned in this document are incorporated by reference. Nothing in this document is to be construed as an admission that the embodiments described in this document are not entitled to antedate such disclosure by virtue of prior invention. As used herein, the term “comprising” means “including, but not limited to”. Additionally, use the term “couple”, “coupled”, or “coupled to” may imply that two or more elements may be directly connected or may be indirectly coupled through one or more intervening elements. 
     In this document, position-identifying terms such as “inflow”, “outflow”, “vertical”, “horizontal”, “front”, “rear”, “top”, and “bottom” are not intended to limit the invention to a particular direction or orientation, but instead are only intended to denote relative positions, or positions corresponding to directions shown when a vascular implant is oriented as shown in the Figures. Accordingly, the provided orienting descriptions of the device do not limit its use to the inflow end of an exclusion graft or device; the device may also be used at the outflow end of an exclusion graft or device. 
     Referring to  FIG.  1   , a radially-compressed (or radially-crimped) cylindrical lattice frame  10  for use in, e.g., a vascular implant, is illustrated. For clarity of illustration, only the foreground portion of cylindrical lattice frame  10  is shown in  FIG.  1   , with the background portion omitted. Frame  10  may be used in conjunction with a transcatheter tube graft implant. Accordingly, frame  10  may be formed of any appropriate biocompatible material, such as stainless steel, gold, titanium, cobalt-chromium alloy, tantalum alloy, nitinol, one or more biocompatible polymers, etc. 
     Frame  10  includes an inflow edge  50  and an outflow edge  52  relative to axial blood flow within a vessel in which the implant is placed. Frame  10  may be formed by a plurality of arms  15  interconnected by a plurality of circumferentially-distributed connection nodes  16  to form a cylindrical lattice structure. The lattice structure of frame  10  may be originally fabricated or cut in the configuration shown in  FIG.  1   . However, it is to be understood that frame  10  may be formed by any appropriate method, and is not limited by the lattice structure illustrated in  FIG.  1   . 
     As shown in  FIG.  1   , when frame  10  is in a radially-compressed state, an axial distance x exists between two random (but approximately circumferentially-aligned) node points  12 ,  17  having respective baselines  14 ,  18 . However, when the cylindrical lattice structure of frame  10  is radially expanded, as illustrated in  FIG.  2   , the overall axial length of frame  10  between points  12  and  17  shortens. For example, in a radially-expanded state, the axial distance between node points  12 ,  17  becomes a distance Fx between baselines  20 ,  18 , with distance Fx being shorter than distance x between baselines  14 ,  18 . Thus, when used in a vascular implant, radial expansion of frame  10  in the direction of the vessel walls leads to axial compression of frame  10 . 
     Referring now to  FIG.  3   , a membrane layer  22  configured for use in conjunction with frame  10  is illustrated. Indicated by arrows, as membrane layer  22  axially shortens from baseline  14  to baseline  20 , a redundant portion  23  of membrane layer  22  is then projected out of plane, corresponding to the radially-outward direction from the underlying frame  10 . This redundant material  23  increases the membrane layer local material density which occupies the space between the frame  10  and the inner surface of the vascular wall, adding to the sealing function of the membrane layer  22 . While shown (for ease of illustration) as a substantially flat sheet in  FIG.  3   , it is to be understood that membrane layer  22  may be cylindrically wrapped or otherwise formed around frame  10  to form a cylindrical, tube-like structure. As will be discussed further below, in accordance with some embodiments, membrane layer  22  may be formed as an axially-complete layer over the entire axial length of frame  10 . However, in accordance with other embodiments, membrane layer  22  may be formed as an axially-incomplete layer of the length of frame  10 . Furthermore, in some embodiments, the axial length of membrane layer  22  may exceed the axial length of frame  10 . Additionally, in some embodiments, the circumferential extent of the membrane layer  22  may not exceed the circumferential extent of underlying frame  10 , while in other embodiments, the circumferential extent of the membrane layer  22  does exceed the circumferential extent of underlying frame  10 . 
     Membrane layer  22  may be formed of any appropriate biocompatible material, such as, for example, processed mammalian pericardium tissue (e.g., porcine or bovine pericardium), a biocompatible fabric, a polymer material (e.g., polytetrafluoroethylene (PTFE)), etc. 
     Membrane layer  22  may be coupled at least partially to an outer surface frame  10  by any appropriate method. For example,  FIG.  4    shows a cross-sectional view of a single side of the membrane layer and frame members at points of interconnection. As shown in  FIG.  4   , portions of membrane layer  22  are coupled to a plurality of circumferentially-distributed and axially-separated connection points  25 ,  26 ,  27  of frame  10  through respective sutures  28 . In one aspect of the present disclosure, a fold  24  may be created during the coupling of membrane layer  22  to an intermediate connection point(s)  26  that is axially between the inflow-side connection point(s)  25  and the outflow-side connection point(s)  27 . For example, referring to configuration “A” of  FIG.  4   , which illustrates the membrane layer  22  coupled to frame  10  when frame  10  is in the radially-compressed configuration shown in  FIG.  1   , two sides of fold  23  at the base of projecting fold  24  are coupled to the intermediate connection point(s)  26  by a suture  28  such that the fold  24  is effectively biased to one side of the intermediate connection point(s)  26 . When frame  10  is radially expanded (as shown in  FIG.  2   ), the accompanying axial compression of at least a portion of frame  10  from an axial distance x to an axial distance Fx causes the coupled membrane layer  22  to similarly compress. Due to two sides of fold  23  being coupled to the intermediate connection point(s)  26 , such axial compression of frame  10  to axial distance Fx also causes membrane layer  22  to radially project outward, away from frame  10 , as is shown in configuration “B” of  FIG.  4   . As will be described further below, this radially-outward projection of membrane layer  22  at fold  24  may provide for improved sealing between the transcatheter tube graft implant and a vessel to mitigate endoleaks around the periphery of the implant. 
     As shown in  FIG.  4   , membrane layer  22  not only projects radially outward away from frame  10 , but also projects at least partially upward (e.g., toward an inflow end relative to blood flow through a vessel). This upward projection is due to the orientation in which the two sides of membrane layer  22  are overlapped when coupled to intermediate connection point(s)  26 . Thus, it is also possible for the membrane layer  22  to be overlapped in the direction opposite of that shown in  FIG.  4   , which would cause membrane layer  22  to project both radially outward and downward away from frame  10 . Furthermore, while not shown, membrane layer  22  may be overlapped and connected to connection point(s)  26  such that the fold  24  may be expanded to project both toward an upward (inflow) end and a downward (outflow) end of the frame. It is to be understood that similar folds in the membrane layer may be configured at other and possibly multiple points of connection or between points of connection by sutures or other means not connecting membrane layer  22  to frame  10 . 
     Referring to  FIG.  5   , a simplified view of an implant  30  in accordance with an aspect of the disclosure is illustrated. For clarity, sutures or other interconnection means between the membrane layer  22  and frame  10  are omitted from  FIG.  5   . As described above with respect to  FIG.  4   , when frame  10  is radially expanded (and axially compressed), the surrounded membrane layer  22  is also axially compressed, resulting in the fold  24  projecting radially outward around the entire circumference of frame  10 . The radial projection formed by fold  24  may act as a seal between the membrane layer  22  and the vessel walls (not shown) when implant  30  is placed in a desired location, with fold  24  of membrane layer  22  blocking some or all of the blood flowing around the periphery of implant  30 , thereby mitigating endoleaks, as indicated by arrows  29 . 
     As shown in  FIG.  6   , implant  30  may include a plurality of sutures  28  utilized to couple the membrane layer to a plurality of connection points of the frame  10 . In addition, a tube graft  32  may be coupled to the outflow side of frame  10 . An inflow side of tube graft  32  may overlap with an outflow side of membrane layer  22 , with the inflow side of tube graft  32  configured to share the sutures  28  coupling membrane layer  22  to frame  10 . Once again, while sutures  28  are illustrated, it is to be understood that any appropriate connection means between the membrane layer, tube graft, and frame may be utilized. 
     Sutures (or other connectors)  28  coupling membrane layer  22  to frame  10  need not lie directly upon an inflow or outflow edge of frame  10 , as only axial separation between the circumferential connection points  25 ,  26 ,  27  (shown in  FIG.  4   ) is needed if there is axial shortening of the corresponding circumferentially-complete underlying portion of the frame  10  upon radially expansion of the frame  10 . Further, the biocompatible membrane layer  22  need not terminate in either inflow or outflow ends of the axial extent of the frame  10 . For example, in one aspect of the present disclosure, the membrane layer  22  may extend at least to and be interconnected along (1) an outflow end of the axial extent corresponding to the outflow edge of the frame  10  and (2) an inflow end of the axial extent between the inflow and outflow edges of the frame  10  approximating the axially mid portion of the frame  10 , such as that which is shown in  FIGS.  5 - 6   . 
     Referring now to  FIGS.  7 - 8   , an implant  34  in accordance with another aspect of the present disclosure is illustrated. Unlike the membrane layer  22  described above with respect to  FIG.  6   , which formed a sealing device separate from tube graft  32 , implant  34  includes a tube graft  36  in which the sealing device is integrally formed on an inflow end of tube graft  36 . Specifically, a portion of tube graft  36  is disposed at least partially around a frame  10  and coupled to frame  10  via sutures  28  in a manner similar to that described above with respect to  FIG.  4   . When frame  10  is radially expanded (as shown in  FIG.  7   ), the portion of tube graft  36  surrounding frame  10  axially compresses, thereby causing one or more folds  46  to project radially outward, allowing this radially projecting portion of tube graft  36  to form a seal against some or all blood flowing around the periphery of implant  34  as indicated by arrows  29 . 
       FIG.  8    illustrates the implant  34  as described above with respect to  FIG.  7    deployed within, e.g., a vessel portion  40  shown in cross-section. As is shown, the radially projecting folds  46  of tube graft  36  are configured to at least partially compress against the inner walls  42  of vessel  40  when frame  10  is radially expanded, thereby providing an effective barrier seal against endoleak or other fluid flow past the outer periphery of implant. In the embodiment shown in  FIG.  8   , folds  46  are shown as being compressed against the inner walls  42  and angled toward the inflow end of the frame. However, as described above, implant  34  could alternatively be configured such that folds  46  are compressed against inner walls  42  and angled toward the outflow end of the frame. 
     While  FIG.  2    shows the entirety of frame  10  being axially compressed when in a radially-expanded state, it is to be understood that, in some embodiments, only a certain axial extent of frame  10  may be axially compressed when in a radially-expanded state. That is, in some embodiments, portions of frame  10  may be capable of remaining substantially constant in axial length, even when frame  10  is expanded radially, while other portions along an axial extent of the frame  10  may axially compress. 
     For example, referring to  FIG.  9   , a plurality of example variations of axial membrane attachment points on a radially-compressed frame are shown, with the axial membrane attachment points being indicated by inwardly-pointed arrows. As is shown in  FIG.  9   , the axial membrane attachment points can be at numerous different locations along the frame between the inflow and outflow edges, including at locations inset from the inflow edge, outflow edge, or both. In variations in which the axial extent of the membrane attachment points does not extend entirely to the inflow and outflow edges (e.g., variations B-F shown in  FIG.  9   ), the portions of the frame located outside of the axial extent between the membrane attachment points do not necessarily need to axially shorten during radial expansion in order to achieve a desired radial projection in the membrane. Accordingly, these portions of the frame located outside of the axial extent between the membrane attachment points may be configured differently than the portions within the axial extent such that all or some of the frame portions located outside of the axial extent do not compress/shorten with radial expansion. 
     Similarly, referring to  FIGS.  10 - 11   , a plurality of example variations in the axial extent and position of the membrane relative to a radially-compressed frame are illustrated. As discussed above with respect to  FIG.  9   , the axial membrane attachment points can be at numerous different locations along the frame between the inflow and outflow edges, including at locations inset from the inflow edge, outflow edge, or both. Accordingly, the membrane itself may also axially extend along less than the entirety of the frame (e.g., variations B-F shown in  FIG.  10   ), dependent upon the axial position of the attachment points. Additionally and/or alternatively, the membrane may extend beyond the inflow and/or outflow edges of the frame (e.g., variations G-K shown in  FIG.  11   ). In such configurations, the membrane portions located between axial membrane attachment points may axially shorten in conjunction with radial expansion of the frame, while the membrane portions located outside of the axial membrane attachment points (and/or outside of the frame itself) may not change in axial length. 
     Referring to  FIG.  12   , a plurality of example variations of suture attachment schemes for the attachment of the membrane to the radially-compressed frame are shown. It is to be understood that the suture attachments schemes shown in  FIG.  12    are not limiting, as different attachment schemes are also possible. In some variations (e.g., variations B-D), suture attachments are placed at a pair of axial locations along the axial length of the membrane. However, in other variations (e.g., variations A, E, F), intermediate suture attachments may also be included along the axial length of the membrane. In accordance with the depiction of the cross-sectional view of the generally cylindrically disposed membrane layer, it is to be understood that the axial position of suture attachments is indicated in  FIG.  12   , but at each indicated axial position the attachments are circumferentially distributed. 
     Next, referring to  FIGS.  13 - 14   , an implant  50  in accordance with another aspect of the disclosure is illustrated. Specifically,  FIG.  13    shows a transverse cross-sectional view of implant  50  having a circumferentially-redundant membrane  52  coupled to an expanded frame  56  along a plurality of attachment points by a plurality of sutures  54  such that the transverse curvilinear extent of the membrane spanning the circumferential separation between two or more points of attachment to the frame exceeds that circumference separation. While frame  56  is shown in an expanded state, it is to be understood that frame  56  may be radially compressed, similar to frame  10  described above. Membrane  52  is sized so as to be circumferentially larger than radially-expanded frame  56 , thereby causing the portions of membrane  52  located between the plurality of attachment points along frame  56  to bulge outward, even when frame  56  is radially expanded. As shown in the inset figure of  FIG.  13   , each radially outward transverse bulge in the membrane may be enhanced by biasing the membrane to the outward radial direction at the points of attachment by the specific means of attachment. In the example shown in the inset figure, the suture attachment  54  is configured to capture and enforce folds  53  in the membrane such that an outward bias in the curve of the bulge is developed. The membrane material may be configured by thickness and stiffness, for example, to create firmness of the bulges suitable to the sealing function. In another biasing mechanism indicated in the inset figure, the two sides of the membrane departing from the point of attachment may be connected at line A-B to each other as by suturing either adjacent the point of attachment alone or along an axial length to form at least a partial seam. Line A-B and points of membrane connection aligned to it may be radially or axially displaced from the underlying frame by an arbitrary distance. Single sutures or seams of suture or other means of connection may be used to create other or multiple folds of arbitrary biasing direction at any place in the membrane layer. 
     As shown in  FIG.  14   , when implant  50  is expanded within a vessel  58 , the outwardly-bulging portions of membrane  52  are compressed against the inner walls of vessel  58  to create a plurality of folds/wrinkles in the membrane  52 , thereby forming a radial and circumferential seal between the implant  50  and the inner walls of vessel  58 . 
     While not shown in  FIGS.  13 - 14   , it is to be understood that the circumferentially-redundant membrane attachment may be employed simultaneously together with the axially-redundant membrane attachment shown and described above with respect to  FIGS.  4 - 8   . 
     While not shown in  FIGS.  6 - 14   , it is to be understood that the sealing device may also be used at the outflow end as well as at the inflow end of a tube graft or EVAR device to mitigate endoleak. 
     In accordance with  FIGS.  1 - 14    described above, various aspects of the present disclosure describe an intravascular device including a frame having an inflow edge, an outflow edge, and a circumferentially complete axial portion that is configured to decrease in axial length upon the radial expansion of the frame from a configuration that is radially compressed to a configuration that is radially expanded, with the radially expanded configuration being associated with the deployed condition of the intravascular device. The intravascular device may also include a layer of biocompatible membrane applied and interconnected to the radially outer surface of the substantially circumferentially-complete axial portion of the frame, with the membrane layer having an axial length that exceeds the axial length of the substantially circumferentially-complete axial portion of the frame when in its expanded configuration. 
     In some aspects of the present disclosure, the frame and, in particular, the circumferentially-complete axial portion of the frame, includes a lattice. 
     The circumference of the biocompatible layer may exceed or not exceed the circumference of the frame portion to which it is interconnected. 
     The biocompatible membrane may be comprised of fabric or polymer material such as PTFE. In some aspects of the present disclosure, the biocompatible membrane is comprised of a cross-linked and processed mammalian tissue, such as porcine or bovine pericardium. The membrane material may be substantially dry, radially compressed, associated to a delivery catheter, sterilized, and pre-packaged with a delivery system prior to use at implantation. 
     In the example where the intravascular device is a framed tube graft for endovascular exclusion of an aneurysmal defect, the biocompatible membrane layer may be interconnected to the frame at a series of circumferentially-distributed points axially displaced from the outflow edge of the frame and at a series of circumferentially-distributed points approximating the outflow edge of the frame. In some aspects of the present disclosure, the points of interconnection correspond to nodes or crossing points of the frame lattice. However, in other aspects, the intravascular device may have alternative uses, such as, for example, transcatheter valves. In such scenarios, the inflow and outflow polarities of the frame may be reversed from that which is described above with respect to  FIGS.  1 - 14   . 
     When the frame including the circumferentially-complete axial portion is deployed from a radially-compressed to a fully radially-expanded condition, the circumferentially-complete axial portion of the frame predictably shortens axially, moving the various circumferential membrane layer interconnection points axially toward each other. Such axial movement causes the membrane layer between the interconnection points to become redundant and, therefore, to project radially outward to form a circumferentially-oriented pleat. This radially-outward projection of the membrane layer is circumferential and causes the radially-outward projection of the membrane layer to be interposed between the frame and the native tissue seat, thereby allowing at least a portion of the membrane layer to act as a barrier seal to block the passage of blood between the inner surface of the vessel and the outer surface of the implant. In the example of an EVAR device, the configuration described above may act to block endoleak. However, the device may be used for other purposes, such as reducing prosthetic paravalvular leak. 
     As long as there is axial separation of these two series of circumferential interconnection points, and there is axial shortening of the corresponding circumferentially complete underlying portion of the frame on expansion from the compressed or crimped configuration, then the interconnection points need not lie directly upon an edge of the frame or upon an edge of that circumferentially complete portion configured to predictably shorten. Further, the biocompatible membrane layer need not terminate in either axial extent at the points of interconnection. In at least one embodiment, the tissue layer extends at least to and is interconnected along (1) an outflow axial extent corresponding to the outflow edge of the frame and (2) an inflow axial extent between the inflow and outflow edges of the frame approximating the axially mid portion of the frame. 
     The above-disclosed features and functions, as well as alternatives, may be combined into many other different systems or applications. Various presently unforeseen or unanticipated alternatives, modifications, variations or improvements may be made by those skilled in the art, each of which is also intended to be encompassed by the disclosed embodiments.