STENT-GRAFTS CONFIGURED FOR POST-IMPLANTATION EXPANSION

An endovascular stent-graft is provided that includes a generally tubular body, which (a) is configured to assume a radially-compressed delivery state and at least first and second radially-expanded deployment states, (b) is shaped so as to define a stepwise expanding portion, and (c) comprises a stent member. The stent member includes a plurality of self-expandable flexible structural stent elements, and at least one circumferential expansion element. The stent member is configured such that application of a force thereto, which is insufficient to cause plastic deformation of the self-expandable flexible structural stent elements and is sufficient to cause plastic deformation of the circumferential expansion element, causes an increase in a circumferential length of the circumferential expansion element, thereby transitioning the tubular body from the first radially-expanded deployment state to the second radially-expanded deployment state, thereby increasing a greatest internal perimeter of the expanding portion.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is the U.S. national stage of International Application PCT/IL2013/050656, filed Jul. 31, 2013, which claims priority from U.S. Provisional Application 61/678,182, filed Aug. 1, 2012, which is assigned to the assignee of the present application and is incorporated herein by reference.

FIELD OF THE APPLICATION

The present application relates generally to prostheses and surgical methods, and specifically to tubular prostheses, including endovascular stent-grafts, and surgical techniques for using the prostheses to maintain patency of body passages such as blood vessels, and treating aneurysms and dissections of arterial walls.

BACKGROUND OF THE APPLICATION

An aneurysm is a localized, blood-filled dilation (bulge) of a blood vessel caused by disease or weakening of the vessel wall. Left untreated, the aneurysm will frequently rupture, resulting in loss of blood through the rupture and death. Endovascular prostheses are sometimes used to treat aortic aneurysms. Such treatment includes implanting a stent or stent-graft within the diseased vessel to bypass the anomaly. Aneurysms may be congenital, but are usually caused by disease or, occasionally, by trauma. Aortic aneurysms include abdominal aortic aneurysms (“AAAs”), which form between the renal arteries and the iliac arteries, and thoracic aortic aneurysms (“TAAs”), which may occur in one or more of the descending aorta, the ascending aorta, and the aortic arch.

“Endoleak” is the persistent flow of blood into the aneurysm sac after implantation of an endovascular prosthesis. The management of some types of endoleak remains controversial, although most can be successfully occluded with surgery, further stent implantation, or embolization. Four types of endoleaks have been defined, based upon their proposed etiology.

A type I endoleak, which occurs in up to 10 percent of endovascular aortic aneurysm repairs, is due to an incompetent seal at either the proximal or distal attachment sites of the vascular prosthesis, resulting in blood flow at the end of the prosthesis into the aneurysm sac. Etiologies include undersizing of the diameter of the endograft at the attachment site and ineffective attachment to a vessel wall that is heavily calcified or surrounded by thick thrombus. Type I failures have also been found to be caused by a continual expansion of the aneurysm neck (the portion of the aorta extending cephalad or caudad from the aneurysm, which is not dilated). This expansion rate has been estimated to be about one millimeter per year. Because the aneurysm neck expands beyond the natural resting diameter of the prosthesis, one or more passageways are defined about the prosthesis in communication with the aneurysm sac. Additionally, type I endoleaks may be caused when circular prostheses are implanted in non-circular aortic lumens, which may be caused by irregular vessel formation and/or calcified topography of the lumen of the aorta.

Type I endoleaks may occur immediately after placement of the prosthesis, or may be delayed. A delayed type I endoleak may be seen during follow-up studies if the prosthesis is deployed into a diseased segment of aorta that dilates over time, leading to a breach in the seal at the attachment site.

Type I endoleaks must be repaired as soon as they are discovered, because the aneurysm sac remains exposed to systemic pressure, predisposing to aneurysmal rupture, and spontaneous closure of the leak is rare. If discovered at the time of initial placement, repair may consist of reversal of anticoagulation and reinflation of the deployment balloon for an extended period of time. These leaks may also be repaired with small extension grafts that are placed over the affected end. These methods are usually sufficient to exclude the aneurysm. Conversion to an open surgical repair may be needed in the rare situation in which the leak is refractory to percutaneous treatment.

Research has shown that the necks of the post-surgical aorta increase in size for approximately twelve months after implantation of a stent-graft, regardless of whether the aneurysm experiences dimensional change. This phenomenon can result in perigraft leaks and graft migration. Furthermore, progressive expansion of the aneurysm sac associated with type I endoleak can lead to compromise of the seal at the neck and is the principal indication for secondary intervention for this condition.

Sizing of aortic endografts is an essential step in successful endovascular treatment of aortic pathology, although there is no consensus regarding the optimal sizing strategy. Some proximal oversizing is necessary to obtain a seal between the stent-graft and the aortic wall and to prevent the graft from migrating, but excessive oversizing might negatively influence the results. In a systematic review, the current literature was investigated to obtain an overview of the risks and benefits of oversizing and to determine the optimal degree of oversizing of stent-grafts used for endovascular abdominal aortic aneurysm repair (J van Prehn et al., “Oversizing of Aortic Stent Grafts for Abdominal Aneurysm Repair: A Systematic Review of the Benefits and Risks,” European Journal of Vascular & Endovascular Surgery 38(1):42-53, July 2009 (published online May 11, 2009)). Prehn et al. conclude that “based on the best available evidence, the current standard of 10-20% oversizing regime appears to be relatively safe and preferable. Oversizing >30% might negatively impact the outcome after EVAR. Studies of higher quality are needed to further assess the relationship between proximal oversizing and the incidence of complications, particularly regarding the impact on aneurysm neck dilatation.”

In light of the above, it appears that the functional lifespan of a stent-graft is limited, because (a) the pathology is progressive and (b) there is an upper limit on desirable oversizing, which if crossed, may itself exacerbate the proximal neck expansion rate and hence contribute to type I endoleak and device migration.

PCT Publication WO 2009/078010 to Shalev, and US Patent Application Publication 2010/0292774 in the national stage thereof, which are assigned to the assignee of the present application and are incorporated herein by reference, describe a system for treating an aneurysmatic abdominal aorta, comprising (a) an extra-vascular wrapping (EVW) comprising (i) at least one medical textile member adapted to at least partially encircle a segment of aorta in proximity to the renal arteries, and (ii) a structural member, wherein the EVW is adapted for laparoscopic delivery, and (b) an endovascular stent-graft (ESG) comprising (i) a compressible structural member, and (ii) a substantially fluid impervious fluid flow guide (FFG) attached thereto. Also described is an extra-vascular ring (EVR) adapted to encircle the neck of an aortic aneurysm. Further described are methods for treating an abdominal aortic aneurysm, comprising laparoscopically delivering the extra-vascular wrapping (EVW) and endovascularly placing an endovascular stent-graft (ESG). Also described are methods to treat a type I endoleak. U.S. Provisional Application 61/014,031, filed Dec. 15, 2007, from which the above-referenced applications claim priority, is also incorporated herein by reference.

SUMMARY OF APPLICATIONS

Applications of the present invention provide endovascular stent-grafts that are configured to be radially expanded during minimally-invasive secondary intervention procedures performed after completion of implantation of the stent-grafts, typically upon detection of type I endoleak or concern of migration. The stent-grafts of the present invention thus minimize the invasiveness of secondary endovascular intervention, and provide techniques that can easily and safely be performed by a surgeon or interventionalist that is skilled in the art of endovascular aortic interventions. These techniques help prevent the need for more invasive and costly intervention, such as implantation of a flared, larger diameter proximal extension cuff, or surgical repair of the endoleak and/or migration.

Each of the stent-grafts of the present invention comprises a generally tubular body. The tubular body is configured to assume (a) a radially-compressed delivery state, typically when the body is initially positioned in a delivery catheter, and (b) at least first and second radially-expanded deployment states. The body typically assumes the first radially-expanded deployment state upon deployment from the delivery catheter, and the second radially-expanded delivery state after deployment, typically during a minimally-invasive secondary intervention procedure. In order to enable a transition from the first radially-expanded deployment state to the second radially-expanded deployment state, the tubular body is shaped so as to define a stepwise expanding portion, a greatest internal perimeter of which increases as the body transitions from the first radially-expanded deployment state to the second radially-expanded delivery state. The tubular body comprises a stent member, and, typically, a generally tubular fluid flow guide comprising a graft material, which is attached to the stent member. The fluid flow guide is configured to accommodate the increasing of the greatest internal perimeter of the expanding portion, as described hereinbelow.

For some applications, the stent member comprises a plurality of self-expandable flexible structural stent elements, and a circumferential expansion element that is coupled to at least two of the self-expandable flexible structural stent elements of the expanding portion of the tubular body. The structural stent elements comprise a self-expanding material, such as a self-expanding metal, such that the body is self-expandable. For some applications, the circumferential expansion element is generally non-elastic. For example, the circumferential expansion element may comprise non-elastic stainless steel, or a cobalt-chromium alloy.

The stent member is configured such that application of a force thereto, which is insufficient to cause plastic deformation of the self-expandable flexible structural stent elements and is sufficient to cause plastic deformation of the circumferential expansion element, causes an increase in a circumferential length of the circumferential expansion element. This increase in length transitions the tubular body from the first radially-expanded deployment state to the second radially-expanded deployment state, thereby increasing the greatest internal perimeter of the expanding portion.

As mentioned above, the fluid flow guide is configured to accommodate the increasing of the greatest internal perimeter of the expanding portion. For some applications, in order to provide such accommodation, when the tubular body is in the first radially-expanded deployment state, the fluid flow guide is shaped so as to define one or more folds in a vicinity of the circumferential expansion element. For some applications, when the tubular body is in the first radially-expanded deployment state, the one or more folds are disposed radially outside the stent member. Alternatively, for some applications, in order to provide such accommodation, at least a portion of the fluid flow guide in a vicinity of the circumferential expansion element comprises a stretchable fabric.

For some applications, the stent-graft comprises a circumferential expansion prevention element, which is coupled to at least two self-expandable flexible structural stent elements of the expanding portion of the tubular body. When intact, the circumferential expansion prevention element restrains the tubular body in the first radially-expanded deployment state, in which the expanding portion has a first greatest internal perimeter. When detached and/or severed, such as by application of a force that increases a distance between the two stent elements to which the circumferential expansion prevention element is coupled, the circumferential expansion prevention element does not restrain the tubular body in the first radially-expanded deployment state. As a result, the tubular body transitions from the first radially-expanded deployment state to the second radially-expanded deployment state. In the second radially-expanded deployment state, the expanding portion has a second greatest internal perimeter, which is greater than the first greatest internal perimeter.

For some applications, the circumferential expansion prevention element comprises a suture, a wire (e.g., comprising metal), a hook, a loop, or a helix. The circumferential expansion prevention element is detached and/or severed, such as by cutting or breaking thereof. For example, a cutting tool may be used, or a balloon may be used to apply a force sufficient to detach and/or sever the element, by increasing a distance between the two stent elements to which the element is coupled.

For some applications, the graft material of the fluid flow guide is shaped so as to define, when the tubular body is in the first radially-expanded deployment state, one or more folds disposed such that at least 50%, e.g., at least 75%, such as 100%, of the graft material of the folds is radially outside the stent member. Disposing of the folds mostly or entirely outside of the stent member reduces or prevents any interfere by the folds with the flow of blood through the fluid flow guide. If the folds instead extended mostly or entirely into the lumen of the fluid flow guide, the folds would reduce the effective cross-section of the lumen and potentially interfere with blood flow and increase the risk of thrombosis. Such interference is particularly undesirable because the stent-graft often remains implanted in the first radially-expanded deployment state for an extended period of time, such as months or years, or even permanently. For some applications, the graft material is shaped so as to define exactly one or exactly two folds when the tubular body is in the first radially-expanded deployment state.

Typically, when the tubular body is in the second radially-expanded deployment state, the graft material of the fluid flow guide is shaped so as to define none of the folds or fewer of the folds than when the tubular body is in the first radially-expanded deployment state.

For some applications, when the tubular body is in the first radially-expanded deployment state, the one or more folds are oriented tangentially to the tubular body, such that a portion of the graft material of the one or more folds is in contact with an outer surface of the tubular body.

For some applications, each of the one or more folds is relatively large with respect to the greatest internal perimeter of the expanding portion, in order to provide a large circumferential buffer for expansion of the expanding portion after implantation. For example, a greatest internal perimeter of the graft material of a first one of the one or more folds, when the first fold is unfolded when the tubular body is in the second radially-expanded deployment state, may be equal to at least 7% of the second greatest internal perimeter.

For some applications, a locking mechanism is provided, which is configured to assume a locked state which restrains the tubular body in the first radially-expanded deployment state, and a released state, which allows the tubular body to transition to the second radially-expanded deployment state.

For some applications, during a primary intervention procedure, a surgeon or interventionalist transvascularly (e.g., transcutaneously) introduces the stent-graft into a blood vessel while the tubular body of the stent-graft is in the radially-compressed delivery state. Thereafter, the surgeon or interventionalist transitions the tubular body to the first radially-expanded deployment state in the blood vessel, in which state the expanding portion has the first greatest internal perimeter and forms a blood-tight seal with a wall of the blood vessel at a neck of an aneurysm and/or a dissection of an arterial wall. The initial implantation procedure is complete.

Over time (typically over a few years), the neck of the aneurysm often progressively dilates, such as because of progressive expansion of the aneurysm sac. Such dilation of the neck may compromise the seal between the expanding portion of the stent-graft and the wall of the anatomical neck, resulting in type I endoleak. In response to detecting such dilation and/or endoleak (typically at least one month, such as at least one year, e.g., a few years, after initial implantation and deployment of the stent-graft), a surgeon or interventionalist, during a minimally-invasive secondary intervention procedure, transitions the tubular body to the second radially-expanded deployment state in the blood vessel. In the second radially-expanded deployment state, the expanding portion has the second greatest internal perimeter, which is greater than the first greatest perimeter.

There is therefore provided, in accordance with an application of the present invention, apparatus including an endovascular stent-graft system, which includes an endovascular stent-graft, which includes a generally tubular body, which:is shaped so as to define a stepwise expanding portion,is configured to assume (a) a radially-compressed delivery state and (b) at least first and second radially-expanded deployment states, in which the expanding portion has respective first and second greatest internal perimeters, the second greater than the first, wherein the tubular body, when in the first radially-expanded deployment state, is restrained from transitioning to the second radially-expanded deployment state, andincludes a self-expandable flexible stent member, and a generally tubular fluid flow guide, which is attached to the stent member and includes a graft material that is shaped so as to define, when the tubular body is in the first radially-expanded deployment state, one or more folds disposed such that at least 50% of the graft material of the folds is radially outside the stent member.

For some applications, at least 75%, such as 100%, of the graft material of the folds is radially outside the stent member when the tubular body is in the first radially-expanded deployment state.

For some applications, when the tubular body is in the second radially-expanded deployment state, the graft material of the fluid flow guide is shaped so as to define none of the folds or fewer of the folds than when the tubular body is in the first radially-expanded deployment state.

For some applications, the second greatest internal perimeter of the expanding portion is at least 10% greater than the first greatest internal perimeter of the expanding portion.

For some applications, when the tubular body is in the first radially-expanded deployment state, the one or more folds are oriented tangentially to the tubular body, such that a portion of the graft material of the one or more folds is in contact with an outer surface of the tubular body. For some applications, wherein, at least when the tubular body is in the radially-compressed delivery state, the one or more folds are removably secured to the outer surface of the tubular body. For some applications, the apparatus further includes a securing mechanism, which removably secures the folds to the outer surface of the tubular body. For some applications, the apparatus further includes a biodegradable adhesive, which removably secures the folds to the outer surface of the tubular body.

For some applications, the expanding portion is disposed at a longitudinal end of the body.

For some applications, a greatest internal perimeter of the graft material of a first one of the one or more folds, when the first fold is unfolded when the tubular body is in the second radially-expanded deployment state, is at least 7% of the second greatest internal perimeter. Alternatively or additionally, for some applications, a greatest internal perimeter of the graft material of a second one of the one or more folds, when the second fold is unfolded, is at least 7% of the second greatest internal perimeter.

For some applications, the stent-graft system further includes a locking mechanism, configured to assume a locked state which restrains the tubular body in the first radially-expanded deployment state, and a released state, which allows the tubular body to transition to the second radially-expanded deployment state. For some applications, the locking mechanism includes a shaft and two or more attachment members coupled to the stent-graft, the shaft passes through the attachment members when the locking mechanism is in the locked state, and the shaft does not pass through the attachment members when the locking mechanism is in the released state. For some applications, the locking mechanism transitions from the locked state to the released state in response to translation of the shaft. For some applications, the translation is longitudinal translation.

For some applications, one of the one or more folds has two end portions at a surface generally defined by the tubular body, and, when the stent-graft is in the first radially-expanded deployment state, a length of the fold, measured along the graft material of the fold at a longitudinal end of the body between the two end portions, is at least 140% of a distance between the two end portions of the fold at the longitudinal end. For some applications, when the stent-graft is in the first radially-expanded deployment state, the length of the fold, measured along the graft material of the fold at the longitudinal end of the body between the two end portions, is at least 167% of the distance between the two end portions of the fold at the longitudinal end. For some applications, when the stent-graft is in the first radially-expanded deployment state, the length of the fold, measured along the graft material of the fold at the longitudinal end of the body between the two end portions, is at least 500% of the distance between the two end portions of the fold at the longitudinal end.

For some applications, the graft material is shaped so as to define exactly one or exactly two folds when the tubular body is in the first radially-expanded deployment state.

For some applications, the stent member includes:a plurality of self-expandable flexible structural stent elements; anda circumferential expansion element that is coupled to at least two of the self-expandable flexible structural stent elements of the expanding portion of the tubular body, andthe stent member is configured such that application of a force thereto, which is insufficient to cause plastic deformation of the self-expandable flexible structural stent elements and is sufficient to cause plastic deformation of the circumferential expansion element, causes an increase in a circumferential length of the circumferential expansion element, thereby transitioning the tubular body from the first radially-expanded deployment state to the second radially-expanded deployment state.

There is further provided, in accordance with an application of the present invention, apparatus including an endovascular stent-graft system, which includes a generally tubular body, which:is shaped so as to define a stepwise expanding portion,is configured to assume (a) a radially-compressed delivery state and (b) at least first and second radially-expanded deployment states, in which the expanding portion has respective first and second greatest internal perimeters, the second greater than the first, wherein the tubular body, when in the first radially-expanded deployment state, is restrained from transitioning to the second radially-expanded deployment state, andincludes a self-expandable flexible stent member, and a generally tubular fluid flow guide, which is attached to the stent member and includes a graft material that is shaped so as to define, when the tubular body is in the first radially-expanded deployment state, one or more folds,wherein a greatest internal perimeter of the graft material of a first one of the one or more folds, when the first fold is unfolded when the tubular body is in the second radially-expanded deployment state, is at least 7% of the second greatest internal perimeter.

For some applications, the first length equals at least 10% of the second greatest internal perimeter.

For some applications, a greatest internal perimeter of the graft material of a second one of the one or more folds, when the second fold is unfolded, is at least 7% of the second greatest internal perimeter.

For some applications, when the tubular body is in the second radially-expanded deployment state, the fluid flow guide is shaped so as to define none of the folds or fewer of the folds than when the tubular body is in the first radially-expanded deployment state.

For some applications, the second greatest internal perimeter is at least 10% greater than the first greatest internal perimeter.

For some applications, the stent-graft system further includes a locking mechanism, configured to assume a locked state which restrains the tubular body in the first radially-expanded deployment state, and a released state, which allows the tubular body to transition to the second radially-expanded deployment state.

There is still further provided, in accordance with an application of the present invention, apparatus including an endovascular stent-graft system, which includes a generally tubular body, which:is shaped so as to define a stepwise expanding portion,is configured to assume (a) a radially-compressed delivery state and (b) at least first and second radially-expanded deployment states, in which the expanding portion has respective first and second greatest internal perimeters, the second greater than the first, wherein the tubular body, when in the first radially-expanded deployment state, is restrained from transitioning to the second radially-expanded deployment state, andincludes a self-expandable flexible stent member, and a generally tubular fluid flow guide, which is attached to the stent member and includes a graft material that is shaped so as to define, when the tubular body is in the first radially-expanded deployment state, exactly one or exactly two folds.

For some applications, the graft material that is shaped so as to define exactly one fold when the tubular body is in the first radially-expanded deployment state.

There is additionally provided, in accordance with an application of the present invention, apparatus including an endovascular stent-graft, which includes a generally tubular body, which tubular body (a) is configured to assume a radially-compressed delivery state and at least first and second radially-expanded deployment states, (b) is shaped so as to define a stepwise expanding portion, and (c) includes a stent member, which includes:a plurality of self-expandable flexible structural stent elements; andat least one circumferential expansion element,wherein the stent member is configured such that application of a force thereto, which is insufficient to cause plastic deformation of the self-expandable flexible structural stent elements and is sufficient to cause plastic deformation of the circumferential expansion element, causes an increase in a circumferential length of the circumferential expansion element, thereby transitioning the tubular body from the first radially-expanded deployment state to the second radially-expanded deployment state, thereby increasing a greatest internal perimeter of the expanding portion.

For some applications, the circumferential expansion element circumscribes an angle of at least 3 degrees, e.g., at least 5 degrees, when the tubular body is in the first radially-expanded deployment state.

For some applications, the circumferential expansion element is coupled to at least two of the self-expandable flexible structural stent elements of the expanding portion of the tubular body. For some applications, a pair of the at least two of the self-expandable flexible structural stent elements to which the circumferential expansion element is coupled are coupled at a peak.

For some applications, the self-expandable flexible structural stent elements of the stent member are shaped so to define at least one circumferential band at the expanding portion, which band is shaped so as to define a plurality of peaks directed in a first longitudinal direction, alternating with a plurality of troughs directed in a second longitudinal direction opposite the first longitudinal direction. For some applications, the at least one circumferential expansion element is positioned alongside one of the self-expandable flexible structural stent elements near an element selected from the group consisting of: one of the peaks and one of the troughs. For some applications, the at least one circumferential expansion element is shaped similarly to a portion of the self-expandable flexible structural stent elements alongside which the at least one circumferential expansion element is positioned.

For some applications, the tubular body further includes a generally tubular fluid flow guide, which (a) includes a graft material, (b) is attached to the stent member, and (c) is configured to accommodate the increasing of the greatest internal perimeter of the expanding portion. For some applications, the at least one circumferential expansion element is attached to the fluid flow guide. For some applications, when the tubular body is in the first radially-expanded deployment state, the fluid flow guide is shaped so as to define one or more folds in a vicinity of the circumferential expansion element, so as to accommodate the increasing of the greatest internal perimeter of the expanding portion. For some applications, when the tubular body is in the first radially-expanded deployment state, the one or more folds are disposed radially outside the stent member.

For some applications, at least a portion of the fluid flow guide in a vicinity of the circumferential expansion element includes a stretchable fabric, so as to accommodate the increasing of the greatest internal perimeter of the expanding portion. For some applications, the fluid flow guide, other than the portion in the vicinity of the circumferential expansion element, includes a fabric that is less elastic than the stretchable fabric.

For some applications, a resistance of the fluid flow guide to lateral expansion is less than 70% of a resistance of the circumferential expansion element to lateral expansion, when the tubular body is in the second radially-expanded deployment state. For some applications, the resistance of the fluid flow guide to lateral expansion is less than 30% of the resistance of the circumferential expansion element to lateral expansion, when the tubular body is in the second radially-expanded deployment state.

For some applications, the circumferential expansion element has a shape selected from the group of shapes consisting of: a U-shape, a V-shape, a W-shape, and an undulating shape, at least when the tubular body is in the first radially-expanded deployment state.

For some applications, the apparatus further includes one or more balloons, configured to apply the force from within the tubular body. For some applications, the one or more balloons include a plurality of balloons have respective different volumes when inflated.

For some applications, the circumferential expansion element includes non-elastic stainless steel.

For some applications, the circumferential expansion element is generally non-elastic. For some applications, an angular segment of the expanding portion that includes the circumferential expansion element expands and contracts at least 50% less per unit circumferential arc angle than an angular segment of the expanding portion that does not include the circumferential expansion element, as the body cycles between being internally pressurized by (a) fluid having a pressure of 80 mmHg and (b) fluid having a pressure of 120 mmHg.

For some applications, the circumferential expansion element includes a cobalt-chromium alloy.

There is yet additionally provided, in accordance with an application of the present invention, apparatus including an endovascular stent-graft, which includes a generally tubular body, which tubular body (a) is configured to assume a radially-compressed delivery state and at least first and second radially-expanded deployment states, (b) is shaped so as to define a stepwise expanding portion, and (c) includes:a stent member, which includes a plurality of self-expandable flexible structural stent elements, which, when unconstrained, are configured to cause the tubular body to assume the second radially-expanded deployment state; anda circumferential expansion prevention element, which is coupled to at least two of the self-expandable flexible structural stent elements of the expanding portion of the tubular body,wherein, when intact, the circumferential expansion prevention element restrains the tubular body in the first radially-expanded deployment state, in which the expanding portion has a first greatest internal perimeter, andwherein, when detached or severed, the circumferential expansion prevention element does not restrain the tubular body in the first radially-expanded deployment state, such that the tubular body transitions from the first radially-expanded deployment state to the second radially-expanded deployment state, in which the expanding portion has a second greatest internal perimeter, which is greater than the first greatest internal perimeter.

For some applications, the tubular body further includes a generally tubular fluid flow guide, which includes a graft material and is attached to the stent member, and is configured to accommodate the increasing of the greatest internal perimeter of the expanding portion during the transitioning.

For some applications, the circumferential expansion prevention element includes an element selected from the group consisting of: a suture, a wire, a hook, a loop, and a helix.

For some applications, the circumferential expansion prevention element circumscribes an angle of at least 3 degrees, e.g., at least 5 degrees, when the tubular body is in the first radially-expanded deployment state.

For some applications, the self-expandable flexible structural stent elements of the stent member are shaped so to define at least one circumferential band at the expanding portion, which band is shaped so as to define a plurality of peaks directed in a first longitudinal direction, alternating with a plurality of troughs directed in a second longitudinal direction opposite the first longitudinal direction; and the circumferential expansion prevention element is coupled to the at least two of the structural elements within 30% of a diameter of the body in its first radially-expanded state of respective ones of the peaks. For some applications, the circumferential expansion prevention element is coupled to the at least two of the structural elements at respective ones of the peaks.

For some applications, when the tubular body is in the first radially-expanded deployment state, the fluid flow guide is shaped so as to define one or more folds in a vicinity of the circumferential expansion prevention element, so as to accommodate the increasing of the greatest internal perimeter of the expanding portion. For some applications, when the tubular body is in the first radially-expanded deployment state, the one or more folds are disposed radially outside the stent member.

For some applications, at least a portion of the fluid flow guide in a vicinity of the circumferential expansion prevention element includes a stretchable fabric, so as to accommodate the increasing of the greatest internal perimeter of the expanding portion. For some applications, the fluid flow guide, other than the portion in the vicinity of the circumferential expansion prevention element, includes a fabric that is less elastic than the stretchable fabric.

For some applications, the apparatus further includes one or more balloons, configured to apply, from within the tubular body, a force sufficient to sever the circumferential expansion prevention element. For some applications, the one or more balloons include a plurality of balloons have respective different volumes when inflated.

There is also provided, in accordance with an application of the present invention, a method including:providing an endovascular stent-graft, which includes a generally tubular body, which (a) is shaped so as to define a stepwise expanding portion, and (b) includes a self-expandable flexible stent member, and a generally tubular fluid flow guide, which includes a graft material and is attached to the stent member;during a minimally-invasive primary intervention procedure, transvascularly introducing the stent-graft into a blood vessel of a human subject while the tubular body of the stent-graft is in a radially-compressed delivery state, and, thereafter, transitioning the tubular body to a first radially-expanded deployment state in the blood vessel, in which state the expanding portion has a first greatest internal perimeter and forms a blood-tight seal with a wall of the blood vessel; andthereafter, during a minimally-invasive secondary intervention procedure separate from the primary intervention procedure, transitioning the tubular body to a second radially-expanded deployment state in the blood vessel, in which state the expanding portion has a second greatest internal perimeter and forms a blood-tight seal with the wall of the blood vessel, which second greatest internal perimeter is greater than the first greatest internal perimeter.

For some applications, transitioning the tubular body to the second radially-expanded deployment state in the blood vessel includes performing the secondary intervention procedure at least one month after performing the primary intervention procedure.

For some applications, the minimally-invasive secondary intervention procedure is a transvascular secondary intervention procedure, and transitioning the tubular body to the second radially-expanded deployment state includes transitioning the tubular body to the second radially-expanded deployment state during the transvascular secondary intervention procedure. For some applications, transitioning the tubular body to the second radially-expanded deployment state in the blood vessel includes transvascularly introducing a balloon into the tubular body, and inflating the balloon.

For some applications, the method further includes, after the minimally-invasive secondary intervention procedure, during a minimally-invasive tertiary intervention procedure separate from the primary and the secondary intervention procedures, transitioning the tubular body to a third radially-expanded deployment state in the blood vessel, in which state the expanding portion has a third greatest internal perimeter and forms a blood-tight seal with the wall of the blood vessel, which third greatest internal perimeter is greater than the second greatest internal perimeter.

For some applications, the method further includes, after transitioning the tubular body to the first radially-expanded deployment state, detecting type I endoleak, and transitioning the tubular body to the second radially-expanded deployment state includes transitioning the tubular body to the second radially-expanded deployment state in response to detecting the type I endoleak.

For some applications, the method further includes identifying that the blood vessel has an aneurysm, transitioning the tubular body to the first radially-expanded deployment state includes transitioning the tubular body to the first radially-expanded deployment state so that the expanding portion forms the blood-tight seal with the wall of the blood vessel at a neck of the aneurysm, and transitioning the tubular body to the second radially-expanded deployment state includes transitioning the tubular body to the second radially-expanded deployment state so that the expanding portion forms the blood-tight seal with the wall of the blood vessel at the neck of the aneurysm.

For some applications, transitioning the tubular body to the second radially-expanded deployment state includes transitioning the tubular body to the second radially-expanded deployment state such that the second greatest internal perimeter of the expanding portion is at least 10% greater than the first greatest internal perimeter of the expanding portion.

For some applications, providing the endovascular stent-graft includes providing the endovascular stent-graft in which the expanding portion is disposed at a longitudinal end of the body.

For some applications, transvascularly introducing the stent-graft includes transvascularly introducing the stent-graft into the blood vessel while a locking mechanism is in a locked state which restrains the tubular body in the first radially-expanded deployment state, and transitioning the tubular body to the second radially-expanded deployment state includes transitioning the locking mechanism to a released state, which allows the tubular body to transition to the second radially-expanded deployment state.

For some applications, transitioning the tubular body to the first radially-expanded deployment state includes transitioning the tubular body to the first radially-expanded deployment state such that the graft material is shaped so as to define one or more folds disposed such that at least 50% of the graft material of the folds is radially outside the stent member. For some applications, transitioning the tubular body to the first radially-expanded deployment state includes transitioning the tubular body to the first radially-expanded deployment state such that the graft material is shaped so as to define one or more folds disposed such that at least 75%, such as 100%, of the graft material of the folds is radially outside the stent member.

For some applications, transitioning the tubular body to the second radially-expanded deployment state includes transitioning the tubular body to the second radially-expanded deployment state such that the graft material of the fluid flow guide is shaped so as to define none of the folds or fewer of the folds than when the tubular body is in the first radially-expanded deployment state.

For some applications, transitioning the tubular body to the first radially-expanded deployment state includes transitioning the tubular body to the first radially-expanded deployment state such that the one or more folds are oriented tangentially to the tubular body, such that a portion of the graft material of the one or more folds is in contact with an outer surface of the tubular body.

For some applications, transitioning the tubular body to the first radially-expanded deployment state includes transitioning the tubular body to the first radially-expanded deployment state such that the graft material is shaped so as to define exactly one or exactly two folds.

For some applications, a greatest internal perimeter of the graft material of a first one of the one or more folds, when the first fold is unfolded when the tubular body is in the second radially-expanded deployment state, is at least 7% of the second greatest internal perimeter. Alternatively or additionally, for some applications, a greatest internal perimeter of the graft material of a second one of the one or more folds, when the second fold is unfolded, is at least 7% of the second greatest internal perimeter.

For some applications, introducing the stent-graft includes introducing the stent-graft into the blood vessel while the graft material is shaped so as to define one or more folds disposed such that at least 50% of the graft material of the folds is radially outside the stent member. For some applications, introducing the stent-graft includes introducing the stent-graft into the blood vessel while the graft material is shaped so as to define one or more folds disposed such that at least 75%, such as 100%, of the graft material of the folds is radially outside the stent member.

For some applications, transitioning the tubular body to the second radially-expanded deployment state includes transitioning the tubular body to the second radially-expanded deployment state such that the graft material of the fluid flow guide is shaped so as to define none of the folds or fewer of the folds than when the tubular body is in the first radially-expanded deployment state.

For some applications, introducing the stent-graft includes introducing the stent-graft into the blood vessel while the one or more folds are oriented tangentially to the tubular body, such that a portion of the graft material of the one or more folds is in contact with an outer surface of the tubular body.

For some applications, introducing the stent-graft includes introducing the stent-graft into the blood vessel while the graft material is shaped so as to define exactly one or exactly two folds.

For some applications, a greatest internal perimeter of the graft material of a first one of the one or more folds, when the first fold is unfolded when the tubular body is in the second radially-expanded deployment state, is at least 7% of the second greatest internal perimeter. Alternatively or additionally, for some applications, a greatest internal perimeter of the graft material of a second one of the one or more folds, when the second fold is unfolded, is at least 7% of the second greatest internal perimeter.

For some applications, transitioning the tubular body to the first radially-expanded deployment state includes transitioning the tubular body to the first radially-expanded deployment state such that the graft material is shaped so as to define one or more folds, and a greatest internal perimeter of the graft material of a first one of the one or more folds, when the first fold is unfolded when the tubular body is in the second radially-expanded deployment state, is at least 7% of the second greatest internal perimeter. For some applications, the first length equals at least 10% of the second greatest internal perimeter.

For some applications, a greatest internal perimeter of the graft material of a second one of the one or more folds, when the second fold is unfolded, is at least 7% of the second greatest internal perimeter.

For some applications, transitioning the tubular body to the second radially-expanded deployment state includes transitioning the tubular body to the second radially-expanded deployment state such that the fluid flow guide is shaped so as to define none of the folds or fewer of the folds than when the tubular body is in the first radially-expanded deployment state.

For some applications, introducing the stent-graft includes introducing the stent-graft into the blood vessel while the graft material is shaped so as to define one or more folds, and a greatest internal perimeter of the graft material of a first one of the one or more folds, when the first fold is unfolded when the tubular body is in the second radially-expanded deployment state, is at least 7% of the second greatest internal perimeter. For some applications, the first length equals at least 10% of the second greatest internal perimeter. For some applications, a greatest internal perimeter of the graft material of a second one of the one or more folds, when the second fold is unfolded, is at least 7% of the second greatest internal perimeter.

For some applications, transitioning the tubular body to the second radially-expanded deployment state includes transitioning the tubular body to the second radially-expanded deployment state such that the fluid flow guide is shaped so as to define none of the folds or fewer of the folds than when the tubular body is in the first radially-expanded deployment state.

For some applications, transitioning the tubular body to the first radially-expanded deployment state includes transitioning the tubular body to the first radially-expanded deployment state such that the graft material is shaped so as to define exactly one or exactly two folds. For some applications, transitioning the tubular body to the first radially-expanded deployment state includes transitioning the tubular body to the first radially-expanded deployment state such the graft material is shaped so as to define exactly one fold.

For some applications, introducing the stent-graft includes introducing the stent-graft into the blood vessel while the graft material is shaped so as to define exactly one or exactly two folds. For some applications, introducing the stent-graft includes introducing the stent-graft into the blood vessel while the graft material is shaped so as to define exactly one fold.

For some applications, providing the endovascular stent-graft includes providing the endovascular stent-graft in which the tubular body further includes a stent member, which includes a plurality of self-expandable flexible structural stent elements, and at least one circumferential expansion element; and transitioning the tubular body to a second radially-expanded deployment state includes causing an increase in a circumferential length of the circumferential expansion element, by applying a force to the stent member, which force is insufficient to cause plastic deformation of the self-expandable flexible structural stent elements and is sufficient to cause plastic deformation of the circumferential expansion element. For some applications, providing the endovascular stent-graft includes providing the endovascular stent-graft in which the circumferential expansion element circumscribes an angle of at least 3 degrees, e.g., at least 5 degrees, when the tubular body is in the first radially-expanded deployment state.

For some applications, providing the endovascular stent-graft includes providing the endovascular stent-graft in which the circumferential expansion element is coupled to at least two of the self-expandable flexible structural stent elements of the expanding portion of the tubular body. For some applications, providing the endovascular stent-graft includes providing the endovascular stent-graft in which a pair of the at least two of the self-expandable flexible structural stent elements to which the circumferential expansion element is coupled are coupled at a peak.

For some applications, providing the endovascular stent-graft includes providing the endovascular stent-graft in which the self-expandable flexible structural stent elements of the stent member are shaped so to define at least one circumferential band at the expanding portion, which band is shaped so as to define a plurality of peaks directed in a first longitudinal direction, alternating with a plurality of troughs directed in a second longitudinal direction opposite the first longitudinal direction. For some applications, providing the endovascular stent-graft includes providing the endovascular stent-graft in which the at least one circumferential expansion element is positioned alongside one of the self-expandable flexible structural stent elements near an element selected from the group consisting of: one of the peaks and one of the troughs. For some applications, providing the endovascular stent-graft includes providing the endovascular stent-graft in which the at least one circumferential expansion element is shaped similarly to a portion of the self-expandable flexible structural stent elements alongside which the at least one circumferential expansion element is positioned.

For some applications, providing the endovascular stent-graft includes providing the endovascular stent-graft in which at least a portion of the fluid flow guide in a vicinity of the circumferential expansion element includes a stretchable fabric, so as to accommodate the increasing of the greatest internal perimeter of the expanding portion.

For some applications, providing the endovascular stent-graft includes providing the endovascular stent-graft in which the circumferential expansion element has a shape selected from the group of shapes consisting of: a U-shape, a V-shape, a W-shape, and an undulating shape, at least when the tubular body is in the first radially-expanded deployment state.

For some applications, transitioning the tubular body to the second radially-expanded deployment state in the blood vessel includes transvascularly introducing a balloon into the tubular body, and inflating the balloon to apply the force from within the tubular body.

For some applications:the method further includes, after the minimally-invasive secondary intervention procedure, during a minimally-invasive tertiary intervention procedure separate from the primary and the secondary intervention procedures, transitioning the tubular body to a third radially-expanded deployment state in the blood vessel, in which state the expanding portion has a third greatest internal perimeter and forms a blood-tight seal with the wall of the blood vessel, which third greatest internal perimeter is greater than the second greatest internal perimeter,the balloon is a first one of a plurality of balloons, andtransitioning the tubular body to a third radially-expanded deployment state includes transvascularly introducing a second one of the plurality of balloons into the tubular body, which second balloon has a larger volume than that of the first balloon, and inflating the second balloon to apply the force from within the tubular body.

For some applications, providing the endovascular stent-graft includes providing the endovascular stent-graft in which the circumferential expansion element includes non-elastic stainless steel.

For some applications, providing the endovascular stent-graft includes providing the endovascular stent-graft in which the circumferential expansion element is generally non-elastic. For some applications, providing the endovascular stent-graft includes providing the endovascular stent-graft in which an angular segment of the expanding portion that includes the circumferential expansion element expands and contracts at least 50% less per unit circumferential arc angle than an angular segment of the expanding portion that does not include the circumferential expansion element, as the body cycles between being internally pressurized by (a) fluid having a pressure of 80 mmHg and (b) fluid having a pressure of 120 mmHg

For some applications, providing the endovascular stent-graft includes providing the endovascular stent-graft in which the circumferential expansion element includes a cobalt-chromium alloy.

For some applications:providing the endovascular stent-graft includes providing the endovascular stent-graft in which the tubular body further includes a stent member, which includes (a) a plurality of self-expandable flexible structural stent elements, which, when unconstrained, are configured to cause the tubular body to assume the second radially-expanded deployment state, and (b) a circumferential expansion prevention element, which is coupled to at least two of the self-expandable flexible structural stent elements of the expanding portion of the tubular body, wherein, when intact, the circumferential expansion prevention element restrains the tubular body in the first radially-expanded deployment state, in which the expanding portion has a first greatest internal perimeter, andtransitioning the tubular body to a second radially-expanded deployment state includes detaching or severing the circumferential expansion prevention element, so that it does not restrain the tubular body in the first radially-expanded deployment state.

For some applications, providing the endovascular stent-graft includes providing the endovascular stent-graft in which the circumferential expansion prevention element includes an element selected from the group consisting of: a suture, a wire, a hook, a loop, and a helix.

For some applications, providing the endovascular stent-graft includes providing the endovascular stent-graft in which the circumferential expansion prevention element circumscribes an angle of at least 3 degrees, e.g., at least 5 degrees, when the tubular body is in the first radially-expanded deployment state.

For some applications, providing the endovascular stent-graft includes providing the endovascular stent-graft in which the self-expandable flexible structural stent elements of the stent member are shaped so to define at least one circumferential band at the expanding portion, which band is shaped so as to define a plurality of peaks directed in a first longitudinal direction, alternating with a plurality of troughs directed in a second longitudinal direction opposite the first longitudinal direction, and the circumferential expansion prevention element is coupled to the at least two of the structural elements within 30% of a diameter of the body in its first radially-expanded state of respective ones of the peaks. For some applications, providing the endovascular stent-graft includes providing the endovascular stent-graft in which the circumferential expansion prevention element is coupled to the at least two of the structural elements at respective ones of the peaks.

The present invention will be more fully understood from the following detailed description of applications thereof, taken together with the drawings, in which:

DETAILED DESCRIPTION OF APPLICATIONS

FIGS. 1A-Band2A-B are schematic illustrations of an endovascular stent-graft20, in accordance with an application of the present invention. Stent-graft20comprises a generally tubular body22. Body22is configured to assume (a) a radially-compressed delivery state, typically when the body is initially positioned in a delivery catheter, and (b) at least first and second radially-expanded deployment states. Body22typically assumes the first radially-expanded deployment state upon deployment from the delivery catheter, and the second radially-expanded delivery state after deployment, typically during a minimally-invasive secondary intervention procedure.FIGS. 1A and 2Ashow the stent-graft with body22in its first radially-expanded deployment state, andFIGS. 1B and 2Bshow the stent-graft with body22in its second radially-expanded deployment state.

Body22is shaped so as to define a stepwise expanding portion23, a greatest internal perimeter of which increases as body22transitions from the first radially-expanded delivery state to the second radially-expanded delivery state. (The “greatest” internal perimeter of the expanding portion means the internal perimeter as measured at the longitudinal location along the expanding portion that has the greatest internal perimeter.) For some applications, expanding portion23is disposed at a longitudinal end25of body22, as shown inFIGS. 1A-Band2A-B. For example, all of expanding portion23may be disposed with a distance of longitudinal end25, measured along an axis of body22, which distance is less than 30%, such as less than 25%, of an axial length of body22. Alternatively or additionally, the distance is less than 120%, such as less than 80%, of an average diameter of the expanding portion when body22is in the first radially-expanded state. For other applications, the expanding portion is disposed elsewhere along stent-graft20.

Body22comprises a stent member24, and, typically, a generally tubular fluid flow guide26. The fluid flow guide and the stent member are attached to each other, such as by suturing or stitching. The fluid flow guide is configured to accommodate the increase in the greatest internal perimeter of expanding portion23, as described hereinbelow. The stent member may be attached to an internal and/or an external surface of the fluid flow guide.

Stent member24comprises a plurality of self-expandable flexible structural stent elements28, which are either indirectly connected to one another by the fluid flow guide (as shown), and/or interconnected with one another (configuration not shown). Optionally, a portion of structural stent elements28may be attached (e.g., sutured) to the internal surface of the fluid flow guide, and another portion to the external surface of the fluid flow guide. Structural stent elements28comprise a self-expanding material, such as a self-expanding metal, such that body22is self-expandable. Typically, structural stent elements28comprise one or more metallic alloys, such as one or more superelastic metal alloys, a shape memory metallic alloy, and/or Nitinol. Typically, stent-graft20is configured to self-expand from the delivery state to the first radially-expanded deployment state. For example, stent member24may be heat-set to cause stent-graft20to self-expand from the delivery state to the first radially-expanded deployment state.

For some applications, flexible structural stent elements28of stent member24are shaped so to define at least one circumferential band29at expanding portion23, such as exactly one circumferential band29or a plurality of circumferential bands29. Circumferential band29is shaped so as to define a plurality of peaks32directed in a first longitudinal direction, alternating with a plurality of troughs34directed in a second longitudinal direction opposite the first longitudinal direction. Circumferential band29may be serpentine-shaped. Typically, stent member24is shaped so as to further define one or more additional circumferential bands29at respective longitudinal locations other than expanding portion23, as shown inFIGS. 1A-2B.

Stent member24further comprises at least one circumferential expansion element30, which is coupled to at least two of self-expandable flexible structural stent elements28of expanding portion23of tubular body22. For some applications, circumferential expansion element30has a shape selected from the group of shapes consisting of: a U-shape, a V-shape, a W-shape, and an undulating shape, at least when tubular body22is in the first radially-expanded deployment state. For some applications, as labeled inFIG. 1B, a pair of the at least two of self-expandable flexible structural stent elements28A and28B to which circumferential expansion element30is coupled are coupled at a peak32A. Circumferential expansion element30may be disposed either radially outside fluid flow guide26, as shown inFIGS. 1A-B, or radially inside fluid flow guide26, as shown inFIGS. 2A-B. Typically, circumferential expansion element30is attached to the fluid flow guide, e.g., sutured to the fluid flow guide (such as in applications in which the fluid flow guide comprises polyester), or encapsulated within the fluid flow guide (such as in applications in which the fluid flow guide comprises ePTFE).

For some applications, stent member24comprises a plurality of circumferential expansion elements30. For some applications, circumferential expansion elements30are alternatively or additionally coupled to at least two of self-expandable flexible structural stent elements28of one or more circumferential bands29positioned at respective longitudinal locations other than expanding portion23, such as described hereinbelow with reference toFIGS. 6A-Bregarding circumferential expansion elements430. Alternatively or additionally, for some applications, circumferential expansion elements30are coupled to a plurality of circumferential bands29, respectively.

For some applications, circumferential expansion element30is generally non-elastic. Alternatively or additionally, circumferential expansion element30is substantially less elastic than structural stent elements28. For example, an angular segment of expanding portion23that comprises circumferential expansion element30may expand and contract at least 30% less, such as at least 50% less, e.g., at least 67% less, per unit circumferential arc angle than an angular segment of expanding portion23that does not comprise circumferential expansion element30, as body22cycles between being internally pressurized by (a) fluid having a pressure of 80 mmHg, typically by blood during diastole in an adult human, and (b) fluid having a pressure of 120 mmHg, typically by blood during systole in an adult human. For example, circumferential expansion element30may comprise non-elastic stainless steel, or a cobalt-chromium alloy.

Fluid flow guide26comprises a graft material, i.e., at least one biologically-compatible substantially blood-impervious flexible sheet. The flexible sheet may comprise, for example, a polyester, a polyethylene (e.g., a poly-ethylene-terephthalate), a polymeric film material (such as a fluoropolymer, e.g., polytetrafluoroethylene), a polymeric textile material (e.g., woven polyethylene terephthalate (PET)), natural tissue graft (e.g., saphenous vein or collagen), Polytetrafluoroethylene (PTFE), ePTFE, Dacron, or a combination of two or more of these materials. The graft material optionally is woven. For some applications, the graft material of fluid flow guide26is generally non- or minimally-elastic.

Stent member24is configured such that application of a force thereto, which is insufficient to cause plastic deformation of self-expandable flexible structural stent elements28and is sufficient to cause plastic deformation of circumferential expansion element30, causes plastic deformation of and an increase in a circumferential length L of circumferential expansion element30, from a first length L1, as shown inFIGS. 1A and 2A, to a second length L2, as shown inFIGS. 1B and 2B. This increase in length transitions tubular body22from the first radially-expanded deployment state, as shown inFIGS. 1A and 2A, to the second radially-expanded deployment state, as shown inFIGS. 1B and 2B, thereby increasing a greatest internal perimeter of expanding portion23, from a first greatest internal perimeter P1(labeled inFIG. 2A) to a second greatest internal perimeter P2(labeled inFIG. 2B). Because of the plastic deformation, circumferential expansion element30retains its increased length L2even after the force is no longer applied.

Typically, circumferential expansion element30, or, for applications in which stent member24comprises a plurality of circumferential expansion elements30, circumferential expansion elements30collectively circumscribe an aggregate angle of at least20degrees, when tubular body22is in the first radially-expanded deployment state, as shown inFIGS. 1A and 2A. For example, the angle may be at least 40 degrees, such as at least 90 degrees. Typically, each of circumferential expansion elements30circumscribes an angle of at least 3 degrees, such as at least 5 degrees, when tubular body22is in the first radially-expanded deployment state, as shown inFIGS. 1A and 2A. For some applications, when tubular body22is the second radially-expanded deployment state, circumferential expansion element30circumscribes an angle that is capable of attaining a value that is at least 30% greater than when tubular body22is the first radially-expanded deployment state. For some applications, a resistance of fluid flow guide26to lateral expansion is less than 70%, e.g., less than 30%, of a resistance of circumferential expansion element30to circumferential expansion.

As mentioned above, fluid flow guide26is configured to accommodate the increase in the greatest internal perimeter of expanding portion23. For some applications, in order to provide such accommodation, when tubular body22is in the first radially-expanded deployment state, fluid flow guide26is shaped so as to define one or more folds40in a vicinity of circumferential expansion element30, such as shown inFIGS. 1A and 2A. For some applications, such as shown inFIGS. 1A and 2A, when tubular body22is in the first radially-expanded deployment state, the one or more folds are disposed radially inside stent member24. For other applications, similar to the configurations shown inFIGS. 4A,5A, and8A, when tubular body22is in the first radially-expanded deployment state, the one or more folds are disposed radially outside stent member24.

Alternatively, for some applications, in order to provide such accommodation, at least a portion of fluid flow guide26in a vicinity of circumferential expansion element30comprises a stretchable fabric (this configuration is not shown inFIGS. 1A-Band2A-B, but is similar to the configuration shown inFIG. 3A, described hereinbelow). For example, the stretchable fabric may comprise expanded polytetrafluoroethylene (ETFE).

For some applications, fluid flow guide26, other than the portion in the vicinity of circumferential expansion element30, comprises a fabric that is less elastic than the stretchable fabric. For example, the fabric of an angular segment of expanding portion23that comprises circumferential expansion element30may expand and contract at least 30% less, such as at least 50% less, e.g., at least 67% less, per unit circumferential arc angle than the fabric of an angular segment of expanding portion23that does not comprise circumferential expansion element30, as body22cycles between being internally pressurized by (a) fluid having a pressure of 80 mmHg, typically by blood during diastole in an adult human, and (b) fluid having a pressure of 120 mmHg, typically by blood during systole in an adult human.

Reference is now made toFIGS. 3A-B, which are schematic illustrations of an endovascular stent-graft120, in accordance with an application of the present invention. Stent-graft120comprises a generally tubular body122. Body122is configured to assume (a) a radially-compressed delivery state, typically when the body is initially positioned in a delivery catheter, and (b) at least first and second radially-expanded deployment states. Body122typically assumes the first radially-expanded deployment state upon deployment from the delivery catheter, and the second radially-expanded delivery state after deployment, typically during a minimally-invasive secondary intervention procedure.FIG. 3Ashows the stent-graft with body122in its first radially-expanded deployment state, andFIG. 3Bshows the stent-graft with body122in its second radially-expanded deployment state.

Body122is shaped so as to define a stepwise expanding portion123, a greatest internal perimeter of which increases as body122transitions from the first radially-expanded delivery state to the second radially-expanded delivery state. (The “greatest” internal perimeter of the expanding portion means the internal perimeter as measured at the longitudinal location along the expanding portion that has the greatest internal perimeter.) For some applications, expanding portion123is disposed at a longitudinal end125of body122, as shown inFIGS. 3A-B. For example, all of expanding portion123may be disposed with a distance of longitudinal end125, measured along an axis of body122, which distance is less than 30%, such as less than 25%, of an axial length of body122. Alternatively or additionally, the distance is less than 120%, such as less than 80%, of an average diameter of the expanding portion when body122is in the first radially-expanded state. For other applications, the expanding portion is disposed elsewhere along stent-graft120.

Body122comprises a stent member124, and, typically, a generally tubular fluid flow guide126. The fluid flow guide and the stent member are attached to each other, such as by suturing or stitching. The fluid flow guide is configured to accommodate the increase in the greatest internal perimeter of expanding portion123, as described hereinbelow. The stent member may be attached to an internal and/or an external surface of the fluid flow guide.

Stent member124comprises a plurality of self-expandable flexible structural stent elements128, which are either indirectly connected to one another by the fluid flow guide (as shown), and/or interconnected with one another (configuration not shown).

Optionally, a portion of structural stent elements128may be attached (e.g., sutured) to the internal surface of the fluid flow guide, and another portion to the external surface of the fluid flow guide. For some applications, self-expandable flexible structural stent elements128of stent member124are shaped so to define at least one circumferential band129at expanding portion123, such as exactly one circumferential band129or a plurality of circumferential bands129. Circumferential band129is shaped so as to define a plurality of peaks132directed in a first longitudinal direction, alternating with a plurality of troughs134directed in a second longitudinal direction opposite the first longitudinal direction. Circumferential band129may be serpentine-shaped. Typically, stent member124is shaped so as to further define one or more additional circumferential bands129at respective longitudinal locations other than expanding portion123, as shown inFIGS. 3A-B.

Self-expandable flexible structural stent elements128of stent member124, when unconstrained, are configured to cause tubular body122to assume the second radially-expanded deployment state. Structural stent elements128comprise a self-expanding material, such as a self-expanding metal. Typically, structural stent elements128comprise one or more metallic alloys, such as one or more superelastic metal alloys, a shape memory metallic alloy, and/or Nitinol. Typically, stent-graft120is configured to self-expand from the delivery state to the first radially-expanded deployment state. For example, stent member124may be heat-set to cause stent-graft120to self-expand from the delivery state to the first radially-expanded deployment state.

Stent-graft120further comprises at least one circumferential expansion prevention element130, which is coupled to at least two of self-expandable flexible structural stent elements128A and128B of expanding portion123of tubular body122. When intact, circumferential expansion prevention element130restrains tubular body122in the first radially-expanded deployment state, in which expanding portion123has a first greatest internal perimeter P3. When detached and/or severed, such as by application of a force that increases a distance between stent elements128A and128B, circumferential expansion prevention element130does not restrain tubular body122in the first radially-expanded deployment state, such that the tubular body transitions from the first radially-expanded deployment state to the second radially-expanded deployment state. In the second radially-expanded deployment state, expanding portion123has a second greatest internal perimeter P4, which is greater than first greatest internal perimeter P3.

For some applications, stent-graft120comprises a plurality of circumferential expansion prevention elements130. For some applications, circumferential expansion prevention elements130are alternatively or additionally coupled to at least two of self-expandable flexible structural stents elements128of one or more circumferential bands129positioned at respective longitudinal locations other than expanding portion123, such as described hereinbelow with reference toFIGS. 6A-Bregarding circumferential expansion elements430.

For some applications, circumferential expansion prevention element130comprises a suture, a wire (e.g., comprising stainless steel, nitinol, poly propylene, polyester, ePTFE), a hook, a loop, or a helix. Circumferential expansion prevention element130is detached and/or severed, such as by cutting or breaking thereof, either at a location along circumferential expansion prevention element130, and/or at the interface with one or both of self-expandable flexible structural stent elements128A and128B. For example, a cutting tool may be used, or a balloon may be used to apply a force sufficient to detach and/or sever the element, by increasing a distance between stent elements128A and128B to which element130is coupled.

For some applications, circumferential expansion prevention element130is coupled to the at least two of the structural elements within a distance of respective ones of the peaks132A and132B, which distance equals 30% of a diameter of body22in its first radially-expanded state. For example, the distance may equal zero, i.e., circumferential expansion prevention element130may be coupled to at least two peaks132A and132B of two structural stent elements128A and128B, as shown inFIG. 3B. For other applications, circumferential expansion prevention element130is coupled to two structural stent elements128A and128B at respective sites thereof other than peaks132A and132B (configuration not shown). Circumferential expansion prevention element130may be disposed either radially outside or radially inside fluid flow guide126.

Fluid flow guide126comprises a graft material, i.e., at least one biologically-compatible substantially blood-impervious flexible sheet. The flexible sheet may comprise, for example, a polyester, a polyethylene (e.g., a poly-ethylene-terephthalate), a polymeric film material (such as a fluoropolymer, e.g., polytetrafluoroethylene), a polymeric textile material (e.g., woven polyethylene terephthalate (PET)), natural tissue graft (e.g., saphenous vein or collagen), Polytetrafluoroethylene (PTFE), ePTFE, Dacron, or a combination of two or more of these materials. The graft material optionally is woven. For some applications, the graft material of fluid flow guide126is generally non- or minimally-elastic.

Typically, circumferential expansion prevention element130, or, for applications in which stent-graft120comprises a plurality of circumferential expansion prevention elements130, circumferential expansion prevention elements130collectively circumscribe an aggregate angle of at least40degrees, when tubular body122is in the first radially-expanded deployment state, as shown inFIG. 3A. For example, the angle may be at least 50 degrees, such as at least 90 degrees. Typically, each of circumferential expansion prevention elements130circumscribes an angle of at least 3 degrees, such as at least 5 degrees, when tubular body122is in the first radially-expanded deployment state, as shown inFIG. 3A.

As mentioned above, fluid flow guide126is configured to accommodate the increase in the greatest internal perimeter of expanding portion123. For some applications, in order to provide such accommodation, at least a portion140of fluid flow guide126in a vicinity of circumferential expansion prevention element130comprises a stretchable fabric For example, the stretchable fabric may comprise expanded polytetrafluoroethylene (ETFE). For some applications, fluid flow guide126, other than the portion in the vicinity of circumferential expansion prevention element130, comprises a fabric that is less elastic than the stretchable fabric. For example, the fabric of an angular segment of expanding portion123that comprises circumferential expansion prevention element130may expand and contract at least 30% less, such as at least 50% less, e.g., at least 67% less, per unit circumferential arc angle than the fabric of an angular segment of expanding portion123that does not comprise circumferential expansion prevention element130, as body122cycles between being internally pressurized by (a) fluid having a pressure of 80 mmHg, typically by blood during diastole in an adult human, and (b) fluid having a pressure of 120 mmHg, typically by blood during systole in an adult human.

Alternatively, for some applications, in order to provide such accommodation, when tubular body122is in the first radially-expanded deployment state, fluid flow guide126is shaped so as to define one or more folds in a vicinity of circumferential expansion prevention element130(this configuration is not shown inFIGS. 3A, but is similar to the configuration shown inFIGS. 1A and 2A). For some applications, when the tubular body is in the first radially-expanded deployment state, the one or more folds are disposed radially outside stent member124, while for some applications, when the tubular body is in the first radially-expanded deployment state, the one or more folds are disposed radially inside stent member124.

Reference is now made toFIGS. 4A-B, which are schematic illustrations of an endovascular stent-graft system210, in accordance with an application of the present invention. Stent-graft system210comprises a stent-graft220, which comprises a generally tubular body222. Body222is configured to assume (a) a radially-compressed delivery state, typically when the body is initially positioned in a delivery catheter, and (b) at least first and second radially-expanded deployment states. Body222typically assumes the first radially-expanded deployment state upon deployment from the delivery catheter, and the second radially-expanded delivery state after deployment, typically during a minimally-invasive secondary intervention procedure.FIG. 4Ashows the stent-graft with body222in its first radially-expanded deployment state, andFIG. 4Bshows the stent-graft with body222in its second radially-expanded deployment state.

Body222is shaped so as to define a stepwise expanding portion223, a greatest internal perimeter of which increases as body222transitions from the first radially-expanded delivery state to the second radially-expanded delivery state. Tubular body22, when in the first radially-expanded deployment state, is restrained from transitioning to the second radially-expanded deployment state. (The “greatest” internal perimeter of the expanding portion means the internal perimeter as measured at the longitudinal location along the expanding portion that has the greatest internal perimeter.) For some applications, expanding portion223is disposed at a longitudinal end225of body222, as shown inFIGS. 4A-B. For example, all of expanding portion223may be disposed with a distance of longitudinal end225, measured along an axis of body222, which distance is less than 30%, such as less than 25%, of an axial length of body222. Alternatively or additionally, the distance is less than 120%, such as less than 80%, of an average diameter of the expanding portion when body222is in the first radially-expanded state. For other applications, the expanding portion is disposed elsewhere along stent-graft220.

Body222comprises a self-expandable flexible stent member224, and a generally tubular fluid flow guide226. The fluid flow guide is attached to stent member224, such as by suturing or stitching. The fluid flow guide is configured to accommodate the increase in the greatest internal perimeter of expanding portion223, as described hereinbelow. The stent member may be attached to an internal and/or an external surface of the fluid flow guide.

Stent member224comprises a plurality of self-expandable flexible structural stent elements228, which are either indirectly connected to one another by the fluid flow guide (as shown), and/or interconnected with one another (configuration not shown). Optionally, a portion of structural stent elements228may be attached (e.g., sutured) to the internal surface of the fluid flow guide, and another portion to the external surface of the fluid flow guide. For some applications, self-expandable flexible structural stent elements228of stent member224are shaped so to define at least one circumferential band229at expanding portion223, such as exactly one circumferential band229or a plurality of circumferential bands229. Circumferential band229is shaped so as to define a plurality of peaks232directed in a first longitudinal direction, alternating with a plurality of troughs234directed in a second longitudinal direction opposite the first longitudinal direction. Circumferential band229may be serpentine-shaped. Typically, stent member224is shaped so as to further define one or more additional circumferential bands229at respective longitudinal locations other than expanding portion223, as shown inFIGS. 4A-B(andFIGS. 5A-B, described hereinbelow).

Self-expandable flexible structural stent elements228of stent member224, when unconstrained, are configured to cause tubular body222to assume the second radially-expanded deployment state. Structural stent elements228comprise a self-expanding material, such as a self-expanding metal, such that body222is self-expandable. Typically, structural stent elements228comprise one or more metallic alloys, such as one or more superelastic metal alloys, a shape memory metallic alloy, and/or Nitinol. Typically, stent-graft220is configured to self-expand from the delivery state to the first radially-expanded deployment state. For example, stent member224may be heat-set to cause stent-graft220to self-expand from the delivery state to the first radially-expanded deployment state.

Fluid flow guide226comprises a graft material250, i.e., at least one biologically-compatible substantially blood-impervious flexible sheet. The flexible sheet may comprise, for example, a polyester, a polyethylene (e.g., a poly-ethylene-terephthalate), a polymeric film material (such as a fluoropolymer, e.g., polytetrafluoroethylene), a polymeric textile material (e.g., woven polyethylene terephthalate (PET)), natural tissue graft (e.g., saphenous vein or collagen), Polytetrafluoroethylene (PTFE), ePTFE, Dacron, or a combination of two or more of these materials. The graft material optionally is woven. For some applications, the graft material of fluid flow guide226is generally non- or minimally-elastic.

As shown inFIG. 4A, graft material250of fluid flow guide226is shaped so as to define, when tubular body222is in the first radially-expanded deployment state, one or more folds230. As used in the present application, including in the claims, a “fold” is a portion of graft material250that is at least doubled upon itself such that two end portions252A and252B of the fold touch or are near each other at the surface generally defined by tubular body222. (The phrase “at least” doubled is to be understood as including multiple doubling of the graft material upon itself, so long as only the two end portions252A and252B of the fold are positioned at the surface generally defined by tubular body222. For example, the fold may be shaped like a generally flattened Greek lower-case omega (w) or epsilon (s).) For some applications, when stent-graft220is in the first radially-expanded deployment state, a distance between end portions252A and252B, measured at longitudinal end225of body222, is less than 50%, such as less than 20%, of a first greatest internal perimeter P5of expanding portion223. Each fold may be disposed circumferentially in one direction (clockwise or counterclockwise, such as shown inFIG. 4A, or both clockwise and counterclockwise, such as shown inFIG. 8A, described hereinbelow). Thus, in accordance with this definition of “fold,” each of the tubular bodies shown inFIGS. 4A and 8A, as well asFIGS. 1A,2A,5A, and7A, defines exactly one fold. In contrast, tubular body422, shown inFIG. 6A, defines a plurality of folds440, one for each circumferential expansion element430(for clarity of illustration, only one of these folds is shown clearly, in the enlargement).

For some applications, as shown inFIG. 4A, when tubular body222is in the first radially-expanded deployment state, one or more folds230are oriented tangentially to tubular body222, such that a portion of graft material250of the one or more folds is in contact with an outer surface of tubular body222. For some applications, at least when tubular body222is in the radially-compressed delivery state, the one or more folds are removably secured to the outer surface of the tubular body. For example, stent-graft system210may further comprise a securing mechanism, which removably secures the folds to the outer surface of the tubular body. Alternatively or additionally, stent-graft system210may further comprise a bio-dissolvable adhesive, e.g. cyanoacrylate, which removably secures the folds to the outer surface of the tubular body.

For some applications, one or more folds230are disposed such that at least 50%, e.g., at least 75%, such as 100%, of graft material250of folds230is radially outside stent member224. Disposing of the folds mostly or entirely outside of the stent member reduces or prevents any interfere by the folds with the flow of blood through fluid flow guide226. If the folds instead extended mostly or entirely into the lumen of the fluid flow guide, the folds would reduce the effective cross-section of the lumen and potentially interfere with blood flow. Although disposing the folds entirely outside the stent member provides the greatest reduction in potential interference with blood flow, this is not always possible because of design considerations. For some applications, graft material250is shaped so as to define exactly one or exactly two folds230when tubular body222is in the first radially-expanded deployment state. For some applications, expanding portion223comprises a plurality of circumferential bands229, and a plurality of the folds230are disposed the plurality of circumferential bands229, respectively (configuration not shown).

Typically, when tubular body222is in the second radially-expanded deployment state, graft material250of fluid flow guide226is shaped so as to define none of folds230(as shown inFIG. 4B) or fewer of folds230than when the tubular body is in the first radially-expanded deployment state. The portion(s) of the graft material that define folds230when the tubular body is in the first radially-expanded deployment state may remain somewhat protruding from stent member224even when the tubular body has transitioned to the second radially-expanded deployment state, but is no longer folded.

As body222transitions from the first radially-expanded delivery state to the second radially-expanded delivery state, a greatest internal perimeter of expanding portion223increases from first greatest internal perimeter P5to a second greatest internal perimeter P6. For some applications, second greatest internal perimeter P6of the expanding portion is at least 10% greater than first greatest internal perimeter P5.

For some applications, each of one or more folds230is relatively large with respect to the greatest internal perimeter of the expanding portion, in order to provide a large circumferential buffer for expansion of the expanding portion after implantation.

For example, a greatest internal perimeter P7of graft material250of a first one of one or more folds230, when the first fold is unfolded when tubular body222is in the second radially-expanded deployment state, may be equal to at least 7% of second greatest internal perimeter P6, such as at least 10%, e.g., at least 12%. For some applications in which graft material250defines at least two folds230, a greatest internal perimeter of graft material250of a second one of one or more folds230, when the second fold is unfolded, may be equal to at least 7% of second greatest internal perimeter P6, such as at least 10%, e.g., at least 12%.

Typically, each of one or more folds230substantially protrudes from or into the stent-graft, i.e., is not a relatively small concavity, convexity, wrinkle, or any other type of deviation from circularity (or ellipticity, in the broader sense) in the graft material of the stent-graft. For example, when stent-graft20is in the first radially-expanded deployment state, as shown inFIG. 4A, a length of a fold230, measured along the graft material of the fold at longitudinal end225of body222between end portions252A and252B of the fold, may be equal to at least 140%, such as at least 167%, at least 300%, or at least 500%, of a distance D between end portions252A and252B of the fold at longitudinal end225. These relative dimensions may also be provided for the folds of the other configurations described herein.

For some applications, the second fold is unfolded when tubular body222is in the second radially-expanded deployment state. For other applications, the second fold remains folded when tubular body222is in the second radially-expanded deployment state, and is unfolded when tubular body222transitions to a third radially-expanded deployment state in which expanding portion223has an even greater greatest internal perimeter than second greatest internal perimeter P6.

For some applications, stent-graft system210further comprises a locking mechanism260, which is configured to assume a locked state which restrains tubular body222in the first radially-expanded deployment state, such as shown inFIG. 4A, and a released state, which allows tubular body222to transition to the second radially-expanded deployment state, such as shown inFIG. 4B.

For some applications, locking mechanism260comprises a shaft262and two or more attachment members264coupled to stent-graft220. Shaft262passes through attachment members264when locking mechanism260is in the locked state, and does not pass through the attachment members when the locking mechanism is in the released state. For some applications, the locking mechanism transitions from the locked state to the released state in response to translation of the shaft, such as longitudinal translation. The shaft may be disposed either within the lumen of stent-graft220, as shown inFIG. 4A, or outside the lumen, such as shown inFIG. 5A, mutatis mutandis.

For some applications, attachment members264are coupled to respective structural stent elements228of circumferential band229. For some applications, structural stent elements228of circumferential band229are arranged in serpentine sections268, each of which comprises two struts270connected at a respective one of peaks232. Two attachment members264are coupled to circumferentially non-adjacent ones of the serpentine sections. Alternatively or additionally, for some applications, locking mechanism260further comprises two or more elongated coupling elements266, which respectively couple attachment members264to structural stent elements228. For some applications, each of coupling elements266is coupled to a structural stent element within a distance of a respective peak, which distance equals 30% of a diameter of body222in its first radially-expanded state. For example, the distance may equal zero, i.e., each of coupling elements266may be coupled to a respective peak, as shown inFIG. 4A. For other applications, coupling elements266are coupled to the structural stent elements at respective sites thereof other than peaks232, such as to respective struts270(this configuration is not shown inFIG. 4A, but is shown inFIG. 5A, described hereinbelow). The coupling elements may be disposed either radially outside or radially inside fluid flow guide226.

For some applications, stent-graft220comprises circumferential expansion element30, described hereinabove with reference toFIGS. 1A-Band2A-B. Alternatively or additionally, for some applications, stent-graft220comprises circumferential expansion prevention element130, described hereinabove with reference toFIGS. 3A-B.

Reference is now made toFIGS. 5A-B, which are schematic illustrations of an endovascular stent-graft system310, in accordance with an application of the present invention. Except for differences described below, stent-graft system310is generally similar to stent-graft system210, described hereinabove with reference toFIGS. 4A-B, and incorporates some or all of the features thereof. Stent-graft system310comprises a stent-graft320, which comprises generally tubular body222. Body222is configured to assume (a) a radially-compressed delivery state, typically when the body is initially positioned in a delivery catheter, and (b) at least first and second radially-expanded deployment states. Body222typically assumes the first radially-expanded deployment state upon deployment from the delivery catheter, and the second radially-expanded delivery state after deployment, typically during a minimally-invasive secondary intervention procedure.FIG. 5Ashows the stent-graft with body222in its first radially-expanded deployment state, andFIG. 5Bshows the stent-graft with body222in its second radially-expanded deployment state.

For some applications, self-expandable flexible structural stent elements228of stent member224are shaped so to define at least one circumferential band229at expanding portion223, such as exactly one circumferential band229or a plurality of circumferential bands229. Circumferential band229is shaped so as to define a plurality of peaks232directed in a first longitudinal direction, alternating with a plurality of troughs234directed in a second longitudinal direction opposite the first longitudinal direction. Circumferential band229may be serpentine-shaped. Typically, stent member224is shaped so as to further define one or more additional circumferential bands229at respective longitudinal locations other than expanding portion23, as shown inFIGS. 5A-2B.

For some applications, stent-graft system310further comprises locking mechanism260, described hereinabove with reference toFIGS. 4A-B. For applications in which locking mechanism comprises shaft262, the shaft may be disposed either radially outside the lumen of stent-graft320, as shown inFIG. 5A, or radially inside the lumen, such as shown inFIG. 4A, mutatis mutandis.

For some applications, attachment members264are coupled to respective structural stent elements228of circumferential band229. For some applications, structural stent elements228of circumferential band229are arranged in serpentine sections268, each of which comprises two struts270connected at a respective one of peaks232. Two attachment members264are coupled to circumferentially non-adjacent ones of the serpentine sections. Alternatively or additionally, coupling elements266are coupled to the structural stent elements at respective sites thereof other than peaks232, such as to respective struts270. The coupling elements may be disposed either radially outside or radially inside fluid flow guide226. Alternatively, for some applications, such as those described in the following two paragraphs, stent-graft system310does not comprise locking mechanism260.

For some applications, serpentine sections268of circumferential band229include at least one generally non-elastic serpentine section280. Struts270of this serpentine section are generally non-elastic. Alternatively or additionally, these struts are substantially less elastic than the other structural stent elements. For example, an angular segment of expanding portion223that comprises non-elastic serpentine section280may expand and contract at least 30% less, such as at least 50% less, e.g., at least 67% less, per unit circumferential arc angle than an angular segment of expanding portion223that does not comprise non-elastic serpentine section280, as body222cycles between being internally pressurized by (a) fluid having a pressure of 80 mmHg, typically by blood during diastole in an adult human, and (b) fluid having a pressure of 120 mmHg, typically by blood during systole in an adult human. For example, the struts of non-elastic serpentine section280may comprise non-elastic stainless steel, or a cobalt-chromium alloy. For some applications, expanding portion223comprises a plurality of circumferential bands229that include respective non-elastic serpentine sections280. For some applications, a resistance of fluid flow guide226to lateral expansion is less than 70%, e.g., less than 30%, of a resistance of non-elastic serpentine section280to circumferential expansion.

Struts270of serpentine section280are closer together when tubular body222is in the first radially-expanded deployment state than when tubular body222is in second first radially-expanded deployment state. Optionally, struts270of serpentine section280are generally parallel to each other (e.g., define an angle of less than 30 degrees) when tubular body222is in the first radially-expanded deployment state. Stent member224is configured such that application of a force thereto, which is insufficient to cause plastic deformation of self-expandable flexible structural stent elements228and is sufficient to cause plastic deformation of struts270of serpentine section280, transitions tubular body222from the first radially-expanded deployment state, as shown inFIG. 5A, to the second radially-expanded deployment state, as shown inFIG. 5B, thereby increasing a greatest internal perimeter of expanding portion223, from a greatest internal perimeter P5(labeled inFIG. 4A) to a greatest internal perimeter P6(labeled inFIG. 4B). Because of their plastic deformation, struts270of serpentine section280retain their increased distance from each other even after the force is no longer applied.

For some applications, stent-graft320comprises circumferential expansion element30, described hereinabove with reference toFIGS. 1A-Band2A-B. Alternatively or additionally, for some applications, stent-graft320comprises circumferential expansion prevention element130, described hereinabove with reference toFIGS. 3A-B.

Reference is now made toFIGS. 6A-B, which are schematic illustrations of an endovascular stent-graft system410, in accordance with an application of the present invention. Except for differences described below, stent-graft system410is similar in some respects to the other stent-graft systems described hereinabove, and incorporates some or all of the features thereof. Stent-graft system410comprises a stent-graft420, which comprises generally tubular body422. Body422is configured to assume (a) a radially-compressed delivery state, typically when the body is initially positioned in a delivery catheter, and (b) at least first and second radially-expanded deployment states. Body422typically assumes the first radially-expanded deployment state upon deployment from the delivery catheter, and the second radially-expanded delivery state after deployment, typically during a minimally-invasive secondary intervention procedure.FIG. 6Ashows the stent-graft with body422in its first radially-expanded deployment state, andFIG. 6Bshows the stent-graft with body422in its second radially-expanded deployment state.

Body422is shaped so as to define a stepwise expanding portion423, a greatest internal perimeter of which increases as body422transitions from the first radially-expanded delivery state to the second radially-expanded delivery state. For some applications, expanding portion423is disposed at a longitudinal end425of body422, as shown inFIGS. 6A-B. For example, all of expanding portion423may be disposed with a distance of longitudinal end425, measured along an axis of body422, which distance is less than 30%, such as less than 25%, of an axial length of body422. Alternatively or additionally, the distance is less than 120%, such as less than 80%, of an average diameter of the expanding portion when body422is in the first radially-expanded state. For other applications, the expanding portion is disposed elsewhere along stent-graft420.

Body422comprises a stent member424, and, typically, a generally tubular fluid flow guide426. The fluid flow guide and the stent member are attached to each other, such as by suturing or stitching. The fluid flow guide is configured to accommodate the increase in the greatest internal perimeter of expanding portion423, as described hereinbelow. The stent member may be attached to an internal and/or an external surface of the fluid flow guide.

Stent member424comprises a plurality of self-expandable flexible structural stent elements428, which are either indirectly connected to one another by the fluid flow guide (as shown), and/or interconnected with one another (configuration not shown). Optionally, a portion of structural stent elements428may be attached (e.g., sutured) to the internal surface of the fluid flow guide, and another portion to the external surface of the fluid flow guide. Structural stent elements428comprise a self-expanding material, such as a self-expanding metal, such that body422is self-expandable. Typically, structural stent elements428comprise one or more metallic alloys, such as one or more superelastic metal alloys, a shape memory metallic alloy, and/or Nitinol. Typically, stent-graft420is configured to self-expand from the delivery state to the first radially-expanded deployment state. For example, stent member424may be heat-set to cause stent-graft420to self-expand from the delivery state to the first radially-expanded deployment state.

For some applications, flexible structural stent elements428of stent member424are shaped so to define at least one circumferential band429at expanding portion423. Circumferential band429is shaped so as to define a plurality of peaks432directed in a first longitudinal direction, alternating with a plurality of troughs434directed in a second longitudinal direction opposite the first longitudinal direction. Circumferential band429may be serpentine-shaped. Typically, stent member424is shaped so as to further define one or more additional circumferential bands429at respective longitudinal locations other than expanding portion423, as shown inFIGS. 6A-B.

Stent member424further comprises one or more circumferential expansion elements430, which are arranged around expanding portion423. Typically, circumferential expansion elements430are generally non-elastic. Alternatively or additionally, circumferential expansion elements430are substantially less elastic than structural stent elements428. For example, an angular segment of expanding portion423that comprises one of circumferential expansion elements430may expand and contract at least 30% less, such as at least 50% less, e.g., at least 67% less, per unit circumferential arc angle than an angular segment of expanding portion423that does not comprise any of circumferential expansion elements430, as body422cycles between being internally pressurized by (a) fluid having a pressure of 80 mmHg, typically by blood during diastole in an adult human, and (b) fluid having a pressure of 120 mmHg, typically by blood during systole in an adult human. For example, circumferential expansion elements430may comprise non-elastic stainless steel, or a cobalt-chromium alloy. For some applications, a resistance of fluid flow guide426to lateral expansion is less than 70%, e.g., less than 30%, of a resistance of each of circumferential expansion elements430to circumferential expansion.

For some applications, as shown inFIGS. 6A-B, circumferential expansion elements430are directly attached to fluid flow guide426, separately from structural stent elements428. For example, the circumferential expansion elements may be sutured to the fluid flow guide (such as in applications in which the fluid flow guide comprises polyester), or encapsulated within the fluid flow guide (such as in applications in which the fluid flow guide comprises ePTFE). For other applications, circumferential expansion elements430are coupled to structural stent elements428, so as to be indirectly attached to fluid flow guide426(configuration not shown).

For some applications, circumferential expansion elements430are positioned alongside respective structural stent elements428near peaks432and/or troughs434of circumferential band429of expanding portion423. For example, the circumferential expansion elements may be positioned within respective curvatures of peaks432(as shown inFIGS. 6A-B) and/or troughs434(configuration not shown), or outside the curvatures of the peaks and/or troughs (configuration not shown). Circumferential expansion elements430typically are shaped similarly to the portions of structural stent elements428alongside which they are positioned. For some applications, circumferential expansion elements430are additionally positioned alongside respective structural stent elements428near peaks432and/or troughs434of one or more additional circumferential bands429positioned along expanding portion423. For example, in the configuration shown inFIGS. 6A-B, circumferential expansion elements430are positioned alongside respective structural stent elements428near peaks432of the two circumferential bands of the expanding portion.

For some applications, circumferential expansion elements430have a shape selected from the group of shapes consisting of: a U-shape, a V-shape, a W-shape, and an undulating shape, at least when tubular body422is in the first radially-expanded deployment state. Circumferential expansion elements430may be disposed either radially outside fluid flow guide426, as shown inFIGS. 6A-B, or radially inside fluid flow guide426.

Fluid flow guide426comprises a graft material, i.e., at least one biologically-compatible substantially blood-impervious flexible sheet. The flexible sheet may comprise, for example, a polyester, a polyethylene (e.g., a poly-ethylene-terephthalate), a polymeric film material (such as a fluoropolymer, e.g., polytetrafluoroethylene), a polymeric textile material (e.g., woven polyethylene terephthalate (PET)), natural tissue graft (e.g., saphenous vein or collagen), Polytetrafluoroethylene (PTFE), ePTFE, Dacron, or a combination of two or more of these materials. The graft material optionally is woven. For some applications, the graft material of fluid flow guide426is generally non- or minimally-elastic.

Stent member424is configured such that application of a force thereto, which is insufficient to cause plastic deformation of self-expandable flexible structural stent elements428and is sufficient to cause plastic deformation of circumferential expansion elements430, causes plastic deformation of and an increase in respective circumferential lengths of circumferential expansion elements430, from a first length, as shown inFIG. 6A, to a second length, as shown inFIG. 6B. This increase in length transitions tubular body422from the first radially-expanded deployment state, as shown inFIG. 6A, to the second radially-expanded deployment state, as shown inFIG. 6B, thereby increasing a greatest internal perimeter of expanding portion423, from a first greatest internal perimeter to a second greatest internal perimeter. Because of the plastic deformation, circumferential expansion elements430retain their increased lengths even after the force is no longer applied. For applications in which a plurality of circumferential expansion elements430is provided, the circumferential expansion is generally distributed over the plurality of elements.

Typically, circumferential expansion element430, or, for applications in which stent member424comprises a plurality of circumferential expansion elements430, circumferential expansion elements430collectively circumscribe an aggregate angle of at least20degrees, when tubular body422is in the first radially-expanded deployment state, as shown inFIGS. 6A. Typically, each of circumferential expansion elements430circumscribes an angle of at least 3 degrees, such as at least 5 degrees, when tubular body422is in the first radially-expanded deployment state, as shown inFIGS. 6A. For example, the angle may be at least 40 degrees, such as at least 90 degrees. For some applications, when tubular body422is the second radially-expanded deployment state, circumferential expansion element430circumscribes an angle that is capable of attaining a value that is at least 30% greater than when tubular body422is the first radially-expanded deployment state.

As mentioned above, fluid flow guide426is configured to accommodate the increase in the greatest internal perimeter of expanding portion423. For some applications, in order to provide such accommodation, when tubular body422is in the first radially-expanded deployment state, fluid flow guide426is shaped so as to define one or more folds440in a vicinity of circumferential expansion element430, such as shown inFIG. 6A. For some applications, such as shown inFIG. 6A, when tubular body422is in the first radially-expanded deployment state, the one or more folds are disposed radially outside stent member424.

Alternatively, for some applications, in order to provide such accommodation, at least a portion of fluid flow guide426in a vicinity of circumferential expansion elements430comprises a stretchable fabric (this configuration is not shown inFIGS. 6A-B, but is similar to the configuration shown inFIG. 3A, described hereinabove). For example, the stretchable fabric may comprise expanded polytetrafluoroethylene (ETFE). For some applications, fluid flow guide426, other than the portion in the vicinity of circumferential expansion element430, comprises a fabric that is less elastic than the stretchable fabric. For example, the fabric of an angular segment of expanding portion423that comprises one of circumferential expansion elements430may expand and contract at least 30% less, such as at least 50% less, e.g., at least 67% less, per unit circumferential arc angle than the fabric of an angular segment of expanding portion423that does not comprise any of circumferential expansion elements430, as body422cycles between being internally pressurized by (a) fluid having a pressure of 80 mmHg, typically by blood during diastole in an adult human, and (b) fluid having a pressure of 120 mmHg, typically by blood during systole in an adult human.

For some applications, stent-graft420further comprises at least circumferential expansion element30, described hereinabove with reference toFIGS. 1A-Band2A-B. Alternatively or additionally, for some applications, stent-graft420comprises at least one circumferential expansion prevention element130, described hereinabove with reference toFIGS. 3A-B. Further alternatively or additionally, for some applications, stent-graft420comprises one or more folds230, described hereinabove with reference toFIGS. 4A-B. Further alternatively or additionally, for some applications, stent-graft420comprises at least one non-elastic serpentine section280, described hereinabove with reference toFIGS. 5A-B.

Reference is now made toFIGS. 7A-B, which are schematic illustrations of an exemplary method for deploying stent-graft20, described hereinabove with reference toFIGS. 1A-Band2A-B, in accordance with an application of the present invention. In this exemplary method, stent-graft20is configured to be implanted in a main blood vessel having an aneurysm and/or a dissection, such as a descending abdominal aorta400(which may have an aneurysm402, typically below renal arteries403, as shown).

During a primary intervention procedure, a surgeon or interventionalist transvascularly introduces stent-graft20into the blood vessel while tubular body22of the stent-graft is in the radially-compressed delivery state. Thereafter, the surgeon or interventionalist transitions the tubular body to the first radially-expanded deployment state in the blood vessel, in which state expanding portion23has first greatest internal perimeter P1and forms a blood-tight seal with a wall404of the blood vessel at a neck406of aneurysm402and/or the dissection. The initial implantation procedure is complete, as shown inFIG. 7A.

Over time (typically over a few several years), neck406often progressively dilates, such as because of progressive expansion of the aneurysm sac. Such dilation of the neck may compromise the seal between expanding portion23of the stent-graft and the wall of neck406, resulting in type I endoleak. In response to detecting such dilation and/or endoleak (typically at least one month, such as at least a few years, after initial implantation and deployment of the stent-graft), a surgeon or interventionalist, during a minimally-invasive secondary intervention procedure, transitions tubular body22to a second radially-expanded deployment state in the blood vessel, as shown inFIG. 7B. In the second radially-expanded deployment state, expanding portion23has a second greatest internal perimeter P2, which is greater than first greatest perimeter P1. Typically, the minimally-invasive secondary intervention procedure is performed transvascularly and most likely transcutaneously.

For some applications, in order to transition tubular body22to the second radially-expanded deployment state in the blood vessel, the surgeon or interventionalist transvascularly introduces a balloon into tubular body22, and inflates the balloon. The balloon applies a force to stent member24to cause plastic deformation of circumferential expansion element30, as described hereinabove with reference toFIGS. 1A-Band2A-B. Optionally, a bare metal stent is further provided, initially disposed over a delivery balloon. This bare metal stent, typically crimped over the balloon, is advanced within tubular body22, while the bare metal stent is in a radially-compressed state and the balloon is deflated. The balloon is then inflated to transition the bare metal stent to a radially-expanded state, in which the bare metal stent has a greater diameter than that of stent-graft20when in the first radially-expanded deployment state. This expansion of the bare metal stent thus transitions stent-graft20to the larger second radially-expanded deployment state. The bare metal stent is typically left in place in stent-graft20. For some applications, the bare metal stent is plastically deformable (e.g., comprises stainless steel), while for other applications the bare metal stent is superelastic (e.g., comprises Nitinol).

For some applications, tubular body22is configured to undergo one or more additional transitions to one or more additional radially-expanded deployment states in which expanding portion23of stent-graft20has respective even greater radially-expanded internal perimeters. Such additional transitions may be effected if neck406of aneurysm402and/or the dissection further dilates after body22has transitioned to the second radially-expanded deployment state, or if the transition to the second radially-expanded deployment state is insufficient to resolve the initial endoleak. For example, body22may be configured to assume a third radially-expanded deployment state, in which expanding portion23of stent-graft20has a third greatest internal perimeter, which is greater than second greatest internal perimeter P2, described hereinabove with reference toFIG. 2B. A surgeon or interventionalist transitions tubular body22to the additional radially-expanded deployment states during respective subsequent minimally-invasive secondary intervention procedures, or during the first secondary intervention procedure if necessary to resolve the endoleak. For example, a plurality of balloons may be provided that have respective different volumes when inflated.

For some applications, in order to enable such additional transitions, stent member24further comprises one or more additional circumferential expansion elements30at additional respective circumferential locations. Alternatively or additionally, for some applications, stent member24comprises a plurality of circumferential expansion elements30at a plurality of circumferential bands29, respectively. Alternatively or additionally, in order to enable such additional transitions, circumferential expansion element30is configured to enable more than one change in circumferential length L thereof (labeled inFIGS. 1A-Band2A-B).

Reference is now made toFIGS. 8A-B, which are schematic illustrations of an exemplary method for deploying stent-graft220, described hereinabove with reference toFIGS. 4A-B, in accordance with an application of the present invention. In this exemplary method, stent-graft220is configured to be implanted in a main blood vessel having an aneurysm and/or a dissection, such as descending abdominal aorta400(which may have aneurysm402, typically below renal arteries403, as shown).

During a primary intervention procedure, a surgeon or interventionalist transvascularly introduces stent-graft220into the blood vessel while tubular body222of the stent-graft is in the radially-compressed delivery state. Thereafter, the surgeon or interventionalist transitions the tubular body to a first radially-expanded deployment state in the blood vessel, in which state expanding portion223has first greatest internal perimeter P5and forms a blood-tight seal with wall404of the blood vessel at neck406of aneurysm402and/or the dissection. The initial implantation procedure is complete, as shown inFIG. 8A.

As mentioned above, over time (typically over several months to several years), neck406often progressively dilates, such as because of progressive expansion of the aneurysm sac. Such dilation of the neck may compromise the seal between expanding portion223of the stent-graft and the wall of neck406, resulting in type I endoleak. In response to detecting such dilation and/or endoleak (typically at least one month, such as at least a few years, after implantation of the stent-graft), a surgeon or interventionalist, during a minimally-invasive secondary intervention procedure, transitions tubular body222to a second radially-expanded deployment state in the blood vessel, as shown inFIG. 8B. In the second radially-expanded deployment state, expanding portion223has a second greatest internal perimeter P6, which is greater than first greatest perimeter P5. Typically, the minimally-invasive secondary intervention procedure is performed transvascularly.

For applications in which stent-graft system210comprises locking mechanism260, in order to transition tubular body222to the second radially-expanded deployment state in the blood vessel, the surgeon or interventionalist transitions the locking mechanism from the locked state to the unlocked state, which allows tubular body222to transition to the second radially-expanded deployment state. For applications in which locking mechanism260comprises shaft262, the surgeon or interventionalist transvascularly translates the shaft in order to unlock locking mechanism260.

For some applications, tubular body222is configured to undergo one or more additional transitions to one or more additional radially-expanded deployment states in which expanding portion223of stent-graft220has respective even greater radially-expanded internal perimeters. Such additional transitions may be effected if neck406of aneurysm402and/or the dissection further dilates after body222has transitioned to the second radially-expanded deployment state, or if the transition to the second radially-expanded deployment state is insufficient to resolve the initial endoleak. For example, body222may be configured to assume a third radially-expanded deployment state, in which expanding portion223of stent-graft220has a third greatest internal perimeter, which is greater than second greatest internal perimeter P6, described hereinabove with reference toFIG. 4B. A surgeon or interventionalist transitions tubular body222to the additional radially-expanded deployment states during respective subsequent minimally-invasive secondary intervention procedures, or during the first secondary intervention procedure if necessary to resolve the endoleak.

For some applications, in order to enable such additional transitions, stent member24further comprises one or more additional folds230and corresponding locking mechanisms260at additional respective circumferential locations, as described hereinabove with reference toFIGS. 4A-B. For applications in which the locking mechanisms comprise respective shafts262, the surgeon or interventionalist transvascularly translates the shafts in respective post-implantation minimally-invasive secondary intervention procedures in order to unlock the respective locking mechanisms.

In order to deploy stent-graft320, described hereinabove with reference toFIGS. 5A-B, the deployment techniques may be used that are described hereinabove with reference toFIGS. 7A-Band/or8A-B, depending on the configuration of stent-graft320. For configurations in which stent-graft320comprises generally non-elastic serpentine section280, the techniques described hereinabove with reference toFIGS. 7A-Bmay be used. Alternatively or additionally, for configurations in which stent-graft system310comprises locking mechanism260, the techniques described hereinabove with reference toFIGS. 8A-Bmay be used.

Stent-graft120, described hereinabove with reference toFIGS. 3A-B, may be deployed using techniques similar to those described hereinabove with reference toFIGS. 7A-B. For some applications, a balloon is expanded within the lumen of stent-graft120to apply a force to and detach and/or sever circumferential expansion prevention element130. Alternatively, a cutting tool may be transvascularly introduced into the stent-graft, and used to cut circumferential expansion prevention element130. For some applications, stent-graft120comprises a plurality of circumferential expansion prevention elements130, located at respective circumferential locations. Detaching and/or severing elements130transitions tubular body122to transition to one or more additional radially-expanded deployment states in which expanding portion123of stent-graft120has respective even greater radially-expanded internal perimeters. In order to effect such additional transitions, the techniques described hereinabove with reference toFIGS. 7A-Bmay be used, mutatis mutandis.

As used in the present application, including in the claims, “tubular” means having the form of an elongated hollow object that defines a conduit therethrough. A “tubular” structure may have varied cross-sections therealong, and the cross-sections are not necessarily circular. For example, one or more of the cross-sections may be generally circular, or generally elliptical but not circular, or circular.

The scope of the present invention includes embodiments described in the following applications, which are assigned to the assignee of the present application and are incorporated herein by reference. In an embodiment, techniques and apparatus described in one or more of the following applications are combined with techniques and apparatus described herein:PCT Application PCT/IL2008/000287, filed Mar. 5, 2008, which published as PCT Publication WO 2008/107885 to Shalev et al., and U.S. application Ser. No. 12/529,936 in the national stage thereof, which published as U.S. Patent Application Publication 2010/0063575 to Shalev et al.U.S. Provisional Application 60/892,885, filed Mar. 5, 2007PCT Application PCT/IL2007/001312, filed Oct. 29, 2007, which published as PCT Publication WO/2008/053469 to Shalev, and U.S. application Ser. No. 12/447,684 in the national stage thereof, which published as US Patent Application Publication 2010/0070019 to ShalevU.S. Provisional Application 60/991,726, filed Dec. 2, 2007PCT Application PCT/IL2008/001621, filed Dec. 15, 2008, which published as PCT Publication WO 2009/078010, and U.S. application Ser. No. 12/808,037 in the national stage thereof, which published as U.S. Patent Application Publication 2010/0292774U.S. Provisional Application 61/219,758, filed Jun. 23, 2009U.S. Provisional Application 61/221,074, filed Jun. 28, 2009PCT Application PCT/IB2010/052861, filed Jun. 23, 2010, which published as PCT Publication WO 2010/150208, and U.S. application Ser. No. 13/380,278 in the national stage thereof, which published as US Patent Application Publication 2012/0150274PCT Application PCT/IL2010/000549, filed Jul. 8, 2010, which published as PCT Publication WO 2011/004374PCT Application PCT/IL2010/000564, filed Jul. 14, 2010, which published as PCT Publication WO 2011/007354, and U.S. application Ser. No. 13/384,075 in the national stage thereof, which published as US Patent Application Publication 2012/0179236PCT Application PCT/IL2010/000917, filed Nov. 4, 2010, which published as PCT Publication WO 2011/055364PCT Application PCT/IL2010/000999, filed Nov. 30, 2010, which published as PCT Publication WO 2011/064782PCT Application PCT/IL2010/001018, filed Dec. 2, 2010, which published as PCT Publication WO 2011/067764PCT Application PCT/IL2010/001037, filed Dec. 8, 2010, which published as PCT Publication WO 2011/070576PCT Application PCT/IL2010/001087, filed Dec. 27, 2010, which published as PCT Publication WO 2011/080738PCT Application PCT/IL2011/000135, filed Feb. 8, 2011, which published as PCT Publication WO 2011/095979PCT Application PCT/IL2011/000801, filed Oct. 10, 2011, which published as PCT Publication WO 2012/049679U.S. Application 13/031,871, filed Feb. 22, 2011, which published as US Patent Application Publication 2011/0208289U.S. Provisional Application 61/496,613, filed Jun. 14, 2011U.S. Provisional Application 61/505,132, filed Jul. 7, 2011U.S. Provisional Application 61/529,931, filed Sep. 1, 2011