WO2007094740A1

WO2007094740A1 - Highly flexible stent

Info

Publication number: WO2007094740A1
Application number: PCT/SG2006/000030
Authority: WO
Inventors: Leon Rudakov; Vimal Raj D
Original assignee: Merlin Md Pte Ltd
Priority date: 2006-02-15
Filing date: 2006-02-15
Publication date: 2007-08-23

Abstract

A stent (10) for treatment of a diseased, damaged or weakened portion of a bodily vessel (11) of a patient at a surgical site, the stent (10) comprising: a plurality of circumferential wave-shaped members (13) in a spaced apart relationship, each wave-shaped member (13) including deformable hinge portions (26, 27) which upon deformation is adapted to enable controlled expansion of the stent (10) from a first position radially outwardly to a second position; and a plurality of linking members (14) extending between adjacent wave-shaped members (13) to maintain the wave-shaped members (13) in the spaced apart relationship, each linking member (14) including at least one deformable hinge portion (25) having a greater flexibility relative to the hinge portions (26, 27) of the wave-shaped members (13); wherein the wave-shaped members (13) have a length to cross-sectional area ratio within a predetermined range so as to enable deployment of the stent (10) within the bodily vessel (11 ) at a predetermined pressure to minimise pressure exerted on the wall of the bodily vessel (11 ) by the stent (10) during expansion to the second position; and wherein the hinge portions (25, 26, 27) of the wave-shaped members (13) and linking members (14) provide local and integral flexibility to allow for delivery of the stent (10) to the surgical site through a tortuous vessel path.

Description

Highly Flexible Stent

Technical Field

The invention concerns a stent for treatment of a diseased, damaged or weakened portion of a bodily vessel of a patient at a surgical site.

Background

An aneurysm is a bulge or a weakening of a wall of an artery. Aneurysms may burst and cause bleeding into a covering around the brain called the subarachnoid space. This is referred to as a subarachnoid hemorrhage. Subarachnoid hemorrhage secondary to a ruptured aneurysm causes a severe headache.

Deployment of existing intracranial stents cause noticeable injury to the healthy sections of the vessel wall near the distal ends of the stent, and also endothelial integrity is injured along the stent struts by expansion of the stent. From observation, this is due to several reasons. Firstly, existing intracranial stents (self- expanding and balloon expandable) lack the requisite flexibility to navigate through a tortuous vessel path to reach the surgical site. Secondly, existing balloon expandable intracranial stents require a significant amount of opening pressure. Consequently, once the opening pressure is applied, the stent expands relatively quickly and abruptly.

Accordingly, there is a desire for a highly flexible stent to treat diseased, damaged or weakened portions of the bodily vessel that minimise the injury to the vessel wall during deployment. Also, there is a desire for a highly flexible stent with an improved crimped profile in order to navigate through tortuous and small vessel paths.

Summary of the Invention

In a first preferred aspect, there is provided a stent for treatment of a diseased, damaged or weakened portion of a bodily vessel of a patient at a surgical site, the stent comprising: a plurality of circumferential wave-shaped members in a spaced apart relationship, each wave-shaped member including deformable hinge portions which upon deformation is adapted to enable controlled expansion of the stent from a first position radially outwardly to a second position; and a plurality of linking members extending between adjacent wave-shaped members to maintain the wave-shaped members in the spaced apart relationship, each linking member including at least one deformable hinge portion having a greater flexibility relative to the hinge portions of the wave-shaped members; wherein the wave-shaped members have a length to cross-sectional area ratio within a predetermined range so as to enable deployment of the stent within the bodily vessel at a predetermined pressure to minimise pressure exerted on the wall of the bodily vessel by the stent during expansion to the second position; and wherein the hinge portions of the wave-shaped members and linking members provide local and integral flexibility to allow for delivery of the stent to the surgical site through a tortuous vessel path.

Preferably, the predetermined pressure for deployment within the bodily vessel is less than four atmospheres.

The wave amplitude of a wave-shaped member may extend in a direction axis parallel to a longitudinal axis of the stent and the wave-shaped members are in a spaced apart relationship with respect to the longitudinal axis of the stent.

The hinge portions of a wave-shaped member may be positioned adjacent to the crest or trough of the wave-shaped member.

Adjacent wave-shaped members may be out of phase with each other.

The phase difference between adjacent wave-shaped members may be about 1.5 the wavelength of the wave-shaped members.

Every third trough of the wave-shaped member may include a substantially straight portion to minimise the lengthening or shortening of the stent during deployment into the bodily vessel.

The linking member may join a first wave-shaped member from the substantially straight portion to an adjacent second wave-shaped member.

The linking member may comprise an "S" portion. The "S" portion of the linking member may be joined to the trough of the adjacent second wave-shaped member to minimise the profile of the stent when in the first position.

The cross-sectional area of the wave-shaped members and linking members may be about 9 x 10^"6 square inches to about 10.2 x 1CT⁶ square inches to minimise the injury score during deployment.

The wave amplitude of the wave-shaped members may be about 0.032" to about 0.042".

The profile of the stent in the first position may be about 0.025".

The stent may be delivered to the bodily vessel at the surgical site over a wire.

Brief Description of the Drawings

An example of the invention will now be described with reference to the accompanying drawings, in which:

Figure 1 is a plan view of a stent as it is being expanded according to a first embodiment of the present invention;

Figure 2 illustrates a plan view of the stent of Figure 1 in a fully expanded state; and

Figure 3 illustrates a plan view of a stent according to a second embodiment of the present invention;

Detailed Description of the Drawings

Referring to Figure 1 , a stent 10 for enabling treatment of diseased, damaged or weakened portion of a bodily vessel 11 of a patient at a surgical site according to a first embodiment is illustrated. The stent 10 may also be used to treat aneurysms, ischemic diseases and haemorrhagic strokes. The stent 10 comprises a plurality of circumferential wave-shaped members 13 and a plurality of linking members 14 extending between adjacent wave-shaped members 13 to maintain the wave- shaped members 13 in the spaced apart relationship. Each of the linking members 14 comprises a substantially straight portion 23 and a deformable hinge portion 25, the deformable hinge portion 25 approximating an S-shape. Each of the wave- shaped members 13 comprises a first deformable hinge portion 26 and a second deformable hinge portion 27.

The first deformable hinge portion 26 and the second deformable hinge portion 27 enable the stent 10 to be crimped down to a first position 15 without distorting or overlapping of the wave-shaped members 13. The first position 15 may be of a profile in a transverse axis 16 of the stent 10, for example, 0.025". The low profile of the first position 15 enables the stent 10 to move easily in the bodily vessel 11 and reach the surgical site where the stent 10 is to be deployed. The bodily vessel 11 may be, for example, a tortuous vessel path with tight radiuses, more specifically a cerebral artery.

A vessel wall 28 of the bodily vessel 11 is susceptible to trauma caused by distortion of the bodily vessel 11. Flexibility along the longitudinal axis 18 of the stent 10 provides a reasonable degree of conformity along the longitudinal axis 18 of the vessel wall 28 if the surgical site is located at a point of natural curvature. Insufficient flexibility of the stent 10 may damage the vessel wall 28 or straighten the vessel wall 28 and disrupt normal blood flow. The wave shaped members 13 and the linking members 14 provide integral and local flexibility to allow for delivery of the stent 10 to the surgical site through the tortuous path.

Each of the plurality of wave-shaped members 13 comprises a strut length 29, a strut width 20 and a strut thickness 21. The strut width 20 may be, for example, less than 0.0032". The strut thickness 21 is dependant on the thickness of the material of the stent 10.

Each of the wave-shaped members 13 comprises an amplitude 17 that extends along an axis parallel to a longitudinal axis 18 of the stent 10. The amplitude 17 may be, for example, within a range of 0.016" to 0.021". As a result, a wave width

19 of each of the plurality of wave-shaped members 13 may be, for example, within a range of 0.032" to 0.042".

The wave-shaped members 13 are in a spaced apart relationship with respect to the longitudinal axis 18 of the stent 10 to enable uniform distribution of a plurality of stent surfaces 24 for enhancement of support and wall coverage of the bodily vessel 11. This reduces the risks of restenosis and tissue prolapsing.

The linking members 14 connect the wave-shaped members 13 and prevent the wave-shaped members 13 from flexing freely. After the stent 10 is positioned at the surgical site, the stent 10 is deployed into the bodily vessel 11 by a deployment means. The deployment means may be, for example, a low pressure inflatable balloon 12. The balloon 12 is mounted within the stent 10 and expanded at a predetermined pressure to deploy the stent 10 from the first position 15 to a second position 22. The predetermined pressure may be low, for example, at less than 4 atmospheres.

When the balloon is expanded, the wave-shaped member 13 expands in the transverse axis 16 to expand the stent 10 to the second position 22. The second position 22 may be dependant on a diameter of the bodily vessel 11. The stent 10 is expanded in a controlled manner to control the expansion rate of the stent 10. The rate of expansion of the stent 10 is dependant on a ratio between the strut length 29 and a cross- sectional area 30 of the stent 10. The ratio may be obtained by dividing the strut length 29 by the cross-sectional area 30 of the stent. The ratio may be from a predetermined range of 0.02379 X 10 ^ square inches to about 0.03417 10.2 X 10^"6 square inches.

The strut length 29 and the cross sectional area 30 is for enabling the expansion of the stent 10 in a controlled manner. The strut length 29 may be varied to accommodate vessels 11 of different diameters. The strut length 29 may be from a range of 0.023" to about 0.0341".

The cross sectional area 30 may be from a range of 9 X 10 ^ square inches to about 10.2 X 10^"6 square inches.

Cerebral arteries are muscular vessels primarily made up of an intima and media with relatively little adventitia. Due to the differences in the properties of cerebral arteries and coronary arteries, the cerebral arteries experience different strains than the coronary arteries for a same range of pressures. As a result, low pressure deployment is highly desirable in treatment of cerebral aneurysms because the walls of the cerebral artery are more fragile relative to coronary arteries and thus more susceptible to trauma caused by sudden and high deployment pressures. By enabling a low pressure deployment, the trauma caused by the expansion of the stent 10 is minimised. This also minimises potential injuries to the healthy part of the vessel 11 at the distal ends of the stent 10. Further, the linking members 14 improve support at the ends of the wave-shaped members 13 and encourage uniform expansion of the stent 10.

Next, the balloon 12 is deflated and removed from the bodily vessel 11 leaving the stent 10 expanded in the second position 22 to hold the tissue of the bodily vessel 11 in place. The stent 10 functions as a mechanical scaffold to enable treatment of the aneurysm. The stent 10 may also be used for treatment of ischemic diseases and haemorrhagic strokes. The stent 10 may be made from a biocompatible material such as, for example, 316L stainless steel.

When the balloon 12 is deflated after the deployment has completed, the balance of forces between the stent 10 and the wall 28 of the bodily vessel 11 results in a slight decrease in a diameter of the stent 10, defined as stent recoil. The linking member 14 minimises the lengthening or shortening of the stent 10 after deployment into the bodily vessel 11. When the stent 10 is fully deployed, the late lumen loss is primarily determined by neointimal proliferation.

The material of the bodily vessel 11 may be, for example, an incompressible, orthotropic material with non-linear elastic properties. As a result of the properties of the bodily vessel 11 being a function of the orientation at a point, it is desirable for the stent 10 to have localized and integral flexibility to adapt to a non-linear elastic response of the bodily vessel 11.

Figure 2 illustrates the stent 10 in the second position 22 in detail. Adjacent wave- shaped members 13 are out of phase with each other. The first hinge portion 26 is positioned adjacent to a crest or a trough of the wave-shaped member 13. The substantially straight portion 23 of the linking member 14 is attached to the first deformable hinge portion 26 at the first deformable hinge portion 26, approximating an E-shaped portion 51 of the stent 10. The first deformable hinge portion 26 may be a third trough of a first wave-shaped member 13.

The deformable hinge portion 25 of the linking member is attached to the second deformable hinge portion 27 of a second wave-shaped member 13 to connect the wave-shaped members 13. A plurality of virtual hinge points 43 in the deformable hinge portion 25 enables a higher flexibility at the second deformable hinge portion 27. The positioning of the linking member 14 with respect to the wave-shaped member 13 is dependant on the number of troughs of the wave-shaped member 13. The phase difference between each of the adjacent wave-shaped members 13 is about 1.5 times of a wavelength of each of the wave-shaped members 13. As there are no linking members 14 attached at each crest or trough 34 of the wave shaped members 13, the wave-shaped members 13 are more flexible about a plurality of virtual hinge points 35.

The geometry of the stent 10 is continuous to minimise any local stresses occurring at areas where the linking member 14 is attached to the wave-shaped members 13. A first end 52 and a second end 53 of the E-shaped portion 51 are rounded to remove any sharp corners. Sharp corners are areas of stress concentration that create possible sites for fatigue if the component is cyclically loaded (even for ductile materials).

After implantation, the stent 10 is subject to the biomechanical stresses and strains of the bodily vessel 11. Stent deformation caused by a movement of the bodily vessel 11 may be small due to the fragility of the cerebral artery. Features of the stent 10 such as rounding the sharp corners may reduce any potential stress concentration at areas surrounding the virtual hinge points 33 and will increase the fatigue reliability of the stent 10 after the stent 10 is implanted into the bodily vessel 11. Rounding is similarly performed on the profile of the "S' portion in the areas surrounding the virtual hinge points 43.

Another deployment means may rely on the stent 10 being self-expandable. In some instances, passive spring characteristics of a preformed elastic stent serve the purpose. For a self-expandable stent, the stent 10 may be of a material such as, but not limited to, nitinol.

Figure 4 illustrates a plan view of a stent 60 according to a second embodiment. The stent 60 is a variation of the first stent 10 described earlier. The deformable hinge portion 65 is attached to a location offset from the center of the second deformable hinge portion 27 of an adjacent wave-shaped member 13.

It will be appreciated by persons skilled in the art that numerous variations and/or modifications may be made to the invention as shown in the specific embodiments without departing from the scope or spirit of the invention as broadly described. The present embodiments are, therefore, to be considered in all respects illustrative and not restrictive.

Claims

WE CLAIM:

1. A stent for treatment of a diseased, damaged or weakened portion of a bodily vessel of a patient at a surgical site, the stent comprising: a plurality of circumferential wave-shaped members in a spaced apart relationship, each wave-shaped member including deformable hinge portions which upon deformation is adapted to enable controlled expansion of the stent from a first position radially outwardly to a second position; and a plurality of linking members extending between adjacent wave-shaped members to maintain the wave-shaped members in the spaced apart relationship, each linking member including at least one deformable hinge portion having a greater flexibility relative to the hinge portions of the wave-shaped members; wherein the wave-shaped members have a length to cross-sectional area ratio within a predetermined range so as to enable deployment of the stent within the bodily vessel at a predetermined pressure to minimise pressure exerted on the wall of the bodily vessel by the stent during expansion to the second position; and wherein the hinge portions of the wave-shaped members and linking members provide local and integral flexibility to allow for delivery of the stent to the surgical site through a tortuous vessel path.

2. The stent according to claim 1 , wherein the predetermined pressure for deployment within the bodily vessel is less than four atmospheres.

3. The stent according to claim 1, wherein the wave amplitude of a wave- shaped member extends in a direction axis parallel to a longitudinal axis of the stent and the wave-shaped members are in a spaced apart relationship with respect to the longitudinal axis of the stent.

4. The stent according to claim 1, wherein the hinge portions of a wave- shaped member are positioned adjacent to the crest or trough of the wave-shaped member.

5. The stent according to claim 1, wherein adjacent wave-shaped members are out of phase with each other.

6. The stent according to claim 5, wherein the phase difference between adjacent wave-shaped members is about 1.5 the wavelength of the wave-shaped members.

7. The stent according to claim 1, wherein every third trough of the wave- shaped member includes a substantially straight portion to minimise the lengthening or shortening of the stent during deployment into the bodily vessel.

8. The stent according to claim 7, wherein the linking member joins a first wave-shaped member from the substantially straight portion to an adjacent second wave-shaped member.

9. The stent according to claim 1, wherein the linking member comprises an "S" portion.

10. The stent according to claim 8, wherein the linking member comprises an "S" portion and the "S" portion of the linking member is joined to the trough of the adjacent second wave-shaped member to minimise the profile of the stent when in the first position.

11. The stent according to claim 1 , wherein the cross-sectional area of the wave-shaped members and linking members is about 9 x 10^"6 square inches to about 10.2 x 10^"6 square inches to minimise the injury score during deployment.

12. The stent according to claim 3, wherein the wave amplitude of the wave- shaped members is about 0.032" to about 0.042".

14. The stent according to claim 1, wherein the profile of the stent in the first position is about 0.025".

15. The stent according to claim 1, wherein the stent is delivered to the bodily vessel at the surgical site over a wire.