WO2006056981A1

WO2006056981A1 - Stent with ratchet-mechanism

Info

Publication number: WO2006056981A1
Application number: PCT/IL2005/001244
Authority: WO
Inventors: Joel Ovil; Ace Ovil
Original assignee: Joel Ovil; Ace Ovil
Priority date: 2004-11-24
Filing date: 2005-11-23
Publication date: 2006-06-01

Abstract

The invention provides a stent (2) formed from a solid sheet of material that is rolled-up to form an elongated cylindrical structure. The sheet of material has a first surface (6) having thereon one or more longitudinal projections (14) and a second surface (8) having therein a plurality of longitudinal grooves (20). In the cylindrical structure, the longitudinal projections (14) engage some of the longitudinal grooves (20) in a ratchet mechanism that allows the cylindrical structure to be expanded from a first caliber to a larger second caliber. The stent of the invention may be used in a method for maintaining the patency of a body passageway.

Description

STENT WITH RATCHET-MECHANISM

FIELD OF THE INVENTION

This invention relates to medical devices and methods, and more specifically to stents and stent delivery systems.

BACKGROUND OF THE INVENTION

Stents are expandable devices that are used to maintain the patency of a body passageway. Stents are commonly used in such passageways as blood vessels, airways, urethras and Eustachian tubes. A stent in a small caliber is delivered to the passageway where it is to be deployed, and is then expanded to a larger caliber in which it applies radially outward forces on the wall of the passageway. In order to maintain the patency of the passageway, the deployed stent must be able to resist radially inward forces applied to it by the passageway wall.

US patent 5,344,426 to Lau et al. discloses a stent having an open, reticulated structure. The stent wall has an array of diamond-shaped apertures and fingers which project into the apertures. The fingers and apertures are engaged in a ratchet mechanism that allows the caliber of the stent to be increased while preventing the caliber of the stent from decreasing.

SUMMARY OF THE INVENTION

The present invention provides a stent for maintaining the patency of a body passageway such as a blood vessel, airway, urethra or Eustachian tube. The stent of the invention is formed from a solid sheet-like material that is rolled into a small caliber cylindrical shape with overlapping edges. In the region of overlap of sheet edges, one or more parallel longitudinal projections on one of the surfaces mate with some of a plurality of parallel longitudinal grooves on the other surface in a ratchet mechanism. The ratchet mechanism allows the stent to be expanded from its initial small caliber to a selectable larger caliber. The ratchet mechanism also provides resistance to any external radially inward forces applied to the stent, so that the stent is stabilized in any selected caliber.

The stent of the invention is preferably made of a biocompatible material such as stainless steel or tungsten. For a vascular stent, the inner surface is preferably provided with a coating that promotes formation of an endothelial layer on the inner surface of the stent. The layer may be made, for example, from woven Dacron. The coating also eliminates contact of the stent material with the blood circulation.

Thus, in its first aspect, the invention provides a stent comprising: a solid sheet of material having a first longitudinal edge, a second longitudinal edge, a first surface and a second surface, the first surface having thereon one or more longitudinal projections adjacent to the first longitudinal edge, the second surface having therein a plurality of longitudinal grooves; whereby the sheet is rolled-up to form an elongated cylindrical structure having a first caliber with the first and second longitudinal edges overlapping and the longitudinal projections engaging some of the longitudinal grooves in a ratchet mechanism allowing the cylindrical structure.

In its second aspect, the invention provides a method for maintaining the patency of a body passageway comprising:

(a) mounting a stent on a distal end of a stent delivery catheter, the stent comprising: a solid sheet of material having a first longitudinal edge, a second longitudinal edge, a first surface and a second surface, the first surface having thereon one or more longitudinal projections adjacent to the first longitudinal edge, the second longitudinal surface having therein a plurality of longitudinal grooves; whereby the sheet is rolled-up to form an elongated cylindrical structure having a first caliber with the first and second longitudinal edges overlapping and the longitudinal projections engaging some of the longitudinal grooves in a ratchet mechanism allowing the cylindrical structure to be expanded from the first caliber to a larger second caliber;

(b) delivering the distal end of the catheter and the stent in the first caliber to the body passageway;

(c) deploying the stent in the body passageway by expanding the stent from the first caliber to a second larger caliber; and

(d) removing the stent from the passageway.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to understand the invention and to see how it may be carried out in practice, a preferred embodiment will now be described, by way of non- limiting example only, with reference to the accompanying drawings, in which:

Fig. 1 shows a stent in accordance with one embodiment of the invention;

Fig. 2 shows a sheet like material for forming the stent of Fig. 1;

Fig. 3 shows the stent of Fig. 1 mounted on a delivery catheter; and

Fig. 4 shows deployment of the stent of Fig. 1 in a body passageway.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

Fig. 1 shows a stent 2 in accordance with one embodiment of the invention. The stent 2 is formed from a sheet-like material 4 shown in Fig. 2 having an outer surface 6 and an inner surface 8. The flat sheet form is shown from two different perspectives in Figs. IA and IB. The flat sheet form shown in Fig. 2 is shaped on a mandrel (not shown) by rolling a longitudinal edge 10 over a longitudinal edge 12 into a small caliber cylindrical shape shown in Fig 2a. In the cylindrical configuration shown in Fig. 1, the outer 6 of the sheet 4 forms the outer surface of the cylinder while the surface 8 of the sheet 4 forms the inner surface of the cylinder that defines a lumen 22. The outer surface 6 is provided with one or more parallel longitudinal projections 14 adjacent to the edge 12. Each projection 14 has a saw tooth profile, a first longitudinal edge 16 perpendicular to the outer surface 6 and facing the edge 22, and a second longitudinal edge 18 oblique to the outer surface 6 and facing the edge 10. When the stent is rolled into the small caliber configuration shown in Fig. Ia₅ the projections 16 mate with some of a plurality of parallel longitudinal grooves 20 in the overlying inner surface 8 of the stent 2 and adjacent to the edge 10. The longitudinal grooves 20 preferably have a saw-tooth profile formed by a surface 21 perpendicular to the surface 8 and a surface 23 oblique to the surface 8. The engagement of the projections 16 and the grooves 20 forms a ratchet mechanism that allows the longitudinal projections 16 to move over the grooves 20 towards the longitudinal edge 10 while preventing the longitudinal projections 16 from moving over the grooves 20 towards the longitudinal edge 12. As explained below, this allows expansion of the stent from the small caliber shown in Fig. Ia to the large caliber shown in Fig. Ib when a balloon is expanded in the lumen 22 of the stent. Moreover, this allows the stent to be expanded to a large caliber that is selectable over a range of calibers depending on the extent of expansion of the stent, and the stent 2 in any caliber is resistant to external radially inward forces subsequently applied to the outer surface 6 of the stent, so that the stent is stabilized in any selected caliber.

The stent 2 is preferably made of a biocompatible material such as stainless steel or tungsten. The flat sheet which forms the stent 2 may be of any suitable length and width and gauge as required in any application. For example, for use in a coronary artery, the length of the stent may be around 1.5 to 4 cm, the diameter of the deployed stent around 0.5 to 1.5 cm and the gauge of the sheet material 4 around 0.02 to 0.125 mm. When the stent 2 is a vascular stent, the inner surface 8 preferably has a layer 9 of woven Dacron glued onto it in order to promote formation of an endothelial layer on the inner surface.

The stent 2 may be used with any stent delivery catheter designed for delivering a stent in its small caliber to a body site and deploying the stent at the body site by expanding the stent to a large caliber. As shown in Fig. 3, a typical stent delivery catheter 22 comprises a slender shaft 24 having a proximal end 30 and a distal end 32, an inflatable balloon 26 located at the distal end of the shaft 24 and a port 28 located at the proximal end of the body 24. The stent 2 in the small caliber shown in Fig. Ia is mounted on the distal end 32 about the balloon 26 so that the balloon 26 is located in the lumen 22 of the stent 2.

The shaft has an outer tube 34 and a coaxial inner tube 35 which define between them an annular inflating lumen 36 for the delivery of an inflation fluid to the interior of the balloon 26 when a source of pressurized fluid (not shown) is connected to the port 28. The pressurized fluid flows in the lumen 36 into the balloon 26 via openings 27 in the outer tube 34 so as to expand the balloon 26. The volume of the pressurized fluid delivered to the balloon 26 is determined so as to achieve a predetermined inflation of the balloon 26 so as to cause the stent 2 to expand from its initial small caliber shown in Fig. Ia to a predetermined large caliber, such as the large caliber shown in Fig. Ib.

The catheter 22 is mountable on a guidewire 38 that is slidably disposed within an inner lumen 40 of inner tube 34. The catheter 22 is provided with a blunt flexible tip 42 at its distal end. A knob 44 attached to the proximal end of the guidewire 38 is used to apply a torque to the proximal end of the guidewire 38 that is transmitted to the tip 42 of the guidewire 38 so that the guidewire can be navigated to a desired body site such as a site within an individual's vascular system or other body passageway.

Fig. 4 shows deployment of the stent 2 in a body passageway such as a stenotic region 44 of an artery 46. The artery 46 has an endothelial layer 47 containing atheromatous plaque 49 in the stenotic region 44. In Fig. 4a, the distal end of the guidewire 38 was navigated through the vascular system to the artery 46. The catheter 22 was then mounted on the guidewire 38, and the distal end 32 of the catheter 22 was guided along the guidewire 38 until the stent 2 in its small caliber and the underlying balloon 26 were positioned in the stenotic region 44. In Fig. 4b the balloon 26 has been inflated to a predetermined diameter by delivering a predetermined amount of a pressurized fluid to the balloon 26 to bring the stent 2 to a predetermined large caliber so as to expand the stenotic region 44 into a dilated state and to maintain the stenotic region 44 in the dilated state. The balloon 26 is then deflated and the deflated catheter 22 is removed from the artery 46 leaving the expanded stent 2 in the artery 46 pressing against the arterial lining, as shown in Fig. 2c. The stent 2 is preferably deployed in a large caliber in which the inner surface 8 of the stent 2 is flush with the endothelium 47 as shown in Figs. 4b and 4c so that an endothelial layer 51 that subsequently forms on the inner surface 8 will be flush with the endothelial layer 47 of the adjacent regions of the blood vessel 46, as shown in Fig. 4d. When the inner surface 8 of the stent 2 has a layer 9 of woven Dacron glued onto it, it can serve as a matrix for the adherence of cells from the blood circulation in order promote the formation of an endothelial layer on the inner surface 8. If, in the future, it should become necessary, the stent can be expanded further by reinserting the balloon 26 into the lumen 22 of the stent and inflating the balloon in order to achieve a still larger caliber of the stent.

The use of a stent having a solid wall prevents penetration of old endothelial cells through the stent wall into the lumen of the stent, and the coating 9 eliminates contact of the stent material from the blood circulation. Overdilation of the stent promotes alignment of the endothelial layer 51 that forms on the stent wall and the previously existing endothelial layer 47 of the blood vessel 46.

Claims

CLAIMS:

1. A stent comprising: a solid sheet of material having a first longitudinal edge, a second longitudinal edge, a first surface and a second surface, the first surface having thereon one or more longitudinal projections adjacent to the first longitudinal edge, the second surface having therein a plurality of longitudinal grooves; whereby the sheet is rolled-up to form an elongated cylindrical structure having a first caliber with the first and second longitudinal edges overlapping and the longitudinal projections engaging some of the longitudinal grooves in a ratchet mechanism allowing the cylindrical structure to be expanded from the first caliber to a larger second caliber.

2. The stent of Claim 1 , wherein said stent is in any caliber is resistant to radially inward forces applied to the stent.

3. The stent according to Claim 1 wherein the longitudinal projections have a saw-tooth profile.

4. The stent according to Claim 1 adapted for use in a blood vessel, airway, urethra or Eustachian tube.

5. The stent according to Claim 1 adapted for use in a blood vessel wherein an inner surface of the cylindrical structure is provided with a coating promoting formation of an endothelial layer on the inner surface.

6. The stent according to Claim 5 wherein the coating is a layer of woven

Dacron.

7. A method for maintaining the patency of a body passageway comprising:

(a) mounting a stent on a distal end of a stent delivery catheter, the stent comprising: a solid sheet of material having a first longitudinal edge, a second longitudinal edge, a first surface and a second surface, the first surface having thereon one or more longitudinal projections adjacent to the first longitudinal edge, the second surface having therein a plurality of longitudinal grooves; whereby the sheet is rolled-up to form an elongated cylindrical structure having a first caliber with the first and second longitudinal edges overlapping and the longitudinal projections engaging some of the longitudinal grooves in a ratchet mechanism allowing the cylindrical structure to be expanded from the first caliber to a larger second caliber;

(d) removing the stent from the passageway.

8. The method according to Claim 7 wherein the stent delivery catheter comprises an inflatable balloon at its distal end, the stent is mounted on the catheter with the balloon in a lumen of the stent, and the stent is deployed by inflating the balloon.

9. The method according to Claim 7 or 8 wherein the body passageway is a blood vessel, airway, urethra, or Eustachian tube.