WO2008148385A1

WO2008148385A1 - A stent

Info

Publication number: WO2008148385A1
Application number: PCT/DK2007/000271
Authority: WO
Inventors: Morten SØRENSEN; Erik Othel-Jacobsen; Henrik Harboe
Original assignee: Pnn Medical A/S
Priority date: 2007-06-06
Filing date: 2007-06-06
Publication date: 2008-12-11
Also published as: WO2008148385A8

Abstract

The invention relates to stent for insertion into and placement inside a body cavity of a human being or an animal. The stent has a first configuration and a second configuration. The stent comprises a retaining part for retaining a lumen inside the body cavity, and at least in the second configuration the retaining part has a substantially truncated, conical configuration. The invention also relates to a stent having an expansion part for fixing a position of the stent inside the body cavity, and wherein the expansion part is overlapping the retaining part of the stent.

Description

A STENT

FIELD OF THE INVENTION

The present invention relates to a stent for insertion into and placement inside a body cavity of a human being or an animal, said stent being made of a material capable of being readily shaped at body cavity temperature and said stent being intended for having a first configuration during insertion into the cavity and said stent, after having been placed in the cavity, being intended for having a second configuration.

BACKGROUND OF THE INVENTION

Stents are generally used for at least retaining, possibly also creating, a lumen in a body cavity. Stents are primarily shaped as a substantially tubular intraluminal prosthesis and are placed inside a body cavity of a human being or an animal. Stents may be used in a variety of body cavities, such as in the urinary canals, the blood vessels, the airways, etc., where occlusion of the body cavity may occur.

A purpose of the retaining part of the stent is to support the inside walls of the body cavity, to enable or preserve flow of fluids such as urine, blood or air through the body cavity if the cross-section of the body cavity is in any way narrowed, compressed, collapsed or in case the lumen of the body cavity is occluded in some other way.

Several different designs of stents have been developed, each type being especially designed for a specific use. Some existing stents have been designed as helically coiled stents, others as stents made from a web-structure, woven from wires or cut from a tube.

For the purpose of anchoring the stent in a specific position inside the body cavity, known stents may be anchored in a desired position inside the body cavity, after insertion, by expanding at least a part of the longitudinal extension of the stent or by providing an already expanded part of the stent, already before insertion. A disadvantage when considering many known stents is that migration of the stents inside the body of the human or animal has been observed. Such disadvantage of stents for implantation in the intraprostatic urethra being positioned between the external urethral sphincter and the bladder has been observed as the stent occasionally migrates towards a position between the colliculus and the bladder. Eventually, the stent migrates all the way to the bladder.

Often however, migration of the stent takes place primarily in one direction, either because forces acting on the stent is primarily orientated in one direction, or because a body organ, e.g. a sphincter muscle in relation to the urethra, is obstructing migration in another direction along the body cavity. And perhaps the body organ limits the possibilities of using an expansion, or at least limits using a stent with a large expansion part, for obviating migration of the stent in the one direction not being obstructed.

US 2003/0139804 describes a stent having cylindrical segments and having conical segments. The stent is having a first proximal segment having proximal and distal ends and a first outer diameter, a second distal segment having proximal and distal ends and a second outer diameter smaller than the said first outer diameter, and a third intermediate segment having a proximal end connected to the distal end of the first segment and a distal end connected to the proximal end of the second segment. With such a configuration the stent has a differential geometry which allows a very strong anchor of the first proximal segment in the body passageway due to the higher radial force at that level. According to the configuration as disclosed in US 2003/0139804, fixation of the stent in the vessel is obtained primarily by means of the first proximal segment.

A disadvantage of some known stents (like the Memokath stent from PNN Medical A/S) having an expandable part extending in prolongation of the retaining part, or where the retaining part of the stent itself has a first configuration during insertion of the stent and a second and different configuration after insertion and when being placed in the body cavity is that not only the cross-section of the stent as viewed perpendicular to a longitudinal axis of the stent, but also the length of the stent as viewed along the longitudinal axis of the stent is different in the second configuration. This implies, that when the stent is inserted to a selected placement within the body cavity, e.g. with one end of the stent abutting a certain body organ or with one end positioned at a certain body cavity opening, the placement of e.g. the one end will be different once the expandable part of the stent is transformed to the second configuration, due to change e.g. of the length.

Another disadvantage of many known stents is that the stents have a tendency of eroding into the tissue surrounding the body cavity. Other known stents produced from metals either being super-elastic or having shape memory effect or being plastically deformable at body temperature are known to apply a pressure on the surrounding tissue of such magnitude so as to cause traumatic damages to the surrounding tissue and may also be seen eroding into the tissue surrounding the body cavity.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a stent for obtaining a satisfactory retainment of the lumen, but also obtaining a reduced risk of the stent migrating, after insertion and when being placed in the body cavity, plus the stent causing only minimal traumatic damages to the tissue surrounding the body cavity and minimal or perhaps no in-growth of the tissue surrounding the body cavity, into which the stent is to be inserted.

This object and the advantages that will be described in the following description of the invention may be obtained by a stent comprising

- at least one retaining part for retaining a lumen inside the body cavity, and

- wherein the retaining part has a substantially truncated, conical configuration along the at least limited longitudinal extension of the retaining part.

Providing a truncated conical configuration has the following advantage when the stent has been inserted into the bodily cavity: The conical configuration may be positioned in the body cavity where natural or induced movements of the body cavity establishes a migrating force in one direction of the vessel, such as in the esophagus, or where other forces than those emanating from the vessel, such as gravitational forces, occur.

If the stent is inserted and positioned in the body cavity in such a manner that the conicity of the truncated configuration of the retaining part is having the conical configuration tapering in the opposite direction as the possible migrating direction, the risk of migration of the stent is reduced, also when no expanded part is provided as part of the stent.

According to preferred embodiments of the invention, the stent either has a circular truncated conical configuration or has a polygonal truncated conical configuration. The choice of either circular or polygonal truncated conical configuration depends on the body cavity into which the stent is to be inserted and also depends on how great a need there is for fixation of the stent towards migration forces.

A circular conical configuration is more gentle to the body cavity, while a polygonal conical configuration may be able to limit displacement, not only along a longitudinal axis of the stent, but possibly also limit displacement around the longitudinal axis of the stent.

The stent is capable of and intended for having a first configuration during insertion of the stent into a body cavity, and the stent is capable of and intended for having a second configuration after having been inserted and when being in place in a body cavity.

According to one aspect of the invention, the first configuration and the second configuration are substantially the same, i.e. at least substantially no change of configuration of the stent occurs in situations of use, i.e. after insertion of the stent and when the stent is in place in the body cavity. According to another aspect of the invention, the first configuration and the second configuration are not the same, i.e. a change of configuration of the stent does occur after insertion of the stent and when the stent is in place in the body cavity. Possibly, the stent further comprises at least one expansion part for maintaining the stent in placement inside the body cavity, and wherein the expansion part has a first cross-sectional extension in the first configuration, and the expansion part has a second, increased cross-sectional extension in the second configuration. An expandable part will further improve avoiding migration of the stent in the body cavity.

Preferably, at least part of the whole stent is formed by a number of helical windings of at least one wire, said wire preferably being made of Shape Memory Alloy being deployable from the first configuration to the second configuration. Helical windings, and possibly made of Shape Memory Alloy, are easily transformed from a first configuration to a second configuration by applying heat or by applying a mechanical force.

Possibly, the retaining part has a first cross-sectional extension, when configured in the first configuration, and where said first cross-sectional extension is substantially the same as a second cross-sectional extension of the retaining part, when being configured in the second configuration. The first cross-sectional extension being substantially the same as the second cross-sectional configuration ensures that the radial loads applied to the walls of the body cavity by the retaining part in the second configuration are the same as the radial loads applied by the retaining part in the first configuration.

Even possibly, at least part of the longitudinal extension of the retaining part of the stent has a cross-sectional extension in the second configuration, said cross- sectional extension being smaller than the normal cross-sectional extension of the body cavity along said longitudinal extension of the retaining part. The cross- sectional extension being smaller than the normal cross-sectional extension of the body cavity ensures that only limited radial loads are applied to the walls of the body cavity by the retaining part in the second configuration.

According to another embodiment of the invention, wherein the retaining part has a substantially truncated, conical configuration along the at least limited longitudinal extension of the retaining part in its second configuration, the retaining part may be expandable from a first low-cross-sectional configuration to a second increased cross-sectional configuration. Hereby the expansion of the retaining part will further improve avoiding migration of the stent in the body cavity, due to the radial forces applied to the walls of the body cavity by the retaining part in the second configuration.

According to an embodiment of the invention, wherein the retaining part has a substantially truncated, conical configuration along the at least limited longitudinal extension of the retaining part, the stent also comprises at least one expansion part for fixing a position of the stent inside the body cavity. The expansion part, when viewed in a plane parallel with the longitudinal axis, and both before and after insertion into the body cavity, is forming either an obtuse angle or an acute angle with the longitudinal axis of the stent.

When the expansion part of the stent forms either the same obtuse angle or the same acute angle with the longitudinal axis, before and after insertion into the body cavity, the expansion part is not as such expandable between the first configuration and the second configuration. The expansion part is in an expanded state in both the first and the second configuration, and the obtuse angle or an acute angle is established already when manufacturing the stent.

According to another embodiment of the invention, wherein the retaining part has a substantially truncated, conical configuration along the at least limited longitudinal extension of the retaining part, the stent also comprises at least one expansion part for fixing a position of the stent inside the body cavity, The expansion part, when viewed in a plane parallel with the longitudinal axis, however, only after insertion into the body cavity, is forming a final obtuse angle or a final acute angle with the longitudinal axis of the stent.

Before insertion and during insertion into the body cavity, the expansion part, when viewed in a plane parallel with the longitudinal axis, may be forming a preliminary obtuse angle with the longitudinal axis of the stent, said preliminary obtuse angle being greater than the final obtuse angle, the expansion part may be forming a preliminary acute angle being with the longitudinal axis of the stent, said preliminary acute angle being minor than the final acute angle. Expansion to the final obtuse or acute angel occurs, when the stent has been fully inserted into the body cavity and when the stent in place in the body cavity.

When the expansion part of the stent forms a final obtuse angle or a final acute angle with the longitudinal axis, only after insertion into the body cavity, the expansion part is as such expandable between the first configuration and the second configuration. The expansion part is in a non-expanded state in the first configuration and in an expanded state in the second configuration, and the final obtuse angle or the final acute angle is established only when the stent is in the second configuration.

In both embodiments, the obtuse angle is between 90 degrees and 180 degrees and the acute angle is between 0 degrees and 90 degrees.

Preferably, an acute angle is between 0 degrees and 45 degrees, possibly between 0 and 30 degrees, even possibly between 30 and 45 degrees, even more possibly between 15 and 45 degrees.

Preferably, an obtuse angle is between 135 degrees and 180 degrees, possibly between 150 and 180 degrees, even possibly between 135 and 150 degrees, even more possibly between 135 and 165 degrees.

Alternatively, an obtuse angle is between 90 degrees and 135 degrees, possibly between 90 and 120 degrees, even possibly between 120 and 135 degrees, even more possibly between 105 and 135 degrees.

The obtuse angle or the acute angle is selected and established in accordance with the body cavity into which the stent is to be employed, and in accordance with the need for fixation of the stent by means of the truncated conical configuration. The obtuse angle or the acute angle selected also depends on the geometry of the expansion part, such as more or less barb-shaped, when the stent is in the second configuration. The object and the advantages that will be described in the following description of the invention may alternatively or additionally be obtained by a stent comprising

- at least one retaining part for retaining a lumen inside the body cavity, and - at least one expansion part for maintaining the stent in placement, and

- at least one expansion part for fixing a position of the stent inside the body cavity, and

- wherein the expansion part of the stent is at least partly overlapping the retaining part of the stent along the at least limited longitudinal extension of the retaining part.

A stent, where the expansion part of the stent is at least partly overlapping the retaining part of the stent along the at least limited longitudinal extension of the retaining part result in the stent being provided with a more or less profound anchoring mechanism for fixation of the stent inside the body cavity after insertion of the stent.

When the expansion part of the stent is at least partly overlapping the retaining part of the stent along the at least limited longitudinal extension of the retaining part the possible migration forces will provide a self-locking effect of the stent by inducing increased abutment between the elements (e.g. helical coils) and by inducing further expansion of the expansion part thus activated by the migration forces.

Additionally, a stent where the expansion part of the stent is at least partly overlapping the retaining part of the stent along the at least limited longitudinal extension of the retaining part result in the total length of the stent being independent from the design and functionality of the expansion part. This facilitates the stent having the same length in both the first possibly non- expanded configuration and in the second expanded configuration. Hereby, exact placement of the stent ends in the desired position within the body cavity is feasible.

In one embodiment, the expansion part of the stent is partly surrounding the retaining part of the stent along the at least limited longitudinal extension of the retaining part. The expansion part overlapping the retaining part by only partly surrounding the retaining part may be capable of providing an anchoring mechanism being supported along only a part of an inner circumference of the walls of the body cavity, because the expansion part may have a configuration of a number of more or less pointed barbs.

In another embodiment, the expansion part of the stent is fully surrounding the retaining part of the stent along the at least limited longitudinal extension of the retaining part. The expansion part overlapping the retaining part by fully surrounding the retaining part may be capable of providing an anchoring mechanism being supported along an entire inner circumference of the walls of the body cavity, because the expansion part may have a configuration of an annular ring not being barbed at all.

The anchoring mechanism may be provided in numerous different ways. The anchoring mechanism may be provided in shape of barbs or the like configuration extending partly or fully around the stent. The anchoring mechanism may also be provided in shape of expanded parts having an increased cross-section compared to the cross-section of the retaining part, but without an effect of barbs or the like. The latter configuration is more gentle to the tissue of the body cavity, but may have a limited fixation effect of the stent.

The embodiment of the invention where the expansion part is at least overlapping the retaining part along at least a limited longitudinal extension of the retaining part may result in a configuration, where the expansion part, before and after insertion into the body cavity, and viewed in a plane parallel with the longitudinal axis, is forming an acute angle with the longitudinal axis along the at least limited longitudinal extension of the retaining part.

When the expansion part of the stent forms substantially the same acute angle with the longitudinal axis, before and after insertion into the body cavity, the expansion part is not as such expandable between the first configuration and the second configuration. The expansion part is in an expanded state in both the first and the second configuration, and the acute angle is established already when manufacturing the stent. The embodiment of the invention where the expansion part is at least partly overlapping the retaining part along at least a limited longitudinal extension of the retaining part may result in a configuration, where the expansion part, at least after insertion into the body cavity, and viewed in a plane parallel with the longitudinal axis, is forming an acute angle with the longitudinal axis along the at least limited longitudinal extension of the retaining part.

When the expansion part of the stent forms an acute angle with the longitudinal axis, at least after insertion into the body cavity, the expansion part is as such expandable between the first configuration and the second configuration. The expansion part is in a non-expanded state in the first configuration and in an expanded state in the second configuration, and the acute angle is established only when the stent is in the second configuration.

In both embodiments, the acute angle is between 0 degrees and 90 degrees, preferably between 30 degrees and 60 degrees, possibly between 30 and 45 degrees.

The acute angle is selected and established in accordance with the body cavity into which the stent is to be employed, and in accordance with the need for fixation of the stent by means of the truncated conical configuration. The acute angle selected also depends on the geometry of the expansion part, such as more or less barb-shaped, when the stent is in the second configuration.

According to one possible embodiment of a stent with an expansion part, either where said extension part is extending in prolongation of the retaining part in the case where at least a limited longitudinal extension of the retaining part has a truncated conical configuration, or where said extension part at least partly is overlapping the retaining part non-dependent of the configuration of the retaining part,

- the expansion part is constituted by at least one section of at least one helical winding in either a clockwise or a counter-clockwise direction, said at least one section being radially expanded clockwise or counter-clockwise. This embodiment refers to a stent where the expansion part is already expanded before insertion of the stent into the body cavity and will remain expanded after insertion and when being in place in the body cavity. The configuration of the expanded part may be a truncated cone, the cone, either extending in prolongation, or surrounding at least a limited longitudinal extension of the retaining part.

According to another possible embodiment of a stent with an expansion part, either where said extension part is extending in prolongation of the retaining part in the case where at least a limited longitudinal extension of the retaining part has a truncated conical configuration, or where said extension part at least partly is overlapping the retaining part non-dependant of the configuration of the retaining part,

- the expansion part is constituted by at least one section of at least one helical winding in either a clockwise or a counter-clockwise direction, said at least one section being radially expandable so that during expansion, the at least one section will be rotating in a clockwise or a counter-clockwise direction.

This embodiment refers to a stent where the expansion part is non-expanded before insertion of the stent into the body cavity and is becoming expanded after insertion and when being in place in the body cavity. The configuration of the expanded part may also be of a truncated cone, the cone either extending in prolongation of the retaining part in the case at least a limited longitudinal extension of the retaining part has a truncated conical configuration, or surrounding at least a limited longitudinal extension of the retaining part non- dependant of the configuration of the retaining part.

According to even another possible embodiment of a stent with an expansion part, either where said extension part is extending in prolongation of the retaining part in the case where at least a limited longitudinal extension of the retaining part has a truncated conical configuration, or where said extension part at least partly is overlapping the retaining part non-dependant of the configuration of the retaining part,

- the expansion part is constituted by at least one first section of at least one helical winding in a clockwise direction and at least one second section of at least one helical winding in a counter-clockwise direction, each of said first and second at least one section being radially expandable so that during expansion, the at least one first section will be rotating in counter-clockwise direction and the at least one second section will be rotating in clockwise direction.

This embodiment refers to a stent where the expansion part is non-expanded before insertion of the stent into the body cavity and is becoming expanded after insertion and when being in place in the body cavity. The configuration of the expanded part may be that of a cylinder, the cylinder either extending in prolongation of the retaining part in the case at least a limited longitudinal extension of the retaining part has a truncated conical configuration, or the cylinder surrounding at least a limited longitudinal extension of the retaining part non-dependant of the configuration of the retaining part.

Additionally, this possible embodiment could have an expansion part being in an expanded state in both the first configuration and the second configuration.

Stents are used to support the inside walls of a body cavity of a human being or animal and thereby enabling and at least retaining flow of liquid or gas through the body cavity in the occurrence of the cross-section of the cavity having in any way been narrowed, compressed, collapsed or the lumen of the cavity having in any other way been occluded.

The retaining part, in the second configuration, may have a cross-sectional extension, along at least part of a longitudinal extension of the retaining part, being smaller than the normal cross-sectional extension of the body cavity along said extension of the retaining part.

At least part of the expansion part, in the second configuration, may have a cross- sectional extension, along a longitudinal extension of the expandable part, being greater than the cross-sectional extension of the body cavity along said extension of the expandable part.

In the remainder of the present description, the part of a stent intended for retaining a lumen inside the body cavity is called a retaining part. In the case the lumen has wholly or partly collapsed, the retaining part may be placed inside the cavity by forcing open the collapsed lumen by means of the stent to enable flow, or the retaining part may be placed inside the cavity for a subsequent transformation of the shape of the stent to open the collapsed lumen.

The stent is placed inside the body cavity at a specific position defined by the position of the occluded lumen inside the human being or animal. For ensuring that the stent maintain the position during natural or inflicted movements of the human being or animal, or during natural or inflicted movements of the tissue surrounding the body cavity, the stent is pre-formed with a truncated conical configuration and/or an expansion part.

By pre-formed is meant that the stent during manufacture of the stent has been provided with a certain truncated conical configuration along at least a limited longitudinal extension of the retaining part and/or has been provided with a certain expansion part, either extending in prolongation, or overlapping, at least a limited longitudinal extension of the retaining part, where the extension in prolongation of at least a limited longitudinal extension of the retaining part or the extension by overlapping at least a part of the retaining part are depending on the embodiment in question.

The manufacture of the stent geometry takes place when the stent is in a second configuration of the stent, said second configuration also being the configuration intended, when the stent is placed inside the body cavity of the human being or animal, ready for fulfilling the purpose of retaining the lumen of the body cavity.

According to one aspect of the invention, the second configuration of the stent, also of the expansion part of the stent, may be substantially the same as the first configuration.

According to another aspect of the invention, the second configuration constitutes an expanded state of the stent and the first configuration constitutes a non- expanded state of the stent. Thus, the second configuration is different than the first configuration.

The expansion in the second configuration is at least established to a part of or to the entire of the expansion part of the stent. Accordingly, the expansion part may consist in one part of the expansion part being expanded in both the first and the second configuration and in a second part of the expansion part only being expanded in the second configuration.

The stent according to the invention, either the stent where at least part of the retaining part, in the second configuration, has a truncated conical configuration, or the stent where the expansion part, in the second configuration, is overlapping at least a limited longitudinal extension of the retaining part, or perhaps a combination of the two different embodiments, may be provided with a curvature along at least part of the retaining part.

Any curvature of the stent may be intended for conforming to a curvature of the lumen of the human being or the animal. Thus, when placed in the lumen, neither the lumen nor the stent need deformation to match the profile of the lumen or of the stent, respectively. Curvature conformity results in reduced localized forces to the internal walls of the lumen.

Conforming of the curvature of the stent to the internal profile of the lumen may be accomplished by mapping the internal profile of the lumen, preferably in 3- dimensional space. Then, curvature of the stent may be formed accordingly, e.g. by heat-treating the stent or by plastically deforming the stent. Alternatively, an apparatus such as a balloon catheter may be formed and adapted for plastically deforming the stent to impose the curvature. Mapping of the body lumen may be accomplished using a variety of techniques, including ultrasound, intravascular ultrasound, angiography, radiography, magnetic resonance imaging, computed tomography and CT angiography.

As an alternative to forming the curvature of the stent or the curvature of apparatus for plastically deforming the stent, a statistical curvature matching technique may be used. The stent or the apparatus may be provided with a standardized curvature that more closely conforms to an average curvature for a specific body cavity lumen within a specific human or animal population. As with curvature conforming to the lumen, statistical curvature matching of the curvature may be facilitated or augmented by pre-mapping the intended body cavity lumen, into which the stent is intended for insertion and placement. As a further alternative, stents may be manufactured in a number of different styles, each having its own predetermined curvature conforming to different specific body cavity lumens of a human being or animal. In this manner, a clinician may select a stent having a degree of curvature most appropriate for the specific lumen presented by the case at hand. As with curvature conforming to the lumen, predetermined curvature matching of the curvature may be facilitated or augmented by pre-mapping the different intended body cavity lumens, into which the stent is intended for insertion and placement.

According to the first aspect of the invention i.e. the first configuration of the stent being the same as the second configuration of the stent,, during manufacture of the stent geometry, and both before, during an after the stent is to be inserted into the body cavity, the stent is maintained in configuration, said configuration both being the first configuration intended during insertion of the stent into the body cavity of the human being or animal, before being ready for fulfilling the purpose of retaining the lumen of the body cavity, and being the second configuration intended after insertion of the stent and when the stent is in place in the body cavity of the human being or animal.

According to the second aspect of the invention i.e. the first configuration of the stent being different than the second configuration of the stent,, subsequent to manufacture of the stent geometry, and when the stent is to be inserted into the body cavity, the stent is transformed to a first configuration, said first configuration being the configuration intended during insertion of the stent into the body cavity of the human being or animal, before being ready for fulfilling the purpose of retaining the lumen of the body cavity. Only after the stent is in place in the body cavity of the human or animal body, the stent is transformed to the second configuration, ready for fulfilling the purpose of retaining the lumen of the body cavity.

In an embodiment of the stent, in which the retaining part may be curved in the second configuration, irrespective of whether the stent has an expansion part or not, and irrespective of the shape of the possible expansion part, the retaining part is preferably transformed to a substantially straight structure in the first configuration for thereby obtaining an easy insertion into the cavity in the first configuration.

In a preferred embodiment according to the second aspect of the invention, i.e. the first configuration of the stent being different than the second configuration of the stent, the material from which the stent is made is a Shape Memory Alloy, having a transformation phase which is a transition phase of the material structure, said transition phase being present at a temperature interval above normal body cavity temperature of the human being or animal, the body cavity for which the stent is intended.

In the preferred embodiment according to the second aspect of the invention, i.e. the first configuration of the stent being different than the second configuration of the stent, the transformation to the second configuration, in which the stent has a truncated conical part and/or an expanded part and/or a curved part, is performed by a thermal influence, such as by flushing the cavity with saline or similar fluid having a higher temperature than the transition temperature of the stent and thereby provoke a change of the crystalline structure of the material, resulting in a geometric change of the stent configuration.

In the one possible embodiment according to the second aspect of the invention, i.e. the first configuration of the stent being different than the second configuration of the stent, the temperature interval of the transition phase of the Shape Memory Alloy is present between 37°C and 75°C, preferably between 37°C and 60⁰C, more preferred between 37°C and 45°C.

Alternatively, the temperature interval of the transition phase of the Shape Memory Alloy is present at a temperature below normal body cavity temperature, of the human being or animal, the body cavity for which the stent is intended, preferably between 0°C and 37°C, more preferably between 25°C and 37°C, most preferred between 30⁰C and 37°C. Hereby, the second configuration having a truncated conical part and/or an expanded part and/or a curved part may be obtained already before or during insertion of the stent. In another embodiment according to the second aspect of the invention, i.e. the first configuration of the stent being different than the second configuration of the stent, the transformation to the second configuration having a truncated conical part and/or an expanded part and/or a curved part is performed by a mechanical influence of the stent or at least part of the stent, by releasing means retaining the stent in the first configuration, such as a cover, a casing or similar means for maintaining the stent in the first configuration. When the means for retaining the stent in the first configuration is released the stent will attain its second configuration by elastic change of the geometry, due to stress-relaxation of the stent.

In the one embodiment according to the other embodiment of the invention, the material from which the stent is made is a Shape Memory Alloy, having a transformation phase which is a transition phase of the material structure, said transition phase being present at a temperature interval that makes the material super-elastic at normal body cavity temperature of the human being or animal, the body cavity for which the stent is intended.

In even another embodiment according to the second aspect of the invention, i.e. the first configuration of the stent being different than the second configuration of the stent, the transformation to the second configuration having a truncated conical part and/or an expanded part and/or a curved part is performed by a mechanical influence of the stent or at least part of the stent, by applying deformation forces onto the stent, such as inflating a balloon inside the stent. Hereby the stent is forced to attain its second configuration by plastic change of the geometry. The material from which the stent is made is in this preferred embodiment a material which is capable of retaining its plastic deformation after removal of the deformation force.

The truncated conical configuration and/or the expansion part of the stent enables maintaining the stent in a fixed position both in a longitudinal extension of the cavity and also maintaining the position of the stent in a transversal extension of the cavity, thereby preventing migration of the stent inside the cavity and/or away from the cavity. The possible curvature of the stent is pre-formed so as to conform to the curvature of the cavity in which the stent is to be placed. When the stent is placed in such a cavity and the stent has a curvature conforming to the curvature of the cavity, the stent does not exert a pressure, or at least the pressure is reduced, towards the inside walls of the cavity. Thereby, any inflicted or natural movements of the walls of the cavity will not, or will at least only to a limited extend, result in a longitudinal movement of the stent.

A stent delivery system may be provided for inserting a stent according to the invention, and in which the stent delivery system comprises a marker element which is detectable from outside the body cavity by at least one of the following detections: optically, tactilely, photographically, electronically or radiologically for being able of obtaining a correct physical placement of the stent in the body cavity. Preferably, the marker element of the stent system is capable of marking a rotational orientation of the stent in respect of a longitudinal axis of the stent.

According to an alternative aspect of the invention, the invention relates to a stent, in which the stent itself comprises a marker element which is detectable from outside the body cavity by at least one of the following detections: optically, tactilely, photographically, electronically or radiologically for being able of obtaining a correct physical placement of the stent in the body cavity. Preferably, the marker element of the stent itself is capable of marking a rotational orientation of the stent in respect of a longitudinal axis of the stent.

A marker element provided in conjunction with a stent delivery system or provided in conjunction with the stent itself result in the possibility of establishing the orientation of the stent after the stent has been inserted into the body cavity. Thereby, it is possible to ensure a correct placement of the stent in the body cavity, either in respect of a longitudinal orientation of the stent or in respect of a rotational orientation of the stent, or in respect of both a longitudinal orientation and rotational orientation of the stent.

A correct longitudinal orientation of the stent is especially necessary in the case where the stent is provided with at least one expandable part. It is necessary for the expandable part to be positioned correctly in relation to the body cavity so that the expandable part will expand towards the proper section of internal walls of the body cavity, which section of the internal walls must be capable of tolerating the pressure from the expandable part.

Also, a correct longitudinal orientation of the stent is necessary in the case where the stent is provided with more expandable parts. It is necessary for the expandable parts to be positioned correctly in relation to the body cavity so that the expandable parts will expand towards the proper sections of internal walls of the body cavity, which sections of the internal walls must be capable of tolerating the pressure from the expandable parts.

A correct rotational orientation of the stent is especially necessary in the case, in which the stent is provided with a curvature. It is necessary for the curvature of the stent to be positioned correctly in relation to the corresponding curvature of the body cavity lumen so that the curvature of the stent will conform to the corresponding curvature of the body cavity lumen.

Also, a correct rotational orientation of the stent is especially necessary in the case, in which the stent is provided with more curvatures. It is necessary for the different curvatures of the stent to be positioned correctly in relation to the corresponding different curvatures of the body cavity lumen so that the different curvatures of the stent will conform to the correct corresponding curvatures of the body cavity lumen.

A combined correct longitudinal orientation and correct rotational orientation is necessary where the stent is provided both with at least one expandable part and with at least one curvature.

The shape of the stent in the second configuration is not readily detectable when the stent during insertion into the body cavity is in the first configuration. Thus, in order to establish the correct placement in the body cavity, and because the shape of the stent when placed in the cavity is not possible to establish until after the stent is in placement, marker elements of the different kinds mentioned, is necessary or at least beneficial. The type of marker element employed, i.e. whether the marker element is optically, tactilely, photographically, electronically or radiologically detectable, depends on the actual type of stent, the body cavity in which the stent is intended for placement, the detection equipment available, the detection equipment necessary or other factors, which clinical personnel will know or will want to employ during insertion of the actual stent in question.

The retaining part of the stent is not intended for expanding into abutment with the inside walls of the cavity for maintaining the position of the stent after placement. The stent is maintained in position by means of the expansion part and/or the truncated conical part and/or the curvature of the stent conforming to the curvature of the cavity. Thereby, the expansion part and/or the truncated conical part and/or the curvature maintains the stent in position, and the stent is maintained in position during any natural or inflicted movements of the human being or animal itself or of the body cavity of the human being or animal.

A stent having the main features of the present invention may in principle be placed in almost any cavity of the body. However, stents having the main features of the present invention are especially suited for placement in body cavities such as the urological tract, the urethra, the biliary tract, the airways, the gastrointestinal tract or the blood vessels in the human or animal body. The stent will ensure passage of liquid, gas or solid inside the natural cavity, in which the stent is placed, and by means of the main features any migration of the stent will be eliminated or at least reduced, while at the same time eliminating or at least reducing to a minimum the traumatic damages to the tissue surrounding the body cavity and/or the in-growth of the tissue surrounding the stent.

According to an embodiment of the second aspect of the present invention, i.e. the first configuration of the stent being different than the second configuration of the stent, the position of the stent, after having been inserted into and having been placed inside the body cavity, is maintained in position by means of the stent comprising at least one retaining part for retaining a lumen inside the body cavity, and furthermore at least one expandable part being the expansion part according to the invention, said expandable part only constituting part of the entire longitudinal extension of the stent. The expandable part is a specific embodiment of the expansion part. The expansion part according to the invention is generic term in relation to either a specific embodiment of an already expanded part according to the first aspect of the invention, i.e. the first configuration of the stent being the same as the second configuration of the stent, or in relation to a specific embodiment of a subsequently expanded part, i.e. an expandable part, according to the second aspect of the invention, i.e. the first configuration of the stent being different than the second configuration of the stent.

Subsequent to the stent having been inserted into and having been placed inside the body cavity, the expandable part is expanded by transformation of the expansion part from the first configuration to the second configuration. The second configuration may be a pre-formed shape of the expandable part, e.g. by means of the expandable part being made of Shape Memory Alloy, said preformed shape of the expandable part being of a larger configuration than during insertion of the stent. The expandable part is intended for expanding outwards towards the inside walls of the body cavity so as to abut the inside walls of the body cavity.

In an embodiment of the invention, in which the stent comprises a curvature of the retaining part and also comprises an expandable part, the interval of the transition phase of the Shape Memory Alloy, which enables activation of the curvature, is present at a temperature below normal body cavity temperature, of the human being or animal, the body cavity for which the stent is intended, preferably between 0⁰C and 37°C, more preferably between 25°C and 37°C, most preferred between 30⁰C and 37°C, and the interval of the transition phase of the Shape Memory Alloy enabling activation of the expansion of the expandable part is present at a temperature above normal body cavity temperature, of the human being or animal, the body cavity for which the stent is intended, preferably between 37°C and 75°C, more preferably between 37°C and 60⁰C, most preferred between 37°C and 45⁰C.

Hereby the shape of the retaining part may be obtained already before or during insertion of the stent, without applying additional heating energy from outside the cavity. The expansion of the expandable part may subsequently be activated by application of heat.

The stent, when having an expansion part being expandable, has a first configuration before insertion into the cavity. In the first configuration, the expandable part is in a compressed configuration when seen in a transverse extension of the stent in comparison to the expanded second configuration of the expandable part of the stent.

The stent according to the present invention may consist of a number of windings of at least one wire. In a preferred embodiment of the stent, the windings are at least partly formed by a number of helical windings of at least one wire.

In one embodiment, at least part of the retaining part is formed by a number of helical windings of at least one wire. In another embodiment, at least part of the expansion part is formed by a number of helical windings of at least one wire. In a still further embodiment, both at least part of the retaining part and at least part of the expansion part is formed by a number of helical windings.

In the embodiment of a stent, in which the retaining part has a truncated conical configuration and in which the retaining part possible also is curved in the second configuration, and irrespective of whether the stent has an expansion part or not, and irrespective of the shape of the possible expansion part, the whole stent may be formed by a number of helical windings extending along the entire extension of the stent.

In the embodiment of a stent, in which the stent is provided with an expansion part, irrespective of whether the retaining part of the stent is straight or curved, and irrespective of the structure of the retaining part of the stent, the whole stent may also be formed by a number of helical windings extending along the entire extension of the stent,

In one embodiment of the invention, the helical windings of the expansion part have in the first configuration a pitch and after expansion, the helical windings of the thus expandable part in the second configuration have substantially the same pitch.

In another embodiment the retaining part and/or the expansion part is formed by a number of helical windings of at least one wire and wherein the mutual distance between the windings is less than 5 mm, preferably less than 3 mm, more preferred less than 1 mm.

The retaining part or the expansion part may in a further embodiment of the invention have another configuration than the rest of the stent, such as a web- structure, a woven structure made from one or more wires or filaments, or the retaining part may be constituted by a perforated tubular body. The web-structure may be constituted by a tubular body provided with cut-outs. The physical structure of the present stent can be made from wire which is wound in different patterns, such as cross- patterns, knitting-patterns or similar.

The stent of the invention may comprise a plurality of retaining parts which are distributed along the longitudinal extension of the stent. The stent of the invention, when provided with one or more curvatures in the second configuration, may comprise more than one curvature so as to conform to a cavity of the human being or animal having, as example an S-form, or even more curvatures.

The stent of the invention, when provided with one or more curvatures in the second configuration, may have one or more curvatures extending in two dimensions or in three dimensions. Thus, the longitudinal axis of the stent along the one or more curvatures may extend in a single plane, i.e. in two dimensions, or the longitudinal axis of the stent along the one or more curvatures may extend in three dimensions.

Either only one curvature or only a limited number of curvatures extend in two dimensions, and the possible remainder of curvatures extend in three dimensions, or the one curvature or all curvatures extend in three dimensions. The extension of the longitudinal axis of the stent along the one or more curvatures depends on the shape of the body cavity into which the stent is to be inserted and in which the stent is to be placed.

In one embodiment, the expansion part is constituted by at least one first section of at least one helical winding which is wound in a clockwise direction and at least one second section of at least one helical winding which is wound in a counterclockwise direction, each of said first and second sections being radially expandable so that during expansion, the at least one first section will be rotating in the counter-clockwise direction and the at least one second section will be rotating in the clockwise direction.

The number of first sections and the number of second sections may vary depending on the stent design and depending on the body cavity into which the stent is to be inserted and is to be placed. Thus, the expansion part of the stent may comprise only one first section consisting of helical windings and only one second section consisting of helical windings. Alternatively, the stent may comprise only one first section consisting of one or more helical windings and a plurality of second sections, each consisting in one or more helical windings. Even in the alternative, the stent may comprise a plurality of first sections, each consisting of one or more helical windings, and only one second section consisting in one or more helical windings.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following, the present invention will be described with reference to the accompanying drawings, in which:

Fig. 1 shows a first embodiment of a stent according to the invention having a non-curved and truncated conical configuration, Fig. 2 shows the first embodiment of a stent after having been inserted into the body cavity and having a curvature and a truncated conical configuration, Fig. 3 shows a second embodiment of a stent according to the invention before insertion into the body cavity and having a substantially cylindrical configuration, Fig. 4 shows the second embodiment of a stent after having been inserted into the body cavity and having a cylindrical retaining part and a truncated expansion part with helical windings extending clock-wise,

Fig. 5 shows a third embodiment of a stent after having been inserted into the body cavity and having a cylindrical retaining part and a cylindrical expansion part with helical windings extending clock-wise,

Fig. 6 shows a fourth embodiment of a stent according to the invention before insertion into the body cavity and having a substantially cylindrical configuration, Fig. 7 shows the fourth embodiment of a stent after having been inserted into the body cavity and having a cylindrical retaining part and a cylindrical expansion part with helical windings extending both clock-wise and counter-clockwise,

Fig. 8 shows a fifth embodiment of a stent according to the invention before insertion into the body cavity and having a substantially cylindrical configuration, Fig. 9 shows the fifth embodiment of a stent after having been inserted into the body cavity and having a cylindrical retaining part and a truncated conical expansion part with windings extending along four U-turns,

Fig. 1Oa-IOd show other embodiments of stents after having been inserted into the body cavity and having curved retaining parts and having expansion parts corresponding to those of Fig. 4, Fig. 5, Fig. 7 and Fig. 9, respectively, Fig. lla-llc show an embodiment of a stent according to the prior art after having been inserted into different body cavities subjecting the stent to migrating forces,

Fig. 12 shows a stent according to the invention having a truncated conical retaining part after having been inserted into a body cavity, Fig. 13a-13b show embodiments of stents according to the prior art having expansion parts after having been inserted into the body cavity and when being subjected to migrating forces,

Fig. 14a-14d show embodiments of stents according to the invention having expansion parts after having been inserted into the body cavity and when being subjected to migrating forces, Fig. 15a-15d show other embodiments of stents after having been inserted into the body cavity and having truncated conical retaining parts and having expansion parts corresponding to those of Fig. 4, Fig. 5, Fig. 7 and Fig. 9, respectively, Fig. 16a-16d show other embodiments of stents before insertion into the body cavity and having truncated conical retaining parts and having expansion parts corresponding to those of Fig. 3, Fig. 6, Fig. 8, respectively, and Fig. 17a-17d show even other embodiments of stents after insertion into the body cavity where Fig. 17a shows a prior art stent and Fig. 17b-17d show stents according to one or both of the two units of the invention.

DETAILED DESCRIPTION OF THE INVENTION

Fig. 1 shows a stent 1 to be inserted inside a body cavity. The stent is intended for insertion into the intraprostatic urethra of a male human being. The stent in this invention is however not limited to insertion into the intraprostatic urethra, as the invention can easily be designed for insertion into other organs, like the ureter, the blood vessels, the airways etc. obvious for those skilled in the art. Fig. 1 shows the stent when being in a first configuration of the stent. The first configuration is an un-stable configuration of the stent, at least when the stent has body cavity temperature. Fig. 1 is also showing a stent when being in a second configuration of the stent. The second configuration is a stable configuration of the stent, at least when the stent has body cavity temperature.

Fig. 2 show the stent 1 in a second configuration having both a curvature 4 and a truncated conical section combined along the longitudinal extension of the retaining part, or at least along part of the longitudinal extension of the retaining part 2. The stent 1 in Fig. 2 is not shown having an expansion part, however, any of the expansion parts shown in the following figures may be combined with the stent 1 having a combined curvature 4 and truncated conical section 2.

The stent shown in Fig. 2 may be straight in the first configuration as shown in Fig. 1, so that the curvature 4 is only provided in the second configuration, according to a second aspect of the invention, where the first configuration of the stent is different than the second configuration of the stent. According to the second aspect of the invention, the stent in Fig. 2 is shown after the material from which the stent is made has passed a transition phase, said transition phase defining the transformation from the first configuration to the second configuration. The stent when being in the second configuration has a configuration which is a pre-formed, non-straight and stable configuration of the stent, at least when the stent has body cavity temperature. Alternatively, the retaining part 2 of the stent 1 as shown in Fig. 2 may already be provided with the curvature 4 in the first configuration.

Fig. 1 and Fig. 2 show the stent 1 comprising only one part, a retaining part 2. In the embodiment shown, the stent 1 is produced by at least one metal wire which is helically wound so that the whole stent consists of a number of helical windings. In the embodiment shown, the stent is made of a Shape Memory Alloy, preferably a nickel-titanium-alloy.

The retaining part 2 is produced so as to have the helical windings fully, or at least substantially, in abutment with each other. The retaining part 2 is designed to retain a lumen in a body cavity, as mentioned the urethra of a male human being, so as to ensure a possible flow of fluid, i.e. urine, through the lumen. The retaining part 2 may furthermore be designed with a curvature 4 in the second configuration to conform to a corresponding curvature of the body cavity, i.e. the intra prostatic curve in the urethra.

When the stent 1, when being in the first configuration as shown in Fig. 1, is inserted into and has been positioned in the intraprostatic urethra, and the stent either before insertion is in the final configuration or subsequent to insertion is transformed to the second configuration, in which truncated conical configuration and curvature formation of the retaining part 2has occurred, the stent 1 will maintain its position without migrating, and will allow urinary passage without obstructing the valve-function of the sphincter.

In an alternative configuration, the stent in the second configuration only exhibits a truncated conical configuration and does not exhibit a curvature. The truncated conical configuration may be applied along the entire longitudinal extension of the stent or may be applied along only a limited part of the longitudinal extension of the stent.

Fig. 3 and Fig. 4 show a stent 1 comprising two parts, a retaining part 2 and an expandable part 3. The stent 1 is produced by at least one metal wire which is helically wound so that the whole stent consists of a number of helical windings. In the embodiment shown, the stent is made of a Shape Memory Alloy, preferably a nickel-titanium-alloy. The stent is an embodiment according to the second aspect of the invention, i.e. the first configuration of the stent being different than the second configuration of the stent.

The expandable part 3 and the retaining part 2 are produced so as to have the helical windings fully, or at least substantially, in abutment with each other. The retaining part 2 is designed to retain a lumen in a body cavity, as mentioned the urethra of a male human being, so as to ensure a possible flow of fluid, i.e. urine, through the lumen.

The stent 1 of Fig. 3 is shown in Fig. 4 as being straight. In the embodiment shown, the retaining part of the stent is straight both in the first configuration and in the second configuration. A transition from the retaining part 2 to the expandable part 3, and vice versa, is abrupt, i.e. no actual junction is provided between the retaining part 2 and the expandable part 3, and vice versa. Thus, there is no distance as such between the retaining part 2 and the expandable part 3, and the retaining part 2 passes directly into the expandable part 3, and vice versa.

The expandable part 3, i.e. the expansion part as defined according to the invention, may be seen as a flange or a collar overlapping a limited longitudinal extension of the retaining part by surrounding the retaining part 2. The windings 10 of the retaining part 2 may e.g. propagate clockwise, and at the transition from the retaining part 2 to the expandable part 3, the winding direction remains clockwise so that the windings 10 of the expandable part 3 also propagate clockwise. In an alternative embodiment, the windings 10 of the retaining part 2 may propagate clockwise, and at the transition from the retaining part 2 to the expandable part 3, the winding direction changes to counter-clockwise so that the windings 10 of the expandable part 3 propagate counter-clockwise, opposite to the propagation of the windings of the retaining part 2. Even in the alternative, the windings of the retaining part may propagate counter-clock-wise and the windings of the expansion part may propagate clockwise.

In the first configuration shown in Fig. 3, the cross-sectional extension of the retaining part 2 may change from a first cross-sectional extension to a smaller second cross-sectional extension for creation of a recess 8 for the expandable part 3, when the flange is in the first configuration as shown in Fig. 3. Alternatively, the cross-sectional extension of the retaining part 2 is unchanged over the length of the stent 1.

In the first configuration of the stent, an outer cross sectional extension of the expandable part 3 may be equal to an outer cross-sectional extension of the retaining part 2, so that an outer cross-sectional extension of the stent 1 is substantially constant in the first configuration as shown in Fig. 3 along the longitudinal extension of the stent 1.

Alternatively, when the expansion part is in the first configuration as shown in Fig. 3, the outer cross sectional extension of the expandable part 3 may be smaller or larger than the outer cross-sectional extension of the retaining part 2. The cross- sectional extension of the expandable part 3 may be substantially constant along the longitudinal extension of the expandable part 3.

In the second configuration shown in Fig. 4, the cross-sectional extension of the expandable part 3 increases along the longitudinal direction, i.e. from left to right in the figure, to form a truncated circular conical configuration as shown, alternatively a hyperbolic, or a parabolic, or a polygonal truncated conical configuration.

In the embodiment shown in Fig. 4, in general terms according to the scope of the invention, the expansion part 3 is substantially circular truncated conical. The expansion part 3 has a cross-section with a linear dimension such as a diameter along a plane being perpendicular to a longitudinal axis of the retaining part 2. The diameter of the expansion part 3 is increasingly larger than a linear dimension such as a diameter of the retaining part along the same plane perpendicular to a longitudinal axis of the retaining part 2.

In the second configuration shown in Fig. 4, an outer cross-sectional extension of the recess 8 may have expanded so that the outer cross-sectional extension of the recess 8 is substantially equal to the outer cross-sectional extension of the first cross-sectional extension of the retaining part 2. Alternatively, the outer cross-sectional extension of the recess 8 does not change between the first configuration shown in Fig. 3 and the second configuration shown in Fig. 4.

Fig. 5 shows a stent 1 in a second configuration, where the cross-sectional extension of the expandable part 3 is larger than the cross-sectional extension of the retaining part 2 and where the cross-sectional extension is constant, or substantially constant, along the longitudinal length of the expandable part 3, i.e. from left to right in the figure.

In the embodiment shown in Fig. 5, in general terms according to the scope of the invention, the expansion part 3 is substantially circular cylindrical. The expansion part has an outer cross-section with a linear dimension such as a diameter along a plane being perpendicular to a longitudinal axis of the retaining part 2. The diameter of the expansion part 3 is substantially larger than a linear dimension such as a diameter of the retaining part along the same plane perpendicular to a longitudinal axis of the retaining part 2.

Fig. 6 shows a stent 1 in a first configuration corresponding to the stent shown in Fig. 3 except from the configuration of the windings of the expandable part 3. The expandable part 3 in Fig. 6 is formed by alternately reversing the propagation of the windings of the expandable part 3 clockwise and counter-clockwise. The retaining part 2 may as shown, or may not, have a recess 8 for taking up the expandable part when being in the first configuration.

In Fig. 6 the expandable part 3 is constituted by at least one first section of at least one helical winding 5 in a clockwise direction and at least one second section of at least one helical winding 6 in a counter-clockwise direction, wherein each of the first and second sections are radially expandable so that during expansion, the first section(s) will rotate in counter-clockwise direction and the second section(s) will rotate in clockwise direction.

Fig. 7 shows the stent 1 of Fig. 6 in the second configuration, where the cross- sectional extension of the expandable part 3 comprising first and second sections is larger than the cross-sectional extension of the retaining part 2, and where the cross-sectional extension is substantially constant along the longitudinal extension of the expandable part 3.

In the embodiment shown in Fig. 7, in general terms according to the scope of the invention, the expansion part 3 is substantially circular cylindrical. The expansion part 3 has an outer cross-section with a linear dimension such as a diameter along a plane being perpendicular to a longitudinal axis of the retaining part 2. The diameter of the expansion part 3 is substantially larger than a linear dimension such as a diameter of the retaining part 2 along the same plane perpendicular to a longitudinal axis of the retaining part 2.

Fig. 8 shows a stent 1 in a first configuration corresponding to the stent shown in Fig. 3 except from the windings of the expandable part 3. The expandable part 3 in Fig. 8 is formed by longitudinal extending U-turns of wire spaced apart from each other so that the U-turns overlap the retaining part 3 by at least partially surround the retaining part 2. The retaining part 2 may as shown, or may not, have a recess 8 for taking up the expandable part 3 when being in the first configuration.

Fig. 9 shows the stent 1 of Fig. 8 in the second configuration where the outer cross-sectional extension of the U-turns forming the expandable part 3 increases along the longitudinal direction to substantially forming generatrices of a truncated square conical configuration as shown, alternatively a hyperboloid, or a parabolic, or a polygonal truncated conical configuration.

In the embodiment shown in Fig. 9, the expansion part 3 is substantially square truncated conical. The expansion part 3 has a cross-section with a linear dimension such as a diagonal along a plane being perpendicular to a longitudinal axis of the retaining part 2 The diagonal of the expansion part is increasingly larger than a linear dimension such as a diameter of the retaining part along the same plane perpendicular to a longitudinal axis of the retaining part 2.

In the embodiments shown in Figs. 3-9, the retaining part 2 is shown having substantially the same cross-sectional area along the entire longitudinal extension of the retaining part. When the stent 1, when being in the first configuration as shown in Fig. 3, Fig. 6 and Fig. 8, is inserted into and has been positioned in the intraprostatic urethra, and the stent subsequently is transformed to the second configuration by expansion of the expandable part 3 of the stent 1, the stent 1 will maintain its position without migrating, and will allow urinary passage without obstructing the valve-function of the sphincter.

Figs. 1Oa-IOd show stents 1 in second configurations corresponding to the stents illustrated in Figures 4, 5, 7 and 9. The stents in Figs 1Oa-IOd differ from the stents shown in figures 4, 5, 7 and 9 by having curvatures 4. In the embodiments shown, the retaining part 2 of the stent 1 is straight in the first configuration, and the curvature 4 is only provided in the second configuration. In alternative embodiments not shown, the retaining part 2 of the stent 1 is already provided with the curvature 4 in the first configuration.

Figs. 11a, lib and lie show examples of a prior art cylindrical stent 1 inserted in a body cavity 31. In Fig 11a, the conic shaped body cavity 31e affects the stent 1 with forces 32. The resulting longitudinal component 33 of the force 32 may act to displace the stent 1 in a longitudinal direction causing migration of the stent 1 from left to right in the figure. In Fig. lib the stent 1 extends into an open body cavity where, in particular, a force 32 at the boundary between the narrow body cavity and the open body cavity acts to displace the stent 1 into the open body cavity. Fig. lie shows how muscular contractions 34 in the walls of the body cavity affects the stent 1 with forces 32 acting to displace the stent 1 in direction of the contractions.

Other examples of body cavities introducing migration forces are body cavities with flow of gas or liquid in one direction, or body cavities affected by external forces like gravity.

Fig. 12 show a stent 1 according to one embodiment of the invention and having a truncated conical shape. The truncated conical shape will apply a radial force onto the walls of the body cavity into which the stent is inserted and placed. Thus, the body cavity will also obtain a truncated conical shape along at least part of the longitudinal extension, where the stent is placed. When the body cavity 31 conforms to the stent 34, any radial force acting from the body cavity 31 to the stent 34 will result in a force 35 with a longitudinal component from right to left in the figure.

Accordingly, the stent 1 having a truncated conical configuration is counter-acting not only the radial components of resulting forces acting on the stent, as generally is the technical effect of a stent, but also the longitudinal components of resulting forces 33 acting on the retaining part of the stent. Therefore, no or at least only a limited magnitude of resulting force will act in the longitudinal direction, thereby avoiding or at least minimising the risk of displacement of the stent in a longitudinal direction.

If the stent 34 shown in Fig. 12 is placed in any of the body cavities shown in fig. lla-llc, the longitudinal force from left to right illustrated in the figures lla-llc may be counteracted by the longitudinal force from right to left, illustrated in fig. 12. By shaping the entire length, or part of the length, of the retaining part 2 to have a truncated conical configuration so that the stent 1 is capable of counteracting any longitudinal forces resulting from natural or applied forces from the walls of the body cavity to the stent, migration of the stent 1 may be avoided, or may at least be reduced, since resulting forces acting to displace the stent 1 in a longitudinal direction are eliminated or at lest minimised.

Fig. 13a-13b show examples of prior art stents having either a cylindrical expansion part, see fig. 13a, extending in prolongation of the retaining part, or a truncated conical expansion parts see fig. 13b, also extending in prolongation of the retaining part,

As illustrated by the arrows, if the retaining part is subjected to forces in the longitudinal direction, the forces will initiate migration of the retaining part. Due to the expansion part, the migration is intended for being avoided or at least minimised. However, not only the helical windings of the retaining part, but also the helical windings of the expansion part will be subjected to the migrating forces in the longitudinal direction. Because the forces are also acting on the helical windings of the expansion part, possibly along the transition between the retaining part and the expansion part, the windings of the expansion will be separated, and the expansion part may rewind so that the windings of the expansion part at some time will end up not having any windings at all or at least the number of windings, and thus the avoidance towards migration, will be reduced. Accordingly, the result of the migrating forces may be that the expansion part is partly or perhaps completely rewound and further migration of the stent is no longer avoided.

Additionally a separation of the windings of the expansion part may result in a longitudinal movement of the fixing point(s) of the expansion part, resulting in a step-wise migration of the stent.

Fig. 14a-14b show examples of stents according to the second embodiment of the invention and having either a cylindrical expansion part, see fig. 14a, fully surrounding a limited longitudinal extension of the retaining part, or a truncated conical expansion part, see fig. 14b, also fully surrounding a limited longitudinal extension of the retaining part,

As illustrated by the arrows, if the retaining part is subjected to forces in the longitudinal direction, the forces will initiate migration of the retaining part. Due to the expansion part, the migration is intended for being avoided or at least minimised. However, not only the helical windings of the retaining part, but also the helical windings of the expansion part will be subjected to the migrating forces in the longitudinal direction.

Because the forces are also acting on the helical windings of the expansion part, possibly along the transition between the retaining part and the expansion part, the windings of the expansion will be forced together, and the expansion part will not rewind. On the contrary, the radial extension of the expansion part will at least be maintained, or as shown in fig. 13d, the radial extension of the expansion part may be increased, due to the forces acting between the windings of the expansion part. Accordingly, the result of the migrating forces will at least be that the expansion part is at least kept in the same expanded state, and further migration of the stent is still avoided by the expansion part. However, the result of the migrating forces may even be that the radial extension of the expansion part is increased, and further migration of the stent will be even further avoided.

Fig. 14a-14d shows the technical effect of the second embodiment of the invention, when the expansion part of the stent is at least partly overlapping the retaining part of the stent along the at least limited longitudinal extension of the retaining part. The possible migration forces shown by arrows along the retaining part of the stent will provide a self-locking effect of the stent by inducing increased abutment between the helical coils and by inducing further expansion of the expansion part thus activated by the migration forces.

The self-locking effect is obtained by the extension part, as shown by the curved arrows, expanding from one expanded state, where no or only minor migration forces are acting on the retaining part, to another more expanded state, where greater migration forces than when the expansion part is in the one state, are acting on the retaining part. The more expanded state will increase the pressure towards the walls of the body cavity, thereby even further preventing, or at least even further reducing, migration of the stent.

Figs. 15a-15d show examples of stents 1 in a second configuration with expansion parts, possibly expandable parts, corresponding to the stents shown in Figs. 4, 5, 7, 9 and 1Oa-IOd. The entire longitudinal extension of the retaining part, or at least part of the longitudinal extension of the retaining part, is provided with a truncated conical configuration. Accordingly, since the stents shown in Figs. 13a- 13d are conically shaped, migration of the stents can be prevented, or at least reduced, partly due to the expansion parts 3 and partly due to the conical configurations of the retaining part.

Figs. 16a-16d show stents 1 in their first configuration with conical sections along at least a limited longitudinal extension of the retaining part, the stents shown in Figs, 16a-16d corresponding to the stents shown with expanded expansion parts 3 in Figs. 15a-15d.

The cross-sectional extension of the retaining part 2 in the first configuration may be smaller than the cross-sectional extension in the second configuration. Similarly, the cross-sectional extension of the retaining part may, in the first configuration, be constant along the longitudinal extension, whereas, in the second configuration, the cross-sectional extension of the retaining part may have a conical configuration.

Fig. 17a is cross-sectional viewed along a longitudinal axis of the stent of a prior art stent (like the Memokath stent from PNN medical A/S). The stent has a circular cylindrical retaining part and a truncated conical expandable part. The prior art stent is preferably made from helically wound wire, said wire preferably being made of Shape Memory Alloy.

Fig. 17b-17c are different shapes of stents having an improved performance compared to prior art stents as the one shown in fig. 17a in relation to avoiding, or at least reducing, the risk of the stent migration of the stent along the body cavity.

Fig. 17b is a stent having a limited part of the retaining part having a truncated conical shape. The retaining part has a proximate end to the left in the drawing, said proximate end having a cylindrical extension. The proximate end passes onto the truncated conical part being an intermediate part of the retaining part, and the truncated conical part passes into a distant end, also having a cylindrical extension with a smaller cross-sectional extension than the cross-sectional extension of the proximate end. An expansion part extends in prolongation of the retaining part and has a truncated conical shape. The expansion part forms an obtuse angle α with the longitudinal axis of the stent. In the embodiment shown, the acute angle is approximately 135 degrees.

Fig. 17c is a stent having a retaining part with a cylindrical shape. In the embodiment shown, the cylindrical shape has the same cross-sectional extension along the entire longitudinal extension of the retaining part. An expansion part overlaps at least a limited longitudinal extension of the retaining part and the expansion part has a truncated conical shape fully surrounding the limited extension of the retaining part. The expansion part forms an acute angle β with the longitudinal axis A of the stent. In the embodiment shown, the acute angle is approximately 45 degrees. Fig. 17d is a stent also having a limited part of the retaining part having a truncated conical shape. The retaining part also has a proximate end to the left in the drawing, said proximate end having a cylindrical extension. The proximate end passes onto the truncated conical part being an intermediate part of the retaining part, and the truncated conical part passes into a distant end, also having a cylindrical extension with a smaller cross-sectional extension than the cross- sectional extension of the proximate end. An expansion part overlaps at least a limited longitudinal extension of the retaining part and has a truncated conical shape fully surrounding the limited extension of the retaining part. The expansion part forms an acute angle β with the longitudinal axis A of the stent. In the embodiment shown, the acute angle is approximately 45 degrees.

The truncated conical configurations of the retaining part in Fig. 17b and Fig. 17c have different cross-sectional dimensions Cm-Cn along different planes Pl-Pn, said planes Pm-Pn being perpendicular to the longitudinal axis A. The cross- sectional dimensions Cm-Cn are increasing continuously along the longitudinal axis A of the stent.

The expansion part overlapping the limited longitudinal extension of the retaining part in Fig. 17c and Fig. 17d has different cross-sectional dimensions D along a plane Px, said plane Px being perpendicular to the longitudinal axis A. The cross- sectional dimension D is larger than cross-sectional dimension d of the retaining part along the same plane Px.

The stent, according to the second embodiment of the invention, is in all embodiments shown as having only one expansion part situated in one end of the stent and only one retaining part constituting the remainder of the stent. The stent 1 may in other embodiments according to the present invention comprise a plurality of lumen retaining parts 2 and/or a plurality of expansion parts 3 distributed along the longitudinal length of the stent 1.

In one embodiment, the stent 1 may have an expansion part 3 situated in both ends of the stent and may have one retaining part 2 situated between the expansion parts 3. In another embodiment, the stent 1 may have a retaining part 2 situated in both ends of the stent and may have one expansion part 3 situated between the retaining parts.

The stents of the present invention is preferably made from a Shape Memory Alloy such as Nickel-Titanium-alloy (Ni-Ti Alloy), but may also be made from other Shape Memory Alloys such as Gold-Cadmium-alloy (Au-Cd Alloy), Copper-Zink- alloy (Cu-Zn Alloy), Indium-Titanium-alloy (In-Ti Alloy), Copper-Zink-Silver-alloy (Cu-Zn-Al Alloy) or other metal alloys exhibiting shape memory characteristics.

Preferably, the Shape Memory Alloy chosen has a shape memory effect above normal body cavity temperature so that the shape of the second configuration has to be inflicted thermally for obtaining the second configuration of the stent. Alternatively, the Shape Memory Alloy chosen may have super-elastic effect at normal body cavity temperature.

In other embodiments of the present invention, the stent may be made from a material being plastically deployable at body cavity temperature such as stainless steel. In even other embodiments of the present invention, the stent may be made of a combination of different materials in order to suit a specific application of the stent. Thus, a combination of different Shape Memory Alloys may be envisaged, or a combination of one or more Shape Memory Alloys and one or more plastically deployable materials may be envisaged.

The Shape Memory Alloy may be an alloy with a transition temperature at normal body cavity temperature of the human being or animal, the body cavity for which the stent 1 is intended. Such an embodiment may be applied where the body cavity is relatively large or is very flexible so that a transformation is possible from the first configuration of the stent to the second configuration of the stent already during insertion. The term Shape Memory Alloy is defined as a metal having transformation from one crystalline phase to another crystalline phase, induced by heating or mechanical stress to the material.

In an alternative embodiment of the stent, containing both a truncated conical configuration along at last part of the retaining part and one or more expandable parts, the Shape Memory Alloy has different transition temperatures defining the activation of the shape of the retaining part and expansion respectively. In this embodiment of the invention the interval of the transition phase of the Shape Memory Alloy enabling activation of the shape of the retaining part is present at a temperature below normal body cavity temperature, of the human being or animal, the body cavity for which the stent is intended, and the interval of the transition phase of the Shape Memory Alloy enabling activation of the expansion of the expandable part is present at a temperature above normal body cavity temperature, of the human being or animal, the body cavity for which the stent is intended.

Hereby the shape of the retaining part may be obtained already before or during insertion of a stent, without applying additional heating energy from outside the cavity. The expansion of the expandable part may subsequently be activated by application of heat.

If the Shape Memory Alloy is a Ni-Ti Alloy the crystalline phase in the first configuration of the material is martensite, and the crystalline phase in the second configuration of the material is austenite. The transformation occurs at a certain temperature range (Austenite Start to Austenite Finish (AS to AF)). Within this temperature range (AS to AF) the expansion of at least part of the stent 1 is initiated and the expansion terminates, when the martensite is transformed into austenite. The stent 1 "remembers" at this temperature range (AS to AF) its original shape, i.e. the pre-formed design that the stent 1 was given during manufacture, before the stent 1 was transformed to the first configuration for enabling insertion into a body cavity.

At another temperature range (Martensite Start to Martensite Finish (MS to MF)) the alloy reverts to the martensite phase. Below this other temperature (MF), the stent 1 is plastically deformable by hand, and the stent 1 may therefore be deformed inside the body cavity. The shape of the deformed stent inside the body cavity may be maintained after deformation, and if the deformed stent has a shape such as a helix, but being elongated, or even having the shape of a elongate wire, and thus having, in the deformed configuration, a reduced cross- sectional area compared to the cross-sectional area in the second configuration, the stent may be retracted through any natural body orifice into which the stent 1 was inserted. Alternatively the stent 1 may be retracted through another natural body orifice than the one through which it was inserted.

The term Shape Memory Alloy may also be a Ni-Ti alloy having super-elastic properties at a certain temperature, such as about 37°C and plasticity at another temperature, such as below 0⁰C. By the wording super-elastic properties is meant an alloy which is elastically deformable until a high level of strain (up to approximately 5%-10%)

The human or animal normal body cavity temperature may vary from human being to human being and from animal to animal. Also, the body cavity temperature may vary depending on which organ the stent is to be inserted into, However, one human being or animal normally has one average body temperature such as around 37 ⁰C for a human being. In another aspect of the present invention the stent 1 may be made of a Shape Memory Alloy having a transition temperature between 37°C and 50⁰C. It is important that the transition temperature in most applications is substantially above the body temperature in that it is not convenient that the stent 1 transforms from the first configuration to the second configuration before the stent 1 is in place inside the body cavity.

The stents of the present invention are primarily produced by using at least one of the different production principles following below, resulting in different possibilities for obtaining the truncated conical configuration and/or for obtaining the expansion of at least part of the stent 1, when it is placed in the desired position inside the body cavity:

1) The stent 1 may in one embodiment be produced in Shape Memory Alloy such as Ni-Ti with a transition temperature above body cavity temperature, in which the transition temperature is the temperature at which the material, of the stent 1, changes from martensite phase to austenite phase. The stent 1 is shaped into a non-curvature and/or a non-truncated conical configuration and/or a low-cross- sectional configuration, in a low temperature state having a martensite structure. After insertion of the stent 1 to its desired position, heat is applied to the stent, thereby elevating the temperature of the stent 1 to above the transition temperature. This results in a transformation of the material from martensite phase to austenite phase causing the stent 1 to change to the second configuration either having a truncated conical configuration with or without a curvature of the retaining part 2 or having an expanded expandable part 3 or having both a truncated conical configuration and an expanded part.

2) The stent 1 may in another embodiment be produced in Shape Memory Alloy such as Ni-Ti, which is super-elastic at body cavity temperature. The stent 1 is shaped into a non-curvature and/or a non-truncated conical configuration and/or a low-cross-sectional configuration and this low-cross-sectional configuration is mechanically retained during the insertion of the stent 1. After insertion of the stent 1 to its desired position, the mechanical retaining of the stent 1 in the low- cross-sectional configuration is released causing the stent 1 to change to the second configuration having a truncated conical configuration with or without a curvature of the retaining part 2 or having an expanded expandable part 3 or having both a truncated conical configuration and an expanded part.

3) Additionally, the stent 1 may also be produced in a material that is plastically deformable, such as stainless steel. The stent 1 is shaped into a non-curvature and/or a non-truncated conical configuration and/or a low-cross-sectional configuration. After inserting the stent 1 to its desired position the stent 1 is plastically deformed to a high-diameter configuration by applying a pressure on the inside wall of the stent 1. This may be done by inflating a balloon inside the stent 1.

The three different principles of transformation from the first configuration to the second configuration are illustrated in the figures based on a stent 1 having a circular cross-section. In other embodiments of the present invention, the stent 1 may have another cross-sectional configuration such as oval or polygonal. However, the different principles of transformation from the first configuration to the second configuration may still be employed to such non-circular cross- sections.

According to an embodiment of the present invention the stent 1 consists of preferably a number of helical windings of only one wire. A stent constituted by only one wire is of particular advantage, when the stent 1 is to be removed or retracted from the body cavity. If the stent is made of a Shape Memory Alloy, and when the temperature of the wire-material of the stent is reduced to below the transition temperature, the stent 1 may be easily removed from the body cavity by grasping any part of the wire and subsequently pulling the wire out of the cavity as one substantial straight wire. This is especially applicable when the stent 1 is produced in Shape Memory Alloy with a transition temperature above the body cavity temperature of the human being or animal in which the stent 1 has been inserted.

The present invention may be provided as part of a delivery device of the stent system according to the invention, said delivery system may comprise a marker element being optically, tactilely, photographically, electronically or radiologically visible from outside the body cavity for being capable of obtaining a correct physical placement of the stent 1.

Alternatively, the present invention may relate to a stent as such according to any of the embodiments shown and described, and further comprising a marker element, on the stent itself, being optically, tactilely, photographically, electronically or radiologically visible from outside the body cavity for being capable of obtaining a correct physical placement of the stent 1.

A correct physical placement of the stent 1 may be a correct longitudinal placement of the stent in the body cavity or a correct rotational placement of the stent in the body cavity or both a correct longitudinal placement and a correct rotational placement of the stent in the body cavity. A correct longitudinal placement of the stent is essential when the stent has an expandable part intended for abutment with a specific part of internal walls of the body cavity, A correct rotational placement of the stent is essential when the stent is provided with a curvature intended for conforming to a corresponding curvature of the body cavity.

For all embodiments of the invention, the retaining part and/or the expansion part, if an expansion part is provided, may in further embodiments of the invention have another configuration than a helically coiled wire, such as a web- structure, a woven structure made from one or more wires or filaments, or the retaining part may be constituted by a perforated tubular body. The web-structure may be constituted by a tubular body provided with cut-outs. The physical structure of the stent, if made from wire, can be made from wire wound in different patterns, such as cross-patterns, knitting-patterns or similar.

Claims

1. A stent for insertion into and placement inside a body cavity of a human being or an animal, said stent capable of having a first configuration, and said stent capable of having a second configuration, wherein said stent comprises

- at least one retaining part for retaining a lumen inside the body cavity, and

- wherein the retaining part, at least in the second configuration, has a substantially truncated, conical configuration along at least a limited longitudinal extension of the retaining part.

2. A stent according to claim 1, where the stent, at least in the second configuration, has a substantially circular truncated conical configuration along the at least limited longitudinal extension of the retaining part.

3. A stent according to claim 1, where the stent, at least in the second configuration, has a substantially polygonal truncated conical configuration along the at least limited longitudinal extension of the retaining part.

4. A stent according to any of the preceding claims, where the substantially truncated conical configuration is geometrically defined as

- a cross-sectional dimension (Cm) along a plane (Pm) perpendicular to a longitudinal axis (A) of the retaining part, and

- a cross-sectional dimension (Cm-Cn) of the retaining part, at least along a limited longitudinal extension of the retaining part, increasing continuously within parallel planes (Pm-Pn) of the cross-sectional dimension,

- said parallel planes (Pm-Pn) each extending perpendicular to the longitudinal axis (A) of the retaining part and successively extending along the at least limited longitudinal extension of the retaining part.

5. A stent according to any of the preceding claims, where the first configuration and the second configuration are substantially the same, i.e. the retaining part, both in the first configuration and in the second configuration, having a substantially truncated, conical configuration along at least a limited longitudinal extension of the retaining part

6. A stent according to any of the preceding claims, where the stent, at least in the second configuration, has a curvature.

7. A stent according to any of the preceding claims, where the retaining part of the stent is expandable from a first low-cross-sectional extension to a second increased cross-sectional extension.

8. A stent according to any of the preceding claims, wherein the stent also comprises at least one expansion part for fixing a position of the stent inside the body cavity, said expansion part having a cross-section viewed in a plane parallel with the longitudinal axis,

- said cross-section, at least in the second configuration, forming an obtuse angle or an acute angle with the longitudinal axis along the at least limited longitudinal extension of the retaining part.

9. A stent according to any of the preceding claims, wherein the stent also comprises at least one expansion part for fixing a position of the stent inside the body cavity, and where the expansion part is expandable between the first configuration and the second configuration, and

- where the expandable part is constituted by at least one first section of at least one helical winding in a clockwise direction and at least one second section of at least one helical winding in a counter-clockwise direction, each of said first and second at least one section being radially expandable so that during expansion, the at least one first section will be rotating in counter-clockwise direction and the at least one second section will be rotating in clockwise direction.

10. A stent according to any of claims 1-8, wherein the stent also comprises at least one expansion part for fixing a position of the stent inside the body cavity, and where the first configuration and the second configuration are substantially the same, and

- where the expansion part is constituted by at least one first section of at least one helical winding in a clockwise direction and at least one second section of at least one helical winding in a counter-clockwise direction.

11. A stent according to any of claims 1-9, wherein the stent also comprises at least one expansion part for fixing a position of the stent inside the body cavity, said expansion part having a cross-section viewed in a plane parallel with the longitudinal axis, and - said cross-section, only in the second configuration, forming an obtuse angle or an acute angle with the longitudinal axis along the at least limited longitudinal extension of the retaining part.

12. A stent according to claim 11, said angle of the expansion part being an acute angle being between 0 degrees and 90 degrees, preferably between 30 and 60 degrees, more preferred between 30 and 45 degrees.

13. A stent according to claim 11, said angle of the expansion part being an obtuse angle being between 90 degrees and 180 degrees, preferably between 120 and 150 degrees, more preferred between 135 and 150 degrees.

14. A stent according to any of the preceding claims, wherein at least part of the whole stent is formed by a number of helical windings of at least one wire.

15. A stent according to any of the preceding claims, wherein at least part of the retaining part is formed by a number of helical windings of at least one wire.

16. A stent according to any of claims 8-15, wherein at least part of the expansion part is formed by a number of helical windings of at least one wire.

17. A stent according to any of the preceding claims, where at least part of the stent is configured by one of the following structures: a web-structure, a woven structure made from one or more wires or filaments, or by a perforated tubular body, and where the possible web-structure preferably is constituted by a tubular body provided with cut-outs and where the possible woven structure preferably is made from wire wound in different patterns.

18. A stent according to any of claims 8-17, wherein the stent has a transition between the expansion part and the retaining part,

- said transition in the first configuration of the stent capable of maintaining a mutual positional relationship between the retaining part and the expansion part, and

- said transition in the second configuration capable of maintaining substantially the same mutual positional relationship between the retaining part and the expansion part.

19. A stent according to claim 18, where the transition, in the first configuration, capable of maintaining a mutual rotational relationship between the retaining part and the expansion part, and wherein said transition, in the second configuration, capable of maintaining substantially the same mutual rotational relationship between the retaining part and the expansion part.

20. A stent according to any of the preceding claims, wherein the expansion part in the first configuration has a longitudinal extension, and where the expansion part in the second configuration has substantially the same longitudinal extension as in the first configuration.

21. A stent according to any of the claims 14-16, wherein at least part of the retaining part is formed by a number of helical windings of at least one wire and wherein the mutual distance between the windings is less than 5 mm, preferably less than 3 mm, more preferred less than 1 mm.

22. A stent according to any of the preceding claims, wherein the material from which the stent is made in the first configuration has a first phase and in the second configuration has a second phase, and where a transition phase of the material is present between the first configuration and the second configuration, and where introduction of the transition between the first configuration and the second configuration may be effected by heating the stent.

23. A stent according to any of claims 1-21, wherein the material from which the stent is made in the first configuration has a first phase and in the second configuration has a second phase, and where a transition phase of the material is present between the first configuration and the second configuration, and where introduction of the transition between the first configuration and the second configuration may be effected by mechanical release of the stent.

24. A stent according to any of the preceding claims, wherein the retaining part has a first cross-sectional extension, when configured in the first configuration, and where said first cross-sectional extension is substantially the same as a second cross-sectional extension of the retaining part, when being configured in the second configuration.

25. A stent according to any of the preceding claims, wherein a central axis of the expansion part and a central axis of the retaining part, when the stent is in the second configuration, are intersecting at a passing between the expandable part and the retaining part.

26. A stent according to any of the preceding claims, wherein a central axis of the expansion part and a central axis of the retaining part, when the stent is in the second configuration, are off-set and not intersecting at a passing between the expandable part and the retaining part.

27. A stent according to any of the preceding claims, wherein the material from which at least part of the stent is made is a Shape Memory Alloy metal having a transition phase above normal body cavity temperature of at the human being or animal, the body cavity for which the stent is intended.

28. A stent according to claim 27, wherein the material is a Shape Memory Alloy metal having

- a transition phase, for activation of the configuration of the truncated conical part, above normal body cavity temperature of the human being or animal, the body cavity for which the stent is intended, preferably between 37°C and 75°C, more preferred between 37°C and 60⁰C, most preferred between 37°C and 45°C.

29. A stent according to any of the preceding claims, wherein the material is a super-elastic metal, said metal being super-elastic at normal body cavity temperature of a human being or animal, the body cavity for which the stent is intended.

5

30. A stent according to any of the preceding claims, wherein the stent is made of a material being plastically deformable at normal body cavity temperature of a human being or animal, the body cavity for which the stent is intended.

10 31. A stent according to any of the preceding claims, wherein the stent itself comprises a marker element being detectable from outside the body cavity by at least one of the following detections: optically, tactilely, photographically, electronically or radiologically for being able of obtaining a correct physical placement of the stent in the body cavity.

15

32. A stent according to claim 31, where the marker element is capable of marking a rotational orientation of the stent in respect of a longitudinal axis of the stent.

20 33. A stent system according to claim 31 or claim 32, where the marker element is capable of marking an axial orientation of the stent in respect of a longitudinal axis of the stent.

34. A stent for insertion into and for placement inside a body cavity of a human 25 being or an animal, said stent capable of having a first configuration, and said stent capable of having a second configuration, wherein said stent comprises

- at least one retaining part for retaining a lumen inside the body cavity, and

- at least one expansion part for fixing a position of the stent inside the body 30 cavity, and

35. A stent according to claim 34, where the expansion part of the stent is partly surrounding the retaining part of the stent along the at least limited longitudinal extension of the retaining part.

36. A stent according to claim 34, where the expansion part of the stent is fully surrounding the retaining part of the stent along the at least limited longitudinal extension of the retaining part.

37. A stent according to any of claims 34-36, where the expansion part at least partly overlapping the retaining part is geometrically defined as

- a the expansion part having a linear dimension (D) measured along a plane (Px) perpendicular to a longitudinal axis (A) of the retaining part,

- said linear dimension (D) of the expandable part being larger than a linear dimension (d) of the retaining part measured along the same plane (Px) perpendicular to the longitudinal axis (A) of the retaining part.

38. A stent according to any of claims 34-37, wherein the cross-section of the expansion part, viewed in a plane parallel with the longitudinal axis of the retaining part, in the second configuration, forms a final acute angle with the longitudinal axis of the retaining part, wherein the final acute angle is different than in the first configuration of the stent.

39. A stent according to any of claims 38, said angle of the expansion part being an acute angle being between 0 degrees and 90 degrees, preferably between 30 and 60 degrees, more preferred between 30 and 45 degrees.

40. A stent according to any of claims 34-39, wherein the retaining part has a first cross-sectional extension, when configured in the first configuration, and where said first cross-sectional extension is substantially the same as a second cross- sectional extension of the retaining part, when being configured in the second configuration.

41. A stent according to any of claims 34-40, where the stent, at least in the second configuration, has a curvature.

42. A stent according to any of claims 34-41, wherein at least the expansion part is expandable between the first configuration and the second configuration, and

- where the expandable part is constituted by at least one first section of at least one helical winding in a clockwise direction and at least one second section of at

5 least one helical winding in a counter-clockwise direction, each of said first and second at least one section being radially expandable so that during expansion, the at least one first section will be rotating in counter-clockwise direction and the at least one second section will be rotating in clockwise direction.

10 43. A stent according to any of claims 34-41, wherein the first configuration and the second configuration, of at least the expansion part, are substantially the same, and

- where the expansion part is constituted by at least one first section of at least one helical winding in a clockwise direction and at least one second section of at

15 least one helical winding in a counter-clockwise direction.

44. A stent according to any of claims 34-43, wherein at least part of the longitudinal extension of the retaining part of the stent has a cross-sectional extension in the second configuration, said cross-sectional extension being smaller

20 than the normal cross-sectional extension of the body cavity along said longitudinal extension of the retaining part.

45. A stent according to any of claims 34-44, wherein at least part of the whole stent is formed by a number of helical windings of at least one wire. 5

46. A stent according to any of claims 34-45, wherein at least part of the retaining part is formed by a number of helical windings of at least one wire.

47. A stent according to any of claims 34-56, wherein at least part of the

30 expansion part is formed by a number of helical windings of at least one wire.

48. A stent according to any of the preceding claims, where at least part of the stent is configured by one of the following structures: a web-structure, a woven structure made from one or more wires or filaments, or by a perforated tubular 5 body, and where the possible web-structure preferably is constituted by a tubular body provided with cut-outs and where the possible woven structure preferably is made from wire wound in different patterns.

49. A stent according to any of claims 34-48, wherein the stent has a transition between the expansion part and the retaining part, and wherein said transition in the first configuration of the stent is capable of maintaining a mutual positional relationship between the retaining part and the expansion part, and wherein said transition in the second configuration is capable of maintaining substantially the same mutual positional relationship between the retaining part and the expandable part.

50. A stent according to claim 40, where the transition in the first configuration is capable of maintaining a mutual rotational relationship between the retaining part and the expansion part, and wherein said transition in the second configuration is capable of maintaining substantially the same mutual rotational relationship between the retaining part and the expansion part.

51. A stent according to any of claims 34-50, wherein the windings of the retaining part propagate clockwise or counter-clockwise, and wherein the winding direction remains clockwise or counter-clockwise when passing a transition from the retaining part to the expansion part, so that the windings of the expandable part propagate in the same direction as the windings of the retaining part.

52. A stent according to any of claims 34-50, wherein the windings of the retaining part propagate clockwise or counter-clockwise, and wherein the winding direction changes to counter-clockwise or clockwise when passing a transition from the retaining part to the expansion part, so that the windings of the expandable part propagate in the opposite direction as the windings of the retaining part.

53. A stent according to any of claims 34-52, wherein the expansion part, in the first configuration, has a longitudinal extension, and where the expansion part, in the second configuration, has substantially the same longitudinal extension as in the first configuration.

54. A stent according to any of claims 34-53, wherein the whole stent, in the first configuration, has a longitudinal extension, and where the whole stent, in the second configuration, has substantially the same longitudinal extension as in the first configuration.

55. A stent according to any of claims 45-47, wherein a mutual distance between the windings is less than 5 mm, preferably less than 3 mm, more preferred less than 1 mm.

56. A stent according to any of claims 34-55, wherein the material from which the stent is made in the first configuration has a first phase and in the second configuration has a second phase, and where a transition phase of the material is present between the first configuration and the second configuration, and where introduction of the transition between the first configuration and the second configuration may be effected by heating the stent.

57. A stent according to any of claims 34-55, wherein the material from which the stent is made in the first configuration has a first phase and in the second configuration has a second phase, and where a transition phase of the material is present between the first configuration and the second configuration, and where introduction of the transition between the first configuration and the second configuration may be effected by mechanical release of the stent.

58. A stent according to any of claims 34-57, wherein the retaining part has a first cross-sectional extension, when configured in the first configuration, and where said first cross-sectional extension is substantially the same as a second cross- sectional extension of the retaining part, when configured in the second configuration.

59. A stent according to any of claims 34-58, wherein a central axis of the expansion part and a central axis of the retaining part, when the stent is in the second configuration, are intersecting at a passing between the expansion part and the retaining part.

60. A stent according to any of claims 34-58, wherein a central axis of the expansion part and a central axis of the retaining part, when the stent is in the second configuration, are off-set and not intersecting at a passing between the expansion part and the retaining part.

61. A stent according to any of claims 34-60, wherein the material from which at least part of the stent Is made is a Shape Memory Alloy metal having a transition phase above normal body cavity temperature of the human being or animal, the body cavity for which the stent is intended.

62. A stent according to claim 61, wherein the material is a Shape Memory Alloy metal having

- a transition phase, for activation of the configuration of the expandable part, above normal body cavity temperature of the human being or animal, the body cavity for which the stent is intended, preferably between 37°C and 75°C, more preferably between 37°C and 60⁰C, most preferred between 37°C and 45°C.

63. A stent according to any of claims 34-62, wherein the material is a super- elastic metal, said metal being super-elastic at normal body cavity temperature of the human being or animal, the body cavity for which the stent is intended.

64. A stent according to any of claims 34-63, wherein the stent is made of a material being plastically deformable at normal body cavity temperature of the human being or animal, the body cavity for which the stent is intended.

65. A stent according to any of claims 34-64, wherein the stent itself comprises a marker element being detectable from outside the body cavity by at least one of the following detections: optically, tactilely, photographically, electronically or radiologically for being able of obtaining a correct physical placement of the stent in the body cavity.

66. A stent according to claim 65, where the marker element is capable of marking a rotational orientation of the stent in respect of a longitudinal axis of the stent.

67. A stent system according to claim 65 or claim 66, where the marker element is capable of marking an axial orientation of the stent in respect of a longitudinal axis of the stent.