Patent Description:
Endovascular delivery catheter assemblies are used to implant prosthetic devices, such as a prosthetic heart valve, at locations inside the body that are not readily accessible by surgery or where less invasive surgery is desirable. For example, aortic, mitral, tricuspid, and/or pulmonary prosthetic valves can be delivered to a treatment site using minimally invasive surgical techniques, including transcatheter delivery methods.

An introducer sheath can be used to safely introduce a delivery apparatus into a patient's vasculature (e.g., the femoral artery). An introducer sheath generally has an elongated sleeve that is inserted into the vasculature and a housing that contains one or more sealing valves that allow a delivery apparatus to be placed in fluid communication with the vasculature with minimal blood loss. A conventional introducer sheath typically requires a tubular loader to be inserted through the seals in the housing to provide an unobstructed path through the housing for the prosthetic implant, such as a heart valve mounted on a balloon catheter. A conventional loader extends from the proximal end of the introducer sheath, and therefore decreases the available working length of the delivery apparatus that can be inserted through the sheath and into the body.

Conventional methods of accessing a vessel, such as a femoral artery, prior to introducing the delivery system include dilating the vessel using multiple dilators or sheaths that progressively increase in diameter. This repeated insertion and vessel dilation can increase the amount of time the procedure takes, as well as the risk of damage to the vessel.

Radially expanding intravascular sheaths reduce the overall profile of the sheath to reduce risk of damage to the vessel. Such sheaths tend to have complex mechanisms, such as ratcheting mechanisms that maintain the shaft or sheath in an expanded configuration once a device with a larger diameter than the sheath's original diameter is introduced.

However, delivery and/or removal of prosthetic devices and other material to or from a patient still poses a risk to the patient. Furthermore, accessing the vessel remains a challenge due to the relatively large profile of the delivery system that can cause longitudinal and radial tearing of the vessel during insertion. The delivery system can additionally dislodge calcified plaque within the vessels, posing an additional risk of clots caused by the dislodged plaque. The addition of radially expanding properties can also hinder a practitioner's ability to push the sheath without it bending or kinking. Thus, there remains a need for further improvements in introducer sheaths for endovascular systems used for implanting heart valves and other prosthetic devices.

Improved introducer sheaths are described in <CIT>, <CIT>, <CIT> and <CIT>. These sheaths advantageously incorporate a longitudinal fold that can be unfolded to allow for radial expansion as an implant passes through. An outer, elastic tubular layer, surrounding the folded inner layer, can urge the expanded inner layer back to the folded configuration. Methods of making an inner layer with a longitudinal fold conventionally involve annealing operations to form the folded profile. The annealing operations are time consuming an require expensive heat shrink tube consumables. There are several thermal bonding operations that form the transition from folded low profile cross section to the large proximally located cross section that is required to mate with the hub/hemostasis valve housing. These operations add time, complexity, and incorporate potential failure locations at the bond joints.

Disclosed herein are expandable introducer sheaths and methods of making and using the same. The sheaths are adapted to temporarily expand a portion of the sheath to allow for the passage of a delivery system for a cardiovascular device, then return to a non-expanded state after the passage of the system. The sheath includes an elongated annular member through which the cardiovascular device and its delivery system pass. In an embodiment, the annular inner member can be formed by coextruding a first and second material. The first material includes a fold, and the second material radially spaces the different parts of the fold from each other during fabrication and provides support for maintaining the tubular structure. The second material is removed once the coextrusion process is complete.

Disclosed herein is a method of making an expandable sheath. The method includes coextruding a first material and a second material. The first coextruded material defines an elongated annular member having a circumferentially extending thick wall portion. The thick wall portion has a first longitudinally extending end and a second longitudinally extending end. The second longitudinally extending end overlaps the first longitudinally extending end to create a folded overlapping segment. The thick wall portion of the annular member is integrally connected to a circumferentially extending thin wall portion. The thin wall portion extends between the first longitudinally extending end and the second longitudinally extending end of the thick wall portion. The first longitudinally extending end is radially closer to a central axis of the elongated annular member than the thin wall portion, and the second longitudinally extending end is radially farther from the central axis the thin wall portion.

The second coextruded material radially spaces the thin wall portion from the thick wall portion in during the coextrusion process. After the coextrusion is finished, the second coextruded material is then removed (by force, for example). The removal of the second extruded material allows for sliding movement of the first longitudinal end relative to the second longitudinal end and radial expansion of the elongated annular member. The second coextruded material can be removed by applying a force to at least one of the first and the second coextruded materials. The second coextruded material can be removed by applying a thermal treatment to at least one of the first and the second coextruded materials. The second coextruded material can be removed by applying a chemical treatment to at least one of the first and the second coextruded materials.

In some embodiments, the second coextruded material extends along the entire circumferential width of the overlapping segment. It can continue to extend circumferentially away from the overlapping segment. Two separate layers of the second coextruded material can be utilized. In some embodiments, a first layer of the second coextruded material is positioned between the first longitudinally extending end and the thin wall portion. In some embodiments, the first layer of the second coextruded material extends circumferentially away from the first longitudinally extending end. The first layer can extend circumferentially along an outer surface of the elongated annular member. A second layer of the second coextruded material is positioned between the second longitudinally extending end and the thin wall portion. The second layer of the second coextruded material can extend circumferentially away from the second longitudinally extending end. In some embodiments, the second layer of the second coextruded material extends circumferentially along an inner surface of the elongated annular member.

In some embodiments, the second coextruded material extends along an inner surface and an outer surface of the elongated member. The second coextruded material can extend around the entire circumference of the inner surface of the elongated member. The second coextruded material can also extend around the entire circumference of the outer surface of the elongated member.

In some embodiments of the method, a taper tube is coextruded near the proximal end of the annular member. The taper tube can have a diameter greater than a diameter of the elongated member. The taper tube is added as part of the coextrusion process, and therefore does not require the use of bonding processes (e.g., thermal bonding, chemical bonding, mechanical bonding). Finally, the annular member can be covered by an elastic outer layer which returns the annular member to a folded configuration after expansion (for example, after an implant passes through).

In the drawings, like reference numbers and designations in the various drawings indicate like elements.

As used in the specification and the appended claims, the singular forms "a," "an" and "the" include plural referents unless the context clearly dictates otherwise.

Throughout the description and claims of this specification, the word "comprise" and variations of the word, such as "comprising" and "comprises," means "including but not limited to," and is not intended to exclude, for example, other additives, components, integers or steps. "Exemplary" means "an example of" and is not intended to convey an indication of a preferred or ideal aspect. "Such as" is not used in a restrictive sense, but for explanatory purposes.

Disclosed herein are expandable introducer sheaths and methods of making and using the same. As will be described in further detail below, the expandable sheaths <NUM> are adapted to allow for temporary expansion of a portion of the sheath to accommodate the passage of a delivery system for a cardiovascular device, then return to a non-expanded state, or "recover" after the passage of the delivery system and device.

<FIG> illustrates an example sheath <NUM> in use with a representative delivery apparatus <NUM> for delivering a prosthetic device <NUM>, such as a tissue heart valve, to a patient. The apparatus <NUM> can include a steerable guide catheter <NUM> (also referred to as a flex catheter), a balloon catheter <NUM> extending through the guide catheter <NUM>, and a nose catheter <NUM> extending through the balloon catheter <NUM>. The guide catheter <NUM>, the balloon catheter <NUM>, and the nose catheter <NUM> in the illustrated embodiment are adapted to slide longitudinally relative to each other to facilitate delivery and positioning of the valve <NUM> at an implantation site in a patient's body, as described in detail below. Generally, a sheath <NUM> is inserted into a vessel, such as the transfemoral vessel, passing through the skin of patient, such that the distal end of the sheath <NUM> is inserted into the vessel. Sheath <NUM> can include a hemostasis valve at the opposite, proximal end of the sheath. The delivery apparatus <NUM> can be inserted into the sheath <NUM>, and the prosthetic device <NUM> can then be delivered and implanted within patient.

The expandable introducer sheath <NUM> is adapted to allow for temporary radial expansion of a portion of the sheath to accommodate the passage of a delivery system for a cardiovascular device (e.g., prosthetic heart valve <NUM>) and to then return to a non-expanded state after the passage of the delivery system with its prosthetic device. The expandable sheath <NUM> includes an elongated annular member <NUM> through which the delivery system and prosthetic heart valve <NUM> pass. As will be described in more detail below, the annular member <NUM> of the expandable sheath <NUM> can include longitudinally extending channels <NUM>, <NUM> that facilitate the sheath's expansion for passage of the prosthetic heart valve <NUM>. The channels <NUM>, <NUM> are positioned such that upon expansion of the annular member <NUM> certain contact surfaces <NUM>, <NUM> are brought into contact with adjacent surfaces of the delivery apparatus <NUM>, thereby reducing friction between the annular member <NUM> and the passing structure. In some embodiments, the radial expansion of the expandable annular member <NUM> at any given portion along its length is due to the ability of base <NUM> and/or bridge members <NUM> of the annular member <NUM> to rotate. The rotation of these sections reduces the surface/contact area of the annular member <NUM> thereby reducing friction with the passing structure. The expandable sheath <NUM> can include an elastic outer layer <NUM>. In some embodiments, the outer layer <NUM> can compress the annular member <NUM> towards a non-expanded configuration.

<FIG> show a cross-section of an example expandable sheath <NUM> in an expanded (<FIG>) and a non-expanded (<FIG>) state. The non-expanded sheath <NUM> includes an inner annular member <NUM> and an outer layer <NUM>. The outer layer <NUM> can be constructed from an elastic material that allows for temporary radial expansion of a portion of the outer layer <NUM> corresponding to the temporary radial expansion of the annular member <NUM> to accommodate the passage of the delivery system for a cardiovascular device (e.g., prosthetic heart valve <NUM>). After passage of the delivery system with its prosthetic device, the annular member <NUM> and outer layer <NUM> return to a non-expanded state (<FIG>). As illustrated in <FIG>, the annular member <NUM> includes a plurality of base members <NUM> arranged around the circumference of the annular member <NUM> and bridge members <NUM> extending between opposing pairs of base members <NUM> (e.g., base member 20a and base member 20b). As illustrated in <FIG>, the base members <NUM> can define a rectilinear shape in cross-section. The base members <NUM> can include an outer edge that define the outer surface/diameter <NUM> of the annular member <NUM> and an inner edge that define the inner surface/diameter <NUM> when the annular member <NUM> is in a non-expanded state. Base members <NUM> can include side walls <NUM> that extend radially between the inner and outer edges. As illustrated in <FIG>, the outer edge has a longer length (around the circumference of the annular member <NUM>) than the inner edge. The side walls <NUM> can meet the inner and outer edges at a curve (illustrated) or angle. The side walls <NUM> can terminate at the bridge member <NUM>. As provided in <FIG>, the side walls <NUM> can meet the bridge members <NUM> at a curve. In other example annular members <NUM> (see e.g., <FIG>) the side wall of the base member <NUM> can meet the bridge member <NUM> at a straight or angled edge/joint. It is further contemplated that the base members <NUM> can define any regular or irregular shape in cross-section including, for example, square, rectangle, trapezoidal, circular, and oval. Likewise, bridge members <NUM> can define any regular or irregular shape. As provided in <FIG>, in the unexpanded state the bridge members <NUM> define a generally S-shape cross-section. That is, in cross-section, the bridge members <NUM> of <FIG> can include a relatively (radially) elongate shape that extends between bends (at joints <NUM>) where the bridge member <NUM> couples to the adjacent base member <NUM>. The bends bracket the ends of the elongate portion and serve as the connection to either the radially inward corner or radially outward corner of adjacent base members. The elongate portion of the bridge member <NUM> can also widen in the outward radial direction. As will be explained in more detail below, during expansion of the annular member <NUM> the shape of the base member <NUM> and/or bridge member <NUM> changes or otherwise deforms.

As illustrated in <FIG>, in the non-expanded state, the annular member <NUM> includes longitudinally extending channels <NUM>, <NUM>. Inward extending channels <NUM> extend radially inward from the outer surface/diameter <NUM> of the annular member <NUM> towards its longitudinal axis <NUM>. The inward extending channels <NUM> are defined between a base member <NUM> and an adjacent bridge member <NUM>. The outward extending channels <NUM> extend radially outward from the inner surface/diameter <NUM> of the annular member <NUM> in a radial direction away from the longitudinal axis <NUM> and are similarly defined between a base member <NUM> and an adjacent bridge member <NUM>.

The inward and outward extending channels <NUM>, <NUM> alternate in inward versus outward directionality, such that each channel of a selected set/direction is positioned circumferentially between two channels of the other set/direction (i.e., each inward extending channel <NUM> is positioned circumferentially between two outward extending channels <NUM>, each outward extending channel <NUM> is positioned circumferentially between two inward extending channels <NUM>).

As depicted in <FIG>, the inward and outward extending channels <NUM>, <NUM> extend radially with respect to the longitudinal axis <NUM> of the annular member <NUM>. For example, the centerline (c) of each of the inward and outward extending channels <NUM>, <NUM> can create a <NUM>-degree angle (α) with a line tangent to the diameter of the annular member <NUM> proximate the opening of the channel.

The inward and outward extending channels <NUM>, <NUM> extend a certain depth (d) into the wall thickness (t) of the annular member <NUM>. For example, as illustrated in <FIG>, the inward and outward extending channels <NUM>, <NUM> can have a depth (d) greater than <NUM>% of the wall thickness (t) of the annular member <NUM>. Though not illustrated, it is contemplated that the depth of the inward and outward extending channels <NUM>, <NUM> can also vary around the circumference of the annular member <NUM>.

The inward and outward extending channels <NUM>, <NUM> can also define a width (w) measured along the length/depth of the channel. The width (w) can be defined between the sidewall of the corresponding bridge member <NUM> and base member <NUM>, i.e., between side wall <NUM> and side wall <NUM>. As illustrated in <FIG>, the width (w) of each channel can be uniform around the annular member <NUM>. It is also contemplated that the width (w) of different channels can vary around the circumference of the annular member <NUM>. The width (w) of the inward and outward extending channels <NUM>, <NUM> can remain constant (see <FIG>) or vary along the depth (d) of the channel. For example, the width (w) of the channel can increase in a direction from the center of the annular member <NUM> towards the perimeter of the annular member <NUM>.

The shape of the inward and outward extending channels <NUM>, <NUM> can remain constant or vary around the circumference of the annular member <NUM>. As depicted in <FIG>, each of the inward and outward extending channels <NUM>, <NUM> have two substantially parallel and straight sides (defined by side wall <NUM> and side wall <NUM>) that terminate at a rounded end <NUM>. It is contemplated that the shape of inward and outward extending channels <NUM>, <NUM> can define any regular or irregular shape and that the shape of each inward and outward extending channel <NUM>, <NUM> can vary (or remain constant) around the circumference of the annular member <NUM>.

In the embodiment shown in <FIG>, the inward and outward extending channels <NUM>, <NUM> are evenly distributed around the circumference of the annular member <NUM> and are similar in size and shape. While it is contemplated that the size and spacing of the base members <NUM>, bridge members <NUM> and corresponding inward and outward extending channels <NUM>, <NUM> can vary, even spacing and uniform size and shape help to prevent tearing of the annular member <NUM> during expansion. For example, during expansion (shown in <FIG>) tension is distributed to many points around the circumference of the annular member <NUM> and not focused at a single location. This distribution of tension reduces the risk of tearing the annular member <NUM>.

As described above, the annular member <NUM> and elastic outer layer <NUM> of the sheath <NUM> are designed to locally expand as the prosthetic device <NUM> is passed through the interior lumen of the sheath <NUM> and then substantially return to their original shape once the prosthetic device has passed through that portion of the sheath <NUM>. That is, in the non-expanded state the outer diameter of the annular member <NUM> and outer layer <NUM> can be substantially constant across the length of the sheath <NUM> from the proximal end <NUM> to the distal end <NUM>. As the prosthetic device <NUM> passes through the interior lumen of the sheath <NUM>, the portion of the annular member <NUM> and outer layer <NUM> proximate the prosthetic device <NUM> expand radially, with the remaining length/portion of the annular member <NUM> and outer layer <NUM> in a substantially non-expanded state. Once the device has passed through a portion of the lumen of the sheath <NUM>, that portion of the sheath <NUM> can substantially return to its original shape and size. <FIG> illustrates the annular member <NUM> and outer layer <NUM> in an expanded state. In the expanded state the outer diameters of the annular member <NUM> and elastic outer layer <NUM> are greater than the non-expanded diameters of the annular member <NUM> and outer layer <NUM>.

To achieve expansion, the orientation of the base members <NUM> and bridge members <NUM> changes. As illustrated in <FIG>, the base members <NUM> rotate during expansion of the annular member <NUM>. For example, the base members <NUM> rotate with respect to the central axis of each corresponding base member <NUM>. Similarly, the bridge members <NUM> rotate and flex at joints <NUM> to extend in a direction around the circumference of the annular member <NUM>, thereby increasing the circumferential distance/spacing between adjacent base members <NUM> and widening/changing the shape of each of the intervening inward and outward extending channels <NUM>, <NUM>. The bridge members <NUM> can be constructed from a flexible material to accommodate flexing at joints <NUM> and/or lengthening/deformation during expansion of the annular member <NUM> and then substantially return to the original, non-expanded shape/configuration. The base members <NUM> can be constructed from a same or different material than the bridge members <NUM>. Accordingly, it is also contemplated that the base members <NUM> can flex and deform during expansion and contraction of the annular member <NUM>.

As illustrated in <FIG>, in the expanded state the orientation of the base members <NUM> and bridge members <NUM> changes. Contact surfaces <NUM>, <NUM> provided on the base members <NUM> now define the inner and outer diameters of the annular member <NUM>, respectively. In the expanded state, the contact surfaces <NUM> define the inner diameter of the outer layer <NUM>. The contact surfaces <NUM> extend towards the interior of the annular member <NUM> and reduce the contact surface area between the annular member <NUM> and the passing device, thereby lowering the coefficient of friction/resistance between the inner surface <NUM> of the annular member <NUM> and the passing device. The contact surfaces <NUM>, <NUM> can define rounded/curved ends <NUM> or linear/angled ends <NUM> when viewed in cross-section. For example, the contact surfaces <NUM>, <NUM> of the expanded embodiments shown in <FIG>, <FIG>, <FIG>, <FIG> and 6C include rounded ends <NUM> in cross-section. In another example, the expanded annular member depicted in <FIG> includes both angled ends <NUM> and rounded ends <NUM> at the contact surfaces <NUM>, <NUM>. Referring back to <FIG>, the shape of the rounded ends <NUM>, including the radii of curvature, can be constant across all base members <NUM> of the annular member <NUM>. It is also contemplated that the shape of the rounded ends <NUM>/contact surfaces <NUM>, <NUM> may vary between base members <NUM>, and vary between contact surface <NUM> and contact surface <NUM> of the same base member <NUM>.

In transition back to the non-expanded state, the base members <NUM> and bridge members <NUM> move back to their original configuration/orientation. The transition back to the non-expanded state can be facilitated by the inclusion of an elastic outer layer <NUM> that extends over the elongated annular member <NUM>. The outer layer <NUM> comprises a material having a lower elastic modulus than the annular member <NUM>, which enables the outer layer <NUM> to force the annular member <NUM> back into the non-expanded state after passage of the cardiovascular device. The annular member <NUM> can be made of a more lubricious material than the outer layer <NUM>. For example, the outer layer <NUM> can be made of, or incorporate, polyurethane, silicone, and/or rubber, and the annular member <NUM> can be made of, or incorporate, high density polyethylene, polytetrafluoroethylene, and/or other fluoropolymers.

<FIG> depict another example sheath <NUM> including an annular member <NUM> and elastic outer layer <NUM>. The annular member <NUM> has a plurality of base members <NUM> arranged around the circumference of the annular member <NUM> and bridge members <NUM> extending between opposing pairs of base members <NUM>. As illustrated in <FIG>, the base members <NUM> and bridge members <NUM> can define a curvilinear shape in cross-section. For example, as depicted in <FIG>, the base member <NUM> can define an elongated portion extending around the outer surface/diameter <NUM> of the annular member and terminating in a rounded end <NUM> contact surface <NUM>, the elongated portion of the base member <NUM> defining the outer diameter of the annular member <NUM> in the non-expanded state. The bridge <NUM> can define an elongated member having substantially linear and parallel sides and terminating at a curved end proximate the inner surface/diameter <NUM> of the annular member <NUM>, the curved end surface of the bridge <NUM> defining the inner diameter of the annular member <NUM> in the non-expanded state.

Similar to the annular member <NUM> depicted in <FIG>, in the non-expanded state the annular member <NUM> of <FIG> includes longitudinally extending channels <NUM>, <NUM> defined between a bridge member <NUM> and adjacent base member <NUM> alternating in inward versus outward directionality around the circumference of the annular member <NUM>. The inward extending channels <NUM> extend inward from the outer surface/diameter <NUM> of the annular member <NUM> and the outward extending channels <NUM> extend outward from the inner surface/diameter <NUM> of the annular member <NUM>. The inward and outward extending channels <NUM>, <NUM> can extend inward or outward from the inner/outer surface <NUM>, <NUM> at an angle, e.g., at an angle other than <NUM>-degrees (with respect to a line tangent to the diameter of the annular member <NUM> proximate the opening of the channel).

As described above, the annular member <NUM> and the elastic outer layer <NUM> of the sheath <NUM> are designed to locally expand in a radial direction between a non-expanded and an expanded state as the prosthetic device <NUM> is passed through the interior lumen of the sheath <NUM>. <FIG> illustrates the annular member <NUM> and outer layer <NUM> in an expanded state. The orientation and/or shape of the base members <NUM> and bridge members <NUM> of the annular member <NUM> change during expansion. As illustrated in <FIG>, the base members <NUM> extend and elongate in a direction around the circumference of the annular member <NUM> when transitioned to the expanded state. The bridge members <NUM> change in orientation during expansion. In the non-expanded state the bridge members <NUM> extend is a direction toward/angled with respect to the longitudinal axis <NUM>/the interior of the annular member <NUM>. Upon expansion of the annular member <NUM> the bridge members <NUM> rotate, elongate and/or extend in a direction around the circumference of the annular member <NUM>. For example, the bridge members <NUM> can flex at joints <NUM> to facilitate their change in orientation with respect to the base members <NUM>. Upon expansion of the annular member <NUM>, the distance/spacing between adjacent base members <NUM> increases, widening and changing the shape of the intervening inward and outward extending channels <NUM>, <NUM> and increasing the overall diameter of the annular member <NUM> and the outer layer <NUM>.

As illustrated in <FIG>, in the expanded state the contact surfaces <NUM> provided on the base member <NUM> and/or bridge member <NUM> define the inner diameter of the annular member <NUM>. Likewise, the contact surface <NUM> defines the outer diameter of the annular member <NUM>, and the corresponding inner diameter of the outer layer <NUM> in the expanded state. The outside surface of the outer layer <NUM> defines the outermost diameter of the combined annular member <NUM>/outer layer <NUM>. Contact surfaces <NUM> reduce the contact surface area between the annular member <NUM> and the passing device, thereby lowering the coefficient of friction/resistance between the inner surface <NUM> and the passing device.

<FIG> depict an example sheath <NUM> including an annular member <NUM> and elastic outer layer <NUM>. The annular member <NUM> has four base members <NUM> arranged around the circumference of the annular member <NUM> and four corresponding bridge members <NUM> extending between opposing pairs of base members <NUM>. In the non-expanded state, the base members <NUM> and bridge members <NUM> can define a curvilinear shape in cross-section. For example, as depicted in <FIG>, the base members <NUM> can define two arcuate portions having substantially similar shape terminating in two substantially linear portions extending in a radial direction with respect to the annular member <NUM>. In the non-expanded state, the arcuate portions of the base members <NUM> define the inner and outer diameter of the annular member <NUM>. In the non-expanded state, the bridge members <NUM> can define an S-shape in cross-section.

Similar to the annular member <NUM> depicted in <FIG> and <FIG>, in the non-expanded state the annular member <NUM> of <FIG> includes longitudinally extending channels <NUM>, <NUM> defined between a bridge member <NUM> and adjacent base member <NUM> alternating in inward versus outward directionality around the circumference of the annular member <NUM>. The inward and outward extending channels <NUM>, <NUM> extend radially with respect to the longitudinal axis <NUM> of the annular member <NUM>. For example, the centerline of each of the inward and outward extending channels <NUM>, <NUM> creates a <NUM>-degree angle with a line tangent to the diameter of the annular member <NUM> proximate the opening of the channel.

As described above, the annular member <NUM> and the elastic outer layer <NUM> are designed to locally expand in a radial direction between a non-expanded and an expanded state as the prosthetic device <NUM> is passed through the interior lumen of the sheath <NUM>. <FIG> illustrates the annular member <NUM> and outer layer <NUM> in an expanded state. The orientation and/or shape of the base members <NUM> and bridge members <NUM> of the annular member <NUM> change during expansion. As illustrated in <FIG>, the base members <NUM> extend and/or elongate in a direction around the circumference of the annular member <NUM> when transitioned to the expanded state. The bridge members <NUM> also change in orientation and/or shape during expansion. In the non-expanded state the bridge members <NUM> extend is a direction toward the longitudinal axis <NUM>/the interior of the annular member <NUM>. Upon expansion of the annular member <NUM> the bridge members <NUM> rotate, elongate and/or extend in a direction around the circumference of the annular member <NUM>. For example, the bridge members <NUM> can flex at joints <NUM> to facilitate their change in orientation with respect to the base members <NUM>. Upon expansion of the annular member <NUM>, the distance/spacing between adjacent base members <NUM> increases, widening and changing the shape of the intervening inward and outward extending channels <NUM>, <NUM> and increasing the overall diameter of the sheath and the outer layer <NUM>.

As illustrated in <FIG>, in the expanded state the contact surfaces <NUM> provided on the base members <NUM> define the inner diameter of the annular member <NUM>. Likewise, the contact surface <NUM> defines the outer diameter of the annular member <NUM>, and the corresponding inner diameter of the outer layer <NUM> in the expanded state. It is contemplated that a portion of the inner surface <NUM> and outer surface <NUM> of the base member <NUM> can also define the inner and outer diameter of the annular member <NUM> in the expanded state. Contact surfaces <NUM> reduce the contact surface area between the annular member <NUM> and the passing device, thereby lowering the coefficient of friction/resistance between the annular member and the passing device.

<FIG> depict another example sheath <NUM> including an annular member <NUM> and elastic outer layer <NUM>. The annular member <NUM> has eighteen base members <NUM> arranged around the circumference of the annular member <NUM> and eighteen corresponding bridge members <NUM> extending between opposing pairs of base members <NUM>. In the non-expanded state, the base members <NUM> and bridge members <NUM> can define a curvilinear shape in cross-section. For example, as depicted in <FIG>, the base members <NUM> can define a semi-rectangular shape. The bridge members <NUM> can define an S-shape in cross-section.

Similar to the annular members <NUM> depicted in <FIG>, <FIG> and <FIG>, in the non-expanded state the annular member <NUM> of <FIG> includes longitudinally extending channels <NUM>, <NUM> defined between a bridge member <NUM> and adjacent base member <NUM> alternating in inward versus outward directionality around the circumference of the annular member <NUM>. The inward and outward extending channels <NUM>, <NUM> extend radially with respect to the longitudinal axis <NUM> of the annular member <NUM>. For example, the centerline of each of the inward and outward extending channels <NUM>, <NUM> creates a <NUM>-degree angle with a line tangent to the diameter of the annular member <NUM> proximate the opening of the channel.

As described above, the annular member <NUM> and the elastic outer layer <NUM> are designed to locally expand in a radial direction between a non-expanded and an expanded state as the prosthetic device <NUM> is passed through the inner lumen of the sheath <NUM>. <FIG> illustrates the annular member <NUM> and outer layer <NUM> in an expanded state. The orientation and/or shape of the base members <NUM> and bridge members <NUM> of the annular member <NUM> change during expansion. As illustrated in <FIG>, the base members <NUM> extend and/or elongate in a direction around the circumference of the annular member <NUM> when transitioned to the expanded state. The bridge members <NUM> also change in orientation and/or shape during expansion. In the non-expanded state the bridge members <NUM> extend in a direction toward the longitudinal axis <NUM>/the interior of the annular member <NUM>. Upon expansion of the annular member <NUM> the bridge members <NUM> rotate, elongate and/or extend in a direction around the circumference of the annular member <NUM>. For example, the bridge members <NUM> can flex at joints <NUM> to facilitate their change in orientation with respect to the base members <NUM>. Upon expansion of the annular member <NUM>, the distance/spacing between adjacent base members <NUM> increases, widening and changing the shape of the intervening inward and outward extending channels <NUM>, <NUM> and increasing the overall diameter of the annular member <NUM> and the outer layer <NUM>.

As illustrated in <FIG>, in the expanded state the contact surfaces <NUM> provided on the base members <NUM> define the inner diameter of the annular member <NUM>. Likewise, the contact surface <NUM> defines the outer diameter of the annular member <NUM>, and the corresponding inner diameter of the outer layer <NUM> in the expanded state. Contact surfaces <NUM> reduce the contact surface area between the annular member <NUM> and the passing device, thereby lowering the coefficient of friction/resistance between the annular member and the passing device.

<FIG> depict another example sheath <NUM> including an annular member <NUM> and elastic outer layer <NUM>. The annular member <NUM> has base members <NUM> arranged around the circumference of the annular member <NUM> and corresponding bridge members <NUM> extending between opposing pairs of base members <NUM>.

In the non-expanded state, the base members <NUM> and bridge members <NUM> can define a curvilinear shape in cross-section. For example, as depicted in <FIG>, the base members <NUM> define a wedge shape. The bridge members <NUM> define an arcuate/curved shape in cross-section.

Similar to the annular members <NUM> depicted in <FIG>, <FIG>, <FIG> and <FIG>, in the non-expanded state the annular member <NUM> of <FIG> includes longitudinally extending channels <NUM>, <NUM> defined between a bridge member <NUM> and adjacent base member <NUM> alternating in inward versus outward directionality around the circumference of the annular member <NUM>. The inward and outward extending channels <NUM>, <NUM> extend radially with respect to the longitudinal axis <NUM> of the annular member <NUM>. For example, the centerline of each of the inward and outward extending channels <NUM>, <NUM> creates a <NUM>-degree angle with a line tangent to the diameter of the annular member <NUM> proximate the opening of the channel. The shape, in cross-section, of the inward and outward extending channels <NUM>, <NUM> as depicted in <FIG> can include two substantially parallel and straight sides (defined by side wall <NUM> and side wall <NUM>) that terminate at a rounded end <NUM>. The rounded end <NUM> can have a width/diameter greater than the width (w) of the corresponding inward and outward extending channels <NUM>, <NUM>.

As described above, the annular member <NUM> and the elastic outer layer <NUM> of the sheath <NUM> are designed to locally expand in a radial direction between a non-expanded and an expanded state as the prosthetic device <NUM> is passed through the interior lumen of the sheath <NUM>. <FIG> illustrates the annular member <NUM> and outer layer <NUM> in an expanded state. The orientation and/or shape of the base members <NUM> and bridge members <NUM> of the annular member <NUM> change during expansion. As illustrated in <FIG>, the base members <NUM> rotate, extend and/or elongate in a direction around the circumference of the annular member <NUM> when transitioned to the expanded state. For example, the base members <NUM> can rotate with respect to the central axis of each corresponding base member <NUM>. Similarly, the bridge members <NUM> also change in orientation and/or shape during expansion. In the non-expanded state the bridge members <NUM> define an arcuate shape that flexes to increase in radius/length upon expansion of the annular member <NUM>. It is also contemplated that the bridge members <NUM> can rotate, elongate and/or extend in a direction around the circumference of the annular member <NUM> upon expansion. Upon expansion of the annular member <NUM>, the distance/spacing between adjacent base members <NUM> increases, widening and changing the shape of the intervening inward and outward extending channels <NUM>, <NUM> and increasing the overall diameter of the annular member <NUM> and the outer layer <NUM>. The wall thickness of the annular member <NUM> is thinner at the bridge members <NUM> than compared to the base members <NUM>. The decreased thickness at the bridge members <NUM> eases the bending of the bridge members <NUM> during expansion, lessening the chance of fracture.

As illustrated in <FIG>, <FIG>, <FIG>, <FIG>, <FIG> and <FIG>, the size, shape, spacing and number of channels can vary. For example, the non-expanded embodiments of <FIG> and <FIG> have twenty four combined inward and outward extending channels <NUM>, <NUM>. The non-expanded embodiments of <FIG> and <FIG> have twenty combined inward and outward extending channels <NUM>, <NUM>, the non-expanded embodiment of <FIG> has eight combined inward and outward extending channels <NUM>, <NUM>, and the non-expanded embodiment of <FIG> has thirty six combined inward and outward extending channels <NUM>, <NUM>.

Sheaths of the present disclosure can be used with various methods of introducing a prosthetic device into a patient's vasculature. Generally, during use, the expandable sheath <NUM> is passed through the skin of patient (usually over a guidewire) such that the distal end region of the expandable sheath <NUM> is inserted into a vessel, such as a femoral artery, and then advanced to a wider vessel, such as the abdominal aorta. The delivery apparatus <NUM> is then inserted through the expandable sheath <NUM>. The prosthetic device is then delivered to the implantation site and implanted within the patient. During the advance of the prosthetic device through the expandable sheath <NUM>, the device and its delivery system exerts a radially outwardly directed force on the portion of the annular member <NUM>, the annular member <NUM> exerts a corresponding radially outwardly directed force on the outer layer <NUM>, causing both the annular member <NUM> and the outer layer <NUM> to expand locally to accommodate the profile of the device. The expansion of the annular member <NUM> widens the longitudinally extending channels <NUM>, <NUM> of the annular member and causes the movement of longitudinally extending contact surfaces <NUM>, <NUM> toward the inner and outer surfaces <NUM>, <NUM> of the annular member <NUM>.

As the prosthetic device and its delivery system passes through the expandable sheath <NUM>, the expandable sheath <NUM> recovers. That is, it returns to its original, non-expanded configuration. In some embodiments, this is facilitated by outer layer <NUM>, which has a lower elastic modulus than annular member <NUM>. The outer layer <NUM> moves the contact surfaces <NUM>, <NUM> of the annular member <NUM> away from the inner and outer surfaces after the passage of the prosthetic valve <NUM>.

As described above, the expandable sheath <NUM> can be used to deliver, remove, repair, and/or replace a prosthetic device. In one example, the expandable sheath <NUM> described above can be used to deliver a tissue heart valve to a patient. For example, a tissue heart valve (in a crimped state) can be placed on the distal end portion of an elongated delivery apparatus and inserted into the sheath. Next, the delivery apparatus and crimped heart valve can be advanced through the patient's vasculature to the treatment site, where the valve is implanted.

Beyond transcatheter heart valves, the expandable sheath <NUM> can be useful for other types of minimally invasive surgery, such as any surgery requiring introduction of an apparatus into a subject's vessel. For example, the expandable sheath <NUM> can be used to introduce other types of delivery apparatus for placing various types of intraluminal devices (e.g., stents, stented grafts, balloon catheters for angioplasty procedures, etc.) into many types of vascular and non-vascular body lumens (e.g., veins, arteries, esophagus, ducts of the biliary tree, intestine, urethra, fallopian tube, other endocrine or exocrine ducts, etc.).

<FIG> show cross-sections of an expandable sheath <NUM> including an annular member <NUM> and outer layer <NUM> similar to the annular member <NUM> and outer layer <NUM> depicted in <FIG>. <FIG> shows a cross-sections of an expandable sheath <NUM> during an intermediate processing step that includes a second material in addition to the material used to form the annular member <NUM>. During processing, a tube is coextruded containing a first material <NUM> and a second material <NUM>. The first material <NUM> defines the annular member <NUM> discussed above. The second material <NUM> does not adhere to the first material <NUM> and defines a first and second set of longitudinally extending ribbons <NUM>, <NUM>. The second material <NUM> could be, or could incorporate, nylon, polyethylene terephthalate, and/or polybutylene terephthalate, for example. The first and second set of ribbons <NUM>, <NUM> form the inward and outward extending channels <NUM>, <NUM> of the annular member <NUM> during the extrusion process. The first set of ribbons <NUM> extends inwardly from the outer surface <NUM> toward the inner surface <NUM> of the annular member <NUM>, and the second set of ribbons <NUM> extends outwardly from the inner surface <NUM> toward the outer surface <NUM> of the annular member <NUM>. Each ribbon of a selected set is positioned circumferentially between two ribbons of the other set.

In some embodiments, the second material <NUM> is a sacrificial material. For example, the ribbons <NUM>, <NUM> of the second material <NUM> shown in <FIG> are removed after coextrusion, exposing the longitudinally extending channels <NUM>, <NUM> described above and as shown in the non-expanded embodiment of <FIG>.

However, some embodiments, such as the one shown in <FIG>, the first material <NUM> and second material <NUM> of the annular member <NUM> are coextruded with a third material <NUM>. This third material <NUM> is in contact with a portion of the first material <NUM> and a portion of the second material <NUM>, and adheres to both the first and second materials <NUM>, <NUM>. Because of the adherent third material <NUM>, the second material <NUM> is not removed. However, it still does not adhere to first material <NUM>. Instead, the third material <NUM> acts as a tie layer to hold the first and second materials <NUM>, <NUM> together during expansion of the annular member <NUM>. This eliminates the need to remove the ribbons <NUM>, <NUM> of the second material <NUM> prior to use, while still allowing a widening of a channel between the non-adherent first <NUM> and second <NUM> materials during the expansion of the annular member <NUM>. The retention of the second material <NUM> also increases the torque of the finished sheath, so that a user finds it easier to twist the sheath.

Some methods include a step of covering the annular member <NUM> with the outer layer <NUM> after coextrusion. As discussed above, the outer layer <NUM> is formed of, or incorporates, a material with a lower elastic modulus than the annular member <NUM>.

<FIG> shows a perspective view of an example sheath <NUM>. In this view, only the outer layer <NUM> is visible. The sheath <NUM> comprises a proximal end <NUM> and distal end <NUM> opposite the proximal end <NUM>. The sheath <NUM> can comprise a hemostasis valve inside the lumen of the sheath <NUM>, at or near the proximal end <NUM>. The sheath <NUM> can include a taper tube <NUM>, a flared proximal end. In some embodiments of the method of making, the taper tube <NUM> is added to the coextrusion. The addition of the second material <NUM> will stabilize the coextrusion process and make it possible to add a taper tube <NUM> during extrusion. This is advantageous because it makes it possible to eliminate the typical taper tube manufacturing steps of flaring (increasing the inner diameter of the sheath) and bonding (increasing the wall thickness after flaring).

Additionally, the sheath <NUM> can comprise a soft distal tip <NUM> at the distal end <NUM>. The soft tip <NUM> can be provided with a lower hardness than the other portions of the sheath <NUM>. In addition to the method of making the expandable sheath described above, a method of making a distal tip <NUM> of an expandable sheath <NUM> is demonstrated in the flow chart of <FIG>. The distal tip <NUM> can be formed on the annual member <NUM>, outer layer <NUM>, or on the annular member <NUM> and outer layer <NUM> combined. The distal tip <NUM> of the expandable sheath <NUM> is softer and more elastic than the more proximal regions of the expandable sheath <NUM> because it must give easily when encountering tissue to reduce the possibility of injury and it must retain the ability to expand after the sealing (reflowing) process wherein the distal tip <NUM> is sealed to prevent blood from entering the space between the annular member <NUM> and the outer layer <NUM>. A first step to making the distal tip <NUM> is to attach a separate distal tube <NUM> to the distal end <NUM> of the expandable sheath <NUM>, for example, by reflowing the materials together. Alternatively, the distal tube <NUM> can be added to the distal end <NUM> of the sheath <NUM> via specialized extrusion technology. The distal tube <NUM> is formed of, or incorporates, a material having greater elasticity than the remainder of the expandable sheath <NUM>. One example material is Pebax.

Next, a portion of the distal tube <NUM> is pinched to create a longitudinally extending outer crease <NUM>. The pinched portion is folded over an outer surface of the distal tube <NUM> in a circumferential direction, creating a longitudinally extending flap <NUM> that is bounded by the outer crease <NUM> and a longitudinally extending inner crease <NUM>. The inner crease <NUM> of the flap <NUM> is cut in a longitudinal direction from the distal edge <NUM> of the distal tube <NUM> to a proximally spaced point along the longitudinal axis of the distal tube <NUM>. This creates a longitudinally extending inner edge <NUM>. The flap <NUM> is cut circumferentially from the outer crease <NUM> to the inner crease <NUM> at the proximally spaced point, such that the longitudinal cut of the inner crease <NUM> meets the circumferential cut at the proximally spaced point. The inner edge <NUM> of the flap is then extended in a circumferential direction around the outer surface <NUM> of the distal tube <NUM> and adhered to the outer surface <NUM>.

In some embodiments, such as the one shown in <FIG>, adhering the inner edge <NUM> of the flap <NUM> to the outer surface <NUM> can include covering the distal end with an outer jacket <NUM>, then reflowing the outer jacket <NUM> with the distal tube <NUM> to form a sealed distal end. The outer jacket <NUM> is also formed of highly elastic materials. One example material is Neusoft. This outer jacket <NUM> can, in some embodiments, be the same layer as the outer layer <NUM> shown in <FIG>. Because the flap <NUM> is unfolded and wrapped around the outer surface <NUM> before reflowing, the final wall thickness of the resulting distal tip varies minimally around its circumference.

<FIG> shows an embodiment of an annular member <NUM> according to the present invention in a radially expanded state The annular member <NUM> has a thick wall portion <NUM> integrally formed and coextruded with a thin wall portion <NUM>. The annular member <NUM> shown in <FIG> is preferably constructed of a relatively stiff material (as compared to the outer layer <NUM>) such as a stiff polymer like high density polyethylene (HDPE) or an equivalent polymer. Integral construction, such as integral extrusion, of the thick and thin wall portions <NUM>, <NUM> advantageously avoids the leakage present in some conventional sheaths that use a split in the sheath to promote expandability. Other conventional sheaths tend to leak close to the proximal end where the sheath is stretched the most during passage of the prosthetic device. Also, integral construction improves the ability to torque the sheath <NUM>.

The thick wall portion <NUM> of the annular member <NUM>, as in the illustrated embodiment of <FIG>, has a C-shaped cross section with a first longitudinally extending end <NUM> and a second longitudinally extending end <NUM>. The first and second ends <NUM>, <NUM> define those portions of the annular member <NUM> where the thickness of the thick wall portion <NUM> starts to narrow or otherwise transition to the thin wall portion <NUM> on the cross-section. That transition extends longitudinally in the direction of the longitudinal axis of the sheath <NUM>, such that the thick wall portion <NUM> forms an elongate C-shaped channel.

The thin wall portion <NUM> extends between the first and second ends <NUM>, <NUM> of the thick wall portion <NUM> which together define the tubular shape of the annular member <NUM>. Central lumen <NUM> extends longitudinally within that tubular shape. <FIG>, in particular, shows the central lumen <NUM> in its expanded diameter which is larger than the initial diameter of the elastic outer layer <NUM>.

<FIG> show the annular member <NUM> in its non-expanded, compressed or folded condition, such that the annular member <NUM> folded up and fit into the initial elastic lumen <NUM> of the elastic outer layer <NUM>. In the compressed condition, the elastic outer layer <NUM> urges the first longitudinally extending end <NUM> under the second longitudinally extending end <NUM> of the annular member <NUM>. As illustrated in <FIG>, compression and folding of the annular member <NUM> positions/layers the thin wall portion <NUM> between the first and second longitudinally extending ends <NUM>, <NUM> and the overlapping sections of the thick wall portion <NUM>.

As will be described in more detail below, the foldable annular member <NUM> shown in <FIG> can be formed by a coextrusion process wherein the annular member <NUM> is coextruded with a second, sacrificial, material while the annular member <NUM> is in a folded state. The second material is then removed, as described above, leaving behind the folded annular member <NUM>.

<FIG> shows a cross-section of the inventive annular member <NUM> of <FIG> during the coextrusion step. During processing, a tubular structure is extruded containing a first coextruded material <NUM> and a second coextruded material <NUM>. The first coextruded material <NUM> defines the annular member <NUM>, discussed above. The second material <NUM> serves to position the folded structure of the annular member <NUM>/first material <NUM>. When the second material <NUM> is removed, the first material <NUM> is left behind in an unexpanded, folded state.

As shown in <FIG>, during processing, the first coextruded material <NUM> defines the elongated annular member <NUM> having the circumferentially extending thick wall portion <NUM> where the thick wall portion <NUM> includes the first and second longitudinally extending ends <NUM>, <NUM> as described above. During the coextrusion process, the second longitudinally extending end <NUM> overlaps and is exterior to the first longitudinally extending end <NUM> along a folded, overlapping segment <NUM>. The thin wall portion <NUM> extends between the first and second longitudinally extending ends <NUM>, <NUM> in a circumferential direction. The thin wall portion <NUM> is positioned radially farther from the central longitudinal axis of the coextruded tubular material than the first longitudinally extending end <NUM> and its adjacent thick wall portion <NUM>. The thin wall portion <NUM> is positioned radially closer to the central longitudinal axis than the second longitudinally extending end <NUM> and its adjacent thick wall portion <NUM>.

The second material <NUM> is coextruded between and in contact with the thick and thin wall portions <NUM>, <NUM>, in a manner that radially spaces the thin wall portion <NUM> from the thick wall portion <NUM>. The second material <NUM> can be coextruded in two separate layers/portions to form the overlapping structure of the thick and think wall portions <NUM>, <NUM>. A first layer <NUM> of the second material <NUM> is positioned between the first longitudinally extending end <NUM> and the thin wall portion <NUM>, and a second layer <NUM> of the second material <NUM> is positioned between the second longitudinally extending end <NUM> and the thin wall portion <NUM>. Each of the first and second layers <NUM>, <NUM> of the second material <NUM> have a generally C-shape in cross section. In some embodiments, the second material <NUM> extends circumferentially along the entire overlapping segment <NUM> and continues to extend away from the overlapping segment <NUM> in either direction, as shown in <FIG>, and around at least a portion of the circumference of the thick wall portion <NUM>. For example, the first layer <NUM> of the second material <NUM> extends circumferentially along the outer surface <NUM> of the annular member <NUM> and between the thin wall portion <NUM> and the thick wall portion <NUM> adjacent the first longitudinally extending end <NUM>. The second layer <NUM> of the second material <NUM> extends circumferentially along the inner surface <NUM> of the annular member <NUM> and between the thin wall portion <NUM> and the thick wall portion <NUM> adjacent the second longitudinal end <NUM>. This circumferential extension of the second material <NUM> provides support to the structure during the fabrication process. In the shown embodiment, the first and second layer <NUM>, <NUM> each extend along the circumference of the annular member <NUM> by about <NUM>-degrees. However, in other embodiments, the first and second layer <NUM>, <NUM> may extend circumferentially only along the overlapping segment <NUM>, about <NUM>-degrees circumferentially, about <NUM>-degrees circumferentially, about <NUM>-degrees circumferentially, about <NUM>-degrees circumferentially, about <NUM>-degrees circumferentially, about <NUM>-degrees circumferentially, or the first and second layers may extend a full <NUM>-degrees circumferentially. The first layer <NUM> and the second layer <NUM> need not extend the same distance circumferentially. As illustrated in <FIG>, the second material <NUM> has a wall thickness (measured in the radial direction) less than the thickness of the first material <NUM>. The thickness of the second material <NUM> is uniform along the entire width of the corresponding first and second layer <NUM>, <NUM>, i.e., the circumferential width the first material extends along the circumference of the annular member <NUM>. It is also contemplated, the that the thickness of the second material <NUM> may vary along the circumferential width of the first and second layers <NUM>, <NUM>. For example, the second material may have a tapering thickness such that the thickness of the second material is thicker in a circumferential central position of the first and second layer <NUM>, <NUM>, than at the edges of the first and second layers <NUM>, <NUM>.

After coextrusion, the second material <NUM> can be removed. In some implementations, the second material <NUM> can be physically removed from the first material <NUM> by force, for example, by applying a force (axial and/or radial) to at least one of the first and/or second materials <NUM>, <NUM>. The second material <NUM> can be formed of a material that does not adhere to the first material <NUM> during the coextrusion process, making its physical removal relatively easy. In other embodiments, the first material and second material can have different chemical properties or melting points, such that chemical or thermal treatments may be used to remove the second material <NUM> from the first material <NUM>. While the first material <NUM> could be, or could incorporate, HDPE, the second material <NUM> could be, or could incorporate, nylon, polyethylene terephthalate, PA12, and/or polybutylene terephthalate, for example. The removal of the second material <NUM> enables the first longitudinal end <NUM> to slide relative to the second longitudinal end <NUM>, such that the annular member <NUM> can be radially expanded.

In some embodiments, the coextrusion process used to form the sheath shown in <FIG> can include the formation of a taper tube <NUM>, such as the one shown in <FIG> (i.e., a bump extrusion). Some methods include a step of covering the annular member <NUM> with the outer layer <NUM> after coextrusion. As discussed above, the outer layer <NUM> is formed of, or incorporates, a material with a lower elastic modulus than the annular member <NUM>.

Claim 1:
An expandable sheath (<NUM>) comprising:
an elongated annular member (<NUM>) having a radially expanded state and a folded state, and comprising a thick wall portion (<NUM>) and a thin wall portion (<NUM>);
wherein the thick wall portion (<NUM>) has a C-shaped cross section with a first longitudinally extending end (<NUM>) and a second longitudinally extending end (<NUM>);
wherein the thin wall portion (<NUM>) extends between the first and second ends (<NUM>, <NUM>) of the thick wall portion (<NUM>) which together define the tubular shape of the annular member (<NUM>);
characterized in that
the thin wall portion (<NUM>) and the thick wall portion (<NUM>) of the annular member are integrally formed and coextruded in the folded state, in which the thin wall portion (<NUM>) is positioned between the first and second longitudinally extending ends (<NUM>, <NUM>) and the overlapping sections of the thick wall portion (<NUM>).