Stent securement system

A stent delivery system having a delivery catheter, a stent mounted thereupon and at least one stent retaining sleeve to retain the stent on the catheter prior to stent delivery. At least a portion of the at least one stent retaining sleeve being further characterized as having a plurality through-holes. The through-holes providing the at least one stent retaining sleeve with reduced radial and columnar strength when compared to a sleeve without through-holes.

CROSS-REFERENCE TO RELATED APPLICATIONS

Not Applicable

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH

Not Applicable

BACKGROUND OF THE INVENTION

The present invention relates to a delivery system in which a catheter carries a stent on its distal end portion. The stent is held in place around the catheter prior to and during percutaneous delivery by means of one and preferably two sleeves. The stent may be self-expanding, such as a NITINOL shape memory stent, or it may be expandable by means of an inflatable portion of the catheter, such as a balloon. The sleeve or sleeves have a plurality of holes which may be bored partially or completely through the material of the sleeve or sleeves. The holes may be mechanically bored or laser bored. The holes are distributed about the surface of the sleeve or sleeves in a uniform pattern but may have a variety of shapes and sizes. The sleeve or sleeves may be composed of an elastic polymer, a non-elastic polymer or a combination thereof.

Stents and stent delivery assemblies are utilized in a number of medical procedures and situations, and as such their structure and function are well known. A stent is a generally cylindrical prosthesis introduced via a catheter into a lumen of a body vessel in a configuration having a generally reduced diameter and then expanded to the diameter of the vessel. In its expanded configuration, the stent supports and reinforces the vessel walls while maintaining the vessel in an open, unobstructed condition.

Both self-expanding and inflation expandable stents are well known and widely available in a variety of designs and configurations. Self-expanding stents must be maintained under a contained sheath or sleeve(s) in order to maintain their reduced diameter configuration during delivery of the stent to its deployment site. Inflation expandable stents are crimped to their reduced diameter about the delivery catheter, then maneuvered to the deployment site and expanded to the vessel diameter by fluid inflation of a balloon positioned between the stent and the delivery catheter. The present invention is particularly concerned with delivery and deployment of inflation expandable stents, although it is generally applicable to self-expanding stents when used with balloon catheters.

In advancing an inflation expandable stent through a body vessel to the deployment site, there are a number of important considerations. The stent must be able to securely maintain its axial position on the delivery catheter without translocating proximally or distally and especially without becoming separated from the catheter. The stent, particularly its distal and proximal ends, must be protected to prevent distortion of the stent and to prevent abrasion and/or reduce trauma of the vessel walls.

Inflation expandable stent delivery and deployment assemblies are known which utilize restraining means that overlie the stent during delivery. U.S. Pat. No. 4,950,227 to Savin et al., relates to an inflation expandable stent delivery system in which a sleeve overlaps the distal or proximal margin (or both) of the stent during delivery. During inflation of the stent at the deployment site, the stent margins are freed of the protective sleeve(s). U.S. Pat. No. 5,403,341 to Solar, relates to a stent delivery and deployment assembly which uses retaining sheaths positioned about opposite ends of the compressed stent. The retaining sheaths of Solar are adapted to tear under pressure as the stent is radially expanded, thus releasing the stent from engagement with the sheaths. U.S. Pat. No. 5,108,416 to Ryan et al., describes a stent introducer system which uses one or two flexible end caps and an annular socket surrounding the balloon to position the stent during introduction to the deployment site. The entire contents of each of the patents cited herein is hereby incorporated by reference.

This invention provides an improvement over the prior art, by providing a stent delivery system wherein the stent retaining sleeves have a reduced radial and columnar strength thereby allowing a delivery catheter to deploy a balloon expandable stent at lower pressures with greater consistency than otherwise would be possible. The lower strength of the sleeves also allows the sleeves to be readily retracted from the stent without additional lubrication, however lubricants may still be applied to a stent delivery catheter using the sleeves described.

BRIEF SUMMARY OF THE INVENTION

This invention provides for a stent delivery system wherein the stent is held onto the stent delivery catheter with one or more tubular shaped stent retaining sleeves. The stent retaining sleeves contain a plurality of through-holes which may be distributed in a predetermined pattern on at least a portion of the sleeve tube. Alternatively, the through-holes may be distributed irregularly on the at least a portion of the sleeve tube.

The through-holes may have a variety of size and shape, or may be uniformly sized and shaped. The through-holes may also be characterized as dimples, indentations, slits or cuts made through the sleeve tube surface.

The presence of the through-holes provide the sleeve or sleeves with reduced radial and columnar strength allowing the sleeve(s) to be more easily retracted and have the capacity to release a stent with greater consistency under reduced pressure, when compared to prior stent retaining sleeves.

DETAILED DESCRIPTION OF THE INVENTION

While this invention may be embodied in many different forms, there are shown in the drawings and described in detail herein specific preferred embodiments of the invention. The present disclosure is an exemplification of the principles of the invention and is not intended to limit the invention to the particular embodiments illustrated.

FIGS. 1 and 2show a first embodiment of a stent delivery system wherein a stent30is mounted upon a stent delivery catheter38.FIG. 1shows the stent delivery system prior to stent delivery.FIG. 2shows the stent delivery system during stent delivery. As may be seen in both figures, a pair of sleeves10aand10bare employed to retain the stent ends32and34on an inflatable portion36of a delivery catheter38prior to stent delivery.

As best seen inFIG. 2when the inflatable portion36is inflated the stent30is expanded radially. As the stent30expands the stent ends32and34are pulled away from sleeves10aand10b. When the inflatable portion36is inflated to a predetermined extent, the stent ends32and34will be completely freed from the sleeves10aand10b.

The sleeves10aand10bof the present invention will typically be distinguished by having a stent retaining portion12which contains a plurality of through-holes14, and an anchored portion16which lacks through-holes.

The through-holes14which are present in the sleeves10aand10bprovide the respective sleeve with reduced radial and columnar strength relative to a sleeve that does not have the through-holes. The reduced radial strength of sleeves10aand10ballows the sleeves to be withdrawn from stent30with less radial expansion than previous sleeve types. Consequently, a balloon expandable stent may be released from the stent retaining sleeves10aand10bwith less inflation pressure than previously required. For example, a particular example of the present invention which includes a pair of sleeves having through-holes, may be withdrawn from the surface of a stent when the stent is expanded under approximately 3.5 atmospheres of pressure. On the other hand, some sleeves without through-holes may require between 4.5 to 5 atmospheres of pressure to be withdrawn from the stent surface.

In addition, the reduced columnar strength of the sleeves10aand10bcauses the sleeves to have a reduced capacity to be retained upon stent ends32and34as they expand outward. As a result, in the present stent delivery system there may be no need to provide lubrication between sleeves10a,10band stent ends32,34to release the stent during expansion. Although a slip coat may still be used for improved performance.

As may be seen inFIG. 3, the through-holes14may be uniformly distributed about stent retaining portion12. Alternatively, the through-holes14may be distributed randomly and/or they may be distributed about the entire sleeve10. The through-holes14may have a variety of sizes and shapes, some examples of suitable hole shapes include ellipsoids such as circles and ovals, but non-uniform shapes may be used as well. Preferably, the through-holes14have a uniform circular shape and diameter such as those shown inFIG. 3. Typically, the through-holes14will have a diameter within the range of 10–1000 microns and preferably within the range of 75–100 microns, however other sizes may also be utilized.

The through-holes14may be bored into or through the sleeve10using a variety of boring methods. Preferably, in order to achieve uniform hole diameter and shape through-holes14are laser bored. Mechanical boring, such as by a mechanical drill and suitably sized bit may also be utilized.

In the embodiment shown inFIG. 4, the through-holes are best characterized as micro-cuts20. The micro-cuts20are made by making an incision on the outside surface22of the sleeve10which passes through the outside surface22to the inside surface24. When the sleeve10is placed on a catheter such as shown inFIG. 1, the user may find it desirable or necessary to apply a lubricant to the stent30which underlies the sleeves10aand10b. The micro-cuts20provide the sleeves10aand10bwith the ability to wick a lubricant or other fluid through the outside surface22to the inside surface24where it will lubricate the stent.

In all embodiments the sleeve10may be constructed from a variety of components. Preferably, sleeve10is made of an elastic polymer or polymers. The sleeve10may also contain non-elastic polymers exclusively or in part, but it may be necessary to process the non-elastic polymers to obtain the more desirable elastic characteristics. In a more preferred embodiment the sleeve10is constructed at least in part of TECOTHANE material and/or CARBOTHANE material. TECOTHANE AND CARBOTHANE are well known trademarked names for respective classes of biocompatable medical grade polyurethanes, both of which are available from Thermedics Inc., located in Woburn, Mass. TECOTHANE is an aromatic polyether based polyurethane having a durometer hardness range, as measured by the Shore D scale, of75A to77D. CARBOTHANE is an aliphatic polycarbonate based polyurethane having a durometer hardness range73A and75D.

In addition to being directed to the embodiments described above and claimed below, the present invention is further directed to embodiments having different combinations of the features described above and claimed below. As such, the invention is also directed to other embodiments having any other possible combination of the dependent features claimed below.

The above examples and disclosure are intended to be illustrative and not exhaustive. These examples and description will suggest many variations and alternatives to one of ordinary skill in this art. All these alternatives and variations are intended to be included within the scope of the attached claims. Those familiar with the art may recognize other equivalents to the specific embodiments described herein which equivalents are also intended to be encompassed by the claims attached hereto.