Abstract:
A stent delivery system to facilitate introduction and placement of a stent, including a catheter having an expandable distal portion constructed and arranged for expanding the outer diameter of the catheter from a contracted state to an expanded state: a stent positioned around the distal portion of the catheter having a contracted condition and being expandable to an expanded condition, and being sized in the contracted condition to closely surround the catheter in the contracted state, the expandable distal portion of the catheter including a balloon within which there is included on the catheter shaft at least one body of a diameter larger than the catheter shaft to which the stent and balloon are fitted, as by crimping, for holding the stent in place until it is released therefrom by expansion of the balloon.

Description:
This is a Continuation application based on U.S. Ser. No. 09/383,174, filed on Aug. 25, 1999 now U.S. Pat. No. 6,270,504, which is a Continuation application based on U.S. Ser. No. 08/917,027, now U.S. Pat. No. 6,068,634, filed Aug. 22, 1997, which is a Continuation-in-part application based on U.S. Ser. No. 08/702,149 now U.S. Pat. No. 5,980,530, filed Aug. 23, 1996, all of which are respectively incorporated by reference in their entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     In typical PTCA procedures, a guiding catheter is percutaneously introduced into the cardiovascular system of a patient through a vessel and advanced through therein until the distal end thereof is at a desired location in the vasculature. A a guidewire and a dilatation catheter having a balloon on the distal end thereof are introduced through the guiding catheter with the guidewire sliding through the dilatation catheter. The guidewire is first advanced out of the guiding catheter into the patient&#39;s coronary vasculature and the dilatation catheter is advanced over the previously advanced guidewire until the dilatation balloon is properly positioned across the lesion. Once in position across the lesion, the flexible, expandable, preformed balloon is inflated to a predetermined size with a liquid or gas at relatively high pressures, such as greater than about four atmospheres, to radially compress the arthrosclerotic plaque of the lesion against the inside of the artery wall and thereby dilate the lumen of the artery. The balloon is then deflated to a small profile so that the dilatation catheter may. be withdrawn from the patients vasculature and blood flow resumed through the dilated artery. 
     In angioplasty procedures of the kind described above, there may be injury to or restenosis of the artery, which either necessitates another angioplasty procedure, a surgical by-pass operation, or some method of repairing or strengthening the area. To strengthen the area and help prevent restenosis, a physician can implant an intravascular prosthesis for maintaining vascular patency, commonly called a stent, inside the artery at the lesion. The stent is expanded to a larger diameter for placement in the vasculature, often by the balloon portion of the catheter. Stents delivered to a restricted coronary artery, expanded to a larger diameter by a balloon catheter, and left in place in the artery at the site of a dilated lesion are shown in U.S. Pat. No. 4,740,207 to Kreamer and U.S. Pat. No. 5,007,926 to Derbyshire, the content of which is incorporated herein by reference. Palmaz et al., 156  Radiology  73 (1985) and U.S. Pat. No. 4,733,665 describe introduction of a stent over a balloon catheter (incorporated herein by reference). A preferred stent for use with this invention is shown in PCT Application No. 960 3092 A1, published Feb. 8, 1996, the content of which is incorporated herein by reference. 
     The present invention is particularly directed to improved arrangements for releasably covering the ends of the stent to prevent the stent ends from flaring and snagging to better facilitate delivery thereof. 
     The art referred to and/or described above is not intended to constitute an admission that any patent, publication or other information referred to herein is “prior art” with respect to this invention. In addition, this section should not be construed to mean that a search has been made or that no other pertinent information as defined in 37 C.F.R. §1.56(a) exists. 
     SUMMARY OF THE INVENTION 
     This invention concerns apparatus suitable for delivery of stents to body cavities. In general, stents are prosthetic devices which can be positioned within a body cavity, for example, a blood vessel of the body of a living human or in some other difficultly accessible place. The stent prosthesis is formed of a generally tubular body, the diameter of which can be decreased or increased. Stents are particularly useful for permanently widening a vessel which is either in a narrowed state, or internally supporting a damaged vessel. Such stents are typically introduced into the body cavity by use of a catheter. The catheter is usually of the balloon catheter type in which the balloon is utilized to expand the stent, which is positioned over the balloon, to place it in a selected location in the body cavity. The present invention is particularly directed to improved arrangements for releasably covering/securing/attaching the stent, particularly the ends thereof, to the catheter to prevent snagging of the stent ends and to facilitate delivery thereof. The stent is held in place on the catheter and kept from flaring upward at its end(s) by means of at least one removable end covering means, or sock/sleeve, over the stent, the stent having been fitted to the catheter over the balloon, as by crimping. Most specifically, this invention is directed to improved modifications to the subject matter of the Savin U.S. Pat. No. 4,950,227 which is incorporated herein by reference. 
     In particular, the invention is directed to an improved stent delivery system designed to securely hold a stent over the balloon on a catheter, via the sleeve arrangements, and to protect the stent from deformation, damage or premature release during delivery intraluminally, as well as snagging during transportation. It is also a purpose of the present invention to provide for easier and smoother removal of the sleeve retaining means. The stent is formed to its lowest geometrical diameter when loaded. In one embodiment, rings or coils are placed over the ends of the stent to retain them and hold them to the balloon beneath the sleeves (unexpanded), and preferably adhered thereto, with little or no relative movement between the ID of the stent and the OD of the balloon/catheter arrangement. The sleeves aid in retaining the stent and hold the stent to the balloon (unexpanded). The rings or coils are each preferably attached (adhered) to the elastomeric socks and the other end of the sleeves are respectively attached to the catheter. Since most stents which are deformed to a low diameter will increase in diameter somewhat after being deformed (spring back), the rings/coils prevent spring back and increase the friction fit between the stent and balloon. When the balloon under the stent is inflated, the stent pushes out of the rings/coils and the sleeves are pushed down the balloon cones to allow the stent to deploy. 
     An alterative embodiment provides for easier and smoother removal of the sock retaining means. In this embodiment the rings or coils are placed over the cone portion of the balloon beneath the socks and preferably adhered thereto. The sleeves aid in retaining the stent and hold the stent to the balloon (unexpanded) with little or no relative movement between the ID of the stent and the OD of the balloon/catheter arrangement. The rings or coils are each preferably attached (adhered) to the elastomeric socks or sleeves. One end of the sleeves cover the ends of the stent and the other end of the sleeves are respectively attached to the catheter. When the balloon under the stent is inflated, the rings/coils, which are positioned on the tapered cone portion of the balloon, are driven primarily axially, resulting in the sleeves being pushed/pulled down the balloon cones to allow the stent to deploy. The positioning of the rings/coils on the cones of the balloon allows for more of an axial force when the balloon inflates rather then a radial force which may be the case if the rings are positioned on the ends of the stent, which may have a flatter profile as apposed to the tapered profile of the cone portion. This allows for a steadier, smoother, more controlled removal of the sleeves. Since most stents which are deformed to a low diameter will increase in diameter somewhat after being deformed (spring back), the sleeves also somewhat prevent spring back and increase the friction fit between the stent and balloon. 
     In a different embodiment, a polymer tube may be formed into a spiral, as by cutting molding or extruding, except for about 1-2 mm on one end; its entire length need only be about 1-2 cm. The uncut portion of the spiral, i.e., the ring end is placed over the end of the stent to retain it as already described. The other end of the coil, a portion of which may be uncut also to form a ring is attached to the catheter. 
     Modifications to this embodiment include replacement of the plastic ring with a metal ring or coil and replacement of the sleeve/ring with a metal or plastic coil or coiled ribbon. Short balloon cone length and/or tension on the spiral can help the spiral move off the stent when the balloon is inflated. 
    
    
     BRIEF DESCRIPTION OF THE FIGURES 
     FIG. 1 is a view, in longitudinal section, of the distal end portion of a balloon catheter having a stent fixed to the catheter by being crimped thereto over the balloon, the ends of the stent being held by a first embodiment of the invention; 
     FIG. 2 is similar to FIG. 1 in which the stent has been released; 
     FIG. 3 is a view of a modification of the embodiment shown in FIGS. 1 and 2; 
     FIG. 4 is a view of another modification to the embodiment of FIGS. 1 and 2; 
     FIG. 5 is a showing of another embodiment of the invention used to hold the ends of the stent; 
     FIG. 6 is a showing of the FIG. 5 arrangement in which the stent has been released; 
     FIG. 7 is a showing of yet another embodiment of the invention used to hold the ends of the stent; 
     FIG. 8 is a showing of the FIG. 7 arrangement in which the stent has been released; 
     FIG. 9 is a view of an alternative embodiment, in longitudinal section, of the distal end portion of a balloon catheter having a stent fixed to the catheter by being crimped thereto over the balloon, the ends of the stent being covered by an alternate embodiment of the invention; 
     FIG. 9A is a partial cross-section view of FIG.  7 . 
     FIG. 10 is similar to FIG. 9 in which the stent has been released; 
     FIG. 11 is a view of a modification of the embodiment shown in FIGS. 9 and 10; 
     FIG. 12 is a view of another modification to the embodiment of FIGS. 9 and 10; 
     FIGS. 13 a-c  are side views of various ring configurations; and 
     FIGS. 14 and 15 are side views of a modification of the embodiment shown in FIGS.  1  and  2 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to FIGS. 1 and 2, a stent delivery system  10  includes a catheter such as an over-the-wire or rapid exchange. Balloon catheters are preferred herein as best examples of catheters having an expandable distal end portion constructed and arranged for expanding the outer diameter of the catheter from a contracted state to an expanded state. A balloon  14  is fixed to the distal end of the catheter by adhesive attachment of the proximal end to the outer shaft  16  of the catheter and the distal end to the inner shaft  18  of the catheter. Other arrangements known in the art may be used. Balloon  14  is shown in FIG. 1 in its contracted state and in FIG. 2 in its expanded state. A stent  20  is fixed about balloon  14  by two overlying retaining sleeves  22  and  24 . 
     Various types of stents may be used with balloon expansion. For example, the stent may be a self-expanding stent which upon release self-expands and is further expanded or is merely aided in release by balloon expansion from the sleeves. Such stents may self-expand elastically or may be thermally induced such as stents formed of Nitinol or other shape memory metals or materials. 
     Any kind of stent may be delivered by the system of the invention, including plastically deformable or elastically deformable and they may be of any configuration or structure so long as they can be loaded at a low diameter and deployed at a larger diameter, i.e., have a contracted condition and being expandable to an expanded condition of large diameter. 
     Stent  20  may be any of the various types known in the art, either balloon expandable or self-expandable. Exemplary stents are shown in U.S. Pat. Nos. 4,735,665; 4,950,227; EPO application No. 707 837 A1, and U.S. Pat. No. 5,445,646. All of these patents are incorporated herein by reference and are intended to be exemplary only and not limiting. Various materials including stainless steel, tantalum, shape memory alloys and plastic may be used. 
     Stent  20  is radially compressed, as by crimping to a contracted condition, against balloon  14  to a relatively small loaded diameter having an OD of 0.044 inches for example, although it has a larger released diameter in the expanded condition. 
     Sleeves  22  and  24  may be formed of polyurethane tubing or the like, having for example an ID of 0.032-0.038 inches and a wall thickness of 0.002-0.004 inches, for example, and are axially fixed along catheter  10  to the proximal end of balloon  14  at  26  and to the distal end of balloon  14  at  27  by means of polyurethane adhesive. The distal end also includes a tapered end  28  which may be formed of the same adhesive. 
     The sleeves may be of an expandable material, preferably elastomers such as polyurethane, silicone, latex or polyether amide, by way of example only. The material should be formable into a thin walled tube. Only one sleeve may be provided at one end of the stent, preferably the distal end. However, the use of a pair of sleeves, one at each end of the stent, is most preferred. 
     Sleeves  22  and  24  overlap stent  20  at each of its ends  30  and  32 , respectively. For example, the overlap may be 0.5-1.5 mm. Reinforcing rings  34  are included under the overlapping portions of sleeves  22  and  24  and in contact with the stent ends. The rings may be attached to the sleeves with adhesive such as a polyurethane adhesive. The rings may be plastic, such as polyimide or polyethylene, or metal, such as platinum, gold, stainless steel or Nitinol, and may be 0.001-0.004 inches and the ID of the ring is to match the desired OD of the stent. The function of the rings is to compress the stent and hold it down. 
     Referring to FIG. 2, in its expanded state balloon  14  has an enlarged diameter with tapered portions  36  and  38  at each end thereof. Stent  20  is released from sleeves  22  and  24  upon expansion of balloon  14  by pulling out of the sleeves and the bunching back of the sleeves. As seen in FIG. 2 the stent deploys. The sleeves contract about balloon  14  when it is deflated. Deflation allows balloon  14  and sleeves  22  and  24  along with catheter  10  to be axially removed from the body. 
     In situations where the stent OD is large relative to the stretched ID of the sleeves; such as 0.060 inches as compared to 0.032-0.038, the fit between the sleeve ID and the balloon end portion tends to be so large as to create difficulty in forming an acceptable profile for the catheter and it is difficult to sufficiently increase the OD of the balloon catheter to provide adequate interference fit of the stent to the balloon. The rings provide increased friction fit in such instances and aid in controlling spring-back of the crimped stent. 
     In assembling the polyurethane sleeves, they can be temporarily swelled by exposure to a solvent such as toluene, alcohol, or others as known in the art, then pushed on the ends of the stent. The sleeves are then bonded to the balloon ends with a polyurethane adhesive or the like. 
     Other embodiments are within the claims to this invention. For example, referring to FIG. 3, the rings  34  seen in FIGS. 1 and 2 may take the form of wire coils  34   a  which may for example be stainless steel or Nitinol or polyamides such as nylon. 
     Referring to FIG. 4, the sleeves  22  and  24  of the preceding Figures may take the form of spiral coils of plastic  22   a  and  24   a  such as polyamide or polyethylene or polyimide for example. The spiral may be cut only partially into the body as a spiral cut or it may be cut all the way through as shown. 
     Referring to FIGS. 5 and 6, the sleeves  22  and  24  of the preceding Figures may be replaced by metal such as stainless steel or Nitinol coils  22   b  (not shown) and  24   b,  for example. FIG. 5 shows such coils engaging stent  20  in the loaded or crimped position, ready for delivery. FIG. 6 shows the coils retracted by balloon expansion with stent  20  partially expanded and ready to be deployed. 
     Referring to FIGS. 7 and 8, metal coils  22   b  (not shown) and  24   b  of FIGS. 5 and 6 may take the form of flat coiled ribbons  22   c  and  24   c  in either metal or plastic of the types already described. In FIG. 7 the coiled ribbons  22   c  and  24   c  are shown engaging the stent  20  in the loaded or crimped position, ready for delivery. FIG. 9A is a cross-sectional view of FIG.  7 . It illustrates the coil  24   c  and a ring  23  attached to the inside of the end of the coil  24   c,  the combination of which secures the end of the stent  20  onto the balloon  21  prior to expansion of the balloons. FIG. 8 shows them retracted by balloon expansion with stent  20  partially expanded ready for deployment. 
     Any body compatible metal and plastic having the requisite strength characteristics, and/or other physical characteristics may be used in the various embodiments of this invention. 
     Alternative embodiments are shown in FIGS. 9-13. These embodiments are basically the same as those mentioned above, except for the positioning of the ring. Combinations of the embodiments may be employed. Referring to FIGS. 9 and 10, a stent delivery system  110  includes a catheter such as an over-the-wire or rapid exchange. Shown is a catheter  110  having a outer shaft  116 , a guidewire lumen  118  with marker band secured thereto  115  and a distal tip  117 . As above, balloon  114  is fixed to the distal end of the catheter by adhesive attachment of the proximal end to the outer shaft  116  of the catheter and the distal end to the inner shaft  118  of the catheter. Other arrangements known in the art may be used. Balloon  114  is shown in FIG. 9 in its contracted state and in FIG. 10 in its expanded state. A stent  120  is fixed about balloon  114  by two overlying retaining sleeves, or socks,  122  and  124 , which cover the ends  130 ,  132  of the stent, respectively. 
     Various types of stents may be used with balloon expansion, as described above. 
     Stent  120  is radially compressed, as by crimping to a contracted condition, against balloon  114  to a relatively small loaded diameter having an OD of 0.044 inches for example, although it has a larger released diameter in the expanded condition. 
     As above, sleeves  122  and  124  may be formed of polyurethane tubing or the like, having for example an ID of 0.032-0.038 inches and a wall thickness of 0.002-0.004 inches, for example, and are axially fixed along catheter  110  to the proximal end of balloon  114  at  126  and to the distal end of balloon  114  at  127  by means of polyurethane adhesive  126 ,  127 . 
     As above, the sleeves may be of an expandable material, preferable elastomers such as polyurethane, silicone, latex or polyether amide, by way of example only, most preferably polyurethane or polyolefin copolymer (POC); Surlyn™. The material should be formable into a thin walled tube. Only one sleeve may be provided at one end of the stent, preferably the proximal end. However, the use of a pair of sleeves, one at each end of the stent, is most preferred. 
     Sleeves  122  and  124  overlap stent  120  at each of its ends  130  and  132 , respectively. For example, the overlap may be 0.5-1.5 mm. Rings  134  are included under, and preferably adhered to, the sleeves  122  and  124  positioned on the cone portion of the balloon  114 , preferably the upper portion, when the balloon is in its collapsed configuration. The rings may be attached to the sleeves with adhesive such as a polyurethane adhesive. The rings may be rigid or any material which effectively retains its substantially annular shape, preferably non-elastomeric material, including plastic, such as polyimide or polyethylene, or metal, such as platinum, gold, stainless steel or Nitinol, and may be 0.25-0.5 mm in length and the ID of the ring is to match the desired OD of the upper portion of the cone portion. In the alternative, the sleeve material may be of a higher Durometer urethane or even merely may have a thicker annular region in the sleeve to function as a ring. The function of the rings is to more effectively and smoothly draw the sleeve off of the ends of the stent, by creating a more axial force on the ring  134 . 
     Referring to FIG. 10, in its expanded state balloon  114  has an enlarged diameter with tapered cone portions  136  and  138  at each end thereof. Stent  120  is released from sleeves  122  and  124  upon expansion of balloon  114  due to the axial force created by the ring which draws the sleeves gradually outward, bunching the sleeve between the rings  134  and the fixed position of the sleeve on the catheter. As the balloon is inflated, a combination of radial and axial forces are applied to the ring  134 . Since the rings resist the radial force, they are driven primarily axially, dragging the sleeve off of the ends of the stent and balloon. The increased axial pressure allows for a more controlled and steady release of the stent and balloon, as opposed to a sudden release which may happen when the primary force on the ring is in the radial direction. As seen in FIG. 10 the stent deploys. The sleeves contract about balloon  114  when it is deflated. Deflation allows balloon  114  and sleeves  122  and  124  along with catheter  110  to be axially removed from the body. 
     The positioning of the rings  134 , which provides for greater axial force, allow the sleeves to be made of softer and thinner material, such as softer grades of urethanes, which include the use of lower Durometer urethane such as 65-95A or 55D (55D Durometer urethane), for example Tecothane 1055D. This is an advantage because the ring is the active movement mechanism pulling the sleeve off the balloon, releasing the stent, and by improving the flexibility of the sleeves improves the overall flexibility of the catheter, thus improving the tracking of the system through the coronary vascular. It is desirous to have the sleeve smoothly slide down the cone of the balloon without appreciably expanding. 
     In assembling the polyurethane sleeves, they can be temporarily swelled by exposure to a solvent such as toluene, alcohol, or others as known in the art, then pushed on the ends of the stent. The sleeves are then bonded to the balloon ends with a polyurethane adhesive or the like. The rings are either held in place by the tension between the sleeves and balloon or the rings are attached to the sleeves. 
     Other embodiments are within the claims to this invention. For example, referring to FIG. 11, the rings  134   a  seen in FIGS. 9 and 10 may take the form of wire coils  134   a  which may for example be stainless steel or Nitinol or polyamides such as nylon. 
     Referring to FIG. 12, the sleeves  122  and  124  of the preceding Figures may take the form of spiral coils of plastic  122   a  and  124   a  such as polyamide or polyethylene or polyimide for example. The spiral may be cut only partially into the body as a spiral cut or it may be cut all the way through as shown. 
     The rings  134  are preferably circular in shape, but may also be any regular polygon. FIG. 13 a-c  illustrate possible designs of the rings  134 . The ring of FIG.  13   a  has a tapered profile to conform to the cones&#39; tapered profiles. FIG. 13 b  illustrates a typical tubular ring and FIG. 13 c  illustrates a coil ring. 
     Any body compatible metal and plastic having the requisite strength characteristics, and/or other physical characteristics may be used in the various embodiments of this invention. 
     As shown in FIGS. 14 and 15, the sleeves  22 ,  24  may include an annular portion or region  33  of increased thickness and rigidity, wherein the annular portion  33  is integral with the sleeve material. As before, the sleeves retain the ends  30 ,  32  of the stent  20  on the balloon  36  when the balloon  36  is in its contracted state (see FIG.  14 ). When the balloon  36  expands, the sleeves  22 ,  24 , including the thickened, rigid annular region, are drawn off the ends  30 ,  32  of the stent  20 , as shown in FIG. 15, thereby releasing the stent from the catheter. 
     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 attached hereto.