Abstract:
An inner member for use within a stent delivery system is provided, wherein the stent delivery system has a stent and a balloon disposed within the stent, the balloon configured to be mounted about the inner member in a collapsed state. The inner member comprises a proximal section, a distal section, and an intermediate section. The proximal and distal sections each have a first outer diameter. The proximal and distal sections have a first and a second lumen therethrough, respectively. The intermediate section having a third lumen therethrough in communication with the first and second lumens and has a second outer diameter larger than the first outer diameter for exerting a retaining force on the stent.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates generally to an intravascular stent deployment apparatus, and more particularly, to an improved, more flexible stent delivery apparatus capable of being advanced to distal locations.  
       BACKGROUND OF THE INVENTION  
       [0002]     In a typical percutaneous transluminal coronary angioplasty (PTCA) procedure, a guiding catheter is percutaneously introduced into the cardiovascular system of a patient. The guiding catheter is advanced through a vessel until its distal end is at a desired location in the vasculature. A guidewire and a dilatation catheter having a balloon on the distal end thereof are introduced into 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. The dilatation catheter is then advanced over the advanced guide wire until the balloon is properly positioned across the lesion. Once in position, the flexible, expandable, preformed balloon is inflated to a predetermined size with a liquid or gas at relatively high pressures (e.g. about ten to twelve atmospheres) to radially compress the artherosclerotic plaque in 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 The balloon is then deflated to a small profile so that the dilatation catheter may be withdrawn from the patient&#39;s vasculature and blood flow resumed through the dilated artery.  
         [0003]     After angioplasty procedures of the kind described above, there may occur a restenosis of the artery; i.e., a re-narrowing of the treated coronary artery which is related to the development of neointinmal hyperplasia that occurs within the artery after it has been treated via PTCA. In a sense, restenosis is scar tissue that forms in response to mechanical intervention within a vascular structure. To prevent restenosis and strengthen the affected area, an intravascular prosthesis, generally referred to as a stent, can be implanted. The stent is typically delivered to the affected area in a collapsed state via a balloon catheter. The stent is expanded to a larger diameter for placement in the vasculature. This is often accomplished by the balloon portion of the catheter. The stent effectively overcomes the natural tendency of the vessel walls of some patients to close back down, thereby maintaining a normal flow of blood through the vessel that would not be possible if the stent was not in place.  
         [0004]     One type of stent which is delivered on a balloon catheter is a generally cylindrical sleeve having a number of openings in its circumference to allow the stent to take on an expanded configuration. In preparation of delivery, the stent is typically collapsed and compressed onto the outside of a collapsed, crimped balloon catheter which may include retainer rings at each end of the stent to help maintain the stent on the balloon. However, the limited securement between the stent and the balloon is not always adequate to insure that the stent will maintain its proper position while being advanced to and through a target lesion. Additionally, the outer surface of the delivery device is uneven because the stent generally extends outwardly beyond the balloon. Thus, the stent may contact a narrow vessel wall and be displaced while the catheter negotiates a narrow vessel and may possibly cause the physician difficulty when attempting to maneuver the stent across the target lesion. In such cases, it may be necessary to pull the stent delivery system back into the guide catheter. In addition, a patient&#39;s vasculature may be extremely tortuous to navigate. Because the balloon catheter is relatively stiff across the portion on which the stent is positioned, at times, the stiffness may cause a physician difficulty in negotiating twists and turns in the patient&#39;s vasculature.  
         [0005]     Thus, a need exists for a stent delivery system that prevents a stent coupled thereto from becoming displaced or dislocated from a predetermined position on the balloon catheter. Moreover, there is a need for a stent delivery system that is flexible so that the ease of navigating a patient&#39;s tortuous vasculature is increased. Other desirable features in characteristics of the present invention will become apparent from the subsequent detailed description and the appended claims taken in conjunction with the accompanying drawings.  
       BRIEF SUMMARY OF THE INVENTION  
       [0006]     According to an aspect of the present invention An inner member configured to be disposed within a stent delivery system is provided, wherein the stent delivery system has a stent and a balloon within the stent, the balloon configured to be mounted about the inner member in a collapsed state. The inner member comprises a proximal section, a distal section, and an intermediate section. The proximal and distal sections each have a first outer diameter, the a first and a second lumen therethrough, respectively. The intermediate section having a third lumen therethrough in communication with the first and second lumens and having a second outer diameter larger than the first outer diameter for exerting a retaining force on the stent.  
         [0007]     According to another aspect of the present invention, an inner member is provided that is configured to be disposed within a stent delivery system, wherein the stent delivery system has a stent and a balloon disposed within the stent, the balloon configured to be mounted about the inner member in a collapsed state and having a length in the collapsed state. The inner member comprises a proximal and a distal section, each having a first outer diameter and a first inner diameter, the proximal and distal sections having a first and a second lumen therethrough, respectively. The inner member further comprises an intermediate section having a third lumen therethrough in communication with and bondedly coupled to the first and second lumens, the intermediate section having a second outer diameter larger than the first outer diameter for exerting a retaining force on the stent and a second inner diameter larger than the first inner diameter. The proximal and distal sections comprise a flexible material and the intermediate section comprises material capable of being formed into a desired shape and size and heat treated to maintain said desired shape and size. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]     The following drawings are illustrative of the particular embodiments of the invention and therefore do not limit its scope. They are presented to assist in providing a proper understanding of the invention. The drawings are not to scale and are intended for use in conjunction with the explanations in the following detailed descriptions. The present invention will hereinafter be described in conjunction with the appended drawings, wherein like reference numerals denote like elements, and;  
         [0009]      FIG. 1  is a longitudinal view of a stent and balloon assembly in a collapsed state and in accordance with the present invention;  
         [0010]      FIG. 2  is a cross-sectional view of the balloon/stent assembly shown in  FIG. 1  taken along line  2 - 2 ;  
         [0011]      FIG. 3  is a longitudinal cross section view of a stent and balloon assembly in an expanded state and in accordance with the present invention; and  
         [0012]      FIG. 4  is a longitudinal cross section view of another embodiment of the stent and balloon assembly in an expanded state and in accordance with the present invention.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0013]     The following detailed description is merely exemplary in nature and is not intended to limit the scope, applicability, or configuration of the invention in any way. Rather, the following description provides a convenient illustration for implementing an exemplary embodiment of the invention. Various changes to the described embodiment may be made in the function and arrangement of the elements described herein without departing from the scope of the invention. A general description of a stent and balloon assembly will now be provided.  
         [0014]      FIG. 1  provides a longitudinal view of a balloon/stent assembly embodying the principles of the present invention. The balloon/stent assembly  20  shown is in a collapsed state and comprises an expandable balloon membrane  22  that is axially mounted around an inner member  24 , an expandable stent  26  axially positioned around the expandable balloon  22 , and optionally, at least one marker band  28 . The inner member  24  comprises a proximal and a distal section  40 ,  42  coupled to one another by an intermediate section  44 . Additionally, a wire lumen  30  extends through the inner member  24 . It will be recognized by those skilled in the art that wire lumen  30  is configured for the insertion of a conventional guidewire (not shown) which will enable the balloon/stent assembly  20  to be guided and positioned at a target location in the vessel to be treated.  
         [0015]     The expandable balloon  22  is mounted on the inner member  24  in a compressed or collapsed state beneath the stent  26  and extends beyond the proximal and distal ends of the stent  26 . The ends of the balloon  22  each sealingly couple and/or adhere to the proximal and distal sections  40 ,  42  of the inner member  24  to thereby define a space within which the intermediate section  44  portion of the inner member  24  resides. The balloon  22  is generally made of a pliable material such as polyethylene, polyethylene terathalate, PEBAX (polyamide block copolymers and polyester block copolymers), polyvinyl chloride, polyolefin, nylon or the like.  
         [0016]     The length of the balloon  22  may be selected to accommodate the particular configuration of the stent to be deployed. When the balloon  22  is collapsed and held beneath the stent  26 , the length of the balloon  22  which contacts the stent  26  is a “balloon working length”  36 . Additionally, the diameter of the balloon  22  may also be selected depending upon the configuration of the stent. The balloon diameter refers to the inner diameter of the balloon  22  while in a collapsed state beneath the stent  26 .  
         [0017]     Turning to  FIG. 2 , a cross-sectional view of one embodiment of the balloon/stent assembly  20  in a collapsed configuration is provided. The cross-section is taken along line  2 - 2  in  FIG. 1 . The balloon  22  is collapsed upon the intermediate section  44 , producing a plurality of folds (in this case four)  58 . Each fold  58  has a longitudinal edge  60 . The wings or folds  58  of balloon  22  are formed by pulling the balloon catheter through a forming tool having a generally cylindrical cross-section and defining a terminal opening configured to produce the desired number of wings or folds in the balloon. For example, the terminal opening may include four slits extending radially outward from the end of the forming tool, the number of slits depending upon the number of folds to be produced. As the balloon catheter is pulled through the forming tool, the balloon is pushed through the terminal opening and exits having, for example, four separate flutes. The balloon catheter bearing the fluted balloon portion is then pulled into a sheath, preferably a two-part sheath made of polytetrafluoroethylene or other suitable material so that the flutes fold and wrap around the catheter in a clockwise direction to form a generally spiral configuration. The sheath/balloon catheter assembly is then heated, preferably by placing the assembly in an oven, to form a crease in substantially the length of each of the folded flutes. Following heating, balloon  22  retains the creases formed in the wings to define a generally symmetrical, cylindrical cross-section as can be seen in  FIG. 2 .  
         [0018]     Referring still to  FIG. 2 , it can be seen that four folds  58  have been formed in balloon  22  each having an edge  60 . It should be appreciated, however, that the number of folds  58  might be varied to accommodate different configurations and/or applications. A variety of adhesives is suitable for this purpose; e.g. ultra-violet cure, instant cure, epoxy type, cyanoacrylate type, etc. The stent  26  may then be crimped or compressed onto balloon  22 .  
         [0019]     Returning to  FIG. 1 , the inner member  24  is generally tubular and, as briefly mentioned above, comprises proximal and distal sections  40 ,  42 , and an intermediate section  44  coupled therebetween. The proximal and distal sections  40 ,  42  are, accordingly, generally tubular in shape and are preferably similarly configured, having substantially similar inner and outer diameters. However, as will be appreciated by those with skill in the art, the proximal and distal sections  40 ,  42  can also be dimensioned so that the proximal section  40  has a smaller inner and/or outer diameter than the distal section  42 , or vice versa, depending on any additional feature that may be added or any purpose for which the balloon/stent assembly  20  may be used. The proximal and distal sections  40 ,  42  are preferably constructed of a flexible, biocompatible material, such as a polyethylene or a polyimide.  
         [0020]     The proximal and distal sections  40 ,  42  each partially define the wire lumen  30 . Accordingly, each section  40 ,  42  has an inner diameter  46   a ,  46   b  that is at least slightly greater than the diameter of a guidewire to be inserted therein and advanced therethrough. To aid in the advancement of any guidewire that may be inserted into the lumen  30 , the proximal and distal sections  40 ,  42  may have inner surfaces that are applied or adhered with a lubricious coating. Alternatively, the proximal and distal sections  40 ,  42  can be constructed of a biocompatible, lubricious material. Examples of such materials include, but are not limited to, varying grades of pebax, or nylon.  
         [0021]     The intermediate section  44  comprises first and second ends  50 ,  52 , and a portion of the wire lumen  30  that extends therebetween. The intermediate section  44  is configured to secure the axial position of the stent  26  when it is in a collapsed configuration on the assembly  20 . To this end, at least a portion of the intermediate section  44  has an outer diameter  48  that is substantially similar to the balloon diameter  38 .  FIG. 2  illustrates a cross section of the portion of assembly  20  with the intermediate section  44 . Thus, when the stent  26  and the crimped balloon  22  are collapsed around the intermediate section  44 , the intermediate section  44  exerts a retaining force  47  against the balloon  22  which is, in turn, exerted on the stent  26  to thereby hold the stent  26  in the desired axial position on the assembly  20 .  
         [0022]     The intermediate section  44  is preferably constructed of a biocompatible, flexible material that permits radial movement so that a physician may mechanically manipulate the intermediate section  44  portion in order to negotiate a patient&#39;s tortuous vasculature. As will be appreciated by those with skill in the art, the intermediate section  44  may be constructed of similar or different material as the other portions of the inner member  24 . In one embodiment of the present invention, the intermediate section  44  is constructed from material capable of being formed and heat-treated into a desired shape and size. In such an embodiment, the heat-treatment may additionally be employed to alter the modulus of the material. This embodiment is illustrated in  FIG. 3 . The intermediate section  44  and the proximal and distal sections  40 ,  42  are integrally formed and/or machined from the same material. However, the portion of the material that comprises the intermediate section  44  is heat treated to maintain a desired configured therein and/or to change the modulus thereof to be sufficiently stiff to maintain the desired shape yet adequately flexible to allow at least some radial movement. Suitable materials include, but are not limited to, thermoplastics, such as polyethylene, pebax, and appropriate metal alloys, such as nickel-titanium alloys.  
         [0023]     In another embodiment, shown in  FIG. 4 , the intermediate section  44  is separately constructed from the proximal and distal sections  40 ,  42  and the expanded member first and second ends  50 ,  52 , are sealingly coupled and/or joined to the proximal and distal sections  40 ,  42 , respectively. This can be achieved by any one of numerous conventional coupling mechanisms or methods. In  FIG. 4 , the ends  50   52  of the separately constructed intermediate section  44  are bonded  53  to the proximal and distal sections  40 ,  42 . Any one of numerous types of bonding may be employed, such as, for example, ultra-violet cure, instant cure, epoxy type, cyanoacrylate type, etc.  
         [0024]     The intermediate section  44  has an outer diameter  48  that is greater than the outer diameters of the proximal and distal sections  40 ,  42  and, as previously mentioned, is substantially similar to the balloon working diameter  38 . The outer diameter  48  of the intermediate section  44  may vary along the length thereof, such as illustrated in  FIGS. 3 and 4 . Accordingly, the intermediate section  44  may comprise at least a portion of tapering proximate the first and second ends  50 ,  52  to provide smooth insertion of the assembly  20  when advanced through the vessels. In one embodiment, the size of the outer diameter  48  is substantially uniform in a middle section  54  so as to be level for at least a portion of the intermediate section  44 . Alternatively, the size of the outer diameter  48  can become larger until reaching a single point or may increase and decrease along the length of the intermediate section  44 , or, can be any other configuration that aids in securing the stent  26  to the assembly  20 .  
         [0025]     The stent  26  may be constructed of any implantable material having good mechanical strength, such as stainless steel, titanium, tantalum, super-elastic nickel-titanium alloys, or high-strength thermoplastic polymers. The exterior of the stent  26  may be selectively plated with platinum or other implantable radiopaque substance to provide visibility during fluoroscopy. The cross-sectional shape of the finished stent  26  may be circular, ellipsoidal, rectangular, hexagonal, square, or any other desired shape, although a circular or ellipsoidal cross-section is preferable. In one embodiment, the stent  26  comprises a plurality of openings  56  that are configured to allow the stent  26  to collapse and expand. The length and width of the stent  26  is generally determined to a large degree by the size of the vessel into which the stent will be deployed. In a preferred embodiment, the stent  26  is sufficiently dimensioned, for example, length-wise, to maintain its axial orientation without shifting its position on the assembly  20  while exposed to the hydraulics of blood flow. The stent  26  is preferably configured to extend across a significant portion of the target lesion area.  
         [0026]     Optionally, marker bands  28 , which may be viewed through fluoroscopy, can be included to assist in positioning the assembly.  
         [0027]     When the assembly is properly located across a lesion, the balloon  22  may be inflated in a conventional manner. This results in the general uniform, symmetrical expansion of the stent  26  and balloon  22 . The amount of inflation and thus the amount of expansion of the stent  26  may be varied as dictated by the lesion itself.  
         [0028]     While at least one exemplary embodiment has been presented in the foregoing detailed description, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration of the invention in any way. Rather, the foregoing detailed description will provide those skilled in the art with a convenient road map for implementing the exemplary embodiment or exemplary embodiments. It should be understood that various changes can be made in the function and arrangement of elements without departing from the scope of the invention as set forth in the appended claims and the legal equivalents thereof.