Abstract:
A catheter having an multilayered shaft section with a first layer formed of a polyimide first material and a second layer formed of a second material. In a presently preferred embodiment, the polyimide material is a thermoset polyimide. However, in alternative embodiments, a thermoplastic polyimide is used. The thermoset polyimide has a very high glass transition temperature (Tg) of approximately 400° C. (as measured by differential scanning calorimetry), and excellent dimensional stability at the processing temperature of polyamides commonly used in catheter components. As a result, during formation and assembly of the catheter, production of a thin polyimide layer with controlled dimensions is facilitated. The polyimide has a high modulus and provides a thin walled yet highly pushable shaft section, while the second layer provides kink resistance. In one embodiment, the second material is selected from the group consisting of a polyamide material and a polyurethane material.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    This invention generally relates to catheters, and particularly intravascular catheters for use in percutaneous transluminal coronary angioplasty (PTCA) or for the delivery of stents.  
           [0002]    In a typical PTCA procedure, a dilatation balloon catheter is advanced over a guidewire to a desired location within the patient&#39;s coronary anatomy where the balloon of the dilatation catheter is positioned within the stenosis to be dilated. The balloon is then inflated with radiopaque liquid at relatively high pressures (generally 4-16 atmospheres) to dilate the stenosed region of the diseased artery. One or more inflations may be needed to effectively dilate the stenosis. Additionally, a stent may be implanted within the artery, typically by delivery to a desired location within the artery in a contracted condition on a balloon of a catheter which is similar in many respects to a balloon angioplasty catheter, and expansion to a larger diameter by inflation of the balloon.  
           [0003]    An essential step in effectively performing a PTCA procedure is properly positioning the balloon catheter at a desired location within the coronary artery. To properly position the balloon at the stenosed region, the catheter must have good pushability and flexibility, to be readily advanceable within the tortuous anatomy of the patient&#39;s vasculature.  
           [0004]    What has been needed is a catheter which is highly trackable within the patient&#39;s anatomy, with improved flexibility and pushability. The catheter of the present invention provides these and other advantages.  
         SUMMARY OF THE INVENTION  
         [0005]    The invention is directed to a catheter having an multilayered shaft section with a first layer formed of a polyimide first material and a second layer formed of a second material. In a presently preferred embodiment, the polyimide material is a thermoset polyimide. However, in alternative embodiments, a thermoplastic polyimide is used. The thermoset polyimide has a very high glass transition temperature (Tg) of approximately 400° C. (as measured by differential scanning calorimetry), and excellent dimensional stability at the processing temperature of polyamides commonly used in catheter components. As a result, during formation and assembly of the catheter, production of a thin polyimide layer with controlled dimensions is facilitated. The polyimide has a high modulus and provides a thin walled yet highly pushable shaft section, while the second layer provides kink resistance.  
           [0006]    In one embodiment, the second material is selected from the group consisting of a polyamide and a polyurethane. In one presently preferred embodiment, the second material is a polyamide, and the polyamide is selected from the group consisting of a nylon and a copolyamide such as polyether block amide (PEBAX). Although discussed below for convenience primarily in terms of a polyamide second layer, it should be understood that other materials such as a polyurethane may be used for the second layer in other embodiments. The polyimide first material is not compatible with the second material (e.g., polyamide or polyurethane), and consequently, the polyimide material is not fusion (i.e., thermal) bondable to the second material. The polyimide material is a high strength material preferably having a higher Shore durometer hardness than the polyamide layer. The high strength of the polyimide material allows the wall thickness of the polyimide first layer to be small for improved shaft flexibility and low profile. The polyamide layer provides a bonding layer which can be fusion bonded to polymeric materials compatible therewith and conventionally used for other catheter components, such as nylon, PEBAX, and polyurethane. Additionally, the polyamide layer contributes to the kink resistance of the catheter. In a presently preferred embodiment, the polyamide second layer is an outer layer forming an outer surface of the multilayered shaft section, and the polyimide first layer is an inner layer forming an inner surface of the multilayered shaft section.  
           [0007]    In a presently preferred embodiment, the catheter is a balloon catheter generally comprising an elongated shaft having a proximal portion and a distal portion, with a balloon on the distal portion of the shaft. The balloon catheters of the invention may comprise a variety of suitable balloon catheters, including coronary and peripheral dilatation catheters, stent delivery catheters, drug delivery catheters, and the like.  
           [0008]    The catheter shaft typically has an outer tubular member with a lumen therein which, in the case of a balloon catheter, is an inflation lumen in fluid communication with the balloon interior. The shaft also has an inner tubular member disposed at least in part within a portion of the outer tubular member lumen, with a lumen therein which is typically a guidewire receiving lumen. At least a section of the outer tubular member is the multilayered section in accordance with the invention. The multilayered shaft section of the invention may extend the full length of the outer tubular member, or alternatively, it may be a distal shaft section, a proximal shaft section, or a midshaft section bonded to an adjacent shaft section(s).  
           [0009]    In one embodiment, the catheter is a rapid exchange type catheter, having a guidewire receiving lumen in a distal section of the catheter shaft. Rapid exchange catheters generally have a distal guidewire port in the distal end of the catheter, a proximal guidewire port spaced a relatively short distance proximally from the distal guidewire port and a relatively long distance from the proximal end of the catheter shaft, and a relatively short guidewire receiving lumen extending therebetween. In an alternative embodiment, the catheter is an over-the-wire type catheter having an elongated shaft with proximal and distal ends, a guidewire port in the proximal end, a guidewire port in the distal end, and a guidewire lumen extending therein from the distal end to the proximal end of the catheter shaft.  
           [0010]    In a presently preferred embodiment, the polyamide second layer is in direct contact with the polyimide first layer around a circumference thereof. Thus, unlike catheter shafts having a braid layer between a first and second layer, the first layer and the second layer of the multilayered shaft section are not in whole or in part separated from one another by a braid, mesh or other layer.  
           [0011]    In a presently preferred embodiment, the polyimide first layer is formed by a solution process, and not by melt extrusion. In a suitable solution forming process, a polyimide solution is dip, or otherwise, coated onto a neckable mandrel, as described in U.S. Pat. Nos. 4,826,706 and 4,659,622, and the Manufacturing Process section of the Phelps Dodge High Performance Conductors brochure, A Primer on Polyimide Tubing, pp. 1, incorporated herein by reference in their entireties, and then separated intact from the mandrel, to thereby produce a tubular member. The dip coated mandrel can be passed through dies to control the outer dimension of the polyimide layer, and the diameter of the removable mandrel determines the inner diameter of the polyimide tube. Similarly, the polyamide or polyurethane second layer is preferably applied as a solution onto the polyimide layer, in order to provide good contact and adhesion between the polyimide layer and the polyamide or polyurethane layer. Thus, although the polyimide material is not fusion bondable to the polyamide or polyurethane material, the solution coating process provides well adhered layers which remain together during component assembly and under the high inflation pressures used during inflation of the catheter balloon. As a result, a separate adhesive or compatibilizing layer is not required between the polyimide first layer and the second layer, and, consequently, the multilayered shaft section of the invention has excellent flexibility, manufacturability, and low profile.  
           [0012]    The catheter of the invention is highly pushable, flexible, and kink resistant due to the synergy of the materials used in the multilayered shaft section. The polyimide material has a high modulus which allows for a very thin walled yet high strength shaft. The high flexural modulus of the polyimide layer provides excellent push transmission along the shaft length during advancement within the patient&#39;s vasculature and across a lesion. Moreover, the high modulus polyimide layer provides the ability to be inflated to high inflation pressure without rupturing during balloon inflation. The thin walled shaft section provides a low profile shaft without sacrificing lumen size. Additionally, the polyamide layer provides an outer layer which is readily fusion bondable with polymeric materials commonly used in other catheter components such as balloons or shaft sections. Thus, the flexible and pushable distal shaft section provides a catheter with excellent trackability, and allows easy advancement over a guidewire and maneuvering within the patient&#39;s tortuous anatomy, to position the operative portion of the catheter at a desired location within the patient. These and other advantages of the invention will become more apparent from the following detailed description of the invention and the accompanying exemplary drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]    [0013]FIG. 1 is an elevational view of a catheter which embodies features of the invention.  
         [0014]    [0014]FIG. 2 is an enlarged view, partially in section, of the portion of the catheter shown in FIG. 1, taken within circle  2 .  
         [0015]    [0015]FIG. 3 is a transverse cross sectional view of the catheter shown in FIG. 2, taken along line  3 - 3 .  
         [0016]    [0016]FIG. 4 is a transverse cross sectional view of the catheter shown in FIG. 2, taken along line  4 - 4 .  
         [0017]    [0017]FIG. 5 is an elevational view of an alternative embodiment of a catheter which embodies features of the invention, having a rapid exchange distal guidewire lumen.  
         [0018]    [0018]FIG. 6 is a transverse cross sectional view of the catheter shown in FIG. 5, taken along line  6 - 6 .  
         [0019]    [0019]FIG. 7 is a transverse cross sectional view of the catheter shown in FIG. 5, taken along line  7 - 7 .  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0020]    FIGS.  1 - 4  illustrate an over-the-wire type balloon catheter  10  embodying features of the invention. Catheter  10  generally comprises an elongated catheter shaft  11  having a proximal end, a distal end, a proximal shaft section  12 , a distal shaft section  13 , an outer tubular member  14 , and an inner tubular member  15 . Inner tubular member  15  defines a guidewire lumen  16  adapted to slidingly receive a guidewire  17 , and the coaxial relationship between outer tubular member  14  and inner tubular member  15  defines annular inflation lumen  18  (see FIGS. 3 and 4, illustrating transverse cross sections of the catheter  10  of FIG. 1, taken along lines  3 - 3  and  4 - 4 , respectively). An inflatable balloon  19  is disposed on the distal shaft section  13 , having a proximal skirt section sealingly secured to the distal end of outer tubular member  14 , and a distal skirt section sealingly secured to the distal end of inner tubular member  15 , so that its interior is in fluid communication with inflation lumen  18 . An adapter  20  at the proximal end of the shaft is configured to provide access to guidewire lumen  17 , and to direct inflation fluid through arm  21  into inflation lumen  18 . Balloon  19  has an inflatable working length located between tapered sections of the balloon. FIG. 1 illustrates the balloon  19  in an uninflated configuration prior to inflation. The distal end of catheter may be advanced to a desired region of a patient&#39;s body lumen in a conventional manner, and balloon  19  inflated to perform a procedure such as dilatation of a stenosis.  
         [0021]    In the embodiment illustrated in FIGS.  1 - 4 , the outer tubular member has a proximal section  25 , and a distal section  26 . As best illustrated in FIG. 2, showing an enlarged longitudinal cross sectional view of the section of the catheter  10  shown in FIG. 1, taken within circle  2 , the proximal section  25  is multilayered with a first layer  27  of a polyimide material and a second layer  28  of a material which is different from the first material, and which is preferably a polyamide material or a polyurethane. A presently preferred polyimide for the first layer is available from Phelps Dodge High Performance Conductors. Preferably, the polyimide is a thermoset polyimide with excellent dimensional stability, which thus has a cross linked 3-dimensional network maintained a high temperatures. A presently preferred polyamide for the second layer is PEBAX, available from Elf Autochem. A presently preferred polyurethane for the second layer is polyurethane N, available from Phelps Dodge High Performance Conductors. The second layer  28  is on an outer surface of the first layer  27 . As illustrated in the figures, the second layer  28  is a solid-walled layer, which is in direct contact with the first layer  27  around a circumference of the first layer  27 . Thus, the second layer  28  is not separated from the first layer  27  by an intermediate layer or braid, and is not itself a braid or mesh.  
         [0022]    In the embodiment of FIGS.  1 - 4 , the second layer  28  of the proximal section  25  forms an outer surface of the multilayered section of the outer tubular member  14 . Thus, although a coating such as a lubricious coating conventionally used on catheter shafts may optionally be provided on at least a section of an outer surface of the multilayered shaft section, a structural or reinforcing layer is not on an outer surface of the second layer  28  in the embodiment of FIG. 1. The first layer  27  forms an inner surface of the multilayered section of the outer tubular member  14 . An optional lubricious inner liner such as a PTFE or HDPE layer may be provided on an inner surface of the first layer  27 , as conventionally known for catheter shafts.  
         [0023]    In the embodiment illustrated in FIG. 1, the distal section  26  of the outer tubular member  14  comprises a single layered tubular member  29 , with a proximal end bonded to a distal end of the proximal section  25  of the outer tubular member  14 . In a presently preferred embodiment, the distal section  26  is formed of a polymeric material, such as polyether block amide (PEBAX), which is compatible with a polyamide material such as PEBAX and nylon, forming the second layer  28  of the proximal section  25 , to allow for fusion bonding the two sections together. However, a variety of suitable methods of bonding can be used including adhesive bonding. Additionally, although a lap joint is illustrated in FIG. 2 between the proximal and distal sections  25 / 26 , a variety of suitable joints may be used including a butt joint, or a lap joint in which the outer diameter of the proximal section  25  is reduced at the joint so that the distal section  26  is flush with the proximal section.  
         [0024]    In an alternative embodiment (not shown), the multilayered section of the outer tubular member  14  is the distal section  26 , and the balloon proximal skirt section is fusion bonded to the second layer  28  of the outer tubular member  14  multilayered distal section.  
         [0025]    FIGS.  5 - 7  illustrate an alternative embodiment of the invention, in which the balloon catheter  50  is a rapid exchange catheter with an outer tubular member  54  having a multilayered distal section  56 . A illustrated in FIG. 5, catheter  50  generally comprises an elongated catheter shaft  51  having a proximal end, a distal end, a proximal shaft section  52 , a distal shaft section  53 , an outer tubular member  54 , and an inner tubular member  55 . Inner tubular member  55  defines a guidewire lumen  56  adapted to slidingly receive a guidewire  57 . Inflation lumen  58  is defined by the outer tubular member  54 . An inflatable balloon  59  is disposed on the distal shaft section  53 , having a proximal skirt section sealingly secured to the distal end of outer tubular member  54 , and a distal skirt section sealingly secured to the distal end of inner tubular member  55 , so that its interior is in fluid communication with inflation lumen  58 . An adapter  60  at the proximal end of the shaft is configured to direct inflation fluid into inflation lumen  58 .  
         [0026]    In the embodiment illustrated in FIG. 5, the outer tubular member  54  comprises a proximal section  61 , a distal section  62 , and a midshaft section  63  having a proximal end bonded to the proximal section  61  and a distal end bonded to the distal section  62 . A guidewire proximal port  64  in a side wall of the midshaft section  63  is in fluid communication with the lumen  56  of the inner tubular member  55 , and with a distal guidewire port in the distal end of the shaft. As shown in FIG. 5, the guidewire  57  exits the catheter proximally from the guidewire proximal port  64  and extends alongside and exteriorly of the proximal section  61  to the proximal end of the catheter  50 . Although the guidewire proximal port  64  is in the midshaft section, in an alternative embodiment (not shown) it is located in the proximal section  61  or the distal section  63 . Additionally, in an alternative embodiment of rapid exchange catheter  50 , the outer tubular member  54  comprises the proximal section  61  directly bonded to the distal section  62 , without a midshaft section therebetween (not shown). A support mandrel  65  is disposed in the inflation lumen  58 , with a distal end distal to the guidewire proximal port  64 . The mandrel is typically a metal member, such as a stainless steel or NiTi member, enhancing the pushability of the catheter  50 .  
         [0027]    In the embodiment illustrated in FIG. 5, the distal section  62  of the outer tubular member  54  is a multilayered section with a first layer  67  of a polyimide material and a second layer  68  of a material which is different from the first material, and which is preferably a polyamide material. The multilayered distal section  62  is similar to the multilayered section of the catheter  10  discussed above in relation to the embodiment of FIGS.  1 - 4 , and the discussion above relating to the first layer  27  and second layer  28  of the multilayered proximal section  25  of catheter  10  applies as well to first and second layers  67 / 68  of the multilayered distal section  62  of catheter  50 . In a presently preferred embodiment, the second layer  68  of the multilayered distal section  62  of the outer tubular member  54  is a polyether block amide (PEBAX) material on the polyimide first layer  61 , providing a highly kink resistant and pushable rapid exchange catheter. Balloon  59  has a proximal skirt section bonded to the second layer  68  of the distal section  62  of outer tubular member  54 .  
         [0028]    When the catheter of the invention is used in an angioplasty procedure, the balloon catheter of the invention is advanced over the guidewire until the balloon is properly positioned across the stenosis. The balloon can be inflated in a conventional manner by introducing inflation fluid through the inflation lumen. After one or more inflations, the balloon is deflated and the catheter removed from the patient. A similar procedure is used when the balloon has a stent (not shown) mounted thereon for implanting the stent in the body lumen.  
         [0029]    The length of the dilatation catheter is generally about 137 to about 145 centimeters, and typically about 140 centimeters for PTCA. The outer tubular member  14 / 54  distal section has an outer diameter (OD) of about 0.028 to about 0.036 inch (0.70-0.91 mm), and an inner diameter (ID) of about 0.024 to about 0.035 inch (0.60-0.89 mm), and the outer tubular member  14 / 54  proximal section has an OD of about 0.017 to about 0.034 inch (0.43-0.87 mm), and an inner diameter (ID) of about 0.012 to about 0.022 inch (0.30-0.56 mm). The inner tubular member  15 / 55  has an OD of about 0.017 to about 0.026 inch (0.43-0.66 mm), and an ID of about 0.015 to about 0.018 inch (0.38-0.46 mm) depending on the diameter of the guidewire to be used with the catheter. In one embodiment, the polyimide layer is about 0.0005 inches (0.0127 mm) to about 0.0015 inches (0.038 mm) thick, and preferably about 0.0005 inches (0.0127 mm) to about 0.00075 inches (0.019 mm) thick, and the second layer (e.g., of polyamide or polyurethane) is about 0.00075 inch (0.019 mm) to about 0.00125 inches (0.03 mm) thick, preferably about 0.001 (0.025 mm) to about 0.00125 inches (0.03 mm) thick. In a presently preferred embodiment, the polyimide first layer has a smaller thickness than the second layer.  
         [0030]    While the present invention has been described herein in terms of certain preferred embodiments, those skilled in the art will recognize that modifications and improvements may be made without departing form the scope of the invention. For example, while the catheter illustrated in the figures has coaxial inner and outer tubular members, other conventional catheter shaft configurations can be used along at least a section of the catheter, such as side-by-side, dual lumen configurations. Moreover, while individual features of one embodiment of the invention may be discussed or shown in the drawings of the one embodiment and not in other embodiments, it should be apparent that individual features of one embodiment may be combined with one or more features of another embodiment or features from a plurality of embodiments