Abstract:
A balloon catheter having a multilayered shaft with variable flexibility along the length of the shaft. In a presently preferred embodiment, the multilayered shaft has a multilayered outer tubular member and an inner tubular member, both the inner and outer tubular members having sections along which the flexibility and/or diameter of the tubular members decrease. These diameter and flexibility transition sections along the outer tubular member are preferably aligned with transitions along the inner tubular member, to provide improved catheter performance.

Description:
BACKGROUND OF THE INVENTION 
   This invention generally relates to medical devices, and particularly to intracorporeal devices for therapeutic or diagnostic uses, such as balloon catheters. 
   In percutaneous transluminal coronary angioplasty (PTCA) procedures, a guiding catheter is advanced until the distal tip of the guiding catheter is seated in the ostium of a desired coronary artery. A guidewire, positioned within an inner lumen of a dilatation catheter, is first advanced out of the distal end of the guiding catheter into the patient&#39;s coronary artery until the distal end of the guidewire crosses a lesion to be dilated. Then the dilatation catheter having an inflatable balloon on the distal portion thereof is advanced into the patient&#39;s coronary anatomy, over the previously introduced guidewire, until the balloon of the dilatation catheter is properly positioned across the lesion. Once properly positioned, the dilatation balloon is inflated with fluid one or more times to a predetermined size at relatively high pressures (e.g., greater than 8 atmospheres) so that the stenosis is compressed against the arterial wall and the wall expanded to open up the passageway. Generally, the inflated diameter of the balloon is approximately the same diameter as the native diameter of the body lumen being dilated so as to complete the dilatation but not overexpand the artery wall. Substantial, uncontrolled expansion of the balloon against the vessel wall can cause trauma to the vessel wall. After the balloon is finally deflated, blood flow resumes through the dilated artery and the dilatation catheter can be removed therefrom. 
   In such angioplasty procedures, there may be restenosis of the artery, i.e. reformation of the arterial blockage, which necessitates either another angioplasty procedure, or some other method of repairing or strengthening the dilated area. To reduce the restenosis rate and to strengthen the dilated area, physicians frequently implant a stent inside the artery at the site of the lesion. Stents may also be used to repair vessels having an intimal flap or dissection or to generally strengthen a weakened section of a vessel. Stents are usually delivered to a desired location within a coronary artery in a contracted condition on a balloon of a catheter which is similar in many respects to a balloon angioplasty catheter, and expanded to a larger diameter by expansion of the balloon. The balloon is deflated to remove the catheter and the stent left in place within the artery at the site of the dilated lesion. 
   The progression of improvements in dilatation catheters generally has been to make catheters with lower profiles and with the proximal portions of the catheter shaft being much stiffer than the distal portions. However, this progression has also increased the difficulty in forming smooth transitions between the various sections of the catheter shaft, and a balance must be struck between the often competing considerations of force transmission (pushability), kink resistance, flexibility, and low profile. 
   What has been needed is a balloon catheter with a shaft having an improved combination of characteristics to provide improved catheter performance. 
   SUMMARY OF THE INVENTION 
   This invention is directed to a balloon catheter having a multilayered shaft with variable flexibility along the length of the shaft. In a presently preferred embodiment, the multilayered shaft has a multilayered outer tubular member and an inner tubular member, both the inner and outer tubular members having sections along which the flexibility and/or diameter of the tubular members decrease. These diameter and flexibility transition sections along the outer tubular member are preferably aligned with transitions along the inner tubular member, to provide improved catheter performance. 
   The balloon catheter generally includes an elongated shaft formed at least in part by the outer tubular member and inner tubular member, and a balloon sealingly secured to a distal section of the shaft. The shaft has an inflation lumen which is defined by the outer tubular member (e.g., the annular space between the inner surface of the outer tubular member and the outer surface of the inner tubular member therein) and which is in fluid communication with the balloon interior, and has a guidewire lumen defined by the inner tubular member. 
   The multilayered outer tubular member has at least first and second (e.g., inner and outer) layers, extending along at least part of the length of the outer tubular member. The first and second layers have different stiffnesses (e.g., are formed of polymers having different Shore durometer hardness values). In one presently preferred embodiment, the first and second layers extend the entire length of the outer tubular member, although in alternative embodiments, at least one of the first and second layers is shorter than the outer tubular member. 
   In a presently preferred embodiment, the multilayered outer tubular member has a relatively stiff proximal section with the first and second layers extending therealong in a first relative proportion which is preferably substantially constant, a relatively flexible distal section with the first and second layers extending therealong in a second relative proportion which is preferably substantially constant and which is different from the first relative proportion, and a transition section between the proximal and distal sections along which the relative proportion of the first and second layers inversely cotapers to transition from the first to the second relative proportion. The transition section has a proximal and a distal portion, and has a tapered portion along which the diameter of the outer tubular member decreases distally. Similarly, the distal section has a tapered portion along which the diameter of the outer tubular member again decreases distally. 
   The inverse cotaper in the transition section is preferably produced by extruding the first layer from an extruder having a first pump at an output end thereof, and extruding the second layer from a second extruder having a second pump at an output end thereof, which in a presently preferred embodiment is formed according to a method set forth in U.S. application Ser. No. 09/707,681 (Carter), incorporated by reference herein in its entirety. However, a variety of suitable conventional coextrusion systems can be used, such as those using on/off valves to control the flow of the polymers making up the two layers. Additionally, U.S. Pat. No. 5,725,814 (Harris), incorporated by reference herein in its entirety, discloses a coextrusion apparatus using gear pumps at the output ends of multiple extruders, which can be used to vary the relative amount of first and second layers. The gear pumps are used to vary the relative amount of the polymers extruded and to thus form an extruded tube having multiple layers, the proportions of which vary along the length of the extruded tube. 
   The shaft inner tubular member is preferably a multilayered tubular member formed of two or more polymeric layers. In a presently preferred embodiment, the inner tubular member has a proximal section, a distal section, and a tapered section extending between the proximal section and the distal section and along which the diameter of the inner tubular member decreases distally. In a presently preferred embodiment, the tapered multilayered inner member is formed according to a method set forth in U.S. Pat. No. 6,579,484 (Tiernan, et al.), incorporated by reference herein in its entirety, using a co-extrusion system including a puller with programmable tapering capabilities. 
   The multilayered outer tubular member transitions to distally decreasing flexibility and diameter, without the need for joining separate tubes together in an end-to-end fashion. Consequently, the stiffness and profile increases caused by such junctions are avoided in the catheter of the invention. The single piece multilayered outer tubular member is completely junctionless (i.e., no bonded junctions between individual longitudinal sections of the outer tubular member), as is the inner tubular member. With the absence of such junctions, the push applied at the proximal end of the shaft is steadily transmitted to the distal portion of the shaft. 
   The catheter has a shaft with a gradual increase in flexibility along the length of the shaft. Moreover, the catheter has optimized inflation/deflation and delivery properties, due at least in part to the multilayered transitioning tubular members and the alignment of one or more transitions of the outer member with a transition of the inner member. For example, in a presently preferred embodiment, the entire length of the inner tubular member tapered section is radially aligned with a location on the outer tubular member located in the transition section of the outer tubular member (i.e., at least part of the outer tubular member transition section extends coextensively with the entire length of the inner tubular member tapered section). 
   The catheter of the invention has excellent pushability, kink resistance, flexibility, and low profile, for improved ability to be advanced through a patient&#39;s tortuous anatomy and position the balloon or other distal end instrumentality across an occluded section of the blood vessel. These and other advantages of the invention will become more apparent from the following detailed description and accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is an elevational view, partially in section, of a stent delivery balloon catheter embodying features of the invention. 
       FIG. 2  is an enlarged, longitudinal cross sectional view of the balloon catheter shown in  FIG. 1 , taken along line  2 - 2 . 
       FIGS. 3-5  are transverse cross sectional views of the balloon catheter shown in  FIG. 2 , taken along lines  3 - 3 ,  4 - 4 , and  5 - 5 , respectively. 
       FIG. 6  an enlarged, longitudinal cross sectional partial view of an alternative embodiment of a balloon catheter embodying features of the invention, having the first and second layers of the outer tubular member extending less than the entire length of the outer tubular member 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1  illustrates an over-the-wire type stent delivery balloon catheter  10  embodying features of the invention. Catheter  10  generally comprises an elongated catheter shaft  12  having an outer tubular member  14 , and an inner tubular member  16  extending in the outer tubular member  14  from the proximal to the distal end of the catheter shaft. Inner tubular member  16  defines a guidewire lumen  18  configured to slidingly receive a guidewire  20 , and the outer tubular member  14  defines an inflation lumen  22 , as best shown in  FIG. 3  illustrating a transverse cross section of the distal end of the catheter shown in  FIG. 1 , taken along line  3 - 3 . In the embodiment of  FIG. 1 , the inflation lumen  22  has an annular shape as a result of the coaxial relationship between outer tubular member  14  and inner tubular member  16 . Guidewire  20  extends out the distal end of the catheter through a distal guidewire port  21 . An inflatable balloon  24  disposed on a distal section of catheter shaft  12  has a proximal skirt section  25  sealingly secured to the distal end of outer tubular member  14  and a distal skirt section  26  sealingly secured to the distal end of inner tubular member  16 , so that the balloon interior is in fluid communication with inflation lumen  22 . An adapter  28  at the proximal end of catheter shaft  12  is configured to provide access to guidewire lumen  18 , and to direct inflation fluid through arm  29  into inflation lumen  22 . In the embodiment illustrated in  FIG. 1 , the balloon  24  is illustrated prior to complete inflation thereof, with an expandable stent  30  mounted on the working length of the balloon  24  for implanting within a patient&#39;s body lumen  27 . The distal end of catheter  10  may be advanced to a desired region of the patient&#39;s body lumen  27  in a conventional manner, the balloon  24  inflated to expand stent  30 , and the balloon deflated, leaving the stent  30  implanted in the body lumen  27 . 
     FIG. 2  illustrates an enlarged, longitudinal cross sectional view of the balloon catheter shown in  FIG. 1 , taken along line  2 - 2 . In the embodiment of  FIG. 2 , the outer tubular member  14  is multilayered with an inner layer  32  and an outer layer  33 . The inner and outer layers  32 ,  33  are typically coextruded, and extend the entire length of the multilayered outer tubular member  14  in the embodiment of  FIG. 2 . The inner layer  32  is formed of a polymeric material having a different stiffness (e.g., a different Shore durometer hardness) than the outer layer  33 . The thickness of each layer  32 ,  33  varies along the length of the outer tubular member  14 , to thereby provide the multilayered outer tubular member with a distal section  35  which is more flexible than a proximal section  34 . In the embodiment illustrated in  FIG. 2 , in order for the distal section  35  to be more flexible than the proximal section  34 , the outer layer  33  is stiffer (e.g., is formed of a polymer having a high Shore durometer hardness) than the inner layer  32 . Although discussed below primarily in terms of an embodiment in which the outer layer  33  is formed of a polymer having a higher Shore durometer hardness than the inner layer  32 , it should be understood that in alternative embodiment (not shown), the inner layer  32  is stiffer than the outer layer  33 , so that the relative proportions of the two layers as discussed in more detail below would be reversed. 
   The outer tubular member  14  has a transition section  36  which extends between and connects the distal end of the proximal section  34  and the proximal end of the distal section  35 . The inner and outer layers  32 ,  33  inversely cotaper along the entire length of the transition section  36 , to thereby transition from the relative proportion of the proximal section  34  to the relative proportion of the distal section  35 . 
   In the illustrated embodiment, in the proximal section  34 , the thickness of the outer layer  33  is about 75% of the total thickness of the two layers  32 ,  33 , and the thickness of the inner layer  32  is about 25% of the total thickness of the two layers  32 ,  33  (i.e., the relative proportion of the inner and outer layers  32 ,  33  is about 25:75). In general, a suitable relative proportion of the inner and outer layers  32 ,  33  along the proximal section  34  in the embodiment of  FIG. 2  is anywhere from about 5:95 to about 40:60, more specifically about 20:80 to about 30:70, depending on the nature of the polymers forming the layers  32 ,  33  and the desired catheter performance. In a presently preferred embodiment, the relative proportion of the inner and outer layers  32 ,  33  is constant along the entire length of the proximal section  34 . However, in alternative embodiments (not shown), the relative proportion may transition to a different relative proportion within the proximal section  34 . It should be understood that in an embodiment in which the outer layer  33  is formed of a more flexible polymer than the inner layer  32 , the outer layer  33  would alternatively be about 25% of the total thickness of the two layers  32 ,  33  along the proximal section  34  in the embodiment of  FIG. 2 . 
   In the illustrated embodiment, the distal section  35  of the outer tubular member  14  has the inner and outer layers  32 ,  33  in a relative proportion of about 50:50. In general, a suitable relative proportion of the inner and outer layers  32 ,  33  along the distal section  35  is anywhere from about 40:60 to about 95:5, more specifically about 40:60 to about 60:40, depending on the nature of the polymers forming the layers  32 ,  33  and the desired catheter performance. Similar to the proximal section  34 , in a presently preferred embodiment, the relative proportion of the inner and outer layers  32 ,  33  is constant along the entire length of the distal section  35 , although it may alternatively vary. 
   The transition section  36  has a length greater than the distal section  35  and less than the proximal section  34  of the outer tubular member  14 . In one embodiment, the transition section  36  is about 33 cm in length, the distal section  35  is about 15 cm in length, and the proximal section  34  is about 91 cm in length. The relatively long length of the transition section  36  provides a gradual change in the flexibility of the shaft as the proportion of the inner and outer layers  32 ,  33  changes there along. 
   In the illustrated embodiment, the transition section  36  of the outer tubular member  14  has a proximal portion  40 , a distal portion  41 , and a tapered portion  42  therebetween. 
   The inner diameter and outer diameter of the outer tubular member  14  decrease distally along the length of the tapered portion  42  of the transition section  36 . Similarly, the inner and outer diameter of the outer tubular member again decrease distally along the length of a tapered portion  43  of the distal section  35 . As a result, the inner diameter of the distal portion  41  of the transition section  36  is less than the inner diameter of the proximal portion  40  of the transition section  36  and is greater than the inner diameter of at least a portion of the distal section  35  of the outer tubular member  14 , and the outer diameter of the distal portion  41  of the transition section  36  is less than the outer diameter of the proximal portion  40  of the transition section  36  and is greater than the outer diameter of at least a portion of the distal section  35  of the outer tubular member  14 . 
   The tapered portions  42  and  43  are typically formed by necking the outer tubular member  14 , by for example pulling the outer tubular member  14  down onto a tapered mandrel while heating at least part of the outer tubular member  14 . The tapered portion  43  in the distal section  35  of the outer tubular member  14  provides a gradual decrease in the outer tubular member outer diameter. The entire length of the tapered portion  43  is typically about 1 to about 8 cm, more specifically about 4 to about 6 cm. Typically, the entire length of the tapered portion  43  is about 15% to about 50% of the entire length of the distal section  35 . The tapered portion  42 , located proximal to tapered portion  43 , is typically less gradual, tapering distally over a length which in one embodiment is about 5 to about 30 mm, more specifically about 10 to about 20 mm. Typically, the entire length of the tapered portion  42  is about 5% to about 10% of the entire length of the transition section  36 . In one embodiment, the wall thickness of the outer tubular member  14  is constant, or is substantially constant (i.e., changes by less than about 10% at tapered portions  42  and  43 ), along the length of the outer tubular member  14 . 
   The inner tubular member  16  is preferably a multilayered tubular member. In the embodiment of  FIG. 2 , the inner tubular member has three layers, namely, an inner layer  50 , middle layer,  51 , and outer layer  52 , of different polymeric materials extending from a proximal end to a distal end of the inner tubular member in a constant relative proportion. The multilayered inner tubular member  16  has a proximal section  54 , a distal section  55 , and a tapered section  56  extending between and connecting a distal end of the proximal section  54  and a proximal end of the distal section  55  and along which the inner diameter and outer diameter of the inner tubular member  14  decrease distally. Thus, the inner diameter of the distal section  55  of the inner tubular member  16  is less than the inner diameter of the proximal section  54  of the inner tubular member  16 , and the outer diameter of the distal section  55  of the inner tubular member  16  is less than the outer diameter of the proximal section  54  of the inner tubular member  16 . 
   At least part of the tapered section  56  of the inner tubular member  16 , and preferably the entire length of the tapered section  56  of the inner tubular member  16  is radially aligned with a location on the outer tubular member located in the transition section  36  of the outer tubular member  14 . In the illustrated embodiment, the distal end of the tapered section  56  is radially aligned with a location on the outer tubular member located at a proximal end of the tapered portion  43  of the distal section  35  of the outer tubular member  14 . The proximal end of the tapered section  56  is radially aligned with a location on the outer tubular member  14  located in the proximal portion  40  of the transition section  36  of the outer tubular member  14 . 
   In a presently preferred embodiment, the tapered section  56  of the inner tubular member  16  is formed during extrusion of the inner tubular member  16 . The entire length of the tapered section  56  of the inner tubular member  16  is typically about 10% to about 25% of the entire length of the inner tubular member  16 , and in one embodiment is about 18 to about 22 cm in length. In one embodiment, the wall thickness of the inner tubular member  16  is constant, or is substantially constant (i.e., changes (e.g., decreases) by less than about 10% at tapered section  56 ), along the length of the inner tubular member  16 . 
   In a presently preferred embodiment, the outer layer  33  of the outer tubular member  14  is formed of a polyamide such as Nylon  12 , and the inner layer  32  is formed of a polyamide block copolymer (PEBAX). The Nylon  12  has a higher Shore durometer hardness than the PEBAX. The Shore durometer hardness of the PEBAX is typically about 63D to about 72D, with the later being more preferred when the catheter  10  is a stent delivery catheter. The Shore durometer hardness of the Nylon  12  is typically about 70D to about 75D. In a presently preferred embodiment, the outer tubular member  14  consisting essentially of the inner and outer polymeric layers  32 ,  33  has sufficient force and torque transmission, so that a braided or coiled reinforcing layer is not provided in the wall of the outer tubular member  14 . The inner tubular member inner layer  50  is typically a lubricious polymer such as HDPE or a fluoropolymer, the middle layer  51  is typically an adhesive polymer capable of bonding the inner and outer layers  50 ,  52  together, and the outer layer  52  is typically hot melt compatible with the polymeric material of the balloon  24 . 
   In the embodiment of  FIG. 2 , the inner and outer layers  32 ,  33  extend the entire length of the outer tubular member  14 . In alternative embodiments, one or both of the layers  32 ,  33  are shorter than the length of the outer tubular member  14 . For example,  FIG. 6  illustrates an enlarged, longitudinal cross sectional partial view of an alternative embodiment of a balloon catheter embodying features of the invention, having first and second layers  32 ,  33  of the outer tubular member  14  extending less than the entire length of the outer tubular member  14 . Specifically, the first (e.g., inner) layer  32  extends only along the distal section  34  and the transition section  36 , whereas the second (e.g., outer) layer  33  extends only along the proximal section  35  and the transition section  36 . Thus, the relative proportion of the first and second layers  32 ,  33  along the proximal section  35  is 0:100, and the relative proportion of the first and second layers  32 ,  33  along the distal section is 100:0. The layers  32 ,  33  inversely cotaper along the transition section  36 , with the first layer  32  proximal end located at the proximal end of the transition section  36 , and with the second layer  33  distal end located at the distal end of the transition section  36 . In alternative embodiments, one of the layers  32 ,  33  extends beyond the transition section  36 , as for example in an embodiment (not shown) similar to the embodiment of  FIG. 6  but having the second layer  33  extending together with the first layer  32  along all or part of the distal section  35  (beyond the distal end of the transition section  36 ), in the second relative proportion as discussed above in relation to the embodiment of  FIG. 2 . 
   The first layer  32  is formed of a first polymer having a lower Shore durometer hardness than the second layer  33 . In embodiment illustrated in  FIG. 6 , the first layer  32  is an inner layer relative to the second layer  33  along the transition section  36 , although in alternative embodiments (not shown) it is an outer layer relative to the second layer  33 . Similar to the embodiment of  FIG. 2 , the inner and outer diameter of the outer tubular member  14  decrease distally at tapered portion  42  of transition section  36 , and at tapered portion  43  of distal section  35 . Although both the inner and outer diameter of the outer tubular member  14  decrease along tapered portions  42 ,  43  in the embodiments of  FIGS. 2 and 6 , in an alternative embodiment (not shown), only the outer diameter decreases. 
   The dimensions of catheter  10  are determined largely by the size of the balloon and guidewire to be employed, the catheter type, and the size of the artery or other body lumen through which the catheter must pass or the size of the stent being delivered. The outer tubular member  14  generally has an outer diameter of about 0.025 to about 0.042 inch (0.064 to 0.11 cm), and a wall thickness of about 0.002 to about 0.008 inch (0.0051 to 0.02 cm), more specifically about 0.005 to 0.007 inch (0.013 to 0.018 cm). The inner tubular member  16  generally has an outer diameter of about 0.02 to about 0.03 inch (0.05 to 0.076 cm), and a wall thickness of about 0.004 to about 0.008 inch (0.01 to 0.02 cm). The overall length of the catheter  10  may range from about 100 to about 150 cm, and is typically about 143 cm. Balloon  24  typically has a length about 0.8 cm to about 6 cm, and an inflated working diameter of about 1.5 to about 10 mm. 
   Although the illustrated embodiment is an over-the-wire stent delivery catheter, the catheter of the invention may comprise other types of intravascular catheters, such as angioplasty catheters and rapid exchange balloon catheters. Rapid exchange catheters generally comprise a distal guidewire port in a distal end of the catheter, a proximal guidewire port in a distal shaft section and typically spaced a substantial distance from the proximal end of the catheter, and a short guidewire lumen extending between the proximal and distal guidewire ports in the distal section of the catheter. Thus, unlike the embodiment of  FIG. 1 , the inner tubular member  14  of a rapid exchange catheter embodiment (not shown) would extend from the distal guidewire port  21  to a proximal guidewire port spaced a substantial distance from the proximal end of the catheter. 
   While the present invention is described herein in terms of certain preferred embodiments, those skilled in the art will recognize that various modifications and improvements may be made to the invention without departing from the scope thereof. Moreover, although individual features of one embodiment of the invention may be discussed herein 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.