Abstract:
A catheter balloon or other expandable tubular medical device or component, having at least a first layer with a first section and a second section longitudinally compacted by more than the first section. In a presently preferred embodiment, the second section of the first layer extends at least in part along a central portion of the length of the first layer. The longitudinal compaction of the material of the first layer preferably results in a balloon or other expandable tubular medical device or component having improved performance characteristics such as compliance and dimensional stability. One aspect of the invention is directed to a method of longitudinally compacting a porous polymeric tube incrementally along the length of the tube, to compact sections of the tube.

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 percutaneous transluminal coronary angioplasty (PTCA) procedures a guiding catheter is advanced in the patient&#39;s vasculature until the distal tip of the guiding catheter is seated in the ostium of a desired coronary artery. A guidewire 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. A 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 inflation fluid one or more times to a predetermined size at relatively high pressures so that the stenosis is compressed against the arterial wall and the wall expanded to open up the vascular 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. After the balloon is finally deflated, blood flow resumes through the dilated artery and the dilatation catheter and the guidewire can be removed therefrom.  
         [0003]     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 of angioplasty alone and to strengthen the dilated area, physicians now normally implant an intravascular prosthesis, generally called 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 or to maintain its patency. A tubular cover formed of synthetic or natural material may be present on an outer or inner surface of the stent. 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 within the patient&#39;s artery 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. See for example, U.S. Pat. No. 5,507,768 (Lau et al.) and U.S. Pat. No. 5,458,615 (Klemm et al.), which are incorporated herein by reference.  
         [0004]     In the design of catheter balloons, characteristics such as strength, compliance, and profile of the balloon vary depending on the desired use of the balloon catheter. A variety of polymeric materials are conventionally used in catheter balloons, and the balloon material and manufacturing procedure are chosen to provide the desired balloon characteristics. Use of polymeric materials such as PET that do not stretch appreciably consequently necessitates that the balloon is formed by blow molding, and the deflated balloon material is folded around the catheter shaft in the form of wings, prior to inflation in the patient&#39;s body lumen. However, it can be desirable to employ balloons, referred to as formed-in-place balloons, that are not folded prior to inflation, but which are instead expanded to the working diameter within the patient&#39;s body lumen from a generally cylindrical or tubular shape (i.e., essentially no wings) that conforms to the catheter shaft.  
         [0005]     Catheter balloons formed of expanded polytetrafluoroethylene (ePTFE) expanded in place within the patient&#39;s body lumen without blow molding the ePTFE tubing have been disclosed. Prior disclosed methods of forming an ePTFE balloon involved wrapping a sheet of ePTFE on a mandrel and heating the wrapped sheet to fuse the layers of wrapped material together to form a tube. The resulting ePTFE tube may be subsequently heated in one or more additional heating steps and otherwise further processed, and typically combined with a nonporous liner to complete formation of the balloon. It would be a significant advance to provide an ePTFE tube for forming a balloon or other expandable medical device or component, with improved performance characteristics and manufacturability.  
       SUMMARY OF THE INVENTION  
       [0006]     This invention is directed to a catheter balloon or other expandable tubular medical device or component, having at least a first layer with a first section, and a second section longitudinally compacted by more than the first section. The second section of the first layer is typically longitudinally adjacent to the first section of the first layer, and preferably extends at least in part along a central portion of the length of the first layer. The longitudinal compaction of the material of the first layer in accordance with the invention results in a balloon or other device or component having improved performance characteristics such as compliance and dimensional stability. One aspect of the invention is directed to a method of longitudinally compacting a porous polymeric tube incrementally along the length of the tube, to compact sections of the tube.  
         [0007]     Longitudinal compaction of a section of the first layer decreases the length of the section and preferably also decreases the porosity of the material forming the section, so that in one embodiment, the first layer first section, which is more highly longitudinally compacted than the first layer second section, has a lower porosity than the first layer second section. The degree of longitudinal compaction is expressed herein as a percentage length reduction. Thus, a section having a precompaction length (i.e., the length of the section just prior to being longitudinally compacted in accordance with the invention) of 2 cm, which is subsequently longitudinally compacted to a length of 1 cm, has a longitudinal compaction of 50% (i.e., (2 cm−1 cm)÷2 cm).  
         [0008]     In a presently preferred embodiment, the medical device tubular component is an inflatable balloon for a catheter. A balloon which embodies features of the invention can be used on a variety of suitable balloon catheters including coronary and peripheral dilatation catheters, stent delivery catheters, drug delivery catheters and the like. A balloon catheter of the invention generally comprises an elongated shaft having a proximal shaft section, a distal shaft section, at least a first lumen, and a balloon on a distal shaft section with an interior in fluid communication with the first lumen of the shaft. Although discussed below primarily in terms of the embodiment in which the medical device component is an inflatable member such as a balloon for a catheter, it should be understood that other expandable medical devices and components are included within the scope of the invention, including stent covers and vascular grafts.  
         [0009]     The catheter balloon typically has a proximal and a distal skirt section secured to the shaft, an inflatable working length section, an inflatable proximal section between the proximal skirt section and the working length which inflates to a tapered configuration (“the proximal tapered section”), and an inflatable distal section between the distal skirt section and the working length which inflates to a tapered configuration (“the distal tapered section”). It should be understood that in at least in one embodiment the balloon is not blow molded or otherwise preexpanded into the inflated configuration prior to use. Thus, the “proximal and distal tapered sections” typically do not have a tapered configuration prior to the balloon being inflated during use of the balloon catheter.  
         [0010]     In a presently preferred embodiment, the section of the first layer located at the central working length section of the balloon (hereafter the first layer working section) has a longitudinal compaction greater than the sections of the first layer located at the proximal and distal tapered sections of the balloon (hereafter the first layer tapered sections). The inflated tapered sections of the balloon form the transition between the skirt sections bonded to the shaft and the inflated working length of the balloon. Thus, depending on the length and the diameter of the inflated tapered sections, this transition can range from a gradual shallow taper to a short sharp transition. In one embodiment, the first layer tapered sections have a longitudinal compaction such that, when inflated, the tapered sections have a desired length and a desired inflated outer diameter tapering between the inflated working length to the skirt section, to decrease the hoop stress and stress concentration at the end of the skirt section. Thus, the  5  rupture pressure of the balloon is increased by increasing the rupture pressure of the bond between the skirt section and the shaft. Specifically, in one embodiment, in the inflated configuration, the tapered sections taper at an angle of about 5° to about 45°, and with an inflated length of about 1 to about 5 mm. Thus, in one embodiment, the longitudinal compaction percentages of the sections are selected to provide a balloon having a desired inflated dimension and shape.  
         [0011]     Additionally, in one embodiment, axial shrinkage of the balloon sections which would otherwise occur during inflation of the balloon is decreased by the longitudinal compaction of the first-layer sections. Specifically, for no axial shrinkage or a minimal amount of axial shrinkage (i.e., less than 5%), the presently preferred the inflatable length of a porous polymeric layer of a balloon has a longitudinal compaction of about 10% to about 60%, preferably about 20% to about 50%. When not compacted, the axial shrinkage is believed to be about 10% to about 30% ofthe length of the balloon.  
         [0012]     In one embodiment, the sections ofthe first layer located at the skirt sections of the balloon (hereafter the first layer skirt sections) have a longitudinal compaction which is less than or at least not greater than the longitudinal compaction of the first layer tapered sections. In one embodiment the first layer skirt sections are not longitudinally compacted, and thus have a longitudinal compaction of 0%. The first layer skirt section preferably has improved flexibility and low profile due to the low or zero percent longitudinal compaction of the skirt section. The skirt sections of the first layer extend along the section of the balloon secured to the shaft. However, the skirt sections of the first layer are not necessarily directly secured to the shaft, and may instead have at least a portion secured to a section of a second (inner) layer of the balloon which is directly secured to the shaft. The terminology “directly secured” to the shaft should be understood to include a variety of bonding methods including fusion and adhesive bonding.  
         [0013]     In a presently preferred embodiment, the polymeric material of the first layer of the balloon comprises a polymer having a porous structure, which in one embodiment is selected from the group consisting of expanded polytetrafluoroethylene (ePTFE), ultra high molecular weight polyolefin such as ultra high molecular weight polyethylene, and porous polyolefins such as polyethylene and polypropylene, and porous polyurethane. In one embodiment, the porous material has a node and fibril microstructure. For example, ePTFE and ultra high molecular weight polyethylene typically have a node and fibril microstructure, and are not melt extrudable. The node and fibril microstructure, when present, is produced in the material using conventional methods. However, a variety of suitable polymeric materials can be used in the method of the invention including conventional catheter balloon materials which are melt extrudable. In one presently preferred embodiment, the polymeric material is typically not formed into a balloon by conventional balloon blow molding, and is instead formed into a balloon by heat fusing wrapped layers of the polymeric material together to form a tubular member. Porous materials such as ePTFE and ultrahigh molecular weight polyethylene typically require a nonporous second layer or liner when used to form an inflatable balloon. Thus, the balloon or other tubular medical device or component having a first layer with longitudinally compacted sections, should be understood to include an embodiment where the first layer forms at least a layer of a multilayered catheter balloon. The balloon first layer is typically longitudinally compacted before being secured to the balloon second layer, and the second layer is typically not longitudinally compacted.  
         [0014]     A method of making a first layer of an expandable tubular medical device or component having at least one layer, generally comprises individually compacting incremental segments of a porous polymeric tube to incrementally compact the porous polymeric tube. In one embodiment, the method comprises placing a porous polymeric tube having a length and an outer diameter on a mandrel, with a diameter limiting member around at least a portion of the tube. In one embodiment, the diameter limiting device is selected from the group consisting of a die, a polymeric tube, and a sheet of polymeric material wrapped around the porous polymeric tube. A mold may also be used as the diameter limiting device, although preferably such that the mold uniformly limits the diameter of the segment of the tube during compaction, to thereby produce uniform compaction along the length of the individual segment avoiding buckling of the segment into an accordion-like configuration during compaction. At least a first compactor member is releasably secured to the tube at a first location on the tube, the secured compactor member being slidably disposed relative to the mandrel, and the compactor member is moved a distance, to thereby compact a first segment of the tube which is within the diameter limiting member and which has a length less than the entire length of the tube. The compactor member is released and repositioned on the tube at a second location on the tube, and the compactor member is releasably secured to the tube at the second location. The compactor member is then moved a distance, to compact a second segment of the tube which is adjacent to the first segment and which is within the diameter limiting member and which has a length less than-the-entire length of the tube. In one embodiment, the incremental compaction method of the invention produces uniform compaction along the length of the porous polymeric tube. In an alternative embodiment, one or more segments are compacted by an amount different than the first segment, so that the incremental compaction method of the invention produces variable compaction along the length of the porous polymeric tube.  
         [0015]     The invention provides a catheter balloon or other expandable tubular medical device or component, having improved performance characteristics due to the longitudinal compaction of sections of the porous polymeric layer. In one embodiment, the compacted sections provide a balloon having an inflated configuration with a desired shape and dimensions, and with reduced stress at the skirt sections. An improved method of compacting porous polymeric material during formation of a tubular medical device or component, provides controllable incremental compaction of the porous polymeric material to produce uniform or variable compaction along the length of the tube. 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  
       [0016]      FIG. 1  is an elevational view, partially in section, of a stent delivery balloon catheter embodying features of the invention.  
         [0017]      FIG. 2  is a transverse cross sectional view of the balloon catheter shown in  FIG. 1 , taken along line  2 - 2 .  
         [0018]      FIG. 3  is a transverse cross sectional view of the balloon catheter shown in  FIG. 1 , taken along line  3 - 3 .  
         [0019]      FIG. 4  illustrates the balloon catheter of  FIG. 1 , with the balloon inflated.  
         [0020]      FIGS. 5   a - d  illustrate an assembly of a tube of polymeric material on a mandrel, partially in section, during longitudinal compaction of portions of the tube to form a layer of the balloon of  FIG. 1 , in a method which embodies features of the invention, in which a block is moved to compact a portion of the tube into a die.  
         [0021]      FIGS. 6   a - c  illustrate an assembly of a tube of polymeric material on a mandrel, partially in section, during longitudinal compaction of portions of the tube to form a layer of the balloon of  FIG. 1 , in an alternative method which embodies features of the invention, in which two blocks are moved together to compact a portion of the tube in a diameter limiting member between the blocks.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0022]      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 . Inner tubular member  16  defines a guidewire lumen  18  configured to slidingly receive a guidewire  20 , and the coaxial relationship between outer tubular member  14  and inner tubular member  16  defines annular inflation lumen  22 , as best shown in  FIG. 2  illustrating a transverse cross section view of the distal end of the catheter shown in  FIG. 1 , taken along line  2 - 2 . 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 its interior is in fluid communication with inflation lumen  22 . An adapter  30  at the proximal end of catheter shaft  12  is configured to provide access to guidewire lumen  18 , and to direct inflation fluid through arm  31  into inflation lumen  22 .  FIG. 1  illustrates the balloon  24  in a low profile tubular configuration prior to complete inflation, with an expandable stent  32  having a stent cover  35 , mounted on the balloon  24  for delivery 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, and balloon  24  inflated to expand covered stent  32 , and the balloon deflated, leaving covered stent  32  implanted in the body lumen  27 .  FIG. 3  illustrates a transverse cross section view of the distal end of the catheter shown in  FIG. 1 , taken along line  3 - 3 .  
         [0023]     In the embodiment illustrated in  FIG. 1 , balloon  24  has a first layer  33  and a second layer  34 . In a presently preferred embodiment, the balloon  24  first layer  33  comprises a microporous polymeric material, and preferably a microporous polymeric material having a node and fibril microstructure, such as ePTFE. In the embodiment illustrated in  FIG. 1 , first layer  33  is formed of ePTFE, and the second layer  34  is formed of a polymeric material preferably different from the polymeric material of the first layer  33 . Although discussed below in terms of one embodiment in which the first layer  33  is formed of ePTFE, it should be understood that the first layer may comprise other materials, including ultrahigh molecular weight polyethylene. The second layer  34  is preferably formed of an elastomeric material, such as polyurethane elastomers, silicone rubbers, styrene-butadiene-styrene block copolymers, polyamide block copolymers, and the like. In a preferred embodiment, layer  34  is an inner layer relative to layer  33 , although in other embodiments it may be an outer layer. Layer  34  formed of an elastomeric material limits or prevents leakage of inflation fluid through the microporous ePTFE to allow for inflation of the balloon  24 , and expands elastically to facilitate deflation of the balloon  24  to a low profile deflated configuration. The elastomeric material forming layer  34  may consist of a separate layer which neither fills the pores nor disturbs the node and fibril structure of the ePTFE layer  33 , or it may at least partially fill the pores of the ePTFE layer.  
         [0024]      FIG. 4  illustrates the balloon catheter  10  of  FIG. 1 , with the balloon in an inflated configuration. The inflated balloon  24  has a central working section with covered stent  32  thereon, a proximal tapered section between the working section and the proximal skirt section  25 , and a distal tapered section between the distal skirt section  26  and the working section. The section of the first layer  33  extending along the working section of the balloon is hereafter referred to as the first layer working section. Similarly, the first layer proximal and distal tapered sections refer to the sections of the first layer  33  extending along the proximal and distal tapered sections of the balloon, and the first layer skirt sections refer to the sections of the first layer  33  extending along the balloon skirt sections  25 ,  26 . In one presently preferred embodiment, the inflated first layer working section has a length of about  8  to about  80  mm, the inflated first layer proximal tapered section has a length of about 1 to about 5 mm, and the inflated first layer distal tapered section has a length of about 1 to about 5 mm. Although the balloon  24  is illustrated in  FIG. 4  with a conventional inflated configuration having a cental working length between two tapered inflatable sections, it should be understood that the inflated balloon may have a variety of suitable configurations including balloon configurations specially shaped for a particular anatomy such as a focal balloon configuration, a conical balloon configuration, and the like, as are conventionally known to-one of skill in the art.  
         [0025]     The first and second layers  33 ,  34  of balloon  24  each extend from the proximal skirt section  25  of the balloon to the distal skirt section  26  of the balloon. The first layer  33  can have a length which is the same as or a shorter than the length of the second layer  34 , or alternatively, can have end sections which extend beyond the end sections of the second layer  34  and directly onto the shaft.  FIG. 4  illustrates one embodiment in which the layers  33 , 34  of the balloon have the same length, so that the skirt sections  25 ,  26  consist of end sections of the second (inner) layer  34  having an inner surface bonded to the shaft, and end sections of the first (outer) layer  33  having an inner surface bonded to the end sections of the second layer  34 . However, in an alternative embodiment (not shown), the ends of the first layer  33  extend beyond the end sections of the second layer  34  and onto the shaft  12 , so that the skirt sections  25 ,  26  are also formed in part by end sections of the first layer  33  which extend beyond the end sections of the second layer  34  and bond directly to the shaft  12  without the second layer  34  therebetween. The lengths of the first layer skirt sections will vary depending on a variety of factors including the method of bonding the balloon to the shaft. In one presently preferred embodiment, the first layer proximal skirt section has a length of about 1 to about 5 mm, and the first layer distal skirt section has a length of about 1 to about 5 mm.  
         [0026]     The ePTFE layer  33  of balloon  24  has sections with different amounts of longitudinal compaction, at least prior to being inflated. Preferably, the ePTFE layer  33  has a first section, and a second section longitudinally adjacent to the first section and extending at least in part along a central portion of the length of the balloon, the second section being longitudinally compacted by more than the first section. In a presently preferred embodiment, the second section of the ePTFE layer  33  is located at the first layer working length (i.e., the section of the first layer  33  extending along the working section of the inflated balloon), and the first section of the ePTFE layer  33  is located at the first layer proximal or distal tapered sections. In a presently preferred embodiment, the section of the first layer located at the working length of the balloon has a greater longitudinal compaction than the sections of the first layer located at both the proximal and the distal inflated tapered sections of the balloon. Thus, in one embodiment, the central working section of the ePTFE layer  33  has a greater longitudinal compaction than the remaining inflatable sections of the ePTFE layer  33 .  
         [0027]     In one embodiment, the first layer working section has a longitudinal compaction of about 10% to about 60%, more specifically about 20% to about 50% of a prelongitudinal compaction length of the section, and the first layer tapered sections have a longitudinal compaction of about 10% to about 40%, more specifically about 15% to about 30% of a prelongitudinal compaction length of the sections. The percent longitudinal compaction values should be understood to refer to values existing prior to inflation of the balloon, and defined as a percentage length reduction from before to after the compaction process. For example, longitudinally compacting an ePTFE tube so that a section corresponding to the first layer working section is compacted from a prelongitudinal compaction length of about 2.86 cm to a compacted length of about 2 cm, produces a 2 cm first layer working section having a longitudinal compaction of about 30% prior to inflation of the balloon.  
         [0028]     The first layer skirt sections have a longitudinal compaction which is not greater than, and preferably is less than the longitudinal compaction of the first layer tapered sections. In a presently preferred embodiment, the first layer skirt sections are not longitudinally compacted, and thus have a longitudinal compaction of 0%. In one embodiment, the first layer skirt sections have a longitudinal compaction of about 0% to about 30%, more specifically about 10% to about 20%.  
         [0029]     Thus, in one presently preferred embodiment, a balloon ePTFE layer having a post-compaction working length of 20 mm compacted by 40%, post-compaction tapered sections of 2 mm compacted by 30%, and post-compaction skirt sections of 2 mm compacted by 20%, had an original pre-compaction working length of 33.3 mm, original pre-compaction tapered sections of 2.86 mm, and original pre-compaction skirt sections of 2.5 mm.  
         [0030]     The first layer working section, prior to inflation of the balloon  24 , preferably has a lower porosity than the first layer proximal and distal tapered sections and lower than the first layer proximal and distal skirt sections. Specifically, in one embodiment, the first layer working section (prior to inflation) has a porosity about 0 to about 40% lower than a porosity of the first layer proximal and distal tapered sections, and about 10 to about 60% lower than a porosity of the first layer proximal and distal skirt sections. In one embodiment, the first layer proximal and distal tapered sections have a porosity lower than the first layer proximal and distal skirt sections, and specifically about 10 to about 30% lower than the porosity of the first layer proximal and distal skirt sections.  
         [0031]     The ePTFE layer  33  is preferably formed according to a method in which an ePTFE tube used to form layer  33  is incrementally compacted. Specifically, the individual sections of layer  33  having specific longitudinal compaction values (e.g., the working length, and the proximal and distal tapered sections) are each produced by compacting multiple smaller length portions of the tube. For example, to produce a working length having a length of 2 cm and a longitudinal compaction of about 30%, 3 portions each having an initial precompaction length of 0.95 cm would each be successively compacted to a compacted length of 0.65 cm (i.e., (0.7)(0.95 cm)), to collectively produce the 2 cm working length having a 30% longitudinal compaction.  
         [0032]      FIGS. 5   a - d  illustrate an assembly with a polymeric tube  40  during incremental longitudinal compaction of the tube  40  in a method which embodies features of the invention. The polymeric material of the tube  40  is ePTFE in the embodiment in which the tube forms ePTFE layer  33  of the balloon  24  of  FIG. 1 . The tube  40  may be provided with uniform longitudinal compaction such that each incremental segment is compacted by the same amount, or alternatively, it may be provided with variable compaction in which one or more incremental segments are longitudinally compacted by different amounts.  
         [0033]     In the embodiment illustrated in  FIG. 5 , the tube  40  is on a mandrel  41  with a portion of the tube  40  in a die  42  having an inlet  43  and an outlet  44 . The mandrel  41  may optionally have a polymeric jacket (not shown) on an outer surface of the metallic body. A compactor member  45  is releasably secured to the tube at a location on the tube  40  spaced from the die inlet  43  by a distance “d”. In the embodiment of  FIG. 5 , the compactor member  45  comprises a block with a bore configured to surround and clamp onto the tube  40  with the mandrel  41  therein, such as with a collet-type clamping mechanism. However, a variety of suitable compactor members may be used including a hydraulic clamp. The compactor member  45  is secured to the tube  40  such that it is slidably disposed relative to the mandrel within the tube. A fixing member  46  releasably secures the tube  40  to the mandrel at a location on the tube adjacent the outlet  44  of the die  42 . In the embodiment of  FIG. 5 , the fixing member  46  comprises a block similar to the compactor member  45 , with a bore configured to surround and clamp onto the tube  40  and mandrel  41  therein. With the compactor member  45  releasably secured to the tube  40  the distance “d” from the inlet  43  of the die  42 , a first segment “S 1 ” of the tube  40  is located between the compactor member  45  and the outlet  44  of the die  42 , as illustrated in  FIG. 5   a . The compactor member  45  is then moved toward the inlet  43  of the die  42  to compact the first segment “S 1 ” of the tube  40  into the die, thereby forming compacted segment “CS 1 ”, as illustrated in  FIG. 5   b . The compacted segment is illustrated in the figures by closer-spaced cross hatching. The difference between the original precompacted length “S 1 ” of the segment, and the compacted length “CS 1 ” of the segment, expressed as a percentage of the original precompacted length “S 1 ”, is the percent longitudinal compaction of the segment. The die may be heated to thereby heat the compacted segment “CS 1 ” in the die, to heat stabilize the compacted segment in the compacted configuration. In a presently preferred embodiment, the die is heated to an elevated temperature of about 320° C. to about 400° C., preferably about 350° C. to about 370° C. to heat stabilize the compacted segment. The compactor member  45  and fixing member  46  are then released, and the tube  40  is repositioned by sliding the compacted segment “CS 1 ” through the die outlet  44  to place another noncompacted portion of the tube  40  in the die lumen, as illustrated in  FIG. 5   c . With the compactor member  45  and fixing member  46  again releasably secured to the tube  40 , the second segment “S 2 ” is compacted as outlined above. The second segment “S 2 ” may be compacted by the same amount as the first segment “S 1 ” in order to continue formation of a first compacted section, or it may be compacted by a different amount in order to provide for a second compacted section.  FIG. 5   d  illustrates the assembly after the compaction of the second segment “S 2 ” to produce compacted segment “CS 2 ”, with the compactor member and fixing member again repositioned and secured on the tube  40 , ready for compaction of a third segment “S 3 ”.  
         [0034]     During compaction, the compactor member  45  may be moved the entire distance “d” to the die inlet  43 , or alternatively, it may be moved a distance less than “d” depending on the amount of longitudinal compaction desired for the segment being compacted. For example, in the embodiments illustrated in  FIGS. 5   a - d , the length of the first, second, and third segments S 1 , S 2 , S 3  are approximately equal, so that the compactor member  45  could be moved the entire distance “d” to produce an amount of compaction in one of the segments, and moved a distance less than “d” in order to produce a smaller amount of compaction in one or more of the remaining segments.  
         [0035]     The inner diameter of the inner chamber of die  42  is sized so that the tube  40  compacts without the outer diameter of the tube increasing. The inner diameter of the inner chamber of die  42  is typically about equal to the outer diameter of the tube  40  on the mandrel  41 . Alternatively, the inner diameter of the inner chamber of die  42  may be smaller than the outer diameter of the tube  40  on the mandrel  41 , so that it provides resistance to movement of the tube  40  therein to increase the percent compaction of the tube  40 . The length of the inner chamber of the die  42  in which tube is compacted is typically about 1 to about 5 cm, preferably about 2 to about 3 cm. The length of the tube  40  is typically about 4 to about 20 cm to produce a layer  33  of a balloon having a length of about 2 to about 10 cm. The length of the segments S 1 , S 2 , S 3  is typically about 5 to about 25 mm, preferably about 5 to about 15 mm. The length of the segment is preferably sufficiently short such that the segment compacts uniformly along the length of the segment and without buckling.  
         [0036]     After being longitudinally compacted, the tube  40  may be heat treated or otherwise further processed and secured to the second layer  34 , to complete formation of the balloon  24 . The tube  40  is typically longitudinally stretched prior to being longitudinally compacted, as for example by being placed on a mandrel and pulled at either end to stretch down on to the mandrel, although it can be longitudinally stretched using a variety of suitable methods. With the tube  40  restrained in the longitudinally stretched configuration, the tube  40  is typically heated, to stabilize the tube in the stretched configuration prior to being longitudinally compacted.  
         [0037]      FIGS. 6   a - c  illustrate an assembly of polymeric tube  40  on mandrel  41  during incremental longitudinal compaction of the tube in an alternative method which embodies features of the invention. Similar to the embodiment of  FIG. 5 , the tube  40  may be provided with uniform longitudinal compaction, or alternatively, with variable compaction.  
         [0038]     In the embodiment illustrated in  FIG. 6 , the tube  40  is on a mandrel  41  with a portion of the tube  40  in a diameter limiting member  52  comprising a sheet of polymeric material wrapped around the tube  40 . In a presently preferred embodiment, the sheet of polymeric material forming the diameter limiting member  52  is ePTFE, although other polymeric materials may be used, including Teflon, and polyolefins such as high density polyethylene (HDPE), low density polyethylene (LDPE), and linear low density polyethylene (LLDPE). At least a first compactor member  53  is releasably secured at a first location to the tube and slidably disposed relative to the mandrel  41 . In the embodiment of  FIG. 6 , the first compactor member  53  is a block similar to the block of the embodiment of  FIG. 5 . In the embodiment of  FIG. 6 , a second compactor member  54  is releasably secured at a second location to the tube  40  longitudinally spaced apart from the first compactor member  53  with at least a portion of the diameter limiting device  52  therebetween. With the first and second compactor members  53 ,  54  releasably secured to the tube  40  a distance apart, a first segment “S 1 ” of the tube  40  is located between the compactor members, as illustrated in  FIG. 5   a . The first and second compactor members  53 ,  54  are then moved toward one another toward a center of the length of the tube  40  to longitudinally compact the first segment “S 1 ” therebetween in the diameter limiting device  52 , thereby forming compacted segment “CS 1 ”, as illustrated in  FIG. 6   b . The compactor members  53 ,  54  are then released and resecured to the tube. In a presently preferred embodiment, the compactor members  53 ,  54  are resecured to the tube  40  at locations further apart on the tube and closer to the ends of the tube  40 , with second segment “S 2 ” greater than “S 1 ” therebetween, as illustrated in  FIG. 6   c . The compactor members  53 ,  54  are illustrated in  FIG. 6   c  ready to be moved toward one another toward a center of the length of the tube  40 , to longitudinally compact the second segment “S 2 ” therebetween in the diameter limiting device  52 . The ePTFE tape  52  typically has a length sufficient to cover the entire length of the tube  40  to be compacted, so that the ePTFE tape  52  does not have to be removed and replaced with a longer length of ePTFE tape  52  between the compaction of each individual segment of tube  40 . In alternative embodiments (not shown) using alternative diameter limiting members such as a tube, die, or mold, the diameter limiting device is typically released from the compacted segment and a longer diameter limiting device is secured to the tube to accommodate the longer length of the next segment to be compacted. The compacted tube  40  may be heated to heat stabilize the compacted segments, as discussed above in relation to the embodiment of  FIG. 5 , as for example by traversing a heating nozzle along the length of the compacted segments. In the illustrated embodiment in which the diameter limiting member  52  is ePTFE tape wound around the tube  40 , the tube may be heated at the end of the compaction of the final segment rather than after each individual compaction, because the ePTFE tape  52  is typically not removed between the compaction of each individual segment of the tube  40 . The length of the segments being compacted is typically about 10 to about 50 mm, preferably about 20 to about 30 mm.  
         [0039]     In an alternative embodiment (not shown), a fixing member is used in place of the second compaction member  54 , which is releasably secures the tube  40  to the mandrel  41 , so that compacting the segment therebetween comprises moving the first compactor member  53  toward the fixing member. The distance between the first compaction member  53  and the fixing member is then increased, for compacting another segment of the tube as described above.  
         [0040]     To the extent not previously discussed herein, the various catheter components may be formed and joined by conventional materials and methods. For example, the outer and inner tubular members  14 ,  16  can be formed by conventional techniques, such as by extruding and necking materials found useful in intravascular catheters such a polyethylene, polyvinyl chloride, polyesters, polyamides, polyimides, polyurethanes, and composite materials.  
         [0041]     The length of the balloon catheter  10  is generally about 108 to about 200 centimeters, preferably about 137 to about 145 centimeters, and typically about 140 centimeters for PTCA. The outer tubular member  14  has an outer diameter (OD) of about 0.017 to about 0.036 inch (0.43-0.91 mm), and an inner diameter (ID) of about 0.012 to about 0.035 inch (0.30-0.89 mm). The inner tubular member  14  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. The balloon  24  is has a length of about 8 mm to about 80 mm, typically about 8 mm to about 38 mm, and an inflated working diameter of about 1.5 mm to about 20 mm, typically about 2 mm to about 10 mm.  
         [0042]     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 from the scope of the invention. For example, although the embodiment illustrated in  FIG. 1  is an over-the-wire stent delivery catheter, balloons of this invention may also be used with other types of intravascular catheters, such as 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 distal of the proximal end of the shaft 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. 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.