Abstract:
The present invention provides an improved balloon catheter. The balloon is of a composite material having the flexibility and elastic characteristics of an elastomeric material, yet exhibiting the growth limits of inelastic materials. The balloon may be treated to maintain a substantially constant length during inflation and deflation. The balloon may be provided with regions of porosity for the delivery of therapeutic agents, and may be treated to exhibit regions of distinct compliance. Also disclosed is an apparatus, which may be used to impart the regions of distinct compliance into the balloon.

Description:
FIELD OF INVENTION  
         [0001]    The present invention generally relates to balloon catheters.  
         BACKGROUND OF THE INVENTION  
         [0002]    Various types of balloon catheters are routinely employed in medical procedures. Typically, balloon catheters consist of elongate thin-walled tubular catheter assemblies with an inflatable balloon attached at the distal end.  
           [0003]    Balloon catheters are commonly used to dilate or remove constrictions, or to deliver and deploy other devices within bodily conduits. In the treatment of constricted conduits, the balloon catheter is inserted within the patient and navigated through the conduit (such as a blood vessel) to the site of blockage. The balloon at the distal end of the catheter is then inflated, causing the balloon to increase in diameter until the desired therapeutic result is achieved. Once the blockage is opened, the balloon is deflated and removed from the patient.  
           [0004]    In a similar fashion, devices such as stents are typically secured onto the distal ends of balloon catheters, the catheters used to deliver the stent to the site of a blockage. Once at the desired location, the underlying balloon is inflated, causing the stent to increase in diameter and thus remodel and support the tissue, which constitutes the blockage within the bodily conduit. Once the therapeutic result is achieved the balloon is deflated and removed from the patient, leaving the stent implanted.  
           [0005]    Balloon catheters may employ various balloon materials depending on the application for which they are used. For example, embolectomy balloon catheters utilize elastomeric balloon materials such as latex or silicone because in such procedures there is no need for the use of high inflation pressures. Angioplasty balloon catheters, on the other hand, utilize relatively inelastic materials such as polyester or nylon because in such procedures the application of high inflation pressure is often required.  
           [0006]    Elastomeric and inelastic balloon materials each have advantages and drawbacks. While elastomeric materials are generally soft and conformable, they lack strength and exhibit continuous diameter growth with the application of increasing inflation pressure until rupture occurs. Elastomeric balloon materials are referred to as compliant. Inelastic balloon materials have very predictable diameter growth characteristics, and distend very little beyond their intended diameter with the application of increasing inflation pressure. Inelastic balloon materials are referred to as non-compliant or semi-compliant depending on their stiffness.  
           [0007]    Due to their stiffness, inelastic balloon materials are not soft and conformable. Balloons made of these materials, such as angioplasty balloons, are carefully wrapped into a small cross-sectional configuration prior to introduction into the patient. During inflation, the balloons unwrap and assume their intended diameters. During subsequent deflation, however, the balloons do not return to their initial small cross-sectional state.  
           [0008]    Angioplasty balloons are often difficult to maneuver through tortuous bodily conduits, posing a challenge in the treatment of blockages within small conduits such as within the coronary vasculature or the neurovasculature. Further, when inflated within a curved conduit, such balloons tend to straighten the conduit because of their lack of conformability. This straightening can result in localized trauma.  
           [0009]    The delivery of devices such as stents via angioplasty balloon catheters can be problematic due to inadequate securement of the stent onto the balloon. The inelastic materials do not provide adequate engagement to the stent, leaving the stent prone to slipping along the length or completely off of the balloon. Also, because the inelastic materials are essentially non-compressible, the edges of a stent, when mounted onto a balloon made of such materials are exposed and vulnerable to being damaged during navigation through narrowed tortuous conduits.  
           [0010]    In addition to the drawbacks mentioned above, there are complications associated with the mechanics of folded balloons. As described, angioplasty balloons are typically folded or wrapped about the catheters to which they are attached. During use, the balloons unfold at very low pressure. In the presence of an obstruction within a conduit, particularly if the obstruction is centered within the length of the balloon, such balloons tend to unfold very quickly at the ends where diameter growth is unimpeded, forming an hourglass shape. As the balloon is inflated to greater pressures, the obstructive tissue is remodeled toward the center of the balloon length, creating a densified lesion and a generally insufficient vessel inner diameter. Similar mechanics may occur during inflation of a stent, particularly if the length of the stent is not carefully matched to the length of the balloon.  
           [0011]    In many cases, blockages occur close to the junction of two conduits. In such situations, particularly if the lesion is located at one end of the balloon, the mechanics described above, rather than densifying the obstructive tissue towards the center of the balloon, redistribute the occlusive tissue into the junction between the two conduits, thus compromising the junction and creating an obstruction within the branching conduit.  
           [0012]    Another complication of balloon angioplasty and stenting is the formation of emboli. Embolic episodes occurring in various anatomical locations, particularly the brain can result in potentially debilitating outcomes or even death.  
         SUMMARY OF THE INVENTION  
         [0013]    The present invention is an improved balloon catheter. The balloon catheter of the present invention comprises a composite balloon material attached to a catheter assembly. The balloon material has the flexibility and elastic characteristics of an elastomeric material, but also has a well-defined growth limit such as exhibited by inelastic balloon materials. The balloon material may be manufactured to maintain a substantially constant length during inflation and subsequent deflation. Various embodiments of the balloon material may be produced to be liquid tight or may be produced with one or more regions of porosity through which various therapeutic agents may be delivered. Additionally, the balloon material may be manufactured with regions of distinct inflation characteristics (compliance) such that one or more regions of the balloon inflate at a faster rate than the remaining region(s). Regions of distinct compliance provide enhanced control during angioplasty and stenting procedures and may be beneficial in reducing the creation of emboli during such procedures. The balloon catheter of the present invention may be provided with a balloon having a substantially constant diameter or may be provided with a balloon having a predetermined shape to further enhance angioplasty and stenting procedures.  
           [0014]    Also disclosed is an apparatus, which may be used to instill the regions of distinct compliance within the balloon. The apparatus may be used to essentially customize the compliance of the balloon such that the balloon optimally serves the needs of the end user. 
       
    
    
     BRIEF DESCRIPTION OF EXEMPLARY DRAWINGS  
       [0015]    Additional aspects of the present invention will be evident upon reviewing the non-limiting embodiments in the specification and the claims, in conjunction with the accompanying figures, where:  
         [0016]    [0016]FIG. 1 is an elevational view of an exemplary balloon catheter of the present invention;  
         [0017]    [0017]FIG. 2 is an enlarged partial longitudinal cross-sectional view of the distal portion of an exemplary balloon catheter of the present invention;  
         [0018]    [0018]FIG. 3 is an enlarged longitudinal cross-sectional view of an exemplary embodiment of the inventive balloon material;  
         [0019]    [0019]FIGS. 4A, 4B, and  4 C are enlarged views of a braided tube used in the manufacture of an exemplary embodiment of the inventive balloon material;  
         [0020]    [0020]FIG. 5 is a graph illustrating the compliance characteristics of an exemplary embodiment of the inventive balloon material; and  
         [0021]    [0021]FIGS. 6A and 6B are partial longitudinal cross-sectional views of exemplary embodiments of inflation molds that may be used to customize the compliance characteristics of the inventive balloon material.  
     
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS  
       [0022]    Referring to the figures, wherein like numerals designate like elements, illustrated in FIG. 1 is an exemplary embodiment of a balloon catheter  100  that includes a proximal adapter  102  located at the proximal end of the device. The proximal adapter includes a wire port  104  and a balloon port  106 , both of which comprise a luer fitting for engagement with other accessory devices. The proximal adapter  102  is attached to an inner catheter member  108  (FIG. 2) and an outer catheter member  110 . The two catheter members are arranged coaxially. The attachment between the proximal adapter  102  and the outer catheter member  110  is enhanced by strain relief member  112 , which provides support to the outer catheter member  110 , minimizing the tendency of the outer catheter member  110  to kink at or near the attachment point.  
         [0023]    At the distal portion of the balloon catheter  100  is balloon  114 . Balloon  114  is attached at its proximal end to outer catheter member  110  and at its distal end to inner catheter member  108  as illustrated in FIG. 2. Also, at the distal portion of balloon catheter  100  is distal tip  116 , which comprises the distal end of inner catheter member  108 .  
         [0024]    Although the embodiment depicted by FIG. 1 comprises two catheter members arranged coaxially, any suitable catheter member arrangement may be employed. For example, a single, dual-lumen catheter member, having a lumen providing communication between the balloon port and the balloon, and another lumen capable of accommodating a guidewire may be employed. Additionally, the assembly of the catheter member(s) may be of any suitable configuration such as, but not limited to, fixed wire, wherein a wire element is included into the catheter tube(s) to add stiffness, over the wire (as depicted by FIG. 1), or rapid exchange.  
         [0025]    The design and manufacture of catheter components and assemblies thereof is well known. Catheter members  108  and  110  may be of any suitable material or combination of materials such as, but not limited to, silicone, polyurethane, nylon, polyethylene, various coploymers such as PolyEther Block Amid (PEBA), or polytetrafluoroethylene (PTFE). In some embodiments catheter members  108  and  110  may suitably contain metallic elements such as, but not limited to, braids, hypodermic tubing and/or wires. Proximal adapter  102  may be configured in any suitable manner and may also be of any suitable material or combination of materials such as, but not limited to, nylon, polycarbonate, polypropylene, PEBA, or polysulfone. Any suitable method may be employed to create the attachments between the various elements of the balloon catheter  100 . Such methods may include, but are not limited to, the use of various adhesives or thermal bonding techniques.  
         [0026]    [0026]FIG. 2 illustrates an enlarged view of the arrangement of catheter members  108  and  110  as well as balloon  114  of the exemplary embodiment of balloon catheter  100 . In this particular embodiment the distal end of outer catheter member  110  is provided with a step  202  which accommodates the proximal end of balloon  114  such that the outer surface of balloon  114  is flush with the outer surface of the outer catheter member  110 . In a similar fashion, inner catheter member  108  is provided with step  204  which accommodates the distal end of balloon  114  such that the outer surface of balloon  114  is flush with the outer surface of distal tip  116  of the inner catheter member  108 . Such an arrangement may be used to create a sleek profile to enhance navigation of the balloon catheter  100  through narrow, tortuous bodily conduits.  
         [0027]    As shown by FIG. 2, inner catheter member  108  may be provided with radiopaque markers  206  and  208 . These markers can be positioned so as to coincide with the edges of balloon  114  while the balloon is inflated, and to provide radiographic visualization of the balloon. Markers  206  and  208 , in this embodiment, are configured as bands attached to inner catheter member  108 . Any suitable configuration of markers  206  and  208  may be employed. Additionally, any suitable method of attaching the markers  206  to the inner catheter member  108  such as, but not limited to, the use of various adhesives, or swaging may be used. Also, markers  206  and  208  may be of any suitable material or combination of materials such as, but not limited to, gold, tantalum, or alloys of platinum and iridium. Markers  206  and  208  may also be printed onto inner catheter member  108  with radiopaque inks.  
         [0028]    Inner catheter member  108  also includes a lumen  210 , which may accommodate a guidewire to aid in navigation of the balloon catheter  100 . In this exemplary embodiment, lumen  210  extends along the entire length of inner catheter member  108 . Guidewire port  104  provides convenient access to lumen  210 . Similarly, outer member  110  includes lumen  212 , which provides communication between balloon port  106  and balloon  114  allowing balloon  114  to be inflated with, for example, saline.  
         [0029]    [0029]FIG. 3 depicts an enlarged cross-sectional view of an exemplary embodiment of the balloon  114  of the present invention. While the illustrated embodiment of balloon  114  comprises 3 layers, it is to be understood, however, that balloon  114  may comprise any suitable number of layers in any suitable manner. It is to be further understood that the layers need not be separate and distinct. Rather, the layers can be co-extruded. In the illustrated exemplary embodiment, inner layer  302  is comprised of silicone tubing having an inner diameter of approximately 1.2 mm and an outer diameter of approximately 1.4 mm.  
         [0030]    To produce the exemplary balloon  114 , an approximately 150 mm length of silicone tubing is fitted coaxially onto an approximately 1.19 mm diameter stainless steel rod. Isopropyl alcohol may be used as a lubricant to facilitate the fitting. With the silicone tubing fitted onto the rod, the rod is preferably placed within an air convection oven set at approximately 70° C. for approximately 10 minutes to evaporate any residual alcohol. While in this embodiment inner layer  302  is comprised of silicone tubing and is liquid tight, any suitable material or combination of materials such as, but not limited to, latex, polyurethane, PEBA, and/or fluoroelastomers may be used. Some embodiments of inner layer  302  may include regions of porosity that allow the passage of fluids there through while still allowing balloon  114  to be inflated. Additionally, various methods or combinations of methods may be employed to create a suitable inner layer  302 . Such methods include, but are not limited to, dipping, application by spraying, and/or molding.  
         [0031]    In this exemplary embodiment, the middle layer  304  comprises 2 layers of a treated braided tube  400 . The 2 layers of treated braided tube  400  are intended to provide strength to the finished embodiment of balloon  114  such that the balloon achieves a well-defined inflation diameter beyond which minimal growth occurs. A suitable braided tube  400  is manufactured by Prodesco, Inc. of Perkasie, Pa. The tube is created from 144 individual strands of 9 denier monofilament polyester yarn, has a relaxed inner diameter of approximately 7 mm, a wall thickness of approximately 0.05 mm, and a braid density of 21.7 pixels per centimeter (55 pixels per inch).  
         [0032]    [0032]FIG. 4A shows an enlarged illustration of the braid pattern of braided tube  400  in a relaxed state. Although this embodiment utilizes polyester braid material, any suitable material or combination of materials such as, but not limited to, nylon, polyethylene, carbon, kevlar, PEBA, and/or PTFE may be used. In some embodiments it may advantageous to combine thin metallic elements into the braid. Additionally, any suitable braid pattern with any suitable strand of any suitable denier, either monofilament, multifilament or any combination thereof may be used. The braid pattern may, for example, employ strands running parallel to the major axis of the tube. It should be understood that any suitable form of textile material or combination of forms such as, but not limited to, woven materials, non-woven materials, knitted materials and/or braided materials may be used to create a suitable middle layer  304 . For example, some embodiments may utilize a textile other than a braid alone or in combination with a braid to create a suitable middle layer  304 .  
         [0033]    Middle layer  304  need not be in the form of a continuous tube and need not be a continuous layer throughout the entire length of the balloon  114 . For example, narrow strips of suitable textiles may be arranged to create an embodiment of middle layer  304 .  
         [0034]    Alternatively, strips of textiles may be arranged helically to create an embodiment of middle layer  304 . Some embodiments of balloon  114  may comprise a middle layer  304  in only a portion or portions of the balloon length. Also, some embodiments of balloon  114  may comprise a middle layer  304  that varies in thickness and/or strength along the length of the balloon.  
         [0035]    As is typical for braided tubes, braided tube  400  exhibits a relationship between its diameter and its length. In order to treat the exemplary braided tube  400  such that it may increase in diameter with substantially no change in length, braided tube  400  is preferably fitted coaxially over an approximately 1.65 mm diameter stainless steel rod. Braided tube  400  is then axially elongated such that it reduces in diameter and fits snugly onto the outer surface of the rod. Each end of braided tube  400  is then secured to the rod with wire, maintaining the axially elongated/reduced diameter condition. FIG. 4B shows an enlarged illustration of the braid pattern of braided tube  400  in the axially elongated/reduced diameter condition.  
         [0036]    With braided tube  400  secured to the rod, thin PTFE film is helically wrapped about the outer surface of the tube to further secure the tube to the stainless steel rod. The wrapping of the PTFE film may be completed manually, with minimal tension. The wires at each end of braided tube  400  are then removed, pen marks are placed at approximately 10 mm intervals along the entire length of the helically wrapped tube, and the tube/rod assembly can be placed into an air convection oven set at approximately 70° C. for a minimum of 15 minutes.  
         [0037]    After the passing of a minimum of 15 minutes the tube/rod assembly is removed from the oven and, while still warm, the tube is axially compressed until the pen marks placed at the approximately 10 mm intervals are spaced consistently at approximately 6.5 mm intervals. The 15 minute, 70° C. parameters are chosen to facilitate the axial compression. Any suitable time and temperature combination may be utilized. During the compression, the braid pattern of the tube  400  densifies and small corrugations form along the surface of the tube. The PTFE film, however, serves to substantially maintain the reduced diameter of braided tube  400  during the axial compression inhibiting the formation of gross corrugations. With braided tube  400  axially compressed, the tube/rod assembly is preferably placed into an air convection oven set at approximately 197° C. for approximately 3.5 minutes and then removed to cool to ambient temperature. Once cool, the PTFE film is removed and braided tube  400  is carefully removed from the rod. At this point the braided tube is capable of undergoing an increase in diameter without a substantial change in length.  
         [0038]    The 3.5 minute 197° C. treatment imparts a thermal set into braided tube  400 , without substantially melting or bonding the strands of the tube, rendering the tube substantially dimensionally stable and easily handled. Any suitable time and temperature combination may be utilized. In some embodiments a more aggressive thermal treatment may be preferred or required such that all or portions of the material(s) used soften and mildly bond to one another. FIG. 4C shows an enlarged illustration of the compression of the braid pattern of braided tube  400 .  
         [0039]    As previously stated any suitable time/temperature combinations may be utilized in the various thermal treatment and axial compression steps described above. Additionally, any suitable means of achieving the compression of the braid pattern of braided tube  400  may be employed. For example, braided tube  400  may be placed within a glass tube having an inner diameter appropriate to cause braided tube  400  to assume an axially elongated/reduced diameter condition. A rod of appropriate material and diameter may then be fitted coaxially within braided tube  400 . Preferably, the rod is slidable yet snugly fit within braided tube  400 . The glass tube/rod assembly may then be suitably heated. With the glass tube/rod assembly heated, tubing of appropriate material, having an outer diameter able to be inserted within the glass tube and having an inner diameter able to accommodate the rod, may be inserted into each end of the glass tube. Preferably, the tubing is slidable within the glass tube and over the rod yet snugly fit to both, acting in a fashion similar to a piston within the glass tube. The tubing at each end of the glass tube may then be slid toward the center of the glass tube causing braided tube  400  to axially compress to the desired amount. Next, the axially compressed braided tube  400 , while in the glass tube, may be suitably thermally treated, then allowed to cool and removed form the glass tube.  
         [0040]    Regardless of the technique employed to achieve the axial compression, various embodiments of balloon  114  may include middle layers with any suitable amount of axial compression. For example, if a braided tube is used within the balloon embodiment the amount of axial compression desired may depend on the braid pattern of the tube. Some braid patterns may not be constant along the length of the braided tube and, as such, may require different amounts of axial compression along the length of the tube. Varying degrees of axial compression may result in varying degrees of corrugations. The formation of the corrugations may also be dependent on the technique employed to achieve the axial compression. In some embodiments of balloon  114  suitable axial compression may be achieved without any formation of corrugations.  
         [0041]    In some embodiments, it may be desirable for balloon  114  to either shorten or lengthen as it is inflated. For example, if balloon catheter  100  is used to deploy a stent that shortens as it grows in diameter, it may be desirable for balloon  114  to shorten in unison with the stent during deployment. Conversely, in such an application of balloon catheter  100 , it may be desirable for balloon  114  to slightly lengthen during inflation to counteract the shortening of the stent being deployed.  
         [0042]    With the axially compressed braided tube  400  completed, one layer is fitted over the silicone tubing comprising inner layer  302 . In this exemplary embodiment braided tube  400  is somewhat loose over inner layer  302 , so the layer of braided tube  400  while over the silicone tubing comprising inner layer  302  is helically wrapped with PTFE film resulting in a more snug fit between the two. The PTFE wrapped inner layer  302  and layer of braided tube  400 , while on the approximately 1.19 mm diameter rod, are placed within an air convection set at approximately 197° C. for approximately 3.5 minutes then removed and allowed to cool to ambient temperature. Once cool, the PTFE film is removed. Another layer of braided tube  400  is then placed over the first and the helical wrapping, the thermal treatment, the cooling, and the removal of the wrapping film are all repeated. Thus 2 layers of braided tube  400  are applied to the inner layer  302 .  
         [0043]    Next, outer layer  306  is applied by covering the outer surface of the 2 layers of compressed braided tube  400  with 2 coats of a 1:1 mixture of MED-1511 Adhesive Silicone (which may be sourced from NuSil of Carpinteria, Calif.) and Heptane. The 1:1 mixture is measured by weight. In this exemplary embodiment of balloon  114  outer layer  306  is intended to encapsulate middle layer  304  and bond to inner layer  302  thus unifying the individual layers into a composite tubular structure. During careful application of the first coat, the mixture penetrates through both layers of the treated braided tube  400  thus coming into contact with inner layer  302 . Once the first coat of the mixture is applied it is allowed to cure in a high humidity environment for a minimum of 18 hours. A second coat of the same silicone/heptane mixture is then applied over the first coat and cured in the same manner as the first coat.  
         [0044]    While in this embodiment outer layer  306  comprises a silicone mixture which after curing results in a uniform silicone layer, any suitable material or combination of materials may be used. Such materials include but are not limited to latex, polyurethane, PEBA, and/or fluoroelastomers. Additionally, various methods or combinations of methods may be employed to create a suitable outer layer  306 . For example, outer layer  306  may comprise a suitable silicone tube that may be fitted coaxially over layers  302  and  304 , and that may be attached to the layers by various elastomers applied as adhesives. Conversely, outer layer  306  may not be attached, or may only be partially attached to layers  302  and/or  304 . Other methods for the creation of an outer layer  306  include, but are not limited to, dipping, application by spraying, and/or molding. Some embodiments of balloon  114  may utilize extrusion as method of creating outer layer  306  over layers  302  and  304 . It may be advantageous in some embodiments to extrude or otherwise mold a suitable material around a treated braided tube or other suitable middle layer  304 , thus creating layers  302  and  306  with one process. Furthermore, some embodiments of balloon  114  may provide outer layer  306  with regions of porosity that allow the passage of fluids there through while still allowing balloon  114  to be inflated.  
         [0045]    Once the second coat is cured, the exemplary balloon  114  is completed. This particular embodiment of balloon  114  is produced to create a liquid tight balloon material. Further processing, however, may be completed in order to create regions of porosity within the balloon material. The processing may completed in any suitable manner, for example, the balloon material may be treated by a laser to create holes of a controlled diameter, or holes may be created with pins. As previously mentioned, the regions of porosity may allow various therapeutic agents to be delivered to bodily conduits while allowing the balloon to inflate.  
         [0046]    When the second coat is cured the exemplary balloon  114  is carefully removed from the approximately 1.19 mm diameter rod. To facilitate the removal of balloon  114  from the rod, small portions of each end of the balloon  114  may be cut off and the rod may be placed in a bath of isopropyl alcohol. The isopropyl alcohol penetrates between the balloon  114  and the rod thus providing lubrication during the removal process. After removal from the rod, the alcohol is allowed to evaporate from the exemplary embodiment of balloon  114 .  
         [0047]    A segment of the exemplary balloon  114 , approximately 30 mm long, is then cut. In order to measure the inflation characteristics (compliance) of the balloon, blunt needles having an outer diameter of approximately 1.3 mm and equipped with luer fittings are inserted into each end of the segment of exemplary balloon  114 . Tuohy-Borst adapters (part mx220, manufactured by Medex, Hilliard, Ohio) may be used to create a watertight seal between the needles and the exemplary balloon  114 . One needle is sealed with a luer cap, while the other is connected to a hand-held inflation syringe filled with water.  
         [0048]    Prior to any inflation, the distance between the two Tuohy-Borst adapters is measured to be approximately 18.27 mm. Also, the outer diameter of the balloon is measured to be approximately 2.36 mm. The balloon is then inflated, at ambient temperature, in increments of approximately 0.1 MPa (1 atm) and the outer diameter of the balloon is measured at each increment until a pressure of approximately 0.6 MPa (6 atm) is achieved. During the inflation, the distance between the Tuohy-Borst adapters is measured to be 18.43 and 18.98 mm at approximately 0.4 and 0.6 MPa (4 and 6 atm) respectively. These data translate into a maximum change in length during inflation of 0.71 mm which, when expressed as a percentage of the balloon length prior to inflation, is approximately 4%. Once all of the measurements are taken, the exemplary balloon  114  is deflated and the outer diameter and distance between the Tuohy-Borst adapters are measured to be 2.31 and 18.27 mm respectively, indicating that the exemplary balloon exhibits an elastic response returning to nearly its original dimensions after being inflated.  
         [0049]    The same test procedure is repeated, yielding compliance data for the exemplary balloon  114  during a second inflation. During this second inflation the distance between the Tuohy-Borst adapters is measured to be 18.58 mm at approximately 0.4 MPa (4 atm), showing a small change in length similar to that of the first inflation. All diameter and length measurements are taken with a pair of digital calipers.  
         [0050]    With the second inflation completed, the blunt needles and Tuohy-Borst adapters are removed and barbed luer fittings (for example, part FTLL210-9 manufactured by Value Plastics Inc., Fort Collins, Colo.) are inserted into each end of the length of exemplary balloon  114 . Wax-coated thread is then tied around each end, providing a watertight seal between the barbed luer fittings and the balloon. Next, one barbed luer fitting is sealed with a luer cap while the other is connected to a hand-held inflation syringe filled with water and the balloon is inflated until rupture occurs.  
         [0051]    The exemplary embodiment of balloon  114  ruptures at approximately 0.8 MPa (8 atm). When tested in the same manner, the silicone tubing comprising inner layer  302  ruptures at approximately 0.1 MPa (1 atm). Therefore, the addition of the 2 layers of treated braided tube  400  (inner layer  304 ) and outer layer  306  results in an approximately eight-fold increase in burst strength.  
         [0052]    [0052]FIG. 5 shows the compliance characteristics of the exemplary embodiment of balloon  114 . As shown in FIG. 5, the compliance signature of exemplary balloon  114  during the first inflation is clearly different from that of the balloon during the second inflation. During the first inflation, most of the diameter growth of exemplary balloon  114  occurs between approximately 0.3 and 0.6 MPa (3 and 6 atm), while very little diameter growth occurs between approximately 0 and 0.3 MPa (0 and 3 atm). During the second inflation, most of the diameter growth of the exemplary balloon occurs between approximately 0 and 0.2 MPa (0 and 2 atm), with a significant change in the slope of the compliance curve occurring at approximately 0.2 MPa (2 atm). The difference in the two compliance signatures is an aspect of balloon  114  that may be tailored and employed to enhance usage of balloon catheter  100 .  
         [0053]    For example, referring to FIGS. 1 and 6A, the distal portion of balloon catheter  100  may be placed within inflation mold  602  with balloon  114  centered lengthwise with respect to the large diameter cavity within the mold. The embodiment of mold  602  may be sized such that the large cavity is approximately half of the length of balloon  114  and of approximately the nominal inflated diameter of the balloon. Balloon  114  may then be inflated within the mold causing the balloon material to adopt the shape of the mold. In this manner, the center region of the balloon  114 , having been inflated to its nominal diameter, will have a compliance signature corresponding to the second inflation curve as shown in FIG. 5. The end regions of the balloon, not having been inflated to a substantially larger diameter, will have a compliance signature corresponding to the curve of the first inflation. Balloon  114  after such a treatment essentially exhibits regions of varying compliance.  
         [0054]    Balloon  114 , treated by inflation within mold  602 , may provide enhanced control during an angioplasty procedure. For example, if the balloon catheter  100  is being used to remodel a stenotic lesion of relatively short length, balloon  114  may be placed, centered lengthwise with respect to the lesion. Upon inflation, the center of balloon  114  inflates first, coming into contact with the stenotic tissue and initiating the angioplasty process. The end regions of balloon  114 , changing in diameter at a lesser rate, remain smaller than the center and do not contribute to the remodeling of the stenotic tissue. Eventually, with increasing pressure all of the regions of balloon  114  reach approximately the same diameter.  
         [0055]    [0055]FIG. 6B shows an inflation mold  608  wherein one half of the mold is of a larger inner diameter than the other half. The larger diameter half of inflation mold  608  may be of approximately the nominal inflated diameter of the balloon  114 . Such an embodiment of an inflation mold, employed in a fashion similar to that described above, may be utilized to create an embodiment of balloon  114  that inflates at a faster rate at one end. Such an embodiment of balloon  114  may enhance the angioplasty process by not only pressurizing and expanding diseased blood vessels, but by also redistributing the diseased tissue in a predetermined lengthwise manner. Such an embodiment of balloon  114  may be utilized, for example, in situations wherein an occlusive lesion is located very close to the origin of a side-branch vessel and redistribution of the diseased tissue away from the side-branch vessel origin is highly advantageous.  
         [0056]    While inflation molds  602  and  608  each have a region that allows an embodiment of balloon  114  to inflate to approximately its fully inflated diameter, embodiments of inflation molds may be created that allow the balloon to inflate only partially. For example, a balloon with a fully inflated diameter of approximately 6 mm may only be allowed to inflate to approximately 4 mm within a mold. Thus, various embodiments of inflation molds may be created. Any suitable inflation mold may be used to create any balloon embodiment having regions of distinct compliance characteristics. Conversely, it may be desirable in some instances to create balloon embodiments that have a single compliance characteristic throughout their entire length. This may be accomplished through the use of an embodiment of an inflation mold having a constant inner diameter. It is to be understood that an inflation mold is not required when an inflation process is used to affect the compliance characteristics of the balloon.  
         [0057]    While any suitable inflation mold geometry may be employed to create any desired balloon embodiment, certain inflation mold embodiments may be used more commonly than others. In order to facilitate routine usage of inflation molds to customize the compliance characteristics of various embodiments of balloon  114 , it may be desirable or otherwise advantageous to provide a set or a kit of inflation molds having commonly used geometries to physicians. In this manner, a single embodiment of a balloon provided by a manufacturer may, by virtue of being customized, be transformed into various embodiments each particularly treated to meet a specific need. In some embodiments it may be desirable to combine the aspect of treating a balloon by inflating it within a mold, with varying the materials or the amount of materials utilized along the balloon length. Such combinations may be utilized to create embodiments of balloon  114  with dramatically different regions of compliance. For example, an embodiment of balloon  114  wherein middle layer  304  is twice as thick at one half of the balloon length may be created. Each half of such an embodiment of balloon  114  would have distinct compliance characteristics than the other, the half with the thinner middle layer  304  being the more compliant of the two. The embodiment of balloon  114  may then be situated within inflation mold  608  such that the half of the balloon with the thicker region of middle layer  304  is located within the region of smaller diameter within mold  608  and suitably inflated within the mold. In such a manner, two of the described aspects may be combined to create various balloon embodiments with regions of different compliance. Balloon embodiments with regions of different compliance that include regions of porosity for the delivery of therapeutic agents may also be created.  
         [0058]    Additionally, the aspect of treating a balloon by inflating it within a mold may be combined with utilizing a braid or other textile having any suitable geometry such as, but not limited to, tapers or teardrop shapes to create balloon embodiments that are suited to specific bodily conduit geometries. Such balloon embodiments may also include regions of porosity for the delivery of therapeutic agents.  
         [0059]    Any suitable method of attachment may be employed to connect the various embodiments of balloon  114  to the various embodiments of the catheter member(s) in order to create various embodiments of balloon catheter  100 . For example, in the exemplary embodiment of balloon  100  described above, balloon  114  may be attached to steps  202  and  204  (FIG. 2) with various adhesives or combinations of adhesives such as, but not limited to, cyanoacrylates, or adhesives that are cured via ultra-violet light. In some embodiments of balloon catheter  100 , balloon  114  may be thermally bonded to the catheter member(s).  
         [0060]    Various techniques may be employed to enhance the connection between balloon  114  and the catheter member(s). For example, reinforcing bands made in any suitable configuration of any suitable material may be placed around balloon  114  coincident to the points at which the balloon is attached to the catheter member(s). Alternatively, the regions of attachment may be wrapped by reinforcing filaments of any suitable material. Usage of thin films may also yield advantageous embodiments.  
         [0061]    Some embodiments of balloon catheter  100  may take advantage of multi-layer embodiments of balloon  114  by integrating any number of any of the balloon layers into the catheter member(s). For example, in the exemplary embodiment of balloon  114  shown in FIG. 3, middle layer  304  may extend beyond the edges of layers  302  and  306 . The portions of middle layer  304  extending beyond the other balloon layers may be integrated into inner and outer catheter members  108  and  110  respectively or into any other suitable catheter member(s).  
         [0062]    By way of further example, a desired length of an embodiment of inner layer  302  may be attached by any suitable method to steps  202  and  204 , or to any suitable embodiment of the catheter member(s). An embodiment of middle layer  304 , suitably longer than inner layer  302  may then be fitted coaxially over inner layer  302 . Additional catheter member material may then be applied over the regions of middle layer  304  that extend beyond the edges of inner layer  302 . The additional catheter material may be applied by any suitable method. For example, the additional material may be injection molded over the regions of middle layer  304  that extend beyond the edges of inner layer  302 . Alternatively, thin tubing may be applied over the regions of middle layer  304  that extend beyond the edges of inner layer  302 . The thin tubing may be attached to the middle layer  304  as well as the catheter member(s) by any suitable method such as the use of an adhesive or various thermal bonding techniques. Various embodiments of distal tip  116  may be formed in such a manner. With middle layer  304  suitably integrated into the catheter member(s), outer layer  306  may be applied by any suitable method such as, but not limited to, application in the form of a mixture (as described above), or alternatively outer layer  306  may comprise a tube similar to inner layer  302 . Regardless of embodiment, outer layer  306  may extend onto the catheter member(s) if desired. Integration of one or more layers of balloon  114  into the catheter member(s) may be advantageous by providing a very sleek profile to the distal region of balloon catheter  100  as well as a very reliable and strong connection between balloon  114  and the catheter member(s).  
         [0063]    The present invention has been described above with reference to various exemplary embodiments. However, changes and modifications may be made to various exemplary embodiments without departing from the scope of the present invention. For example various embodiments of the distal portion of balloon catheter  100 , particularly with regard to the arrangement of catheter members  108  and  110  and balloon  114  may be provided. Additionally, various changes in the configuration and the materials of balloon  114  may be provided. These and other changes or modifications are intended to be included within the scope of the present invention as set forth in the appended claims.