Abstract:
A device and method for making medical balloons such as for angioplasty. The device has fibers that may be of different materials, shapes, sizes, and directions, with the interstitium filled by a polymer materials to render it waterproof and able to be pressurized. The device exhibits improved strength and flexibility. Preferably, the device is steerable, radiopaque, and can operate at very high inflation pressures in order to facilitate low impedance angioplasty.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]    This application claims priority from U.S. Provisional Application Serial No. 60/238,957 filed Oct. 9, 2000, entitled A NOVEL METHOD OF CATHETER FABRICATION AND A NOVEL METHOD OF MEDICAL BALLOON FABRICATION. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    The field of the invention includes materials suitable for use in making medical balloons and catheters, such as for angioplasty. Current angioplasty balloons are fabricated from polymer sheets, and are thus isotropic. The material exhibits no differential properties of elasticity or mechanical compliance as a function of bend direction. Anisotropic balloon characteristics must thus be attained through variations in material thickness, layering, and the like, such as is the case with biaxially oriented balloons.  
           [0003]    There are several features of current balloons that represent areas for improvement. Current balloon devices do not typically exhibit the flexibility optimal for delivery, with or without a stent, to lesion sites targeted for angioplasty. In the case of coronary angioplasty, for example, the delivery path is usually very tortuous, requiring significant bending of the device to reach the target site.  
           [0004]    Another problem associated with current balloons pertains to balloon compliance. When a balloon is being used for stent delivery, compliance of those portions of the balloon that protrude past the ends of the stent is thought to be responsible for vessel injury and further predisposes the artery for neointimal formation as a result of the injury done by the balloon. The balloon inflates uniformly until the stent reaches a maximum diameter. Continued inflation results in compliant expansion of those portions of the balloon that extend beyond the stent while the portion of the balloon constrained by the stent can no longer comply with the increased fluid volume. A shape, similar to a dog bone, results with compliant bulging past either end of the stent. This bulging creates unhealthy stresses in the walls of the vessel being treated, typically resulting in significant injury to the vessel wall. A balloon with lower radial compliance is needed as a stent delivery device, both in coronary and peripheral vessels. Preferably, the balloon would exhibit self-restraining qualities regardless of whether a stent surrounds the balloon. A balloon that is appropriately compliant, yet capable of very high pressures, (equal to or greater than 40 atmospheres) would permit appropriate stent expansion, yet minimal “dog boning” effects as the stent cannot resist such high balloon pressures.  
         BRIEF SUMMARY OF THE INVENTION  
         [0005]    The present invention pertains generally to a fiber-based membrane for use in a medical balloon or catheter. The fibers are preferably woven or braided. Fiber directions and numbers are chosen to create an anisotropic material. As opposed to current polymer membranes of angioplasty balloons, which are isotropic, that is, the elasticity is uniform for all directions of stress and tension within the polymer, the anisotropic material of the present invention provides compliance only in chosen directions.  
           [0006]    For example, an anisotropic structure may have vertical members of a strong, inelastic material, while the cross members may be of a different, more compliant material. One aspect of the invention provides that one of the materials is metallic, such as approved stainless steel. The fibers are sealed, or otherwise contained, within a thin polymer coating that makes them yield a differential expandability. Preferably, one or more of the fibers is radiopaque.  
           [0007]    Importantly, if the fibers are made to run circumferentially, the fibers will impart increased radial strength to the device, encouraging the device to expand longitudinally when pressurized. This will provide longitudinal compliance coupled with reduced radial compliance, thereby creating an anisotropic expansion characteristic which minimizes the potential for imparting damage to the vessel walls during introduction. Moreover, if the balloon having circumferential fibers is elongate, so as to form a cylinder, longitudinal flexibility is preserved. If the existence of the fibers allows a membrane to be used that is thinner than would be required in the absence of the fibers, longitudinal flexibility may even be increased.  
           [0008]    The circular symmetry of the present invention results in a balloon having excellent trackability, in a deflated state, because the longitudinal compliance allows it to snake around corners. If a spiral pattern is used to arrange the fibers around the circumference of the balloon, varying the pitch of the spiral provides different degrees of inflated and deflated longitudinal compliance.  
           [0009]    In order to provide a fluid-tight surface, a polymer is placed within the interstices of the spiraled support fibers or coils. The polymer may be a different material than that of the support coils. The polymer may be a polymer film, formed between the fibers to make the balloon fluid-tight and able to hold pressurized or non-compressible fluids.  
           [0010]    The fibers of the balloon, in addition to providing radial rigidity and preserving longitudinal compliance, may be used to further control the expansion characteristics of the balloon during inflation, more specifically, predetermined, incremental balloon sizes may be obtained. This will allow one balloon size (pre-inflation) to serve a variety of applications requiring different inflation sizes. For example, one balloon-stent may be useful for the 3.0-4.0 mm size range. Typically, three balloon sizes are used to cover this range: 3.0, 3.5, and 4.0 mm. The present invention replaces this with one balloon which can be selectively inflated to each of these diameters. An initial inflation brings the balloon to 3.0 mm in diameter. Overcoming a first pressure threshold causes an incremental increase in the diameter of the support coil, thus “stepping” the diameter of the inflated balloon up to 3.5 mm. A second pressure threshold, once reached, again allows the diameter of the inflated balloon to step up, this time to 4.0 mm. This feature eliminates the need for stepwise balloon sizing, thus reducing the quantity of balloons stocked in a catheter lab by two-thirds. Numerous sizes can be devised using a wide range of pressure thresholds.  
           [0011]    Another aspect of the present invention provides a balloon material having a plurality of elongate, hollow fibers running longitudinally down the length of the balloon. The proximal ends of the fibers are fluidly connectable to a fluid pressure source. They may be connected to the fluid pressure source such that the fibers are selectively in fluid communication with the source, or such that each fiber is connected to a different pressure source. The fibers may thus be selectively inflated, thereby causing the balloon to bend around corners when fibers on one side of the balloon are inflated more than those on the other side. These hollow fibers are also useable in a catheter to similarly steer the catheter using selective inflation techniques. Incorporating radiopaque fibers allows an attending physician a viewing aid for steering the balloon or catheter. This bending aspect allows a balloon or catheter to bend through a tight curve having a very small radius, and may be particularly useful for steering a guidewire into difficult to reach, arterial locations. If the device is made to retroflex, it can easily guide a wire into a sidebranch. A three chambered system is preferably used to provide the ability to steer the device in any direction. Differential pressurization of the septa will cause the balloon to bend through a tight radius of curvature as well. The fibers in this design can be elastic and biased at a predetermined level so that the balloon can bend in any direction.  
           [0012]    Yet another aspect of the present invention pertains to the balloon&#39;s unique ability to withstand high pressures. The high pressure expansion characteristic made possible by the fibers allows the balloon to be expanded using either high or low pressures. During standard dilatations and stent expansions, if a stent is expanded at 8 atmospheres of pressure, resistance to expansion by a lesion being treated may demand a higher internal balloon pressure, and the external force which arises when this demand is answered creates a dog bone effect as the balloon on either sides of the lesion expands more than that part of the balloon adjacent the lesion, thereby giving the balloon a relative constriction or “waist” at the point of artery or stent location. Increasing the balloon pressure will generally break the resistance to allow additional radial expansion. Conversely, if the balloon is expanded under high balloon tension (high pressure) the device will not dog-bone or form a waist. Referring to the resistive force exhibited by the artery or stent as “expansion-impedance” (I), a relationship between the expansion-impedance, the radial expansion (E) and the tension in the balloon (T) can be represented as:  
       I   ∝     E   T                           
 
           [0013]    such that when the expansion occurs under high pressure, the impedance is quite low. Expanding a stent or dilating an artery (or both simultaneously) is facilitated by this low impedance expansion since, as the balloon is loaded by the resistive force of the stent or artery, it expands without being impeded and achieves a more uniform expansion.  
           [0014]    In addition to the aforementioned expansion advantages that the use of fibers provide, it is envisioned that the fibers may be constructed and arranged to form a device, such as a filter or cage, at the distal tip of the balloon. The distal device can be used to manage the particulate matter, such as arterial plaque, dislodged from the walls of the vessel during expansion. A filter, for example, can be used to prevent the particulate matter from entering the catheter when the catheter is being used in a suction capacity. A cage can be fashioned to trap and extract the particulate matter when the catheter is removed.  
           [0015]    Using the fiber technology of the present invention to form catheters allows a catheter to be formed having segments of varying flexibility. Flexibility may be varied by changing the weave pattern of the fibers. For example, a circumferentially spiraling fiber may extend down the length of the catheter, interwoven with uniformly spaced longitudinal fibers. Increasing the pitch of the circumferential fiber decreases the weave density and, thus, increases the flexibility. Thus, a catheter could be formed with such a circumferential fiber having segments of increased and decreased pitch to create desired segments of varying flexibility. For example, a coronary catheter could be fashioned having a relatively stiff proximal end, thereby permitting good torque transmission for straightening tortuous vessels. The catheter could also have a relatively soft tip curves to avoid arterial injury. Portions of the tip may be stiffer than others to permit guide support.  
           [0016]    Portions of the catheter could also be provided with varying characteristics by altering the thickness of the interstitial polymer or even varying the types of polymer used along the length. For example, the catheter may provide a segment in which the woven fibers are uncoated or weakly coated with the polymer in order to provide a segment that allows fluid to escape from the lumen in a controlled manner, such as may be desired with the introduction of a contrast agent.  
           [0017]    The fibers can be woven or braided in a fashion to change the shape of the balloon from a cylinder to a tapered cylinder. The fibers could be woven to make the shape of the balloon oval, wedge like, dog bone, reverse taper, and so on. Two balloons could be made from one piece of fabric to create a unique shape with balloons side by side. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0018]    [0018]FIG. 1 is a graph generally depicting compliant inflation behavior;  
         [0019]    [0019]FIG. 2 is a graph generally depicting the expansion behavior of the device of the present invention when filled with a compressible fluid;  
         [0020]    [0020]FIG. 3 is a graph generally depicting the expansion behavior of the device of the present invention when filled with an incompressible fluid;  
         [0021]    [0021]FIG. 4 is a graph generally depicting the expansion behavior of an embodiment of the device of the present invention whereby no compliant behavior is exhibited;  
         [0022]    [0022]FIG. 5 is a side elevation view of a pleated balloon embodiment of the present invention;  
         [0023]    [0023]FIG. 6 is a plan view of the embodiment of FIG. 5;  
         [0024]    [0024]FIG. 7 is a partially inflated side elevation view of the embodiment of FIG. 5;  
         [0025]    [0025]FIG. 8 is a perspective view of a fabric sleeve balloon of the present invention;  
         [0026]    [0026]FIG. 9 is a plan view of the fabric sleeve balloon of FIG. 8;  
         [0027]    [0027]FIG. 10 is a perspective view of the fabric sleeve balloon of FIG. 8 in a partially inflated state;  
         [0028]    [0028]FIG. 11 is a top plan view of an alternative embodiment of the fabric sleeve balloon of the present invention;  
         [0029]    [0029]FIG. 12 is a perspective view of a fill yarn critical sleeve embodiment of the present invention inflated to a first diameter;  
         [0030]    [0030]FIG. 13 is a perspective view of the fill yarn critical sleeve of FIG. 12 inflated to a second diameter;  
         [0031]    [0031]FIG. 14 is a perspective view of a section of material useable to make a balloon of the present invention which inflates to multiple, distinct diameters;  
         [0032]    [0032]FIG. 15 is a perspective view of a section of material useable to make a balloon of the present invention which inflates to multiple, distinct diameters;  
         [0033]    [0033]FIG. 16 is a section view of a thread pattern useable to create a material of the present invention which exhibits anisotropic stretching characteristics;  
         [0034]    [0034]FIG. 17 is a perspective section view of a catheter of the present invention;  
         [0035]    [0035]FIG. 18 is a perspective view of an alternative catheter of the present invention;  
         [0036]    [0036]FIG. 19 is a perspective view of a segment of material usable to form a catheter having a weeping effect;  
         [0037]    [0037]FIG. 20 is a perspective view of an embodiment of a balloon of the present invention whereby the fibers are constructed and arranged to form a filter external to the balloon; and,  
         [0038]    [0038]FIG. 21 is a perspective view of an embodiment of a balloon of the present invention whereby the fibers are constructed and arranged to form a cage external to the distal end of the balloon.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0039]    Conventional angioplasty balloons may be described as “compliant”, meaning that the diameter of the inflated balloon is directly proportional to the inflation pressure over a defined pressure range. This behavior is illustrated in FIG. 1, which shows a graph of balloon diameter “D” versus inflation pressure “P” for a typical compliant angioplasty balloon. The plot displays a linear region  10  which describes the compliant aspect of the balloon where there is a direct proportional relation between the diameter and the inflation pressure. The graph is continuous indicating that the balloon diameter increases or decreases in a continuous manner as a function of the inflation pressure. There is a point, however, where the elastic limit of the material comprising the balloon is exceeded and the balloon increases unpredictably, usually significantly in diameter in proportion to a further increase in the pressure. The elastic limit is indicated at point  12  which marks the end of linear behavior of the balloon. The pressure may be increased further, but a point is eventually reached where the ultimate strength of the balloon material is exceeded and the balloon bursts as indicated at point  14 .  
         [0040]    The invention concerns balloons useful in angioplasty procedures, as well as for other purposes. The balloons, according to a first aspect of the invention, have a plurality of pressure ranges over which compliant behavior is manifest (i.e., the diameter is substantially linearly proportional to the inflation pressure), the ranges of compliant behavior being separated by points wherein the diameter increases in a discontinuous jump between a relatively smaller diameter and a relatively larger diameter such that the behavior of the balloon over its entire useful pressure range may be described as “non-compliant”. In a second aspect of the invention the balloon diameter jumps substantially discontinuously between discrete diameters with increases in inflation pressure without any significant compliant behavior of the balloon between the various diameters.  
         [0041]    [0041]FIG. 2 presents a graph which generally illustrates the “non-compliant” behavior of balloons according to the first aspect of the invention. The graph shows the balloon diameter “D” as a function of inflation pressure “P”. Such balloons may initially exhibit compliant behavior as shown in the linear region  16  up to a first predetermined pressure P 1  corresponding to a maximum diameter D 1 . Increase in pressure P beyond P 1  does not result in an increase in diameter D of the balloon until a second predetermined pressure P 2  is reached. If the balloon is pressurized with a gaseous fluid, the balloon diameter jumps discontinuously to a relatively larger diameter D 2  once the predetermined pressure P 2  is reached. Further, increasing the pressure P beyond P 1  need not be accompanied by an increase in the length of the balloon as gaseous fluid may be compressed. The balloon behavior may then again be compliant between P 2  and a third predetermined pressure P 3  as evidenced by the linear region  18  of the graph. At and above P 3 , there will again be no significant increase in balloon diameter as the pressure is increased until a fourth predetermined pressure P 4  is reached. At P 4 , the diameter of the balloon will jump discontinuously to a larger diameter D 3  and then behave compliantly over a further range of pressures above P 4  as indicated at  20 . These characteristics featuring regions of compliant behavior separated by discrete, discontinuous jumps in diameter can be repeated but eventually practical considerations will place a limit on the behavior and the balloon will eventually reach the end of its ability to stretch and burst when the balloon&#39;s ultimate strength is exceeded, as indicated at  22 . It is noted that the graphs shown are representative of general principles for explanatory purposes only.  
         [0042]    If a liquid fluid is used to pressurize the balloon, there will not be significant abrupt jumps in balloon diameter at the transition points between the regions of compliant behavior. This is due mainly to the fact that liquids tend to be substantially incompressible and the increases in pressure within the balloon are hydraulically transmitted through the liquid without significant amounts of additional liquid entering the balloon. Once the critical pressure marking the transition point is exceeded, however, and the balloon is free to expand further, the balloon may be inflated to a larger diameter in a controlled manner by forcing more liquid into it. Use of liquid to inflate the balloon, thus, prevents the balloon from suddenly expanding at a transition point and causing an injury or a rupture in a blood vessel, for example. FIG. 3 is a graph showing the behavior of a liquid filled balloon. There is a relatively small jump  24  in the balloon diameter at point P 2  between the ranges of linear behavior  16  and  18 . Notably, this small jump  24  in balloon diameter may be accompanied by a small decrease in pressure until fluid is introduced to the newly created space resulting from the increase in balloon diameter.  
         [0043]    [0043]FIG. 4 illustrates the behavior of a balloon according to the second aspect of the invention. For such balloons, there is a first diameter D 1  which the balloon achieves over a relatively large pressure range  26  and a second diameter D 2  achieved over another pressure range  28 , but there are no regions of compliant behavior where the balloon diameter is continuously variable as a function of the inflation pressure. Various balloon embodiments corresponding to both aspects of the invention are described in detail below.  
         [0044]    The pleated balloon  30  shown in FIGS. 5 through 7 has an envelope  32  preferably comprised of a flexible, resilient, elastic material such as rubber or similar synthetic polymer. A plurality of pleats  34  are formed in the envelope by folding it, preferably inwardly in a series of reverse folds  36  as shown in FIG. 6. Reverse folds  36  have facing portions  38  and  40  which are releasably adhered to one another, for example, by an adhesive layer  42 , which will hold the pleats together until a predetermined critical pressure is achieved within the balloon.  
         [0045]    The balloon with pleats  34  initially displays compliant behavior, expanding linearly or otherwise proportionally with increasing inflation pressure until the predetermined critical pressure is reached. Pressure within the balloon places the pleats under tension and the adhesive releases the pleats at the predetermined critical pressure to allow the balloon to abruptly expand from a first diameter D 1  shown in FIG. 5, to a second, larger diameter D 2  shown in FIG. 7. Note that not all of the pleats  34  have released at the critical pressure. It is possible to arrange for different pleats to release at different internal pressures, thus, allowing the balloon to have multiple compliant behavior regimes separated by multiple discrete jumps in diameter. Release pressures for the pleats may be controlled, for example, by using several adhesives having different strengths to secure different pleats. Pleats secured with a relatively weak adhesive will separate at a lower pressure than pleats secured with a stronger adhesive. It is also possible to control the release pressure by using the same adhesive on all pleats but forming the adhesive bond over a relatively larger surface area between the facing portion  38  and  40  of the pleat when a stronger bond, corresponding to a higher critical pressure, is desired.  
         [0046]    Pleats  34  may also be secured by other means including ultrasonic bonding and thermal bonding. The envelope  32  may alternately be comprised of materials such as polyurethane, PET, Silicone, nylon, or acrylic, to name a few. When resilient elastic material is used for the envelope, the pleated balloon behaves according to the first aspect of the invention with expansion characteristics as shown in FIG. 2.  
         [0047]    FIGS.  8 - 11  show a fabric sleeve balloon  46 . This embodiment has fabric sleeve  48 , preferably woven and comprised of polymer yarns, fibers or monofilaments of materials such as polyester, polypropylene, or nylon, as well as liquid crystal polymers such as Spectra, PBO zylon, Vectran. Although of woven construction, the sleeve  48  may itself have a coating or film of resin, silicone or polyurethane causing it to be fluid tight, or it may enshroud a fluid tight membrane  50  as depicted in FIG. 8.  
         [0048]    Sleeve  48  is formed preferably by arranging a single woven tube having a relatively large diameter into a plurality of smaller diameter tubes, three tubes numbered  52 ,  54  and  56  being shown by way of example. The tubes are arranged substantially parallel to each other and each is separated from another by a respective rip-stop seam  58  and  60 . One of the tubes,  52 , is inflatable and, when pressurized, places tension forces on the rip-stop seams  58  and  60  between tube  52  and tubes  54  and  56  respectively. Seams  58  and  60  are designed to release when a predetermined tension force corresponding to a predetermined pressure within tube  52  is reached. The release force may be different for each seam.  
         [0049]    The fabric sleeve balloon  46  may be inflated to a first diameter D 1  shown in FIG. 8 and remain at that diameter while the inflation pressure is increased until a first predetermined critical pressure is reached, at which point the tension forces on the seam  58  exceed the strength of the seam and the seam parts allowing the fabric sleeve balloon to expand in a discrete jump to a larger diameter D 2  shown in FIG. 10. Note that seam  60 , which has a relatively higher strength, is still intact and holds tube  56  in place. When a second predetermined critical pressure is reached, seam  60  will also part and allow the balloon to expand in a discrete jump to another larger diameter.  
         [0050]    Seams such as  58  and  60  are formed by weaving together warp fibers or yarns  62  along the length of the seam. Normally during weaving the shuttle carrying the fill yarns  64  moves in a “figure  8 ” path which causes the warp and fill yarns to cross over one another. However, to create tubes  52 ,  54  and  56  according to the invention, the shuttle is moved across the top and bottom faces of the tube and does not cross at the seam, resulting in multiple warp fibers being captured by fill fibers or yarns along the seam. The strength of seams  58  and  60  is mainly determined by the strength of the warp yarns, but other parameters such as the number of warp yarns and their denier also affect the seam strength. Separation of the seam is effected by the parting of the warp yarns along the seam, the circumferential yarns remaining intact and maintaining the integrity of the fabric sleeve balloon  46 .  
         [0051]    The fabric sleeve balloon  46  may exhibit aspects of compliant behavior as illustrated in FIG. 2, or it may be totally non-compliant and jump between diameters exhibiting no significant compliant behavior as shown in FIG. 3. Compliant behavior will occur if elastic resilient yarns are used to form the sleeve  48 . This will allow tube  52  to increase in diameter linearly as a function of inflation pressure until the tension forces on a seam exceed the strength of the seam, causing the seam to part and allowing a discontinuous jump to a larger diameter. If the yarns comprising the sleeve are inelastic, then the only significant changes in diameter will occur when the inflation pressure causes seams to part and a discontinuous diameter change results.  
         [0052]    While the tubes  54  and  56  are shown positioned on the outside of tube  52 , this is for clarity of illustration. It is preferred that the tubes  54  and  56  be arranged on the inside of tube  52  as shown in FIG. 11. The inside configuration allows the balloon to have a regular circular shape so as to pass readily through vessel and catheter lumens.  
         [0053]    [0053]FIGS. 12 and 13 show a fill yarn critical sleeve balloon  66  according to the invention. Balloon  66  comprises a woven sleeve  68  which may itself be fluid tight or may have an inflatable membrane  70  within. Sleeve  68  is woven with circumferential yarns  72  and  74  having different characteristics as described below which allow the balloon  66  to display both compliant and non-compliant behavior.  
         [0054]    Preferably, circumferential fill yarns  72  have a first, relatively low tensile strength, and circumferential fill yarns  74  have a relatively higher tensile strength. Furthermore, fill yarns  74  are overfed upon weaving, and thus are longer than fill yarns  72 . If fill yarns  72  are elastic, then the balloon  66  will expand continuously when inflated to a maximum first diameter D 1  (see FIG. 12) limited by the strength of the fill yarns  72 . Increasing the pressure above a predetermined critical value will cause fill yarns  72  to part and the balloon  66  will expand discontinuously to a second diameter D 2  (see FIG. 13) established by the length and elasticity of fill yarns  74 . Due to their relatively greater length, due to overfeeding, fill yarns  74  do not take any significant load until fill yarns  72  part. If fill yarns  74  are elastic, then the balloon  66  may be further expanded by increasing the inflation pressure. If the fill yarns  74  are relatively inelastic, then the diameter will remain substantially constant with increases in inflation pressure until the tensile strength of the fill yarns  74  is exceeded.  
         [0055]    If circumferential yarns  72  and  74  are relatively inelastic, then the balloon  66  will have essentially two discrete diameters determined by the relative lengths of the fill yarns and the balloon will display no significant compliant behavior in between the two discrete diameters.  
         [0056]    The relative strengths of the fill yarns  72  and  74  may be controlled by choice of the materials comprising the yarns and their denier, as well as the ratio of number of one type of fill yarn  72  to the other  74  comprising the sleeve  68 . Relative elasticity may also be used to establish the critical pressures and discrete diameters defining the non-compliant behavior of the balloon  66 . For example, if fill yarns  72  are fully oriented and fill yarns  74  are partially oriented then fill yarns  72  will be relatively inelastic and take the load when the balloon is inflated while fill yarns  74 , being relatively elastic, will stretch and not bear any significant load until the inflation pressure is reached where the relatively inelastic fill yarns  72  part and the balloon expands discontinuously until yarns  74  take up the load and resist further expansion of the balloon.  
         [0057]    As shown in FIG. 14, this overfeeding approach can be used to create more than one distinct jumps in diameters. Here, fill yarns  73  and  74  have been overfed, thereby each creating somewhat of a sine wave, when compared to relatively straight fibers  72 . The “wavelength” of the sine wave of yarns  74  is shorter than that of yarns  73 , making yarns  74  longer than the yarns  73 . Thus, as the device inflates, a first diameter will be determined by the yarns  72  until they break, the diameter will then jump up to a second diameter, defined by the yarns  73  until they break, at which time the diameter will jump up to a third diameter, defined by the yarns  74 .  
         [0058]    Looking at FIG. 15, it can be seen that this same effect can be obtained using circumferential fibers  72  and  74  which are elastic, rather than inelastic. These elastic fibers have different yield points and thus, break at different pressures and stretched lengths. The fibers  74  are shown as being thicker and, thus, stronger, however it may be desired to provide similarly sized fibers  72  and  74  that attain different elastic profiles because they are made of different materials, as opposed to having different thicknesses.  
         [0059]    Preferred materials for the fill yarn critical sleeve balloon include polymer yarns, fibers or monofilaments of materials such as polyester, polypropylene, or nylon, as well as liquid crystal polymers such as Spectra, PBO zylon, Vectran.  
         [0060]    The principles of the present invention can be practiced to provide medical devices exhibiting anisotropic stretching characteristics. Anisotropic materials stretch differently in different directions when exposed to a relatively uniform stress, such as when they are being inflated. By providing a balloon that stretches along one direction, but is relatively nondistensible in another direction, many of the problems described in the background can be avoided.  
         [0061]    Referring now to FIG. 16, there is shown a section of material  78  having distensible fibers or yarns  80  and nondistensible fibers or yarns  82 . Thus the material  78  exhibits elastic properties in a first direction, indicated by arrows  84 , but little to no elastic properties in a second direction, indicated by smaller arrows  86 .  
         [0062]    Using such a material  78  to create a balloon or catheter of the present invention provides control over the expansion characteristics of the device. For example, if the material  78  were used to create a balloon, and oriented such that the distensible fibers  80  run longitudinally, while the nondistensible fibers run circumferentially, a balloon is created which can expand in length but maintains a relatively constant radius. This balloon avoids the dog-boning problems of the prior art.  
         [0063]    Notably, if the elastic membrane  88  used to make the balloon fluid-tight is strong enough for its intended purpose, and the circumferential fibers  82  are impregnated into, or otherwise securely fastened to the balloon membrane  88 , it may be unnecessary to provide the longitudinal fibers  80 . However, inclusion of the longitudinal fibers  80  provides more control over the elasticity of the balloon  78  in a given direction and also predictably controls the yield point of the balloon  78 . The balloon  78  can thus be inflated rapidly, using higher than usual pressures, such as on the order of 40 atmospheres, thereby overcoming resistance imposed by an area such as a lesion of the vessel being treated, thus expanding uniformly without creating a waist.  
         [0064]    Using the fiber technology of the present invention to form catheters allows a catheter to be formed having segments of varying flexibility. Referring to FIG. 17, it can be seen that flexibility may be varied by changing the weave pattern of the fibers. For example, a circumferentially spiraling fiber  90  may extend down the length of the catheter  92 , interwoven with uniformly spaced longitudinal fibers  94 . Increasing the pitch of the circumferential fiber  90  decreases the weave density and, thus, increases the flexibility. Thus, a catheter  92  could be formed with such a circumferential fiber  90  having segments of increased pitch  96  to create segments  96  of varying flexibility.  
         [0065]    Insofar as fibers  94  are distensible, the catheter can be made to be steerable by using hollow, inflatable fibers  94 . When the fibers  94  are inflated, they increase in length. Inflating some of the fibers  94 , while leaving others deflated, causes one side of the catheter  92  to become longer than the other side, necessarily bending the catheter in the direction of the fibers  94  that are not inflated.  
         [0066]    [0066]FIG. 18 shows how the areas of increased flexibility  96  can be combined with the characteristics of the hollow fibers  94  to provide a desired result. The catheter  92  has a spiraling circumferential fiber  90  extending down the length of the catheter  92 . The spiraling fiber  90  has an increased pitch at the distal end of the catheter  92  thereby creating a segment of increased flexibility  96 . The catheter also has three inflatable fibers  94  imbedded within a membrane  98  making up the body of the catheter. When the inflatable fibers  94  are inflated at different pressures in order to cause the catheter  92  to bend toward the fibers  94  which are least inflated, the catheter  92  will bend more at the segment of increased flexibility  96  because it will experience less resistance to bending at that segment  96 . This significantly decreases the radius of the bend and makes the catheter  92  very steerable.  
         [0067]    Portions of the catheter  92  could also be provided with varying characteristics by altering the thickness of the interstitial polymer  98  or even varying the types of polymer used along the length. Referring to FIG. 19, a material  100  is shown for use in devising a catheter  92  having a fluid tight body  98  with a weeping section  102 . The polymer  98  comprising the body is so thin in section  102  that small holes  104  are created in the interstices of the fibers  90  and  94 . These holes  104  allow fluid introduced through the lumen of the catheter  92  to escape into the treated vessel. If the holes  104  are numerous, the pressure of the fluid escaping will be low, thereby creating a weeping effect.  
         [0068]    As seen in FIGS. 20 and 21, in addition to the aforementioned expansion advantages that the use of fibers provide, it is envisioned that the fibers may be constructed and arranged to form a device  110 , such as a filter  112  or cage  114 , at the distal tip of the balloon or catheter. The distal device  110  can be used to manage the particulate matter, such as arterial plaque, dislodged from the walls of the vessel during expansion. A filter, for example, can be used to prevent the particulate matter from entering the catheter when the catheter is being used in a suction capacity. A cage  114  can be fashioned to trap and extract the particulate matter when the catheter is removed. FIG. 20 shows a device  110  comprising a balloon  116  having fibers of the present invention that are woven into and out of the balloon  116  in order to form an external filter  112 . FIG. 21 shows a device  110  comprising a balloon  116  wherein the fibers of the present invention extend from the distal end of the balloon  116  to form a cage  114 .The fabric we used to make the balloons are woven into near net shape structures. The fabric is woven to resemble a standard angioplasty balloon. The fabric ends are tapered. The advantage of this is that the end balloon cones are not as thick as standard balloons. Furthermore, the shape of the fabric reduces any need for seams or overlapping balloons material.  
         [0069]    [0069]FIG. 20 shows a device  110  whereby the fibers of the balloon extend radially to form a filter  112 . Fibers thus raised from the surface, either completely or just partially, may also serve other purposes. For example, textured balloon surfaces can be made by covering the inside of the fabric only. In other words, the membrane is attached to the inside of the mesh, leaving a textured mesh surface on the outside of the balloon. The textured surface reduces balloon slippage inside a calcified lesion. The textured surface also helps anchor a stent during delivery before expansion. Additionally, by changing the size of the yarns, the surface texture can be altered. For example, every 5 th  to 10 th  yarn could be replaced with a larger yarn. This would reduce fabric bulk and increase fabric texture/roughness.  
         [0070]    Large protrusions on the balloons surface, such as is seen in FIG. 20, could also be used to help “cut” or break highly calcified lesions. The large protrusions may be made by incorporating large diameter yarns/wires into the fabric surface during the textile manufacturing process. The yarns could be axial or radially placed. Radially placed at some predetermined pitch could help reduce balloon stiffness and crossing profile.  
         [0071]    Although the invention has been described in terms of particular embodiments and applications, one of ordinary skill in the art, in light of this teaching, can generate additional embodiments and modifications without departing from the spirit of or exceeding the scope of the claimed invention. Accordingly, it is to be understood that the drawings and descriptions herein are proffered by way of example to facilitate comprehension of the invention and should not be construed to limit the scope thereof.