Abstract:
A medical device for insertion and expansion within a bifurcated lumen is described. An expansion region of the device has regions thereon which, in some cases, enable the device to fold into a predetermined configuration upon deflation. The regions may be defined by differing modulus of the device material.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority to U.S. Provisional Application No. 61/059,243 filed on Jun. 5, 2008, the entire contents of which is hereby incorporated by reference. 
         [0002]    This application is related to U.S. application Ser. No. 11/599,049, filed Nov. 14, 2007, and U.S. application Ser. No. ______ (Attorney Docket No. 1001.2385101) filed on even date herewith, which claims the benefit of U.S. Provisional Application Ser. No. 61/059,250 filed Jun. 5, 2008, the entire contents of all of which are hereby incorporated by reference. 
     
    
     TECHNICAL FIELD 
       [0003]    This disclosure relates to the treatment of bifurcated lumens with a balloon. 
       BACKGROUND 
       [0004]    The body includes various passageways including blood vessels such as arteries, and other body lumens. These passageways sometimes become occluded or weakened. For example, they can be occluded by a tumor, restricted by plaque, or weakened by an aneurysm. When this occurs, the passageway can be reopened or reinforced, or even replaced, with a medical endoprosthesis. An endoprosthesis is an artificial implant that is typically placed in a passageway or lumen in the body. Many endoprostheses are tubular members, examples of which include stents, stent-grafts, and covered stents. 
         [0005]    Many endoprostheses can be delivered inside the body by a catheter. Typically the catheter supports a reduced-size or compacted form of the endoprosthesis as it is transported to a desired site in the body, for example, the site of weakening or occlusion in a body lumen. Upon reaching the desired site, the endoprosthesis is installed so that it can contact the walls of the lumen. 
         [0006]    One method of installation involves expanding the endoprosthesis. The expansion mechanism used to install the endoprosthesis may include forcing it to expand radially. For example, the expansion can be achieved with a catheter that carries a balloon in conjunction with a balloon-expandable endoprosthesis reduced in size relative to its final form in the body. The balloon is inflated to deform and/or expand the endoprosthesis in order to fix it at a predetermined position in contact with the lumen wall. The balloon can then be deflated, and the catheter withdrawn. 
         [0007]    Body lumens often include bifurcated regions with branching pathways. Treatments, such as angioplasty and stent delivery, are sometimes required at locations proximate the branching physiology. A balloon configured for use with a bifurcated endoprosthesis can have a non-linear portion that expands the bifurcated portion of the endoprosthesis. It is desirable that upon deflation, the balloon forms a predictable low profile configuration that facilitates withdrawal from the body and is not likely to become caught on the endoprosthesis during removal. 
       SUMMARY 
       [0008]    The following summary is provided to facilitate an understanding of some of the innovative features unique to the present disclosure and is not intended to be a full description. A full appreciation of the disclosure can be gained by taking the entire specification, claims, drawings, and abstract as a whole. 
         [0009]    In one embodiment, a medical device for treating a bifurcated lumen is described. The medical device may include a catheter shaft having a proximal region, a distal region, and a longitudinal axis. A main balloon may be disposed about the distal region of the catheter shaft along the longitudinal axis. A secondary balloon may be coupled to the distal region of the catheter shaft and may be disposed offset from the longitudinal axis. The secondary balloon may have an inflatable portion including a first section and a second section where the first section may be more flexible than the second section. 
         [0010]    In another embodiment, a method of forming a medical device for treating a bifurcated lumen is described. The method may include providing a balloon system disposed about a distal region of a catheter shaft, the balloon system including a first inflatable portion along a longitudinal axis of the catheter shaft and a second inflatable portion offset from the longitudinal axis of the catheter shaft, and modifying a region of the second inflatable portion of the balloon system to form a first section and a second section in the second inflatable portion having varying crystallinity and/or thickness, wherein the first section is more flexible than the second section. 
         [0011]    In yet another embodiment, a medical device for treating a bifurcated vessel is described. The medical device may include a catheter shaft having a proximal region and a distal region. A first balloon may be disposed about the distal region of the catheter shaft. A second balloon may be coupled to the distal region of the catheter shaft. The second balloon may include a first section and a second section forming a pattern where the first section being more flexible than the second section. The first section and the second section may cause the balloon to collapse into a predetermined configuration having one or more pleats. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0012]    The invention may be more completely understood in consideration of the following detailed description of various illustrative embodiments of the disclosure in connection with the accompanying drawings, in which: 
           [0013]      FIGS. 1A-1D  are cross-sectional views illustrating delivery and deployment of a stent in a bifurcated lumen; 
           [0014]      FIG. 2A  is a cross-sectional view through a portion of a balloon catheter; 
           [0015]      FIG. 2B  is a perspective view illustrating a portion of a balloon catheter; 
           [0016]      FIG. 3A  is a side view of a balloon with ablated stripes in an inflated state; 
           [0017]      FIGS. 3B and 3C  are side and cross-sectional views of a balloon with ablated stripes in a collapsed state; 
           [0018]      FIG. 4A  is a side view of a balloon with stripes of increased crystallinity in an inflated state; 
           [0019]      FIGS. 4B and 4C  are side and cross-sectional views of a balloon with stripes of increased crystallinity in a collapsed state; 
           [0020]      FIG. 5  is a schematic of a balloon being laser treated; 
           [0021]      FIG. 6  is a scanning electron microscope image of a modified surface; 
           [0022]      FIGS. 7-9  are alternative ablation or increased crystallinity patterns on inflated balloons; and 
           [0023]      FIG. 10  is a perspective view of a balloon with ablated stripes. 
       
    
    
     DETAILED DESCRIPTION 
       [0024]    The following detailed description should be read with reference to the drawings in which similar elements in different drawings are numbered the same. The drawings, which are not necessarily to scale, depict illustrative embodiments and are not intended to limit the scope of the invention. 
         [0025]    Referring to  FIGS. 1A-1D , a body lumen  10 , such as a blood vessel, that has a bifurcated region  11  is treated with a catheter  12  carrying a stent  14  over an inflatable balloon system  15 . At the bifurcated region  11 , the body lumen  10  forms a first branch  16  and a second branch  18 . Referring particularly to  FIG. 1A , the catheter  12  may be delivered through a tortuous pathway over a guidewire  13  to the treatment site about the bifurcated region  11 . Referring as well to  FIGS. 1B and 1C , the balloon system  15  is expanded to expand the stent  14  into contact with the wall of the body lumen  10 . Referring to  FIG. 1D , the balloon system  15  is then deflated and the catheter  12  withdrawn, leaving the stent  14  in place. 
         [0026]    The stent  14  is arranged such that it can be placed in the bifurcated region  11 . In this embodiment, the stent  14  includes distal  20  and proximal  22  openings as well as a side opening  24  such that the stent  14  will not obstruct the second branch  18  when it is positioned to span the bifurcated region in the first branch  16 . In addition, the stent  14  includes a main axis region  26  which is along the axis A (shown in  FIG. 1D ) of the stent  14  and is expanded into contact with the first branch  16  and an off-axis region  28  that is expanded into contact with the second branch  18 . The balloon system  15  likewise includes a main axis region  30 , for expanding the main axis  26  of the stent, and an off-axis region  32  that expands the off-axis region  28  of the stent. 
         [0027]    Referring to  FIGS. 2A and 2B , a cross section and perspective view, respectively, of the distal end of a balloon catheter  33  suitable for placement in a body lumen  16 . As in, for example,  FIGS. 1A and 1B , the catheter  33  includes an inner shaft  34  defining a guidewire lumen  36 , an outer shaft  38 , and a dual balloon system. The concentric inner and outer shafts define an annular lumen  37  through which inflation fluid can be directed to the balloon system. The dual balloon system has a first, main balloon  42  including a region  54  that inflates in a generally cylindrical profile along the axis B of the catheter to expand the stent in the first branch  16  of the lumen. The main balloon  42  also includes proximal and distal sleeves or waists  56 ,  58 , that are attached to the catheter. The system also includes a second, off-axis balloon  44  that expands off the axis of the catheter into the second branch  18  of the lumen. The off-axis balloon  44  extends along and around a portion of the main balloon and includes a base portion  41 , an apex or dome  43 , and proximal and distal sleeves  51 ,  53 . The proximal sleeves of both balloons are attached at a region  47  of outer shaft  38  and the distal sleeves of both balloons are attached to a distal region  49  of the inner shaft of the catheter. The proximal sleeve  51  or leg of the off-axis balloon  44  provides a pathway  50  for inflation fluid to the interior of the balloon  44 . In some cases, the distal sleeve  53  of the balloon  44  may be sealed to prevent inflation fluid from passing substantially beyond the off axis inflatable portion of the balloon. In this embodiment, inflation fluid delivered through the lumen  37  is directed to the main and off-axis balloons so that the balloons are inflated substantially simultaneously. In other embodiments, the off-axis and main balloons are arranged sequentially along the catheter axis. In other embodiments, the off-axis and main balloons can be provided on separate catheters that are delivered simultaneously or sequentially. In other embodiments, a single balloon is provided that has main and off-axis inflatable regions. Exemplary stent and catheter arrangements are described in U.S. Patent Application Publication No. 2005/0102023, and in U.S. Pat. Nos. 6,325,826; 6,210,429; 6,706,062; 6,596,020; and 6,962,602, all of which are incorporated herein by reference in their entireties. 
         [0028]    Referring to  FIG. 3A  an off-axis balloon  144  has flexible and less flexible portions. Specifically, the balloon  144  has regions  104  that are more flexible than the surrounding balloon material  120 . Referring to  FIGS. 3B and 3C , the more flexible regions  104  tend to fold inward upon deflation of the balloon  144 . 
         [0029]    Referring to  FIG. 4A , a balloon  144 ′ has stiffer regions  114 , as compared to the surrounding balloon material  120 , Referring as well to  FIGS. 4B and 4C , the stiffer regions  114  tend to stay on the outside of the balloon as it deflates and folds. The regions  104 ,  114  shown in  FIGS. 3A  et seq. and  4 A et seq., respectively, form a pattern of stripes that are parallel to an axis C along which the sleeve  53  lies. A stripe pattern causes the dome of the balloon  144  to fold in an accordion manner, that is, the balloon  144  tends to form pleats as it collapses onto itself. 
         [0030]    Referring to  FIG. 5 , the regions  104 ,  114  can be formed by treating the balloon material  120 , such as by ablating or modifying the crystallinity of the balloon material by exposing the balloon to radiation, such as ultraviolet radiation. Ultraviolet radiation from a laser  30  can be modulated by controlled by a controller  32  to deliver selected energy to the exposed regions. For example, to ablate material the laser fluence is controlled to exceed the ablation threshold of the material. Chemical bonds are broken and the material is fractured into energetic fragments which leave the ablation zone. It is theorized that most of the energy is deposited in the ejected material so there is little thermal damage to surrounding materials. The high energy input to regions  104  removes some of the thickness of the material and therefore reduces the stiffness of these regions more than regions exposed to lower total energy or the unmodified polymer. The more flexible regions  104  tend to fold and collapse more readily as the balloon is deflated, forming valleys, as shown in  FIGS. 3B and 3C . 
         [0031]    To modify the crystallinity of the polymer without ablation, the laser fluence is controlled such that it is below the ablation threshold. In embodiments, the same laser  30  and controller  32  can be used to form regions  114  as used for forming regions  104 . The regions  114  that are treated with the lower energy have increased crystallinity, which increases the stiffness or modulus of these regions. The increased stiffness causes the treated regions to be less flexible than the unmodified regions and thus the balloon is less likely to bend in the stiffer regions than in the unmodified regions. The stiffer regions  114  form the apexes of the accordion folds upon refolding as shown in  FIGS. 4B and 4C . Whether the regions are ablated or have increased crystallinity, the balloon can have at least two modified regions. If the modified regions are in the form of stripes, the balloon can have two stripes or more, such as three stripes, as shown in  FIGS. 3A and 4A , or even more stripes, such as four, five, size, seven or eight stripes. In embodiments, the balloon includes both regions  104 ,  114 , e.g. in an alternating pattern. 
         [0032]    The amount of ablation or degree of crystallinity modification can be selected to facilitate a desirable deflation profile. If the balloon is ablated, the amount of material removed can be for example, about 0.1-15%, such as 0.5 to 2.5% of the balloon wall thickness. If the balloon&#39;s crystallinity is modified without substantial ablation effects, the crystallinity of the polymer can be increased by about 2 to 90%, e.g., 2-5%, 5-10%, 10-20%, 20-40%, 40-60%, 60-70%, 70-80%, 80-90% or 20-80%, compared to the unmodified polymer. In some embodiments, the crystallinity percentage can be two, three or four times after modification than prior to modification. The thickness of the balloon in the crystallinity-modified regions and untreated regions can be substantially the same. With some materials, an increase in crystallinity is exhibited by nodules on the surface of the material. Crystallinity can be increased by heating the polymer material to between the glass transition temperature and the melt flow temperature. Within this temperature range, crystals begin to form, or crystals that were previously present grow larger. The amount of change in crystallinity can be controlled by controlling the energy delivered to the exposed regions, such as by controlling the time of exposure, the fluence and/or the wavelength of radiation. Crystallinity can be increased by increasing the exposure time at a low fluence. As noted above, the fluence threshold depends on the balloon material and on the type of wavelength of energy input into the material. Suitable UV lasers for treating the balloon have a wavelength between about 150-450 nm, such as 157, 193, 248, 308 or 351 nm. For treating a PET or a PEBAX® balloon with a 193 nm multigas laser, less than about 150 mJ/cm 2 , such as between about 60-70 mJ/cm 2  will avoid ablating the balloon material. Other combinations of materials and lasers will have different thresholds of fluence to avoid ablation. Ultraviolet ablation is further described in U.S. Pat. No. 4,911,711. Suitable ablation and control systems are available from Coherent Lambda Physiks, in Goettingen, Germany. Crystallinity can be measured by WAX/SAX x-ray diffraction. Crystallinity measurements can be made at various vendors, such as the University of Minnesota Shepard characterization lab. 
         [0033]    Crystallinity can be changed only on the surface or can be changed throughout the depth of the balloon wall. Suitable techniques for inputting heat into the balloon, such as UV lasers, affect primarily the surface of the balloon. For example, a UV laser may penetrate only part way into a polymer surface, such as 1-60 Angstroms into the balloon. Other heating techniques can penetrate more deeply into the material. With some methods of applying energy, the energy not only penetrates into the material, but radiates isotropically. This heating is considered to be massive or bulk heating of the material, because more than just the surface of the material is heated. A laser, such as a CO 2  laser, an IR laser, a YAG laser, a diode laser, excimer laser, or any another suitable photon source, or a heat stick, i.e., a conductive material connected to a heat cartridge, or an RF generator can be used to apply heat to the balloon. In the case of an RF generator, a jelly having metal particles can be applied to the regions to be treated. If a laser is used to apply heat to the balloon, the balloon can be filled with a fluid to absorb the heat and prevent other portions of the balloon from being simultaneously treated. As noted herein, the amount of crystallinity can be controlled, such as by controlling the amount of time that energy is input into the balloon or controlling the energy output by the energy input device. To focus the heat on particular regions of the balloon, a mask can be used or the device for applying the heat can be focused only in the region where crystallization is desired. With some methods of treating the balloon, the depth of the crystallization can determine whether the treated region ends up on the apex or the valley of a fold. Surface treatment with a UV laser tends to form treated regions that are in the valleys of the folds of the balloon, where treatment with a CO 2  laser or hot stick forms treated regions that are on the apex of the folds a balloon. 
         [0034]    Flexibility or stiffness variations can also be created by other techniques, such as ion beam exposure and mechanically by cutting regions of the balloon wall. All of these techniques can be used in any combination to provide desired properties to the balloon. Ion beam treatment is further described in U.S. application Ser. No. 11/533,588, filed Sep. 20, 2006, and U.S. application Ser. No. 11/355,392, filed Feb. 16, 2006, both of which are incorporated herein by reference in their entirety. The treated regions can be formed by application of energy on the balloon directly or on a polymer tubular parison that is subsequently formed or blown into a balloon, e.g. by free inflation or blow molding. Balloon formation is described further in U.S. Pat. No. 4,963,313. 
         [0035]    Referring to  FIG. 6 , an effect of some heat applications, such as application of UV laser, is to rearrange material at the surface of the balloon. A magnified view of a balloon surface that is crystallized using a UV laser shows nodules  52 . The balloon is a TAXUS® Liberté™ OTW (PEBAX® 7233) polymer balloon available from Boston Scientific, Natick, Mass., and is exposed to UV radiation using a Lambda 210i, multigas UV excimer laser (available from Coherent Lambda Physiks, in Goettingen, Germany) operating at a wavelength of 193 nm with an attenuator set at 30 VA to achieve an output of 30 mJ/cm 2 . Forming the nodules  52  does not remove polymer material from the balloon wall, but rearranges the material on the balloon surface and can reduce the effective wall thickness between the nodules. A non-treated balloon wall would appear smooth and free of nodules. Nodules  52  are observed when the balloon is treated with a UV laser, but are not observed with other treatments, such as CO 2  laser or hot stick. The UV laser treated regions also appear to be opaque, due to the surface modification. 
         [0036]    Polymers suitable for forming the balloon include biaxially oriented polymers, thermoplastic elastomers, engineering thermoplastic elastomers, polyethylenes, polyethylene terephthalate (PET), polybutylenes, polyamides (e.g. nylon  66 ), polyether block amides (e.g., PEBAX®), polypropylene (PP), polystyrene (PS), polyvinyl chlorides (PVC), polytetrafluorethylene (PTFE), polymethylmethacrylate (PMMA), polyimide, polycarbonate (PC), polyisoprene rubber (PI), nitrile rubbers, silicone rubbers, ethylene-propylene diene rubbers (EPDM), butyl rubbers (BR), ethyl-ester thermoplastic elastomers (e.g., ARNITEL®), thermoplastic polyurethanes (PU) (e.g., those based on a glycol ether and an isocyanate, such as PELLETHANE®). In particular embodiments, a poly(ether-amide) block copolymer having the general formula 
         [0000]    
       
                 
         
             
             
         
       
     
         [0000]    in which PA represents a polyamide segment, e.g., nylon  12 , and PE represents a polyether segment, e.g., poly(tetramethylene glycol) is utilized. Such polymers are commercially available from ARKEMA under the tradename PEBAX®. The balloon can be formed of single polymer or of multiple polymers, e.g. by coextrusion. 
         [0037]    In addition to the linear treated regions described, the treated regions can be arranged in other configurations to enhance refolding. In some embodiments, the treated regions spiral around the dome of the balloon, so that the spiral winds around an axis that is perpendicular to the axis along which the sleeves extend. The spiral region can be one continuous region or can be series of non-contiguous regions that generally are in a spiral pattern. Referring to  FIG. 7 , the treated regions are not formed in a contiguous line, but are formed as a series of dots  150 , dashes or shapes which together determine where the balloon will fold upon deflation. Referring to  FIG. 8 , the treated regions  155  can form stripes that are at an angle to the axis C of the sleeves, such as at an angle between about 30° and 60°, for example a 45° angle to the axis. Referring to  FIG. 9 , the treated region  160  can be wider on one side of the dome, that is on a side closer to a proximal sleeve  51  than on the other side of the dome, that is, the side closer to the distal sleeve  53 . Regardless of the pattern, between about 20% and 80% of the balloon&#39;s dome can be treated to create regions of greater or lesser flexibility, such as 50±5% can be treated. In embodiments, the width of the treated regions is about 2 mm or less, such as about 0.1 to 0.5 mm. In some embodiments, ablation is performed only on the portion of the dome closest to the sleeves and not on the apex of the dome. In some bifurcation balloons, the apex of the dome tends to be the thinnest portion of the dome, having a thickness of only a few ten thousandths of an inch. Therefore, in such balloons, ablation may be avoided in the very thin parts of the balloon. Crystallinity modification, however, can be performed on the balloon dome portions closest to the sleeves or can be also on the apex of the dome. 
         [0038]    Referring to  FIG. 10 , a bifurcation balloon  170  with five parallel treated regions 
         [0039]    172 is shown. The top of the dome  174  is free of treated regions  172 . As the balloon  170  deflates, the sides of the dome will collapse into pleats, causing the deflated balloon  170  to reduce down to a predictable shape so that the balloon  170  can be more easily pulled through a lumen than a non-treated balloon in a collapsed state. 
         [0040]    Treating selected portions of a bifurcated balloon cause a bifurcation balloon to collapse in a predictable way when the balloon is deflated. The collapsed state can be selected so that the balloon folds in a compact manner. The more compact the balloon is when collapsed, the easier it may be to remove the balloon from a lumen after the balloon inflation and deflation. Moreover, a more compactly folded balloon may be less likely to catch on an expanded stent upon removal. Unlike cylindrical balloons, the bifurcation balloons tend to be in a naturally expanded state, even when they are not inflated. Thus, treating the balloons to enhance folding can add particular folding characteristics that the balloon would not otherwise have. 
       Example 
       [0041]    A 2.0×2.75 mm bifurcation PEBAX® polymer balloon made by Boston Scientific, Natick, Mass., is exposed to UV radiation using a Lambda LPX210i, multigas UV excimer laser (available from Coherent Lambda Physiks, in Goettingen, Germany) using an argon fluoride gas mixture operating at a pulse duration of 29 ns, a repetition rate of 25 Hz and at a wavelength of 193 nm with an attenuator set at 100% VA to deliver a fluence of 100 mJ/cm 2 , which is above the ablation threshold of PEBAX®, which is around 60-70 mJ/cm 2 . The homogenized beam from the laser is about 9 mm wide and about 9 mm long. Five parallel linear regions approximately 0.14 mm in width spaced equidistantly up the side of the dome of the balloon are exposed through a mask. Three of the regions are exposed at a shot spacing of 75 microns. Two of the regions are exposed at a shot spacing of 100 microns. The exposed regions became opaque. 
         [0042]    Embodiments may include one or more of the following advantages. Balloon treatment of bifurcated lumens can be facilitated by reducing the likelihood that the balloon fold into a predictable configuration upon deflation. The profile of the side branch balloon on deflation after angioplasty or stent delivery can be reduced, e.g. by folding or forming into a desired, predictable configuration that facilitates withdrawal from a body lumen. It can require less withdrawal force to remove a balloon that has been folded compactly from a lumen than to remove a similar balloon that has not been folded compactly from the same lumen. 
         [0043]    A number of embodiments of the invention have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. It should be understood that this disclosure is, in many respects, only illustrative. Changes may be made in details, particularly in matters of shape, size, and arrangement of steps without exceeding the scope of the disclosure. The invention&#39;s scope is, of course, defined in the language in which the appended claims are expressed.