Abstract:
A balloon geometry is utilized herein where the balloon is inflatable from an initial unexpanded state to an expanded state. The balloon includes first and second portions; the first portion having a first diameter with the balloon being in the expanded state, the second portion having a second diameter with the balloon being in the expanded state, the first diameter being different from the second diameter. With a stent being mounted onto the balloon, expansion of the balloon results in the first portion of the balloon assisting a first portion of the stent to radially expand more than a second portion of the stent located adjacent to the second portion of the balloon. Preferably, the stent is formed of shape memory polymer. With the subject invention, one or both ends of the stent can be formed with larger diameters, or flares, in vivo at the point of implantation. The flared ends provide engagement points for the stent to a surrounding bodily passageway. Although the balloon may have various applications, it is particularly well-suited for use with shape memory polymer stents, which can be expanded and deformed in vivo.

Description:
FIELD OF THE INVENTION 
       [0001]    This invention relates to balloons for radially expanding stents, and more particularly, to balloons for radially expanding shape memory polymer (SMP) stents. 
       BACKGROUND OF THE INVENTION 
       [0002]    Shape memory polymer (SMP) stents are known in the prior art. The following disclosures, which are all incorporated by reference herein, disclose suitable materials and geometries for SMP stents: U.S. Published Patent Appl. No. 2005/0010275; PCT Published Patent Appl. No. WO 2004/032799; U.S. Published Patent Appl. No. 2005/0216074; U.S. Published Patent Appl. No. 2005/0251249; U.S. Published Patent Appl. No. 2005/0245719; U.S. Published Patent Appl. No. 2004/0116641; PCT Published Patent Appl. No. WO 2004/033515; U.S. Published Patent Appl. No. 2004/0122174; PCT Published Patent Appl. No. WO 2004/033539; U.S. Published Patent Appl. No. 2004/0083439; PCT Published Patent Appl. No. WO 2004/033553; U.S. Published Patent Appl. No. 2005/0075625; and, PCT Published Patent Appl. No. WO 2005/009523. 
         [0003]    Stents are often used in the gastrointestinal tract to treat malignant or benign strictures as palliative or supporting treatment to chemotherapy or surgery. With biliary stent applications, plastic stents are often used. Plastic stents are typically 2-3 mm in diameter and need to be exchanged relatively often (e.g., every three months) due to occlusion from bile. Metal stents, such as self-expanding metal stents, are also useable and tend to have a longer patency than plastic stents because of their larger diameters, typically 8-10 mm. However, plastic stents may be removable, whereas, metal stents generally are not. Common practice calls for removing stents when treatment of benign strictures is completed. Accordingly, metal stents are generally restricted to use where malignant, not benign, strictures are present. 
         [0004]    A need had developed in the prior art for a stent having relatively large diameters in the range of metal stents, e.g., 8-10 mm, yet, be removable. SMP stents satisfy this need with SMP stents both being useable at the relatively large diameters, thereby providing good patency, and being removable, thus allowing for use with both benign and malignant applications. 
         [0005]    SMP stents are formable as tubular structures (which may be cut or etched or otherwise have material removed) or as coiled structures resembling coil springs. With either configuration, a straight, generally cylindrical shape may not be desired, due to the possibility of migration within a bodily passageway. A method has been developed of pre-forming SMP stents with one or both ends flared, with the SMP stents recovering this configuration in vivo at the point of implantation. However, in preparing the SMP stents, the stents are initially pre-formed with the flared-end configuration and then contracted to a minimized diameter for insertion into a catheter (in being readied for implantation) and later expanded. Alternatively, the SMP stents may be formed at a reduced profile and expanded to a desired size. The pre-expansion profile of the SMP stents resembles proportionately the profile of the fully-expanded stents, with the ends being likewise flared. With the smallest possible profile being sought for insertion into a patient, the flared-end configurations of the contracted SMP stents may be undesirable. 
       SUMMARY OF THE INVENTION 
       [0006]    A balloon geometry is utilized herein where the balloon is inflatable from an initial unexpanded state to an expanded state. The balloon includes first and second portions; the first portion having a first diameter with the balloon being in the expanded state, the second portion having a second diameter with the balloon being in the expanded state, the first diameter being different from the second diameter. With a stent being mounted onto the balloon, expansion of the balloon results in the first portion of the balloon assisting a first portion of the stent to radially expand more than a second portion of the stent located adjacent to the second portion of the balloon. Preferably, the stent is formed of SMP. With the subject invention, one or both ends of the stent can be formed with larger diameters, or flares, in vivo at the point of implantation. The flared ends provide engagement points for the stent to a surrounding bodily passageway. Although the balloon may have various applications, it is particularly well-suited for use with SMP stents, which can be expanded and deformed in vivo. 
         [0007]    The balloon is catheter mounted and useable in various bodily passageways for implanting a stent, including, but not limited to, the gastrointestinal tract (e.g, bile ducts, colon, duodenum), esophagus, bronchi, trachea, urine tract (e.g., urethra, ureter, prostate) and vasculature (e.g., coronary blood vessels, peripheral blood vessels, intracranial blood vessels). 
         [0008]    These and other features will be better understood through a study of the following detailed description and accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]      FIG. 1  is a schematic of an assembly including a catheter, with a balloon in an unexpanded state being located thereon, and a stent mounted onto the balloon in accordance with one embodiment of the invention; 
           [0010]      FIG. 2  is a schematic of a balloon in an expanded state in accordance with one embodiment of the invention; 
           [0011]      FIGS. 3(   a )-( e ) are schematics of various alternative balloon geometries in accordance with alternate embodiments of the invention; 
           [0012]      FIG. 4  is a schematic of an expanded balloon located in a bodily passageway having a tubular stent thereabout in accordance with one embodiment of the invention: 
           [0013]      FIG. 5  is a schematic of an expanded balloon having a coiled stent thereabout in accordance with one embodiment of the invention; and, 
           [0014]      FIGS. 6(   a )-( c ) are schematics of alternative balloon configurations in accordance with alternate embodiments of the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0015]    A balloon  10  is provided herein for expanding and/or deforming a stent  12  in vivo at the point of implantation. The balloon  10  is located on a catheter  14 , as is known in the art. The catheter  14  may be formed in accordance with any known design and includes a proximal end  16  and a distal end  18 . With the distal end  18  being intended for insertion into a patient, it is preferred that the balloon  10  be located in proximity to the distal end  18 . 
         [0016]    With reference to  FIG. 2 , the balloon  10  may extend along a longitudinal length of the catheter  14  and includes first and second ends  20  and  22 , respectively, and an intermediate portion  24  therebetween. The balloon  10  is expandable from an initial unexpanded state to an expanded state. 
         [0017]    With the subject invention, at least one portion of the balloon  10  is formed to expand to a different, e.g. larger, diameter than one or more other portions of the balloon  10 . For example, as shown in  FIG. 2 , a first portion  26 , located in proximity to the first end  20 , is expandable to a diameter D 1 . A second portion  28  of the balloon  10 , which may coincide with a length of the intermediate portion  24 , is expandable to a diameter D 2 . The diameter D 1  is different from, e.g., greater than, the diameter D 2 . With this arrangement, the balloon  10  can be used to selectively assist in expanding and/or deforming one or more portions of the stent  12  to larger diameters than other portions of the stent  12 . Preferably, the first portion  26  is positioned to coincide with one of the ends  30  of the stent  12 , while the second portion  28  is positioned to coincide with an intermediate section  32  of the stent  12 , the intermediate section  32  being spaced from the ends  30 . In this manner, at least one of the ends  30  of the stent  12  may be flared. 
         [0018]    Optionally, a third portion  34  of the balloon  10  may be formed with a diameter D 3  that is different from, e.g., larger, than the diameter D 2 . D 3  may approximately equal D 1 . Preferably, the second portion  28  is located between the first and third portions  28 ,  34  and, more preferably, the third portion  34  is located in proximity to the second end  22 . In addition, the third portion  34  is preferably positioned to coincide with one of the ends  30  of the stent  12 . With locating the diameter D 2  between the diameters D 1  and D 3 , two of the ends  30  of the stent  12  may be flared. 
         [0019]    To allow for smooth transitions between the first, second and third portions  26 ,  28 ,  34 , one or more transition surfaces  36  may be provided for the balloon  10 . For example, the transition surfaces  36  may be tapered or arcuate. With the arrangement of  FIG. 2 , the transition surfaces  36  are arcuate with the intermediate portion  24  being generally concave. End transition surfaces  38  may also be provided to connect the first and seconds  20 ,  22  with the first and third portions  26 ,  34 , respectively. 
         [0020]    The first and third portions  26 ,  34  may be formed generally cylindrically, as shown in  FIG. 2 , with varying longitudinal lengths. The spacing between the first and third portions  26 ,  34  should be evaluated in view of the longitudinal length of the stent  12 . The spacing between the first and third portions  26 ,  34  may affect the extent of flaring and overall expansion of the stent  12  which is achievable. The diameters D 1 , D 2 , D 3  should also be evaluated in view of the construction of the stent  12  (e.g., inherent material characteristics; permissible ratio of diameters (e.g., extent of flaring)). The profile of the balloon  10  in an expanded state will generally match the profile of the stent  12  in an expanded state. 
         [0021]    As will be appreciated by those skilled in the art, the balloon  10  may be formed with various geometries beyond that shown in  FIG. 2 . With reference to  FIGS. 3(   a )-( e ), various alternative configurations of the first, second and third portions  26 ,  28 ,  34 , respectively, are depicted. These configurations are by way of non-limiting examples and any geometry consistent with the principles herein may be utilized. As shown in  FIG. 3(   a ), the third portion  34  need not be provided. Here, the first portion  26  allows for the flaring of one of the ends  30  of the stent  12 . With reference to  FIG. 3(   b ), the first and third portions  26  and  34  may be both provided, with the diameter D 3  being smaller than the diameter D 1 . Both diameters D 1  and D 3 , however, are greater than the diameter D 2 . This arrangement allows for different degrees of flaring of the ends  30  of the stent  12 . 
         [0022]      FIG. 3(   c ) shows that the first and third portions  26 ,  34  may be formed with different shapes. For example, the first portion  26  may be generally spherous, with the first diameter D 1  being defined as generally the diameter of the spherous form. The third portion  34  may be generally cylindrical at the diameter D 3  and extend coextensively with a portion of the catheter  14 , same as in the configuration of  FIG. 2 . 
         [0023]    As shown with  FIGS. 3(   d ) and ( e ), the first or third portions  26 ,  34  may be formed to extend only partially circumferentially about the catheter  14 . With the other shown configurations, the first and third portions  26 ,  34  extend fully circumferentially about the catheter  14 . In  FIGS. 3(   d ) and ( e ), the third portion  34  is shown to extend no greater than half the circumference of the catheter  14 . The portion of the balloon  10  above the third portion  34  is generally coextensive with the second portion  28  (i.e., coextensive with the diameter D 2 ). This configuration allows for a partial flaring of the ends  30  of the stent  12 —the entire circumference of the ends  30  need not be flared. 
         [0024]    The balloon  10  may be formed of any conventional material used in balloon formation, including, but not limited to, PET, Pebax, Hytrel, nylon and combinations thereof. To allow for a non-constant profile, the balloon  10  may be initially manufactured into the desired shape. For example, the balloon  10  may be blown or molded into the finished shape, within a mold cavity resembling the final desired shape. With the balloon  10  being in the unexpanded state, excess material of the balloon  10  corresponding to the first and third portions  26 ,  34  collects or bunches about the catheter  14  and extends radially outwardly from the catheter  14 . As shown in  FIG. 1 , material of the balloon  10  used in forming the first portion  26  is shown to be bunched together. Advantageously, the bunched material of the first portion  26  extends radially outwardly from the catheter  14  further than the second portion  28  and the stent  12 . Consequently, the bunched material of the first portion  26  inhibits axial movement of the stent  12  along the longitudinal length of the catheter  14 . With the first and third portions  26  and  34  being utilized, bunched material of the first and third portions  26 ,  34  in the unexpanded state may simultaneously inhibit axial movement of the stent  12  in both longitudinal directions along the length of the catheter  14 . 
         [0025]    Optionally, the balloon  10  may be formed with varying wall thickness to allow for differing extents of expansion. With thinner walls, portions of the balloon  10  (e.g., the first portion  26 ) may be expanded to greater diameters than portions of the balloon  10  having thicker wall portions (e.g., the second portion  28 ). The balloon  10  may be also formed of different materials having different resistances to expansion (e.g., different durometers). A weaker material will allow for greater expansion than a stronger, more rigid material. 
         [0026]    The balloon  10  may be selectively expanded and deflated via the catheter  14  as required. Known techniques may be used. As discussed below, certain SMP stents require heat and, optionally, pressure for expansion. To permit heating by the balloon  10 , the balloon inflation fluid may be heated, with heat from the balloon  10  being conducted to the balloon  10 . Optionally, the catheter  14  may carry a heating device, e.g. a resistive heater or RF heater within the interior of the balloon  10 . A heated balloon catheter is described in U.S. Pat. Nos. 5,496,311 and 4,955,377, the disclosures of which are incorporated by reference herein. 
         [0027]    The stent  12  may be formed as a tubular structure, which may be cut or etched or otherwise have material removed or may be formed as a coiled structure resembling a coil spring. Preferably, the stent  12  is formed of SMP. As discussed in the disclosures set forth above, by way of non-limiting examples, SMP&#39;s may include polynorbornene and copolymers of polynorbornene, blends of polybornene with KRATON® (thermoplastic elastomer) and polyethylene, styrenic block copolymer elastomers (e.g., styrene-butadiene), polymethylmethacrylate (PMMA), polyethylene, polyurethane, polyisoprene, polycaprolactone and copolymers of polycaprolactone, polylactic acid (PLA) and copolymers of polyactic acid, polyglycolic acid (PGA) and copolymers of polyglycolic acid, copolymers of PLA and PGA, polyenes, nylons, polycyclooctene (PCO), polyvinyl acetate (PVAc), polyvinylidene fluoride (PVDF), blends of polyvinyl acetate/polyvinylidine fluoride (PVAc/PVDF), blends of polymethylmethacrylate/polyvinyl acetate/polyvinylidine fluoride (PVAc/PVDF/PMMA) and polyvinylchloride (PVC) and blends and/or combinations thereof. 
         [0028]    With the stent  12  being formed of SMP, the stent  12  is pre-formed to an initial diameter. Optionally, the stent  12  may be heated near or above melt or glass transition and mechanically deformed to a smaller, contracted diameter, suitable for delivery. Alternatively, the stent  12  remains at or about its initial diameter. The stent  12  is cooled and assembled onto the catheter  14 , delivered into the body of a patient, and expanded with application of heat to the melt or glass transition, while inflating the balloon  10 . With the subject invention, the first portion  26  of the balloon  10  may be used to assist the expansion of a portion of the stent  12  to a diameter greater than the pre-formed initial diameter. As such, the first portion  26  may deform the stent  12  in vivo at the point of implantation. Advantageously, this allows for the stent  12  to be pre-formed without one or both of the ends  30  being initially flared, (as shown in  FIG. 1 ), thereby allowing for a smaller overall profile for implantation. Optionally, the stent  12  may be pre-formed with some flaring at one or both of the ends  30 , but with less flaring than is desired with the final configuration. In this manner, the profile of the stent  12  may be minimized, yet some shape definition may be imparted to the stent  12  to aid in formation of the flared ends. 
         [0029]    It should also be noted that the subject invention need not deform the stent  12 . Rather, the stent  12  may be pre-formed with one or both of the ends  30  being fully flared as desired. The first portion  26  and/or the third portion  34  may act to expand one or both of the ends  30  to the pre-formed flared configuration to ensure full and proper expansion into the desired pre-formed configuration, without deformation. 
         [0030]    With reference to  FIG. 4 , the stent  12  is shown to have a tubular construction. Prior to implantation, the balloon  10  and the stent  12  are assembled, as shown in  FIG. 1 , with the stent  12  being mounted about the balloon  10  in an unexpanded state. The stent  12  is in a contracted or unexpanded state. A sheath or additional catheter may be placed about the assembly of  FIG. 1  for implantation. To initiate implantation, the distal end  18  of the catheter  14  is inserted into the patient and guided, using known techniques, to the intended bodily passageway. The stent  12  is located within the bodily passageway at a desired location by the catheter  14  using known techniques (e.g., utilizing radiopaque markers). Thereafter, the balloon  10  is expanded, with expansion of the balloon  10  assisting flaring of one or both of the ends  30  of the stent  12 . As discussed above, with the stent  12  being formed of SMP, heat is required for proper expansion. The balloon  10  and/or the catheter  14  may provide the heating as discussed above. Alternatively, the heat may be applied from a remote location outside the body. For example, as discussed in U.S. published Patent Appl. No. 2005/0010275, the SMP forming the stent  12  may be compounded to include magnetic particles, which are susceptible to heating by magnetic effects, such as hysteresis effects. A magnetic field can be imposed on the stent  12  by a source on the catheter  14  or outside the body. Heating by magnetic effects is discussed in U.S. Pat. No. 6,056,844, the disclosure of which is incorporated herein. In addition, heat may be applied by ultrasound; interfering electromagnetic beams (e.g., light beams); body heat; and/or, warm fluid through the catheter  14  (e.g., warm saline). 
         [0031]    Once the stent  12  is expanded to its target diameter, the balloon  10  is caused to deflate as is known in the art. The catheter  14  is thereafter retracted. The flared ends  30  of the stent  12  help to anchor the stent  12  within the bodily passageway. Removal of the stent  12  can be achieved in reverse order, with heat being applied to the stent  12  to allow for its deformation to a contracted diameter. 
         [0032]      FIG. 5  shows the stent  12  having a coiled configuration. In all basic respects, the stent  12  in the coiled configuration is expanded and implanted in the same manner as discussed above with respect to the tubular configuration. 
         [0033]    As an additional feature, the balloon  10  may be provided with one or more raised or textured features to enhance the gripping force applied to the stent  12 . For example, with reference to  FIGS. 6(   a )-( c ), the balloon  10  may be formed with: one or more rings  40  which circumscribe the circumference of the balloon  10 ; one or more spirals  42  which coil about the circumference of the balloon  10 ; and/or, one or more protrusions  44 . The rings  40 , spirals  42 , and protrusions  44  may be unitarily formed with the balloon  10  and may be raised portions, such as defined by thickened regions of the balloon  10 . The rings  40 , spirals  42 , and protrusions  44  are positioned to at least partially underlie the stent  12  when mounted to the balloon  10 . 
         [0034]    The stent  12  may be provided with biological and/or anti-microbial agents, as is known in the art. The stent  12  may also be provided with radiopacity. 
         [0035]    As will be appreciated by those skilled in the art, the balloon  10  may be used with stents of various materials, including metal. For example, a metal stent (e.g., of shape memory metal (such as nitinol)) may be expanded by the balloon  10  to obtain a flared configuration. The expansion may occur below the transition temperature of the constituent metal. 
         [0036]    As is readily apparent, numerous modifications and changes may readily occur to those skilled in the art, and hence it is not desired to limit the invention to the exact construction operation as shown and described, and accordingly, all suitable modification equivalents may be resorted to falling within the scope of the invention as claimed.