Abstract:
The present invention is directed to balloon catheter having a compression member securing one or more balloon skirts to the catheter shaft. The compression member may be a band or coil that sealing secures the balloon skirt to a catheter shaft. Metallic compression members may be swaged to compress the skirt against the shaft, and thus provide a uniform seal between the balloon skirt and the catheter shaft. The compression members are especially useful when the balloon is formed of a fluoropolymer, such as expanded polytetrafluoroethylene (ePTFE) or polyterafluoroethylene (PTFE).

Description:
BACKGROUND OF THE INVENTION 
   This invention generally relates to medical devices, and particularly intracorporeal devices for therapeutic or diagnostic uses, such as balloon catheters. 
   In percutaneous transluminal coronary angioplasty (PTCA) procedures, a guiding catheter is advanced until the distal tip of the guiding catheter is seated in the ostium of a desired coronary artery. A guidewire, is first advanced out of the distal end of the guiding catheter into the patient&#39;s coronary artery until the distal end of the guidewire crosses a lesion to be dilated. Then the dilatation catheter having an inflatable balloon on the distal portion thereof is advanced into the patient&#39;s coronary anatomy, over the previously introduced guidewire, until the balloon of the dilatation catheter is properly positioned across the lesion. Once properly positioned, the dilatation balloon is inflated with fluid one or more times to a predetermined size at relatively high pressures (e.g. greater than 8 atmospheres) so that the stenosis is compressed against the arterial wall and the wall expanded to open up the passageway. Generally, the inflated diameter of the balloon is approximately the same diameter as the native diameter of the body lumen being dilated so as to complete the dilatation but not overexpand the artery wall. Substantial, uncontrolled expansion of the balloon against the vessel wall can cause trauma to the vessel wall. After the balloon is finally deflated, blood flow resumes through the dilated artery and the dilatation catheter can be removed therefrom. 
   In such angioplasty procedures, there may be restenosis of the artery, i.e. reformation of the arterial blockage, which necessitates either another angioplasty procedure, or some other method of repairing or strengthening the dilated area. To reduce the restenosis rate and to strengthen the dilated area, physicians frequently implant an intravascular prosthesis, generally called a stent, inside the artery at the site of the lesion. Stents may also be used to repair vessels having an intimal flap or dissection or to generally strengthen a weakened section of a vessel. Stents are usually delivered to a desired location within a coronary artery in a contracted condition on a balloon of a catheter which is similar in many respects to a balloon angioplasty catheter, and expanded to a larger diameter by expansion of the balloon. The balloon is deflated to remove the catheter and the stent left in place within the artery at the site of the dilated lesion. 
   In the manufacture of catheters, one difficulty has been the bonding of dissimilar materials together. The fusion bonding of a dissimilar material to a substrate material can be extremely difficult if the substrate has a low surface energy. For example, balloons formed of fluoropolymers such as expanded polytetrafluoroethylene (ePTFE) are not easily bonded to shafts without detrimentally effecting the ePTFE material. Specifically, one difficulty has been adhesively bonding ePTFE, absent some pretreatment causing decomposition of the fibril structure or the use of adhesives interlocking in the pore structure of the ePTFE. Chemical modification involving decomposition (i.e., defluoronation) of the ePTFE using compounds including bases (i.e., alkali metal compounds) such as sodium napthalide, or using plasma etching processes such as oxygen or trifluoroamine etching, have disadvantageous effects on the structural integrity of the ePTFE material. Additionally, lubricious materials such as high density polyethylene (HDPE) and polytetrafluoroethylene (PTFE), often used to form inner tubular members of catheters to provide good guidewire movement therein, have low surface energies of 31 dynes/cm and 18 dynes/cm, respectively, that make bonding to balloons formed of a dissimilar material such as a polyamide, e.g. PEBAX, difficult. Prior attempts to address this problem involved providing a multilayered shaft having an outer layer on the shaft configured to be bondable to the balloon. However, a decrease in shaft collapse pressure resistance may result in some cases when the outer layer has a lower stiffness than the shaft material. While adhesives may be used in some cases to bond dissimilar materials together, they are not ideal because they can increase stiffness of the component at the bond and some materials do not bond well to adhesives commonly used in medical devices. 
   It would be a significant advance to provide a balloon catheter with improved bonding of the balloon to the catheter shaft. 
   SUMMARY OF THE INVENTION 
   The present invention is directed to a balloon catheter having a compression member mounted about a balloon skirt section, securing the balloon skirt section to the catheter shaft. The compression member provides a low profile, a fluid tight seal, and is particularly advantageous when the balloon and/or shaft are fabricated from dissimilar materials or materials which are hard to bond. 
   A balloon catheter of the invention generally comprises an elongated shaft having a proximal section, a distal section, at least one lumen therein, and a balloon located on the distal section of the elongated shaft with an interior in fluid communication with the at least one lumen of the elongated shaft and having at least one skirt, and a compression member on the balloon skirt. In a presently preferred embodiment, the compression member is selected from a group consisting of a band and a coil. 
   In one embodiment, the compression member is swaged about the skirt section of the balloon in order to secure the balloon onto the catheter shaft, as well as provide a uniform seal around the entire circumference of the compression member. Swaging, as used herein, refers to the method of applying radially compressing force uniformly around the entire circumference of an object. Thus, unlike crimping in which a radially compressive force is applied at merely intermittent points around the circumference, a swaged member, such as a band of the present invention, provides a uniform seal at all points around the entire circumference of the swaged band. Consequently, the balloon is sealingly secured to the shaft in an improved manner around the entire circumference of the balloon skirt. 
   The compression member is mounted on at least one of the proximal or the distal skirt sections of the balloon. In a presently preferred embodiment, both the proximal and the distal skirt sections of the balloon have a compression member thereon securing both skirt sections to the shaft. 
   In one embodiment of the present invention, the compression member has an outer diameter around the circumference of the compression member which is not greater than an outer diameter of a first portion of the balloon skirt section directly adjacent to a second portion of the skirt section about which the compression member is mounted. Thus, the compression member compresses a part (i.e. second portion) of the skirt section so that the compression member outer diameter is equal to or less than the outer diameter of an adjacent part (i.e., first portion) of the balloon skirt section. Consequently, the compression member does not increase the profile of the catheter. 
   In one embodiment, the compression member, located on the skirt section of the balloon and sealingly securing the skirt section of the balloon to a portion of the distal section of the shaft, has an outer surface with a circumferential shape corresponding to a circumferential shape of an outer surface of the portion of the distal section of the shaft. Circumferential shape, as used herein, refers to the transverse cross-sectional shape extending around the entire circumference of the compression member&#39;s and the catheter shaft&#39;s outer surface. For example, in one embodiment, the outer surface of the catheter shaft has an overall circular transverse cross-section. Thus, the compression member having a corresponding circumferential shape would be of a similar circular shape around the entire circumference thereof and matching the shape of the circular shaft around the entire circumference thereof. The outer surface of the catheter shaft may, however, have a variety of suitable shapes, including oblong, triangular, elliptical, or rectangular, with a compression member having a similar corresponding circumferential shape. 
   A variety of suitable materials can be used to form the compression member of the invention including composite materials such as platinum-iridium, gold based alloys, stainless steel, platinum alloys, cobalt-chromium alloys, carbon fibers, polymeric materials such as nylon, polyamides, polyethelenes, polymides, polyester, shrink tubing or FEP, shape memory or superelastic materials such as nitinol, and radiopaque metals such as gold or tungsten, as wells as those materials previously mentioned. In addition to securing the balloon to the shaft, the compression members made from radiopaque materials are visible under fluoroscopy and thus can indicate the position of the balloon in a patient. 
   It should be noted that the features of the present invention and the compression members taught therein, can prove particularly useful with catheters having balloons formed of various fluoropolymers such as polytetrafluoroethylene (PTFE) or expanded polytetrafluoroethylene (ePTFE). As discussed above, it can be difficult to secure such balloons to a catheter shaft. The present invention, however, is not limited to use with catheters having fluoropolymer balloons. A variety of balloon materials can be used in the catheter of the present invention including material conventionally used in balloon catheter formation, particularly nylon polyether block amide (PEBAX), a nylon/PEBAX blend, polyamide, polyethylene (PE), high density polyethylene (HDPE), ultra-high density polyethylene (UHDPE), rubber (latex), polyisoprene, polyethylene terephthalate (PET), polyurethanes, and other hard to bond materials such as polypropylene and polyimide. 
   Additionally, the balloon catheter of the present invention has an improved fluid tight seal between the balloon and the shaft due to the compression member. The compression member provides a low profile, sealed portion and facilitates the securing of dissimilar or hard to bond materials together. These and other advantages of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying exemplary drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is an elevational view, partially in section, of a balloon catheter that embodies features of the invention. 
       FIG. 2  is an enlarged, longitudinal cross section of a distal end of the catheter shown in  FIG. 1 . 
       FIG. 3  is a transverse cross-section of the catheter shown in  FIG. 1 , taken along line  3 - 3 . 
       FIG. 4  is a transverse cross-section of the catheter shown in  FIG. 1 , taken along line  4 - 4 . 
       FIG. 5  is a longitudinal cross section of a swaging apparatus useful in a method that embodies features of the invention, in which a compression member comprising a band is swaged to a balloon skirt section disposed around a catheter shaft. 
       FIG. 6  is a transverse cross section of the swaging apparatus illustrated in  FIG. 5 , taken along line  6 - 6 . 
       FIG. 7  is an enlarged, elevational view of the distal end of an alternative embodiment of a balloon catheter embodying features of the invention, having compression members comprising coils. 
       FIG. 8  is an enlarged longitudinal cross section of the balloon catheter shown in  FIG. 7 , taken along line  8 - 8 . 
   

   DETAILED DESCRIPTION OF THE INVENTION 
     FIGS. 1-4  illustrate a balloon catheter  10  embodying features of the present invention. The catheter  10  generally comprises an elongated catheter shaft  12  having an outer tubular member  14  and an inner tubular member  16 . The inner tubular member  16  defines a guidewire lumen  18  configured to slidingly receive a guidewire  20 , as best illustrated in  FIG. 2  showing an enlarged longitudinal cross section of the distal end of the catheter illustrated in  FIG. 1 . The coaxial relationship between outer tubular member  14  and inner tubular member  16  defines an annular inflation lumen  22 , as best illustrated in  FIG. 3  showing a transverse cross section of the catheter of  FIG. 1  taken along line  3 - 3 . 
   An inflatable balloon  30  is disposed on a distal section of catheter shaft  12 . The balloon  30  has a proximal skirt  32  sealingly secured to the distal end of outer tubular member  14  and a distal skirt  34  sealingly secured to the distal end of inner tubular member  16 . The balloon interior is in fluid communication with the annular inflation lumen  22 . An adapter  36  at the proximal end of catheter shaft  12  is configured to provide access to the guidewire lumen  18  and to direct inflation fluid through arm  38  into the inflation lumen  22 . The balloon  30  has an inflatable working length  33  located between the skirt sections  32 ,  34  of the balloon  30  and a stent  60  mounted on the balloon  30  for implanting in a patient&#39;s body lumen.  FIG. 1  illustrates the balloon  30  in an uninflated configuration. The distal end of catheter  10  may be advanced to a desired region of a patient&#39;s body lumen in a conventional manner and the balloon  30  inflated. 
   In the embodiment illustrated in  FIG. 1 , a proximal compression member  40  and a distal compression member  42  sealingly secure the balloon  30  to the outer tubular member  14  and the inner tubular member  16 , respectively. The compression members  40 ,  42  are bands with a first outer diameter that allow the bands to be placed around an outer surface of the balloon and which contracts to a second, smaller diameter which then secures the balloon  30  to the shaft  12 . In one embodiment, compression members  40 ,  42  are radiopaque marker bands.  FIGS. 1 and 2  also illustrates an outer diameter around the circumference the compression members  40 ,  42  which is not greater than the outer diameter of a first portion  44  of the skirt section  32  directly adjacent to a second portion  46  of the skirt section about which the compression member is mounted. However, in an alternative embodiment, the compression members  40 ,  42  may have an outer diameter, which is greater than the outer diameter of the directly adjacent portion of the balloon. 
     FIGS. 3 and 4  illustrate the compression members  40 ,  42  having an outer surface with a circumferential shape corresponding to the circumferential shape of the outer surface of the portion of the catheter shaft onto which the compression member is mounted and secured. Although the circumferential shape of the compression members and the shaft is circular in the illustrated embodiments, a variety of suitable shapes can be alternatively used. 
   In a presently preferred embodiment, bands  40 ,  42  are formed of a super elastic material such as NiTi (Nitinol). The coils may also be formed from other types of materials commonly used in medical devices and that have a large thermal expansion coefficient. 
     FIG. 5  illustrates the method of swaging compression members  40 ,  42  onto a balloon skirt section to sealing secure the balloon  30  onto catheter shaft  12  with a mandrel  44  in place in the outer tubular member  14  for support. The compression member  40  is positioned on the outer surface of a balloon skirt. The assembly is then positioned in swaging apparatus  46 , and the swaging apparatus  46  applies a radially compressive force uniformly around the entire circumference of the compression member.  FIG. 6  illustrates a transverse cross section of the swaging apparatus  46  taken along line  6 - 6  in  FIG. 5 . The swaging apparatus  46  applies a radially compressive force uniformly around the entire circumference of the compression member  40 . As a result of the uniform pressure applied by the swaging apparatus  46  to the compression member, a uniform seal is provided around all points around the entire circumference of the swaged member or band. Consequently, a balloon can be secured onto a catheter shaft in an improved manner around the entire circumference of the balloon skirt. A suitable commercially available swaging apparatus is model Torrington Model 100 available from Torrington, Swager &amp; Vaille. 
     FIGS. 7 and 8  illustrates another embodiment of the invention, having compression members  50  and  52  comprising coils securing the balloon  30  to the catheter shaft  12 . Proximal compression member  50  secures the proximal skirt section  32  of the balloon to the distal end of the outer tubular member  14 , and a distal compression member  52  on the distal skirt section  34  of the balloon sealingly secures the balloon  30  to a distal section of the inner tubular member  16 . 
     FIG. 8  illustrates an enlarged longitudinal cross section of the catheter taken along line  8 - 8  at the proximal end of the balloon illustrated in  FIG. 7 . Similar to the embodiment of  FIG. 1 , compression members  50 ,  52  have an outer surface which has a circumferential shape that corresponds to the circular circumferential shape of the outer surface of the distal section of the shaft. The compression members  50 ,  52  can be contracted about the balloon skirt section  32 ,  34  by a variety of suitable methods such as swaging and heating to undergo a shape memory transition. In a presently preferred embodiment, the coils  50 ,  52  are formed of stainless steel or Nitinol. However, the coils can be made from any material commonly used in medical devices that has a large thermal expansion coefficient. In the embodiments illustrated in  FIGS. 1 and 7 , the balloon  30  is a wingless balloon which expands from low profile configuration which does not have deflated wings folded around the balloon circumference. In one embodiment, the balloon  30  is formed of ePTFE. Although for ease of illustration the balloon is shown as a single-layered balloon, balloon  30  formed of ePTFE would typically have a first layer formed of ePTFE, and a second layer formed of a different material such as an elastomeric polymer which limits or prevents leakage of inflation fluid through the porous ePTFE to allow for inflation of the balloon  30  and expands elastically to facilitate deflation of the balloon  30  to a low profile deflated configuration. The ePTFE layer is typically an outer layer and the elastomeric layer is typically an inner layer. While the present invention is described herein in terms of certain preferred embodiments, those skilled in the art will recognize that various modifications and improvements may be made to the invention without departing from the scope thereof. For example, in the embodiment illustrated in  FIG. 1 , the catheter is over-the-wire stent delivery catheter. However, one of skill in the art will readily recognize that other types of intravascular catheters may be used, such as and rapid exchange dilatation catheters having a distal guidewire port and a proximal guidewire port and a short guidewire lumen extending between the proximal and distal guidewire ports in a distal section of the catheter. Moreover, to the extent not otherwise described herein, the materials and methods of construction and the dimensions of conventional catheters may be employed with the catheter of the present invention. The features disclosed with one embodiment may be employed with other described embodiments as well. While the description of the invention is directed to embodiments for coronary applications, various modifications and improvements can be made to the invention without departing therefrom. Additionally, reference to the terms “members”, “elements”, “sections” and terms of similar import in the claims which follow shall not be interpreted to invoke the provisions of 35 U.S.C. §112, paragraph 6 unless reference is expressly made to the term “means” followed by an intended function.