Abstract:
A catheter balloon is formed from a mold process in which raised dimples or shallow divots are formed on the outer surface using indentations or raised beads on the mold surface. The dimples or divots are located at the transition between the body portion of the catheter balloon and the neck or taper section. The presence of the dimples or divots serves the dual purpose of identifying the transition between the two regions for placing a visual marker on the balloon to be used in positioning the balloon, and also to assist in the retention of a vascular stent on the balloon.

Description:
BACKGROUND 
       [0001]    This invention generally relates to intravascular balloon catheters such as those used in percutaneous transluminal coronary angioplasty (PTCA) and stent delivery, and more particularly to a catheter balloon and mold for creating a balloon that permits reliable securement of positioning markers and stents. 
         [0002]    PTCA is a widely used procedure for the treatment of coronary heart disease. In this procedure, a balloon dilatation catheter is advanced into the patient&#39;s coronary artery and the balloon on the catheter is inflated within the stenotic region of the patient&#39;s artery to open up the arterial passageway and thereby increase the blood flow there through. To facilitate the advancement of the dilatation catheter into the patient&#39;s coronary artery, a guiding catheter having a preshaped distal tip is first percutaneously introduced into the cardiovascular system of a patient by the Seldinger technique or other method through the brachial or femoral arteries. 
         [0003]    The catheter is advanced until the preshaped distal tip of the guiding catheter is disposed within the aorta adjacent the ostium of the desired coronary artery, and the distal tip of the guiding catheter is then maneuvered into the ostium. A balloon dilatation catheter may then be advanced through the guiding catheter into the patient&#39;s coronary artery over a guidewire until the balloon on the catheter is disposed within the stenotic region of the patient&#39;s artery. The balloon is inflated to open up the arterial passageway and increase the blood flow through the artery. 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 over expand the artery wall. After the balloon is finally deflated, blood flow resumes through the dilated artery and the dilatation catheter can be removed. 
         [0004]    In a large number of angioplasty procedures, there may be a restenosis, i.e. reformation of the arterial plaque. To reduce the restenosis rate and to strengthen the dilated area, physicians may implant an intravascular prosthesis or “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 then deflated to remove the catheter and the stent is left in place within the artery at the site of the dilated lesion. 
         [0005]    To accurately place the balloon at the desired location, visual markers on the balloon are utilized that are read by machines outside the body. For example, in the case where a balloon catheter is used with an fluoroscope, the radiopaque marker may be observed visually on a screen while the procedure is taking place. In many cases, the markers must be precisely located to ensure accurate placement of the balloon in the affected area. When stents are being deployed the location of the beginning and ending point of the stent can be crucial to the success of the procedure. In such cases, it is preferred that the markers be located very specifically at the junction of the body portion of the balloon with the neck portion. However, it is also important that the marker not be located on the neck portion of the balloon. Unfortunately, the manufacturing process does not readily lend itself to a precise determination as to where to apply the marker such that it is at the extreme end of the working portion of the balloon but does not extend to the neck portion. 
       SUMMARY OF THE INVENTION 
       [0006]    The present invention addresses the problem above by using a modified mold to create visual locators on the balloon that identify the proper position of the marker. A ring of visual locators on the balloon can be created by putting indentions or beads on the mold used to form the balloon, causing the balloon to have raised dimples in the case of indentations or shallow cavities in the case of beads on the working portion of the balloon right before the taper or neck portion. Henceforth the application shall refer to the visual markers as dimples but it is to be understood that cavities or divots would serve the same purpose and are considered part of the invention. The raised dimples enable the manufacturing operators who are tasked with placing the visual markers on the balloon to quickly and easily locate the visual markers precisely before the neck region but in the working area of the balloon every time. This also aids in the placement of stents that are mounted on the balloon in procedures that use this feature. The raised dimples also can assist in the retention of the stent on the balloon as it passes through the patient&#39;s vascular, where the raised dimples provide a resistance against slippage of the stent off of the balloon. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]      FIG. 1  is an elevated view partially in section of a balloon catheter of the present invention; 
           [0008]      FIG. 2  is a transverse cross sectional view of the balloon catheter of  FIG. 1  taken along lines  2 - 2 ; 
           [0009]      FIG. 3  is a transverse cross sectional view of the balloon catheter of  FIG. 1  taken along lines  3 - 3 ; 
           [0010]      FIG. 4  is an enlarged view of the balloon catheter of  FIG. 1  with a vascular stent mounted thereon; 
           [0011]      FIG. 5  is an enlarged view of the stent of  FIG. 4  disposed in a patient&#39;s vascular after removal of the balloon; 
           [0012]      FIG. 6 . is an even more enlarged view of the distal end of the balloon and stent of  FIG. 4  showing the raised dimples; 
           [0013]      FIG. 7  is a cut-away view of a mold for forming the balloon of the present invention and a balloon tubing prior to forming; and 
           [0014]      FIG. 8  is a cut-away view of the mold of  FIG. 7  after pressurization and heating to form the balloon of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0015]      FIG. 1  shows a balloon catheter that can be used to illustrate the features of the invention. The catheter  10  of the invention generally comprises an elongated catheter shaft  11  having a proximal section  12 , a distal section  13 , an inflatable balloon  14  on the distal section  13  of the catheter shaft  11 , and an adapter  17  mounted on the proximal section  12  of shaft  11 . In  FIG. 1 , the catheter  10  is illustrated within a greatly enlarged view of a patient&#39;s body lumen  18 , prior to expansion of the balloon  14 , adjacent the tissue to be injected with therapeutic agents. 
         [0016]    In the embodiment illustrated in  FIG. 1 , the catheter shaft  11  has an outer tubular member  19  and an inner tubular member  20  disposed within the outer tubular member and defining, with the outer tubular member, inflation lumen  21 . Inflation lumen  21  is in fluid communication with the interior chamber  15  of the inflatable balloon  14 . The inner tubular member  20  has an inner lumen  22  extending therein which is configured to slidably receive a guidewire  23  suitable for advancement through a patient&#39;s coronary arteries. The distal extremity of the inflatable balloon  14  is sealingly secured to the distal extremity of the inner tubular member  20  and the proximal extremity of the balloon is sealingly secured to the distal extremity of the outer tubular member  19 . 
         [0017]      FIGS. 2 and 3  show transverse cross sections of the catheter shaft  11  and balloon  14 , respectively, illustrating the guidewire receiving lumen  22  of the guidewire&#39;s inner tubular member  20  and inflation lumen  21  leading to the balloon interior  15 . The balloon  14  can be inflated by a fluid such as air, saline, or other fluid that is introduced at the port in the side arm  25  into inflation lumen  21  contained in the catheter shaft  11 , or by other means, such as from a passageway formed between the outside of the catheter shaft  11  and the member forming the balloon  14 , depending on the particular design of the catheter. The details and mechanics of the mode of inflating the balloon vary according to the specific design of the catheter, and are omitted from the present discussion. 
         [0018]      FIG. 4  illustrates an embodiment of the catheter of  FIG. 1  with a vascular stent  16  mounted thereon. The stent  16  can be made in many ways. One method of making the stent is to cut a thin-walled tubular member, such as stainless steel tubing to remove portions of the tubing in the desired pattern for the stent, leaving relatively untouched the portions of the metallic tubing which are to form the stent  16 . The stent  16  also can be made from other metal alloys such as tantalum, nickel-titanium, cobalt-chromium, titanium, shape memory and superelastic alloys, and the Nobel metals such as gold or platinum. It is preferred to cut the tubing in the desired pattern by means of a machine-controlled laser as is well known in the art. Stents function to hold open a segment of a blood vessel or other body lumen such as a renal or coronary artery. At present, there are numerous commercial stents being marketed throughout the world. While some of these stents are flexible and have the appropriate radial rigidity needed to hold open a vessel or artery, there typically is a tradeoff between flexibility and radial strength and the ability to tightly compress or crimp the stent onto a catheter so that it does not move relative to the catheter or dislodge prematurely prior to controlled implantation in a vessel. Currently, to secure a stent  16  on a balloon  14 , after the stent is crimped onto the deflated balloon such that the balloon partially protrudes through the stent struts. During this process, the balloon and stent are placed in a heated mold and pressurized. The balloon protrusions then acts as holds to secure the stent in place. 
         [0019]    In a typical procedure to implant stent  16 , the guide wire  23  is advanced through the patient&#39;s vascular system by well known methods so that the distal end of the guide wire is advanced past the location for the placement of the stent in the body lumen  18 . Prior to implanting the stent  16 , the cardiologist may wish to perform an angioplasty procedure or other procedure (i.e., atherectomy) in order to open the vessel and remodel the diseased area. Thereafter, the stent delivery catheter assembly  10  is advanced over the guide wire  23  so that the stent  16  is positioned in the target area. The balloon  14  is inflated so that it expands radially outwardly and in turn expands the stent  16  radially outwardly until the stent  16  bears against the vessel wall of the body lumen  18 . The balloon  14  is then deflated and the catheter withdrawn from the patient&#39;s vascular system, leaving the stent  16  in place to dilate the body lumen. The guide wire  23  typically is left in the lumen for post-dilatation procedures, if any, and subsequently is withdrawn from the patient&#39;s vascular system. As depicted in  FIG. 4 , the balloon  14  is fully inflated with the stent  16  expanded and pressed against the vessel wall, and in  FIG. 5 , the implanted stent  16  remains in the vessel after the balloon has been deflated and the catheter assembly and guide wire have been withdrawn from the patient. 
         [0020]      FIG. 6  illustrates a close up section of the balloon  14  showing raised dimples  26  in a circumferential ring at the juncture of the body section  27  of the balloon  14  and the onset of the neck section  29 . Again, the dimples can be replaced with shallow divots or cavities as long as the structural integrity of the balloon is not compromised. The dimples  26  are shown as rectangular in shape although other shapes are possible. The dimples  26  form a ring or perimeter around the balloon  14  defining the end of the balloon body or working portion  27  of the balloon, and consequently coinciding with the edge  24  of the stent  16 . For example, in a first preferred embodiment the dimples  26  are located one millimeter from the beginning of the taper or neck section of the balloon. Between dimples  26  a radiopaque marker  28  is secured to the balloon that can be used to locate both the balloon  14  and the stent  16 . It is to be understood that a similar ring of dimples  26  will ordinarily be formed at the proximal end of the working section  27  of the balloon  14  where it tapers into the proximal neck portion  30 . The markers  28  (shown as diamond shaped but can be any shape or size) are observed under the fluoroscope or other means and can be used to precisely locate the catheter, the balloon  14 , and the stent  16 . The dimples  26  also ensure that the markers  28  are not placed by the distal seal operators at the taper sections of the balloons. The raised dimples  26  can also assist in stent retention, as the perimeter of raised dimples can assist the anchoring of the stent  16  as it is mounted on the balloon  14  and passed through the patient&#39;s vascular system. That is, the dimples  26  act as a retaining barrier that abuts the stent to keep it positioned properly on the balloon. 
         [0021]    The balloon  14  is formed using conventional balloon technologies, such as blow molding as illustrated in  FIGS. 7 and 8 . A tube  60  of balloon material is inserted into a mold  62  having the desired balloon shape. The mold  62  has a constant radius wall  70  and an increasing radial section  72  at a first end and a decreasing radial section  74  at a second end, and further includes a series of cavities/indentations (or beads)  64  on the constant radius wall section at the transition to the radially increasing and decreasing portions. The indentations  64  fill with balloon material as the tube is expanded and heated to form a balloon with the desired raised dimples at the edges of the working section of the balloon  14 . Alternatively, the beads form a slight cavity in the balloon producing a visual identifier of the edge of the working section. The balloon material is maintained in the heated and pressurized state until the balloon is formed to cause the tubing  60  to expand to the final shape within the mold  62 , including the formation of the dimples or cavities  26  in the indentation. This will result in a balloon that includes the rings of dimples  26  shown in  FIGS. 4 and 6 . 
         [0022]    While particular forms of the invention have been illustrated and described, it will be apparent to those skilled in the art that various modifications can be made without departing from the spirit and scope of the invention. Accordingly, it is not intended that the invention be limited except by the appended claims.