Abstract:
A medical catheter for inserting into a body includes a bump tubing section with proximal and distal ends, wherein the proximal end is configured to mate with a hub. The bump tubing section has an intermediate portion extending away from the proximal end with a substantially constant outer diameter and thickness, and a taper portion adjacent the distal end with generally decreasing inside and outside diameters to provide a gradually increasing flexibility toward the distal end of the bump tubing section. The bump tubing section is comprised of a polymer having a predetermined flexural modulus. A tip section is disposed distally of the distal end of the bump tubing section comprising a distal liner and a distal cover such that at least a majority of the tip section has a substantially constant stiffness and a flexural modulus substantially equal to or greater than the predetermined flexural modulus.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     Not Applicable. 
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH 
     Not Applicable. 
     BACKGROUND OF THE INVENTION 
     The present invention relates in general to a medical catheter with multiple stiffness sections, and, more specifically, to a medical catheter and an efficient manufacturing method employing bump tubing and a relatively stiffened distal end incorporating radiopaque markers. 
     Many medical procedures require entry into a patient&#39;s blood vessel for purposes of accessing a desired site, e.g., angioplasty, stenting, and other treatments for chronic total occlusions. In order to gain access to the desired site, a catheter is advanced through the blood vessel. Once in place within the patient&#39;s vessel, various types of medical instrumentation can be fed through the catheter and positioned at the desired site so that the procedure may be performed. 
     To initially gain access to a particular site within a patient, a needle is used to puncture the patient&#39;s skin and gain entry to a desired blood vessel. During insertion of the catheter through the blood vessels, it may be required to follow a tortuous path. Therefore, the distal end of the catheter has been made more flexible than the proximal end. The flexible distal end provides trackability, while the stiffer proximal end provides pushability. As shown in U.S. Pat. No. 7,896,861, a catheter may include a proximal shaft section of a polymer with a relatively high durometer and a distal shaft section of a polymer with a relatively low durometer. However, mechanical bonding or welding of the different sections creates a potential site for kinking of the catheter. 
     Bump tubing has been used in catheters to provide a decreased tube diameter at the distal end for navigating small vessels and to provide an increased tube diameter at the proximal end for accommodating medical devices to be used during a medical procedure. Bump tubing, also known as a taper tube, may be formed by extruding a polymeric tube in a manner that varies the diameter during the extrusion. As a consequence of the changing diameter, the tube stiffness is reduced along with the diameter without creating a potential site for kinking. 
     To assist in locating the distal tip by fluoroscopy during a procedure, radiopaque markers are applied to the distal tip. Platinum or platinum blends have been applied to the tubing for this purpose. However, previous markers have been subject to wear and other damage while passing through particularly tortuous anatomies. 
     It would be desirable to combine the use of bump tubing with efficient assembly methods that lower the risk of kinking and provide protection for radiopaque markers. 
     SUMMARY OF THE INVENTION 
     The present invention includes the discovery that performance may be improved if the distal tip is not made to be the softest, most flexible portion of the catheter because the softer grades of plastics being used have an increased coefficient of friction. Instead, a transition zone with increasing flexibility is located proximal to a distal tip, the distal tip having substantially constant stiffness and a flexural modulus substantially the same as or greater than the transition zone. The transition zone is comprised of a bump tubing section wherein both the inside and outside diameters are decreasing. A distal cover protects any radiopaque markers. Further, a fusing process employing shrink tubing may be used to join separate components with reduced kinking. 
     In one aspect of the invention, a catheter is provided for inserting into a body. A bump tubing section has proximal and distal ends, wherein the proximal end is configured to mate with a hub. The bump tubing section has an intermediate portion extending away from the proximal end with a substantially constant outer diameter and thickness, and a taper portion adjacent the distal end with generally decreasing inside and outside diameters to provide a gradually increasing flexibility toward the distal end of the bump tubing section. The bump tubing section is comprised of a polymer having a predetermined flexural modulus. A tip section is disposed distally of the distal end of the bump tubing section comprising a distal liner and a distal cover such that at least a majority of the tip section has a substantially constant stiffness and a flexural modulus substantially equal to or greater than the predetermined flexural modulus. 
     In another aspect of the invention, a catheter is provided for inserting into a body. A bump tubing section has proximal and distal ends, wherein the proximal end is configured to mate with a hub. The bump tubing section has an intermediate portion extending away from the proximal end with a substantially constant outer diameter and thickness, and a taper portion adjacent the distal end with generally decreasing inside and outside diameters to provide a gradually increasing flexibility toward the distal end of the bump tubing section. The bump tubing section is comprised of a polymer having a predetermined flexural modulus A tip section is disposed distally of the distal end of the bump tubing section comprising a distal liner and a distal cover such that at least a majority of the tip section has a substantially constant inside diameter and outside diameter. Radiopaque markers are disposed between the distal liner and the distal cover. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a plan view of a catheter according to one embodiment of the present invention. 
         FIG. 2  is a cross-sectional view of a catheter of the invention. 
         FIG. 3  is a cross-sectional view showing a distal end of a catheter of the invention in greater detail. 
         FIG. 4  is a partial cross section showing the application of radiopaque markers during the manufacturing of a catheter. 
         FIG. 5  is a partial cross section showing the fusing of a distal cover and distal liner around the radiopaque markers. 
         FIG. 6  illustrates the fusing of a distal tip section with a bump tubing section on a mandrel. 
         FIGS. 7 and 8  illustrate the fusing of a distal cover in an embodiment wherein the distal liner is comprised of an extension of the bump tubing section. 
         FIG. 9  shows a partial braiding pattern for covering a portion of the is catheter. 
         FIG. 10  shows a coil pattern for covering a portion of the catheter. 
         FIG. 11  is a flowchart representing various embodiments of a manufacturing method of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Referring now to  FIG. 1 , a catheter  10  has a proximal end having a hub  11  and a stress release section  12  of conventional design. A bump tubing section spanning the major portion of catheter  10  includes an intermediate portion  13  with a substantially constant outer diameter and thickness and a taper portion  14  with a generally decreasing inside and outside diameter to provide a gradually increasing flexibility toward the distal end of the bump tubing section. As shown in  FIG. 1 , the intermediate portion may include a conventional braided or coiled material around the bump tubing section for increasing stiffness and pushability. 
     A tip section  15  is disposed distally of the bump tubing section and is made from a material having a flexural modulus substantially equal to or greater than the flexural modulus of the material in the taper section  14 . In one embodiment, both can be made from the same material. A plurality of radiopaque markers  16  are provided within distal tip  15 . 
     An embodiment of the invention is shown in cross-section in  FIG. 2 . A catheter  20  has a hub section  21 , an intermediate section  22 , a taper section  23 , and a tip section  24 . In this embodiment, catheter  20  includes a bump tubing piece  25  and a distal tubing piece  26  attached together at a joint  27 . Pieces  25  and  26  can be made from polyolefins, polyethylene, polypropylene, polypropylene copolymers, or thermoplastic elastomers (such as TPO, TPU, TPV, polyester elastomers such as Hytrel, polyamide elastomers such as PEBAX, nylons, fluoropolymers including FEP, PFA, of ETFE, and the like). Within intermediate section  22 , bump tubing piece  25  preferably has a substantially constant inside and outside diameter. The diameters may increase in hub section  21  to accommodate instruments or connecting devices. In taper section  23 , bump tubing piece  25  has decreasing inside and outside diameters while approaching the distal end. Preferably, the inside diameter decreases less than the outside diameter so that bump tubing piece  25  also becomes thinner, thereby providing a greater increase in flexibility. After taper section  23 , bump tubing piece  25  may have an optional straight segment  28  at its distal end. Distal tubing piece  26  preferably has matching inside and outside diameters with straight segment  28  providing a substantially seamless connection at  27 . 
     As shown in greater detail in  FIG. 3 , distal tubing piece  26  preferably includes a distal liner  30  and a coaxial distal cover  31  with a plurality of annular markers  32  sandwiched between distal liner  30  and distal cover  31 . By encapsulating markers  32 , they are protected against damage and wear. 
     In one preferred embodiment, bump tubing piece  25  was extruded using a material known as PEBAX 7233 available from Arkema, Inc., of Philadelphia, Pa. This material has a flexural modulus of about 107,000 psi, which is a relatively inflexible material compared to conventional distal tips, and provides good pushability. In one embodiment of the catheter, the intermediate section of the bump tubing piece had an outside diameter of 0.063 inches and an inside diameter of 0.043 inches. Over a transition zone of about 9 inches in length, the outside diameter linearly decreased to about 0.054 inches and the inside diameter decreased to about 0.038 inches. The bump tubing section continued on for a straight segment having a length of about 7 inches. This embodiment accommodates a guide wire with a diameter of 0.035 inches. Continuing with this embodiment, distal liner  30  and distal cover  31  were likewise formed using PEBAX 7233 materialcorrected. The final inside and outside diameters of the liner and cover after they are joined match those of the distal end of the bump tubing piece, but they start out as larger diameters which are shrunk during manufacturing as described below. 
     Since distal tip  26  is formed of materials having the same flexural modulus and since the diameter and thickness are the same, the flexibility of tip  26  is the same as at the distal end of bump tubing piece  25 . Alternatively, an even harder material with a higher flexural modulus could be employed in distal tip  26 . 
     The distal tubing piece forming tip  26  can be manufactured according to a method shown in  FIGS. 4 and 5 . A cylindrically shaped mandrel  35  having a diameter corresponding to the desired diameter of the internal lumen of the catheter receives distal liner tube  30 . Liner tube  30  may originally have an inside diameter slightly larger than the diameter of mandrel  35  making it easy to fit liner tube  30  onto mandrel  35 . Moreover, mandrel  35  may be coated with a lubricant to facilitate removal after shrinking of liner tube  30  as described below. After fitting distal liner tube  30  to mandrel  35 , annular rings for markers  32  are placed over liner tube  30 . The rings could be made of various radiopaque substances such as barium, bismuth, gold, hafnium, iridium, molybdenum, niobium, platinum, palladium, rhodium, rhenium, silver, tantalum, titanium, tungsten, or alloys or composites of these radiopaque substances. Placement of the rings on distal liner  30  can be evenly spaced or in any suitable pattern. After alignment, markers  32  are reduced in diameter by swaging (e.g., radial compression by a swaging tool placed over the rings). 
       FIG. 4  shows markers  32  prior to swaging. After swaging, markers  32  press into the surface of distal liner  30  as shown in  FIG. 5 . A distal cover  31  in the form of another polymeric tube with an inner diameter slightly larger than the outer diameter of the distal liner  30  is placed over distal liner  30  and markers  32 . A piece of shrink tubing  36  is then placed over distal cover tubing  31  in preparation for joining the elements of the distal tubing piece. In its unshrunken state, shrink tubing  36  has an inside diameter slightly greater than the outside diameter of distal cover tubing  31 . Upon heating to a sufficient temperature, shrink tubing  36  “recovers” its reduced diameter. Shrink tubing  36  may be comprised of a polyolefin heat shrink tubing available from Tyco Electronics Corporation of Berwin, Pa., for example. By heating all the components to a sufficiently high temperature (e.g., 120° C.), liner tubing  30  and cover tubing  31  soften sufficiently so that upon being squeezed equally from all sides by shrink tubing  36  they are squeezed against mandrel  35 , causing the interface surface between liner tubing  30  and cover tubing  31  to fuse together. After cooling, heat shrink tubing  36  is removed by cutting into it with a razor blade and peeling it off. 
     Distal tip section  26  can then be joined with a preformed bump tubing section  25  as shown in  FIG. 6 . Bump tubing section  25  is fit onto mandrel  35  to abut both the distal liner tube and the distal cover tube of distal end piece  26 . The tube can be connected by welding methods known in the art such as ultrasonic, RF, laser, induction, vibration, or microwave welding. A bonding material could also be placed between the abutting surfaces. Preferably, the pieces are joined by fusing, welding, or bonding in the presence of heating while being covered with another heat shrink tubing  37 . Thus, after abutting bump tubing piece  25  and distal tip piece  26 , shrink tubing segment  37  is placed over the abutment and heat shrink tubing segment  37  and pieces  25  and  26  are heated for bonding them together. Heat shrink tubing  37  ensures a smooth transition across the interface. After cooling, heat shrink tubing  37  is cut using a razor blade and removed. 
       FIG. 7  shows an alternative embodiment employing a bump tubing piece  40  with an intermediate portion  41  and a taper portion  42 . In this embodiment, the distal liner is comprised of an extension  43  formed as a continuous extrusion extending from tapered portion  42  of bump tubing piece  40 . After being placed on a mandrel, radiopaque markers  45  are swaged onto extension  43 . Then a distal cover  44  is fit over markers  45  and subsequently compressed over them using heat shrink tubing  46  shown in phantom. The distal end of the resulting distal tip formed by liner  43  and cover  44  may be trimmed and or shaped as desired (not shown). 
       FIG. 8  shows an alternative embodiment wherein only the longitudinal ends of distal cover  44  are fused using heat shrink tubing  47  and  48  applied at the opposite edges. 
     As previously discussed, portions of the bump tubing section may be covered with a braid formed from fibers wrapped over the bump tubing. Suitable materials for the fiber include Kevlar, NOMEX, Technora, Twaron, Vectran, glass, or stainless steel. The braiding can be woven in various patterns such as a conventional crisscross pattern shown in  FIG. 9 . The braiding may cover any desired portions of the intermediate section or the tapered section of the bump tubing. Furthermore, braiding could also be placed over a portion of the distal tip (not shown). 
     In an alternative embodiment shown in  FIG. 10 , a coiled layer  51  may be disposed over the intermediate portion or the taper portion of the bump tubing. The coil layer may be comprised of a metal wire made from stainless steel, gold, silver, platinum, copper, iridium, titanium, molybdenum, or combinations thereof. The braid or coiled layers increase the rigidity of the corresponding portions of the catheter and increase its pushability. 
     The braided or coiled fibers or wire  50  or  51  in  FIGS. 9 and 10  would be preferably coated with a cover layer  52  or  53 , respectively. The cover layer can be applied with a heat shrink operation, as an extrusion, or by dipping in a solution, for example. The coating layer may be between 0.0005 and 0.010 inches thick. 
     The flowchart of  FIG. 11  summarizes methods for manufacturing the catheters of the present invention. In step  60 , a release agent or lubricant is applied to the mandrel. This may include a permanent or semi-permanent coating of PTFE or other fluoropolymer. In step  61 , the distal liner is fit to the mandrel. As noted above, the distal liner may be a separate cylindrical tubing piece or may be an extension of the bump tubing section. In the case of a separate distal liner piece, multiple distal tips could be manufactured on the mandrel simultaneously either as distinct units or as one longer piece of tubing that is subsequently trimmed or cut into separate tip pieces after the addition of markers and a distal cover. 
     Radiopaque markers are swaged over the distal liner in step  62 . In step  63 , an oversized distal cover is slid over the liner and markers. In step  64 , a piece of heat shrink tubing is placed over the distal cover. The heat shrink tubing, distal cover, and distal liner are heated in step  65  to cause the shrinkage of the heat shrink tubing and the fusing together of the distal cover and distal liner, thereby encapsulating the markers. The heat may be supplied by a hot air box placed around the tubing pieces and mandrel supplying hot air from a nozzle, whereby all the components are heated substantially evenly. 
     The hot air box is removed and the tubing pieces are allowed to cool in step  66 . In step  67 , the heat shrink tubing is cut longitudinally using a razor blade or other knife and then removed. The end or ends of the distal tip are trimmed as necessary. 
     In the event that the distal tip was not made using an extension of the bump tubing as the distal liner, then the distal tip must be joined with the bump tubing. In step  70 , the bump tubing is fit to the mandrel to abut the distal liner/distal cover combination. In step  71 , the bump tubing and the tip are welded/fused/bonded together. Step  71  may be performed in the presence of heat shrink tubing. In that case, the heat shrink tubing is removed in step  72 . 
     In the event that the distal liner is being formed using an extension of the bump tubing, then following the removal of shrink tubing in step  67 , there may be a second application of heat shrink tubing in step  75  in order to smooth the edges of the distal cover. After any necessary trimming, the completed catheter is removed from the mandrel.