Abstract:
An intraluminal catheter, particularly a dilatation catheter for angioplasty procedures, which has a shaft section formed of a blend of lubricous and bonding polymeric components in proportions to maintain a low coefficient of friction while maintaining the ability to bond non-lubricous polymeric material, such as polyethylene terephthalate, nylon, or PEBAX, to the segment.

Description:
This application is a continuation-in-part application of copending application Ser. No. 08/976,447, filed Nov. 25, 1997, which is a continuation of application Ser. No. 08/587,330, filed Jan. 16, 1996, now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates to catheters for performing intravascular procedures such as percutaneous transluminal coronary angioplasty (PTCA) and more specifically to elongated shafts for such catheters. 
     PTCA is now one of the most widely used treatment modalities for heart disease. The procedure basically comprises advancing a dilatation catheter, having an inflatable balloon on its distal extremity, into the patient&#39;s coronary anatomy over a guidewire until the balloon of the dilatation catheter is properly positioned across the lesion to be dilated. Once properly positioned, the dilatation balloon is inflated with liquid to a predetermined size at relatively high pressures, e.g. up to 20 atmospheres or more, to expand the arterial 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. After the balloon is finally deflated, blood flow resumes through the dilated artery and the dilatation catheter can be removed therefrom. 
     In most PTCA procedures, a guiding catheter having a preshaped distal tip is first percutaneously introduced into the cardiovascular system of a patient by means of a conventional Seldinger technique and advanced therein until the preshaped distal tip of the guiding catheter is disposed within the aorta adjacent to the ostium of the desired coronary artery. The guiding catheter is twisted or torqued from its proximal end, which extends out of the patient, to guide the distal tip of the guiding catheter into the desired coronary ostium. Once the guiding catheter is in proper position within the patient&#39;s vasculature, the dilatation catheter with a guidewire slidably disposed within an inner lumen of the dilatation catheter is positioned within the inner lumen of the guiding catheter. The guidewire is first advanced out the distal tip of the guiding catheter seated in the coronary ostium into the patient&#39;s coronary artery and directed to the region of the patient&#39;s coronary anatomy where the procedure is to occur. A torque may be applied to the proximal end of the guidewire, which extends out of the proximal end of the guiding catheter, to guide the curved or otherwise shaped distal end of the guidewire into a desired branch of the coronary artery. The advancement of the guidewire within the selected artery continues until it crosses the lesion to be dilated. The dilatation catheter is then advanced over the previously advanced guidewire, until the balloon on the distal extremity of the dilatation catheter is properly positioned across the lesion which is to be dilated. 
     Current intravascular catheter designs are limited by the need to incorporate conflicting characteristics. For example, most dilatation catheters are designed to be introduced into a body lumen over an in-place guidewire which is slidably received within an inner lumen within the catheter. As such, it is desirable to minimize the friction between the guidewire and the surface of the inner lumen of the catheter by constructing the catheter from a lubricous material such as a high density polyethylene. However, lubricous polymeric materials frequently lack other desirable properties, including, for example, the ability to readily bond to incompatible polymeric materials such as polyethylene terephthalate and nylon. Due to the high inflation pressures (up to 300 psi or more) associated with coronary balloon angioplasty, it is imperative to provide a strong bond between one or more ends of the dilatation balloon and the catheter shaft. Polyolefin balloons can be effectively fusion bonded to a polyethylene shaft but balloons made of nylon and other polyamide materials, and balloons made of polyesters such as polyethylene terephthalate do not easily bond to polyolefinic materials. Nylon and polyethylene terephthalate balloons usually require surface treatment and the use of a suitable adhesive to bond to polyolefin materials such as polyethylene. The additional manufacturing steps of surface treatments and incorporating and curing an adhesives, greatly complicate the manufacturing process and can introduce significant quality control problems. A catheter shaft should also have adequate strength for pushability and resistance to buckling or kinking. As another example, it may be desirable to provide a catheter shaft with elastomeric properties to improve flexibility. However, most lubricous materials are not elastomeric. 
     U.S. Pat. No. 5,304,134 to Kraus et al., which is hereby incorporated in its entirety by reference, attempts to provide a solution to the poor bonding of lubricous by providing the catheter shaft with an inner tubular member having a lubricous proximal portion and a non-lubricous, bondable distal portion. However, this approach does not represent a complete solution, because the lubricous proximal portion must still be bonded to the non-lubricous distal portion. The Kraus et al. system also requires that some portion of the guidewire lumen be formed from a non-lubricous material which restricts guidewire movement within the lumen. 
     A different approach involves forming the dilatation balloon as an integral portion of the catheter shaft itself, but this requires the balloon and the shaft to be formed from the same material, which is not always desirable because the property requirements for the balloon and the shaft can be quite different, particularly for dilatation catheters for PTCA . 
     Accordingly, there remains a need to provide a catheter shaft having a lubricous inner surface defining a guidewire lumen while allowing an easy, secure bond with a dilatation balloon or other catheter components formed of non-lubricous polymeric materials. The present invention satisfies these and other needs. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to an intraluminal catheter, such as a balloon dilatation catheter for performing angioplasty procedures, which has a shaft or shaft segment which is both lubricous and is capable of readily bonding to other catheter components such as a balloon formed of essentially non-lubricous polymers. 
     In one embodiment of the invention, the catheter shaft or catheter shaft segment is formed of a polymeric blend comprising at least about 30% by weight, preferably at least about 50% by weight, of a lubricous polymeric component not more than about 60%, preferably not more than about 40%, of a bonding polymeric component and up to about 30%, preferably not more than about 10%, of a polymeric component for compatiblizing the lubricous and bonding components. Optionally, up to 25% by weight, usually not more than about 10% by weight of the blend could be a catalytic material to facilitate cross linking the shaft material to enhance compatiblizing. The lubricous component and the bonding component are not compatible, or miscible in the molten state. As used herein the term “compatible” and words of similar import mean that two polymer materials readily form an intimate mixture when they are melt processed together. However, the relative amounts of the different polymeric components of the polymeric blend will depends upon, and will therefore vary with, the nature of the polymeric materials. 
     Suitable lubricious polymeric components include polyolefins, such as polyethylene and polypropylene. One preferred lubricious polymeric material is high density polyethylene (HDPE), and most preferably high molecular weight HDPE having a molecular weight of about 50,000 to about 200,000. High density polyethylene has a density of at least about 0.94. The high molecular weight material has a high modulus of about 220,000 psi which provides improved collapse resistance for a given catheter shaft wall thickness. 
     In one embodiment, the bonding component comprises a polyamide polymeric material. Suitable polyamide materials include nylon, such as nylon  6 , nylon  6 , 12 , nylon  6 , 6 , nylon  11 , nylon  12 . The preferred nylons are typically semicrystalline, although suitable amorphous nylons may also be used. In one embodiment, nylon  11  and nylon  12  are preferred due to their advantageously low moisture absorption, however, the lower nylons such as nylon  6  may also have low sensitivity to moisture when blended with the polyolefin lubricious polymeric component. Other suitable polyamide materials are copolyamides, including polyether block amides such as PEBAX available from Elf Atochem or PEBA available from Huls AG. Preferably the polyamides or copolyamides have a Shore D hardness of about 63 to about 75. Commercially available polyamide-polyolefin alloys or blends may be used, such as ORGALLOY resins, available from Elf Atochem. In the embodiment having a polyamide bonding component, the catheter shaft or shaft segment is preferably formed of a polymeric blend of at least about 20% by weight, preferably at least about 40% by weight, of a lubricious polymeric component; not more than about 80% by weight, preferably not more than about 60% by weight of a polyamide or copolyamide (bonding polymeric component); and about 5 to about 20% by weight of a compatiblizer. In one embodiment, the polymeric blend is about 20 to about 60% by weight of a lubricious polymeric component, about 40 to about 80% by weight of a polyamide or copolyamide bonding polymeric component, and about 5 to about 10% of a compatiblizer. Suitable compatiblizers for the polyamide containing blends include ethylene acrylic acid copolymer such as PRIMACOR from Dow Chemical, ethylene acrylate anhydride terpolymer such as LOTADER, or epoxy modified LOTADER, including AX8840, AX8900, AX9820 or AX8930 grades of LOTADER. An optional polymeric catalyst is preferably about 1 to about 10% by weight of the polymeric blend. Suitable. polymeric catalysts include ethylene acrylic ester-maleic anhydride terpolymer such as LOTADER XX1275, with 6% aliphatic tertiary amine. The catheter shaft having a polyamide polymeric bonding component, such as nylon or PEBAX, readily fusion bonds to a nylon or PEBAX polyamide balloon shaft. 
     In another embodiment, the bonding component comprises a copolyester such as HYTREL. The catheter shaft or shaft segment is formed of a polymeric blend comprising less than about 30% by weight, preferably less than about 50% by weight, of a lubricious polymeric component; and at least about 60%, preferably at least about 40%, of a copolyester (bonding polymeric material); and about 5 to about 20%, preferably about 5 to about 10%, compatiblizer. In one presently preferred embodiment, the catheter or catheter segment is formed of a blend of about 40-50% polyethylene (a lubricous component), about 50-60% of a copolyester such as Hytrel® (the bonding component), and up to about 5% of a compatiblizing agent such as ethylene acrylate anhydride terpolymer or epoxy modified ethylene acrylate anhydride terpolymer, or ethylene acrylic ester copolymer. A balloon formed of polyethylene terephthalate (PET) or copolyester such as HYTREL readily fusion bonds to the outer surface of the tubular member. 
     The polymer components are intimately mixed and extruded into a tubular product which is utilized as the inner tubular member of an intravascular catheter. The surface defining an inner lumen of the tubular member has a kinematic frictional coefficient of about 0.08 to about 0.3 on a smooth glass. 
     These and other advantages of the invention will become more apparent from the following detailed description of the invention when taken in conjunction with the accompanying exemplary drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an elevational view, partially in section, of an over-the-wire dilatation catheter having an inner tubular member embodying features of the invention. 
     FIG. 2 is a transverse cross section of the embodiment shown in FIG. 1 taken along the lines  2 - 2 . 
     FIG. 3 is an elevational view, partially in section, of the distal section of a rapid exchange type dilatation catheter having an inner tubular member embodying features of the invention. 
     FIG. 4 is a transverse cross section of the embodiment shown in FIG. 3 taken along the lines  4 - 4 . 
     FIG. 5 is an elevational view, partially in section, of an alternative embodiment wherein the distal section of the catheter shaft is formed of an extrusion of a polymer blend. 
     FIG. 6 is a transverse cross section of the embodiment shown in FIG. 5 taken along the lines  6 - 6 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Reference is made to FIGS. 1 and 2 which illustrate a balloon dilatation catheter  10  embodying features of the invention. Generally, the catheter  10  comprises an outer tubular member  11 , an inner tubular member  12 , a dilatation balloon  13  on a distal portion of the catheter and an adapter  14  on the proximal end of the catheter. The inner tubular member  12  has a guidewire receiving inner lumen  15  which slidably receives guidewire  16 . The outer surface of the inner tubular member  12  and the inner surface of the outer tubular member  11  define an annular inflation lumen  17  which is in fluid communication with the interior of balloon  13  and side arm  18  of adapter  14 . 
     The distal skirt or shaft  20  of balloon  13  is bonded, preferably fusion bonded, to the exterior of the inner tubular member  12  and the proximal skirt  21  is fusion bonded to the exterior of the outer tubular member  11 . The fusion bonds are preferably formed by applying laser energy to the exterior of the skirts  20  and  21  which causes the interface between the skirts and the exterior of the outer and inner tubular members  11  and  12 . In one presently preferred embodiment, both the outer and inner tubular members  11  and  12  are formed of a polymer blend in accordance with the invention, having a lubricious polymeric component and a bonding polymeric component. 
     FIGS. 3-4 depict another embodiment of the invention directed to a rapid exchange type dilatation catheter  30 . The catheter  30  includes a relatively stiff proximal shaft  31  formed of hypotubing and a relatively flexible distal shaft section  32 . The distal shaft section  32  includes an inner tubular member  33 , an outer tubular member  34  and a dilation balloon  35 . The inner tubular member  33  has a guidewire receiving inner lumen  36  which is in fluid communication with a distal guidewire port  37  in the distal end of the catheter  30  and a proximal guidewire port  38  disposed a short distance, e.g. about 10 to about 45 cm from the proximal end of the balloon  35 . The proximal shaft  31  comprises a metallic hypotube  40  (e.g. stainless steel or NiTi alloys) and an outer polymer jacket  41  formed of suitable polymer material such as high density polyethylene. The distal end  42  of the. hypotube  40  is truncated and fits into the interior of the outer tubular member  34  and bonded thereto by suitable adhesive. Support tube  43 , preferably formed of polyimide, is disposed between the inner and outer tubular members  33  and  34  and defines inflation lumen  44 . As shown in more detail in FIG. 4, the outer tubular member is partially bonded to the inner tubular member  33  and partially to the support tube  43 . A filler material  46 , such as 75/25 high density/low density polyethylene, is disposed between the outer tubular member  34  and the support tube  43 . 
     In the embodiment of FIGS. 3-4 the inner tubular member  33  is formed of a polymer blend in accordance with the present invention. The distal skirt  47  of balloon  35  is fusion bonded to the exterior of the inner tubular member  33  as in the previously discussed embodiment shown in FIGS. 1 and 2. The proximal skirt  48  of the balloon  35  forms the outer tubular member  34  and is formed of essentially the same material as the balloon. In an alternative embodiment not shown the outer tubular member  34  may be a member separate and distinct from the balloon and formed of a polymer blend in accordance with the present invention. In this latter case the proximal skirt of the balloon  35  is fusion bonded to the exterior of the outer tubular member. 
     FIGS. 5 and 6 illustrate yet another embodiment of the invention wherein the catheter  50  has a distal shaft  51  which is of a dual lumen construction and is formed by extruding a polymer blend in accordance with the present invention. A tubular extension  52  extends through the interior of the dilatation balloon  53  and has a distal guidewire port  54  in its distal end. The balloon  53  has a distal skirt  55  fusion bonded to the distal end of the tubular extension  52  and a proximal skirt  56  fusion bonded to the distal shaft  51  as shown in the drawings. 
     One presently preferred polymer blend includes about 40 to about 60% high density polyethylene, about 40 to about 60% nylon, including nylon  12  or nylon  11 , and about 5 to about 20% epoxy modified ethylene methyl acrylate such as LOTADER AX8900. Another preferred polymer blend comprises polyamidepolyolefin alloys, including alloys having nylon  6 , and including ORGALLOY resins such as ORGALLOY RS, LE and LT grade resins, and preferably ORGALLOY LE 6000, 60XV, and LT 5050 extrudable grade resins. These blends readily fusion bond to balloons formed of polyamides such as nylon or PEBAX. 
     Another presently preferred polymer blend includes about 50% high density polyethylene, about 45% HYTREL (available from Dupont) and about 5% ethylene methyl acrylate such as epoxy modified LOTADER AX8900 (available from Elf ATOCHEM). This blend readily fusion bonds to a PET balloon and has a coefficient of friction of about 0.1-0.2. In one embodiment, the compatiblizing component is a polymeric material having a functional group selected from the group consisting of epoxy, anhydride, or acid functional groups. In another embodiment, the compatiblizing component is an alkyl acrylate copolymerized from monomers having about 2 to about 5 carbon atoms. 
     Although individual features of embodiments of the invention may be shown in some of the drawings and not in others, those skilled in the art will recognize that individual features of one embodiment of the invention can be combined with any or all the features of another embodiment. A variety of modifications can be made to the present invention without departing from the scope thereof.