Abstract:
A method and apparatus for forming catheters and catheter curves using ferromagnetic materials exposed to an alternating magnetic field. Heat is generated in the exposed ferromagnetic material. The temperature of the ferromagnetic material is allowed to reach a desired temperature, preferably the Curie temperature of the ferromagnetic material containing portion. The heat generated is transferred to a catheter, wherein the catheter can be selectively formed or assembled and bonded at the desired elevated temperature.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention is related generally to medical devices. More specifically, the present invention is related to catheters. The present invention includes apparatus and methods for forming catheters and catheter curves.  
         BACKGROUND OF THE INVENTION  
         [0002]    A wide variety of intravascular catheters have been developed to diagnose and treat vascular diseases. Some types of catheters include a curved or shaped distal portion. The curved or shaped portion is used in order to facilitate navigation of the catheter through the vasculature. The curved or shaped portion allows the catheter to make sharp bends or follow tortuous passages not easily achieved using other catheters.  
           [0003]    Some catheters used for diagnosing and treating vascular diseases are generally comprised of an inner layer, a reinforcing layer, and an outer layer. The outer layer may include a plurality of segments placed along the length of the catheter. The segments may have different mechanical properties and/or materials, thus varying the rigidity, flexibility, and torqueability of the catheter along its shaft. For example, in selecting a useful combination of segments in forming the outer layer, a catheter may be created having a flexible distal region while maintaining a more rigid proximal region with a higher torqueability. The flexible distal tip region will allow the catheter to navigate tortuous regions of the vasculature while the more rigid proximal region will allow the catheter to be longitudinally pushed through the vasculature. It is necessary to bond these segments of varying properties or materials together or to the rest of the catheter shaft in order to create a generally continuous catheter shaft.  
         SUMMARY OF THE INVENTION  
         [0004]    The present invention relates generally to methods for forming catheters and catheter curves and apparatus used to form catheters and catheter curves. More specifically the present invention relates to forming catheters and catheter curves using electromagnetic induction heating created by an alternating magnetic field in combination with a ferromagnetic material. The ferromagnetic material is placed in the alternating magnetic field generating heat due to hysteresis loss. The heat generated from the ferromagnetic material is transferred to a catheter tube through conduction and/or convection. Heating of catheters in contact with or in close proximity to the ferromagnetic material can be performed quickly, uniformly, and controllably.  
           [0005]    One embodiment of the present invention includes a catheter tube and a mandrel having a ferromagnetic material. The ferromagnetic material may be embedded in the outer surface of the mandrel or contained in a coating on the mandrel. Alternatively, the mandrel may be made of a mixture of a polymer and a ferromagnetic material or the mandrel may comprise a non-ferromagnetic material having a ferromagnetic core. The mandrel may have multiple portions having different compositions or particle size or concentration of particles of a ferromagnetic material corresponding generally to segments of different materials or mechanical properties in the catheter. The mandrel may have a desired curve shape formed at the distal portion. Alternatively, the mandrel may be substantially straight or readily bendable into a desired curve shape.  
           [0006]    The mandrel may be inserted into the lumen of the catheter tube forming a desired curve in the catheter tube, preferably at the distal end, or retaining the catheter tube substantially straight. The mandrel and the catheter tube are then exposed to an alternating magnetic field. Heat is generated in the mandrel due to the hysteresis effect from the ferromagnetic particles. The mandrel, and therefore the adjacent portion of the catheter tube, is allowed to reach a desired temperature, preferably the Curie temperature of the ferromagnetic material. The Curie temperature is the temperature above which the material becomes paramagnetic and no longer heats. A desired Curie temperature can be reached by controlling characteristics such as the particle size and the volume fraction of the ferromagnetic material. If a mandrel with multiple portions designed to reach different Curie temperatures is used, different segments of the catheter tube may reach different temperatures corresponding to desired forming or fusing temperatures related to varying melting points of the segments of the catheter tube.  
           [0007]    Once the mandrel and the catheter tube have reached the desired temperature, they are removed from the alternating magnetic field and allowed to cool. The mandrel may then be removed from the catheter tube. A new catheter tube may be disposed on the mandrel and the forming process repeated.  
           [0008]    Another embodiment of the invention includes a catheter tube and a fixture for containing the catheter tube. The fixture may have a top portion and a bottom portion in order to completely surround at least a portion of the catheter tube. The fixture may include a chamber designed to receive at least a portion of the catheter tube. The chamber may have a desired curve shape or may be substantially straight. The fixture may be designed to receive inserts having a chamber forming a desired curve shape. The inserts may be substituted to form additional curve shapes. The chamber or inserts may be made of or coated with a ferromagnetic material, wherein different portions of the chamber or different inserts having different compositions of the ferromagnetic material may be designed to reach different desired temperatures. The regions of varying temperatures correspond generally to different segments of the catheter comprising materials with different melting points or other mechanical properties. Certain segments can include insulating inserts placed between ferromagnetic inserts. These segments would aid in preventing overheating of a shaft segment adjacent a higher temperature insert.  
           [0009]    At least a portion of the catheter tube may be received in the chamber of the fixture. The catheter tube, therefore, forms to the shape of the chamber. A top portion of the fixture may be placed over the catheter tube, thus enclosing at least a portion of the catheter tube. The fixture and the catheter tube are then exposed to an alternating magnetic field. Heat is generated in the fixture due to the hysteresis effect from the ferromagnetic material. The fixture, and therefore the adjacent portion of the catheter tube, is allowed to reach a desired temperature, preferably the Curie temperature of the ferromagnetic containing material. As stated above, the fixture can be precisely designed to reach a desired Curie temperature. If a fixture with multiple portions designed to reach different Curie temperatures is used, different segments of the catheter tube may reach different temperatures corresponding to varying melting or fusing temperatures or points of the segments of the catheter tube.  
           [0010]    Once the fixture and the catheter tube have reached the desired temperature, they are removed from the alternating magnetic field and allowed to cool. The catheter tube may then be removed from the fixture. A new catheter tube may be disposed in the fixture and the forming process repeated.  
           [0011]    Additional applications such as forming angioplasty balloons or other medical device balloons may also utilize this forming process. It may be desirable to subject different sections of a balloon to varying temperatures. For example, it may be desirable to expose the end sections to a higher temperature than the center section. A fixture using different compositions of ferromagnetic materials may be designed to allow the end sections to reach a higher Curie temperature than the center section. Exposing the fixture enclosing a balloon to an alternating magnetic field may heat the balloon portions to the desired temperatures. Following the forming of a balloon or other member, the ferromagnetic heat source may be cooled at a controlled rate to improve resulting polymer properties, as by annealing. This application may also be useful in securing the balloon end portions to a catheter shaft while not deforming the center section of the balloon. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]    [0012]FIG. 1 is a plan view of a catheter having a plurality of segments;  
         [0013]    [0013]FIG. 1A is a cross-sectional view of the catheter of FIG. 1 taken along line  1 A depicting multiple layers and a reinforcing member;  
         [0014]    [0014]FIG. 2 is a side view of a catheter having a curved shape distal portion;  
         [0015]    [0015]FIG. 3 is a perspective view of a fixture for receiving a catheter tube with the fixture chamber walls having a ferromagnetic material including varied segment concentrations depicted on the surface;  
         [0016]    [0016]FIG. 4 is a perspective view of a fixture including removable inserts, with the inserts having chamber walls having a ferromagnetic material of varied concentration;  
         [0017]    [0017]FIG. 5 is a perspective view of a catheter tube positioned in a fixture;  
         [0018]    [0018]FIG. 6 is a side view of a mandrel having a plurality of ferromagnetic portions;  
         [0019]    [0019]FIG. 7 is a perspective view of a catheter tube having a mandrel disposed within the lumen; and  
         [0020]    [0020]FIG. 8 is a perspective view of a fixture for forming an angioplasty balloon. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0021]    The following description should be read with reference to the drawings wherein like reference numerals indicate like elements throughout the several views. The drawings, which are not necessarily drawn to scale, depict selected embodiments and are not intended to limit the scope of the invention. Those skilled in the art will recognize that the examples may have suitable alternative embodiments that may be utilized.  
         [0022]    [0022]FIG. 1 shows a catheter  10  having a plurality of segments  12 ,  14 ,  16 . Although the catheter  10  depicted includes three segments  12 ,  14 ,  16 , the invention is not limited by the number of segments of the catheter  10  or their position along the shaft  18 . In one embodiment, the segments  12 ,  14 ,  16  each comprise different materials having distinct properties. However the segments may be comprised of substantially the same polymeric material having different mechanical properties. In one embodiment, the first segment  12 , at the distal portion  20 , is relatively flexible for navigating tortuous vasculature; the second segment  14  is somewhat less flexible; and the third segment  16  is relatively rigid to facilitate advancing the catheter through a lumen in a vasculature. The properties of the catheter  10  are only illustrative and not intended to limit the scope of the invention.  
         [0023]    [0023]FIG. 1A shows a cross-sectional view of catheter  10  depicted in FIG. 1. Catheter  10  comprises an inner layer  22  having at least one lumen  28  therethrough, a reinforcing layer  24 , and an outer layer  26  disposed over the reinforcing layer  24 . Although catheter  10  comprises three layers  22 ,  24 ,  26 , this example is only illustrative, and the invention is not limited by the number of layers or the arrangement of the layers comprising the catheter  10 . In one embodiment, only the outer layer  26  includes segments  12 ,  14 ,  16  having distinctive properties.  
         [0024]    [0024]FIG. 2 shows a catheter  30  having a plurality of segments  12 ,  14 ,  16  and a distal portion  40  having a desired curve shape  38 . Although the distal portion  40  may be relatively flexible, the catheter  30  may be biased to retain the curve shape  38 . The curve shape  38  of the catheter  30  facilitates navigation and positioning of the catheter  30  within tortuous vasculature. The segments  12 ,  14 ,  16  each may be comprised of substantially the same material, or they may be comprised of different materials having distinct properties. The catheter  30  may be formed using a plurality of layers such as the catheter  10  of FIG. 1. In one embodiment, only the outer layer  26  has a plurality of segments  12 ,  14 ,  16 .  
         [0025]    [0025]FIGS. 3 and 4 depict two variations of a fixture which can be utilized with the present invention. Elements of one embodiment may be incorporated into another embodiment as necessary. FIG. 3 shows a fixture  50  for forming a catheter such as the catheter  10  depicted in FIG. 1 or a catheter curve such as the catheter curve  38  of the catheter  30  depicted in FIG. 2. The fixture  50  may include a top section  52  and a bottom section  54 , or it may only include one section. One skilled in the art will understand that the scope of the invention shall not be limited by the number of sections comprising the fixture. The sections may have a means for securing the sections to one another such as a hinge  68  shown in FIG. 4. The sections  52 ,  54  may also or alternatively have a means for aligning the sections  52 ,  54 . As in FIG. 4, the bottom section  54  may include tabs  56  and the top section  52  may include slots  58  for receiving the tabs  56 .  
         [0026]    The fixture  50  has a chamber  60  for receiving at least a portion of the catheter  10 ,  30 . The chamber  60  may have a desired curve shape resembling the desired curve shape  38  of the catheter  30  as FIG. 2 illustrates, or the chamber  60  may be substantially straight as shown in FIG. 4. In one embodiment, the chamber  60  has a plurality of portions  62 ,  64 ,  66  having a ferromagnetic material; a first portion  62  having a first selected composition including a ferromagnetic material, a second portion  64  having a second selected composition including a ferromagnetic material, and a third portion  66  having a third selected composition including a ferromagnetic material. Although the chamber  60  shown in FIG. 3 includes three portions  62 ,  64 ,  66 , the invention is not intended to be limited by the number of portions in the chamber  60 .  
         [0027]    The selected composition for each portion  62 ,  64 ,  66  may be chosen for its unique properties including the Curie temperature of the ferromagnetic material containing portion. A desired Curie temperature may be chosen to correspond to the melting point of the material of the catheter segment  12 ,  14 ,  16  in contact with a selected portion  62 ,  64 ,  66  of the chamber  60 . By having multiple portions  62 ,  64 ,  66  with distinct compositions, it is possible to heat different segments  12 ,  14 ,  16  of the catheter  10 ,  30  to different temperatures corresponding to different melting temperatures. Further, selected segments could include insulating material to protect adjacent areas from overheating.  
         [0028]    [0028]FIG. 4 shows an alternative fixture  70  having a plurality of inserts  72 ,  74 ,  76 . The inserts  72 ,  74 ,  76  are disposed in a channel  80  in the fixture  70 . Although FIG. 4 shows a substantially straight channel  80  having inserts  72 ,  74 ,  76 , the channel  80  may have a curve shape  58  such as the fixture  50  of FIG. 3 for receiving curved inserts. The inserts  72 ,  74 ,  76  have a chamber  60  for receiving at least a portion of a catheter  10 ,  30 . In one embodiment, the inserts  72 ,  74 ,  76  include a ferromagnetic material. In another embodiment, the inserts have a coating  78  including a ferromagnetic material. As in the chamber  60  of FIG. 3, each insert  72 ,  74 ,  76  may include the same ferromagnetic material or it may include a distinct ferromagnetic material. The fixture  70  may have a top section  52  and a bottom section  54  as shown in FIG. 4, or it may only have one section. The top section  52  can include identical inserts to corresponding areas of the bottom section  54 . One skilled in the art will understand that the scope of the invention shall not be limited by the number of sections comprising the fixture. A hinge  68  allows the top section  52  to be lifted off the bottom section  54 , yet remain coupled together. Additionally or alternatively, tabs  56  of the bottom section  54  may be disposed in slots  58  of the top section  52  in order to securely align the sections  52 ,  54 .  
         [0029]    Similarly to the fixture  50  of FIG. 3, the selected composition of a ferromagnetic material for each insert  72 ,  74 ,  76  may be chosen for its unique properties such as the Curie temperature of the ferromagnetic material. Further, certain inserts can be made of insulating material to protect adjacent segments from overheating. As explained above, different segments  12 ,  14 ,  16  of a catheter  10 ,  30  may be heated to different temperatures in relation to the Curie temperature of each insert  72 ,  74 ,  76 .  
         [0030]    [0030]FIG. 5 demonstrates one example of the catheter forming process. A fixture  50  having a chamber  60  for receiving at least a portion of a catheter  30  is provided. The chamber  60  has a plurality of portions  62 ,  64 ,  66 , each having a composition including a ferromagnetic material. The catheter  30  such as the catheter of FIG. 2 includes a plurality of segments  12 ,  14 ,  16  comprising the outer layer  26 . A portion of the catheter  30  is placed in the chamber  60 , wherein the catheter segments  12 ,  14 ,  16  may correspond to the portions  62 ,  64 ,  66  of the chamber  60  having a ferromagnetic composition. The fixture  50  and at least a portion of the catheter  30  are exposed to an alternating magnetic field  90 . In one embodiment, the alternating magnetic field  90  may be made by using an alternating electrical current. Heat is generated in the fixture  50  due to the hysteresis loss in the ferromagnetic material exposed to the alternating magnetic field  90 . The ferromagnetic material may be heated to its corresponding Curie temperature above which point the material no longer heats. A desired Curie temperature may be reached by selectively choosing the particle size and volume fraction of the ferromagnetic material, as well as controlling the effect of oxidation during heat generation. Electromagnetic induction heating in this fashion allows for quick, uniform, controlled, and selective heating of a desired material.  
         [0031]    The selected Curie temperature of the ferromagnetic material may be chosen to correspond to the fusing or melting temperature of the segments  12 ,  14 ,  16  of the catheter  30 . It is, therefore, possible to allow each segment  12 ,  14 ,  16  of the catheter  30  to reach its unique fusing or melting point without overheating another portion of the catheter  30 . In this fashion, the segments  12 ,  14 ,  16  of the catheter  30  may be bonded to the catheter  30  and/or to each other. Additionally or alternatively, a curve shape  38  may be formed in a portion of the catheter  30  through the heating process.  
         [0032]    Once the fixture  50  and the selected portion of the catheter  30  reach their desired temperatures, the fixture  50  and the catheter  30  may be removed from the alternating magnetic field  90  and allowed to cool. Another catheter may be placed in the fixture  50  and this process repeated.  
         [0033]    [0033]FIG. 6 shows a mandrel  100  having a plurality of portions  162 ,  164 ,  166 . The mandrel  100  has a first portion  162  having a first composition including a ferromagnetic material, a second portion  164  having a second composition including a ferromagnetic material, and a third portion  166  having a third composition including a ferromagnetic material. Although the mandrel  100  in FIG. 6 includes three portions  162 ,  164 ,  166 , the scope of the invention is not limited by the number of portions of the mandrel  100 . The portions  162 ,  164 ,  166  may include distinct compositions including a ferromagnetic material or they may be substantially the same. The mandrel  100  in FIG. 6 includes a curved distal region  158 , but the mandrel  100  may also be substantially straight.  
         [0034]    There are a number of possible ways that the mandrel  100  may include a ferromagnetic material. The mandrel  100  may include ferromagnetic particles embedded in the outer surface, or a coating having a composition of a ferromagnetic material. Alternatively, the mandrel may be formed with a mixture of a polymer and ferromagnetic materials or have a core having a ferromagnetic material. The mandrel may be substantially rigid or may be flexibly manipulated.  
         [0035]    [0035]FIG. 7 demonstrates another example of a catheter forming process similar to that of FIG. 5. The mandrel  100  of FIG. 6 is disposed within the lumen  110  of a catheter  30  such as in FIG. 2. In one embodiment, the plurality of portions  162 ,  164 ,  166  of the mandrel  100  corresponds to the plurality of segments  12 ,  14 ,  16  of the catheter  30 . A curve shape  38  may be formed in at least a portion of the catheter  30  disposed around the mandrel  100 , or the catheter  30  may be retained substantially straight. The mandrel  100  and at least a portion of the catheter  30  are exposed to an alternating magnetic field  90 . The mandrel  100  and the portion of the catheter  30  are allowed to reach a desired temperature preferably selected by designing the portions  162 ,  164 ,  166  of the mandrel  100  to have predetermined Curie temperatures. Desired Curie temperatures may be controlled by selectively including a ferromagnetic material in the mandrel  100  as explained above. In this way, the segments  12 ,  14 ,  16  of the catheter  30  may reach different temperatures such as their corresponding melting or fusing temperatures without overheating another segment of the catheter  30 . As the segments  12 ,  14 ,  16  of the catheter  30  reach their respective melting or fusing temperatures, they may be bonded to the catheter  30  and/or to another segment. Additionally or alternatively, a curve shape  38  may be formed in a portion of the catheter  30  through the heating process. Once the catheter  30  is heated to its desired temperature, the mandrel  100  and the catheter  30  may be removed from the alternating magnetic field  90  and allowed to cool. The cooling rate may be controlled to give an annealing effect to the polymers if desired. The mandrel  100  may be removed from the catheter  30  and the forming process repeated.  
         [0036]    Other forming processes similar to those discussed above may prompt a similar use of a ferromagnetic material exposed to an alternating magnetic field  90 . FIG. 8 shows a fixture.  120  for forming an angioplasty balloon to a catheter using a similar forming process. The fixture  120  may have a top section  152  and a bottom section  154  and may have similar securing features such as the fixtures  50 ,  70  of FIGS. 3 and 4. The fixture  120  has a chamber  160  for receiving a tubular member which is blow-molded to form a balloon (not shown). Such processes of balloon formation are disclosed in commonly assigned U.S. Pat. No. 5,087,394, the disclosure of which is incorporated herein by reference. The chamber  160  includes a center portion  176  and two end portions  172 ,  174 . The end portions  172 ,  174  may have a different ferromagnetic material or material concentration/particle size than the center portion  176 . Therefore, the end portions  172 ,  174  may be able to reach a different temperature than the center portion  176  when the fixture  120  is exposed to an alternating magnetic field  90 . In this instance, the end portions  172 ,  174  may reach a higher temperature, which may be desirable due to greater end portion thicknesses while retaining the center portion of the balloon at or below a desired maximum temperature of the center balloon material. Therefore, the balloon could be heat treated preferentially in the fixture during heating and cooling cycles.  
         [0037]    It should be understood that this disclosure is, in many respects only illustrative. Changes may be made in details, particularly in matters of shape, size, arrangement of parts, and order of steps without departing from the scope of the invention. The language of the appended claims shall define the scope of the invention.