Abstract:
A microcatheter comprises a coil formed over an inner liner. The coil is covered with a series of outer jacket segments that decrease in durometer relative to proximally adjacent segments. Preferably, these segments have angled ends that allow each segment to be inserted and bonded into the segment prior to it. The outer jacket ultimately terminates at a distal of the microcatheter with the segment having the lowest durometer.

Description:
This application claims priority to U.S. Provisional Application Ser. No. 61/121,525 filed Dec. 10, 2008 entitled Microcatheter, the contents of which are incorporated in their entirety herein. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates generally to medical devices and methods of manufacturing the same. More particularly, this invention relates to microcatheters and methods for making microcatheters used in performing endovascular medical procedures. 
     BACKGROUND OF THE INVENTION 
     Microcatheters are used in a variety of medical procedures for the diagnosis and treatment of conditions and diseases occurring in remote, highly tortuous vascular sites. Typically, a microcatheter is introduced to the vascular system of a patient at a first location and then is advanced through the patient&#39;s vessels until the distal end of the microcatheter reaches a desired target location. 
     The process of advancing the microcatheter often involves applying force proximal of its distal end. Hence, as some prior art microcatheters advance deeper into the vascular system, it can become difficult to properly push and maneuver the distal end of the microcatheter. In this respect, it is desirable that a microcatheter exhibit superior pushability and trackability. Pushability is often understood as the ability to transmit force from the proximal end of the microcatheter to the distal end of the microcatheter while minimizing or eliminating kinking. Trackability is often understood as the ability to navigate the microcatheter through tortuous vasculature. 
     While prior art microcatheters are typically capable of performing their intended task within a patient, it is always desirable to have improved catheter performance, such as improved trackability and pushability. 
     SUMMARY OF THE INVENTION 
     In one preferred embodiment according to the present invention, a microcatheter comprises a coil formed over an inner liner. The coil is covered with a series of outer jacket segments or transition segments that decrease in durometer relative to proximally adjacent segments. Preferably, these segments have angled ends that allow each segment to be inserted and bonded into the segment prior to it. The outer jacket ultimately terminates at a distal of the microcatheter with the segment having the lowest durometer. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other aspects, features and advantages of which embodiments of the invention are capable of will be apparent and elucidated from the following description of embodiments of the present invention, reference being made to the accompanying drawings, in which 
         FIG. 1A  illustrates a side cross sectional view of a microcatheter according to a preferred embodiment of the present invention; 
         FIG. 1B  illustrates a magnified view of a distal region of the microcatheter of  FIG. 1A  taken from area  1 B; 
         FIG. 1C  illustrates a cross sectional view of the microcatheter of  FIG. 1A  taken along lines  1 C; 
         FIG. 2A  illustrates the microcatheter of  FIG. 1A  having a curved distal region; 
         FIG. 2B  illustrates a distal region of the microcatheter from area  2 B with the outer jacket partially removed; 
         FIG. 3  illustrates different example segments forming the outer jacket of the microcatheter according to a preferred embodiment of the present invention; 
         FIG. 4  illustrates different example segments forming the outer jacket of the microcatheter according to a preferred embodiment of the present invention; 
         FIG. 5A  illustrates a side view of two outer jacket segments with opposing or oppositely oriented diagonal angled ends; 
         FIG. 5B  illustrates a side view of two outer jacket segments with similarly oriented diagonal angled ends; and, 
         FIG. 5C  illustrates a side perspective view of a jacket segment with a diagonal angled end region. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Specific embodiments of the invention will now be described with reference to the accompanying drawings. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. The terminology used in the detailed description of the embodiments illustrated in the accompanying drawings is not intended to be limiting of the invention. In the drawings, like numbers refer to like elements. 
     Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein. 
       FIG. 1A  illustrates a preferred embodiment of a microcatheter  100  comprising an elongated tubular member  101  connected to a hub member  102 . The proximal end  108  of the tubular member  101  is coupled to a distal end of the hub  102  and is further covered by a strain relief member  106 . At least one center lumen in the tubular member  101  is in communication with a passage within the hub  102 , thereby forming catheter passage  104 . In the present example embodiment, a guide wire  112  is positioned through passage  104 , exiting at a distal end  110  of the tubular member. 
     The hub  102  is preferably bonded to the proximal portion  108  with DYMAX medical adhesion or a similar adhesive. The strain relief portion  106  may be installed onto the hub  102  by friction, adhesive or similar connection techniques. 
     As best seen in  FIGS. 1B and 1C , the passage  104  is formed by an inner liner  114  about which is wound a coil  124 . The coil  124  is covered by an outer jacket  116  that is formed from a plurality different section. Each section of the outer jacket  116  preferably has a durometer that is less that the section proximal to it. In this respect, the outer jacket  116  generally increases in flexibility towards the distal end  110  relative to the proximal end  108 . 
     As seen in  FIG. 2A , the outer jacket preferably includes a hydrophilic coating along a portion of its length. Preferably, this coating is about 100-120 cm from the distal tip of the microcatheter  100 . 
     As seen in the cross sectional view of  FIG. 1B  and the view of  FIG. 2B , the distal end  110  includes two radiopaque markers  118  and  120  that are bonded between the coil layer  124  and the outer jacket  116 . In one example arrangement, the marker  120  is located at or near the distal tip of the catheter  100 , while the marker  118  is located about 3 cm proximal of marker band  120 . As best seen in  FIG. 1B , these markers  118  and  120  can provide raised or elevated areas that can be used to secure an implant device such as a stent. 
     In one example, the microcatheter  100  is approximately 150 cm, as measured from the distal tip of the strain relief portion  106  to the distal end of the distal portion  110 . The central lumen  104  has an inner diameter of approximately 0.0165 to 0.017 inches. The distal portion  110  preferably includes a region approximately 40 cm long that is approximately 1.9 French. The proximal portion  108  preferably includes a region of approximately 2.4 French. The outer jacket  116  is about 0.025 inches. 
     The inner liner  114  is preferably composed of polytetrafluroethelyene, PTFE, or other similar material and has a wall thickness in the range of about 0.0005 and 0.007 inches. Preferably, the inner liner  114  is “necked” or stretched to reduce wall thickness. This stretching can also selectively orient the molecular structure of the material and thereby impart additional performance characteristics. For example, such stretching can increase burst strength and/or increase compliance or suppleness as compared with similar, non-stretched material of the same thickness. 
     In this respect, a smaller portion of the microcatheter  100  is used for the inner liner  114  while the thickness of other portions can be increased without increasing the outer diameter or reducing the inner diameter of the microcatheter  100 . In other words, stretching the inner liner  114  allows a different thickness ratio between the inner liner  114  and other portions of the microcatheter, such as the outer jacket  116 . 
     For example, in a 10 system microcatheter having an inner lumen diameter in the range of about 0.0165 to 0.017 inches and an outer diameter of about 0.025 inches, there is a ratio of outer jacket  116  thickness to inner liner  114  thickness greater than about 70% and more preferably about 78% while achieving desirable performance results. 
     Preferably, the inner liner  114  is stretched prior to assembly by applying heat and tension to the liner  114 . For example, a temperature between about 250° F. and 600° F. can be applied to the liner  114  while a tension between about 50 g to 750 g at a speed between 0.5 and 12 inches per minute. In another example, the inner liner  114  can be stretched at room temperature with similar or stronger forces and similar or quicker speeds. 
     In one preferred embodiment, the inner liner  114  can have a uniform thickness along its length. In another preferred embodiment, the inner liner  114  can increase in thickness towards its proximal end, thereby imparting additional burst strength. 
     The coil layer  124  is preferably formed of a round wire with an outer diameter of approximately 0.001 inch filar. The pitch of coil  124  is preferably in the range of about 0.002 to 0.004 inches. In certain embodiments of the microcatheter  100 , coil  124  may also be formed with a tighter pitch. 
     In one example, the outer jacket  116  is formed of a plurality of segments of polyether block amide, Pebax, of varying durometer bonded to one another (e.g., heat bonded or adhesive bonding). As illustrated in  FIG. 5C , a first jacket segment  116 A includes a biased or angled end  116 D. In other words, the segment end  116 D is nonperpendicular to an axis  116 E along the length of the segment  116 A. Preferably, this angle can be within a range of about 5-75 degrees relative to the axis  116 E. 
     As seen in  FIG. 5A , segment  116 A is angle-bonded within jacket segment  116 B. The angled cut end  116 D is oriented such that it is in an opposite rotational position relative to the angled cut end  116 C. In other words, the angles of ends  116 D and  116 C are positioned so as to form a triangular or trapezoid shape. 
     Preferably, segments  116 A and  116 B are bonded by first placing the angled cut end  116 D against angled cut end  116 C. Next, a heat shrink tube is positioned over the two segments  116 A and  116 B. Finally, heat is applied, causing the heat shrink tube to shrink in diameter, pushing segment  116 A within segment  116 B. Both the heat and the force of the heat shrink tube cause the segments  116 A and  116 B to bond together. Finally, the heat shrink tube can be removed from the jacket segments. 
     As illustrated in  FIG. 5B , segment  116 A may also be oriented such that the angled cut end  116 D is positioned in the same direction and orientation as angled end  116 C. While both segments are shown having angled ends, it is also contemplated that only a single segment may include an angled or biased end. The angled bonding as described in the examples of  FIGS. 5A and 5B  can reduce kinking that may otherwise occur by providing additional axial strength while maintaining flexibility. 
     Preferably, the outer jacket  116  has seven segments, each of which having a lower durometer than the segment proximally adjacent to it. In this respect, the outer jacket  116  becomes more flexible towards the distal end  110 . 
     Turning to  FIG. 3 , an example outer jacket  116  is shown having various segments. Segment  150  represents a segment on the proximal end  108  while segment  162  represents a segment on the distal end  110 . In one example, the segments are composed as follows: 
     
       
         
               
               
               
               
               
             
           
               
                   
               
               
                 Jacket 
                   
                 Length 
                 Internal Diameter 
                 Outer Diameter 
               
               
                 Segment Number 
                 Material 
                 (approximate) 
                 (approximate) 
                 (approximate) 
               
               
                   
               
             
             
               
                 150 
                 Grilamid L25 
                 85 cm 
                 0.026 inches 
                 0.035 inches 
               
               
                 152 
                 Pebax 72 
                  5 cm 
                 0.026 inches 
                 0.035 inches 
               
               
                 154 
                 Pebax 63D1 
                  5 cm 
                 0.026 inches 
                 0.033 inches 
               
               
                 156 
                 Pebax 55D1 
                  5 cm 
                 0.026 inches 
                 0.032 inches 
               
               
                 158 
                 Pebax 45D2 
                 20 cm 
                 0.026 inches 
                 0.031 inches 
               
               
                 160 
                 Pebax 45D1 
                 15 cm 
                 0.026 inches 
                 0.030 inches 
               
               
                 162 
                 Pebax 35D 
                 15 cm 
                 0.026 inches 
                 0.029 inches 
               
               
                   
               
             
          
         
       
     
     Turning to  FIG. 4 , an example outer jacket  116  is shown having various segments. Segment  164  represents a segment on the proximal end  108  while segment  176  represents a segment on the distal end  110 . In one example, the segments are composed as follows: 
     
       
         
               
               
               
               
               
             
           
               
                   
               
               
                 Jacket 
                   
                 Length 
                 Internal Diameter 
                 Outer Diameter 
               
               
                 Segment Number 
                 Material 
                 (approximate) 
                 (approximate) 
                 (approximate) 
               
               
                   
               
             
             
               
                 164 
                 Grilamid L25 
                 84 cm 
                 0.026 inches 
                 0.035 inches 
               
               
                 166 
                 Pebax 72D 
                  5 cm 
                 0.026 inches 
                 0.034 inches 
               
               
                 168 
                 Pebax 63D1 
                  5 cm 
                 0.026 inches 
                 0.033 inches 
               
               
                 170 
                 Pebax 55D1 
                 35 cm 
                 0.026 inches 
                 0.032 inches 
               
               
                 172 
                 Pebax 45D2 
                 10 cm 
                 0.026 inches 
                 0.031 inches 
               
               
                 174 
                 Pebax 45D1 
                 15 cm 
                 0.026 inches 
                 0.030 inches 
               
               
                 176 
                 Pebax 35D 
                  1 cm 
                 0.026 inches 
                 0.029 inches 
               
               
                   
               
             
          
         
       
     
     It will be recognized that suitable alternatives to Pebax and Grilamid are known in the field and may be employed accordingly. It will further be recognized that the wall thickness of the inner liner  114  and the outer jacket  116  may be altered so as to emphasize or enhance certain characteristics, such as the trackability, pushability, internal diameter, and/or outer diameter, of the microcatheter  100  as desired in order to perform the intended procedure. 
     Certain embodiments of the present invention provide for superior tip-shapeability and enhanced tip-shape retention in the microcatheter  100 . With respect to tip-shapeability, the microcatheter  100  is formed in a straight, i.e. not pre-shaped, configuration that can be steam-shaped as desired by a physician prior to use. The catheter  100  can be steam-shaped in a manner well known in the field. The tip-shape retention of the microcatheter  100  is greater that 55 percent. In a preferred embodiment the tip-shape retention is 58 percent and in another preferred embodiment the tip-shape retention is 67 percent. 
     Tip-shape retention is enhanced by employing a thinner inner liner  114  which, in turn, allows for incorporation of a thicker walled, shapeable, outer jacket  116 . Tip-shape retention is further enhanced by incorporating the coil  124  having a tight pitch between the inner liner  114  and the shapeable outer jacket  116 . The tight pitch coil  124  is disposed concentrically about the inner liner  114  such that the shapeable section of the microcatheter  100 , i.e. the distal portion  110 , is not significantly subjected to a straightening force by the coil  124 . This is in contrast to prior art microcatheters that employ a braided or a longer pitch coil configuration that disposes wire or other filaments in the shapeable section of the microcatheter in a manner that exert a straightening force to the microcatheter tip. 
     Although the invention has been described in terms of particular embodiments and applications, one of ordinary skill in the art, in light of this teaching, can generate additional embodiments and modifications without departing from the spirit of or exceeding the scope of the claimed invention. Accordingly, it is to be understood that the drawings and descriptions herein are proffered by way of example to facilitate comprehension of the invention and should not be construed to limit the scope thereof.