Abstract:
Flexible microcatheter having regions of different flexibility integrally and strategically placed along and about the length of a one-piece composite catheter tube. Distally the flexible microcatheter exhibits pronounced flexibility with respect to locations or regions of flexibility located proximally for navigation along tortuous vascular paths. Different regions of flexibility are formed by applying resins of different Shore hardness readings either singularly or in combination along and about a braid which overlies an inner resin layer. The encapsulated braid provides resistance to kinking and bending of the flexible microcatheter as well as providing for torque transmission and pushability along the length of the flexible microcatheter.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention pertains to a catheter, and more particularly, pertains to a flexible microcatheter having continuous variability of stiffness or flexibility along and about the length of the flexible catheter. Embedded flexible braid wires surrounded by layers of varied hardness flexible plastic allows flexibility in different degrees for tracking and navigating along a tortuous vascular or other path. 
     2. Description of the Prior Art 
     Prior art catheter devices for use in small and tortuous vascular paths required catheters of minimum profile while yet requiring a great degree of flexibility. A catheter of minimum profile often could be flexible to a fault in that the catheter would tend to kink in a tight radius path, thereby causing a lumen flow restriction or stoppage. Difficulty could also be encountered in advancing the catheter along a path or application of torque-transfer, as the minimum profile structure did not provide the structural integrity required for advancement or twisting without the tube bending or kinking at various points along the catheter length. 
     The present invention provides a flexible microcatheter which overcomes the problems of prior art devices. 
     SUMMARY OF THE INVENTION 
     The present invention, a flexible microcatheter, is fashioned, in part, by a one-piece composite catheter tube composed of several layers of plastic including a polyethylene or polyamide copolymer or fluoroplastic inner layer or polyether block amide, a stainless steel or other braid material aligned over and about the inner layer to provide kink resistance and to increase torque transfer, and an outer layer of two polyamide and polyether or polyurethane based materials along and about the braid material and the inner layer. The inner layer has a constant hardness or flexibility while the length of the outer layer is comprised of regions of continually varying or different hardness or flexibility as determined by the composition of resin used to fashion the regions of the outer layer. The regions included are the distal region, a mid region of continually varying hardness located proximally and adjacent to the distal region and a proximal region located adjacent to and proximal to the mid region. The distal region exhibits the greatest amount of flexibility followed by regions of increasingly lesser flexibility in each successively and proximally located region of flexibility. 
     According to one embodiment of the present invention there is provided a flexible microcatheter having a Luer adapter, a strain relief and a one-piece composite catheter tube extending therefrom. The one-piece tube is comprised of a flexible plastic inner layer of constant hardness, a braid aligned over and about and along the inner layer and a flexible plastic outer layer having regions of different or continually varying hardness aligned over, about and along the braid and the inner layer. Marker bands and a distally located tip are included distally on the one-piece composite catheter tube. 
     One significant aspect and feature of the present invention is a flexible microcatheter having a variable degree of flexibility along its length. There is a mid region of flexibility which is continually varying. 
     Another significant aspect and feature of the present invention is a flexible microcatheter having a one-piece composite catheter tube. 
     Yet another significant aspect and feature of the present invention is a flexible microcatheter which encapsulates a braid between an inner and outer plastic layer, and is resistant to kinking and ovalization with bending. 
     Still another significant aspect and feature of the present invention is a flexible microcatheter which allows torque transfer. 
     A further significant aspect and feature of the present invention is a flexible microcatheter having a relatively stiff proximal region for application of push force to the distal flexible region(s). 
     A still further significant aspect and feature of the present invention is being able to vary stiffness without varying the outer dimension. 
     Having thus described one embodiment of the present invention, it is the principal object hereof to provide a flexible microcatheter. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other objects of the present invention and many of the attendant advantages of the present invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, in which like reference numerals designate like parts throughout the figures thereof and wherein: 
     FIG. 1 illustrates an isometric view of a flexible microcatheter, the present invention; 
     FIG. 2 illustrates a cutaway and partially exploded view of the flexible microcatheter; and, 
     FIG. 3 illustrates a longitudinal cross sectional view of the flexible microcatheter. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 illustrates an isometric view of a flexible microcatheter  10 , the present invention. Visible on the exterior of the flexible microcatheter  10  are a Luer connector  12 , a strain relief  14  concentrically located with the Luer connector  12  and extending outwardly and distally therefrom, a one-piece composite catheter tube  16  extending through the strain relief  14  from the Luer connector  12 , and a distally located atraumatic tip  18 . Although not visible to the naked eye, the one-piece composite catheter tube  16  includes a distally located region of flexibility  20  juxtaposing the atraumatic tip  18 , a mid region of flexibility  22  located proximal to the distally located region of flexibility  20 , and a proximally located region of flexibility  24  located proximal to the mid region of flexibility  22 . For purposes of example and illustration, the length of the one-piece composite catheter tube  16  measured from the strain relief to the atraumatic tip  18  can range from approximately 100 to 160 cm where the distal region of flexibility  20  can range from 10 to 30 cm, the mid region of flexibility  22  can range from 10 to 30 cm and the proximal region of flexibility  24  can range from 80 to 100 cm. Each region of flexibility, which is part and parcel of an outer layer  26 , is formed in a continuous fashion which can be, but is not limited to, an extrusion process to provide composition of either one or another resin or a combination or mixture of resins over and about a braid and an inner layer (FIG. 2) to provide staged or graduated degrees or continuously variable degrees of flexibility according to a durometer reference. Through the extrusion process, an inner layer  34  and the outer layer  26  are thermally bonded. Application of one or more resins having different hardness or flexible qualities is a one step continuous application where resins are furnished and applied over the braid and the inner layer as a pure form or a mixed form to provide the proper hardness or flexibility. A single resin  28  having specific hardness qualities (25 D to 35 D) and which can be, but is not limited to, thermoplastics, polyether block amide, polyamide, polyurethane, or polyethylene, is applied over the braid and inner layer to form a part of the outer layer  26  designated as the distal region of flexibility  20  having, for purpose of example and illustration, a 25 D Shore hardness value within a Shore hardness range of 25 D to 63 D. Another single resin  30  which also can be, but is not limited to, thermoplastics, polyether block amide, polyamide, polyurethane, or polyethylene and having specific hardness qualities (70 D to 80 D) which are harder than the resin  28  and which is incorporated in the proximal region of flexibility  24 , is then mixed as part of the continual process with resin  28  having lesser hardness qualities to form a combination resin  32 , to be continually applied and bonded to and over the braid and inner layer to form a part of the outer layer  26  designated as the mid region of flexibility  22  having, for purpose of example and illustration, a middle range of 25 D to 75 D Shore hardness value. The mix of the combination resin  32  is changed during extrusion and is continuously variable to increase stiffness, or decrease flexibility, in a proximal direction to continuously and upwardly increase the Shore reading proximally. Single resin  30 , as part of the continual application process, is applied over the braid and inner layer to form a part of the outer layer  26  designated as the proximal region of flexibility  24  having, for purpose of example and illustration, a 72 D Shore hardness value within a Shore hardness range of 50 D to 75 D. Although three regions of flexibility are described, any number of regions of flexibility can be utilized and shall not be limiting to the scope of the invention. The flexible microcatheter  10  which is provided is distally more flexible, which allows insertion of the atraumatic tip  18  and adjacent distal region of flexibility  20  into, and navigation of the balance of the flexible catheter structure along, tortuous vascular paths. 
     FIG. 2 illustrates a cutaway and partially exploded view of the flexible microcatheter  10 , where all numerals correspond to those elements previously or otherwise described. Central to the flexible microcatheter  10  is an inner layer  34  having a lumen  36 . The inner layer  34  is formed over a mandrel or otherwise suitably formed from another single resin  38  having specific hardness qualities which can be, but is not limited to, thermoplastics, fluroplastics polyamide, polyethylene, or polyether block amide. The inner layer  34 , for purposes of example and illustration, preferably can have a 50 D to 75 D Shore hardness value distributed constantly along its length, but in the alternative, can include regions of flexibility as required to provide various hardness or flexibility attributes. A braid  40  is aligned over and about the length of the inner layer  34  and extends from the atraumatic tip  18  to the interior of the Luer connector  12 . The braid  40 , which can include from four to  64  braid wires, can be of flat or round stainless steel or polyamide based filament or other such suitable material and can be spiral or cross wound and varying from 10 to 100 picks or pitches per inch. The braid  40  imparts flexibility to the flexible microcatheter  10  while at the same time providing structure to preclude kinking or adverse bending or ovalization along the length of the flexible microcatheter  10 , especially in the regions of reduced hardness (i.e., increased flexibility). The braid  40  also provides for structural integrity and for superior torque transmission qualities during rotation of the flexible microcatheter  10  during navigation and penetration of tortuous or other vascular paths. The outer layer  26  of resin, the attributes of which were described previously, is applied over and about and is formed to the braid  40  and inner layer  34 , also comprised of resin, to form a one-piece composite catheter tube  16 . Radio-opaque marker  44  can also be included at the distal end of the inner layer  34  in close proximity to the atraumatic tip  18  and a radio-opaque marker  42  can be located along the catheter shaft over the inner layer  34 . 
     FIG. 3 illustrates a longitudinal cross sectional view of the flexible microcatheter  10 , where all numerals correspond to those elements previously or otherwise described. Illustrated in particular are the outer and inner layers  26  and  34 , respectively, having the braid  40  encapsulated therebetween to form the one-piece composite catheter tube  16 . Also shown is the conically shaped cavity  46  located central to the Luer connector  12  which connects to the lumen  36  of the one-piece composite catheter tube  16 . The operation of the microcatheter is based on the doctor&#39;s preference. 
     Various modifications can be made to the present invention without departing from the apparent scope hereof. 
     FLEXIBLE MICROCATHETER 
     PARTS LIST 
       10  flexible microcatheter 
       12  Luer connector 
       14  strain relief 
       16  one-piece composite catheter tube 
       18  atraumatic tip 
       20  distal region of flexibility 
       22  mid-region of flexibility 
       24  proximal region of flexibility 
       26  outer layer 
       28  resin, soft 
       30  resin, hard 
       32  resin, combo, medium 
       34  inner layer 
       36  lumen 
       38  resin, single 
       40  braid 
       42  radio-opaque marker 
       44  radio-opaque marker 
       46  conical cavity