Patent Publication Number: US-2018042506-A1

Title: Segmented electrode and method

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This Non-Provisional Patent Application claims the benefit of the filing date of U.S. Provisional Patent Application Ser. No. 62/375,369, filed Aug. 15, 2016, entitled “SEGMENTED ELECTRODE AND METHOD,” which is herein incorporated by reference. 
    
    
     BACKGROUND 
     This disclosure relates to segmented electrodes configured for sensing and/or stimulation within a biological application. In some embodiments, ring electrodes are provided on the distal end of a lead for sensing or stimulation within a human body. The distal end of a lead is placed adjacent tissue that is to be sensed or stimulated and the ring electrodes either transmit or receive energy. In some cases, it is useful to have very discrete locations energized, and accordingly, use only a segment of a ring electrode, rather than the entire ring. Manufacturing discrete electrode segments can be difficult, particularly where multiple electrode segments are desired on a small diameter lead. For these and other reasons, there is a need for the present disclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates a side view of a medical lead with segmented electrodes in accordance with one embodiment. 
         FIG. 2  illustrates a perspective view of an electrode assembly for a lead in accordance with one embodiment. 
         FIG. 3  illustrates an exploded perspective view of a strut and electrode assembly with wiring for a lead in accordance with one embodiment. 
         FIG. 4  illustrates a perspective view of an electrode assembly with wiring for a lead in accordance with one embodiment. 
         FIG. 5  illustrates a partial perspective view of an electrode assembly with wiring for a lead in accordance with one embodiment. 
         FIG. 6A  illustrates an end view of an electrode assembly with wiring before centerless grinding in accordance with one embodiment. 
         FIG. 6B  illustrates an end view of an electrode assembly with wiring after centerless grinding in accordance with one embodiment. 
         FIG. 7A  illustrates a top view of an electrode assembly with wiring for a lead in a mold cavity in accordance with one embodiment. 
         FIG. 7B  illustrates a perspective view of an electrode assembly with wiring for a lead after grinding in accordance with one embodiment. 
         FIG. 8  illustrates a perspective view of a strut for a lead in accordance with one embodiment. 
         FIG. 9  illustrates a perspective view of an electrode assembly with wiring for a lead in accordance with one embodiment. 
         FIG. 10  illustrates an end view of an electrode assembly before centerless grinding in accordance with one embodiment. 
         FIG. 11  illustrates a partial perspective view of an electrode assembly with wiring for a lead in accordance with one embodiment. 
         FIG. 12  illustrates a perspective view of a strut for a lead in accordance with one embodiment. 
         FIG. 13  illustrates a perspective view of an electrode from an electrode assembly for a lead in accordance with one embodiment. 
         FIG. 14  illustrates a perspective view of an electrode from an electrode assembly for a lead in accordance with one embodiment. 
         FIG. 15  illustrates perspective views of wire sleeves for use in an electrode for a lead in accordance with one embodiment. 
         FIGS. 16A-16B  illustrate side and perspective views of a lead with segmented electrodes in accordance with one embodiment. 
         FIGS. 17A-17B  illustrate side and perspective views of a lead with segmented electrodes in accordance with one embodiment. 
         FIG. 18  illustrates a method of forming a medical lead with segmented electrodes in accordance with one embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     In the following Detailed Description, reference is made to the accompanying drawings, which form a part hereof, and in which is shown by way of illustration specific embodiments in which the embodiments may be practiced. In this regard, directional terminology, such as “top,” “bottom,” “front,” “back,” “leading,” “trailing,” etc., is used with reference to the orientation of the Figure(s) being described. Because components of embodiments can be positioned in a number of different orientations, the directional terminology is used for purposes of illustration and is in no way limiting. It is to be understood that other embodiments may be utilized and structural or logical changes may be made without departing from the scope of the embodiments. The following detailed description, therefore, is not to be taken in a limiting sense, and the scope of the embodiments is defined by the appended claims. 
       FIG. 1  illustrates a side view of a medical lead  10  with segmented electrodes  20 ,  22 ,  24 ,  26  in accordance with one embodiment. In one embodiment, lead  10  includes, adjacent its distal end  12 , four electrodes  20 ,  22 ,  24 ,  26 , each of which is segmented such that each has a plurality of individually accessible electrode segments. Specifically, first electrode  20  includes multiple electrode segments  20   a ; second electrode  22  includes multiple electrode segments  22   a ; third electrode  24  includes multiple electrode segments  24   a ; and fourth electrode  26  includes multiple electrode segments  240   a . In one various embodiments, there are two, three, four or five electrode segments  20   a ,  22   a ,  24   a ,  26   a , for each of electrodes  20 ,  22 ,  24 ,  26 . 
     In operation, lead  10  may be configured for use within a human body. Once within a human body, each of electrode segments  20   a ,  22   a ,  24   a ,  26   a  may be used for directional stimulation or for positional feedback sensing. Rather than using a single ring electrode that spans the entire 360° circumference of the lead, lead  10  includes electrode segments  20   a ,  22   a ,  24   a ,  26   a , which only span a portion of the circumference of lead  10  (for example, 180°, 90° degrees or less), such that directional stimulation or positional feedback sensing can be much more precisely controlled relative to a given target within the human body. 
     Furthermore, lead  10  in accordance with embodiments described herein, allow for the manufacture of leads having increased density of electrode segments. Increased density of electrode segments is useful in a variety of applications. For example, lead  10  can be used in deep brain stimulation (DBS), in which lead  10  delivers electrical pulses into one or several specific sites within the brain of a patient to treat various neurological disorders, such as chronic pain, tremors, Parkinson&#39;s disease, dystonia, epilepsy, depression, obsessive-compulsive disorder, and other disorders. In other applications, lead  10  may be configured for spinal cord stimulation, peripheral nerve stimulation, dorsal root stimulation, cortical stimulation, ablation therapies, cardiac rhythm management leads, various catheter configurations for sensing, and various other therapies where directional sensing or stimulation are needed. 
     In one embodiment, the manufacture of lead  10  begins with electrode assembly  30 , such as illustrated in  FIG. 2 . Electrode assembly  30  includes first electrode  20 , second electrode  22 , third electrode  24 , and fourth electrode  26 . Each electrode is coupled to at least on other electrode with coupling segments  32 . Each electrode  20 ,  22 ,  24 ,  26  is provided with a plurality of grooves  20   b ,  22   b ,  24   b ,  26   b , respectively, on the outer periphery of the electrode. The number of grooves provided in each electrode  20 ,  22 ,  24 ,  26  corresponds to the number of electrode segments  20   a ,  22   a ,  24   a ,  26   a  that will be provided for each electrode. A flexible conductor (not illustrated in  FIG. 2 ) will be coupled within each groove  20   b ,  22   b ,  24   b ,  26   b , thereby provided independent electrical access to each electrode segment  20   a ,  22   a ,  24   a ,  26   a.    
     Electrode assembly  30  can be formed in a variety of way consistent with the embodiments. For example, electrode assembly  30  can be formed by machining, metal injection molding, 3-D printing and/or metal screen printing. Fabrication of electrode assembly  30  in this way simplifies the manufacturing process and provides precise and consistent electrodes. Forming electrode assembly  30  as a single part, with electrodes  20 ,  22 ,  24 ,  26  coupled together with coupling segments  32  also ensures that precise spacing between adjacent electrodes is maintained in the final lead  10 , which can be important in many applications. 
     Electrode assembly  30  is illustrated in  FIG. 3  coupled to a plurality of flexible conductors  40 . Strut  50  is illustrated exploded away from electrode assembly  30 . In one embodiment, a flexible conductor  42 ,  44 ,  46 ,  48  is placed in each groove  20   b ,  22   b ,  24   b ,  26   b  of each electrode  20 ,  22 ,  24 ,  26 . For example, where each electrode  20 ,  22 ,  24 ,  26  includes four grooves  20   b ,  22   b ,  24   b ,  26   b , the plurality of flexible conductors  40  includes a total of  16  flexible conductors. Once the plurality of flexible conductors  40  are coupled within the respective grooves  20   b ,  22   b ,  24   b ,  26   b , strut  50  is placed within electrode assembly  30 , thereby supporting the plurality of flexible conductors  40  between strut  50  and electrode assembly  30 . 
       FIG. 4  illustrates strut  50  assembled within electrode assembly  30 . In one embodiment, strut  50  is provided with a stop  53  and a plurality of helical channels  52 . During assembly, strut  50  is inserted into electrode assembly  30  up to stop  53 , such that stop  53  is adjacent electrode  20  as illustrated in  FIG. 4 . Stop  53  ensures proper axial alignment of strut  50  within electrode assembly  30 , such that the length of strut  50  extends within each of electrodes  20 ,  22 ,  24 ,  26  and supports the plurality of flexible conductors  40  therein. In one embodiment, strut  50  is also provided with a center lumen  51 , illustrated in  FIG. 5 , where stop  53  is removed to reveal center lumen  51  and the plurality of helical channels  52  in the end view. 
     In one embodiment where  16  flexible conductors make up the plurality of flexible conductors  40 , four helical channels  52  are provided in strut  50 . In this way, each flexible conductor  42 ,  44 ,  46 ,  48  that is coupled to a groove  20   b ,  22   b ,  24   b ,  26   b  is then placed into a helical channel  52  of strut  50 . Each channel  52  is configured to accommodate up to four flexible conductors. For example, each of the four flexible conductors  42  coupled within the four grooves  20   b  of first electrode  20  are each placed in one of the four channels of strut  50 . Then, moving down the length of electrode assembly  30 , four more flexible conductors  44  that are coupled within the four grooves  22   b  of second electrode  22  are each placed in one of the four channels of strut  50  adjacent the flexible conductors from second electrode  22 . Again, moving down the length of electrode assembly  30 , four more flexible conductors  46  that are coupled within the four grooves  24   b  of third electrode  24  are each placed in one of the four channels of strut  50  adjacent the flexible conductors from first and second electrodes  20  and  22 . Finally, once flexible conductors  48  are coupled to fourth electrode  24 , there will be four flexible conductors in each of the four channels  52  of strut  50 . As such, each of the flexible conductors are well supported during subsequent molding processes and during use of lead  10 . 
     In one embodiment, the plurality of flexible conductors  40  are secured to electrodes  20 ,  22 ,  24 ,  26  using wedges  20   c ,  22   c ,  24   c ,  26   c , as illustrated in  FIG. 5  (not all wedges are shown for simplification of the figure). Once a flexible conductor is placed in a groove, such as groove  20   b  illustrated in  FIG. 5 , wedge  20   c  is then placed within groove  20   b  over the flexible conductor  42 , thereby securing flexible conductor  42 . In one embodiment, wedge  20   c  is of the same material as electrode  20  and can be resistance or laser welded into place. 
     Because the plurality of flexible conductors  40  are supported by strut  50  and secured to electrodes  20 ,  22 ,  24 ,  26 , flexible conductors are wires or cables that are flexible and easily threaded up into electrodes  20 ,  22 ,  24 ,  26 , thereby simplifying the manufacturing process. In some previous designs, hypotubes, or stiff metal tubes were welded to the inner periphery of electrodes. Using the stiff metal tubes complicates both the assembly and the welding process.  FIG. 6A  illustrates an end view of first electrode  20  with wedges  20   c  secured within each of four grooves  20   b  on the outer periphery of electrode  20 . Flexible conductors  42  are illustrated firmly secured under each of wedges  20   c . Strut  50  is also illustrated within electrode  20 . For illustration purposes, stop  53  is removed so that four helical channels  52  are illustrated, each one for supporting one of the four flexible conductors  42  secured within grooves  20   b . Strut  50  supporting the plurality of flexible conductors  40  in this way minimizes strain on the flexible conductors and secures during subsequent molding processes, as will be further discussed. 
     Once each of flexible conductors  42  are secured within grooves  20   b , electrode  20  is then ground from its outer periphery inward to grind line  60  in order to define electrode segments  20   a . In one embodiment, a centerless grinding process is used to grind down to grind line  60 . In its original configuration as part of electrode assembly  30 , electrode  20  includes openings  62  along its inner periphery. As electrode  20  is ground down to grind line  60 , openings  62  are then exposed in the post-grind outer periphery of electrode  20 , thereby defining electrode segments  20   a.    
       FIG. 6B  illustrates electrode  20  after the grinding process. For each of electrode segments  20   a  defined between openings  62 , flexible conductors  42  are embedded and secured between the outer periphery  21  and inner periphery  19  of electrode segments  20   a . Furthermore, each electrode segment  20   a  is electrically isolated from each other segment by opening  62  and can be individually accessed via each of the four flexible conductors  42 .  FIGS. 6A and 6B  illustrate the processing of electrode  20  before and after grinding, but processing the other electrodes  22 ,  24  and  26  is directly analogous. The number of openings  62  provided in the electrodes  20 ,  22 ,  24 ,  26  of electrode assembly  30  determines the number of electrode segments that will be defined after grinding. Although four openings are illustrated, two, three, four or five openings can be provided to respectively define two, three, four or five electrode segments  20   a . The number of flexible conductors  42  provided also matches the number of electrode segments  20   a  so that each can be independently accessed. 
     In one embodiment, the centerless grinding process can be done before the electrode assembly is molded, and in another embodiment, the centerless grinding process is done after the assembly is molded.  FIG. 7A  illustrates the later embodiment, where strut  50  assembled within electrode assembly  30  and coupled to the plurality of flexible conductors  40  (such as illustrated in  FIG. 4 ), is placed within injection mold  75 . Injection mold  75  includes mold cavity  75   b , in which electrode assembly  30  is placed, and mold gates  75   a . Once mold cavity  75   b  is closed against its mirror image cavity (not illustrated), molding material, such as thermoplastic or elastomer insulation, is flowed into cavity  75   b  via mold gates  75   a . The mold material fills all spaces within electrode assembly  30 , including filing around the combination of strut  50  and the plurality of flexible conductors  40  between each of the electrodes  20 ,  22 ,  24 ,  26 , and also filing any small spaces within each of electrodes  20 ,  22 ,  24 ,  26 . Because the plurality of flexible conductors  40  are supported within strut  50 , they are not significantly disturbed by the force with which the mold material enters cavity  75   b , and are instead supported and held in place between strut  50  and within each of electrodes  20 ,  22 ,  24 ,  26 . 
     After the mold material solidifies, the entire assembly is removed and centerless ground to form lead  10 , as illustrated in  FIG. 1 . Molding material fills the spaces between each of electrode segments  20   a ,  22   a ,  24   a ,  26   a  such that each is electrically isolated from each other by the insulative molding material. Each of the plurality of flexible conductors  40  are surrounded and firmly secured with the molding material. 
     When an elastomer is used as the mold material, lead  10  has some flexibility, which is useful in some applications, such as where lead  10  is incorporated into a catheter configured to navigate the tortuous vasculature of a human body. In such case, the helical configuration of the strut  50 , with the plurality of flexible conductors  40  following the helical configuration, allows relief to the flexible conductors as the lead  10  bends as it moves through the vasculature. If the flexible conductors are all aligned parallel, rather than twisted around the helical configuration, too much bending can cause too much strain on the flexible conductors. 
       FIG. 7B  illustrates further processing of lead  10  in accordance with one embodiment. As illustrated, each of electrodes  20 ,  22 ,  24 ,  26  have been ground to define a plurality of electrode segments  20   a ,  22   a ,  24   a ,  26   a  (four segments in the illustrated example, although only three are visible in the view). Four each of flexible conductors  42 ,  44 ,  46 ,  48  are respectively embedded in electrode segments  20   a ,  22   a ,  24   a ,  26   a  such that the plurality of flexible conductors  40  include a total of  16 . Each of the plurality of flexible conductors  40  are secured within the helical channels  52  of strut  50 . In order to further illustrate the internal portions of lead  10 , all molding material has been removed from the illustration. 
     With the centerless grinding process, in addition to removing an outer periphery of each of electrodes  20 ,  22 ,  24 ,  26 , the grinding also removes each of the coupling segments  32  between the electrodes. The axial location of each of the electrodes relative to each other, however, is maintained by strut  50 , which is secured within electrode assembly  30  before the grinding process. Strut  50  within electrode assembly  30  is configured to extend through each of electrodes  20 ,  22 ,  24 ,  26  and thereby constrain the axial distance and axial orientation of each of the electrodes  20 ,  22 ,  24 ,  26  even after the coupling segments  32  have been ground away. 
     In one embodiment, lead  10  also includes marker bands  72  and  74 . Marker bands are useful in locating lead  10  once inserted in a human body via magnetic imaging. Accordingly, by locating the marker bands, the axial location and orientation of the electrode segments  20   a ,  22   a ,  24   a ,  26   a  can be determined. 
       FIG. 8  illustrates strut  80  in accordance with one embodiment. Strut  80  is analogous to strut  50  illustrated in  FIG. 4 . In one embodiment, strut  80  includes a stop  90 , a center lumen  81 , and four ribs  82 ,  84 ,  86 ,  88 , thereby defining four channels  83 ,  85 ,  87 ,  89 , each channel defined between two adjacent ribs. In one embodiment, multiple flexible conductors from a plurality of flexible conductors  120  can be placed in each channel  83 ,  85 ,  87 ,  89 , in order to support and maintain the position of the flexible conductor, and isolate flexible conductors in one channel from those in other channels. 
       FIG. 9  illustrates an electrode assembly  110  coupled over strut  80  with a plurality of flexible conductors  120  coupled thereto. As with the electrode assembly  30  previously described, electrode assembly  110  includes first, second, third and fourth electrodes  100 ,  102 ,  104 ,  106 , which are coupled over strut  80 . In one embodiment, each of electrodes  100 ,  102 ,  104 ,  106  will be segmented with a centerless grinding process to form four electrode segments each. In other embodiments, two, three or five segments are possible for each electrode. In the illustrated embodiment with four electrode segments, each electrode  100 ,  102 ,  104 ,  106  couple with four flexible conductors—one connected to each of its segments, as will be more fully described. As such, strut  50  accommodates four flexible conductors in each of its four channels  83 ,  85 ,  87 ,  89  between each of its four ribs  82 ,  84 ,  86 ,  88 , thereby supporting the plurality of flexible conductors  120  between strut  80  and electrodes  100 ,  102 ,  104 ,  106 . 
     During assembly, strut  80  is inserted into electrode assembly  110  up to stop  90 , such that stop  90  is adjacent electrode  106  as illustrated in  FIG. 9 . Stop  90  ensures proper axial alignment of strut  80  within electrode assembly  110 , such that the length of strut  80  extends within each of electrodes  100 ,  102 ,  104 ,  106  and supports the plurality of flexible conductors  120  therein, and separates them into channels  83 ,  85 ,  87 ,  89 . In one embodiment, strut  80  is also provided with a center lumen  81 , illustrated in  FIG. 8 . 
       FIG. 10  illustrates an end view of the electrode assembly  110  and strut  80  from  FIG. 9 . Electrode  100  includes openings  92 . In one embodiment, four openings  92  are provided so that four electrode segments  110   a  are defined by the grinding process. As previously described relative to electrode assembly  30  and strut  50 , electrode assembly  110  and strut  80  are ground from the periphery down to grind line  125 . This grinding exposes openings  92 , thereby defining electrode segments  100   a , each of which are electrically isolated from each other by openings  92 . Each on openings  92  are filled with molding material by the molding process described above relative to electrode assembly  30 . 
     Electrode  100  also includes notches  115 . Notches  115  provide a flexible conductor retaining feature, analogous to that provided by grooves  20   b ,  22   b ,  24   b ,  26   b  in electrode assembly  30 , which facilitates attaching one flexible conductor of the plurality of flexible conductors  120  to each electrode segment  100   a.    
       FIG. 11  illustrates a more detailed view of a portion of electrode assembly  110 , and connections between the plurality of flexible conductors  120  and electrode segments  106   a . The electrode assembly  110  illustrated is after a grinding process, such that electrode segments  106   a  have been defined, and molding material is either not yet added or has been removed for illustration purposes. Each electrode segment  106   a  includes a shoulder  125 . Notches  115  are provided in shoulder  125  for each electrode segment  106   a . Accordingly, four flexible conductors  121  of the plurality of flexible conductors  120  are attached to the four notches  115 , one for each of the four electrode segments  106   a.    
     In one embodiment, each flexible conductor  121  includes a bend at its end  130 , such that it is more readily inserted into notch  115  and can easily be welded into place. In one embodiment, the bend at end  130  is approximately 90 degrees. Flexible conductors  121  are fed through channels  83 ,  85 ,  87 ,  89  and up to one of the electrodes. The bend at the flexible conductor end  130  is then placed into notch  115  and welded there, for example, resistance or laser welded. As illustrated in  FIG. 11 , each flexible conductor  121  coupling to each electrode segment  106   a  is in a separate channels  83 ,  85 ,  87 ,  89 , and thus, separated from each other by a rib  82 ,  84 ,  86 ,  88 . This affords management of the plurality of flexible conductors  120  and streamlines the assembly process and avoids confusing flexible conductors  121 . Furthermore, each of the flexible conductors are well supported during subsequent molding processes and during use of lead  10 . 
     Once all flexible conductors are attached to electrode segments  100   a ,  102   a ,  104   a ,  106 , the assembly is placed in a mold, such as mold  75  in  FIG. 7A  and overmolded as previously described. After the mold material solidifies, the entire assembly is removed and centerless ground to form lead  10 , as illustrated in  FIG. 1 . As with previous designs, the centerless grinding process can be done before the electrode assembly is molded, or the centerless grinding process may be done after the assembly is molded. 
       FIG. 12  illustrates strut  150  in accordance with one embodiment. Strut  150  is analogous to struts  50  and  80  previously described and can be used in any of the previous embodiments. In one embodiment, strut  150  further includes positioning arms  162 ,  164 ,  166 ,  168 . Each positioning arm is configured with a catch  162   a ,  164   a ,  166   a ,  168   a . Strut  150  may be used as strut  50  or  80  described previously, but also provide additional positioning of electrodes. For example, any of electrode  20 ,  22 ,  24 ,  26  in  FIG. 2  can be fed over strut  150  and snapped into place via positioning arms  162 ,  164 ,  166 ,  168  and catches  162   a ,  164   a ,  166   a ,  168   a . First electrode  20  can be moved over each of the positioning arms  162 ,  164 ,  166 ,  168  and snapped into place in fourth positioning arm  168 . Catch  168   a  will then engage a feature in electrode  20  such that it cannot be moved back in the direction from which it was assembled. The next three electrodes  22 ,  24 ,  26  can be assembled over the three remaining positioning arms  162 ,  164 ,  166  in the same way. 
     In preventing back movement of each electrode, positioning arms  162 ,  164 ,  166 ,  168  and catches  162   a ,  164   a ,  166   a ,  168   a  ensure that each electrode is precisely positioned along the length of strut  150  correctly and ensures that the relative distance between each electrode is precisely controlled. This is important in many applications where positioning of the electrode segment relative to tissue in the human body must be very precise. Also, catches  162   a ,  164   a ,  166   a ,  168   a  preventing backward movement along the length of strut  150  is useful during the injection molding process. Even where significant flow forces are generated by molten molding material moving into the mold cavity, catches  162   a ,  164   a ,  166   a ,  168   a  prevent electrodes from being moved axially by these forces. 
       FIG. 13  illustrates an electrode  200  in accordance with one embodiment. Electrode  200  is analogous to those previously described and can be used in any of the previous embodiments. Electrode  200  includes grooves  202  and openings  204 . In the Figure, four grooves  202  and openings  204  are illustrated, but other amounts, for example, two, three or five, are possible. In each groove  202 , sleeve  210  is provided over a flexible conductor. Sleeve  210  helps facilitate a good connection between the plurality of flexible conductors  40 ,  120  and electrode  200 . 
     Although only a single sleeve  210  is illustrated in  FIG. 13  for ease of illustration, in assembly of lead  10  a sleeve  210  is inserted in each of the four grooves  202 . In one embodiment, each flexible conductor is inserted into a sleeve  210  and then a crimp  210   a  is made on sleeve  210  to secure the flexible conductor within sleeve  210 . Once the flexible conductor is secure within sleeve  210 , sleeve  210  is placed within groove  202  and can be welded into place. In one embodiment, sleeve  210  is welded at each of its ends. 
       FIG. 14  illustrates an electrode  220  in accordance with one embodiment. Electrode  220  is analogous to those previously described and can be used in any of the previous embodiments. Electrode  220  includes grooves  222  and openings  224 . In the Figure, four grooves  222  and openings  224  are illustrated, but other amounts, for example, two, three or five, are possible. In each groove  222 , sleeve  242  is provided over a flexible conductor. Sleeve  242  helps facilitate a good connection between the plurality of flexible conductors  40 ,  120  and electrode  220 . 
     Although only a single sleeve  242  is illustrated in  FIG. 14  for ease of illustration, in assembly of lead  10  a sleeve  242  is inserted in each of the four grooves  222 . In one embodiment, each flexible conductor is inserted into a sleeve  242  and then a crimp is made on sleeve  242  to secure the flexible conductor within sleeve  242 . Once the flexible conductor is secure within sleeve  242 , sleeve  210  is slid into groove  222  and can be welded into place. In one embodiment, sleeve  242  is welded at its end. 
       FIG. 15  illustrates various embodiments of sleeves  210 ,  240 ,  242 ,  244  over flexible conductors  210   a ,  240   a ,  242   a ,  244   a  for use in the electrodes previously described. As illustrated, sleeves  210 ,  240 ,  242 ,  244  for use in electrodes, such as electrodes  200 ,  220  illustrated in  FIGS. 13-14 , can be of various configurations. Sleeve  210  is generally cylindrical and over flexible conductor  210   a , similar to that illustrated in groove  202  of  FIG. 13 . Sleeve  242  is also generally cylindrical with a longitudinal slot along its length. Sleeves  240  and  244  are generally rectangular, sleeve  244  being closed and sleeve  240  has an open slot. Each of sleeves  210 ,  240 ,  242 ,  244  can include a crimp over flexible conductors  210   a ,  240   a ,  242   a ,  244   a  to ensure the respective sleeve tightly retains the flexible conductor. Each sleeve can then be welded into the respective groove of an electrode. 
       FIGS. 16A and 16B  illustrate side and perspective views of lead  310  in accordance with one embodiment. Lead  310  includes four electrodes  320 ,  322 ,  324 ,  326  out toward its distal tip  312 . Each of the four electrodes  320 ,  322 ,  324 ,  326  are segmented such that each has independently accessible electrode segments  320   a ,  322   a ,  324   a ,  326   a . In the illustrated embodiment, each of the electrode segments  320   a ,  322   a ,  324   a ,  326   a  are radially aligned. For example, each electrode segment  320   a  of electrode  320  is aligned with each electrode segment  322   a  (and the other segments  324   a ,  236   a ), such that their edges lie on a continuous straight line along the length of lead  310 . This configuration may be useful in certain application for ensuring proper location of the electrode segments relative to tissue that is being stimulated or sensed. 
       FIGS. 17A and 17B  illustrate side and perspective views of lead  410  in accordance with one embodiment. Lead  410  includes four electrodes  420 ,  422 ,  424 ,  426  out toward its distal tip  412 . Each of the four electrodes  420 ,  422 ,  424 ,  426  are segmented such that each has independently accessible electrode segments  420   a ,  422   a ,  424   a ,  426   a . In the illustrated embodiment, each of the electrode segments  420   a ,  422   a ,  424   a ,  426   a  are radially offset. For example, each electrode segment  420   a  of electrode  420  is radially rotated slightly relative to each electrode segment  422   a  (and the other segments  324   a ,  236   a ), such that none of their edges lie in a straight line along the length of lead  310 . This configuration may be useful in certain application for accessing certain locations of the electrode segments relative to tissue that is being stimulated or sensed. 
       FIG. 18  illustrates a method of forming a segmented electrode lead, such as leads  10 ,  310  and  410  in accordance with one embodiment. First, at step  502 , an electrode assembly, such as previously described is formed. The electrode assembly may be formed by any of a variety of processing, including machining, metal injection molding, 3-D printing and/or metal screen printing. The formed electrode assembly has a plurality of electrodes, for example, two, three, four or five. In one embodiment, each of the electrodes in the electrode assembly are each configured with opening and grooves. The grooves are useful in coupling conductors and the openings will define electrode segments. 
     At step  504 , a plurality of flexible conductors are attached to each of the plurality of electrodes. In one embodiment, a single flexible conductor is attached to each portion of each electrode that will be formed into an electrode segment. For example, if an electrode will be formed into three electrode segments, then three flexible conductors will be attached to that electrode, one flexible conductors connected at each of the segments. In one embodiment, a single flexible is coupled in each groove provided in the electrodes. 
     At step  506 , the plurality of flexible conductors are arranged relative to a strut. In some embodiments, the flexible conductors are helically wrapped in channels of the strut. In other embodiments, the flexible conductors are sorted into separate channels of the strut. Once the flexible conductors are arranged, the strut is inserted into the electrode assembly, such that the strut is within each of the electrodes in the assembly. 
     At step  508 , the combination of the flexible conductors, the strut and the electrode assembly are placed into a mold cavity, and molding material is injected into the cavity. Gaps between the flexible conductors, the strut and the electrode assembly are filled with the molding material, which is allowed to solidify. 
     At step  510 , the molded electrode assembly is ground inward from its outer periphery. In one embodiment, a centerless grinding process is used to grind the molded electrode assembly down to a grind line that exposed the openings that are formed in each electrode. In so doing, each electrode is segmented, such that a plurality of electrode segments are defined wherein each is electrically isolated from each other. 
     The various described steps are not necessarily required in a particular order. For example, a centerless grinding process may be applied to the combination of the flexible conductors, the strut and the electrode assembly before the combination is placed into a mold cavity. The injection molding process can then be the last step in producing the finished lead. 
     Although specific embodiments have been illustrated and described herein, it will be appreciated by those of ordinary skill in the art that a variety of alternate and/or equivalent implementations may be substituted for the specific embodiments shown and described without departing from the scope. This application is intended to cover any adaptations or variations of the specific embodiments discussed herein. Therefore, it is intended that these embodiments be limited only by the claims and the equivalents thereof.