Abstract:
In one embodiment, a method of fabricating a stimulation lead for stimulation of tissue of a patient, the method comprises: providing a plurality of cables, wherein each of the cables comprises a plurality of wires twisted about a core support and disposed within an outer sheath, wherein each of the plurality of wires comprises a coating of insulative material to electrically isolate each wire from each other wire within the respective cable, each of the plurality of wires being disposed in a single layer circumferentially about a central axis of the respective cable; wrapping the plurality of cables about a central core in a helical manner to form a cable assembly.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Application No. 61/267,275, filed Dec. 7, 2009, which is incorporated herein by reference. 
     
    
     TECHNICAL FIELD 
       [0002]    This application is generally related to a stimulation lead for stimulation of tissue of a patient and a method of fabricating the same. 
       BACKGROUND 
       [0003]    Neurostimulation systems are devices that generate electrical pulses and deliver the pulses to nerve tissue to treat a variety of disorders. Spinal cord stimulation (SCS) is the most common type of neurostimulation. In SCS, electrical pulses are delivered to nerve tissue in the spine typically for the purpose of chronic pain control. Applying electrical energy to the spinal cord associated with regions of the body afflicted with chronic pain can induce “paresthesia” (a subjective sensation of numbness or tingling) in the afflicted bodily regions which can effectively mask the transmission of non-acute pain sensations to the brain. 
         [0004]    Neurostimulation systems generally include a pulse generator and one or more leads. The pulse generator is typically implemented using a metallic housing that encloses circuitry for generating the electrical pulses, control circuitry, communication circuitry, a rechargeable battery, etc. The pulse generating circuitry is coupled to one or more stimulation leads through electrical connections provided in a “header” of the pulse generator. 
         [0005]    Each stimulation lead includes a lead body of insulative material that encloses wire conductors. The distal end of the stimulation lead includes multiple electrodes that are electrically coupled to the wire conductors. The proximal end of the lead body includes multiple terminals, which are also electrically coupled to the wire conductors, that are adapted to receive electrical pulses. The distal end of a respective stimulation lead is implanted at the location adjacent or within the tissue to be electrically stimulated. The proximal end of the stimulation lead is connected to the header of the pulse generator or to an intermediate “extension” lead. 
         [0006]    In certain cases, it is desirable to use a larger number of conductor wires within the lead body to permit the use of a larger number of electrodes. For example, deep brain stimulation leads may employ multiple groups of segmented electrodes disposed axially from the distal tip of the stimulation lead. The segmented electrodes enable greater directional control of the stimulation field. Also, cortical leads and paddle leads may employ larger numbers of electrodes. 
         [0007]    Fabrication of lead bodies with larger numbers of conductor wires can be a relatively complex process. In one known fabrication process, a first layer of conductor wires are wound about a mandrel and, then, a second layer of conductor wires are wound about the first layer to form the lead body of the stimulation lead. During the wire winding process, insulative material is provided to embed the conductor wires. Electrode attachment occurs by exposing individual conductor wires by removing insulative material from the lead body. However, exposing an individual conductor wire within the interior layer without exposing any of the other wires can be challenging and time consuming. Accordingly, manufacturing costs can be excessive and manufacturing yields can be less than optimal. 
       SUMMARY 
       [0008]    In one embodiment, a method of fabricating a stimulation lead for stimulation of tissue of a patient, the method comprises: providing a plurality of cables, wherein each of the cables comprises a plurality of wires twisted about a core support and disposed within an outer sheath, wherein each of the plurality of wires comprises a coating of insulative material to electrically isolate each wire from each other wire within the respective cable, each of the plurality of wires being disposed in a single layer circumferentially about a central axis of the respective cable; wrapping the plurality of cables about a central core in a helical manner to form a cable assembly, wherein during the wrapping each cable of the plurality of cables is rotated so that each wire of a respective cable is disposed at an exterior surface of the cable assembly at respective axial positions of the cable assembly; providing an outer insulative layer over the cable assembly; forming a lead body assembly from the cable assembly; and fabricating a plurality of electrodes and terminals that are electrically coupled to wires of the plurality of cables of the lead body assembly to form a stimulation lead. 
         [0009]    The foregoing has outlined rather broadly certain features and/or technical advantages in order that the detailed description that follows may be better understood. Additional features and/or advantages will be described hereinafter which form the subject of the claims. It should be appreciated by those skilled in the art that the conception and specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the appended claims. The novel features, both as to organization and method of operation, together with further objects and advantages will be better understood from the following description when considered in connection with the accompanying figures. It is to be expressly understood, however, that each of the figures is provided for the purpose of illustration and description only and is not intended as a definition of the limits of the appended claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1  depicts a process for fabricating a stimulation lead according to one representative embodiment. 
           [0011]      FIG. 2  depicts a stainless steel mandrel for use in the process of  FIG. 1 . 
           [0012]      FIG. 3  depicts a portion of a lead body in a side view according to one representative embodiment. 
           [0013]      FIG. 4  depicts a micro cable for use in fabricating a lead body according to one representative embodiment. 
           [0014]      FIG. 5  depicts a lead body according to one representative embodiment. 
           [0015]      FIG. 6  depicts another lead body according to one representative embodiment. 
           [0016]      FIG. 7A  depicts a stimulation lead according to one representative embodiment. 
           [0017]      FIG. 7B  depicts a stimulation system according to one representative embodiment. 
       
    
    
     DETAILED DESCRIPTION 
       [0018]    In one embodiment, a process for fabricating lead body material for stimulation leads begins with a continuous working material  10  shown in  FIG. 1 . In one embodiment, the working material  10  is a polytetrafluoroethylene (PTFE) coated stainless steel mandrel wire  12  (shown in  FIG. 2 ). Referring again to  FIG. 1 , the working material  10  is then helically wrapped with a set of micro cables  14  at a wire wrapping system  15 . While seven micro cables  14  are used in one embodiment, those skilled in the art will recognize that any suitable number of micro cables  14  may be wrapped onto mandrel  12  according to other embodiments. 
         [0019]    In one preferred embodiment, micro cables  14  are wrapped about working material  10  in an axially repeating pattern of groups  301  of closely spaced wires with each group  301  separated by distance  302  that is larger than the spacing between adjacent wires within each group ( FIG. 3 ). The distance between groups in  FIG. 3  is by way of example and any suitable distance may be employed according to some embodiments. The wrapping of micro cables  14  in this manner may occur using the wire wrapping system disclosed in U.S. Patent Application Ser. No. 61/247,264, entitled “SYSTEM AND METHOD FOR FABRICATING A STIMULATION LEAD,” which is incorporated herein by reference. 
         [0020]    Referring again to  FIG. 1 , in step  18 , an outer sheath is provided over the working material  10  (which now includes the helically wound micro cables  14 ) using any suitable method. Upon provision of the outer sheath of insulative material, working material  10  may now be spooled and later unspooled (not shown) or fed directly to the next step in the process. In the next step, working material  10  may optionally be heated in reflow oven  19 . Micro cables  14  are heated to a temperature that causes insulative material of micro cables  14  to approach or achieve a phase change, thereby becoming soft and adherent and ultimately fusing together, by heating, melting and re-solidifying. 
         [0021]    At this point, the working material  10 , now comprising mandrel  12  having micro cables  14  at least partially fused about it, may now be spooled onto a spool and stored for later work. Continuous working material  10  is cut (step  24 ) into individual lead bodies  21 . Each individual lead body  21  may have a length anywhere from about 10 cm (4 in) to about 150 cm (60 in). 
         [0022]    After the lead bodies  21  have been cut to length, mandrel  12  is removed from within in a mandrel removal step  28 . This task may be facilitated by a coating of mandrel  12  that will ease removal, such as a PTFE coating. The mandrel removal step  28  may be a simple hand operation by a human worker. 
         [0023]    Next, in an electrode creation step  30 , electrodes and terminals are provided on the distal and proximal ends of the lead body, respectively. Any suitable technique or process may be employed to provide the electrodes and terminals. Also, the lead body could alternatively be connected to a paddle structure which holds electrodes in a planar arrangement as is well known in the art. 
         [0024]    Micro cable  14  is shown in greater detail in  FIG. 4 . A length of micro cable  14  is preferably fabricated by using a standard serving process (using any suitable commercially available serving system) to twist stranded wires or other suitable conductors  401  around center support core  402 . Center support core  402  may be a monofilament or a metallic wire as examples. Each conductor  401  may be a stranded wire (e.g. of a diameter of approximately 0.003 inches) coated with a thin coating of insulative material with suitable properties (a perfluoroalkoxy copolymer (PFA), polytetrafluoroethylene, liquid crystal polymer (LCP), etc.). In one embodiment, the coating is perfluoroalkoxyethylene. In one embodiment, five conductors  401  are wound about central support core  402 , although any suitable number of conductors  401  may employed depending upon the total number of conductors selected for the final lead configuration. Outer sheath  403  of insulative material is then provided about the wound conductors  401  (e.g., using an extrusion process). In one embodiment, the diameter of micro cable  14  is approximately 0.012 inches. The length of micro cable  14  is then cut into separate segments and wound onto respective spools. 
         [0025]      FIG. 5  depicts lead body assembly  500  according to one representative embodiment. In this embodiment, seven micro cables  14  are helically wound about inner wall  501  of insulative material, although any suitable number could be employed. As depicted in  FIG. 5 , each conductor  401  within each micro cable  14  is twisted so that the conductors  401  rotate with each micro cable  14  to expose a different conductor  401  at each different axial position along lead body  500 . That is, a different conductor  401  within each micro cable  14  is closest to exterior insulative sheath  502  at different axial positions along lead body  500 . This is achieved by using a suitable wire wrapping system to twist conductors  401  about central support core  402 . Also, as shown in  FIG. 5 , gap  503  is provided that is empty of micro cables  14 . The presence of gap  503  facilitates the elongation of lead body  500  according to some embodiments. 
         [0026]    In one embodiment, the diameter of lead body  500  is approximately 0.055 inches which is approximately equal to the diameter of commercially available neurostimulation leads. However, lead body  500  encloses 35 conductors for connection to electrodes and terminals, which is considerably larger than known commercially available neurostimulation leads adapted for long term implantation. Also, because each conductor  401  within each micro cable  14  is located near the surface of lead body  500  at various points, access to each conductor  401  for electrode and terminal fabrication is relatively straight forward and only involves removal of a small amount of insulation from sheath  502  (i.e., it is not necessary to ablate through insulative material to a separate interior layer). In some embodiments, different visual characteristics (e.g., different colors) may be employed to permit an operator to distinguish between respective conductors  401  within each cable  14 . 
         [0027]    The dimensions for lead body  500  and components thereof are by way of example. Other suitable dimensions may be employed. Also, other configurations of conductor  401  and micro cables  14  may be employed. For example, 4 conductor/8 micro cables or 6 conductor/6 micro cables may be selected for other embodiments. 
         [0028]    Further, in some embodiments, lead body  500  is fabricated such that lead body  500  is capable of elastic elongation under relatively low stretching forces. Also, after removal of the stretching force, lead body  500  is capable of resuming its original length and profile. For example, in one embodiment, relatively low durometer, elastic polymer material (e.g. CARBOSIL™) is used for inner wall  501  and outer sheath  502 . The combination of the selection of the insulative materials, the helically wrapping of the micro cables, and the repeating groups of micro cables with separating gaps enables the stretching according to the relatively low stretching forces. For example, the lead body may stretch 10%, 20%, 25%, 35%, or even up to 50% at forces of about 0.5, 1.0, and/or 2.0 pounds of stretching force. For additional description of a lead body capable of elastic elongation, reference is made to U.S. Patent Publication No. 2007/0282411, entitled “COMPLIANT ELECTRICAL STIMULATION LEADS AND METHODS OF FABRICATION,” which is incorporated herein by reference. 
         [0029]      FIG. 6  depicts lead body  600  according to one representative embodiment. Lead body  600  is substantially similar to lead body  500  except that in lieu of gap  503 , lead body  600  includes a plurality of elastic spacer threads  601  wound about inner wall  501  with micro cables  14 . The elastic spacer threads facilitate the elastic characteristics of lead body  600  while ensuring that micro cables  14  remain in their respective angular positions within lead body  600 . The elastic spacer threads may be subsequently fused with the insulative material of inner wall  501  and outer sheath  502  using suitable application of heat and, optionally, pressure to form a uniform fused matrix of insulative material enclosing conductors  401  according to some embodiments. 
         [0030]      FIG. 7A  depicts cortical paddle lead  775  according to one representative embodiment. Cortical paddle lead  775  comprises a relatively large number of electrodes  701  disposed on paddle structure  702 . The larger number of electrode sites for selection by a clinician may be beneficial for cortical stimulation in which targeting the appropriate cortical tissue can be challenging. Electrodes  701  are electrically coupled to terminals  703  through the conductors  401  (not shown in  FIG. 7 ) of lead body  500  (or any other lead body according to some representative embodiments). Although a cortical paddle is shown in  FIG. 7A , any suitable stimulation lead for stimulation of tissue of a patient may utilize lead bodies according to some representative embodiments. For example, spinal cord stimulation leads, deep brain stimulation leads, peripheral nerve stimulation leads, cardiac leads may employ lead bodies according to some embodiments described herein. Also, any suitable number and arrangement of electrodes may be employed according to other embodiments. For example, ring electrodes or segmented electrodes may be disposed about the outer diameter of lead body  500  in lieu of being disposed on paddle structure  702 . 
         [0031]      FIG. 7B  depicts stimulation system  700  according to one representative embodiment. Neurostimulation system  700  includes pulse generator  720  and one or more stimulation leads  775 . Pulse generator  720  is typically implemented using a metallic housing that encloses circuitry for generating the electrical pulses for application to neural tissue of the patient. Control circuitry, communication circuitry, and a rechargeable battery (not shown) are also typically included within pulse generator  720 . Pulse generator  720  is usually implanted within a subcutaneous pocket created under the skin by a physician. 
         [0032]    Lead  775  is electrically coupled to the circuitry within pulse generator  720  using header  710 . Lead  775  includes terminals  703  (shown in  FIG. 7A ) that are adapted to electrically connect with electrical connectors (e.g., “Bal-Seal” connectors which are commercially available and widely known) disposed within header  710 . The terminals  703  are electrically coupled to conductors (not shown in  FIG. 7B ) within lead body  500  of lead  775 . The conductors conduct pulses from the proximal end to the distal end of lead  775 . The conductors are also electrically coupled to electrodes  701  to apply the pulses to tissue of the patient. Lead  775  can be utilized for any suitable stimulation therapy. An “extension” lead (not shown) may be utilized as an intermediate connector if deemed appropriate by the physician. 
         [0033]    Pulse generator  720  preferably wirelessly communicates with programmer device  750 . Programmer device  750  enables a clinician to control the pulse generating operations of pulse generator  720 . The clinician can select electrode combinations, pulse amplitude, pulse width, frequency parameters, and/or the like using the user interface of programmer device  750 . The parameters can be defined in terms of “stim sets,” “stimulation programs,” (which are known in the art) or any other suitable format. Programmer device  750  responds by communicating the parameters to pulse generator  720  and pulse generator  720  modifies its operations to generate stimulation pulses according to the communicated parameters. 
         [0034]    Although certain representative embodiments and advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the appended claims. Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, composition of matter, means, methods and steps described in the specification. As one of ordinary skill in the art will readily appreciate when reading the present application, other processes, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed that perform substantially the same function or achieve substantially the same result as the described embodiments may be utilized. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps.