Abstract:
In one embodiment, a system for wrapping biomedical conductor wires about core material, comprises: a payout assembly and a take-up assembly for controllably paying out the core material and taking up the core material with the wrapped conductor wires; a turntable; a plurality of carriers, disposed on the turntable, for letting out the conductor wires; and a die for applying force to the conductor wires as the wires are wrapped about the core material, the die adapted to rotate according to group rotation of the plurality of carriers by the turntable during operation of the system, wherein the die comprises one or more features asymmetrically arranged about a circumference of the die, the one or more features adapted to direct the conductor wires from the plurality of carriers onto the core material in an axially repeating pattern of groups of closely spaced wires with each group separated by a distance larger than the spacing between adjacent wires within each group.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 61/247,264, filed Sep. 30, 2009, which is incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     This application is generally related to a system for wrapping conductor wires about core material for fabrication of a stimulation lead and a method of fabricating a stimulation lead for stimulation of tissue of a patient. 
     BACKGROUND 
     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. 
     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. 
     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 to the pulse generator or to an intermediate “extension” lead. 
     The manufacture of stimulation leads is a relatively complex process. Some manufacturing techniques involve wrapping conductor wires with insulative coatings about a mandrel in a helically manner. An example of a system adapted to perform such winding is shown in U.S. Pat. No. 7,287,366, entitled “Method for producing a multielectrode lead,” which is incorporated herein by reference. The system described in the &#39;366 patent draws a mandrel through wire wrapping structure. As the mandrel is drawn into a spool, conductor wires are let out in controlled manner by a plurality of “payout carriers.” The plurality of payout carriers are rotated as a group about the mandrel. Also, each payout carrier is rotated independently about its own axis to compensate for twist imparted by the group rotation to minimize the amount of residual force left on the wound wires. The final product in the &#39;366 patent is a product with multiple conductor wires wound about the mandrel in helical manner. This product is then cut into separate lengths for fabrication of stimulation leads including attachment of electrodes and terminals. 
     Also, in known wire wrapping systems, force is applied to the wires as the wires are served onto the mandrel to permanently deform or “preform” the wires to maintain the wires around the mandrel when the winding tension is released. The application of force may be implemented using a “winding die.” In operation, the individual wires pass over one or more radii of a circular or toroidal die where the assembly of the wires and the mandrel pass through a center hole of the die. 
     SUMMARY 
     In one embodiment, a system for wrapping biomedical conductor wires about core material, comprises: a payout assembly and a take-up assembly for controllably paying out the core material and taking up the core material with the wrapped conductor wires; a turntable; a plurality of carriers, disposed on the turntable, for letting out the conductor wires; and a die for applying force to the conductor wires as the wires are wrapped about the core material, the die adapted to rotate according to group rotation of the plurality of carriers by the turntable during operation of the system, wherein the die comprises one or more features asymmetrically arranged about a circumference of the die, the one or more features adapted to direct the conductor wires from the plurality of carriers onto the core material in an axially repeating pattern of groups of closely spaced wires with each group separated by a distance larger than the spacing between adjacent wires within each group. 
     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 
         FIG. 1  depicts a process for fabricating a lead body according to one representative embodiment. 
         FIG. 2  depicts a mandrel for use in fabricating a lead body. 
         FIG. 3  depicts a segment of a lead body fabricated according to one representative embodiment. 
         FIG. 4  depicts a wire wrapping system according to one representative embodiment. 
         FIG. 5  depicts a portion of the system shown in  FIG. 4  according to one representative embodiment. 
         FIG. 6  depicts a set of gears for use in the system of  FIG. 4  according to one representative embodiment. 
         FIGS. 7-9  depict a plurality of payout carriers for use in the system of  FIG. 4  according to one representative embodiment. 
         FIG. 10  depicts another view of a wire wrapping system according to one representative embodiment. 
         FIG. 11  depicts a die for use in a wire wrapping system according to one representative embodiment. 
         FIG. 12  depicts another die for use in a wire wrapping system according to one representative embodiment. 
         FIG. 13  depicts another die for use in a wire wrapping system according to one representative embodiment. 
         FIG. 14  depicts another die for use in a wire wrapping system according to one representative embodiment. 
         FIG. 15  depicts a cross-sectional view of lead body assembly  1500  according to one representative embodiment. 
         FIG. 16  depicts a lead body fabricated according to one representative embodiment. 
         FIG. 17  depicts a stimulation lead fabricated according to one representative embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     In one embodiment, a process for fabricating lead body material for stimulation leads begins with a continuous core material  10  shown in  FIG. 1 . In one embodiment, the core material  10  is a polytetrafluoroethylene (PTFE) coated stainless steel mandrel wire  12  (shown in  FIG. 2 ), although additional insulative layers may also be provided according to other embodiments. Referring again to  FIG. 1 , the core material  10  is then helically wrapped with a set of insulated wires  14  at a wire wrapping system  15 . Each of the wires  14  may include one or more layers of insulation. In one embodiment, each wire  14  comprises an inner thin layer of perfluoroalkoxy (PFA) and outer thicker layer of a thermoplastic silicone polycarbonate urethane (e.g., CARBOSIL™). While eight insulated wires are used in one embodiment, those skilled in the art will recognize that any suitable number of wires may be wrapped onto mandrel  12  according to other embodiments. In other embodiments, additional layers of wires  14  may be wound over the initial layer(s) of wires. 
     In one preferred embodiment, wires  14  are wrapped about core 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. 
     Referring again to  FIG. 1 , core material  10 , now comprising mandrel  12  and helically wrapped insulated wires  14  may now be spooled and later unspooled (not shown) or fed directly to the next step in the process. In this next step, core material  10  may be selectively and repeatedly heated in a reflow oven  18 . The wires  14  are heated to a temperature that causes the insulation  16  of insulated wires  14  to approach or achieve a phase change, thereby becoming soft and adherent and ultimately fusing together, by heating, melting and re-solidifying after removal from reflow oven  18 . 
     At this point, the core material  10 , now comprising mandrel  12  having insulated wires  14  at least partially fused about it, may now be spooled (step  19 ) onto a spool and stored for later work. Alternatively, step  19  is not performed and core material  10  proceeds directly to the remaining steps. Continuous core material  10  is cut (step  24 ) into individual lead bodies  21 . Each individual lead body  21  may have a length of from about 10 cm (4 in) to about 150 cm (60 in). 
     After the lead bodies  21  have been cut to length, mandrel  12  must be 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. 
     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. Exemplary electrode and terminal fabrication processes are described in U.S. Pat. No. 6,216,045, entitled “Implantable lead and method of manufacture,” and U.S. Pat. No. 7,039,470, entitled “Medical lead and method for medical lead manufacture,” which are incorporated herein by reference. 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. 
     Wire wrapping system  15  is shown in greater detail in  FIG. 4 . Portions of wire wrapping system  15  are omitted from  FIG. 4  for the sake of clarity. For example, only two wires are shown in  FIG. 4  being wrapped about mandrel  12  and only the corresponding structures for these two wires are shown in  FIG. 4 . It shall be appreciated that the depicted structures may be duplicated in wire wrapping system  15  in a given implementation according to any suitable number of wires selected to be wrapped about mandrel  12 . 
     The wire wrapping process begins with mandrel payout assembly  80  and core material take up assembly  86  that together maintain core material  10  in well regulated motion and tension along its path. Simultaneously, controls and displays assembly  88  controls a power and linkage assembly  82 , which powers a wire payout assembly  84 . Although one preferred embodiment permits the use of a keyboard for user input of control parameters, as indicated in  FIG. 4 , an alternative embodiment provides a simple set of manual controls, such as knobs, for controls and display assembly  88 . 
     Assembly  84  includes turntable  114  upon which a set of payout carriers  112  are supported. Wire wrapping system  15  is configured to permit a variable degree of back twist compensation, which is implemented by rotating carriers  112  relative to turntable  114  at an operator specified rate. In one embodiment, an operator manipulates controls and display assembly  88  to place the right amount of back twist compensation onto wires  14 . In an alternative embodiment, the operator enters the wire and mandrel dimensions and the pitch at which the wires are to be wrapped and control and display assembly  88  computes the degree of back twist compensation necessary to prevent residual stress being placed onto wires  14 . 
     Avoiding the placement of residual stress on wires  14  is important so that this stress does not cause the wires to move spontaneously later in the process, causing a deformation in the final shape of the lead body  10 , or inconsistent wire locations. After wrapping is complete, wrapped mandrel is spooled by core material take up assembly  86 , which maintains a constant tension to avoid deforming the core material  10 . In an alternative preferred embodiment, core material  10  is not spooled but progresses immediately to the next stage of processing (e.g., reflow and fusing of the insulative coating material about wires  14 ). 
     In greater detail, the progress of core material  10  is maintained by the payout assembly  80  and the take up assembly  86 . Payout assembly  80  includes a mandrel payout spool  100 , a payout motor  102 , and a dancer arm tension measurement device (not shown). Motor  102  is responsive solely to the tension measurement, thereby maintaining constant tension on core material  10 . In take up assembly  86 , core material take up spool  105  is also motor driven (not shown) and solely responsive to tension measurement dancer arm  103 . Take up spool  105  is moved cyclically into and out of the plane of  FIG. 4 , thereby causing core material  10  to spool in a repeated pattern. The tension placed on core material  10  can be changed by changing the weighting on either dancer arm  103  or the dancer arm of payout assembly  80 . 
     An additional portion of take up assembly  86  is the capstan  106 , which includes an equal-diameter pair of wheels  108  and  110 , about which core material  10  is looped several times. Each wheel  108  and  110  bears several grooves along its exterior rim, to permit this looping while preventing the core material  10  from ever rubbing against itself. Capstan  106  is driven by an electric motor (not shown) and serves the function of stabilizing core material  10  as it is drawn through the system. 
     As shown in  FIG. 4 , core material  10  passes through the center of die  900 . Wires  14  pass around one or more radii of die  900 . Preferably, die  900  applies force to wires  14  to deform wires  14  for wrapping about core material  10 . As shown in  FIG. 4 , die  900  is held by support struts  902  which are, in turn, coupled to support columns  901 . Support columns  901  are mounted on platform  903 . In one embodiment, platform  903  is mechanically coupled to a drive shaft that is also coupled to turntable  114 . Accordingly, platform  903  and die  900  rotate at the same rate as turntable  114 . In alternative embodiments, die  900  is not mechanically coupled to turntable  114 , but is independently driven to rotate the same rate as turntable  114 . An isometric view of die  900  with support struts  902 , support columns  901 , platform  903 , and turntable  114  is shown in  FIG. 10 . 
     Die  900  is asymmetrically designed so that die  900  causes wires  14  to be wrapped about core material  10  in an axially repeating pattern of groups of closely spaced wires with each group separated by a distance larger than the spacing between adjacent wires within each group (see  FIG. 3 ). 
     In some embodiments, wire wrapping system  15  controls the wire wrap pitch using the ratio between the capstan  106  rotation rate and the turntable  114  rotation rate  96  (which equals the rotation rate of a turntable drive motor  132  ( FIG. 5 )) may be set prior to beginning a wire wrapping run. Likewise the backtwist compensation ratio  96 , which is the ratio of a payout carrier drive motor  134  rate ( FIG. 5 ) to the turntable drive motor  132  rate, may be set at the same time. Then, during operation, the speed of the entire process may be changed by changing the turntable rotation rate command, which changes the capstan  106  turn rate and payout carrier drive motor  134  rate, automatically. In other words, during operation, the capstan  106  drive and the payout carrier drive motor  134  are slaved to the turntable drive motor  132 . The rate of capstan  106  effectively controls the turn rate of take up spool  105  ( FIG. 4 ) and pay out spool  100  ( FIG. 4 ). 
     Referring to  FIGS. 5 and 6 , power and linkage assembly  82  includes an inner shaft  122  which drives the turntable  114 , and an outer shaft  124  which drives the payout carriers  112 , by way of a system of gears  126 . Inner shaft and outer shaft are driven by a first pulley  128  and a second pulley  130 , respectively. Each of these pulleys  128 ,  130  are driven by belts  129  and  131  respectively that are in turn driven by the turntable motor  132  and the payout carrier motor  134 , respectively. 
     The two motors  132  and  134  are managed by the control assembly  88  ( FIG. 4 ), which regulates their relative speed within a range of relative speeds. As noted previously, the turn rate ratio of these two motors is set before a production run is begun. In one preferred embodiment this range extends from equal speed (payout carriers  112  stationary relative to the turntable  114 ) to the case where the outer shaft rotates at one half the speed of the inner shaft (payout carriers  112  stationary relative to an absolute frame of reference). 
     A slip ring  140  (shown in  FIG. 5 ) permits electric power to be transmitted to the rotating inner assembly that includes shafts  122  and  124 . On turn table  114 , each payout carrier  112  includes a slip ring  142  near its base for supplying electricity to the payout carrier  112 . Each payout carrier  112  includes an electric wire tension control assembly  144  that maintains a constant tension on the insulated wire  14  that is being threaded onto core material  10 . Bearing assemblies  150 ,  152 ,  154  and  156  facilitate the rotation of shafts  122  and  124 . Plates  160  and  162  support power and linkage assembly  82 . A spider  164  supports a wire guide wheel  166  for each payout carrier  112 , to further restrain the wires  14  as turntable  114  rotates. 
     Referring to  FIGS. 7-9 , each electric wire tension control assembly  144  includes an electric motor  170  that drives a spool  172 , both of which are mounted on a payout carrier frame  173 . Only four assemblies  144  are depicted in  FIG. 7  for the sake of clarity. Any suitable number of assemblies  144  may be included according to some embodiments. A respective wire  14  follows a path defined by a dancer arm  174  which is rotatably mounted by way of an axle  175  to frame  173 . Dancer arm  174  has a first dancer arm guide wheel  176  and a second dancer arm guide wheel  178  about which wire  14  is threaded in an “S pattern.” Wire  14  proceeds about a frame guide wheel  180  and through a payout carrier exit guide  182 . A dancer arm position measurement unit  184  monitors the position of arm  174  and sends this information to an electric motor controller  186 . Controller  186  commands the rate at which electric motor  170  turns. This arrangement permits control of the tension in wire  14  to an accuracy of about +1%. 
       FIG. 11  depicts die  1101  for wire wrapping system  15  according to one representative embodiment. As shown in  FIG. 11 , die  1101  comprises a plurality of features (only one feature  1102  is annotated for the sake of clarity) asymmetrically arranged about a circumference of an inner surface of die  1101 . In this embodiment, the plurality of features  1102  define a plurality of inner surfaces which form an array of planes that intersect at the central axis of the die. In this embodiment, the features  1102  are equally spaced about a limited arc of the circumference of the inner surface leaving gap  1103  along the circumference. In this embodiment, the features  1102  are equally spaced about the limited arc (about 315° for eight features  1102 ), although other spacings (even or uneven) could be employed. Gap  1103  controls the spacing between respective groups of wires  14  applied to the core material  10 . 
       FIG. 12  depicts die  1201  for wire wrapping system  15  according to one representative embodiment. As shown in  FIG. 12 , die  1201  also comprises a plurality of features asymmetrically arranged about a circumference of an inner surface of die  1201 . In lieu of the features having inner surfaces, die  1201  comprises a plurality of holes  1202  disposed over a limited arc of a circumference of an inner surface of die  1201 . Wires  14  (not shown in  FIG. 12 ) travel through holes  1202  of die  1201  during the wire wrapping process. Die  1201  also comprises gap  1203  to control the spacing between respective groups of wires  14  applied to the core material  10  (not shown in  FIG. 12 ). Also, each hole  1202  comprises an appropriate radii to preform its wire  14  as necessary for the wire wrapping process. 
       FIG. 13  depicts die  1301  for wire wrapping system  15  according to one representative embodiment. As shown in  FIG. 13 , die  1301  also comprises a plurality of features asymmetrically arranged about a circumference of an inner surface of die  1301 . In the case, the plurality of features comprises protrusions  1302  and larger protrusion  1303 . Wires  14  (not shown in  FIG. 13 ) proceed through the slots defined between adjacent ones of protrusions  1302  and  1303 . The size of protrusion  1303  controls the spacing between respective groups of wires  14  applied to the core material  10  (not shown in  FIG. 13 ). The protrusions  1302  and  1303  may be appropriately shaped (e.g., possess appropriate radii) to preform wire  14  as necessary for the wire wrapping process. 
       FIG. 14  depicts die  1401  for wire wrapping system  15  according to one representative embodiment. Die  1401  includes a single feature  1402  over a limited arc of a circumference of an inner surface of die  1401 . Feature  1402  is essentially a tab that extends above the remaining portion of die  1401 . Feature  1402  separates wires  14  (not shown in  FIG. 14 ) to define the spacing between respective groups of wires  14  applied to the core material  10  (not shown in  FIG. 14 ). Wires  14  are otherwise left to find their own angular positions and are preformed as they pass over the radii of die  1401  in a manner similar to conventional dies. 
     In one embodiment, a lead body is fabricated, in part, using wire wrapping system  15  such that the lead body is capable of elastic elongation under relatively low stretching forces. Also, after removal of the stretching force, the lead body is capable of resuming its original length and profile. For example, in one embodiment, relatively low durometer, elastic polymer material is used for the material of the lead body. The combination of the selection of the materials, the helically wrapping of the wires, and the repeating groups of wires 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. 
       FIG. 15  depicts a cross-sectional view of lead body assembly  1500  according to one representative embodiment. Lead body assembly  1500  comprises stainless steel mandrel  1520  which is coated with layer  1501  of PTFE. Inner layer  1502  of CARBOSIL™ is extruded or otherwise provided over the inner layer of PTFE. The mandrel  1520  with layers  1501  and  1502  is utilized as core material  10  in wire wrapping system  15 . Each wire  1510  (only one wire is annotated for the sake of clarity) is preferably stranded wire coated with a thin layer of PFA and a thicker layer of CARBOSIL™. Wire wrapping system  15  wraps a plurality of wires  1510  about mandrel  1520 , layer  1501 , and layer  1502  in the manner discussed above. An outer layer  1503  of CARBOSIL™ is also provided. Shrink wrap tubing  1504  is then provided on the exterior of the assembly. 
     Lead body  1500  is cut to length and lead body assembly  1500  is subjected to heating above the melting point of the thermoplastic material. The heat and pressure (e.g., from heat shrinkable tubing) causes the thermoplastic insulative material (e.g., the CARBOSIL™ material) to flow. After the thermoplastic material is cooled, the thermoplastic material re-solidifies into a lead body  1600  of fused insulative material enclosing the respective conductors  1510 . Also, as shown in  FIG. 16 , gap  1610  is provided within lead body  1600  where no conductors are located within gap  1610 . That is, gap  1610  is entirely filled with insulative material. 
     Lead body  1600  is then cut into appropriate lengths and electrodes and terminals are provided using any known or later developed process to form stimulation lead  1700  as shown in  FIG. 17 . Although lead  1700  is shown to fabricated as a “percutaneous lead,” other lead designs may also be employed such as paddle-style leads. Also, although some embodiments have discussed fabrication of neurostimulation leads, other medical leads may be fabricated according to other embodiments, such as cardiac leads, mapping leads, ablation leads, etc. 
     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.