Abstract:
In one embodiment, a method of fabricating an implantable stimulation paddle comprises: providing a sheet of conductive material coupled to a first insulative layer; laser removing portions of the conductive material to form a pattern of conductive material, the pattern of conductive material including a plurality of isolated metal traces; providing a second insulative layer over the pattern of conductive material so that the pattern of conductive material is interposed between the first and second insulative layers; and exposing portions of the metal traces to form electrodes on the paddle for delivering electrical stimulation.

Description:
RELATED APPLICATION 
       [0001]    This application is a divisional of U.S. application Ser. No. 11/740,507, filed Apr. 26, 2007, pending, which claims the benefit of U.S. Provisional Application No. 60/745,882, filed Apr. 28, 2006, the disclosures of which are incorporated herein by reference. 
     
    
     BACKGROUND 
       [0002]    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 an example of neurostimulation in which electrical pulses are delivered to nerve tissue in the spine for the purpose of chronic pain control. While a precise understanding of the interaction between the applied electrical energy and the nervous tissue is not fully appreciated, it is known that application of an electrical field to spinal nervous tissue (i.e., spinal nerve roots and spinal cord bundles) can effectively mask certain types of pain transmitted from regions of the body associated with the stimulated nerve tissue. Specifically, 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. Thereby, paresthesia can effectively mask the transmission of non-acute pain sensations to the brain. 
         [0003]    Neurostimulation systems typically include a pulse generator and one or several leads. The pulse generator is the device that generates the electrical pulses. The pulse generator is typically implanted within a subcutaneous pocket created under the skin by a physician. The leads are used to conduct the electrical pulses from the implant site of the pulse generator to the targeted nerve tissue. The leads typically include a lead body of an insulative polymer material with embedded wire conductors extending through the lead body. Electrodes on a distal end of the lead body are coupled to the conductors to deliver the electrical pulses to the appropriate nerve tissue. 
         [0004]    Stimulation paddle leads dispose a plurality of electrodes (for example, two, four, eight, or sixteen) arranged in one or more columns on a paddle structure. It is typical that implanted SCS paddles are transversely centered over the physiological midline of a patient. In such position, multiple columns of electrodes are well suited to address both unilateral and bilateral pain. A multi-column SCS paddle also enables reliable positioning of a plurality of electrodes that does not deviate over time. In particular, the probability of migration of an SCS paddle after implantation is significantly lower than the probability of migration of percutaneous leads. Additionally, SCS paddles are capable of being sutured in place. 
         [0005]    However, given the dimensions of conventional SCS paddles, a surgical procedure is necessary for implantation. The surgical procedure (a “partial laminectomy”) requires the resection and removal of certain vertebral structures to allow both access to the dura and proper positioning of the SCS paddle. The invasive nature of the surgical procedure requires some amount of time for patient recovery and, in some cases, could cause long-term complications for the patient. Additionally, due to the relatively complicated nature of the surgical procedure, the procedure is typically performed by a neurosurgeon. 
         [0006]    Additionally, it is noted that typical assembly procedures for electrically coupling a lead body to a paddle structure are not only cumbersome and expensive, but also create a number of natural, easy breakage points. Specifically, conventional couplings between lead bodies and paddle structures involve welding a jumper wire between contacts and conductive wires of the lead body. Accordingly, conventional paddle lead fabrication methods may involve undue expense and lower than desired manufacturing yields. 
       SUMMARY 
       [0007]    In one embodiment, a method of fabricating an implantable stimulation paddle comprises: providing a sheet of conductive material coupled to a first insulative layer; laser removing portions of the conductive material to form a pattern of conductive material, the pattern of conductive material including a plurality of isolated metal traces; providing a second insulative layer over the pattern of conductive material so that the pattern of conductive material is interposed between the first and second insulative layers; and exposing portions of the metal traces to form electrodes on the paddle for delivering electrical stimulation. 
         [0008]    In another embodiment, an implantable medical lead for delivering electrical energy to stimulate a patient comprises: a lead body comprising a plurality of helically wound conductive wires embedded in insulative material; and a paddle comprising a metal layer disposed between insulative layers, wherein a plurality of electrically isolated metal traces are patterned in the metal layer, each metal trace comprises an electrode exposed through one or several insulative layers, and each electrode is electrically coupled to a conductive wire of the lead body. 
         [0009]    In another embodiment, a system for electrically stimulating a patient comprises: an implantable pulse generator (IPG) for generating electrical stimulation; a lead body comprising a plurality of helically wound conductive wires, embedded in insulative material, for conducting electrical stimulation from the IPG; and a paddle comprising a metal layer disposed between insulative layers, wherein a plurality of electrically isolated metal traces are patterned in the metal layer, each metal trace comprises an electrode exposed through one or several insulative layers, and each electrode is electrically coupled to a conductive wire of the lead body. 
         [0010]    In another embodiment, a method comprises: providing a lead body having a plurality of conductive wires, wherein the plurality of conductive wires are helically wound at a wire spacing pitch; providing a stimulation paddle, the stimulation paddle comprising a metal layer between insulative layers, wherein a plurality of electrically isolated metal traces are patterned in the metal layer, each metal trace comprises a contact and an electrode exposed through one or several insulative layers, and the contacts of the metal traces are disposed together on the stimulation paddle and spaced according to the wire spacing pitch; placing the lead body in contact with the stimulation paddle such that an exposed segment of the lead body abuts the contacts of the metal traces; and transmitting energy onto each contact so that the respective contact becomes welded to an abutting conductive wire of the medical lead thereby electrically coupling the abutting conductive wire to a respective electrode of the stimulation paddle. 
         [0011]    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. 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 
         [0012]    Exemplary embodiments are illustrated in referenced figures of the drawings. It is intended that the embodiments and figures disclosed herein are to be considered illustrative rather than restrictive. 
           [0013]      FIG. 1  is an expanded top perspective view of a stimulation paddle shaped work piece, at an early stage in the production process. 
           [0014]      FIG. 2  is an expanded top perspective view of a of the work piece of  FIG. 1 , at a further stage in the production process. 
           [0015]      FIG. 3  is an expanded top view of a connector portion of the work piece of  FIG. 1 , as indicated by the rectangle marked “FIG.  3 ” in  FIG. 2 . 
           [0016]      FIG. 4  is an expanded top view of the connector portion of  FIG. 3  showing the result of further machining of the work piece of  FIG. 1 , after removal of a window of dielectric material to expose a portion of the traces, which had been entirely embedded. 
           [0017]      FIG. 5  is a plan view of a completed SCS paddle, resulting from the manufacturing process shown in  FIGS. 1   4 . 
           [0018]      FIG. 6  is an expanded top view of the connector portion of  FIG. 5  placed with the window over a portion of a multiconductor cable. 
           [0019]      FIG. 7  is an expanded top view of the connector portion and lead body of  FIG. 5 , showing the exposed traces of the connector portion after being laser welded to the underlying conductive wires of the lead body. 
           [0020]      FIG. 8  is an expanded top view of a connector portion of an alternative preferred embodiment of a stimulation paddle work piece, at the same stage of manufacturing as is the work piece of  FIG. 4 . 
           [0021]      FIG. 9  shows an alternative preferred embodiment of a paddle head having a polymeric coating on the back side of the connection contact sites, which are spaced further apart from each other than in previously shown embodiments. 
           [0022]      FIG. 10  shows an alternative preferred embodiment of a paddle head that is similar in concept to the paddle of  FIG. 9 , but is adapted for the case in which the paddle is positioned perpendicular to the lead body. 
       
    
    
     DETAILED DESCRIPTION 
       [0023]    One preferred embodiment takes the form of a method of making a spinal cord stimulation lead in the form of a paddle for stimulation of tissue (e.g., an “SCS paddle”). Referring to  FIG. 1 , in a preferred method, an SCS paddle work piece  10  begins to take form as a thin layer of nervous-tissue-compatible conductive metal  14  adhered or otherwise coupled to a layer of nervous-tissue-compatible dielectric material  12 . The shape of the work piece  10  can be described as including a body  15 , a neck  17  and a head  19 . 
         [0024]    Laser  16  is used to create a set of traces  18  (not completed in  FIG. 1 ) by forming separating trenches  21  in metal layer  14 . Sufficient power is applied by laser  16  to ablate a small portion of the metal layer  14  preferably without ablating through the layer of dielectric material  12 . Once completed, each trace  18  is electrically isolated from each other trace  18 . Also, each trace  18  joins an electrode site  20  in body  15  to a device contact  28  ( FIG. 4 ), in the form of a finger, in head  19 . 
         [0025]    Referring to  FIG. 2 , an additional layer of nervous-tissue-compatible dielectric material  22  is then added on top of metal layer  14 , thereby covering electrode sites  20 , traces  18  ( FIG. 3 ) and device contacts  28 . A solid film can be adhered to metal layer  14 . Additionally or alternatively, a spin coat of insulative material could be applied to metal layer  14 . Layer  22  is then patterned with a second laser  16 ′ (adapted for machining dielectric material) to create a set of apertures  24 , which reveal the electrode sites  20 . In an alternative preferred embodiment, the same laser is used for both removing metal and dielectric material. Also, in alternative embodiments, the electrode sites  20  could be exposed using manual or other mechanical means. 
         [0026]    Referring to  FIGS. 3 and 4 , a window  26  is then created by laser  16 ′, revealing the device electrical contacts  28 . The completed SCS paddle  10  is shown in  FIG. 5 . Referring to  FIG. 6 , SCS paddle  10  is then placed over a medical lead  30 , so that the device electrical contacts  28  are each aligned with and placed over a conductive wire  32  of lead  30 . At this point, the insulation of lead  30  has been partially removed to expose conductive wires  32  which are co-located with contacts  28 . It shall be appreciated that the relative dimensions of the contacts  28 , lead  30 , and conductive wires  32  are not depicted to scale in  FIG. 6 . 
         [0027]    A laser beam, from the first laser  16  ( FIG. 1 ), is then focused so that part of its footprint covers a part of a device electrical contact  28  and/or part covers a portion of the corresponding exposed conductive wire  32 . The energy, transmitted quickly, heats device electrical contact  28  and conductive wire  32 , melting the end of contact  28  and causing it to be securely welded to conductive wire  32 , as shown in  FIG. 7 . This procedure is repeated for each device electrical contact  28 . In an alternative preferred embodiment, each electrical contact  28  is micro-spot welded to conductive wire  32 . In this technique a microprobe touches and transmits electrical energy onto the free face of electrical contact  28 . As the system is grounded, this causes a large flow of electrical energy, which melts portions of contact  28 , welding it to conductive wire  32 . 
         [0028]      FIG. 8  shows the connective portion of an alternative preferred embodiment of a stimulation paddle work piece in which device electrical contacts  28 ′ extend all the way across window  26 ′. The welding of device electrical contacts  28 ′ to the lead  30  ( FIG. 6 ) may be essentially identical to the welding of device electrical contacts  28  as described above. The preferred embodiment of  FIG. 8  may afford a greater stability to device electrical contacts  28 ′, versus device electrical contacts  28 , as contacts  28 ′ are anchored on both sides of window  26 ′. 
         [0029]      FIG. 9  shows an alternative preferred embodiment of a head  19 ′ with a polymeric coating  12 ′ on the back side of contact sites  28 ″, which are spaced further apart from each other. In one preferred method the polymeric coating  12 ′ is melted or ablated off by laser  16  ( FIG. 1 ) as contact sites  28 ″ are laser welded to a cable. The head  19 ″ of  FIG. 10  is similar in concept to the head of  FIG. 9 , but is adapted for the case in which the lead is arranged in a manner perpendicular to the cable. 
         [0030]    A range of nervous system tissue compatible polymeric materials, sold under the trade designation Bionate® and sold in sheets that may be laminated together are available from Polymer Technology Group of Berkeley, Calif. Metal  14  ( FIG. 1 ) may be gold or a platinum-iridium alloy. First laser  16  may be a ND:YAG laser, which in one preferred embodiment is frequency multiplied, and second laser  16 ′ may be a frequency multiplied ND:YAG laser or a CO2 laser. Conductive wires  32  ( FIG. 6 ) may be made of an alloy that is referred to by the trade designation MP35N and is available from Fort Wayne Metals of Fort Wayne, Ind. 
         [0031]    It shall be appreciated that these material selections are by way of example and any other suitable materials could be substituted without departing from the scope of the appended claims. Also, although some embodiments have been discussed in terms of SCS paddles, stimulation paddles for other indications can be fabricated according to other embodiments. For example, stimulation paddles can be fabricated according to some embodiments for cardiac stimulation, cortical stimulation, deep brain stimulation, peripheral nerve stimulation, gastric pacing, etc. 
         [0032]    The above described methods of paddle fabrication are quite highly automated; thereby requiring far fewer manual operations compared with previously available production techniques for known stimulation paddles. This potentially lowers the costs of manufacturing and reduces the reject rate. Moreover, the process permits the creation of a set of paddles that are more precisely uniform to one another, thereby permitting a medical professional to have confidence that a particular paddle will not fail over time due to inaccurate fabrication processes. 
         [0033]    The disclosed combination of physical dimensions and mechanical characteristics further enables SCS paddles to be inserted within the epidural space of a patient without performing a partial laminectomy. Specifically, by utilizing relatively thin layers of material, SCS paddles can be folded or otherwise deformed for placement within an insertion tool. The insertion tool can be inserted through spacing in the vertebral structures into the epidural space. The SCS paddle is then passed through the end of the insertion tool. The shape memory characteristic of the metal layer and, perhaps, the dielectric backing enables the SCS paddle to resume its original shape upon exiting the insertion tool thereby exposing the electrodes of the paddle to deliver the electrical stimulation. 
         [0034]    Additionally, the physical dimensions and mechanical characteristics of the paddle reduce the probability of causing spinal cord compression. In some alternative embodiments, the paddle can also be made thick enough to be retained in place by the compressing force between the vertebrae and the spinal cord. 
         [0035]    Skilled persons will appreciate that by using the above described method it is possible to create and connect an electrical probe having features that are on the order of 0.1 mm 2  in area without the risk of leaving trace amounts of photolithography agents on the probe. This is particular important in that nervous system tissue is highly sensitive and easily damaged by a wide range of compounds (even in very small concentrations). 
         [0036]    Although 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 from this disclosure, 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 corresponding embodiments described herein may be utilized without departing from the scope of the appended claims. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps.