Patent Publication Number: US-2022218985-A1

Title: An implantable electrical stimulation device with a flexible electrode

Description:
FIELD 
     The present disclosure relates to an implantable stimulation device for providing electrical stimulation comprising a flexible electrode. It also relates to a stimulation system comprising such an implantable stimulation device. 
     BACKGROUND 
     Implantable electrical stimulation systems may be used to deliver electrical stimulation therapy to patients to treat a variety of symptoms or conditions such as headaches, lower back pain and incontinence. 
     In many electrical stimulation applications, it is desirable for a stimulation device, typically comprising a therapeutic lead (a lead comprises electrodes and electrical connections), to provide electrical stimulation to one or more precise locations within a body in many cases, precisely aligning of the stimulation electrodes during implantation may be difficult due to the curvature of tissues and anatomical structures. A mismatch in curvature of the electrode section of a lead may create unexpected and/or unpredictable electrical resistance between one or more electrode and the underlying tissue. In addition, repeated movement of the relevant areas of the body may even worsen the mismatch. A particular problem with subcutaneous implants is that even small differences in flexibility between the implant and surrounding tissue may affect patient comfort, and can cause irritation of the overlying skin. 
     More recently, use has been made of polymers, which have an inherent flexibility. However, implants for electrical stimulation require low resistance conductors for stimulation electrodes, return electrodes and interconnections which conventionally use metal for wires and contacts. These conductors reduce the flexibility, and the problem becomes worse as the size of electrodes increases due to a desire to offer a higher degree of customization, to provide more functionality or to lower the electrical resistance. 
     US application US 2015/099959 describes an implantable electrode array including an organic substrate material configured to be implanted into an in vivo environment and to optionally dissolve and be absorbed, and an electrode mounted to the organic substrate material and configured to acquire signals generated by the in vivo environment. The electrode array includes a connection pad mounted to the organic substrate, and an MRI-compatible conductive trace formed between the electrode and the connection pad. 
     PCT application WO 2018/122824 describes a cortical stimulating and recording electrode comprising a flexible support element for at least one conductive element, with a head end and a tail end. The conductive element has at least one head contact and at least one tail contact, arranged at the head end and tail end respectively of the flexible support element, such that said conductive element transmits signals from said head contact to said tail contact and vice versa. Moreover the conductive element is composed of a conductive track formed of a layer of conductive ink deposited on said flexible support element. 
     US application US 2018/0008821 describes thin film devices and methods of manufacturing and implanting the same. In one implementation, a shaped insulator is formed having an inner surface, an outer surface, and a profile shaped according to a selected dielectric use. A layer of conductive traces is fabricated on the inner surface of the shaped insulator using biocompatible metallization. An insulating layer is applied over the layer of conductive traces. An electrode array and a connection array are fabricated on the outer surface of the shaped insulator and/or the insulating layer, and the electrode array and the connection array are in electrical communication with the layer of conductive traces to form a flexible circuit. The implantable thin film device is formed from the flexible circuit according to the selected dialectic use. 
     It is an object of the invention to provide an improved implantable stimulation device with a plurality of conductors that provides a higher degree of conformity with surrounding tissues and anatomical structures. 
     General Statements 
     According to a first aspect of the present disclosure, there is provided an implantable stimulation device comprising: an elongated substrate, disposed along a longitudinal axis, the substrate having a first and second surface disposed along substantially parallel transverse planes, the substrate further comprising: a flexible electrode, comprised in the first or second surface, and configured, in use, to be in contact with human or animal tissue; and one or more interconnections, disposed between the first and second surface; the flexible electrode further comprising: a first portion, disposed along a first portion plane, and a second portion, disposed along a second portion plane, the first portion and second portion being in direct electrical connection through the one or more interconnections and being separated by one or more bending interruptions, wherein one or more bending interruptions are configured and arranged to have a lower bending resistance than the first and second portion whereby an orientation of the first portion plane is allowed to deviate from an orientation of the second portion plane at the one or more bending interruptions; wherein the first portion and second portion are in direct electrical connection through the one or more interconnections. 
     A highly-configurable flexible electrode is provided by disposing it on a surface of an elongated substrate and including one or more bending interruptions. In addition, the portions on opposite sides of the bending points are electrically connected by low resistance interconnections, which allows the mechanical bending and the electrical connections to be optimized separately. One or more bending interruptions allows at least the electrode portion of an implantable device to conform to neighboring anatomical and tissue structures. This may also increase the tissue contact area of the flexible electrode. The presence of one or more interconnections allows the bending characteristics to be optimized without substantially affecting the electrical characteristics of the flexible electrode. The flexible electrode may be configured and arranged as a return electrode or stimulation electrode. A plurality of flexible electrodes may be provided. 
     Additionally or alternatively, the conformable shape of the flexible electrode in cross-section comprises one or more bending interruptions separating two portions having a higher rigidity than the bending interruptions. 
     According to a further aspect of the present disclosure, there is provided an implantable stimulation device, wherein the flexible electrode has a longitudinal extent along the longitudinal axis; and the one or more bending interruptions being configured and arranged to allow a deviation around a longitudinal axis. Alternatively or additionally, the flexible electrode has a transverse extent along a first transverse axis, the transverse axis being substantially perpendicular to the longitudinal axis; the one or more bending interruptions being configured and arranged to allow a deviation around a transverse axis. 
     Bending around a longitudinal axis and/or transverse axis allows a highly configurable implantable substrate. This means that substrate sections with electrodes (leads) that closely confirm to a high degree to surrounding tissue. It also allows very accurately shapeable substrate sections to be produced for specific anatomical dispositions, and even personalized shaping for highly-variable anatomical dispositions. 
     According to another aspect of the present disclosure, there is provided an implantable stimulation device wherein the tissue contact surface of the first portion is disposed along the first portion plane, and the tissue contact surface of the second portion is disposed along the second portion plane. 
     If a substrate section is made highly configurable, a high degree of tissue contact surface may be provided, up to the total surface area of the flexible electrode portions. This means that the actual tissue stimulation area of the one or more electrodes may be more predictable. 
     According to a still further aspect of the present disclosure, the flexible electrode further comprises one or more contiguous portions proximate the one or more bending interruptions, configured and arranged to increase or to maintain the bending resistance between the first and second portions. This may be described as a deformable electrode, allowing it to be bent into desired shapes and profiles which may be wholly or partially retained. 
     This allows the conductive properties between the electrode portions and the bending resistance to be separately optimized. Configuring and arranging the contiguous portion to increase or to maintain the bending resistance at the bending axes (for example, making the contiguous portion thinner and/or narrower), may be performed without substantially effecting the conductivity and without substantially affecting the operation of the flexible electrode. When suitably configured, it also allows a substrate section to retain a bending profile this may be advantageous when a healthcare professional is preparing the substrate section for implantation. 
     According to yet another aspect of the present disclosure, the one or more bending interruptions comprise one or more openings. 
     Openings may be advantageous because they are relatively straightforward to create using lithographic and etching techniques, and they also may provide a visual clue to a healthcare professional who is implanting the substrate section where the bending axes are disposed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Features and advantages of some embodiments of the present invention, and the manner in which the same are accomplished, will become more readily apparent upon consideration of the following detailed description of the invention taken in conjunction with the accompanying drawings, which illustrate preferred and exemplary embodiments, and which are not necessarily drawn to scale, wherein: 
         FIGS. 1A, 1B and 1C  depicts a first example of an implantable distal end of a stimulation device; 
         FIGS. 2A, 2B and 2C  depicts a second example of an implantable distal end of a stimulation device; 
         FIGS. 3A, 3B and 3C  depicts a third example of an implantable distal end of a stimulation device; 
         FIGS. 4A and 4B  depicts a fourth and fifth example of an implantable distal end of a stimulation device; 
         FIG. 5  and  FIG. 6  depict examples of nerves that may be stimulated to treat headaches; 
         FIG. 7  depicts examples of nerves that may be stimulated for other treatments; 
         FIG. 8  depicts a view of the first surface of an implantable distal end of a stimulation device; and 
         FIG. 9  depicts an example of configuring and arranging a device to be conformable to a predetermined curvature. 
     
    
    
     DETAILED DESCRIPTION 
     In the following detailed description, numerous non-limiting specific details are given to assist in understanding this disclosure. 
       FIGS. 1A, 1B &amp; 1C  depict longitudinal cross-sections through a first embodiment  100  of an implantable distal end of a stimulation device comprising:
         an elongated substrate  300 , disposed along a longitudinal axis  600 , the substrate having a first  310  and second  320  surface disposed along substantially parallel transverse planes  600 ,  700 . For substrates  300  with a degree of flexibility, the degree to which the first  310  and second  320  surface are along substantially parallel transverse planes  600 ,  700  may be determined by laying the substrate  300  on a substantially flat surface. As depicted, the first surface  310  lies in a plane comprising the longitudinal axis  600  and a first transverse axis  700 —the first transverse axis  700  is substantially perpendicular to the longitudinal axis  600 . As depicted, the plane of the first surface  310  is substantially perpendicular to the plane of the cross-section drawing (substantially perpendicular to the surface of the paper). The substrate  300  has a thickness or extent along a second transverse axis  750  this second transverse axis  750  is substantially perpendicular to both the longitudinal axis  600  and the first transverse axis  700  it lies in the plane of the drawing (along the surface of the paper) as depicted. The first surface  310  is depicted as an upper surface and the second surface  320  is depicted as a lower surface.       

     To clarify the different views, the axes are given nominal directions:
         the longitudinal axis  600  extends from the proximal end (not depicted) on the left, to the distal end, depicted on the right of the page;   the first transverse axis  700  extends into the page as depicted; and   the second transverse axis  750  extends from bottom to top as depicted.       

     For example, the elongated substrate  300  may comprise an elastomeric distal end composed of silicone rubber, or another biocompatible, durable polymer such as siloxane polymers, polydimethylsiloxanes, polyurethane, polyether urethane, polyetherurethane urea, polyesterurethane, polyamide, polycarbonate, polyester, polypropylene, polyethylene, polystyrene, polyvinyl chloride, polytetrafluoroethylene, polysulfone, cellulose acetate, polymethylmethacrylate, polyethylene, and polyvinylacetate. Suitable examples of polymers, including LCP Liquid Crystal Polymer), are described in “Polymers for Neural Implants”, Hassler, Boretius, Stieglitz, Journal of Polymer Science: Part B Polymer Physics, 2011, 49, 18-33 (DOI 10.1002/polb.22169), In particular, Table 1 is included here as reference, depicting the properties of Polyimide (UBE U-Varnish-S), Parylene C (PCS Parylene C), PDMS (NuSil MED-1000), SU-8 (MicroChem SU-8 2000 &amp; 3000 Series), and LCP (Vectra MT1300). 
     Flexible substrates  300  are also preferred as they follow the contours of the underlying anatomical features very closely. Very thin substrates  300  have the additional advantage that they have increased flexibility. 
     Preferably, the flexible substrate  300  comprises an LCP, Parylene and/or a Polyimide. LCPs are chemically and biologically stable thermoplastic polymers which allow for hermetic sensor modules having a small size and low moisture penetration. 
     Advantageously, an LCP may be thermoformed allowing complex shapes to be provided. Very thin and very flat sections of an LCP may be provided. For fine tuning of shapes, a suitable laser may also be used for cutting. For example, LCP substrates  300  with thicknesses (extent along the second transverse axis  750 ) in the range 50 microns (um) to 720 microns (um) may be used, preferably 100 microns (um) to 300 microns (um). For example, values of 150 um (micron), 100 um, 50 um, or 25 um may be provided. Similarly, substrate widths (extent along the first transverse axis  700 ) of 2 mm to 20 mm may be provided using LCP, for example. 
     At room temperature, thin LCP films have mechanical properties similar to steel. This is important as implantable substrates  300  must be strong enough to be implanted, strong enough to be removed (explanted) and strong enough to follow any movement of the neighboring anatomical features and/or structures. 
     LCP belongs to the polymer materials with the lowest permeability for gases and water. LCPs can be bonded to themselves, allowing multilayer constructions with a homogenous structure. 
     In contrast to LCPs, polyimides are thermoset polymers, which require adhesives for the construction of multilayer substrates. Polyimides are a thermoset polymer material with high temperature and flexural endurance. 
     An LCP may be used, for example, to provide a substrate having multilayers (not depicted) in other words, several layers of 25 um (micron) thickness. Electrical interconnections and/or interconnect layers may also be provided by metallization using techniques from the PCB (Printed Circuit Board) industry, such as metallization with a bio-compatible metal such as gold or platinum. Electro-plating may be used. These electrical interconnections and/or interconnect layers may be used to provide electrical energy to any electrodes. 
     Preferably, a low aspect ratio is used for the elongated substrate to reduce the chance of implantation problems for example a ratio of width (extent along the first transverse axis  700 ) to height (thickness or extent along the second transverse axis  750 ) of less than 10, such as 0.3 mm high and 10 mm wide. 
     The device  101  of  FIG. 1  further comprises:
         a flexible electrode  400 , comprised in the first surface  310 , and configured, in use, to be in contact with human or animal tissue. The flexible electrode  400  comprises two or more portions  400   a ,  400   b  ( 400   ab ), separated by one or more bending interruptions  500 . It is configured as a return electrode  400 .       

     “Comprised in” the first or second surface means that flexible electrode  400  is relatively thin, and attached to the first  310  or second  320  surface. The electrode  400  may also be embedded in the first  310  or second  320  surface. 
     The first portion  400   a  and second portion  400   b  are disposed on opposing sides of the one or more interruptions  500 . In some cases, they may oppose each other, as depicted in  FIG. 1 . In terms of this disclosure, there is no substantial functional difference between “a” and “b” portions—they may be interchanged. Conductor material disposed between two or more bending interruptions  500  may comprise one or more “a” portions and one or more “b” portions. 
     The portions  400   ab  are considered to be comprised in the same electrode (portions of the same electrode), because they are in direct electrical connection—in other words, they are connected such that the stimulation energy applied by a stimulation system (not depicted) is substantially the same at substantially the same time instance (usually measured as a voltage, a current, a power or any combination thereof) in each portion  400   ab  of the flexible return electrode  400 . 
     This is not the same as two adjacent electrodes. Adjacent electrodes are configured and arranged to provide substantially different energies at substantially the same time, and/or substantially the same energy at substantially different times. In the context of this disclosure, electrodes that have separate electrical connections to an electrical energy source are considered “adjacent” they are not considered portions of the same electrode. 
     The device  101  of  FIG. 1  further comprises:
         one or more bending interruptions  500  between two portions  400   ab  of the flexible electrode  400 , configured and arranged to allow the flexible return electrode  400  to deform by bending at the disposition of the one or more bending interruptions  500 . In other words, if a first portion  400   a  is disposed along a first portion plane and a second portion  400   b  is disposed along a second portion plane, the one or more bending interruptions  500  between these two portions  400   ab  is configured and arranged to deviate from an orientation of the second portion plane at the one or more bending interruptions  500 .       

     The device  101  of  FIG. 1  further comprises:
         one or more interconnections  450 , configured and arranged to directly electrically connect two or more portions  400   ab . Additionally, the one or more interconnections  450  may be configured to provide the flexible return electrode  400  with electrical energy from a stimulation system (not depicted). The one or more interconnections  450  are disposed between the first  310  and second surface  320 . They may comprise one or more conductors, such as a metal, formed as required for example, in one or more conductive: wire, strand, foil, lamina, plate, and/or sheet. They may be a substantially contiguous (one conductor). They may also comprise more than one conductor, configured and arranged to be, in use, electrically connected with each other proximate the corresponding bending interruption  500  in other words, the one or more conductors are configured and arranged to be substantially electrically contiguous in use.       

     An interconnection  450  in the context of this disclosure is not configured or arranged to be, in use, in contact with human or animal tissue. For example, by embedding the one or more interconnections  450  in a low conductance or insulating substrate  300 , such as LCP. Note that an interconnection  450  may be comprised in the first  310  or second surface  320  if it is configured and arranged to be low conductance and/or insulating by including one or more layers between the interconnection  450  and any human or animal tissue. 
     “Comprised in” the first  310  or second  320  surface means that the interconnection  450  is relatively thin, and attached to the first  310  or second  320  surface. The interconnection  450  may also be embedded in the first  310  or second  320  surface. 
     Additionally or alternatively, the substrate  300  may be a multilayer, comprising one or more electrical interconnections and/or electrical interconnect layers  450 . If an LCP multilayer is used, the thickness (extent of the substrate  300  along the second transverse axis  750  or the perpendicular distance between the first surface  310  and the second surface  320 ) may be typically approximately 150 um (micron) in the sections with no electrode portions  400   ab  or interconnections  450 , 250 um in the sections with an electrode  220 , and 180 um in the sections with an electrical interconnection  250 . If multilayers are used, one or more electrical interconnection layers of 25 um (micron) thickness may be used, for example. 
     Alternatively, the flexible return electrode  400  may also be comprised in the second surface  320 . The device may comprise a plurality of flexible return electrodes  400  comprised in the first  310  and/or second  320  surface. 
     In this example, the flexible electrode  400  is configured as a return electrode it is configured to provide, in use, an electrical return for one or more stimulation electrode  220 . In other words, the electrical return  400  closes the electrical circuit. It may also be similarly configured to provide an electrical ground for a correspond electrical energy source. 
     The device  101  of  FIG. 1  further comprises:
         one or more stimulation electrodes  200 , comprised in the second surface  320  and configured to transmit energy, in use, to human or animal tissue (after implantation).   one or more electrical interconnections  250 , configured to provide the one or more stimulation electrodes  200  with electrical energy from a stimulation system (not depicted). The flexible electrode  400  is configured to provide, in use, an electrical return for these one or more stimulation electrode  220 .       

     “Comprised in the second surface” means that the one or more stimulation electrode  200  is relatively thin, and attached to the second surface  320 . The electrode  200  may also be embedded in the second surface  320 . 
     Additionally or alternatively, the device may comprise one or more stimulation electrodes  200 , comprised in the first surface  310 . 
     In general, one or more stimulation electrodes  200  may be provided. The number, dimensions and/or spacings of the stimulating electrodes  200  may be selected and optimized depending on the treatment for example, if more than one electrode  200  is provided, each electrode  200  may provide a separate stimulation effect, a similar stimulation effect or a selection may be made of one or two electrodes  200  proximate the tissues where the effect is to be created. Two or more stimulation electrodes  200  may be made active if stimulation over a larger area is required and/or at a disposition between the active electrodes  200 . The electrodes  200  may comprise a conductive material such as gold, silver, platinum, iridium, and/or platinum/iridium alloys and/or oxides. An implantable device with a distal end (or lead) suitable for implant may comprise, for example, 12 stimulation electrodes over a length of 15 cm. A stimulation electrode may have dimensions on the order of 6 to 8 mm along the longitudinal axis  600  and 3 to 5 mm along the first transverse axis  700 , so approximately 18 to 40 square mm (mm 2 ). If a strip of 4 mm wide (extent along the first transverse axis  700 ) is provided as a return electrode, then a length (extent along the longitudinal axis  600 ) 4.5 to 10 mm also provides a contact area of 18 to 40 square mm (mm 2 ). The electric field is more concentrated between the strip and the corresponding stimulation electrode. 
       FIG. 1B  depicts a view of the second surface  320  of the implantable end of the stimulation device  100  depicted in  FIG. 1A . In other words, the second surface  320  is depicted in the plane of the paper, lying along the longitudinal axis  600  (depicted from bottom to top) and in the first transverse axis  700  (depicted from left to right). The second transverse axis  750  extends into the page. This is the view facing the animal or human tissue which is stimulated (in use). The first surface  310  is not depicted in  FIG. 1B , but lies at a higher position along the second transverse axis  750  (into the page), and is also substantially parallel to the plane of the drawing. 
     The one or more interconnections  250  are disposed between the second  320  surface and the first  310  surface, as depicted in  FIG. 1A . In  FIG. 1B , they are depicted as dotted lines, representing wire (or wire-like) interconnections  250  that have been provided for each of the stimulation electrodes  200  in this example. 
     The substrate  300  extends along the first transverse axis  700  (considered the width of the stimulation device  100 ) from a first transverse extent  330  (depicted on the left-hand side) to a second transverse extent  340  (depicted on the right-hand side). 
     The device  100  may be implanted by first creating a tunnel and/or using an implantation tool. 
     The return electrode  400  is depicted in  FIGS. 1A and 1B , but not in  FIG. 1C . 
     As depicted in  FIG. 1B , the stimulation electrode  200  has a longitudinal extent along the longitudinal axis  600  and a transverse extent along the first transverse axis  700 . Although depicted as similar, in practice, each stimulation electrode  200  may vary in shape, transverse cross-section, and size (or extent). 
       FIG. 1C  depicts a view of the first surface  310  of the implantable distal end of the device  100 , depicted in  FIGS. 1A and 1B . In other words, the first surface  310  is depicted in the plane of the paper, lying along the longitudinal axis  600  (depicted from bottom to top) and in the first transverse axis  700  (depicted from right to left). The second transverse axis  750  extends out of the page. The second surface  320  is not depicted in  FIG. 1C , but lies at a lower position along the second transverse axis  750  (into the page), and is also substantially parallel to the plane of the drawing. 
     The one or more interconnections  450  are disposed between the first  310  surface and the second  320  surface, as depicted in  FIG. 1A . In  FIG. 1C , they are not depicted the one or more interconnections  450  are comprised in an interconnection layer  450  just underneath the first surface  310 , with through connections (not depicted) to each of the portions  400   ab  in this example. 
     It may be convenient to manufacture this first embodiment  100  such that the longitudinal extent  600  of the flexible electrode  400  portions  400   ab  are substantially similar this provides a similar degree of bending flexibility at a plurality of longitudinal  600  dispositions. 
     After implantation of the device  100 , a source of energy may be configured and arranged to provide, in use, electrical energy to the stimulation electrode  200  with respect to the electrical return applied to each portion  400   ab  of the corresponding return electrode  400 . As the portions of the return electrode  400  are each directly electrically connected, the electrical return applied is substantially the same for all points along the return electrode portions  400   ab.    
     It is advantageous to provide one or more return electrodes  400  proximate the corresponding one or more stimulation electrodes  200  as that may allow a more concentrated electrical field to be used. It may be advantageous to configure and arrange the one or more proximal return electrodes to be disposed within less than 8 mm, preferably less than 6 mm, from the one or more corresponding (active) stimulation electrodes. However, when there is a change in the one or more stimulation electrodes  200  being used for stimulation, it may not be possible to configure an electrode proximate the changed stimulation electrode  200  as an electrical return. 
     If a plurality of selectable return electrodes  400  are provided, the complexity of the implantable stimulation device may increase, and/or require a more complicated control system. An alternative is to provide a ground electrode  400  with an increased longitudinal  600  and transverse  700  extent, compared to conventional devices however, this may increase the rigidity (increase the bending resistance) of the corresponding section of the substrate due to the metal layer. 
     Thicker metal layers are generally preferred over thinner metal layers for electrodes  200 ,  400  because they can be subjected to bodily substances that may dissolve the metal. However, thicker metal layers typically increase rigidity. 
     An additional design factor is a preference to provide a combined active tissue contact area of the one or more return electrode  400  equal to or more than the active tissue contact area of the one or more active stimulation electrodes  200 . The contact areas to be considered are not the total contact surface areas, but the contact areas configured to be active during use and the contact areas that are actually in contact with the surrounding tissue. In general, the ratio between the tissue contact areas does not need to be determined exactly they should be of a similar order of magnitude. For example, it may be sufficient if the combined active tissue contact area of the one or more return electrodes is equal to or more than 70% to 100% of the active tissue contact area of the one or more stimulation electrodes. 
     By providing one or more bending interruptions  500 , the tissue contact area may be optimized due to the enhanced ability of the distal end of a stimulation device to conform to the shape of surrounding tissues and anatomical features. In the example depicted in  FIG. 1 , one return electrode  400  is provided, and the optimized contact area is up to a maximum of the total contact areas of the two or more electrode portions  400   ab.    
     As depicted in  FIG. 1C , the one or more bending interruptions  500  have a transverse  700  extent comparable with the transverse extent of the substrate  300  (in other words, from edge  340  to edge  330 ). They are disposed substantially along the first transverse axis  700 , and are disposed approximately perpendicular to the longitudinal axis  600 . 
     A number of parameters and properties may be considered when configuring and arranging the one or more bending interruptions  500 , such as:
         the required curvature orientation in this example, substantially about a plurality of longitudinal  600  dispositions. This may be influenced, for example, by the orientation of the one or more bending interruptions  50  and the separation between the first  400   a  and second  400   b  portions.   the maximum radius of curvature of the substrate  300  at this longitudinal disposition  600 . This may be influence, for example, by the separation between the first  400   a  and second  400   b  portions, and the bending resistance between the first  400   a  and second  400   b  portions.       

     The bending resistance between the first  400   a  and second  400   b  portions depends on parameters such as:
         the transverse  700  and/or longitudinal extent  600  of the one or more interruptions   the thickness of the substrate  300 , or distance between the first surface  310  and the second surface  320     the materials comprised in the substrate  300  within the region of the one or more interruptions, and their physical properties. The bending resistance of the substrate  300  material may be increased by including different materials of different thicknesses and different rigidities and/or resilience, such as a reinforcement filament, a metal wire and/or LCP strip.   the presence of interconnections  250 ,  450  and/or interconnection layers  450  between the first surface  310  and second surface  320 .   the presence of one or more reinforcement coatings, such as a sputtered layer of chrome.   the presence of one or more indentations in the first surface  310  and/or second surface  320 .   the presence of one or more electrodes  200 ,  400  at the longitudinal  600  and/or transverse  700  disposition of the one or more interruptions  500 . For example, the stimulation electrodes  200  depicted in  FIG. 1A  are longitudinally  600  disposed at interruptions between the first  400   a  and second  400   b  portions this may increase the bending resistance at these interruptions.       

     As depicted in  FIGS. 1A and 1C , the spacing between the portions  400   ab  of the flexible return electrode  400  are approximately the same, but the skilled person will realize that each bending interruption may be configured and arranged separately to provide one or more predetermined bending resistances. 
     One of the insights upon which an aspect of the invention is based is that the inherent flexibility of some substrate materials offers advantages of a high degree of conforming with the shape of surrounding tissue. However, the presence of one or more electrodes  200 ,  400  may affect the flexibility, resulting in sections of the substrate that are rigid adjacent to more flexible sections. Regions of the electrode surface may be thinned, thickened or removed to provide an optimal bending profile, but this may affect the electrical characteristics of the electrode by affecting the degree to which the different portions of electrode surface area remain substantially contiguous. 
       FIGS. 2A, 2B and 2C  depict longitudinal cross-sections through a second embodiment  101  of an implantable distal end of a stimulation device comprising. It is similar to the first embodiment  100 , depicted in  FIG. 1  except:
         instead of one or more separate stimulation electrodes  200 , a further flexible electrode  200  is provided, comprised in the second surface  320 , and configured, in use, to be in contact with human or animal tissue. This flexible stimulation electrode  200  comprises two or more portions  400   a ,  400   b  ( 400   ab ), separated by one or more bending interruptions  500 .   the portions  200   ab  of the flexible stimulation electrode  200  are disposed at substantially the same longitudinal  600  dispositions as the portions  400   ab  of the flexible return electrode  400 . In other words, the bending interruptions  500  of the flexible stimulation electrode  200  are disposed at substantially the same longitudinal  600  dispositions as the bending interruptions  500  of the flexible return electrode  400 .   the one or more interconnections  450  for the return electrode portions  400   ab  are still an electrical interconnect layer  450 . However, they are disposed further away from the first surface  310  (in other words, closer to the second surface  320 ). In this case, the return electrical interconnect layer  450  includes conductors that connect to each portion  400   ab . As before, these conductors are substantially electrically contiguous in use.   the one or more electrical interconnections  250  for the stimulation electrode  200 , implemented as wires in  FIG. 1 , are replaced here by one or more interconnections  250  comprised in a further electrical interconnect layer  250 . In this case, they are disposed further away from the second surface  320  (in other words, closer to the first surface  310 ). In this case, the stimulation electrical interconnect layer  250  includes conductors that connect to each portion  200   ab . As before, these conductors are substantially electrically contiguous in use.       

     By aligning the longitudinal  600  positions of the bending points  500  comprised in the first  310  and second  320  surfaces, a very flexible substrate is provided  300 , with a high uniformity of bending resistance as the interruptions are configured and arranged substantially the same. 
     Alternatively, the flexible stimulation electrode  200  may also be comprised in the first surface  310 . The device may comprise a plurality of flexible stimulation electrodes  200  comprised in the first  310  and/or second  320  surface. 
     Although the electrodes comprised in the top surface  310  are indicated as one or more return electrodes  400 , and the electrodes comprised in the bottom surface  320  are indicated as stimulation electrodes  200 , the skilled person will realize that the functionalities of the electrodes  200 ,  400  may be modified by changing the electrics connections to the distal end. This may be advantageous if it is uncertain whether the implantable distal end is above or below the targeted tissue for example, above or below a nerve. 
       FIGS. 3A, 3B and 3C  depict longitudinal cross-sections through a third embodiment  102  of an implantable distal end of a stimulation device. It similar to the second embodiment  101  depicted in  FIG. 2  except:
         instead of a flexible stimulation electrode  200  comprised in the second surface  320 , a flexible stimulation electrode  200  is comprised in the first surface  310 . No electrodes are comprised in the second surface  320 .   the portions  400   ab  of the flexible return electrode  400  and the portions  200   ab  of the flexible stimulation electrode  200  are comprised in the first surface  310  and alternated (interposed).   the one or more interconnections  450  for the return electrode portions  400   ab  are implemented in this example as a wire or wire-like (depicted in  FIG. 3B  as a dashed line). In this case, the interconnections  450  are comprised in the second surface  320  and include conductors that connect to each portion  400   ab  passing through almost the whole thickness of the substrate  300 . In this case, the one or more return interconnections  450  context of this disclosure are not configured or arranged to be, in use, in contact with human or animal tissue. For example, they are rendered low conductance and/or insulating by including one or more layers (not depicted) between the interconnection  450  and any human or animal tissue.   the one or more interconnections  250  for the stimulation electrode portions  200   ab  are implemented in this case as a wire or wire-like (depicted in  FIG. 3B ). In this case, the interconnections  450  are comprised between the first surface  310  and the second surface  320 , include conductors that connect to each portion  400   ab  passing through almost the whole thickness of the substrate  300 .       

     The advantage of this embodiment may be increased local field strengths due to the low degree of separation between the stimulation  200   ab  electrode portions and the return  400   ab  portions. 
     Alternatively, the flexible stimulation electrode  200  and return flexible electrode  400  may be comprised in the second surface  320 . The device may comprise a plurality of flexible stimulation electrodes  200  comprised in the first  310  and/or second  320  surface. 
     For clarity, no contiguous portions  470  are depicted, but the bending points  500  may be of any configuration described above in relation to  FIG. 4A  and  FIG. 4B . 
       FIGS. 4A and 4B  depict a fourth  103  and fifth  104  example of an implantable distal end of a stimulation device in both cases a view of the first surface  310  of the implantable distal end of these devices. They are modifications of the return electrode  400  depicted in  FIG. 1C  or  FIG. 2C .  FIGS. 4A and 4B  also depict a flexible electrode  400  with a longitudinal extent along the longitudinal axis  600 , and a transverse extent along the first transverse axis  700 , the transverse axis  700  being substantially perpendicular to the longitudinal axis  600 . The flexible electrode  400  comprises, in general, one or more bending interruption  500 . 
       FIG. 4A  depicts a flexible return electrode  400  comprising a plurality of pairs of portions, separated by four differently configured specific bending interruptions  371 ,  372 ,  373 ,  374 . Three of them  371 ,  373 ,  374  provide bending around approximately transverse bending axes  771 ,  773 ,  774 . One of the bending interruptions  372  provides bending around a bending axis  772  at an angle to the first transverse axis  700  in other words, it allows diagonally-oriented bending. 
       FIG. 4B  depicts a flexible return electrode  400  comprising a one pair of portions, separated by bending interruptions  375 , configured and arranged to allow bending around approximately the substrate longitudinal axis  600 . 
     Each bending point in  FIGS. 4A and 4B  comprise one or more bending interruptions,  371 ,  372 ,  373 ,  374 ,  375  configured and arranged to allow an orientation of each corresponding first portion plane to deviate from an orientation of each corresponding second portion plane at the one or more bending interruptions  371 ,  372 ,  373 ,  374 ,  375  in other words, they allow bending around the corresponding bending axes  771 ,  772 ,  773 ,  774 ,  600 . However, in these cases, each of the bending interruptions,  371 ,  372 ,  373 ,  374 ,  375  provides a different possible deviation and/or bending resistance. 
       FIG. 4A  depicts a first bending interruption  371 , approximately disposed along the first transverse axis  700 . It is disposed along a first bending axis  771  to provide a first bending point  771 —the interruption  371  is an area of increased flexibility compared to the immediately proximate portions of the electrode  400 . This may be achieved by providing a region with a variation in a relevant parameter such as those indicated above—for example, a region of substantially thinner electrode, a region of no electrode material (an opening) and/or a region comprising a different electrode material and/or coating. As the first bending interruption  371  is disposed approximately along the first transverse axis  700 , the first bending interruption  371  is configured and arranged to allow the plane of a first portion of the first  310  surface between the first bending interruption  371  and the distal end (more positive along the longitudinal axis  600 ) to deviate from the plane of a second portion of the first  310  surface between the first bending interruption  371  and the proximal end (more negative along the longitudinal axis  600 ). By suitable configuration, the substrate  300  may allow bending away from the first surface  310  and/or away from the second surface  320 . 
     Optionally, the first bending interruption  371  may comprise one or more openings—in other words, the flexible electrode  400  is no longer contiguous at this point and bending is mainly determined by the properties of the substrate. Openings may be advantageous because they are relatively straightforward to create, and they also may provide a visual clue to a healthcare professional who is implanting the substrate section where the bending axes are disposed. 
     Additionally, it may be advantageous to provide a further connection between adjacent portions separated by the one or more interruptions  371  this further connection comprises one or more contiguous portions proximate the one or more bending interruptions  371 —here one contiguous portion  470  is depicted between a transverse edge of the interruption  371  and the edge  340  of the substrate  300 . 
     As in the configurations described above, the electrical connection between the portions is provided through the one or more interconnections  450 , disposed between the first  310  and second  320  surfaces. 
     The contiguous portion  470  forms part of the electrode conductive layer, and may therefore be considered as an additional electrical connection. But, this contiguous portion  470  therefore may be substantially configured to increase or to maintain the bending resistance at the bending axes, and any effect on the conductivity (for example, due to making the contiguous portion  470  thinner and/or narrower) does not substantially affect the operation of the flexible electrode  400 . 
     One of the insights upon which an aspect of the invention is based is that the shape of the conductive electrode material may be configured and arranged to maintain or to increase the bending resistance at a bending axis. One or more regions of the electrode proximate a bending interruption may be thinned, thickened or shaped to provide a predetermined bending resistance using a region of the electrode that remains contiguous. The presence of interconnections allows a very high degree of bending resistance configurability without affecting the electrical characteristics of the flexible electrode  200 ,  400 . 
     The one or more bending interruptions  371  and/or one or more openings may be formed using any suitable material removal (or partial removal) techniques, such as lithography, chemical etching, using a laser, using a mechanical scribe and any combination thereof. It is therefore straightforward to provide relatively complex shapes. 
     Additionally or alternatively, a similar configuration and arrangement may be achieved by increasing the amount of material present proximate the first bending interruption  371 , using, for example, coatings and/or ridges made of substrate material  300 . 
     The skilled person will realize that the degree of bending, the direction of the bending and the disposition may be provided by a suitable arrangement and configuration of the one or more bending interruptions  371  and a suitable arrangement and configuration of the optional one or more openings. For example, the skilled person may predetermine the degree of bending by configuring the length (longitudinal extent  600 ), the width (transverse extent  700 ) and the shape. The shape may include, for example, such geometries as rectangle, square, trapezium, polygon. 
       FIG. 4A  further depicts a second bending interruption  372 , disposed at approximately 20 degrees to the first transverse axis  700 . It is similar to the first bending interruption  371 , except:
         the second bending interruption  372  is disposed along a second bending axis  772 , which is at an angle of approximately 20 degrees to the first transverse axis  700  and approximately 70 degrees to the longitudinal axis  600 .       

     Similarly, a proximate contiguous portion  470  is provided to increase or maintain bending resistance. 
     Any angle may be used to provide a corresponding angle of bending axis/point  772 . 
       FIG. 4A  further depicts a third bending interruption  373 , disposed along a third bending axis  773  which is approximately also along the first transverse axis  700 . It is similar to the first bending interruption  372 , except for:
         an additional contiguous portion  470  is provided between an edge  330  of the substrate  300  and the transverse edge of the interruption  373 .       

     Both contiguous portions  470  may be configured and arranged to increase or maintain bending resistance. 
       FIG. 4A  further depicts a fourth bending point comprising three interruptions  374 , disposed along a fourth bending axis  774 , which is approximately also along the first transverse axis  700 . It is similar to the third bending interruption  373 , except for:
         comprising three bending interruptions  374 , each one having less than one-third of the transverse extent of the third bending interruption  373 ,   comprising four contiguous portions  470 .       

     Both contiguous portions  470  may be configured and arranged to increase or maintain bending resistance. 
       FIG. 4B  depicts a fifth example  104  of an implantable distal end of a stimulation device. 
     The fifth example  104  comprises a fifth bending point comprising two interruptions  375 , approximately disposed approximately along a longitudinal axis  600 . The interruptions  375  are similar to the bending interruptions described above in relation to  FIG. 4A . 
     In this case, a contiguous portion  470  is provided proximate and between the two bending interruptions  375 , disposed approximately along the longitudinal axis  600 . 
     The contiguous portion  470  may be configured and arranged to increase or maintain bending resistance. 
     The skilled person will realize that any number of interruptions may be provided, as well as any number of contiguous portions, to provide the desired bending resistance, the desired degree of flexibility, and at the desired angle. This allows the substrate  300  to conform to neighboring anatomical tissue if made flexible enough, with a low degree of bending resistance, the substrate  300  may conform by being pressed against neighboring tissue at the point of implantation. Additionally or alternatively, the flexibility may be slightly less, allowing a health professional to bend the substrate to the appropriate conformation shape before and/or during implantation. 
     In addition, a plurality of interruptions may be provided at different angles, allowing different shapes of the electrode portions. For example, one or more electrode portions  200   ab ,  400   ab , separated by one or more interruptions may be provided to provide a substrate  300  that bends in two or more directions. The electrode portions may be, for example, polygonal, rectangular, square, trapezoidal in shape. 
     Alternatively or additionally, such bending interruption  371 ,  372 ,  373 ,  374 ,  375  may be comprised in a flexible stimulation electrode  200  comprised in the first surface  310 . Alternatively or additionally, one or more bending interruptions  371 ,  372 ,  373 ,  374 ,  375  may be comprised in a flexible electrode  200 ,  400  comprised in the second surface  320 . 
       FIG. 9  depicts an example of configuring and arranging a device to be conformable to a predetermined curvature. A substrate  300  is depicted in longitudinal cross-section, elongated along a longitudinal axis  600 . The longitudinal axis  600  is depicted with the desired curvature. The substrate  300  has a first  310  and second  320  surface disposed along substantially parallel curved transverse planes  600 ,  700 . 
     As depicted, the first surface  310  lies in a plane comprising the longitudinal axis  600  and a first transverse axis  700 —the first transverse axis  700  is substantially perpendicular to the longitudinal axis  600 . As depicted, the curved plane of the first surface  310  and second surface  320  are substantially perpendicular to the plane of the cross-section drawing (substantially perpendicular to the surface of the paper). The substrate  300  has a thickness or extent along a second transverse axis  750  of D this second transverse axis  750  is substantially perpendicular to both the longitudinal axis  600  and the first transverse axis  700  it lies in the plane of the drawing (along the surface of the paper) as depicted. 
     A flexible electrode  200 ,  400  is provided, separated into four portions  200   ab ,  400   ab , comprised in the curved second surface  320 . This may be any of the stimulation electrodes and/or return electrodes described above. The electrode  200 ,  400  comprises three bending interruptions  500 , providing three bending points/axis (not depicted) approximately along the first transverse axis  700 . For clarity, no contiguous portions  470  are depicted, but the bending points  500  may be of any configuration described above in relation to  FIG. 4A  and  FIG. 4B . 
     As depicted, the nominal curvature of the substrate  300  is R1—from the center point of the curvature to the central plane which is midway between the first  310  and second  320  surface along the second transverse axis  750 . The conformed curvature of the substrate  300  is R2 from the center point of the curvature to the curved second surface  320 . The thickness of the electrodes (extent along the second transverse axis  750 ) is labelled as L. The thickness of the substrate  300  (extent along the second transverse axis  750 ) is labelled as D. W2 is the pitch between portions. W1 is the longitudinal extent  600  of the electrode portion. 
     Typical values are:
         R1: 100 mm   D/L: 0.150 mm   L: 0.050 mm       

     Calculation is as follows with typical values: 
         R 2= R 1−( D/ 2+ L )
 
         W 2/ W 1=2π R 2/2π R 1= R 2/ R 1
 
         R 2/ R 1=( R 1−( D/ 2+ L ))/ R 1=1−( D/ 2+ L )/ R 1
 
     With these typical values, W2/W1=0.998 or 99.8% 
     So, by providing bending interruptions  500  with an extent along the longitudinal axis of 1.2% compared to the electrode portion  200   ab ,  400   ab , and the substrate  300  comprises a sufficiently flexible substrate, then the device may be bent to conform with a radius of curvature of 100 mm or less. A smaller radius of curvature means a higher degree of bending. 
     Typically, curvatures that the implantable distal end of a stimulation device must conform to may be determined by measurement of patients. 
     Additionally or alternatively, databases such as the DINED database (from  2004 ) of body measurements may be used to determine typical values. Dimensions of these 3D human models are based on anthropometric data from a survey done in the Netherlands in 2004. P50 refers to the percentile of people participating in the study:
         for a frontal implant, male P50 curvatures from  2004  are horizontal radius 75.124 mm, vertical radius 96.615 mm;   for a frontal implant, female P50 curvatures from  2004  are horizontal radius 71.089 mm, vertical radius 93.108 mm;   for an occital implant, male P50 curvatures from  2004  are horizontal radius 74.916 mm, vertical radius 96.095 mm;   for an occital implant, female P50 curvatures from  2004  are horizontal radius 70.641 mm, vertical radius 91.42 mm;       

     So, by suitable configuration, a radius of curvature of 90 mm to 96 mm may be provided. 
     Dimensions of these 3D human models are based on anthropometric data from a survey done in the Netherlands in 2004. P50 refers to the percentile of people participating in the study. For both the frontal and occipital area, the radius of the most curved edges is defined by means of an osculating circle:
         for male P50, the radius frontal osculating circle 63.019 mm;   for male P50, the radius occipital osculating circle 60.458 mm;   for female P50, the radius frontal osculating circle 58.195 mm;   for female P50, the radius occipital osculating circle 56.228 mm;       

     So, by suitable configuration, a radius of curvature of 55 mm to 65 mm may be provided. 
     Dimensions of these 3D human models are based on anthropometric data from a survey done in the Netherlands in 2004. P5 and P95 refers to the percentile of people participating in the study, with P5 representing the smallest person and P95 the largest person of the total sample. 
     For both the frontal and occipital area, the radius of the most curved edge is defined by means of an osculating circle:
         for male P95, the horizontal radius 79.00 mm, the vertical radius 100.477 mm and the radius frontal osculating circle 67.361 mm;   for male P95, the horizontal radius 79.423 mm, the vertical radius 102.003 mm, the radius occipital osculating circle 66.237 mm;   for female P5, the horizontal radius 64.68 mm, the vertical radius 83.336 mm and the radius frontal osculating circle 49.585 mm; and   for female P5, the horizontal radius 65.578 mm, the vertical radius 85.21 mm and the radius occipital osculating circle 48.035 mm       

     So, by suitable configuration, a radius of curvature of 45 mm to 80 mm may be provided. 
       FIG. 8  depicts a view of the first surface  310  of a sixth  105  example of an implantable distal end of a stimulation device. 
     It is a modification of the flexible return electrode  400  depicted in  FIG. 4A . It also depicts a flexible electrode  400  with a longitudinal extent along the longitudinal axis  600 , and a transverse extent along the first transverse axis  700 , the transverse axis  700  being substantially perpendicular to the longitudinal axis  600 . The flexible electrode  400  comprises, in general, one or more bending interruption  500 . 
       FIG. 8  differs from  FIG. 4A :
         it comprises a plurality of electrode portions  400   ab , separated by six bending interruptions  371  (as depicted in  FIG. 4A ), configured and arranged to provide substantially the same bending properties and substantially the same bending resistance between each of the portions  400   ab , around a plurality of bending axes  771 . In this case, the bending axis  771  is approximately the same as the first transverse axis  700 . A high uniformity of bending resistance is provided due to the interruptions  771  being configured and arranged to be substantially the same.       

       FIG. 5  and  FIG. 6  depict examples of nerves that may be stimulated using a suitably configured implantable distal end of stimulation devices  100 ,  101 ,  102 ,  103 ,  104 ,  105 ,  106 ,  107  to provide neuro stimulation to treat, for example, headaches or primary headaches. 
       FIG. 5  depicts the left supraorbital nerve  910  and right supraorbital nerve  920  which may be electrically stimulated using a suitably configured device.  FIG. 6  depicts the left greater occipital nerve  930  and right greater occipital nerve  940  which may also be electrically stimulated using a suitably configured device. 
     Depending on the size of the region to be stimulated and the dimensions of the part of the device to be implanted, a suitable location is determined to provide the electrical stimulation required for the treatment. Approximate implant locations for the distal part of the stimulation device comprising stimulation devices  100 ,  101 ,  102 ,  103 ,  104 ,  105 ,  106 ,  107  are depicted as regions:
         location  810  for left supraorbital stimulation and location  820  for right supraorbital stimulation for treating chronic headache such as migraine and cluster.   location  830  for left occipital stimulation and location  840  for right occipital stimulation for treating chronic headache such as migraine, cluster, and occipital neuralgia.       

     In many cases, these will be the approximate locations  810 ,  820 ,  830 ,  840  for the implantable device  100 ,  101 ,  102 ,  103 ,  104 ,  105 ,  106 ,  107 . 
     For each implant location,  810 ,  820 ,  830 ,  840  a separate stimulation system may be used. Where implant locations  810 ,  820 ,  830 ,  840  are close together, or even overlapping, a single stimulation system may be configured to stimulate at more than one implant location  810 ,  820 ,  830 ,  840 . 
     A plurality of stimulation devices  100 ,  101 ,  102 ,  103 ,  104 ,  105 ,  106 ,  107  may be operated separately, simultaneously, sequentially or any combination thereof to provide the required treatment. 
       FIG. 7  depict further examples of nerves that may be stimulated using a suitably configured improved implantable device  100 ,  101 ,  102 ,  103 ,  104 ,  105 ,  106 ,  107  to provide neurostimulation to treat other conditions. The locations depicted in  FIG. 5  and  FIG. 6  ( 810 ,  820 ,  830 ,  840 ) are also depicted in  FIG. 7 . 
     Depending on the size of the region to be stimulated and the dimensions of the part of the device to be implanted, a suitable location is determined to provide the electrical stimulation required for the treatment. Approximate implant locations for the part of the stimulation device comprising stimulation electrodes are depicted as regions:
         location  810  for cortical stimulation for treating epilepsy;   location  850  for deep brain stimulation for tremor control treatment in Parkinson&#39;s disease patients; treating dystonia, obesity, essential tremor, depression, epilepsy, obsessive compulsive disorder, Alzheimer&#39;s, anxiety, bulimia, tinnitus, traumatic brain injury, Tourette&#39;s, sleep disorders, autism, bipolar; and stroke recovery;   location  860  for vagus nerve stimulation for treating epilepsy, depression, anxiety, bulimia, obesity, tinnitus, obsessive compulsive disorder and heart failure;   location  860  for carotid artery or carotid sinus stimulation for treating hypertension;   location  860  for hypoglossal &amp; phrenic nerve stimulation for treating sleep apnea;   location  865  for cerebral spinal cord stimulation for treating chronic neck pain;   location  870  for peripheral nerve stimulation for treating limb pain, migraines, extremity pain;   location  875  for spinal cord stimulation for treating chronic lower back pain, angina, asthma, pain in general;   location  880  for gastric stimulation for treatment of obesity, bulimia, interstitial cystitis;   location  885  for sacral &amp; pudendal nerve stimulation for treatment of interstitial cystitis;   location  885  for sacral nerve stimulation for treatment of urinary incontinence, fecal incontinence;   location  890  for sacral neuromodulation for bladder control treatment; and   location  895  for fibular nerve stimulation for treating gait or footdrop.       

     Other condition that may be treated include gastro-esophageal reflux disease and inflammatory diseases. 
     The descriptions thereof herein should not be understood to prescribe a fixed order of performing the method steps described therein. Rather the method steps may be performed in any order that is practicable. Similarly, the examples are used to explain the algorithm, and are not intended to represent the only implementations of these algorithms the person skilled in the art will be able to conceive many different ways to achieve the same functionality as provided by the embodiments described herein. 
     Many types of implantable distal ends of stimulation devices are depicted. But this does not exclude that the rest of the device is implanted. This should be interpreted as meaning that at least the electrode section of the distal end is preferably configured and arranged to be implanted. 
     In general, for any of the configurations described and depicted in this disclosure, any electrode  200 ,  400  may be connected as either a stimulating  200  or return electrode  400 . This may be advantageous if it is uncertain whether the implantable distal end is above or below the targeted tissue for example, above or below a nerve. 
     Although the present invention has been described in connection with specific exemplary embodiments, it should be understood that various changes, substitutions, and alterations apparent to those skilled in the art can be made to the disclosed embodiments without departing from the spirit and scope of the invention as set forth in the appended claims. 
     REFERENCE NUMBERS USED IN DRAWINGS 
     
         
           100  a first implantable distal end of a stimulation device 
           101  a second implantable distal end of a stimulation device 
           102  a third implantable distal end of a stimulation device 
           103  a fourth implantable distal end of a stimulation device 
           104  a fifth implantable distal end of a stimulation device 
           105  a sixth implantable distal end of a stimulation device 
           106  a first implantable distal end of a stimulation device 
           200  one or more stimulation electrodes 
           200   ab  one or more stimulation electrode portions 
           250  one or more stimulation electrical interconnections 
           300  an elongated substrate 
           310  a first substantially planar transverse surface 
           320  a second substantially planar transverse surface 
           371  a first bending interruption 
           372  a second bending interruption 
           373  a third bending interruption 
           374  a fourth bending interruption 
           375  a fifth bending interruption 
           400  one or more return electrodes 
           400   ab  one or more return electrode portions 
           450  one or more return electrical interconnections 
           470  one or more contiguous portions 
           500  a bending interruption 
           600  a longitudinal axis 
           700  a first transverse axis 
           750  a second transverse axis 
           771  a first bending axis/point 
           772  a second bending axis/point 
           773  a third bending axis/point 
           774  a fourth bending axis/point 
           810  location for left supraorbital nerve or cortical stimulation 
           820  location for right supraorbital stimulation 
           830  location for left occipital nerve stimulation 
           840  location for right occipital nerve stimulation 
           850  location for deep brain stimulation 
           860  location for vagus nerve, carotid artery, carotid sinus, phrenic nerve or hypoglossal stimulation 
           865  location for cerebral spinal cord stimulation 
           870  location for peripheral nerve stimulation 
           875  location for spinal cord stimulation 
           880  location for gastric stimulation 
           885  location for sacral &amp; pudendal nerve stimulation 
           890  location for sacral neuromodulation 
           895  location for fibular nerve stimulation 
           910  left supraorbital nerve 
           920  right supraorbital nerve 
           930  left greater occipital nerve 
           940  right greater occipital nerve