Abstract:
High reliability electrical connections between a helical strand and flat electrodes, such us strip electrodes found in implantable neurostimulator system, are described. The connection consists of a crimp joint in which an inside diameter mandrel is used to provided the coil with sufficient radial rigidity to ensure structural integrity of the crimp. The mandrel is made of a relatively soft biocompatible material that deforms rather than damages the fine wires of the helical strand during crimping. The crimping is acomplished by radial deformation of an annular or semi-annular crimping member that receives the helical strand/mandrel assembly.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application is a divisional of U.S. application Ser. No. 10/968,310, filed Oct. 19, 2004, which claims priority from provisional application Ser. No. 60/512,739, filed Oct. 20, 2003. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     This invention relates to high reliability electrical attachments between coiled leads and flat electrodes, such as strip electrodes found in implantable neurostimulator systems. The requirements for the attachment are biocompatibility, isolation from body fluids, and long-term mechanical/electrical continuity under cyclic stress.  
         [0003]     A typical strip electrode consists of a thin, flat electrical contact of biocompatible, conductive material. A typical lead consists of a tightly wound coil of one or more helical strands of fine, fatigue resistant wire or filar elements. After attachment of the helical strand to the electrical contact, the entire assembly is potted or embedded in a flat sheet of elastomer so that only the face of the contact is exposed to body fluids.  
         [0004]     Implantable leads are made of wires typically about 0.002 inches to 0.004 inches in diameter. These wires are formed into coils or helical strands about 0.015-inches in diameter. Leads are coiled so they can withstand constant flexing and bending forces as a result of body movement. Because of the very fine wire diameters, however, the resulting helical strands are difficult to attach to electrical contacts by laser welding. Crimping is the preferred attachment method. In that respect, the present invention is directed to ensuring that the crimped connection between a helical strand and an electrical contact maintains the same degree of reliability as is built into the coiled lead itself.  
       SUMMARY OF THE INVENTION  
       [0005]     The connection between a coiled lead or helical strand and an electrical contact consists of a crimp joint in which an inside diameter mandrel is used to provide the coil with sufficient radial rigidity to ensure structural integrity of the crimp. The mandrel is made of a relatively soft biocompatible material that deforms rather than damages the fine wires of the helical strand during crimping. The crimp is accomplished by radial deformation of an annular or semi-annular crimping member that receives the helical strand/mandrel assembly.  
         [0006]     In one embodiment, the crimping member is a porous, deformable disk having an axial hole that receives the electrical contact and a radial hole that receives the helical strand/mandrel assembly. This deformable crimping member is subjected to a cold coining process that provides a secure crimp joint to the helical strand/mandrel assembly with a portion of the crimping member being extruded into a circumferential groove or channel in the central electrical contact. In that manner, the deformed crimping member creates a secure connection to the helical strand comprising the lead as well as to the electrical contact.  
         [0007]     In another embodiment, there is no deformable crimping member. Instead, the electrical contact made of a porous sintered material is itself deformable. That way, the electrical contact is provided with a radial bore that receives the mandrel supported in the lumen at the distal end of the helical strand. This assembly is inserted into the radial bore in the contact, which is then deformed into a locking relationship with the helical strand and mandrel.  
         [0008]     In another embodiment, as before, the integrity of the crimp is enabled by the presence of a relatively soft mandrel positioned inside the diameter of the helical strand. The mandrel has a distal portion that is secured to the back of the electrical contact by means of a weld, braze, or solder joint. Alternatively, the distal portion of the mandrel is inserted into a through-hole in the electrical contact, secured from the top face, and then bent over until the helical strand/mandrel connection is parallel to the back face of the contact. In any event, the crimping member consists of an annular or semi-annular crimp socket surrounding the helical strand/mandrel assembly.  
         [0009]     These and other aspects of the present invention will become more apparent to those skilled in the art by reference to the following description and to the appended drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]      FIG. 1  is a perspective view, partly in phantom, showing an implantable medical device  10  connected to a pair of strip electrodes  20  and  22  by respective coiled leads  16  and  18 .  
         [0011]      FIG. 2  is a cross-sectional view along line  2 - 2  of  FIG. 1 .  
         [0012]      FIG. 3  is a side elevational view, partly in cross-section, showing a helical strand  16 D of the coiled lead  16  crimped to an electrical contact  30  according to the present invention and encased in an elastomeric material  32 .  
         [0013]      FIG. 4  is a side elevational view, partly in cross-section, showing the electrical contact  30  prior to being moved into the central opening  56  in a deformable crimping member  46  and the helical strand  16 D/mandrel  44  prior to being moved into an axial bore  58  in the crimping member.  
         [0014]      FIG. 5  is a side elevational view, partly in cross-section, of the electrical contact  30  seated in the deformable crimping member  46 .  
         [0015]      FIG. 6  is a side elevational view, partly in cross-section, of the helical strand  16 D/mandrel  44  seated in the deformable crimping member  46 .  
         [0016]      FIG. 7  is a side elevational view, partly in cross-section, showing an annular punching ram  72  prior to deformation of the crimping member  46 .  
         [0017]      FIG. 8  is a side elevational view, partly in cross-section, showing the crimping member  46  being deformed by the punching ram  72 .  
         [0018]      FIG. 9  is a side elevational view, partly in cross-section, of another embodiment of a helical strand  114 /mandrel  112  assembly prior to being moved into the axial bore  110  of a deformable electrical contact  102 .  
         [0019]      FIG. 10  is a side elevational view, partly in cross-section, showing the helical strand  114 /mandrel  112  of  FIG. 11  moved into the bore  110  in the deformable electrical contact  102 .  
         [0020]      FIG. 11  is a side elevational view, partly in cross-section, showing a punching ram  116  beginning to deform the electrical contact  102 .  
         [0021]      FIG. 12  is a side elevational view, partly in cross-section, showing the helical strand  114  crimped to the electrical contact  102  and encased in an elastomeric material  116 .  
         [0022]      FIG. 13  illustrates another embodiment of an electrical contact  102 A having its upper surface  106 A spaced above the elastomeric material  116 .  
         [0023]      FIG. 14  is a side elevational view, partly in cross-section, showing a connection for a helical strand  124  to the electrical contact  102 .  
         [0024]      FIG. 15  is a side elevational view, partly in cross-section, showing the present invention connection of the helical strand  114  to the electrical contact  102 .  
         [0025]      FIG. 16  is a side elevational view, partly in cross-section, of another embodiment of a headed mandrel  136  crimped to a helical strand  134  secured to an electrical contact  132  and encased in an elastomeric material  148 .  
         [0026]      FIG. 17  is a side elevational view, partly in cross-section, of another embodiment of a mandrel  156  supported by a helical strand  154  secured to an electrical contact  152  and encased in a elastomeric material  166 .  
         [0027]      FIG. 18  is a side elevational view, partly in cross-section, of another embodiment of a mandrel  178  crimped to a helical strand  174  secured to the land  190  of an electrical contact  172  and encased in an elastomeric material  194 .  
         [0028]      FIG. 19  is a side elevational view, partly in cross-section, of another embodiment of a mandrel  208  crimped to a helical strand  204  secured to an electrical contact  202  provided with a flange  216  and encased in an elastomeric material  220 .  
         [0029]      FIG. 20  is a side elevational view, partly in cross-section, of another embodiment of a mandrel  238  crimped to a helical strand  234  secured to a deep drawn electrical contact  232  and encased in an elastomeric material  252 .  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0030]     Referring now to the drawings,  FIG. 1  illustrates an implantable medical device  10  comprising a housing  12  supporting a header  14  connecting coiled leads  16  and  18  to respective strip electrodes  20  and  22 . The housing  12  is of a conductive material, such as of titanium or stainless steel. Preferably, the medical device housing  12  comprises mating clamshell portions  24  and  26  in an overlapping relationship. The clamshell housing portions are hermetically sealed together, such as by laser or resistance welding, to provide an enclosure for control circuitry (not shown) connected to a power supply (not shown), such as a battery. There may also be a capacitor for a medical device such as a defibrillator. U.S. Pat. No. 6,613,474 to Frustaci et al. contains a more detailed description of a housing comprising mating clamshell portions. This patent is assigned to the assignee of the present invention and incorporated herein by reference. The housing  12  can also be of a deep drawn, prismatic and cylindrical design, as is well known to those skilled in the art.  
         [0031]     The header  14  is mounted on the housing  12  and comprises a body of molded elastomeric material supporting terminal blocks (not shown) that provide for plugging the proximal ends of leads  16  and  18  therein to electrically connect them to the control circuitry and power supply contained inside the housing. The distal ends of the leads  16 ,  18  connect to the respective strip electrodes  20  and  22 . For a more detailed description of the header assembly, reference is made to U.S. Pat. No. 7,167,749 to Biggs et al., which is assigned to the assignee of the present invention and incorporated herein by reference.  
         [0032]     The strip electrodes are surgically secured to body tissue whose proper functioning is assisted by the medical device. In that respect, the implantable medical device  10  is exemplary of any one of a number of known implantable therapeutic devices such as spinal cord stimulation devices, vagus nerve stimulation devices for epilepsy, and functional electrical stimulation devices for paralysis, and the like. For example, in an implantable pulse generator for spinal cord stimulation to control pain, the circuitry provides a pulsed stimulating signal that can be current controlled or voltage controlled. The signal is delivered to nerves entering the spinal cord by means of implanted insulated coiled leads terminating at strip electrodes such as those shown in  FIG. 1 .  
         [0033]     The strip electrodes  20  and  22  can be similar or different in construction. Strip electrode  20  comprises four electrical contacts  24 ,  26 ,  28  and  30 , each having a circular shape in plan view and potted in an elastomeric material  32 . Strip electrode  22  comprises four electrical contacts  34 ,  36 ,  38  and  40  potted in an elastomeric material  42 . These contacts are square, triangular, hexagonal, and rectangular in plan view, respectively. In that respect, the present invention is not limited to the exact shape of the electrical contact and is adaptable to contacts having a myriad of shapes in plan form. Nonetheless, the present invention will be described with respect to strip electrode  20  shown in greater detail in  FIG. 2  with the understanding that strip electrode  22  is generally similar in construction.  
         [0034]     As shown, each electrical contact  24 ,  26 ,  28  and  30  is individually connected to the medical device  10  by a helical strand or filar of the coiled lead  16 . Suitable materials for the electrical contacts include carbon such as pyrolytic carbon, titanium, zirconium, niobium, molybdenum, palladium, hafnium, tantalum, tungsten, iridium, platinum, gold, and alloys thereof. Stainless steel, MP35N®, ELGILOY® are other suitable alloys. The helical strands can be co-axial or they can be coiled side-by-side along the length of the coiled lead  16  until it enters the elastomeric material  42  of the strip electrode  20 . There, the individual helical strands  16 A,  16 B,  16 C and  16 D separate from the bundle and connect to the individual electrical contacts  24 ,  26 ,  28  and  30 , respectively. Each helical strand is formed of a conductive, fatigue resistant material such as ELGILOY® (cobalt 40%, chromium 20%, nickel 15%, molybdenum 7%, manganese 2%, carbon&lt;0.10%, beryllium&lt;0.10%, and iron 5.8%, by weight) or MP35N® (nickel 35%, cobalt 35%, chromium 20%, and molybdenum 10%, by weight) alloys. The coiled leads comprised of the helical strands exhibit the desired mechanical properties of low electrical resistance, high corrosion resistance, flexibility, strength and fatigue resistance required for long term duty inside a human body, and the like.  
         [0035]      FIG. 3  shows a cross-sectional view of helical strand  16 D secured to electrical contact  30 . A deformable mandrel  44  is inserted into the distal end of the helical strand  16 D. Suitable materials for the mandrel include stainless steel, titanium, zirconium, niobium, molybdenum, palladium, hafnium, tantalum, tungsten, iridium, platinum, gold, and alloys thereof. A crimping member  46  is then coined into locking contact with the helical strand  16 D and the surrounded electrical contact  30 . The process for coining the helical strand  16 D into this locking relationship will now be described in greater detail in the progression of FIGS.  4  to  8 .  
         [0036]     As shown in  FIG. 4 , the deformable crimping member  46  in the form of a porous sintered disc has an annular outer sidewall  48  and an annular inner sidewall  50 , both extending to an upper surface  52  and a lower surface  54 . A circular, axial opening  56  is formed in the disc by the inner annular sidewall  50 . A radial bore  58  extends from the outer annular sidewall  48  to the inner annular sidewall  50  and the circular opening  56 . The radial bore  58  is located approximately an equal distance from the upper and lower surfaces  52 ,  54  and is sized to receive the electrical contact  30 . The electrical contact  30  has a circular cross-section comprising an annular sidewall  60  extending to an upper face  62  and a lower face  64 . An annular groove or channel  66  recessed in the sidewall  60  surrounds the electrical contact and is spaced closer to the lower face  64  than the upper face  62 .  
         [0037]     As shown in  FIGS. 4 and 5 , the electrical contact  30  is received in the circular opening  56  in the deformable crimping member  46  such that the disc sidewall  60  is in a tight-fitting relationship with the inner annular sidewall  50  thereof.  
         [0038]     As shown in FIGS.  4  to  6 , the helical strand  16 D provides a lumen  68  receiving the tapered mandrel  44  at its distal end. The mandrel  44  has a cylindrically shaped sidewall received in the helical strand lumen in a tight-fitting relationship. Preferably, the mandrel diameter is slightly larger than the inside diameter of the helical strand so it stays in place inside the coil while it is being assembled. A planar distal end  70  of the mandrel  44  is recessed somewhat inside the distal end of the strand  16 D. The reason for this is to have the helical strand/mandrel contact interface as great as possible. A proximal end thereof tapers toward the longitudinal axis of the mandrel  44 . The taper has a radiused profile with the radius being about 10 to about 20 times the diameter of the mandrel. The helical strand  16 D and mandrel  44  received in the lumen  68  thereof is then received in the axial bore  58  of the deformable crimping member  46  with the planar distal mandrel end  70  spaced from the inner disc annular sidewall  50  defining the opening  56 . In this position, the longitudinal axis of the mandrel is spaced somewhat toward the upper surface  52  of the deformable crimping member  46  with respect to the center of the annular groove  66 .  
         [0039]     As shown in  FIG. 7 , this assembly is loaded in an open-die punching fixture having an annular ram  72  sized to the exact shape of the upper surface  52  of the deformable crimping member  46  surrounding the electrical contact  30 . The porous crimping member is formed by low-pressure pressing or by loose bed sintering of powdered stainless steel, titanium, platinum, or platinum alloy. The powder may be atomized spherical powder particles, or, preferably, “sponge” powder (such as powders reduced from a metal chloride), which have higher strength at the relatively low densities used in the present crimping member. A sintering profile is typically 1,150° C. for three hours at temperature in vacuum for titanium and stainless steel, or 1,625° C. for three hours at temperature in air for platinum to produce a low-density structure combined with a high degree of sintering. The sintered particles have relatively large diameter interparticle necks, but at a relative density of only about 60% to 70%. This allows the porous crimping member to undergo cold coining to a density of around 80% during the crimping process while maintaining its structural integrity.  
         [0040]     In that respect, a sufficient amount of force is exerted on the crimping member  46  to compress it into a final shape having its upper surface  52  spaced a relatively short distance from the groove  66 . As this occurs, material  46 A comprising the crimping member  46  flows by plastic deformation into the groove  66  to lock the deformable disc to the electrical contact  30 . This deformation also causes the crimping member  46  to lock onto the rugosity of the helical strand  16 D/mandrel  44  assembly. A typical cold coining pressure is about 10,000 psi, which is sufficient to increase the density of the deformable crimping member  46 , form the crimp, and intrude the inside diameter material of the crimping member into the electrical contact without pinching off the fine wires of the helical strand  16 D.  
         [0041]     As shown in the final assembly of  FIG. 3 , encasing the deformable crimping member  46 , helical strand  16  and electrical contact  30  in the biocompatible elastomeric material  32 , such as silicone or polyurethane, completes the strip electrode. After cold coining, a longitudinal axis of the mandrel  44  is substantially centered with the trough of the groove  66 . After cold coining, the annular outer sidewall of the crimping member assumes the shape of a bulge  48 A, which helps lock the polymer material  32  to the crimping member  46 . Before deformation, electrical contact  30  is shown having a circular cross section. However, it may also have a frusto-conical shape before deformation to further improve the interlock with the elastomeric material.  
         [0042]     Only the upper face of the electrical contact  30  is left exposed. This surface may be impregnated with liquid silicone or other biocompatible resin that is then polymerized to seal the porosity, and to keep body fluids from infusing into the porous electrode and reaching the coiled lead. The remaining surfaces of the electrical contact  30  exposed to the elastomeric material is preferably roughened by grit blasting, machining marks, knurling, and the like to improve adhesion of the potting material to the electrode and stabilize the electrode position.  
         [0043]     FIGS.  9  to  12  illustrate another embodiment of a strip electrode  100  according to the present invention. The electrode comprises a porous sintered deformable electrical contact  102  having a surrounding sidewall  104  extending to upper and lower surfaces  106  and  108 . Suitable materials for the contact  102  include titanium, zirconium, niobium, molybdenum, palladium, hafnium, tantalum, tungsten, iridium, platinum, gold, and alloys thereof. An annular bore  110  enters the body from the sidewall  104 , spaced closer to the lower surface  108  than the upper surface  106 .  
         [0044]     As shown in  FIG. 10 , a tapered mandrel  112 , similar to the previously described mandrel  44 , supported in the lumen at the distal end of a helical strand  114  are received in the bore  110 . A pressing ram  116  then deforms the electrical contact  102  into locking contact with the rugosity provided by the coils of the helical strand  114 . The electrical contact  102  has a relative density of about 60% to about 70% prior to being deformed under the compression pressure and about 80% after being deformed into the locking relationship.  
         [0045]     Encasing the deformed electrical contact  102  and helical strand  114  in a biocompatible elastomeric material  116 , such as silicone or polyurethane, completes the electrode  100 . After cold coining, the surrounding sidewall of the electrical contact assumes the shape of a bulge  104 A. This helps lock the polymer material  116  to the contact. only the upper active surface  106  of the electrical contact  102  is left exposed. In a similar manner as the contact  30  in FIGS.  1  to  8 , this upper surface  106  may be impregnated with liquid silicone or other biocompatible resin that is then polymerized to seal the porosity and to keep body fluids from infusing into the porous electrode and reaching the coiled lead.  
         [0046]     In  FIG. 12 , the upper surface  106  of the electrical contact  102  is substantially coplanar with that of the elastomeric material  116 . In  FIG. 13 , the upper surface  106 A of the electrical contact  102 A is spaced above the upper surface of the elastomeric material.  
         [0047]     An important aspect of the present embodiments illustrated in FIGS.  1  to  12  is that the extended, tapered mandrels  44 ,  112  distribute the bending, flexing and twisting strain forces caused by body movement over a greater length of the helical strands  16 D,  114  than in a mandrel having a blunt end. This is shown in  FIG. 15  by the gap of arrows designated  118  in comparison to the strain distribution indicated by the gap of arrows  120  afforded by a mandrel  122  having the blunt end construction shown in  FIG. 13 . The length of gap  118  is about 1 to 5 diameters of the helical strand, preferably about 2 to 3 diameters. In the blunt end mandrel  122 , strain forces on the helical strand  124  moving along a 20° arc are significantly more concentrated in comparison to a similar degree of movement in the present construction.  
         [0048]     Another embodiment of a strip electrode  130  comprising an electrical contact  132  secured to a helical strand  134  according to the present invention is shown in  FIG. 16 . Machining, stamping, metal injection molding, drawing, and any other suitable method can make the contact  132 . In the case of machining and metal injection molding, the mandrel/contact assembly may also be formed as a single integral unit. This electrode comprises a mandrel  136  having a tapered nose  138  received in the lumen of the helical strand  134 . A significant portion of the mandrel  136  extends out the distal end of the helical strand  134 . A distal end of the mandrel  136  is in the shape of a spherical ball  140  sized about 0.010 inches larger in diameter than that of the mandrel. The distal ball  140  is secured to the back face  142  of the electrical contact  132  by braze, weldment, or solder joint  146 . An effective braze load is about 10 mg of gold at a temperature of about 1,100° C. for two seconds at temperature. Many other braze materials other than gold can be used, however, for example gold-tin or copper-silver braze alloys.  
         [0049]     An annular or semi-annular socket  146  is positioned on the distal end of the helical strand  134  with the mandrel received in the lumen thereof. The crimp is accomplished by radial deformation of the socket  146 . That way, the material of the socket  146  plastically deforms into the rugosity of the helical strand  134  that, in turn, tightly surrounds the cylindrical intermediate section of the mandrel  136 . Materials appropriate for the socket  146  include stainless steel, titanium, niobium, zirconium, platinum and platinum alloys, and other biocompatible deformable materials. The entire assembly is encased in a elastomeric material  148  such as silicone or polyurethane with only the active surface  150  of the electrical contact  132  being left exposed. This construction provides improved isolation of the crimp joint from body fluids that may diffuse along the electrical contact/elastomer interface.  
         [0050]      FIG. 17  illustrates a further embodiment of a strip electrode  150  comprising an electrical contact  152  secured to a helical strand  154  according to the present invention. A mandrel  156  has its distal end received in an axial opening  158  in the contact  152 . A braze, weldment or solder joint  160  secures the mandrel to the contact. Then, the mandrel  156  is bent until the longitudinal axis of the helical strand  154  is substantially parallel to the upper contact face  162 .  
         [0051]     Connection of the mandrel  156  to the helical strand  154  is similar to that shown in  FIG. 16  with a deformable socket  164  clamped onto the helical strand receiving the mandrel. Finally, the entire assembly is encased in an elastomeric material  166 , such as silicone or polyurethane, with only the active contact face  164  left exposed.  
         [0052]      FIG. 18  illustrates a further embodiment of a strip electrode  170  comprising an electrical contact  172  secured to a helical strand  174  by a deformable crimp socket  176  according to the present invention. A cylindrically shaped mandrel  178  having a tapered nose  180  is received in the lumen of the helical strand  174 . A distal portion  182  of the mandrel  178  extends out the distal end of the helical strand  174 . The electrical contact  172  comprises a contact face  184  extending downwardly and outwardly to form a chamfered edge  186 . The back face  188  has a protruding land  190  to which the distal portion  182  of the mandrel is secured by braze, weldment or solder joint  192 . To further enhance this connection, the distal portion  182  of the mandrel may have a flat surface received in a coinciding groove or channel in the land  190 . This assembly is then encased in an elastomeric material  194 , such as silicone or polyurethane, with only the contact face  184  left exposed.  
         [0053]      FIG. 19  illustrates a further embodiment of a strip electrode  200  comprising an electrical contact  202  secured to a helical strand  204  by a deformable crimp socket  206  according to the present invention. A mandrel  208  having a tapered nose  210  is received in the lumen of the helical strand  204 . A distal portion  212  of the mandrel  208  extends out the distal end of the helical strand  204 . The electrical contact  202  comprises a contact face  214  extending downwardly to a flange  216 . As with the strip electrode  170  of  FIG. 18 , the distal portion  212  of the mandrel is cylindrical, flattened or of some other cross-section received in a coinciding groove or channel on the back face  216  of the contact  202  secured thereto by a braze, weldment or solder joint  218 . This assembly is then encased in a elastomeric material  220  with only the contact face  214  left exposed.  
         [0054]      FIG. 20  illustrates a further embodiment of a strip electrode  230  comprising a deep drawn electrical contact  232  secured to a helical strand  234  by a deformable crimp socket  236  according to the present invention. A mandrel  238  having a tapered nose  240  is received in the lumen of the helical strand  234 . A distal portion  242  of the mandrel  238  extends out the helical strand  234 . The electrical contact  232  is made of a conductive metal such as any one previously described as useful for the contacts shown in alternate embodiments of the present invention. The electrical contact  232  has an upper contact face  244  connected to a frusto-conical portion  246  extending downwardly and outwardly to a surrounding rim  248 . The rim  248  is generally parallel to the plane of the contact face  244 . The distal portion  242  of the mandrel is secured to the rim  248  by braze, weldment or solder joint  250 . Preferably, the distal portion of the mandrel  238  and that portion of the rim  248  supporting the mandrel have coinciding shapes for added strength to the connection. This assembly is then encased in an elastomeric material  252  with only the contact face  244  left exposed.  
         [0055]     Thus, the present invention has been described with respect to various structures and methods for making high reliability electrical attachments between coiled leads and flat electrodes such as strip electrodes found in implantable neurostimulator systems. The attachment requirements of biocompatibility, isolation from body fluids, and long-term mechanical/electrical continuity under cyclic stress are met by the novel mandrel received in the helical strand connected to the electrical contact by the deformable crimping member, the deformable contact itself, or by the mandrel being secured to the contact through a braze, weldment or solder joint.  
         [0056]     It is appreciated that various modifications to the inventive concepts described herein may be apparent to those of ordinary skill in the art without departing from the spirit and scope of the present invention as defined by the appended claims.