Abstract:
A medically implantable electrical connector includes a housing having a bore with an internal V-groove or a flat bottom groove therein along with radial garter spring disposed in the V-groove or an axial garter spring disposed in the flat bottom groove. A pin is provided and sized for insertion in the housing bore. The housing, spring and pin are formed from a combination of medically implantable materials in order to control electrical resistivity between the housing, the garter spring and the pin.

Description:
This application claims the benefit of Provisional Application No. 60/357,360 filed Feb. 15, 2002. 
    
    
     The present invention is directed to medically implantable electrical connectors and is more particularly directed to medical connectors which have tailored connect and disconnect forces. Such connectors can be used in a number of medical devices such as, for example, pace makers defibrillators, and neuro-stimulators. Medically implantable electrical connectors are adherently different than a vast majority of other electrical connections due to the environment and critical nature of their use. Such medical connectors must not only be made of materials suitable for implanting within a body, but also must provide positive and unvarying conductivity thereacross in order to insure reliability of a functioning medical device. 
     Heretofore, implantable electrical connectors have utilized a lead wire, or pin, and a housing with the lead wire removably fixed to the housing by a set screw. It should be appreciated that such set screws are small, thus losable. In addition, a set screw is very torque sensitive and requires a tool for installation. 
     The present invention provides for an implantable electrical connector with reduced resistivity and reduced resistivity variability under static and dynamic loading without the necessity of an installation tool. 
     SUMMARY OF THE INVENTION 
     A medically implantable electrical connector in accordance with the present invention generally includes a housing having a bore with an internal groove therein along with a garter spring disposed in a groove. 
     A pin is sized for insertion into the housing bore and may include an external groove for capturing the spring in order to removably latch the pin within a housing bore. 
     Reduced resistivity across the connector including the housing spring and pin is achieved through the use of a shaped V-groove and by forming the housing, spring and pin from a combination of medically implantable materials in order to control the resistivity. Preferably, the spring is formed from platinum iridium. 
     In one embodiment of the present invention, the pin does not include the external groove and the housing groove is a V-groove. More particularly, the V-groove may have an included angle of about 135° and in the embodiment including the pin groove a cross-section of the pin groove may include a flat center portion subtended by angled sides. As hereinafter described a V-groove with a radial spring provides for greater conductivity of the connector with enhanced conductivity stability than a flat bottom groove with a radial spring. 
     Still more particularly, the angled sides may be disposed at about a 45° with a flat center. 
     In all of the embodiments of the present invention, one of the housing pin, or spring is preferable formed from platinum iridium with the most preferred being a platinum iridium spring. The remaining components, namely the housing and pin may be formed from MP35N or titanium grade-5 or stainless steel. 
     Other embodiments of the present invention include a connector with a housing V-groove and a radial garter spring, or a connector with a housing flat groove and an axial spring. The axial spring provides for greater conductivity with a housing with flat grooves in view of the fact that the axial spring motion produces a scraping action that removes oxides thus decreasing resistivity. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will be better understood by reference to the accompanying drawings, in which: 
     FIG. 1 is a view of one embodiment of the present invention, in partial cross section, generally showing a housing having a V-groove, a spring disposed therein along with a pin having a external groove. 
     FIGS. 1 b - 1   f  show the embodiment of FIG. 1 a  in stepwise illustration of insertion, connect-latch, and disconnect in one direction and connect latch and disconnect in an opposite direction; 
     FIGS. 2 a - 2   d  show an alternative embodiment of the present invention in stepwise connect and disconnect fashion as shown in FIGS. 1 a - 1   f  utilizing a non-grooved pin; 
     FIGS. 3 a - 3   d  illustrate yet another alternative embodiment of the present invention utilizing a housing having a flat bottom and a grooveless pin and further showing stepwise insertion and disconnect of the pin from the housing; and 
     FIGS. 4 a - 4   d  show a further alternative embodiment of the present invention similar to that shown in FIGS. 3 a - 3   d  except the radial spring of FIGS. 3 a - 3   d  is replaced with an axial spring  76 . 
    
    
     DETAILED DESCRIPTION 
     In general, two types of connectors will be hereinafter described. One type is for latching as shown in FIGS. 1 a - 1   f  in which the connector  10  includes a pin  12  retained in a housing  14  by a spring  16  within a bore  22  (See FIG. 1 b ), only one half of the pin  12  and housing  14  being shown as indicated by a centerline  24 . 
     Shown in FIGS. 2 a - 2   d ,  3   a - 3   d  and  4   a - 4   d  are connectors  30 ,  50 ,  70  for holding pins  32 ,  52 ,  72  within respective housings  34 ,  54 ,  74  with bores  35 ,  55 ,  75  by the friction force derived by compressing a canted coil spring  36 ,  56 ,  76 . Similar to FIGS. 1 a - 1   f  only one half of the pins  32 ,  52 ,  72  and housings  34 ,  54 ,  74  are shown as indicated by centerlines  37 ,  57 ,  77 . 
     The springs  16 ,  36 ,  56 ,  76  may be radial canted coil springs  16 ,  36 ,  56 , with a housing V-groove  15 ,  38 , or axial canted coil springs  76  with a flat bottom-housing groove  78 . It has been found that axial springs are preferable for a flat bottom housing groove  78  inasmuch as there is a greater coil density, i.e. more coils per arcuate distance, disposed against the pin and a scraping motion of the axial spring  76  removes oxides. 
     The springs  16 ,  36 ,  56 ,  76  may be inserted clockwise or counterclockwise with a back angle on the inside or the outside. Suitable springs are taught in U.S. Pat. Nos. 5,108,076, FIGS. 1-6, U.S. Pat. No. 4,893,795, FIGS. 4, 5a, 5b, 5c, 5d, 5e, 6a, and 6b and U.S. Pat. No. 5,139,243, FIGS. 1a, 1b, 2a, and 2b to Balsells. All of these patents are to be incorporated herewith for teaching suitable spring designs for the present invention. 
     The springs  16 ,  36 ,  56 ,  76  are generally made with an outside diameter slightly larger than the housing groove I.D.s so that upon assembling the spring  16 ,  36 ,  56 ,  76  into the grooves  18 ,  38 ,  58  and  78  it creates interference with the outside diameter of the spring and the inside diameter of the housing groove  18 ,  38 ,  58 ,  78 . With regard to springs  16 ,  36 ,  56 , the interference provides a radial compression load that retains the spring  16 ,  36 ,  56  in the housing  14 ,  34 ,  54 . The springs  16 ,  36 ,  56 ,  76  may be inserted clockwise or counter clockwise. 
     With regard to the spring  76 , the interference provides an axial compression load that retains the spring  76  within the housing  74 . In this manner, the springs  16 ,  36 ,  56 ,  78 , are firmly retained in place. It also insures conductivity between the outside diameter of the spring  16 ,  36 ,  56 ,  76  and the housing  14 ,  34 ,  54 ,  74 . 
     As hereinabove noted, resistivity is a very important factor since the greater the resistivity the more electrical energy is dissipated as heat across the connector  10 ,  30 ,  50 ,  70 , which is drawn from a battery. (not shown), thus, limiting the life of the battery. 
     It has been discovered that by utilizing a V-groove  18 ,  38  substantially lower resistivity is achieved with a radial spring compared with a flat bottom groove with a radial spring. At the same time, with a V-type groove  18 ,  38  the spring  16 ,  36  is more constrained resulting in more consistent resistivity and less shuttling occurs. 
     The area of contact between the springs  16 ,  36  coils and the housing  14 ,  34  also effects the resistivity. The greater the area of contact of the springs  16 ,  36  with the housing  14 ,  34 , the lower the resistivity. 
     It should be appreciated that it is very important that during operation, the resistivity, or conductivity, remains constant. The geometry of the spring  14 ,  84  and groove  18 ,  38  minimizes the amount of movement that may occur. 
     Connector  10  provides for latching. That is, the pin groove  20 , when aligned with the housing groove  18  with the spring  16  therebetween, provides latching action as well as conductivity. At the same time such V-grooves  18  in the housing  14  assures consistent retention and resistivity. 
     It should be appreciated that while FIGS. 1 a - 1   f  illustrate the spring  16  being retained in the housing  14 , the spring  16  may also be retained on the pin  12 . 
     The type of V-groove  18 , as hereinabove noted, effects the position, constraint of the spring and reduces the variability of resistivity. The V-groove  18  and the housing  14  may have various angles less than 180° to an included angle of about 135° or 90°, among others as shown in FIGS. 1 a - 1   f  and FIGS. 2 a - 2   d . It has been found that a 45° (90° included angle) constrains the coils, allows good retention in the coils and provides reduced resistivity. 
     Increasing the deflection of the coils will tend to increase the force. The increase in force will reduce resistivity and increase the constraint of the spring  16 ,  36 ,  56 ,  76  minimizing the variability of resistivity, especially under dynamic loads. The force may be varied by various manners, such as, for example, the back or front angle of the coils, wire diameter, ratio of coil height to wire diameter among others. All these parameters are discussed in the hereinabove referenced U.S. Patents which have been incorporated herewith. 
     The ratio of disconnect to connect force can be controlled within a ratio of about 1 to 1 to about 10 to 1. With a high disconnect to connect force ratio conductivity is maintained. A number of condition for providing force ratios include: 
     1. Directional. Higher ratio when the pin contacts the front angle first on insertion. This is indicated by the black dot on the coil along the major axis at insertion or disconnect and the direction of insertion. 
     2. Higher disconnect to connect ratios are obtained when the centerline of the coil along the major axis is closer to the pin or shaft load point. 
     3. The following parameters also affect the force differential: 
     a. Ratio of coil height to wire diameter. 
     b. Ratio of coil width to coil height. 
     c. The back and front angle of the coil. 
     d. The coil height. 
     e. Coil width. 
     f. Wire diameter. 
     g. Material properties of the material, such as tensile, elongation, and modulus of elasticity. 
     h. The location of the centerline of the coil along the major axis relative to the pin or shaft load point. 
     i. The geometry of the housing. 
     j. The spring orientation. 
     Flat bottom groove with axial spring compared to flat bottom groove with radial spring. These are two differences that are very important. Axial spring is compressed at assembly along the minor axis of the coil and in doing so increases the force acting on the walls of such groove and the more the squeeze between the coil height and the groove width the higher the radial force that is generated. This affects the radial force required to pass the pin through the housing contacting the spring. Such added force has an effect on the conductivity and resistivity that is not linear. 
     The referenced patents also discuss the relationship between the angles of the pin, angles on the housing and shape of the coil, be it round or elliptical, such that it maximizes the area of contact between group services and the spring coils. 
     Operation in the stepwise manner of inserting the pins  12 ,  32 ,  52 ,  72  and the housings  14 ,  34 ,  54 ,  74  for latch or resistive hold are shown in a stepwise manner in FIGS. 1 a - 1   f ,  2   a - 2   d ,  3   a - 3   d  and  4   a - 4   d  respectively. 
     It has been discovered that combining different materials of construction for the connection  10 ,  30 ,  50 ,  70  provides a method for substantially effecting the resistivity of the connectors  10 ,  30 ,  50 ,  70 . Materials for medical applications must be of the type that are stable in implant applications, such as, for example, stainless steel type 316L, MP35N, platinum-iridium, titanium and others. 
     It has been unexpectedly found that the use of platinum iridium in the pin  12 ,  32 ,  52 ,  72 , housing  14 ,  34 ,  54 ,  74 , or spring  16 ,  36 ,  56 ,  76  reduces resistivity. This is particularly the case when the spring is formed of platinum iridium. The housing  14 ,  34 ,  54 ,  74  and pin  12 ,  32 ,  52 ,  72  may be formed from another material such as MP35N or titanium grade-5. With all of these materials the surface finish of the mating parts effects resistivity with the better the surface condition, the more intimate contact between mating parts and the lower force that is required to maintain resistivity. 
     Table 1 shows condensed data on resistivity of different types of groove springs and materials all made with a common dimensions. 
     
       
         
               
             
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 CONDENSED DATA ON RESISTIVITY OF DIFFERENT TYPES OF GROOVES, SPRINGS 
               
               
                 AND MATERIAL 
               
             
          
           
               
                   
                   
                   
                   
                 % Variation 
                   
                 % Variation 
               
               
                   
                   
                   
                   
                 Between 
                   
                 Between 
               
               
                   
                   
                 Flat Bottom- 
                 V-Bottom 
                 Flat Bottom 
                 Flat Bottom 
                 Flat Bottom 
               
               
                   
                   
                 RADIAL 
                 RADIAL 
                 Radial and 
                 AXIAL 
                 Radial and 
               
               
                 Item 
                 Material 
                 Resistance Ω 
                 Resistance Ω 
                 V-Bottom 
                 Resistance Ω 
                 Flat Bottom 
               
             
          
           
               
                 No. 
                 Housing 
                 Spring 
                 Pin 
                 Average Value 
                 Average Value 
                 Radial 
                 Average Value 
                 Axial 
               
               
                   
               
             
          
           
               
                 1 
                 PT-IR 
                 MPN 
                 MPN 
                 0.320 
                 0.203 
                 36.7% 
                 0.127 
                  52.6% 
               
               
                 2 
                 TNM5 
                 MPN 
                 MPN 
                 .671 
                 0.488 
                 27.2% 
                 0.296 
                 137.9% 
               
               
                 3 
                 MPN 
                 MPN 
                 MPN 
                 1.964 
                 1.065 
                 45.7% 
                 0.590 
                 300.3% 
               
               
                 4 
                 S.S. 
                 MPN 
                 MPN 
                 2.611 
                 1.496 
                 42.7% 
                 0.860 
                 410.1% 
               
               
                   
               
               
                 NOTE: Data Sorted by Average V-Bottom Housing Resistance  
               
             
          
         
       
     
     In Table 1 the symbol S.S. is a stainless steel type 316L, PT-IR is platinum-iridium, MPN is MP35N and TNM-5 is titanium grade-5. 
     As shown in Table 1 when using an axial spring  76  a groove  78  the lowest resistivity is produced in each case. The next lowest resistivity is achieved when using a radial spring  16  in a V-bottom groove  18 . The reduction in percentage of resistivity between a flat bottom groove  58  with a radial spring  56  and a V-bottom groove  38  with a radial spring  36  along with a flat bottom groove  78  with an axial spring  76  illustrates a significant advantage in the selection of groove and spring types. 
     However, it is important to recognize that the use of platinum iridium leads to lowest resistivity of the connectors  10 ,  30 ,  50 ,  70 . 
     Although there has been hereinabove described specific electrical connectors with conductivity means for holding and latching in accordance with the present invention for the purpose of illustrating the manner in which the invention may be used to advantage, it should be appreciated that the invention is not limited thereto. That is, the present invention may suitably comprise, consist of, or consist essentially of the recited elements. Further, the invention illustratively disclosed herein suitably may be practiced in the absence of any element which is not specifically disclose herein. Accordingly, any and all modifications, variations or equivalent arrangements which may occur to those skilled in the art, should be considered to be within the scope of the present invention as defined in the appended claims.