Abstract:
The limbs of a bipolar forceps for RF coagulation are produced from a bimetal material, wherein an outer layer ( 18 ) consists of stainless steel and determines the mechanical properties of the forceps, while an inner layer ( 20 ) consists of a sliver alloy. An electrode ( 30 ) is formed from the inner layer at the distal end of the limbs ( 16 ). The inner layer ( 20 ) brings about good heat dissipation from the electrodes ( 30 ) and prevents the tissue from sticking thereto during coagulation.

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to a bipolar forceps, more particularly for RF coagulation, as per the preamble of patent claim  1 . 
     In surgery, bipolar forceps are used for coagulating the tissue of a patient. To this end, radiofrequency AC current is generally conducted through the tissue in order to heat and coagulate the latter. The forceps used for this purpose have differently shaped limbs, depending on intended use, with respectively one electrode being formed at the distal tips of the two limbs. The tissue to be coagulated is brought between the electrodes. The RF current is supplied via a plug-in connector attached proximally on the forceps and conducted through tissue via the electrodes. 
     A problem in the case of these bipolar forceps is that the RF current heats not only the tissue situated between the electrodes. The electrical contact resistance between the tissue and the contact areas of the electrodes touching the tissue also leads to heating of the electrodes. The heating of the electrodes can lead to the tissue sticking to the contact area of the electrodes. This leads to dirtying of the contact areas by the stuck-on tissue and increases the contact resistance for subsequent coagulations. Moreover, the tissue sticking-on can lead to stuck-on tissue parts being carried along when the forceps is removed and the tissue being damaged as a result of this. 
     In order to counteract this sticking-on of the tissue, the heating of the electrodes is known to be reduced by providing the electrodes with a metal, which has a high thermal conductivity for dissipating heat from the contact area of the electrodes. Moreover, this metal must have good electrical conductivity in order to conduct the RF current. Finally, the metal must be biocompatible, i.e. it must not damage the tissue chemically. Suitable metals with these properties are, in particular, the precious metals silver and gold, wherein silver should be preferred, more particularly also for reasons of cost. In the case of a bipolar forceps known from EP 1 210 022 B1, the distal tips of the limbs, consisting of stainless steel, of the forceps are for this purpose surrounded by a layer of silver or gold. This layer forms the electrodes with the contact areas thereof and at the same time forms a heat reservoir with a relatively large heat capacity for absorbing heat dissipated from the contact area. In the case of a bipolar forceps known from DE 10 2008 022 889 A1, a channel leading to the contact area of the electrodes is worked into the distal ends of the limbs, consisting of stainless steel, of the forceps, which channel is filled with silver to form a heat conduction channel for dissipating the heat from the contact areas. In these known bipolar forceps, the formation of the heat dissipation is connected with additional work steps during the production of the forceps. 
     BRIEF SUMMARY OF THE INVENTION 
     The invention is based on the object of simplifying the production of a bipolar forceps as per the preamble of claim  1 . 
     According to the invention, this object is achieved by a bipolar forceps with the features of patent claim  1 . According to the invention, such a forceps is produced by a method as per patent claim  9 . 
     Advantageous embodiments of the invention are specified in the dependent claims. 
     In the case of the bipolar forceps according to the invention, the two limbs of the forceps are each produced from a bimetal material, which consists of a first layer of an elastically resilient metal and a second layer made of a metal with high electrical and thermal conductivity. The bimetal material is produced in a fashion known per se by placing a strip made of the elastically resilient metal and a strip made of the metal with the high conductivity flat on top of one another and connecting them integrally. The integral connection is usually brought about by cold welding under pressure, more particularly by rolling. The limbs of the forceps are made by deformation from the bimetal strip produced thus. To this end, the limbs of the forceps are stamped out of the bimetal strip, preferably available in the form of a large-area metal strip, and deformed under pressure. This affords the possibility of producing the blanks of the limbs of the forceps from the bimetal strip in a single work step by stamping and compression processing by means of a press. 
     The first layer made of the elastically resilient metal in the process forms the outer side of the limbs, while the second layer made of the metal with the high electrical and thermal conductivity forms the inner sides of the limbs facing one another. Here, the first layer provides the limbs of the forceps with the mechanical rigidity and the resilient properties for opening and closing the forceps. The electrodes are formed at the distal end of the limbs from the metal of the second layer. As a result of its areal extent, the second layer has a high heat capacity, with the high thermal conductivity ensuring rapid dissipation of the heat from the electrodes into the volume of the second layer. 
     The first layer, which forms the outer side of the limbs of the forceps, preferably consists of stainless steel. Silver or a silver alloy is preferably selected as biocompatible metal with high thermal and electrical conductivity for the second layer. 
     The second layer should preferably at least extend over half the length of the limb at the distal end of the limb in order to provide a sufficient volume of this layer and hence sufficient heat capacity for absorbing the dissipated heat. However, the second layer preferably extends over the entire inner surface of the limbs. A first advantage of this is the particularly high thermal capacity, and it also simplifies the production in particular because the blanks of the limbs can be stamped out of a bimetal strip with two layers throughout. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the following text, the invention will be explained in more detail on the basis of an exemplary embodiment illustrated in the drawing, in which: 
         FIG. 1  shows a bimetal strip as basic material for producing the limbs of a bipolar forceps, 
         FIG. 2  shows a section through the bimetal strip, 
         FIG. 3  shows a blank of a limb of the forceps formed from the bimetal strip, in a view from the outer side and from the inner side, 
         FIG. 4  shows a side view of the limb, 
         FIG. 5  shows an enlarged view of the distal end of the limb, 
         FIG. 6  shows a perspective view of the bipolar forceps and 
         FIG. 7  shows a side view of this forceps. 
     
    
    
     In the drawing, a bipolar forceps for RF coagulation is, as an example, illustrated in an embodiment with straight limbs. Forceps with other limb shapes, e.g. curved limbs, are likewise conventional. Since the invention relates to the structure of the limbs of the forceps and not to the shape thereof, all shapes of forceps that have the structure explained below fall within the scope of the invention. 
     DETAILED DESCRIPTION OF THE INVENTION 
     In order to produce the forceps, a bimetal strip  10  is firstly produced as basic material. To this end, a strip  12  of a sheet made of an elastically resilient material and a strip  14  of a sheet made of a biocompatible metal with high electrical and thermal conductivity are placed flat on top of one another. The strip  12  preferably consists of stainless steel. The strip  14  preferably consists of silver or a silver alloy, more particularly of AgNiO.15. The strip  12  for example has a material thickness of 1.5 mm and the strip  14  for example has a material thickness of 1 mm. The strips  12  and  14  lying flat on top of one another are rolled onto one another under pressure, or are pressed onto one another, as a result of which a non-detachable integral connection is created in the contact zone by cold welding and the bimetal strip  10  is formed. 
     In a press, a blank of a limb  16  of the forceps is stamped out of the bimetal strip  10  in a single work stroke of the press and deformed under pressure. Depending on the areal dimensions of the bimetal strip  10 , one or more limbs  16  can be produced in one work stroke of the press. 
     As shown in  FIGS. 3 to 5 , the limb  16  has a first layer  18 , which forms the outer side of the limb  16  and is formed from the deformed strip  12  of e.g. stainless steel. The inner side of the limb  16  is formed by a second layer  20 , which is formed from the strip  14  of e.g. a silver alloy. In the illustrated exemplary embodiment, the first layer  18  and the second layer  20  extend with their areas substantially parallel over the entire length and width of the limb  16 . 
     In the longitudinal direction, the limb  16  has a proximal end region  22 , a central region  24  and a distal end region  26 . In the proximal end region  22 , the limb  16  has a reduced width and is deformed to have a low material thickness, wherein the material thickness of the outer first layer  18  and inner second layer  20  is approximately equal. The central region  24  has a greater width, with the outer first layer  18  being formed to make a serrated recessed grip  28 . The inner second layer  20  is not deformed in this region, and so the material thickness of the inner second layer  20  in conjunction with the width of the central region  24  forms a large volume with a high heat capacity. 
     The distal end region  26  of the limb  16  has a small width and tapers towards the distal tip of the limb. The second layer  20  is formed to be an electrode  30  in the region of the distal tip. In the region of this electrode  30 , the material thickness of the second layer  20  is enlarged, and so the electrode  30  projects over the plane of the inner side of the limb  16  with a raised contact area  32 . The second layer  20  ensures a good thermally conducting connection between the electrode  30  and the volume of the second layer  20  in the region of the recessed grip  28 , and so rapid heat dissipation is ensured from the electrode  30  to the thermal capacity of the second layer  20  in the region of the recessed grip  28 . With the exception of the raised electrode  30 , the second layer  20  forms a continuous planar surface over the entire inner side of the limb  16 . 
     As shown by  FIGS. 6 and 7 , two limbs  16  are joined together in a mirror-symmetric fashion with inner sides facing one another in order to form the forceps. In the process, the proximal end regions  22  of the two limbs are encapsulated by molding by an insulating plastic material. This plastic material forms an electrical insulation  34  between the inner faces facing one another of the proximal end regions  22  of the two limbs  16 . Furthermore, the plastic material forms an outer collar  36 , which surrounds the proximal end regions  22  of the two limbs  16  and holds these together mechanically. The end of the limbs  16  projecting beyond the outer collar  36  in the proximal direction forms a plug  38  of a plug-in connection for an RF current supply with the first layers  18 , which are respectively exposed on the outer side. On the distal side of the outer collar  36 , the limbs  16  are coated by a plastic insulation that, it goes without saying, leaves at least the contact areas  32  of the electrodes  30  exposed. 
     During use, the forceps is connected to an RF current supply via the plug  38 . For the purposes of tissue coagulation, the tissue to be coagulated is gripped with the distal tip of the forceps such that the two limbs  16  of the forceps each touch the tissue to be coagulated with the contact areas  32  of the electrodes  30 . A radiofrequency current can now be conducted through the tissue via the electrodes  30 , as a result of which the tissue between the electrodes  30  is heated and coagulates. Heat generated at the contact areas  32  is absorbed by the electrode  30  and very rapidly dissipated from the electrode  30  to the large volume of the second layer  20  as a result of the high thermal conductivity of the second layer  20  and the relatively large cross section thereof. As a result, it is possible to prevent the contact areas  32  from being heated and tissue from sticking onto the contact areas  32  as a result thereof. 
     LIST OF REFERENCE SIGNS 
     
         
         
           
               10  Bimetal strip 
               12  Stainless steel strip 
               14  Silver strip 
               16  Limb 
               18  First layer 
               20  Second layer 
               22  Proximal end region 
               24  Central region 
               26  Distal end region 
               28  Recessed grip 
               30  Electrode 
               32  Contact area 
               34  Insulation 
               36  Outer collar 
               38  Plug