Patent Publication Number: US-9848938-B2

Title: Compressible jaw configuration with bipolar RF output electrodes for soft tissue fusion

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application is a continuation of an claims the benefits of and priority to U.S. patent application Ser. No. 12/879,505 which was filed on Sep. 10, 2010, now U.S. Pat. No. 8,945,125, which is a continuation of U.S. patent application Ser. No. 10/712,486 which was filed on Nov. 13, 2003, now U.S. Pat. No. 7,799,026, the entire contents of both of which are incorporated by reference. 
    
    
     BACKGROUND 
     1. Technical Field 
     The present disclosure relates to electrosurgical instruments and, more particularly, to open or endoscopic electrosurgical instruments having compressible or elastomeric end effector assemblies for use in sealing various tissues. 
     2. Background 
     A hemostat or forceps is a simple plier-like tool which uses mechanical action between its jaws to constrict vessels and is commonly used in open surgical procedures to grasp, dissect and/or clamp tissue. Electrosurgical forceps utilize both mechanical clamping action and electrical energy to effect hemostasis by heating the tissue and blood vessels to coagulate, cauterize and/or seal. 
     By utilizing an electrosurgical forceps, a surgeon can either cauterize, coagulate/desiccate and/or simply reduce or slow bleeding, by controlling the intensity, frequency and duration of the electrosurgical energy applied through the jaw members to the tissue. The electrode of each jaw member is charged to a different electric potential such that when the jaw members grasp tissue, electrical energy can be selectively transferred through the tissue. 
     In order to seal large vessels, two predominant mechanical parameters must be accurately controlled—the pressure applied to the vessel and the gap distance between the electrodes—both of which are affected by the thickness of the sealed vessel to be sealed. More particularly, accurate application of pressure is important to oppose the walls of the vessel; to reduce the tissue impedance to a low enough value that allows enough electrosurgical energy through the tissue; to overcome the forces of expansion during tissue heating; and to contribute to the end tissue thickness which is an indication of a good seal. It has been determined that a typical fused vessel wall is optimum between 0.001 and 0.005 inches. Below this range, the seal may shred or tear and above this range the opposing tissue layers may not be properly or effectively sealed. 
     With respect to smaller vessels, the pressure applied to the tissue tends to become less relevant whereas the gap distance between the electrically conductive surfaces becomes more significant for effective sealing. With smaller vessels, the chances of the two opposed electrically conductive surfaces of the electrosurgical forceps touching during activation increases as the size of the vessel becomes smaller. 
     The process of coagulating small vessels is fundamentally different than electrosurgical vessel sealing. For the purposes herein, “coagulation” is defined herein as a process of desiccating tissue wherein the tissue cells are ruptured and dried. “Vessel sealing” meanwhile is defined herein as a process of liquefying the collagen elastin and ground substances in the tissue so that it reforms into a cohesive, fused mass. Coagulation of small vessels is sufficient to permanently close the vessel lumen. Larger vessels need to be sealed to assure permanent closure. 
     U.S. Pat. No. 2,176,479 to Willis, U.S. Pat. Nos. 4,005,714 and 4,031,898 to Hiltebrandt, U.S. Pat. Nos. 5,827,274, 5,290,287 and 5,312,433 to Boebel et al., U.S. Pat. Nos. 4,370,980, 4,552,143, 5,026,370 and 5,116,332 to Lottick, U.S. Pat. No. 5,443,463 to Stern et al., U.S. Pat. No. 5,484,436 to Eggers et al. and U.S. Pat. No. 5,951,549 to Richardson et al., all relate to electrosurgical instruments for coagulating, cutting and/or sealing vessels or tissue. However, some of these designs may not provide uniformly reproducible pressure to the opposing tissue layers which in turn may result in an ineffective or non-uniform seal. For example and with particular respect to variously-sized tissues, many of these references disclose instruments which unevenly compress the tissue across the jaw surface which is not conducive to consistent or effective tissue sealing. 
     Many of these instruments rely on clamping pressure alone to procure proper sealing thickness and are not designed to take into account gap tolerances and/or parallelism and flatness requirements which are parameters which, if properly controlled, can assure a consistent and effective tissue seal. For example, it is difficult to adequately control thickness of the resulting sealed tissue by controlling clamping pressure alone for either of many reasons: 1) if tissue is initially thin or if too much force is applied, there is a possibility that the two electrically conductive surfaces of the instrument will touch and energy will not be transferred through the tissue resulting in an ineffective seal; 2) if tissue is thick or too low a force is applied, the tissue may pre-maturely move prior to activation and sealing and a thicker, less reliable seal may be created; or 3) if the tissue is thick, over compression may lead to tissue vaporization and a less reliable seal may be created. 
     Moreover, the performance of certain existing clamping RF delivery systems is limited due to their inherent tendency to arc and short once the directly opposing electrodes have been drawn into close proximity with one another. Maintaining a functional and reliable system with a directly opposed configuration requires tight tolerances on specific parameters such as electrode gap and jaw parallelism. 
     Thus, a need exists to develop an electrosurgical instrument which effectively and consistently seals variously-sized tissue and solves many of the aforementioned problems known in the art. 
     SUMMARY 
     The present disclosure relates to electrosurgical instruments having compressible or elastomeric end effector assemblies for use in sealing various tissues. In accordance with one aspect of the present disclosure, an electrosurgical instrument for sealing vessels includes a housing having a shaft attached thereto and an end effector assembly attached to a distal end of the shaft, wherein the end effector assembly includes first and second jaw members attached thereto. The jaw members are movable relative to one another from a first position for approximating tissue to at least one additional position for grasping tissue therebetween. 
     Preferably, each of the jaw members includes an elastomeric material disposed on an inner facing tissue contacting surface thereof. Each of the elastomeric materials includes an electrode disposed therein. Preferably, the electrodes are offset a distance X relative to one another such that when the jaw members are closed about the tissue and when the electrodes are activated, electrosurgical energy flows through the tissue in a generally coplanar manner relative to the tissue contacting surfaces. Preferably, the offset distance X is in the range of about 0.005 inches to about 0.0.200 inches. It is envisioned that at least one of the jaw members includes means for regulating the distance X dependent upon tissue thickness or tissue type. 
     It is envisioned that the elastomeric material is either silicone, polyurethane or other thermoplastic elastomers such as santoprene (or combinations thereof). One or more of the above substances may also be combined to form an alloy with one or more of the following substances: nylon, syndiotactic polystryrene, Polybutylene Terephthalate (PBT), Polycarbonate (PC), Acrylonitrile Butadiene Styrene (ABS), Polyphthalamide (PPA), Polymide, Polyethylene Terephthalate (PET), Polyamide-imide (PAI), Acrylic (PMMA), Polystyrene (PS and HIPS), Polyether Sulfone (PES), Aliphatic Polyketone, Acetal (POM) Copolymer, Polyurethane (PU and TPU), Nylon with Polyphenylene-oxide dispersion or Acrylonitrile Styrene Acrylate. Preferably, the compressible material has a comparative tracking index (CTI) value of about 300 to about 600 volts. 
     It is envisioned that the electrosurgical system include at least one sensor which provides information to a feedback circuit for regulating the electrosurgical energy through the tissue. Preferably, the sensor measures at least one of tissue impedance, tissue temperature, tissue pressure, light transmission, and tissue thickness. 
     Preferably, at least one of the jaw members includes a plurality of electrodes across the width thereof and the electrosurgical instrument includes means for selecting one of the plurality of electrodes for electrically opposing the electrode disposed on the other of the jaw members. The selecting means includes a sensor which measures at least one of tissue impedance, tissue temperature and tissue thickness. 
     In one embodiment, the electrodes are wire electrodes which project from the tissue contacting surfaces of the elastomeric material into contact with the tissue. In another embodiment, the elastomeric material on each of the jaw members includes an electrode which is partially disposed therein. It is envisioned that upon grasping of tissue between the jaw members, each of the electrodes deflect inwardly relative to the tissue contacting surfaces in response to the tissue reaction forces. 
     In yet another embodiment, the electrodes are recessed within the elastomeric material. It is further contemplated that the tissue contacting surface of each electrode is substantially crowned. 
     In another aspect of the present disclosure, the electrosurgical instrument includes an end effector assembly attached to a distal end of the shaft. The end effector assembly includes first and second jaw members attached thereto. The jaw members are movable relative to one another from a first position for approximating tissue to at least one additional position for grasping tissue therebetween. 
     In the present embodiment each of the jaw members includes an electrically insulative material (e.g., a material having a high CTI value) disposed on an inner facing tissue contacting surface thereof and an elastomeric material disposed between each jaw member and a respective insulative material. It is envisioned that the elastomeric material is may also be made from one or more electrically insulative materials. Each of the insulative materials includes an electrode disposed therein. The electrodes are offset a distance X relative to one another such that when the jaw members are closed about the tissue and when the electrodes are activated, electrosurgical energy flows through the tissue in a generally coplanar manner relative to the tissue contacting surfaces. 
     It is envisioned that the insulative material on each of the jaw members includes an electrode which is partially disposed therein. It is further envisioned that each of the electrodes are recessed within the insulative material. 
     Other objects and features of the present disclosure will become apparent from consideration of the following description taken in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other objects and features of the present invention will become apparent from the following detailed description considered in connection with the accompanied drawings. It should be understood, however, that the drawings are designed for the purpose of illustration only and not as a definition of the limits of the invention. 
         FIG. 1  is a perspective view of an exemplary electrosurgical instrument in accordance with the present disclosure, and associated with an electrosurgical generation; 
         FIG. 2  is a transverse, cross-sectional end view of one embodiment according to the present invention showing a pair of opposing jaw members each having a resilient tissue contact surface with an electrode housed therein; 
         FIG. 3  is a transverse, cross-sectional end view of another embodiment according to the present disclosure wherein the electrodes are partially housed within the resilient tissue contacting surface; 
         FIG. 4  is a transverse, cross-sectional end view showing a wire electrode disposed in each of the resilient tissue contacting surfaces; 
         FIG. 5  is a transverse, cross-sectional end view showing a resilient member disposed between the tissue contacting surface and an outer periphery of each of the jaw members; 
         FIG. 6  is a transverse, cross-sectional end view showing an alternate embodiment of the present disclosure wherein the electrodes are disposed on the same jaw member; and 
         FIG. 7  is a transverse, cross-sectional end view showing another alternate embodiment of the present disclosure wherein the jaw members include a series of stop members for controlling the gap distance between jaw members during sealing. 
     
    
    
     DETAILED DESCRIPTION 
     Preferred embodiments of the presently disclosed electrosurgical instrument are described in detail herein with reference to the drawing figures wherein like reference numerals identify similar or identical elements. In the drawings and in the description which follows, the term “proximal”, as is traditional will refer to the end of the electrosurgical instrument which is closest to the operator, while the term “distal” will refer to the end of the instrument which is furthest from the operator. 
     Referring initially to  FIG. 1 , there is seen a perspective view of an electrosurgical instrument system in accordance with an exemplary embodiment of the present disclosure, generally indicated as reference numeral  10 . Electrosurgical instrument system  10  includes an electrosurgical energy generator  12  and electrosurgical forceps  14 . A cable  16  electrically connects forceps  14  to generator  12  via clips  18  and  20 . 
     Forceps  14  include a housing  22 , a handle assembly  24 , a rotating assembly  26 , a trigger assembly  28  and an end effector assembly  100  which mutually cooperate to grasp and divide tubular vessels and vascular tissue. More particularly, forceps  14  include a shaft  32  which has a distal end  34  dimensioned to mechanically engage end effector assembly  100  and a proximal end  36  which mechanically engages housing  22 . While the illustrated forceps  14  are intended for use in minimally invasive endoscopic surgical procedures, the principles of the present disclosure are equally applicable to forceps designed for use in open surgical procedures. 
     Handle assembly  24  includes a fixed handle  40  and a movable handle  50 . Fixed handle  40  is integrally associated with housing  22  and movable handle  50  is movable relative to fixed handle  40  as explained in more detail below with respect to the operation of forceps  14 . Rotating assembly  26  is preferably attached to a distal end of housing  22  and is rotatable in either direction about a longitudinal axis “A” of shaft  32 . 
     As mentioned above, end effector assembly  100  is attached to distal end  34  of shaft  32  and includes a pair of opposing jaw members  110 ,  120 . Movable handle  50  of handle assembly  24  is ultimately connected to a drive rod (not shown) which, together, mechanically cooperate to impart movement of jaw members  110 ,  120  from an open position wherein jaw members  110 ,  120  are disposed in spaced relation relative to one another to a clamped or closed position wherein jaw members  110 ,  120  cooperate to grasp tissue therebetween. 
     It is envisioned that forceps  14  may be designed such that it is fully or partially disposable depending upon a particular purpose or to achieve a particular result. For example, end effector assembly  100  may be selectively and releasably engageable with the distal end  34  of shaft  32  and/or the proximal end  36  of shaft  32  may be selectively and/or releasably engageable with housing  22  and handle assembly  24 . In either of these two instances, forceps  14  would be considered “partially disposable” or “reposable”, i.e., a new or different end effector assembly  100  (or end effector assembly  100  and shaft  32 ) selectively replaces the old end effector assembly  100  as needed. 
     An exemplary electrosurgical energy generator  12  is disclosed in U.S. Pat. No. 6,068,627 to Orszulak, et al. and available from Valleylab—a division of Tyco Healthcare, LP as the Ligasure™ vessel sealing generator and includes an identifying circuit (not shown) therein which is responsive to information and which transmits a verification signal to generator  12  and further includes a switch (not shown) connected to the identifying circuit which is responsive to the signaling of the identifying circuit. 
     Each jaw member  110 ,  120  is manufactured from a sufficiently rigid material (i.e., stainless steel) which is resistant to deformation as a result of clamping forces acting thereon. Preferably, jaw members  110 ,  120  are manufactured from an electrically non-conductive material, such as, for example, a polymer, carbon-fiber, a ceramic-like material or a combination thereof (i.e., Teflon polytetreflouroethylene) which is also resistant to deformation forces. 
     Preferably, each jaw member  110 ,  120  is at least partially enveloped in an elastomeric material or shell  114 ,  124 , respectively. As elastomeric material is defined herein as a macromolecular material that return rapidly to approximately the initial dimensions and shape after substantial deformation by a weak stress and release of the stress (strain ˜100 to 200%). As seen in  FIGS. 2-4 , elastomeric shells  114 ,  124  substantially surround the outer periphery of jaw members  110 ,  120 . Preferably, the elastomeric shells  114 ,  124 , cover the opposing tissue contacting surfaces  115 ,  125  of jaw members  110 ,  120 , respectively, and are dimensioned to at least partially house an electrode  116 ,  126  therein. 
     Preferably, the elastomeric shells  114 ,  124  are at least partially made from a compressible, electrically non-conductive elastomeric material having a high CTI (Comparative Tracking Index) value of about 300 to about 600 volts in order to reduce surface tracking and possible collateral damage to tissue. It is envisioned that the elastomeric material includes either silicone, polyurethane or another thermoplastic elastomers such as santoprene (or combinations thereof). It is also envisioned that one or more of the above substances may also be combined to form an alloy with one or more of the following substances: nylons and syndiotactic polystryrenes such as QUESTRA® manufactured by DOW Chemical, Polybutylene Terephthalate (PBT), Polycarbonate (PC), Acrylonitrile Butadiene Styrene (ABS), Polyphthalamide (PPA), Polymide, Polyethylene Terephthalate (PET), Polyamide-imide (PAI), Acrylic (PMMA), Polystyrene (PS and HIPS), Polyether Sulfone (PES), Aliphatic Polyketone, Acetal (POM) Copolymer, Polyurethane (PU and TPU), Nylon with Polyphenylene-oxide dispersion and Acrylonitrile Styrene Acrylate. Preferably, the elastomeric materials have a low moisture absorption (e.g., less than about 4%) in order to maintain material performance after continual use in fluid rich environments. It has also been discovered that certain coatings can be utilized either alone or in combination with one of the above materials in order to reduce other electrosurgical effects at the tissue contacting site, e.g., flashover. 
     Each electrode  116 ,  126  of jaw member  110 ,  120 , respectively, is electrically coupled to generator  12  for delivering bipolar energy across the tissue “T” when grasped. More particularly, electrode  116  is connected to a first electrical potential and electrode  126  is connected to a second electrical potential such that, when energized, electrosurgical energy is transferred through tissue “T” disposed between respective jaw members  110  and  120 . 
     Electrodes  116 ,  126  are each at least partially disposed within respective elastomeric shells  114 ,  124  of each jaw member  110 ,  120  and are preferably disposed on opposite sides of jaw members  110 ,  120 . More particularly, and as best seen in the end views of  FIGS. 2-5 , electrodes  116 ,  126  are spaced a transverse distance “X” from one another. Preferably, in accordance with the present disclosure, distance “X” is from about 0.005 inches to about 0.200 inches, a range of about 0.050 inches to about 0.150 inches is preferred to insure proper seal width. Accordingly, when jaw members  110 ,  120  are in the closed position, electrodes  116 ,  126  create an electrical path therebetween which is substantially coplanar to opposing tissue engaging surfaces  115  and  125  as will be explained in more detail below. 
     It is envisioned that the outer surface of electrodes  116 ,  126  may include a nickel-based material, coating, stamping, and/or metal injection molding which is designed to reduce adhesion between electrodes  116 ,  126  and the surrounding tissue during activation and sealing. Moreover, it is also contemplated that the tissue contacting surfaces of electrodes  116 ,  126  may be manufactured from one (or a combination of one or more) of the following materials: nickel-chrome, chromium nitride, MedCoat 2000 manufactured by The Electrolizing Corporation of OHIO, Inconel 600 and tin-nickel. It is further envisioned that tissue contacting surfaces  115 ,  125  may also be coated with one or more of the above materials to achieve the same result, i.e., a “non-stick surface”. For example, Nitride coatings (or one or more of the other above-identified materials) may be deposited as a coating on another base material (metal or nonmetal) using a vapor deposition manufacturing technique. Preferably, the non-stick materials are of a class of materials that provide a smooth surface to prevent mechanical tooth adhesions. As can be appreciated, reducing the amount that the tissue “sticks” during sealing improves the overall efficacy of the instrument. 
     It is also contemplated that the tissue contacting surfaces  115 ,  125  of jaw members  110 ,  120  can include or be coated with these non-stick materials (not shown). When utilized on contacting surfaces  115 ,  125 , these materials provide an optimal surface energy for eliminating sticking due in part to surface texture and susceptibility to surface breakdown due to electrical effects and corrosion in the presence of biologic tissues. It is envisioned that these materials exhibit superior non-stick qualities over stainless steel and should be utilized on forceps  14  in areas where the exposure to pressure and electrosurgical energy may create localized “hot spots” more susceptible to tissue adhesion. 
     One particular class of materials disclosed herein has demonstrated superior non-stick properties and, in some instances, superior seal quality. For example, nitride coatings which include, but not are not limited to: TiN, ZrN, TiAlN, and CrN are preferred materials used for non-stick purposes. CrN has been found to be particularly useful for non-stick purposes due to its overall surface properties and optimal performance. Other classes of materials have also been found to reduce overall sticking. For example, high nickel/chrome alloys with a Ni/Cr ratio of approximately 5:1 have been found to significantly reduce sticking in bipolar instrumentation. One particularly useful non-stick material in this class is Inconel 600. Bipolar instrumentation having contact surfaces  115 ,  125  made from or coated with Ni200, Ni201 (˜100% Ni) also showed improved non-stick performance over typical bipolar stainless steel electrodes. 
     By way of example, chromium nitride may be applied using a physical vapor deposition (PVD) process that applies a thin uniform coating to the entire electrode surface. This coating produces several effects: 1) the coating fills in the microstructures on the metal surface that contribute to mechanical adhesion of tissue to electrodes; 2) the coating is very hard and is a non-reactive material which minimizes oxidation and corrosion; and 3) the coating tends to be more resistive than the base material causing electrode surface heating which further enhances desiccation and seal quality. 
     The Inconel 600 coating is a so-called “super alloy” which is manufactured by Special Metals, Inc. located in Conroe, Tex. The alloy is primarily used in environments which require resistance to corrosion and heat. The high Nickel content of Inconel makes the material especially resistant to organic corrosion. As can be appreciated, these properties are desirable for bipolar electrosurgical instruments which are naturally exposed to high temperatures, high RF energy and organic matter. Moreover, the resistivity of Inconel is typically higher than the base electrode material which further enhances desiccation and seal quality. 
     Turning back to  FIGS. 2-5 , when jaw members  110 ,  120  are actuated to grasp tissue “T”, a gap “G” is defined between opposing surfaces  117 ,  127  of elastomeric shells  114 ,  124 . In accordance with the present disclosure, the material of elastomeric shells  114 ,  124  is selected such that when jaw members  110 ,  120  are closed onto tissue “T’, elastomeric shells  114 ,  124  will compress and deform in order to maintain a substantially uniform gap “G” across the portion of the jaw which is in contact with the tissue. In particular, each elastomeric shells  114 ,  124  will have a compression or deflection of about 0.001 inches to about 0.015 inches when the clamping force is between about 40 p.s.i. to about 230 p.s.i. (120 p.s.i. nominal) distributed over tissue contacting surfaces  115 ,  125  of jaw members  110 ,  120 . In addition, it is envisioned that the elastomeric shells  114 ,  124  of the present disclosure allow for local pressure compensation along the length thereof to allow for sealing across non-homogeneous structures found within the individual tissue or tissue “T” (such as, for example, bronchi and/or vascular structures found in the lung). More particularly, the elastomeric shells  114 ,  124  compensate for the reaction forces of vessels and tissues so that end effector assembly  100  (i.e., jaw members  110 ,  120 ) will not unintentionally damage the tissue “T” (i.e., over-compress the tissue) during the sealing process. 
       FIG. 2  shows one embodiment according to the present disclosure wherein electrodes  116 ,  126  are encased in pockets  119 ,  129 , in shells  114  and  124 , respectively. Electrodes  116 ,  126  preferably include an outer edge radius “R” which is designed to reduce negative tissue effects during activation. The electrodes  116 ,  126  may also be crowned to reduce negative tissue effects during activation. Preferably, the radiused edge “R” includes a radius of about 0.005 inches at the exposed tissue contacting edges. It is envisioned that the radiused edges, in conjunction with placing electrodes  116 ,  126  within pockets  119 ,  129  of the elastomeric shells  114 ,  124  reduces current densities at the inner most corner of electrodes  116 ,  126 . Areas of high current densities may result in the unintentional damage to the tissue during sealing. 
     It is believed that the distance “X” between adjacent electrodes  116  and  126  plays an important role in sealing vessels. Using computer simulations and histological evidence, it has been demonstrated that a non-uniform power-density exists due to the electrical and thermal properties of tissue. This results in a non-uniform temperature distribution in which temperature is greater in a region centrally located between the electrodes. Impedance in this central region can rise quickly creating an insulative barrier to further current flow across the tissue, resulting in inadequate sealing at the electrode edges. The greater the distance “X” is between the electrodes  116 ,  126  the greater the effect of the non-uniform temperature distribution. On the other hand if the distance “X” is too small, the resulting seal width may be inadequate to insure effective seal strength. Thus, it has been determined that the distance “X”, the distribution of energy across the seal and the relative size of the seal itself are all important parameters which must be properly considered during the sealing process. As a result, it has been found that the preferred distance “X,” as described above, is from about 0.005 inches to about 0.200 inches. 
     It is envisioned that all of these parameters may be monitored and regulated as a part of the disclosures herein. For example, the electrosurgical system may include one or more sensors  145 ,  155 , respectively, which measure tissue temperature, tissue impedance, tissue pressure, light transmission, or tissue thickness prior to, during, or after the sealing process. These parameters can be relayed back to the generator  12  in a feedback loop circuit  160  to predetermine the proper amount of electrosurgical energy required to effectively seal the tissue or monitor and adjust the electrosurgical energy during the overall sealing process. Moreover, it is envisioned that the jaw members  110 ,  120  may be constructed such that the distance “X” is variable depending upon tissue thickness. This can be accomplished by constructing the electrodes  116 ,  126  such that at least one is moveable transversely across the sealing surface or by having an array of electrodes across the sealing surfaces  115 ,  125 . When utilizing an array of electrodes, each electrode is electrically coupled to the generator  12  to automatically select the appropriate opposing electrode pairs to effect the proper seal across the tissue depending upon the tissue thickness and tissue type. 
       FIG. 3  shows an alternate embodiment of the present disclosure wherein the electrodes  116   a ,  126   a  are partially disposed within the shells  114   a ,  124   a , respectively. It is envisioned that partially disposing the electrodes  116   a ,  126   a  within shell  114   a ,  124   a  will allow the electrodes  116   a ,  126   a  to partially deflect when the jaw members  110  and  120  cooperate to grasp tissue “T”. As such, gap “G” is maintained across the portion of the jaw members  110 ,  120  which are closed about tissue “T”. In addition, portions  114   a ,  124   a  act to further insulate electrodes  116   a ,  126   a  from support members  112 ,  122 . Accordingly, support members  112 ,  122  can be fabricated from electrically conductive materials without interfering (i.e., shorting or arcing) with the electrical fields being transmitted between electrodes  116   a ,  126   a . It is contemplated that electrodes  116   a ,  126   a  may be radiused in the same manner as electrodes  116 ,  126  of  FIG. 2 . 
     Turning now to  FIG. 4 , another embodiment of the present disclosure, discloses a pair of opposing wire electrodes  116   b ,  126   b  disposed at least partially within elastomeric shells  114  and  124 , respectively, more particularly, electrodes  116   b ,  126   b  are embedded in respective elastomeric shells  114 ,  124  such that only a portion of electrodes  116   b ,  126   b  are exposed at contacting surfaces  117 ,  127  of elastomeric shells  114 ,  124 . It is envisioned that wire electrodes  116   b ,  126   b  create the same effect as radiused electrode edges and function to disperse current density. Moreover and similar to the  FIG. 3  embodiment depicted above, wire electrodes  116   b ,  126   b  permit a certain degree of deflection at the tissue contacting surfaces  117 ,  127  which is believed to create a more uniform seal. 
     Turning now to  FIG. 5  which shows yet another embodiment of the present disclosure wherein the jaw members  110 ,  120  each include a layer of elastomeric compressible material  114   b ,  124   b  disposed thereon. More particularly, each jaw member  110 ,  120  preferably further includes an insulating member  118 ,  128 , respectively, having a respective layer of compressible material  114   b ,  124   b  disposed therebetween. A pair of electrodes  116   c ,  126   c  are disposed in the insulating members  118 ,  128  and are spaced a distance “X” across the respective contacting surfaces  117 ,  127 . When jaw members  110 ,  120  close about tissue “T”, the insulating members  118 ,  128  and the electrodes deflect by virtue of the disposition of the compressible material  114   b ,  124   b  between the jaw members  110 ,  120  and insulating members  118 ,  128 . Electrically insulative spaces may be incorporated on the tissue contacting surface (or surfaces) to control gap “G”. As such, a gap “G” is uniformly maintained across the width of jaw members  110 ,  120  when jaw members  110 ,  120  are closed about tissue “T”. 
     As can be appreciated and in accordance with the present disclosure, the end effector assembly  100  does not necessarily require a fixed electrode gap (created via a stop member between jaw members—See  FIG. 7 ) or jaw parallelism to reduce the incidents of arcing, shorting and fluid wicking between electrodes  116 ,  126 . In fact, due to the adjacent disposition of the opposing electrodes  116 ,  126 , opposing surfaces  117 ,  127  of jaw members  110 ,  120  may contact with each other without causing any incidents of arcing, shorting or fluid wicking. 
     Moreover, the opposing offset configuration of electrodes  116 ,  126  according to the present disclosure also tends to minimize collateral electrical fields or current flows which, in turn, reduces unwanted thermal damage to adjacent tissue “T” located outside of the intended sealing area. In other words, the positioning of electrodes  116 ,  126  on opposite jaw members  110 ,  120  limits current flow to between the intended sealing area such that stray currents do not extend to tissue outside the lateral boundaries of jaw members  110 ,  120 . Accordingly, enhanced current flow through the tissue is achieved. 
       FIG. 6  shows an alternate embodiment of the present disclosure wherein the electrode  116 ,  126  are disposed on the same jaw member, e.g., jaw member  120 . The elastomeric material  114  is disposed on the opposite jaw member  110 .  FIG. 7  shows another embodiment of the present disclosure wherein at least one of the jaw members includes a stop member  135   a  (or series of stop members  135   a - 135   d ) disposed on the tissue contacting surface  117 ,  127  to regulate the gap distance “G” between opposing jaw members  110  and  120 . The electrodes  116  and  126  are diametrically opposed to one another and are supported within each jaw member  110  and  120  by an elastomeric material  114   a ,  114   b , respectively. It is envisioned that this configuration allows the electrodes  116 ,  126  to self-align if the alignment between the two electrodes  116 ,  126  is slightly skewed or non-parallel. 
     Although the subject apparatus has been described with respect to preferred embodiments, it will be readily apparent to those having ordinary skill in the art to which it appertains that changes and modifications may be made thereto without departing from the spirit or scope of the subject apparatus. 
     For example, it is envisioned that electrodes  116 ,  126  and/or electrodes  116 ,  126  and elastomeric shells  114 ,  124  may be selectively removable from jaw members  110 ,  120  (i.e., snap-fit over jaw members  110 ,  120 ) depending on the particular purpose. Alternatively, it is envisioned that electrodes  116 ,  126  can be conductive strips adhered to the elastomeric shells  114 ,  124 . 
     It is also envisioned that the opposing surfaces  115 ,  125  of jaws  110 ,  120  may be crowned in order to effectively stretch the tissue from the centerline of jaws  110 ,  120  outwardly upon the clamping or closing of jaws  110 ,  120 . By crowning the opposing surfaces  115 ,  125 , the elastomeric shells  114 ,  124  progressively collapse from the center outwardly towards their respective lateral ends thus substantially squeezing blood and other fluids out of the tissue prior to sealing. It is believed that this facilitates the sealing process by preventing entrapment of air, blood and excess fluids while placing the tissue under tension. 
     It is contemplated that the relative length of the electrodes  116 ,  126  may be regulated depending on the size of the tissue being sealed and/or the location and accessibility of the tissue being sealed. 
     It is further contemplated that opposing surfaces  115 ,  125  can be provided with gripping or grasping features, e.g., knurling, teeth, ridges, ribs, or the like, (not shown) in order to facilitate grasping of tissue “T” between jaw members  110 ,  120 . It is still further contemplated that the jaw members  110 ,  120  may be constructed to close in a non-parallel manner about the tissue “T”. For example, it is envisioned that the jaw members  110 ,  120  may be constructed to close in a tip biased, heal biased, or independently floating manner with respect to parallel about tissue “T”. It is also envisioned that only one jaw member may include the elastomeric material and the opposite jaw member may be rigid. For example, the elastomeric material  114  may be disposed on the tissue engaging surface of the jaw member  110  and the opposite jaw member  120  may be made from a rigid, non-conductive material. As can be appreciated, either jaw member  110 ,  120  in this instance could feasibly house the electrodes  116  and  126 . 
     It is further envisioned that the electrically active and insulative components may be designed to minimize thermal masses in order to improve the overall thermal control of end effector assembly  100 . 
     It is also contemplated that the end effector assembly  100  may include a dividing mechanism, such as, for example, a knife blade (not shown), which may be longitudinally reciprocable between the opposing jaws members  110 ,  120  to effectively and accurately separate the tissue “T” along the tissue seal. 
     While several embodiments of the disclosure have been shown in the drawings, it is not intended that the disclosure be limited thereto, as it is intended that the disclosure be as broad in scope as the art will allow and that the specification be read likewise. Therefore, the above description should not be construed as limiting, but merely as exemplifications of preferred embodiments. 
     Those skilled in the art will envision other modifications within the scope and spirit of the claims appended hereto.