Patent Publication Number: US-8979843-B2

Title: Electrosurgical cutting and sealing instrument

Description:
BACKGROUND 
     The present invention relates to medical devices and methods. More particularly, the present invention relates to electrosurgical instruments and methods for sealing and transecting tissue. 
     In various circumstances, a surgical instrument can be configured to apply energy to tissue in order to treat and/or destroy the tissue. In certain circumstances, a surgical instrument can comprise one or more electrodes which can be positioned against and/or positioned relative to the tissue such that electrical current can flow from one electrode, through the tissue, and to the other electrode. The surgical instrument can comprise an electrical input, a supply conductor electrically coupled with the electrodes, and/or a return conductor which can be configured to allow current to flow from the electrical input, through the supply conductor, through the electrodes and the tissue, and then through the return conductor to an electrical output, for example. In various circumstances, heat can be generated by the current flowing through the tissue, wherein the heat can cause one or more hemostatic seals to form within the tissue and/or between tissues. Such embodiments may be particularly useful for sealing blood vessels, for example. The surgical instrument can also comprise a cutting element that can be moved relative to the tissue and the electrodes in order to transect the tissue. 
     By way of example, energy applied by a surgical instrument may be in the form of radio frequency (“RF”) energy. RF energy is a form of electrical energy that may be in the frequency range of 300 kilohertz (kHz) to 1 megahertz (MHz). In application, RF surgical instruments transmit low frequency radio waves through electrodes, which cause ionic agitation, or friction, increasing the temperature of the tissue. Since a sharp boundary is created between the affected tissue and that surrounding it, surgeons can operate with a high level of precision and control, without much sacrifice to the adjacent normal tissue. The low operating temperatures of RF energy enables surgeons to remove, shrink or sculpt soft tissue while simultaneously sealing blood vessels. RF energy works particularly well on connective tissue, which is primarily comprised of collagen and shrinks when contacted by heat. 
     In various open, endoscopic, and/or laparoscopic surgeries, for example, it may be necessary to coagulate, seal, and/or fuse tissue. One means of sealing tissue relies upon the application of electrical energy to tissue captured within an end effector of a surgical instrument in order to cause thermal effects within the tissue. Various mono-polar and bi-polar radio frequency (RF) surgical instruments and surgical techniques have been developed for such purposes. In general, the delivery of RF energy to the captured tissue elevates the temperature of the tissue and, as a result, the energy can at least partially denature proteins within the tissue. Such proteins, such as collagen, for example, may be denatured into a proteinaceous amalgam that intermixes and fuses, or “welds”, together as the proteins renature. As the treated region heals over time, this biological “weld” may be reabsorbed by the body&#39;s wound healing process. 
     In certain arrangements of a bi-polar radio frequency (RF) surgical instrument, the surgical instrument can comprise opposing first and second jaws, wherein the face of each jaw can comprise an electrode. In use, the tissue can be captured between the jaw faces such that electrical current can flow between the electrodes in the opposing jaws and through the tissue positioned therebetween. Such instruments may have to seal or “weld” many types of tissues, such as anatomic structures having walls with irregular or thick fibrous content, bundles of disparate anatomic structures, substantially thick anatomic structures, and/or tissues with thick fascia layers such as large diameter blood vessels, for example. With particular regard to sealing large diameter blood vessels, for example, such applications may require a high strength tissue weld immediately post-treatment. 
     The foregoing discussion is intended only to illustrate various aspects of the related art in the field of the invention at the time, and should not be taken as a disavowal of claim scope. 
     SUMMARY 
     In one embodiment, an electrosurgical instrument may comprise a handle, an elongate shaft extending distally from the handle, where the elongate shaft defines a longitudinal axis, and a trigger coupled to the elongate shaft. The electrosurgical instrument may also comprise an end effector coupled to the distal end of the elongate shaft that comprises a first jaw member and a second jaw member. The first jaw member may be movable relative to the second jaw member between an open and a closed position. The electrosurgical instrument may also comprise an axially movable member configured to open and close the jaws and a tissue-cutting element positioned at a distal end of the axially movable member configured to translate with respect to the first jaw and the second jaw, and an electrode. The electrosurgical instrument may also comprise a spring operably coupled to the trigger, the spring to release energy and distally translate the axially movable member. 
     In another embodiment, an electrosurgical instrument may comprise a handle, an elongate shaft extending distally from the handle, where the elongate shaft defines a longitudinal axis, and a trigger coupled to the elongate shaft. The electrosurgical instrument may further comprise an internal shaft, where the internal shaft defines a longitudinal axis that is substantially perpendicular to the longitudinal axis of the elongate shaft, and an end effector coupled to the distal end of the elongate shaft. The end effector may comprise a first jaw member and a second jaw member, where the first jaw member is movable relative to the second jaw member between an open and a closed position, an electrode, and a tissue-cutting element configured to translate with respect to the first jaw and the second jaw. The electrosurgical instrument may further comprise an axially moveable member configured to open and close the jaws. The tissue-cutting element may be positioned at a distal end of the axially movable member. The electrosurgical instrument may further comprise a spring operably connected to the trigger to regulate the distal translation the moveable cutting member. 
     In yet another embodiment, an electrosurgical instrument may comprise a handle, an elongate shaft extending distally from the handle, and an end effector coupled to the distal end of the elongate shaft. The end effector may comprise a first jaw member and a second jaw member, where the first jaw member is movable relative to the second jaw member between an open and a closed position. The end effector may also comprise a tissue-cutting element configured to translate with respect to the first jaw and the second jaw and an electrode. The electrosurgical instrument may further comprise an axially moveable member configured to open and close the jaws with the tissue-cutting element be positioned at a distal end of the axially movable member and a trigger coupled to the moveable cutting member. The electrosurgical instrument may further comprise an advance biasing member operably connected to the trigger and the moveable cutting member, and a return biasing member operably connected to the moveable cutting member and the handle. 
     In one embodiment, an electrosurgical instrument may comprise a handle, an elongate shaft extending distally from the handle, and an end effector coupled to the distal end of the elongate shaft. The end effector may comprise a first jaw member and a second jaw member, where the first jaw member is movable relative to the second jaw member between an open and a closed position. The end effector may also comprise a tissue-cutting element configured to translate with respect to the first jaw and the second jaw and an electrode. The electrosurgical instrument may further comprise an axially moveable cutting member configured to open and close the jaws and a trigger coupled to the axially moveable cutting member. The tissue-cutting element may be positioned at a distal end of the axially movable member. The electrosurgical instrument may further comprise a linear actuator coupled to the axially moveable cutting member. 
     In another embodiment, an electrosurgical instrument may comprise a handle, an elongate shaft extending distally from the handle, and an end effector coupled to the distal end of the elongate shaft. The end effector may comprise a first jaw member and a second jaw member, where the first jaw member is movable relative to the second jaw member between an open and a closed position. The end effector may also comprise a tissue-cutting element configured to translate with respect to the first jaw and the second jaw and an electrode. The electrosurgical instrument may further comprise an axially moveable cutting member configured to open and close the jaws, where the moveable cutting member comprises a distal stop and a proximate stop, and a trigger coupled to the axially moveable cutting member movable between a first position, a second position, and a third position. The tissue-cutting element may be positioned at a distal end of the axially movable member. The electrosurgical instrument may further comprise a linear actuator coupled to a nut, where the nut is coupled to the axially moveable cutting member intermediate the distal stop and the proximate stop. 
     In yet another embodiment, an electrosurgical instrument may comprise a handle, an elongate shaft extending distally from the handle, and an end effector coupled to the distal end of the elongate shaft. The end effector may comprise a first jaw member and a second jaw member, where the first jaw member is movable relative to the second jaw member between an open and a closed position. The end effector may also comprise a tissue-cutting element configured to translate with respect to the first jaw and the second jaw and an electrode. The electrosurgical instrument may further comprise an axially moveable cutting member configured to open and close the jaws and a trigger coupled to the axially moveable cutting member, where the trigger is movable between a first position and a second position. The tissue-cutting element may be positioned at a distal end of the axially movable member. The electrosurgical instrument may further comprise a linear actuator coupled to the axially moveable cutting member and a load cell coupled to the axially moveable cutting member, where the load cell is configured to output a load signal, and where the linear actuator distally drives the axially moveable cutting member at a variable speed, where the variable speed is at least partially based on the load signal. 
     In one embodiment, an electrosurgical instrument may comprise a handle, an elongate shaft extending distally from the handle, a trigger moveable between a first position and a second position, and an end effector coupled to the distal end of the elongate shaft. The end effector may comprise a first jaw member and a second jaw member, where the first jaw member is movable relative to the second jaw member between an open and a closed position. The end effector may also comprise a tissue-cutting element configured to translate with respect to the first jaw and the second jaw, and an electrode. The electrosurgical instrument may further comprise an axially moveable cutting member configured to open and close the jaws, and a damper coupled to the trigger and the axially moveable cutting member. The tissue-cutting element may be positioned at a distal end of the axially movable member. 
     In another embodiment, an electrosurgical instrument may comprise a handle, an elongate shaft extending distally from the handle, and an end effector coupled to the distal end of the elongate shaft. The end effector may comprise a first jaw member and a second jaw member, where the first jaw member is movable relative to the second jaw member between an open and a closed position. The end effector may also comprise a tissue-cutting element configured to translate with respect to the first jaw and the second jaw and an electrode. The electrosurgical instrument may further comprise an axially moveable cutting member configured to open and close the jaws and a trigger moveable between a first position and a second position, where the trigger is coupled to the axially moveable cutting member. The tissue-cutting element may be positioned at a distal end of the axially movable member. The electrosurgical instrument may further comprise a damper positioned in the handle, where the damper is positioned to engage the trigger and oppose movement of the trigger from the first position to the second position. 
     In yet another embodiment, an electrosurgical instrument may a handle, an elongate shaft extending distally from the handle, and an end effector coupled to the distal end of the elongate shaft. The end effector may comprise a first jaw member, a second jaw member, where the first jaw member is movable relative to the second jaw member between an open and a closed position. The end effector may also comprise a tissue-cutting element configured to translate with respect to the first jaw and the second jaw, and an electrode. The electrosurgical instrument may further comprise an axially moveable cutting member configured to open and close the jaws, a trigger moveable between a first position and a second position, and a damper, where the damper comprises a barrel and a plunger, where the plunger is coupled to the axially moveable cutting member and the trigger. The tissue-cutting element may be positioned at a distal end of the axially movable member. 
     In one embodiment, an electrosurgical instrument may comprise a handle, an elongate shaft extending distally from the handle, a trigger moveable between a first position and a second position, an electromagnetic brake, and an end effector coupled to the distal end of the elongate shaft. The end effector may comprise a first jaw member, a second jaw member, where the first jaw member is movable relative to the second jaw member between an open and a closed position, and a tissue-cutting element configured to translate with respect to the first jaw and the second jaw. The end effector may also comprise an axially moveable cutting member configured to open and close the jaws, and an electrode. The tissue-cutting element may be positioned at a distal end of the axially movable member. 
     In another embodiment, an electrosurgical instrument may comprise a handle, an elongate shaft extending distally from the handle, a trigger moveable between a first position and a second position, and an electrically activated brake comprising an engaging portion. The engaging portion may be configured to move from a non-engaged position to an engaged position. The electrosurgical instrument may further comprise a controller and an end effector coupled to the distal end of the elongate shaft. The end effector may comprise a first jaw member, a second jaw member, where the first jaw member is movable relative to the second jaw member between an open and a closed position, a tissue-cutting element configured to translate with respect to the first jaw and the second jaw, and a sensor in electrical communication with the controller. The electrosurgical instrument may further comprise an axially moveable cutting member configured to open and close the jaws. The tissue-cutting element may be positioned at a distal end of the axially movable member. 
     In yet another embodiment, an electrosurgical instrument may comprise a handle, an elongate shaft extending distally from the handle, a trigger comprising a rotor moveable between a first position and a second position, and an electromagnetic brake configured to selectively engage the rotor. The electrosurgical instrument may further comprise an end effector coupled to the distal end of the elongate shaft. The end effector may comprise a first jaw member and a second jaw member, where the first jaw member is movable relative to the second jaw member between an open and a closed position. The end effector may also comprise a tissue-cutting element configured to translate with respect to the first jaw and the second jaw, and an electrode. The electrosurgical instrument may further comprise an axially moveable cutting member configured to open and close the jaws. The tissue-cutting element may be positioned at a distal end of the axially movable member. 
     In one embodiment, an electrosurgical instrument may comprise a handle, an elongate shaft extending distally from the handle, a trigger, and an end effector coupled to the distal end of the elongate shaft. The end effector may comprise a first jaw member and a second jaw member, where the first jaw member is movable relative to the second jaw member between an open and a closed position. The end effector may also comprise a tissue-cutting element configured to translate with respect to the first jaw and the second jaw, and an electrode. The electrosurgical instrument may further comprise an axially moveable cutting member configured to open and close the jaws, an electromagnet positioned proximate to the trigger, and an electromagnet engaging surface positioned proximate to the trigger. The tissue-cutting element may be positioned at a distal end of the axially movable member. 
     In another embodiment, an electrosurgical instrument may comprise a handle, an elongate shaft extending distally from the handle, a trigger movable between a plurality of positions, and an end effector coupled to the distal end of the elongate shaft. The end effector may comprise a first jaw member and a second jaw member, where the first jaw member is movable relative to the second jaw member between an open and a closed position. The end effector may also comprise a tissue-cutting element configured to translate with respect to the first jaw and the second jaw, and an electrode. The electrosurgical instrument may further comprise an axially moveable cutting member configured to open and close the jaws and a plurality of electromagnetic gates. The tissue-cutting element may be positioned at a distal end of the axially movable member. 
     In yet another embodiment, an electrosurgical instrument may comprise a handle, an elongate shaft extending distally from the handle, a trigger movable between a plurality of positions during a trigger stroke, and a first electromagnetic gate and a second electromagnetic gate. The first electromagnetic gate and a second electromagnetic gate may each be positioned to sequentially pass proximate to an electromagnet engaging surface during the trigger stroke. The electrosurgical instrument may further comprise an end effector coupled to the distal end of the elongate shaft that comprises a first jaw member and a second jaw member, where the first jaw member is movable relative to the second jaw member between an open and a closed position. The end effector may also comprise a tissue-cutting element configured to translate with respect to the first jaw and the second jaw and an electrode. The electrosurgical instrument may further comprise an axially moveable cutting member configured to close the jaws during the trigger stroke. The tissue-cutting element may be positioned at a distal end of the axially movable member. 
     In one embodiment, an electrosurgical instrument may comprise a handle with an indicator configured to provide a serial series of feedback signals during an operational stroke and an elongate shaft extending distally from the handle. The electrosurgical instrument may further comprise an end effector coupled to the distal end of the elongate shaft. The end effector may comprise a first jaw member and a second jaw member, where the first jaw member is movable relative to the second jaw member between an open and a closed position. The end effector may also comprise a tissue-cutting element configured to translate with respect to the first jaw and the second jaw, an electrode, and a sensor. The electrosurgical instrument may further comprise an axially moveable cutting member configured to open and close the jaws and a trigger coupled to the axially moveable cutting member. The tissue-cutting element may be positioned at a distal end of the axially movable member. 
     In another embodiment, an electrosurgical instrument may comprise a handle, an elongate shaft extending distally from the handle, and an indicator configured to provide a sequence of feedback signals during the operational stroke. The electrosurgical instrument may further comprise an end effector coupled to the distal end of the elongate shaft. The end effector may comprise a first jaw member and a second jaw member, where the first jaw member is movable relative to the second jaw member between an open and a closed position. The end effector may also comprise a tissue-cutting element configured to translate with respect to the first jaw and the second jaw, an electrode, and an impedance sensor. The electrosurgical instrument may further comprise an axially moveable cutting member configured to close the jaws during the operational stroke and a ratcheting trigger coupled to the axially moveable cutting member, where the ratcheting trigger is movable between a plurality of discrete positions during an operational stroke. The tissue-cutting element may be positioned at a distal end of the axially movable member. 
     In yet another embodiment, an electrosurgical instrument may comprise a handle, an elongate shaft extending distally from the handle, and an end effector coupled to the distal end of the elongate shaft. The end effector may comprise a first jaw member and a second jaw member, where the first jaw member is movable relative to the second jaw member between an open and a closed position to clamp tissue in the closed position. The end effector may also comprise a tissue-cutting element configured to translate with respect to the first jaw and the second jaw and an electrode. The electrosurgical instrument may further comprise an axially moveable member configured to distally translate during the operational stroke to close the jaws and a ratcheting trigger coupled to the axially moveable cutting member, where the ratcheting trigger is movable between a plurality of discrete positions during an operational stroke. The tissue-cutting element may be positioned at a distal end of the axially movable member. The electrosurgical instrument may further comprise an indicator configured to verify an independence level in a section of the clamped tissue during the operational stroke. 
     The foregoing discussion should not be taken as a disavowal of claim scope. 
    
    
     
       FIGURES 
       Various features of the embodiments described herein are set forth with particularity in the appended claims. The various embodiments, however, both as to organization and methods of operation, together with advantages thereof, may be understood in accordance with the following description taken in conjunction with the accompanying drawings as follows. 
         FIG. 1  is a perspective view of a surgical instrument according to a non-limiting embodiment. 
         FIG. 2  is a side view of a handle of the surgical instrument of  FIG. 1  with a half of a handle body removed to illustrate some of the components therein. 
         FIG. 3  is a perspective view of an end effector of the surgical instrument of  FIG. 1  illustrated in an open configuration; the distal end of an axially moveable member is illustrated in a retracted position. 
         FIG. 4  is a perspective view of the end effector of the surgical instrument of  FIG. 1  illustrated in a closed configuration; the distal end of the axially moveable member is illustrated in a partially advanced position. 
         FIG. 5  is a perspective sectional view of a portion of an axially moveable member of the surgical instrument of  FIG. 1 ; the axially moveable member is shown at least partially shaped like an I-beam. 
         FIG. 6  is a sectional view of the end effector of  FIG. 1   
         FIG. 7  is a schematic representation of an actuation assembly in accordance with one non-limiting embodiment. 
         FIG. 8  a cross-sectional view of the engagement between the internal shaft of  FIG. 7  and the moveable locking member in accordance with one non-limiting embodiment. 
         FIG. 9  is a schematic representation of an actuation assembly in accordance with one non-limiting embodiment. 
         FIG. 10  is a simplified representation of an actuation assembly in accordance with one non-limiting embodiment. 
         FIG. 10A  is a close-up view of the damper of  FIG. 10  in accordance with one non-limiting embodiment. 
         FIG. 11  is a simplified representation of an actuation assembly in accordance with one non-limiting embodiment. 
         FIGS. 12-15  illustrate a representation of an electrosurgical instrument comprising a linear actuator in accordance with one non-limiting embodiment. 
         FIG. 16  is a block diagram of a control system of an electrosurgical instrument in accordance with one non-limiting embodiment. 
         FIG. 17  is a flow chart of the operation of an electrosurgical instrument having a linear actuator in accordance with one non-limiting embodiment. 
         FIGS. 18-21  illustrate an electrosurgical instrument having a damper in accordance with one non-limiting embodiment. 
         FIG. 18A  is an enlarged cross-sectional view of the damper in  FIGS. 18-21 . 
         FIGS. 22-25  illustrate an electrosurgical instrument with a damper having two check valves 
         FIG. 22A  is an enlarged cross-sectional view of the damper in  FIGS. 22-25 . 
         FIG. 26  illustrates a damper that is coupled to a tab of a trigger in accordance with one non-limiting embodiment. 
         FIG. 26A  is an enlarged view of the damper in  FIG. 26 . 
         FIG. 27  illustrates a rotary damper in accordance with one non-limiting embodiment. 
         FIG. 27A  is a cross-sectional view of the damper in  FIG. 27  taken along line  27 A- 27 A. 
         FIG. 28  illustrates an electrosurgical instrument incorporating an electromagnetic brake assembly in accordance with one non-limiting embodiment. 
         FIG. 29  illustrates an electromagnetic brake assembly in accordance with one non-limiting embodiment. 
         FIG. 30  illustrates an electromagnetic brake assembly in accordance with one non-limiting embodiment. 
         FIG. 31  is a partial cut-away view of an electrosurgical instrument having an electromagnetic brake assembly in accordance with one non-limiting embodiment. 
         FIG. 32  illustrates an enlarged view of a brake pad in accordance with one non-limiting embodiment. 
         FIGS. 33A and 33B , illustrate the electromagnetic brake assembly in  FIG. 31  in various stages of operation. 
         FIG. 34  is a partial cut-away view of an electrosurgical instrument having an electromagnetic brake assembly in accordance with one non-limiting embodiment. 
         FIG. 35  illustrates an electrosurgical instrument having electromagnetic gates to regulate the operational stroke in accordance with one non-limiting embodiment. 
         FIGS. 36A ,  36 B, and  36 C are enlarged side views of the trigger web and the electromagnet engaging surface in  FIG. 35  during an operational stroke in accordance with one non-limiting embodiment. 
         FIG. 37  is a partial cut-away view of an electrosurgical instrument having a feedback indicator in accordance with one non-limiting embodiment. 
         FIGS. 38A ,  38 B,  38 C, and  38 D illustrate the progression of feedback signals provided by the feedback indicator in  FIG. 37  in accordance with one non-limiting embodiment. 
     
    
    
     Corresponding reference characters indicate corresponding parts throughout the several views. The exemplifications set out herein illustrate various embodiments of the invention, in one form, and such exemplifications are not to be construed as limiting the scope of the invention in any manner. 
     DETAILED DESCRIPTION 
     Various embodiments are directed to apparatuses, systems, and methods for the treatment of tissue. Numerous specific details are set forth to provide a thorough understanding of the overall structure, function, manufacture, and use of the embodiments as described in the specification and illustrated in the accompanying drawings. It will be understood by those skilled in the art, however, that the embodiments may be practiced without such specific details. In other instances, well-known operations, components, and elements have not been described in detail so as not to obscure the embodiments described in the specification. Those of ordinary skill in the art will understand that the embodiments described and illustrated herein are non-limiting examples, and thus it can be appreciated that the specific structural and functional details disclosed herein may be representative and illustrative. Variations and changes thereto may be made without departing from the scope of the claims. 
     Reference throughout the specification to “various embodiments,” “some embodiments,” “one embodiment,” or “an embodiment”, or the like, means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment. Thus, appearances of the phrases “in various embodiments,” “in some embodiments,” “in one embodiment,” or “in an embodiment”, or the like, in places throughout the specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. Thus, the particular features, structures, or characteristics illustrated or described in connection with one embodiment may be combined, in whole or in part, with the features structures, or characteristics of one or more other embodiments without limitation. 
     The entire disclosures of the following non-provisional United States patents are hereby incorporated by reference herein: 
     U.S. Pat. No. 7,381,209, entitled ELECTROSURGICAL INSTRUMENT; 
     U.S. Pat. No. 7,354,440, entitled ELECTROSURGICAL INSTRUMENT AND METHOD OF USE; 
     U.S. Pat. No. 7,311,709, entitled ELECTROSURGICAL INSTRUMENT AND METHOD OF USE; 
     U.S. Pat. No. 7,309,849, entitled POLYMER COMPOSITIONS EXHIBITING A PTC PROPERTY AND METHODS OF FABRICATION; 
     U.S. Pat. No. 7,220,951, entitled SURGICAL SEALING SURFACES AND METHODS OF USE; 
     U.S. Pat. No. 7,189,233, entitled ELECTROSURGICAL INSTRUMENT; 
     U.S. Pat. No. 7,186,253, entitled ELECTROSURGICAL JAW STRUCTURE FOR CONTROLLED ENERGY DELIVERY; 
     U.S. Pat. No. 7,169,146, entitled ELECTROSURGICAL PROBE AND METHOD OF USE; 
     U.S. Pat. No. 7,125,409, entitled ELECTROSURGICAL WORKING END FOR CONTROLLED ENERGY DELIVERY; and 
     U.S. Pat. No. 7,112,201, entitled ELECTROSURGICAL INSTRUMENT AND METHOD OF USE. 
     Various embodiments of systems and methods of the invention relate to creating thermal “welds” or “fusion” within native tissue volumes. The alternative terms of tissue “welding” and tissue “fusion” may be used interchangeably herein to describe thermal treatments of a targeted tissue volume that result in a substantially uniform fused-together tissue mass, for example, in welding blood vessels that exhibit substantial burst strength immediately post-treatment. The strength of such welds is particularly useful for (i) permanently sealing blood vessels in vessel transection procedures; (ii) welding organ margins in resection procedures; (iii) welding other anatomic ducts wherein permanent closure is required; and also (iv) for performing vessel anastomosis, vessel closure or other procedures that join together anatomic structures or portions thereof. The welding or fusion of tissue as disclosed herein is to be distinguished from “coagulation”, “hemostasis” and other similar descriptive terms that generally relate to the collapse and occlusion of blood flow within small blood vessels or vascularized tissue. For example, any surface application of thermal energy can cause coagulation or hemostasis—but does not fall into the category of “welding” as the term is used herein. Such surface coagulation does not create a weld that provides any substantial strength in the treated tissue. 
     At the molecular level, the phenomena of truly “welding” tissue as disclosed herein may result from the thermally-induced denaturation of collagen and other protein molecules in a targeted tissue volume to create a transient liquid or gel-like proteinaceous amalgam. A selected energy density is provided in the targeted tissue to cause hydrothermal breakdown of intra- and intermolecular hydrogen crosslinks in collagen and other proteins. The denatured amalgam is maintained at a selected level of hydration—without desiccation—for a selected time interval which can be very brief. The targeted tissue volume is maintained under a selected very high level of mechanical compression to insure that the unwound strands of the denatured proteins are in close proximity to allow their intertwining and entanglement. Upon thermal relaxation, the intermixed amalgam results in protein entanglement as re-crosslinking or renaturation occurs to thereby cause a uniform fused-together mass. 
     It will be appreciated that the terms “proximal” and “distal” may be used throughout the specification with reference to a clinician manipulating one end of an instrument used to treat a patient. The term “proximal” refers to the portion of the instrument closest to the clinician and the term “distal” refers to the portion located furthest from the clinician. It will be further appreciated that for conciseness and clarity, spatial terms such as “vertical,” “horizontal,” “up,” and “down” may be used herein with respect to the illustrated embodiments. However, surgical instruments may be used in many orientations and positions, and these terms are not intended to be limiting and absolute. 
     Various embodiments disclosed herein provide electrosurgical jaw structures adapted for transecting captured tissue between the jaws and for contemporaneously welding the captured tissue margins with controlled application of RF energy. The jaw structures may comprise a scoring element which may cut or score tissue independently of the tissue capturing and welding functions of the jaw structures. The jaw structures may comprise first and second opposing jaws that carry positive temperature coefficient (PTC) bodies for modulating RF energy delivery to the engaged tissue. 
     A surgical instrument can be configured to supply energy, such as electrical energy and/or heat energy, to the tissue of a patient. For example, various embodiments disclosed herein provide electrosurgical jaw structures adapted for transecting captured tissue between the jaws and for contemporaneously welding the captured tissue margins with controlled application of RF energy. In some embodiments, the electrosurgical jaw structures may be adapted to coagulate the captured tissue rather than weld the captured tissue. All such arrangements and implementations are intended to be within the scope of this disclosure. 
     Referring now to  FIG. 1 , an electrosurgical system  100  is shown in accordance with various embodiments. The electrosurgical system  100  includes an electrosurgical instrument  101  that may comprise a proximal handle  105 , a distal working end or end effector  110  and an introducer or elongate shaft  108  disposed in-between. The end effector  110  may comprise a set of openable-closeable jaws with straight or curved jaws—an upper first jaw  120 A and a lower second jaw  120 B. The first jaw  120 A and the second jaw  120 B may each comprise an elongate slot or channel  142 A and  142 B (see  FIG. 3 ), respectively, disposed outwardly along their respective middle portions. 
     The electrosurgical system  100  can be configured to supply energy, such as electrical energy, ultrasonic energy, and/or heat energy, for example, to the tissue of a patient. In one embodiment, the electrosurgical system  100  includes a generator  145  in electrical communication with the electrosurgical instrument  101 . The generator  145  is connected to electrosurgical instrument  101  via a suitable transmission medium such as a cable  152 . In one embodiment, the generator  145  is coupled to a controller, such as a control unit  102 , for example. In various embodiments, the control unit  102  may be formed integrally with the generator  145  or may be provided as a separate circuit module or device electrically coupled to the generator  145  (shown in phantom to illustrate this option). Although in the presently disclosed embodiment, the generator  145  is shown separate from the electrosurgical instrument  101 , in one embodiment, the generator  145  (and/or the control unit  102 ) may be formed integrally with the electrosurgical instrument  101  to form a unitary electrosurgical system  100 . 
     The generator  145  may comprise an input device  147  located on a front panel of the generator  145  console. The input device  147  may comprise any suitable device that generates signals suitable for programming the operation of the generator  145 , such as a keyboard, or input port, for example. In one embodiment, various electrodes in the first jaw  120 A and the second jaw  120 B may be coupled to the generator  145 . A cable  152  may comprise multiple electrical conductors for the application of electrical energy to positive (+) and negative (−) electrodes of the electrosurgical instrument  101 . The control unit  102  may be used to activate electrical source  145 . In various embodiments, the generator  145  may comprise an RF source, an ultrasonic source, a direct current source, and/or any other suitable type of electrical energy source, for example. 
     In various embodiments, the electrosurgical system  100  may comprise at least one supply conductor  139  and at least one return conductor  141 , wherein current can be supplied to electrosurgical instrument  101  via the supply conductor  139  and wherein the current can flow back to the generator  145  via return conductor  141 . In various embodiments, the supply conductor  139  and the return conductor  141  may comprise insulated wires and/or any other suitable type of conductor. In certain embodiments, as described below, the supply conductor  139  and the return conductor  141  may be contained within and/or may comprise the cable  152  extending between, or at least partially between, the generator  145  and the end effector  110  of the electrosurgical instrument  101 . In any event, the generator  145  can be configured to apply a sufficient voltage differential between the supply conductor  139  and the return conductor  141  such that sufficient current can be supplied to the end effector  110 . 
     Moving now to  FIG. 2 , a side view of the handle  105  is shown with half of a first handle body  106 A (see  FIG. 1 ) removed to illustrate various components within second handle body  106 B. The handle  105  may comprise a lever arm  128  (e.g., a trigger) which may be pulled along a path  129 . The lever arm  128  may be coupled to an axially moveable member  140  disposed within elongate shaft  108  by a shuttle  146  operably engaged to an extension  127  of lever arm  128 . The shuttle  146  may further be connected to a biasing device, such as a spring  141 , which may also be connected to the second handle body  106 B, to bias the shuttle  146  and thus the axially moveable member  140  in a proximal direction, thereby urging the jaws  120 A and  120 B to an open position as seen in  FIG. 1 . Also, referring to  FIGS. 1 and 2 , a locking member  131  (see  FIG. 2 ) may be moved by a locking switch  130  (see  FIG. 1 ) between a locked position, where the shuttle  146  is substantially prevented from moving distally as illustrated, and an unlocked position, where the shuttle  146  may be allowed to freely move in the distal direction, toward the elongate shaft  108 . The handle  105  can be any type of pistol-grip or other type of handle known in the art that is configured to carry actuator levers, triggers or sliders for actuating the first jaw  120 A and the second jaw  120 B. The elongate shaft  108  may have a cylindrical or rectangular cross-section, for example, and can comprise a thin-wall tubular sleeve that extends from handle  105 . The elongate shaft  108  may include a bore extending therethrough for carrying actuator mechanisms, for example, the axially moveable member  140 , for actuating the jaws and for carrying electrical leads for delivery of electrical energy to electrosurgical components of the end effector  110 . 
     The end effector  110  may be adapted for capturing and transecting tissue and for the contemporaneously welding the captured tissue with controlled application of energy (e.g., RF energy). The first jaw  120 A and the second jaw  120 B may close to thereby capture or engage tissue about a longitudinal axis  125  defined by the axially moveable member  140 . The first jaw  120 A and second jaw  120 B may also apply compression to the tissue. In some embodiments, the elongate shaft  108 , along with first jaw  120 A and second jaw  120 B, can be rotated a full 360° degrees, as shown by arrow  117  ( FIG. 1 ), relative to handle  105  through, for example, a rotary triple contact. The first jaw  120 A and the second jaw  120 B can remain openable and/or closeable while rotated. 
       FIGS. 3 and 4  illustrate perspective views of the end effector  110  in accordance with one non-limiting embodiment.  FIG. 3  shows end the effector  110  in an open configuration and  FIG. 4  shows the end effector  110  in a closed configuration. As noted above, the end effector  110  may comprise the upper first jaw  120 A and the lower second jaw  120 B. Further, the first jaw  120 A and second jaw  120 B may each have tissue-gripping elements, such as teeth  143 , disposed on the inner portions of first jaw  120 A and second jaw  120 B. The first jaw  120 A may comprise an upper first jaw body  161 A with an upper first outward-facing surface  162 A and an upper first energy delivery surface  175 A. The second jaw  120 B may comprise a lower second jaw body  161  B with a lower second outward-facing surface  162 B and a lower second energy delivery surface  175 B. The first energy delivery surface  175 A and the second energy delivery surface  175 B may both extend in a “U” shape about the distal end of the end effector  110 . 
     Referring briefly now to  FIG. 5 , a portion of the axially moveable member  140  is shown. The lever arm  128  of the handle  105  ( FIG. 2 ) may be adapted to actuate the axially moveable member  140  which also functions as a jaw-closing mechanism. For example, the axially moveable member  140  may be urged distally as the lever arm  128  is pulled proximally along the path  129  via the shuttle  146 , as shown in  FIG. 2  and discussed above. The axially moveable member  140  may comprise one or several pieces, but in any event, may be movable or translatable with respect to the elongate shaft  108  and/or the jaws  120 A,  120 B. Also, in at least one embodiment, the axially moveable member  140  may be made of  17 - 4  precipitation hardened stainless steel. The distal end of axially moveable member  140  may comprise a flanged “I”-beam configured to slide within the channels  142 A and  142 B in jaws  120 A and  120 B. The axially moveable member  140  may slide within the channels  142 A,  142 B to open and close first jaw  120 A and second jaw  120 B. The distal end of the axially moveable member  140  may also comprise an upper flange or “c”-shaped portion  140 A and a lower flange or “c”-shaped portion  140 B. The flanges  140 A and  140 B respectively define inner cam surfaces  144 A and  144 B for engaging outward facing surfaces of first jaw  120 A and second jaw  120 B. The opening-closing of jaws  120 A and  120 B can apply very high compressive forces on tissue using cam mechanisms which may include movable “I-beam” axially moveable member  140  and the outward facing surfaces  162 A,  162 B of jaws  120 A,  120 B. 
     More specifically, referring now to  FIGS. 3-5 , collectively, the inner cam surfaces  144 A and  144 B of the distal end of axially moveable member  140  may be adapted to slidably engage the first outward-facing surface  162 A and the second outward-facing surface  162 B of the first jaw  120 A and the second jaw  120 B, respectively. The channel  142 A within first jaw  120 A and the channel  142 B within the second jaw  120 B may be sized and configured to accommodate the movement of the axially moveable member  140 , which may comprise a tissue-cutting element  148 , for example, comprising a sharp distal edge.  FIG. 4 , for example, shows the distal end of the axially moveable member advanced at least partially through channels  142 A and  142 B ( FIG. 3 ). The advancement of the axially moveable member  140  may close the end effector  110  from the open configuration shown in  FIG. 3 . In the closed position shown by  FIG. 4 , the upper first jaw  120 A and lower second jaw  120 B define a gap or dimension D between the first energy delivery surface  175 A and second energy delivery surface  175 B of first jaw  120 A and second jaw  120 B, respectively. In various embodiments, dimension D can equal from about 0.0005″ to about 0.040″, for example, and in some embodiments, between about 0.001″ to about 0.010″, for example. Also, the edges of the first energy delivery surface  175 A and the second energy delivery surface  175 B may be rounded to prevent the dissection of tissue. 
       FIG. 6  is a sectional view of the end effector  110  in accordance with one non-limiting embodiment. In one embodiment, the engagement, or tissue-contacting, surface  175 B of the lower jaw  120 B is adapted to deliver energy to tissue, at least in part, through a conductive-resistive matrix, such as a variable resistive positive temperature coefficient (PTC) body, as discussed in more detail below. At least one of the upper and lower jaws  120 A,  120 B may carry at least one electrode  170  configured to deliver the energy from the generator  145  to the captured tissue. The engagement, or tissue-contacting, surface  175 A of upper jaw  120 A may carry a similar conductive-resistive matrix (i.e., a PTC material), or in some embodiments the surface may be a conductive electrode or an insulative layer, for example. Alternatively, the engagement surfaces of the jaws can carry any of the energy delivery components disclosed in U.S. Pat. No. 6,773,409, filed Sep. 19, 2001, entitled SURGICAL SYSTEM FOR APPLYING ULTRASONIC ENERGY TO TISSUE, the entire disclosure of which is incorporated herein by reference. 
     The first energy delivery surface  175 A and the second energy delivery surface  175 B may each be in electrical communication with the generator  145 . The first energy delivery surface  175 A and the second energy delivery surface  175 B may be configured to contact tissue and deliver electrosurgical energy to captured tissue which are adapted to seal or weld the tissue. The control unit  102  regulates the electrical energy delivered by electrical generator  145  which in turn delivers electrosurgical energy to the first energy delivery surface  175 A and the second energy delivery surface  175 B. The energy delivery may be initiated by an activation button  124  ( FIG. 2 ) operably engaged with the lever arm  128  and in electrical communication with the generator  145  via cable  152 . In one embodiment, the electrosurgical instrument  101  may be energized by the generator  145  by way of a foot switch  144  ( FIG. 1 ). When actuated, the foot switch  144  triggers the generator  145  to deliver electrical energy to the end effector  110 , for example. The control unit  102  may regulate the power generated by the generator  145  during activation. Although the foot switch  144  may be suitable in many circumstances, other suitable types of switches can be used. 
     As mentioned above, the electrosurgical energy delivered by electrical generator  145  and regulated, or otherwise controlled, by the control unit  102  may comprise radio frequency (RF) energy, or other suitable forms of electrical energy. Further, the opposing first and second energy delivery surfaces  175 A and  175 B may carry variable resistive positive temperature coefficient (PTC) bodies that are in electrical communication with the generator  145  and the control unit  102 . Additional details regarding electrosurgical end effectors, jaw closing mechanisms, and electrosurgical energy-delivery surfaces are described in the following U.S. patents and published patent applications: U.S. Pat. Nos. 7,087,054; 7,083,619; 7,070,597; 7,041,102; 7,011,657; 6,929,644; 6,926,716; 6,913,579; 6,905,497; 6,802,843; 6,770,072; 6,656,177; 6,533,784; and 6,500,176; and U.S. Pat. App. Pub. Nos. 2010/0036370 and 2009/0076506, all of which are incorporated herein in their entirety by reference and made a part of this specification. 
     In one embodiment, the generator  145  may be implemented as an electrosurgery unit (ESU) capable of supplying power sufficient to perform bipolar electrosurgery using radio frequency (RF) energy. In one embodiment, the ESU can be a bipolar ERBE ICC 350 sold by ERBE USA, Inc. of Marietta, Ga. In some embodiments, such as for bipolar electrosurgery applications, a surgical instrument having an active electrode and a return electrode can be utilized, wherein the active electrode and the return electrode can be positioned against, adjacent to and/or in electrical communication with, the tissue to be treated such that current can flow from the active electrode, through the positive temperature coefficient (PTC) bodies and to the return electrode through the tissue. Thus, in various embodiments, the electrosurgical system  100  may comprise a supply path and a return path, wherein the captured tissue being treated completes, or closes, the circuit. In one embodiment, the generator  145  may be a monopolar RF ESU and the electrosurgical instrument  101  may comprise a monopolar end effector  110  in which one or more active electrodes are integrated. For such a system, the generator  145  may require a return pad in intimate contact with the patient at a location remote from the operative site and/or other suitable return path. The return pad may be connected via a cable to the generator  145 . 
     During operation of electrosurgical instrument  101 , the user generally grasps tissue, supplies energy to the captured tissue to form a weld or a seal, and then drives a tissue-cutting element  148  at the distal end of the axially moveable member  140  through the captured tissue. According to various embodiments, the translation of the axial movement of the axially moveable member  140  may be paced, or otherwise controlled, to aid in driving the axially moveable member  140  at a suitable rate of travel. By controlling the rate of the travel, the likelihood that the captured tissue has been properly and functionally sealed prior to transection with the cutting element  148  is increased. 
       FIG. 7  is a schematic representation of an actuation assembly  200  in accordance with one non-limiting embodiment with some of the components thereof omitted for clarity. Additionally various components of the actuation assembly  200  have been expanded or altered in scale for convenience. The actuation assembly  200  may be used, for example, with instruments similar to electrosurgical instrument  101  in order to regulate or otherwise control the axial movement of an axially moveable member  240 . The actuation assembly  200  may comprise an axially moveable member  240  which has at its distal end  242  a tissue-cutting element, such as a sharp distal edge  243 , for example. The axially moveable member  240  may define a longitudinal axis  246 . The axially moveable member  240  may also comprise a rack  244  configured to engage a drive gear  246 . The drive gear  246  may be coupled to an internal shaft  248 , which may define a longitudinal axis  250 . In one embodiment the longitudinal axis  250  of the internal shaft  248  is substantially perpendicular to the longitudinal axis  246  of the axially moveable member  240 . In some embodiments, a trigger gear  252  may also be coupled to the internal shaft  248 . A portion of a trigger assembly  227  may comprise a rack  254  that is configured to engage the trigger gear  252 . The actuation assembly  200  may also comprise a moveable locking member  256  this is selectably engagable with the internal shaft  248  or other component of the actuation assembly  200 . The actuation assembly  200  may also comprise a spring, such as torsional spring  251 , which distally drives the axially moveable member  240 . One end of the torsional spring  251  may be coupled to the internal shaft  248  when the other end the torsional spring  251  may be attached to a portion of the actuation assembly  200  that remains stationary relative to the rotating internal shaft  248 . Rotation of the internal shaft  248  winds the torsional spring  251  to generate potential energy which may be selectably transferred to the internal shaft  248 , as described in more detail below. 
     Referring briefly to  FIG. 8 , a cross-sectional view of the engagement between the internal shaft  248  and the moveable locking member  256  is provided in accordance with one non-limiting embodiment. The internal shaft  248  may comprise a plurality of facets  258  positioned around its circumference. The facets  258  may longitudinally span the entire internal shaft  248 , or may be positioned on a portion of the internal shaft  248 , such as the portion proximate the moveable locking member  256 . The movable locking member  256  may comprise a pawl  260  that engages the facets  258  of the internal shaft  248 . The movable locking member  256  may be able to pivot in the direction indicated by arrow  262  to allow the internal shaft  248  to rotate in a first direction indicated by arrow  264 . When the pawl  260  is engaged with a facet  258 , the internal shaft  248  is prohibited from rotating in a second direction indicated by arrow  266 . When the pawl  260  is disengaged from the facet  248 , such as by movement of the pawl in the direction indicated by arrow  268 , the internal shaft  248  may rotate in the directions indicated by arrow  266  and arrow  264 . 
     Referring again to  FIG. 7 , the operation of the actuation assembly  200  allows for a controlled distal translation of the axially moveable member  240 . In accordance with one embodiment, at the beginning of the operational stroke, the portion of a trigger assembly  227  comprising the rack  254  is moved in the direction indicated by arrow  270 . As the rack  254  translates relative to the trigger gear  252 , the trigger gear  252  rotates in the direction indicated by arrow  271 . As the trigger gear  252  rotates, the internal shaft  248  rotates as well, which winds the torsional spring  251 . The drive gear  246  also rotates in the direction indicated by arrow  271 , which due to its engagement with the rack  244  of the axially moveable member  240 , draws the axially moveable member  240  in the proximal direction indicated by arrow  272 . The moveable locking member  256  keeps the internal shaft  248  from rotating in the direction indicated by arrow  274 , despite the rotational force of the torsional spring  251  bearing on the internal shaft  248 . When the activation button  124  ( FIG. 2 ) is pressed, the movable locking member  256  may withdraw from engagement with the internal shaft  248 . The coupling of the activation button  124  to the movable locking member  256  may be made using any suitable technique, such as a mechanical linkage, for example. In some embodiments, a tab on the trigger assembly  227  contacts the movable locking member  256  to move it from engagement with the internal shaft  228  once the torsional gear  251  is wound. Accordingly, any suitable technique may be used to disengage the movable locking member  256  from the internal shaft  248 . 
     With the movable locking member  256  no longer locking the internal shaft  248 , the internal shaft  248  rotates in the direction indicated by arrow  274  as the torsional spring  251  unwinds. Consequently, the drive gear  246  also rotates, and through its engagement with the rack  244 , the axially moveable member  240  is driven in the distal direction indicated by arrow  276 . The rate of travel of the axially moveable member  240  is generally dependent on the spring constant of the torsional spring  251 , as opposed to the user&#39;s interaction with the trigger. 
     In various embodiments, the parameters of the components of the actuation assembly  200  may be altered to achieve the desired performance. For example, the size or strength of the torsional spring  251  may be changed. In one embodiment the gear ratio between the trigger gear  252  and the drive gear  246  may be a  1 : 1  ratio, while in other embodiments a different ratio is used. In some embodiments, as shown in  FIG. 9 , a single gear  280  may engage both the rack  254  of the trigger assembly  257  and the rack  244  of the axially moveable member  240 . In some embodiments, a dashpot, such as damper  312  ( FIG. 10 ), may be used to further control the translation of axially moveable member  240 . 
       FIG. 10  is a simplified representation of an actuation assembly  300  in accordance with one non-limiting embodiment with some of the components thereof omitted for clarity. The actuation assembly  300  is associated with a handle  302  and an axially moveable member  306  extending distally from the handle. An end effector similar to the end effector  110  illustrated in  FIG. 3  may be coupled to the distal end of an elongate shaft  304 . The axially moveable member  306  may extend from the end effector and into the handle  302 . As described in more detail below, a trigger  307  is operably coupled to the axially moveable member  306 . In various embodiments, an advance spring  308  and a return spring  310  are each operably connected to the axially moveable member  306 . The advance spring  308  and the return spring  310  may have different spring constants. In one embodiment, the advance spring  308  has a higher spring constant than the return spring  310 . The actuation assembly  300  may further comprise a damper  312  configured to regulate (i.e., slow) the translation of the axially moveable member  306 . 
       FIG. 10A  provides a close-up view of the damper  312  in accordance with one non-limiting embodiment. The damper  312  comprises a barrel  314  and a plunger  316 , wherein an outer surface of the plunger  316  is in sealing engagement with an inner surface of the barrel  314  to create a variable volume cavity  315 . While the damper  312  is illustrated as having a barrel and plunger arrangement, any suitable damping device may be used, such as mechanical or hydraulics dashpots, for example. This disclosure is not limited to any particular damper arrangement. The plunger  316  may be coupled to, for example, the proximal end of the axially moveable member  306 . The plunger may be movable between a first and second position within the barrel  314 . The damper  312  may define a first port  318  having a first flow path and a second port  320  having a second flow path. In one embodiment, the damper  312  comprises a check valve  322  positioned in the second flow path. During operation, air may flow in both directions through the first flow path, while air may only exit the variable volume cavity  315  through the second flow path. As is to be appreciated, the size and number of ports in the barrel  314  may be varied to achieve the desired dampening. 
     Referring again to  FIG. 10 , the trigger  307  may pivot or rotate about a pivot  324  such that as the bottom trigger portion  307   a  is rotated in the direction indicated by arrow  326 , the top trigger portion  307   b  is rotated in the direction indicated by arrow  328 . The top trigger portion  307   b  may be coupled to an end of the advance spring  308 . The other end of the advance spring  308  may be coupled to the axially moveable member  306 , such as via a linkage  324 . One end of the return spring  310  may also be coupled to the axially moveable member  306 , such as via the linkage  324 . The other end of the return spring  310  may be fixed to a mount  326 . The advance spring  308  and the return spring  310  may exert biasing forces on the axially moveable member  306  in generally opposite longitudinal directions. 
     When the bottom trigger portion  307   a  is squeezed by a user, the top trigger portion  307   b  exerts a longitudinal force on both the advance spring  308  and the return spring  310  in the direction indicated by arrow  328 . As described above, the squeezing of the trigger  307  may close the jaws of an associated end effector to capture tissue. As the user squeezes the trigger  307 , both springs  308 ,  310  expand, the axially moveable member  306  distally translates in order to transect the captured tissue. The rate of travel of the axially moveable member  306  is regulated as a function of the spring constants of the springs  308 ,  310  and the dampening effects of the damper  312 . Referring to  FIG. 10A , as the plunger  316  distally translates in the barrel  314 , the variable volume cavity  315  expands and a low pressure, below atmosphere, is generated. In order to reach equilibrium, ambient air enters the variable volume cavity  315  through the first port  318 . In the illustrated embodiment, the check valve  322  prohibits air form entering the variable volume cavity  315  through the second port  320 . As is to be appreciated, the damping coefficient of the damper  312  is a function of the rate of the ingress of the air through the first port  318 . In some embodiments, the size of the first port  318  may be variable to provide a selectable damping coefficient. As the user continues to squeeze and rotate the bottom trigger portion  307   a , the top trigger portion  307   b  will continue to exert a substantially linearly applied force on the springs  308 ,  310  which continue to expand. Since the advance spring  308  is stronger (i.e., has a higher spring constant) than the return spring  310 , the axially moveable member  306 , via the linkage  324 , will be drawn distally in order to transect captured tissue. As the axially moveable member  306  is translated distally by the force applied through the advance spring  308 , the return spring  310  expands between the linkage  324  and the mount  326 . 
     When the user releases the trigger assembly  307 , the expanded return spring  310  exerts a linear force on the linkage  324  to proximally translate axially moveable member  306 . The proximal translation of the axially moveable member  306  will drive the plunger  316  ( FIG. 10A ) into the barrel  314 , thus reducing the size of the variable volume chamber  315 . Air will be expelled from the variable volume chamber  315  via both the first portion  318  and the second port  320 . Thus, when the plunger  316  travels in the proximal direction, the damping coefficient of the damper  312  is less than when the plunger  316  travels distally. 
     The advance spring  308  and the return spring  310  may be any suitable types of biasing members, such as pistons, coil springs, rubber bands, and/or any other suitable elastic member, for example. In one embodiment, illustrated in  FIG. 11 , linear compression springs may be used as biasing members.  FIG. 11  is a simplified representation of an actuation assembly  340  in accordance with one alternative non-limiting embodiment with some of the components thereof omitted for clarity. As illustrated, the actuation assembly  340  may comprise a return spring  342  and an advance spring  344 . The overall operation of the actuation assembly  340  may be generally similar to the operation of the actuation assembly  300  illustrated in  FIG. 10 , with the exchange of linear compression springs for linear expansion springs. Accordingly, as the lower trigger portion  307   a  is rotated in the direction indicated by arrow  326 , the upper trigger portion  307   b  compresses the springs  342 ,  344  similar to the above. The damper  312  serves to regulate the rate of distal and proximal translation of the axially moveable member  306 . 
     According to various embodiments, the pacing of the axial movement of the axially moveable member may driven by an electric motor or any other type of suitable linearly actuating device, such as an electroactive polymer (EAP) actuator, for example.  FIGS. 12-15  illustrate a representation of an electrosurgical instrument  400  comprising a linear actuator  402  in accordance with one non-limiting embodiment. For clarity, various components have been omitted. The electrosurgical instrument  400  may comprise a proximal handle  405 , a distal working end or end effector  410  and an introducer or elongate shaft  408  disposed in-between. An axially moveable member  440  may couple the end effector  410  and a trigger assembly  407 . The end effector  410  may comprise a set of openable-closeable jaws with straight or curved jaws, similar to the end effector  110  illustrated in  FIG. 3 , for example. In one embodiment, the linear actuator  402  comprises a lead screw  420  and an electric motor  422  coupled to the lead screw  420 . The electric motor  422  may be coupled to a power  121  supply  425  via cabling  426 . As is to be appreciated, the power supply  425  may be any suitable power source and may be a separate unit (as illustrated), or carried on-board the electrosurgical instrument  400 . In some embodiments, other techniques may be used to impart linear motion to the axially moveable member  440 . For example, similar to  FIG. 9 , the axially moveable member  440  may comprise a rack and the motor  422  may rotate a drive gear operably engaged to the rack. 
     A nut assembly  424  may be slideably engaged to the axially moveable member  440  and the lead screw  420 . The nut assembly  424  may interface the axially moveable member  440  at a clearance  429 . The clearance  429  may be, for example, a portion of the axially moveable member  440  having a reduced diameter. Either end of clearance  429  may have a proximal stop  428  and a distal stop  430 . The proximal and distal stops  428 ,  430  may each be a lip, as illustrated. It is noted that the clearance  429  illustrated in  FIGS. 12-15  has been expanded for clarity and is not necessarily drawn to any particular scale. As discussed in more detail below, the clearance  429  generally allows for the opening and closing of the jaws of the end effector  410 , while prohibited the cutting of tissue until the tissue has been properly sealed. 
     The trigger assembly  407  may be operatively engaged with axially moveable member  440  at a trigger interface  432 . The trigger interface  432  may include a distal sensor  434  and a proximal sensor  436 . The trigger interface  432  may also include a distal trigger stop  433  and a proximal trigger stop  435 . The electrosurgical instrument  400  may also comprise a button  438 . When the button  438  is engaged, electrical energy (i.e., RF energy) may be supplied to captured tissue via the end effector  410 . 
     With reference to  FIGS. 12-15 , the operation of the electrosurgical instrument  400  in accordance with one non-limiting embodiment will be described. In  FIG. 12 , the jaws of the end effector  410  are in an open position allowing tissue to be captured therebetween. A gap  444  is present between the nut assembly  424  and the proximal stop  428 . In  FIG. 13 , the trigger assembly  407  has been rotated (i.e., squeezed) in the direction indicated by arrow  446 . As the trigger assembly  407  rotates it engages the distal trigger stop  433  which is coupled to the axially moveable member  440 . As the axially moveable member  440  moves in the direction indicated by arrow  448 , the jaws of the end effector  410  are closed, similar to the end effector  110  illustrated in  FIG. 4 . The progression of the axially moveable member  440  in the direction indicated by arrow  448  is impeded when the proximal stop  428  engages the nut assembly  424 . Accordingly, at this stage in the operational stroke, the distance of travel of axially moveable member  440  is generally limited to the length of the gap  444  ( FIG. 12 ). In one embodiment, this distance is long enough to cause the jaws of the end effector  410  to clamp tissue, while keeping a cutting element at the distal end of the axially moveable member  440  from contacting the captured tissue. Generally, by providing the clearance  429  on the axially moveable member  440 , a relatively small amount of trigger assembly manipulation may be performed by the user to open and close the jaws of the end effector without distally driving the cutting element into the tissue. The cutting element is only driven through the tissue when the linear actuator  402  is activated. As is to be appreciated, the clearance  429  may sized based on the particular arrangement of the electrosurgical instrument  400 . For example, in one embodiment, the clearance  429  may be less than about 0.5 inches in length as measured between the proximal stop  428  and a distal stop  430 . In one embodiment, the clearance  429  may be less than about 0.2 inches, for example, in length as measured between the proximal stop  428  and a distal stop  430 . As is to be appreciated, the size of the clearance  429  for any electrosurgical instrument  400  will at least partially depend on the relative size of the nut assembly  424  since a gap  444  is required between the nut assembly  424  and the distal stop  430 . 
     Referring now to  FIG. 14 , when the button  438  is activated by the user, energy flows through electrodes in the end effector  410  to energize the captured tissue (not illustrated). When the button  438  is activated and the trigger  407  is squeezed, the motor  422  of the linear actuator  402  rotates lead screw  420  in the direction indicated by arrow  450  ( FIG. 15 ). In one embodiment, the motor  422  will only be activated when both the button  438  is activated to deliver the RF energy to the tissue and the trigger  407  is squeezed. By requiring the user to complete both actions before activating the linear actuator  402 , the possibility of a “cold cut” (e.g., cutting the tissue before it has been welded) is greatly reduced or eliminated. The squeezing of the trigger  407  may be sensed by the distal sensor  434 . The distal sensor  434  may be, for example, a pressure sensor that supplies a signal to an associated controller. As the lead screw  420  rotates, the nut assembly  424  travels in the direction indicated by arrow  448 , owing to the operative engagement of threads on the lead screw  420  and a threaded aperture in the nut assembly  424 . As the nut assembly  424  travels along the lead screw  420 , the nut assembly  424  will engage the axially moveable member  440  at the distal stop  430 . The nut assembly  424  will then push the axially moveable member  440  in the distal direction as the user continues to squeeze the trigger  407  and lead screw  420  continues to rotate. A cutting element  452  positioned on the distal end of the axially moveable member  440  progresses through and transects the captured tissue. When the user opens the trigger  407 , the trigger  407  can move toward and activate the proximal sensor  436 . Activation of the proximal sensor  436  will cause the motor  422  to rotate the lead screw  420  in the opposite direction, and owing to the threaded engagement between the lead screw  420  and the nut assembly  424 , the nut assembly  424  will translate through the gap  444  ( FIG. 12 ) and engage the axially moveable member  440  at the proximal stop  428 . The nut assembly  424  will then push the axially moveable member  440  in the proximal direction as the user continues to open the trigger  407  and lead screw  420  continues to rotate. In one embodiment, the motor  422  may rotate the lead screw  420  faster during the proximal progression of the axially moveable member  440  as compared to the distal progression. As is to be appreciated, a controller  502  ( FIG. 16 ) may be used to receive the inputs from various components of the electrosurgical instrument  440 , such as the button  438  and the sensors  434 ,  436 , and selectively supply energy to the motor  422 . 
     The speed of the motor  422  may be changed based on any particular application. In one embodiment, at least one of the proximal sensor  436  and the distal sensor  434  measures the amount of force exerted by the user during the trigger actuation. In one embodiment, the displacement of the trigger is monitored. In any event, as the force exerted by the user increases (or the displacement of the trigger increases), the speed of the motor  422  is also increased. Therefore, for applications involving large amounts of captured tissue, for example, the user can selectively increase or decrease the speed of the motor through manipulation of the trigger. 
     The maximum rate of travel of the axially moveable member  440  is determined by the linear actuator  402 . In various embodiments, the rate of travel of the axially moveable member  440  may be adjustable by the user. In some embodiments, the electrosurgical instrument  400  may comprise a force transducer  442 . The force transducer  442  may be any type of load cell suitable to produce a signal indicative of the force. The force transducer  442  may supply information to the controller indicative to characteristics of the captured tissue. For example, thicker tissue will generally require more time to properly seal and will provide more resistance to the axially moveable member  440  as it passes through the tissue. Comparatively, thinner tissue will generally require less time to properly seal and will provide less resistance to the axially moveable member  440  as it passes through the tissue. Information from the force transducer  442  may be supplied to the controller  502  ( FIG. 16 ) and the speed of the motor  422  may be adjusted to compensate for the tissue characteristics. Accordingly, the rotational speed of the lead screw  420  may be reduced when cutting thicker tissue in order to lengthen the amount of time the captured tissue is exposed to the RF energy. The rotational speed of the lead screw  420  may be increased when cutting thinner tissue to shorten the amount of time the captured tissue is exposed to the RF energy and reduce the likelihood of charring or excess heating. In any event, the use of the linear actuator  402  helps to ensure a steady and regulated translation of the axially moveable member through the tissue, even with end effectors having a relatively long jaw length. 
     In various embodiments, the electrosurgical instrument  440  may have an encoder  460  associated with the linear actuator  402 . The encoder  460  may supply information to an associated controller to aid in the cutting of the captured tissue, such as speed data. The encoder  460  may be any type of suitable encoder, such as a rotary encoder to monitor the rotation of the lead screw  420 . The linear displacement of the axially moveable member  440  may then be determined as a function of the threaded coupling between the nut assembly  424  to the lead screw  420 . 
       FIG. 16  is a block diagram of a control system  500  of an electrosurgical instrument in accordance with one non-limiting embodiment. A controller  502  receives various inputs from the components, such as an encoder  560 , a force transducer  542 , a button  538 , a distal sensor  534 , and a proximal sensor  536 . When an activation signal is received from the button  538 , the controller  502  may send a signal to an RF source  504  which, in turn, provides RF energy to an electrode  506 . When the controller  502  receives an activation signal from both the button  538  and the distal sensor  534 , the controller  502  may supply current to the motor  522 . As described above, information received from the encoder  560  and the force transducer  542  may provide a feedback loop to aid in the motor control. For example, the encoder  560  may indicate that the axially moveable member has reached the distal end of its stroke indicating to the controller  502  to cease supplying current to the motor  522 . When the proximal sensor  536  supplies a signal to the controller  502 , the controller  502  may rotate the motor  522  in an opposite direction. The encoder  560  may indicate that the axially moveable member has reached the proximal of its stroke indicating to the controller  502  to cease supplying current to the motor  522 . 
       FIG. 17  is a flow chart  580  of the operation of an electrosurgical instrument having a linear actuator in accordance with one non-limiting embodiment. At  582 , the instrument is in a standby mode. In standby mode, the jaws are in the open position and ready to engage tissue. At  584 , a main trigger, such as trigger  407  ( FIG. 14 ) is moved from a first position to a second position in order to capture tissue between the jaws. At  586 , a button, such as button  538 , for example, or any other type of triggering or activation device, is activated to supply electrical energy to the captured tissue. At  588 , while the button is activated, the main trigger is moved from the second position to a third position to activate a linear actuator and cut the captured tissue. At  590 , an axially moveable member is distally advanced using a linear actuator. At  592 , the main trigger is moved from the third position back to the first position and the linear actuator is activated to move the axially moveable member in the proximal direction to open the jaws of the end effector. 
     In various embodiments, a dashpot may be coupled to a trigger-actuated axially moveable member in order to regulate the rate of travel of axially moveable member.  FIGS. 18-21  illustrate an electrosurgical instrument  600  with various components removed, or otherwise simplified, for clarity. The electrosurgical instrument  600  has a handle  602  and an elongate shaft  604  extending distally from the handle. An end effector  610  similar to the end effector  110  illustrated in  FIG. 3  may be coupled to the distal end of the elongate shaft  604 . An axially moveable member  606  may extend from the distal end of the elongate shaft  604  into the handle  602 . A trigger  607  is coupled to the axially moveable member  606 . The electrosurgical instrument  600  may further comprise a damper  612  (shown in cross-section) configured to regulate the translation of the axially moveable member  606 . Generally, movement of the trigger  607  corresponds to movement of the axially moveable member  606  in the distal and proximal direction due to a pivot  616  and a linkage  614  connecting the trigger  607  to the axially moveable member  606 . 
     The damper  612  may be associated with the axially moveable member  606  such that it controls the speed of the axially moveable member  606  during the operational stroke of the electrosurgical instrument  600 .  FIG. 18A  is an enlarged cross-sectional view of the damper  612  in accordance with one non-limiting embodiment. In one embodiment, the damper  612  comprises a barrel  620  and a plunger  622 , wherein an outer diameter of the plunger  622  is in sealing engagement with an inner diameter of the barrel  620 . As is to be appreciated, an o-ring  640 , or other type of sealing device may be positioned around the periphery of the plunger  622  to aid in creating a seal with the barrel  620 . Furthermore, as illustrated, the plunger  622  may be coupled to the axially moveable member  606 . The plunger  622  may be formed unitary with the axially moveable member  606  or otherwise coupled thereto. The damper  612  may also have a spring  624 , or other biasing element, to bias the axially moveable member  606  in the proximal direction. In the illustrated embodiment, a spring  624  is positioned intermediate the plunger  622  and a distal end  626  of the damper  612 . 
     Still referring to  FIG. 18A , the distal end  626  may have at least one inlet orifice  628  and at least one outlet orifice  630 . The inlet orifice  628  may have a check valve  632  which permits air to flow into the barrel  620  while restricting air to flow out of the barrel  620  through that orifice. The check valve  632  may pivot in the direction indicated by arrow  633 . In one embodiment, the outlet orifice  630  is an open aperture allowing free flow of air (or other fluid) in and out of the barrel  620 . The inlet orifice  628  and the outlet orifice  630  may have different cross sectional areas, with the outlet orifice  630  being smaller than the inlet orifice  630 . In some embodiments, the area of the outlet orifice  630  is variable. The distal end  626  may also have a center orifice  634  which is sized to accommodate the axially moveable member  606 . In various embodiments, a o-ring  636 , or other sealing device, may be used to maintain a seal between the distal end  626  of the damper  612  and the axially moveable member  606 . The barrel  620  and the distal surface of the plunger  622  define a variable volume cavity  642 . The volume of the variable volume cavity  642  decreases as the plunger  622  is distally translated and increases in volume as the plunger  622  is proximally translated. 
     Referring again to  FIGS. 18-21 , the operation of the electrosurgical instrument  600  in accordance with one non-limiting embodiment will now be described. In  FIG. 18  the electrosurgical instrument  600  is configured to begin the operational stroke. The plunger  622  is positioned at the proximal end of the barrel  620  and the jaws of the end effector  610  are in an open position.  FIG. 19  illustrates the electrosurgical instrument  600  as the trigger  607  is rotated (or squeezed) in the direction indicated by arrow  650 . As the trigger  607  is rotated, the plunger  622  is translated in the direction indicated by arrow  652 . The biasing force of the spring  624  is overcome and the variable volume cavity  642  is reduced in the volume. Air is expelled from the variable volume cavity via the outlet port  630  ( FIG. 18A ). Due to the operation of the check valve  632 , air is not expelled, or substantially expelled, through the inlet port  628  ( FIG. 18A ). Thus, when the user actuates the trigger  607 , the speed of the axially moveable member  606  is controlled by the cross sectional area of the outlet port  630 . The expelling of air (or other fluid) from the variable volume cavity  642  acts as a resistive force to the rotation of the trigger  607  to slow the operational stroke of the axially moveable member  606 . As the plunger  622  translates within the barrel  620  the axially moveable member  606  is distally translated and the end effector  610  closes its jaws to capture and transect tissue therebetween with a cutting element  607 . As the plunger  622  distally translates within the barrel  620 , the spring  624  is compressed to create a stored energy which biases the end effector  610  open at the end of the cycle. 
     As shown in  FIG. 20 , the axially moveable member  606  may continue to distally translate to move the plunger  622  toward the distal end  626  of the barrel  620 . The spring  624  is compressed between the plunger  622  and the distal end  626  of the barrel  620 . As is to be appreciated, energy may be introduced into the captured tissue to sufficiently weld the tissue prior to and during the operational stroke. As illustrated in  FIG. 21 , rotation of the trigger  607  in the direction indicated by arrow  654  translates the plunger  622  in the direction indicated by arrow  656  (e.g., proximally). As the plunger  622  is translated proximally, the volume of the variable volume cavity  642  is increased. The increase in volume generates a low pressure which draws air (or other fluid) into the variable volume cavity  642 . Due to the operation of the check valve  632  ( FIG. 18A ), air is permitted to enter the variable volume cavity  642  through both the inlet port  628  and the outlet port  630 . Therefore, the plunger  622  may translate proximally with less resistance as compared to distal translation. 
       FIGS. 22-25  illustrates the electrosurgical instrument  600  with a damper  660  having two check valves. The spring  624  is positioned external to the damper  660  such that it provides a biasing force to the trigger  607 .  FIG. 22A  is an enlarged cross-sectional view of the damper  660 . The damper  660  comprises a barrel  662  which receives the plunger  622 . A variable volume cavity  664  is formed between the plunger  622  and the distal end  666  of the barrel  662 . The damper  660  further has a first orifice  668  and a second orifice  670  positioned in the distal end  666  of the barrel  662 . A first check valve  672  is positioned proximate the first orifice  668  and a second check valve  674  is positioned proximate the second orifice  670 . The first check valve  672  defines a first outlet  676  and the second check valve  674  defines a second outlet  678 . When the plunger  622  is translated in the distal direction, air is forced from the variable volume cavity  664  through the first outlet  676  and the second outlet  678 . When the plunger  622  is translated in the proximal direction, the check valves  672 ,  674  open and air is drawn into the variable volume cavity  664  through the first orifice  668  and the second orifice  670 . The total cross-sectional area of the first and second orifices  668 ,  670  may be greater than the total cross-sectional area of the first and second outlets  676 ,  678 . 
     A damper may be coupled to the trigger and/or axially moveable member of an electrosurgical instrument using any suitable configuration.  FIG. 26  illustrates an embodiment of a damper  680  that is coupled to a tab  682  of the trigger  607  via a shaft  686 . The damper  680  comprises a barrel  688  that may have an inlet port  681  and outlet port  683  arrangement similar to the configuration illustrated in  FIG. 18A . As is to be appreciated, however, any suitable configuration of orifices may be used. The shaft  686  is coupled to a plunger  684 . In some embodiments, the shaft  686  and/or the plunger  684  may be integral with the trigger  607 . Rotation of the trigger  607  in the direction indicated by arrow  650  drives the plunger  684  into the barrel  688 . As the plunger  684  drives into the barrel  688 , the volume of a variable volume cavity  690  inside the barrel  688  is reduced. Fluid inside the variable volume cavity  690  is expelled through outlet port  683 . Thus, the damper  680  regulates the translation of axially moveable member  606  by providing resistance to the trigger  607  when the user attempts to squeeze the trigger too fast.  FIG. 26A  is an illustration of the damper  680  in accordance with another non-limiting embodiment. A sealing member  694  (e.g., an o-ring) may establish a seal between the shaft  686  and an orifice  695  of the barrel  688 . The barrel  688  may be filled with a highly viscous fluid  692 . The plunger  684  may separate the barrel  688  into a first cavity  691  and a second cavity  693 . As the plunger  684  is translated within the barrel  688 , one of the cavities increases in volume while the other cavity decreases in volume. The highly viscous fluid  692  may flow between the two cavities via a gap  696  between the plunger  684  and the inner wall of the barrel  688 . In some embodiments, the plunger  684  may have orifices that fluidly couple the first cavity  691  to the second cavity  693 . During the operational stroke, the plunger  684  is translated in the barrel  688  and the highly viscous fluid  692  generally opposes the motion of the plunger  684  to ultimately regulate the translation of the axially moveable member. 
     As is to be appreciated, any type of damper may be used. As illustrated in  FIG. 27 , in some embodiments, a rotary damper  700  may be used to regulate the movement of an axially moveable member  702 . The rotary damper  700  may comprise a sealed volume  704 . In one embodiment, the sealed volume  704  is a cavity formed within a trigger  706 . The trigger may be rotatable about a pivot  708 . At least one fin  710  may be fixed with respect to the trigger  706 . As illustrated, the fins  710  may radiate from the pivot  708 . While two fins  710  are illustrated in  FIG. 27 , it is to be appreciated that any number of fins  710  may be used. Furthermore, the fins  710  may be straight, curved, or a combination of straight and curved sections. In some embodiments, the fins may be attached to inner surface of the  712  of the sealed volume  704  and extend toward the pivot  708 . In any event, the sealed volume  704  may be filled with a fluid  714 , such as a highly viscous silicone fluid, for example. Protrusions  713  may extend into the sealed volume  704  and move relative with respect to the fins  710  during rotation of the trigger  706 . The protrusions  713  may be any size or shape. As the trigger  706  is rotated in the direction indicated by arrow  716 , the interaction of the viscous fluid  714 , the fins  710 , and the protrusions  713  will provide a resistive force to slow the rotation of the trigger.  FIG. 27A  is a cross-sectional view of the damper  700  taken along line  27 A- 27 A. The damper  700  is rotatable about a central axis  701 . While the fins  710  are illustrated in  FIG. 27A  as being generally rectangular, it is to be appreciated that any suitable shape may be used. Furthermore, the fins  710  and/or protrusions  713  may be solid, as illustrated, or may be discontinuous (e.g., vented or perforated) to achieve the desired fluid flow during rotation of the damper  700 . 
     Referring again to  FIG. 27 , a return spring  720 , or other biasing element, may be coupled to the trigger  706  and the handle  722  in order to urge the trigger  706  to its starting position after it is moved in the direction indicated by arrow  724 . During an operational stroke, the amount of counter force the trigger  706  experiences, (e.g., the dampening effect) will depend at least partially on the size of a gap  718  between the pivot  708  and protrusions  713 . As with the other dampers described herein, the faster the trigger  706  is rotated, the higher the resistive force supplied by the rotary damper  700  will be. In other words, the resistive force may be proportional to the velocity of the trigger actuation. If the user actuates the trigger  706  in a slow and controlled manner, the rotary damper  700  will provide relatively little resistive force. If, however, the user actuates the trigger  706  aggressively, the rotary damper  700  will provide a higher resistive force to slow the trigger actuation  716 . 
     As is to be appreciated, any suitable type of damper may be used to regulate the stroke of the trigger. For example, in some embodiments, the damper may comprise a magnetorheological fluid damper or a solenoid having a variable resistance. 
     In some embodiments, other techniques may be used to regulate the translation of the axially moveable member.  FIG. 28  illustrates an electrosurgical instrument  800  incorporating an electromagnetic brake assembly  802  in accordance with one non-limiting embodiment. The electrosurgical instrument  800  may have an end effector (not illustrated) similar to the end effector  110  illustrated in  FIG. 3  coupled to the distal end of an elongate shaft  804 . An axially moveable member  806  may extend from the distal end of the elongate shaft  804  into the handle  808 . A trigger  810  is coupled to the axially moveable member  806 . In one embodiment, the trigger  810  comprises a toothed section  812  and the axially moveable member  806  comprises a rack  814 . The toothed section  812  of the trigger  810  is engaged to the rack  814  such that rotational movement of the trigger  810  about a pivot  816  is transferred into distal and proximal linear movement of the axially moveable member  806 . The rack  814  may have two general sections  818 ,  820 . During an operational stroke, the toothed section  812  first engages a first section  818  and the end effector captures and clamps tissue between two jaws, for example. As a second section  820  of the rack  814  engages the toothed section  812 , a cutting element may be driven through the captured tissue as described in greater detail below. The electromagnetic brake assembly  802  may regulate the stroke of the moveable cutting element  806  when the second section  820  of the rack  814  is engaged to the toothed section  812 . By regulating this portion of the stroke, the likelihood of advancing the moveable cutting element  806  too quickly (e.g., before the captured tissue has been sufficiently welded) is reduced. Some embodiments may comprise other implementations of electrically actuated brake assemblies. For example, the brake assembly may comprise an element that responds to external electrical stimulation by displaying a significant shape or size displacement, such as an electroactive polymer (EAP), for example. In some embodiments, the brake assembly may comprise a other components, such as a solenoid, a magnetorheological fluid damper, a reed relay, and/or a stepper motor, for example. All such embodiments are intended to be included in this disclosure. 
       FIG. 29  is an illustration of the electromagnetic brake assembly  802  in accordance with one non-limiting embodiment. The electromagnetic brake assembly  802  may comprise a collar  830 . When a controller  832  supplies current from a power source  834  a magnetic field around the collar  830  is generated. The axially moveable member  806  is positioned proximate the collar  830  and is has a ferrous component, for example, that is attracted to or repulsed by magnetic fields. The controller  832  may receive information via an input  836  to determine if a magnetic field should be generated and/or the strength of the magnetic field. The input  836  may be an indication of tissue temperature, tissue impedance, or time, for example. In one embodiment, if the captured tissue has not reached suitable temperature to sufficiently weld tissue, the electromagnetic brake  802  may be activated. Specifically, a magnetic field may be generated to attract the axially moveable member  806  to the collar  830 . When the axially moveable member  806  is attracted to the collar  830 , the distal progression of the axially moveable member  806  is halted or slowed depending on the intensity of the magnetic field generated. Once the temperature of the captured tissue has reached a sufficient level, the magnetic field of the collar  830  may be reduced or eliminated to allow the axially moveable member  806  to continue its distal translation. 
     As is to be appreciated, while the collar  830  is illustrated as having a ringed cross-sectional shape, any suitable cross-sectional shape may be used. For example, the collar  830  may have a rectangular, triangular, trapezoidal, or other closed-form shape. In some embodiments, multiple collars  830  having the same or different shapes may be used. This disclosure is not limited to any particular size, shape, or arrangement of the collar(s)  830 .  FIG. 30  is an illustration of an electromagnetic brake assembly  840  in accordance with another non-limiting embodiment. In this embodiment, a brake element  842  is positioned proximate the trigger  810 . When the brake element  842  is energized by the controller  832  a magnetic field is generated which attracts the trigger  810 . Similar to the collar  830  illustrated in  FIG. 29 , the brake element  842  may serve to regulate to movement of axially moveable member  806  by selectively engaging the trigger  810 . When the trigger  810  is attracted to the brake element  842 , the distal progression of the axially moveable member  806  is halted or slowed depending on the intensity of the magnetic field generated. 
       FIG. 31  is a partial cut-away view of an electrosurgical instrument  900  having an electromagnetic brake assembly in accordance with one non-limiting embodiment. A partial cross-section is provided to illustrate an electromagnetic brake assembly  902 . For the sake of clarity, various components have been omitted from the electrosurgical instrument  900 . The electrosurgical instrument  900  may have an end effector (not illustrated) similar to the end effector  110  illustrated in  FIG. 3  coupled to the distal end of an elongate shaft  904 . An axially moveable member  906  may extend from the distal end of the elongate shaft  904  into the handle  908 . A trigger  910  is coupled to the axially moveable member  906 . In one embodiment, the trigger  910  comprises a pivot  912 . A surface  914  of the trigger  910  may comprise a series of trigger ridges  916 . In one embodiment, the trigger ridges  916  radiate outward from the pivot  912 . The trigger ridges  916  are dimensioned to engage a brake pad  918 .  FIG. 32  illustrates an enlarged view of the brake pad  918 . The brake pad  918  may comprise pad ridges  920  with troughs  922  positioned intermediate adjacent pad ridges  920 . The troughs  922  are dimensioned to receive the trigger ridges  916 . 
     Referring again to  FIG. 31 , the brake pad  918  may be coupled to an electromagnetic solenoid  924 , or other component capable of selectably translating the brake pad  918  between a disengaged position and an engaged position (e.g., an electroactive polymer actuator). The solenoid  924  may be energized by a controller  832  ( FIG. 30 ). When the solenoid  924  is activated, the brake pad  918  is driven toward the trigger ridges  916  such that they engage with the pad ridges  920 . When the ridges  916 ,  920  are engaged, the trigger  910  is locked and may not be further rotated by the user. When the solenoid  924  is de-activated, the brake pad  918  is retracted and the trigger ridges  916  disengage from the pad ridges  920  to allow the trigger  910  to continue its rotation. During operation, the user may simply apply pressure to the trigger  910  and the electromagnetic brake assembly  902  will continually lock and un-lock the trigger  910  in order to regulate the stroke. Similar to the embodiments illustrated in  FIGS. 29 and 30 , a controller may use information from various inputs to determine if the trigger  910  should be locked or unlocked. As is to be appreciated, the trigger ridges  916  and the brake pad  918  may be made from any suitable material or polymer, such as a thermal set rigid plastic, for example. In some embodiments, the polymer is a nylon or rubber polymer, for example. In other embodiments, the trigger ridges  916  and the brake pad  918  are made from a metal alloy, such as medical grade stainless steel, for example. 
       FIGS. 33A and 33B , illustrate the electromagnetic brake assembly  902  in various stages of operation. The brake pad  918  is coupled to a pad housing  926  that is coupled to the solenoid  924 . While the ridges  916 ,  920  are illustrated in a saw tooth configuration, it is appreciated that any suitable type of ridge shapes may be implemented. As illustrated, the operation of the solenoid may be controlled by a controller  932 . The controller  932  may receive information from a sensor  934 . The information may be, for example, tissue temperature information or tissue impedance information. In  FIG. 33A , the brake pad  918  is separated (i.e., disengaged) from the trigger ridges  916  of the trigger  910 . In this position, the trigger  910  may rotate with respect to the brake pad  918 . In  FIG. 33B , the solenoid  924  has translated the brake pad  918  in the direction indicated by arrow  930 . In this position, the brake pad  918  is engaged to the trigger ridges  916  of the trigger  910  to inhibit the rotation of the trigger  910  with respect to the brake pad  918 . This position may be maintained until any number of conditions are satisfied, such as a tissue temperature condition or a time-based condition. In at least one embodiment, the brake pad  918  can lock the trigger  910  in position until the temperature and/or impedance of the tissue being treated has exceeded a certain temperature and/or impedance. In such an embodiment, the advancement of movable member  906 , and cutting member associated therewith, can be delayed until a sufficient quantity of energy has been supplied to the tissue, as indicated by the sensed temperature and/or impedance. In such circumstances, the tissue may not be incised until the tissue has received a minimum amount of energy. In some embodiments, the brake can be operated on a time delay, i.e., an amount of time between the initial application of energy to the tissue and the release of the brake. 
       FIG. 34  is a partial cut-away view of an electrosurgical instrument having an electromagnetic brake assembly  902  in accordance with one non-limiting embodiment. As illustrated, the trigger ridges  916  are positioned around a periphery of the trigger  910 . The brake pad  918  is positioned to engage the trigger ridges  916  when the brake pad  918  is moved toward the trigger  910  by the solenoid  924 . The brake pad  918  may have a curved portion  920  to mate with the periphery of the trigger  910 . As is to be appreciated, while  FIG. 31  and  FIG. 34  illustrate two embodiments of the brake pad  918 , the present disclosure is not limited to any particular brake pad configuration. 
       FIG. 35  illustrates an electrosurgical instrument  1000  having electromagnetic gates to regulate the operational stroke. The electrosurgical instrument  1000  may have an end effector  1010  similar to the end effector  110  illustrated in  FIG. 3  that is coupled to the distal end of an elongate shaft  1004 . An axially moveable member  1006  may extend from the distal end of the elongate shaft  1004  into a handle  1002 . A trigger  1007  is coupled to the axially moveable member  1006 . In one embodiment, the trigger  1007  comprises a trigger web  1008  that is received by the handle  1002  during a trigger stroke. The electrosurgical instrument  1000  may be electrically coupled to an electrical source  1045 . The electrical source  1045  may be connected to the electrosurgical instrument  1000  via a suitable transmission medium such as a cable  1052 . In one embodiment, the electrical source  1045  is coupled to a controller  1046 . 
     The electrosurgical instrument  1000  may comprise an electromagnet engaging surface  1014  positioned proximate the trigger  1007  in the handle  1002 . In various embodiments, the electromagnet engaging surface  1014  may be ferrous. The electrosurgical instrument  1000  may also comprise a plurality of electromagnetic gates  1012  positioned proximate to the trigger  1007 . In one embodiment, the plurality of electromagnetic gates  1012  are coupled to the trigger web  1008  such that they pass proximate the electromagnet engaging surface  1014  during a trigger stroke. The electromagnetic gates  1012  may be selectively magnetized and de-magnetized by the controller  1046  in order to control the trigger actuation during the operational stroke. 
       FIGS. 36A-C  are enlarged side views of the trigger web  1008  and the electromagnet engaging surface  1014  during an operational stroke in accordance with one non-limiting embodiment. As illustrated in  FIG. 36A , electromagnetic gates  1012   a - c  are coupled to the trigger web  1008  and are in electrical communication with the controller  1046  via signal lines. In one embodiment, at the start of an operational stroke, all of the electromagnetic gates  1012   a - c  are energized such that they create a corresponding magnetic field. The electromagnet engaging surface  1014  is attracted to the magnetic field of first electromagnetic gate  1012   a . The trigger  1007  will remain in this position until the first electromagnetic gate  1012   a  is deactivated. Once the first electromagnetic gate  1012   a  is deactivated, the user may actuate the trigger  1007  to move the trigger  1007  in the direction indicated by arrow  1016 . The electromagnet engaging surface  1014  will then be attracted to the magnetic field of the second electromagnetic gate  1012   b  ( FIG. 36B ). The trigger  1007  will remain in this position until the second electromagnetic gate  1012   b  is deactivated. Once the second electromagnetic gate  1012   b  is deactivated, the user may actuate the trigger  1007  to move the trigger  1007  in the direction indicated by arrow  1016 . The electromagnet engaging surface  1014  will then be attracted to the magnetic field of the third electromagnetic gate  1012   c  ( FIG. 36C ). The trigger  1007  will remain in this position until the third electromagnetic gate  1012   c  is deactivated. Once the third electromagnetic gate  1012   c  is deactivated, the user may actuate the trigger  1007  to move the trigger  1007  in the direction indicated by arrow  1016  to complete the operational stroke, if the operational stroke has not yet been completed. 
     While  FIGS. 36A-C  illustrate three electromagnetic gates  1012   a - c , it is to be appreciated that any number of electromagnetic gates may be used. For example, in some embodiments, two electromagnetic gates may be used, while in other embodiments, thirty electromagnetic gates may be used, for example. Additionally, similar to embodiments illustrated in  FIG. 33A-B , various sensors  934  may supply information to the controller  1046  which is used to determine which electromagnetic gates to activate or deactivate. Such information may include, for example, tissue temperature information, tissue impedance information, or time delay information. Furthermore, in some embodiments, the electromagnet engaging surface  1014  may be coupled to the trigger  1007  and the electromagnetic gates  1012  may be coupled to the handle  1002 . In either event, the advancement of the axially moveable member  1006  can be staggered such that the axially moveable member  1006  can be moved incrementally in the distal direction. In at least one such embodiment, the movement of the axially movable member  1006 , and a cutting member associated therewith, can be delayed until a significant amount of energy has been applied to the tissue being treated. In some circumstances, the tissue may not be incised until the tissue has received a minimum amount of energy. In certain circumstances, the rate in which the axially movable member  1006  may be moved distally may be impeded, or slowed, until a certain amount of energy has been applied, and/or a certain temperature or impedance of the tissue has been reached, wherein, thereafter the axially movable member  1006  may be permitted to move distally at a faster rate or at a rate which is unimpeded by the gates. Thus, in certain embodiments, the trigger may be sequentially held at every gate for the same amount of time while, in other embodiments, the trigger may be held at different gates for different amounts of time. 
     In various embodiments, feedback signals may be provided to the user during the operational stroke of the electrosurgical instrument.  FIG. 37  is a cut-away view of an electrosurgical instrument  1100  having a feedback indicator  1102  in accordance with one non-limiting embodiment. For the sake of clarity, various components have been omitted from the electrosurgical instrument  1100 . The electrosurgical instrument  1100  may have an end effector (not illustrated) similar to the end effector  110  illustrated in  FIG. 3  coupled to the distal end of an elongate shaft  1104 . An axially moveable member  1106  may extend from the distal end of the elongate shaft  1104  into the handle  1108 . A trigger  1110  is coupled to axially moveable member  1106 . 
     The trigger  1110  may be a ratcheting trigger that has multiple positions along the operational stroke. As illustrated, the trigger  1110  may comprise a hub  1164  that rotates about a pivot  1166  during an operational stroke. The hub may define a plurality of notches or detents  1168  that rotate past a pawl  1160  during an operational stroke. The pawl  1160  may be biased toward the hub by a spring  1162 . The pawl  1160  may comprise, for example, a ball bearing to engage the individual detents  1168 , for example. The number of detents  1168  may correspond to the number of discrete trigger positions along the operational stroke. The detents  1168  may be evenly spaced around the periphery of the hub  1168  or the distance separating adjacent detents may vary. When the user actuates the trigger, the engagement of the pawl  1160  with the detent  1168  provides tactile feedback to the user. The discrete positions may be implemented using a pawl and ratchet, or any other suitable technique. In one embodiment, the trigger has at five positions (e.g., five detents), for example, although any suitable number of positions may be used. 
     Still referring to  FIG. 37 , in a first position  1112 , the trigger  1110  is un-actuated and the jaws on the end effector are open and capable of grasping tissue. At a second position  1114 , the axially moveable member  1106  is distally advanced to close the jaws of the end effector. At this point in the operational stroke, energy may be applied to the captured tissue. At a third position  1116 , the axially moveable member  1106  has started to transect the captured tissue. At a fourth position  1118 , the axially moveable member  1106  has continued to travel through the captured tissue and at the fifth position  1120  the tissue has been completely transected. As is to be appreciated, various embodiments the operational stroke may have more or less discrete positions, as determined by the number of detents  1168 . 
     The feedback indicator  1102  is configured to convey operational information to the user. In one embodiment, the feedback indicator  1102  is a series of lights (e.g., light emitting diodes). In one embodiment, the feedback indicator  1102  is positioned proximate the trigger  1110  and provides a vibratory signal to the hand of the user. In one embodiment, the feedback indicator  1102  is a sound-emitting device that provided audio signals to the user. In one embodiment, the feedback indicator  1102  is a combination of multiple forms of feedback, such as a tactile and audio, for example. In one embodiment, the feedback indicator  1102  is located in a position remote from the electrosurgical device  1100 , such as on an external power supply, for example. For illustration purposes only, the operation of the feedback indicator  1102  will be described in the context of a series of lights mounted on the handle  1108  of the electrosurgical instrument  1100 . 
       FIGS. 38A-D  illustrate the progression of feedback signals provided by the feedback indicator  1102  in accordance with one non-limiting embodiment. The feedback indicator comprises a first indicator  1131 , a second indicator  1132 , a third indicator  1133 , and a fourth indicator  1134 . In one embodiment indicators,  1131 - 1134  are light emitting diodes (LEDs) which may be toggled between a green indication and a red indication during the operational stroke. In some embodiments, the LEDs may be white LEDs that are toggled between an on and an off state during an operational stroke. In other embodiments, other forms of visual indicators may be used, such as an LCD screen, for example. As illustrated in  FIG. 33A , the feedback indicator  1102  may be electrically coupled to a controller  1140 . The controller  1140  may receive information from a sensor  1148 , such as a tissue impedance sensor. The controller  1140  may comprise one or more processors  1142  and one or more computer memories  1146 . For convenience, only one processor  1142  and only one memory  1146  are shown in  FIG. 38A . The processor  1142  may be implemented as an integrated circuit (IC) having one or multiple cores. The memory  1146  may comprise volatile and/or non-volatile memory units. Volatile memory units may comprise random access memory (RAM), for example. Non-volatile memory units may comprise read only memory (ROM), for example, as well as mechanical non-volatile memory systems, such as, for example, a hard disk drive, an optical disk drive, etc. The RAM and/or ROM memory units may be implemented as discrete memory ICs, for example. 
     The feedback indicator  1102  may provide information to the user during various stages in the operational stroke. For example, it may provide information to the user which helps the user control the pacing of the operational stroke to increase the likelihood that an adequate tissue seal has been created. In one embodiment, the feedback indicator  1102  provides feedback when the jaws are closed and the axially moveable member is about to transect the captured tissue (e.g., the second position  1114 ). The movement of the trigger  1110  into the second position can be detected by the controller. Upon detecting the change in the position, the controller may illuminate the first indicator  1131 . When the first indicator  1131  is illuminated, the user may apply energy to the captured tissue. For example, the user may depress a button  1150  ( FIG. 37 ) positioned on the trigger  1110 . The sensor  1148  may monitor a characteristic or property the captured tissue, such as impedance, and when the tissue has reached a certain impedance level, the second indicator  1132  may be illuminated, as illustrated in  FIG. 38B . When the user sees the second indicator  1132  illuminate (or otherwise toggle its state), the user may actuate the trigger  1110  to the next position (e.g., the third position  1116 ) to begin the cutting stroke. The sensor  1148  may continue monitor the characteristic or property the captured tissue, such as impedance, for example, and when the tissue has reached a certain impedance level, the third indicator  1133  may be illuminated, as illustrated in  FIG. 38C . When the user sees the third indicator  1133  illuminate (or otherwise toggle its state), the user may actuate the trigger  1110  to the next position (e.g., the fourth position  1118 ) to continue its cutting stroke. The sensor  1148  may continue monitor the characteristic or property the captured tissue, such as impedance, for example, and when the tissue has reached a certain impedance level, the fourth indicator  1134  may be illuminated, as illustrated in  FIG. 38D . When the user sees the fourth indicator  1134  illuminate (or otherwise toggle its state), the user may actuate the trigger  1110  to the next position (e.g., the fifth position  1120 ) to complete its cutting stroke. 
     The embodiments of the devices described herein may be introduced inside a patient using minimally invasive or open surgical techniques. In some instances it may be advantageous to introduce the devices inside the patient using a combination of minimally invasive and open surgical techniques. Minimally invasive techniques may provide more accurate and effective access to the treatment region for diagnostic and treatment procedures. To reach internal treatment regions within the patient, the devices described herein may be inserted through natural openings of the body such as the mouth, anus, and/or vagina, for example. Minimally invasive procedures performed by the introduction of various medical devices into the patient through a natural opening of the patient are known in the art as NOTES™ procedures. Some portions of the devices may be introduced to the tissue treatment region percutaneously or through small—keyhole—incisions. 
     Endoscopic minimally invasive surgical and diagnostic medical procedures are used to evaluate and treat internal organs by inserting a small tube into the body. The endoscope may have a rigid or a flexible tube. A flexible endoscope may be introduced either through a natural body opening (e.g., mouth, anus, and/or vagina) or via a trocar through a relatively small—keyhole—incision incisions (usually 0.5-1.5 cm). The endoscope can be used to observe surface conditions of internal organs, including abnormal or diseased tissue such as lesions and other surface conditions and capture images for visual inspection and photography. The endoscope may be adapted and configured with working channels for introducing medical instruments to the treatment region for taking biopsies, retrieving foreign objects, and/or performing surgical procedures. 
     The devices disclosed herein may be designed to be disposed of after a single use, or they may be designed to be used multiple times. In either case, however, the device may be reconditioned for reuse after at least one use. Reconditioning may include a combination of the steps of disassembly of the device, followed by cleaning or replacement of particular pieces, and subsequent reassembly. In particular, the device may be disassembled, and any number of particular pieces or parts of the device may be selectively replaced or removed in any combination. Upon cleaning and/or replacement of particular parts, the device may be reassembled for subsequent use either at a reconditioning facility, or by a surgical team immediately prior to a surgical procedure. Those of ordinary skill in the art will appreciate that the reconditioning of a device may utilize a variety of different techniques for disassembly, cleaning/replacement, and reassembly. Use of such techniques, and the resulting reconditioned device, are all within the scope of this application. 
     Preferably, the various embodiments of the devices described herein will be processed before surgery. First, a new or used instrument is obtained and if necessary cleaned. The instrument can then be sterilized. In one sterilization technique, the instrument is placed in a closed and sealed container, such as a plastic or TYVEK® bag. The container and instrument are then placed in a field of radiation that can penetrate the container, such as gamma radiation, x-rays, or high-energy electrons. The radiation kills bacteria on the instrument and in the container. The sterilized instrument can then be stored in the sterile container. The sealed container keeps the instrument sterile until it is opened in the medical facility. Other sterilization techniques can be done by any number of ways known to those skilled in the art including beta or gamma radiation, ethylene oxide, and/or steam. 
     Although the various embodiments of the devices have been described herein in connection with certain disclosed embodiments, many modifications and variations to those embodiments may be implemented. For example, different types of end effectors may be employed. Also, where materials are disclosed for certain components, other materials may be used. The foregoing description and following claims are intended to cover all such modification and variations. 
     Any patent, publication, or other disclosure material, in whole or in part, that is said to be incorporated by reference herein is incorporated herein only to the extent that the incorporated materials does not conflict with existing definitions, statements, or other disclosure material set forth in this disclosure. As such, and to the extent necessary, the disclosure as explicitly set forth herein supersedes any conflicting material incorporated herein by reference. Any material, or portion thereof, that is said to be incorporated by reference herein, but which conflicts with existing definitions, statements, or other disclosure material set forth herein will only be incorporated to the extent that no conflict arises between that incorporated material and the existing disclosure material.