Abstract:
A surgical instrument for being endoscopically or laparoscopically inserted into a surgical site for simultaneous stapling and severing of tissue includes load sensing pressure transducers strategically placed for closed loop control and monitoring. Load sensing within a staple applying assembly (end effector) may provide feedback for preventing firing with insufficient or too much tissue, or to sense appropriate presence buttress material, to deploy buttress material after firing is sensed.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
   This application is a Continuation in Part of U.S. patent application Ser. No. 11/082,495, entitled “Surgical Instrument Incorporating an Electrically Acutated Articulation Mechanism”, filed on Mar. 17, 2005, the disclosure of which is hereby incorporated by reference in its entirety. 

   FIELD OF THE INVENTION 
   The present invention relates in general to surgical stapler instruments that are capable of applying lines of staples to tissue while cutting the tissue between those staple lines and, more particularly, to improvements relating to stapler instruments and improvements in processes for forming various components of such stapler instruments including adding bolstering material to the severed and stapled tissue. 
   BACKGROUND OF THE INVENTION 
   Endoscopic and laparoscopic surgical instruments are often preferred over traditional open surgical devices since a smaller incision tends to reduce the post-operative recovery time and complications. The use of laparoscopic and endoscopic surgical procedures have been relatively popular and has provided additional incentive to develop the procedures further. In laparoscopic procedures, surgery is performed in the interior of the abdomen through a small incision. Similarly, in endoscopic procedures, surgery is performed in any hollow viscus of the body through narrow endoscopic tubes inserted through small entrance wounds in the skin. 
   Laparoscopic and endoscopic procedures generally require that the surgical region be insufflated. Accordingly, any instrumentation inserted into the body must be sealed to ensure that gases do not enter or exit the body through the incision. Moreover, laparoscopic and endoscopic procedures often require the surgeon to act on organs, tissues and/or vessels far removed from the incision. Thus, instruments used in such procedures are typically long and narrow while being functionally controllable from a proximal end of the instrument. 
   Significant development has gone into a range of endoscopic surgical instruments that are suitable for precise placement of a distal end effector at a desired surgical site through a cannula of a trocar. These distal end effectors engage the tissue in a number of ways to achieve a diagnostic or therapeutic effect (e.g., endocutter, grasper, cutter, staplers, clip applier, access device, drug/gene therapy delivery device, and energy device using ultrasound, RF, laser, etc.). 
   Known surgical staplers include an end effector that simultaneously makes a longitudinal incision in tissue and applies lines of staples on opposing sides of the incision. The end effector includes a pair of cooperating jaw members that, if the instrument is intended for endoscopic or laparoscopic applications, are capable of passing through a cannula passageway. One of the jaw members receives a staple cartridge having at least two laterally spaced rows of staples. The other jaw member defines an anvil having staple-forming pockets aligned with the rows of staples in the cartridge. The instrument includes a plurality of reciprocating wedges which, when driven distally, pass through openings in the staple cartridge and engage drivers supporting the staples to effect the firing of the staples toward the anvil. 
   Small videoscopes of various types (e.g., endoscopes) are relied upon to monitor proper positioning and operation of the surgical stapler. While effective to a degree, it is desirable to have improved monitoring of operation of the surgical stapler, especially if such monitoring enables closed loop control of various actuations performed by the surgical stapler. 
   Consequently, a significant need exists for an improved surgical stapling and severing instrument that incorporates a load sensing capability. 
   BRIEF SUMMARY OF THE INVENTION 
   The invention overcomes the above-noted and other deficiencies of the prior art by providing a surgical instrument that incorporates an electrical pressure sensor positioned to receive a compressive load when the surgical instrument is actuated. Control circuitry that monitors the electrical pressure sensor then generates a control signal responsive to that sensed compressive load to enhance operation of the surgical instrument. 
   In one aspect of the invention, a surgical instrument has a staple applying assembly with first and second opposing compression surfaces that clamp tissue to be stapled and imparts a compressive force thereby to a pressure transducer. The staple applying assembly is closed by a handle portion and actuated by a firing member moved by the handle portion through a shaft. Control circuitry responds to the sensed compression load of the staple applying assembly to send a control signal to an electrical actuator. Thereby, a desired sequence of events may be enforced that are dependent upon first successfully clamping a desired amount of tissue, avoiding dry firing of an actuator in the absence of sufficient tissue or ineffective activation of the actuator in the presence of too much tissue. 
   In another aspect of the invention, a surgical instrument has an end effector that is attached to a shaft and in turn to a handle portion. A firing member is translated by the handle portion and received for longitudinal reciprocation in the shaft to actuate the end effector and to thereby impart a compressive load upon a pressure transducer. Control circuitry is responsive to a signal received from the pressure transducer to generate a control signal. Thereby, a desired sequence of events may be enforced that are dependent upon firing having commenced or having been successfully completed. 
   In yet another aspect of the invention, a surgical instrument has an articulated shaft that allows for articulating an end effector. Control circuitry receives a signal from a sensor in an articulation joint of the shaft that is representative of an articulation angle so that a control signal may be generated. Thereby, a desired sequence of events may be enforced that are dependent upon achieving a desired angle of articulation of the shaft and end effector. 
   These and other objects and advantages of the present invention shall be made apparent from the accompanying drawings and the description thereof. 

   
     BRIEF DESCRIPTION OF THE FIGURES 
     The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention, and, together with the general description of the invention given above, and the detailed description of the embodiments given below, serve to explain the principles of the present invention. 
       FIG. 1  depicts a partially cutaway side elevation view of a surgical stapling and severing instrument with a staple applying assembly in an open position, a lower buttress pad removed to expose a staple cartridge, and an elongate shaft partially cutaway to expose components of a closed loop control system consistent with the present invention including components in a handle portion shown in phantom. 
       FIG. 2  is a block diagram of the closed loop control circuitry of the surgical stapling and severing instrument of  FIG. 1 . 
       FIG. 3  is a left front isometric view of an elongate staple channel of the staple applying assembly of  FIG. 1  incorporating elongate electroactive polymer (EAP) sensor strips for load sensing. 
       FIG. 4  is a left front isometric view of the elongate staple channel of the staple applying assembly of  FIG. 1  incorporating an aligned series of EAP sensor strips for load sensing. 
       FIG. 5  is a top view of an articulation joint of a frame ground assembly of an elongate shaft of the surgical stapling and severing instrument of  FIG. 1 . 
       FIG. 6  is a top view of the articulation joint of  FIG. 5  in a leftward articulated state. 
       FIG. 7  is a isometric exploded view of an elongate shaft incorporating a firing bar sensor for the surgical stapling and severing instrument of  FIG. 1 , omitting a buttress deployment system and including alternate EAP fiber articulation actuators. 
       FIG. 8  is an isometric view of the elongate shaft of the surgical stapling and severing instrument of  FIG. 7  with a closure sleeve and staple applying assembly omitted to expose the firing bar sensor and firing bar. 
       FIG. 9  is an isometric detail view of a proximal end of the firing bar activating the firing bar sensor in the elongate shaft of the surgical stapling and severing instrument of  FIG. 8 . 
       FIG. 10  is a detail view of a distal portion of an elongate staple channel of  FIG. 8  including an alternative firing bar sensor positioned at a distal end of a firing bar channel slot. 
       FIG. 11  is an isometric exploded view of an alternative staple cartridge incorporating elongate EAP pressure sensors positioned to detect staple driving for the surgical stapling and severing instrument of  FIG. 1 . 
       FIG. 12  is an isometric exploded view of an additional alternative staple cartridge incorporating an aligned series of EAP pressure sensors positioned to detect staple driving for the surgical stapling and severing instrument of  FIG. 1 . 
       FIG. 13  is an isometric exploded view of the staple cartridge and a distal portion of the firing bar having a distal EAP pressure sensor positioned to abut a wedge sled that drives staples during firing for the surgical stapling and severing instrument of  FIG. 1 . 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Turning to the Drawings, wherein like numerals denote like components throughout the several views, in  FIG. 1 , a surgical stapling and severing instrument  10  includes a handle portion  12  that manipulates to position an implement portion  14  formed from a fastening end effector, specifically a staple applying assembly  16 , distally attached to an elongate shaft  18 . The implement portion  14  is sized for insertion through a cannula of a trocar (not shown) for an endoscopic or laparoscopic surgical procedure with an upper jaw (anvil)  20  and a lower jaw  22  of the staple applying assembly  16  closed by depression of a closure trigger  24  toward a pistol grip  26  of the handle portion  12 . 
   Once inserted into an insufflated body cavity or lumen, the surgeon may rotate the implement portion  14  about its longitudinal axis by twisting a shaft rotation knob  27  that engages across a distal end of the handle  12  and a proximal end of the elongate shaft  18 . The surgeon may selectively move to either lateral side an articulation control lever  28  on the handle portion  12  to cause a distal portion of the elongate shaft  18  and the staple applying assembly  16  to articulate about an articulation joint  30 . Thereby, the staple applying assembly  16  may approach tissue otherwise obscured by other tissue or allow for an endoscope to be positioned behind the staple applying assembly  16 . Thus positioned, the closure trigger  24  may be released, opening the anvil  20  so that tissue may be grasped and positioned. Once satisfied, the surgeon depresses the closure trigger  24  until locked against the pistol grip  26 , clamping the staple applying assembly  16 . Then a firing trigger  32  is depressed, perhaps multiple times referencing firing progress on a firing indicator gauge  33 . The firing trigger  32  is drawn toward the closure trigger  24  and pistol grip  26 , thereby distally advancing a firing member, depicted as including a proximal firing rod  34  attached to a distal firing bar  36 , that is supported within a frame ground assembly  38  that connects the handle portion  12  to the staple applying assembly  16 . An outer closure sleeve  40  longitudinally translates upon the frame ground assembly  38  to pivot the anvil  20  in response to the closure trigger  24 . 
   To assist in stapling a thin layer and/or a thick layer of tissue, buttress material of an upper buttress pad  42  and a lower buttress pad  44  may be held on each inner surface of the anvil  20  and upon a staple cartridge  46  engaged within an elongate staple channel  47  of the lower jaw  22 . After firing of the staple applying assembly  16 , the buttress pads  42 ,  44  which are severed and stapled along with the clamped tissue, are disengaged by actuating upper and lower buttress clamps  48 ,  50  to remain with the two stapled and severed ends of tissue as the firing trigger  32  is released and a closure release button  52  is depressed to unlock the closure trigger  24  to open the staple applying assembly  16 . 
   It should be appreciated that a distal end of the firing bar  36  includes or is coupled to a knife that traverses a vertical slot in the staple cartridge  46  to sever clamped tissue and the buttress pads  42 ,  44 . The knife is coupled to a wedge assembly that cams staples upwardly out of the staple cartridge  46  through the clamped tissue and buttress pads  42 ,  44  to close and form against the anvil  20 . Thereafter, the firing bar  36  is withdrawn by an end-of-firing-travel release mechanism and a retraction bias in the handle portion  12 . The surgeon may abort after partial firing and/or effect manual retraction of the firing member  34 ,  36  by actuating a manual retraction lever  54  on the top of the handle portion  12 . 
   In  FIGS. 1-2 , consistent with the present invention, a closed loop control system  55  enhances operation of the surgical stapling and severing instrument  10  by monitoring proper operation and electrically controlling various features. A power switch  56  may be depressed by the user to activate the closed loop control system  55 , drawing upon a power supply, depicted as a battery  58 . A visual confirmation (status indicator) on the handle portion  12  may be incorporated into power switch  56  to indicate what the state of the closed loop control system  55  (e.g., color/flash illumination and/or alphanumeric message of the power button  56 ), such as “POWER ON”, “OPERATIONAL-SELF-TEST PASSED”, “LOAD STAPLE CARTRIDGE”, “LOAD BUTTRESS PADS”, “SYSTEM LOADED/AWAITING FIRING”, “FAULT DETECTED”, etc. Additional programming flexibility may be achieved by incorporating a wired or wireless (e.g., BLUETOOTH) protocol to interface the closed loop control system  55  to an external graphical user interface (e.g., personal computer). 
   The closed loop control system  55  includes a controller  60  that advantageously receives signals from electrical sensors that monitor operation of the surgical stapling and severing instrument  10 . In particular, a load sensor, such as an elongate electroactive polymer (EAP) load strip  62  ( FIG. 3 ) or aligned series of EAP strips  63  ( FIG. 4 ) between the staple cartridge  46  and the elongate staple channel  47 , monitors the amount of clamping force in the staple applying assembly  16 . Determination that a proper clamping force has been achieved may then be used as a condition precedent by the controller  60  before firing, such as by activating a firing lockout actuator  64  that prevents inadvertent firing. 
   A useful feature of EAP is its sensing (transduction) capabilities. For instance, an excellent dynamic response (sensing mode) may be achieved with an EAP strip in a loaded cantilever form. A damped electric response is observed that is highly repeatable with a high bandwidth up to about 100 Hz. Such direct mechanoelectric behaviors are related to the endo-ionic mobility due to imposed stresses. It means that, if we impose a finite soft-phase flux but do not allow a current flux, it creates a certain conjugate electric field that can be dynamically monitored. In this sense, EAP is truly multifunctional: structural, actuating, and sensing capabilities in one body. EAP actuators are described in greater detail below. 
   Illustrative firing lockout actuators  64  may be incorporated into the handle portion  12  as described in co-pending and commonly owned U.S. patent application Ser. No. 11/095,428 entitled “Surgical Instrument Incorporating EAP Complete Firing System Lockout Mechanism” and filed on Mar. 31, 2005, the disclosure of which is hereby incorporated by reference in its entirety. Alternatively or in addition, firing lockout actuators  64  may be incorporated into the implement portion  14  as described in co-pending and commonly owned U.S. patent application Ser. No. 11/066,371 entitled “Surgical Stapling Instrument Having An Electroactive Polymer Actuated Single Lockout Mechansim For Prevention Of Firing” and filed on Feb. 25, 2005, the disclosure of which is hereby incorporated by reference in its entirety. 
   Continuing with  FIGS. 1-2 , the controller  60  also receives a signal from one or more articulation sensors  70 . The signal is responsive to an angle of articulation of the articulation joint, either continuously and/or a discrete articulation limit threshold. This information may be used to perform closed loop control of an articulation actuator  72 . Illustrative versions of electrically actuated articulation are described in three co-pending and commonly-owned patent applications (1) U.S. patent application Ser. No. 11/082,495 entitled “Surgical Instrument Incorporating an Electrically Actuated Articulation Mechanism” and filed on Mar. 17, 2005; (2) U.S. patent application Ser. No. 11/096,096 entitled “Surgical Instrument Incorporating an Electrically Actuated Pivoting Articulation Mechanism” and filed on Mar. 31, 2005; and (3) U.S. patent application Ser. No. 11/096,158 entitled “Surgical Instrument Incorporating an Electrically Actuated Articulation Mechanism” and filed on Mar. 31, 2005, the disclosures of which are hereby incorporated by reference in their entirety. Once at a desired articulation angle, the controller  60  may reengage an electrically actuated articulation lock  74  to maintain the articulation. An illustrative articulation lock is described in co-pending and commonly-owned U.S. patent application Ser. No. 11/092,053 entitled “Surgical Instrument Incorporating an Electrically Actuated Articulation Locking Mechanism”, filed on Mar. 29, 2005, the disclosure of which is hereby incorporated by reference in its entirety. 
   It should be appreciated given the benefit of the present disclosure that applications consistent with the present invention may incorporate a mechanically articulated and/or mechanically locked shaft rather than an electrical articulated and/or electrically locked shaft. Moreover, a control signal from the controller  60  may merely provide a visual and/or aural indication to the user confirming that the desired articulation angle has been achieved so a command to further articulate may be discontinued and/or the articulation joint may be manually locked. 
   In  FIGS. 4-5 , an illustrative articulation joint  30  includes a proximal frame ground portion  80  of the frame ground assembly  38  has a cylindrical pin recess  82  that communicates with a vertical recess  84  formed between left and right distally projecting frame arms  86 ,  88 . A distal frame ground portion  90  of the frame ground assembly  38  includes a tapered, proximally projecting arm  92  that terminates in a cylindrical pin  94  pivotally received within the cylindrical pin recess  82  of the proximal frame ground portion  80 . 
   In a distal portion of the vertical recess  84 , left and right actuating/sensing EAP laminate stacks  96 ,  98  are inserted on respective sides of the tapered, proximally projecting arm  92  attached respectively to the left and right distally projecting frame arms  86 ,  88 . The left actuating/sensing EAP laminate stack  96  comprises a left EAP articulation actuator  100  with a left thin EAP pressure sensor  102  attached across its inner surface against the tapered, proximally projecting arm  92 . Similarly, the right actuating/sensing EAP laminate stack  98  comprises a right EAP articulation actuator  104  with a right thin EAP pressure sensor  106  attached across its inner surface against the tapered, proximally projecting arm  92 . As a selected EAP articulation actuator  104  is activated (expands), a pressure reading may be sensed by the left and/or the right thin EAP pressure sensors  102 ,  106 , representative of the articulation angle of the articulation joint  30 . 
   Alternatively or in addition to continuous articulation angle sensing, left and right thin EAP limit sensors  108 ,  110  are positioned in a proximal portion of the vertical recess  84  on respective left and right pivot stops  112 ,  114  angled to abut the tapered, proximally projecting arm  92  at a maximum allowed articulation angle. 
   Returning to  FIGS. 1-2 , the controller  60  also receives signals from a firing bar sensor  120  that detects distal firing travel. The controller  60  may thus advantageously activate a buttress deployment system  121 , (e.g., upper and lower buttress clamps  48 ,  50 ) described in co-pending and commonly owned U.S. patent application Ser. No. 11/181,471 entitled “Surgical Stapling Instrument Having an Electroactive Polymer Actuated Buttress Deployment Mechanism” and filed on Jul. 14, 2005, the disclosure of which is hereby incorporated by reference in its entirety, to automatically deploy the buttress pads  42 ,  44  after firing. Alternatively or in addition, the controller  60  may thus advantageously activate a medical substance dispensing actuator  122  during firing to enhance a therapeutic result (e.g., coagulant, adhesive, antibiotic, etc.), such as described in co-pending and commonly owned U.S. patent application Ser. No. 11/157,767 entitled “Surgical Stapling Instrument Having an Electroactive Polymer Actuated Medical Substance Dispenser” and filed on Jun. 1, 2005, the disclosure of which is hereby incorporated by reference in its entirety. Alternatively or in addition, the controller  60  may thus advantageously selectively enable and/or disable an anti-backup actuator  123  at the end of the firing stroke to allow for automatic retraction, as described in co-pending and commonly owned U.S. patent application Ser. No. 11/181,046 entitled “Anti-Backup Mechanism for a Multi-Stroke Endeffector Using Electrically Active Polymers” and filed on Jul. 14, 2005, the disclosure of which is hereby incorporated by reference in its entirety. 
   In  FIGS. 7-10 , the firing bar sensor  120  comprises an EAP stack actuator that is positioned within an alternative elongate shaft  124  to contact a portion of the firing member as full firing travel is reached. In particular, the firing member comprises a clevis  126  at a distal end of a firing rod  34  that receives an upwardly hooked end  128  of the firing bar  36 . The laterally widened profile of the clevis  126  hits the firing bar sensor  120 , which is attached inside of a firing member slot  130  formed inside of the frame ground assembly  38 . 
   In  FIG. 7 , the staple cartridge  46  includes a bottom tray  134  with a proximally open longitudinal slot  136 . A plurality of staple drivers  138  sit upon the bottom tray  134  on either side of the longitudinal slot  136 , upon which in turn sit a plurality of staples (not shown). A staple body  140  sits down upon the staple drivers  138 , providing suitable recesses (not shown) for the staple drivers  138  to be actuated upward by a distally driven wedge sled  142  ejecting the staples from staple apertures  144  formed in the staple body  140 . The assembled staple cartridge  46  is received in the elongate staple channel  47  with the proximally open longitudinal slot  136  in the bottom tray  134  vertically aligned with a channel slot  146  in the elongate staple channel  47 . 
   In  FIGS. 7-8 , the distal end of the firing bar  36  is an E-beam  148  having a lower foot  150  that slides along a bottom surface of the elongate staple channel  47  as a middle pin  152  slides along a top surface of the bottom tray  134  inside of the staple cartridge  46 . A distal driving surface  154  of the E-beam  148  abuts and drives the wedge sled  142 . Above the distal driving surface  154 , a recessed cutting surface  156  traverses along and above a top surface of the staple cartridge  46  to cut tissue. A top pin  158  of the E-beam  148  engages an anvil (upper jaw)  160  (which omits buttress clamps) to maintain spacing. An alternative flexing closure sleeve  162  encompasses the frame ground assembly  38 . 
   With particular reference to  FIG. 7 , articulation differs from the previously described version in that upper left and right EAP fiber articulation actuators  164 ,  166  are attached at their inner ends to an upper articulation arm  168  that projects from an upper distally projecting tang  170  from a proximal frame ground portion  172  with outer ends attached to respective opposite inner surfaces of a distal frame ground portion  174 . Similarly, lower left and right EAP fiber articulation actuators  176 ,  178  are attached at their inner ends to a lower articulation arm  180  that projects from a lower distally projecting tang  182  from the proximal frame ground portion  172  with outer ends attached to respective opposite inner surfaces of the distal frame ground portion  174 . Upper and lower proximally projecting tangs  184 ,  186  from the distal frame ground portion  174  are pinned for rotation respectively to the upper and lower distally projecting tangs  170 ,  182  of the proximal frame ground portion  172 . 
   In  FIGS. 7 ,  10 , alternatively or in addition to a proximally positioned firing bar sensor  120 , a distally positioned EAP pressure sensor  190  may be positioned on the elongate staple channel  47  to contact the wedge sled  142  upon full distal travel. 
   In  FIG. 11 , left and right elongate EAP pressure sensors  200 ,  202  are placed on each side of the longitudinal slot  136  in the bottom tray  134  to sense the progress of the wedge sled  142  during firing. In  FIG. 12 , a series of left and right EAP pressure sensors  204 ,  206  are placed on each side of the longitudinal slot  136  on the bottom tray  134 . In  FIG. 13 , alternatively or in addition, a firing bar sensor is depicted as an EAP pressure sensor  210  placed on the distal driving surface  154  of the E-beam  148  to register a force during firing, especially an increase in sensed force when the wedge sled  142  reaches full distal travel. 
   It should be appreciated given the benefit of the present disclosure that a firing sensor may be incorporated into a handle instead of or in addition to a firing bar sensor in the implement portion  14 . An illustrative version of the handle portion  12  without the closed loop control system  55  is described in U.S. patent application Ser. Nos. 11/052,387 entitled “Surgical Stapling Instrument Incorporating A Multi-Stroke Firing Mechanism With Return Spring Rotary Manual Retraction System” to Shelton et al., filed on Feb. 7, 2005, the disclosure of which is hereby incorporated by reference in its entirety. 
   It should be appreciated given the benefit of the present disclosure that a controller  60  may comprise a microcontroller with memory containing a program that monitors sensors and generates control signal(s) for electrically activated components. Alternatively, a controller  60  may comprise a programmable logic array, lumped component logic gates, optical logic components, or other electronic circuitry. In addition portions of a closed loop control system  55  consistent with aspects of the invention may be remote to the surgical stapling and severing instrument  10 . 
   ELECTROACTIVE POLYMERS. While a number of electrical actuators (e.g., solenoids) may be integrated into the surgical stapling and severing instrument  10 , illustrative versions described herein advantageously employ electroactive polymers (EAP), which are conductive doped polymers that change shape when electrical voltage is applied. In essence, the conductive polymer is paired to some form of ionic fluid or gel and electrodes. Flow of the ions from the fluid/gel into or out of the conductive polymer is induced by the voltage potential applied and this flow induces the shape change of the polymer. The voltage potential ranges from 1V to 4 kV, depending on the polymer and ionic fluid used. Some of the EAPs contract when voltage is applied and some expand. The EAPs may be paired to mechanical means such as springs or flexible plates to change the effect that is caused when the voltage is applied. 
   There are two basic types of EAPs and multiple configurations of each type. The two basic types are a fiber bundle and a laminate version. The fiber bundle consists of fibers around 30-50 microns. These fibers may be woven into a bundle much like textiles and are often called EAP yarn because of this. This type of EAP contracts when voltage is applied. The electrodes are usually made up of a central wire core and a conductive outer sheath that also serves to contain the ionic fluid that surrounds the fiber bundles. An example of a commercially available fiber EAP material is manufactured by Santa Fe Science and Technology, is sold as PANION™ fiber and is described in U.S. Pat. No. 6,667,825, which is hereby incorporated by reference in its entirety. 
   The other type is a laminate structure, which consists of a layer of EAP polymer, a layer of ionic gel and two flexible plates that are attached to either side of the laminate. When a voltage is applied, the square laminate plate expands in one direction and contracts in the perpendicular direction. An example of a commercially available laminate (plate) EAP material is from Artificial Muscle Inc, a division of SRI Laboratories. Plate EAP material is also available from EAMEX of Japan and is referred to as thin film EAP. 
   It should be noted that EAPs do not change volume when energized; they merely expand or contract in one direction while doing the opposite in the transverse direction. The laminate version may be used in its basic form by containing one side against a rigid structure and using the other much like a piston. The laminate version may also be adhered to either side of a flexible plate. When one side of the flexible plate EAP is energized, it expands flexing the plate in the opposite direction. This allows the plate to be flexed in either direction, depending on which side is energized. 
   An EAP actuator usually consists of numerous layers or fibers bundled together to work in cooperation. The mechanical configuration of the EAP determines the EAP actuator and its capabilities for motion. The EAP may be formed into long stands and wrapped around a single central electrode. A flexible exterior outer sleeve will form the other electrode for the actuator as well as contain the ionic fluid necessary for the function of the device. In this configuration when the electrical field is applied to the electrodes, the strands of EAP shorten. This configuration of EAP actuator is called a fiber EAP actuator. Likewise, the laminate configuration may be placed in numerous layers on either side of a flexible plate or merely in layers on itself to increase its capabilities. Typical fiber structures have an effective strain of 2-4% where the typical laminate version achieves 20-30%, utilizing much higher voltages. 
   For instance, a laminate EAP composite may be formed from a positive plate electrode layer attached to an EAP layer, which in turn is attached to an ionic cell layer, which in turn is attached to a negative plate electrode layer. A plurality of laminate EAP composites may be affixed in a stack by adhesive layers therebetween to form an EAP plate actuator. It should be appreciated that opposing EAP actuators may be formed that can selectively bend in either direction. 
   A contracting EAP fiber actuator may include a longitudinal platinum cathode wire that passes through an insulative polymer proximal end cap through an elongate cylindrical cavity formed within a plastic cylinder wall that is conductively doped to serve as a positive anode. A distal end of the platinum cathode wire is embedded into an insulative polymer distal end cap. A plurality of contracting polymer fibers are arranged parallel with and surrounding the cathode wire and have their ends embedded into respective end caps. The plastic cylinder wall is peripherally attached around respective end caps to enclose the cylindrical cavity to seal in ionic fluid or gel that fills the space between contracting polymer fibers and cathode wire. When a voltage is applied across the plastic cylinder wall (anode) and cathode wire, ionic fluid enters the contracting polymer fibers, causing their outer diameter to swell with a corresponding contraction in length, thereby drawing the end caps toward one another. 
   While the present invention has been illustrated by description of several embodiments and while the illustrative embodiments have been described in considerable detail, it is not the intention of the applicant to restrict or in any way limit the scope of the appended claims to such detail. Additional advantages and modifications may readily appear to those skilled in the art. 
   For example, while EAP actuator and sensors are described as having advantageous features, applications consistent with the present invention may incorporate other types of actuators and electrical transducers 
   For another example, while a manually operated surgical stapling and severing instrument  10  is depicted for clarity, it should be appreciated that robotically manipulated and/or controlled fastening devices may incorporate load sensing transducers for closed control and/or monitoring. Such sensors may be particularly useful to replace tactile feedback to a surgeon. 
   As yet another example, while a surgical stapling and severing instrument particularly suited for endoscopic or laparoscopic use is illustrated herein, applications consistent with aspects of the present invention may be for open surgical use or perform similar surgical procedures. In additions, a circular stapler may incorporate electrical sensors and/or electrical actuators for purposes such as load sensing. 
   For yet another example, applications consistent with the present invention may include various combinations of the sensors and/or actuators described herein. For instance, a fully mechanical closure and firing system may include electrical sensors that are monitored by a controller and a status displayed. The surgeon thus “closes the loop” by discontinuing if a warning is presented. In addition, certain features may be omitted such as articulation or buttressing. 
   As yet a further example, although separate closure and firing mechanisms, including separate triggers, are described in the illustrative versions, applications consistent with the present invention may incorporate a single firing trigger that sequentially effects closure and firing. 
   As yet an additional example, while EAP pressure sensors are an advantageous way to sense clamping, firing and articulation, other electrical sensors may be incorporated in addition to or in the alternative, such as proximity sensors (e.g., Hall effect), capacitive sensors, microswitches, and position sensors (e.g., potentiometers).