Abstract:
A surgical instrument for being endoscopically or laparoscopically inserted to a surgical site for simultaneous stapling and severing of tissue includes electrically actuated deployment of buttress pads held on inner surfaces of upper and lower jaws of a staple applying assembly. Thereby, thick or thin layers may be stapled and severed without improper staple formation nor with nonoptimal deployment of the buttress pads. Electroactive polymer (EAP) actuated latches, an EAP channel, or a rigid channel with an EAP pinch lock reliably hold the buttress pad until deployment is desired with a low force to separate the stapled and severed buttress pad/tissue combination with the respective EAP mechanism activated for deployment.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application claims the benefit of U.S. provisional application Ser. No. 60/591,694, entitled “SURGICAL INSTRUMENT INCORPORATING AN ELECTRICALLY ACTUATED ARTICULATION MECHANISM” to Shelton IV, filed 28 Jul. 2004. 
     
    
     FIELD OF THE INVENTION  
       [0002]     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  
       [0003]     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 has 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.  
         [0004]     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 the proximal end of the instrument.  
         [0005]     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.).  
         [0006]     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.  
         [0007]     One known problem with using surgical staplers in this fashion has been the formation of air leaks in stapled lung tissue. The leaks can occur in the cut line, and/or in the staple holes themselves. Frequently, the diseased lung tissue is thin and friable and can tear at the staples as the lungs re-inflate. These air leaks can be persistent and can extend the hospital stay for a patient by weeks. To alleviate these leakage problems, surgeons reinforce the staple line by applying a buttress or pledget material to the desired stapling site and stapling through the buttress material. The buttress material provides reinforcement to the friable tissue. The tissue is compressed against the staple holes resulting in increased pneumostasis. This reduces the chances of tissue tearing at the staple line, and reduces staple pullout in friable tissue.  
         [0008]     These reinforcement materials are typically releasably mounted onto the jaw members of a surgical stapling device such that upon firing, the reinforcement material is stapled to the lung tissue. Optimally the lung tissue is “sandwiched” between two layers of this reinforcement material. Alternately, buttress materials can be used in a number of other surgical procedures such as but not limited to: an ovarian hysterectomy, a gastric bypass, an anastomosis of intestinal tissue, or any other procedure that requires reinforcement of a staple line or increased hemostasis in tissue.  
         [0009]     Releasably attaching the buttress material to the jaw members of the surgical stapling device presents a special challenge. The buttress material must be fastened securely to the jaws of the surgical stapling device so that it will not fall off during normal operation, yet the material must be easily released from the surgical stapling device after the staples are fired. A variety of adhesive and mechanical attachment means are known. Both adhesive and mechanical attachment means are discussed below, and both have their deficiencies.  
         [0010]     One example of a device which attaches a buttress material to a linear cutter with an adhesive is described in U.S. Pat. No. 5,441,193 by Gravener et al. This device attaches buttress materials to a surgical instrument with a biocompatible cyanoacrylate adhesive. The adhesive bonding is applied along the edge portions of the buttress material and dashed lines of perforations are placed within the buttress material (adjacent to the glue line) so that the unglued central portion of the buttress material can be torn from the glued edge portions. However, the portions of the buttress material having the adhesive applied thereto are not releasable from the device. As a consequence, removing the buttress from the instrument (after firing) can be especially difficult, as all of the material between the perforations must be torn simultaneously to release the surgical stapling device from tissue. An improved approach to adhesively engaged buttress material was subsequently disclosed in U.S. Pat. No. 6,656,193 to Grant that included both mechanical alignment features in combination with a reliable adhesive with beneficial characteristics for attachment and detachment.  
         [0011]     It is also known to employ various mechanical attachments of the buttress material to the surgical stapling and severing instrument. Many methods of mechanical attachment exist, and a common one is the placement of a sleeve over the clamping members of the surgical stapling device. The sleeves can be formed from flexible fabric such as buttress material, or can contain a releasable strip of buttress material attached to a different fabric. Many of these sleeves are described in U.S. Pat. Nos. 5,503,638 and 5,549,628 by Cooper et al, in U.S. Pat. No. 5,702,409 by Rayburn et al., in U.S. Pat. No. 5,810,855 by Rayburn et al., and in U.S. Pat. No. 5,964,774 by McKean et al.  
         [0012]     While sleeves can effectively be used to attach the buttress material to the end effector of the surgical stapling device, sleeves can cause other complications during surgery. For example, if the sleeve is formed from a solid sleeve of buttress material, such as in U.S. Pat. Nos. 5,902,312 and 5,769,892, firing the surgical stapling device staples the buttress and tissue and severs the buttress sleeve and tissue between the staple lines. This action leaves the portions of tissue (on either side of the cut line) attached together by a sheet of buttress material. This requires the surgeon to go in and sever the cut sleeve of the buttress to separate the severed tissue, and remove any unwanted portion of the buttress material.  
         [0013]     It is also known to incorporate frangible features that are a compromise between a strong hold to prevent inadvertent detachment and unduly high force to detach after stapling. For instance, in U.S. Pat. Nos. 5,542,594, 5,908,427, and 5,964,774 to McKean et al., buttress material is pinned onto end effector surfaces. In U.S. Pat. Nos. 5,702,409 and 5,810,855 to Rayburn et al., porous polytetrafluoroethylene (PTFE) tubes fit over each jaw with each having a tear away flat face. As a compromise, it would be desirable that retention force be higher prior to stapling and reduced after stapling.  
         [0014]     Consequently, a significant need exists for an improved surgical stapling and severing instrument that may reliability position buttress material on each side of tissue that is to be stapled and severed with the buttress material thereafter easily deployed from the instrument.  
       BRIEF SUMMARY OF THE INVENTION  
       [0015]     The invention overcomes the above-noted and other deficiencies of the prior art by providing a surgical instrument that reliably engages buttress material to a tissue compression surface of a fastener applying assembly by use of an electrically actuated retention member. Thereby, a strong engagement avoids inadvertent deployment yet the electrically actuated retention member may be switched to a disengaged state to effect deployment of the buttress material after fastening to tissue without need for subsequent surgical procedures.  
         [0016]     In one aspect of the invention, a surgical instrument for fastening buttress material to tissue has a staple applying assembly distally attached to an elongate shaft that responds to distal motion of a firing member to form staples between opposing tissue compression surfaces through first and second buttress pads and interposed compressed tissue. Electrically actuated retention members selectively positioned between an engaged position holding a selected buttress pad to a selected tissue compression surface are controlled by circuitry to effect a selected one of retaining and deploying the buttress pad. Thereby, reliance of a static amount of retention force is replaced by a selectable amount of force.  
         [0017]     In another aspect of the invention, a surgical instrument for fastening buttress material to tissue incorporates the advantages of electroactive polymers to serve as a means for engaging a buttress pad to each of a pair of tissue compression surfaces and to remotely electrically control deployment of the buttress pads after their stapling to interposed tissue. Thereby, an implement portion of such a surgical instrument may be desirably small in transverse cross section for insertion through a cannula of a trocar for endoscopic or laparoscopic procedures.  
         [0018]     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  
       [0019]     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.  
         [0020]      FIG. 1  depicts a partially cutaway side elevation view of a surgical stapling and severing instrument in an open position with an electrically actuated buttress deployment mechanism with a lower buttress pad exploded off a lower jaw and an elongate shaft partially cut away.  
         [0021]      FIG. 2  depicts a left side view in elevation of a staple applying assembly of the surgical stapling and severing instrument of  FIG. 1 .  
         [0022]      FIG. 3  depicts a left front perspective view of a replaceable staple cartridge removed from the lower jaw of the staple applying assembly of  FIG. 2 .  
         [0023]      FIG. 4  is a left front perspective disassembled view of the replaceable staple cartridge of  FIG. 3 .  
         [0024]      FIG. 5  is a front view of a right side of the lower jaw taken in cross section along lines  5 - 5  of  FIG. 2  with a lower, lateral electroactive polymer (EAP) buttress latch in a locked state.  
         [0025]      FIG. 6  is a front view of the right side of the lower jaw taken in cross section along lines  5 - 5  of  FIG. 2  with the lower, lateral EAP buttress latch in an unlocked state.  
         [0026]      FIG. 7  is a left side detail view of an aft EAP buttress latch in an unlocked state.  
         [0027]      FIG. 8  is a left perspective view of an upper jaw (anvil) of the staple applying assembly of  FIG. 2 .  
         [0028]      FIG. 9  is a left perspective, disassembled view of the upper jaw (anvil) of the staple applying assembly of  FIG. 2 .  
         [0029]      FIG. 10  is a front view of the upper jaw (anvil) of the staple applying assembly of  FIG. 2  taken in cross section through lines  10 - 10  with an upper, lateral EAP latch engaged to a buttress pad.  
         [0030]      FIG. 11  is a front view of the upper jaw (anvil) of the staple applying assembly of  FIG. 2  taken in cross section through lines  10 - 10  with the upper lateral EAP latch actuated and the deployed buttress pad omitted.  
         [0031]      FIG. 12  is a left side view in elevation of an alternative staple applying assembly for the surgical stapling and severing instrument of  FIG. 1  with a lower, front EAP latch engaged to a lower buttress pad.  
         [0032]      FIG. 13  is a front left perspective view of a replaceable staple cartridge removed from the lower jaw of the alternative staple applying assembly of  FIG. 12 .  
         [0033]      FIG. 14  is a left side detail view of the lower jaw of  FIG. 12  with the lower, front EAP latch activated to disengage from an omitted deployed buttress pad.  
         [0034]      FIG. 15  is a left perspective disassembled view of the lower jaw of  FIG. 12  with a slotted buttress pad.  
         [0035]      FIG. 16  is a front perspective view of an alternative replaceable staple cartridge with EAP latching channels for the lower jaw for the staple applying assembly of  FIG. 2 .  
         [0036]      FIG. 17  is a front perspective view of the alternative replaceable staple cartridge of  FIG. 16  taken in cross section through lines  17 - 17  through the deactivated (contracted) EAP latching channel engaged to a buttress pad.  
         [0037]      FIG. 18  is a front perspective view of the alternative replaceable staple cartridge of  FIG. 16  taken in cross section through lines  17 - 17  through an activated (expanded) EAP latching channel disengaged from an omitted deployed buttress pad.  
         [0038]      FIG. 19  is a front perspective of a right side of an additional alternative lower jaw for the staple applying assembly of  FIG. 2  taken in transverse cross section through a rigid buttress channel with an EAP pinching lock depicted in a deactived, expanded position locking a buttress pad.  
         [0039]      FIG. 20  is a front perspective of the right side of the additional alternative lower jaw of  FIG. 19  for the staple applying assembly of  FIG. 2  taken in transverse cross section through the rigid buttress channel with the EAP pinching lock depicted in an activated, contracted position unlocked from an omitted deployed buttress pad.  
         [0040]      FIG. 21  is a perspective view of a circular surgical stapler with an EAP buttress latching mechanism. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0041]     Turning to the Drawings, wherein like numerals denote like components throughout the several views, in  FIGS. 1-2 , 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. Advantageously, an electrically actuated buttress deployment mechanism  20  reliability retains upper and lower buttress pads  22 ,  24  respectively on an upper jaw (anvil)  26  and a lower jaw  28  until tissue clamped within the staple applying assembly  16  is stapled and severed. Thereafter, the electrically actuated buttress deployment mechanism  20  deploys the buttress pads  22 ,  24  without undue force or ancillary surgical procedures (e.g., use of a grasper).  
         [0042]     The surgical stapling and severing instrument  10  is in an initial state as depicted in  FIG. 1 , with a closure trigger  30  and a more distal firing trigger  32  both released from a pistol grip  34 . Release of the closure trigger  30  proximally draws a closure sleeve  36 , which is an outer portion of the elongate shaft  18  that pivots the anvil  26 . The lower jaw  28  is supported by a frame ground  38  that is encompassed by the closure sleeve  36  and is rotatably engaged to the handle portion  12 . A rotation knob  40  allows reciprocating longitudinal motion of the closure sleeve  36  while engaging the closure sleeve  36  and frame ground  38  for rotation about a longitudinal axis of the elongate shaft  18 . The firing trigger  32  is either directly or intermittently coupled to a firing member, specifically a firing rod  42 , guided by the frame ground  38  that transfers a firing motion to the staple applying assembly  16  to effect stapling and severing.  
         [0043]     A power button  44  may be depressed by the user to activate a control module  46  of the electrically actuated buttress deployment mechanism  20 , powered by a battery  48 . A visual confirmation on the handle portion  12  may be given to the user as to the state of the electrically actuated buttress deployment mechanism  20  (e.g., color/flash illumination of the power button  44 ). For instance, the power button  44  and/or other user interfaces (not shown) may advantageously be depressed a number of times to toggle through several available operational states of the electrically actuated buttress deployment mechanism  20 , such as “POWER ON”, “BUILT-IN TEST PASSED”, INSERT BUTTRESS PADS, “SYSTEM LOADED/AWAITING FIRING”, “FAULT DETECTED”, and “BUTTRESS OVERRIDE/FIRING WITHOUT INSTALLED BUTTRESS PADS”. Additional programming flexibility may be achieved by incorporating a wired or wireless (e.g., BLUETOOTH) protocol to interface the control module  46  to an external graphical user interface (e.g., personal computer). In the initial state, the control module  46  electrically actuated buttress retention elements, in the version depicted, comprise upper and lower latch arms  50 ,  52  that are electrically urged outwardly so that the upper buttress pad  22  may be inserted against an inner surface of the anvil  26  as depicted and a lower buttress pad  24  may be placed upon and latched to an inner surface of the lower jaw  28 , in particular, upon a replaceable staple cartridge  54  that is engaged in an elongate staple channel  56  of the lower jaw  28 .  
         [0044]     With the buttress pads  22 ,  24  inserted and the power button  44  depressed again to latch, the implement portion  14  may be inserted endoscopically or laparoscopically to a surgical site. The closure trigger  30  is depressed and released as necessary until an amount of tissue is gripped in the staple applying assembly  16 . Drawing the closure trigger  30  fully to the pistol grip  34  causes the closure trigger  30 , and thus the anvil  26 , to clamp in a closed position. Then, the firing trigger  32  is depressed, either in a single stroke or in a series of strokes depending upon the configuration of the handle portion  12  causing full firing travel of the firing rod  42 . For multiple firing strokes, a firing indicator wheel  58  on the handle portion  12  gives a visual indication as to the amount of firing that has occurred. It should be appreciated that a distal end of the firing rod  42  includes or is coupled to a knife that traverses a vertical slot in the staple cartridge  54  to sever clamped tissue and the buttress pads  22 ,  24 . The firing rod is also coupled to a wedge assembly that cams staples upwardly out of the staple cartridge  54  through the clamped tissue and buttress pads  22 ,  24  to close and form against the anvil  26 . Thereafter, the firing rod  42  is withdrawn by an end-of-firing travel release mechanism and a retraction bias in the handle portion  12 . For manually releasing and/or manually retracting the firing rod  42 , a manual retraction lever  60  may be rotated upwardly on the handle portion  12 . The control module  46  of the electrically actuated buttress deployment mechanism  20  advantageously senses that firing has been accomplished, such as by being responsive to a firing position sensor  62  in the handle portion  12 . With the unclamping of the closure trigger  30  by depressing a closure release button  64 , the severed ends of buttressed, stapled tissue (not shown) is released from the staple applying assembly  16 .  
         [0045]     An illustrative version of the handle portion  12  without an electrically actuated buttress deployment mechanism  20  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., the disclosure of which is hereby incorporated by reference in its entirety.  
         [0046]     Electroactive Polymers.  
         [0047]     While a number of electrical actuators (e.g., solenoids) may be integrated into the staple applying assembly  16 , 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.  
         [0048]     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, manufactured by Santa Fe Science and Technology and sold as PANION™ fiber, is described in U.S. Pat. No. 6,667,825, which is hereby incorporated by reference in its entirety.  
         [0049]     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.  
         [0050]     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.  
         [0051]     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.  
         [0052]     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.  
         [0053]     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.  
         [0054]     In  FIGS. 3-7 , the lower latch arms  52  of the electrically actuated buttress deployment mechanism  20  selectively hold the lower buttress pad  24  by electrically actuating cylindrical EAP actuators  74  positioned in holes  76  formed in left and right lateral lips  78 ,  79  of a staple cartridge body  80  of the replaceable staple cartridge  54 . With particular reference to  FIG. 4 , the polymeric staple body  80  has an aft vertical slot  82  that receives a knife of a firing bar (not shown). A plurality of vertical staple apertures  84  are formed in the polymeric staple body  80  with each containing a staple supported by staple drivers (not shown). A staple cartridge tray  85  underlies and laterally encompasses the polymeric staple body  80  to retain these components. Left and right aft rectangular EAP actuators  86 ,  88  extend out of left and right aft rectangular apertures  90 ,  92  formed in the staple cartridge body  80  on each side of the aft vertical slot  82 . Left and right aft latch arms  94 ,  96  are formed into the staple cartridge tray  85  attached at their aft portion and horizontally extending distally to bend front upwardly as the respective aft rectangular EAP actuators  86 ,  88  expand ( FIG. 7 ). Separate left and right side brackets  98 ,  100  each include a plurality of opposing and inwardly bent top and bottom flanges  102 ,  104  that grip respective left and right lateral lips  78 ,  79 . The lower latch arms  52  are formed from the left and right side brackets  98 ,  100  as L-shaped flanges that overlie and are spaced away from the respective left and right lateral lips  78 ,  79 . Each side latch arm  52  and aft latch arm  94 ,  96  has a down turned inward edge  106  that assists in gripping the lower buttress pad  24  ( FIGS. 3, 5 ). In  FIG. 6 , electrical activation of cylindrical EAP actuators  74  rotates the lower latch arms  52  upwardly and laterally allowing the lower buttress pad  24  to deploy away from a top compression surface  108  of the replaceable staple cartridge  54 .  
         [0055]     In  FIGS. 8-11 , the upper latch arms  50  of the electrically actuated buttress deployment mechanism  20  are curved to closely overlay the anvil  26  with inwardly curved left and right tips  120 ,  122  that parallel a respective outer edge of the anvil  26 . Each upper latch arm  50  is electrically actuated by a pair of cylindrical EAP actuators  124  that extend out of a respective left and right holes  126 ,  128  formed into arm recess  130  that is formed laterally across a top surface  132  of the anvil  26 . At a longitudinal apex of the anvil  26 , each upper latch arm  50  is fastened to the anvil  26  by a fastener  134 . Thus expansion of the pair of cylindrical EAP actuators  124  on each side of the respective fastener  134  causes the left and right tips  120 ,  122  of each upper latch arm  50  to raise and rotate away from the retained upper buttress pad  22  allowing deployment from a staple forming inner compression surface  136  of the anvil  26  ( FIG. 11 ).  
         [0056]     In  FIGS. 12-15 , a version of a replaceable staple cartridge  54 ′ of a lower jaw  28 ′ of a staple applying assembly  16 ′ as otherwise described in  FIGS. 3-6  further includes a lower distal latch  140  that is a plate bent into an obtuse angle corresponding to a beveled lead edge  142  and the top compression surface  108  of a staple cartridge body  80 ′. A lower distal EAP actuator  144  extends out of a distal EAP recess  146 , adhered to both the staple cartridge body  80 ′ and the lower distal latch  140  for pulling a hooked proximal end  148  of the lower distal latch  140  down into engagement with a distal side of a lower buttress pad  24 ′ or for pushing the hooked proximal end  148  up and out of engagement. A distal longitudinal slot  150  in the lower buttress pad  24 ′ corresponds to a proximal longitudinal slot  152  formed in the lower distal latch  140  to assist in achieving engagement without contact with the knife or for incomplete severing of the lower buttress pad  24 ′.  
         [0057]     In  FIGS. 16-18 , alternative left and right EAP buttress latches  200 ,  202  for an electrically actuated buttress deployment mechanism  20 ′ are formed as inwardly open C-channels of EAP material embedded into left and right lateral lips  78 ′,  79 ′ of a staple cartridge body  80 ″ and are configured to vertically contract when deactivated ( FIG. 17 ) to grip a lower buttress pad  24  and to expand when actuated to deploy ( FIG. 18 ).  
         [0058]     In  FIGS. 19-20 , an alternative EAP locking actuator  74 ′ is used in the replaceable staple cartridge  54  along with alternative left and right side brackets  100 ′ (the latter depicted) with increased vertical spacing from the top compression surface  108  of the staple cartridge body  80  to loosely hold the lower buttress pad  24 . The EAP locking actuator  74 ′ has a vertically expanded locking state ( FIG. 19 ) that pushes the lower buttress pad  24  upwardly into tight engagement in an upper flange  240  of the respective side bracket  100 ′. The EAP locking actuator  74 ′ has a retracted unlocking state ( FIG. 20 ) that allows deployment. It should be appreciated that recessing the EAP locking actuator  74 ′ into the staple cartridge body  80  provides for a desired amount of extension to deform the buttress pad  24 . Alternatively or in addition, an EAP actuator may be placed in an opposing position under the upper flange  240 .  
         [0059]     In  FIG. 21 , a circular stapler instrument  310  has distal and proximal buttress rings  312 ,  314  depicted as exploded away from distal and proximal circular compression surfaces  316 ,  318 . EAP latches  320  extending inwardly from the compression surfaces  316 ,  318  and controlled from a handle  322  selectively engage and deploy the buttress rings  312 ,  314 .  
         [0060]     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.  
         [0061]     For example, while a staple applying assembly  16  is depicted in the illustrative version, it should be appreciated that electrically actuated buttress deployment may be advantageously used in fastener instruments that utilize clips, anchors, sutures, etc.  
         [0062]     For another example, while a manually operated surgical stapling and severing instrument  10  is depicted for clarity, it should be appreciated that a robotically manipulated and/or controlled fastening device may incorporate electrically actuated buttress retention members consistent with aspects of the invention.  
         [0063]     For yet another example, sensing of tissue thickness and/or presence of buttress material may advantageously enable or disable firing to avoid inadvertent firing when buttress material is warranted but not installed or buttress material is installed but not warranted.  
         [0064]     For yet a further example, an electrically actuated buttress retention element may comprise a combination of a passive resilient member (e.g., compression spring) that provides a power off retention bias within a buttress gripping channel with an active electrical component. For instance, an EAP fiber actuator passing through the compression spring to a cap may be activated to contract, compressing the compression spring for deployment of a buttress pad.  
         [0065]     As yet another example, a staple cartridge may be manufactured with a buttress pad attached to a compression surface by pins, crimped-on clamps, etc., or may be forcibly deployed by an underlying EAP actuator that deforms the buttress pad and/or the attachment to effect separation.  
         [0066]     As yet a further example, applications consistent with the present invention may incorporate electrically actuated retention members that are activated to perform engagement to the buttress pad and/or activated to disengage for deployment of the buttress pad. For instance, a retention member may have a loose frictional engagement without power that allows insertion of buttress pads prior to use. Powered activation of a locking EAP actuator thereafter may effectively lock the buttress pad prior to use. Alternatively or in addition to such a locking EAP actuator, activation after stapling of a deployment EAP actuator may effectively reduce engagement or frictional engagement of the buttress pad facilitating deployment.  
         [0067]     As yet another additional example, while endosocopic and laparoscopic applications benefit from aspects of the present invention, it should be appreciated that open surgical procedures may also benefit.