Patent Publication Number: US-10772623-B2

Title: Coupling system, applicator tool, attachment ring and method for connecting a conduit to biological tissue

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a divisional of application Ser. No. 14/808,350, filed Jul. 24, 2015, now U.S. Pat. No. 9,848,870, which is a divisional of application Ser. No. 13/406,511, filed Feb. 27, 2012, now U.S. Pat. No. 9,125,648, which claims the benefit of Provisional Application No. 61/446,996, filed Feb. 25, 2011 and Provisional Application No. 61/603,140, filed Feb. 24, 2012, all of which applications are incorporated herein by reference for all purposes. 
    
    
     FIELD OF THE INVENTION 
     The invention relates to a coupling system, applicator tool, attachment ring and method for connecting a conduit to biological tissue, and more particularly, for connecting a conduit to the heart. 
     BACKGROUND OF THE INVENTION 
     Surgical procedures for connecting a conduit to biological tissue, such as blood vessels and the heart, have required manually suturing the conduit or coupling device to the biological tissue. Manual suturing can be difficult due to limited access to, location of, and/or type of biological tissue. When the procedure is performed on a blood vessel, blood flow may need to be blocked temporarily to avoid the loss of large amounts of blood during the time required for manual suturing and/or to stop pulsatile motion which can make accurate placement of sutures difficult. When the procedure is performed on the heart, the patient is connected to a heart-lung bypass machine and the heart is stopped for a period of time during the procedure. 
     There is a continuing need to make the procedure for connecting a conduit easier and faster to perform. There is also a need to be able to connect a conduit to the heart, such as during implantation of a ventricular assist device (VAD), with the option of allowing the heart to continue to beat and not having to resort to using a heart-lung bypass machine. 
     SUMMARY OF THE INVENTION 
     Briefly and in general terms, the present invention is directed to an assembly for retaining a plurality of clips deployed to connect the assembly to tissue, and to an attachment ring. 
     In aspects of the present invention, an assembly, for retaining a plurality of clips deployed to connect the assembly to tissue, comprises a main body, a first device, and a second device. The main body is configured to contain a medial segment of each clip. The first device is configured to trap a forward segment of each clip. The second device is configured to cinch each clip while the forward segments of the clips are trapped by the first device. 
     In aspects of the present invention, an attachment ring comprises a main body, an annular cuff, and a clamping ring. The main body includes a cylindrical wall encircling an axial centerline. The annular cuff is attached to the main body. The clamping ring is movable relative to the main body in a direction substantially parallel to the axial centerline. The clamping ring is configured to engage a lock feature on the main body. 
     The features and advantages of the invention will be more readily understood from the following detailed description which should be read in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1A-1E  are perspective views of an exemplary applicator tool for anchoring an attachment ring to biological tissue using securement clips, the applicator tool shown fully assembled in  FIG. 1A , disassembled in  FIGS. 1B-1D , and close-up in  FIG. 1E . 
         FIG. 1F  is a partial cross-section view of an exemplary clip holder of the applicator tool of  FIG. 1A . 
         FIGS. 2A-2D  are perspective views of an exemplary attachment ring, the attachment ring shown fully assembled in  FIGS. 2A-2C  (viewed from the top, side, and bottom), and disassembled in  FIG. 2D . 
         FIG. 3A-3D  are perspective and other views of an exemplary securement clip to be loaded into and deployed out of an applicator tool. 
         FIG. 4  is a side view of another exemplary securement clip similar to that of  FIGS. 3A-3D . 
         FIG. 5  is a cross-section view of an exemplary applicator tool forward end. 
         FIG. 6  is a cross-section of another exemplary attachment ring similar to that of  FIGS. 2A-2D . 
         FIG. 7  is a cross-section view of the attachment ring of  FIG. 6  mounted on the forward segment of  FIG. 5  to form a coupling system, the view showing the front segment of the coupling system in an initial, undeployed condition on top of biological tissue. 
         FIG. 8  is a cross-section view of the coupling system after  FIG. 7 , showing the coupling system in a deployed condition. 
         FIG. 9  is a cross-section view of the coupling system after  FIG. 8 , showing the coupling system in a clamped condition. 
         FIG. 10  is a cross-section view of the coupling system after  FIG. 9 , showing the coupling system in a cinched condition. 
         FIG. 11  is a cross-section view of the attachment ring after  FIG. 10 , showing the applicator tool removed and a clamp and valvular structure attached to the attachment ring. 
         FIG. 12  is a cross-section view of the attachment ring and valvular structure after  FIG. 11 , showing an exemplary instrument inserted through the attachment ring and valvular structure. 
         FIG. 13  is a cross-section view of the attachment ring and valvular structure after  FIG. 12 , showing a through-hole cut into the biological tissue by the instrument. 
         FIG. 14  is a cross-section view of the attachment ring and valvular structure after  FIG. 13 , showing an exemplary cannula inserted into the attachment ring, valvular structure, and through-hole in the biological tissue. 
         FIG. 15  is a cross-section view of the attachment ring after  FIG. 14 , showing the valvular structure removed and a fluid conduit connected to the cannula. 
         FIGS. 16-18  are perspective, perspective cutaway, and detailed cutaway views of an applicator tool similar to that of  FIG. 1 . 
         FIG. 19  is a detailed cutaway view of the applicator tool of  FIG. 18  with some parts absent from the illustration to more clearly show other parts. 
         FIG. 20-27  are partial sectional views of the applicator tool of  FIGS. 16-19 , showing sequential operation of the applicator tool for deploying and cinching a plurality of clips. 
         FIGS. 28-30  are exploded and assembled views of exemplary attachment rings that can be mounted on biological tissue using the applicator tool of  FIGS. 16-19 . 
         FIGS. 31-33  are perspective, detailed perspective, and perspective cutaway views of a valvular structure that can be mounted on the attachment rings herein. 
         FIGS. 34 and 35  are perspective and perspective cutaway views of an exemplary cannula that can be mounted on the attachment rings herein. 
     
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     As used herein, any term of approximation such as, without limitation, near, about, approximately, substantially, essentially and the like mean that the word or phrase modified by the term of approximation need not be exactly that which is written but may vary from that written description to some extent. The extent to which the description may vary will depend on how great a change can be instituted and have one of ordinary skill in the art recognize the modified version as still having the properties, characteristics and capabilities of the modified word or phrase. For example and without limitation, a first structure that is described as “substantially parallel” in reference to a second structure encompasses an orientation that is perfectly parallel and an orientation that one skilled in the art would readily recognize as being parallel even though distances between corresponding locations on the two respective structures are not exactly the same. 
     As used herein, a “through-hole” refers to a lumen that extends from one surface of a structure completely through the structure to another surface of the structure such that, if desired, a fluid could pass completely through the structure. 
     Referring now in more detail to the exemplary drawings for purposes of illustrating exemplary embodiments of the invention, wherein like reference numerals designate corresponding or like elements among the several views, there is shown in  FIG. 1A  applicator tool  10  for anchoring attachment ring  30  to biological tissue. Although attachment ring  30  is shown and described together with applicator tool  10 , it will be appreciated that other applicator tools may be used to anchor attachment ring  30  to biological tissue.  FIGS. 1B-1D  shows applicator tool  10  without attachment ring  30  and in varying states of disassembly.  FIG. 1E  shows a detailed view of an exterior portion of applicator tool  10  on which attachment ring  30  could be carried. Exemplary attachment ring  30  is a type of prosthesis suitable for implantation within a human or animal body. Attachment ring  30  is a coupling for a conduit, graft, or other structure that is to be connected to biological tissue. In various embodiments, attachment ring  30  is configured for attaching a device (e.g. a prosthesis, therapy device, a diagnostic device, etc.) to a body lumen or organ. Forward segment  12  of applicator tool  10  is configured to engage attachment ring  30 . Rear segment  14  has grip  16 . Clip deployment handle  18 , clamp release  21 , and disengagement knob  24  are used to control various elements in forward segment  12 . As described below, clip deployment handle  18  also provides clamping and cinching functions. 
       FIGS. 2A-2C  show various views of attachment ring  30  in a fully assembled state after completion of clip deployment and clamping processes described below.  FIG. 2D  shows attachment ring  30  in a disassembled state. 
     Referring to  FIG. 2B , attachment ring  30  has bottom end  32  and top end  34 . Bottom end  32  is secured to biological tissue and top end  34  is configured to engage forward segment  12  of applicator tool  10 . Attachment ring  30  includes features configured to connect with a conduit, such as an inflow conduit of a ventricular assist device (VAD), after attachment ring  30  has been secured to biological tissue, such as the ventricular apex of the heart. Methods for securing an inflow conduit to the ventricular apex by means of an attachment ring are described in U.S. Application Publication Nos. 2011/0118766 A1, 2011/0118833 A1, and 2011/0118829 A1, which are incorporated herein for all purposes by reference. While the attachment ring and applicator tool will be described in terms of attaching a conduit to a biological tissue such as a body lumen or organ wall, one will appreciate that the devices and methods described herein may be applied equally to a variety of applications. 
     As shown in  FIG. 2D , attachment ring  30  comprises main body  70 , cinching ring  86  and clamping ring  100 . When used with applicator tool  10 , cinching ring  86  is located within main body  70 . Main body  70  and cinching ring  86  collectively form ring assembly  71  which is releasably attached to connector mechanism  28  of applicator tool  10 . Connector mechanism  28  ( FIG. 1E ) includes movable lock elements  29  capable of selectively engaging and releasing internal annular groove  77  of attachment ring main body  70 . As shown in  FIG. 1A , clamping ring  100  is releasably attached to the outer surface of cinching tube  58  and abuts forward end of clamping tube  64  (also referred to as a clamp pusher). In  FIG. 1E , clamping ring  100  would be located at a region of applicator tool  10  designated generally by arrow A. 
     As shown in  FIG. 2D , attachment ring main body  70  comprises cylindrical wall  72 , ratchet members  76  attached to cylindrical wall  72 , and base  74  attached to the bottom of cylindrical wall  72 . Main body  70  can be made of titanium, other metal, or other material suitable for implantation within a human or animal body as would be understood by one of skill in the art from the description herein. Cylindrical wall  72  encircles interior space  73 . Ratchet members protrude into interior space  73  and face toward axial centerline  78  of cylindrical wall  72 . Through-holes  80  are formed through base  74 . 
     Flexible, annular cuff  82  (illustrated in broken line in  FIG. 2B ) can be attached to base  74  by a suture or thread passing through annular cuff  82  and through-holes  80  of base  74 . Annular cuff  82  can be attached to base  74  by an adhesive. Central through-hole of annular cuff  82  is substantially centered upon axial centerline  78 . Annular cuff  82  can be made of polytetrafluoroethylene (PTFE) felt, polyethylene terephthalate (PETE) felt, other polyester fibers, titanium, other metals, silicone rubber, any combination thereof, or other material suitable for implantation within a human or animal body as would be understood by one of skill in the art from the description herein. In various embodiments, annular cuff  82  is capable of forming a hemostatic connection with biological tissue when attachment ring  30  is anchored to the biological tissue. 
     Dimensions for annular cuff  82  may be selected based on the type of surgical procedure that is being performed and the type and condition of the biological tissue to which attachment ring  30  is to be anchored. In one embodiment, annular cuff  82  has an outer diameter from about 30 mm to about 50 mm, and an inner diameter from about 10 mm to 25 mm. 
       FIG. 3A  shows exemplary clip  36  for anchoring attachment ring  30  to biological tissue.  FIGS. 3B-3C  show various views of clip  36  of  FIG. 3A . In  FIGS. 3A-3D , clip  36  is shown in its natural and unconstrained state prior to being loaded into applicator tool  10 . Clip  36  can be made of titanium or other material suitable for implantation within a human or animal body or a mammalian body. In one embodiment, clip  36  is made of a nickel-titanium alloy (e.g. Nitinol), copper-zinc-aluminum alloy, or other material having shape memory and/or superelastic properties. 
     In use, clips  36  are contained within forward end  12  of applicator tool  10 . Each clip  36  includes wire body  38  having forward segment  40  and rear segment  42 . Forward segment  40  has sharp tip  44  for piercing a portion of attachment ring  30  and underlying biological tissue. Catch  46  protrudes out from rear segment  42  and is pushed forward during operation of applicator tool  10 . Clips  36  are constrained in a straightened configuration within forward end  12  of applicator tool  10 . In various embodiments, the clips are formed of shape memory material and make use of the shape memory properties. When deployed out of forward end  12 , exemplary clips  36  will autonomously coil radially outward away from axial centerline  54  ( FIG. 1E ) in a direction away from forward end  12  due to elastic memory of wire body  38 . In various embodiments, the clips have a generally straight shape in a stowed or undeployed condition and a relatively curved shape when deployed. In various embodiments, at least a portion of the clips extend outwardly away from the forward end without the use of external forces when they are unconstrained. One will appreciate that the shapes and configurations of the clips in the deployed and undeployed conditions may be modified depending on the application. For example, the clips may have a relatively straighter shape when deployed. 
     Referring to  FIG. 1E , clips  36  are constrained within a plurality of clip holders  47  forming parts of clip tube  48 . Clip tube  48  is a hollow, cylindrical sleeve. Each clip holder  47  comprises clip groove  52  formed within walls of clip tube  48 . Clip groove  52  has axial slot opening  53  that faces radially outward, away from axial centerline  54  of clip tube  48 . An end portion of catch  46  of each clip  36  extends out of axial slot opening  53  of clip groove  52 . One exemplary catch  46  is shown for ease of illustration, and it will be understood there will be a catch protruding out of each clip groove  52  that contains clip  36 . Clip pusher surface  51  abuts catch  46  from behind and is configured to push clips  36  out of forward opening  61  of clip groove  52 . 
     Clip grooves  52  have sidewalls  57  that extend substantially parallel to axial centerline  54  and substantially non-perpendicular to outer surface  45  of clip tube  48 . In other embodiments, sidewalls  57  are substantially perpendicular to outer surface  45 . 
     Catch  46  of each clip  36  abuts sidewalls  57  of clip groove  52 , which prevents clip  36  from twisting about its central axis  39  while contained inside clip groove  52 . Catch  46  and sidewalls  57  help to ensure that the curved trajectory of tip  44  will be in the desired direction relative to attachment ring  30 . The direction followed by tip  44  is controlled in part by the angle of sidewalls  57  and by the initial shape of clip  36  prior to being loaded in applicator tool  10 . As shown in  FIG. 1E , sidewalls  57  are at an oblique angle measured from radial line  54 R. Radial line  54 R is a radial line that extends out from the center of clip tube  48  and is perpendicular to axial centerline  54 . The oblique angle, indicated by arrow B, can be from about 10 degrees to about 80 degrees, and more narrowly from about 30 degrees to about 60 degrees, and more narrowly at about 45 degrees. In some embodiments, the angle of sidewalls  57  causes clips  36  to deploy into biological tissue at the oblique angle relative to radial line  54 R. A change in oblique angle B changes the distance between the center of applicator tool  10  and the point at which the clip tip  44  exits the biological tissue, and thus changes the size of the clip foot print. Oblique angle B is important since clip tip  44  should exit the biological tissue at a point slightly beyond the outer circumference of attachment ring  30 . A larger oblique angle B results in a smaller clip footprint and thereby increases hemostasis and stabilization of attachment ring  30  to the biological tissue. The term “clip footprint” refers to the surface area of biological tissue encircled by a plurality of deployed clips. 
     In  FIG. 1E , oblique angle B is the same for sidewalls  57  of all clip grooves  52 . In other embodiments, clip grooves  52  can have varying oblique angles. For example, a first group of clip grooves  52  at a first area of clip tube  48  have sidewalls  57  oriented at oblique angle B that is different than that of a second group of clip grooves  52  at a second area of clip tube  48 . For example, on the same clip tube, oblique angle B can be 30 degrees for some clip grooves  52 , and 45 degrees for other clip grooves, and 60 degrees for other clip grooves  52 . 
       FIG. 1F  shows a cross-section view of clip holder  47 . Clip groove  52  has bottom portion  180  that is shaped and sized to receive and contain clip  36 . Bottom portion  180  is shaped and sized to receive and contain bumps  176  and barbed head  170  of clip  36 . Axial slot opening  53  at the top of clip groove  52  is narrower than the space within bottom portion  180  in order to prevent forward segment  40 , medial segment  174 , and rear segment  42  of clip from passing through axial slot opening  53 . The space or gap within axial slot opening  53  is less than the diameter of clip wire body  38 . The relatively narrow space or gap within slot opening  53  prevents clip  36 , while contained in applicator tool  10 , from moving from a straight configuration to its natural curved configuration (shown in  FIGS. 3A-3D ). Catch  46  of clip  36  is sized to pass through axial slot opening  53 , which allows catch  46  to be pushed by clip pusher surface  51  ( FIG. 1E ). 
     There are twelve clip holders  47  circumferentially arranged on clip tube  48  at substantially equal angular spacing of about 30 degrees apart from each other. In other embodiments, a fewer number or a greater number of clip holders  47  are arranged around the clip tube than what is shown in  FIG. 1E . The number of clip holders and clips depends upon a variety of factors, such as the type of surgical procedure that is being performed and the type and condition of the biological tissue to which attachment ring  30  is to be anchored. In other embodiments, the clip holders are not arranged at equal angular spacing, such that the clip holders are closer to each other at one area of clip tube  48  as compared another area of the clip tube  48 . 
     Cinching tube  58  is a hollow, cylindrical sleeve. Cinching tube  58  contains and is substantially coaxial with clip tube  48 . Clip pusher surface  51  ( FIG. 1E ) is located at the forward end of cinching tube  58 . Cinching pins  60  are attached to cinching tube  58  and protrude axially in front of clip pusher surface  51 . Cinching tube  58  is controlled by clip deployment handle  18  ( FIG. 1 ). Clamping tube  64  is a hollow, cylindrical sleeve. Clamping tube  64  contains and is substantially coaxial with clip tube  48  and cinching tube  58 . Clamping tube  64  is controlled by handle  18 . 
     A method for anchoring attachment ring  30  will now be described together with applicator tool  10 , though it should be understood that other applicator tools may be used to perform the method. It is to be understood that, depending on the type of applicator tool used and depending on clinical need, some steps described below may be performed simultaneously as a single step, performed in a sequence other than described below, or may be omitted. 
     Exemplary steps for applicator tool stabilization are as follows. Referring to  FIG. 1A , a user such as a medical practitioner grasps grip  16  to position main body  70  of attachment ring over biological tissue. Suction may be applied to tube fitting  25  which conveys the suction to suction cup  26  ( FIG. 1E ) at the front of applicator tool  10 . Suction cup  26  engages the biological tissue and stabilizes applicator tool  10  against movement relative to the biological tissue. Steps for stabilization can be performed whenever needed, which can be before, during, and/or after any of the steps for clip deployment, clamping, and cinching described below. 
     As used herein, the phrase “clip deployment” refers to forward movement of clips  36  out of applicator tool  10 , through attachment ring  30 , and into biological tissue. 
     Exemplary steps for clip deployment are as follows. The user rotates handle  18  to begin deployment of clips  36  out of applicator tool  10 . Handle rotation causes clamping tube  64  ( FIG. 1A ), cinching tube  58 , and clamping ring  100  to slide axially forward onto clip tube  48  in the direction of arrow C. Forward end of cinching tube  58  has clip pusher surface  51  ( FIG. 1E ) that pushes clips  36  out of applicator tool  10 , through cinching ring  86  and attachment ring main body  70 , and into the biological tissue. As clip pusher surface  51  continues to push rear segment  42  of clips  36 , sharp tips  44  of clips  36  follow a curved path into and then out of the biological tissue. At the conclusion of clip deployment, clips  36  are completely pushed out of applicator tool  10 . Catch  46  of each clip  36  is located between the forward end of clip tube  48  and top surface  91  ( FIG. 2D ) of cinching ring  86 . Sharp tip  44  of each clip  36  is located between clamping ring  100  and clamp surface  67  ( FIGS. 1A and 2D ) of attachment ring main body  70 . 
     As used herein, the phrase “clamping” refers to moving clamping ring  100  ( FIG. 1A ) closer to attachment ring main body  70  in order to prevent sharp tips  44  of clips  36  from pulling backwards into the biological tissue. 
     Exemplary steps for clamping are as follows. After clip deployment, the user pulls clamp release  21  ( FIG. 1A ) downward, which allows clamping tube  64  to slide forward over cinching tube  58 . The user rotates handle  18  to move clamping tube  64  and clamping ring  100  axially forward over cinching tube  58  and toward attachment ring main body  70 . 
     As shown in  FIG. 2D , clamping ring  100  includes flexible arms  700  with radially inward facing catch members  702 . Each catch member  702  is in the form of a pawl that locks clamping ring  100  onto attachment ring main body  70 . As clamping ring  100  is pushed onto main body  70 , flexible arms  700  bend as leading face  702 A of each catch member  702  slides over and is pushed radially outward by cylindrical wall  72  of attachment ring main body  70 . Catch members  702  enter lock feature  704  in the form of groove formed into the outer surface of cylindrical wall  72 . Rear face  702 B of each catch member  702  engage lock feature  704  and prevents clamping ring  100  from sliding off attachment ring main body  70 . 
     At the conclusion of clamping, clamping ring  100  covers clamp surface  67  of attachment ring main body  70 . Ridges or teeth  706  are arranged around the outer perimeter of clamping ring  100  and are configured to trap at least a portion of clip forward segment  40  ( FIG. 3A ) between clamping ring  100  and attachment ring main body  70 . Each groove or space  708  between teeth  706  is sized to allow passage of clip wire body  38  ( FIG. 3A ) and to prevent passage of barbed head base  172  and bumps  176  on clip forward segment  40 . 
     After clip deployment and clamping, there may be some slack or excess length of clip  36  below the biological tissue due to curvature, thickness, and/or density of biological tissue or due to other factors. The slack or excess length of clip  36  can result in a gap between clip wire body  38  and the interior surface of the biological tissue. 
     As used herein, the word “cinching” refers to tightening of clips  36  against the biological tissue. The tightening of clips  36  may include a reduction of slack or excess length of clip  36  that may exist between clip wire body  38  and the interior surface of the biological tissue after clip deployment and clamping. 
     Exemplary steps for cinching are as follows. After completion of clip clamping, the user rotates handle  18  which causes cinching tube  58  to rotate relative to clip tube  48  and connector mechanism  28  ( FIG. 1E ). During rotation of cinching tube  58 , cinching pins  60  ( FIG. 1E ) on cinching tube  58  engage cinching feature  89  ( FIGS. 2A and 2D ) on cinching ring  86 , and forces cinching ring  86  to rotate relative to attachment ring main body  70 . During rotation of cinching ring  86 , top surface  91  ( FIG. 2D ) of cinching ring  86  engages catch  46  ( FIG. 3A ) of each of clips  36 . As a result, rear segment  42  of clips  36  are pulled circumferentially within chamber  75  ( FIG. 2D ) enclosed between attachment ring main body  70  and cinching ring  86 . Pulling of rear segment  42  of clips  36 —while tips  44  of clips  36  are trapped between clamping ring  100  and clamp surface  67  ( FIG. 2D ) of main body  70 —causes clips  36  to tighten against the biological tissue. 
     The above described rotation and pulling during cinching is generally in the circumferential direction of arrow D ( FIG. 2D ). However, it will be appreciated that rotation can be in the opposite circumferential direction for other embodiments. 
     Exemplary steps for separating attachment ring  30  from applicator tool  10  are as follows. The user discontinues any suction that may have been applied to suction cup  26  ( FIG. 1E ). The user pulls disengagement knob  24  which controls movable lock elements  29  of attachment mechanism  26 . The pulling allows lock elements  29  to move and disengage internal annular groove  77  of attachment ring main body  70 . Next, the user pulls applicator tool  10  away from attachment ring main body  70 , while main body  70  remains secured by clips  36  to the biological tissue, and while clamping ring  100  and cinching ring  86  remain locked onto main body  70 . 
     Further details of applicator tool  10  are as follows.  FIG. 1B  shows clamping tube  64  removed to expose L-shaped guide slot  718  formed in cinching tube  58 .  FIG. 1C  shows clamping tube  64  and cinching tube  58  removed to expose stationary tube  720  which is fixed to clip tube  48  and grip  16 . L-shaped guide slot  722  is formed in stationary tube  720 .  FIG. 1D  shows stationary tube  720  removed to expose drive member  724 , in the shape of a worm gear or Archimedes screw, which is fixed to deployment handle  18 . Helical slot  726  is formed in drive member  724  and receives drive pin  730  ( FIGS. 1A and 1B ) coupled to clamping tube  64  and cinching tube  58 . When the user rotates handle  18 , helical slot  726  pushes drive pin  730  through guide slots  718  and  722 , which are sized and shaped to cause clamping tube  64  and cinching tube  58  to move as described above for clip deployment, clamping, and cinching. 
     Further details of attachment ring  30  are as follows. Cinching ring  86  ( FIGS. 2A and 2D ) is contained within interior space  73  of cylindrical wall  72  of main body  70 . Central through-hole  88  of cinching ring  86  is substantially centered upon axial centerline  78  of main body  70 . Peripheral through-holes  90  are formed through axial top surface  91  of cinching ring  86  and have a diameter sized to receive clips  36  ( FIG. 3A ) contained within forward segment  12  of applicator tool  10 . The passageway of the through-holes  90  intersects annular cuff  82 . Cinching feature  89  extends axially upward from top surface  91  of cinching ring  86 . During the cinching process described above, cinching feature  89  engage cinching pins  60  ( FIG. 1E ) at the forward portion of cinching tube  58  of applicator tool  10 . As shown in  FIG. 2D , ratchet catch  96 , in the form of a flexible arm, extends circumferential around and protrudes out from radially outward facing surface  94  of cinching ring  86 . At the free end of each ratchet catch  96  there is pawl  97  that protrudes axially downward and is configured to engage ratchet members  76  of attachment ring main body  70 . In use, cinching ring  86  is capable of rotating within main body  70  in only one direction. During such rotation, ratchet catch  96  bends as the ramped shape of leading edge  97 A of pawl  97  slides over and is pushed upward by ratchet member  76  of main body  70 . In the reverse direction, rear edge  97 B pawl  97  engages ratchet member  76  of main body  70  and prevents rotation of cinching ring  86  in the reverse direction. 
     As shown in  FIGS. 2A and 2D , attachment ring main body  70  includes interior cylindrical wall  732 . Internal annular groove  77  is formed into interior cylindrical wall  732  for engagement with attachment device  28  of applicator tool  10  and for subsequent engagement with a cannula. The cannula can be as described in  FIGS. 34 and 35  or any of the VAD inflow conduits described in U.S. Application Publication No. 2011/0118766 A1, which is incorporated herein for all purposes by reference. 
     Interior cylindrical wall  732  has annular lip  734  configured to retain cinching ring  86  within main body  70 . Annular lip  734  forms one side of a retention groove and includes four recesses  736 , each recess sized to receive one of four tabs  738  of cinching ring  86 . Two tabs  738  are visible in  FIG. 2D . The angular spacing between tabs  738  is the same as the angular spacing between recesses  736 . When tabs  738  and recesses  736  are aligned, tabs  738  can pass axially through recesses  736 . After tabs  738  are received into recesses  736 , rotation of cinching ring  86  causes tabs  738  to slide within the retention groove and move out of alignment relative to recesses  736 . Thereafter, annular lip  734  prevents cinching ring  86  from pulling apart from attachment ring main body  70 . The angular spacing between tabs  738  is such that with continued rotation of cinching ring  86 , only one tab  736  comes into alignment with any of recesses  736 . A complete 360-degree rotation is needed to allow realignment of all the tabs  738  and recesses  736  and to allow removal of cinching ring  86  from main body  70 . 
     Further details of clip  36  are as follows. As shown in  FIGS. 3A-3D , clip  36  has a non-uniform thickness. Central axis  39  extends axially through the center of wire body  38  which extends from sharp tip  44  to catch  46 . Wire body  38  forms a spiral or helix. Sharp tip  44  forms the point of barbed head  170 . Barbed head  170  flares radially outward from central axis  39  so that barb head  170  widens from tip  44  to base  172 . Base  172  is attached to and abuts thinner portion  40 A of forward end  40 . Base  172  is wider or thicker than thinner portion  40 A. Thinner portion  40 A of forward end  40  has thickness  173 A that is perpendicular to central axis  39  and is less than the thickness of base  172 . Base  172  can be shaped and sized to engage teeth  706  of clamping ring  100 , which inhibits or prevents tip  44  from pulling out of attachment ring  30  after clip deployment and clamping. 
     Forward end  40  of clip  36  is substantially straight so that tip  44  moves in a substantially straight path for an initial period of time after the start of clip deployment out of applicator tool  10 . The axial length of forward end  40  is selected to control the depth of clip penetration into the biological tissue. As clip deployment continues, tip  44  moves in a substantially curved direction due to the natural curvature of medial segment  174  of wire body  38 . 
     Wire body  38  includes a series of bumps  176  that protrude radially outward from central axis  39 . Although four bumps  176  are illustrated, a lesser or greater number of bumps  176  can be implemented. These bumps are designed for purpose of securing the wire body by engaging with a corresponding mating part. Thus, as an alternative or in combination with bumps  176 , other securing features such as a void or depression into clip wire body can also be used for purpose of securement. In forward segement  40 , bumps  176  may engage teeth  706  of clamping ring  100 . In rear segment  42 , bumps  176  may engage cinching ring  86  during the cinching process, and may accommodate variations in the thickness of biological tissue. In other embodiments, bumps  176  can be located on medial segment  174 . 
     As shown in  FIG. 3A , rear segment  42  includes L-bend portion  178  that is narrower or thinner than other parts of rear segment  42 . Catch  46  forms the free end of L-bend portion  178 . Other parts of rear segment  42  have thickness  173 C which is perpendicular to central axis  39  and is greater than the thickness of L-bend portion  178  and catch  46 . L-bend portion  178  and catch  36  can be formed by stamping, coining, or flattening the free end of rear segment  42  so that L-bend portion  178  and catch  46  are narrower or thinner than other parts of clip  36 . The reduced thickness of catch  46  allows it to pass through axial slot  53  ( FIG. 1E ) of clip tube  48 . Other parts of wire body  38  have thicknesses that are too large to pass through axial slot  53 . 
       FIG. 3B  shows a view of clip  36  along axis  740  substantially perpendicular to radius of curvature  742  of medial segment  174 . Radius of curvature  742  and/or length of medial segment  174  are selected to ensure that tip  44  moves to a position between clamping ring  100  and camp surface  67  of attachment ring main body  70  during clip deployment. As viewed along axis  740 , medial segment  174  forms a complete 360-degree loop. 
     As shown in  FIG. 3C , medial segment  174  includes a coil portion  744  and s-curve portion  746 . Coil portion  744  connects to forward segment  40  at line  748  and connects to s-curve portion  746  at line  750 . S-curve portion  746  is s-shaped in the sense that it includes concave downward part  746 A, concave upward part  746 C, and inflection point  746 B between parts  746 A and  746 C. S-curve portion  746  connects to rear segment  42  at line  752 . S-curve portion  746  is shaped and oriented to reduce the circumferential pulling force needed during cinching. The helix formed by the entire wire body  38  is in the same direction as cinching. Also, the helix formed by the entire wire body  38 , at its natural state shown in  FIGS. 3A-3D  before being loaded into applicator tool  10 , simulates the shape of clip  36  after clip deployment, clamping, and cinching. 
     In some embodiments, the diameter of wire body  38  can range approximately from about 0.010 inch to about 0.025 inch. The diameter of wire body  38  corresponds to thickness  173 A and  173 C described above. The diameter of bumps  176  can range approximately from about 0.030 inch to about 0.040 inch. The height of bumps  176  ranges approximately from about 0.005 inch to about 0.010 inch from base to peak. The depth of depressions into clip wire body ranges approximately from about 0.005 inch to about 0.010 inch from base to valley. The bump height or depression depth corresponds to the radial distance from the bump peak to bump base or from the diameter of the wire body to the valley of the depression. The overall length of clip  36  from tip  44  to L-bend portion  178  ranges approximately from about 0.75 inch to about 2 inch. Deployment angle (oblique angle B described above) can vary from 0 degree up to 90 degrees. 
     In some embodiments, the clip may have no bumps  176 . 
     In some embodiments, the clip may have no s-curve portion  746 . 
     In some embodiments, the clip has an alternative configuration shown in  FIG. 4 . Medial segment  174  forms a loop of less than 360 degrees. 
     In some embodiment, the clips contained within and deployed out of applicator tool  10  do not have the same length and shape. For example, some clips in one area of clip tube  48  may be longer and/or have a different curvature than other clips in another area of clip tube  48 . 
       FIGS. 5 and 6  show an applicator tool and an attachment ring according to other embodiments. Applicator tool forward end  12  is configured such that clip tube  48  is disposed within cinching tube  58 , and cinching tube  58  is disposed within clamping tube  64 . Clip grooves  52  are formed into an interior surface of clip tube  48  such that clip catch  46  points radially inward toward central axis  54 . Clip pusher surface  51  is disposed within clip tube  48 . As shown in  FIG. 6 , attachment ring  30  includes main body  70 , clamping ring  100 , and cinching ring  86 .  FIG. 7  shows applicator tool forward end  12  engaged to attachment ring  30  at the start of clip deployment. Attachment ring  30  is disposed over biological tissue  110 . Biological tissue  110  can be any hollow organ or other anatomical structure to which a conduit, graft, cannula, or similar structure is to be coupled. For example, when preparing the heart for attachment with a VAD, biological tissue  110  can be myocardium at the ventricular apex of the heart. 
       FIG. 8  shows the result of forward axial movement of clip pusher surface  51  at the conclusion of clip deployment. Tip  44  of clip  36  is disposed between clamping ring  100  and base  74  of attachment ring main body  70 . While clip pusher surface  51  pushes catch  46  of clip  36 , tip  44  pierces and enters biological tissue  110 , wire body  38  of clip  36  bends outward away from the center of attachment ring  30 . The bending occurs due to a natural tendency of wire body  38  to return to its original shape prior to being loaded in a straight configuration within the applicator tool. In various embodiments, the clip is constrained in the straight configuration by the inner walls of the applicator tool in which it is loaded. Tip  44  follows a curved path. In various embodiments, the curved path has a generally uniform radius of curvature along its length. In various embodiments, the curved path has a compound or complex curvature. In various embodiments, the tip is pre-disposed to move to a curved shape configured to promote insertion through the attachment ring and/or biological tissue. Tip  44  passes out from a first point  114  on interior surface  116  of biological tissue  110 , and reenters at a second point  118  on interior surface  116  at a distance away from first point  114 . Tip  44  continues up and out of top surface  120  of biological tissue  110  and enters clamp gap  105  between base  74  and clamping ring  100 . 
       FIG. 9  shows the result of forward axial movement of clamping tube  64  at the conclusion of clip clamping. Tip  44  of clip  36  is trapped between clamping ring  100  and base  74  of attachment ring main body  70 . Forward segment  40  of clips  36  are prevented from pulling back into biological tissue  110 . 
     Due to curvature, thickness, and/or density of biological tissue  110  or due to other factors, there may be some slack or excess length of clip  36  below biological tissue  110 . The slack or excess length of clip  36  is evident, for example, by gap  122  between wire body  38  and interior surface  116  of biological tissue  110 . 
       FIG. 10  shows the result of rearward axial movement of cinching tube  58  at the conclusion of cinching. The slack is taken out by cinching clips  36  against interior surface  116  of biological tissue  110 . Cinching ring  86  has been moved axially relative to attachment ring main body  70  and further separated from base  74  of main body  70 . Cinching ring  86  is locked in position by ratchet members  76  which hold ratchet catch  96  on cinching ring  86 . As cinching ring  86  moves upward, ratchet catch  96  engages ratchet members  76  on cylindrical wall  72 . After cinching, applicator tool forward end  12  is detached from attachment ring  30 . 
     As shown in  FIG. 11 , after removing applicator tool forward end  12 , clamp  130  can be secured onto attachment ring  30  to stabilize the position of attachment ring  30  and underlying biological tissue  110 . Valvular structure  140  is attached to top end  34  of attachment ring  30  so that there is a substantially liquid-tight seal between valvular structure  140  and attachment ring  30 . The liquid-tight seal can be accomplished with a press-fit, a resilient gasket, helical screw threads, interlocking/mating features, mechanical fasters or a combination thereof on either one or both of valvular structure  140  and top end  34  of attachment ring  30 . 
     Installation of valvular structure  140  allows an incision to be made in biological tissue  110  through attachment ring  30  without extensive loss of body fluid from the incision. For example, when preparing the heart for attachment with a VAD, valvular structure  140  prevents significant loss of blood and thus allows an incision to be made in the ventricular apex of the heart while the heart is beating and without the use of a heart-lung bypass machine. Depending on the type of surgical procedure and anatomical structure on which attachment ring  30  is anchored, it may not be desired or necessary to place valvular structure  140  on attachment ring  30 . For example, placement of valvular structure  140  need not be placed on attachment ring  30  when preparing the heart for attachment with a VAD while the patient is connected to a heart-lung bypass machine. 
     Referring to  FIGS. 11-13 , valvular structure  140  includes a housing  142 , seal  144 , and valve  146 . Seal  144  and valve  146  are elastic and are configured to bend in response to passage of instrument  150  through them and to autonomously return to their original shape after instrument  150  is withdrawn. Seal  144  and valve  146  can be made of silicone rubber, polyurethane or other blood compatible polymers with elastic resiliency known in the art. Instrument  150  can be a slitting tool in one instance and a coring knife in a later instance. Suitable slitting tools and coring knives for use with attachment ring  30  and valvular structure  140  include without limitation the slitting tools and coring knives described in U.S. Application Publication No. 2011/0118766 A1, which is incorporated herein for all purposes by reference. 
     Annular seal  144  is attached to housing  142  and has a circular seal opening  148  substantially centered upon axial centerline  78  of attachment ring  30 . Seal opening  148  is sized smaller than the outer diameter of instrument  150 . As instrument  150  is passed through seal opening  148 , a substantially liquid-tight seal is formed between the exterior surface of instrument  150  and annular seal  144 , which prevents flow of body fluid therebetween. 
     Valve  146  is attached to housing  142  and is movable to and from a closed configuration ( FIGS. 9 and 11 ) and an open configuration ( FIG. 10 ). In the closed configuration, valve  146  provides a liquid-tight seal and substantially prevents flow of body fluid past valve  146  in the distal direction indicated by arrow  152 . Valve  146  is a quadcuspid (i.e., four-leaflet) valve similar in configuration and function to quadcuspid valves described in U.S. Application Publication No. 2011/0118766 A1, which is incorporated herein for all purposes by reference. Valve  146  includes flexible members  154  configured to flex open in response to insertion instrument  150  and to close autonomously ( FIG. 11 ), due to elastic resiliency of flexible members  154 , upon removal of instrument  150 . 
     In other embodiments, the valve of valvular structure  140  can be a tricuspid valve (similar to U.S. Application Publication No. 2011/0118766 A1, FIG. 14a), a bicuspid valve (similar to FIG. 15a of U.S. U.S. Application Publication No. 2011/0118766 A1), a dome valve, a diaphragm valve (similar to U.S. U.S. Application Publication No. 2011/0118766 A1, FIG. 15f), and combinations thereof, the entire contents of which publications are incorporated herein for all purposes by reference. 
     As shown in  FIG. 13 , instrument  150  has made a circular through-hole  156  in biological tissue  110 . Any body liquid beneath biological tissue  110  is substantially prevented by valve  146  from flowing out of valvular structure  140 . 
     Referring to  FIG. 14 , cannula  158 , or other tubular structure, can be inserted through valvular structure  140 , attachment ring  30 , and through-hole  156  in biological tissue  110 . Cannula  158  is a type of prosthesis suitable for implantation within a human or animal body. Cannula  158  includes tube body  160 , securement member  162  on tube body  160 , and a removable plug  164  within tube body  160 . As tube body  160  is passed through seal opening  148  ( FIG. 11 ), a substantially liquid-tight seal is formed between the exterior surface of tube body  160  and annular seal  144 , which prevents flow of body fluid therebetween. Plug  164  temporarily prevents any body liquid from escaping. When preparing a patient&#39;s heart for attachment with a VAD, cannula  158  can be any of the VAD inflow conduits described in U.S. Application Publication No. 2011/0118766 A1, which is incorporated herein for all purposes by reference. Plug  164  need not be present when escape of body fluid is not a concern, such as when the patient is connected to a heart-lung bypass machine during preparation for attachment with a VAD. 
     Referring to  FIG. 13 , after installation of cannula  158 , valvular structure  140  can be removed from attachment ring  30  by dismantling or opening housing  142  of valvular structure  140 . Valvular structure  140  includes a housing first portion and a housing second portion that are configured to be selectively locked together and moved apart from each other. The first housing portion is connected to the second housing portion by a slide member that locks the housing first portion and the housing second portion together. Valvular structure  140  can by any of the valvular structures described in U.S. Application Publication No. 2011/0118766 A1 (for example, FIGS. 10A-11C, 40G, 56A-56D and FIGS. 57A-57D), which is incorporated herein for all purposes by reference. 
     After the valvular structure  140  is removed from attachment ring  30 , cannula  158  is pushed down until it contacts attachment ring  30 . Securement member  162  is secured to attachment ring  30  so as to form a liquid-tight seal with attachment ring  30 . Attachment can be accomplished with a press-fit, a resilient gasket, helical screw threads, interlocking/mating features, mechanical fasters or a combination thereof on either one or both of securement member  162  and attachment ring  30 . After attachment of securement member  162  on attachment ring  30 , plug  164  can be removed and fluid conduit  166  can be attached to cannula  158  by any suitable method. Examples of suitable methods include clamping, suturing, helical screw threads, interlocking/mating features, mechanical fasters or a combination thereof. Fluid conduit  166  can be a vascular graft, an anatomical lumen, a fluid connection to a VAD, or other tubular structure depending on the type of surgical procedure being performed. 
       FIGS. 16-27  show exemplary applicator tool  310  for anchoring attachment ring  500  of  FIGS. 28-30  to biological tissue. Attachment ring  500  is a type of prosthesis suitable for implantation within a human or animal body. Applicator tool  310  includes forward segment  312  and rear segment  314 . Forward segment  312  is configured to carry attachment ring  500  to a desired location on biological tissue. Rear segment  314  includes grip  316  and contains various controls to be manipulated by a person. Axial center line  315  extends axially through the center of forward segment  312 . 
     As used in connection with applicator tool  310 , “forward direction” is a direction generally parallel to arrow  317  on axial center line  315 , “rearward direction” is a direction generally parallel to arrow  319  on axial center line  315 , and “radial direction” is a direction generally perpendicular to axial center line  315 . 
     When a user actuates deployment handle  318 , clips  36  are pushed out of applicator tool  310  and into attachment ring  500  and biological tissue. Due to shape memory and/or elasticity of clips  36 , tip  44  of each clip follows a loop or curved trajectory in which tip  44  initially travels in a forward direction, then away from attachment ring  500 , and then returns toward attachment ring  500 . Continuous actuation of deployment handle  318  moves clamp pusher  326  in a forward direction within forward segment  312  of applicator tool  310  for pushing each clip out of the applicator tool  310 . When moved forward, clamp pusher  326  (also referred to as a clamping tube) causes a portion of attachment ring  500  to clamp down on and/or trap tips  44  of clips  36 . 
     After tips  44  of clip  36  are trapped within attachment ring  500  and when the user actuates cinching handle  322 , catch  46  of all clips  36  are pulled by applicator tool  310  in a rearward direction away from attachment ring  500 , causing clips  36  to cinch or to tighten whereby any slack or excess length of clips  36  below biological tissue is reduced. 
     In other embodiments, the clips  36  are cinched by pulling catch  46  in a circumferential direction within attachment ring  500  instead of pulling catch  46  in a rearward, vertical direction away from attachment ring  500 . 
     After clips  36  are cinched or tightened, the user actuates disengagement knob  324 . As a result, connector mechanism  328  is moved to an unlocked position which allows applicator tool  310  and attachment ring  500  to disengage and be pulled apart from each other. After disengagement, attachment ring  500  remains attached to biological tissue by clips  36 . 
     As indicated above, applicator tool  310  is used to carry attachment ring  500  to a desired location on biological tissue.  FIGS. 16-20  show applicator tool  310  without attachment ring  500 .  FIGS. 21-26  show applicator tool  310  with attachment ring  500 . 
     As shown in the dissembled view of  FIG. 28 , attachment ring  500  comprises flexible cuff  502 , bottom mount  504  (also called a base), main body  506  (also called a ring body), top plate  508  (also called a cinch plate), and clamping ring  510 . Flexible cuff  502 , bottom mount  504 , main body  506 , top plate  508 , and clamping ring  510  are each ring-shaped and are, in some embodiments, rotationally symmetrical about axial centerline  511 . When assembled for use with applicator tool  310 , cuff has been secured to mount  504  with sutures, adhesive and/or other attachment methods known in the art. Also, bottom mount  504 , main body  506  and top plate  508  have been secured to each other with screws, mechanical clips, adhesive and/or other attachment methods known in the art. In some embodiments, at least bottom mount  504  and/or top plate  508  are an integral part of main body  506 . Cuff  502 , mount  504 , main body  506 , and top plate  506  collectively form ring assembly  512 . 
     During use within a patient, connector mechanism  328  ( FIG. 21 ) of applicator tool  310  retains ring assembly  512  while clamp pusher  326  ( FIG. 21 ) pushes clamping ring  510  onto ring assembly  512 . Clamping ring  510  includes a plurality of cantilevered and flexible arms  516 . Ramped catch members  514  protrude radially inward from flexible arms  516  and are configured to enter into and engage lock feature  518  on an exterior surface  520  of main body  506 . Lock feature  518  is in the form of a depression or recess in exterior surface  520 . 
       FIGS. 17 and 18  show applicator tool  310  with connector mechanism  328  in an unlocked position.  FIG. 19  shows applicator tool  310  illustrated without connector mechanism  328  to more clearly show other components of applicator tool  310 .  FIGS. 20-27  show a partial cross-sectional view of forward segment  312  of applicator tool  310 , with only the structures above axial center line  315  shown for ease of illustration. Forward segment  312  is substantially symmetrical about axial center line  315 . It is to be understood that that structures below axial center line  315 , are present although not illustrated or shown, are substantially the same as the structures above axial center line  315 . 
     Features of connector mechanism  328  are shown in  FIGS. 18 and 20 . A plurality of first lock elements  406  are carried within connector ring  400  of connector mechanism  328 . Second lock element  410  is controlled by disengagement knob  324  ( FIG. 16 ) and causes first lock elements  406  to move from a disengaged position ( FIG. 20 ), in which the first lock element is contained entirely within connector ring  400 , to an engaged position ( FIG. 21 ), in which first lock element protrudes out of connector ring  400 . When in the engagement position, first lock elements  406  retain ring assembly  512  onto applicator tool  510 . 
     As described below, a method for connecting a conduit to tissue can include (1) mounting attachment ring  500  to applicator tool  310 ; (2) moving applicator tool  310  with the mounted attachment ring  500  to place attachment ring  500  in contact with biological tissue; (3) deploying clips  36  out of applicator tool  310  and through both attachment ring  500  and biological tissue; (4) clamping and/or trapping tips  44  of clips  36  after penetration through the biological tissue on attachment ring  500 ; (5) cinching clips  36  by pulling catch  46  of clips  36  away from attachment ring  500  and biological tissue; (6) releasing clips  36  from applicator tool  310 ; and (7) releasing attachment ring  500  from applicator tool  310 . 
       FIG. 21  shows attachment ring  500  mounted to forward segment  312  of applicator tool  310  and placed in contact with top surface  120  biological tissue. Connector mechanism  328  temporarily retains ring assembly  512  of attachment ring  500 . Second lock element  410  keeps first lock element  406  at the engaged position so that first lock element  406  protrudes into and engages internal annular groove  521  ( FIGS. 28 and 29 ) formed in an interior surface of ring assembly  512 . Clamping ring  510  of attachment ring  500  is temporarily retained at a location adjacent clamp pusher  326 . Applicator tool  310  is positioned by the user so that cuff  502  and suction cap  416  make contact with top surface  120  of biological tissue. 
     Suction cap  416  is configured to maintain suction over top surface  120  of biological tissue. Suction cap  416  is tubular in shape and comprises forward end  418  and rear end  420 . Rear end  420  is slideably coupled to applicator tool body  311 . Suction cap  416  contains resilient O-ring gasket  422  adjacent rear end  420 . O-ring gasket  422  maintains a substantially fluid-tight seal between suction cap  416  and applicator tool body  311 . In use, forward end  418  of suction cap  416  is placed over the surface  120  of a target site on the biological tissue, then the user can apply a vacuum or suction through hollow shaft  402  to prevent relative movement between the biological tissue and the cuff  502  of attachment ring  500  during deployment of clips  36  into the biological tissue. To accommodate a variety of possible curvatures in the biological tissue, the user may slide suction cap  416  in a forward or rearward direction relative to applicator tool body  311  so that cuff  502  of attachment ring  500  and forward end  418  of suction cap  416  simultaneously contact top surface  120  of biological tissue. 
     Suction cap  416  ensures the good contact between the applicator tool and the biological tissue. Suction cap  416  ensures that the deployment site is clear of external elements. Suction cap  416  deforms the tissue to more ideal deployment shape. Suction cap  416  reduces the movement of the tissue relative to the applicator tool. 
     Still referring to  FIG. 21 , clip  36  is contained in clip holder  347  of clip tube  348 . Although one clip is illustrated, clip tube  348  can include any number of clip holders  347  and clips  36 . Clip holder  347  includes clip groove  352  having axial slot opening  353  and bottom portion  380 . Catch  46  of clip  36  protrudes out of axial slot opening  353 . The remainder of clip  36  is retained in bottom portion  380  of clip groove  352  since axial slot opening  353  is narrower in width than clip  36  except for catch  46 . Clip pusher surface  351  abuts catch  46 . 
       FIG. 22  shows clip  36  deployed out of the forward opening of clip groove  352  after catch  46  of clip  36  has been pushed in a forward direction by clip pusher surface  351 . Barbed head  170  of clip  36  has passed through ring assembly  512 , into and out of biological tissue, and onto clamp surface  522  of ring assembly  512 . Clip  36  extends through peripheral through-hole  530  formed into top plate  508  of ring assembly  512 . 
       FIG. 23  shows tip  44  of clip  36  clamped and/or trapped by attachment ring  500  after clamping ring  510  has been pushed from its initial position ( FIG. 24 ) by clamp pusher  326 . Tip  44  is retained between clamping ring  510  and clamp surface  522  of attachment ring  500 . Forward segment  40  of clip  36  passes through one of the plurality of grooves  524  ( FIG. 28 ) formed in a forward facing surface of clamping ring  510 . Grooves  524  are at least as wide as forward segment  40  of clip  36  and are narrower in width than base  172  ( FIG. 20 ) of barbed head  170  on clip  36 . Ridges  526  ( FIG. 28 ) on each side of groove  524  engage base  172  of clip  36 . In some embodiments, attachment ring  500 ′ ( FIG. 30 ) has no grooves  524 , and tip  44  is retained by other types of grooves, by pressure and/or by other features. 
     In some embodiments, clamp surface  522  includes annular groove  528  ( FIG. 28 ) configured to engage base  172  of barbed head  170  on clip  36 . In other embodiments, clamp surface  522  includes a plurality of concentric annular grooves  528  ( FIG. 30 ). 
       FIG. 24  shows clip  36  after it has been cinched or tightened. Catch  46  of clip  36  has been pulled in a rearward direction while tip  44  of clip  36  is trapped within attachment ring  500 . Catch  46  is pulled rearward by cinching ring  444  which is fixedly attached to or is an integral part of clip tube  348 . 
       FIG. 25  shows clip  36  after it has been released from applicator tool  310 . Movable barrier  327  has moved in a rearward direction away from cinching ring  444  so as to uncover the exit opening of radial cut  448  formed through cinching ring  444 . Due to its shape memory and/or elasticity, clip  36  has a natural tendency to autonomously move to a curved configuration from a straight configuration. Thus, when movable barrier  327  moves away from exit opening of radial cut  448 , the shape memory and/or elasticity causes rear segment  42  and catch  46  of clip  36  autonomously pass out of the exit opening of radial cut  448  and become detached from applicator tool  310 . The ability of clip  36  to pass out of radial cut  448  is evident from  FIG. 19  in which movable barrier  327  is absent from the illustration. After its release, the rear segment of clip  36  is prevented by top plate  508  from moving in toward top surface  120  of biological tissue. Top plate  508  engages bumps  176  of clip  36 . 
     After cinching and release of clip  36  and in order to prevent subsequent loosening of clip  36 , engagement between attachment ring  500  and bumps  176  of clip  36  can be the result of (1) the shape memory and/or elasticity of clip  36 , (2) one or more elements within attachment ring  500 , or (3) a combination thereof. 
     In  FIG. 29  peripheral through-holes  530  of top plate  508  are key-hole in shape. As shown in  FIG. 29 , key-hole shaped through-holes  530  have wide area  530   a  and narrow area  530   b . Wide area  530  is sized to receive barbed head  170  and bumps  176  of clip  36 . Bumps  176  are unable to pass through narrow area  530   a . Narrow area  530   a  is sized to receive wire body  38  ( FIGS. 3A and 4 ) of clip  36 . In some embodiments, the shape memory and/or elasticity of clip  36  causes clip medial segment  174  ( FIGS. 3A  and  4 ) to bend autonomously and move from wide area  530   a  toward narrow area  530   b  of through-holes  530 . This movement helps bumps  176  engage top plate  508  of attachment ring  500  and prevent clip  36  from loosening after being cinched. Attachment ring  500  includes chamber  532  ( FIG. 28 ) enclosed by top plate  508  and main body  506 . Chamber  532  can be sized to allow clip  36  to bend autonomously after being released from applicator tool  310  so that bumps  176  engage top plate  508 . 
     In  FIG. 30 , attachment ring  500 ′ can include annular element  534  that is movable within annular chamber  532  of main body  506  for preventing loosening of clip  36  after the clip is cinched. Compression spring  536  is disposed between movable element  534  and post  538  of main body  506 . Spring  536  pushes and biases movable element  534  to move toward an engaged orientation at which movable element  534  restricts a passageway through which clip  36  passes when clip  36  is deployed through attachment ring  500 ′. Though one spring  536  and post  538  is illustrated, there can be a plurality of springs and posts to provide a greater amount of force on movable element  534 . At the engaged orientation, movable element  534  limits bumps  176  of clip  36  to one-way movement through the restricted passageway. At the engaged orientation, movable element  534  allows movement of bumps  176  in a rearward direction (away from the biological tissue) during cinching of clip  36  by applicator tool  310 , and prevents movement of bumps  176  in a forward direction (toward the biological tissue) after release of clip  36  from applicator tool  310 . Element  534  includes a plurality of leaf springs  540 . The one-way movement is provided by leaf springs  540  which restrict the clip passageway. Each clip  36  is acted upon by one leaf spring  540 . Each leaf spring  540  abuts a surface of chamber  532  in main body  506 . Each leaf spring  540  is configured to move in a rearward direction and is prevented from moving in a forward direction due to contact with main body  506 . Prior to and during deployment of clip  36  through attachment ring  500 ′, movable element  534  is held in a disengaged orientation at which movable element  534  does not restrict the passageway through which clip  36  passes. Movable element  534  is held in the disengaged orientation, against spring  536 , by restraining pins that pass through axial apertures  542  in top plate  508 . The restraining pins abut and keep movable element  534  in the disengaged orientation until the restraining pins are pulled out of axial apertures  542 . In some embodiments, the restraining pins can be fixedly attached to or form an integral part of clip tube  348  of applicator tool  310 . Restraining pins are pulled out of axial apertures  542  when clip tube  348  is retracted in a rearward direction during the process of cinching of clip  36  (such as in  FIG. 24 ), thereby allowing movable element  534  to move to its engaged orientation before clip  36  is released from applicator tool  310 . 
       FIG. 26  shows connector mechanism  328  of applicator tool  310  in an unlocked position after a user has pulled disengagement knob  324  ( FIG. 17 ) in a rearward direction. Second lock element  410  has moved out of axial aperture  408 , which allows first lock element  406  to move to its disengaged position ( FIG. 26 ) from its engaged position ( FIG. 25 ). With first lock element  406  is at its disengaged position, forward segment  312  of applicator tool  310  can be lifted away from attachment ring  500  and top surface  120  of biological tissue, as shown in  FIG. 27 . 
     After applicator tool  310  is separated from attachment ring  500 , the method can proceed in the same or similar manner as was described in connection with  FIGS. 11-15 . For example, the method can include: temporarily mounting valvular structure  140  on attachment ring  500 ; using instrument  150  to make a circular through-hole in biological tissue; inserting cannula  158 , or other tubular structure, through valvular structure  140 , attachment ring  500 , and the through-hole in biological tissue; and attaching fluid conduit  166  to cannula  158 . 
     The valvular structure in the above describe methods can be as shown in  FIGS. 31-33 . Alternative valvular structure  550  of  FIGS. 31-33  is configured to perform the same or similar function as valvular structure  140  of  FIGS. 11-14 . Alternative valvular structure  550  is configured to receive instrument  150  of  FIG. 12 . Alternative valvular structure  550  includes an integrated handle  552 , so clamp  130  of  FIG. 11  is not necessary to hold alternative valvular structure  550 . Handle  552  is fixedly attached to housing  554 . Housing  554  includes housing first portion  556  and housing second portion  558  that are configured to be selectively locked together and moved apart from each other. First housing portion  556  is temporarily connected to second housing portion  558  by movable lock members  560 . Lock members  560  have a locked orientation in which lock members  560  keep first housing portion  556  and second housing portion  558  in fluid-tight sealing engagement with each other. A user may move lock members  560  to an unlocked orientation in which first housing portion  556  and second housing portion  558  can be disengaged from other. Housing  554  contains valve  562 , which can have the same or similar configuration as valve  154  of  FIG. 11 . Valve  562  can have the same or similar configuration as quadcuspid valves, bicuspid valves, dome valve, or diaphragm valve described in U.S. Application Publication No. 2011/0118766 A1. 
     As shown in  FIG. 32 , the bottom or forward edge  567  of housing  554  includes a plurality of L-shaped hook members  564  configured to enter and engage elongate slots  544  ( FIGS. 28-30 ) in top plate  508  of attachment ring  500  and  500 ′. After hook members  564  enter elongate slots  544 , rotation of housing  554  about its central axis  555  causes hook members  564  to engage top plate  508  and thereby lock alternative valvular structure  550  onto the attachment ring  500  or  500 ′. Subsequent rotation of housing  554  in the opposite direction allows causes hook members  564  to disengage top plate  508  and thereby allow valvular structure  550  to detach from attachment ring  500  or  500 ′. 
     As shown in  FIG. 32 , the bottom or forward edge  567  of housing  554  includes a plurality of movable lock pins  566  configured to engage lock recesses  546  ( FIGS. 28-30 ) in top plate  508  of attachment ring  500  and  500 ′. When housing  554  is rotated about its central axis  555 , lock pins  566  enter lock recesses  546  when hook members  564  have engaged top plate  508 . With lock pins  566  in lock recesses  546 , rotation of housing  554  in the opposite direction is prevented, which also prevents alternative valvular structure  550  from detaching from attachment ring  500  or  500 ′. Lock pins  566  are spring-loaded or biased to axially protrude in a forward direction from circular edge  567  of housing  554 . Lock pins  566  are coupled to release handles  568 . When a user moves release handles  568  in a rearward direction, lock pins  566  move in a rearward direction out of lock recesses  546  of attachment ring  500 . When lock pins  566  are pulled out of lock recesses  546 , the user may rotate housing  554  in the opposite direction and then detach valvular structure  550  from attachment ring  500  or  500 ′. 
     The cannula in the above describe methods can be as shown in  FIGS. 34 and 35 . Cannula  600  of  FIGS. 34 and 35  is configured to perform the same or similar function as cannula  158  of  FIGS. 14 and 15 . Cannula  600  is a type of prosthesis suitable for implantation within a human or animal body. Cannula  600  can be, in some embodiments, a conduit of a ventricular assist device. Front end  602  of cannula  600  can be inserted through valve  562  ( FIG. 31 ) of valvular structure  550 , then into attachment ring  30 ,  500  or  500 ′, and then into circular through-hole in biological tissue. Thereafter, a conduit can be secured to rear end  604  of cannula  600 . 
     Cannula  600  includes tubular cannula body  606 , first lock members  608  in the form of a sphere, ring  609  containing first lock members  608 , second lock member  610  in the form of a sleeve, cover sleeve  612 , and control member  614  in the form of a rotatable knob. Cannula body  606  includes a non-porous inner surface that defines central fluid passageway  620  from front end  602  to rear end  604 . Central axis  622  extends through the center of fluid passageway  620 . Each of first lock members  608 , ring  609 , second lock member  610 , cover sleeve  612 , and control member  614  extends around central axis  622  and is attached to cannula body  606  at a location outside central fluid passageway  620 . Control member  614  and cannula body  606  each have helical threads that mate with each other to allow control member  612  to be selectively positioned in either an axially forward position or an axially rearward position. Control member  614  is illustrated in its rearward position. 
     First coil spring  616  is contained within a cavity between second lock member  610  and cover sleeve  612 . First coil spring  616  pushes cover sleeve  612  in a forward direction toward front end  602 , so that cover sleeve  612  covers first lock member  508 . Cover sleeve  612  is illustrated in a retracted position after it has been moved in a rearward direction toward rear and  604 , so that first lock members  508  are exposed. 
     Second coil spring  618  is contained within a cavity between second lock member  610  and control member  614 . Second coil spring  618  pushes second lock member  610  in a forward direction toward front end  602 , so that second lock member  610  is in a lock position between first lock members  608  and cannula body  606 . When second lock member  610  is in the lock position, first lock members  608  are forced radially outward through apertures in ring  609 . Second lock member  610  is illustrated in a retracted position after it has been moved in a rearward direction, which allows first lock members  608  to move radially inward. 
     At the start of the process of mounting cannula  600  onto attachment ring  30 ,  500  or  500 ′, cannula  600  can be held such that second lock member  610  is in its retracted position. For example and not limitation, cannula  600  can be held with a mounting clamp (not illustrated) which pulls second lock member  610  toward control member  614 . 
     While forward end  602  of cannula  600  is moved in a forward direction and enters valvular structure  550 , cover sleeve  612  passes through valve  562  and annular gasket  570  ( FIG. 33 ). In some embodiments, annular gasket  570  is configured to provide a fluid-tight seal against the outer surface of cover sleeve  612  and/or against top plate  508  of attachment ring  500  or  500 ′ and/or Interior cylindrical wall  732  ( FIG. 2A ) of attachment ring main body  70 . 
     While forward end  602  of cannula  600  is moved in a forward direction and enters attachment ring  30 ,  500  or  500 ′, cover sleeve  612  abuts top plate  508  ( FIGS. 29 and 30 ) and is pushed rearward to its retracted position, so that first lock members  608  become exposed. With second lock member  610  at its retracted position, first lock members  608  are allowed to move radially inward. When they move radially inward, first lock members  608  are able to travel past top plate  508  ( FIGS. 29 and 30 ) of attachment ring  500  or  500 ′ or cinching ring  86  ( FIG. 2A ) of attachment ring  30 , then enter annular groove  521  ( FIGS. 30 and 31 ) or  77  ( FIG. 2A ) of the attachment ring. Thereafter, second lock member  610  can be released, such as by removing a mounting clamp (not illustrated), so that second coil spring  618  pushes second lock member  610  into the cavity between first lock members  608  and cannula body  606 . First lock members  608  are pushed radially outward and become engaged within annular groove  521  ( FIGS. 30 and 31 ) or  77  ( FIG. 2A ) of the attachment ring, which prevents cannula  550  from separating from the attachment ring. To prevent second lock member  610  from retracting or moving rearward, the user can rotate control member  614  to its forward position where it presses against second lock member  610 . 
     O-ring seal  624  is attached to ring  609  and faces radially outward. O-ring seal  624  is made of an elastic material and is sized and shaped to form a fluid-tight seal with an inner surface of main body  506  ( FIGS. 30 and 31 ) or  70  ( FIG. 2A ) of the attachment ring. After attachment ring  30 ,  500  or  500 ′ is secured to biological tissue, the fluid-tight seal substantially prevents a body fluid such as blood from leaking out between cannula  600  and the attachment ring. 
     While several particular forms of the invention have been illustrated and described, it will also be apparent that various modifications can be made without departing from the scope of the invention. It is also contemplated that various combinations or subcombinations of the specific features and aspects of the disclosed embodiments can be combined with or substituted for one another in order to form varying modes of the invention. Accordingly, it is not intended that the invention be limited, except as by the appended claims.