Patent Publication Number: US-2007123917-A1

Title: Anastomotic device promoting tissue necrosis

Description:
FIELD OF THE INVENTION  
      The invention relates broadly to an anastomosis device, and more particularly to an anastomosis device formed from a woven tube of shape-memory wire where, when deployed, the anastomosis device can hold tissues of an anastomotic site in apposition.  
     BACKGROUND OF THE INVENTION  
      During many surgical procedures, the surgeon will have to close or ligate various blood vessels and other ducts before severing them in order to prevent excessive bleeding, and reduce the risk of other complications to the patient. One ligation technique is to tie a suture about the vessel to close the vessel. Alternatively, a surgeon can place a clip having a pair of legs connected at their proximal ends about the vessel, and urge or squeeze the legs together to close the vessel.  
      One drawback associated with some current clips used for ligating vessels is that the legs of the clip may tend to separate to some extent following release from a clip applier. This phenomenon is called duck-billing. Duck-billing can result in insufficient ligation of a vessel, thus leading to excessive blood loss and/or unnecessary damage to the vessel. Further, some known ligation clips are often difficult to preload into a clip applier because of resistance between the tissue disposed between the jaws and the gripping features on the clip legs.  
      Accordingly, there remains a need for an improved surgical instrument and method, and in particular for surgical clips used for ligating blood vessels, other ducts, and the like.  
     BRIEF SUMMARY OF THE INVENTION  
      Embodiments of the present invention generally provide anastomosis devices for securing layers of tissue, such as the walls of a small intestine and an upper stomach pouch, in apposition. An anastomosis device, in one embodiment of the invention, generally includes a body that can be formed from a woven shape-memory wire having a central lumen. The body can be configurable between an expanded position, in which the body can assume a generally tubular configuration having a wire mesh wall adapted for insertion into a lumen of an anastomotic site, and a rest position, in which the body can assume an annular configuration having a plurality of petals with petal tips that define an outer periphery. The rest position is effective to hold opposed tissues of the anastomotic site in apposition and can apply a pressure to the opposed tissues such that the pressure decreases from an outer periphery to an inner periphery of the device. The plurality of petals can be configured to apply the pressure to the opposed tissues to cause necrosis of the opposed tissues in a contact region, such as a region about the outer periphery of the device. In one embodiment, in the rest position, the tips of the petals are adapted to contact the opposed tissues along a distance greater than approximately 5% of the circumference of the outer periphery of the device.  
      In one embodiment of the anastomosis device, the plurality of petals can include a superior set of adjacent petals and an inferior set of adjacent petals where the device is adapted to receive the opposed tissues between the inferior and superior sets of petals. In a rest position, each petal of the superior set and inferior set of adjacent petals can be formed by adjacent arms connected by a tip that extends along a portion of the outer periphery of the device. Each petal tip can have a first radius and each arm can be connected to the tip at a bend having a second radius, where the first radius is greater than the second radius. The tips of the superior set of adjacent petals have midpoints that can be staggered about a circumference of the device relative to midpoints of the tips of the inferior set of adjacent petals or that can be substantially aligned with midpoints of the tips of the inferior set of adjacent petals.  
      The superior and inferior petals of the device can be configured with a variety of geometries. In one embodiment, when the device is configured in the rest position, the adjacent arms and tip of each petal can be oriented in a substantially planar configuration in a plane that is substantially perpendicular to a central axis extending through the central lumen of the device. In another embodiment, the adjacent arms of each petal can be oriented in a plane that is substantially perpendicular to a central axis extending through the central lumen of the device where at least a portion of the adjacent arms of the superior set of petals include an arc portion having an inferior facing opening, and at least a portion of the adjacent arms of the inferior set of petals include an arc portion having a superior facing opening. The adjacent arms of the superior set of petals can include a bend portion disposed between the arc portion and the tip that can orient the tip in the plane that is substantially perpendicular to a central axis extending through the central lumen of the device and the adjacent arms of the inferior set of petals can include a bend portion disposed between the arc portion and the tip. The bend portion of the adjacent arms can orient the tip in the plane that is substantially perpendicular to a central axis extending through the central lumen of the device. In yet another embodiment, the tip of each petal can have a peak portion that defines an inferior facing opening and a trough portion that defines a superior facing opening.  
      In another embodiment, the anastomosis device can include a first wire circumferentially coupled to the petal tips of the superior set of adjacent petals and a second wire circumferentially coupled to the petal tips of the inferior set of adjacent petals. When the device is configured in the rest position, the first wire and the second wire can contact the opposed tissues along a distance greater than approximately 90% of the circumference of the outer periphery of the device.  
      Methods for coupling tissue layers are also provided. In one embodiment, the method can include delivering an anastomosis device, formed from a woven shape-memory wire having a wire mesh wall defining a central lumen and configured in an expanded, tubular position, through a lumen defined by two opposed tissues. The method can also include deploying the anastomosis device to hold the opposed tissues in apposition such that, upon deployment, the device assumes an annular configuration having a plurality of petals with petal tips that define an outer periphery. As so deployed, the device is effective to apply a pressure to the opposed tissues such that the pressure decreases from the outer periphery to an inner periphery of the device.  
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The invention will be more fully understood from the following detailed description taken in conjunction with the accompanying drawings, in which:  
       FIG. 1  is a top view of a prior art anastomosis device shown in a deployed state;  
       FIG. 2  is a side view of one embodiment of a tissue-necrosing type anastomosis device in an expanded elongate tubular configuration;  
       FIG. 3A . is a top view of one embodiment of a tissue-necrosing type anastomosis device in a deployed state having staggered petals with non-overlapping tips;  
       FIG. 3B  is a side view of the anastomosis device of  FIG. 3A ;  
       FIG. 3C  is a perspective view of the anastomosis device of  FIG. 3A  having a tissue material disposed between a portion of the opposed petals;  
       FIG. 4A  is a top view of one embodiment of a tissue-necrosing type anastomosis device in a deployed state having staggered overlapping petals;  
       FIG. 4B  is a side view of the tissue-necrosing type anastomosis device of  FIG. 4A ;  
       FIG. 4C  is a perspective view of the embodiment of the tissue-necrosing type anastomosis device of  FIG. 4A  having a tissue material disposed between a portion of the opposed petals;  
       FIG. 4D  is a side view of another embodiment of the tissue-necrosing type anastomosis device of  FIG. 4A ;  
       FIG. 5A  is a top view of one embodiment of a tissue-necrosing type anastomosis device in a deployed state having staggered overlapping petals;  
       FIG. 5B  is a side view of the anastomosis device of  FIG. 5A ;  
       FIG. 5C  is a perspective view of the anastomosis device of  FIG. 5A  having a tissue material disposed between a portion of the opposed petals;  
       FIG. 6A  is one embodiment of a tissue-necrosing type anastomosis device in a deployed state having aligned overlapping petals;  
       FIG. 6B  is a side view of the anastomosis device of  FIG. 6A ;  
       FIG. 6C  is a perspective view of the anastomosis device of  FIG. 6A  having a tissue material disposed between a portion of the opposed petals;  
       FIG. 7  illustrates an embodiment of a tissue-necrosing type anastomosis device in a deployed state having a pressure distribution ring disposed about the tips of the petals;  
       FIG. 8  illustrates the anastomosis device of  FIG. 7  prior to formation of the pressure distribution rings;  
       FIG. 9A  is a top view of one embodiment of an anastomosis device configured to promote growth of tissue about an inner periphery of the device;  
       FIG. 9B  is a perspective view of the anastomosis device of  FIG. 9A ; and  
       FIG. 9C  is a perspective view of the anastomosis device of  FIG. 9A  deployed at an anastomosis site. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
      Certain exemplary embodiments will now be described to provide an overall understanding of the principles, structure, function, manufacture, and use of the devices and methods disclosed herein. One or more examples of these embodiments are illustrated in the accompanying drawings. Those skilled in the art will understand that the devices and methods specifically described herein and illustrated in the accompanying drawings are non-limiting exemplary embodiments and that the scope of the present invention is defined solely by the claims. The features illustrated or described in connection with one exemplary embodiment may be combined with features of other embodiments. Such modifications and variations are intended to be included within the scope of the present invention.  
      The present invention generally provides an anastomosis device that can be used to couple two or more layers of tissue in apposition. In an exemplary embodiment, the device can be formed from one or more woven wires that can be configured to have a generally tubular shape in a first, expanded position for insertion to an anastomosis site and a generally annular, ring-shape in a second, resting or deployed position for securing tissue in apposition at the anastomosis site. The device can be adapted either to cause necrosis of the tissue layers around an outer periphery of the device or to promote growth of tissue about an inner periphery of the device.  
      The device can be formed from a variety of materials, but in an exemplary embodiment, it is formed from a shape-memory wire woven into a mesh. The shape-memory wire is formed into an annular ring such that, when the anastomosis device is expanded into an elongate tubular form, it will return to its annular, ring-shaped configuration that is necessary during use of the device. Suitable shape-memory materials include, by way of non-limiting example, a shape-memory metal, such as an alloy of titanium and nickel (e.g., nitinol), that changes its shape upon the application of a force, such as a tension, and that returns to its deployed state upon removal of the force. A person skilled in the art will appreciate that the wire forming the anastomosis device can also be formed from other materials as well. For example, the wire can be formed from a spring material or from a compressible wire material. The device can also be formed from superelastic metal materials, such as alloys of titanium and nickel, that have the ability to undergo a relatively large elastic deformation when mechanically loaded. Additionally, one skilled in the art will understand that the wire can have a variety of cross-sectional shapes and thicknesses or diameters. For example, the wire can have a round, square, or hexagonal shape and can have a thickness or diameter in the range of about 0.008 inches to 0.023 inches.  
      As indicated above, the present invention provides both necrosing and non-necrosing anastomosis devices.  FIGS. 2-7  show various exemplary embodiments of anastomosis devices that are adapted to cause necrosis of tissue at an anastomosis site. In general, each device has a ring shaped configuration in a resting or deployed state with an inner and outer periphery. The inner and outer peripheries are configured such that, in the deployed state, pressure is highest at the outer periphery of the deployed device and decreases from the outer periphery to the inner periphery of the device. The relatively high pressure can impede blood flow to the tissue about the outer periphery, thereby causing the tissue inside the outer periphery of the device to become necrotic in this region. As the tissue necroses over time, the device can become separated from the healthy tissue at the anastomosis site and can be passed through the digestive system of the patient.  
       FIG. 2  illustrates one embodiment of an anastomosis device  200  in the expanded elongated tubular configuration, which can be achieved by applying a force, such as a tension, to the device. As shown, the device  200  has a wire mesh wall  242  that includes first  248  and second  250  ends and a midportion  245  disposed between the ends  248 ,  250 . The wire mesh wall  242  also defines a central lumen or opening  204  extending along a central or longitudinal axis  246 . The central lumen  204  allows the device  200  to be disposed on the shaft of a delivery device to be delivered to an anastomosis site. As the anastomosis device  200  is deployed from the delivery device, the device  200  will collapse from the elongated state to a resting state to secure opposed tissue layers in apposition. In particular, the wire mesh wall  242  of the tube will contract in the direction of the longitudinal axis  246 , the midportion  245  of the device will collapse inward to form an inner periphery of the ring, and ends  248 ,  250  of the tube will evert to form an outer periphery of the ring. The device  240  will thus have a generally annular configuration in the resting or deployed position, as shown in  FIGS. 3A-3C . In particular, the anastomosis device  200  has an annular, ring-shaped configuration with an inner periphery  202  that defines an opening  204  and petals  206  extending from the inner periphery  202  and defining an outer periphery  208 . The inner periphery  202  of the device  200  is defined by overlapping of the meshed wire and the outer periphery  208  is defined by the opposed ends of the tube which form opposing superior and inferior petals  206 ′,  206 ″. In the deployed state as shown, the inner periphery  202  can maintain a passageway between two apposed tissue layers at an anastomosis site to allow fluid and/or other substances to be passed between the layers and the superior and inferior petals  206 ′,  206 ″ can engage and apply pressure to tissue captured therebetween. In an exemplary embodiment, the superior and inferior petals  206 ′,  206 ″ can be configured to apply pressure to particular regions of tissue disposed therebetween to facilitate necrosis.  
      In the embodiment shown in  FIGS. 3A-3C , the petals  206  are adapted to apply a pressure to tissue such that the pressure is highest at the outer periphery  208  and decreases from the outer  208  to the inner periphery  202 . In particular, each petal  206  can be formed by adjacent arms  210 ,  212  connected by a tip  214  that extends along a portion of the outer periphery  208  of the device  200 . The tip  214  has a bend  215  with a first radius  216 , and each arm  210 ,  212  is connected to the tip  214  at a bend  218  that has a second radius  220 . In one aspect, the first radius  216  is greater than the second radius  220 . By way of example, the bend  215  can have a radius  216  of approximately 0.44 inches, while the bends  218 , which can form transitions between each arm  210 ,  212  and the tip  214 , have a radius  220  of approximately 0.04 inches.  
      Additionally, as indicated in  FIG. 3B , the adjacent arms  210 ,  212  of each petal  206  can be curved relative to a plane  227  of the device  200  (e.g., in the deployed state) that is substantially perpendicular to a central axis  228  extending through the opening or lumen  204  of the device  200 . For example, each of the arms  210 ′,  212 ′ forming each of the superior petals  206 ′ can include an arc portion  230  that extends away from the plane  227  along a first longitudinal direction  233  and that defines an opening  232  that faces (e.g., opposes) the inferior set of petals  206 ″. Additionally, each of the arms  210 ″,  212 ″ forming each of the inferior petals  206 ″ can include an arc portion  234  that extends away from the plane  227  along a second longitudinal direction  235  and that defines an opening  236  that faces (e.g., opposes) the superior set of petals  206 ′. The arc portions  230 ,  232  of the opposed petals  206 ′,  206 ″ are configured to orient the respective petal tips  214 ′,  214 ″ relative to the plane  227  of the device  200  such that the petal tips  214 ′,  214 ″ cross the plane  227  of the device  200  (e.g., where the tips  214 ′ of the superior petals  206 ′ extend below the plane  227  and the tips  214 ″ of the inferior petals  206 ″ extend above the plane  227  of the device  200 ). In use, the curved arc to the arms  210 ,  212  of the petals  206  can help to focus pressure applied by the petals  206  to the outer periphery  208  of the device  200 .  
      The superior and inferior petals  206 ′,  206 ″ can also be positioned at particular locations relative to one another to effect tissue necrosis at the outer periphery  208  of the device  200 . As shown in  FIG. 3A , for example, the tips  214  of the superior and inferior petals  206 ′,  206 ″ can be staggered relative to each other about the outer periphery of  208  to distribute pressure to tissue about the circumference or outer periphery  208  of the device  200 . In particular, the tips  214 ′ of each of the superior petals  206 ′ have midpoints  222  that are staggered or offset from the midpoints  224  of the adjacent tips  214 ″ of the inferior petals  206 ″. While the midpoints  222 ,  224  of adjacent, opposed petals  206 ′,  206 ″ can be staggered by any amount, in one embodiment, the midpoints  222 ,  224  are staggered by an amount in the range of about 15° to 20°, and more preferably by about 18°. As further illustrated in  FIG. 3A , the petals  206  are configured such that the tips  214  of opposed, adjacent superior and inferior petals  206 ′,  206 ″ do not cross each other, however the arms  210 ,  212  forming each of the petals  206  are configured to cross at multiple locations about the circumference of the device  200 . For example, an arm  212 ′ of a superior petal  206 ′ crosses an arm  210 ″ of an inferior petal  206 ″ to form a crossing location  226 . When the device  200  is deployed at an anastomosis site, the arms  210 ,  212  of the opposing petals  206  can contact or clamp tissue disposed between the opposed petals  206  at the crossing locations  226  and can apply a relatively large pressure to tissue at the locations  226  while each tip  214  is able to contact and apply pressure to the tissue disposed between adjacent locations  226  to limit or prevent blood flow thereto and to cause the tissue to become necrotic.  
      The number and size of petals  206  can also vary to obtain a desired result. In the embodiment illustrated in  FIGS. 3A-3C , the device  200  includes ten superior petals and ten inferior petals. However, other numbers of petals  206  can be used. For example, a device can be formed with fewer superior and inferior petals  206 ′,  206 ″ to increase the stiffness of the device  200  and thus increase the amount of pressure applied by the device  200  on tissue at the outer periphery of the device  200 . In another example, a device can be formed with additional superior and inferior petals  206 ′,  206 ″ to decrease the stiffness of the device  200  and thus decrease the amount of pressure applied by the device  200  on tissue at the outer periphery of the device  200 .  
      The anastomosis devices described herein can be deployed using a delivery device of the type known in the art, such as that described in U.S. Patent Application Publication No. 2003/0120292, which is hereby incorporated by reference. In use, such as in a side-to-side intestinal anastomosis, the anastomosis device  200  can be expanded into an elongate tubular configuration, such as illustrated in  FIG. 2 , and disposed about a delivery device. The delivery device can then be inserted within a patient and advanced intraluminally to an anastomosis site. At the anastomosis site, two tissue layers, such as a tissue wall forming an upper stomach pouch and a tissue wall forming a portion of the patient&#39;s small intestine, can be brought into apposition. Openings can then be formed within the walls of the tissue such as by a retractable cutting instrument associated with the delivery device. The anastomosis device  200  can then be deployed from the delivery device at the juncture of the apposed openings such that the device  200  collapses from the elongated state to the resting, annular, ring-shaped configuration with the superior petals  206 ′ and the inferior petals  206 ″ disposed on opposite sides of the two tissue layers.  
      Once the anastomosis device  200  has collapsed from the elongated to the resting state, opposing arms  210 ,  212  of adjacent petals  206  apply a relatively large pressure to the tissue disposed between the superior and inferior petals  206 ′,  206 ″ at locations  226 , thereby limiting or preventing blood from flowing to these tissue regions. Additionally, the tips  214  of each petal  206  can apply a pressure to the tissue disposed at the outer periphery  208 . For example, each tip  214  can apply a load to the tissue disposed between adjacent locations  226  at the outer periphery  208  to limit or prevent blood from flowing to the tissue disposed at the outer periphery  208  of the device  200 . Over time, as a result of the pressure applied by the petals  206  on the tissue, the tissue can become necrotic at the outer periphery  208  and inbound of the outer periphery  208 , thereby allowing the device to become separated from the healthy tissue at the anastomosis site and passed through the digestive system of the patient.  
       FIGS. 4A-4C  illustrate another embodiment of an anastomosis device  400 , in the resting state, that is adapted to necrose tissue. In this embodiment, each petal  406  can be formed by adjacent arms  410 ,  412  connected by a tip  414  that extends along a portion of the outer periphery  408  of the device  400 . As illustrated in  FIGS. 4B and 4C , the adjacent arms  410 ,  412  of each petal  406  can be curved relative to a plane  427  of the device  200 . For example, each of the arms  410 ′,  412 ′ of the superior set of petals  406 ′ can include an arc portion  430  that extends away from the plane  427  in a first longitudinal direction  433  and a bend portion  434  that orients the tip  414 ′ substantially parallel to the plane  427  of the device  400 . Additionally, each of the arms  410 ″,  412 ″ of the inferior set of petals  406 ″ can include an arc portion  434  that extends away from the plane  227  in a second longitudinal direction  435  and a bend portion  436  that orients the tip  414 ″ substantially parallel to the plane  427  of the device  400 . In use, the curved arc of the arms  410 ,  412  of the petals  406  can focus pressure applied by the petals  206  to the outer periphery  408  of the device  400 .  
      The superior and inferior petals  406 ′,  406 ″ can also be positioned at particular locations relative to one another to facilitate necrosis formation at the outer periphery  408 . As shown in  FIG. 4A , opposed petals  406  are staggered relative to each other and portions of the tips  414  of adjacent petals  406  are configured to cross at multiple locations  426  about the circumference of the of the device  400 . For example, each tip  414 ′ of superior petal  406 ′ crosses the tips  414 ″ of two adjacent inferior petals  406 ″ at locations  426 - 1 ,  426 - 2 . Once deployed in tissue, opposing tips  414  can contact (e.g., clamp) tissue at each of the locations  426  and can apply a relatively large pressure (e.g., localized pressures calculated to be in the range of approximately 40 psi to 70 psi) to the tissue to limit or prevent blood flow thereto and to cause the tissue to become necrotic at the outer periphery  408  and inbound of the outer periphery  408 . Also, the amount of overlap of the tips  414 , relative to a circumference of the device  400 , can affect the degree of tissue necrosis at the outer periphery  408 . For example, in the embodiment of  FIGS. 4A-4C , opposing petal tips  414  can overlap and clamp tissue along approximately 40% of the outer periphery  408  or circumference of the deployed device  400  and, as a result, can cause substantially uniform necrosis of the tissue about the outer periphery  408 , thereby allowing the anastomosis device  400  as well as the necrotic tissue to separate from the healthy tissue and pass through the digestive system of a patient.  
      One skilled in the art will understand that the tips  414  of the petals  406  can be configured in a variety of different ways. In one embodiment of the device  400 ′, as shown in  FIG. 4D , the tips  414  of the petals  406  can be arced or curved relative to the plane  427  of the device  400 ′. For example, the tip  414  of each of the superior and inferior petals  406 ′,  406 ″ has a peak portion  430  that defines an inferior facing opening and a trough portion  434  that defines a superior facing opening. With the opposed superior and inferior petals  406 ′,  406 ″ petals being staggered relative to each other, the peaks  430  and troughs  434  of opposed superior and inferior petals  406 ′,  406 ″ can be aligned along the outer periphery. For example, a peak portion  430 ′ of the superior petal  406 ′ can be aligned with a peak portion  430 ″ of a first inferior petal  406 - 1 ″ and a trough portion  434 ′ of the superior petal  406 ′ can be aligned with a trough portion  434 ″ of a second inferior petal  406 - 2 ″. The overlapping peaks  430  and troughs  434  of the opposed petals  406  form a relatively long circumferential path about the outer periphery  408 . As such, tissue disposed at the outer periphery  408  can become stretched by the overlapping peaks  430  and troughs  434  of the opposed petals  406  and, as a result, the thickness of the affected tissue will decrease. Such a decrease in tissue thickness can result in the tissue being exposed to relatively high pressures as applied by the device  400 . In use, the overlapping peaks  430  and troughs  434  of opposed petals  406  can clamp tissue along approximately 50% of the outer periphery  408  of the device  400  and can apply a relatively large force (e.g., localized pressures calculated to be in the range of about 75 to 80 psi) to tissue disposed at the outer periphery  408  to cause substantially uniform necrosis of the tissue.  
       FIGS. 5A-5C  illustrate an embodiment of an anastomosis device  500 , in the resting state, having opposed petals  506  in which the adjacent arms  510 ,  512  and tip  514  of each petal  506  are oriented in a substantially planar configuration and where the petal tips  514  of the opposed petals  506  have midpoints  522 ,  524  that are staggered or offset relative to each other. As shown in  FIG. 5B , the arms  510 ,  512  and tips  514  are oriented to be substantially parallel to a plane  527  that is perpendicular to a central axis  528  of the device  500 . Further, the tips  514  of the opposing petals  506  cross at multiple locations  526  about an outer periphery  508  of the device  500 . By way of example, the crossing portions  526  of the tips  514  can overlap and clamp tissue along approximately 85% of the outer periphery  508  of the deployed device  500 .  
       FIGS. 6A-6C  illustrate another embodiment of an anastomosis device  600  that is adapted to necrose tissue. In this embodiment, opposed petals  606  are substantially aligned with each otherabout an outer periphery  608  of the device  600 . That is, the tips  614 ′ of each of the superior petals  606 ′ have midpoints  622  that are substantially aligned with midpoints  624  of the tips  614 ″ of the inferior petals  606 ″. As a result, the tips  614  of the aligned superior and inferior petals  406 ′,  406 ″ cross at multiple locations  626  about the outer periphery  608  of the of the device  600  to clamp tissue along approximately 77% of the outer periphery  608 . In use, opposing tips  614 ′,  614 ″ can clamp tissue at each of the locations  626  to apply a relatively large pressure (e.g., localized pressures calculated to be in the range of about 20 to 25 psi) to the tissue to limit or prevent blood flow thereto and to cause the clamped tissue to become necrotic.  
       FIG. 7  illustrates another embodiment of an anastomosis device  700 , in a resting state, that is adapted to necrose tissue. As shown, the anastomosis device  700  has an annular, ring-shaped configuration with an inner periphery  702  that defines an opening  704  and petals  706  extending from the inner periphery  702  and defining an outer periphery  708 . The inner periphery  702  of the device  700  is defined by overlapping of the meshed wire and the outer periphery  708  is defined by the tips  714  of the superior and inferior petals  706 . The outer periphery  708  of the anastomosis device  700  also includes opposing pressure distribution rings  715  disposed about to the tips  714  of each set of the opposed petals  716 . For example, the device  700  includes an upper ring  715  disposed about the tips  714  of the superior petals  706 ′ and a lower ring (not shown) disposed about the tips  714  of the inferior petals  706 ″. In use, the pressure distribution rings  715  can distribute pressure from the petal tips  714  to tissue disposed substantially along the entire outer periphery  708  of the device  700  to create a substantially uniform blood flow barrier about the outer periphery  708  of the device  700 . For example, the anastomosis device  700  can clamp tissue along approximately 90% of the outer periphery  708  to apply a substantially uniform pressure of approximately 35 psi to the tissue disposed at the outer periphery  708 .  
      One skilled in the art will understand that the pressure distribution rings  715  can be formed at the outer periphery  708  of the device  700  in a number of ways. For example, as described below with respect to  FIG. 8 , when the anastomosis device  700  is manufactured, two wires can be woven together to form a mesh wall  702  such that, at the end of the weaving process, portions  716 ,  717 ,  718 ,  719  of the two wires can extend from the device  700 . Two of the end wires can then be removed from the device  700  while the remaining two end wires can be used to form the pressure distribution rings  715 . For example, the wire portions  718  and  719  can be removed from the mesh wall  702 , the wire portion  716  can be interwoven with the tips  720  of a first end  722  of the device  700  to form a first pressure distribution ring, and the wire portion  719  can be interwoven with the tips  723  of a second end  724  of the device  700  to form a second pressure distribution ring. Once the wire portions  716 ,  719  have been woven to form the pressure distribution rings, the respective free ends  726 ,  728  of the wire portions  716 ,  719  can remain uncoupled to the mesh wall  702 . In use, as the device  700  is deployed from an applier and collapses from an expanded, tubular shape to an annular, deployed shape, the free ends  726 ,  728  of the wire portions  716 ,  719  can slide through the tips  720 ,  723  to allow the pressure distribution rings  715  of the device  700  to expand from a collapsed state to an expanded state. When deployed, the pressure distribution rings  715  can distribute pressure from the petal tips  714  to tissue disposed substantially along the entire outer periphery  708  of the device  700 .  
      While the pressure distribution rings  715  can be formed at the outer periphery  708  of the device  700  using two of the wire portions  716 ,  717 ,  718 ,  719  that extend from the device  700 , one skilled in the art will understand that the pressure distribution rings  715  can be formed from separate wires that are added to the device  700 . For example, at the end of the weaving process, all of the wire portions  716 ,  717 ,  718 ,  719  can be removed from the device  700  and separate wire elements can be attached. In particular, wire elements having a larger or smaller diameter than that of the wire forming the mesh wall  702  or wire elements formed of a material that is different than the wire forming the mesh wall  702  can be attached to the device  700 .  
      The various anastomosis devices described above are adapted to cause necrosis of the clamped tissue. It is sometimes desirable, however, for an anastomosis device to allow tissue to overgrow the device at an anastomosis site. A non-necrosing anastomosis device is similar to necrosing anastomosis devices in that it has a ring shaped configuration in a resting or deployed state with an inner and outer periphery.  
       FIGS. 9A-9C  show one embodiment of a non-necrosing type anastomosis device  900  in a resting or deployed state. As shown, the anastomosis device  900  has an annular, ring-shaped configuration with an inner periphery  902  that defines an opening  904  and petals  906  extending from the inner periphery  902  and defining an outer periphery  908 . One characteristic of such a non-necrosing anastomosis device  900  is that the inner periphery  902  of the device  900  is formed from nonoverlapping wire segments  909 . For example, as illustrated in  FIG. 9B , the device  900  can be woven such that in the deployed state the wire segments  909  disposed at the inner periphery  902  of the device  900 , within a lumen  917  formed between opposed tissues  914 ,  916 , do not contact each other. Instead, the wires forming the arms of adjacent superior or inferior petals  906  can contact each other at locations  915 . For example as illustrated in  FIG. 9B , an arm  912 - 1  of a first superior petal  906 - 1  is disposed beneath an arm of a second superior petal  906 - 2  at location  915 - 1 , an arm  910 - 1  of the first superior petal  906 - 1  is disposed over an arm of a third superior petal  906 - 3  at location  915 - 2 , and the arms of the second and third superior petals  906 - 2 ,  906 - 3  contact each other at location  915 - 3 . It is believed that such a design discourages the growth of bacteria or biofilms which can limit or prevent tissue growth due to the lack of contact between wire segments  909  at the inner periphery. Thus, tissue at the inner periphery  902  is able to grow over the wire segments  909 . Accordingly, when the device  900  is in the deployed state as shown in  FIG. 9C , the wire segments  909  forming the inner periphery  902  maintain a passageway between the two apposed tissue layers  914 ,  916  at an anastomosis site to allow fluid and/or other substances to be passed between the layers  914 ,  916  and promote tissue overgrowth of the segments  909  at the inner periphery  902 . The device  900  still enables the superior and inferior petals  906  to engage the tissue layers  914 ,  916  and apply a pressure to the layers  914 ,  916  that is sufficient to maintain apposition of the tissue layers  914 ,  916  but that is below a threshold that can cause the tissues to become necrotic. For example, the opposing superior and inferior petals  906 ′,  906 ″ can overlap at locations  926  about the outer periphery  908  to apply a pressure of less than about 2 psi to the tissue layers  914 ,  916  at each of the locations  926 .  
      One skilled in the art will appreciate further features and advantages of the invention based on the above-described embodiments. Accordingly, the invention is not to be limited by what has been particularly shown and described, except as indicated by the appended claims. All publications and references cited herein are expressly incorporated herein by reference in their entirety.