Abstract:
Tissue anchoring devices in the form of microanchors that partially penetrate tissue, thereby avoiding full thickness penetration of the tissue, yet are secure enough to enable reliable device fixation and easy removal of the device while maintaining normal GI tract functions.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority to U.S. application Ser. No. 61/681,673, filed Aug. 10, 2012. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention is directed to microanchors for anchoring devices to body tissues, and more particularly, to microanchoring devices that enable reliable device fixation and easy removal of the device, while maintaining normal gastrointestinal (GI) tract function. 
       BACKGROUND OF THE INVENTION 
       [0003]    Implantable devices such as intestinal sleeves are known in the industry. A common difficulty associated with such devices that are designed for implantation in the GI tract is reliable anchoring of the devices. The GI tract is a very dynamic area of the body. There is much movement, flow, and other disruptive action that exerts forces on the implanted device. Anchoring the device so that it stays in place without migration in these dynamic locations is very difficult. The tissue anchors must be secure enough to anchor endolumenally delivered devices in the GI tract and yet produce minimal impact to normal physiological functions of the GI tract, such as motility, blood supply to the surrounding tissue, secretions, patency, etc.). In addition, the tissue anchors must avoid causing pain to the patient. 
         [0004]    An even greater challenge is presented with temporary implantable devices—those that are designed to be anchored in the body for a limited period of time, and then removed. The tissue anchors for these devices must meet all of the same criteria for reliable fixation and allowing normal GI tract functions, but must also permit endolumenal removal of the device. A tissue anchor satisfying all of these needs is highly desirable. 
       SUMMARY OF THE INVENTION 
       [0005]    The present invention provides tissue anchors in the form of microanchors, the length of which ensure penetration of only the submucosa of the tissue, yet are secure enough to enable reliable device fixation and easy removal of the device while maintaining normal GI tract functions. The invention includes several embodiments of these microanchors. 
         [0006]    In a first embodiment, the present invention provides a microanchor comprising a first tissue engagement member, a second tissue engagement member, and a strain relieving connector joining the first tissue engagement member to the second tissue engagement member, wherein said device has a retracted state and an engaged state, the first tissue engagement member and said second tissue engagement member forming a pincer in the engaged state. 
         [0007]    In another embodiment, the present invention provides a microanchor for fixating a device within a body lumen comprising a first portion attached to said device, a second portion having at least one tissue engagement member for insertion into a wall of the body lumen, and a reversibly deformable and recoverable segment located between the first portion and the second portion. 
         [0008]    In a third embodiment, the present invention provides a microanchor comprising a central hub and at least three tissue engagement members radially oriented on the central hub, wherein the device has a constrained state and an engaged state, and wherein the tissue engagement members are in apposition to each other in the engaged state. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]      FIG. 1A  is a perspective view of an exemplary embodiment of the invention in a retracted state. 
           [0010]      FIG. 1B  is a perspective view of the microanchor of  FIG. 1A  in an engaged state. 
           [0011]      FIG. 1C  is a perspective view of microanchors of  FIG. 1A  mounted on a stent graft attached to a graft. 
           [0012]      FIG. 1D  is a perspective view of microanchors of  FIG. 1A  mounted on a sleeve. 
           [0013]      FIG. 2A  is a perspective view of another exemplary embodiment of the present invention. 
           [0014]      FIG. 2B  is a perspective view of microanchors of  FIG. 2A  mounted on a sleeve 
           [0015]      FIG. 3A  is a perspective view of another exemplary embodiment of the present invention in a retracted state. 
           [0016]      FIG. 3B  is a perspective view of the microanchor of  FIG. 3A  in an engaged state. 
           [0017]      FIG. 3C  is a perspective view of microanchors of  FIG. 3A  coupled to an implantable device. 
           [0018]      FIG. 3D  is a perspective view of microanchors of  FIG. 3A  coupled to an implanted device in an engaged state. 
           [0019]      FIG. 4A  is a perspective view of another exemplary embodiment of the present invention 
           [0020]      FIG. 4B  is a perspective view of microanchors of  FIG. 4A  coupled to an end portion of an implantable sleeve device. 
           [0021]      FIG. 4C  is a perspective view of microanchors of  FIG. 4A  coupled to an end region of an implantable sleeve device. 
           [0022]      FIG. 4D  is a perspective view of microanchors of  FIG. 4A  coupled to an implantable device comprising a stent portion and a graft portion. 
           [0023]      FIG. 5  is a perspective view of another exemplary embodiment of the present invention 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0024]    The present invention will now be described with reference to exemplary embodiments. In a first embodiment illustrated in  FIGS. 1A and 1B , a microanchor device  1  is illustrated having a first tissue engagement member  10  and second tissue engagement member  11  joined by a connector  12 . Connector  12  in this embodiment is a coil spring made of a metal such as nitinol or stainless steel. Other biocompatible materials may also be used provided that they can be repeatedly retracted and engaged as described herein including but not limited to chrome cobalt alloys such as Elgiloy or L605 and titanium alloys such as Titanium Beta 3.  FIG. 1A  illustrates the microanchor device  1  in a retracted state. In this retracted state, first tissue engagement member  10  and second tissue engagement member  11  are physically wound against the tension of the spring such that they are in proximity to each other. The engagement members  10  and  11  are then physically constrained using external means such as a suture or ligament or line  15 . Line  15  is tied around both engagement members  10  and  11  to physically constrain them in retracted state. The force of the spring coil connector  12  is stored as potential energy in this retracted state. It should be understood that the use of tethers to restrain tissue engagement members is merely exemplary and that any thermal or mechanical means to initially restrain tissue engagement members could be employed. In one embodiment, a rigid sheath could be employed to restrain tissue engagement members. 
         [0025]    In use, a plurality of microanchor devices  1  as illustrated in  FIG. 1A  are mounted around a portion of a device to be anchored within the body. For example, as illustrated in  FIG. 1C , microanchor devices  1  are mounted at various locations on a stent frame  19  of a device to be anchored within a body. As illustrated in  FIG. 1C , microanchor devices  1  are mounted at the apices of the stent frame and are depicted in their restrained state. The stent frame is optionally used in combination with a graft member  16  which may extend any desired length, including beyond the stent frame  19 . 
         [0026]    For insertion into a body, the stent frame  19  and any associated graft  16  are diametrically compressed into a small configuration suitable for insertion into a catheter device, for example. The stent frame  19  and any associated graft  16  are then advanced along the catheter to the desired point of deployment within the body. At that point, the stent frame  19  and any associated graft  16  are deployed from the catheter and expand to the desired diametrical size to engage the tissue or vessel walls. 
         [0027]    After deployment of stent, the operator, typically a doctor, will manipulate tether lines  15  (as shown in  FIG. 1A ), which will in turn release first tissue engagement member  10 , and second tissue engagement member  11 . At that point, as illustrated in  FIG. 1B , microanchor device  1  releases the stored potential energy within connector  12  and forces first tissue engagement member  10  and second tissue engagement member  11  into an engaged state, illustrated in  FIG. 1B . In this engaged state, first tissue engagement member  10  and second tissue engagement member  11  form a pincer. By “pincer” as used herein is meant a configuration in which first tissue engagement member  10  and second tissue engagement member  11  are essentially two grasping jaws working on a pivot used for gripping tissue  18 . 
         [0028]    With reference again to  FIG. 1C , once all of the microanchor devices  1  have been deployed from their retracted state to their engaged state, the stent frame  19  and any associated graft  16  are anchored securely to the body tissue. Although this anchoring is secured, it is not necessarily permanent. Microanchor device  1  is designed to penetrate only the sub-mucosa of the tissue. The microanchors described herein, typically penetrate less than one millimeter into the tissue. As a result, with the application of appropriate force in the appropriate direction, microanchor device  1  can be disengaged or removed from the tissue  18 . In this way, the stent frame  19  and any associated graft  16  can be removed from the body after disengaging microanchor devices  1 . 
         [0029]    An alternate device configuration is illustrated in  FIG. 1D  where a plurality of microanchor devices  1  as illustrated in  FIG. 1A  are mounted at various locations of a sleeve device  16  to be anchored within a body without the use of a stent. As illustrated in  FIG. 1D , microanchor devices  1  are mounted directly on graft member  16  and are depicted in their restrained state. The anchoring devices  1  may mounted on a portion of the graft, such as the proximal length of the graft, or may mounted throughout the length of the graft (figure not shown). The microanchors could be attached individually to the sleeve and oriented in parallel to resist distal movement of the sleeve. Alternatively, the anchors could be randomly oriented. In another embodiment, the microanchors could be attached to one another to form a chain which is subsequently attached to the sleeve. 
         [0030]    The device shown in  FIG. 1D  may be packed into a small configuration suitable for insertion into a catheter device. For deployment the packed device may be advanced along the catheter to the desired point of deployment within the body. After deployment the tissue engagement members on graft  16  may be put in the proximity of the tissue, through a tissue approximation mechanism. An example of the tissue approximation mechanism is use of an inflating balloon to put graft  16  and the microanchor device  1  in proximity of the tissue that it will engage. 
         [0031]    After approximating the microanchor device  1  to the tissue, the operator, typically a doctor, will manipulate tether lines  15 , which will in turn release first tissue engagement member  10 , and second tissue engagement member  11 , by releasing (as illustrated in  FIG. 1B ) the stored potential energy within connector  12  and forming the pincer as described earlier to engage the tissue. 
         [0032]    A second embodiment of the present invention is illustrated in  FIG. 2A . In  FIG. 2A , a microanchor device  2  is shown. The microanchor device  2  has a first portion  20 , a second portion  21 , and a connector portion  23  connecting the first portion  20  to the second portion  21 . The first portion  20  is adapted for attachment to an apparatus to be anchored within the body. The second portion  21  of the microanchor device  2  has a tissue engagement member  22  adapted for insertion into body tissue. The tissue engagement member  22  may be a microanchor that is dimensioned to only extend into the submucosa of the tissue upon implantation and deployment of the microanchor device  2 . The size of the tissue engagement member  22  is limited so that the anchoring member  22  does not extend through the wall of the tissue and so that upon removal the tissue engagement member does not tear the tissue. 
         [0033]    The first portion  20  and second portion  21  of the microanchor device  2  are coupled together through a reversibly deformable or resilient connector portion  23 . Upon implantation of the apparatus in a body, the tissue engagement member  22  is engaged with a body tissue and the first portion  20  is coupled to the apparatus. As the body exerts forces on the implanted apparatus, the apparatus may move in response to these external forces. The resilient or reversibly deformable portion  23  may provide a strain relief that may absorb these forces by stretching or deforming along the length of the deformable portion  23 . The dissipation of the force should reduce the likelihood of the engagement member  22  disengaging from the tissue. The application of a force to the apparatus will cause connector segment  23  to stretch or deform, thus absorbing the shock or energy from the force without directly exerting that force through the tissue engagement member on the tissue itself. 
         [0034]    In the embodiment illustrated in  FIG. 2A , connector segment  23  is formed of the same wire as the rest of the microanchor device, which can be a material such as nitinol or stainless steel or other reversibly deformable (resilient) material. Connector segment  23  in the illustrated embodiment is shaped in the form of an “S”. Upon application of a force to first portion  20 , the “S” connector segment  23  straightens out or substantially straightens out (stretches or lengthens) to absorb the shock. The deformation of the “S” shape may reduce the amount of force that will transfer through the first portion  20  of the microanchor device  2  to the second portion  21  and the engagement member  22 . The connector segment  23  absorbs the force in order to reduce the likelihood of tissue engagement member  22  pulling out of the tissue. Upon release of the force, connector segment  23  then reversibly regains its initial “S” shape, ready to deform again to absorb further forces on microanchor device  2 . In this way, when a plurality of microanchor devices  2  of this embodiment are disposed around an apparatus anchored within a body, the microanchor devices  2  are able to absorb the repeated shock of forces applied to the device, such as within the intestine. The apparatus anchored within the intestine is thereby securely maintained. 
         [0035]    As with the microanchor device illustrated in  FIGS. 1A-1C , the tissue engagement member  22  of microanchor device  2  only penetrates the submucosa of the tissue. Therefore upon application of an appropriate force to tissue engagement member  22 , it may be removed from the tissue, thereby allowing the apparatus to be removed from the body with minimal injury or tearing to the tissue wall. 
         [0036]    In use, a plurality of microanchor devices as illustrated in  FIG. 2A  can be mounted around a portion of a device to be anchored within the body. For example, as illustrated in  FIG. 2B , a plurality of microanchor devices  2  are mounted at various locations of a sleeve device  16  to be anchored within a body without the use of a stent. The microanchors could be attached individually to the sleeve and oriented in parallel to resist distal movement of the sleeve. Alternatively, the anchors could be randomly oriented. 
         [0037]    The device shown in  FIG. 2B  may be packed into a small configuration suitable for insertion into a catheter device. For deployment the packed device may be advanced along the catheter to the desired point of deployment within the body. After deployment, the tissue engagement members of microanchor devices  2  on graft  16  may be put in the proximity of the tissue, through a tissue approximation mechanism. An example of the tissue approximation mechanism is use of an inflating balloon to put graft  16  and the microanchor device  2  in proximity of the tissue that it will engage. 
         [0038]    After approximating the microanchor device  2  to the tissue, the operator, typically a doctor, will manipulate the engagement members with the tissue by pulling on the catheter, which would set the engagement members into the tissue. 
         [0039]    Another embodiment of the present invention is illustrated in  FIGS. 3A-3D . As shown in  FIG. 3A , a microanchor device  3  has a central hub  30  and a plurality of tissue engagement members  31  extending therefrom. Typically this microanchor device  3  is formed of a shape memory material such as nitinol. The configuration illustrated in  FIG. 3A  depicts the device in a retracted state. A plurality of microanchor devices  3  may be mounted around an apparatus to be anchored within a body, such as around a stent frame of such device, as shown in  FIGS. 3C &amp; 3D . Upon insertion and deployment of the apparatus at the desired location within the body, microanchor device  3  is released from its retracted state into an engaged state, as illustrated in  FIG. 3B . Typically, with shape memory metals, this release from retracted state to engaged state is stress induced, however, it is envisioned that this activation could be thermally induced as well. In an engaged state, tissue engagement members  31  are in apposition to each other. This means that they are facing substantially toward one another in a configuration that effectively grips the body tissue. As with the previous two embodiments, microanchor device  3  is adapted to only penetrate the submucosa, approximately one millimeter, in the tissue. As a result, upon application of suitable force, it can be removed from the tissue. Nonetheless, the apparatus anchored by the microanchor device  3  is securely maintained at its position within the body, enduring the forces and shock experienced by the apparatus, holding it securely in place. The multiple directions of the anchor members allow the device to withstand the forces that are within a body lumen. These forces may not be in a single direction and the multiple directions of the anchor members allow the device to be maintained within the lumen. 
         [0040]    Turning now to  FIGS. 3C and 3D , the microanchor device  3  is shown coupled to an implant. The microanchor device  3  may be coupled directly to an end of a tubular member in an evenly spaced distribution around the outside surface of the tubular member. In  FIG. 3C  the microanchor device is shown in a retracted state on the outside surface of a tubular member  16  and in  FIG. 3D  the microanchor device  3  is shown in an engaged state on the outside surface of the tubular member  16 . The location of the anchoring devices  3  with respect to the tubular member or implanted device may be coupled together in any pattern. 
         [0041]    In  FIGS. 4A-4D , another alternative embodiment of the present invention is shown. The microanchor device  4  is similar to the embodiment of  FIGS. 2A and 2B . The microanchor device  4  may have two tissue engaging portions  42 . Each of the tissue engaging portions  42  may be coupled to a device engagement portion  44  with a connector portion  46  therebetween. The tissue engagement member  42  of the microanchor device  4  may allow the device to couple to a body tissue when implanted into a patient. The size and shape of the tissue engagement member  42  is designed to limit the depth of tissue wall penetration to the submucosa layer of the tissue wall. The limit on tissue penetration depth may allow the microanchor device  4  to be removed from the tissue wall and also limit any damage that may be caused by the tissue engagement member  42 . 
         [0042]    The connector portions  46  may provide a strain relief when the microanchor device  4  is implanted into a body lumen. As forces from the body act upon a device (See  FIGS. 4B-4D ) coupled to the microanchor device  4 , the connector portions  46  may stretch or deform in order to reduce the force that may be translated to the tissue engaging portions  42 . The reduction of force on the tissue engagement portions  42  may prevent the tissue engagement portions from pulling out of the tissue wall and also may prevent an implanted device from migrating or moving from the implanted location. A device might consist of a sleeve device  16  as shown in  FIGS. 4B and 4C , or a stent frame  19  in combination with a sleeve device  16  as shown in  FIG. 4D . Including multiple microanchor devices  4  on an implantable device may further reduce the likelihood of a device from being removed prematurely from an implant site. 
         [0043]    In another embodiment, similar to the embodiment in  FIG. 1A , illustrated in  FIG. 5 , a microanchor device  5  in an open configuration is illustrated having a first tissue engagement member and second tissue engagement member joined by a connector  12 . Connector  12  in this embodiment is two coil springs made of a metal such as nitinol or stainless steel. The spacing between the coil springs can be changed to provide greater or lesser distance between the tissue engagement members. Multiple coil springs, such as two or three or more, may be used to provide different anchoring forces and angles to suit the different microanchor requirements of the anatomy. 
         [0044]    Other embodiments contemplated include using a combination of the micoanchor devices described herein by coupling one or more of microanchor devices  1 - 5 , in any array or pattern, to any implantable device. In some embodiments, this plurality of varying anchoring devices, will extend along the length of the implantable device. The microanchor devices may be coupled to the implantable device in varying directions. The different angular placement of the microanchor devices will allow the individual microanchor devices to absorb forces from multiple directions when implanted into the body. 
         [0045]    While particular embodiments of the present invention have been illustrated and described herein, the present invention should not be limited to such illustrations and descriptions. It should be apparent that changes and modifications may be incorporated and embodied as part of the present invention within the scope of the following claims. 
       EXAMPLE  
       [0046]    A microanchor similar to that depicted in  FIG. 1  was produced by first obtaining 0.018″ diameter nitinol wire (Ft. Wayne Metals, Ft. Wayne, Ind.). A metal fixture was made having three rods mounted parallel to one another with a small gap therebetween. The nitinol wire was then wound in serpentine fashion around the three rods and secured such that the two ends of the wire wrapped completely around the outer two rods. Heat treatment of the serpentine shaped nitinol wire was accomplished by placing the fixture with the nitinol wire in a fluidized bed furnace at 480° C. for 7 minutes. The fixture having the nitinol wire was removed from the oven and quenched in water. After quenching, the nitinol wire was removed from the fixture. As a result of the thermal treatment, the wire retained its serpentine configuration. The outer loops were then trimmed to produce sharp points at a position approximately 200 degrees around the outer rods respectively. 
         [0047]    The serpentine shaped nitinol wire was then preloaded by wrapping it around a single small diameter rod until it generally assumed the shape shown in  FIG. 1A . A piece of suture was used to tie a quick-release knot at the crossover portion of the loaded nitinol wire. 
         [0048]    Next, the trained and locked nitinol microanchor was evaluated for tissue retention performance. To simulate a stent frame, the locked microanchor was affixed to a small diameter rod. A piece of canine duodenum was used as the representative tissue. The microanchor was held against the tissue and the suture quick-release pulled to release the microanchor. The microanchor immediately unwound so that the two pincer ends of the microanchor anchor themselves into the tissue. 
         [0049]    Load bearing performance of the anchored microanchor was determined by tying a string to the loop of the microanchor and vertically hanging a weight on the opposite end of this string. A starting weight of 20 gm was used. The weight was allowed to hang for approximately 5 minutes. If there were no signs of tissue tearing or the microanchor releasing, an additional 20 gm was added. This process was repeated until the weight reached 200 gm. With 200 gm hanging from the microanchor and after about 3 minutes the microanchor released itself from the tissue. There was no tearing of the tissue.