Abstract:
Release mechanism for medical device includes a bushing having a proximal end, a distal end and a channel extending therethrough. Plurality of extend proximally from the distal end are biased toward a release configuration in which engagement surfaces at distal ends thereof retract radially into the channel. A core pin insertable through the channel applies a radially expansive pressure to move the arms radially outward to a locking configuration. Engagement surfaces of the first and second arms connect to a retaining surface of a tissue treatment device containing capsule, which extends at an angle relative to the engagement surfaces selected so that a first portion of a force transmitted along an axis of the bushing moves the arms radially inward toward the release configuration before a second portion of the force exceeds a threshold level associated with the removal of a tissue treatment device from gripped tissue.

Description:
PRIORITY CLAIM 
     The application claims the priority to the U.S. Provisional Application Ser. No. 61/382,624, entitled “Release Mechanism for Hemostasis Clip” filed Sep. 14, 2010. The specification of the above-identified application is incorporated herewith by reference. 
    
    
     BACKGROUND 
     Pathologies of the gastrointestinal (“GI”) system, the biliary tree, the vascular system and other body lumens and hollow organs are often treated through endoscopic procedures, many of which require active and/or prophylactic hemostasis to control bleeding. Hemostatic clips are often deployed via endoscopes to stop internal bleeding by holding together the edges of wounds or incisions to allow natural healing processes to close the wound. Specialized endoscopic clipping devices are used to deploy the clips at desired locations of the body after which the clip delivery device is withdrawn, leaving the clip within the body. Deployment of such clips in the body is often complicated, requiring multiple steps before the clip is released from an insertion device. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to a release mechanism for a medical device comprising a bushing having a proximal end, a distal end and a channel extending therethrough, the bushing comprising first and second arms extending proximally from the distal end, the first and second arms being biased toward a release configuration in which engagement surfaces at a distal ends thereof are retracted radially into the channel. The release mechanism also comprises a core pin insertable through the channel and configured to apply a radially expansive pressure to move the arms radially outward from the release configuration into a locking configuration. A clip containing capsule is connected to the bushing by engagement between the engagement surfaces of the first and second arms and a retaining surface of the capsule, the retaining surface of the capsule extending at an angle relative to the engagement surfaces selected so that a first portion of a force transmitted along an axis of the bushing to the first and second arms moves the arms radially inward toward the release configuration before a second portion of the force transmitted by the first and second arms to the capsule exceeds a threshold level associated with the removal of a clip from tissue with which it has been engaged. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows an exemplary bushing according to the present invention in an operative configuration with a hemostatic clipping device; 
         FIG. 2  shows a partial cross-sectional view of a bushing according to a first exemplary embodiment of the present invention in a biased, non-stressed configured; 
         FIG. 3  shows a partial cross-sectional view of the bushing of  FIG. 1  in a stressed configuration; 
         FIG. 4  shows a partial cross-sectional view of the bushing of  FIG. 1  while being attached to a capsule of the hemostatic clipping device; 
         FIG. 5  shows a perspective view of the bushing of  FIG. 1  in a stressed configuration; 
         FIG. 6  shows a partial cross-sectional view of the bushing of  FIG. 1  in a non-stressed configuration; and 
         FIG. 7  shows partial cross-sectional view of the bushing of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION 
     The present application may be further understood with reference to the following description and the appended drawings, wherein like elements are referred to with the same reference numerals. The present invention relates to devices for hemostatic clipping and, in particular, to a hemostatic clip deployed through a single stage process. Exemplary embodiments of the present invention provide a bushing including angled bushing fingers at an end thereof to permit removable attachment of the bushing to a capsule of a hemostatic clipping device as described, for example, in U.S. Patent Application Ser. No. 60/915,806, to Adam L. Cohen, Bryan R. Ogle, Russell F. Durgin, Gregory R. Furnish, Michael Goldenbogen, Gary A. Jordan, Benjamin E. Morris, Mark A. Griffin, William C. Mers Kelly and Vasily P. Abramov filed May 7, 2007 and entitled “Single Stage Mechanical Hemostasis Clipping Device,” the entire disclosure of which is hereby incorporated by reference in its entirety. The exemplary bushing of the present invention connects a capsule including a hemostatic clip to a flexible delivery member of a hemostatic clip delivery system improves a deployment mechanism usable for both single and two piece hemostatic clips as well as on a mechanism for separation of the capsule from the flexible delivery member. The exemplary embodiment of the present invention permits attachment and removal of such a clip from the bushing any number of times without breaking and without damage to the hemostatic clipping device or surrounding tissue. It is noted that embodiments of the present invention also relate to and may be employed with various types of clipping devices including, but not limited to, clips for fastening tissue layers together and clips for closing openings in one or more layers of tissue. For example, the bushing of the present invention may be used with a clipping device for closing wounds and/or incisions for hemostasis of natural or surgical bleeding, “stitching” a wound, occluding a vessel or lumen, plicating a hollow organ, attaching tissues, tissue approximation, etc. The bushing may further be used with any medical device requiring detachment from a catheter or tube. 
     As shown in  FIGS. 1-7 , a bushing  100  according to a first exemplary embodiment of the present invention comprises a substantially cylindrical body  102  extending from a proximal end  103  which is coupled to a flexible insertion member  30  of a hemostatic clipping device  10 . The hemostatic clipping device  10  comprises an elongated flexible insertion member  30  extending between a proximal end coupled to a handle  20  and a distal end connected to the bushing  100 . As those skilled in the art will understand, the insertion member  30  is preferably formed of a substantially flexible material to allow it to be advanced through a natural body lumen without damaging the tissue thereof and should have a length suited to the requirements of a clipping procedure being performed. The device  10  further comprises a control member  107  extending through the insertion member  30  between the handle  20  and the clip  40 . The control member  107  extends from a proximal end connected to the handle  20  via a pin  50 , through the bushing  100  and into the capsule  200  to a distal end connected to the clip  40 . The bushing  100  of the present invention extends from a proximal end  103  coupled to a distal end of the insertion member  30  to a distal end  104  and defining a channel  106  extending therethrough. The distal end  104  comprises fingers  108  (in this example, 2 fingers  108 ) each of which is formed by a pair of longitudinal slits  110  extending through the cylindrical body  102 . Each of the fingers  108  is biased toward a release position in which a distal ends thereof is drawn radially inward into the channel  106  out of engagement with a corresponding finger engaging window  202  in the capsule  200  an angle described in greater detail hereinafter. The fingers  108  may be formed of a material having polymer components and may be sized and shaped to exhibit predetermined deflective properties, as will be described in greater detail later. In one embodiment, the fingers  108  may be annealed or otherwise treated to exhibit the desired properties. In another embodiment, the fingers  108  may comprise holes or other portions of removed material in order to enhance their flexibility as would be understood by those skilled in the art. 
     As shown in  FIGS. 2-7 , two pairs of slits  110  are formed on opposing sides of the cylindrical body  102  so that each of the fingers  108  is separated from the other by an angle of approximately 180°. As would be understood by those skilled in the art, although the bushing  100  according to this embodiment is described with two fingers, any other number of fingers may be employed without deviating from the scope of the present invention. The width of the fingers  108  is selected to permit a desired engagement between the distal end of each of the fingers  108  and the corresponding window  202 . In one embodiment, the thickness of the fingers  108  is approximately 0.127 mm., although any other thickness may be used without deviating from the spirit and scope of the present invention. The material thickness of the fingers  108  is preferably selected such that a required force applied by the control member  107  to the clip  40  and subsequently, the capsule  200  does not cause the fingers  108  to disengage from the windows  202 . As described above, in an unstressed state, the fingers  108  are withdrawn toward the center of the channel  106  allowing the distal end  104  of the bushing  100  to be inserted into the proximal end of a capsule  200 . As will be described in greater detail with respect to the exemplary method of the present invention, a core pin  109  is inserted over the control member  107  into the bushing  100  after the distal end  104  has been inserted into the capsule  200  and advanced distally through the channel  106  to move the fingers  108  radially outward so that they engage the corresponding windows  202  of the capsule locking the busing  100  to the capsule  200 . As the core pin  109  is moved into the channel  106 , the fingers  108  are deflected radially outward from their unstressed state between 20 and 80 microns and more preferably by approximately 25.4-76.2 microns to lockingly engage windows  202  in the capsule  200 . It is noted, however, that this range is exemplary only and that any other range may be employed without deviating from the scope of the invention. Specifically, the fingers  108  are configured so that, when in the biased configuration of  FIG. 2 , the bushing  100  is insertable into the capsule  200 . Once inserted, the fingers  108  may be configured to deflect radially outwardly by any range. In one embodiment, the core pin  109  is formed as a disc having an outer diameter greater than a non-stressed diameter of the fingers  108 , as shown in  FIGS. 2 and 3 , with a central opening through which the control member  107  may slide. As would be understood by those skilled in the art, the core pin  109  may be formed in any shape so long as it is sized to move through the channel  106  and is wide enough to move the fingers  108  from the unstressed position into locking engagement with the windows  202 . For example, the core pin  109  may also be formed with a conical shape or any other shape without deviating from the spirit and scope of the present invention. 
     After the core pin  109  has been positioned to lock the bushing  100  to the capsule  200 , the clip  40  may be deployed, as would be understood by those skilled in the art, by applying increasing tension to the control member  107  via the handle  20  until the connection between the clip  40  of the distal assembly and the control member  107  is severed. At this point, the core pin  109  of the control member  107  or a separate abutting member  111  attached thereto, is drawn with the control member  107  proximally through the capsule  200 . The control member  107  moves proximally until the core pin  109  no longer contacts the fingers  108 , thus freeing the fingers  108  to return to the unstressed position in which they are retracted radially into the channel  106  out of engagement with the windows  202  of the capsule  200 . Thus, the capsule  200  is separated from the bushing  100  and the clip  40  may be left in place within the body as the bushing  100  and the control member  107  are withdrawn therefrom. 
     A distal end of each of the fingers  108  comprises a hook-shaped lip with a first curved section  112  extending into the channel  106  to define a reduced diameter neck of the channel  106  and a second section  114  extending distally from the first section  112 . The second section  114  increases in diameter in a distal direction so that, when the core pin  109  is in position urging the fingers  108  radially outward, a diameter of the bushing  100  is greatest at a distal end of a distal section  116 . In one embodiment, the bushing  100  comprises a substantially cylindrical proximal section  118  having a first substantially uniform outer diameter with a tapered distal section  116  extending therefrom tapering down in diameter in a distal direction. The second section  114  of each finger  108  extends along an axis angled relative to an axis of the distal section  116 . In one embodiment, an angle α between the axis of the second section  114  and the axis of the distal section  116  is greater than 90° and smaller than 180° and preferably approximately 110°-115° and in an exemplary embodiment, approximately 110°. 
     As described above, in an operative configuration, the first and second sections  112 ,  114  are configured to be received in the windows  202  formed through a proximal end  204  of the capsule  200 , as shown in  FIGS. 2-6 . The windows  202  are formed on opposite sides of the proximal end  204  and separated from one another by an angle of approximately 180° or another angle selected to conform to the placement of the fingers  108  over the distal end  104  of the bushing  100 . To couple the bushing  100  to the capsule  200 , a first one of the fingers  108  is inserted into a first one of the windows  202  by pivoting the bushing  100  by, for example, approximately 20° relative to a longitudinal axis of the capsule  200  as shown in  FIG. 4 . It is noted however that the bushing  100  may be pivoted by any other angle as called for by the dimensions of the bushing  100 , first and second sections  110 ,  112  and capsule  200 . Once the first and second sections  110 ,  112  of the first finger  108  have been positioned within the first window  202 , the second finger  108  is positioned adjacent to a second window  202  by returning the bushing  100  to longitudinal alignment with the capsule  200 . 
     In operation, the bushing  100  remains coupled to the capsule  200  during insertion to a target location within a body (e.g., through a body lumen accessed via a natural body orifice). Once the capsule  200  has been properly positioned and clipped over a target portion of tissue, the user retracts the core member  107  proximally by operating the handle  20  until the control member is separated from the clip  40  (by any known mechanism) so that the control member  107  is drawn proximally to contact the core pin  109 , driving the core pin  109  proximally out of engagement with the fingers  108 . Proximal retraction of the core pin  107  causes the fingers  108  to return to their biased configuration in which the outer diameter of the first and second sections  110 ,  112  is smaller than a diameter of the capsule  200  at the windows  202 . 
     As those skilled in the art will understand, in some cases the bushing  100  may be damaged during, for example, insertion into the body or may be otherwise deformed. In one such case, the bushing  100  may not separate from the capsule  200  upon retraction of the core pin  109  (i.e., distal ends of the fingers  108  may not be sufficiently withdrawn into the channel  106  after the core pin  109  has been removed therefrom retaining the connection between the bushing  100  and the capsule  200 ). The bushing according to the present invention still permits a user to separate the bushing  100  from the capsule in these situations by applying a proximally directed force to the flexible insertion member  30 . That is, as the clip  40  is now locked in place on target tissue, drawing the flexible insertion member  30  proximally places the flexible insertion member  30  under tension and exerts a force on the connection between the fingers  108  of the bushing  100  and the capsule  200 . The angle of the distal ends of the fingers  108  relative to the edge of the windows  202  against which they abut allows the force required to separate the bushing  100  from the capsule in these conditions to be smaller than a force required to dislodge a properly placed clip  40  from the tissue over which it has been clipped. Thus, as will be described in greater detail hereinafter, the exemplary system according to the present invention is configured so that the bushing  100  will separate from the capsule  200  when subjected to a force less than that required to pull a properly deployed clip  40  from tissue. In an exemplary embodiment of the present invention, the capsule  200  and bushing  100  may be configured with a singular connection so that, once the bushing  100  has been separated from the capsule  200 , a reconnection therebetween is not permitted. In another embodiment however (not shown), the capsule  100  and bushing  200  may configured to permit multiple connections therebetween. 
     In one embodiment, as depicted in  FIG. 7 , the angles of the first and second sections  112 ,  114  convert the force F TOTAL  to a vector force comprising a first proximally directed force, F 1  and a second force F 2  extending at an angle to the force F 1 . As those skilled in the art will understand, the direction and magnitude of each of the forces F 1  and F 2  depend upon the configuration of the first and second sections  112 ,  114 . In one embodiment, the second section  114  is angled with respect to the tapered distal section  116  at an angle of approximately 110-115°, as shown in  FIG. 2 . 
     The angle at which the second section  114  extends relative to the distal section  116  is selected to achieve a desired coupling strength between the capsule  200  and the bushing  100  while permitting the bushing to be pulled proximally out of engagement with the capsule  200  by a force less than that required to dislodge a clip from tissue on which it has been placed. As would be understood by those skilled in the art, the greater the angle of the second section  114  relative to the distal section  116 , the smaller the force required to deflect the finger  108  radially inward out of engagement with the window  202 . In an exemplary embodiment, the angle α is selected so that the force F 2  is sufficient to dislodge the fingers  108  from the windows  202  while the force F 1  remains below the level required to dislodge a deployed clip  40 . In this manner, the force transmitted to the clip  40  is always less than that required to dislodge the clip  40  as the bushing  100  is disengaged from the capsule  200  before the force transmitted to the capsule exceeds this threshold level. For example, the total force required to dislodge the clip  40  from the tissue for an exemplary clip is approximately 0.947 N. However, this force may vary depending on the type of tissue being clipped, the mechanical strength of the clip  40  and a plurality of other factors known in the art. It is therefore respectfully submitted that this force is described herein for descriptive purposes only and that the angle of the second section  114  relative to the distal section  116  may be altered based on the characteristics of the procedure for which the clip  40  is intended. Each of the fingers  108  would be subject to one half of the force transmitted linearly along the insertion member  30 . Where the force required to dislodge a clip  40  is 0.947 N, the force transmitted by each of the fingers  108  to the capsule  202  should be no more than 0.474 N. The desired angle of the second section  114  may then be determined using the following formulas:
 
β=α±2°-90°,
 
wherein β is the angle of the second section  114  relative to an axis extending perpendicularly to the proximally directed force;
 
γ=90°-β,
 
wherein γ is the complementary angle of β
 
F 2 =cos(γ)·0.474 N
 
which, when simplified, yields:
 
F 2 =cos(180°-α±2°)·0.474 N
 
From this determination, we can determine the total radial displacement each of the fingers  108  into the channel  106  upon application of the proximally directed force F TOTAL . In one embodiment, displacement of the fingers  108  along the x-axis shown in  FIG. 7  can be determined so that the distance remaining between the fingers  108  is less than the inner diameter of the capsule  200 , which in an exemplary embodiment may be approximately 1.94 mm. The exact required deflection distance of the fingers  108  may vary based on an amount of damage sustained by each of the fingers  108  during manipulation. That is, if the fingers  108  return to their original configuration after engagement with the capsule  200 , the amount of required deflection may be smaller than if the fingers  108  fail to recover to their neutral configuration. In one embodiment, if the angle α is selected to be 105°, β will be 15°, γ will be 75°, and F 2  will be 0.123 N. In this embodiment, the total displacement of each of the fingers  108  along the x-axis will be 22.86 microns. The chart below depicts a list of values for three exemplary measurements of α. It is noted that any measurement of a within the range of 90-180° is also acceptable.
 
                                             α   β   γ   F 2     X-displacement                   105°   15°   75°   0.1227N   22.86 μm       110°   20°   70°   0.1621N   30.48 μm       115°   25°   65°   0.2003N    38.1 μm                    
After separating into the vector forces, the resultant force F 1  aids in the longitudinal separation of the fingers  108  from the windows  202  of the capsule  200 , thus separating the damaged or deformed bushing  100  from the capsule  200  as depicted in  FIG. 6 .
 
     It will be understood by those of skill in the art that the capsule  200  may be repeatedly moved between an engaged and disengaged position with the bushing  100  as desired by removing the core pin  109  from engagement with the fingers  108  and disengaging the fingers  108  from the windows  202  as described above. The bushing  100  may then be re-coupled to the capsule  200  when desired. 
     It will be apparent to those skilled in the art that various modifications can be made in the structure and the methodology of the present invention, without departing from the spirit or scope of the invention. Thus, it is intended that the present invention cover the modifications and variations of this invention provided that they come within the scope of the appended claims and their equivalents.