Patent Document

CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a divisional of U.S. patent application Ser. No. 10/283,873, entitled “Linearly Expandable Ureteral Stent,” filed Oct. 30, 2002 (now abandoned), the entirety of which is incorporated herein by reference. 
    
    
     BACKGROUND 
     The invention generally relates generally to medical devices for the drainage of fluids, and more specifically to ureteral stents. 
     A ureter is a tubular passageway in a human body that conveys urine from a kidney to a bladder. The ureter begins with the renal pelvis and ends at the trigone region of the bladder, i.e., the triangulated area between both ureteral orifices and the bladder neck. Urine is transported through the ureter under the influence of hydrostatic pressure, assisted by contractions of muscles located within the walls (lining) of the ureter. Some patients experience a urological condition known as ureteral blockage or obstruction. Some common causes of ureteral blockage are the formation of tumors or abnormalities within the ureteral lining, or the formation and passage of kidney stones. 
     Ureteral stents are used to facilitate urinary drainage from the kidneys to the bladder in patients having a ureteral obstruction or injury, or to protect the integrity of the ureter in a variety of surgical manipulations. Stents may be used to treat or avoid ureter obstructions (such as ureteral stones or ureteral tumors) which disrupt the flow of urine from the kidneys to the bladder. Serious obstructions may cause urine to back up into the kidneys, threatening renal function. Ureteral stents may also be used after endoscopic inspection of the ureter. 
     A stent may be uncomfortable to a patient because of intramural tunnel pain, imposed by the stent itself or in combination with intraoperative trauma inflicted from device passage. Pain may also be caused by urine reflux back up the ureter during increased bladder pressure, e.g., during voiding. Further, pain may stem from trigome irritation resulting from constant irritation, imposed by the bladder anchoring features or in combination with intraoperative trauma inflicted from device passage. Moreover, discomfort may arise from flank pain, caused by reflux or kidney anchoring. 
     Ureteral stents typically are tubular in shape, terminating in two opposing ends: a kidney distal end and a bladder proximal end. Existing ureteral stents compensate for the motion between the kidney and bladder by employing a pair of coil end-effectors, with one effector placed in the bladder proximal end and the other in the kidney distal end. As motion occurs, the ureter slides up and down the stent body. Any other travel results in an uncurling of the end effector(s). 
     SUMMARY 
     It is an objective of the invention to provide a patient, male or female, with a flexible device designed to maintain the patency of the ureter and enable fluid drainage while minimizing the pains and discomfort commonly associate with an in-dwelling device. 
     Discomfort may be related to the stent rubbing against a wall of the ureter, caused by the constant relative motion between the kidney and the bladder. This motion may be as much as 5 centimeters (cm) (approximately 2 inches) and cycles with each breath of the patient. This is equal to approximately 17,000 cycles per day, assuming 1 breath every 5 seconds. The present invention alleviates discomfort by providing a stent that, like the ureter, linearly expands and contracts in response to relative motion between the kidney and the bladder, thereby reducing friction caused by a stent rubbing against a wall of the ureter. 
     In one aspect, the invention features a ureteral stent having an elongated member defining a lumen. The member has a solid sidewall defining a spiral-shaped opening such that the member is linearly expandable along a longitudinal axis of the lumen. A distal retention structure is connected to a distal end of the elongated member for retention in a kidney, and a proximal retention structure is connected to a proximal end of the elongated member for retention in a bladder. 
     One or more of the following features may also be included. The member includes a spring having a spring force of less than one pound. The member includes a wire spring. The wire spring includes a metal alloy, that may include at least one of titanium, nickel, copper, cobalt, vanadium, and iron. The metal alloy includes nitinol. The wire spring is coated with a polymer. The polymer includes at least one of urethane, nylon, thermoplastic polyurethane (TPU), thermoplastic polyester elastomer, polyethyl, and silicone. 
     The stent has an elongated member including a tube having the solid sidewall and defining the lumen. The spiral-shaped opening is defined by a slit formed in the sidewall of the tube. The elongated member may include a polymer, such as at least one of urethane, nylon, TPU, thermoplastic polyester elastomer, polyethyl, and silicone. 
     The elongated member includes an inner liner and an outer cover. A wire spring is sandwiched between the inner liner and the outer cover, with the spiral-shaped opening being defined by slits formed in the inner liner and the outer cover, between a plurality of coils of the wire spring. The wire spring includes a metal alloy including, e.g., at least one of titanium, nickel, copper, cobalt, vanadium, and iron. The metal alloy includes nitinol. At least one of the inner liner and the outer cover includes a polymer. The polymer includes at least one of urethane, nylon, TPU, thermoplastic polyester elastomer, polyethyl, and silicone. 
     A removable introducer is sized for placement within the lumen. 
     In another aspect of the invention, a ureteral stent includes an elongated member defining a lumen, the member having a solid sidewall with at least one slit formed therein such that the member is linearly expandable along a longitudinal axis of the lumen. A distal retention structure is connected to a distal end of the elongated member for retention in a kidney, and a proximal retention structure is connected to a proximal end of the elongated member for retention in a bladder. 
     In yet another aspect of the invention, a method of facilitating urinary drainage from a kidney to a bladder in a patient that reduces discomfort to the patient includes positioning a ureteral stent in a ureter of a patient, the ureteral stent having an elongated member defining a lumen, the member having a solid sidewall defining a spiral-shaped opening such that the member is linearly expandable along a longitudinal axis of the lumen, a distal retention structure connected to a distal end of the elongated member for retention in the kidney, and a proximal retention structure connected to a proximal end of the elongated member for retention in the bladder. The elongated member is allowed to linearly expand and contract between an expanded position and a retracted position, based on at least one of: relative positioning of organs within the patient, a breathing pattern of the patient, and relative positions of the kidney and the bladder. In addition, the elongated member can be biased to the retracted position. 
     In yet another aspect of the invention, a method of manufacturing a linearly expandable ureteral stent includes providing an elongated member defining a lumen, the member having a solid sidewall defining a spiral-shaped opening such that the member is linearly expandable along a longitudinal axis of the lumen. The stent also includes a distal retention structure and a proximal retention structure. The distal retention structure is connected to a distal end of the elongated member, and the proximal retention structure is connected to a proximal end of the elongated member. 
     The following features may be included. Providing the elongated member includes providing a wire spring. Providing the wire spring includes coating the wire spring with a polymer. Providing the wire spring includes sandwiching the wire spring between an inner lining and an outer cover. The inner lining and outer cover include extruded sheets. The inner lining and outer cover are shrunk, and slits are formed through the inner lining and outer cover between a plurality of coils of the wire spring. The inner lining and the outer cover are melted, and slits are formed through the inner lining and outer cover between a plurality of coils of the wire spring. The elongated member is provided by forming a tube including a polymer, and forming a spiral slit through the tube. 
     In yet another aspect of the invention, a method of placing a ureteral stent in a patient includes providing a ureteral stent. The ureteral stent includes an elongated member defining a lumen, the member having a solid sidewall defining a spiral-shaped opening such that the member is linearly expandable along a longitudinal axis of the lumen. The ureteral stent also includes a distal retention structure connected to a distal end of the elongated member, and a proximal retention structure connected to a proximal end of the elongated member. The ureteral stent is inserted into a ureter of the patient. The ureteral stent is positioned in the patient with the distal retention structure substantially within the kidney of the patient, the elongated member substantially within the intramural tunnel portion of the ureter, and the proximal retention structure substantially within the bladder of the patient. In a detailed embodiment, the ureteral stent can further include a removable introducer sized to fit within the lumen and inserting the ureteral stent includes inserting the stent with the removable introducer into the ureter. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the drawings, like reference characters generally refer to the same parts throughout the different views. Also, the drawings are not necessarily to scale, emphasis instead generally being placed upon illustrating the principles of the invention. 
         FIG. 1A  is a schematic view of a human urinary tract, illustrating the placement of one embodiment of the invention within the ureter of a patient, in an expanded position; 
         FIGS. 1B-1C  are detailed sectional views of a portion of the embodiment of the invention of  FIG. 1A ; 
         FIGS. 2A-2B  are schematic representations of the embodiment of the invention illustrated in  FIGS. 1A-1C  in a retracted position; 
         FIGS. 3A-3B  are schematic representations of another embodiment of the invention in an expanded position; 
         FIGS. 4A-4C  are schematic representations of the embodiment of the invention illustrated in  FIGS. 3A-3B  in a retracted position; 
         FIGS. 5A-5C  are schematic representations of yet another embodiment of the invention at various stages of fabrication; 
         FIGS. 6A-6C  are schematic representations of yet another embodiment of the invention in retracted and expanded positions; and 
         FIG. 7  is a schematic representation of an introducer. 
     
    
    
     DETAILED DESCRIPTION 
     The invention features temporary ureteral stents that, when positioned within the ureter of a patient, significantly reduce discomfort to the patient. As used herein, proximal refers to the end of a stent closest to a medical professional when placing a stent in a patient. As used herein, distal refers to the end of a stent furthest from a medical professional when placing a stent in a patient. 
     Referring to  FIG. 1A , a human urinary tract  100  includes a ureter  105  that transports urine from a kidney  110  to a bladder  115 . When ureter  105  becomes blocked or obstructed due to, for example, post-kidney stone fragmentation/removal and ureteral stricture therapy, fluid drainage can become restricted. Ureteral stents are medical devices that are implanted within ureter  105  to restore patency and fluid drainage. A ureteral stent  120  is located within the ureter  105  of a patient, with a distal retention structure  125  in a pelvis  130  of kidney  110 , and a proximal retention structure  135  in the bladder  115 , proximate ureteral orifice  136 . A lumen  137  extends within distal retention structure  25 , an elongated member  140 , and proximal retention structure  135  to provide for the passage of fluid. Distal retention structure  125  is connected to a distal end  142  of elongated member  120 , and proximal retention structure  135  is connected to a proximal end  144  of elongated member  140 . Distal retention structure  125  secures distal end  142  of elongated member in or proximate to kidney  110 . Proximal retention structure  135  secures proximal end  144  of elongated member  140  in or proximate bladder  115 , as well as facilitates the removal of stent  120  by providing a loop suitable for grasping by a hook. 
     Distal retention structure  125  and proximal retention structure  135  can be fabricated of materials such as nylon, polyurethane, or the like. Heat bonding of these materials to elongated member  140  is conveniently accomplished by, for example, using an RF heat source as is commonly employed for plastic tubes and catheters. The desired shape of distal and proximal retention structures  125 ,  135  can be formed by injection molding or extrusion. They can also be heat-formed, for example, by flaring the working piece over an anvil of an appropriate shape, with the application of heat. The shape of distal retention structure  125  can be, for example, a coil, a pig-tail coil, J-shaped, or a helical coil. The shape of proximal retention structure  135  can be, for example, a coil, a pig-tail coil, J-shaped or a helical coil. In the illustrated embodiment, both distal and proximal retention structures  125 ,  135  are J-shaped. 
     Referring to  FIGS. 1A-1C , elongated member  140  includes a tube  145  having a solid sidewall  150 . A slit  155  is formed in sidewall  150 , defining a spiral-shaped opening  160 , so that elongated member  140  is linearly expandable along a longitudinal axis  165  of lumen  137 . Elongated member  140  can be formed from a polymer, such as, e.g., urethane, nylon, TPU, thermoplastic polyester elastomer, polyethyl, and silicone. 
     Elongated member  140  can be manufactured by, for example, injection molding or extrusion and optionally a combination of subsequent machining operations. Extrusion processes, for example, can be used to provide a uniform shape, such as a single monolithic tube. Spiral-shaped opening  160  can be created in the desired locations by a subsequent machining operation. 
     Referring also to  FIGS. 2A and 2B , elongated member  140  is linearly expandable between an expanded position (see, e.g.,  FIGS. 1A-1B ) and a retracted position (see  FIGS. 2A-2B ). When elongated member  140  is retracted, spiral-shaped opening  160  is closed. A difference in an expanded length L 1  of elongated member  140  in its expanded position and a retracted length L 2  of elongated member  140  in its retracted position can be approximately 5 cm (approximately 2 inches). For example, elongated member  140  can be sized so that retracted length L 2  is approximately 8 cm to 30 cm, and expanded length L 1  is approximately 13 cm to 35 cm. Elongated member  140  can have, in its retracted position, an outer diameter d 1  corresponding to approximately 3.7 French to 14.0 French. Lumen  137  can have a diameter d 2  when elongated member  140  is in its retracted position, to allow the introduction of a guide wire. 
     In use, elongated member  140  can expand linearly up to 2 inches to expanded length L 1 , to provide comfort to the patient by compensating for at least one of: relative positioning of organs within the patient, a breathing pattern of the patient, and relative positions of kidney  110  and bladder  115 . Because of the possibility of linear expansion, a physician may be able to select ureteral stent  120  with a smaller size than would be required with a conventional stent. 
     Referring to  FIGS. 3A-3B , in another embodiment, ureteral stent  300  has an elongated member  310  including a spring  315 . Distal retention structure  125  is connected to a distal end  312  of elongated member  310 , and proximal retention structure  135  is connected to a proximal end  314  of elongated member  310 . 
     Spring  315  has a plurality of coils  320  having, in some embodiments, a spring force less than one pound. Spring  315  includes a wire  325  formed from a superelastic material. Materials with superelastic properties make it possible to configure a component into a particular shape, such as a coil or a sleeve, and then modify reversibly the geometry of the component, such as by straightening it out. Once the device is straightened, after removal of the straightening force, the component reverts spontaneously to its predetermined configuration, thereby regaining its former geometry. In so doing, the component provides a biasing force back to its original configuration. 
     Superelastic materials can include alloys of In—Ti, Fe—Mn, Ni—Ti, Ag—Cd, Au—Cd, Au—Cu, Cu—Al—Ni, Cu—Au—Zn, Cu—Zn—Al, Cu—Zn—Sn, Cu—Zn—Xe, Fe 3 Be, Fe 3 Pt, Ni—Ti—V, Fe—Ni—Ti—Co, and Cu—Sn. Preferably, wire  325  includes a superelastic material comprising a nickel and titanium alloy, known commonly as nitinol, available from Memory Corp. of Brookfield, Conn. or SMA Inc. of San Jose, Calif. The ratio of nickel and titanium in nitinol can be varied. Examples include a ratio of about 50% to about 52% nickel by weight, or a ratio of about 48% to about 50% titanium by weight. Nitinol has shape retention properties in its superelastic phase. 
     Wire  325  can have a coating  330  including a biocompatible material, such as a polymer like urethane, nylon, TPU, thermoplastic polyester elastomer, polyethyl, or silicone. Coating  330  can be applied to wire  325  by various methods, such as spray coating or painting. 
     Ureteral stent  300  has an expanded position (see, e.g.,  FIGS. 3A-3B ) and a retracted position (see, e.g.,  FIGS. 4A-4C ). In the retracted position, coils  320  abut each other, defining a lumen  332  that is substantially enclosed. In the expanded position, coils  320  define a spiral-shaped opening  335 , formed by a plurality of gaps  340  between coils  320 . Elongated member  310  is linearly expandable along a longitudinal axis  345  of lumen  332 . 
     Referring to  FIGS. 5A-5C , in another embodiment, a stent  500  is formed by placing a wire spring  510 , having a plurality of coils  512 , between an inner lining  515  and an outer cover  520 . Wire spring  510  can be made from a metal alloy including, for example, titanium, nickel, copper, cobalt, vanadium, or iron. The metal alloy can include nitinol, a material including nickel and titanium. Inner lining  515  and outer cover  520  can each be formed from an extruded sheet. Inner lining  515  and outer cover  520  can each be made from a polymer, such as urethane, nylon, TPU, thermoplastic polyester elastomer, polyethyl, and silicone. 
     Inner lining  515  and outer cover  520  are deformed at elevated temperatures to fully surround wire spring  510 . For example, inner lining  515  and outer cover  520  can be shrunk by, e.g., exposure to a heat lamp. Alternatively, inner lining  515  and outer cover  520  can be melted by, e.g., heating in an oven. After deformation, a plurality of slits  525  are formed through inner lining  515  and outer cover  520  between coils  512  to form an elongated member  530 . Elongated member  530  is linearly expandable along a longitudinal axis  535  of a lumen  540  extending through elongated member  530 . Elongated member  530  is connected at a distal end  545  to a distal retention structure  125 , and at a proximal end  555  to a proximal retention structure  135 . 
     Referring to  FIGS. 6A-6C , in yet another embodiment, a stent  600  has an elongated member  610  connected to distal retention structure  125  for retention in a kidney and proximal retention structure  135  for retention in a bladder. Elongated member  610  defines a lumen  620 , and has a solid sidewall  625 . Solid sidewall  625  can be made of a biocompatible material, such as a polymer, e.g., urethane, nylon, TPU, thermoplastic polyester elastomer, polyethyl, or silicone. Solid sidewall  625  has at least one slit  630  formed in it, so that elongated member  610  is linearly expandable along a longitudinal axis  635  of lumen  620 . 
     Referring to  FIG. 7 , in another aspect, the invention provides an apparatus for delivering a stent into a patient. An introducer  700  includes a guide wire  710 . A proximal end  720  of guide wire  710  includes a grip  725  to assist in using the device. 
     Referring to  FIG. 7  and also to  FIG. 1A , in use, a stent, (e.g., stent  120 ) is mounted on introducer  700 . Distal retention structure  125  is threaded over guide wire  710 , and most of its inherent curvature is removed. Next, the guide wire  710  is inserted into bladder  115  through ureteral orifice  136  up ureter  105 , and into kidney  110 . A pusher (not shown) is then moved along guide wire  710 , pushing stent  120  along guide wire  710  towards kidney  110 . Proximal end  144  of elongated member  140  can be positioned either at or distal to ureteral orifice  136 . Stent  120  can also be positioned such that proximal retention structure  135  is at or distal to ureteral orifice  136 . 
     Once the surgeon has achieved the desired positioning of stent  120 , guide wire  710  is removed, while holding the pusher stationary to maintain stent  120  in position. Finally, the pusher is removed from within the patient, leaving stent  120  in place. Using this method, the stent of the invention can be precisely positioned within ureter  105  of the patient. The method can also be used to accurately position proximal retention structure  135  in bladder  115 , and distal retention structure  125  within kidney  110 . 
     In one embodiment of the invention, the guide wire, pusher, and stent are inserted into ureter  105  percutaneously through a surgical opening. In another embodiment, they are inserted into the ureter via the urinary tract of the patient. 
     While the invention has been particularly shown and described with reference to specific preferred embodiments, it should be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.

Technology Category: 1