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 fig1 a , 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 fig1 a - 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 fig2 a and 2b , elongated member 140 is linearly expandable between an expanded position ( see , e . g ., fig1 a - 1b ) and a retracted position ( see fig2 a - 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 fig3 a - 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 ., fig3 a - 3b ) and a retracted position ( see , e . g ., fig4 a - 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 fig5 a - 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 fig6 a - 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 fig7 , 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 fig7 and also to fig1 a , 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 .
a method includes placing a ureteral stent on an insertion tool . the ureteral stent includes an elongate member having a distal end coupled to a distal retention member . the elongate member includes a solid spring wire having a plurality of coils defining a lumen . a first portion of the insertion tool is disposed within the lumen , and the distal retention member , which has a nominally curved shape , is disposed about a second portion of the insertion tool such that the distal retention member is substantially linear . the insertion tool is inserted into the body of the patient and the ureteral stent is moved along the insertion tool such that at least a portion of the distal retention member is disposed within the kidney and a portion of the elongate member is disposed within the ureter .