Patent Publication Number: US-11654009-B2

Title: Helical hollow strand ureteral stent

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present patent application is a continuation of U.S. application Ser. No. 15/359,830, filed Nov. 23, 2016, issuing as U.S. Pat. No. 10,517,710 on Dec. 31, 2019, which claim the benefit of priority to U.S. Provisional U.S. Patent Application Ser. No. 62/262,634, filed Dec. 3, 2015, the entirety of each are hereby incorporated by reference. 
    
    
     FIELD 
     The present disclosure relates to medical devices and more specifically to stents. 
     BACKGROUND 
     The statements in this section merely provide background information related to the present disclosure and may not constitute prior art. 
     A stent is a tubular device that is placed into a body lumen, such as a blood vessel, of a patient to for example provide support to a weakened area or to maintain patency of a lumen within the body. Ureteral stents are a specific type of stents that are optimized for use in a patient&#39;s ureter. A ureteral, or ureteric, stent may be used to support a weakened ureter due to a variety of complications or to reopen a ureter that has been obstructed by a kidney stone. 
     The majority of ureteral stents used today are flexible polymer tubes that include drainage side ports and loops at each end ( FIG.  1   ). A guide wire is inserted into the patient&#39;s ureter and the stent is delivered over the guide wire and positioned within the patient&#39;s ureter. Polymer ureteral stents are designed to be flexible to reduce patient discomfort. However, polymer ureteral stents have several drawbacks. First, polymers degrade at a greater rate than other biocompatible materials and therefore they are only approved to be used for a short period of time (e.g. 6 months) before they must be removed from the patient and replaced. Second, polymers have a high surface friction, thus necessitating the use of a hydrophilic coating to prevent unwanted friction between the stent and the ureteral wall to prevent or limit damage to the ureteral wall. Third, polymer stents have low radial strength, meaning they are unsuitable for use in patients where a high radial strength is necessary to properly support the ureteral wall. Fourth, because the polymer stents are designed to be flexible, tensile strength and torque-ability is sacrificed, which may result in insufficient support of the ureteral wall. 
     Thus, it is desirable to provide a ureteral stent with high tensile, torque, compressive, and radial strength while maintaining maximum flexibility for patient comfort. Additionally, it is desirable to provide a ureteral stent that allows for passage over a guide wire and may remain indwelled in a patient for a long period of time. 
     SUMMARY 
     In one form of the present disclosure, a stent is provided. The stent comprises a body extending between a distal end and a proximal end. The body is defined by a plurality of elongated members, each elongated member extending between a distal end that is coterminous with the distal end of the body and a proximal end that is coterminous with the proximal end of the body. Further, each of the plurality of elongated members are arranged so as to define a lumen extending along the length of the respective plurality of elongated members, the lumen extending between the distal and proximal ends of the body so as to form a lumen length. Also, each of the plurality of elongated members are configured to permit drainage of a fluid from within the lumen to an environment external the stent along the entire lumen length. 
     Further, the stent may have each of the plurality of elongated members extend in a helical pattern to define a surface of the body and the lumen. The stent may also include the plurality of elongate members comprising a first plurality of elongated members and a second plurality of elongated members, wherein the first plurality of elongated members form an inner layer to define the lumen, and the second plurality of elongated members form an outer layer that surrounds the inner layer. The first plurality of elongated members may extend around and along the lumen in a clockwise helical pattern while the second plurality of elongated members may extend around and along the lumen in a counterclockwise helical pattern. The lumen may also be configured so as to allow the passage of a wire guide therethrough. The stent may further comprise a distal portion, a proximal portion, and a central portion, wherein one or both of the distal and proximal end portions are biased into a shape other than straight. 
     In another form of the present disclosure, a method for placing a ureteral stent is provided. This method comprises providing a stent that comprises a body extending between a distal end and a proximal end. The body is defined by a plurality of elongated members, each elongated member extending between a distal end that is coterminous with the distal end of the body and a proximal end that is coterminous with the proximal end of the body. Further, each of the plurality of elongated members are arranged so as to define a lumen extending along the length of the plurality of elongated members, the lumen extending between the distal and proximal ends of the body so as to form a lumen length. Also, each of the plurality of elongated members are configured to permit drainage of a fluid from within the lumen to an environment external the stent along the entire lumen length. The method further comprises advancing the ureteral stent into a ureter of a patient until the ureteral stent is positioned within the ureter. 
     The method may also comprise advancing a guide wire into the ureter before the step of advancing the ureteral stent into the ureter wherein the step of advancing the ureteral stent into the ureter further comprising advancing the ureteral stent over the guide wire. The method may also comprise removing the guide wire from the ureter. Additionally, the method may include removing the ureteral stent from the ureter. 
     Further areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. 
    
    
     
       DRAWINGS 
       The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way. 
         FIG.  1    is a side view of a known ureteral stent design; 
         FIG.  2    is a side view of a ureteral stent constructed in accordance with the teachings of the present disclosure; 
         FIG.  3    is a cross-sectional view of a ureteral stent; 
         FIG.  4    is an exemplary schematic of a ureteral stent with two layers of filars; 
         FIG.  5    is an orthogonal view of a filar of a ureteral stent; 
         FIG.  6    is a cross-sectional view of one example of a ureteral stent; 
         FIG.  7 A  is a cross-sectional view of an inner filar of a ureteral stent; and 
         FIG.  7 B  is a cross-sectional view of an outer filar of a ureteral stent. 
     
    
    
     DETAILED DESCRIPTION 
     The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses. It should be understood that throughout the drawings, corresponding reference numerals indicate like or corresponding parts and features. It should also be understood that various cross-hatching patterns used in the drawings are not intended to limit the specific materials that may be employed with the present disclosure. The cross-hatching patterns are merely exemplary of preferable materials or are used to distinguish between adjacent or mating components illustrated within the drawings for purposes of clarity. 
     Referring to  FIG.  2   , a ureteral stent  10  is provided. The ureteral stent  10  may have a body  7  with a distal end  11 , and proximal end  13 , a distal portion  12 , central portion  14 , and proximal portion  16 . The ureteral stent  10  may further include a lumen  18  that extends through the entire length  9  of the stent  10 . As can be seen, the central portion  14  of the ureteral stent  10  may be substantially straight along the entire length thereof. In contrast, one or both the distal portion  12  and proximal portion  16  may be straight or biased into loops, pigtails, or any other shape other than straight. The loops or other shapes may be formed by mechanical or plastic deformation or by heat setting the metal formed around a jig. The loops or other shapes may allow urine to travel through the center lumen as well as the sidewalls. 
       FIG.  3    shows a cross-section view of the ureteral stent  10 . As can be seen, the body  7  of the ureteral stent  10  may be defined by a plurality of thin, elongated members, or filars  20 , that each extend between a distal end that is coterminous with the distal end  11  of the body  7  and a proximal end that is coterminous with the proximal end  13  of the body  7 . The filars  20  need not extend completely from the distal end  11  to the proximal end  13  of the body  7  to be considered coterminous, as long as the filars  20  extend a substantial portion of that distance. Each of the plurality of elongated members are arranged to form and define a lumen  18 . The lumen  18  may extend along the entire length  9  of the stent  10 : from the proximal end  13  to the distal end  11 . Alternatively, the lumen  18  may extend along only a portion of the length  9  of the stent  10 . Each filar  20  may have a proximal end  17  and a distal end  19  ( FIG.  5   ). The filars  20  may each include a length  21  ( FIG.  5   ) along which the filars  20  are aligned so as to form the tube. As shown in  FIG.  3   , the filars  20  may be wound in a helical pattern along the lengths  21  of the filars  20  and around the lumen  18 . The filars  20  may extend around and along the lumen  18  at varying pitch magnitudes, including a pitch magnitude that allows for multiple helical revolutions around the lumen  18  between the distal end  11  and the proximal end  13  of the body  7 . In one non-limiting example, the pitch may range from 50-200 threads per inch. Alternatively, the filars  20  may extend straight along their entire lengths  21 , or in some other common pattern. The present embodiment also has two separate layers of filars  20 : an inner layer  22  and an outer layer  24 . The inner layer  22  may define the lumen  18  and the surface  23  of the lumen  18 , while the outer layer  24  surrounds the inner layer  22 . The filars  20  of both the inner and outer layers may be wound helically in the same direction along their lengths  21  (i.e. clockwise or counterclockwise). Alternatively, the filars  20  of the inner layer  22  may be wound helically in a clockwise direction along their lengths  21  while the outer layer  24  of the filars  20  may be wound helically in a counterclockwise direction, or vice versa.  FIG.  4    shows an exemplary stent  10  with a portion of the outer layer  22  removed so as to clearly show the inner layer  22  and outer layer  24  where the filars  20  are wound in opposite helical directions.  FIG.  4    is merely a schematic, and the stent  10  may have different numbers of filars  20  per layer, including a different number of filars  20  for each layer. The inner layer  22  filars  20  may extend around and along the lumen  18  at the same or varying pitch magnitudes as the outer layer  24  filars  20 . To prevent the filars  20  from unwinding and separating, the ends of the filars  20  may be bonded, soldered, welded, or otherwise mechanically or chemically attached together. Additionally, the ends of the filars  20  may be electropolished or otherwise finished to provide a smooth end of the stent  10  to ease introduction of the stent  10  into the patient. Alternative means of securing the ends or any other portion of the filars  20  together may be used. Additionally, the filars  20  may be bonded together at various locations along the lengths  21  of the filars  20 . Optionally, one or both ends of the stent  10  may be tapered, so as to ease introduction of the stent  10  into the patient. For example, the stent  10  with two layers  22 ,  24  of filars  20  may be tapered and then welded together at the end of the stent  10  to form a smooth, rounded end. The end may then be electropolished to ensure a smooth end of the stent  10 . 
     While the embodiment shown in  FIG.  3    includes two layers  22 ,  24  of filars  20 , any number of layers is contemplated, including a single layer or three or more layers of filars  20 . Additionally, the embodiment in  FIG.  3    includes 18 individual filars  20  for each of the inner and outer layers  22 ,  24  for a total of 36 filars  20 . However, any number of filars  20  may be used, including a different number of filars  20  for each layer. Further, the diameter of the lumen  18 , or inner diameter, and the outside diameter of the stent  10 , may be varied as desired by altering the size and number of filars  20 . The design of the filars  20  may be varied as well. The filars  20  may have varying cross-sections, such as circular or rectangular. However, the filars  20  in this embodiment have a cross-section as shown in  FIG.  5   . Each filar  20  in this embodiment may include an inner surface  30 , an outer surface  32 , and two side surfaces  34 ,  36 . The inner surface  30  may have a curved concave shape such that when the filars  20  are arranged together, a smooth, circular inner surface is provided to form the lumen  18 . Similarly, the outer surface  32  may have a curved, convex shape such that when the filars  20  are wound together, a smooth, cylindrical outer surface is provided along the entire length  9  of the stent  10 . 
     The filars  20  may be made of a variety of biocompatible materials. Ideally, due to its strength properties and resilience, a biocompatible metal may be used. However, the filars  20  may be made of other materials such as polymers. Other material examples for the filars  20  include, but are not limited to: nitinol, cobalt chrome alloys, 35N LT, MP35N, 304V and 304LV stainless, L605, FWM 1058, FWM 1537, Titanium Ti6Al-4V ELI, or any other material with a high corrosion resistance. 
     As shown in  FIG.  1   , typical ureteral stents include drainage ports  6  along the length of the stent  2 . These drainage ports  6  provide fluid communication between the lumen  4  of the stent  2  and an environment external the stent  2 . Ureteral stents must provide drainage along a substantial length of the stent due to blockages that may form in the lumen due to encrustation or biofilm formation. Due to the composition of urine, calcifications may form around the ureteral stent which can cause obstructions and potentially infection. Including drainage ports along the entire length of the stent limits the possibility that the stent may become entirely obstructed. In contrast to the ureteral stent  2  shown in  FIG.  1   , the ureteral stent  10  shown in  FIGS.  2  and  3    does not include any drainage ports. Drainage ports are not necessary in the present design because the filars  20  may be designed and arranged in such a way so as to allow drainage through the side walls of the inner and outer layers along a portion of the length of the stent (such as the central portion, for example), or along the entire length  9  of the stent  10 . When designed properly, small, imperceptible gaps exist between neighboring filars  20  that are large enough to allow a fluid to flow from the lumen  18 , through these gaps, and into an environment external to the stent  10  along the entire length  9  of the stent  10 , or a portion of the length of the stent  10 . While many factors may affect the rate at which the fluid may drain from the lumen  18  to an environment external the stent  10 , research has shown that altering the shape of the individual filars  20  so as to provide larger gaps along the lengths  21  of the filars  20  may increase the drainage rate. Additionally, reducing the number of filar layers may also increase the drainage rate. However, one of ordinary skill in the art upon a thorough review of this specification will understand that the drainage rate should be optimized while also maintaining appropriate strength and flexibility of the stent  10  for usage within the desired body lumen. 
     While the filars  20  of the ureteral stent  10  may include many variations, such as dimensions, amount, and number of layers, the following example shown in  FIG.  6    has been experimentally determined to provide adequate liquid flow through from the lumen of the stent and through the side walls of the stent while maintaining sufficient strength and flexibility for successful maintenance of patency through the ureter. 
     In some embodiments, the outer diameter  50  of the stent  10  may be about 0.072 inches while the inner diameter  52  of the stent  10 , which corresponds to the lumen  18  diameter, may be about 0.044 inches. These dimensions allow the stent  10  to be used with a standard 0.038 inch guide wire. In some embodiments, the stent may be two layers of filars: an outer layer  54  made up of nine outer layer filars  58  and an inner layer  56  made up of nine inner layer filars  60 . An exemplary outer layer filar  58  is shown in  FIG.  7 A , and an exemplary inner layer filar  60  is shown in  FIG.  7 B . Ideally, all nine of the inner layer filars  60  are identical in shape and size and all nine of the outer layer filars  58  are identical in shape and size. In this example, each outer layer filar  58  and inner layer filar  60  has a diameter of 0.007 inches. Further, in this embodiment, there may be pigtail loops on both the distal and proximal portions  12 ,  16  with diameters of around 1.5 centimeters. 
     The ureteral stent  10  described herein has various advantages over conventional plastic ureteral stent designs. As mentioned above, the need for drainage ports has been eliminated in the present design because the filars  20  allow for fluid to drain naturally from the lumen to a point external the patient along the entire length  9  of the stent. Additionally, the ureteral stent  10  has excellent tensile, torque, compressive, and radial force properties, thus ensuring the required strength to stabilize the ureter and maintain patency of the ureter and allow urine flow therethrough. However, despite the excellent strength properties of the ureteral stent  10 , flexibility has not been sacrificed, thus ensuring minimal patient discomfort. Additionally, because the stent  10  includes openings at both ends of the lumen  18 , the stent  10  may be fed over a guide wire during the insertion process. The stent  10  may also be made of a biocompatible metal that is corrosion resistant, thus allowing the stent  10  to remain in the patient for long periods of time before requiring replacement. 
     In use, to insert the ureteral stent  10  into a patient&#39;s ureter, a guide wire may first be provided. The guide wire may be inserted into a patient&#39;s ureter using conventional techniques. Next, the stent  10  may be advanced along the guide wire by inserting the guide wire into the lumen  18  of the stent  10 . The stent  10  may be advanced into the patient&#39;s ureter until it is positioned at the desired location, such as spanning between the kidney and the bladder. Then, the guide wire may be removed from the patient&#39;s ureter, while the stent  10  remains in place. When no longer necessary or requiring replacement, the stent  10  may be removed from the patient&#39;s ureter through the use of a variety of well-known removal methods. Alternatively, the stent  10  may be inserted into the patient&#39;s ureter without the use of a guide wire. 
     The description of the disclosure is merely exemplary in nature and, thus, variations that do not depart from the substance of the disclosure are intended to be within the scope of the disclosure. Such variations are not to be regarded as a departure from the spirit and scope of the disclosure.