Abstract:
A biodegradable double stent is used for various organs such as a biliary tract, an esophagus, an airway and a ureter. A biodegradable stent having a hollow cylindrical body woven out of a separate wire made of biodegradable polymer so as to have a plurality of rhombic spaces is fixed to an intermediate portion of a primary stent having a cylindrical body. When administered into the organ, the biodegradable stent has its original function of expanding the organ, and is firmly supported in the inner wall of a narrowed passage of the organ by pressurizing the inner wall of the narrowed passage of the organ. After a predetermined time period has elapsed, the biodegradable stent is gradually degraded away by bodily fluids, thereby enabling the primary stent to be easily removed from the organ.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates, in general, to a stent that is used for a patient who does not suffer from a malignant tumor but rather from chronic obstructive pulmonary disease (COPD) in which microtubules such as terminal tracts, bronchioles, etc. of the lungs are blocked, or a patient who suffers from tract stenosis that temporarily manifests itself after various organs such as a biliary tract, an esophagus, an airway and a ureter as well as the surroundings thereof are operated. More particularly, the present invention relates to a biodegradable double stent, in which a biodegradable stent having a hollow cylindrical body woven out of a separate wire made of biodegradable polymer so as to have a plurality of rhombic spaces is fixed to an intermediate portion of a primary stent having a cylindrical body, and in which the biodegradable stent maintains a firmly supported state by pressurizing the inner wall of an organ when inserted into the organ, and then is gradually degraded away by bodily fluids while a lesion area is being cured, thereby enabling the primary stent to be easily removed from the organ. 
         [0003]    2. Description of the Related Art 
         [0004]    Generally, in order to keep narrowed excretory passages expanded at places where microtubules such as terminal tracts, bronchioles, etc. of the lungs are blocked due to chronic obstructive pulmonary disease (COPD) rather than a malignant tumor, and in order to widen the excretory passages of various organs, such as such as a biliary tract, an esophagus, an airway and a ureter, which are narrowed by lesions or which are temporarily narrowed when surroundings of the organs are resected and sutured, various stents are used. 
         [0005]    However, the stents administered to the microtubules of the lungs and particularly to narrowed excretory passages, have a problem because they deviate from the narrowed excretory passages without maintaining a firmly supported state due to inspiratory or expiratory pressure caused by respiration. 
         [0006]    In order to solve this problem, a stent administrated into a narrowed tract of a lung, a biliary tract, a large intestine, a small intestine, an esophagus, or the like has been disclosed, wherein curved catch ridges protrude from an outer circumference of the middle of the stent. 
         [0007]    In detail, as illustrated in  FIG. 1 , when the stent  1  is fabricated using a wire  1 , curved catch ridges  3  protrude from an outer circumference of the middle of the stent. 
         [0008]    This stent is administrated into the narrowed passage of the lung, the biliary tract, the large intestine, the small intestine, the esophagus, or the like, and thus the curved catch ridges  3  formed on the outer circumference of the middle of the stent offer close contact support with an inner wall of the narrowed passage. 
         [0009]    However, the conventional stent is configured such that the curved catch ridges  3  formed on the outer circumference of the middle thereof offer close contact support with an inner wall of the narrowed passage. As such, the stent does not firmly resist external pressure or force. 
         [0010]    In other words, the stent is not firmly maintained in the narrowed tract, because of the inspiratory or expiratory pressure caused by respiration of the lung or the force of substances such as bile of the biliary tract or food passing through the large intestine, the small intestine or the esophagus. 
         [0011]    After surroundings of the organ are excised and then sutured, the passage of the organ is temporarily narrowed during the healing process. Thus, this stent is used to expand the narrowed passage, and then must be removed after a lesion area has completely cured. At the time of removal, the catch ridges greatly inhibit the stent from being removed from the organ. 
       SUMMARY OF THE INVENTION 
       [0012]    Accordingly, the present invention has been made keeping in mind the above problems occurring in the related art, and embodiments of the present invention provide a biodegradable double stent, which is firmly maintained without a change in position such as sliding after being administered into a lesion area, and which is allowed to be easily removed after the lesion area has cured. 
         [0013]    According to one aspect of the present invention, there is provided a double-tube type biliary stent, which includes a primary stent having a hollow cylindrical body that has a plurality of rhombic spaces formed by weaving an alloy wire made of superelastic shape memory alloy or stainless steel so as to be crossed and that is inserted into and expands an excretory passage of an organ, and a biodegradable stent having a hollow cylindrical body that has a plurality of rhombic spaces formed by weaving a separate wire made of biodegradable polymer so that they criss-cross each other and that has a curved portion curved outwards at an intermediate portion thereof. 
         [0014]    According to embodiments of the present invention, the biodegradable double stent is used for temporary administration followed by removal after a predetermined time period has elapsed. 
         [0015]    At this time, when the biodegradable double stent is administrated into the passage of an organ, the biodegradable stent made of biodegradable polymer supports an inner wall of the passage of the organ by exerting a predetermined pressure, so that it can be firmly maintained in the passage of the organ. 
         [0016]    The biodegradable double stent is firmly maintained without changes in its position caused by sliding and the like, after being administered into the passage of the organ. After a predetermined time period has elapsed, the biodegradable stent is gradually degraded away by bodily fluids when a lesion area of the passage of the organ has completely cured. 
         [0017]    This degradation of the biodegradable stent can remove the primary stent from the passage of the organ with ease. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0018]    The above and other objects, features and advantages of the present invention will be more clearly understood from the following detailed description when taken in conjunction with the accompanying drawings, in which: 
           [0019]      FIG. 1  is a front view illustrating a conventional biliary stent; 
           [0020]      FIG. 2  is a disassembled perspective view illustrating a biodegradable double stent according to an exemplary embodiment of the present invention; 
           [0021]      FIG. 3  is an assembled perspective view of the biodegradable double stent of  FIG. 2 ; 
           [0022]      FIGS. 4A and 4B  are sectional views of the biodegradable double stent of  FIG. 2 ; 
           [0023]      FIGS. 5A through 10  illustrate a biodegradable double stent according to another embodiment of the present invention; 
           [0024]      FIGS. 11 through 14  illustrate the operation of a biodegradable double stent according to another embodiment of the present invention; and 
           [0025]      FIGS. 15 through 22  illustrate a biodegradable double stent according to another embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0026]    Reference will now be made in greater detail to an exemplary embodiment of the invention, an example of which is illustrated in the accompanying drawings. Wherever possible, the same reference numerals will be used throughout the drawings and the description to refer to the same or like parts. 
         [0027]    An exemplary embodiment of the present invention is characterized in that a biodegradable stent having a hollow cylindrical body that has a plurality of rhombic spaces formed by weaving a separate wire made of biodegradable polymer is fixed to an intermediate portion of a primary stent having a hollow cylindrical body that has a plurality of rhombic spaces formed by weaving a superelastic shape memory alloy wire or a stainless steel wire so as to be criss-crossed. 
         [0028]    In detail, as illustrated in  FIGS. 2 through 4B , a biodegradable double stent includes: a primary stent  10  having a hollow cylindrical body  15  that has a plurality of rhombic spaces  12  formed by weaving an alloy wire  11  made of superelastic shape memory alloy or stainless steel so as to be criss-crossed and that is inserted into and expands the excretory passage of an organ; and a biodegradable stent  23  having a hollow cylindrical body  15 ′ that has a plurality of rhombic spaces  12 ′ formed by weaving a separate wire  21  made of biodegradable polymer so as to be criss-crossed and that has a curved portion  22  curved outwards at an intermediate portion thereof. Here, the biodegradable stent  23  is located on an outer circumference of the primary stent, and is connected to the primary stent  10  at one of opposite ends thereof using a connecting thread or a connecting wire  20 . 
         [0029]    The biodegradable stent  23  is made of a separate wire  21  of biodegradable polymer. The biodegradable polymer includes one selected from poly L-lactic acid (PLLA), poly lactic acid (PLA), polyglycolic acid (PGA), poly glycolide-co-L-lactide acid (PGLA), polydioxanone (PDO), poly glycolide-co-caprolactone (PGCL), and so on. 
         [0030]    However, it should be noted that the biodegradable polymer for the biodegradable stent  23  can use any material innocuous to the human body because it is configured to facilitate removal of the primary stent  10  after the predetermined time period which it takes to be gradually degraded away by bodily fluids has elapsed. 
         [0031]    Further, herein, the biodegradable stent  23  is installed on an outer circumference of the primary stent  10 . However, the biodegradable stent  23  may be installed on a part, for instance, a middle portion or one end, of the outer circumference of the primary stent  10  if necessary. 
         [0032]    Further, the biodegradable stent  23  may be connected to the primary stent  10  at either end thereof in the state in which it is installed on the outer circumference of the primary stent  10 . If necessary, the biodegradable stent  23  may be connected to the primary stent  10  at opposite ends thereof in the state in which it is installed on the outer circumference of the primary stent  10 . 
         [0033]    In this manner, the biodegradable stent  23  can be variously modified. 
         [0034]    As illustrated in  FIGS. 5A, 5B, 5C and 5D , the biodegradable double stent  24  is configured so that the biodegradable stent  23  is installed on the outer circumference of the primary stent  10 , wherein the biodegradable stent  23  is formed as a hook-shaped stent  100  curved in a downward direction and is fastened to the primary stent  10  at opposite ends thereof using a fasting means  101 . 
         [0035]    At this time, at least one hook-shaped stent  100  is installed on the outer circumference of the primary stent  10 . In detail, the two hook-shaped stents  100  can be installed so as to be opposite to each other in a diametrical direction. In addition, the numerous hook-shaped stents  100  can be installed in one or more rows at regular intervals in a longitudinal direction. 
         [0036]    Further, as illustrated in  FIGS. 6A and 6B , the several hook-shaped stents  100  can be installed so as to be opposite to each other in a diametrical direction of the primary stent  10 . In addition, the numerous hook-shaped stents  100  can be installed in one or more rows at regular intervals in a longitudinal direction of the primary stent  10 . 
         [0037]    As illustrated in  FIG. 7 , the numerous hook-shaped stents  100  can be installed in a zigzag shape in a longitudinal direction of the primary stent  10 . 
         [0038]    At this time, each hook-shaped stent  100  is made of a separate wire  21  of biodegradable polymer. The biodegradable polymer includes one selected from poly L-lactic acid (PLLA), poly lactic acid (PLA), polyglycolic acid (PGA), poly glycolide-co-L-lactide acid (PGLA), polydioxanone (PDO), poly glycolide-co-caprolactone (PGCL) and so on. 
         [0039]    Further, the biodegradable stent  23  can be implemented as illustrated in  FIGS. 8 and 9 . 
         [0040]    As described above, the biodegradable stent  23  is made of a separate wire  21  of biodegradable polymer, and is configured so that one end thereof is formed as a pressurization end  200  protruding outwardly from the outer circumference of the primary stent  10  and that the rest thereof is interwoven with the primary stent  10 . 
         [0041]    This structure is preferably formed on opposite sides of the primary stent  10 . In this case, the pressurization end  200  of the biodegradable stent  23  is formed in a linear shape as illustrated in  FIG. 8 , or otherwise in a hook shape as illustrated in  FIG. 10 . 
         [0042]    Now, the operation and effects of the biodegradable double stent having the aforementioned configuration will be described below. 
         [0043]    It should be noted that the description of  FIGS. 11 and 12  is merely made for the illustrative purpose but not for the purpose of limiting the invention to application in a lung  50 . 
         [0044]    First, the biodegradable double stent is administrated on the desired area of an organ using separate surgical tools. 
         [0045]    When this administration is performed, the primary stent  10  expands the excretory passage of a lesion area for its original purpose, and particularly is inserted into narrowed excretory passages of various organs or microtubules such as terminal tracts, bronchioles, etc. of the lungs of a person who does not suffer from a malignant tumor, or temporarily narrowed excretory passages occurring when surroundings of such organs are excised and sutured using insertion tools, and thereby expands the narrowed excretory passages. 
         [0046]    At this time, the biodegradable stent  23  located outside the primary stent  10  supports and pressurizes an inner wall of the excretory passage of the administrated organ, and thus is caught on the inner wall of the excretory passage. In detail, the curved portion  22  of the biodegradable stent  23 , an intermediate portion of which protrudes in an outward direction, supports and pressurizes the inner wall of the excretory passage of the organ where it was administered, and thus is caught on the inner wall of the excretory passage. 
         [0047]    This catching action allows the biodegradable double stent to be firmly maintained in an inner wall of the excretory passage without deviation from the inner wall of the excretory passage. 
         [0048]    More specifically, the biodegradable double stent does not deviate from the administered position, because the biodegradable stent  23  pressurizes the inner wall of the excretory passage although the primary stent  10  be forcibly pushed in a downward direction by excessive force caused by endocrine secretion or food passing through the excretory passage of the organ. 
         [0049]    Further, as illustrated in  FIG. 12 , although the primary stent  10  attempts to slide downwards due to this external force, the primary stent  10  stands against the external force in interaction with the biodegradable stent  23  because the primary stent  10  is coupled with the biodegradable stent  23 , and because the biodegradable stent  23  pressurizes the inner wall of the excretory passage of the organ. Thus, the biodegradable stent  23  resists against the sliding due to the pressurizing force of the biodegradable stent  23  which is applied to the inner wall of the excretory passage of the organ, and thus the biodegradable stent  23  is contracted to undergo an increase in its diameter in proportion to such contraction, so that the biodegradable stent  23  further pressurizes the inner wall of the excretory passage of the organ in an outward direction. 
         [0050]    Thus, although the primary stent  10  is pushed outwards by such temporary external force, the primary stent  10  is temporarily pushed without deviation from the administered position, and then is returned to its original position again thanks to the supporting force of the biodegradable stent  23  when the external force is removed. 
         [0051]    In particular, when the biodegradable double stent  24  is administered to the lesion area of a pulmonary disease, the aforementioned action allows the primary stent  10  to be firmly maintained without deviation from the administered position because the curved portion  223  of the biodegradable stent  23  pressurizes the inner wall of the narrowed excretory passage of the organ in the event of respiration, i.e. inspiration or expiration. 
         [0052]    When the lesion area is completely cured with the lapse of time after the administration of the stent, it is necessary to remove the biodegradable double stent  24  from the administered position. 
         [0053]    The biodegradable stent  23  made of biodegradable polymer is gradually degraded away by bodily fluids while a lesion area is being cured. 
         [0054]    When the biodegradable stent  23 , which is made of biodegradable polymer and firmly maintains the biodegradable double stent  24  itself at the administered position by supporting the inner wall of the excretory passage of the organ, is degraded away, the primary stent  10  of the biodegradable double stent  24  becomes free from the administered position. 
         [0055]    This free primary stent  10  has to be removed using separate tools such as surgical tools. 
         [0056]    Similarly, as illustrated in  FIG. 13 , the hook-shaped stent  100  prevents the primary stent  10  from easily sliding due the external force, because the hook-shaped stent  100  also pressurizes the inner wall of the excretory passage of the organ after administration. As the primary stent  10  attempts to move downwards due to strong external force, the hook-shaped stent  100  still more strongly pressurizes the inner wall of the excretory passage of the organ in an outward direction. As a result, the primary stent  10  is prevented from deviating from the administered position. 
         [0057]    At this time, similar to the biodegradable stent  23  made of biodegradable polymer, the hook-shaped stent  100  is also gradually degraded away by bodily fluids while the lesion area is being cured. 
         [0058]    When the hook-shaped stent  100 , which firmly maintains the biodegradable double stent  24  itself at the administered position by supporting the inner wall of the excretory passage of the organ, is degraded away, the primary stent  10  of the biodegradable double stent  24  becomes free from the administered position. 
         [0059]    This free primary stent  10  has to be removed using separate tools such as surgical tools. 
         [0060]    Further, as illustrated in  FIG. 14 , when the pressurization end  200  of the biodegradable stent  23  protruding outwards from the primary stent  10  is administered, the pressurization end  200  of the biodegradable stent  23  pressurizes the inner wall of the excretory passage of the organ. 
         [0061]    This configuration prevents the primary stent  10  from sliding downwards due to the application of an external force. Further, since the biodegradable stent  23  is made of biodegradable polymer, the biodegradable stent  23  is gradually degraded away by bodily fluids while the lesion area is being cured. Thus, the primary stent  10  of the biodegradable double stent  24  becomes free from the administered position. 
         [0062]    This free primary stent  10  has to be removed using separate tools such as surgical tools. 
         [0063]    According to an embodiment of the present invention, the biodegradable double stent  24  as described above can be applied to a trumpet-shaped stent  45  having expanded portions  43 , which are greater than the diameter of the cylindrical body  15  of the primary stent  10  at the opposite ends of the primary stent  10 . For example, this trumpet-shaped stent  45  includes one having the expanded portions  43 , each of which has a taper face  42  inclined at a predetermined angle as illustrated in  FIG. 15  or each of which has a flat face  41  formed in a step shape as illustrated in  FIG. 16 . 
         [0064]    Further, as illustrated in  FIGS. 17, 18 and 19 , the biodegradable double stent  24  as described above can be applied to a thin-film-coated stent  50  or a thin-film-coated trumpet-shaped stent  60  in which a thin film  25  made of polytetrafluoroethylene (PTFE) or silicon can be formed on an inner and/or outer circumference of the primary stent  10  or the trumpet-shaped stent  45 . This thin-film-coated stent  50  or the thin-film-coated trumpet-shaped stent  60  is used for preventing the lesion area from penetrating into the primary stent  10  while the aforementioned lesion area grows. 
         [0065]    In this case, as illustrated in  FIGS. 20, 21 and 22 , if necessary, in order to maintain the biodegradable double stent at the lesion area for a long time after the biodegradable double stent has been administered, the inner circumference of the primary stent  10  or the trumpet-shaped stent  45  is selectively coated with PETE or silicon, while the outer circumference of the primary stent  10  or the trumpet-shape stent  45  is coated with a material, which is different from that coated on the inner circumference of the primary stent  10  or the trumpet-shaped stent  45 . For example, if the inner circumference of the primary stent  10  or the trumpet-shaped stent  45  is coated with PETE, the outer circumference of the primary stent  10  or the trumpet-shaped stent  45  is coated with silicon. 
         [0066]    In the latter case, since the inner and outer circumferences of the primary stent  10  or the trumpet-shaped stent  45  are coated with the different materials, the time required for degradation of the biodegradable stent  23  by bodily fluids is prolonged, as compared to the former case in which one of the inner and outer circumferences of the primary stent  10  or the trumpet-shaped stent  45  is coated with PETE or silicon. As such, the biodegradable double stent is maintained in the human body in proportion to the prolonged time, so that it can secure the excretory passage of the organ through outward pushing of the lesion area. 
         [0067]    Although an exemplary embodiment of the present invention has been described for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.