Patent Publication Number: US-2007123974-A1

Title: Vascular stent which is specially designed for the multiple drug loading and better drug elution

Description:
CROSS-REFERENCE TO RELATED PATENT APPLICATION  
      This application claims the benefit of Korean Patent Application No. 10-2005-0100276, filed on Oct. 24, 2005, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.  
     BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to a vascular stent which is specially designed for multiple drug loading and improved drug elution, and more particularly to a vascular stent used in percutaneous coronary intervention (PCI), which effectively inhibits restenosis by loading a large amount of a drug or various types of drugs in multiple layers in slots of struts in the vascular stent and controlling elution of the drugs from the vascular stent to blood vessels, and can be easily installed in a serpentine coronary artery with excellent flexibility.  
      2. Description of the Related Art  
      Percutaneous coronary intervention (PCI) is a treatment procedure for obstructive coronary artery diseases such as myocardial infarction and angina pectoris. The procedure involves dilating the narrowed coronary artery by inserting a guidewire and then a balloon catheter into the obstructed coronary artery segment through arteries in the wrists or groins and expanding a balloon to expand the narrowed lesion. PCI is widely known as the most effective way to treat obstructed coronary arteries. It is estimated that more than 1 million patients in U.S.A., more than 100,000 patients in Japan, and more than 15,000 patients in Korea undergo PCI each year.  
      In PCI, the narrowed coronary arterial wall is expanded using the balloon catheter. In over 70% of patients undergoing PCI, a stent, which is a thin stainless steel or cobalt chrome mesh tube, is inserted in a vascular wall and thus the expanded vascular wall is continuously sustained.  
       FIGS. 1A through 1D  are schematic cross sectional views of blood vessels illustrating a PCI treatment process using a conventional stent and a restenosis formation;  
      Referring to  FIGS. 1A through 1D , a PCI treatment process using a balloon catheter with a stent will be described.  
      First, a balloon catheter  2  including a balloon  2   a  and a stent  1   a  optimized in conditions such as the length of a stenotic lesion and the diameter of a blood vessel, etc. is selected and inserted into a stenotic lesion L of a coronary artery (CA) ( FIG. 1A ). When the balloon catheter  2  reaches an accurate location of the stenosis region L, the balloon  2   a  is expanded to expand the stent  1   a  which is mounted on the balloon  2   a , so that the stent  1  is expanded by plastic deformation( FIG. 1B ). Then, the expanded balloon  2   a  is deflated to remove the balloon catheter  2  including the balloon  2   a , and thus the stent la is left installed in the coronary artery to keep the vascular region L open and prevent the coronary artery from being renarrowed ( FIG. 1C ). However, since the stent  1   a  itself is a foreign material in the human body, the cells in the vascular wall which withstand pressure from the installed stent  1   a  sustain barotrauma, and thus rapidly proliferate. If the rapidly proliferated cells excessively cover the stent  1   a , the vascular wall is narrowed again resulting in restenosis L′ ( FIG. 1D ). The risk of restenosis increases as the length of the stent  1   a  increases and as the diameter of the stent  1   a  decreases, and restenosis occurs in approximately 17 to 25% of patients. Restenosis mainly occurs within 1 to 3 months after PCI, and rarely occurs after 6 months.  
      Restenosis has been one of the major limitations of PCI. Accordingly, various methods of preventing restenosis have been developed. Recently, stents coated with drugs which can inhibit tissue overgrowth on the stent and prevent restenosis have been widely used in PCI treatment, resulting in a remarkable decrease in the incidence of restenosis after PCI.  
      Drugs such as rapamycin or paclitaxel which have anti-cancer activities are coated on the stents to inhibit restenosis after PCI treatment. When the drug coated stents are installed in the coronary artery, the restenosis rate is about 4% at a proximal end P and about 2 to 3% at a distal end D. It is assumed that the restenosis rate is relatively higher at the proximal end P than at the distal end D since the drugs coated on the stents to inhibit restenosis are washed by the bloodstream from the proximal end P to the distal end D.  
      Stents coated with drugs which can prevent restenosis are expected to become more widely used in coronary intervention in the future. Stents coated with drugs which can prevent restenosis have already been widely used. However most of the currently used drug coated stents use their preexisting stents and are not specifically designed for drug coating purpose. Stent design also has limitations that some stents are rigid to conform and track to the tortuous vessel and in side branch accessibility.  
      Thus, newly-designed stents for loading a sufficient amount of a drug or drug combinations which can sustainedly elute the drugs for a long period of time are required.  
      One of the inventors of the present invention recognized that conventional stents should be modified and filed a patent application (Korean Patent Application No. 2003-3465) reciting a stent for PCI which can be coated with a vascular restenosis-preventing drug with the Korean Intellectual Property Office. The structure of the stent is illustrated in  FIGS. 2A and 2B .  
       FIG. 2A  is a perspective view of an expanded stent  1   b  for PCI according to another invention of the inventor of the present invention, and  FIG. 2B  is an open form of the stent  1   b . The stent  1   b  is formed by disposing several first ring structures  10  and several second ring structures  20  in the longitudinal direction of the stent  1   b . Each of the first ring structures  10  includes a plurality of struts  11  disposed in a zigzag formation and connected to each other to form a cylindrical loop. A hole filled with drugs  12   a  penetrates each of a plurality of round ends  12  connecting each of the struts  11  and faces the center of the stent  1   b . A groove filled with drugs  11   a  is formed on the surface of each of the struts  11  in the longitudinal direction of the struts  11 .  
      Meanwhile, each of the second ring structures  20  includes a plurality of struts  21  having a thread  22  and a chase  23  disposed in a zigzag formation and connected to each other to form a cylindrical loop. The second ring structure  20  also includes a plurality of bridges  30  connecting one point of the struts  11  of the first ring structure  10  and the threads  22  of the second ring structure  20 . The bridges  30  are used to connect the first ring structures  10  and the second structures  20  to each other to form a net, and the bridges  30  includes a N-type serpentine link  31  in the center thereof.  
      The stent  1   b  illustrated in  FIGS. 2A and 2B , which was invented by one of the inventors of the present invention, has an excellent effect on eluting drugs inhibiting restenosis by loading the drugs on the stent  1   b . However, a vascular stent needs to be newly designed for loading a large amount of drugs inhibiting restenosis which occurs after PCI, extending the elution time of the drugs by separating a plurality of drugs in multiple layers, and controlling the elution time.  
      In addition, a vascular stent needs to be newly designed to be inserted into and installed in a serpentine coronary artery with excellent flexibility and to have open cell structures through which another balloon catheter with a stent can be inserted into and installed in a branched artery.  
     SUMMARY OF THE INVENTION  
      The present invention provides a specially designed vascular stent for multiple drug loading and improved drug elution which effectively elutes drugs for a long period of time by loading a large amount of a drug or various types of drugs in multiple layers in slots of struts in the vascular stent.  
      The present invention also provides an open cell type vascular stent with excellent flexibility having an open gap through which a balloon catheter with a stent can be inserted.  
      According to an aspect of the present invention, there is provided a vascular stent which is specially designed for multiple drug loading and better drug elution including:  
      a plurality of ring structures extending in the longitudinal direction of the vascular stent, comprising a plurality of struts disposed in a zigzag formation and connected to each other to form a cylindrical loop; and  
      a plurality of link structures disposed between the ring structures and connecting the ring structures in the longitudinal direction of the vascular stent,  
      wherein each of the struts in a ring structure is connected to adjacent struts in the same ring structure through one of a plurality of linking ends, a slot is formed in the strut in the longitudinal direction of the strut, and a multi-layer structure comprising a plurality of layers of drugs is loaded in the slot.  
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The above and other features and advantages of the present invention will become more apparent by describing in detail exemplary embodiments thereof with reference to the attached drawings in which:  
       FIGS. 1A through 1D  are schematic cross sectional views of blood vessel illustrating a percutaneous coronary intervention (PCI) treatment process using a conventional stent and a restenosis formation;  
       FIG. 2A  is a perspective view of an expanded stent  1   b  for PCI according to another invention of the inventor of the present invention;  
       FIG. 2B  is an open form view of the stent  1   b  illustrated in  FIG. 2A ;  
       FIG. 3  is a perspective view of a vascular stent  1  for multiple drug loading and improved drug elution according to an embodiment of the present invention;  
       FIG. 4  is an open form view of the vascular stent  1  of  FIG. 3 , according to an embodiment of the present invention;  
       FIG. 5  is an open form view of the vascular stent  1  of  FIG. 3  when expanded, according to an embodiment of the present invention;  
       FIG. 6  is an enlarged view of a section of the vascular stent  1  of  FIG. 4 , according to an embodiment of the present invention;  
       FIGS. 7A and 7B  are cross sectional views of a strut  120  in the enlarged vascular stent  1  of  FIG. 6  taken along an arbitrarily drawn cut-line VII-VII of  FIG. 6 , illustrating a rectangular slot  121  loaded with one drug, and a rectangular slot  121  loaded with a plurality of layers of drugs, respectively, according to an embodiment of the present invention;  
       FIG. 8A  schematically illustrates a vascular stent  1  in which a rectangular slot  121  is loaded with one drug and the external surface of the vascular stent  1  is coated with another drug, according to an embodiment of the present invention;  
       FIG. 8B  is a graph illustrating the concentration of drugs eluted from the vascular stent of  FIG. 8A  according to time, according to an embodiment of the present invention;  
       FIG. 9A  schematically illustrates a vascular stent  1  in which a rectangular slot  121  is loaded with a plurality of layers of drugs and the external surface of the vascular stent  1  is coated with another drug, according to an embodiment of the present invention;  
       FIG. 9B  is a graph illustrating the concentration of coated drugs eluted from the stent of  FIG. 9A  according to time, according to an embodiment of the present invention;  
       FIG. 10  is an enlarged perspective view of a partial stent  1  in which an open gap  210  is formed between S-type links  200 ′ of a link structure  200 , according to an embodiment of the present invention;  
       FIGS. 11A through 11D  illustrate procedures of inserting a balloon catheter  2  with a second vascular stent  1 ″ into a branched artery BA through an open gap  210  formed between S-type links  200 ′ of a first vascular stent  1 ′ installed in a coronary artery CA, and installing the second vascular stent  1 ″ in the branched artery BA when stenosis regions L 1  and L 2  are found in each of the coronary artery CA and the branched artery BA, according to an embodiment of the present invention;  
       FIG. 12  is a schematic view of a stent  1  installed in a serpentine blood vessel, according to an embodiment of the present invention;  
       FIGS. 13A and 13B  illustrate sizes of elements of a stent  1  according to an embodiment of the present invention;  
       FIG. 14  illustrates an open form of a stent  1  according to another embodiment of the present invention;  
       FIG. 15  illustrates an open form of a stent  1  according to another embodiment of the present invention; and  
       FIG. 16  illustrates an open form of a stent  1  according to another embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
      Hereinafter, the structure and effect of a vascular stent of the present invention which is specially designed for multiple drug loading and improved drug elution will be described more fully with reference to the accompanying drawings, in which exemplary embodiments of the invention are shown. The invention may, however, be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the concept of the invention to those skilled in the art.  
       FIG. 3  is a perspective view of a vascular stent  1  which is specially designed for multiple drug loading and improved drug elution according to an embodiment of the present invention.  FIG. 4  is an open form view of the vascular stent  1  of  FIG. 3 , and  FIG. 5  is an open form view of the vascular stent  1  of  FIG. 3  when expanded;  
      Referring to  FIGS. 3 through 5 , the stent  1  according to the current embodiment of the present invention includes ring structures  100  in which struts  120  are connected to each other by linking ends  110  in a zigzag formation, and link structures  200  including S-type links  200   a  connecting the ring structures  100 . In the ring structures  100 , rectangular slots  121  loaded with drugs are formed in the struts  120  in the longitudinal direction of the struts  120  and penetrating the struts  120 . One end of each of the struts  120  is connected to a corresponding one of the linking ends  110  having an open ring shape.  
      In the link structures  200  connecting the ring structures  100  of the stent  1 , each of both ends of each of the S-type links  200   a  is connected to a corresponding one of the linking ends  110  of a first ring structure  100  and a corresponding one of the linking ends  110  of a second ring structure  100 . The thickness of the S-type links  200   a  is less than the width of the struts  120  to facilitate bending and expansion of the vascular stent  1 . Due to such property, the vascular stent according to the current embodiment of the present invention can be installed in a serpentine blood vessel.  
      The amount of ring structures  100  and link structures  200  may vary according to the length of the vascular stent  1 . The vascular stent  1  typically has 6 to 8 ring structures  100 , and ring structures  100  should be disposed at both ends of the vascular stent. The vascular stent  1  illustrated in  FIG. 3  consists of 6 ring structures  100  and  5  link structures  200 .  
      When the struts  120  get twisted or bent during the expansion of the struts  120 , drugs may leak out of the rectangular slots  121  loaded with drugs. Referring to  FIGS. 3 and 4 , the thickness of the linking ends  110  may be less than that of the struts  120  in the ring structures  100  in order to facilitate expansion of the vascular stent  1  by easily spreading both ends of the linking ends  110  during the expansion of a balloon and not to deform the struts  120 .  
      In the vascular stent  1  according to the current embodiment of the present invention, the rectangular slots  121  loaded with drugs are formed in the struts  120  in the longitudinal direction of the struts  120  and penetrating the struts  120  to contain a larger amount of drugs than a conventional stent. Only one drug may be loaded in the rectangular slots  121 , or a plurality of layers of drugs may be loaded in the rectangular slots  121  ( FIG. 7B and 9A ). The size of the rectangular slots  121  loaded with drugs may vary according to the size and length of the vascular stent  1 .  
      Generally, the rectangular slots  121  loaded with drugs may have an area of from 0.05 inch (1.27 mm)×0.002 inch (0.05 mm) to 0.20 inch (5.0 mm)×0.008 inch (0.2 mm).  
      The amount of struts  120  to be included in one ring structure  100  may be determined in consideration of the diameter of the vascular stent  1  when the vascular stent  1  is expanded. That is, if the diameter of the vascular stent  1  is about 3.0 to 3.5 mm when the vascular stent  1  is expanded, each of the ring. structures  100  of the vascular stent  1  may have 12 to 14 struts  120  since it is preferable to have 12 to 14 rectangular slots  121  loaded with drugs. When the diameter of the vascular stent  1  is greater than about 3.5 mm, the amount of struts  120  is required to be increased.  
      Referring to  FIGS. 3 through 5 , the S-type links  200   a  in the link structures  200  of the vascular stent  1  may have a width of about 0.05 mm in order not to cause any difficulty during the installation of the vascular stent  1  in a blood vessel. In  FIGS. 3 through 5 , the S-type links  200   a  are illustrated. However, other types of links such as “N”-type links, “V”-type links and “W”-type links can be used as illustrated in  FIGS. 14 through 16 .  
      In addition, all of the links  200   a  in the link structures  200  of the vascular stent  1  are not disposed in the same direction. The links  200   a  are disposed in asymmetric formation in which a couple of links  200   a  are symmetric to each other to form an open gap as large as possible between the links  200   a . When stenosis regions are found in a coronary artery CA and a branched artery BA, a first stent may be installed in the coronary artery CA and a second stent with a balloon catheter may be easily inserted through the obtained large open gap between the links and installed in the branched artery BA as illustrated in  FIGS. 11A through 11D .  
       FIG. 6  is an enlarged open form view of part of the vascular stent  1  of  FIG. 4 .  FIGS. 7A and 7B  are cross sectional views of one of the struts  120  in the vascular stent  1  taken along an arbitrarily drawn cut-line VII-VII of  FIG. 6 , illustrating a rectangular slot  121  loaded with one drug, and a rectangular slot  121  loaded with a plurality of layers of drugs, respectively, according to an embodiment of the present invention.  
      In  FIG. 7A , the top of the rectangular slot  121  is in contact with an inner vascular wall and the bottom of the rectangular slot  121  is disposed toward the inside of a blood vessel. A base layer  122  is formed at the bottom of the rectangular slot  121  to prevent drugs from leaking into the blood vessel. A drug  1  (D 1 ) is loaded onto the base layer  122 , and an isolation layer  122   d  is formed at the top of the rectangular slot  121 , that is, the isolation layer  122   d  is in contact with the inner vascular wall. As illustrated not in  FIGS. 6 and 7 A, but in  FIGS. 8A and 9A , the external surface of the vascular stent  1  may be coated with another drug, and thus the isolation layer  122   d  should be formed on the top of the rectangular slot  121  to prevent interference by the coated drug.  
       FIG. 7B  illustrates a rectangular slot  121  loaded with a plurality of layers of drugs. In  FIG. 7B , a base layer  122  is formed on the bottom of the rectangular slot  121  of the strut  120 . The base layer  122  is disposed toward the inside of a blood vessel, and a drug  4  (D 4 ), an isolation layer  122   a , a drug  3  (D 3 ), an isolation layer  122   b , a drug  2  (D 2 ), an isolation layer  122   c , a drug  1  (D 1 ), and an isolation layer  122   d  are sequentially loaded on the base layer  122 . When a plurality of drugs are loaded in a multi-layer structure, the drugs may be sequentially eluted. Thus, drug elution time can be controlled, and the effect of the drugs can be sustained for a long period of time.  
       FIG. 8A  schematically illustrates a vascular stent  1  in which a rectangular slot  121  is loaded with one drug B and the external surface of the vascular stent  1  is coated with another drug A, according to an embodiment of the present invention.  FIG. 8B  is a graph illustrating the concentration of drugs eluted from the vascular stent  1  of  FIG. 8A  according to time. In the vascular stent  1  of  FIG. 8A , since drug A which is coated on the external surface of the vascular stent  1  is eluted and then drug B is eluted, the concentration of drug A (curve (a)) is high at the initial stage and the concentration of drug B (curve (b)) increases while the concentration of drug A decreases as illustrated in  FIG. 8B .  
       FIG. 9A  schematically illustrates a vascular stent  1  in which a rectangular slot  121  is loaded with a plurality of layers of drugs (drugs C, D, E, and F) and the external surface of the vascular stent  1  is coated with another drug A, according to an embodiment of the present invention.  FIG. 9B  is a graph illustrating the concentration of coated drugs eluted from the vascular stent  1  of  FIG. 9A  according to time. According to  FIG. 9B , the concentration of drug A (curve (a)) is high at the initial stage and the drug elution effects of drug F, drug E, drug D, and drug C are sequentially obtained (curves (f), (e), (d), and (c))  
       FIG. 10  is an enlarged perspective view of a portion of a vascular stent  1  in which an open gap  210  is formed between S-type links  200   a  of a link structure  200 , according to an embodiment of the present invention  
       FIGS. 11A through 11D  illustrate procedures of inserting a balloon catheter  2  with a vascular stent  1 ″ into a branched artery BA through an open gap  210  formed between S-type links  200   a  of a vascular stent  1 ′ installed in a coronary artery CA, and installing the vascular stent  1 ″ in the branched artery BA when stenosis regions L 1  and L 2  are found in each of the coronary artery CA and the branched artery BA.  
      As illustrated in  FIG. 11A , more than one stenosis region may be found in the vicinity of a branch point  400  in the coronary artery CA. In such case, the balloon catheter  2  including a balloon  2   a  with a vascular stent  1 ′ is inserted into the coronary artery CA to treat a first stenosis region L 1  as illustrated in  FIG. 11A , and the balloon  2   a  is expanded to install the vascular stent  1 ′ as illustrated in  FIG.11B . Then, another balloon catheter  2  including a balloon  2   a  with a vascular stent  1 ″ is inserted into the branched artery BA through an open gap between the S-type links  200   a  of a link structure  200  of the vascular stent  1 ′ to treat a second stenosis region L 2  as illustrated in  FIG. 11C , and the balloon  2   a  is expanded to install the vascular stent  1 ″ as illustrated in  FIG. 11D .  
      The stent of an embodiment of the present invention includes the link structure  200  arranged in an open cell type and the links  200   a  which is disposed in a mirror-symmetric manner in which a couple of links  200   a  are facing each other to form an open gap  210  between the links  200   a  larger than that of a conventional stent.  
       FIG. 12  is a schematic view of a vascular stent  1  which is installed in a serpentine blood vessel, according to an embodiment of the present invention. The vascular stent  1  may have excellent flexibility since links  200   a  of the vascular stent  1  are thin. Thus, the vascular stent  1  can be easily installed in the serpentine blood vessel.  
       FIGS. 13A and 13B  illustrate details of a vascular stent  1  according to an embodiment of the present invention. A material that is used to form the vascular stent  1  may be stainless steel or cobalt-chrome, and a material in a cylindrical shape may be laser-cut to form the vascular stent  1 .  
      According to an embodiment of the present invention, the entire length Xl of the vascular stent  1  including 6 ring structures  100  and 5 link structures  200  may be 0.7087 inch. The length X 2  of each of the ring structures  100  may be 0.0931 inch, and the width Y 1  of each of the ring structures  100  when not expanded may be 0.2041 inch. In addition, the distance Y 2  between linking ends  110  may be 0.0340 inch, and the length X 3  of each of the link structures  200  may be 0.03 inch ( FIG. 13A ).  
      Meanwhile, referring to  FIG. 13B , the external diameter Z 1  of the vascular stent  1  when not expanded may be 1.65 mm (0.065 inch), and the thickness Z 2  of the strut  120  may be 0.004 inch.  
      The sizes of each part of the vascular stent  1  are not limited thereto and may vary according to various conditions and purposes for which the vascular stent  1  are to be used. 90% of stent products that are commonly used in the art are made of a cobalt-chrome alloy, since cobalt-chrome stents are effective for preventing restenosis in blood vessels without drug coatings, and have excellent corrosion resistance and long fatigue life compared to conventionally-used stainless steel stents. Thus, cobalt-chrome stents can have advantages compared with stainless steel stents.  
      A method of manufacturing a vascular stent according to an embodiment of the present invention may include the following processes. A stainless steel or cobalt-chrome material having a cylindrical shape is laser-cut, in which metal is burned to be removed, to form a vascular stent. Then, the rough surface of the vascular stent is polished using a polishing process such as a chemical etching process to form a smooth surface.  
      Since the surface of the s vascular tent is directly in contact with vascular walls in the human body, the surface of the vascular stent need to be as smooth as possible and accordingly the polishing process affects the quality of the vascular stent. In an experiment, a laser-cut stent was polished three times, five times and eight times, and the results were compared with each other. While the surface of the vascular stent became smoother as the number of polishing processes increased, the manufacturing costs for the vascular stent increased, and the thickness and width of the metal parts of the vascular stent decreased. Accordingly, the optimum amount of polishing processes may be determined to achieve the desired manufacturing costs and quality of the vascular stent, and the size of the material to be used to form the vascular stent needs to be sufficient in consideration of the amount removed during the polishing process.  
      Then, drugs are loaded in a slot of the vascular stent and coated on the external surface of the vascular stent. Drugs which can prevent the proliferation of smooth muscle cells and prevent restenosis, such as rapamycin, paclitaxel or newer drugs having this property may be used. When the drugs which can prevent the proliferation of smooth muscle cells (and also may enhance reendothelization) are delivered to a damaged vascular wall due to a coronary intervention, the drugs inhibit the cell cycle regulators of proliferation in vascular cells, and thus restenosis can be prevented. In addition, inflammation inhibitors such as dexamethasone, gene therapy products, and the like can be used as restenosis preventing drugs, and estrogen based drugs containing the female hormone may also be used. A drug which inactivates metalloproteinase which is involved in collagenous fiber generation during cell proliferation may also be used. Any restenosis inhibiting drug may be loaded as much as possible in the vascular stent according to an embodiment of the present invention, so that the drug may be sustainedly eluted over a long period of time. In the specially designed stent of the present invention, conventional drugs may be loaded, and any drug that is to be developed in the future may also be loaded.  
      Meanwhile, a spray or dipping method or other methods may be used to coat the surface of the vascular stent. In the spray method, surface tension of the drug increases, and thus loading the drugs in the slot, which may be narrow, may be difficult. Any method that has been used or is to be developed, to coat drugs may be applied to the vascular stent manufacturing process.  
      In another embodiment of the present invention, “N”-type links, “V”-type links and “W”-type links may be used in addition to S-type links.  
       FIG. 14  illustrates an open form of a vascular stent  1  having an N-type link structure  201 , according to another embodiment of the present invention.  FIG. 15  illustrates an open form of a vascular stent  1  having a V-type link structure  202 , according to another embodiment of the present invention and  FIG. 16  illustrates an open form of a stent  1  having a W-type link structure  203 , according to another embodiment of the present invention.  
      The stents having such link structures according to embodiments of the present invention can be easily expanded, and flexibly bent, and thus can be easily and safely installed in blood vessels.  
      As described above, a vascular stent according to the present invention which is specially designed for multiple drug loading and improved drug elution, effectively elutes drugs inhibiting restenosis for a long period of time by loading a large amount of a drug or various types of drugs in multiple layers in rectangular through-hole slots in struts in the vascular stent.  
      In addition, the vascular stent according to the present invention has a plurality of link structures and a plurality of linking ends having improved flexibility, and thus the vascular stent can be easily installed even in serpentine blood vessels.  
      The link structures of the vascular stent according to the present invention are disposed in a symmetric structure to form a larger open gap compared to a conventional stent, and thus an additional coronary intervention may be performed in a branched artery without a stent jail when the vascular stent is installed at a branch point of a coronary artery.  
      While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the following claims.