Patent Publication Number: US-2021161691-A1

Title: Delivery device and delivery system for controlling release of stent in a stepwise manner

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     The present disclosure claims priorities to Chinese patent application No. 201810899863.5, entitled “DELIVERY DEVICE AND DELIVERY SYSTEM FOR CONTROLLING RELEASE OF STENT IN A STEPWISE MANNER” filed on Aug. 9, 2018, Chinese patent application No. 201821276305.5, entitled “DELIVERY DEVICE AND DELIVERY SYSTEM FOR CONTROLLING RELEASE OF STENT IN A STEPWISE MANNER” filed on Aug. 9, 2018, Chinese patent application No. 201810899886.6, entitled “A DELIVERY DEVICE” filed on Aug. 9, 2018, and Chinese patent application No. 201821276778.5, entitled “A DELIVERY DEVICE” filed on Aug. 9, 2018, each of which is incorporated by reference herein in its entirety. 
     TECHNICAL FIELD 
     The present invention relates to the technical field of medical devices, and particularly to a delivery device and a delivery system for controlling release of a stent in a stepwise manner. 
     BACKGROUND 
     An aortic aneurysm refers to the abnormal local or diffuse expansion of the aortic wall, which compresses the surrounding organs and causes symptoms. Aortic aneurysms can be classified into true aortic aneurysms, pseudoaneurysms, and dissecting aortic aneurysms according to the structures. An aortic aneurysm causes increased pressure in the inner side of the blood vessel, so it expands progressively. If it has been developed for a long time, the aortic aneurysm eventually ruptures, and the larger the aneurysm, the greater possibility for rupture. According to statistics, without surgical treatment, 90% of patients with thoracic aortic aneurysms die within 5 years, and 75% of patients with abdominal aortic aneurysms die within 5 years. 
     Thoracic aortic endovascular repair (TEVAR) is currently used to treat aortic ectasia lesions such as aortic dissection, aortic penetrating ulcer, aortic intermural hematoma, thoracic aortic aneurysm, and pseudoaneurysm, etc. Since the first case of abdominal aortic endovascular repair (EVAR) was reported to have been used in the treatment of abdominal aortic aneurysms in the 1990s, it has been rapidly developed in just two decades, because of its advantages such as less trauma, shorter operation and hospitalization time, faster postoperative recovery, lower mortality and complication rate, etc. 
     Expandable stents are often used as treatment devices for TEVAR and EVAR. In order to maintain well conforming with the blood vessel to be repaired, the diameter of the unfolded stent is generally about 10% greater than the diameter of the blood vessel, and the completely released stent presses against the blood vessel and cannot be re-adjusted if the release position is inaccurate. Thus, the surgeon is required to have rich experience and spend more time and energy to make sure an accurate releasing angle of the stent before the stent is released, which is much time-consuming. Therefore, it is necessary to develop a delivery device and a delivery system for controlling the release of the stent in a stepwise manner, which is convenient to adjust the position of the stent. 
     SUMMARY 
     The technical problem to be solved by the embodiments of the present disclosure is, providing a delivery device and a delivery system for controlling the release of the stent in a stepwise manner, which is convenient to adjust the position of the stent, and facilitates time-saving and energy saving. 
     In order to solve the aforementioned technical problem, embodiments in a first aspect of the present disclosure provide a delivery device for controlling the release of the stent in a stepwise manner, which is configured to deliver a stent and release the stent in a stepwise manner, the delivery device includes: 
     a core assembly; 
     an outer sheath, which is hollow and mounted around an outer periphery of the core assembly, with a delivering gap defined between the outer sheath and the core assembly, wherein the delivering gap has a distal end for receiving a folded stent; and a stent restraining assembly, configured to enable the stent to be partly unfolded so as to restrain an outer diameter of a released part of the stent when the stent is in a partly released state and to enable the stent to be fully unfolded when the stent is in a completely released state. 
     In one embodiment of the first aspect of the present disclosure, the delivery device further includes a control handle connected with the outer sheath, wherein the control handle controls the outer sheath to move axially relative to the core assembly so as to enable the folded stent to be in a partly released state or in a completely released state. 
     In one embodiment of the first aspect of the present disclosure, the stent restraining assembly includes at least one control wire, and the control wire enters the delivering gap through a proximal end of the delivering gap and extending to the distal end of the delivering gap, and wherein the control wire has a distal end configured to circumferentially restrain the released part of the stent. 
     In one embodiment of the first aspect of the present disclosure, the stent restraining assembly further includes a pull-tab secured to a proximal end of the control wire, the pull-tab is configured to apply a force to a proximal end of the delivery device so as to release the restraining of the control wire to the stent. 
     In one embodiment of the first aspect of the present disclosure, the delivery device further includes a first locking assembly configured to lock the movement of the stent restraining assembly to avoid releasing the restraining of the control wire to the stent unintentionally. 
     In one embodiment of the first aspect of the present disclosure, a sheath joint is secured to an outer periphery of the outer sheath, and the control handle includes: 
     a support body, with the sheath joint provided therein, wherein when being subjected to an axial force, the sheath joint moves axially within the support body to drive the outer sheath to move axially; 
     a fixed handle, mounted outside a distal end of the support body and secured thereto; and 
     a sliding handle, mounted outside the support body adjacent to a proximal end of the fixed handle, the sliding handle being rotatable at the outside of the support body so as to drive the sheath joint to move axially. 
     In one embodiment of the first aspect of the present disclosure, an elongated hole is defined on the support body and extends in an axial direction, a tooth block is mounted outside the support body at a position corresponding to the elongated hole, the sheath joint includes a joint body, and an abutment block and a distal protrusion provided on the joint body, the abutment block and the distal protrusion extend through the elongated hole and abut against a proximal end and a distal end of the tooth block, respectively, in such a way to limit an axial movement of the tooth block relative to the sheath joint, the sliding handle is provided with an internal thread, the tooth block is provided with an external thread engaging with the internal thread, and wherein when the sliding handle rotates, the sliding handle drives the sheath joint to move axially through the tooth block, the abutment block and the distal protrusion, and in turn drives the outer sheath to move axially. 
     In one embodiment of the first aspect of the present disclosure, the sliding handle is axially slidable on the support body, an unlocking button is embedded in the fixed handle, the unlocking button extends to the side of the sliding handle with a hook, and the hook hooks the sliding handle in such a way that the sliding handle is arranged next to the fixed handle and prevented from axially sliding. 
     In one embodiment of the first aspect of the present disclosure, the delivery device further includes a push-rod, wherein the push-rod has a distal end disposed in the delivering gap, and the push-rod is configured to abut against the stent to prevent the stent from moving towards the proximal end of the delivering gap when the control handle controls the outer sheath to axially move relative to the core assembly towards the proximal end. 
     In one embodiment of the first aspect of the present disclosure, the delivery device further includes a support tube, wherein the support tube has a distal end disposed in the delivering gap, and the push-rod is disposed in the support tube. 
     In one embodiment of the first aspect of the present disclosure, the push-rod defines therein a through passage extending in an axial direction thereof, and the control wire enters the through passage from a proximal end thereof and extends out of the through passage from a distal end thereof. 
     In one embodiment of the first aspect of the present disclosure, the delivery device further includes a pre-embedded guidewire, wherein the pre-embedded guidewire enters the delivering gap through the proximal end of the delivering gap and extends to the distal end of the delivering gap, the pre-embedded guidewire has a distal end configured to enter an inside of the stent from an outside thereof via a fenestration defined on the stent, and the pre-embedded guidewire is configured to guide a branch guidewire to extend out of the stent via the fenestration of the stent. 
     In one embodiment of the first aspect of the present disclosure, a second locking assembly is provided at a proximal end of the delivery device and configured to lock the pre-embedded guidewire to be prevented from moving. 
     Embodiments in a second aspect of the present disclosure provide a delivery system for controlling the release of a stent in a stepwise manner, the delivery system includes a stent and a delivery device, wherein the stent includes a tubular membrane and an annular support frame, and the delivery device includes: 
     a core assembly; 
     an outer sheath, which is hollow and mounted around an outer periphery of the core assembly, with a delivering gap defined between the outer sheath and the core assembly, wherein the delivering gap has a distal end receiving the folded stent; and 
     a stent restraining assembly, configured to restrain a released part of the stent to be partly unfolded so as to restrain an outer diameter of the released part of the stent when the stent is in a partly released state, and to enable the stent to be fully unfolded when the stent is in a completely released state. 
     In one embodiment of the second aspect of the present disclosure, a plurality of connecting members are provided on the tubular membrane and extend from a proximal end of the tubular membrane towards a distal end of the tubular membrane, and the plurality of connecting members are arranged in at least two columns which are circumferentially arranged spaced apart. 
     In one embodiment of the second aspect of the present disclosure, the stent restraining assembly is controlled to bound at least two columns of the connecting members together to restrain the stent to be partly unfolded when the stent is in the partly released state, and the stent restraining assembly releases the bound to the connecting members so as to make the stent be fully unfolded when the stent is in the completely released state. 
     In one embodiment of the second aspect of the present disclosure, a fenestration is provided on the tubular membrane, and the fenestration is located on a released part of the tubular membrane when the stent is in the partly released state. 
     In one embodiment of the second aspect of the present disclosure, the stent restraining assembly includes at least one control wire which enters the delivering gap through a proximal end of the delivering gap and extending to the distal end of the delivering gap, and the control wire has a distal end restraining the released part of the stent circumferentially. 
     In one embodiment of the second aspect of the present disclosure, the delivery device further includes a control handle connected with the outer sheath, the control handle controls the outer sheath to move axially relative to the core assembly so as to enable the folded stent to be in a partly released state or in a completely released state. 
     The embodiments of the present disclosure have advantages as follows. 
     Since the delivery device for controlling the release of stent in a stepwise manner includes a stent restraining assembly, which is used to restrain a released part of the stent to be partly unfolded when the stent is in a partly released state so as to restrain an outer diameter of the released part of the stent, and to make the stent be fully unfolded when the stent is in a completely released state. The released part of the stent would not tightly conform the blood vessel as the released part of the stent is partly unfolded and the outer diameter thereof is relatively small. In this way, when the stent is released to an inaccurate position, there is no resistance between the fully released part of the stent and the blood vessel, the delivery device can easily drive the stent to move. The delivery device in the embodiments is convenient to adjust the position of the stent, which facilitates time-saving and energy saving of the operator. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In order to more clearly illustrate the technical solutions of the embodiments according to the present application or the existing technology, drawings used in the description of the embodiments according to the present application or the existing technology will be briefly introduced below. It should be appreciated that the drawings described below merely illustrate some embodiments of the present application, and other drawings may be obtained by those skilled in the art without departing from the scope of the drawings. 
         FIG. 1  is a perspective view of a delivery device for controlling the release of a stent in a stepwise manner according to an embodiment of the present disclosure. 
         FIG. 2  is a cross-sectional view of the delivery device for controlling the release of a stent in a stepwise manner according to the embodiment of the present disclosure, viewed from one direction. 
         FIG. 3  is a cross-sectional view of the delivery device for controlling the release of a stent in a stepwise manner according to the embodiment of the present disclosure viewed from another direction. 
         FIG. 4  is an enlarged view of a circled portion A of  FIG. 2 . 
         FIG. 5  is an enlarged view of a circled portion B of  FIG. 2 . 
         FIG. 6  is an enlarged view of a circled portion D of  FIG. 3 . 
         FIG. 7  is an enlarged view of a circled portion C of  FIG. 2 . 
         FIG. 8  is an enlarged view of a circled portion E of  FIG. 3 . 
         FIG. 9  is a schematic view of the delivery device for controlling the release of a stent in a stepwise manner according to the embodiment of the present disclosure, viewed from one aspect, in which a stent is in a partly released state. 
         FIG. 10  is a schematic view of the delivery device for controlling the release of a stent in a stepwise manner according to the embodiment of the present disclosure, viewed from another aspect, in which the stent is in a partly released state. 
         FIG. 11  is a schematic view showing the stent according to the embodiment of the present disclosure in a completely released state. 
     
    
    
     Reference numbers shown in the drawings refer to: 
       1000 —delivery device;  100 —core assembly;  110 —inner core;  120 —outer tube;  130 —leading head;  131 —internal lumen;  140 —stent securing assembly;  142 —positioning sleeve;  143 —securing anchor;  150 —outer tube fastener;  160 —inner core securing steel sleeve;  170 —rear releasing knob;  200 —outer sheath;  210 —delivering gap;  220 —sheath joint;  221 —abutment block;  222 —joint body;  223 —distal protrusion;  300 —control handle;  310 —support body;  311 —elongated hole;  320 —fixed handle;  321 —unlocking button;  322 —hook;  323 —button support;  324 —positioning post;  330 —sliding handle;  332 —rotating knob;  333 —inner flange;  334 —friction-reducing protruding ring;  340 —tooth block;  400 —stent restraining assembly;  410 —control wire;  420 —pull-tab;  500 —first locking assembly;  510 —pull-tab fastener;  520 —proximal releasing knob;  610 —push-rod;  611 —through passage;  651 —rear sliding passage;  620 —support tube;  630 —push-rod fastener;  640 —rear fastener;  650 —rear slideway;  670 —luer joint;  680 —outer cover;  710 —pre-embedded guidewire;  720 —second locking assembly;  721 —wire fastener;  722 —fixed annular protrusion;  723 —blocking member;  800 —stent;  810 —tubular membrane;  811 —fenestration  820 —annular support frame;  830 —connecting member;  840 —bare stent;  2000 —delivery system;  3001 —TPU flexible tube;  3002 —three-way valve. 
     DESCRIPTION OF THE EMBODIMENTS 
     The technical solutions in the embodiments of the present disclosure will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present disclosure. Obviously, the described embodiments are only a part of the embodiments of the present disclosure, not all of the embodiments. Based on the embodiments of the present disclosure, all other embodiments obtained by those skilled in the art without inventive work shall fall within the protection scope of the present disclosure. 
     The terms “include”, “comprise”, “have” and any variations thereof in the specification, claims and drawings of the present disclosure are intended to cover non-exclusive inclusions. For example, a process, method, system, product or device including a series of steps or elements, is not limited to the steps or elements listed herein, but optionally includes other steps or elements that are not listed herein, or optionally further includes steps or elements inherent to such process, method, product or device. Furthermore, the terms “first,” “second,” and “third,” etc. are used to distinguish between different objects and are not used to describe a particular order. 
     For clarity of description, one end of the delivery device close to the operator is defined as a proximal end of the delivery device, and the other end relatively far from the operator is defined as a distal end of the delivery device; one end of the stent close to the patient&#39;s heart is defined as a proximal end of the stent, and the other end relatively far from the heart is defined as a distal end of the stent. The terms “proximal end” and “distal end” for the delivery device and the stent are defined according to different references. 
     A delivery device for controlling the release of a stent in a stepwise manner is provided according to an embodiment of the present disclosure, which is configured to deliver a stent and control release of the stent in a stepwise manner. Herein, the stent is loaded within the delivery device. The delivery device releases the stent in a step-by-step manner after the stent is delivered to an appropriate location in a blood vessel. Specifically, as shown in  FIGS. 9 and 10 , a part of the stent  800  is released first from the outer sheath  200 . Here, the part of the stent  800  refers to a proximal side of the stent  800 , and the remaining part of the stent  800  is remained within the delivery device. Meanwhile, the released proximal side of the stent  800  is still restrained by the delivery device, and the stent  800  is in a partly released state (which will be discussed hereinafter). Since the partly released stent  800  has an outer diameter smaller than the diameter of the blood vessel, it is possible to adjust the position of the stent  800 . The remaining part of the stent  800  may be released after the stent  800  has been adjusted in place, at that time, the stent  800  is completely released (as shown in  FIG. 11 ), i.e., in a completely released state. Alternatively, in other embodiment of the present disclosure, the stent  800  may be released in multiple steps, not limited to two steps. 
     As shown in  FIGS. 1 to 3 , the delivery device  1000  for controlling the release of a stent in a stepwise manner includes a core assembly  100 , an outer sheath  200  and a stent restraining assembly  400 . 
     Specifically, in this embodiment, referring to  FIGS. 2 and 4 , the core assembly  100  includes an inner core  110  and an outer tube  120 . The outer tube  120  is hollow and mounted around the inner core  110 . The outer tube  120  is slidable relative to the inner core  110  in an axial direction. 
     In this embodiment, the delivery device  1000  further includes a leading head  130  and a stent securing assembly  140 . The leading head  130  is conical and has a distal end being cuspidal. The leading head defines an internal lumen  131  in a center thereof in the axial direction. The inner core  110  has a distal end secured to a proximal end of the leading head  130 . The inner core  110  is hollow and communicates with the internal lumen  131  of the leading head  130 . The stent securing assembly  140  is provided adjacent to the proximal end of the leading head  130 . The stent securing assembly  140  includes a positioning sleeve  142  and a securing anchor  143 . The securing anchor  143  is secured to a distal end of the outer tube  120 . The securing anchor  143  is columnar and provided with a plurality of protrusions evenly spaced from one another in a circumference thereof for securing a bare stent  840  (as shown in  FIG. 11 ) at a proximal end of the stent  800 , so as to position the proximal end of the stent  800 . That is, the proximal end of the stent  800  surrounds the securing anchor  143  and is connected thereto. The positioning sleeve  142  has a distal end connected to the leading head  13  by insert molding. The positioning sleeve  142  is hollow and has a proximal end mounted around the securing anchor  143 . A limiting gap is defined between the securing anchor  143  and an inner wall of the positioning sleeve  142 , and the proximal end of the stent  800  is disposed in the limiting gap. 
     In this embodiment, the outer sheath  200  is hollow and is mounted around an outer periphery of the core assembly  100 . Specifically, the outer sheath  200  is mounted around an outer periphery of the outer tube  120 , and is slidable relative to the outer tube  120  in an axial direction. A delivering gap  210  is defined between the outer sheath  200  and the core assembly  100 . Specifically, the delivering gap  210  is defined between the outer sheath  200  and the outer tube  120 . Herein, the delivering gap  210  refers to a space between an inner wall of the outer sheath  200  and an outer wall of the outer tube  120 . The whole securing anchor  143  and the proximal end of the positioning sleeve  142  are disposed in the delivering gap  210 . The delivering gap  210  has a distal end for receiving the folded stent  800 . Herein, the stent  800  is forced by an external force to have a compressed profile so as to be received in the delivering gap  210 . The bare stent  840  at the proximal end of the stent  800  is positioned on the protrusions of the securing anchor  143 . The stent  800  is completely received in the delivering gap  210 . 
     In order to prevent a problem in that a released part of the stent  800  is fully unfolded when the stent  800  is in the partly released state, which results in that the released part of the stent  800  conform the blood vessel tightly (the fully unfolded stent  800  may have a diameter generally about 10% larger than that of the blood vessel) and thus it is impossible to adjust the position of the stent  800  when the stent  800  has been released to an inaccurate position, in this embodiment, as shown in  FIGS. 1 to 3 and 8 , the stent restraining assembly  400  is provided to restrain the released part of the stent  800  to be partly unfolded when the stent  800  is in the partly released state, so as to restrain the outer diameter of the released part of the stent  800 . The released part of the stent  800  refers to a part of the stent  800  not restrained by the outer sheath  200 , i.e., the part of the stent  800  which is exposed from the outer sheath  200 . Herein, the outer diameter of the released part of the stent  800  when folded is smaller than or equal to 90% of the outer diameter of the released part of the stent  800  when fully unfolded. Since the released part of the stent  800  is partly unfolded and the outer diameter thereof is relatively small, the released part of the stent  800  would not tightly conform the blood vessel. In this way, when the stent  800  is released to an inaccurate position, for example, the stent  800  is inaccurately aligned in a circumferential direction, or a fenestration  811  (as shown in  FIG. 10 ) on the stent  800  is inaccurately positioned, without resistance between the released part of the stent  800  and the blood vessel, the delivery device  1000  can easily drive the stent  800  to move, for example, rotate or move axially, so as to adjust the position of the stent  800  conveniently, for example, to adjust the circumferential alignment of the stent  800 . After the stent  800  is adjusted in place, the outer sheath  200  may be operated to move towards the proximal end of the delivery device  100  in the axial direction to completely release the stent  800 , and the stent  800  is fully unfolded and tightly conform the blood vessel. The delivery device  1000  in this embodiment can adjust the stent  800  conveniently, which facilitates time-saving and energy saving for the operator. In this embodiment, the stent restraining assembly  400  may make the released part of the stent  800  be fully unfolded as soon as the stent  800  is adjusted in place, or may make the stent  800  be fully unfolded until the stent  800  is in the completely released state. Additionally, in other embodiments of the present disclosure, the delivery device  1000  may be operated to adjust the position of the stent  800  by the operator when the stent  800  is inaccurately positioned in the axial direction. 
     Still referring to  FIGS. 1 to 3, and 8 , in this embodiment, the stent restraining assembly  400  includes at least one control wire  410 . Herein, one control wire, or two or more control wires  410  may be provided. The control wire  410  may be made of stainless steel. The control wire  410  enters the delivering gap  210  through the proximal end of the delivering gap  210  and extends to the distal end of the delivering gap  210 . 
     As shown in  FIG. 11 , the stent  800  includes a tubular membrane  810  and an annular support frame  820 . A plurality of connecting members  830  are provided on the tubular membrane  810  and extend axially from a proximal end of the tubular membrane  810  towards a distal end of the tubular membrane  810 . The connecting members  830  are arranged in at least two columns which are spaced apart in a circumferential direction of the tubular membrane  80 . Preferably, the connecting member  830  has a proximal end located at the proximal end of the tubular membrane  810  and a distal end located at the middle of the tubular membrane  810 . The tubular membrane  810  is provided with at least one fenestration  811  thereon, which is disposed between the proximal end and the middle of the tubular membrane  810 . When the stent  800  is in the partly released state, the tubular membrane  810  is released from its proximal end towards its distal end, but generally not beyond the middle of tubular membrane  810 , and at that time the fenestration  811  is located on the released part of the stent  800 . The control wire  410  bounds at least two columns of the connecting members  830  together to restrain the stent  800  to be partly unfolded, so as to restrain the outer diameter of the released part of the stent  800 . The outer diameter of the released part of the stent  800  is smaller than the diameter of the blood vessel, which facilitates adjust the position of the stent  800 , for example, adjust the stent  800  to make the fenestration  811  align with a branch vessel. Preferably, a circumferential length between two columns of the connecting members  410  bounded by the control wire  410  may result in 10% or above reduction of the outer diameter of the released part of the stent  800 , that is, the ratio of the outer diameter of the released part of the stent  800  when folded to the outer diameter of the released part of the stent  800  when unfolded is smaller than or equal to 90%. 
     In this embodiment, as shown in  FIGS. 1, 2 and 8 , the stent restraining assembly  400  further includes a pull-tab  420  which is secured to a proximal end of the control wire  410 , to facilitate handling of the control wire  410  in operation. Specifically, a force applied to the proximal end of the delivery device  1000  by the operator through the pull-tab  420  may release the bound of the control wire  410  to the stent  800 , so as to achieve unfolding of the restrained part of the stent  800 . 
     In order to improve security for use of the device, in this embodiment, the delivery device  1000  further includes a first locking assembly  500  configured to lock the movement of the stent restraining assembly  400 , so as to avoid releasing the restraining of the control wire  410  to the stent  800  unintentionally. In this embodiment, the first locking assembly  500  is configured to lock the movement of the pull-tab  420 , so as to avoid releasing the restraining of the control wire  410  to the stent  800  unintentionally. In addition, in other embodiments of the present disclosure, the first locking assembly  500  may be configured to lock the movement of the control wire  410 , so as to avoid releasing the restraining of the control wire  410  to the stent  800  unintentionally. In this embodiment, the first locking assembly  500  includes a pull-tab fastener  510  and a proximal releasing knob  520 . The pull-tab fastener  510  is connected to a proximal end of a rear slideway  650  (described hereafter) by a threaded connection. The pull-tab fastener  510  defines a through-hole configured for positioning the pull-tab  420 , and a first groove for engaging with the proximal releasing knob  520 . The proximal releasing knob  520  is rotatably mounted at a proximal end of the pull-tab fastener  510 . An L-shaped protrusion is provided inside a distal end of the proximal releasing knob  520 , which has a relatively long arm extending in a circumferential direction of the proximal releasing knob  520  and a relatively short arm extending from one end of the relative long arm towards the distal end in an axial direction of the proximal releasing knob  520 , so as to define a second groove. A second protrusion is provided at a distal end of the pull-tab  420  and extends outwards. After the pull-tab  420  is inserted in the through-hole and secured therein, the proximal releasing knob  520  is rotated to make the second protrusion enter into the second groove, such that the pull-tab  420  is locked there. In this way, the pull-tab  420  is unable to drive the control wire  410  to move towards the proximal end, so as to avoid releasing the restraining to the stent  800  unintentionally. When the proximal releasing knob  520  is rotated such that the second protrusion disengaged from the second groove, the pull-tab  420  is able to be operated to drive the control wire  410  to move towards the proximal end, so as to release the restraining to the stent  800 . 
     In order to control the release of the stent  800  in a stepwise manner, in this embodiment, as shown in  FIGS. 1 and 2 , the delivery device  1000  includes a control handle  300  connected with the outer sheath  200 . The control handle  300  is configured to control the movement of the outer sheath  200  to move axially relative to the core assembly  100 . Specifically, the control handle  300  is configured to control the outer sheath  200  to move axially relative to the outer tube  120 . The axial direction refers to a direction extending between the left side and the right side in  FIG. 1 . With the control handle  300  controlling the outer sheath  200  to move axially, the folded stent  800  in the delivering gap  210  is enabled to be in a partly released state or in a completely released state. Herein, referring to  FIGS. 9 and 10 , the partly released state refers to a state in which the proximal end of the stent  800  is released and the released part of the stent  800  is no more restrained by the outer sheath  200 , in which the position of the stent  800  is adjustable. As shown in  FIG. 11 , the completely released state refers to a state in which the whole stent  800  is no more restrained by the outer sheath  200 , that is an outer periphery of the stent  800  is not surrounded by the outer sheath  200 . 
     In order to adjust an axial position of the outer sheath  200 , in this embodiment, referring to  FIGS. 1, 2 and 5 , the outer sheath  200  is secured to a sheath joint  220 . In this embodiment, an outer periphery of a proximal end of the outer sheath  200  is secured to the sheath joint  220 . When the sheath joint  220  moves axially, the outer sheath  200  is driven to move axially with the sheath joint  220 . The control handle  300  includes a support body  310 , a fixed handle  320  and a sliding handle  330 . The support body  310  is hollow and the sheath joint  220  is provided therein. When a force is applied to the sheath joint  220  in the axial direction, the sheath joint  220  moves axially within the support body  310  and drives the outer sheath  200  to move axially. The fixed handle  320  is mounted outside a distal end of the support body  310  and secured thereto. The sliding handle  330  is mounted outside the support body  310  and adjacent to a proximal end of the fixed handle  320 . The sliding handle  330  is rotatable relative to the support body  310  and drives the sheath joint  220  to move axially. That is, the rotation of the sliding handle  330  is transformed into the axial movement of the sheath joint  220 . 
     Specifically, an elongated hole  311  is defined on the support body  310  and extends in the axial direction thereof. A tooth block  340  is provided outside the support body  310  at a position corresponding to the elongated hole  311 . The sheath joint  220  includes a joint body  222 , an abutment block  221  and a distal protrusion  223  that are provided on the joint body  222 . The abutment block  221  and the distal protrusion  223  extend through the elongated hole  311  and abut against a proximal end and a distal end of the tooth block  340 , respectively, so as to limit an axial movement of the tooth block  340  relative to the sheath joint  220 . That is, the tooth block  340  is disposed between the abutment block  221  and the distal protrusion  223  in the axial direction. The sliding handle  330  is provided with an internal thread inside, and the tooth block  340  is provided with an external thread outside engaging with the internal thread. When the sliding handle  330  is rotated, the tooth block  340  is driven by the sliding handle  330  to move axially, and thus drives the abutment block  221  and the distal protrusion  223  to move in the axial direction within the elongated hole  311 , and in turn the outer sheath  200  is driven to move axially, such that it is possible to enable the stent  800  take the partly released state or take the completely released state. 
     In this embodiment, the sliding handle  330  is further axially slidable on the support body  310 , that is, the sliding handle  330  is axially slidable relative to the fixed handle  320 . In order to hold the sliding handle  330  axially in position to enhance the security of the operation, in this embodiment, as shown in  FIG. 6 , an unlocking button  321  is embedded in the fixed handle  320 . A hook  322  extends from the unlocking button  321  to the side of the sliding handle  330 . A button support  323  is provided below the unlocking button  321  and secured on the support body  310 . Two positioning posts  324  are provided between the unlocking button  321  and the button support  232  and arranged opposite to each other. A spring is mounted around the two positioning posts  324 , disposed between the unlocking button  321  and the button support  232 , and configured to urge the hook  322  in position. The hook  322  hooks the sliding handle  330 , such that the sliding handle  330  is arranged next to the fixed handle  320  and prevented from axially sliding. Specifically, the sliding handle  330  includes a rotating knob  332  disposed at a distal end of the sliding handle  330 . The rotating knob  332  has an inner flange  333 , and the hook  322  may extend into the rotating knob  332  and engage with the inner flange  333 . One side of the inner flange engaging with the hook  322  is defined as an annular positioning groove. That is, the hook  322  is positioned within the positioning groove, such that an axial position of the hook  322  is limited, while allowing the sliding handle  330  to rotate relative to the fixed handle  320 . In this embodiment, two friction-reducing protruding rings  334  are coaxially provided on the rotating knob  332 . The friction-reducing protruding rings  334  are disposed on a sidewall of a distal end of the rotating knob  322 . Due to the friction-reducing protruding ring  332 , contact between the fixed handle  320  and the sliding handle  330  is line contact instead of surface contact, which greatly reduces a contact area therebetween and thus reduces friction when they move relative to each other, resulting in a smoother and more accurate release of the stent  800 . 
     In this embodiment, referring to  FIGS. 1 to 3, and 7 , the delivery device  1000  further includes a push-rod  610  and a support tube  620 . The support tube  620  is disposed between the outer sheath  200  and the outer tube  120 . That is, the support tube  620  is at least partly disposed in the delivering gap  210 . The support tube  620  serves to enhance the support. The push-rod  610  is disposed between the support tube  620  and the outer tube  120 , with a distal end thereof disposed in the delivering gap  210 . When the control handle  300  controls the outer sheath  200  to axially move relative to the core assembly  100  towards the proximal end, the distal end of the push-rod  610  is configured to abut against the stent  800  so as to prevent the stent  800  from moving towards the proximal end of the delivering gap  210 . In the meanwhile, the push-rod  610  serves to support the stent  800 . In addition, in this embodiment, the push-rod  610  defines a through passage  611  inside in an axial direction. The through passage  611  is configured to allow the control wire  410  and a pre-embedded guidewire  710  to pass therethrough. Specifically, the control wire  410  and the pre-embedded guidewire  710  enter the through passage  611  from a proximal end thereof and extends out of the through passage  611  from a distal end thereof. 
     In this embodiment, the delivery device  1000  further includes a push-rod fastener  630  and a rear fastener  640 . The push-rod fastener  630  is fixedly connected to the proximal ends of the push-rod  610  and the support tube  620 . The push-rod fastener  630  has a distal end disposed at an inner side of a proximal end of the support body  310  and secured to the proximal end of the support body  310 . The rear fastener  640  is mounted around an outer periphery of the proximal end of the support body  310 , and has a distal end secured to the proximal end of the support body  310 . In addition, a connecting port extends out from the push-rod fastener  630 , which is configured to be connected to an end of a TPU flexible tube  3001 . Another end of the TPU flexible tube  3001  is connected with a three-way valve  3002 . 
     In this embodiment, the rear fastener  640  has a proximal end secured to a rear slideway  650  which has a distal end disposed at an inner side of the rear fastener  640 . The rear slideway  640  is provided therein with an outer tube fastener  150 , which is disposed at a position in proximity to the middle of the rear slideway  650  and secured to an outer periphery of the proximal end of the outer tube  120 . An outer cover  680  is provided adjacent to the proximal end of the rear slideway  650  and mounted around the rear slideway  650 . 
     In this embodiment, as shown in  FIGS. 1 to 3, 7 and 8 , an inner core securing steel sleeve  160  and a rear releasing knob  170  are provided at the proximal end of the rear slideway  650 . The inner core securing steel sleeve  160  is disposed inside the rear slideway  650 . The inner core securing steel sleeve  160  is secured to the inner core  110  and disposed outside the inner core  110 . The rear releasing knob  170  is disposed outside the proximal end of the rear slideway  650 . The rear releasing knob  170  is secured to the inner core securing steel sleeve  160 . An elongated hole is defined at the proximal end of the rear slideway  650  which extends in an axial direction. The rear releasing knob  170  can drive the inner core securing steel sleeve  160  to move in the axial direction within the elongated hole, so as to control a later release of the stent  800 . In this embodiment, the proximal end of the rear slideway  650  is secured to the distal end of the pull-tab fastener  510 . In this embodiment, the inner core  110  has a proximal end secured to a Luer joint  670 . 
     In general, an arterial blood vessel of a human body is connected to a plurality of branch vessels, and when the arterial blood vessel is repaired by the stent  800 , the branch vessels sometimes are required to repair simultaneously. In that case, a branch stent is required to enter the branch vessel via the stent  800  to repair the branch vessel. In order to deliver the branch stent to the branch vessel conveniently, in this embodiment, as shown in  FIGS. 1, 2 and 4 , the delivery device  1000  also includes a pre-embedded guidewire  710  that enters the delivering gap  210  through the proximal end and extends to the distal end thereof. The pre-embedded guidewire  710  has a distal end configured to enter into the stent  800  from an outside thereof via the fenestration  811  on the stent  800 . The pre-embedded guidewire  710  is configured to guide a branch guidewire to pass through the fenestration  811  from inside to outside of the stent  800 . At that time, the connection between the pre-embedded guidewire  710  and the branch guidewire may be released. Thereafter, since the fenestration  811  is aligned with the branch vessel, the branch guidewire may be pushed further by the operator to enter the branch vessel. Thereafter, the branch stent may be guided into the branch vessel by the branch guidewire. In addition, in this embodiment, the distal end of the pre-embedded guidewire passes through the push-rod. 
     In this embodiment, referring to  FIG. 1 , the proximal end of the delivery device  1000  is provided with a second locking assembly  720 . Specifically, the second locking assembly  720  is arranged on the rear slideway  650  and configured to lock the movement of the pre-embedded guidewire  710 . 
     Specifically, referring to  FIG. 7 , the rear slideway  650  defines therein a hollow rear sliding passage  651  extending in an axial direction. The rear sliding passage  651  communicates with the delivering gap  210 , and the pre-embedded guidewire  710  enters the rear sliding passage  651 . The second locking assembly  720  includes a wire fastener  721 , a fixed annular protrusion  722  secured on the rear slideway  650  and a blocking member  723  secured inside the rear sliding passage  651 . The pre-embedded guidewire  710  enters the rear sliding passage  651  from a gap between the blocking member  723  and the wire fastener  721 . Herein, the wire fastener  721  and the fixed annular protrusion  722  may be movably connected by a threaded connection. When the pre-embedded guidewire  710  is pressed tightly by the wire fastener  721  onto the blocking member  723 , the movement of the pre-embedded guidewire  710  is locked, such that the pre-embedded guidewire  710  is prevented from being pulled to an improper position by mistake. 
     A delivery system for controlling the release of a stent in a stepwise manner is provided according to an embodiment of the present disclosure. As shown in  FIGS. 1 to 4, and 9 to 11 , the delivery system  2000  for controlling the release of a stent in a stepwise manner includes a stent  800  and a delivery device  1000 . The stent  800  includes a tubular membrane  810  and an annular support frame  820 . The delivery device  1000  includes a core assembly  100 , an outer sheath  200  and a stent restraining assembly  400 . The outer sheath  200  is hollow, and is mounted around an outer periphery of the core assembly  100 . A delivering gap  210  is defined between the outer sheath  200  and the core assembly  100 . The delivering gap  210  has a distal end for receiving the folded stent  800 . When the stent  800  is in a partly released state, the stent restraining assembly  400  makes the released part of the stent  800  be partly unfolded, so as to restrain an outer diameter of the released part of the stent  800 , and makes the stent  800  be fully unfolded when the stent  800  is in a completely released state. 
     In this embodiment, a plurality of connecting members  830  are provided on the tubular membrane  810  which extend from a proximal end of the tubular membrane  810  towards a distal end of the tubular membrane  810 . The connecting members  830  are arranged in at least two columns which are spaced apart in a circumferential direction. The connecting members  830  may be flexible rings. One to six connecting member(s), preferably three to five connecting members may be provided in a column. The connecting members arranged in a column in the axial direction may prevent the stent from being shortened when the stent restraining assembly is used. When the stent  800  is in the partly released state, the stent restraining assembly  400  is controlled to bound at least two columns of the connecting members to enable the stent  800  to be partly unfolded. When the stent  800  is in the completely released state, the stent restraining assembly  400  releases the bound to the connecting members  830 , so as to enable the stent to be fully unfolded. 
     A fenestration  811  is provided on the tubular membrane  810 . When the stent  800  is in the partly released state, the fenestration  811  is located on the released part of the tubular membrane. The specific structure of the stent  800  in this embodiment has been discussed in detail in a co-pending Chinese patent application No. 201711483955.7 early filed, the disclosed content of which is incorporated herein by reference. 
     In this embodiment, the stent restraining assembly  400  includes at least one control wire  410 . The control wire  410  enters the delivering gap  210  through a proximal end of the delivering gap  210  and extends to a distal end of the delivering gap  210 . The control wire  410  has a distal end bounding the released part of the stent  800  circumferentially. The control wire  410  ties at least two columns of the connecting members to restrain the stent  800  to be partly unfolded circumferentially. 
     In addition, the delivery device further includes a control handle  300  connected with the outer sheath  200 . The control handle  300  controls the outer sheath  200  to move axially relative to the core assembly  100 , so as to enable the folded stent  800  to be in a partly released state or in a completely released state. Detail descriptions of the delivery device have been provided above in the aforementioned embodiment, and will not be described here again. 
     It should be noted that each embodiment in this specification is described in a progressive manner and focuses on the differences from the other embodiments, and the same parts between those embodiments may be referred to each other. The above disclosure merely describes preferred embodiments of the present disclosure without intention to limit the scope of the present disclosure, and thus equivalent changes made in accordance with the claims fall within the scope of the present disclosure.