JP2006141555A - Stent and its production method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a stent for which slack and wrinkles are not generated on polymer in the state that it is inserted into a lumen such as a blood vessel and an extension amount for tightly adhering it to a lumen inner wall can be small, and its production method. <P>SOLUTION: For the stent 1, both inner and outer peripheral surfaces of a stent main body 10 are coated with a polymer film 2. The stent main body 10 is made of a shape memory alloy such as a nickel titanium alloy, and the transformation temperature of the shape memory alloy is lower than the body temperature of a living body. The stent main body 10 is slightly reduced in a diameter at a temperature lower than the transformation temperature and is coated with the polymer film 2. In the state where the stent 1 is placed at a temperature higher than the transformation temperature and forcible extension by a balloon is not executed, the stent 1 is turned to a quasi-maximum diameter slightly smaller than the maximum diameter. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a stent placed in a lumen such as a blood vessel and a method for manufacturing the stent. Specifically, the present invention relates to a stent in which a self-expanding stent body made of a shape memory alloy is covered with a flexible polymer film, and a manufacturing method thereof.

  Conventional treatment of ischemic heart disease is percutaneous transluminal coronary angioplasty (PTCA), that is, a balloon catheter is carried through a lumen in a blood vessel to, for example, a stenotic site, and then the balloon is expanded with a liquid such as physiological saline. Treatment methods were common. However, with this method, there is a high probability that coronary occlusion in the acute phase and re-stenosis (so-called restenosis) at the site where PTCA is performed occur. In order to solve these problems, an intraluminal graft called a stent has been developed and recently put into practical use and has become widespread. Recent data show that nearly 75% of balloon catheter surgery has already been replaced by stent surgery.

  The stent body is an intraluminal graft that is carried through the inside of a lumen such as a blood vessel and supported by an action from the inside by expanding its diameter at the treatment site of the lumen. Although it is mainly used in the above-mentioned coronary artery surgery, it is mainly described here, but the stent is a ureter, ureter, fallopian tube, aortic aneurysm, peripheral artery, renal artery, carotid artery, It can also be used for other luminal parts of the human body such as cerebral blood vessels. In particular, in order to understand the present invention, it is expected that the field of use of stents will expand further, that stents will be used in many surgeries in the future, and that the importance of ultrafine stents will increase with the use in the field of brain surgery. The

  Restenosis can be drastically prevented by the spread of surgery using stents. However, since the metallic stent body is a foreign substance in the body, thrombosis develops within a few weeks after insertion of the stent body. In other words, since the metal stent itself has thrombogenicity, when exposed to blood, it contacts with plasma proteins such as albumin and fibrinogen and aggregation occurs due to adhesion of platelets. It is also pointed out that the placement of a metal stent body promotes intimal thickening, which is one cause of restenosis.

  As a solution to this problem, a stent has been proposed in which the outer peripheral surface of a metal stent body is covered with a flexible polymer film having fine holes (for example, WO 2004/022150 A1).

  It is also known that the stent body is made of nickel / titanium shape memory alloy. For example, laser processing is performed on a cylindrical tube made of a shape memory alloy made of Ni44-Ti47-Nb9 with a composition having an Af temperature of about 30 ° C., and a large number of rhombus-shaped openings are drilled, and this is made at 400 ° C. for about 10 minutes. Stents that have been annealed and memorized in shape are known. The stent is reduced in diameter and placed in the sheath, sent to a planned placement position in the blood vessel, and released from the sheath. Since the released sheath has a temperature of Af or higher, it can be expanded to a memorized diameter.

A covered stent in which a shape memory alloy stent is covered with a polymer such as urethane is also known.
WO2004 / 022150 A1

  Conventional stents made by coating a stent body made of shape memory alloy with a polymer are heat treated to store the shape of the stent body, and the polymer coating is applied in a state where the diameter is kept above the transformation temperature and the maximum diameter is maintained. It is manufactured.

  When the stent thus manufactured does not have the maximum diameter when inserted into a lumen such as a blood vessel, the polymer is slackened or wrinkled, and various problems occur.

  On the contrary, when the polymer coating is applied with the stent below the transformation temperature and having a small diameter equal to the inner diameter of the sheath, the elongation of the polymer layer at the time of expansion becomes excessive, resulting in damage to the polymer layer or a decrease in strength. .

  The present invention provides a stent that does not loosen or wrinkle in a polymer when inserted into a lumen such as a blood vessel, and that requires only a small amount of expansion to be in close contact with the inner wall of the lumen, and a method for manufacturing the stent. For the purpose.

  The stent according to claim 1 is made of a shape memory alloy whose transformation temperature is lower than the body temperature of a living body, has a small diameter at a temperature lower than the transformation temperature, and expands to a large diameter at a temperature higher than the transformation temperature; In a stent having a polymer layer covering at least the outer peripheral surface of the stent body, the stent body has a diameter when there is no restraint by the polymer layer in an environment at a temperature higher than the transformation temperature. The quasi-maximum aperture is slightly smaller than the maximum aperture, and further expansion is restricted by the polymer layer.

  The stent according to claim 2 is characterized in that, in claim 1, the quasi-maximum aperture is 30 to 80% of the maximum aperture.

  The stent according to claim 3 is characterized in that in the stent according to claim 1 or 2, the stent can be expanded in diameter by a balloon inserted therein when the stent body is in a quasi-maximum diameter. It is what.

  A stent according to a fourth aspect is characterized in that, in any one of the first to third aspects, the Young's modulus of the polymer layer is 0.05 MPa to 30.00 MPa.

  A stent according to a fifth aspect is characterized in that, in any one of the first to fourth aspects, the polymer layer is provided with a plurality of fine holes communicating the inner peripheral side and the outer peripheral side of the stent. It is.

  A stent according to a sixth aspect is characterized in that, in any one of the first to fifth aspects, the main body of the stent is slidable with respect to the inner peripheral surface of the cylindrical polymer layer surrounding from the outer peripheral side. is there.

  The stent according to claim 7 is characterized in that, in claim 6, the inner peripheral surface of the cylindrical polymer layer is subjected to a slidability imparting treatment.

  The stent of claim 8 is the stent according to claim 7, wherein the slidability imparting treatment comprises a composition comprising gelatin modified with xanthene dye and a hydrogen donor such as thiol, reducing sugar, polyphenol or a compound having a dialkylamino group. It is the process which irradiates light after coat | covering, It is characterized by the above-mentioned.

  The stent according to claim 9 is the stent according to claim 7, wherein the slidability imparting treatment uses the stent body as an electrode to perform glow discharge to generate a radical active site in the polymer layer and graft polymerize dimethylacrylamide to the radical active site. It is a process.

  The method for manufacturing a stent according to claim 10 is a method for manufacturing the stent according to any one of claims 1 to 9, wherein the stent body is lower than the transformation temperature and lower than the quasi-maximum diameter. The stent body is inserted into the cylindrical polymer layer, and then the stent body is expanded to a temperature higher than the transformation temperature to adhere to the inner peripheral surface of the cylindrical polymer layer. It is characterized by making it.

  The stent manufacturing method according to claim 11 is characterized in that, in claim 10, when the temperature of the stent body is increased after being inserted into the cylindrical polymer layer, the diameter expansion rate of the stent body is 10% or less. It is what.

  According to a twelfth aspect of the present invention, there is provided a stent manufacturing method according to the tenth or eleventh aspect, wherein the cylindrical polymer layer is subjected to a slidability imparting treatment.

  The method for producing a stent according to claim 13 is the method according to claim 12, wherein the slidability imparting treatment comprises gelatin modified with xanthene dye and a hydrogen donor such as a compound having thiol, reducing sugar, polyphenol or dialkylamino group. It is a treatment characterized by light irradiation after coating the composition.

  The method for producing a stent according to claim 14 is the method for producing a stent according to claim 12, wherein the slidability imparting treatment generates a radical active site in the polymer layer by glow discharge using the stent body as an electrode, and dimethylacrylamide is added to the radical active site. It is a process for graft polymerization.

  The stent manufacturing method according to claim 15 is a method for manufacturing the stent according to any one of claims 1 to 9, wherein the polymer is maintained in a state where the stent body is maintained at a diameter smaller than the quasi-maximum diameter. A layer is formed.

  The stent manufacturing method according to claim 16 is characterized in that, in claim 15, the polymer layer is formed in a state where the stent body is externally fitted to a rod-like body at a temperature lower than the transformation temperature. It is.

  The stent manufacturing method according to claim 17 is characterized in that, in claim 15, the polymer layer is formed in a state in which the stent body is fitted into a cylindrical body at a temperature higher than the transformation temperature. It is.

  The stent provided by the present invention has a stent body made of a shape memory alloy and a polymer layer covering at least the outer periphery of the stent body. When the stent is in a temperature environment above the transformation temperature, the stent body attempts to expand to the maximum memorized diameter, but the polymer layer prevents further expansion. In other words, when the stent is placed at a temperature higher than the transformation temperature of the stent body, the polymer layer is pressed in the expansion direction from the stent body, so that the polymer layer becomes taut with no looseness or wrinkles. ing.

  The stent is first placed in a lumen such as a blood vessel, and then expanded and placed by a balloon or the like as necessary. Therefore, even when the tube diameter of a blood vessel or the like is larger than the maximum diameter of the stent body, the stent is expanded to a larger diameter than the maximum diameter by a balloon and placed in close contact with the inner peripheral surface of the blood vessel or the like. Can be made.

  In the stent of the present invention, in the state immediately after the stent is delivered into the blood vessel, the stent body is in a quasi-maximum diameter, and as described above, the polymer layer has an expanded diameter of the stent body. Is in a state of tension with no slack or wrinkles. Therefore, in the indwelling state in which the stent is further expanded, the polymer layer is naturally free from sagging and wrinkles.

  Also, the stent polymer layer only expands as the stent body expands from the quasi-maximum aperture to the indwelling aperture. Therefore, the elongation of the polymer layer is smaller than when the stent is expanded from the inner diameter of the stent delivery sheath to the indwelling diameter by the expansion force of the balloon. As described above, in the present invention, during the operation of placing the stent, the elongation of the polymer layer accompanying the expansion of the stent becomes small, and the load on the polymer layer can be reduced. By reducing the load on the polymer layer, it is possible to prevent damage to the polymer layer and improve durability, and to increase the degree of freedom in selecting the polymer material.

  In the present invention, the polymer layer may be formed in a pre-formed cylindrical shape, and the stent body may be in close contact with the inner peripheral surface of the cylindrical polymer layer by the expansion force. In this case, the stent body can be slidable with respect to the polymer during the indwelling treatment by not bonding the stent body and the polymer. In this case, even when the stent is complicatedly deformed or twisted during the treatment, the polymer layer and the stent body slide, and wrinkles and wrinkles are prevented from occurring in the polymer layer.

  Hereinafter, embodiments will be described with reference to the drawings. 1 is a perspective view of the stent, FIG. 2 is a cross-sectional view taken along the line II-II of FIG. 1, FIG. 3 is a cross-sectional view showing a method for manufacturing the stent, and FIGS. FIG. 3B is a sectional view taken along line IIIb-IIIb in FIG. 1 to 3 are schematic views, and particularly the thickness is shown to be significantly thicker than actual. 4 is a perspective view of the stent body, and FIG. 5 is a perspective view of the expanded stent body.

  In the stent 1 according to this embodiment, both the inner and outer peripheral surfaces of the stent body 10 are covered with the polymer film 2.

  The stent body 10 is preferably a tube having a length of about 2 to 40 mm and a diameter of about 10 to 100% of the length. The stent body 10 is preferably in the form of a mesh so that the diameter can be expanded flexibly. In particular, the stent body 10 is preferably in the form of an oblique grid as shown in FIG.

  The stent body 10 is made of a shape memory alloy such as a nickel / titanium alloy, and the transformation temperature (Af) of the shape memory alloy is lower than the body temperature of the living body. In the case of human use, the transformation temperature of the shape memory alloy is preferably about 4 to 30 ° C, particularly about 20 to 25 ° C.

  The stent main body 10 made of the shape memory alloy is heat-treated at, for example, 350 to 600 ° C., subjected to a shape memory treatment, and rapidly cooled as it is.

  The stent body 10 ′ in the maximum diameter state not covered with the polymer film 2 shown in FIG. 5 is pressed in the direction of diameter reduction at a temperature lower than the transformation temperature to obtain the small diameter state shown in FIG. When the pressure is released and the temperature is higher than the transformation temperature, the original shape is restored and the maximum aperture state shown in FIG. 5 is obtained.

  When the stent 1 is in a temperature environment higher than the transformation temperature and is not forcedly expanded by the balloon, the stent body 10 in the stent 1 has a slightly smaller diameter than the maximum diameter. The quasi-maximum aperture. At this time, the stent body 10 attempts to expand to the maximum diameter, but the expansion is restricted by the polymer film 2. Therefore, the polymer film 2 is tensioned in this state.

When the maximum diameter (diameter) is D ₁ and the quasi-maximum diameter (diameter) is D ₂ , the quasi-maximum diameter D ₂ is preferably 20 to 80% of D ₁ , particularly 30 to 60%.

  The material used as the flexible polymer film 2 is preferably a high-flexibility polymer elastomer, such as polystyrene, polyolefin, polyester, polyamide, silicone, urethane, fluorine resin, natural rubber, etc. These elastomers and their copolymers or their polymer alloys can be used. Among them, segmented polyurethane is most suitable because it is highly flexible and strong. The polymer film 2 preferably has a Young's modulus of about 0.05 MPa to 30.00 MPa.

  A segmented polyurethane polymer has a flexible polyether portion as a soft segment and a portion rich in aromatic rings and urea bonds as a hard segment, and the soft segment and hard segment phase separate to form a fine structure. It is what. This segmented polyurethane polymer film is excellent in antithrombotic properties. Moreover, it is excellent in properties such as strength and elongation, and can be sufficiently expanded without breaking even when the stent is expanded in diameter.

  This segmented polyurethane polymer film preferably has a thickness of 10 to 100 μm, in particular 20 to 50 μm.

  The polymer film is provided with a plurality of fine holes. The fine holes may be randomly arranged, but preferably the fine holes are perforated at substantially uniform intervals. The fact that the micropores are perforated at a substantially uniform interval does not mean that the intervals are the same, but that the micropores are arranged at a substantially constant interval by a controlled method. Accordingly, the substantially uniform interval includes diagonal, circular, and elliptical arrangements that appear to be randomly arranged at first glance. The micropore may have any size and shape as long as the endothelial cells can enter and exit. Preferably, it is a circle having a diameter of 5 to 500 μm, most preferably 20 to 100 μm. Needless to say, other shapes such as an ellipse, a square, and a rectangle are also included. These are the states before expansion, and when the stent body is expanded and placed in the lumen, the circle is deformed into an oval shape, and the diameter changes accordingly.

  In the present invention, since the expansion amount of the stent at the time of indwelling is small, the stretching of the polymer film at the time of stent expansion is small, and therefore the deformation of the micropores of the polymer film 2 is also small.

  If the arrangement density of the micropores is too high, the strength of the polymer film is lowered and the intimal tissue penetrates too much. If the density is too low, the endothelial cells do not sufficiently grow inside the stent. Therefore, the micropores are arranged on a plurality of straight lines at intervals of 50 to 500 μm, preferably 100 to 300 μm. The plurality of straight lines include, for example, 10 to 50 straight lines arranged at a predetermined constant angular interval in the axial direction of the stent.

  These fine holes are preferably provided by applying a polymer film on both the inner and outer peripheral surfaces of the stent body and then drilling with a laser or the like.

  In the present invention, a base polymer film such as a segmented polyurethane polymer film may be coated with a biodegradable polymer. Examples of such biodegradable polymers include gelatin, polylactic acid, polyglycolic acid, caprolactone, lactic acid-glycolic acid copolymer, polygioxanone, and chitin.

  The biodegradable polymer may contain a therapeutic agent such as an antiplatelet agent, an antithrombotic agent, a growth promoter, a growth inhibitor, or an immunosuppressant. This therapeutic agent is released into the body along with the degradation of the biodegradable polymer, and is effective in suppressing the formation of thrombus or promoting the proliferation of endothelial cells and obtaining early endothelialization.

  This treatment includes heparin, low molecular weight heparin, hirudin, argatroban, formacholine, bapiprost, prostamorin, prostakyrin congeners, dextran, lofepro-algchloromethylketone, dipyridamole, glycoprotein platelet membrane receptor antibody, combination Reversible hirudin, thrombin inhibitor, vascular peptin, vascular tensin converting enzyme inhibitor, steroid, fibroblast growth factor antagonist, fish oil, omega-3 fatty acid, histamine, antagonist, HMG-CoA reductase inhibitor, ceramine, Examples include serotonin blocking antibodies, thioprotein inhibitors, trimazole pyridimine, interferon, vascular endothelial growth factor (VEGF), rapamycin, FK506, and the like.

  The biodegradable polymer coating layer can be formed by immersing the stent in a biodegradable polymer solution. The polymerization may be promoted by ultraviolet rays after being dipped in the polymer solution and pulled up. When a polymer film is formed by a centrifugal molding method described later, the biodegradable polymer layer may also be formed by a centrifugal molding method. When the therapeutic agent is blended in the biodegradable polymer solution, a coating containing the therapeutic agent is formed. By adjusting the biodegradable polymer type, molecular weight, coating thickness, and the like, it is possible to set the time and period during which the therapeutic agent is released into the body.

  The outer surface of the stent of the present invention may be coated with a lubricious polymer in order to smoothly move in fine blood vessels in the human body. Examples of such a lubricious polymer include polyethylene glycol, polyacrylamide, and polyvinyl pyrrolidone.

  The stent 1 can be manufactured by, for example, an insertion method, a dipping method, a cover strip method, or a centrifugal molding method.

(1) Insertion method A polymer tube having an inner diameter slightly smaller than the quasi-maximum diameter is manufactured, and an elastic force is applied by applying an external force at a temperature lower than the transformation temperature so that the diameter is smaller than the quasi-maximum diameter. A stent body having a temperature lower than the transformation temperature reduced in diameter is inserted. Next, the external force is released to expand the stent body, and the stent body is brought into close contact with the inner peripheral surface of the polymer tube. Next, laser processing is performed to drill fine holes in the polymer film.

  In this case, the inner peripheral surface of the stent body is not covered with the polymer layer, but the inner peripheral surface may be further covered with the polymer layer. The coating on the inner peripheral surface can be formed by the following dipping method, cover strip method, and centrifugal molding method.

  When the external force is released after inserting the stent body into the polymer tube, the stent body expands and the tube slightly expands to a quasi-maximum diameter. In this case, the expansion ratio of the stent body is preferably 10% or less.

(2) Immersion method In order to manufacture the stent of the present invention by this immersion method, a mandrill made of a cylindrical or cylindrical rod-like body having a diameter D slightly smaller than the inner diameter of the stent body 10 in the quasi-maximum aperture state is used. Use. The mandrill is immersed in a polymer solution such as polyurethane to coat the polymer in a cylindrical shape. Next, the stent body whose diameter has been reduced by applying a force in the diameter reduction direction at a temperature lower than the transformation temperature is placed on the coating layer.

  Thereafter, the mandrill and the stent body 10 are further immersed in a polymer solution to form a film, and the outer surface of the stent body 10 is coated. Next, laser processing is performed to form fine holes in the polymer film, and then the films on both ends are cut off. Thereafter, the stent is expanded in diameter by placing it at a temperature higher than the transformation temperature, and is extracted from the mandrill.

(3) Cover Strip Method To manufacture a stent by this cover strip method, a cylindrical cover strip with one end sealed is manufactured, and this is attached to the outer peripheral surface and inner peripheral surface of the stent body. In order to attach the cover strip to the outer peripheral surface of the stent body, a gas is sent into the cover strip and the cover strip is sufficiently opened, and the temperature is lower than the transformation temperature fitted to the mandrill. A stent having a diameter slightly smaller than the quasi-maximum diameter is inserted into the cover strip, and the cover strip is contracted by stopping the blowing of gas to be brought into close contact with the outer peripheral surface of the stent. Thereafter, in order to attach the cover strip to the inner peripheral surface of the stent body, the diameter of the stent body 10 is increased at a temperature higher than the transformation temperature, and the stent body 10 is extracted from the mandrill. At this time, the stent body has a quasi-maximum diameter. Thereafter, the cover strip is inserted into the stent body, and then the gas is supplied into the cover strip to expand the diameter, and is brought into close contact with the inner peripheral surface of the stent body. Excess cover strips that protrude from the stent body are excised. Next, laser processing is performed to drill fine holes in the polymer film.

(4) Centrifugal molding The stent of the present invention can be molded by centrifugal molding.
That is, a cylindrical mold is rotated at high speed around its axis, and a polymer film resin material solution is supplied to mold an outer layer polymer film. The resin material liquid may be a polymer solution or a polymerizable resin material liquid such as a monomer. If necessary, after performing a curing treatment by drying or ultraviolet irradiation, the stent body 10 whose diameter is reduced at a temperature lower than the transformation temperature is inserted into the mold, and then the temperature is set higher than the transformation temperature. The stent body 10 is expanded and brought into close contact with the outer layer polymer film in the mold. Next, the mold is rotated at a high speed, and the interior polymer film is supplied by supplying the resin material liquid of the interior polymer film into the interior of the mold. The interior polymer film is cured by drying, ultraviolet irradiation, etc., and then demolded. Next, laser processing is performed to drill fine holes in the polymer film.

  The stent 1 manufactured as described in the above (1) to (4) has a balloon catheter inserted into the stent 1 in a state where the diameter is reduced to the minimum diameter at a temperature lower than the transformation temperature of the stent body 10, and the delivery is performed. Inserted into the distal end of the sheath of the system. The sheath has an inner diameter smaller than the above-mentioned quasi-maximum diameter, and the stent expands when the temperature exceeds the transformation temperature of the stent body, and is in close contact with the inner peripheral surface of the sheath. After the sheath 1 is sent to the intended placement position in the lumen and then the stent 1 is sent into the lumen, the stent 1 whose sheath is released is expanded to the quasi-maximum diameter.

  If the inner diameter of the blood vessel is smaller than this quasi-maximum diameter, this will place the stent.

  When the inner diameter of the blood vessel is larger than the quasi-maximum diameter, the stent 1 is sent out into the lumen in this way, and then the stent 1 is expanded by a balloon and brought into close contact with the inner surface of the lumen. The stent 1 can be expanded until the stent body 10 has the maximum diameter, but adheres to the inner surface of the lumen before the maximum diameter is reached. Therefore, the stent 1 is placed by deflating the balloon and taking it out of the body.

  Immediately after being sent into the lumen, the stent 1 has a quasi-maximum diameter. In this quasi-maximum diameter, the polymer is already in a tensioned state without wrinkles or slack, so that the stent does not have wrinkles or slack even in the expanded state. Further, the amount of expansion required from the quasi-maximum aperture to the indwelling state is small. Therefore, since the amount of stretching of the polymer film 2 accompanying expansion is small, the load applied to the polymer film 2 is small, and the strength and durability of the polymer film 2 are good.

  When the polymer film 2 is attached to the stent body 10 by the insertion method (1) or the cover strip method (3), the stent body 10 and the polymer film 2 on the outer peripheral side are simply overlapped, The polymer film 2 on the outer peripheral side and the stent body 10 may be slidable. If the polymer film 2 on the outer peripheral side and the stent body 10 are merely overlapped, and the stent body 10 is slidable with the outer cover cover strip during the indwelling operation, the stent 1 is twisted or deformed in a complicated manner. Even if it happens, wrinkles and wrinkles are prevented from occurring in the polymer film 2 on the outer peripheral side.

  In order to improve the slidability, the inner peripheral surface of the polymer film 2 on the outer peripheral side may be surface-treated. As an example of this treatment, light irradiation may be mentioned after coating a composition comprising gelatin modified with a xanthene dye and a hydrogen donor such as thiol, reducing sugar, polyphenol or a compound having a dialkylamino group. Further, as surface treatment, dimethylacrylamide may be graft-polymerized to radical active sites by glow discharge using the stent body as an electrode.

It is a perspective view of a stent. FIG. 2 is a cross-sectional view of the stent of FIG. It is sectional drawing of the stent and stent main body which show the manufacturing method of a stent. It is a perspective view of a stent main body. It is a perspective view of the stent main body expanded in diameter.

Explanation of symbols

1 Stent 2 Polymer film 10 Stent body

Claims (17)

The stent body is made of a shape memory alloy whose transformation temperature is lower than the body temperature of the living body, has a small diameter at a temperature lower than the transformation temperature, and expands to a large diameter at a temperature higher than the transformation temperature;
In a stent having a polymer layer covering at least the outer peripheral surface of the stent body,
In an environment where the temperature is higher than the transformation temperature, the stent body has a quasi-maximum diameter slightly smaller than the maximum diameter, which is the diameter when not restrained by the polymer layer. A stent characterized in that the above diameter expansion is constrained.   The stent according to claim 1, wherein the quasi-maximum diameter is 30 to 80% of the maximum diameter.   3. The stent according to claim 1, wherein the stent can be expanded in diameter by a balloon inserted therein when the main stent body has a quasi-maximum diameter.   The stent according to any one of claims 1 to 3, wherein the polymer layer has a Young's modulus of 0.05 MPa to 30.00 MPa.   The stent according to any one of claims 1 to 4, wherein the polymer layer is provided with a plurality of micropores communicating the inner peripheral side and the outer peripheral side of the stent.   The stent according to any one of claims 1 to 5, wherein the main stent body is slidable with respect to an inner peripheral surface of a cylindrical polymer layer surrounding from the outer peripheral side.   The stent according to claim 6, wherein a sliding property imparting process is applied to an inner peripheral surface of the cylindrical polymer layer.   8. The treatment according to claim 7, wherein the slidability imparting treatment is performed by coating a composition comprising gelatin modified with a xanthene dye and a hydrogen donor such as a compound having a thiol, a reducing sugar, a polyphenol, or a dialkylamino group. A stent characterized in that   8. The slidability imparting treatment according to claim 7, wherein the slidability imparting treatment is a treatment in which a radical active site is generated in the polymer layer by glow discharge using the stent body as an electrode, and dimethylacrylamide is graft-polymerized to the radical active site. Stent.   A method for producing a stent according to any one of claims 1 to 9, wherein the stent body is formed at a temperature lower than the transformation temperature and smaller than the quasi-maximum diameter, and the stent body is cylindrical. The stent is inserted into the polymer layer, then heated to a temperature higher than the transformation temperature to expand the stent body, and is in close contact with the inner peripheral surface of the cylindrical polymer layer. .   The stent according to claim 10, wherein when the stent body is inserted into the cylindrical polymer layer and then heated to a temperature higher than the transformation temperature, the diameter expansion rate of the stent body is 10% or less. Manufacturing method.   The method for producing a stent according to claim 10 or 11, wherein a slidability imparting treatment is applied to an inner peripheral surface of the cylindrical polymer layer.   The slidability imparting treatment according to claim 12, wherein the slidability imparting treatment is performed by irradiating light after coating a composition comprising gelatin modified with xanthene dye and a hydrogen donor such as thiol, reducing sugar, polyphenol, or a compound having a dialkylamino group. A method for producing a stent, characterized in that   The slidability imparting treatment according to claim 12, wherein the slidability imparting treatment is a treatment in which a radical active site is generated in the polymer layer by glow discharge using the stent body as an electrode, and dimethylacrylamide is graft-polymerized to the radical active site. A method for manufacturing a stent.   10. The method for producing a stent according to claim 1, wherein the polymer layer is formed in a state in which a stent body is maintained at a diameter smaller than the quasi-maximum diameter. Manufacturing method.   16. The method for manufacturing a stent according to claim 15, wherein the polymer layer is formed in a state where the stent body is externally fitted to the rod-like body at a temperature lower than the transformation temperature.   16. The method for manufacturing a stent according to claim 15, wherein the polymer layer is formed in a state in which the stent body is fitted into the cylindrical body at a temperature higher than the transformation temperature.

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