Balloon for balloon catheter

Abstract

Provided is a balloon for a balloon catheter, which can be easily prevented from the breakage in the peripheral direction even when the balloon is broken.　A balloon for a balloon catheter wherein: when the position where the balloon has the thinnest average film thickness Tx in the central section is referred to as the thinnest position X, the amount of film thickness change, which is obtained by dividing the difference between the average film thickness Tp at the proximal position P and the average film thickness Tx by 1 / 4 of the length of a straight pipe section, and the amount of film thickness change, which is obtained by dividing the difference between the average film thickness Td at the distal position D and the average film thickness Tx by 1 / 4 of the length of the straight pipe section, are both 2.0×10-4 or less; and the average film thickness Tx is 30 μm or less.

Description

Balloon for balloon catheter

[0001] The present invention relates to a balloon for a balloon catheter and a balloon catheter including the same.

[0002] Angioplasty, a minimally invasive treatment in which a balloon catheter is inserted into a narrowed portion of a blood vessel and the balloon is inflated to expand the blood vessel and ensure blood flow, is widely used. Angioplasty is used to treat diseases such as myocardial infarction caused by narrowing of the coronary arteries of the heart, and to treat stenosis occurring in shunts for dialysis. The balloon used in a balloon catheter typically has a cylindrical shape with tapered distal and proximal ends, and the cylindrical part with the largest diameter is used to expand the blood vessel.

[0003] When dilating a stenotic area using a balloon catheter, an inflation pressure appropriate to the target area is applied to the balloon, but if the internal pressure of the balloon becomes excessive due to unexpected internal pressure being applied to the balloon during the procedure, the balloon may break. If the balloon breaks circumferentially in this case, there is a serious risk that fragments of the balloon distal to the breakage will remain inside the body. Therefore, even if the balloon breaks, a technology is needed to ensure that the balloon breaks longitudinally rather than circumferentially.

[0004] For example, Patent Documents 1 to 3 disclose balloons in which the pressure resistance is improved by controlling the molecular orientation of the resin that constitutes the balloon. Patent Document 4 discloses that a balloon having a membrane-like body with a non-elastomer-containing intermediate layer and outer and inner layers containing an elastomer disposed on the outer and inner surfaces of the intermediate layer has been obtained, and that by setting the average thickness of the intermediate layer to 30% to 70% of the average thickness of the entire balloon, compliance is improved and a balloon with a good balance between pressure resistance and passage performance is obtained.

[0005] Japanese Patent Application Laid-Open No. 2004-298354 Japanese Patent Application Laid-Open No. 9-38195 International Publication No. 2014 / 141382 International Publication No. 2013 / 145479

[0006] If a balloon were to break inside the body during a procedure using a balloon catheter, and if the balloon were to break circumferentially, there would be a serious risk that fragments of the balloon distal to the breakage would remain inside the body. However, with conventional balloons such as those described above, it was difficult to reliably prevent circumferential cracking.

[0007] In view of the above circumstances, an object of the present invention is to provide a balloon for a balloon catheter that can easily suppress circumferential cracking even in the event of balloon destruction.

[0008] One embodiment of a balloon for a balloon catheter of the present invention that has solved the above-mentioned problems is a balloon having a proximal end and a distal end in the longitudinal axis direction, a straight tube section, a proximal tapered section located proximal to the straight tube section, and a distal tapered section located distal to the straight tube section, wherein, at a predetermined position in the longitudinal axis direction, the film thickness is measured at eight points equally spaced 45° apart in a 360° circumferential direction of the balloon, and when the average of the eight points is taken as the average film thickness at the predetermined position, the proximal end of the straight tube section is taken as the 0% position and the distal end is taken as the 100% position in the longitudinal axis direction. The position where the balloon has the thinnest average thickness Tx in the central section from the 30% position to the 70% position is defined as the thinnest position X, the position away from the thinnest position X on the proximal side by a length of ¼ of the length of the straight tube portion is defined as the proximal position P, and the position away from the thinnest position X on the distal side by a length of ¼ of the length of the straight tube portion is defined as the distal position D. The thickness change amount obtained by dividing the difference between the average thickness Tp and the average thickness Tx at the proximal position P by the length of ¼ of the length of the straight tube portion, and the thickness change amount obtained by dividing the difference between the average thickness Td and the average thickness Tx at the distal position D by the length of ¼ of the length of the straight tube portion were both 2.0 × 10 －４ The average thickness Tx is 30 μm or less.

[0009] When internal pressure is applied to a thin-walled cylindrical shell such as a balloon, stress concentrates in areas where the thickness changes, potentially leading to cracks. If there is a portion where the thickness changes suddenly along the longitudinal axis, stress concentrates in that portion along the circumferential direction, potentially resulting in circumferential cracks. However, the balloon for a balloon catheter according to an embodiment of the present invention, with its configuration described above, can gently change the thickness from the thinnest point X in the central section of the balloon along the longitudinal axis, thereby suppressing circumferential stress concentration and preventing circumferential cracks. This avoids the risk of fragments of the balloon for a balloon catheter remaining in the body, enabling safe treatment using a balloon catheter.

[0010] At the thinnest position X, the coefficient of variation of the film thickness at the eight points is 1.5×10 －２ This makes it easier to prevent stress concentration in the circumferential direction when internal pressure is applied to the balloon.

[0011] It is preferable that the position where the average film thickness is thinnest in the entire section of the straight pipe portion from the 0% position to the 100% position among the predetermined positions is the same as the thinnest position X.

[0012] The present invention also provides a balloon catheter comprising the above-mentioned balloon for a balloon catheter.

[0013] The balloon for a balloon catheter described above can prevent circumferential stress concentration in the area including the thinnest point of the central section, even in the event of balloon rupture, thereby easily preventing the occurrence of circumferential cracks and cross-shaped cracks formed by a combination of longitudinal cracks and circumferential cracks. As a result, the risk of fragments of the balloon for a balloon catheter remaining in the body can be avoided, enabling safe treatment using a balloon catheter.

[0014] 1 is a plan view of a balloon catheter according to one embodiment of the present invention. It is a plan view of a balloon of the balloon catheter shown in FIG. 1. It is a plan view when a longitudinal crack has occurred in the balloon. It is a plan view when a circumferential crack has occurred in the balloon. It is a plan view when a cross-shaped crack has occurred in the balloon. It is a cross-sectional view taken along line VI-VI of the balloon shown in FIG. 2. It is a diagram showing the results of film thickness measurement of a balloon according to one embodiment of the present invention. It is a graph showing the average film thickness along the longitudinal axis of a balloon according to one embodiment of the present invention. It shows a stress-strain curve of a polyamide-based resin. It is a cross-sectional view showing the state of a parison placed in a mold according to one embodiment of the present invention. It is a cross-sectional view showing the state during a first stretching step according to one embodiment of the present invention. It is a cross-sectional view showing the state during a second stretching step according to one embodiment of the present invention. It is a cross-sectional view showing the state after completion of the second stretching step according to one embodiment of the present invention. It is a diagram showing the results of film thickness measurement of a balloon obtained in Example 1. It is a diagram showing the results of film thickness measurement of another balloon obtained in Example 1. It is a diagram showing the results of film thickness measurement of yet another balloon obtained in Example 1. It is a diagram showing the results of film thickness measurement of yet another balloon obtained in Example 1. It is a diagram showing the results of film thickness measurement of yet another balloon obtained in Example 1. It is a diagram showing the results of film thickness measurement of a balloon obtained in Comparative Example 1. 1A is a diagram showing the results of film thickness measurement of another balloon obtained in Comparative Example 1. FIG. 1B is a diagram showing the results of film thickness measurement of yet another balloon obtained in Comparative Example 1. FIG. 1C is a diagram showing the results of film thickness measurement of yet another balloon obtained in Comparative Example 1.

[0015] The present invention will be described below based on the embodiments, but the present invention is not limited to the following embodiments and can be implemented with appropriate modifications within the scope of the above and below-described purposes, and all such modifications are included within the technical scope of the present invention. In addition, hatching and component symbols may be omitted in each drawing for convenience. In such cases, please refer to the specification or other drawings. Furthermore, the dimensions of various components in the drawings may differ from the actual dimensions, as priority is given to helping understand the features of the present invention.

[0016] A balloon for a balloon catheter according to an embodiment of the present invention has a proximal end and a distal end in the longitudinal axis direction, and has a straight tube section, a proximal tapered section located proximal to the straight tube section, and a distal tapered section located distal to the straight tube section. At a predetermined position in the longitudinal axis direction, the film thickness is measured at eight points equally spaced 45° apart around 360° of the balloon in the circumferential direction, and the average of the eight points is taken as the average film thickness at the predetermined position. In the longitudinal axis direction, the proximal end of the straight tube section is taken as the 0% position and the distal end is taken as the 100% position. The position where the balloon has the thinnest average thickness Tx in the central section from the 30% position to the 70% position is defined as the thinnest position X, the position away from the thinnest position X on the proximal side by a length of 1 / 4 of the straight tube section is defined as the proximal position P, and the position away from the thinnest position X on the distal side by a length of 1 / 4 of the straight tube section is defined as the distal position D. The thickness change amount obtained by dividing the difference between the average thickness Tp and the average thickness Tx at the proximal position P by the length of 1 / 4 of the straight tube section, and the thickness change amount obtained by dividing the difference between the average thickness Td and the average thickness Tx at the distal position D by the length of 1 / 4 of the straight tube section, were both 2.0 × 10 －４ The average thickness Tx is 30 μm or less.

[0017] When internal pressure is applied to a thin-walled cylindrical shell such as a balloon, stress can concentrate in areas where the thickness changes, potentially leading to cracks in those areas. If there is a portion where the thickness suddenly changes along the longitudinal axis, stress can concentrate in that portion along the circumferential direction, potentially resulting in circumferential cracks. For this reason, with conventional balloons for balloon catheters, it has been difficult to eliminate the possibility of circumferential cracks in the central section or cross-shaped cracks formed by a combination of longitudinal cracks and circumferential cracks. However, with the balloon for balloon catheters according to the embodiment of the present invention, as described above, the average thickness Tx at the thinnest point X is 30 μm or less, and the thickness changes of the average thickness Tp at the proximal position P and the average thickness Td at the distal position D relative to the average thickness Tx at the thinnest point X of the balloon central section are both 2.0 × 10 －４By satisfying the following conditions, it is possible to make the change in film thickness from the thinnest point X of the central section of the balloon along the longitudinal axis gentle, thereby suppressing the concentration of circumferential stress and preventing circumferential cracking. This avoids the risk of fragments of the balloon for a balloon catheter remaining in the body, allowing for safe treatment using a balloon catheter.

[0018] Hereinafter, a balloon for a balloon catheter according to an embodiment of the present invention will be described with reference to FIGS. 1 to 8. FIG. 1 is a plan view of a balloon catheter according to an embodiment of the present invention. FIG. 2 is a plan view of the balloon of the balloon catheter shown in FIG. 1. FIGS. 3 to 5 are plan views showing examples of cracks occurring in a balloon for a balloon catheter according to an embodiment of the present invention, respectively showing examples of longitudinal cracks, circumferential cracks, and cross-shaped cracks. FIG. 6 is a cross-sectional view of the balloon shown in FIG. 2 taken along line VI-VI and illustrating a method for determining the average film thickness at a predetermined position. FIG. 7 is a diagram showing the results of film thickness measurements of a balloon according to an embodiment of the present invention. FIG. 8 is a graph showing the average film thickness at various positions along the longitudinal axis of a balloon according to an embodiment of the present invention. In this specification, a balloon for a balloon catheter may be simply referred to as a "balloon."

[0019] As shown in Fig. 1, a balloon 20 is used for a balloon catheter 1. The balloon 20 is connected to the distal side of the shaft 3, and the balloon 20 can be expanded by introducing a fluid through the lumen of the shaft 3, and can be deflated by discharging the fluid. The fluid is introduced or discharged using an indeflator (a balloon pressurizer), and the expansion and contraction of the balloon 20 can be controlled. The fluid may be pressurized fluid pressurized by a pump or the like.

[0020] The balloon 20 has a longitudinal axis direction x, a circumferential direction z along the outer edge of the balloon 20 in a cross section perpendicular to the longitudinal axis direction x, and a radial direction y connecting the centroid of the outer edge of the balloon 20 to a point on the outer edge of the balloon 20 in a cross section perpendicular to the longitudinal axis direction x. In this specification, the direction toward the user's hand in the longitudinal axis direction x is referred to as the proximal side, and the direction opposite to the proximal side, i.e., the direction toward the treatment target, is referred to as the distal side.

[0021] The balloon 20 has a proximal end and a distal end in the longitudinal axis direction x, and includes a straight tube section 23, a proximal tapered section 22 located proximal to the straight tube section 23, and a distal tapered section 24 located distal to the straight tube section 23. The straight tube section 23 preferably has approximately the same diameter in the longitudinal axis direction x, but may have different diameters in the longitudinal axis direction x. The proximal tapered section 22 and the distal tapered section 24 are preferably formed so that their diameters decrease with increasing distance from the straight tube section 23. By having the straight tube section 23 have the largest diameter, when the balloon 20 is expanded at a lesion such as a stenosis, the straight tube section 23 can be in sufficient contact with the lesion, facilitating treatment such as dilation of the lesion. Furthermore, since the proximal tapered portion 22 and the distal tapered portion 24 are reduced in diameter, when the balloon 20 is deflated, the outer diameter of the proximal end and distal end of the balloon 20 can be reduced, thereby reducing the step between the shaft 3 and the balloon 20, making it easier to insert the balloon 20 into a body cavity.

[0022] The balloon 20 may have a proximal sleeve portion 21 proximal to the proximal tapered portion 22 and a distal sleeve portion 25 distal to the distal tapered portion 24. At least a portion of the proximal sleeve portion 21 and the distal sleeve portion 25 may be fixed to the shaft 3.

[0023] As shown in FIG. 2, the straight tube portion 23 of the balloon 20 has a proximal end at a 0% position L ０ The distal end is at the 100% position L １００ When this is done, the 30% position L ３０ From 70% position L ７０23C, an end portion proximal to the central section 23C, and an end portion distal to the central section 23C.

[0024] When the balloon 20 is manufactured using a conventional manufacturing method, such as blow molding, the thinnest part of the balloon 20 is typically located in the central section 23C. Therefore, cracks may occur in the central section 23C when the internal pressure of the balloon 20 becomes excessive. When internal pressure is applied to a thin-walled cylindrical shell such as the balloon 20, the stress in the circumferential direction z is twice the stress in the longitudinal direction x. Therefore, longitudinal cracks, as shown in FIG. 3, are likely to occur in a typical thin-walled cylindrical shell. Therefore, even with conventional balloons, longitudinal cracks are theoretically dominant. However, with conventional balloons, it has been difficult to achieve a statistically significant reduction in the incidence of circumferential cracks, as shown in FIG. 4, or cross-shaped cracks, formed by a combination of longitudinal cracks and circumferential cracks, as shown in FIG. 5. However, even a small percentage of circumferential cracks can lead to serious medical accidents in clinical settings. In this regard, the balloon 20 according to the present invention can easily and reliably prevent circumferential cracks by adjusting the thickness to a predetermined condition, thereby improving the safety of procedures using the balloon catheter 1.

[0025] A method for measuring the film thickness will be described with reference to FIG. 6 . FIG. 6 is a cross-sectional view of the balloon 20 shown in FIG. 2 taken along line VI-VI, perpendicular to the longitudinal axis direction x at a predetermined position on the straight tube section 23. The average film thickness of the balloon 20 at a predetermined position in the longitudinal axis direction x is determined by measuring the film thickness at eight points equally spaced by 45° in the circumferential direction z of the balloon 20 over a 360° range and calculating the average of the film thicknesses at these eight points. That is, when point a in FIG. 6 is defined as the 0° point in the circumferential direction z of the balloon 20, points b, c, d, e, f, g, and h are defined as points where the central angle θ is 45°, 90°, 135°, 180°, 225°, 270°, and 315°, respectively. The film thicknesses at points a to h are measured at the predetermined position in the longitudinal axis direction x, and the average of the film thicknesses at points a to h is defined as the average film thickness at the predetermined position. The greater the number of predetermined positions in the longitudinal axis direction x, the more detailed the film thickness of the balloon 20 can be determined. The number of predetermined positions may be, for example, 1000 in the longitudinal axis direction x. In this case, the film thickness is measured at 1000 x 8 = 8000 points. However, the number of predetermined positions is not limited to 1000.

[0026] The membrane thickness can be measured, for example, by a laser displacement measuring device while the balloon 20 is pressurized to the extent that it can maintain its cylindrical shape. Fig. 7 shows an example of a chart obtained by actual measurement. The horizontal axis of Fig. 7 represents the position x in the longitudinal axis direction of the straight pipe portion 23, and 0 at the left end represents the 0% position L ０ , the right end 150 is the 100% position L １００ The vertical axis of Fig. 7 represents the central angle θ in the circumferential direction z, and the gray scale represents the film thickness (thickness, unit: mm). The lines in the chart of Fig. 7 are isopleths connecting points having the same film thickness.

[0027] In the example shown in Fig. 7, the film thickness is measured at eight points out of 1000 predetermined positions in the longitudinal axis direction x. The average film thickness at each predetermined position is calculated from the average of the eight points, and a graph showing the relationship between position and average film thickness can be obtained, as shown in Fig. 8.

[0028] As shown in Figures 7 and 8, the measurement results indicate the position X in the central section 23C where the balloon 20 has the thinnest average thickness Tx, the average thickness Tp at a proximal position P that is 1 / 4 of the length of the straight tube section 23 proximally from position X in the longitudinal axis direction x, and the average thickness Td at a distal position D that is 1 / 4 of the length of the straight tube section 23 distally from position X in the longitudinal axis direction x.

[0029] In the examples shown in Figures 7 and 8, the thinnest position in the entire straight pipe section 23 coincides with the thinnest position X in the central section 23C, but these do not necessarily have to coincide, and there may be a position in a part other than the central section 23C that has a film thickness thinner than the thinnest position in the entire straight pipe section 23, i.e., the average film thickness Tx at the thinnest position X.

[0030] In the balloon 20, the amount of change in film thickness obtained by dividing the difference between the average film thickness Tp at the proximal position P and the average film thickness Tx at the thinnest position X by ¼ of the length of the straight tube portion 23, and the amount of change in film thickness obtained by dividing the difference between the average film thickness Td at the distal position D and the average film thickness Tx at the thinnest position X by ¼ of the length of the straight tube portion 23, are both 2.0 × 10 －４ The straight pipe section 23 has an average thickness Tx of 30 μm or less at the thinnest position X of the central section 23C, and the amount of change in thickness relative to the average thickness Tx in a predetermined section in the longitudinal axis direction x is within the above range, so that the change in thickness can be made gradual in the region from the thinnest position X of the central section 23C of the straight pipe section 23 along the longitudinal axis direction x. As a result, if there is a portion where the thickness suddenly changes along the longitudinal axis direction x, stress concentration occurs in that portion along the circumferential direction z, which could result in circumferential cracking. However, in the balloon 20, stress concentration in the circumferential direction z can be suppressed, making it possible to prevent circumferential cracking.

[0031] 8, the amount of change in film thickness obtained by dividing the difference between the average film thickness Tp at the proximal position P and the average film thickness Tx at the thinnest position X by one-quarter of the length of the straight tube section 23 corresponds to the slope of the line Lp, and the amount of change in film thickness obtained by dividing the difference between the average film thickness Td at the distal position D and the average film thickness Tx at the thinnest position X by one-quarter of the length of the straight tube section 23 corresponds to the slope of the line Ld. Here, the average film thickness Tx is the average film thickness at the thinnest position X in the central section 23C of the straight tube section 23, and therefore the difference between the average film thickness Tp and the average film thickness Tx at the proximal position P and the difference between the average film thickness Td and the average film thickness Tx at the distal position D are always positive values, and therefore the amount of change in film thickness is the absolute value of the slope of the lines Lp and Ld.

[0032] The average film thickness Tx at the thinnest position X is preferably 28 μm or less, more preferably 25 μm or less, and even more preferably 24 μm or less. If the upper limit of the average film thickness Tx at the thinnest position X is within the above range, stress concentration in the circumferential direction z can be easily suppressed when the film thickness change amount is within the above range, and circumferential cracking can be easily prevented. Furthermore, since the balloon 20 can be made flexible, the insertability of the balloon 20 can be improved. The average film thickness Tx at the thinnest position X is preferably 15 μm or more, more preferably 18 μm or more, and even more preferably 20 μm or more. If the lower limit of the average film thickness Tx at the thinnest position X is within the above range, the strength of the balloon 20 can be ensured.

[0033] The amount of change in film thickness obtained by dividing the difference between the average film thickness Tp and the average film thickness Tx by one-quarter of the length of the straight pipe portion 23, and the amount of change in film thickness obtained by dividing the difference between the average film thickness Td and the average film thickness Tx by one-quarter of the length of the straight pipe portion 23, are 1.9×10 －４ The following is preferred: 1.85 x 10 －４ More preferably, 1.8×10 or less －４ If the upper limit of the change in film thickness is within the above range, stress concentration can be easily suppressed by gradually changing the film thickness in the region along the longitudinal axis direction x from the thinnest position X of the central section 23C of the straight pipe portion 23, and it is possible to prevent circumferential cracks. The lower limit of the change in film thickness is not particularly limited, but is, for example, 1.2 × 10 －４ That's it, 1.3 x 10 －４ That's it, 1.4 x 10 －４ It may be more than that.

[0034] To determine the average film thickness, the film thickness is measured at eight points spaced at 45° intervals in the circumferential direction z at a predetermined position. At the thinnest position X, the coefficient of variation of the film thickness at these eight points is 1.5×10 －２ It is preferable that the coefficient of variation of the film thickness is equal to or greater than this value. The coefficient of variation of the film thickness is the standard deviation of eight measurements taken at eight points divided by the average value of the eight measurements, and indicates the degree of variation of the film thickness at the eight points. At the thinnest position X of the central section 23C of the straight pipe section 23, by having the coefficient of variation of the film thickness at the eight points be equal to or greater than this value, it is possible to configure the balloon 20 so that the film thickness at the thinnest position X at the eight points in the circumferential direction z is not too uniform. When the film thickness in the circumferential direction z at the thinnest position X is uniform, that is, when the coefficient of variation of the film thickness at the eight points is 1.5×10 －２ If the thickness is less than 1.5×10, the portion having the thinnest film thickness will be uniformly distributed in the circumferential direction z, and therefore, when stress is applied to the thinnest position X, stress will be concentrated in the circumferential direction z, which may lead to circumferential cracks. However, it is necessary to prevent the film thickness in the circumferential direction z at the thinnest position X from being too uniform, that is, to set the variation coefficient of the film thickness at eight points to 1.5×10. －２ By doing so, it is possible to configure the portions with the thinnest film thickness to be different from each other in the circumferential direction z, and therefore it is possible to more easily prevent stress concentration in the circumferential direction z when stress is applied to the thinnest position X.

[0035] The coefficient of variation of the film thickness at eight points is 1.8 × 10 －２ More preferably, 2.0 × 10 －２ More preferably, 2.1 × 10 －２ That's it, 2.3 x 10 －２ That's it, 2.5 x 10 －２ That's it, 2.8 x 10 －２ or more, and may be 3.5 × 10 －２ Preferably, the value is 3.2 x 10 －２ The following is more preferable: If the coefficient of variation is within the above range, the variation in film thickness in the circumferential direction z at the thinnest point X can be kept within a predetermined range while not becoming too uniform, and circumferential cracking can be easily prevented.

[0036] The positions in the longitudinal direction x where the coefficient of variation is within the above range preferably extend over a certain range in the longitudinal direction x from the thinnest position X. The coefficient of variation is preferably within the above range in sections each of which is 1 / 20 of the length of the straight pipe section 23 in the longitudinal direction x from the thinnest position X to the proximal and distal sides, and more preferably within the above range in sections each of which is 1 / 10 of the length. By configuring the film thickness in the longitudinal direction x so that it is not too uniform in the circumferential direction z over a certain range from the thinnest position X, stress concentration in the circumferential direction z can be more easily prevented.

[0037] The coefficient of variation, i.e., whether the film thickness is uniform in the circumferential direction z, can be visually seen from the chart shown in Fig. 7. The lines in the chart are contour lines connecting points with the same film thickness, so the straighter the vertical line in the chart, the smaller the coefficient of variation, i.e., the more uniform the film thickness is in the circumferential direction z.

[0038] Among the predetermined positions for determining the average film thickness, the 0% position L ０ From 100% position L １００ It is preferable that the position where the average film thickness is thinnest in all sections of the straight pipe section 23 up to the central section 23C is the same as the thinnest position X. In other words, it is preferable that the average film thickness Tx at the thinnest position X of the central section 23C is the thinnest film thickness in all sections of the straight pipe section 23. This makes it possible to configure sections other than the central section 23C so that there are no sections where the film thickness is thinner than the average film thickness Tx at the thinnest position X, thereby preventing cracks from occurring in sections other than the central section 23C. If a crack occurs at an end of the straight pipe section 23 other than the central section 23C, the crack may extend to the tapered section, which has a relatively thick film thickness, and cause an L-shaped or J-shaped crack, which is a circumferential crack in the tapered section. However, the above configuration can prevent such a problem.

[0039] Examples of materials constituting the balloon 20 include polyolefin-based resins such as polyethylene, polypropylene, and ethylene-propylene copolymer; polyester-based resins such as polyethylene terephthalate and polyester elastomer; polyurethane-based resins such as polyurethane and polyurethane elastomer; polyphenylene sulfide-based resins; polyamide-based resins such as polyamide and polyamide elastomer; fluorine-based resins; silicone-based resins; and natural rubbers such as latex rubber. These materials may be used alone or in combination. Among these, polyamide-based resins, polyester-based resins, and polyurethane-based resins are preferred, with polyamide-based resins such as nylon 12 and nylon 11 being more preferred, and nylon 12 being particularly preferred. From the standpoint of thinning and flexibility of the balloon 20, it is preferable to use an elastomer resin, and polyamide elastomers such as polyamide ether elastomers are preferably used.

[0040] The balloon 20 can be manufactured by placing a parison made of the above-mentioned material in a mold and biaxially stretching and blow molding the parison. A preferred method for manufacturing the balloon 20 will be described later.

[0041] The present invention also provides a balloon catheter 1 including the above-described balloon 20. As described above, the balloon 20 is connected to the distal side of the shaft 3.

[0042] The shaft 3 is preferably made of resin, metal, or a combination of resin and metal. Using resin as the material for the shaft 3 facilitates imparting flexibility and elasticity to the shaft 3. Furthermore, using metal as the material for the shaft 3 improves the pushability of the balloon catheter 1. Examples of resins that can be used to form the shaft 3 include polyamide-based resins, polyester-based resins, polyurethane-based resins, polyolefin-based resins, fluorine-based resins, vinyl chloride-based resins, silicone-based resins, and natural rubber. These may be used alone or in combination. Among these, the resin that can be used to form the shaft 3 is preferably at least one of polyamide-based resins, polyolefin-based resins, and fluorine-based resins. This enhances the lubricity of the surface of the shaft 3 and improves the insertability of the balloon catheter 1 through a body cavity. Examples of metals that can be used to form the shaft 3 include stainless steels such as SUS304 and SUS316, platinum, nickel, cobalt, chromium, titanium, tungsten, gold, Ni-Ti alloys, Co-Cr alloys, and combinations thereof.

[0043] The shaft 3 may be a single shaft 3 extending from the distal side to the proximal side, or may include a distal shaft and a proximal shaft that are separate members, with the proximal end of the distal shaft connected to the distal end of the proximal shaft. The distal shaft and the proximal shaft may further be composed of multiple tubular members. When the shaft 3 is composed of a distal shaft and a proximal shaft, for example, the distal shaft and the proximal shaft may both be made of resin, or the distal shaft may be made of resin and the proximal shaft may be made of metal. The shaft 3 may also have a layered structure made of different materials or the same material.

[0044] The shaft 3 preferably has an internal fluid flow path and also has a guidewire insertion path. A configuration in which the shaft 3 has an internal fluid flow path and a guidewire insertion path can be achieved, for example, by configuring the balloon catheter 1 as an over-the-wire type having a guidewire insertion path from the distal side to the proximal side of the shaft 3, as shown in Fig. 1 , in which the shaft 3 has an outer tube and an inner tube, the inner tube functions as a guidewire insertion path, and the space between the inner tube and the outer tube functions as a fluid flow path. In this configuration in which the shaft 3 has an outer tube and an inner tube, it is preferable that the inner tube extends from the distal end of the outer tube and penetrates distally beyond the balloon 20, the distal side of the balloon 20 is joined to the inner tube, and the proximal side of the balloon 20 is joined to the outer tube.

[0045] Alternatively, although not shown, the balloon catheter 1 according to an embodiment of the present invention may be a rapid exchange type having a guidewire port midway from the distal side to the proximal side of the shaft, with a guidewire insertion passage provided from the guidewire port to the distal side of the shaft.

[0046] The balloon 20 and the shaft 3 can be joined by bonding with an adhesive, welding, or by attaching a ring-shaped member to the overlapping portion of the end of the balloon 20 and the shaft 3 and crimping the end. Among these, it is preferable that the balloon 20 and the shaft 3 are joined by welding. By welding the balloon 20 and the shaft 3, the bond between the balloon 20 and the shaft 3 is unlikely to come loose even when the balloon 20 is repeatedly expanded or contracted, and the bond strength between the balloon 20 and the shaft 3 can be easily increased.

[0047] A tip member is preferably provided at the distal end of the balloon catheter 1. The tip member may be provided at the distal end of the balloon catheter 1 as a separate member from the shaft 3 and connected to the distal end of the balloon 20, or the shaft 3 (e.g., the inner tube) extending distally beyond the distal end of the balloon 20 may function as the tip member.

[0048] To enable confirmation of the position of the balloon 20 under X-ray fluoroscopy, radiopaque markers may be placed on the balloon 20 and / or on the shaft 3 at the portion where the balloon 20 is located in the longitudinal axis direction x. The radiopaque markers are preferably placed so that the positions of both ends of the straight tube portion 23 of the balloon 20 can be confirmed, or may be placed so that the center position of the straight tube portion 23 can be confirmed.

[0049] As shown in FIG. 1 , the balloon catheter 1 may have a hub 4 provided on the proximal side of the shaft 1. The hub 4 preferably has a fluid injection section 6 connected to a fluid flow path for supplying fluid to the interior of the balloon 20. The hub 4 may also have a guidewire insertion section 5 connected to a guidewire insertion passage. This configuration facilitates the operation of supplying fluid to the interior of the balloon 20 to inflate or deflate the balloon 20, and the operation of delivering the balloon catheter 1 to a treatment site along the guidewire. While FIG. 1 shows a so-called over-the-wire balloon catheter 1 in which a guidewire is inserted from the distal side to the proximal side of the shaft 3, the balloon 20 can also be applied to a so-called rapid exchange balloon catheter in which a guidewire is inserted partway from the distal side to the proximal side of the shaft 3. In the case of a rapid exchange type, the guidewire port is provided partway from the distal side to the proximal side of the shaft 3, so the hub 4 does not need to have a bifurcated structure.

[0050] The shaft 3 and the hub 4 can be joined by, for example, bonding with an adhesive or welding. Of these, it is preferable that the shaft 3 and the hub 4 are joined by adhesive. By bonding the shaft 3 and the hub 4, the bond strength between the shaft 3 and the hub 4 can be increased, thereby improving the durability of the balloon catheter 1, even when the shaft 3 and the hub 4 are made of different materials, such as when the shaft 3 is made of a highly flexible material and the hub 4 is made of a highly rigid material.

[0051] When the balloon catheter 1 is an over-the-wire type, it is preferable that an appropriate coating be applied to the outer wall of the shaft 3 (e.g., the outer tube).When the balloon catheter 1 is a rapid exchange type, it is preferable that an appropriate coating be applied to the outer wall of the shaft 3 on the distal and / or proximal sides of the guidewire port, and it is more preferable that a coating be applied to the outer wall of the shaft 3 on the distal and proximal sides of the guidewire port.

[0052] The coating can be a hydrophilic coating or a hydrophobic coating depending on the purpose, and can be applied by immersing the shaft 3 in a hydrophilic coating agent or a hydrophobic coating agent, by applying a hydrophilic coating agent or a hydrophobic coating agent to the outer wall of the shaft 3, or by covering the outer wall of the shaft 3 with a hydrophilic coating agent or a hydrophobic coating agent. The coating agent may contain drugs or additives.

[0053] Examples of hydrophilic coating agents include hydrophilic polymers such as polyvinyl alcohol, polyethylene glycol, polyacrylamide, polyvinylpyrrolidone, methyl vinyl ether maleic anhydride copolymer, and the like, or hydrophilic coating agents made from any combination thereof.

[0054] Examples of hydrophobic coating agents include polytetrafluoroethylene (PTFE), fluorinated ethylene propylene (FEP), perfluoroalkoxyalkane (PFA), silicone oil, hydrophobic urethane resin, carbon coat, diamond coat, diamond-like carbon (DLC) coat, ceramic coat, and substances terminated with alkyl groups or perfluoroalkyl groups and having low surface free energy.

[0055] Next, a method for manufacturing a balloon 20 will be described with reference to FIGS. 9 to 13. FIG. 9 shows a stress-strain curve for a polyamide resin. FIG. 10 shows a cross-sectional view of a parison placed in a mold according to one embodiment of the present invention. FIG. 11 shows a cross-sectional view of a parison stretched in the longitudinal axis direction x while heating the mold in a first stretching step according to one embodiment of the present invention. FIG. 12 shows a cross-sectional view of a parison stretched in the first stretching step, further stretched while being heated under a higher internal pressure than in the first stretching step, in a second stretching step according to one embodiment of the present invention. FIG. 13 shows a cross-sectional view of a state after the second stretching step is completed.

[0056] The balloon 20 can be manufactured by a first stretching step followed by a second stretching step. In the first stretching step, a parison is placed in a mold, and while the mold is heated, the parison is stretched to a necking region R of the stress-strain curve of the resin constituting the balloon 20, as shown in FIG. ｎ In the subsequent second stretching step, the film is stretched in the longitudinal axis direction x until the necking region R ｎ The parison stretched to exceed this value is further stretched while being heated in a state where the internal pressure of the parison is higher than in the first stretching step.

[0057] In many resins, in the stress-strain curve shown in Figure 9, stress acts so that the molecular chains in a bent state stretch in the elastic deformation region up to the yield point B. After the yield point B, the molecular chains that have been attracting each other by intermolecular forces begin to displace in the shear direction, causing plastic deformation. Once the molecular chains begin to displace, some resins exhibit a phenomenon in which the molecular chains become loose and the stress decreases down to the lower yield point L. After that, a region showing a flat stress is seen for a while, and this region is called the necking region R. ｎ The necking region R ｎ In the case of the necking region R, the molecular chains are displaced by strain, resulting in a certain stress. However, when the strain exceeds a certain level, the molecular chains approach each other and are closely oriented, generating a strong intermolecular force between the molecular chains. ｎ In the region beyond this, the stress increases steadily. ｎFirst, the parison is stretched in the longitudinal axis direction x until it exceeds the necking region R ｎ The parison stretched to exceed this value is heated under high internal pressure and further stretched. By this manufacturing method, the average film thickness Tx at the thinnest position X of the central section 23C of the straight pipe section 23 is 30 μm or less, and the film thickness change amount in a predetermined section in the longitudinal axis direction x is 2.0×10 －４ A balloon 20 can be manufactured that is as follows:

[0058] First, a parison 30 made of resin is prepared. The parison 30 is a tubular member having an inner cavity 31 and can be produced by, for example, extrusion molding. The parison 30 has one end and the other end and extends in the longitudinal axis direction x from one end to the other end.

[0059] The cross-sectional shape of the parison 30 in a direction perpendicular to the longitudinal axis direction x, i.e., in the radial direction y, may be substantially uniform along the longitudinal axis direction x. Alternatively, as shown in Figure 10, the cross-sectional shape of the parison 30 in the radial direction y may vary depending on the position along the longitudinal axis direction x. Parts of the parison 30, for example, parts corresponding to the straight tube portion 23, proximal tapered portion 22, and distal tapered portion 24 of the balloon 20, may have bubbles, i.e., enlarged diameter portions, in which the outer diameters of the parts are larger than those of the other parts.

[0060] Since the parison 30 is a component that is molded into the balloon 20, the material that constitutes the parison 30 can refer to the material that constitutes the balloon 20 described above.

[0061] Next, a mold 40 is prepared, which has a lumen 46 and an inner wall surface forming the lumen 46 that has a straight pipe portion 43, a proximal tapered portion 42 located proximal to the straight pipe portion 43, and a distal tapered portion 44 located distal to the straight pipe portion 43. The inner wall surface forming the lumen 46 of the mold 40 may have a proximal sleeve portion 41 located proximal to the proximal tapered portion 42 and a distal sleeve portion 45 located distal to the distal tapered portion 44.

[0062] The mold 40 may be composed of one member or multiple members. For example, the mold 40 may be composed of multiple halves, i.e., multiple mold members may be connected so as to be separable in the radial direction, or multiple mold members may be connected so as to be separable in the longitudinal direction.

[0063] 10 , the parison 30 is placed in the lumen 46 of the mold 40. At this time, if the parison 30 has a portion with a larger outer diameter, i.e., if it has bubbles corresponding to the straight tube section 23, proximal tapered section 22, and distal tapered section 24 of the balloon 20, it is preferable that the parison 30 be placed so that the bubbles are located in the straight tube section 43 of the mold 40. This makes it easier to form the straight tube section 23, proximal tapered section 22, and distal tapered section 24 of the balloon 20 by stretching the relevant portion.

[0064] 11, a first stretching step is performed in which the parison 30 is stretched in the longitudinal axis direction x while the mold 40 is heated. At this time, the parison 30 is stretched in the necking region R of the stress-strain curve of the resin constituting the parison 30. ｎ The necking region R ｎ As described above, the region R indicates a flat stress region after the yield point B and the lower yield point L, and in this region, the molecular chains of the resin that have started to plastically deform are displaced by the stress. ｎ The parison 30 is stretched until it exceeds the stretch limit.

[0065] The internal pressure of the parison 30 in the first stretching step is preferably lower than the internal pressure of the parison 30 in the second stretching step, so that in the first stretching step, the parison 30 can be stretched in the longitudinal axis direction x while being suppressed from stretching in the circumferential direction z.

[0066] When the parison 30 is prepared by extrusion molding, for example, and the parison 30 is prepared by being stretched to a certain extent in the longitudinal axis direction x before the first stretching step, the necking region R ｎThe amount by which the parison 30 is stretched in the longitudinal direction x until it exceeds this value varies depending on the degree of stretching of the parison 30 in the preparation stage, such as during extrusion molding. That is, if the parison 30 has been stretched in the longitudinal direction x to some extent in the preparation stage, the amount by which the parison 30 is stretched in the longitudinal direction x in the first stretching step may be reduced accordingly.

[0067] 12 , after the first stretching step is completed, a second stretching step is performed in which the parison 30 is further stretched while the mold 40 is heated, with the parison 30 being under a higher internal pressure than in the first stretching step. Because the internal pressure of the parison 30 is higher in the second stretching step than in the first stretching step, in the first stretching step the parison 30 is stretched in the longitudinal axis direction x while being restricted from stretching in the circumferential direction z, whereas in the second stretching step the parison 30 is stretched in the radial direction y and also in the longitudinal axis direction x.

[0068] In this way, a balloon 20 as shown in Fig. 13 can be obtained. By performing the first stretching step and the second stretching step, the average thickness Tx at the thinnest position X of the central section 23C of the straight pipe section 23 is 30 µm or less, and the thickness change amount in a predetermined section in the longitudinal axis direction x is 2.0 × 10 －４ The balloon 20 may be:

[0069] The stress-strain curve shown in FIG. 9 shows the necking region R ｎ However, depending on the resin, the region of constant stress may be short or the flat region may be unclear. In such cases, the first point after the stress-strain curve exceeds the yield point B where the differential coefficient of the stress-strain curve is 5% or more of the average rate of change up to the yield point B is defined as the necking region R. ｎ The first stretching step may be carried out until the strain exceeds this value.

[0070] The heating temperature in the first stretching step and the second stretching step can be set to a temperature close to the glass transition temperature of the resin forming the balloon 20. As a heating means for the mold 40, a known heater or the like can be used as appropriate.

[0071] In the first stretching step, a fluid is preferably introduced into the cavity 31 of the parison 30 to pressurize the interior of the parison 30, and the pressure is preferably 3 MPa or less. Alternatively, the pressure in the cavity 31 of the parison 30 and the pressure outside the parison 30 may be the same, i.e., the cavity 31 of the parison 30 may not be pressurized.

[0072] In the second stretching step, a fluid is preferably introduced into the lumen 31 of the parison 30 to pressurize the interior of the parison 30. The pressure is higher than the pressure applied to the lumen 31 of the parison 30 in the first stretching step, and is, for example, preferably 1 MPa or higher, more preferably 1.5 MPa or higher, and even more preferably 2 MPa or higher. The pressure is also preferably 5 MPa or lower, more preferably 4.5 MPa or lower, even more preferably 4 MPa or lower, and may be 3 MPa or lower. With such an internal pressure, the parison 30 stretched in the longitudinal axis direction x to the state shown in FIG. 13 can be further stretched in the radial direction y and the longitudinal axis direction x to be blow-molded into the final balloon shape shown in FIG. 13.

[0073] In the first stretching step, the parison 30 is not pressurized, and in the second stretching step, the necking region R ｎ It is preferable that pressure is applied to the parison 30 after the change in thickness in a predetermined section in the longitudinal axis direction x exceeds 2.0×10 －４ This makes it easier to form the balloon 20 as follows:

[0074] This application claims the benefit of priority based on Japanese Patent Application No. 2022-67321, filed on April 15, 2022. The entire contents of the specification of Japanese Patent Application No. 2022-67321, filed on April 15, 2022, are incorporated herein by reference.

[0075] The present invention will be described below with reference to examples. The present invention is not limited to the following examples, and can of course be practiced with appropriate modifications within the scope of the above-mentioned and below-mentioned aims, and all such modifications are included within the technical scope of the present invention.

[0076] Example 1: A parison with a bubble length of 71 mm was extruded from a polyamide ether elastomer. The parison was placed in a mold with a straight tube section measuring 150 mm in the longitudinal direction. While the mold was heated to 60°C, the parison was stretched in the longitudinal direction at a stretching rate of 10 mm / s under an internal pressure of 20 bar (2 MPa). Next, while the mold was heated to 60°C, the parison was blow-molded under a pressure of 38 bar (3.8 MPa) at a stretching rate of 140 mm / s. The extruded parison was then annealed at 130°C for 50 seconds to obtain a balloon.

[0077] Five balloons, No. 1 to No. 5, were fabricated using the same method. The film thickness of the straight tube section of each balloon was measured using a Keyence CL-PT010. The resulting charts are shown in Figures 14 to 18, the film thickness change in the section from the thinnest position to a predetermined position in the longitudinal direction is shown in Table 1, and the film thickness and coefficient of variation at eight points at the thinnest position are shown in Table 2. The film thickness change shown in Table 1 is the value of the change in the section from the thinnest position to a predetermined position on the proximal or distal side if the film thickness change is the same, or the larger value if the film thickness change is different.

[0078]

[0079]

[0080] Thirty more balloons were fabricated using the same method as in Example 1. Internal pressure was applied to these 30 balloons until they were broken, and the state of cracks after the breakage was observed. All 30 balloons had longitudinal cracks, but none had circumferential cracks.

[0081] Comparative Example 1 A parison was prepared in the same manner as in Example 1. The parison was placed in the cavity of the same mold as in Example 1, and the mold was heated to 60° C. while applying an internal pressure of 32.5 bar (3.25 MPa) to the parison and blow-molding it at a stretching speed of 140 mm / s. The parison was then annealed at 130° C. for 50 seconds to obtain a balloon.

[0082] Four balloons, No. 6 to No. 9, were fabricated using the same method. The film thickness of the straight tube section of each balloon was measured using a Keyence CL-PT010. The resulting charts are shown in Figures 19 to 22, the film thickness change in the section from the thinnest position to a predetermined position in the longitudinal direction is shown in Table 1, and the film thickness and coefficient of variation at eight points at the thinnest position are shown in Table 2. The film thickness change shown in Table 1 is the value of the change in film thickness in the section from the thinnest position to a predetermined position on the proximal or distal side if the film thickness change is the same, or the larger value if the film thickness change is different.

[0083] Thirty more balloons were fabricated using the same method as in Comparative Example 1. Internal pressure was applied to these 30 balloons until they were broken, and the state of cracks after the breakage was observed. Cracks along the longitudinal axis were observed in all 30 balloons, and in two of them, cross-shaped cracks were observed, where a crack along the longitudinal axis was combined with a crack along the circumferential axis.

[0084] The balloons produced in Example 1 and Comparative Example 1 all had a film thickness of about 25 μm at the thinnest position, but the film thickness change in a predetermined section in the longitudinal axis direction was 1.62 × 10 for balloons No. 1 to No. 5 of Example 1. －４ ~1.83 x 10 －４ In contrast, the values ​​for balloons No. 6 to No. 9 in Comparative Example 1 were 2.09 × 10 －４ ~2.43 x 10 －４ As a result, in the balloon fabricated by the manufacturing method of Comparative Example 1, there was a portion where the film thickness in the longitudinal direction suddenly changed, and it is believed that this portion caused stress concentration in the circumferential direction, resulting in the cross-shaped cracks. In the balloon fabricated by the manufacturing method of Example 1, the film thickness change in the longitudinal direction was gradual, which is thought to have suppressed stress concentration in the circumferential direction, resulting in only longitudinal cracks.

[0085] 14 to 22, the contour lines in Figures 19 to 22 for Comparative Example 1 tended to be vertically straight near the thinnest position, whereas the contour lines in Figures 14 to 18 for Example 1 had almost no vertically straight portions near the thinnest position. This is also thought to have contributed to the absence of circumferential cracks or cross-shaped cracks.

[0086] 1: Balloon catheter 3: Shaft 4: Hub 5: Guidewire insertion section 6: Fluid injection section 20: Balloon 21: Proximal sleeve section 22: Proximal tapered section 23: Straight tube section 23C: Central section 24: Distal tapered section 25: Distal sleeve section 30: Parison 31: Lump of parison 40: Mold 41: Proximal sleeve section of mold 42: Proximal tapered section of mold 43: Straight tube section of mold 44: Distal tapered section of mold 45: Distal sleeve section of mold 46: Lump of mold a-h: 8 points X: Thinnest position P: Proximal position D: Distal position Tx: Average film thickness at thinnest position Tp: Average film thickness at proximal position Td: Average film thickness at distal position L ０ : 0% position L ３０ : 30% position L ７０ : 70% position L １００ : 100% position B: Yield point L: Lower yield point R ｎ : necking region x: longitudinal direction y: radial direction z: circumferential direction

Claims

1. A balloon having a proximal end and a distal end in a longitudinal axis direction, and having a straight tube portion, a proximal tapered portion located proximally of the straight tube portion, and a distal tapered portion located distally of the straight tube portion, At a predetermined position in the longitudinal axis direction, the film thickness is measured at eight points equally spaced 45° apart around 360° in the circumferential direction of the balloon, and the average of the eight points is defined as the average film thickness at the predetermined position. In the longitudinal axis direction, the proximal end of the straight tube portion is defined as the 0% position, and the distal end is defined as the 100% position. The position where the balloon has the thinnest average thickness Tx in the central section from the 30% position to the 70% position is defined as the thinnest position X. The proximal position P is defined as the position away from the thinnest position X proximally by a length of ¼ of the straight tube portion. The distal position D is defined as the position away from the thinnest position X distally by a length of ¼ of the straight tube portion. The thickness change amount obtained by dividing the difference between the average thickness Tp and the average thickness Tx at the proximal position P by the length of ¼ of the straight tube portion, and the thickness change amount obtained by dividing the difference between the average thickness Td and the average thickness Tx at the distal position D by the length of ¼ of the straight tube portion, were both 2.0×10 －４ is as follows: At the thinnest position X, the coefficient of variation of the film thickness at the eight points is 1.5×10 −2 or more; A balloon for a balloon catheter, wherein the average thickness Tx is 30 μm or less.

2. 2. The balloon for a balloon catheter according to claim 1, wherein the position where the average film thickness is thinnest is the same as the thinnest position X in the entire section of the straight tube portion from the 0% position to the 100% position among the predetermined positions.

3. A balloon catheter comprising the balloon for a balloon catheter according to claim 1 or 2.