Method and device for manufacturing hollow cylinder for medical use

Abstract

The invention relates to a method for producing a hollow cylinder, and also to a hollow cylinder, in particular a magnesium alloy-based hollow cylinder, produced by the method, and to a device for carrying out the method.

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a hollow cylinder for medical technology or for medical products, in particular for implants. The method comprises a first step (i), in which a blank at least partially inserted into a receptor is extruded by pressing a punch through a die or by pressing both the punch and the die into a receptor chamber of the receptor, and a mandrel is driven into the blank such that a hollow cylinder having an inner diameter defined by the mandrel and an outer diameter defined by the die is formed. After step (i), there is a step (ii) in which the hollow cylinder is guided through a nip defined by at least two rollers. Furthermore, the present invention also relates to a hollow cylinder manufactured by this method, in particular a hollow cylinder based on a magnesium alloy, and a device for implementing this method. Background Art

[0002] Workpieces or semi-finished products in the form of hollow cylinders are used in many fields of medical technology. Particularly important are implants for keeping hollow orifices or blood vessels open, in particular stents. Such stents have a body in the form of a tubular or hollow cylindrical basic grid, which is open at both longitudinal ends. Usually, a hollow cylindrical semi-finished product serves as the initial shape for such a body, and then, for example, the basic grid is cut out of the semi-finished product by means of a laser.

[0003] Stents are used in blood vessels, particularly in coronary arteries, to prevent them from occluding again after dilation; this type of treatment is called stent angioplasty. On the other hand, stents are used in cancer treatment to keep open constrictions in the airways (trachea), bile ducts, or esophagus caused by malignant tumors. In addition to the main goal of preventing new blood vessel occlusions, stents can also fix vascular deposits and improve blood flow in the vessels, since they smooth the inner surface of the vessels by pressing against the vessel walls.

[0004] In principle, the required workpieces or semi-finished products in the form of hollow cylinders can be manufactured by forming methods. One possible method is extrusion or impact extrusion, which is a well-known method for manufacturing thin-walled tubes. In this method, a drilled blank is placed on the mandrel of a punch, which serves as an internal tool and thus defines the final inner diameter of the hollow cylinder, and then it is pressed through a die, which serves as an external tool for defining the outer diameter of the cylinder. A relatively high degree of formability can be achieved in a single method step, thus allowing for good mechanical properties, namely small grains, high strength, and medium elongation at break. However, the high degree of formability deteriorates the resulting cylinder geometry, i.e., the continuity of the outer diameter or wall thickness becomes worse.

[0005] In medical applications, the pressing method is usually additionally supported by a traction or traction / torsion device. In this case, the device grasps the hollow cylinder at the tool outlet and pulls or pulls and twists the hollow cylinder with a high force and / or torsional moment. Depending on the stress level occurring, the microstructure is further improved for medical applications, but the geometry is further deteriorated.

[0006] Alternatively, a pure stretching method is used. In this method, the blank is stretched on a mandrel, which is usually a pin (also called a free-floating mandrel), in a number of successive production steps. Between the manufacturing steps, a recrystallization-annealing method is carried out to restore the formability of the tube for subsequent steps. Due to the many steps, grain growth occurs due to the many intermediate annealing steps, so a very good geometry is achieved at the expense of mechanical properties.

[0007] In summary, extrusion or impact extrusion with or without a tension or tension / torsion device has the following disadvantages: the resulting geometric properties of the hollow cylinder are not ideal. In particular, the variations in the outer diameter and wall thickness are relatively large. On the other hand, stretching results in a coarser structure with large grains and thus poorer mechanical properties. In addition, in order to form the final hollow cylinder, multiple forming steps are required, usually 10 or more. Summary of the Invention

[0008] Therefore, the present invention is based on the task of circumventing these disadvantages and provides a method and a device for implementing the method, by means of which a geometrically highly precise hollow cylinder, in particular also a hollow cylinder made of a magnesium alloy, with very good mechanical properties can be manufactured with as few method steps as possible.

[0009] This task is solved by the invention having the features of claims 1 and 9.

[0010] A method according to the invention for producing a semi-finished product for medical technology or for medical products, in particular for implants, comprises the following steps:

[0011] In step (i), direct or indirect extrusion is possible. In direct extrusion, a material block (the so-called blank) is inserted into a surrounding receptor and pressed through a die by means of a punch. The characteristic of this method variant is that the receptor and the die are stationary.

[0012] The indirect variant of extrusion is characterized in that the punch and the die are pressed into the receptor together. This method results in less friction because there is no relative movement between the punch and the receptor. Therefore, the efficiency of the pressing movement is higher than that of the direct extrusion method. In addition, there is also no relative movement between the blank and the receptor, which facilitates the use of longer blanks.

[0013] The drilling in the blank can be foreseen to more precisely position the mandrel. The drilling can be designed as a blind hole or completely open. The blank and the punch can be joined by means of the mandrel first and then inserted into the receiving chamber of the receiver, or the blank can be inserted into the receiving chamber first and then the mandrel and the punch.

[0014] However, the mandrel must have a length greater than the length of the resulting hollow cylinder. In the first variant, the mandrel can be guided through the punch and driven into the blank independently of its movement so that it completely penetrates the blank, thereby producing a hollow cylinder. In the second variant, the mandrel is attached to the punch and has completely penetrated the blank during insertion, which requires a tubular design of the blank, so a complete opening is necessary.

[0015] In all variants, the hollow cylinder is constructed to have an inner diameter formed by the mandrel and an outer diameter formed by the die. Then, in step (ii) after step (i), the hollow cylinder emerging from the die in the feed direction is guided through a roll gap defined by at least two rolls.

[0016] This has the advantage that a tensile force or a torsional moment can be applied by the rolls. Thereby, residual stresses are introduced into the material, which is beneficial for recrystallization and the grain orientation is formed.

[0017] One way to carry out this method is to apply a tension between 20 N and 100 N when the blank has a cross-sectional profile of about 1 mm 2 If it is advantageous to carry out such conduction at a lower temperature because favorable mechanical properties are observed.

[0018] The method according to the invention is particularly advantageous if another method step is foreseen, so that in the absence of additional rolls, due to the interaction of this other step with the relative movement of the blank, the punch and the receiver towards the die, there is a risk of upsetting during the forming method from the blank to the hollow cylinder.

[0019] In this context, it is particularly worthwhile to have an additional step (iii) in which the hollow cylinder is pulled by means of a pulling device. The device grips the end of the manufactured hollow cylinder facing away from the punch and pulls it in the feed direction. This improves the geometry of the obtained hollow cylinder, especially the straightness of the resulting tube.

[0020] This pulling can be carried out with or without simultaneous torsion, whereby the additional torsion further increases the internal stress in the semi-finished product.

[0021] Advantageously, the stretching device stretches the hollow cylinder through a stretching ring surrounding the cylinder, thereby additionally smoothing the outer surface and / or reducing the diameter of the tube.

[0022] At this time, the diameter reduction by stretching is only very small and only reaches a few hundredths of a millimeter in the production of the stent. Therefore, it is not necessarily necessary to use a mandrel, also known as an internal free-floating mandrel, to support the inside of the tube during stretching. However, its use has proven to be advantageous, especially in the area of the stretching ring. By using a mandrel, the inner shell of the hollow cylinder can also become smooth and contribute to a possible reduction in the outer diameter.

[0023] As an alternative or supplement to using a stretching ring, a machining tool can be used, through which or along which the hollow cylinder is stretched by a stretching device, and thus the material of the cylinder is removed. In particular, turning, but also milling or grinding are suitable methods for forming.

[0024] It is particularly advantageous to use a stretching ring and at least one machining tool simultaneously, because this means that even more complex geometries can be manufactured in only a few steps.

[0025] Preferably, the blank together with the punch is heated in the receiver at 200 to 300 °C, and in some cases in the range of 250 to 280 °C. This enables more uniform forming in terms of the grain size distribution.

[0026] If the method, especially the consecutive steps (i), (ii) and (iii) are carried out continuously by directly moving the resulting hollow cylinder, the advantages of the present invention are particularly effective, because the advantages of the individual methods regarding the microstructure are not negatively affected by intermediate processing pauses.

[0027] The method is advantageously carried out in a device designed for this purpose. The device is designed by the features of claim 9. First of all, such a device for manufacturing a hollow cylinder for medical applications or for medical products (especially for implants) includes an extrusion device. All features of the method should also apply to their formation in the device according to the invention and vice versa.

[0028] Such an extrusion device can receive a blank in the receiving chamber of the receiver, optionally with a drill hole. The extrusion device also includes a punch, which is characterized by a pressure plate and a mandrel, both of which are configured to be at least partially inserted into the receiving chamber. In addition, the extrusion device includes a die, also known as a matrix. The punch is arranged in such a way that its pressure plate can press the blank through the die in the feed direction with the end face, or the punch together with the die is pressed into the receiver so that a hollow cylinder is formed.

[0029] Secondly, at least two rollers are arranged downstream of the extrusion device in the feed direction. These rollers define a roll gap through which the hollow cylinder is guided. Thereby, a support tension can be applied to the material in the described manner, which minimizes or even prevents material upsetting or compression and improves the mechanical properties of the hollow cylinder.

[0030] Advantageously, if a pulling device (also known as a stretching device) is provided downstream of the roller in the feed direction, the mechanical properties can be further improved, and the pulling device at least partially surrounds the tube. Particularly advantageously, a stretching ring is arranged between the roller and the pulling device, the stretching ring surrounds the hollow cylinder and additionally smoothes the outer surface of the hollow cylinder.

[0031] Additionally or alternatively, at least one processing tool can be provided after the roller and / or before or after the stretching ring. This allows for further adaptation of the geometric properties of the hollow cylinder.

[0032] This can be done, for example, by removing or screwing out. Thus, buckling of the hollow cylinder can be prevented, and in the case of stent production, the buckling of the hollow cylinder has very small dimensions in terms of outer diameter, inner diameter, and wall thickness.

[0033] In summary, the method and the associated device offer the possibility of maintaining very good mechanical properties despite a high degree of shaping. Additionally, these mechanical properties can be further improved by supported tensile or torsional stresses.

[0034] Optimization of the geometric properties, particularly with regard to the possibility of reducing outer diameter and wall thickness variations, is first achieved by stretching with a stretching ring. The stretching method with the stretching ring simultaneously enables hardening of the tube surface or the edge layer to achieve better mechanical properties due to the applied pressure.

[0035] Particularly for indirect extrusion methods and particularly for relatively long dies, it has proven advantageous to support the dies to prevent them from bending or even breaking. This is achieved by at least one support device for the dies. To enable complete movement of the dies without being hindered by the support function, a particularly advantageous design provides that the at least one support device can move in such a way that when approaching the die, it moves away from its position, enabling the substrate to move completely towards the receptor.

[0036] In addition to the improvement of the mechanical and geometric properties of the hollow cylinders produced in this way, a significant increase in production efficiency has also been noted. On the one hand, this is due to the reduction in the number of working steps compared to pure stretching methods, but at the same time, the proportion of defective products due to variations in outer diameter and wall thickness can be significantly minimized, which means that smaller manufacturing tolerances can be achieved. The latter also improves the quality of all hollow cylinders produced. This is particularly applicable to the production of stents, which must meet special quality requirements.

[0037] As already described, the use of stents produced by this method can widen the constricted area in blood vessels. However, such foreign objects in the body carry the risk of the stent gradually growing inwards, which in the worst case may lead to complete occlusion of the blood vessel.

[0038] One way to solve this problem is to manufacture implants, especially stents, from biodegradable materials. Biodegradation is understood as the result of hydrolytic, enzymatic, and other metabolic degradation processes in living organisms, which is mainly caused by the contact of body fluids with the biodegradable material of the implant and leads to the gradual dissolution of the structure of the implant containing the biodegradable material. Due to this process, the implant loses its mechanical integrity at a certain point. The term biocorrosion is usually used synonymously with the term biodegradation. The term bioresorption additionally includes the subsequent resorption of degradation products by living organisms.

[0039] Materials suitable for the body of biodegradable implants may include, for example, polymers or metals. Biodegradable magnesium implants, especially magnesium stents, have proven particularly promising for the above-mentioned degradation target corridors.

[0040] In addition to any semi-finished products or hollow cylinders obtained by the method according to the invention, the present invention particularly protects the method of using magnesium alloys and the implementation of hollow cylinders made of magnesium alloys by the method according to any one of claims 1 to 8.

[0041] Other objects, features, advantages, and possible applications of the present invention can also be obtained from the following description of the drawings and embodiments. All features described and / or shown, alone or in any combination, form the subject matter of the present invention, independent of their inclusion in the individual claims or their reverse references. Description of the Drawings

[0042] Figure 1 is a schematic diagram of the device according to the present invention. Detailed Description

[0043] Figure 1 The device 1 according to the present invention is shown. The device is characterized by an extrusion device 10, which includes a receiver 11, a punch 13, and a die 16.

[0044] A receiver chamber 12 is provided in the receiver 11. The receiver chamber 12 is designed such that the punch 13 and the blank 40 can be at least partially inserted. The punch 13 is designed such that the punch has a pressure plate 15 on one side, by means of which the punch can press on the blank 40. In addition, a mandrel 14 is provided on the pressure plate 15, which can at least partially penetrate the blank 40.

[0045] During the pressing method, the die 16 and the punch 13 are moved relative to each other by moving the punch and the pressure plate 15 towards the die 16 or by moving the die 16 in the opposite direction into the receiving chamber 12. This deforms the blank 40 such that its outer diameter assumes a circular shape defined by the die 16 and, at the same time, the mandrel 14 penetrates its interior in such a way as to form a cylindrical cavity. Thus, forming produces a hollow cylinder 41, which is characterized by an outer diameter determined by the die 16 and an inner diameter determined by the mandrel 14.

[0046] After this extrusion device 10, there is a roller device 20 having at least two rollers 21, the two rollers 21 defining a nip through which the hollow cylinder 41 is guided and thus optimized in terms of its mechanical and geometric properties.

[0047] Optionally, additional tools can be located downstream as optimization devices 30. In the illustrated variant, this is a pulling device 31, which stretches the hollow cylinder 41 and optionally also twists the hollow cylinder 41. For smoothing the exterior, stretching can be effected by means of a stretching ring 32. Smoothing and / or stabilizing of the interior can be achieved by means of pins 33.

[0048] In principle, it is also possible to use at least one machining tool as a supplement or alternative to this illustration.

[0049] List of reference numerals

[0050] 1 Device according to the invention

[0051] 10 Extrusion device

[0052] 11 Receiver

[0053] 12 Receiver chamber

[0054] 13 Punch

[0055] 14 Mandrel

[0056] 15 Pressure plate

[0057] 16 Die

[0058] 20 Roller device

[0059] 21 Roller

[0060] 22 Nip

[0061] 30 Optimization device

[0062] 31 Pulling device

[0063] 32 Stretching ring

[0064] 33 Pin

Claims

1. A method for manufacturing a hollow cylinder for medical technology or for medical products, in particular for implants, the method comprising a first step (i) in which a blank at least partially inserted into a receiving chamber of a receiver is extruded by pressing a punch through a die or by pressing both the punch and the die into the receiver, and a mandrel is driven into the blank such that a hollow cylinder having an inner diameter defined by the mandrel and an outer diameter defined by the die is formed, characterized in that, Step (i) is followed by step (ii), in which the hollow cylinder is guided through a nip defined by at least two rollers.

2. The method according to claim 1, characterized in that, Step (ii) is followed by step (iii), in which the hollow cylinder is pulled by a pulling device.

3. The method according to claim 2, characterized in that, The pulling is carried out with or without simultaneous twisting.

4. The method according to claim 2 or 3, characterized in that, In step (iii), the hollow cylinder is pulled by means of the pulling device through a stretching ring surrounding it, thereby being flattened.

5. The method according to claim 4, characterized in that, In step (iii), during at least part of the pulling, pins are introduced to support the inner hollow cylinder.

6. The method according to claim 2 or 3, characterized in that, In step (iii), the hollow cylinder is stretched by a machining tool and thus material is removed.

7. The method according to claim 4 or 5, characterized in that, In step (iii), the hollow cylinder is stretched by both the stretching ring and the machining tool.

8. The method according to any one of the preceding claims, characterized in that, All steps (i) to (ii) or steps (i) to (iii) follow one another in a continuous process.

9. An apparatus (1) for manufacturing a hollow cylinder (41) for medical technology or for medical products, in particular for implants, comprising an extrusion device (10), the extrusion device (10) comprising a receiver (11) having a receiving chamber (12) for receiving a blank (40), a punch (12) guided in the receiving chamber (12) by a pressure plate (15), a mandrel (14) for forming the inner diameter of the hollow cylinder (41), and a die (16) for forming the outer diameter of the hollow cylinder (41), wherein, At least two rollers (21) are provided downstream of the extrusion device (10), wherein the rollers (21) define a nip (22) through which the hollow cylinder is guided.

10. The apparatus according to claim 9, characterized in that, A pulling device (31) is provided downstream of the rollers (21), the pulling device (31) being designed to at least partially surround the hollow cylinder (41) formed by the extrusion device (10) and to pull the hollow cylinder (41) through a stretching ring (31) for smoothing, and / or a machining tool is provided downstream of the rollers (21).

11. The apparatus according to claim 9 or 10, characterized in that, At least one support device is provided, which is removably arranged between the receiver (11) and the die (16), the support device being designed to be removable when the punching plate (15) and the die (16) are brought close together.

12. A hollow cylinder made of a magnesium alloy for medical applications or for medical products, in particular for implants, manufactured by the method according to any one of claims 1 to 8.

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