DE102017222168B4 - Method for manufacturing a stent and stent manufactured by the method - Google Patents

Abstract

Process for the production of stents for implantation in blood vessels in which a cylindrical or hollow cylindrical shaping rod or filament, which is formed with a polymer as an organic material, is provided on its outer surface with a metallic coating that forms the stent material using a thin-film process and then provided the organic material is removed and, after the removal of the material of the metallic tube obtained, further material for forming the filigree stent structure is removed with an energy beam, by wire EDM or mechanically.

Description

The invention relates to a method for producing stents, in particular for cardiovascular intervention, and stents produced therewith.

In the prior art, the starting product for the manufacture, in particular of coronary stents, are thin tubes, which are typically manufactured by tube drawing. In this process, bars are gradually cold-formed into a seamless tubular shape using a mandrel. Recrystallization in the form of heat treatment is necessary between each cold forming step. For coronary stents, tubes with diameters in the order of magnitude of 2 mm and thicknesses typically around 130 μm (stainless steel stents) are usually required. Numerous cold forming and recrystallization steps are necessary for this. Due to the large number of process steps, production is associated with considerable expenditure of time and energy. Therefore the manufacturing process of thin tubes is very time consuming and costly. The filigree stent structure is then created by laser cutting or wire erosion, which can be expanded outwards by plastic expansion as a result of radial pressure and thus permanently constricted blood vessels can be expanded.

It is therefore the object of the invention to propose a method for the production of thin tubes as a preliminary product for stent production, with which the production is significantly simpler, faster and more cost-effective.

For example, US 2011/0 253 525 A1 discloses an object made from a thin shape memory alloy and a method for production.

An inflatable object for medical applications is described in US 2009/0301 643 A1.

US 2009/0 035 859 A1 relates to a method and a stent for cardiovascular use.

A folded stent is disclosed in US 2005/0 090 888 A1.

According to the invention, this object is achieved with a method which has the features of claim 1. Claim 10 relates to a stent which has been produced using the method. Advantageous refinements and developments of the invention can be implemented with features identified in the subordinate claims.

The core of the present invention is the production of thin tubes by coating cylindrical or hollow cylindrical shaping rods or filaments on their radially outer surface with a thin metal layer. The rods or filaments are made of a polymer and are coated with the respective metal using thin-film technology. The organic material that gives the shape is then removed. This can advantageously be achieved with a thermal treatment in which the polymer of the respective shaping rod or filament is converted into the gaseous phase, which can be achieved in particular by means of pyrolysis.

The polymer can also be removed alone or in addition to the thermal treatment by etching or dissolving in a suitable etchant or solvent for the respective polymer. Suitable etchants or solvents are known, in particular for suitable polymers. An etchant or solvent should only not attack or influence the metal forming the semifinished product, or only to a minor extent. By etching or dissolving, for example, part of the organic material and then the remainder can be removed with a thermal treatment.

In this way, metallic tubes are created that can then be finally reshaped or recrystallized again if necessary. Furthermore, the resulting tubes can be used as in the prior art and the filigree stent structure is formed by laser cutting or wire erosion and the stent is expanded by plastic expansion due to radial pressure outward.

If the tubes obtained in this way are of appropriate length, several individual stents can also be obtained by cutting. The cutting can be achieved with an energy beam, in particular a laser beam, or by wire EDM. Mechanical breaking at predetermined breaking points that have been formed during the formation of the metal layer is also possible.

Cylindrical or hollow-cylindrical templates made of a polymer material, which reproduce the inner shape of the metallic tube with their radially outer lateral surface, are used as the starting material for this procedure. This rod-like or filament-like shape is to be made with polymers that can easily be thermally decomposed by a heat treatment. Examples of highly suitable polymers are polyethylene (PE) or polyoxymethylene (POM), which are known to be used as feedstock for metal powder injection molding. Polymethyl methacrylate (PMMA) also has a proven favorable thermal decomposition behavior.

The forming rods or filaments can be coated with the metal layer by means of physical vapor deposition (PVD), chemical vapor deposition (CVD) or galvanic deposition. The first-mentioned method is particularly suitable for the production of stent tubes, since this method also allows coating with alloys. A so-called target can be bombarded with an electron or laser beam and thus the target material can be vaporized. The metal vapor condenses on the surface of a shaping rod or filament and, after the transition from the liquid to the solid phase, forms the metal layer on the radially outer lateral surface of the respective rod or filament.

The coating can take place in a chamber at working pressures in the range 10 ^-4 Pa to 10 Pa. The metal vapor particles spread in a straight line from the target. The rod or filament to be coated can be introduced rotating around its longitudinal axis into the formed metal vapor flow in order to form a uniform coating on the entire surface to be coated, in particular with regard to the layer thickness and the material composition. The required layer thicknesses of 75 µm to 175 µm, in particular 100 µm - 150 µm, are comparatively high; plasma-activated high-rate vapor deposition can be used here. This enables deposition rates of up to 3000 nm / s.

The metallic base material for stents is often a stainless steel (for example the Ni-Cr steel 1.4404), but CoCr, PtCr and, more recently, biodegradable magnesium alloys have also been used. But it is also possible to manufacture tubes from molybdenum or molybdenum-rhenium alloys. These alloys can be processed using the PVD process.

The polymer can then be removed by thermal debinding. The respective polymer is thermally decomposed in a heat treatment under a flow of protective gas. The process is also used for metal powder injection molding and usually takes place in a nitrogen, argon, hydrogen atmosphere or mixtures of these gases. Such debinding typically takes place at different temperature levels. The polymer backbone breaks down at around 450 ° C. For some polymers, additional steps at higher temperatures are required, for example PE has typical decomposition temperatures of around 650 ° C. In order not to cause damage to the metallic coating structures due to excessive internal pressure in the temperature ranges of high decomposition activity, these areas must be approached with low heating rates in the range 0.1 K / min to 1 K / min, preferably 0.5 K / min . The duration of the holding times depends on the material volume of the rods or filaments. In the case of cylindrical or hollow cylindrical shaping rods or filaments, this depends on the respective length, the outer diameter and possibly the inner diameter and is in the order of 60 min - 120 min.The outer diameter of a rod or filament should be in the range 0.5 mm to 5 mm lie.

In order to avoid residues of the template structures containing hydrocarbons in the metallic material, the thermal treatment should take place up to 1100 ° C., depending on the metal. This reduction takes place through thermochemical reactions, for example in the case of stainless steel through carbothermal reduction at 1050 ° C. In this way, the metallic tubes remain as semi-finished products for a stent or several stents with thicknesses in the required order of magnitude.

Typically, an accuracy of ± 3% - 20% of the metal layer thickness can be achieved with high-rate vapor deposition. If the deviations from the target value are too great, the thermal removal of the organic components can be followed by a further cold forming step with subsequent recrystallization. This can be achieved by pulling or pressing the hollow body over a mandrel that is conical and / or whose diameter is larger than the smallest inner diameter of the hollow body, and / or by a die with a hole diameter that is smaller than the largest outer diameter of the hollow body . In comparison to the prior art, however, this step is only a calibration step.

In the formation of the metal layer, at least one mask can also be used, which keeps metal vapor formed locally defined from the surface of the radially outer jacket surface of the respective rod or filament and the predetermined filigree stent structure is reproduced on the surface of the radially outer jacket surface.

A filigree stent structure can also be reproduced in that small rods are used which have a corresponding structure with corresponding elevations and / or depressions on their radially outer lateral surface on which the metal layer is formed.

It is also possible to coat the radially outer lateral surface in a locally defined manner in order to achieve this effect. In this way, locally defined areas of the metal layer can be formed that are thicker, thinner or without a metal coating. Such coatings are particularly advantageous when the metal layer is formed by electroplating.

With the above-mentioned options, predetermined breaking points can also be formed, which can be used advantageously when separating several stents from a tube or forming the filigree stent structure, since a mechanical breaking of the metal material can be achieved there in a locally defined manner.

A tube produced as a semi-finished product can now be brought into the desired stent shape by means of laser cutting or wire erosion, as is known in the prior art. In the prior art, a surface treatment (e.g. electropolishing) is usually followed up; this can be done in the same way here.

Claims (10)

Process for the production of stents for implantation in blood vessels in which a cylindrical or hollow cylindrical shaping rod or filament, which is formed with a polymer as an organic material, is provided on its outer surface with a metallic coating that forms the stent material using a thin-film process and then provided the organic material is removed and, after the removal of the material of the metallic tube obtained, further material for forming the filigree stent structure is removed with an energy beam, by wire EDM or mechanically. Procedure according to Claim 1 , characterized in that the removal of the organic material with a thermal treatment in which the organic components of the respective shaping rod or filament are converted into the gas phase is achieved by etching and / or dissolving in a solvent. Method according to one of the preceding claims, characterized in that the formation of the metal layer on the radially outer jacket surface of the shaping rod or filament is carried out by means of physical vapor deposition (PVD), chemical vapor deposition (CVD), plasma-activated high-rate vapor deposition or galvanic deposition. Method according to one of the preceding claims, characterized in that a metal layer with a steel alloy, in particular a Ni-Cr, CoCr or PtCr steel, or a biodegradable magnesium alloy, is formed with molybdenum or a molybdenum-rhenium alloy and / or polyethylene (PE), polyoxymethylene (POM) or polymethyl methacrylate (PMMA) is used as a polymer for a shaping rod or filament. Method according to one of the preceding claims, characterized in that the metal layer is formed with a thickness in the range 75 µm to 175 µm, in particular 100 µm to 150 µm and / or a shaping rod or filament with an outer diameter in the range 0.5 mm to 5 mm is used. Method according to one of the preceding claims, characterized in that a shaping rod or filament is used which has structural elements on its outer jacket surface which correspond to the filigree stent structure to be formed. Method according to one of the preceding claims, characterized in that the filigree stent structure is specified or taken into account when forming the metal layer by means of at least one mask or by applying a further material to the radially outer lateral surface of the shaping rod or filament. Method according to one of the Claims 2 to 7th , characterized in that during a thermal treatment to remove the organic components of the organic material, a heating rate in the range 0.1 K / min to 1 K / min, preferably 0.5 K / min, is maintained and / or after the thermal treatment for Removal of the organic components, a temperature increase up to a maximum of 1100 ° C is carried out. Method according to one of the Claims 3 to 8th , characterized in that during the formation of the metal layer by means of physical vapor deposition (PVD), chemical vapor deposition (CVD) or plasma-activated high-rate vapor deposition, the shaping rod or filament is rotated around its longitudinal axis. Stent produced by a method according to one of the preceding claims.