Implant and method for production thereof

Abstract

An implant, in particular an intraluminal endoprosthesis, or a semi-finished part for an implant, having a hollow cylindrical body, wherein the body includes magnesium, and the body is enriched with gallium or a gallium alloy in a region close to a surface.

Claims

1. An intraluminal endoprosthesis comprising a body that comprises a WE 43 magnesium alloy characterized as 4%, Y, 2%, Nd, 0.5% Gd, 0.5% Dy, 0.5% Zr, and a remainder Mg, and the body is enriched with a gallium alloy in a region close to a surface.

2. The intraluminal endoprosthesis according to claim 1, wherein the endoprosthesis has a hollow cylindrical body.

3. An intraluminal endoprosthesis comprising a body that comprises magnesium, and the body is enriched with a gallium alloy in a region close to a surface.

4. The endoprosthesis according to claim 3, the body further comprising a polymer coating.

5. The intraluminal endoprosthesis according to claim 3, wherein the endoprosthesis has a hollow cylindrical body.

6. An implant, in particular an intraluminal endoprosthesis, comprising a body that comprises magnesium, and the body is enriched with a gallium alloy in a region close to a surface, wherein the gallium alloy comprises indium, tin and 65 to 95% gallium.

7. An implant, in particular an intraluminal endoprosthesis that comprises magnesium, and the body is enriched with gallium or a gallium alloy in a region close to a surface, wherein the region close to the surface comprises a depth of up to 40 μm from the surface.

8. The implant according to claim 7, wherein the region close to the surface comprises a depth of at least 10 μm from the surface.

9. The implant according to claim 7, wherein the depth is at least 15 μm from the surface.

10. An intraluminal endoprosthesis comprising a body that comprises magnesium, and the body is enriched with a gallium alloy in a region close to a surface, the gallium alloy comprising 65 to 95% gallium.

Description

DESCRIPTION OF THE DRAWINGS

(1) The drawings illustrate schematically:

(2) FIG. 1 a cross-section of a semifinished article according to the invention (for example, for a stent) according to step b) of the method according to the invention, and

(3) FIG. 2 the binary status diagram for the magnesium/gallium system.

DETAILED DESCRIPTION

(4) It should first be noted that the indications of concentrations of a material contained in the following description are given in wt %, unless otherwise indicated at the relevant site.

(5) A tubular or hollow cylindrical sleeve made of a magnesium alloy, for example, having the composition WE 43 (4% Y, 2% Nd, 0.5% Gd, 0.5% Dy, 0.5% Zr, remainder Mg) is subjected to an extrusion process for the purpose of producing an implant semifinished article, for example, for a stent. Prior to the extrusion process, GALINTSAN having a composition of 68.5% Ga, 21.5% In and 10% Sn, by way of example, is applied to the surface of the extrusion tool as a lubricant, in places where the surface of the extrusion tool will come into contact with the sleeve. In addition, the ram that will determine the interior geometry and/or the die that will determine the later outer surface can also be provided with the lubricant.

(6) The gallium-containing lubricant is applied in the form of drops to the outer tool (ram) and/or to the inner tool (die) prior to the extrusion process. The tools and the blank, which is arranged on the ram and will be shaped (dimensions, e.g., outer diameter 3 mm to 10 mm, inner diameter 1 mm to 5 mm, length 3 mm to 15 mm), are then heated to the process temperature, which lies between 300° C. and 500° C. The heating process lasts approximately 1 minute to 10 minutes. This is followed by the actual shaping process, in which the cylindrical blank arranged on the ram is extruded in the die to a semifinished article 10 in the form of a sleeve (dimensions, e.g., outer diameter 2 mm, inner diameter 1.6 mm, length 50 mm to 200 mm). The press speed can range between 1 mm/min and 100 mm/min, for example, so that the extrusion process is completed after approximately 30 seconds to 200 minutes.

(7) With the introduction of the ram into the blank (also called the slug) situated in the die and the preceding heating of the sleeve to the process temperature of approximately 400° C., gallium first imparts its effect as a lubricant due to its extremely low shear forces, which are particularly pronounced in the molten state.

(8) During shaping, the elements of the gallium-containing lubricant diffuse into the resulting new inner and/or outer surface of the semifinished article 10, and begin to form an alloy with the magnesium.

(9) The extruded semifinished article 10 is then removed from the tool and cools within a few minutes to nearly room temperature.

(10) This is followed by a tempering step, preferably at 300° C. to 500° C., for eliminating stresses (so-called low-stress annealing), over a period of 1 minute to 60 minutes in air or under inert gas such as argon. In this, two processes take place in the zones close to the surface. For one, the diffusion of the elements of the lubricant into the volume of the semifinished article continues, and for another, an alloy of Mg and Ga forms. In this process, either the gallium becomes partially embedded in the Mg lattice as a substituent in accordance with the binary status diagram Mg/Ga illustrated in FIG. 2, or intermetallic compounds, e.g., Mg.sub.5Ga.sub.2, Mg.sub.2Ga and MgGa form in a region 12 (or layer) close to the surface. As a result, mixed phases are produced, which form according to the phase diagram (see FIG. 2) on the basis of the process holding time of several minutes, to a depth of up to 40 μm. By adjusting the above-described process parameters of temperature and time, the diffusion depth of the gallium into the semifinished article can be varied to an order of magnitude of between 20 μm (at 450° C./10 min) and 40 μm (470° C./40 min), measured from the respective surface of the semifinished article.

(11) FIG. 1 shows the increased gallium concentration in the boundary region 12 close to the surface, on only the abluminal side. Depending upon the application of the lubricant in the tool, the luminal side of the semifinished article can alternatively or additionally have a boundary region of this type close to the surface with an increased gallium concentration.

(12) An overdosing of lubricant is not possible, because at the end of the process, excess lubricant either remains on the tool or is stripped off of it.

(13) The additional process steps are structured similarly to the known methods for producing implants by means of laser beam methods, which have been described many times, and comprise final shaping processes such as laser cutting, deburring, scouring and electropolishing. It is particularly important to mention within this context that the scouring and electropolishing steps are run in phosphoric acid-containing solutions at room temperature, over periods of between 0.5 minutes and 4 minutes (preferably 2 minutes). The scouring and electropolishing include a removal of material. For example, the removal of material by scouring over a period of 2 minutes amounts to between 10 μm and 20 μm of the wall thickness. Therefore, at the end of the production process the implant, e.g., the stent, still has a wall thickness of between 140 μm and 170 μm, wherein the wall thickness of the semifinished article, after extrusion and tempering and before electropolishing and/or scouring, amounts to 180 μm to 190 μm. However, when the described process parameters are applied, it is ensured that the diffusion depth of the gallium in the magnesium matrix material is greater than the removal of material that occurs as a result of the scouring and/or polishing step.

(14) The finished implant, similarly to the semifinished article 10, also has an increased gallium concentration in a boundary region, close to the surface, of the outer side and/or the inner side of its struts.

(15) It is advantageous that this is achieved in the semifinished article 10 as a result of the “interleaving”, produced in a metallurgical process, in the region close to the surface that is rich with gallium, with the base material. This means that in the finished implant, no delamination phenomena occur with bending, shearing or torsion stress under the conditions of use of the implant.

(16) As was already mentioned above, the binary status diagram for the gallium/magnesium system is illustrated in FIG. 2, wherein the gallium concentration in wt % or atom % is plotted on the X axis and the temperature in ° C. is plotted on the Y axis. The letter L is used to identify the liquid range.

(17) It will be apparent to those skilled in the art that numerous modifications and variations of the described examples and embodiments are possible in light of the above teaching. The disclosed examples and embodiments are presented for purposes of illustration only. Other alternate embodiments may include some or all of the features disclosed herein. Therefore, it is the intent to cover all such modifications and alternate embodiments as may come within the true scope of this invention.

LIST OF REFERENCE SIGNS

(18) 10 Semifinished article 12 Region close to the surface L Liquid range