Implant made of a magnesium alloy and method for the production thereof

Abstract

A method for manufacturing a bioresorbable implant, wherein a magnesium alloy is formed into an implant. A melt is pressed into a die and gases in the die induce turbulence in the inflowing melt, thereby enclosing gas, so that the porous implant is formed with a porosity, which increases from outside inwardly. The surface of the implant is substantially free from open pores.

Claims

1. A method for manufacturing a bioresorbable implant, comprising pressing a magnesium alloy melt into a high pressure casting die without first evacuating the die, so that porosity in the implant is produced solely from air in the die inducing turbulence in and being enclosed in the melt, so that a porous implant is formed with a porosity which increases from outside inwardly, and which has a surface which is substantially free of open pores.

2. The method of claim 1, wherein the magnesium alloy comprises from about 1 to about 9% of Y, and from about 0.1 to about 1.5% of other rare earth metals.

3. The method of claim 1, wherein the pressure under which the melt is compressed in the die during a die casting process is more than about 100 bars.

4. The method of claim 1, wherein a casting temperature is above about 600 C.

5. The method of claim 1, wherein a casting rate more than about 20 cm/s is used.

6. The method of claim 1, wherein the implant is formed in a form selected from the group consisting of: a screw, a cage, a suture anchor, and a suture wound anchor.

7. The method of claim 1, wherein the magnesium alloy comprises from about 1 to about 9% of Y and between from about 0.1 and to about 1.5% of other rare earth metals, and wherein the amount of Zn is less than about 0.4%.

8. The method of claim 1, wherein a closed surface retards corrosive attack in an initial period following placement.

9. The method of claim 1, wherein the surface is formed which has less than 3 open pores with a diameter of more than 100 m/cm2.

10. The method of claim 1, wherein a degree of porosity in a first region close to the surface is less than 3%.

11. The method of claim 10, wherein the region close to the surface is defined by a maximum depth of 0.5 mm.

12. The method of claim 10, wherein the degree of porosity in a second region, away from the surface, is more than 3%.

13. The method of claim 12, wherein the second region away from the surface is defined by a depth of more than 0.6 mm.

Description

DESCRIPTION OF THE DRAWINGS

(1) The invention will now be described in detail with reference to the drawings of FIG. 1 to FIG. 10.

(2) FIG. 1 schematically shows a section through an implant 1, here in form of an interference screw. The interference screw of this exemplary embodiment has a central passage 2.

(3) Implant 1 is produced by a die cast method from a magnesium alloy and has a surface 3 which is substantially free of pores and closed.

(4) Interiorly, i.e. in a region 4 away from the surface, implant 1 has a considerably higher porosity than at the surface 3.

(5) Since passage 2 is not defined by drilling but already by the casting die, the surface of passage 2 is equally free of pores and closed.

(6) Following placement of the implant in the body, the decomposition rate at surface 3 of the implant is considerably reduced compared to the decomposition rate in a core 4 of the implant.

(7) In this way, an implant can be provided which maintains its required mechanical properties for a relatively long period.

(8) The implant 1 can have a coating (not shown) which substantially prevents degradation of the implant 1 following placement in the body. The coating can be melted away at a later time by application of electromagnetic waves, or by induction. In this way, the mounted implant is uncovered and subjected to degradation.

(9) FIG. 2 schematically shows a plate 5 which is used, for example, for joining bone fragments.

(10) For fixing, the plate 5 has at least threads 6 or alternatively a drilling hole, through which a screw is threaded into the bone.

(11) Thread 6 is preferably formed during die casting by means of a threaded pin which is introduced into the casting die and which is threaded out upon ejection of plate 5. In this way, the surface of thread 6 also has a casting skin. Alternatively, thread 6 can be cut. In fact, this destroys the casting skin; following placement, however, thread 6 is protected by a screw.

(12) FIG. 3 schematically shows a screw 7 which, e.g., may serve for fixing the plate illustrated in FIG. 2. This represents an angularly stable system wherein head 8 of the screw 7 has an external thread for engaging the thread of the plate. Screw body 9 is provided with a thread for threading into the bone, the thread having a self-cutting portion 10 at the tip.

(13) FIG. 4 schematically shows a pin 11 which is placed by means of an appropriate tool. This pin, too, is produced in a die cast process and is interiorly porous. Pin 11 is especially intended for smaller fractures.

(14) FIG. 5 shows a cage 12 for stiffening vertebral bodies. Cage 12 consists of a substantially tubular portion which is filled with bone granules in its interior 13. The bone granules cause generation of bone such that after degradation of the portion made from a magnesium alloy the vertebral bodies are grown together.

(15) With reference to FIGS. 6 and 7, a method for manufacturing an implant 1 will be described.

(16) FIG. 7 illustrates a sectional view of a casting die which comprises an upper portion 15 and a lower portion 14. A magnesium alloy comprising an amount of yttrium is compressed in this die under high temperature and high pressure. The melt solidifies within fractions of a second. In this way, a fine-grained casting skin is formed at the surface of implant 1, while inside the implant a porous structure with a coarser texture is formed, assumable due to turbulences and the relatively poor flow behavior of the alloy used.

(17) Subsequently, as depicted in FIG. 7, the die comprised of upper portion 15 and lower portion 14 is opened and the implant is ejected.

(18) It will be understood that the die is depicted in fairly schematic manner and that in practical use it will comprise other portions and components. In particular, a die is contemplated which comprises at least four parts.

(19) FIG. 8 shows an alternative embodiment of a cage 12 which is adapted to be placed in the cervical spine. This cage 12 also has an opening 13 which can be filled with bone granules.

(20) FIG. 9 and FIG. 10 show different embodiments of a suture anchor 16.