MAGNESIUM ALLOY, BIODEGRADABLE IMPLANT AND METHOD FOR PRODUCING A BIODEGRADABLE IMPLANT

Abstract

The invention relates to a magnesium alloy which comprises: Zn: 0.5-2 wt %, Mn: 0.2-1 wt %, Ca: 0.1-2 wt %, wherein the magnesium alloy comprises 0.6 wt % or more Mn or 0.6 wt % or more Ca, between 0.5 wt % and 1.5 wt % Mn and Ca in sum, and wherein Mg and impurities account for the remaining content in the alloy that is missing up to 100 wt %. The invention further relates to an implant of a calcium containing magnesium alloy, which is coated with a calcium phosphate layer. The invention further relates to a method of producing a biodegradable implant.

Claims

1.-22. (canceled)

23. A magnesium alloy for a biodegradable implant, having the following composition: Zn: 0.5-2 wt %, Mn: 0.2-1 wt %, Ca: 0.1-1.3 wt %, wherein the magnesium alloy comprises 0.6 wt % or more Mn or 0.6 wt % or more Ca, between 0.5 wt % and 1.5 wt % Mn and Ca in sum, and wherein Mg and impurities account for the remaining content in the alloy that is missing up to 100 wt %.

24. The magnesium alloy of claim 23, having the following composition: Zn: 1-2 wt %, Mn: 0.3-1 wt %, and Ca: 0.2-1 wt %.

25. The magnesium alloy of claim 23, having the following composition: Zn: 1.2-1.8 wt %, Mn: 0.3-0.9 wt %, and Ca: 0.3-0.7 wt %.

26. The magnesium alloy of claim 23, having the following composition: Zn: 1.2-1.8 wt %, Mn: 0.6-0.8 wt %, and Ca: 0.2-0.4 wt %.

27. The magnesium alloy of claim 23, wherein said magnesium alloy comprises between 0.8 wt % and 1.2 wt % Mn and Ca in sum.

28. The magnesium alloy of claim 23, wherein said alloy comprises less than 0.5 wt %.

29. The magnesium alloy of claim 23, wherein said alloy comprises less than 0.1 wt % impurities.

30. The magnesium alloy of claim 23, wherein the magnesium alloy is free from Y.

31. The magnesium alloy of claim 23, wherein the magnesium alloy is free from rare earth elements.

32. The magnesium alloy of claim 23, wherein the magnesium alloy is extruded in two steps.

33. A medical device comprising the magnesium alloy of claim 23, wherein the medical device is an implant.

34. A method of controlling the corrosion of a biodegradable magnesium alloy, comprising: producing an alloy which comprises: 0.5-2 wt % Zn, 0.2-1 wt % Mn and 0.1-2 wt % Ca, and controlling a corrosion rate by varying the content of Zn, Mn, and Ca.

35. A biodegradable implant comprising a body of a magnesium alloy, wherein said magnesium alloy comprises Ca, and wherein said magnesium alloy is coated with a coating which comprises Ca.

36. The biodegradable implant according to claim 35, wherein said coating is a calcium phosphate coating.

37. The biodegradable implant according to claim 35, wherein said magnesium alloy comprises at least 0.1 wt % Ca.

38. The biodegradable implant according to claim 35, wherein said magnesium alloy comprises 0.2-3 wt % Mn, 0.5-5 wt % Zn and/or 0.1-3 wt % Ca and/or a ratio of Ca/Mn between 3:1 and 1:3 and/or a ratio of Zn to the sum of Ca and Mn between 2:1 and 1:1.

39. The biodegradable implant according to claim 35, wherein said coating is a hydroxyapatite coating.

40. The biodegradable implant according to claim 35, wherein said coating is applied by a method of plasma electrolytic oxidation and/or wherein the magnesium alloy of the body gradually transitions to said coating.

41. The biodegradable implant according to claim 35, wherein the magnesium content at least at the surface of the coating is more than 10 wt % and less than 70 wt %.

42. The biodegradable implant according to claim 35, wherein the magnesium content at least at the surface of the coating is more than 30 wt % and less than 60 wt %.

43. The biodegradable implant according to claim 35, wherein the surface of said coating comprises 5-30 wt % Ca, 15-50 wt % 0 and/or 3-10 wt % P.

44. The biodegradable implant according to claim 35, wherein said coating comprises a ceramic-metal-matrix.

45. The biodegradable implant according to claim 35, wherein said coating has a thickness of 1 to 100 m.

46. The biodegradable implant according to claim 35, wherein said coating has a thickness of 3 to 25 m.

47. A method of producing a biodegradable implant, wherein an implant body comprising a calcium containing magnesium alloy is coated with a calcium phosphate coating by using a plasma electrolytic oxidation method.

48. The method according to claim 47, wherein said plasma electrolytic oxidation process is performed in an electrolytic bath comprising calcium phosphate particles, in particular hydroxyapatite particles.

49. The method according to claim 47, wherein the electrolyte comprises water glass and/or a dissolved phosphate.

50. The method according to claim 47, wherein the electrolyte comprises water glass and sodium phosphate, each in an amount of at least 0.1%.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0076] FIG. 1 shows am implant.

[0077] FIG. 2 a schematic cross sectional view of an implant.

[0078] FIG. 3 is a table showing the corrosion rate of an implant.

[0079] FIG. 4 is a graph showing the corrosion rate of two implants according to the invention and of a comparative example.

[0080] FIG. 5 is an illustration of the controlled corrosion of the alloy.

[0081] FIG. 6 is a SEM image of the surface of a coated implant.

[0082] FIG. 7 is an EDS analysis of the surface of the coated implant.

[0083] FIGS. 8 and 9 are SEM images of a sliced coated implant.

[0084] FIG. 10 is an EDS analysis of the transition region between the alloy substrate and the coating.

[0085] FIG. 11-FIG. 14 are images of an element mapping of the surface region for the elements calcium, oxygen, phosphorous and magnesium.

DETAILED DESCRIPTION

[0086] FIG. 1 is a schematic view of an implant 1. The implant 1 is formed in this embodiment as a bone plate, comprising a body 2 with holes 3 for inserting bone screws.

[0087] The implant body consists of a non-porous, massive magnesium alloy, preferably of an alloy composition, according to one of the examples. The material of the implant can also be densified, in particular by using an extrusion process.

[0088] The implant body 2 is covered with a calcium phosphate coating, which is shown in the schematic drawing according to FIG. 4.

[0089] The surface of the body 2 is coated by using the plasma electrolytic oxidation method.

[0090] The plasma electrolytic oxidation method is performed by introducing calcium phosphate, in particular hydroxyapatite particles, into an electrolytic bath, and by generating a plasma discharge at the surface of the implant body 2.

[0091] By using such a plasma electrolytic oxidation process, a calcium phosphate layer 5 is formed on the surface of the body.

[0092] Due to the high energy of the plasma discharge, an intermediate layer 4 forms, which comprises magnesium, in particular magnesium oxide, as well as calcium phosphate.

[0093] FIG. 3 is a table showing the corrosion rate (mmpy) of an implant, which is immersed into a 0.9% NaCl solution at a temperature of 37 C.

[0094] The table shows the corrosion rate of an alloy, according to Examples 1, 2, and 3. The corrosion rate of a machined implant made of the alloy according to Example 1 is also shown.

[0095] The table further shows a comparative example of another magnesium alloy. This alloy has a manganese content of 0.5%, a calcium content of 0.3% and a zinc content of 1.3%.

[0096] It can be seen that the corrosion rate of the alloy, according to Example 1 and Example 3, is lower than the corrosion rate of the comparative example, especially in the initial phase after implantation. In further, the corrosion rate is not significantly weakened by machining the alloy.

[0097] FIG. 4 is a graph showing the corrosion rate of above-mentioned comparative example and Example 1 and 3, dependent on the immersion time.

[0098] It can be seen that the corrosion rate of Example 1 is less than 1 mmpy over the entire period.

[0099] The corrosion rate of Example 3 is substantially higher and is similar to the comparative example after an immersion time of 24 hours.

[0100] However, the corrosion rate in the initial phase after immersion of the comparative example is substantially higher, in particular the corrosion rate reaches more than 3 mmpy.

[0101] This results in an increased gas bubble formation after implantation, which can be disadvantageous, depending on the application.

[0102] FIG. 5 shall illustrate that it is, according to the invention, possible to control the corrosion by at least varying the content of zinc, manganese, and calcium.

[0103] In further, the corrosion rate can also be controlled by the manufacturing method, in particular by using an at least two step extrusion process and by providing a coating, in particular a protective calcium phosphate coating.

[0104] With the invention-controlled degradation of biodegradable implants, a sophisticated ingrowth of bone tissue can be achieved.

[0105] FIG. 6 is a SEM image of a calcium phosphate coating, which is applied onto a calcium containing magnesium alloy by using a plasma electrolytic oxidation method.

[0106] The coating consists of plateaus of a calcium phosphate layer, which are separated by meander-shaped grooves.

[0107] FIG. 7 is an EDS analysis of the surface of the coating. The coating comprises also a high amount of amount of magnesium oxide.

[0108] In this embodiment, the coating comprises 40-60 wt % Mg.

[0109] Preferably, the coating comprises at least at its surface 5-30 wt % Ca, 15-50 wt % 0 and 3-10 wt % P.

[0110] Since the used electrolyte also comprises water glass, the coating also comprises Si and Na.

[0111] FIG. 8 is an SEM image of a sliced pin of a magnesium alloy comprising a calcium phosphate coating.

[0112] FIG. 9 is a detailed view of the coating. There is nearly no visible transition between the coating and the substrate.

[0113] FIG. 10 is an EDS analysis of the transition region between the coating and the substrate.

[0114] In comparison to coating as shown in FIG. 7, the amount of calcium and oxygen is substantially lower.

[0115] However, it can be shown that the ca containing alloy gradually transitions to a coating which comprises MgO, Ca and P as main components.

[0116] In particular, the coating comprises hydroxyapatite, which is formed from the Ca and P containing electrolyte.

[0117] Without being bond to this theory, the Ca in the alloy enables the gradual transition, which results in an extreme strong bond of the coating.

[0118] The coating reduces the corrosion of the implant in the initial phase after insertion.

[0119] FIG. 11-FIG. 14 are images of an element mapping of the surface region of a coated implant for the elements calcium, oxygen, phosphorous and magnesium.

[0120] As shown in FIG. 11, the Ca content in the coating is substantially higher as in the alloy. However, also the alloy comprises Ca in order to enable a gradual transition of the substrate to the coating.

[0121] FIG. 12 shows that the alloy is substantially free of oxide. The coating has an oxygen content of at least 15 wt %, which is predominantly bonded as MgO.

[0122] FIG. 13 shows that only the coating comprises phosphorous, in particular to be embodied as a hydroxyapatite containing layer.

[0123] FIG. 14 shows that also the coating comprises magnesium. However, since the magnesium in the coating is bonded predominantly in the form of MgO, also this oxide contributes the protective property of the coating.