Bioerodible Magnesium Alloy Microstructures for Endoprostheses

Patent metadata

Field	Value
Publication number	US-2016263288-A1
Application number	US-201615068132-A
Country	US
Kind code	A1
Filing date	Mar 11, 2016
Priority date	Mar 11, 2015
Publication date	Sep 15, 2016
Grant date	—

Abstract

A bioerodible endoprosthesis includes a bioerodible body including an alloy comprising at least 85 weight percent magnesium and at least one high-melting-temperature element having a melting temperature of greater than 700° C. The alloy has a microstructure including equiaxed magnesium-rich phase grains and optionally high-melting-temperature intermetallic phases. The equiaxed magnesium-rich phase grains have an average grain diameter of less than or equal to 10 microns. High-melting-temperature intermetallic phases, if present, can have an average longest dimension of 3 microns or less.

First claim

What is claimed is:

1 . A bioerodible endoprosthesis comprising:
a bioerodible body comprising an alloy comprising at least 85 weight percent magnesium and at least one high-melting-temperature element having a melting temperature of greater than 700° C., the alloy having a microstructure comprising equiaxed magnesium-rich phase grains and optionally high-melting-temperature intermetallic phases, the equiaxed magnesium-rich phase grains having an average grain diameter of less than or equal to 10 microns and the high-melting-temperature intermetallic phases, if present, comprising at least 20 weight percent of one or more high-melting-temperature elements and having an average longest dimension of 3 microns or less.

2 . The endoprosthesis of claim 1 , wherein the at least one high-melting-temperature element is a rare earth metal.

3 . The endoprosthesis of claim 1 , wherein the at least one high-melting-temperature element has a melting temperature of at least 1,000° C.

4 . The endoprosthesis of claim 1 , wherein the at least one high-melting-temperature element is selected from the group consisting of neodymium, tin, yttrium, cerium, lanthanum, and gadolinium.

5 . The endoprosthesis of claim 1 , wherein the alloy comprises between 0.5 and 5.0 weight percent of the at least one high-melting-temperature element.

6 . The endoprosthesis of claim 1 , wherein the high-melting-temperature intermetallic phases are primarily centered upon grain boundaries between equiaxed magnesium-rich phase grains and do not extend into the equiaxed magnesium-rich phase grain interior by more than 0.3 microns from a grain boundary when viewed at 200-500× magnification on a metallography plane.

7 . The endoprosthesis of claim 1 , wherein the alloy further comprises aluminum, zinc, manganese, or a combination thereof.

8 . The endoprosthesis of claim 7 , wherein the microstructure further comprises low-melting-temperature intermetallic phases having an average longest dimension of 1 micron or less, the low-melting-temperature intermetallic phases comprising aluminum, zinc, manganese, or a combination thereof.

9 . The endoprosthesis of claim 8 , wherein the low-melting-temperature intermetallic phases comprise Mg 17 Al 12 .

10 . The endoprosthesis of claim 1 , wherein the alloy has an elastic modulus of between 39 GPa and 44 GPa, a 0.2% offset yield strength of between 150 MPa and 350 MPa, an ultimate tensile strength of between 250 MPa and 400 MPa, and a tensile reduction in area of at least 30%.

11 . The endoprosthesis of claim 1 , wherein the alloy maintains its initial elastic modulus, yield strength, ultimate tensile strength, and a tensile RIA within ±10% following storage for 180 days at a temperature of between 20° C. and 25° C. and a relative humidity of less than 30%.

12 . The endoprosthesis of claim 11 , wherein the bioerodible body comprises between 5 and 11 weight percent aluminum, between 0.1 and 3.0 weight percent zinc, up to 0.3 weight percent manganese, and between 0.6 and 1.5 weight percent neodymium, and balance magnesium.

13 . The endoprosthesis of claim 1 , wherein the endoprosthesis is a stent comprising a plurality of struts, wherein the struts have a width to thickness ratio of less than 1.2.

14 . A method of forming an endoprosthesis comprising:
cooling a solution comprising at least 85 weight percent magnesium and at least one high-melting-temperature element from a temperature of equal to or greater than the melting temperature of the at least one high-melting-temperature element to a temperature of 650° C. or less at a rate of at least 3.0° C. per second to form a cast alloy; and performing at least one high-strain process on the cast alloy to form a microstructure of equiaxed magnesium-rich phase grains and high-melting-temperature intermetallic phases, the equiaxed magnesium-rich phase grains having an average grain diameter of less than or equal to 10 microns and the high-melting-temperature intermetallic phases having an average longest dimension of 3 microns or less.

15 . The method of claim 14 , wherein the solution is cooled from a temperature of equal to or greater than the at least one rare earth metal to a temperature of 650° C. or less at a rate of at least 30° C. per second.

16 . The method of claim 14 , wherein the at least one high-strain process is an equal-channel, high-strain process performed at a temperature of less than 400° C.

17 . The method of claim 16 , wherein the cooling of the solution forms a supersaturated flake, further comprising consolidating the supersaturated flake into a billet, wherein the billet is processed through at least two equal-channel, high-strain processes at different temperatures, wherein a first equal-channel, high-strain process occurs at a first time and is performed at a higher temperature than a second equal-channel, high-strain process that occurs at a second time occurring after the first time, wherein the first equal-channel, high-strain process is performed at a temperature of between 250° C. and 400° C. and the second equal-channel, high-strain process is performed at a temperature of between 150° C. and 300° C.

18 . The method of claim 14 , wherein the solution further comprises aluminum, zinc, manganese, or a combination thereof.

19 . The method of claim 18 , wherein the microstructure further comprises low-melting-temperature intermetallic phases having an average longest dimension of 1 micron or less, the low-melting-temperature intermetallic phases comprising aluminum, zinc, manganese, or a combination thereof.

20 . The method of claim 14 , wherein the solution comprises between 5 and 11 weight percent aluminum, between 0.1 and 3.0 weight percent zinc, up to 0.3 weight percent manganese, and between 0.6 and 1.5 weight percent neodymium, and balance magnesium.

Assignees

• Boston Scient Scimed Inc

Inventors

• Edick Jacob Drew
• Stinson Jonathan S

Classifications

• A61F2/82

  Devices providing patency to, or preventing collapsing of, tubular structures of the body, e.g. stents (stent-grafts for tubular structures of the body other than blood vessels A61F2/04; stent-grafts for blood vessels A61F2/07) · CPC title

• A61F2240/001

  Designing or manufacturing processes · CPC title

• A61L31/022 Primary

  Metals or alloys · CPC title

• A61L31/148

  Materials at least partially resorbable by the body · CPC title

• A61F2/06

  Blood vessels · CPC title