Magnesium-based absorbable alloys
A magnesium alloy contains a small amount of lithium, zinc, calcium, and manganese. For example, the magnesium alloy may include between 1-5 wt. % lithium, between 0.2-2.0 wt. % zinc, between 0.1-0.5 wt. % calcium, and between 0.1-0.8 wt. % manganese. These alloying elements are all nutrient elements, such that the present alloy can be safely broken down in vivo, then absorbed and/or expelled from the body. Li, Zn, Ca and Mn each contribute to solid-solution strengthening of the alloy. Ca also acts as a grain refiner, while Zn and Ca both form strengthening and corrosion-controlling intermetallic compounds. Optionally, the alloy may also include a small amount of yttrium for added strength and corrosion resistance.
1. An alloy for use in an absorbable medical device, the alloy comprising:
between 1.0-5.0 wt. % lithium;
between 0.2-2.0 wt. % zinc;
between 0.1-0.5 wt. % calcium;
between 0.1-0.8 wt. % manganese; and
balance magnesium and inevitable impurities.
2. The alloy of claim 1 , wherein the alloy has no retained cold work and exhibits an ultimate tensile strength reaching 34 ksi.
3. The alloy of claim 1 , wherein the alloy has 75% retained cold work and exhibits an ultimate tensile strength reaching 64 ksi.
4. The alloy of claim 1 , wherein the alloy has no retained cold work and exhibits a yield strength reaching 26 ksi.
5. The alloy of claim 1 , wherein the alloy has 75% retained cold work and exhibits a yield strength reaching 56 ksi.
6. The alloy of claim 1 , wherein the alloy has no retained cold work and exhibits a ductility sufficient to allow elongation of 14% before rupture.
7. The alloy of claim 1 , wherein the alloy has 75% retained cold work and exhibits a ductility sufficient to allow elongation of 7% before rupture.
8. The alloy of claim 1 , wherein the alloy has no retained cold work and exhibits a mean survival of at least 30 hours in Hanks' Balanced Salt Solution maintained at 37° C. and 7.4 pH while also being held at an initial stress of 110 MPa.
9. The alloy of claim 1 , wherein the alloy has at least 50% retained cold work and exhibits a mean survival of at least 30 hours in Hanks' Balanced Salt Solution maintained at 37° C. and 7.4 pH while also being held at an initial stress of 110 MPa.
10. The alloy of claim 1 , wherein the alloy has no retained cold work and exhibits:
an ultimate tensile strength reaching 34 ksi;
a yield strength reaching 26 ksi;
a ductility sufficient to allow elongation of 14% before rupture; and
a mean survival of at least 30 hours in Hanks' Balanced Salt Solution maintained at 37° C. and 7.4 pH while also being held at an initial stress of 110 MPa.
11. The alloy of claim 1 , wherein the alloy has at least 50% retained cold work and exhibits:
an ultimate tensile strength reaching 64 ksi;
a yield strength reaching 56 ksi;
a ductility sufficient to allow elongation of 7% before rupture; and
a mean survival of at least 30 hours in Hanks' Balanced Salt Solution maintained at 37° C. and 7.4 pH while also being held at an initial stress of 110 MPa.
12. The alloy of claim 1 , further comprising yttrium in an amount up to 2.5 wt. %.
13. The alloy of claim 12 , wherein the alloy has no retained cold work and exhibits an ultimate tensile strength reaching 39 ksi.
14. The alloy of claim 12 , wherein the alloy has 75% retained cold work and exhibits an ultimate tensile strength reaching 61 ksi.
15. The alloy of claim 12 , wherein the alloy has no retained cold work and exhibits a yield strength reaching 33 ksi.
16. The alloy of claim 12 , wherein the alloy has 75% retained cold work and exhibits a yield strength reaching 45 ksi.
17. The alloy of claim 12 , wherein the alloy has no retained cold work and exhibits a ductility sufficient to allow elongation of 19% before rupture.
18. The alloy of claim 12 , wherein the alloy has 75% retained cold work and exhibits a ductility sufficient to allow elongation of 10% before rupture.
19. A wire formed from the alloy of claim 1 .
20. A medical device formed from an alloy comprising:
between 1.0-5.0 wt. % lithium;
between 0.2-2.0 wt. % zinc;
between 0.1-0.5 wt. % calcium;
between 0.1-0.8 wt. % manganese; and
balance magnesium and inevitable impurities.
21. The medical device of claim 20 , wherein the medical device is a vascular device.
22. The medical device of claim 20 , wherein the medical device is an orthopedic fixation device.
23. The medical device of claim 20 , wherein the medical device is a surgical intervention device.