Magnesium single crystal for biomedical applications and methods of making same

Abstract

A biomedical implant ( 16, 18 ) is formed from magnesium (Mg) single crystal ( 10 ). The biomedical implant ( 16, 18 ) may be biodegradable. The biomedical implant ( 16, 18 ) may be post treated to control the mechanical properties and/or corrosion rate thereof said Mg single crystal ( 10 ) without changing the chemical composition thereof. A method of making a Mg single crystal ( 10 ) for biomedical applications includes filling a single crucible ( 12 ) with more than one chamber with polycrystalline Mg, melting at least a portion of said polycrystalline Mg, and forming more than one Mg single crystal ( 10 ) using directional solidification.

What is claimed is: 
     
         1 . A biomedical implant formed from Mg single crystal. 
     
     
         2 . The biomedical implant of  claim 1  wherein the implant is for use as an implant in a mammal. 
     
     
         3 . The biomedical implant of  claim 1  wherein said Mg single crystal is formed by fully or partially melting polycrystalline Mg and solidifying it in a controlled manner effective to form a single crystal. 
     
     
         4 . The biomedical implant of  claim 3  wherein controlled crystallization of said Mg crystallization is caused by directional solidification from the Mg melt utilizing at least one of the Czochralski method, Bridgman method, and floating zone method. 
     
     
         5 . The biomedical implant of  claim 3  wherein said implant is formed by forming polycrystalline Mg in a desired shape, growing said Mg single crystal by placing said preformed polycrystalline Mg implant into a mold conforming to the shape of said preformed polycrystalline Mg implant, and converting said preformed polycrystalline Mg implant to a Mg single crystal. 
     
     
         6 . The biomedical implant of  claim 1  wherein growth of said Mg single crystal is based on gas phase transport of Mg and related Mg-containing species to a crystal growth zone by chemical vapor deposition, physical vapor deposition, or a combination thereof. 
     
     
         7 . The biomedical implant of  claim 1  wherein said Mg single crystal is grown from a starting material, said starting material being Mg having a purity of 99.99% and greater. 
     
     
         8 . The biomedical implant of  claim 1  wherein said Mg single crystal is grown from a starting material, said starting material being a Mg alloy. 
     
     
         9 . The biomedical implant of  claims 1 ,  7 , and  8  wherein said Mg single crystal is grown from a melt exposed to a soaking time from 1 to 50 hr and a constant soaking temperature of 10 to 150° C. above the melting point of magnesium. 
     
     
         10 . The biomedical implant of  claim 9  wherein said Mg single crystal is grown from a melt exposed to a soaking time of 30 hr and a constant soaking temperature of 75° C. above the melting point of magnesium. 
     
     
         11 . The biomedical implant of  claim 8  wherein segregation of said Mg alloy during growth of said Mg single crystal is eliminated by varying a growth rate. 
     
     
         12 . The biomedical implant of  claim 8  wherein segregation of said Mg alloy during growth of said Mg single crystal is eliminated by applying an annealing procedure in argon at a temperature maintained below the magnesium melting point for 1 to 50 hrs. 
     
     
         13 . The biomedical implant of  claim 12  wherein the temperature is 645° C. and the annealing procedure is applied for 14 hrs. 
     
     
         14 . The biomedical implant of  claim 1  wherein said Mg single crystal is grown with a preset shape and size. 
     
     
         15 . The biomedical implant of  claim 1  wherein said Mg single crystal is grown with a preset orientation using a seed crystal with defined crystal orientation. 
     
     
         16 . The biomedical implant of  claim 15  wherein said seed crystal is a Mg seed crystal. 
     
     
         17 . The biomedical implant of  claim 15  wherein said seed crystal is a Zr seed crystal. 
     
     
         18 . The biomedical implant of  claim 1  wherein said Mg single crystal is post treated to control mechanical properties of said Mg single crystal without changing the chemical composition thereof. 
     
     
         19 . The biomedical implant of  claim 18  wherein said post treatment is cold working. 
     
     
         20 . The biomedical implant of  claim 18  wherein said post treatment is one of electron beam irradiation, gamma irradiation, and neutron irradiation. 
     
     
         21 . The biomedical implant of  claim 18  wherein said post treatment is anodization. 
     
     
         22 . The biomedical implant of  claim 1  wherein said Mg single crystal is post treated to control a corrosion rate of said Mg single crystal without changing the chemical composition thereof. 
     
     
         23 . The biomedical implant of  claim 22  wherein said post treatment is polishing and chemical etching. 
     
     
         24 . The biomedical implant of  claims 18  and  22  wherein said Mg single crystal is polished using grit silicone carbide paper in isopropyl alcohol, sonicated in ethanol, chemically etched for 10 to 100 seconds, and rinsed using ethanol. 
     
     
         25 . The biomedical implant of  claim 24  wherein a chemical etchant used to chemically etch said Mg single crystal is made of nitric acid, methanol and ethanol in the ratio 1:2:1. 
     
     
         26 . The biomedical implant of  claim 1  wherein said Mg single crystal is machined to a desired shape and size. 
     
     
         27 . The biomedical implant of  claim 1  wherein said Mg single crystal is subjected to forging to provide a desired shape and size. 
     
     
         28 . The biomedical implant of  claim 1  wherein said biomedical implant is selected from the group consisting of ACL interference screws, temporomandibular joint, temporomandibular devices, bone fixation plates, and bone screws. 
     
     
         29 . A method of making a Mg single crystal for biomedical applications comprising:
 filling a single crucible including more than one chamber with polycrystalline Mg;   melting at least a portion of said polycrystalline Mg; and   forming more than one Mg single crystal using directional solidification.   
     
     
         30 . The method of  claim 30  wherein said polycrystalline Mg is a polycrystalline Mg alloy. 
     
     
         31 . A method of making a Mg single crystal for biomedical applications comprising:
 filling a crucible designed with desired shape with polycrystalline Mg;   melting at least a portion of said polycrystalline Mg; and   forming a Mg single crystal with the shape of crucible using directional solidification.   
     
     
         32 . A method of making a Mg single crystal for biomedical applications comprising:
 filling a split mold crucible locked with a carbon nanotube (CNT) thread or a CNT sheet with polycrystalline Mg;   melting at least a portion of said polycrystalline Mg; and   forming Mg single crystal using directional solidification thus enabling easy release of the grown crystal.   
     
     
         33 . A hydrogen storage device formed from Mg single crystal.