Dynamic, non-homogeneous shape memory alloys

Abstract

Composite alloys comprising a first alloy portion comprising nickel and titanium and a second alloy portion comprising nickel and titanium in a different stoichiometry than the first alloy portion are disclosed, along with related methods of manufacture and use. Particularly, the composite alloys may be used in customized medical devices where a shape memory effect would be beneficial.

What is claimed is: 
     
         1 . A composite alloy, comprising:
 a first alloy portion comprising a first composition of 45 to 55 wt. % nickel (Ni) and 45 to 55 wt. % titanium (Ti); and   a second alloy portion comprising a second composition of 45 to 55 wt. % nickel (Ni) and 45 to 55 wt. % titanium (Ti);   wherein said first and said second compositions are different; and   wherein said first alloy portion and said second alloy portion are adjacent and interconnected through a functional gradient interface.   
     
     
         2 . The composite alloy of  claim 1 , wherein said composite alloy is formed into a medical device selected from the group consisting of an implantable spine rod, an external medical brace, a component of an external medical brace, a bone plate, a screw, an intramedullary nail, a vertebral spacer and a pin. 
     
     
         3 . The composite alloy of  claim 1 , wherein said first and/or said second composition(s) further comprise up to 10 wt. % of at least one element selected from the group consisting of zirconium (Zr), aluminum (Al), niobium (Nb), vanadium (V), copper (Cu), iron (Fe) and combinations thereof. 
     
     
         4 . The composite alloy of  claim 1 , wherein said first and/or said second composition(s) comprise 0 wt. % to 2 wt. % of at least one element selected from the group consisting of Zr, Al, Nb, V, Cu, Fe and combinations thereof. 
     
     
         5 . The composite alloy of  claim 1 , wherein the first alloy portion and the second alloy portion occupy first and second locations respectively. 
     
     
         6 . The composite alloy of  claim 5 , wherein the first and second locations are distributed non-uniformly throughout the composite alloy. 
     
     
         7 . The composite alloy of  claim 1 , wherein at least one of the first and the second alloy is a shape memory alloy. 
     
     
         8 . The composite alloy of  claim 1 , wherein said first alloy is a superelastic alloy and said second alloy is a shape memory alloy, or wherein said first alloy is a superelastic alloy and said second alloy is a different superelastic alloy, or wherein said first alloy is a shape memory alloy and said second alloy is a different shape memory alloy. 
     
     
         9 . The composite alloy of  claim 1 , wherein said composite alloy is trained to undergo a transition from a first desired shape to a second desired shape. 
     
     
         10 . The composite alloy of  claim 9 , wherein the total strain experienced by the composite alloy over the course of the transition is less than 0.2. 
     
     
         11 . The composite alloy of  claim 9 , wherein the rate of strain experienced by the composite alloy over the course of the transition is less than 2000 με/day. 
     
     
         12 . The composite alloy of  claim 1 , wherein the density of the first alloy portion is between 30% and 100% of theoretical maximum density for the first alloy, and the density of the second alloy portion is between 30% and 100% of theoretical maximum density for the second alloy. 
     
     
         13 . The composite alloy of  claim 1 , wherein a porosity of said first alloy portion and/or said second alloy portion is between 0% and 70% on the basis of image analysis or Archimedes principle. 
     
     
         14 . The composite alloy of  claim 1  further comprising a coating. 
     
     
         15 . The composite alloy of  claim 14 , wherein the coating is selected from the group consisting of a metal, a metal alloy, a ceramic, a polymer, titanium hydroxide (Ti(OH) 2 ), titanium hydride (TiH 2 ), titanium nitride (TiN), titanium dioxide (TiO 2 ), collagen, bone morphogenic proteins and combinations thereof. 
     
     
         16 . The composite alloy of  claim 1 , wherein the functional gradient interface is predominantly oriented along a longitudinal axis of the composite alloy. 
     
     
         17 . The composite alloy of  claim 1 , wherein the functional gradient interface is predominantly oriented along a lateral axis of the composite alloy. 
     
     
         18 . The composite alloy of  claim 1 , wherein the functional gradient interface is non-linear. 
     
     
         19 . The composite alloy of  claim 1  further comprising a third alloy portion comprising a third composition. 
     
     
         20 . The composite alloy of  claim 19 , wherein the third alloy portion is adjacent and interconnected through another functional gradient interface with the first alloy portion or the second alloy portion.