Devices configured from strain hardened Ni Ti tubing

Abstract

Cold worked nickel-titanium alloys that have linear pseudoelastic behavior without a phase transformation or onset of stress-induced martensite as applied to a medical device having a strut formed body deployed from a sheath is disclosed. In one application, an embolic protection device that employs a linear pseudoelastic nitinol self-expanding strut assembly with a small profile delivery system for use with interventional procedures is disclosed. Linear pseudoelastic nitinol is used in the medical device as distinct from non-linear pseudoelastic (i.e., superelastic) nitinol. The expandable strut assembly is made from a small diameter tubing of cold worked nickel-titanium alloys. The self-expanding struts that deploy the filter element is laser cut from a large diameter cold worked nickel-titanium alloy, then joined to the small diameter tubing.

What is claimed is:  
     
         1 . A medical device for use in a body lumen, comprising: 
 a tubular body formed from small diameter tubing;    a plurality of struts formed from a large diameter tubing and disposed on the tubular body such that the struts project radially outward in an unconstrained state;    wherein the large diameter tubing includes a cold formed nickel-titanium alloy, and the nickel-titanium alloy is in a martensitic phase only regardless of stress applied to the alloy; and    a sheath at least partially enveloping the body and restraining the struts in a compressed state for delivery and retrieval of the device to and from the body lumen.    
     
     
         2 . The medical device of  claim 1 , wherein the strut includes a long beam extending from a wide base, and the tubular body includes apertures formed therein, and wherein each aperture receives the wide base of the strut therein.  
     
     
         3 . The medical device of  claim 2 , wherein the long beam of the strut includes a sloped profile.  
     
     
         4 . The medical device of  claim 2 , wherein the aperture has a beveled interior edge and the wide base has a matching beveled edge.  
     
     
         5 . The medical device of  claim 2 , wherein the medical device includes a sleeve that slidably engages the tubular body and covers the wide bases of the struts thereby retaining the struts to the body.  
     
     
         6 . The medical device of  claim 1 , wherein the tubular body has been heat treated and a hysteresis curve of the nickel-titanium alloy does not include a stress plateau.  
     
     
         7 . The medical device of  claim 1 , wherein the struts assume a shape imparted by cold forming.  
     
     
         8 . The medical device of  claim 7 , wherein the cold forming occurs below the recrystallization temperature of the nickel-titanium alloy.  
     
     
         9 . The medical device of  claim 1 , wherein the ingot transformation temperature of the nickel-titanium alloy is set above 37 degrees C.  
     
     
         10 . The medical device of  claim 1 , wherein the small diameter tubing includes a nickel-titanium alloy.  
     
     
         11 . A medical device for delivery to, deployment within, and removal from a lumen of a mammalian body, comprising: 
 a tubular body derived from small diameter tubing having a plurality of apertures formed therein;    a plurality of struts derived from a large diameter tubing;    wherein the apertures receive the struts therein and in an unstressed state bend away from the tubular body;    wherein the small and large diameter tubing include a cold formed nickel-titanium alloy, and the nickel-titanium alloy is in a martensitic phase only regardless of stress applied to the alloy; and    a sheath at least partially enveloping the body and restraining the struts in a compressed state for delivery and retrieval of the device to and from the lumen.    
     
     
         12 . The medical device of  claim 11 , wherein the strut is cold formed to provide a curvature in a profile thereof.  
     
     
         13 . The medical device of  claim 11 , wherein the strut includes a long beam extending from a wide base, and the wide base includes a radius of curvature matching a radius of curvature of the tubular body.  
     
     
         14 . The medical device of  claim 13 , wherein some of the apertures have a first shape and the wide bases of the struts have a second shape complementary to the first shape so that at least a portion of the struts is recessed into the tubular body when attached thereto.  
     
     
         15 . The medical device of  claim 11 , wherein the strut includes a long beam extending from a wide base, and the wide base includes a beveled periphery that wedges against a beveled periphery of the aperture.  
     
     
         16 . The medical device of  claim 11 , wherein the strut has been heat treated and a hysteresis curve of the nickel-titanium alloy does not include a stress plateau.  
     
     
         17 . The medical device of  claim 11 , wherein the nickel-titanium alloy has received low temperature heat treating and does not undergo a phase transformation when stressed.  
     
     
         18 . The medical device of  claim 11 , wherein the struts are bonded to the tubular body.  
     
     
         19 . A method for providing a medical device for use in a body lumen, comprising: 
 providing a small diameter tubing;    forming the small diameter tubing into a tubular body;    providing a large diameter tubing wherein the large diameter tubing includes a cold formed nickel-titanium alloy wherein the nickel-titanium alloy is in a martensitic phase only regardless of stress applied to the alloy;    fashioning a plurality of struts from the large diameter tubing;    disposing the struts on the tubular body such that the struts project radially outward in an unconstrained state; and    providing a sheath that at least partially envelopes the body and restrains the struts in a compressed state for delivery and retrieval of the device to and from the body lumen.    
     
     
         20 . The method for providing a medical device of  claim 19 , wherein the method further comprises providing a small tubing including a cold formed nickel-titanium alloy wherein the nickel-titanium alloy is in a martensitic phase only regardless of stress applied to the alloy.  
     
     
         21 . The method for providing a medical device of  claim 19 , wherein the strut is cold formed to achieve a curved profile.  
     
     
         22 . The method for providing a medical device of  claim 19 , wherein method includes low temperature heat treat of the nickel-titanium alloy.  
     
     
         23 . A medical device for use in a body lumen, comprising: 
 a tubular body formed from small diameter tubing;    a plurality of struts formed from a large diameter tubing and disposed on the tubular body such that the struts project radially outward in an unconstrained state;    wherein the large diameter tubing includes a cold formed nickel-titanium alloy that includes heat treating, and the nickel-titanium alloy is in a martensitic phase only regardless of stress applied to the alloy; and    a sheath at least partially enveloping the body and restraining the struts in a compressed state for delivery and retrieval of the device to and from the body lumen.