Stent design

Abstract

The present invention is directed to an expandable stent which is relatively flexible along its longitudinal axis to facilitate delivery through tortuous body lumens, but which is stiff and stable enough radially in an expanded condition to maintain the patency of a body lumen such as an artery when implanted therein. The struts of the present invention have a specific trapezoidal, triangular or a reduced radii configuration projecting radially outward that functions to reduce the forces necessary to penetrate the vessel wall thereby minimizing trauma or damage imparted to the wall during deployment. In addition, this design feature of the present invention helps secure the expanded stent so that it does not move once it is implanted and furthermore, minimizes projections into the blood stream. The invention generally includes a plurality of radially expandable loop elements which are relatively independent in their ability to expand and to flex relative to one another. The individual radially expandable elements of the stent are dimensioned to minimize the strut from twisting or rotating during expansion. Interconnecting elements or a backbone extends between the adjacent loop elements to provide increased stability and a preferable position for each loop to prevent warping of the stent upon the expansion thereof. The resulting stent structure is a series of radially expandable loop elements which are spaced longitudinally close enough so that the obstruction, vessel wall and any small dissections located at the treatment site of a body lumen may be dilated or pressed back into position against the lumenal wall. The manufacturing process of the present invention utilizes optimized stress-strain curve characteristics to achieve, unlike other non-wire stent designs, improved mechanical properties throughout the stent. The optimized stress-strain curve of the materail increases both the yield strength and the ultimate tensile strength of the expanded stent, increasing its resistance to structural failure (fracture) or stent crushing.

I claim:  
     
         1 . A low pressure stent for implanting in a vessel comprising; 
 a plurality of substantially cylindrical loop elements which are independently expandable in the radial direction and which are interconnected to generally align said cylindrical loop elements in a common longitudinal axis;    one or more connecting elements for interconnecting said cylindrical loop elements; and    an outer surface on said cylindrical loop elements, said outer surface comprising a converging configuration projecting radially from said longitudinal axis prior to expansion of said stent, said converging configuration maintaining its radial projection as said stent is expanded radially outwardly from a first diameter to a second, enlarged diameter.    
     
     
         2 . A low pressure stent as recited in  claim 1 , wherein said converging configuration of said outer surface of the loop element comprises a trapezoidal configuration.  
     
     
         3 . A low pressure stent as recited in  claim 1 , wherein said converging configuration of said outer surface of the loop element comprises a triangular configuration.  
     
     
         4 . A low pressure stent as recited in  claim 1 , wherein said converging configuration of said outer surface of the loop element comprises a reduced radii configuration.  
     
     
         5 . A low pressure stent as recited in  claim 1 , wherein said loop elements include an undulating, alternating loop or serpentine pattern.  
     
     
         6 . A low pressure stent as recited in  claim 1 , wherein said outer surface of said loop elements are embedded into the vascular wall of the body lumen in order to more firmly attach said stent to the vascular wall.  
     
     
         7 . The low pressure stent as recited in  claim 1 , wherein said loop elements are capable of maintaining their expanded condition upon expansion thereof  
     
     
         8 . The low pressure stent as recited in  claim 1 , wherein said stent is formed of a material selected from the group of materials consisting of stainless steel, platinum, gold alloy, or a gold/platinum alloy.  
     
     
         9 . The low pressure stent as recited in  claim 1 , wherein said stent is formed from a single piece of tubing.  
     
     
         10 . The low pressure stent as recited in  claim 1 , further comprising coating said stent with a biocompatible coating.  
     
     
         11 . The low pressure stent as recited in  claim 1 , wherein said loop elements have a yield strength greater than 35,000 psi.  
     
     
         12 . The low pressure stent as recited in  claim 1 , wherein said loop elements have an ultimate tensile strength greater than 65,000 psi.  
     
     
         13 . A low pressure stent for implanting in a vessel comprising; 
 a plurality of substantially cylindrical loop elements which are independently expandable in the radial direction and which are interconnected to concentrically align said cylindrical loop elements in a common longitudinal axis;    one or more connecting elements for interconnecting said cylindrical loop elements, so that said stent, when expanded radially outward, retains its overall length without appreciable shortening; and    an outer surface on said loop elements, said outer surface comprising a converging configuration projecting radially from said longitudinal axis prior to expansion of said stent, said converging configuration maintaining its radial projection as said stent is expanded radially outwardly from a first diameter to a second, enlarged diameter.    
     
     
         14 . A low pressure stent as recited in  claim 13 , wherein said converging configuration of said outer surface of the loop element comprises a trapezoidal configuration.  
     
     
         15 . A low pressure stent as recited in  claim 13 , wherein said converging configuration of said outer surface of the loop element comprises a triangular configuration.  
     
     
         16 . A low pressure stent as recited in  claim 13 , wherein said converging configuration of said outer surface of the loop element comprises a reduced radii configuration.  
     
     
         17 . A low pressure stent as recited in  claim 13 , wherein said loop elements include an undulating, alternating loop or serpentine pattern.  
     
     
         18 . A low pressure stent as recited in  claim 13 , wherein said outer surface of said loop elements are embedded into the vascular wall of the body lumen in order to more firmly attach said stent to the vascular wall.  
     
     
         19 . The low pressure stent as recited in  claim 13 , wherein said loop elements are capable of maintaining their expanded condition upon expansion thereof.  
     
     
         20 . The low pressure stent as recited in  claim 13 , wherein said stent is formed of a material selected from the group of materials consisting of stainless steel, stainless steel, platinum, gold alloy, or a gold/platinum alloy.  
     
     
         21 . The low pressure stent as recited in  claim 13 , wherein said stent is formed from a single piece of tubing.  
     
     
         22 . The low pressure stent as recited in  claim 13 , further comprising coating said stent with a biocompatible coating.  
     
     
         23 . The low pressure stent as recited in  claim 13 , wherein said loop elements have a yield strength greater than 35,000 psi.  
     
     
         24 . The low pressure stent as recited in  claim 13 , wherein said loop elements have an ultimate tensile strength greater than 65,000 psi.  
     
     
         25 . A low pressure stent for implanting in a vessel comprising; 
 a plurality of substantially cylindrical loop elements which are independently expandable in the radial direction and which are interconnected to concentrically align said loop elements in a common longitudinal axis;    one or more connecting elements for interconnecting said cylindrical loop elements, so that said stent, when expanded radially outward, retains its overall length without appreciable shortening; and    said loop elements having a yield strength of at least 35,000 psi.    
     
     
         26 . A low pressure stent for implanting in a vessel comprising; 
 a plurality of substantially cylindrical loop elements which are independently expandable in the radial direction and which are interconnected to concentrically align said cylindrical loop elements in a common longitudinal axis;    one or more connecting elements for interconnecting said cylindrical loop elements, so that said stent, when expanded radially outward, retains its overall length without appreciable shortening; and    said loop elements having an ultimate tensile strength of at least 65,000 psi.    
     
     
         27 . The method of deploying a stent having a plurality of substantially cylindrical loop elements which are independently expandable in the radial direction and which are interconnected and generally aligned with said cylindrical loop elements in a common longitudinal axis, one or more connecting elements for interconnecting said loop elements, an outer surface on said loop elements, said outer surface comprising a converging configuration or reduce radius projecting radially from said longitudinal axis prior to expansion of said stent, said converging configuration or reduced radius maintaining its radial projection as said stent is expanded radially outwardly from a first diameter to a second, enlarged diameter; 
 providing a catheter with an expandable member on its distal end and positioning said stent coaxially on said expandable member;    positioning said expandable member with said stent at a selected implantation site within a vessel of a patient;    expanding the expandable member radially to expand said stent within a lumen of said vessel;    contracting said expandable member; and    removing said catheter from said patient.    
     
     
         28 . A method of deploying a stent as recited in  claim 27 , further comprising the step of implanting said stent within a vessel wall after the step of expanding said expandable member within said lumen of said vessel.