Retrieval device made of precursor alloy cable

Abstract

A medical retrieval device for retrieving foreign objects from a patient and the method of constructing the device are disclosed. The device incorporates a wire cable composed of a precursor alloy to a superelastic material to improve durability of the device. Because precursor alloys exhibit a linear stress-strain relationship and a yield point associated with a relatively high stress level, the device transfers greater stresses before experiencing deformation. Thus, greater crushing forces can be achieved using a device of this type. These crushing forces may be needed when the foreign object is too large to remove intact. This property also facilitates the device in dilating ducts to retrieve foreign objects. Using the precursor alloy additionally eliminates the need for heat treatment of the cables used in constructing the device. A retrieval device made of precursor alloy cable also is less susceptible to permanent deformation and unwinding during use.

What is claimed is:  
     
         1 . A medical retrieval device for retrieving foreign objects from a patient's body, comprising: 
 a retrieval assembly including a cable preformed into a configuration adapted to capture and remove said foreign objects, wherein said cable includes a core wire made of a precursor alloy to a superelastic material and a plurality of wire strands surrounding the core wire.    
     
     
         2 . The device of  claim 1 , wherein said precursor alloy exhibits a stress-strain curve that is linear extending to a yield point.  
     
     
         3 . The device of  claim 2 , wherein said stress-strain curve has no phase transformation point.  
     
     
         4 . The device of  claim 2 , wherein said stress-strain curve extends to a yield point without passing through a substantially constant stress plateau while strain is varied.  
     
     
         5 . The device of  claim 1 , wherein said retrieval assembly is capable of crushing said foreign objects.  
     
     
         6 . The device of  claim 1 , wherein the plurality of wire strands includes at least five wire strands.  
     
     
         7 . The device of  claim 1 , further comprising a nosepiece attached to a distal end of said retrieval assembly.  
     
     
         8 . The device of  claim 1 , wherein said plurality of wire strands includes strands made of stainless steel.  
     
     
         9 . The device of  claim 1 , wherein said plurality of wire strands includes strands made of the precursor alloy.  
     
     
         10 . The device of  claim 9 , wherein said superelastic material is Nitinol.  
     
     
         11 . The device of  claim 1 , further comprising a coupling tube attached to a proximal end of said retrieval assembly.  
     
     
         12 . The device of  claim 11 , wherein said coupling tube includes a retaining cannula.  
     
     
         13 . The device of  claim 1 , wherein said cable is preformed by bending said cable beyond a yield point of said precursor alloy.  
     
     
         14 . The device of  claim 13 , wherein said cable is preformed to a basket configuration.  
     
     
         15 . A method of manufacturing a medical retrieval device for retrieving foreign objects from a patient's body, comprising the steps of: 
 constructing a cable including a core wire made of a precursor alloy to a superelastic material and a plurality of wire strands surrounding the core wire; and    forming a retrieval assembly by preforming said cable into a configuration adapted to capture and remove said foreign objects.    
     
     
         16 . The method of  claim 15 , wherein said precursor alloy exhibits a stress-strain curve that is linear extending to a yield point.  
     
     
         17 . The device of  claim 15 , wherein said stress-strain curve has no phase transformation point.  
     
     
         18 . The device of  claim 15 , wherein said stress-strain curve extends to a yield point without passing through a substantially constant stress plateau while strain is varied.  
     
     
         19 . The method of  claim 15 , wherein the plurality of wire strands includes at least five wire strands.  
     
     
         20 . The method of  claim 15 , further comprising the step of attaching a nosepiece to a distal end of said retrieval assembly.  
     
     
         21 . The method of  claim 15 , wherein said plurality of wire strands are made of stainless steel.  
     
     
         22 . The method of  claim 15 , wherein said plurality of wire strands includes strands made of the precursor alloy.  
     
     
         23 . The method of  claim 22 , wherein said superelastic material is Nitinol.  
     
     
         24 . The method of  claim 15 , further comprising the step of attaching a coupling tube to a proximal end of said retrieval assembly.  
     
     
         25 . The method of  claim 24 , wherein said coupling tube includes a retaining cannula.  
     
     
         26 . The method of  claim 15 , wherein preforming said cable includes bending said cable beyond a yield point of said precursor alloy.  
     
     
         27 . The method of  claim 26 , wherein said cable is preformed to a basket configuration.  
     
     
         28 . A medical retrieval device for retrieving foreign objects from a patient's body, comprising: 
 a plurality of cables interconnected to form a retrieval basket, each of said plurality of cables including a core wire and a plurality of wire strands surrounding the core wire,    wherein the core wire and the plurality of wire strands each consist of a precursor alloy to a superelastic material so that an elongation of the core wire corresponds with similar elongation of the plurality of wire strands.    
     
     
         29 . The device of  claim 28 , wherein the basket is capable of repeatedly retrieving the foreign objects without permanent deformation.  
     
     
         30 . The device of  claim 29 , wherein the precursor alloy used for each of the core wire and the plurality of wire strands has a plastic yield point.  
     
     
         31 . A medical retrieval device for retrieving foreign objects from a patient's body, comprising: 
 a plurality of cables interconnected to form a retrieval basket, each of said plurality of cables including a core wire and a plurality of wire strands surrounding said core wire;    wherein the core wire and the plurality of wire strands each consist of a precursor alloy to a superelastic material so that the basket is capable of withstanding a relatively large stress without permanently deforming the basket.    
     
     
         32 . The device of  claim 31 , wherein the basket is capable of withstanding stress associated with dilating a duct during the retrieval of the foreign objects.  
     
     
         33 . The device of  claim 31 , wherein the basket is capable of withstanding a stress associated with a retention of said basket in a retaining cannula.  
     
     
         34 . The device of  claim 31 , wherein the basket is capable of withstanding stress associated with a force required to crush foreign objects.  
     
     
         35 . The device of  claim 34 , wherein the basket is capable of withstanding a force of at least 50 pounds without permanent deformation.  
     
     
         36 . The device of  claim 35 , wherein the basket is capable of repeatedly retrieving the foreign objects without permanent deformation.  
     
     
         37 . The device of  claim 36 , wherein the precursor alloy used for each of the core wire and the surrounding wire strands has a plastic yield point.