Abstract:
Baskets with atraumatic distal tips allow the capture of material from difficult-to-reach areas of the body, while reducing the risk of tissue damage.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. application Ser. No. 09/756,093, filed Jan. 8, 2001, which is a continuation of U.S. application Ser. No. 09/296,327, filed Apr. 22, 1999, which is based on and claims priority to provisional U.S. patent application Ser. No. 60/082,810 which was filed on Apr. 23, 1998, and U.S. provisional patent application Ser. No. 60/105,448 which was filed on Oct. 23, 1998. 
    
    
     TECHNICAL FIELD 
     The invention relates generally to medical devices for retrieving material from within a body. More particularly, the invention relates to medical retrieval baskets that have atraumatic distal ends that are contoured or tipless both to minimize the chances of damage to tissue during use and to enhance the ability of the basket to capture material (e.g., stones) disposed or lodged in “pockets” or other areas that are difficult to access in the body. 
     BACKGROUND INFORMATION 
     Known stone retrieval devices typically have baskets that are constructed by joining multiple legs together at a base of the basket and at a distal end or tip of the basket such that a “cage” is formed. At the distal tip, the individual legs are joined by soldering, adhesives, etc. such that a protruding tip results. This protrusion or outward projection at the distal end of the basket can poke tissue and cause tissue trauma. In general, the tips or ends of known baskets protrude outward and thus can cause damage by poking or piercing tissue. Also, the protruding tips of known baskets generally do not permit access to or intimate contact with certain areas within the body such as “pockets,” and thus stones residing in such areas are difficult or impossible to retrieve with known baskets. 
     SUMMARY OF THE INVENTION 
     It is an object of the invention to provide a medical retrieval basket that does not have a substantially protruding distal basket end or basket tip. That is, a basket according to the invention is atraumatic and does not have any significant distal protrusion or outward projection that can poke tissue, pierce tissue, or otherwise cause trauma to tissue. 
     It is another object of the invention to provide a medical retrieval basket that permits access to and/or intimate contact with certain areas within the body such as “pockets” where material to be retrieved (e.g., stones) might reside or be lodged, impacted, or embedded. A tipless or contoured tip basket arrangement can access these areas and retrieve material from those areas whereas a conventional basket with a traumatic tip would not be able to do so because of the traumatic protruding tip that prevents intimate contact between the distal end of the basket and body tissue. 
     It is yet another object of the invention to provide a method of using such baskets to retrieve material from within a body. The material can be biological or foreign matter. The material can be, for example, urological stones or any of a variety of other types of material found in the body. 
     A basket according to one aspect of the invention is tipless and thus lacks a protruding end or tip. At least a distal end portion of the basket can be formed from a single piece of material to achieve the desired tipless feature. The one-piece construction of at least the distal end portion of the tipless basket can be achieved by removing the desired profile from a flat sheet of construction material or by using an injection mold process. With this type of single unit, one-piece construction, the basket legs require joining only at the base of the basket where the basket is attached to a cable, coil, wire, etc., that connects the basket to a proximal handle mechanism. This single unit feature of baskets according to the invention can be achieved in a variety of ways including stamping, photoetching, laser cutting, and injection molding. Also, various materials can be used to form the tipless one-piece unit or the entire basket such as metal, polymers, ceramics, powdered metals, thermal plastic composites, etc. Combinations of these or other materials also may be used to manufacture a basket according to the invention. 
     The invention generally relates to a medical retrieval device that comprises a sheath, a handle, and an atraumatic basket. The sheath has a proximal end and a distal end. The handle is located at the proximal end of the sheath. The basket can remove material from a body, and it has a collapsed position where the basket is enclosed within the sheath and an expanded position where the basket extends from the distal end of the sheath. The basket can have three or more legs (e.g., four, five, or six legs). At least a distal end portion of the basket is substantially tipless and defined by a shape or profile which comprises a single continuous unit. In another embodiment of the invention, the atraumatic basket is formed by a plurality of wires, each wire forming a loop with a small protrusion at the very distal end of the basket. 
     In accordance with one aspect of the invention, the atraumatic basket has a distal end portion defined by a single continuous, one-piece unit. The atraumatic basket can include the following features. The distal end portion of the atraumatic basket can be non-perforated or perforated to, for example, allow a guidewire or lithotripsy device (laser) to extend through the sheath and through the end of the basket. The shape of the distal end portion of the atraumatic basket can be formed from, for example, metal, metal alloys, a ceramic material, a powdered metal, or a polymer. The basket legs, each of which has an inner surface and an outer surface, can have at least a portion of their inner surfaces coated with an anti-slip material, textured, or roughened in some manner to enhance the ability of the basket to grip and hold material. The atraumatic basket can be made by one-piece construction forming, as a single continuous one-piece unit, a shape having three or more legs, for example, a y-shape, x-shape, t-shape or star-shape, and then bending the legs of the shape to form at least a distal portion of a three-dimensional basket structure that is useful for retrieving objects. Other shapes such as a double loop may be used to form the distal portion of the basket. Shapes other than the ones described here also may be used to form the distal portion of the basket. The shape can be stamped, etched, and/or cut from a continuous sheet of material. Alternatively, the shape could be achieved by injection molding. 
     In another embodiment of an atraumatic wire basket, the distal ends of the basket wires insert into an inverted cap at the distal basket tip. 
     Another aspect of the invention relates to a method for manufacturing a basket for a medical retrieval device comprising the steps of forming, as a single continuous unit, a shape having three or more legs and bending the legs of the shape to form at least a portion of a three-dimensional basket structure for retrieving objects. The shape can be stamped, etched or cut from a continuous sheet of material. The shape can also be injection molded. 
     Yet another aspect of the invention features a method for retrieving material from a body including the steps of inserting an extractor into a body, the extractor including a basket having three or more legs and wherein at least a distal end portion of the basket is defined by a shape which comprises a single continuous unit, capturing the material within the basket and withdrawing the extractor from the body to remove the material from the body. 
     The foregoing and other objects, aspects, features, and advantages of the invention will become more apparent from the following description and from the claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the drawings, like reference characters generally refer to the same parts throughout the different views. Also, the drawings are not necessarily to scale, emphasis instead generally being placed upon illustrating the principles of the invention. 
         FIG. 1A  illustrates a top view of an X-profile embodiment of a one-piece construction of at least a distal end portion of a medical retrieval basket removed from a single piece of substantially flat material according to the invention. 
         FIG. 1B  illustrates a side view of an embodiment according to the invention of a three-dimensional atraumatic tipless basket formed by bending and shaping the legs of the X-profile illustrated in FIG.  1 A. 
         FIG. 1C  illustrates a side view of an embodiment according to the invention of the X-profile illustrated in FIG.  1 A. 
         FIG. 1D  illustrates an embodiment according to the invention of an end view of the X-profile illustrated in FIG.  1 A. 
         FIG. 1E  illustrates one embodiment of a medical retrieval device with an atraumatic basket according to the invention with the basket in an expanded position. 
         FIG. 1F  illustrates one embodiment of a medical retrieval device with an atraumatic basket according to the invention with the basket in a collapsed position. 
         FIG. 1G  illustrates a side view of one embodiment of the invention of a distal end portion of a basket formed by bending and shaping the legs of the X-profile illustrated in FIG.  1 A. 
         FIG. 1H  illustrates an embodiment of the medical retrieval device according to the invention with a lithotriptic device extending into the basket lumen; 
         FIG. 2A  illustrates a top view of one embodiment of an X-profile, one-piece construction of a distal end portion of the basket of the invention. 
         FIG. 2B  illustrates details of the center of the X-profile illustrated in FIG.  2 A. 
         FIG. 2C  illustrates details of the end of one leg of the X-profile illustrated in FIG.  2 A. 
         FIG. 2D  illustrates embodiments of a cross-section of one of the legs illustrated in FIG.  2 A. 
         FIG. 2E  illustrates another embodiment of a cross-section of one of the legs illustrated in FIG.  2 A. 
         FIG. 2F  illustrates one embodiment of a modification of the end of a basket leg; 
         FIG. 3A  illustrates a top view of a parachute-shaped profile embodiment of a one-piece construction of a medical retrieval basket removed from a single piece of substantially flat material according to the invention. 
         FIG. 3B  illustrates a side view of an embodiment according to the invention of a three-dimensional atraumatic tipless basket formed by bending and shaping the profile of the parachute shape illustrated in FIG.  3 A. 
         FIG. 3C  illustrates the basket of  FIG. 3B  enclosed within a sheath. 
         FIG. 3D  illustrates the basket of  FIG. 3B  extended from the distal end of the sheath. 
         FIG. 4A  illustrates a top view of a web-shaped profile embodiment of a one-piece construction of at least a distal end portion of a medical retrieval basket removed from a single piece of substantially flat material according to the invention. 
         FIG. 4B  illustrates a side view of an embodiment according to the invention of a three-dimensional atraumatic basket formed by bending and shaping the profile of the web-shaped profile illustrated in FIG.  4 A. 
         FIG. 5A  illustrates a top view of a double loop-shaped profile embodiment of a one-piece construction of at least a distal end portion of a medical retrieval basket removed from a single piece of substantially flat material according to the invention. 
         FIG. 5B  illustrates a side view of an embodiment according to the invention of a three-dimensional atraumatic tipless basket formed by bending and shaping the profile of the double-loop shaped profile illustrated in FIG.  5 A. 
         FIG. 6A  is a top view of a stamped profile that can be formed into a basket or a portion of a basket by bending the legs of the shape, in accordance with the invention. 
         FIG. 6B  is an embodiment according to the invention of a three-dimensional tipless basket with a distal end portion constructed from the profile illustrated in FIG.  6 A. 
         FIG. 7A  is an embodiment according to the invention of a three-dimensional tipless basket structure formed from a single continuous piece of material, for example, the stamped shape illustrated in FIG.  6 A. 
         FIG. 7B  is the distal end profile illustrated in  FIG. 6A  including a textured inner surface of one leg. 
         FIG. 8  is a top view of an embodiment according to the invention of another stamped shape that can be formed into a basket or a portion of a basket by bending the legs of the shape, according to the invention. 
         FIG. 9  illustrates an embodiment according to the invention of a basket with an atraumatic spot-welded tip. 
         FIG. 10  illustrates an embodiment according to the invention of a basket with an atraumatic looped tip. 
         FIG. 11A  illustrates a loop of a basket according to the invention. 
         FIG. 11B  illustrates an embodiment of a three-dimensional basket according to the invention formed from a plurality of basket loops illustrated in  FIG. 11A   
         FIG. 11C  illustrates a loop of a basket according to the invention having an atraumatic protrusion with a radius at the distal end. 
         FIG. 11D  illustrates an embodiment of a three-dimensional basket according to the invention formed from a plurality of basket loops illustrated in FIG.  11 C. 
         FIG. 12A  illustrates another embodiment of the basket loop having multiple shoulders illustrated in FIG.  11 C. 
         FIG. 12B  illustrates yet another embodiment of the basket loop illustrated in FIG.  12 A. 
         FIG. 12C  illustrates an embodiment of a three-dimensional basket formed from basket loops having multiple shoulders illustrated in  12 A. 
         FIG. 12D  illustrates an embodiment of a three-dimensional basket formed from basket loops illustrated in FIG.  12 B. 
         FIG. 13A  illustrates an inverted cap embodiment of a tipless basket. 
         FIG. 13B  illustrates the distal end portion of the inverted cap, tipless basket illustrated in  FIG. 13A  before the ends of the basket legs are affixed together at the proximal end of the basket. 
         FIG. 13C  illustrates the details of the inverted cap illustrated in  FIGS. 13A and 13B . 
         FIG. 14  illustrates a metal ring inserted into a polyimide sheath before the metal ring is ground flush with the end of the polyimide sheath. 
     
    
    
     DESCRIPTION 
     All of the following embodiments of the invention generally have at least one thing in common, a basket of a medical retrieval device having a substantially atraumatic tip according to the invention. The basket  10 , shown by way of example in  FIG. 1F , is the type that can be collapsed within a sheath  12  for entry into the body. A medical device or extractor that includes the basket  10  of the invention also includes the sheath  12  and a proximal handle  8 . The handle  8 , sheath  12 , and basket  10  illustrated in  FIGS. 1E  and  1 F are not shown in their correct size or proportion to each other. The size of the entire sheath is dimensioned to fit the requirements of its application in the body. For example, for urological applications, the size of the device is typically 1.7-8.0 Fr. The sheath  12  has at least one lumen  14  therein, may be made from a single material, and extends from the handle  8  to a distal sheath end  16 . An elongated member such as a cable, coil, shaft, guidewire or mandril wire  18  extends within the lumen  14  from an actuating mechanism  4  at the device handle  8  to the base  20  of the basket  10 , where the cable  18  is attached to the basket base  20 . Operation of the actuating mechanism  4  by an operator causes the basket  10  to move in and out of the sheath  12  between a collapsed position within the sheath  12  as illustrated in  FIG. 1F  to an extended position outside of the sheath  12  where the basket  10  is open/expanded and extending beyond the distal end of the sheath  16  as shown in FIG.  1 E. Alternatively, the mechanism  4  can cause movement of the sheath  12  to advance the sheath  12  over the stationary basket  10  and cable  18  combination, to thereby collapse the basket  10  within the sheath  12 , and the mechanism  4  can slide the moveable sheath  12  back to expose the stationary basket  10  and allow it to open/expand. In general, both types of basket/sheath movement configurations and related handle mechanisms are known, and can be seen in existing product designs available from, for example, Boston Scientific Corporation (Natick, Mass.). With the basket collapsed within the sheath  12  as shown in  FIG. 1F , the sheath  12  can be inserted into the body by an operator to a site in the body where the material to be retrieved is located (e.g., a stone in the ureter). By putting the basket  10  into its open/expanded position, as illustrated in  FIG. 1E , the basket  10  dilates the body tract in which it has been placed and can be manipulated by the operator to entrap or capture material within the basket  10 . The basket  10  and/or the sheath  12  can then be moved to cause the legs  11   a ,  11   b ,  11   c ,  11   d  of the basket  10  to close around the material and capture it. The captured material is then withdrawn from the body along with the sheath and the basket that is holding the material. 
     In one aspect, according to the invention, a basket  10  of a device for retrieving biological or foreign material from a body has a plurality of legs, for example, as shown in  FIG. 1B , four legs  11   a ,  11   b ,  11   c ,  11   d . An end-on view of the basket  10  in  FIG. 1D  illustrates a substantially tipless or atraumatic distal end  100 . A small, insubstantial protrusion or depression may remain at the distal tip as a result of the manufacturing process. Such features on the basket tip do not poke, tear, pierce, perforate, bruise or otherwise inflict injury or cause trauma to the tissue and may enhance basket performance. In one embodiment, for example, the legs  11   a ,  11   b ,  11   c ,  11   d  and the atraumatic basket  10  can be cut, etched, stamped or otherwise removed as a single shape or profile from a substantially flat piece of material  101  as illustrated in FIG.  1 A. In another embodiment, referring to  FIGS. 1E ,  1 G and  6 B, just the distal end portion  5  of the basket  10  is removed as a single shape or profile from a single piece of substantially flat material. Alternatively, the basket  10  or distal end portion  5  can be injection molded into the desired shape by, for example, plastic injection molding, metal-injection-molding (MIM) or by compression of metal powders. As illustrated in FIG.  1 A and  FIG. 1C , the starting profile for the basket  10  or the basket end portion  5  can be an X-profile or X-shape. After removal of the X-profile from the flat material, the three-dimensional basket  10  or distal end portion  5  of the basket  10  can be formed by bending and shaping the legs of an X-profile. The starting profile may be asymmetrical. For example, in other embodiments, the starting profile of the basket  10  or the distal end portion  5  can be y-shaped, t-shaped or star-shaped. 
     With continued reference to  FIGS. 1B and 1D , the distal end  100  of the basket  10  is uniform, contoured, and substantially without any protruding surface features. That is, in accordance with the invention, the distal end  100  of the basket  10  is substantially devoid of knobs, protrusions, fasteners, or outward projections. The distal end  100  of the basket  10  may be perforated  20  as illustrated in  FIG. 1G  to permit a guidewire (not shown) to extend through the sheath  12  and out the end of the basket  10  through the perforation  20 . Referring to  FIG. 1H , alternatively, a ram-rod, laser or other lithotriptic device  9  is longitudinally disposed in a channel  200  of sheath  12 . Channel  200  extends through the proximal end  20  of the basket  10 . In operation, a stone  50  is captured in the lumen of the basket  10 . The lithotriptic device is advanced beyond the proximal basket end into the basket until the lithotriptic device approaches the stone  50 . The stone  50  is then fragmented by lithotripsy. The fragmented stones are removed from the body while entrapped within the basket  10 . 
     No adhesive or any other attachment material or device is used at the distal end  100  of the basket  10  to hold the legs together as at least the distal ends of the legs are formed by a profile including distal leg portions extracted from a single piece of sheet-like material as illustrated in  FIGS. 1A and 1C  to form a tipless atraumatic three-dimensional basket as illustrated in FIG.  1 B. The distal end  100  of the basket  10  is substantially atraumatic in that it has no substantial outward projections or protrusions that might cause injury or trauma to tissue and/or that might present an impediment to contacting the distal end  100  of the basket  10  directly and intimately with tissue. 
     In one embodiment, referring to  FIGS. 2A-2E , a medical device of the invention includes a plurality of legs forming the basket  10 . The legs can have various cross-sectional shapes, for example, as shown in  FIGS. 2D and 2E . Other cross-sectional shapes for the legs of the basket  10  include, but are not limited to, a D-shape, a V-shape, a B-shape, rectangular, and cylindrical (not shown). Typically, the length of the legs  11   a ,  11   b ,  11   c ,  11   d  is about 0.5 to 3.5 inches, for example, 1.1 to 1.5 inches, the width of the leg is about 0.005 inches to 0.015 inches and the thickness of the legs is 0.028 inches to 0.045 inches. The ends  1  of the basket legs  11  may be modified by narrowing, enlarging or grooving the end for example, as shown in  FIG. 2F , to ease assembly and/or strengthen the basket when the ends of the basket legs are brought together. 
     Referring to  FIGS. 2A-2C  and  2 E, a typical basket end portion may have the following features. The basket end portion can have four legs, the legs being approximately 90° apart. The leg length d 1  is 1.1 inches to 1.25 inches, leg width d 2  is 0.010 inches to 0.012 inches, leg width d 3  is 0.006 inches to 0.008 inches, and leg thickness d 4  is 0.005±0.0003 to 0.0032±0.003 inches. At the intersection  121  of the four legs, the four corners have a slight radius as shown in FIG.  2 B. The ends  1  of the legs as illustrated in  FIG. 2C  have a full radius. Notches or cut-outs  123  are located 0.100 inches (d 6 ) from the end  1  of the leg and have a radius of 0.003-0.004 inches with a minimum distance (d 5 ) of 0.004 inches between the apex of the notches. The “X” profile illustrated in  FIG. 2A  may be removed from a flat annealed, superelastic, nickel-titanium sheet having a pickled surface and active A f  of 15±5° C. 
     The basket  10  or distal end  100  of the basket  10  can be formed from various materials such as stainless steel, metal alloys, superelastic materials, shape memory materials, powdered metals, ceramics, thermal plastic composites, ceramic composites, polymers, etc. Also, combinations of these and other materials can be used. 
     The atraumatic basket  10  can assume shapes more complex than one with three or more legs running parallel and longitudinally from the distal end of the basket to the basket base. For example, referring to  FIG. 3A , a single-unit hourglass profile  22  can be removed from a single piece of sheet-like material  101  by stamping, etching, or cutting, for example, according to the invention. A three-dimensional basket  10  can be created by folding the single-unit hourglass profile, as illustrated by the arrows in  FIG. 3A , into a substantially parachute-shaped configuration as shown in FIG.  3 B. Heat treatment, cold-forming, or other shaping processes using a ball-shaped die is then performed on the parachute-shaped configuration to shape the profile into a three-dimensional basket  10 . The distal end  100  of this basket  10  is tipless and atraumatic. The proximal end  24  of basket  10  can be joined to a cable  18  within a sheath  12  as illustrated in FIG.  3 C. The basket  10  is moveable relative to the sheath  12  from a collapsed basket position, shown in  FIG. 3C  to an open basket position shown in FIG.  3 D. 
     In another embodiment, the basket can be made by extracting a single unit web-shaped profile  26 , as illustrated in  FIG. 4A , from a single piece of sheet-like material. The web-profile is removed from a single piece of sheet-like material by stamping, etching or cutting, for example. The web-profile is subsequently shaped and molded around a ball shape by heat treatment, cold-forming, or other shaping processes to achieve a basket  10  as illustrated in FIG.  4 B. The distal end  100  of this basket  10  is atraumatic and substantially tipless. The proximal end  24  of basket  10  can be joined to a cable (not shown) and the basket can be moved within the lumen of a sheath relative to the sheath in a manner similar to the basket illustrated in  FIGS. 3C and 3D . 
     Referring to  FIG. 5 , another embodiment of the basket can be made by extracting a single unit double-loop profile  28  from a single piece of material by stamping, etching, or cutting, for example. The double-loop profile  28  is shaped and molded around a ball shape by heat treatment, cold-formed, or by other shaping processes, to form the basket  10  illustrated in FIG.  5 B. The distal end  100  of the basket  10  is substantially tipless and atraumatic. The proximal end  24  of the basket can be joined to a cable (not shown) and the basket can be moved within the lumen of a sheath, relative to the sheath in a manner similar to the basket illustrated in  FIGS. 3C and 3D . 
     To manufacture a basket according to the invention, a single piece of flat material, such as a sheet of metal, or a single piece of material contoured to conform to the basket radius is used to form the distal basket tip. When starting with a single piece of flat material, at least the distal basket tip is defined by a shape or profile that is removed from the single piece of construction material. The profile can be removed from the material by a variety of methods including, for example, stamping, etching, photoetching, or laser cutting as illustrated in  FIG. 1A  or  3 A. The profile removed from the single piece of material is then shaped by heat treatment, cold-forming process or by other processes known in the art to form at least a distal end portion  5  as illustrated, for example, in  FIGS. 1G and 6B  having an atraumatic distal tip, or a three-dimensional basket structure, for example, as illustrated in  FIGS. 1B ,  3 B,  4 B and  5 B having an atraumatic distal tip. Alternatively, the basket legs may be rotated or twisted slightly around their longitudinal axis to achieve a helical basket, for example, as shown in FIG.  1 D. 
     A basket according to the invention also can be formed by injection molding the distal basket portion or desired basket profile. Alternatively, with a metal or plastic injection molding process, the three-dimensional distal basket portion or basket design can be injected into a three-dimensional mold thereby obviating the step of shaping the distal basket portion or basket structure following removal of the profile from a single piece of construction material by molding into a final shape. 
     The basket  10  and basket designs described below are joined at the basket proximal end to the distal end of the elongated member  18  to form a subassembly. The basket/elongated member subassembly is inserted into the sheath  12  and joined to the handle  8  to form the medical retrieval device according to the invention. 
     The “X” profile that is shown in  FIG. 6A , for example, can be replaced by any other shape that lends itself to clinical efficiency and manufacturability and that results in a substantially tipless atraumatic basket. The “X” or other profiles can have a small, atraumatic protrusion or depression at the distal basket tip. Also, the “X” profile or other profile, can be shaped to make a distal end portion  5  of the basket  10 , and leg extensions  3   a ,  3   b ,  3   c ,  3   d  can be added to end-sections  1   a ,  1   b ,  1   c ,  1   d  of legs  11   a ,  11   b ,  11   c ,  11   d  to form all of or a portion of the basket legs  11   a ,  11   b ,  11   c ,  11   d  as shown in FIG.  6 B. Alternatively, the end-sections  1   a ,  1   b ,  1   c ,  1   d  of the basket legs  11   a ,  11   b ,  11   c ,  11   d  of the “X” profile or any other profile can be secured together at the base  20  of the basket  10  illustrated in FIG.  7 A. 
     All or a portion of the inner surface (side toward basket center) of one or more of the basket legs can be treated to enhance the ability of the basket to grasp and hold material to be retrieved. For example, an anti-slip coating, such as a rubberized or plastic coating can be applied to at least a portion of the inner surface of at least one of the basket legs as illustrated on the inner surface  15  of leg  11   b  in FIG.  7 A. The coating can be applied directly to the single piece of sheet-like material from which the basket profile is extracted before basket formation or to the inner surface of the basket legs after basket formation. An enhanced grasping and/or fragmentation capability also can be achieved by adding texture to at least the inner surface of at least one of the basket legs by, for example, creating serrations, teeth, or points on the inner surface(s). This can be achieved by, for example, etching, pitting, bending, stamping or machining the texture/roughness into the inner surface(s) by application of these methods directly to the single piece of sheet-like material from which the basket or basket distal end shape is extracted before basket formation, or directly to the inner surface of the basket legs after basket formation. 
     Referring to  FIGS. 6A ,  7 B, and  8 , according to one embodiment of the invention, a profile stamped from a single piece of sheet-like material has end-sections  1  that are brought together at a basket base  20  to form a three-dimensional basket  10 . Alternatively, as illustrated in  FIGS. 6A and 6B , just the distal end portion  5  of the basket can be formed from the single piece of construction material with the legs of the basket extending from the end-sections  1   a ,  1   b ,  1   c ,  1   d  of the profile and then drawing the end-sections  1   a ,  1   b ,  1   c ,  1   d  down and bringing the end-sections together at the basket base  20  to form the basket  10 . As shown in  FIG. 8 , it is possible to have more than three or four basket legs by forming the basket distal end from, for example, an eight-leg  11   a ,  11   b ,  11   c ,  11   d ,  11   e ,  11   f ,  11   g ,  11   h  star-shape profile  28  extracted as a single unit from a single piece of sheet-like material. The shape forming the distal end portion of the basket may be asymmetrical. 
     Baskets that are atraumatic and tipless may also have each leg  11   a ,  11   b ,  11   c ,  11   d  joined at the distal end  100  of the basket in a variety of ways such as by spot welding the legs at the distal end  100  as illustrated in  FIG. 9  or by looping two or more wires  17   a ,  17   b  together at the distal end  100  as illustrated in FIG.  10 . The wires are looped together by forming a loop in a mid-portion of the first wire  17   a . Second wire  17   b  is passed through the loop of the first wire  17   a . The second wire  17   b  is looped within and is held by the loop of the first wire  17   a.    
     Referring to  FIGS. 11A and 11B , in another embodiment of the invention, a tipless end  130  of the atraumatic basket  10  is constructed by using single wires to form loops  120   a ,  120   b  having legs  11   a ,  11   b ,  11   c ,  11   d  extending from the apex  130   a ,  130   b  of the loops  120   a  and  120   b , respectively, the apex  130   a ,  130   b  positioned at the basket distal end  100 . A plurality of pre-formed wire loops is included in a three-dimensional, atraumatic basket. Wire loops may be formed from plastics, superelastic materials, stainless steel, shape memory metals, ceramic composites, other composites, or other materials and may have any of a variety of cross sectional shapes such as D-shape, B-shape, U-shape, round, half-round, oval, rectangular or ribbon-like. In this embodiment of an atraumatic wire basket, two wire loops  120   a ,  120   b , for example, may be used to form a basket with four legs  11   a ,  11   b ,  11   c ,  11   d  as shown in  FIG. 11A , and three wire loops  120   a ,  120   b ,  120   c  may be used to form a basket with six legs  11   a ,  11   b ,  11   c ,  11   d ,  11   e ,  11   f  as shown in FIG.  11 B. Additional wire loops may be used to form a basket with more than the four or six legs shown. The apex  130  of each wire loop  120  intersects the apex  130  of the other wire loops  120  of the basket  10  at the basket distal end  100 . The wire loops  120  at the basket distal end  100  are free to slide by one another, i.e., they are not affixed, fused, soldered, welded, glued, joined, secured or attached to one another. The advantages of this configuration of the basket is that the basket end  100  is atraumatic and provides flexibility thereby enhancing the ease by which stones are captured. The two end-sections  1 ,  1 ′ of each wire loop are brought together at the basket base  20  and held in place by welding, soldering, ligating, gluing, crimping or any other means known in the art. In one embodiment, the end-sections  1 ,  1 ′ of the wire loops are affixed (not shown) to a cable, coil, shaft, mandril wire or guidewire  18  that runs longitudinally in a sheath  12  as shown in FIG.  1 E and FIG.  1 F. 
     Referring to  FIGS. 11C and 11D , the tipless end  100  of the atraumatic basket can also be constructed by using single pre-formed wires to form modified loops  120 , each modified loop having a pair of legs  11   a ,  11   b  extending from the apex  130  of the loop  120 , the apex  130  positioned at the basket distal end  100 . The apex  130  of a pre-formed wire loop  120  forming pairs of basket legs is modified to stabilize the basket tip. For example, as illustrated in  FIG. 11C , the apex  130  of a wire loop  120  is modified by a protrusion  140  with a radius, such as a semi-circular protrusion. A basket may be formed by a plurality of wire loops  120   a ,  120   b , each wire loop having a small protrusion  140   a ,  140   b  with a radius, as illustrated in FIG.  11 D. Each semi-circular protrusion on the basket wire has a convex surface  142  and a concave surface  144  as illustrated in FIG.  11 C. In this embodiment, the convex surface  142  of the semi-circular protrusion  140  of wire loop  120   a  meets the concave surface  144  of the semi-circular protrusion  140  of the outer wire loop  120   b  where the wires of the basket cross one another at the basket distal tip  100  as illustrated in FIG.  11 D. At the apex  130  where the loops cross one another at the distal end of the basket, the wires forming the loops are not adhered, affixed, fused, soldered, welded, glued or joined to one another. Typically, two or more wires (i.e., loops), each with a semi-circular protrusion, are used to form an atraumatic wire basket. 
     Wire loops  120  may be formed from superelastic materials, stainless steel, shape memory metals, ceramic composites, other composites, or other materials and may have any of a variety of cross sectional shapes such as D-shape, B-shape, U-shape, round, half-round, oval, rectangular, or ribbon-like. In this embodiment of an atraumatic wire basket, for example, two wire loops  120   a ,  120   b  may be used to form a basket with four legs as shown in  FIG. 11C , or three wire loops may be used to form a basket with six legs (not shown), and so on. Additional wire loops may be used to form a basket with more than the four or six legs shown. Referring to  FIG. 11C , the two end-sections  1 ,  1 ′ of each wire loop are brought together at the basket base  20  and held in place by welding, soldering, ligating, gluing, crimping or any other means known in the art. The end-sections  1 ,  1 ′ of the wire loops can be affixed as shown in  FIG. 11D  to a cable, coil, shaft, mandril wire or guidewire  18  that runs longitudinally in a sheath  12  as shown in FIGS.  1 E and  FIG. 1F. A  channel  200  may run through the sheath  12  and the proximal end  20  of the basket  10  to accommodate a ram-rod, laser or other lithotriptic device  9  as shown in FIG.  1 H and described earlier. 
     A basket of the invention having two or more wire loops  120   a ,  120   b  each with semi-circular protrusions  140  at the apex  130  of the loops  120   a ,  120   b , has enhanced basket stability and dilatative strength without substantially compromising basket flexibility. In this embodiment of the invention (FIGS.  11 C and  11 D), the wires are unlikely to slide by one another at the distal tip. The semi-circular protrusions also help to reduce the stress on the basket legs while closing the basket. 
     The legs of an atraumatic wire basket  10  illustrated in  FIGS. 11A-11D  and  FIGS. 12A-12D  may be gently curved or may have a plurality of angular bends. In one embodiment, illustrated in  FIG. 12A , each of the legs  11   a ,  11   b  of a loop  120   a  have five angular bends,  17   a ,  17   a ′,  17   a ″,  17   a ″′,  17   a ″″ forming at least two shoulders  15 ′ and  15 ″ on each leg  11   a ,  11   b  of the wire loop  120 . A three-dimensional basket shape formed by two loops  120   a ,  120   b  of the type illustrated in  FIG. 12A  is shown in FIG.  12 B.  FIG. 12A  illustrates a wire loop  120  configuration where all of the angles  17  of the loop are obtuse. A three-dimensional basket shape formed by two loops  120   a ,  120   b  of the type illustrated in  FIG. 12A  is shown in FIG.  12 C. An infinite number of obtuse angles in both legs of the wire loop results in a smoothly curved loop as illustrated in  FIG. 12B. A  largely oval or round, atraumatic three-dimensional basket shape  10  formed by two basket loops  120   a ,  120   b  of the type illustrated in  FIG. 12B  is shown in FIG.  12 D. The legs  11   a ,  11   b ,  11   c ,  11   d  of the baskets illustrated in  FIGS. 11B ,  11 D,  12 C and  12 D may be pre-formed, and their cross-section may be B-shaped, D-shaped, U-shaped, round, half-round, oval, rectangular, ribbon-like, or a variety of other cross-sectional shapes such as those shown in  FIGS. 2D and 2E . 
     In yet another embodiment of an atraumatic wire basket illustrated in  FIG. 13A , the distal ends  3   a ,  3   b ,  3   c ,  3   d  of the basket wires  3  insert into a cap  160  with a core  170  at the basket tip  100  as shown in FIG.  13 C. The distal ends  3   a ,  3   b ,  3   c ,  3   d  of the wires are affixed to the cap  160  by soldering, gluing or any means known in the art. The wires emerging from the cap are bent and then drawn down proximally as indicated by the arrows in  FIG. 13B  to form basket legs  11   a ,  11   b ,  11   c ,  11   d . The end-sections of the legs  1   a ,  1   b ,  1   c ,  1   d  are gathered together at the basket base  20  to form an atraumatic wire basket  10  as shown in FIG.  13 A. The end-sections  1   a ,  1   b ,  1   c ,  1   d  can be joined to a cable, shaft or coil (not shown). 
     In some embodiments of the invention, the sheath  12  of the medical retrieval device is manufactured from polyimide, PTFE, composites or similar materials. In order to prevent the distal end  16  of a polyimide sheath  12  from splitting, a metal ring  180 , as illustrated in  FIG. 14 , is inserted into the lumen  14  of the distal end  16  of a polyimide sheath  12 . The metal ring  180  is flush with the end  16  of the polyimide sheath or may protrude slightly beyond the end of the sheath as illustrated in FIG.  14 . 
     In yet another aspect, the invention relates to a method for retrieving material from a body such as a body tract or body canal. Material (e.g., biological or foreign) can be retrieved from a body by using a tipless basket where at least a distal portion of the basket is defined by a shape which comprises a single unit or by using an atraumatic wire loop basket, each basket wire forming a loop with a distal atraumatic protrusion. The basket of the retrieval device has a tipless or an atraumatic distal end and thus allows the capture of material that is located in pockets or other difficult-to-access areas within the body. Because the distal basket end is atraumatic, it can make intimate contact with the surface of tissue, even the walls or lining of a pocket-type area, and allows the retrieval of stones or other materials that are unrecoverable with conventional tipped baskets that can cause tissue trauma and are limited, by the existence of the protruding tip, in how close the basket can approach the tissue. A method for retrieving material from a body includes inserting a retrieval device with an atraumatic basket into the body, moving the tipless basket into the extended position, maneuvering the basket via one or more actuators on the proximal handle (which is located outside of the body) of the retrieval device until the material (e.g., stone) is entrapped within the three-dimensional basket structure, and capturing the material within the basket by moving the basket relative to the sheath to close the basket legs around the material. With the material so gripped or held by the basket, the basket can be withdrawn from the body to remove the material from the body. Before the basket is withdrawn from the body with the captured material, the material can be broken apart by, for example, laser energy or lithotripsy. Mechanisms for breaking up the material before its removal from the body can be part of the retrieval device or can be separate tools/devices that are also inserted into the body and utilized at the appropriate time in the stone removal procedure. The material that can be captured with tipless baskets according to the invention includes a thrombus, embolus, foreign body, calculus, or a stone, such as a kidney stone, a ureteral stone, a urinary bladder stone, a gall bladder stone, a stone within the biliary tree, tumor, polyp or foreign body. 
     Variations, modifications, and other implementations of what is described herein will occur to those of ordinary skill in the art without departing from the spirit and the scope of the invention as claimed. Accordingly, the invention is to be defined not by the preceding illustrative description but instead by the spirit and scope of the following claims.