Variable strength sheath

[0002] This is based on and claims priority to provisional U.S. patent application Ser. No. 60/138,950 which was filed on Jun. 11, 1999.

[0003] This invention generally relates to medical devices for manipulating matter in a body. More particularly, the invention relates to a medical device including an object-engaging unit, such as a retrieval device or a surgical blade, and a sheath for introduction of the object-engaging unit directly into a body opening or cavity or into a body through an endoscope or a laparoscope channel, for example.

[0004] Medical devices can be used in a body opening, cavity, or tract to manipulate material within the body. Such medical devices may be used through an endoscope or a laparoscope.

[0005] One such medical device has a sheath and an object-engaging unit, such as a basket, that is moveable relative to the sheath from a collapsed state within the sheath to another state in which the unit extends past the distal end of the sheath. Typically, the object-engaging unit is in an operational mode when the object-engaging unit is extended beyond the distal end of the sheath. The sheath typically extends from a handle, located at the proximal end (i.e., the end away from the patient) of the sheath to the object-engaging unit which is located at the distal end of the sheath (i.e., the end near the patient and that goes into the patient).

[0006] One purpose of the sheath is to collapse and release the object-engaging unit by sliding the sheath over (to collapse) or away from (to release) the object-engaging unit, or by moving the object-engaging unit into (to collapse) and out of (to release) the sheath.

[0007] The object-engaging unit is, for example, a grasping force-like assembly, a basket assembly, or any type of tissue and/or object manipulating, capturing, and/or retrieving assembly. In addition, the object-engaging unit can be, for example, a retractor, probe, scissors, or a surgical blade. When the object-engaging unit is enclosed within the sheath, the object-engaging unit is inoperative and in its collapsed or withdrawn state. For example, object-engaging units, such as baskets, assume a collapsed, reduced diameter profile when the basket is enclosed within the distal end of the sheath. When the sheath is retracted relative to the basket or the basket is extended beyond the distal end of the sheath, the basket expands to a relatively larger diameter than when the basket is enclosed and collapsed within the sheath. In the expanded position, the basket is positioned and is operable at least to capture material in the body, such as kidney stones. If the object-engaging unit is, for example, a blade, it would be withdrawn when not needed to cut, and then extended at least partially out beyond the distal end of the sheath to allow cutting with the blade. The sheath also serves other purposes. For example, the sheath serves to encompass and protect the object-engaging unit as it is inserted into the body cavity. The sheath also serves to protect the body cavity from damage that may be introduced by the object-engaging unit itself if it were released, expanded, or extended during passage of the sheath into the body. Also, the sheath must provide sufficient strength and rigidity to allow its insertion into the body while also providing sufficient flexibility to permit the sheath to navigate through the tortuous channels of the body cavity, opening, or tract in which it is inserted.

[0008] It is an object of the invention to provide a medical device comprising a sheath with sufficient flexibility to locate and engage material at a site in a body, such as the renal pelvis. That is, the distal end of the sheath is sufficiently flexible to navigate the turns and curves of the body tract into which the medical device is introduced in order to manipulate target material at the remote body site.

[0009] It is another object of the invention to provide a medical device including a sheath that has sufficient strength at the proximal and distal end portions of the sheath to locate, engage, and retrieve target material at a remote body site, and to actuate an object-engaging unit without distorting or deforming the distal end portion of the sheath.

[0010] It is yet another object of the invention to provide a method of using medical devices including such sheaths to retrieve material at a remote site in a body.

[0011] In one aspect, the invention relates to a device for use in manipulating material at a site within a body. The device includes a handle and a sheath extending from the handle. The sheath includes a lumen, a distal end, a proximal portion, an intermediate portion, and a distal portion. The intermediate portion of the sheath is more flexible than both the proximal portion and the distal portion of the sheath. The device also includes an object-engaging unit. The object-engaging unit and the sheath are moveable relative to each other to achieve a collapsed state of the object-engaging unit in which the object-engaging unit is collapsed within the lumen of the distal portion of the sheath, and another state in which the object-engaging unit extends from the distal end of the sheath.

[0012] In one embodiment of the device according to this aspect of the invention, the outside diameter of the intermediate sheath portion is more narrow than the outside diameter of the proximal and distal sheath portions. The intermediate sheath portion may, in another embodiment, have one or more fewer layers than the proximal and distal sheath portions, and in this case the outside diameter of the intermediate sheath portion may or may not have the same outside diameter as the proximal and distal sheath portions.

[0013] Also, in accordance with this aspect of the invention, the layers of the sheath in all portions of the sheath can comprise various materials, such as fluorinated ethylenepropylene (FEP), polytetrafluoroethylene (PTFE), stainless steel braid, or polyamide. Regardless of the materials or the number of layers of material used to make the proximal, intermediate, and distal sheath portions, the diameter of the sheath lumen can be the same or different in the proximal, intermediate, and distal sheath portions.

[0014] In another aspect, the invention relates to a sheath for a medical device, wherein the sheath comprises a wall extending from a proximal end of the sheath to a distal end of the sheath. The wall defines a lumen extending from the proximal sheath end to the distal sheath end. The wall includes a proximal portion, an intermediate portion, and a distal portion. The intermediate portion is more flexible than the proximal and distal portions. The lumen in the distal portion of the sheath wall is adapted for receiving an object-engaging unit.

[0015] In still other aspects of the invention, methods of manipulating material in a body include inserting into a body (either directly or through some other mechanism such as an endoscope channel), a medical device including a sheath of the type described above. The steps of the methods include moving the object-engaging unit from a collapsed state to another state in which the object-engaging unit is extended beyond the distal end of the sheath, engaging the material in the body, and ultimately withdrawing the device from the body.

[0016] 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.

[0017] FIG. 1 illustrates a stone lodged in a remote body site.

[0018] FIG. 2A illustrates a plan view of an embodiment of a medical device including a sheath according to the invention with an object-engaging unit in a fully extended or open position.

[0019] FIG. 2B illustrates the device illustrated in FIG. 2A with the object-engaging unit in a collapsed or retracted position within the distal end of the sheath.

[0020] FIG. 3A illustrates a plan view of another embodiment of a medical device including a sheath according to the invention with an object-engaging unit in a fully extended, open position.

[0021] FIG. 3B illustrates the device illustrated in FIG. 3A with the object-engaging unit in a collapsed or retracted position within the distal end of the sheath.

[0022] 4A illustrates a plan view of an embodiment of the sheath according to the invention.

[0023] FIG. 4B illustrates a plan view of a sheath when the intermediate sheath portion is flexed.

[0024] FIG. 5A illustrates a cross-section of an embodiment of the distal portion of a sheath according to the invention.

[0025] FIG. 5B illustrates a cross-section of an embodiment of the intermediate portion of the sheath illustrated in FIG. 5A according to the invention.

[0026] FIG. 6A illustrates a cross-section of another embodiment of a proximal portion of the sheath according to the invention.

[0027] FIG. 6B illustrates a cross-section of an embodiment of the intermediate portion of the sheath illustrated in FIG. 6A according to the invention.

[0028] FIG. 7A is a plan view of an embodiment of a sheath according to the invention including an attenuated sheath wall in the intermediate portion of the sheath.

[0029] FIG. 7B illustrates a cross-section of the embodiment of the proximal sheath portion illustrated in FIG. 7A taken at line 7b—7b.

[0030] FIG. 7C illustrates a cross-section of the embodiment of the intermediate sheath portion illustrated in FIG. 7A taken at line 7c—7c.

[0031] FIG. 7D illustrates a cross-section of the embodiment of the distal sheath portion illustrated in FIG. 7A taken at line 7d—7d.

[0032] FIG. 8A shows another embodiment of a sheath according to the invention including an attenuated wall in the intermediate portion of the sheath.

[0033] FIG. 8B shows another embodiment of a sheath according to the invention including an attentuated wall in the intermediate portion of the sheath.

[0034] FIG. 8C shows another embodiment of a sheath according to the invention including an attentuated wall in the intermediate portion of the sheath.

[0035] FIG. 8D shows another embodiment of a sheath according to the invention including an attenuated wall in the intermediate portion of the sheath.

[0036] FIG. 9A illustrates a plan view of the long axis of a sheath according to the invention, the intermediate portion of the sheath including numerous slits in the external wall of the sheath.

[0037] FIG. 9B shows a cross-section in perspective of the embodiment of the intermediate portion of the sheath illustrated in FIG. 9A at 9b—9b.

[0038] FIG. 9C shows a cross-section in perspective of another embodiment of the intermediate portion of a sheath according to the invention including numerous depressions in the external wall of the sheath.

[0039] FIG. 10A illustrates a first step in a method for retrieving material located in a body cavity using a medical device including a sheath according to the invention.

[0040] FIG. 10B illustrates a second step in a method for retrieving material from a body cavity using a medical device including a sheath according to the invention.

[0041] FIG. 10C shows a third step in a method for retrieving material from a body cavity using a medical device including a sheath according to the invention.

[0042] One of the problems encountered when an elongated medical device, such as a retrieval device in a sheath, is used reach a remote location in the body, is negotiating the turns or curves in the body tract to reach the remote body location. As illustrated in FIG. 1, by way of example, a stone 100 lodged in the renal calyx 42 can not be approached via the ureter 40 without encountering at least one curve 102 illustrated by arrow 104. The rigid elongate member of a medical device can not effectively negotiate curves, such as the one illustrated, without causing tissue trauma in order to reach the remote tissue location.

[0043] According to the invention, positioning a flexible sheath portion near the distal end of the sheath, addresses this problem. The embodiments of the invention described below, all have the common feature of a flexible sheath portion positioned near the distal end of the elongate sheath.

[0044] All of the following embodiments of the invention have at least one thing in common, the sheath of the invention has sufficient flexibility in an area adjacent the distal end portion (at the “intermediate portion” of the sheath) to allow engagement of a stone, tissue, or other material, and sufficient strength or rigidity at the most distal end portion of the sheath to enclose the object engaging unit in the inoperative or collapsed state and permit the object-engaging unit to move in and out of the distal end portion of the sheath without the distal end portion of the sheath deforming or failing.

[0045] Referring to FIGS. 2A, 2B, 3A, and 3B, one embodiment of a medical device, according to the invention, includes a handle portion 16, an actuator 20, a sheath 14, a sheath lumen 15, an elongated member 18 that passes within the sheath lumen 15, and an object-engaging unit 10, such as the grasping forceps illustrated in FIGS. 2A and 2B. The handle 16, the sheath 14, and the object-engaging unit 10 are not shown in their correct size or proportion to each other. The sheath 14 typically is much longer and narrower than the handle 16 or the grasping forceps 10 to allow insertion into a body cavity or tract.

[0046] Referring to FIG. 4A, a sheath 14 according to the invention comprises at least three segments: a proximal segment 30, an intermediate segment 32, and a distal segment 34. The proximal segment 30 of the sheath is located nearest to the handle 16. The distal portion of the sheath 34 is that region of the sheath at the distal end of the medical device opposite to the handle 16 where the object-engaging unit 10 is collapsed and from which the object-engaging unit 10 is extended. The intermediate portion 32 of the sheath is positioned distal to the proximal portion 30 of the sheath and proximal to the distal portion 34 of the sheath. The proximal end of the intermediate portion 32 of the sheath is located about 3 inches to 6 inches, preferably 4.75 inches from the distal end 26 of the sheath.

[0047] The object-engaging unit 10 is collapsed within the distal portion of the sheath 34 for direct entry into the body or for entry into the body via the operating channel of an endoscope or laparoscope. The object-engaging unit 10 can be a grasping-type device, as illustrated in FIGS. 2A and 2B. Such grasping type object-engaging units are described in U.S. Ser. No. 09/064,704, the disclosure of which is expressly incorporated by reference herein. Other types of object-engaging units that can be used with the sheath of the invention are retrieval basket-type devices, as illustrated in FIGS. 3A and 3B, such as those described in U.S. Ser. No. 09/065,158, U.S. Ser. No. 09/027,534, U.S. Ser. No. B09/084,135, U.S. Ser. No. 09/296,327, U.S. Ser. No. 09/268,484, and U.S. Ser. No. 09/369,226, the disclosures of which are expressly incorporated by reference herein. Other suitable object-engaging units are forceps, probes, retractors, elevators, blades, needles, and the like.

[0048] Referring now to FIGS. 2A, 2B, 3A and 3B, the sheath 14, according to the invention, has at least one lumen 15 therein, and it extends from the handle 16 to a distal sheath end 26. In one embodiment, an elongated member 18, such as a cable, coil, shaft, guidewire, or mandril wire, extends within the lumen 15 from the actuating mechanism 20 in the handle portion 16 to a base 13 of the object engaging unit 10 where the elongated member 18 is joined to the object-engaging unit base 13. Operation of the actuating mechanism 20 by an operator causes the object-engaging unit 10 to move relative to the sheath 14 between a collapsed state within the distal sheath portion 34, as illustrated in FIG. 3B, to an extended state outside of the distal end 26 of the sheath 14 where the object-engaging unit 10 is open and extending beyond the distal end 26 of the sheath, as shown in FIG. 3A. Alternatively, in another embodiment of the invention, operation of the actuating mechanism 20 by an operator causes the sheath 14 to move relative to the object-engaging unit 10 and the elongated member 18, such that the object-engaging unit 10 is moved between a collapsed position within the distal sheath portion 34, illustrated in FIG. 2B, to an extended position outside of the sheath 14 where the object-engaging unit 10 is open and extending beyond the distal end of the sheath 26 as illustrated in FIG. 2A.

[0049] With the object-engaging unit 10 withdrawn into and collapsed within the distal sheath portion 34, as shown in FIGS. 2B and 3B, the object-engaging unit 10 is inserted into the body directly, or via an endoscope channel, to a remote internal site in the body where the target material is located. The object-engaging unit 10 is then moved relative to the sheath 14 and placed in the extended position illustrated in FIGS. 2A and 3A, such that the object-engaging unit 10, in its operative position, is manipulated by the operator to engage the target material or tissue in the remote body site. The object-engaging unit 10 can then be used to manipulate the material in the body. Following manipulation of the material by the object-engaging unit 10, the object-engaging unit 10 is at least partially withdrawn into the lumen 15 of the distal sheath portion 34, as illustrated in FIG. 3B, by moving the elongated member 18 axially relative to the sheath 14 with the object-engaging unit 10 attached to its distal end, or by moving the sheath 14 axially relative to the object-engaging unit 10, as illustrated in FIG. 2B. The medical device, including the object-engaging unit 10 and the sheath 14, are withdrawn from the body cavity.

[0050] The overall length of the sheath 14, according the invention, can range between 40 inches to 75 inches, preferably about 49.5 inches to 52.5 inches. The proximal portion 30 of the sheath is 35 inches to 55 inches in length, preferably 44.75 inches to 48.25 inches in length, the intermediate portion 32 of the sheath is 3 inches to 6 inches in length, preferably 4.75 inches, and the distal portion 34 of the sheath is 0.5 inches to 1.0 inch in length, preferably 0.75 inches.

[0051] The outside diameter 11 of the sheath, indicated between the arrows 11 in FIG. 4A, may or may not be uniform from the proximal end of the sheath 24 to the distal end of the sheath 26. In general, the outside diameter 11 of the proximal sheath portion 30 may range from 0.0135 inches to 0.0414 outside diameter 11 of the intermediate sheath portion 32 may range from 0.03 inches to 0.04 inches, and the outside diameter 11 of the distal sheath portion 34 may range from 0.0315 inches to 0.0414 inches.

[0052] Sheath flexibility varies along the sheath's long axis from the proximal end 24 of the sheath to the distal end 26 of the sheath. In one embodiment, according to the invention, the intermediate portion 32 of the sheath 14 is more flexible than either the proximal sheath portion 30 or the distal sheath portion 34. That is, the proximal sheath portion 30 and the distal sheath portion 34 are more rigid than the intermediate sheath portion 32. The flexibility of the proximal sheath portion 30 and the distal sheath portion 34 can be the same or can differ. However, the proximal sheath portion 30 and the distal sheath portion 34 are less flexible, i.e., more rigid, than the intermediate sheath portion 32. The intermediate portion 32, as illustrated in FIG. 4B, can be flexed to as much as 170 degrees to 180 degrees

[0053] Enhanced flexibility of the intermediate portion 32 of the sheath 14 is achieved in several ways. Referring to FIGS. 4A, 4B, 5A, 5B, 6A and 6B in one embodiment of a sheath 14, according to the invention, the sheath 14 is constructed by adding layers of material from the luminal side of the sheath wall 19 to the outside 17 of the sheath wall. The wall 12 of the sheath, according to the invention, can include multiple concentric layers of the same or different materials. The intermediate sheath portion 32, like the proximal sheath portion 30 and the distal sheath portion 34, can include multiple concentric layers, however, the intermediate sheath portion 32 has at least one fewer layer or at least one different layer of material than the layers of material in the proximal sheath portion 30 and the distal sheath portion 34.

[0054] For example, as illustrated by a cross-section of distal sheath 34 in FIG. 5A, in one embodiment of the sheath, according to the invention, the distal sheath portion 34 and the proximal sheath portion 30 (not shown) are manufactured from four layers of material including, from inside of the sheath wall 19 to outside of the sheath wall 17, a first layer (a) of polytetrafluoroethylene (PTFE), a second layer (b) of 304 braided stainless steel, a third layer (c) of polyamide, and a fourth layer (d) of fluorinated ethylenepropylene (FEP). Each material is arranged in a concentric layer around the circumference of the sheath wall 12. In the same sheath, the intermediate sheath portion 34, illustrated in FIG. 5B, has one fewer of the layers a-d than the proximal and distal sheath portions. The materials in intermediate sheath portion 32, from the inside 19 of the sheath wall 12 to the outside 17 of the sheath wall, include a first inner layer (a) of PTFE, a second layer (b) of stainless steel braid, no third layer, and a fourth layer (d) of FEP, each material arranged in a concentric layer around the circumference of the sheath wall 12. The relative thickness of each layer, illustrated in FIGS. 5A and 5B, is merely intended to be illustrative and is not limited to that illustrated. The thickness of one or more of the layers of the sheath wall 12 may be greater or lesser than the thickness of one or more of the other layers. Thus, the outer diameter 11 of the intermediate sheath portion 32 may be less than or the same as the outer diameter 11 of proximal sheath portion 30 and distal sheath portion 34. However, the internal diameter 13 of the intermediate sheath portion 32 is the same as the internal diameter 13 of proximal sheath portion 30 and distal sheath portion 34. That is, the diameter of the lumen 15 of the sheath 12 is uniform from the proximal end 24 of the sheath to the distal end 26 of the sheath. By maintaining a constant internal diameter 13 throughout the length of the sheath 14, the object-engaging unit 10 and the elongated member 18 may move in the lumen 15 relative to the sheath 14 without becoming snagged.

[0055] In an alternate embodiment, the proximal sheath portion 30 and the distal sheath portion 34 are manufactured from a different combination of materials. For example, the first or inner layer is FEP, followed by a second layer of stainless steel braid, followed by a third layer of polyamide, and followed by a fourth, outer layer of PTFE. The intermediate sheath portion 32 of this embodiment of the sheath includes a first inner layer (a) of FEP, a second layer (b) of stainless steel braid, no third layer, and a fourth, outer layer (d) of PTFE.

[0056] In yet another embodiment of the sheath of the invention, the proximal sheath portion 30, illustrated in FIG. 6A, and the distal sheath portion 34 each have five layers, each layer made from the same material. In this embodiment of the sheath, the intermediate sheath portion 32, illustrated in FIG. 6B, has four layers of materials identical to the materials used in the five layers of the proximal 30 and distal 34 sheath portions. Other materials and different number of layers are also contemplated by the invention and are not limited to those illustrated in FIGS. 5A, 5B, 6A and 6B. Whatever the combination of materials and numbers of layers, the intermediate sheath portion 32 is always more flexible than the proximal sheath portion 30 and distal sheath portion 34, and the internal diameter 13 of the sheath is uniform from the proximal end 24 of the sheath to the distal end 26 of the sheath.

[0057] In another embodiment of the sheath, according to the invention, a first polymer having a certain characteristic stiffness is used to manufacture the sheath wall in the intermediate sheath portion 32 and a second polymer having a different characteristic stiffness than the first polymer can be used in the proximal sheath portion 30 and the distal sheath portion 34 (not shown). For example, a polymer-metal composition may be used in the intermediate sheath portion 32 whereas a more rigid or stiff type of polymer can be used in the proximal sheath portion 30 and the distal sheath portion 34. In general, any type of material may be used in the intermediate sheath portion 32 that is a suitable material having the appropriate strength, flexibility and biocompatibility characteristics.

[0058] Other materials that can be included in one or more layers of the sheath are PEEK, 100 density or 130 density stainless steel braid.

[0059] Referring now to FIG. 7A, in another embodiment, according to the invention, the thickness of sheath wall 12 in the intermediate portion 32, i.e., the outer diameter 11 of the sheath wall, is less than the thickness of the sheath wall at the proximal portion 32 and the thickness of the sheath wall at the distal sheath portion 34. As illustrated by cross-sections of proximal sheath portion 30 in FIG. 7B, and distal sheath portion 34 in FIG. 7D, the thickness of sheath wall 12 is the same in the proximal sheath portion 30 and distal sheath portion 34. As illustrated by cross-section of intermediate sheath portion 32 in FIG. 7C, the thickness of the intermediate sheath portion 32 is less than either the proximal sheath portion 30 illustrated in FIG. 7B and the distal sheath portion 34 illustrated in FIG. 7D. The inside diameter 13 of the sheath in the intermediate portion 32 of the sheath, illustrated in FIG. 7C, is unchanged relative to the inside diameter 13 of proximal sheath portion 30, illustrated in FIG. 7B, and distal sheath portion 34, illustrated in FIG. 7D. By maintaining a uniform inside diameter 13 from the proximal end 24 of the sheath to the distal end 26 of the sheath, illustrated in FIG. 7A, the object-engaging unit can move smoothly in the lumen 15 of the sheath without risk of snagging in dilated or constricted regions of the inner wall 13 of the sheath caused by the presence of a lumen having non-uniform dimensions

[0060] The transition in wall 12 thickness along the intermediate portion 32 of the sheath is gradual in one embodiment as illustrated in FIG. 7A. Alternatively, the transition in wall thickness of the intermediate sheath portion 32, relative to the wall thickness of proximal sheath portion 30 and distal sheath portion 34, is incremental, i.e., occurs in multiple stages, segments, or steps as illustrated in FIG. 8A. The number of possible incremental steps is without limit. The increments can be non-uniformly distributed along the long axis of intermediate sheath portion 32 as illustrated in FIGS. 8B and 8C. The inside diameter 13 of the sheath wall 12 is uniform in the proximal sheath portion 30, the intermediate sheath portion 32, and the distal sheath portion 34. As a result, the diameter of the sheath lumen 15 is unchanged throughout the length of the sheath from the proximal end 24 to the distal end 26 of the sheath.

[0061] Referring to FIG. 8D, in another embodiment of the sheath of the invention, the external sheath wall 17 of the intermediate sheath portion 32 is thrown into circumferential folds to achieve an accordion-like effect. This accordion-like effect enhances the flexibility of the intermediate sheath portion 32 relative to the rest of the sheath 14. The inner diameter of the sheath in the intermediate sheath portion 32 is unchanged relative to the inner diameter of proximal sheath portion 30 and distal sheath portion 34. The diameter of the lumen 15 of the sheath, therefore, is constant from the proximal end 24 of the sheath to the distal end 26 of the sheath.

[0062] Referring to FIGS. 9A-9C, in another embodiment of the invention, flexibility may be added to the intermediate portion 32 of the sheath by modification of the external sheath wall 17 with slits, grooves, or other depressions. Slits, grooves, or depressions can be distributed completely or partially around the circumference of the sheath wall 12 in the intermediate sheath portion 32 as illustrated in FIG. 9A. As illustrated by cross-section in perspective of intermediate sheath portion 32 in FIG. 9B, the modifications in the external sheath wall 17 of the intermediate sheath portion 32 extend part way through the full thickness of the sheath wall 12 and not through the inner sheath wall 19. Sheath wall modifications, such as slits or grooves, are oriented with their long axis parallel to or perpendicular to the long axis of the sheath.

[0063] As illustrated in FIG. 9C, in yet another embodiment of the sheath of the invention, scattered dimples or other shapes are introduced into the outer sheath wall 17 of the intermediate sheath portion 32. Like the grooves or slits illustrated in FIG. 9B, dimples extend from the outer wall 17 partially into the sheath wall 12 but not through the inner sheath wall 19. Thus, as illustrated in FIGS. 9B and 9C, the inner diameter 13 of the sheath and, therefore, the sheath lumen 15, is uniform throughout the length of the sheath beginning at the proximal end 24 of the sheath, extending through the intermediate portion 32 of the sheath, to the distal end 26 of sheath 14.

[0064] The surface of the sheath 14 from the proximal portion 24 to the distal portion 26 can be made or coated with any suitable material with a low friction coefficient, such as a polymeric material, a polyethylene glycol, a photopolyacrylamide-heparin complex, hyaluronic acid, polyvinylpyrrolidine material, and others. These low-friction materials can be materials included in the composition of the sheath wall during manufacturing or can be applied to the surface of the sheath after the sheath is manufactured.

[0065] The sheath of the invention provides numerous advantages. For example, the flexible intermediate portion 32 of the sheath allows an increase in the deflection capability of the sheath 14. When inserted into a flexible scope, for example, the flexible intermediate portion 32 of the sheath 14 overcomes the rigidity of the distal end 26 of the sheath that is necessary for the proper actuation of the object-engaging unit 10. The flexible intermediate portion 32 coincides and deflects with a bending portion of the flexible scope. The distal portion 34 of the sheath holds and surrounds the object-engaging unit 10 when it is in the collapsed state or partially collapsed state, without radial deformation of the sheath 14. The flexible intermediate portion 32 of the sheath allows more steerability than possible with conventional sheaths.

[0066] In another aspect, the invention relates to a method for manipulating material or tissue in a body, such as a body tract or body canal, with a medical device including a sheath. The sheath, as part of the medical device, may be introduced directly into the body cavity or may be introduced through a channel in an endoscope or laparoscope. Sheaths, according to the invention, provide the requisite rigidity at the proximal sheath portion 30 for effective manipulation by an operator for locating, engaging, and retrieving stones, and the requisite rigidity at the distal sheath portion 34 to enclose the object-engaging unit 10 in the collapsed or partially collapsed state without deformation or distortion of the distal end of the sheath. Sheaths of the invention can be introduced into an endoscope or laparoscope without the need for introducers or other means. The flexible intermediate portion 32 of the sheath of the invention offers an improvement in sheath deflection from about 130 to 140 degrees in prior art devices to 170 to 180 degrees in sheath deflection for the sheath according to the invention. Sheaths of variable strengths, according to the invention, are used with medical retrieval devices or a variety of other medical devices. Also, the sheaths of the invention can be used in urology, endoscopy, laparoscopy, biliary, and lithotripsy procedures as well as a variety of other applications.

[0067] Referring to FIGS. 10A-10C, a method for retrieving material from a body includes inserting into the body a medical device including a sheath according to the invention. The medical device including the sheath according to the invention may be directly introduced into the body or may be introduced via a channel 50 of an endoscope or laparoscope for medical devices as illustrated in FIG. 10A. For example, the endoscope 50 is advanced by an operator via the lumen of the ureter 40 until the distal end of the endoscope 50 enters the body site, such as the renal pelvis 42, where the target material 100 is located. The medical device, including the object-engaging unit 10 collapsed within the distal end portion 34 of the sheath, is passed into the endoscope 50, until the distal end 26 of the sheath approaches the distal end 51 of the endoscope 50. As shown in FIG. 10B, the flexible intermediate portion 32 of the sheath coincides and deflects with the bending portion of the flexible endoscope 50. The object-engaging unit 10 is extended from the distal end 26 of the sheath 12 to manipulate the material or tissue 100 within the remote body site 42. The distal end portion 34 of the sheath is of sufficient strength and rigidity to resist deformation of the sheath as the object-engaging unit 10 is moved relative to the sheath.

[0068] As shown in FIG. 10C, after the material or tissue 100 within the remote body site 42 is manipulated, the object-engaging unit 10 is withdrawn partially or completely into the distal end portion 34 of the sheath either by axial movement of the elongated member 18, attached to the base 13 of the object-engaging unit 10, or by movement of the sheath 12 over the stationary object-engaging unit 10.

[0069] The medical device including the sheath according to the invention can be directly inserted (not shown) into a body cavity without an endoscope or an introducer. The steps are similar to those described above for use of the medical device in an endoscope. The flexible intermediate portion of the sheath 32 deflects against the wall of the body tract as the sheath housing the object-engaging unit is advanced in the body tract. The object-engaging unit extends from the distal end of the sheath in the manner described above for using the medical device in an endoscope. After the material in the body site is manipulated, the object-engaging unit is withdrawn partially or completely into the distal sheath portion. The medical device including the sheath is withdrawn from the body tract.

[0070] Variations, modifications, and other instrumentations of what is described herein will occur to those of ordinary skill in the art without departing from the spirit and 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 20 claims.