SYSTEMS, DEVICES AND METHODS OF MAKING HIGHLY ELASTIC SUTURE NEEDLES FOR MINIMALLY INVASIVE SURGERY

Abstract

An elastic suture needle for passing through a smaller cannula used in minimally invasive surgery includes an elongated body having a proximal end, a distal end, a length extending from the proximal end to the distal end, a top surface extending along the length of the elongated body, and a bottom surface extending along the length of the elongated body. The elongated body has dimensions that are calculated using the equation T/L.sub.N < (2*.sub.σ)/(πE), where T is the thickness of the elongated body, L.sub.N is the length of the neutral axis of the elongated body, σ is the yield strength of the elongated body, and E is the Young’s modulus of the elongated body. The elongated body is made of stainless steels such as martensitic stainless steels, austenitic stainless steels, martensitic-aged (mar-aged) stainless steels, and stainless steels sold under the registered trademark ETHALLOY® Needle Alloy.

Claims

1. An elastic suture needle comprising an elongated body having a proximal end, a distal end, a length extending from the proximal end to the distal end, a top surface extending along the length of said elongated body, and a bottom surface extending along the length of said elongated body, wherein said elongated body has dimensions that are calculated using the equation T/L.sub.N < (2*σ)/(πE), where T is the thickness of said elongated body, L.sub.N is the length of the neutral axis of said elongated body, σ is the yield strength of said elongated body, and E is the Young’s modulus of said elongated body.

2. The elastic suture needle as claimed in claim 1, wherein said elongated body comprises stainless steel.

3. The elastic suture needle as claimed in claim 2, wherein said stainless steel is selected from the group of stainless steels consisting of martensitic stainless steels, austenitic stainless steels, martensitic-aged (mar-aged) stainless steels, and stainless steels sold under the registered trademark ETHALLOY Needle Alloy.

4. The elastic suture needle as claimed in claim 1, further comprising a suture attachment barrel proximal to the proximal end of said elongated body and a tip distal to the distal end of said elongated body.

5. The elastic suture needle as claimed in claim 1, wherein said top surface of said elongated body includes a flat top surface that extends along the length of said elongated body, and wherein said bottom surface of said elongated body include a flat bottom surface that extends along the length of said elongated body.

6. The elastic suture needle as claimed in claim 5, wherein the thickness T of said elongated body is a distance between said flat top surface of said elongated body and said flat bottom surface of said elongated body.

7. The elastic suture needle as claimed in claim 1, wherein said elongated body is curved with said top surface of said elongated body defining a concave aspect of said curved elongated body and said bottom surface defining a convex aspect of said curved elongated body.

8. The elastic suture needle as claimed in claim 1, wherein said elongated body comprises martensitic-aged stainless steel having a yield strength of about 1500-2200 MPa and a Young’s modulus of about 200-205 GPa.

9. An elastic suture needle comprising an elongated stainless steel body having a proximal end, a distal end, a length extending from the proximal end to the distal end, a flat top surface extending along the length of said elongated stainless steel body, and a flat bottom surface extending along the length of said elongated stainless steel body, wherein said elongated body has dimensions that are calculated using the equation T/L.sub.N < (2*σ)/(πE), where T is the thickness defined as a distance from said flat top surface to said flat bottom surface of said elongated stainless steel body, L.sub.N is the length of the neutral axis of said elongated stainless steel body, σ is the yield strength of said elongated stainless steel body, and E is the Young’s modulus of said elongated stainless steel body.

10. The elastic suture needle as claimed in claim 9, wherein said elongated stainless steel body is curved with said flat top surface of said elongated stainless steel body defining a concave aspect of said curved elongated body and said flat bottom surface of said elongated stainless steel body defining a convex aspect of said curved elongated body.

11. The elastic suture needle as claimed in claim 9, wherein said stainless steel is selected from the group of stainless steels consisting of martensitic stainless steels, austenitic stainless steels, martensitic-aged (mar-aged) stainless steels, and stainless steels sold under the registered trademark ETHALLOY Needle Alloy.

12. The elastic suture needle as claimed in claim 9, wherein said elongated body comprises martensitic-aged stainless steel having a yield strength of about 1500-2200 MPa and a Young’s modulus of about 200-205 GPa.

13. The elastic suture needle as claimed in claim 9, wherein said elastic suture needle comprises: a tip located at a distal-most end of said elongated stainless steel body; a suture attachment barrel located at a proximal-most end of said elongated stainless steel body.

14. A method of making an elastic suture needle comprising: obtaining an elongated body having a proximal end, a distal end, a top surface extending between the proximal and distal ends, and a bottom surface extending between the proximal and distal ends, wherein said elongated body has a predetermined yield strength and a predetermined Young’s modulus; using the equation T/L.sub.N < (2*σ)/(πE) for determining a thickness and a length of said elongated body, where T is the thickness of said elongated body that is defined as a distance from said top surface to said bottom surface of said elongated body, L.sub.N is the length of the neutral axis of said elongated body that extends from the proximal end to the distal end of said elongated body, σ is the yield strength of said elongated body, and E is the Young’s modulus of said elongated body.

15. The method as claimed in claim 14, wherein said elongated body comprises stainless steel.

16. The method as claimed in claim 15, wherein said stainless steel is selected from the group of stainless steels consisting of martensitic stainless steels, austenitic stainless steels, martensitic-aged (mar-aged) stainless steels, and stainless steels sold under the registered trademark ETHALLOY Needle Alloy.

17. The method as claimed in claim 14, wherein said top surface of said elongated body includes a flat top surface that extends along the length of said elongated body, and wherein said bottom surface of said elongated body include a flat bottom surface that extends along the length of said elongated body, and wherein the thickness T of said elongated body is a distance between said flat top surface of said elongated body and said flat bottom surface of said elongated body.

18. The method as claimed in claim 14, wherein said elastic suture needle has a curved shape defining a first height H.sub.1.

19. The method as claimed in claim 18, further comprising: obtaining a cannula having a proximal end, a distal end, and a conduit that extends from the proximal end to the distal end of said cannula, wherein said conduit of said cannula has an inner diameter defining a second height H.sub.2 that is less than the first height H.sub.1 of said elastic suture needle; with said elastic suture needle at the first height H.sub.1, positioning said elastic suture needle adjacent the proximal end of said cannula; passing said elastic suture needle through said conduit and from the proximal end to the distal end of said cannula, wherein during the passing step said elastic suture needle flattens out for transforming to a third height H.sub.3 that is less than or equal to the second height H.sub.2 of said conduit; after the passing step, removing said elastic suture needle from the distal end of said cannula whereupon said elastic suture needle transforms to a fourth height H.sub.4 that is greater than the second height H.sub.2 of said conduit.

20. The method as claimed in claim 19, wherein the fourth height H.sub.4 is about 90% of the first height H.sub.1.

21. The method as claimed in claim 20, wherein the fourth height H.sub.4 is about 95% of the first height H.sub.1.

22. The method as claimed in claim 21, wherein said fourth height H.sub.4 is substantially equal to said first height H.sub.1.

Description

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0058] Referring to FIGS. 1A and 1B, in one embodiment, an elastic suture needle 100 preferably includes an elongated body 102 having a proximal end 104 and a distal end 106. In one embodiment, the elongated body 102 of the suture needle 100 is curved. In one embodiment, the suture needle 100 defines a half circle or a semi-circle.

[0059] In one embodiment, the elastic suture needle 100 preferably includes a suture attachment barrel 108 that is adjacent the proximal end 104 of the elongated body 102, which preferably has a suture attachment opening 110 formed in a proximal face thereof. In one embodiment, a distal end of a surgical suture may be inserted into the suture attachment opening 110 of the suture attachment barrel 108 and the suture attachment barrel may be swaged for securing the surgical suture to the proximal end 104 of the elongated body 102 of the elastic suture needle 100.

[0060] In one embodiment, the elastic suture needle 100 preferably includes a tip 112, such as a sharpened or pointed tip, that is integral to the distal end 106 of the elongated body 102 and that preferably defines a leading or distal-most end of the suture needle 100. In one embodiment, the tip 112 is preferably sharpened for piercing tissue to facilitate passing the distal end 106 of the elongated body 102 of the suture needle 100 through tissue during a suturing operation.

[0061] In one embodiment, the elongated body 102 of the elastic suture needle 100 preferably includes a top surface 114 that extends along the inside of the curve of the curved elongated body 102 (i.e., the concave curved surface), and a bottom surface 116 that extends along the outside of the curve of the curved elongated body 102 (i.e., the convexly curved surface). The top and bottom surfaces 114, 116 of the elongated body 102 preferably define the thickness T of the elongated body 102 of the suture needle 100, whereby the axis for measuring the thickness T is perpendicular to the longitudinal axis of the elongated body 102 of the suture needle 100. In one embodiment, the top and bottom surfaces 114, 116 include flat surfaces that extend over the respective top and bottom sides of the elongated body of the suture needle. In other preferred embodiments, the top and bottom surfaces of the elongated body may include concave surfaces, convex surfaces, ribbed surfaces, and combinations of one concave surface and one convex surface, as will be described in more detail herein.

[0062] In one embodiment, the elongated body 102 of the elastic suture needle 100 is not made of a superelastic material, such as Nitinol, but is preferably made of stainless steel such as high strength stainless steel. In one embodiment, an external force (e.g., tension, compression) may be applied to the elastic suture needle to elastically deform the elongated body of the suture needle, and the elongated body of the suture needle will not be plastically deformed by the external force so that the elongated body will spring back to its original shape and/or configuration when the external force is removed.

[0063] Referring to FIG. 1B, in one embodiment, when the elastic suture needle 100 is in its original, half-circle configuration, the elongated body 102 of the elastic suture needle 100 defines a height H.sub.1. As will be described in more detail herein, when external forces are exerted upon the outer surface of the elongated body 102 of the elastic suture needle 100 (e.g., when passing the suture needle through a cannula), the elongated body will preferably flex, bend, straighten, and/or flatten out for transforming into an elongated body having a lower height or profile than the original height H.sub.1.

[0064] Referring to FIGS. 1B and 1B-1, in one embodiment, the elongated body 102 of the elastic suture needle 100 preferably has a length L.sub.N extending along the neutral axis of the elongated body 102 between the proximal end 104 and the distal end 106 (FIG. 1) hereinafter referred to as the neutral length of the suture needle 100. In one embodiment, the elongated body 102 of the elastic suture needle 100 preferably has a top length L.sub.T that extends along the top surface 114 of the elongated body 102 from the proximal end 104 to the distal end 106 of the elongated body, and a bottom length L.sub.B that extends along the bottom surface 116 of the elongated body 102 from the proximal end 104 to the distal end 106 of the elongated body 102.

[0065] In one embodiment, the neutral length L.sub.N, the top length L.sub.T and the bottom length L.sub.B are the distances that extend from the proximal end 104 and the distal end 106 of the elongated body 102, and the extra lengths of the suture needle provided by the suture attachment barrel 108 and the tip 112 are not used to calculate the respective lengths L.sub.N, L.sub.T, and L.sub.B of the elongated body 102 of the suture needle 100.

[0066] In one embodiment, the elongated body of the elastic suture needle may have a bendable region provided thereon, which facilitates changing the shape and/or configuration of the suture needle to fit through a cannula (e.g., a 5 mm cannula), as disclosed in commonly assigned U.S. Pat. Application Ser. No. 16/282,604, filed on Feb. 22, 2019, and U.S. Pat. Application Ser. No. 16/282,652, filed on Feb. 22, 2019, the disclosures of which are hereby incorporated by reference herein.

[0067] Referring to FIGS. 2A and 2B, in one embodiment, a clamping element such as a needle driver 130 may be utilized for securing a suture needle, such as the elastic suture needle 100 shown in FIGS. 1A, 1B and 1B-1, to remove the suture needle from a suture needle package and/or to advance the suture needle through a cannula to a surgical site for performing a suturing operation. In one embodiment, the shape of the elongated body of the elastic suture needle may change as the needle driver 130 advances the suture needle through the cannula. For example, the suture needle may be an elastic suture needle that normally has a half circle shape with a first height. As the needle driver 130 advances the suture needle through a cannula having an inner diameter that is smaller than the first height of the elongated body of the suture needle (e.g., height H.sub.1 shown in FIG. 1B), the inner walls of the cannula may exert an external force upon the elongated body of the suture needle whereupon the elongated body of the suture needle will flatten out or become straighter along at least one segment of the elongated body of the elastic suture needle for transforming to a smaller, second height for fitting through the smaller inner diameter of the cannula. Upon being extracted from the end of the cannula, the inner walls of the cannula no longer exert an external force upon the suture needle, whereupon the elongated body of the elastic suture needle will preferably transform back (e.g., spring back) to its original half circle shape having the first height H.sub.1 (FIG. 1B).

[0068] In one embodiment, the needle driver 130 preferably includes an elongated shaft 132 having a proximal end 134 and a distal end 136 with a clamping assembly 138 that is movable between open and closed positions. In one embodiment, the clamping assembly 138 preferably includes a lower jaw 140 and an opposing upper jaw 142 that is movable between open and closed positions. In one embodiment, with the clamping assembly 138 in the open position, the lower and upper jaws 140, 142 may be guided into alignment with the tip 112 of the suture needle 100 (FIG. 1A). In one embodiment, after the lower and upper jaws are aligned with the tip of the suture needle, the jaws may be moved to the closed position for clamping and/or gripping the distal end 106 (FIG. 1A) of the suture needle with the tip 114 preferably positioned between and surrounded by the opposing lower and upper jaws.

[0069] Referring to FIG. 2B, in one embodiment, the lower jaw 140 may be stationary, rigidly secured, and/or integral to the distal end 136 of the elongated shaft 132 of the needle driver 130 so that the lower jaw 140 is fixed and does not move relative to the distal end 138 of the elongated shaft 132 of the needle driver 130. In one embodiment, the lower jaw 140 preferably includes a substantially flat top surface 144 that is adapted to be aligned with the tip 114 (FIG. 1A) of the suture needle. In one embodiment, the substantially flat top surface 144 of the lower jaw 140 may include a surface roughening such as knurling for enhancing gripping of the distal end of the elastic suture needle when the clamping assembly 138 is in the closed position.

[0070] In one embodiment, the upper jaw 142 of the clamping assembly 138 is desirably pivotally secured to the distal end 136 of the elongated shaft 132 of the needle driver 130 via a pivot 146, which pivotally secures a proximal end of the upper jaw 142 to the distal end 136 of the elongated shaft 132. The upper jaw 142 preferably includes a substantially flat bottom surface 148 that opposes the substantially flat top surface 144 of the lower jaw 140. The substantially flat bottom surface 148 of the upper jaw 142 may include surface roughening such as knurling for gripping the distal end of the elastic suture needle when the clamping assembly 138 is in the closed position.

[0071] Referring to FIGS. 1A and 2B, in one embodiment, when the lower and upper jaws 140, 142 are in the closed position for clamping, gripping and/or securing the distal end 106 of the elongated body 102 of the elastic suture needle, the top surface 144 of the lower jaw 140 engages the bottom surface 116 of the elongated body at the distal end 106 of the suture needle 100, and the bottom surface 148 of the upper jaw 142 preferably engage the top surface 114 of the elongated body 102 at the distal end 106 of the suture needle 100, with the tip 112 of the suture needle being located between the opposing jaws. In one embodiment, when the jaws are closed, the top and bottom surfaces 144, 148 of the respective lower and upper jaws 140, 142 may be spaced away from the tip 112 so that the tip is not marred, bent, damaged, or dulled by the jaws of the clamping assembly. The closed jaws preferably surround the outer perimeter of the tip as the suture needle is passed through a cannula for preventing the tip from scratching or being damaged by the inner wall of the cannula.

[0072] In one embodiment, a suture needle package may hold the elastic suture needle 100, such as the suture needle shown in FIGS. 1A and 1B, so that the tip 112 of the suture needle 100 is pre-positioned at a location that will facilitate aligning the tip 112 between the top and bottom surfaces 144, 148 of the respective lower and upper jaws 140, 142 of the clamping assembly 138 of the needle driver 130.

[0073] Referring to FIG. 3A, in one embodiment, after the clamping assembly 138 of the needle driver 130 has been closed for clamping onto the distal end 106 of the elongated body 102 of the elastic suture needle 100, the needle driver 130 may be utilized for advancing the suture needle 100 through a cannula 160 to position the suture needle at a surgical site for performing a suturing operation. In one embodiment, the cannula 160 preferably has an elongated conduit 162 having an inner diameter that defines a second height H.sub.2. The elongated conduit 162 preferably extends to an opening 164 at a distal end 166 of the cannula 160. The clamping assembly 138 of the needle driver 130, clamped onto the distal end 106 of the elongated body 102 of the suture needle 100, may be advanced toward the distal end of the conduit 162 of the cannula 160 for pulling the elastic suture needle 100 through the cannula. As the suture needle 100 is pulled by the clamping assembly 138 of the needle driver 130 toward the distal end 166 of the cannula 160, the suture needle 100 is required to fit through the smaller conduit 162 having the second height H.sub.2 that is less than the original, first height H.sub.1 (FIG. 1B) of the suture needle 100. Because the suture needle 100 is capable of elastically deforming, the elongated body 102 of the suture needle 100 preferably elastically deforms (e.g., straightens out, becomes flatter) as shown in FIG. 3A. In FIG. 3A, a mid-section 120 of the elongated body 102 of the elastic suture needle 100 straightens or flattens for reducing the overall height of the suture needle to a third height H.sub.3 that is less than the second height H.sub.2 of the conduit 162 of the cannula 160. At the smaller third height H.sub.3, the transformed suture needle may pass through the smaller conduit 162 of the cannula 160. As will be described in more detail herein, the suture needle is designed to be substantially elastically deformed as it passes through the smaller cannula, changing from the first height H.sub.1 to the third height H.sub.3.

[0074] Referring to FIG. 3B, after the elastic suture needle 100 has been removed from the opening 164 at the distal end 166 of the cannula 160, the elastic suture needle 100 springs back to the original curved configuration (e.g., a half circle shape) having the fourth height H.sub.4 that is greater than the second height H.sub.2 of the conduit 162 of the cannula 160. Surgical personnel may utilize the curved suture needle 100 for performing a suturing operation at the surgical site.

[0075] In one embodiment, after being removed from the distal end 166 of the cannula 160, the elastic suture needle 100 preferably springs back to the fourth height H.sub.4 that substantially matches the original, first height H.sub.1 (FIG. 1B) of the suture needle. In one embodiment, the fourth height H.sub.4 is about 90% of the original, first height H.sub.1. In one embodiment, the fourth height H.sub.4 is about 95% of the original, first height H.sub.1. In one embodiment, the fourth height H.sub.1 substantially matches the original, first height H.sub.1.

[0076] Referring to FIG. 3C, in one embodiment, at the conclusion of a suturing operation, the curved suture needle 100 having the fourth height H.sub.4 may be removed from a patient by retracting the suture needle through the cannula 160. In one embodiment, the clamping assembly 138 of the needle driver 130 is again closed for securing the distal end 106 of the elongated body 102 of the curved suture needle 100 between the lower jaw 140 and the upper jaw 142 of the needle driver 130.

[0077] Referring to FIG. 3D, in one embodiment, the needle driver 130 preferably retracts the elastic suture needle 100 through the conduit 162 of the cannula 160. Because the second height H.sub.2 of the conduit of the cannula is smaller than the fourth height H.sub.4 (FIG. 3B) of the suture needle 100, the mid-section 120 of the elongated body 102 of the suture needle 100 preferably straightens or flattens out to the third height H.sub.3 so that the suture needle may be extracted through the conduit 162 of the cannula 160. As the elastic suture needle 100 is withdrawn through the cannula 160, the lower and upper jaws 140, 142 of the needle driver 130 preferably engage the distal end 106 of the elongated body 102 of the suture needle 100 and surround the tip 112 (FIG. 1A) of the suture needle to protect the tip from being damaged as the needle is pulled and/or retracted through the cannula 160.

[0078] In one embodiment, the suture needle is designed to exhibit elasticity for passing through a smaller cannula (e.g., a 5 mm cannula) without being plastically deformed. In one embodiment, the elastic suture needle is made of stainless steel such as high strength stainless steel. In one embodiment, knowing the yield strength and the Young’s modulus for the stainless steel used to make the suture needle, the elongated body of the suture needle may be designed with flat surfaces having thickness and length dimensions that will make the suture needle elastically deformable without being plastically deformed.

[0079] The yield point for a material is the point on a stress-strain curve that indicates the limit of elastic behavior for the material and the beginning of plastic behavior. Yield strength or yield stress is the material property defined as the stress at which a material begins to deform plastically whereas yield point is the point where nonlinear (elastic + plastic) deformation begins. Prior to the yield point the material will deform elastically and will return to its original shape when the applied stress is removed. Once the yield point is passed, however, some fraction of the deformation will be permanent and non-reversible. The yield point determines the limits of performance for mechanical components, since it represents the upper limit to forces that can be applied without permanent deformation.

[0080] The Young’s modulus of a material is one way to measure the modulus of elasticity of a material. A modulus of elasticity is a quantity that measures an object’s resistance to being deformed elastically (i.e., non-permanently) when a stress is applied to it. The modulus of elasticity of an object is defined as the slope of its stress-strain curve in the elastic deformation region. A stiffer material will have a higher modulus of elasticity.

[0081] Specifying how stress and strain are to be measured, including directions, allows for many types of elastic moduli to be defined. Young’s modulus (E) describes tensile elasticity, or the tendency of an object to deform along an axis when opposing forces are applied along that axis. It is defined as the ratio of tensile stress to tensile strain. It is often referred to simply as the elastic modulus.

[0082] In one embodiment, the elongated body of the suture needle is preferably elastically deformable from a half-circle shape to a flatter shape having a straightened section without plastically deforming the elongated body of the suture needle. As a result, when the elastic suture needle is passed through the smaller cannula and is extracted at a surgical site, the elongated body of the suture needle will preferably spring back to its original half circle shape.

[0083] Referring to FIG. 4A, in one embodiment, the suture needle 100 preferably has the curved elongated body 102 that extends from the proximal end 104 to the distal end 106, a suture attachment barrel 108 having a suture attachment opening 110 located at the proximal end 104 of the elongated body 102, and the tip 112 located at the distal-most end of the suture needle. In a first configuration, the elongated body 102 of the elastic suture needle 100 is preferably curved and has the top surface 114 that extends along the concave top side of elongated body 102 and the bottom surface 116 that extends along the convexly curved bottom side of the elongated body 102.

[0084] In one embodiment, the top and bottom surfaces 114, 116 of the curved elongated body 102 preferably define the thickness T (FIG. 5B) of the suture needle 100, whereby the axis for measuring the thickness T is perpendicular to the longitudinal axis of the elongated body 102 of the suture needle 100. In one embodiment, the top and bottom surfaces 114, 116 define flat surfaces that extend longitudinally and laterally over the respective top and bottom sides of the elongated body of the suture needle.

[0085] Referring to FIGS. 4A and 4B, in one embodiment, the elongated body 102 of the elastic suture needle 100 preferably has the neutral length L.sub.N that extends along the center of the elongated body 102 and between the proximal end 104 and the distal end 106 of the elongated body 102, the top length L.sub.T that extends along the top surface 114 of the elongated body 102, and the bottom length L.sub.B that extends along the bottom surface 116 of the elongated body 102. The axis for the neutral length L.sub.N is located between the top surface 114 and the bottom surface 116 of the elongated body 102. The distance between the flat top surface 114 and the flat bottom surface 116 preferably defines the thickness T of the elongated body 102.

[0086] Referring to FIG. 5, in one embodiment, the suture needle 100, made of materials having a known yield strength and a known Young’s modulus, is designed to be elastic so that it can be transformed from the half circle configuration of FIGS. 4A and 4B to the flattened or straightened configuration (mid-section 120) of FIG. 3A without substantially plastically deforming the elongated body 102 of the suture needle. As a result, when external forces are no longer applied to the elongated body 102 of the suture needle, the elongated body will substantially spring back from the straightened configuration of FIGS. 3A and 5 to the original half circle shape shown in FIGS. 4A-4B.

[0087] Referring to FIG. 5, in one embodiment, when the mid-section 120 (FIG. 3A) of the elongated body 102 of the suture needle 100 is straightened for passing through a smaller cannula, tension and compression forces are applied at the respective top and bottom surfaces 114, 116 of the elongated body 102 of the suture needle 100. For the straightened mid-section 120 of the elongated body 102 shown in FIG. 5B, the top surface 114 of the elongated body 102 is under tension. The bottom surface 116 of the elongated body 102 is under compression. The part of the elongated body 102 that extends along the axis that defines the neutral length L.sub.N is under neither tension nor compression. The elastic strain calculation associated with transforming the half circle suture needle (FIGS. 4A-4B) to the straightened suture needle (FIGS. 3A and 5) may be calculated using the equation ε = ΔL/L.sub.N, where ΔL is the change in the top length L.sub.T of the suture needle at the top surface 114 of the elongated body or the change in the bottom length L.sub.B of the suture needle at the bottom surface 116 of the elongated body, and L.sub.N is the neutral length of the elongated body of the suture needle that is mid-way between the top and bottom surfaces 114, 116 of the elongated body.

[0088] For a half circle suture needle, the diameter d of a circle may be calculated using the following equation d = 2*L.sub.N/π, where L.sub.N is the neutral length of the elongated body of the suture needle.

[0089] The strain associated with straightening out the curved needle is calculated using the following equation: ε = [½π(d+½T)-½πd] / (½πd), where ½π(d+½T) is the length at the outside of the suture needle, ½πd is the length L.sub.N of the neutral axis of the elongated body of the suture needle, and T is the thickness of the elongated body of the suture needle that extends from the flat top surface 114 to the flat bottom surface 116 (FIG. 5B) of the elongated body.

[0090] In one embodiment, a suture needle made of high strength stainless steel may be designed to exhibit elasticity and prevent plastic deformation and loss of the original curvature. In one embodiment, the minimum elastic strain that a suture needle is required to exhibit to prevent plastic deformation and loss of its original curvature is calculated using the following equation ε = πT/4L.sub.N, where T is the thickness of the elongated body of the suture needle measured between the top and bottom flat surfaces of the elongated body, and L.sub.N is the neutral length of the elongated body of the suture needle.

[0091] Controlling for engineering properties such as yield strength and Young’s modulus, the maximum amount of stress that may be exerted upon a suture needle while maintaining elasticity and preventing plastic deformation may be calculated using the following equation σ = (πT/4L.sub.N)*E, where σ is the Yield Strength of the material, and E is the Young’s Modulus of the material.

[0092] Rearranging the above equation, a ratio for the maximum thickness T of the elongated body to the neutral length L.sub.N of the elongated body may be calculated using the following equation T/L.sub.N < (2*σ)/(πE), where T is the thickness of the elongated body of the suture needle, L.sub.N is the neutral length of the elongated body of the suture needle, σ is the Yield Strength of the material used to make the suture needle, and E is the Young’s modulus of the material used to make the suture needle.

[0093] Referring to FIG. 6, in one embodiment, the elongated body 102 of an elastic suture needle has a substantially flat top surface 114 and a substantially flat bottom surface 116. The substantially flat top and bottom surfaces 114, 116 define the thickness T of the elongated body 102.

[0094] Referring to FIG. 7, in one embodiment, an elongated body 202 of an elastic suture needle has a convex top surface 214 and a convex bottom surface 216. The thickness T of the elongated body 202 is defined by the distance between the highest part of the convex top surface 214 and the lowest part of the convex bottom surface 216.

[0095] Referring to FIG. 8, in one embodiment, an elongated body 302 of an elastic suture needle has a concave top surface 314 and a concave bottom surface 316. The thickness T of the elongated body 302 is defined by the distance between the highest part of the concave top surface 214 and the lowest part of the concave bottom surface 216.

[0096] Referring to FIG. 9, in one embodiment, an elongated body 402 of an elastic suture needle has a top surface 414 with top ribs 415 and a bottom surface 416 with bottom ribs 425, as disclosed in commonly assigned U.S. Pat. No. 3,160,157 to Chisman, the disclosure of which is hereby incorporated by reference herein. The thickness T of the elongated body 402 is defined by the distance between the outermost part of the top ribs 415 and the outermost part of the bottom ribs 425.

[0097] Referring to FIG. 10, in one embodiment, an elongated body 502 of an elastic suture needle has a concave top surface 514 and a convex bottom surface 516. The thickness T of the elongated body 502 is defined by the distance between the highest part of the concave top surface 514 and the lowest part of the convex bottom surface 516.

[0098] FIG. 11 is a graph that plots the thickness and length dimensions that may be used for making suture needles that will elastically deform but not plastically deform during passage through smaller cannulas used in minimally invasive surgery. Knowing the yield strength and the Young’s modulus of stainless steels used to make the suture needles, the elongated body’s thickness T versus the elongated body’s neutral length L.sub.N may be designed into suture needles to achieve elastic recovery during minimally invasive surgery. For example, a suture needle made of high yield strength ETHALLOY Needle Alloy (2200 MPa) having an elongated body thickness T of <0.25 mm and an elongated body neutral length L.sub.N of 30 mm will achieve complete elastic recovery after passing through a smaller cannula, however, a suture needle made of the same high yield strength ETHALLOY Needle Alloy (2200 MPa) having an elongated body thickness T of 0.51 mm inches and an elongated body neutral length L.sub.N of 30 mm will suffer some partial plastic deformation when passing through the smaller cannula.

[0099] The stainless steels used to make the elastic suture needles disclosed herein may include martensitic stainless steels (420SS), austenitic stainless steels (302SS), and martensitic-aged (mar-aged) stainless steels (455SS).

[0100] Martensitic stainless steels (420SS) can be high-carbon or low-carbon steels built around the Type 420 composition of iron, 12% chromium, and up to 0.4% carbon. Martensitic stainless steel is hardenable by heat treatment (e.g., by quenching, or by quenching and tempering). The alloy composition and the high cooling rate of quenching enable the formation of martensite. Tempered martensite provides steel with good hardness and high toughness. It is often used for making medical devices and tools such as scalpels, razors and suture needles. See https://en.wikipedia.org/wiki/Martensitic_stainless_steel.

[0101] Austenitic stainless steels (302SS) possess austenite as their primary crystalline structure. The austenite crystalline structure is achieved by sufficient additions of the austenite stabilizing elements nickel, manganese and nitrogen. Due to their crystalline structure austenitic steels are not hardenable by heat treatment and are essentially non-magnetic. See https://en.wikipedia.org/wiki/Austenitic_stainless_steel. Nevertheless, exceptionally high strength may be achieved via work hardening especially in the wire drawing process used to produce feedstock for needle manufacturing.

[0102] Martensitic-aged (mar-aged) stainless steels (455SS) are steels that are known for possessing superior strength and toughness without losing malleability. The “aging” portion of the word Mar-aged refers to the extended heat-treatment process. These steels are a special class of low-carbon, ultra-high-strength steels that derive their strength not from carbon, but from precipitation of intermetallic compounds. Typically, the principal alloying element is 7 to 25 wt.% nickel. Secondary alloying elements, which include cobalt, molybdenum and titanium, are added to produce intermetallic precipitates. See https://en.wikipedia.org/wiki/Maraging_steel

[0103] One type of martensitic-aged alloy that was specifically developed for suture needles and that provides levels of strength far exceeding that of alloys previously used for making suture needles is sold under the registered trademark ETHALLOY Needle alloy. The ETHALLOY Needle Alloy is strengthened by a combination of work hardening and thermal processing (precipitation strengthening).

[0104] While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, which is only limited by the scope of the claims that follow. For example, the present invention contemplates that any of the features shown in any of the embodiments described herein, or incorporated by reference herein, may be incorporated with any of the features shown in any of the other embodiments described herein, or incorporated by reference herein, and still fall within the scope of the present invention.