Niti-type medical guide wire and method of producing the same

Claim 1

An NiTi-based medical guidewire comprising an NiTi-based alloy wire made of a wire produced by mechanical straightening a cold drawn NiTi-based alloy wire and (1) having a straightness of 20 mm/1.5 m as determined by the suspension method and having a shape and characteristics of the stress-strain curve in a wire tensile test which satisfy the following requirements (2) to (5) and thereby displaying excellent pushability, torque transmission, and reusability as a medical guidewire: (2) a monotonous increase in loading up to a strain of 4% without any yield points or inflection points and no stress-induced martensitic transformation shown at all; (3) high elasticity characteristics over a wide range of strain and an apparent modulus of elasticity of 3000 kgf/mm 2 or more at a strain of 4%; (4) a residual strain after loading up to a strain of 4%, then unloading, of not more than 0.15%; and (5) a stress difference, between loading and unloading, at a strain of 2% after loading up to 4% strain, then unloading, of not more than 15 kgf/mm 2 .

Claim 7

A method of producing an NiTi-based medical guidewire comprising an NiTi-based alloy wire made of a wire produced by mechanical straightening a cold drawn NiTi-based alloy wire and (1) having a straightness of 20 mm/1.5 m as determined by the suspension method and having a shape and characteristics of the stress-strain curve in a wire tensile test which satisfy the following requirements (2) to (5) and thereby displaying excellent pushability, torque transmission, and reusability as a medical guidewire: (2) a monotonous increase in loading up to a strain of 4% without any yield points or inflection points and no stress-induced martensitic transformation shown at all; (3) high elasticity characteristics over a wide range of strain and as apparent modulus of elasticity of 3000 kgf/mm 2 or more at a strain of 4%; (4) a residual strain after loading up to a strain of 4%, then unloading, of not more than 0.15%; and (5) a stress difference, between loading and unloading, at a strain of 2% after loading up to 4% strain, then unloading, of not more than 15 kgf/mm 2 , the method including a step of applying a tension of 18 kgf/mm 2 or more to a cold drawn NiTi-based alloy wire and mechanically straightened it under conditions defined by the relationship of a torsional shear strain (TSS) and a temperature (T) and within a domain defined a polygon of points a-b-c-d-e-f-g-a, where a is a point of TSS=50% at T=100° C., b is a point of TSS=17% at T=100° C., c is a point of TSS=5% at T=150° C., d is a point of TSS=2.5% at T=200° C., e is a point of TSS=2.0% at T=250° C., f is a point of TSS=2.0% at T=275° C., and g is a point of TSS=50% at T=275° C.

Claim 8

A method of producing an NiTi-based medical guidewire comprising an NiTi-based alloy wire made of a wire produced by mechanical straightening a cold drawn NiTi-based alloy wire and (1) having a straightness of 20 mm/1.5 m as determined by the suspension method and having a shape and characteristics of the stress-strain curve in a wire tensile test which satisfy the following requirements (2) to (5) and thereby displaying excellent pushability, torque transmission, and reusability as a medical guidewire: (2) a monotonous increase in loading up to a strain of 4% without any yield points or inflection points and no stress-induced martensitic transformation shown at all; (3) high elasticity characteristics over a wide range of strain and as apparent modulus of elasticity of 3000 kgf/mm 2 or more at a strain of 4%; (4) a residual strain after loading up to a strain of 4%, then unloading, of not more than 0.15%; and (5) a stress difference, between loading and unloading, at a strain of 2% after loading up to 4% strain, then unloading, of not more than 15 kgf/mm 2 , the method including a step of applying a tension of 18 kgf/mm 2 or more to a cold drawn NiTi-based alloy wire and mechanically straightened it under conditions defined by the relationship of a torsional shear strain (TSS) and a temperature (T) and within a domain defined a polygon of points a-b-c-d-e-f-g-a, where a is a point of TSS=50% at T=100° C., b is a point of TSS=17% at T=100° C., c is a point of TSS=5% at T=150° C., d is a point of TSS=2.5% at T=200° C., e is a point of TSS=2.0% at T=250° C., f is a point of TSS=2.0% at T=275° C., and g is a point of TSS=50% at T=275° C.