Niti-type medical guide wire and method of producing the same
AssigneesFurukawa Techno Material Co., Ltd., Furukawa Electric Co., Ltd.
InventorsHiroshi Horikawa, Kaisuke Shiroyama, Kengo Mitose
Life of this patent
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Abstract
A medical guidewire comprised of an NiTi-based alloy having a high elasticity over a wide range of strain, excellent straightness, and preferable shape and characteristics of a stress-strain curve in a tensile test. The wire is obtained by applying a predetermined tension to a cold drawn NiTi-based alloy wire and mechanical straightening it under conditions of a predetermined torsional shear strain and temperature and shows superior pushability, torque transmission, and reinsertability as a medical guidewire, so is preferable for a catheter guidewire, endoscope guidewire, etc.
Claims9
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/mm2 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/mm2.
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/mm2 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/mm2,
- the method including a step of applying a tension of 18 kgf/mm2 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.
Dependencies are inferred from the claim text.