초록

A process is provided for the manufacture of a two-way shape memory alloy and device. The process of the invention allows a reversible adjustment of the characteristic transformation temperatures, as well as the direction of the two-way shape memory effect, at the final stage of manufacture.

대표청구항 ▼

[ We claim:] [14.] A process for the manufacture of a medical stent from a wire made of a NiTi alloy having a first diameter, the stent having either the form of a wire with a second diameter or a form of a band, the stent exhibiting a two-way shape memory effect (SME) having an austenitic and a mar

[ We claim:] [14.] A process for the manufacture of a medical stent from a wire made of a NiTi alloy having a first diameter, the stent having either the form of a wire with a second diameter or a form of a band, the stent exhibiting a two-way shape memory effect (SME) having an austenitic and a martensitic memory state with associated austenitic and martensitic shapes, respectively, the process comprising the steps of:(a) heating a sample of the wire at a temperature of about 450.degree.-550.degree. C. for about 0.5-2.5 hours, and then testing the sample for temperature difference between A.sub.s and A.sub.f wherein A.sub.s, is a temperature wherein austenitic transformation, namely transformation between the martensitic to the austenitic state, begins, and A.sub.f is a temperature where the austenitic transformation ends;(b) subjecting the wire to a first heat treatment based on the A.sub.f -A.sub.s difference obtained in step (a), as follows:where the difference is less than about 7.degree. C., heat treating the wire at a temperature of about 450.degree.-500C. for about 0.5-1.0 hours;where the difference is more than about 7.degree. C., heat treating the wire at a temperature of about 510.degree.-550.degree. C. for about 1.0-2.5 hours;(c) subjecting the wire to a thermo-mechanical treatment, comprising warm roiling of the wire at a strain rate of less than 5 sec.sup.-1, with simultaneous internal heating of a portion of the wire where the deformation occurs, by electro-stimulation at a current density of about 500-2000 A/cm.sup.2, the deformation in this step being less than 55%;(d) where the deformation in step (c) did not yield a cross-sectional shape of the final form, subjecting wire to an intermediate heat treatment at a temperature of about 500.degree.-550.degree. C., for about 0-2 hours and then repeating step (c); and(e) subjecting the wire to a final heat treatment and to a memorizing treatment, which comprises:(i) winding the wire or band obtained in step (c) on a mandrel having a conditioning diameter being different than the diameter to be assumed by the stent in the austenitic state,(ii) subjecting the wire to a heat treatment at about 450.degree.-500.degree. C. for about 0.5-2 hours, then to polygonization and solution treatment about 600.degree.-800.degree. C. for about 2-50 mins., and then to aging treatment at about 350.degree.-300.degree. C. for about 0-2 hours,(iii) winding the wire or band on a mandrel having a diameter to be assumed by the stent in the austenitic state,(iv) subjecting the alloy to a memorizing heat treatment at about 500.degree.-600.degree. C. for more than about 10 mins., and then to aging treatment at about 350.degree.-500.degree. C. for about 0.15-2.15 hours;whereby a stent is obtained having an austenitic state with a diameter into which the wire was formed in step (iii), and a martensitic state in which the stent has a diameter which is an intermediate diameter between the conditioning diameter and the diameter of the stent in the austenitic state.