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1. (WO1998049363) MANUFACTURE OF TWO-WAY SHAPE MEMORY DEVICES
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CLAIMS:

1. A process for treating a raw NiTi alloy having an initial form to obtain an alloy with a final form in which it exhibits a two-way shape memory effect (SME) whereby it has an austenitic and a martensitic memory state with associated austenitic and martensitic shapes, respectively, the process comprising the steps of:
(a) testing the raw NiTi-based alloy so as to obtain an estimate of the alloy's internal structure, by measuring the difference between As and Af;
(b) subjecting the raw NiTi alloy to a first heat treatment based on results obtained in (a) so as to yield alloys with an initial internal structure condition having essentially equal random dislocation density;
(c) subjecting the alloy to thermo-mechanical treatment (TMT), comprising plastic deformation of the alloy with simultaneous heating during a dynamic ageing process, to yield a polygonal sub-grain dislocation structure decorated by precipitation;
(d) if the deformation in step (c) did not yield the final form, subjecting the alloy to an intermediate heat treatment to conclude one cycle of sub-grain dislocation structure formation;
(e) repeating steps (c) and (d) until yielding said final form; and

(f) subjecting the alloy to a final heat treatment and to a memorizing treatment.
2. A process according to Claim 1, comprising the steps of:
(a) heating a sample of the raw Niti alloy, to a temperature of about 450-550°C for about 0.5-2.5 hours, and then testing the sample for temperature difference between Aj and Af;
(b) subjecting the raw Niti alloy to a first heat treatment based on the At-As difference obtained in step (a), as follows: where the difference is less than about 7°C, heat treating the alloy to a temperature of about 450-500°C for about 0.5-1.0 hours;
where the difference is more than about 7°C, heat treating the alloy to a temperature of about 510-550°C for about

1.0-2.5 hours;
(c) subjecting the alloy to TMT, comprising plastic deforming the alloy at a strain rate, of less than 5 sec-1, with simultaneous internal heating of a portion of the alloy where the deformation occurs to a temperature of about 250-550°C, the deformation of this step being less than 55%, preferably less than 40%;
(d) if the deformation in step (c) did not yield the final form, subjecting the alloy to an intermediate heat treatment at a temperature of about 500-550°C, for about 0.5-2 hours, and then repeating step (c); and
(e) subjecting the alloy to a final heat treatment and to a memorizing treatment.
3. A process according to Claim 1 or 2, wherein the final heat and memorizing treatment comprises:
(i) forming the alloy into the form to be assumed by it in the austenitic state,
(ii) subject the alloy to a polygonization heat treatment to yield arrangement of random dislocation, then to solution treatment to release non arranged dislocation from precipitation and provide for their rearrangement and then to an ageing treatment;
(iii) deforming the alloy to assume a conditioning form and treating it to memorize said austenitic state, which is the state into which it was formed under (i) above, and a martensitic state, in which the alloy has a martensitic form with an intermediate degree of deformation between the austenitic form and the conditioning form.

4. A process according to Claim 3, wherein the final heat heat and memorizing treatment comprises:
(i) forming the alloy into the form to be assumed by it in the austenitic state;
(ii) subjecting the alloy to a polygonization heat treatment at about

450-550°C for about 0.5-1.5 hours, then to solution treatment at about 600-800°C for about 2-50 mins., and then to an aging treatment at about 350-500° for about 0.15-2.5 hours, and (iii) deforming the alloy to assume a conditioning form, the deforma- tion being less than about 15%, and preferably less than 7%, and being performed at a temperature T, which meets the following formula
T < Ms + 30°C
wherein Ms is a temperature where the martensitic transformation begins, and then heating the alloy to a temperature of or above that in which the austenitic transformation of the alloy ends.

5. A process according to Claim 4, wherein the deformation of the alloy to asume the conditioning form in step (e) (iii), is less than about 7%.

6. A process according to Claim 1 or 2, wherein the final heat and memorizing treatment comprises:
(i) forming the alloy into a form other than the form to be assumed by it in the austenitic state,
(ii) subjecting the alloy first to heat treatment, then to polygonization and solution treatment and then optionally to ageing treatment; (iii) forming the alloy into a form to be assumed by it in the austenitic state,
(iv) subjecting the alloy to a memorizing heat treatment and to an ageing treatment;
whereby the alloy is conditioned to memorize an austenitic state in which it has an austenitic form assumed by it in (iii) above, and a martensitic state, wherein it has a martensitic form being a form with an intermediate degree of deformation between the form in which the alloy was formed in (i) above and the austenitic form.
7. A process according to Claim 6, wherein the final heat and memorizing treatment comprising:
(i) forming the alloy into a form other than the form to be assumed by it in the austenitic state,
(ii) subjecting the alloy to a heat treatment at about 450-500°C for about 0.5-2 hours, then subjecting the alloy to polygonization and solution treatment at about 600-800°C for about 2-50 mins., and then subjecting the alloy to aging treatment at about 350- 500°C for about 0-2 hours,
(iii) forming the alloy into a form to be assumed by it in the austenitic state, and
(iv) subjecting the alloy to a memorizing heat treatment at about 500- 600°C for more than about 10 mins., and then subjecting the alloy to aging treatment at about 350-500°C for about 0.15-2.5 hours.
8. A process according to Claim 4 or 7, comprising:
(a) adjusting the temperature in which the austenitic transformation occurs, by either
an aging treatment at a temperature of about 350-500°C, to increase the temperature in which the austenitic transformation occurs, or
a solution treatment at a temperature of about 510-800°C, to decrease the temperature in which the austenitic transformation occurs.
9. A process according to Claim 2 or 6, wherein the deformation in step (c) is less than 40%.
10. A process according to Claim 4 or 7, wherein the internal heating in step (c) comprises electro-stimulation with a current density of about

500-2000 A/cm2.

11. A process for preparing a medical device comprising a shape memory alloy (SMA) embodying a two-way shape memory effect, comprising treating the SMA in accordance with the process defined in Claim 1 or 4.
12. A process according to Claim 11, wherein said medical device is a stent.
13. A process for the manufacture of a medical stent from a Niti alloy, being a wire 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 Niti wire to a temperature of about 450- 550°C for about 0.5-2.5 hours, and then testing the sample for temperature difference between A and Af, wherein As is a temperature wherein austenitic transformation, namely transformation between the martensitic to the austenitic state, begins, and Af is a temperature where the austenitic transformation ends;
(b) subjecting the wire to a first heat treatment based on the Af-As difference obtained in step (a), as follows:
where the difference is less than about 7°C, heat treating the wire to a temperature of about 450-500°C for about 0.5-1.0 hours;
where the difference is more than about 7°C, heat treating the wire to a temperature of about 510-550°C for about
1.0-2.5 hours;
(c) subjecting the wire to a thermo-mechanical treatment, comprising warm rolling of the wire at a strain rate of less than 5 sec-1, with simultaneous internal heating of a portion of the wire where the deformation occurs, the heating by electro-stimulation at a current density of about 500-2000 A/cm2, 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 500-550°C, for about 0.5-2 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 diameter to be assumed by the stent in the austenitic state,
(ii) subjecting the wire to a polygonization heat treatment at about 450-550°C for about 0.5-1.5 hours, then to solution treatment at about 600-800°C for about 2-50 mins., and then to an aging treatment at about 350-500°C for about 0.15-2.5 hours,
(iii) deforming the wire by winding it on a mandrel having a conditioning diameter, the deformation being less than about 7%, and being performed at a temperature T, which meets the following formula
T < Ms + 30°C
wherein Ms is a temperature where the martensitic transformation begins, and then heating the wire or band to a temperature at or above that in which the austenitic transformation ends;
whereby a stent is obtained with an austenitic state in which it has a diameter assumed in (i) above and a martensitic state in which it has a diameter which is an intermediate diameter between the conditioning diameter and the austenitic diameter. 14. A process for the manufacture of a medical stent from a Niti wire 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 Nitinol wire to a temperature of about 450-550°C for about 0.5-2.5 hours, and then testing the sample for temperature difference between A,, and Af, wherein Aj is a temperature wherein austenitic transformation, namely transformation between the martensitic to the austenitic state, begins, and Af is a temperature where the austenitic transformation ends;
(b) subjecting the wire to a first heat treatment based on the Af-As difference obtained in step (a), as follows:
where the difference is less than about 7°C, heat treating the wire to a temperature of about 450-500°C for about 0.5-1.0 hours;
where the difference is more than about 7°C, heat treating the wire to a temperature of about 510-550°C for about
1.0-2.5 hours;
(c) subjecting the wire to a thermo-mechanical treatment, comprising warm rolling of the wire at a strain rate of less than 5 sec"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/cm2, 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 500-550°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 450-500°C for about 0.5-2 hours, then to polygonization and solution treatment at about 600-800°C for about 2-50 mins., and then to aging treatment at about 350-500°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 500-600°C for more than about 10 mins., and then to aging treatment at about 350-500°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.
15. A process for the manufacture of tooth root implant from a NiTi alloy, exhibiting a two way SME having an austenitic and a martensitic memory states with associated austenitic and martensitic shapes, respectively, the process comprising the steps of:
(a) heating a sample of a NiTi rod to a temperature of about 450- 550°C for about 0.5-2.5 hours, and then testing the sample for temperature difference between As and Af, wherein As is a temperature wherein austenitic transformation, namely transformation between the martensitic to the austenitic state, begins, and Af is a temperture where the austenitic transformation ends;

(b) subjecting the rod to a first heat treatment based on the Af-As difference obtained in step (a), as follows:
where the idfference is less than about 7°C, heat treating the wire to a temperature of about 450-500°C for about 0.5-1.0 hours;

where the difference is more than about 7°C, heat treating the wire to a temperature of about 510-550°C for about 1.0-2.5 hours.
(c) subjecting the rod to a TMT comprising warm drawing with a strain rate less than 5sec_1 with simultaneous heating, the total strain 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 the rod to an intermediate heat treatment at a temperature of about 500-550°C, for about 0.5-2 hours and then repeating step (c);
(e) maching the rod to yield the shape of the implant;
(f) subjecting the implant to the final heat treatment and to a memorising treatment, which comprises:
(i) expanding implant's force segments to a diameter to be assumed by the implant in the austenitic state,
(ii) subjecting the implant to a poligonization heat treatment at about 450-550°C for about 0.5-1.5 hours, then to solution treatment at about 600-800°C for about 2-50 min, and then to an ageing treatment at about 350-500°C for about 0.15- 2.5 hours,
(iii) deforming the implant force segments to a conditioning diameter with a stain less than about 7% and being performed at temperature T < Ms + 30°C, wherein Ms is a temperature where the martensitic transformation begins and then heating the implant to a temperature at or above that in which the austeritic transformation ends;
whereby an implant is obtained with an austenitic state in which it has a diameter assumed in (i) above and a martensitic state in which it has a diameter, which is an intermediate diameter between the conditioning diameter and the austenitic diameter.
16. A process for the manufacture of tube coupling from a NiTi alloy, exhibiting a two sway SME having an austenitic and a martensitic memory stakes with associated austenitic and martensitic shapes, respectively, the process comprising the steps of:
(a) heating a sample of a NiTi rod to a temperature of about 450- 550°C for about 0.5-2.5 hours, and then testing the sample for temperature difference between As and Af, wherein As is a temperature wherein austenitic transformation, namely transformation between the martensitic to the austenitic state, begins, and Af is a temperature where the austenitic transformation ends;

(b) subjecting the rod to a first heat treatment based on the Af-As difference obtained in step (*a), as follows:
where the difference is less than about 7°C, heat treating the wire to a temperature of about 450-500°C for about 0.5-1.0 hours;
where the diference is more than about 7°C, heat treating the wire to a temperature of about 510-550°C for about

1.0-2.5 hours;
(c) subjecting the rod to a TMT comprising warm drawing with a strain rate less than 5sec_1 with simultaneous heating, the total strain 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 the rod to an intermediate heat treatment at a temperature of about 500-550°C, for about 0.5-2 hours and then repeating step (c); and
(e) machining the rod to yield the shape of the implant;
(f) subjecting the implant to the final heat treatment and to a memorising treatment, which comprises:
(i) subjecting the coupling to a poligonizatin heat treatment at bout 450-550°C for about 0.5-1.5 hours, then to solution treatment at about 600-800°C for about 2-50 min and then to an ageing treatment at about 350-500°C for about 0-2.5 hours, (ii) expanding the coupling to a diameter to be assumed by the coupling in the austenitic state,
(iii) subjecting the coupling to a memorizing heat treatment at about 500-600°C for more than about 10 mins, and then to an ageing treatment at about 350-500°C for about 0.15-2.5 hours,
whereby a coupling is obtained having an austenitic with a diameter into which it was formed in step (ii) and a martensitic state in which the oupling has a diameter which is intermediate diameter between the conditioning ID and the diameter of the coupling in the austenitic state.