Method of loading a medical device into a delivery system
A method of loading a medical device into a delivery system includes providing a two-stage shape memory alloy at a temperature at which at least a portion of the alloy includes austenite. A stress which is sufficient to form R-phase from at least a portion of the austenite is applied to the medical device at the temperature. A delivery configuration of the medical device is obtained, and the medical device is loaded into a restraining member. Preferably, the delivery configuration of the medical device includes stress-induced R-phase.
1. A method of loading a medical device into a delivery system, the method comprising:
providing a medical device comprising a two-stage shape memory alloy at a temperature at which at least a portion of the alloy is austenite;
applying a stress to the medical device at the temperature, the stress being sufficient to form R-phase from at least a portion of the austenite and not exceeding 200 MPa;
obtaining a delivery configuration of the medical device; and
loading the medical device in the delivery configuration into a restraining member, wherein the delivery configuration comprises stress-induced R-phase.
2. The method of claim 1 wherein the stress applied to the medical device is not sufficient to form martensite from the R-phase.
3. The method of claim 2 wherein the delivery configuration does not include stress-induced martensite.
4. The method of claim 1 wherein the stress-induced R-phase is present in the delivery configuration of the medical device in regions of maximum strain.
5. The method of claim 1 wherein the stress applied to the medical device is sufficient to form martensite from at least a portion of the R-phase.
6. The method of claim 5 wherein the delivery configuration of the medical device further comprises stress-induced martensite.
7. The method of claim 1 wherein the temperature is between about A s and A s +10° C. of the shape memory alloy.
8. The method of claim 1 wherein the temperature is at or above A f of the shape memory alloy, the alloy being fully austenitic at the temperature.
9. The method of claim 1 further comprising, prior to applying the stress to the medical device, processing the shape memory alloy to maximize a difference between a martensite start temperature and an R-phase start temperature of the alloy.
10. The method of claim 1 wherein applying the stress to the medical device comprises radially compressing the medical device and wherein the medical device is a self-expanding stent.
11. A method of loading a medical device into a delivery system, the method comprising:
providing a medical device comprising a two-stage shape memory alloy, the alloy being at a temperature at which the alloy includes a parent phase, the parent phase not being R-phase;
applying a stress of no more than 200 MPa to stress-induce the R-phase from the parent phase in at least a portion of the alloy at the temperature;
obtaining a delivery configuration of the medical device; and
loading the medical device in the delivery configuration into a restraining member, wherein the delivery configuration comprises stress-induced R-phase.
12. The method of claim 11 , wherein the parent phase is austenite.
13. The method of claim 11 , wherein the parent phase is martensite.
14. The method of claim 11 , further comprising stress-inducing martensite from at least a portion of the stress-induced R-phase.
15. The method of claim 11 , wherein the delivery configuration of the medical device further comprises stress-induced martensite.
16. The method of claim 11 further comprising, prior to applying the stress to the medical device, processing the shape memory alloy to maximize a difference between a martensite start temperature and an R-phase start temperature of the alloy.
17. A method of loading a medical device into a delivery system, the method comprising:
providing a medical device comprising a two-stage shape memory alloy at a temperature at which at least a portion of the alloy is austenite;
applying a stress to the medical device at the temperature, the stress being sufficient to form R-phase from at least a portion of the austenite;
obtaining a delivery configuration of the medical device; and
loading the medical device in the delivery configuration into a restraining member, wherein the delivery configuration comprises stress-induced R-phase,
wherein, prior to applying the stress to the medical device, the shape memory alloy is processed to maximize a difference between a martensite start temperature and an R-phase start temperature of the shape memory alloy.
18. A method of loading a medical device into a delivery system, the method comprising:
providing a medical device comprising a two-stage shape memory alloy, the alloy being at a temperature at which the alloy includes a parent phase, the parent phase not being R-phase;
stress-inducing the R-phase from the parent phase in at least a portion of the alloy at the temperature;
obtaining a delivery configuration of the medical device; and
loading the medical device in the delivery configuration into a restraining member, wherein the delivery configuration comprises stress-induced R-phase,
wherein, prior to stress-inducing the R-phase, the shape memory alloy is processed to maximize a difference between a martensite start temperature and an R-phase start temperature of the shape memory alloy.