Implantable medical devices of shape memory alloy

• US 5,876,434 A
• Filed: 08/12/1997
• Issued: 03/02/1999
• Est. Priority Date: 07/15/1997
• Status: Expired due to Term

• Current Assignee: Litana Limited
• Original Assignee: Litana Limited
• Inventors: Flomenblit, Josef, Budigina, Nathaly
• Primary Examiner(s): Milano, Michael J.
• Application Number:
  US08/910,030
• Time in Patent Office: 567 Days
• Field of Search: 623/1, 623/12, 623/16, 433/172, 433/173, 433/225
• US Class Current: 623/1.18
• CPC Class Codes: A61C 2201/007 using shape memory effect
• CPC Class Codes: A61C 8/0033 Expandable implants; Implants with extendable elements
• CPC Class Codes: A61F 2/82 Devices providing patency to, or preventing collapsing of, tubular structures of the body, e.g. stents stent-grafts for tubular structures of the body other than blood vessels A61F2/04; stent-grafts for blood vessels A61F2/07; instruments specially adapted for placement or removal of stents or stent-grafts A61F2/95; for closing wounds, or holding wounds closed A61B17/04 - A61B17/115; dilators A61M29/00
• CPC Class Codes: A61F 2/88 the wire-like elements formed as helical or spiral coils forming a net-like or mesh-like structure A61F2/90
• CPC Class Codes: A61F 2210/0042 using a fluid, e.g. circulating
• CPC Class Codes: A61F 2310/00023 Titanium or titanium-based alloys, e.g. Ti-Ni alloys
• CPC Class Codes: A61L 2400/16 Materials with shape-memory or superelastic properties
• CPC Class Codes: A61L 27/06 Titanium or titanium alloys
• CPC Class Codes: A61L 31/022 Metals or alloys
• CPC Class Codes: C22F 1/006 Resulting in heat recoverable alloys with a memory effect

Abstract

A medical device which comprises a shape memory alloy (SMA) portion which is deformable from an undeformed first configuration assumed by it in an austenitic state of the SMA to a deformed second configuration, whereby the SMA is converted into a strain-induced martensite or partial martensite. This conversion increases the temperature of transformation (A_s) from an initial transformation temperature A_s ° to a temperature A_s '"'"'. When the SMA, once in the second configuration, is heated to a temperature higher than A_s '"'"', it transforms to an at least partial austenite and it transforms towards the undeformed first configuration with a decrease of A_s from A_s '"'"' to A_s °. A_s ° is below body temperature such that when the device is deployed in the body, after placing it in its target location with the SMA portion in the second configuration and then heating it to assume its first configuration, the SMA is stable in the at least partial austenite at body temperature.

Claims

1. A medical device comprising a shape memory alloy (SMA) portion having an austenitic and a martensitic state with a different configuration in each of these states, the SMA being transformable from a martensitic to an austenitic state by an austenitic transformation occurring in a temperature range between A_s, a start temperature of the austenitic transformation, to A_f, a finish temperature of the austenitic transformation, and being transformable from an austenitic state to a martensitic state by a martensitic transformation occurring in a temperature range lower than body temperature between M_s, a start temperature of a martensitic transformation and M_f, a finish temperature of the martensitic transformation, A_s being lower than body temperature in an undeformed state;

the device being characterized in that;

the SMA portion is deformable from an undeformed first configuration assumed by it in the austenitic state to a deformed second configuration, such that the deformation converts it into a strain-induced martensitic or partial martensite with an increase in A_s from its original temperature A_s °

, to a temperature A_s '"'"'; and

in that

when the SMA portion, once in said second configuration, is heated to a temperature higher than A_s '"'"', it transforms to an at least partial austenitic state, which transformation results in a change in configuration from the deformed second configuration towards the undeformed first configuration and in a decrease of A_s from A_s '"'"' to A_s °

, such that the SMA portion is stable in the at least partial austenitic state at the body temperature.

2. A medical device according to claim 1, wherein the shape memory alloy is nitinol.

3. A medical device according to claim 1, wherein at least one portion of the SMA is deformable to a higher strain than the remainder of the SMA such that said at least one portion has an A_s '"'"' temperature t₂ which is greater than the A_s '"'"' temperature of the remainder SMA, t₁.

4. A medical device according to claim 3, to be deployed in the body by heating the SMA to a temperature higher than t₁ but less than t₂, whereby said at least one portion remains in a martensitic state during deployment and the remainder of the SMA transforms to austenitic.

5. A medical device according to claim 1, wherein A_s '"'"' is above body temperature.

6. A medical device according to claim 1, wherein A_s '"'"' is below body temperature and A_f '"'"' is above body temperature.

7. A medical device according to claim 1, being a member of the group consisting of a medical stent, a tooth implant, a bone fracture healing device, a heart implant, a bone plate and an intrauterine contraceptive device.

8. A method of deploying a medical device within the human body, the medical device comprising a shape memory alloy (SMA) portion having an austenitic and a martensitic state with a different configuration in each of these states and having associated M_s, M_f, A_s and A_f temperatures, being start and finish temperatures of the SMA'"'"'s martensitic transformation and the start and finish temperature of the SMA'"'"'s austenitic transformation, respectively, A_s having the value A_s °

which being less than body temperature, when the medical device is in an undeformed state, and M_s being less than A_s, the method comprising the steps of;

heating the SMA to a temperature greater than A_s, thereby placing the SMA in at least a partial austenitic state;

cooling the medical device to a temperature between A_s and M_s ;

deforming the medical device from an undeformed first configuration assumed by it in the austenitic state to a deformed second configuration, said deforming resulting in an increase in A_s from A_s °

to A_s '"'"', the SMA portion being in a martensitic or partial martensitic state after said deforming;

positioning the medical device to a target location within the body, the SMA portion remaining in the martensitic or partial martensitic state during said positioning; and

transforming the SMA portion from the martensitic or partial martensitic state to at least a partial austenitic state by heating it to a temperature higher than A_s '"'"', said transforming resulting in a change in the configuration of the SMA portion from the deformed second configuration towards the undeformed first configuration, the change in configuration resulting in a decrease in A_s from A_s '"'"' to A_s °

such that the medical device is stable in at least a partially austenitic state while deployed in the body.

9. A method according to claim 8, wherein the shape memory alloy is nitinol.

10. A method according to claim 8, wherein at least one portion of the SMA is deformed to a higher strain than the remainder of the SMA during said deforming, such that the at least one portion has an A_s '"'"' temperature t₂, higher than the A_s '"'"' temperature of the remainder of the SMA, t₁.

11. A method according to claim 10, wherein the SMA is heated to a temperature higher than t₁ but less than t₂ such that the at least one portion remain in a martensitic state and the remainder of the SMA transforms to austenite.

12. A method according to claim 11, further comprising heating the SMA to a temperature higher than t₂ after said transforming step, thereby transforming the at least one portion from a martensitic state to an austenitic state.

13. A method according to claim 11, further comprising removing the medical device from the body by gripping the at least one portion of a higher strain which had been transformed during heating to a temperature about t₂.

14. A method of deploying a medical device within the human body, the medical device comprising a shape memory alloy (SMA) portion having an austenitic and a martensitic state with a different configuration in each of these states and having associated M_s, M_f, A_s and A_f temperatures, being start and finish temperatures of the SMA'"'"'s martensitic transformation and the start and finish temperature of the SMA'"'"'s austenitic transformation, respectively, A_s having the value A_s °

, which is less than body temperature, when the medical device is in an undeformed state, the method comprising the steps of;

deforming the medical device by transforming it from an undeformed first configuration assumed by it in the austenitic state to a deformed second configuration, said deforming resulting in an increase in A_s from A_s °

to A_s '"'"', the SMA portion being in a strain-induced martensitic or partial martensitic state after said deforming;

positioning the medical device to a target location within the body, the SMA portion remaining in the strain-induced martensitic or partial martensitic state during said positioning; and

transforming the SMA portion from said martensitic or partial martensitic state to at least a partial austenitic state by heating it to a temperature higher than A_s '"'"', said transforming resulting in a change in the configuration of the SMA portion from the deformed second configuration towards the undeformed first configuration, the change in configuration resulting in a decrease in A_s from A_s '"'"' to A_s °

such that the medical device is stable in at least a partially austenitic state while deployed in the body.