Thin-film shape memory alloy device and method

• US 20010039449A1
• Filed: 01/24/2001
• Published: 11/08/2001
• Est. Priority Date: 01/24/2000
• Status: Active Grant

• Current Assignee: Stryker European Operations Holdings, LLC (Stryker Corporation)
• Original Assignee: Scimed Life Systems Incorporated (Boston Scientific Corporation)
• Inventors: Gupta, Vikas, Martynov, Valery V., Bose, Arani, Johnson, A. David
• Granted Patent: US 6,533,905 B2
• Time in Patent Office: Days
• US Class Current: 623/1.19
• 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 2/91 made from perforated sheet material or tubes, e.g. perforated by laser cuts or etched holes
• CPC Class Codes: A61F 2/915 with bands having a meander structure, adjacent bands being connected to each other
• CPC Class Codes: A61F 2002/91533 characterised by the phase between adjacent bands
• CPC Class Codes: A61F 2002/9155 Adjacent bands being connected to each other
• CPC Class Codes: C22F 1/006 Resulting in heat recoverable alloys with a memory effect
• CPC Class Codes: C23C 14/0005 Separation of the coating from the substrate
• CPC Class Codes: C23C 14/14 Metallic material, boron or silicon

Abstract

A thin film device, such as an intravascular stent, is disclosed. The device is formed of a seamless expanse of thin-film (i) formed of a sputtered nitinol shape memory alloy, defining, in an austenitic state, an open, interior volume, having a thickness between 0.5-50 microns, having an austenite finish temperature A_f below 37° C.; and demonstrating a stress/strain recovery greater than 3% at 37° C. The expanse can be deformed into a substantially compacted configuration in a martensitic state, and assumes, in its austenitic state, a shape defining such open, interior volume. Also disclosed is a sputtering method for forming the device.

Claims

1. A thin film device comprising a seamless thin-film expanse

(i) formed of a sputtered nitinol shape memory alloy;

(ii) defining, in an austenitic state, an open, interior volume;

(iii) having a thickness between 0.5-100 microns;

(iv) having an austentite finish temperature A_f below 37°

C.; and

(v) demonstrating a stress/strain recovery greater than 3% at 37°

C.;

where the expanse can be deformed into a substantially compacted configuration in a martensitic state, and the expanse assumes, in its austenitic state, a shape defining such open, interior volume.

2. The device of

claim 1

, which further includes a skeletal member to which the expanse is attached, said member having a thickness greater than the thickness of the expanse.

3. The device of

claim 1

, wherein the expanse is in the form of a sock closed at one end, and the skeletal member forms a circumferential or longitudinal rib in the sock.

4. The device of

claim 1

, wherein the stent'"'"'s thin-film expanse is fenestrated.

5. The device of

claim 1

, for use as an intravascular stent, wherein the thin-film expanse is a cylindrical expanse.

6. The device of

claim 5

, wherein the stent'"'"'s thin-film expanse is fenestrated.

7. The device of

claim 1

, wherein the device is a hemispherical thin-film structure.

8. A method of forming the thin-film device of

claim 1

, comprising

placing in a magnetron sputtering device, a mandrel having an exposed, etchable outer layer that corresponds to the open, interior volume of the device to be formed,

providing the sputtering apparatus with a TiNi alloy target composed of between 45-55% each of titanium and nickel,

sputter depositing material from the target adjacent said mandrel under low-pressure, low-oxygen conditions,

during said sputter depositing, moving the mandrel relative to said target, to achieve substantially uniform sputter deposition over the entire exposed surface of the mandrel,

continuing said sputtering until a desired thin-film alloy thickness between 0.5 and 100 microns is formed on the mandrel,

heating the thin-film on the mandrel under annealing conditions, and

releasing the thin-film device so formed from the mandrel.

9. The method of

claim 8

, wherein the mandrel has an etchable surface, and said releasing includes the mandrel and deposited thin-film to an etchant, under conditions effective to dissolve the outer layer of the mandrel, and removing the thin-film device so formed from mandrel.

10. The method of

claim 8

, wherein said target has a composition of between about 48 to 51 atomic percent nickel to 52 to 49 atomic percent titanium.

11. The method of

claim 8

, wherein said sacrificial layer material is selected from the group consisting of chromium, aluminum, and copper, and the etchant is selected from the group consisting of chrome etch, potassium hydroxide, and nitric acid.

12. The method of

claim 8

, wherein said mandrel is rotated during said sputtering step, thus to achieve substantially uniform sputter deposition over the entire exposed surface of the mandrel.

13. The method of

claim 8

wherein the mandrel is coated with a smooth surface such as polyimide before sputtering to ensure a continuous layer of deposited material.

14. The method of

claim 8

, wherein the exposed mandrel surface has a shape selected from the group consisting of (i) cylindrical, (ii) sock-like, and (iii) hemispherical.

15. The method of

claim 8

, wherein said depositing is carried out until a film thickness of between 2 and 50 microns is reached.

16. The method of

claim 8

, which further includes applying structural members to the mandrel, prior to depositing the thin film thereon, thus to form structural members in the formed device.

17. The method of

claim 8

, for use in forming a fenestrated thin-film device, which further includes forming on the annealed thin film, a resist layer containing a pattern of openings, exposing the coated thin film with a solvent under conditions effective to create fenestrations in the thin film corresponding to the pattern of openings.

18. The method of

claim 17

, wherein the fenestrations have dimensions and interfenestration spacings of between about 10-50 microns.