Ultra-low fractional area coverage flow diverter for treating aneurysms and vascular diseases
A flow diverter is described and fabricated using ultra-thin porous thin-film Nitinol, and is configured for implantation to a treatment site within a vessel for significant reduction in an intra-aneurismal flow velocity and vorticity. Using small size pores in a coverage area of only 10%, a 90% reduction in flow velocity into a pseudo-aneurysm can be achieved, with an almost immediate cessation of flow into an anatomical feature such as aneurysm sac in vivo. The size of the holes can be tailored to be any shape and range in size from 1-400 μm using photolithography and from 5-1000 nm using ebeam lithography.
1. A flow diversion apparatus for diverting blood flow from a treatment region, comprising:
a thin-film stent cover configured to be positioned adjacent the treatment region, the thin-film stent cover comprising a plurality of fenestrations and fabricated with a lift-off process comprising the steps of:
creating a plurality of trenches using photolithography and deep reactive ion etching (DRIE) on a substrate;
depositing a metal sacrificial layer on the substrate;
depositing Nitinol on the metal sacrificial layer by sputtering to form a thin-film Nitinol comprising the fenestrations;
removing the metal sacrificial layer;
crystallizing the thin-film Nitinol to form the thin-film stent cover; and
elongating the thin-film stent cover;
wherein the fenestrations are diamond-shaped subsequent to the elongating of the thin-film stent cover;
wherein the thin-film stent cover is hyper-elastic, such that it is capable of elongating to at least 400% without failure; and
wherein the thin-film stent cover has a surface coverage of less than 20% after the elongation.
2. The flow diversion apparatus of claim 1 , wherein the thin-film stent cover has a thickness between 12 microns and 2 microns.
3. The flow diversion apparatus of claim 1 , wherein the fenestrations have a pore size of 300 microns prior to the elongating and a pore size of 200 microns subsequent to the elongating, or a pore size of 500 microns prior to the elongating and a pore size of 400 microns subsequent the elongating.
4. The flow diversion apparatus of claim 1 , wherein the thin-film stent cover has a surface coverage of between 5% and 20% subsequent to the elongating.
5. The flow diversion apparatus of claim 1 , wherein the thin-film stent cover comprises at least one super-hydrophilic surface.
6. The flow diversion apparatus of claim 5 , wherein the at least one super-hydrophilic surface has a water contact angle of less than 5 degrees.
7. The flow diversion apparatus of claim 5 , wherein the at least one super-hydrophilic surface is configured to deter platelet adhesion at a rate of less than 3 parts per mm 2 when subjected to platelet rich plasma for 3 or more hours.
8. The flow diversion apparatus of claim 1 , further comprising: a collapsible stent; wherein the thin-film stent cover is disposed over the stent.
9. The flow diversion apparatus of claim 1 , wherein the thin-film stent cover is capable of accommodating strain to at least 800% without failure.
10. The flow diversion apparatus of claim 1 , wherein the substrate comprises a Si substrate.
11. The flow diversion apparatus of claim 1 , wherein the depositing of the metal sacrificial layer comprises depositing a Cu sacrificial layer by e-beam evaporation.
12. The flow diversion apparatus of claim 1 , further comprising depositing a SiO 2 barrier layer by plasma-enhanced chemical vapor deposition (PECVD) on the metal sacrificial layer prior to the depositing of the Nitinol.
13. The flow diversion apparatus of claim 1 , wherein the depositing of the Nitinol comprises depositing the Nitinol by a direct current (DC) sputtering process.
14. The flow diversion apparatus of claim 1 , wherein the depositing of the Nitinol comprises a hot-target sputter deposition.
15. The flow diversion apparatus of claim 1 , wherein the crystallizing comprises placing the thin-film Nitinol at 500° C. for 120 minutes.
16. The flow diversion apparatus of claim 1 , wherein each fenestration of the plurality of fenestrations has a pore size of 150 microns prior to elongation.
17. The flow diversion apparatus of claim 1 , wherein the thin-film stent cover is capable of elongating to at least 400% without substantial deformation.