A smart guidewire using nitinol materials was designed, manufactured and evaluated the device functionality, such as bending performance, trackability, thermal effects, and thrombogenic response. Two types of nitinol material were partially used to enhance the guidewire trackability. A proposed smart guidewire system uses either one- or two-way shape-memory alloy nitinol (1W-SMA, 2W-SMA) wires (0.015, 381µm nitinol wire). Bending stiffness was measured using in vitro test system, which contains the NI USB-9162 data logger and LabView Signal Express 2010. Temperature distribution and displacement were evaluated via recording a 60Hz movie using a SC325 camera. Hemocompatibility was evaluated by scanning electron microscopy after one heating cycle of nitinol under the Na-citrate porcine whole blood circulation. A smart guidewire showed 30 degrees bending after applying or disconnecting electrical current. While the temperature of the nitinol wires increased more than 70 °C, the surrounding temperature with the commercially available catheter coverings showed below human body temperature showing 30 ̴ 33 °C. There was no significant platelet attachment or blood coagulation when the guidewire operates. Novel smart guidewires have been developed using shape memory alloy nitinol, which may represent a novel alternative to typical commercially available guidewires for interventional procedures.
A proof of concept of low-profile flow sensor has been designed, fabricated, and subsequently tested to demonstrate its feasibility for monitoring hemodynamic changes in cerebral aneurysm. The prototype sensor contains three layers, i.e., a thin polyurethane layer was sandwiched between two sputter-deposited thin film nitinol layers (6μm thick). A novel superhydrophilic surface treatment was used to create hemocompatible surface of thin nitinol electrode layers. A finite element model was conducted using ANSYS Workbench 15.0 Static Structural to optimize the dimensions of flow sensor. A computational fluid dynamics calculations were performed using ANSYS Workbench Fluent to assess the flow velocity patterns within the aneurysm sac. We built a test platform with a z-axis translation stage and an S-beam load cell to compare the capacitance changes of the sensors with different parameters during deformation. Both LCR meter and oscilloscope were used to measure the capacitance and the resonant frequency shifts, respectively. The experimental compression tests demonstrated the linear relationship between the capacitance and applied compression force and decreasing the length, width and increasing the thickness improved the sensor sensitivity. The experimentally measured resonant frequency dropped from 12.7MHz to 12.48MHz, indicating a 0.22MHz shift with 200g ( 2N) compression force while the theoretical resonant frequency shifted 0.35MHz with 50g ( 0.5N). Our recent results demonstrated a feasibility of the low-profile flow sensor for monitoring haemodynamics in cerebral aneurysm region, as well as the efficacy of the use of the surface treated thin film nitinol for the low-profile sensor materials.
A novel hyper-elastic thin film nitinol (HE-TFN) covered stent has been developed to promote aneurysm
quiescence by diminishing flow across the aneurysm's neck. Laboratory aneurysm models were used to assess the
flow changes produced by stents covered with different patterns of HE-TFN. The flow diverters were constructed by
covering Wingspan stents (Boston Scientific) with HE-TFNs (i.e., 82 and 77% porosity) and deployed in both in
vitro wide-neck and fusiform glass aneurysm models. In wide-neck aneurysms, the 82% porous HE-TFN stent
reduced mean flow velocity in the middle of the sac by 86.42±0.5%, while a 77% porous stent reduced the velocity
by 93.44±4.99% (n=3). Local wall shear rates were also significantly reduced by about 98% in this model after
device placement. Tests conducted on the fusiform aneurysm revealed smaller intra-aneurysmal flow velocity
reduction to 48.96±2.9% for 82% porous and to 59.2±6.9% for 77% porous stent, respectively. The wall shear was
reduced by approximately 50% by HE-TFN stents in fusiform models. These results suggest that HE-TFN covered
stents have potential to promote thrombosis in both wide-necked and fusiform aneurysm sacs.
Micro features were created in thin film nitinol using a novel lift-off process to create an endovascular
biomedical device. This manuscript describes fabrication problems with wet etching and introduces an effective way,
named "Lift-off" process to solve undercut and non-uniform pattern issues. Two lift-off processes (i.e., lift-off I and II)
are discussed. Lift-off I process has fracture issues and the film peels off the substrate due to high aspect ratio post structures. Lift-off II process use the film on the top of the Si substrate to fabricate various shape patterns (i.e., ellipse, diamond, circle, square, etc.) in the range of 5~60μm. The lift-off II process shows smooth and well aligned micro patterns in thin film nitinol. In-vivo tests in swine were performed to evaluate the endothelial tissue growth through fabricated micro patterns. Angiography and SEM images show patency of the artery and a uniform endothelial layer covering the device without thromobosis.
Thin film NiTi produced by sputter deposition was used in the design of small vessel grafts intended to
treat small vessel aneurysms. Thin film small vessel grafts were fabricated by "hot-target" DC sputter
deposition. Both stress-strain curves and DSC curves were generated for the film used to fabricate small
vessel grafts. The films used for small vessel grafts had an Af temperatures of approximately 36 degrees
allowing for body activated response from a micro-catheter. Thin film small vessel grafts were tested in
a pulsatile flow loop in vitro. Small vessel grafts could be compressed into and easily delivery in < 3 Fr
catheters. Theoretical frictional and wall drag forces on a thin film NiTi small vessel vascular graft were calculated and the radial force exerted by thin film small vessel grafts was evaluated theoretically and experimentally. <i>In-vivo</i> studies in swine confirmed that thin film NiTi small vessel grafts could be deployed accurately and consistently in the swine vascular system.