Mechanically Optimized Bypass Grafts for Treating Patients with Peripheral Artery Disease in the Lower Limb

Courtney Keiser Author

04/06/2021 Added

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Courtney's graduate research work developing mechanically optimized vascular bypass grafts for treating patients with PAD

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[00:00:00.780]Hi,
[00:00:01.530]my name is Courtney Keiser and I'm a fifth year PhD student in mechanical and
[00:00:05.190]materials engineering. Today.
[00:00:06.930]I'm going to be giving you a brief overview of my research,
[00:00:09.360]developing mechanically optimized,
[00:00:11.130]vascular bypass graphs for treating patients with peripheral artery disease.
[00:00:15.780]Peripheral artery disease often refers to an obstruction of the femoral
[00:00:19.110]popliteal artery,
[00:00:20.070]which is your main artery in your leg that decreases blood flow to the lower
[00:00:23.430]limbs and affects 8.5 million adult Americans,
[00:00:27.210]which is close to roughly five times.
[00:00:28.860]The population of Nebraska total annual costs for hospitalizations for patients
[00:00:33.840]with pad is an excess of 21 billion per year.
[00:00:37.560]This high cost is attributed to a high operation and high intervention failure
[00:00:41.430]rate, which leads to poor treatment outcomes and a need for reintervention.
[00:00:45.810]The images on the right showed the femoropopliteal artery and the two sites
[00:00:49.740]of PAD occlusion that are clinically seen the most are above and below the knee.
[00:00:55.500]The treatment typically involves surgically implanted conduits called bypass
[00:00:59.400]graphs that redirect the blood flow around the occluded area.
[00:01:02.880]The image on the far right shows the greater saphenous vein being used,
[00:01:06.630]unfortunately, 20 to 45% of patients do not have this fan available.
[00:01:10.710]And its ability to stay open is very low within the first year.
[00:01:16.620]A synthetic graft is the next best solution,
[00:01:18.930]but they fail frequently with recent evidence suggesting that this is because
[00:01:22.470]they're high stiffness promotes kinking and tortuosity during limb flection.
[00:01:27.450]My research objective was to develop a reinforced bypass graft with resistance
[00:01:32.100]to kinking and tortuosity by optimizing the graphs mechanical properties to
[00:01:36.180]mimic young, healthy artery.
[00:01:37.890]The images on the LEFT are CT scans of living young and old subjects that
[00:01:42.390]demonstrates a loss of longitudinal tension in the femoral popliteal artery that
[00:01:46.680]prevents kinking and tortuosity during limb flection.
[00:01:50.190]The images on the right are a 2d angiogram and a 3d CT scan from
[00:01:54.750]patients treated with this stiff commercial PTFE bypass grafts.
[00:02:00.180]The black arrows are showing blood flow disturbances from where the graft is
[00:02:04.320]kinking and the red arrows show the graphs tortuosity these
[00:02:09.210]clinical results demonstrate a need to make grafts that are resistant to
[00:02:14.070]kinking and tortuosity.
[00:02:17.370]Bypass.
[00:02:17.850]Grafts were made by electro spinning technique that uses an electric field to
[00:02:21.600]draw out a charged polymer solution to create a non-woven elastomeric nanofiber fabric
[00:02:25.860]fiber fabric between the layers I worked on developing a polymer reinforcement
[00:02:30.030]material and a deposition technique that would allow for kink resistance and
[00:02:34.020]radial support mechanical properties were optimized by modulating the elastomer
[00:02:38.610]ratios,
[00:02:39.330]wall thickness reinforcement material in pattern and nanofiber orientation to
[00:02:43.140]match those of healthy human arteries.
[00:02:46.020]I used uniaxial tensile tests of human femoropopliteal arteries that were
[00:02:50.040]generously donated that were generously donated from live on Nebraska to guide
[00:02:54.900]the fabrication process here, I've created a database of,
[00:02:59.440]of longitudinal mechanical properties of human arteries from different age
[00:03:02.800]groups to understand the amount of force required to stretch the artery as you
[00:03:06.640]move from left to right, the age bracket increases.
[00:03:09.160]And one can see from the increased slope in the curves that with age or arteries
[00:03:12.970]are stiffening and requiring more force to stretch.
[00:03:17.080]The top left plot shows the force versus stretch characteristics of some of my
[00:03:21.400]better graft prototype. The top right plot shows a commercial.
[00:03:26.170]It shows a commercial reinforced bypass graft to notice in yellow,
[00:03:29.500]which is stiff and requires a lot of force to stretch.
[00:03:32.800]Then there are my bypass grafts that are red,
[00:03:35.230]orange and green that are slowly converging on being similar
[00:03:40.090]to a young, healthy artery, which is denoted in blue.
[00:03:44.080]The bottom of image.
[00:03:45.100]It shows some of my prototypes and their reinforcement patterns and the bottom
[00:03:48.550]right, demonstrates my reinforced grafts ability to stretch longitudinally,
[00:03:54.850]to test my grafts resistance to tortuosity. I designed in 3d printed,
[00:03:59.770]a simulated limb flection device on the far left a commercial bypass graft is
[00:04:04.690]mounted and show significant tortuosity when the hinge has been,
[00:04:08.290]the middle panel shows my bypass graft without any longitudinal tension that is
[00:04:12.790]inherent to the femoral popliteal artery.
[00:04:15.010]And you can see there's mild tortuosity on the far right panel is my bypass
[00:04:19.180]graft with 30% pre-stretch.
[00:04:22.480]And my graft is able to have minimal tortuosity compared to the middle and left.
[00:04:26.950]Panel.
[00:04:29.470]On the bottom image,
[00:04:30.850]you can see that my graft is able to resist kinking compared to the commercial
[00:04:34.180]graft to take these tests. One step further.
[00:04:38.200]I was able to test my grafts resistance to tortuosity in a perfused human
[00:04:42.730]cadaver model.
[00:04:45.100]Computerized tomography images were taken of the limbs in different
[00:04:50.080]postures to measure 3d deformations of the FPA with my bypass graft in a
[00:04:54.250]commercial PTFE graft. The results demonstrated that my graft,
[00:04:58.750]which is shown in green,
[00:05:00.520]was able to accommodate limb flection with minimal tortuosity compared to the
[00:05:04.030]standard supported PTFE graft, which is shown in purple.
[00:05:08.050]The red arrows are pointing to locations of graph tortuosity and actually
[00:05:11.290]coincide very well with what is clinically seen. So in conclusion,
[00:05:16.330]our results suggest bypass graphs with longitudinal compliance tuned to young,
[00:05:20.320]healthy human arteries,
[00:05:21.700]reduce kinking and tortuosity during limb flection and could potentially lead to
[00:05:25.510]better clinical performance for arterial repairs.
[00:05:28.540]And this might spark the development of a next generation vascular bypass graft
[00:05:32.980]current in future work involves compliance between human arteries and bypass
[00:05:37.240]grafts on a flow circuit that I designed in the bottom ripe cyto toxicity
[00:05:41.920]testing and future animal studies.
[00:05:46.090]I'd like to thank my advisor, Dr. Alexey Kamenskiy, my co-advisor Dr.
[00:05:49.750]Jason McTaggart and my mentor, Dr.
[00:05:51.880]Kaspar's Maleckis for all of their help and guidance throughout my research.
[00:05:55.210]And I'd also like to thank my UN MC collaborators, my UNL collaborators,
[00:05:59.200]and my UNL collaborators for all their help.

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Mechanically Optimized Bypass Grafts for Treating Patients with Peripheral Artery Disease in the Lower Limb

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