Mechanically Optimized Bypass Grafts for Treating Patients with Peripheral Artery Disease in the Lower Limb
Courtney's graduate research work developing mechanically optimized vascular bypass grafts for treating patients with PAD
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- [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.
- [00:02:17.850]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
- [00:02:39.330]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.
- [00:04:29.470]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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