Faculty advisor: Robert TranquilloThis research was supported by the Undergraduate Research Opportunities Program (UROP)

Patel, Puja

University of Minnesota Digital Conservancy

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Evaluation of Leaflet Washout in Vein Valves
Puja Patel
Tranquillo Laboratory, Department of Biomedical Engineering
University of Minnesota - Twin Cities
Background and Goals
Background:
• Professor Tranquillo’s Lab is developing engineered tissue 
vein valves, composed of two leaflets that function at low 
pressures.
• During development, testing must be done in order to 
determine if vein valves are ready for implantation.
• Washout testing can be performed by putting a valve in a 
closed flow loop, injecting dye behind the leaflets, and cycling 
fluid through the flow loop while measuring the amount of time 
it takes for the dye to washout from behind the leaflets 
(Tanner, 2013).
• Washout testing is mainly used to determine if all the fluid 
behind the leaflets washes out at a given flow rate. 
• Washout testing is also applicable because of the threat of 
leaflet fusion to side walls of the vein. When blood flow is 
stagnant for long periods the valve can remain open, leading 
to clotting and thus fusion to the walls 
Goals:
• Determine an optimal valve design using washout testing, by 
creating various vein valves and conducting washout testing 
on each of them.
• Determine if shorter leaflets are viable and do not have a 
detrimental effect on the valves’ efficiency.
Materials/Methods
Washout Testing Methods
Method 1: Dye injection during cyclic flow
• Pulse duplicator was kept on, so the valve was opening and 
closing while injecting dye
• Washout time: time from when injection stopped to when the 
color of the chamber remained the same (the dye washed out 
to the fullest extent possible) 
• The time to peak intensity: time from when injection stopped 
to when the chamber showed the most intense color (visually 
determined)
• The injection time: time from when injection started to when 
no more dye was visibly added
Method 2: Dye injection prior to cyclic flow
• Injection of the dye before the pulse duplicator was turned on
• Washout time: time from the opening of the valve to when the 
color in the chamber of the pulse duplicator system remained 
constant
• The time to peak intensity: time from the opening of the valve 
to when the chamber showed the most intense color
Note: Measured times were converted to cycles using time for one 
cycle of opening and closing of the valve. 
Data Analysis
Data Analysis
T-Tests
• There was no significant difference between the washout time 
and time to peak intensity between the two methods 
• There was no significant difference in washout time and time 
to peak intensity between the different leaflet sizes
• Significance level of 0.05 was chosen 
Images of Flow Over Time
Conclusions
References
• There was not a large difference in the washout times and 
time to peak intensity between the different leaflet sizes.
• Smaller leaflet size does not compromise the integrity of the 
valve and efficiency of the valve. However, smaller leaflets 
prevent the leaflets from touching the walls, and thus allows 
for decreased risk of fusion to the walls.
• The time to peak intensity and washout times were also not 
found to be different between the two methods.  Thus, either 
method can be used.
• Washout time is based more on fluid flow and stroke volume. 
It doesn’t matter which method is used for a given leaflet size 
because the amount of fluid the leaflets move through the 
valve is the same, and the flow is held constant between 
methods. 
• Future work could include further testing in order to confirm 
the results and to understand the effects of different leaflet 
sizes on efficiency of vein valves. A total of 10 trials were 
conducted in this experiment. 
Dalsing, M. C. (2018). Phlebolymphology.org. Retrieved from Artificial Venous Valve: An
Ongoing Quest to Treat End-Stage Deep Venous
Insufficiency: https://www.phlebolymphology.org/artificial-venous-valves-an-ongoing
-quest-to-treat-end-stage-deep-venous-insufficiency/
Tanner, D. E. (2013). Design, Analysis, Testing, and Evaluation of a Prosthetic Venous 
Valve. Georgia Institute of Technology, 101-103.
• Engineered tissue samples were used to create vein valves.
• The tissue samples were cut into slabs that represented the 
leaflets, and were sewn together on the edges.
• The leaflets were then attached to a stent. 
• Leaflet lengths :  16, 18 and 20 mm. 
• Leaflet height: 7 mm. 
• Stented tissue engineered vein valves were then placed into a 
pulse duplicator system with a camera to view the valve’s 
motion. 
• A dye injection device was also built and attached
• 0.2 mL of dye were injected during each test
• Windows Movie Maker was used to determine washout time, 
time to peak dye intensity, and injection time. 
OPTIONAL
LOGO HERE
OPTIONAL
LOGO HERE
Acknowledgements
Thank you to Zeeshan Syedain, UROP for funding this work, and the 
Minnesota Partnership for Biotechnology and Medical Genomics Grant 
(to RTT) for the main funding of this project. 
Dye Injection During Cyclic Flow (cycles)
Leaflet 
Length
Washout 
Time Avg.
Washout 
Time St Dev
Time to Peak 
Intensity Avg.
Time to Peak 
Intensity St Dev
16 mm 13 0 2 0
18 mm 10.67 1.25 2.67 0.94
20 mm 6.5 0.5 1.5 0.5
Dye Injection Prior to Cyclic Flow (cycles)
Leaflet 
Length
Washout 
Time Avg.
Washout Time 
St Dev
Time to Peak 
Intensity Avg.
Time to Peak 
Intensity St Dev
16 mm 10.5 0.5 3 0
18 mm 10.75 0.75 2.5 0.5
0
2
4
6
8
10
12
14
Washout Time Time to Peak Intensity
C
yc
le
s
Dye Injection During Cyclic Flow
16 mm
18 mm
20 mm
0
2
4
6
8
10
12
14
Washout Time Time to Peak Intensity
C
yc
le
s
Dye Injection Prior to Cyclic Flow
16 mm
18 mm
Leaflet Length (mm) 16 18 20 
Area of Valve Opening (mm^2) 40.52 45.32 47.99
36
38
40
42
44
46
48
50
16 mm 18 mm 20 mm
V
al
ve
 O
p
en
in
g 
A
re
a 
(m
m
^2
)
Leaflet Size (mm)
Effect of Leaflet Length on Area of Valve Opening
16 mm
18 mm
20 mmFigure 1:Top View of Stented 
Vein Valve 
Figure 3: Front View Diagram of Different Leaflet Lengths. A Closed 
Valve is shown on the Left, Increasing Leaflet Lengths Going Right   
Green dot is injection point
Figure 4: Dye Injection System
Dye Injection System
Figure 2: Front View of Stented 
Valve in Pulse Duplicator System
Figure 6: Area of Valve Opening for each Leaflet Size Tested. 
• The area of the valve opening was calculated using ImageJ 
and the photographs that were obtained from the original 
setup
• Increasing leaflet size decreased how much leaflets touched 
the walls 
Figure 7: Washout Time and Time to Peak Intensity for Three Leaflet 
Sizes using Method 1 (Dye Injection During Cyclic Flow) 
Figure 8: Washout Time and Time to Peak Intensity for Three Leaflet 
Sizes using Method 2 (Dye Injection Prior to Cyclic Flow) 
Comparing ‘Dye into Continuous Flow’ to ‘Dye Prior’
Washout Time Time to Peak Intensity
p value 0.95 0.85
Comparing 16 mm to 18 mm
Washout Time Time to Peak Intensity
p value 0.81 0.5
0 frames (beginning) 30 frames 120 frames 296 frames (end)
Figure 9: Images of Flow during Method 2 (Dye Injection Prior to Cyclic 
Flow
0 frames (beginning) 30 frames 120 frames 296 frames (end)
Figure 8: Images of Flow during Method 1 (Dye Injection During Cyclic 
Flow
Flow of dye through the valves over time. 
• Images collected from videos of the valves in the pulse 
duplicator system
• Time to peak intensity and washout time varied between 
trials
• Third image in Figure 8 (120 frames) was close to what the 
valve would have looked like at time to peak intensity 
• The valve looked similar to what was seen at the end for both 
Figures 8 and 9 (296 frames) at the completion of washout 
Figure 5: Stented Vein Valve 
in Dye Injection System 


Evaluation of Leaflet Washout in Vein Valves

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Evaluation of Leaflet Washout in Vein Valves

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