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Department of Bioengineering

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Uniaxial Suture Strength Testing
Group TB2
Brandon Chen
Stephen Cifelli
Robert Metter
Ek Kia Tan
Department of Bioengineering
Background:
In Experiment 5 (Imaging Techniques for Displacement
Measurements), it was determined that the running locked stitch
experienced less displacement at a particular force than the
interrupted stitch (0.0015 mm/g vs. 0.0032 mm/g). In each trial, it
was the actual fabric that ruptured before the stitching broke.
Therefore, we will suture rubber samples and apply force with
the Instron, likely causing the suture to rupture before the rubber.
This will allow us to determine which stitch can withstand the
most force before breaking.
Hypothesis:
The running locked stitch will be able to withstand a significantly
greater force than the interrupted stitch before rupturing.
Department of Bioengineering
Methods & Protocol:
• Cut rubber into 20 pieces measuring 0.75 in. x 1.25 in. Suture
5 pairs on the short sides using the running locked stitch and the
other 5 pairs using the interrupted stitch.
• Use 5 stitches for each sample with equal separation.
• Using the Instron 4444, run a uniaxial tensile test on each
sample and obtain force vs. displacement data.
• Analyze the graphs to determine the maximum force that each
sample could withstand.
• Perform a paired one-tailed t-test between the running locked
stitch group and the interrupted stitch group to determine if there
is a significant difference in the maximum suture strength and to
determine which stitch is stronger.
Department of Bioengineering
Proposed Deliverables/Findings:
We will obtain a force vs. displacement plot for each sample similar
to the plot below (from Experiment 3). From each graph, we will
determine the maximum force applied to the rubber and suture (the
peak of the graph).
Force vs. Displacement (Rubber)
50
45
40
Force (N)
We expect that the running locked
stitch will rupture at a higher applied
force than the interrupted stitch after
performing the t-test.
35
30
25
20
15
10
5
0
0
20
40
60
80
Displacement (mm)
Department of Bioengineering
100
120
Potential Pitfalls:
• Suture variability: It must be ensured that all stitchings are
uniform. Stitches should be evenly spaced, at an equal distance
from the center, and have uniform tightness. Variations in any of
these factors could influence rupture force, e.g. leading to
rupture of one stitch before the others.
• Distance of sutures from gap: An effective distance for the
stitches from the gap must be determined so that the rubber
does not tear before stitch failure.
• Suture rupture: The stitches could break all at once or one at
a time. It should be determined in which fashion they will break
in order to determine how the force vs. displacement graph will
be analyzed to determine the maximum force.
Department of Bioengineering
Equipment and Budget & Justification:
• Equipment: Instron Model 4444 – used to perform the uniaxial tensile test
on the samples because it can apply force at a uniform rate and will
produce data necessary to construct a force vs. displacement plot
• Supplies:
• Scissors – to cut rubber, Needles – to thread stitches
• Rubber – 2 sheets of 6” x 4” x 0.06” Ultra-Soft Polyurethane
(8824T125 from McMaster-Carr – $10.93 each)
• Tensile Strength: 209 psi
• Thread – 1 spool of 500’ (0.058” diameter) Polished Cotton Fiber Rope
(1931T51 from McMaster-Carr – $5.15)
• Tensile Strength: 48 lb.
• Newly Purchased Equipment: Screw Side Action Grips for Instron
(2710-205 from Instron - $820.00) – used to ensure that rubber
does not slip out of grips
• Rated capacity: 5 kN, specimen width: up to 0.6”
• Serrated Jaw Faces for Flats (2702-141 from Instron – $290.00)
Department of Bioengineering
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