Department of Bioengineering

Brandon ChenStephen CifelliRobert MetterEk Kia Tan

Uniaxial Suture Strength Testing

Group TB2

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)

0

5

10

15

20

25

30

35

40

45

50

0 20 40 60 80 100 120

Displacement (mm)

Fo

rce

(N

)

We expect that the running locked stitch will rupture at a higher applied force than the interrupted stitch after performing the t-test.

Department of Bioengineering

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)