1. Department of Bioengineering Modeling of Wound Closures Under Uniaxial Tensile Loading 101A3 Tefesehet Mesfin – Background & Hypothesis Ryan Stuckert – Methods & Protocol Dan Hoang – Proposed Deliverables/Findings Lindsay Pordon – Potential Pitfalls Ryan Stuckert – Equipment & Budget

2. Department of Bioengineering Background: This experiment combines the Instron tensile and camera experiments to test the properties of wound closures: sutures and staples. The optimum closure would have high strength under tensile stress. Force displacement data as collected by the Instron could be used to calculate the force at the failure point of the closure. The type of failure (punching through of sutures or staples, or tearing of the wound) could be observed by taking successive pictures. Hypothesis & Aims or Objectives: Sutures will be a more optimum closure than staples for a one inch slit in rubber under uniaxial tensile stress. Staples will fail at a lower tensile force than sutures. Sutures will make the wound more resistant to further tearing. Tefesehet Mesfin Types of Failure:

3. Department of Bioengineering Methods & Protocol: 1.Setup Instron & camera as in Labs 3 & 5 of the lab manual. 2.Cut 12 rubber samples into 2”x4” strips, & cut a 1” slit in the center of each sample parallel to the 2” sides. 3.Using 1 or 2 rubber samples, standardize your testing methods. 4.Suture closed the slit with the pulley stitch method using 4 equally spaced stitches, & using your standardized methods, load a sample with the cut parallel & 1” from each clamp. 5.Test the sample, using the Instron & the camera. Note when and how the sample began to fail. 6.Repeat Steps 4 & 5 using the other 4 prepared samples (N=5). 7.Repeat Steps 4 & 5 using staples instead of sutures to close the slit for the remaining 5 rubber samples (N=5). 8.Analyze the results using a paired t-test to compare the force at the point of failure for the stitches & the staples. Ryan Stuckert Sample and loading technique.

4. Department of Bioengineering Proposed Deliverables/Findings: Dan Hoang Force vs. Displacement Graph: Instron Output The ultimate force of the wound closures is measured by the maximum force of the Force vs. Displacement Graph at failure. Two-Tailed T-Test: Significance Test This experiment should yield at least a set of 5 ultimate forces for sutures and a set of 5 for staples. A p-value of less than 0.05 for a two-tailed t-test comparing both sets will yield a significant difference in ultimate force. Failure Pattern: Pictures from Camera Under tensile loading, the sutures and staples can fail by further lengthening the slit or punching through the rubber. These qualitative measurements of the failure pattern can be used to determine the optimum wound closure. The group can determine which failure pattern is less desirable in a wound closure. Failure Point Group 1 Group 2 Average Ultimate Force (N)22.529.8 # of Samples55 t-Test, p-value0.075

5. Department of Bioengineering Potential Pitfalls: Rubber slips out of clamps. Some samples punch through while others tear. Each staple/suture may not act the same. Sutures rip before rubber tears. Staples bend before rubber tears. The black and white pictures may make it difficult to place markers for displacement. To prevent slipping, the group should change the loading rate and possibly use paper towels to increase friction. Failure is defined as the force at which punching through or full tearing occurs, so the samples can all be compared. Note observations (bending/ripping), but continue testing. Make marks as visible as possible and place camera for optimum resolution. Lindsay Pordon

6. Department of Bioengineering Equipment/Materials and Budget & Justification: Major Equipment: Instron & CCD camera. These will be used to measure force & displacement and displacement & failure type, respectively. Lab Equipment & Supplies: Ruler, scissors, scalpel, cutting board, weight set, string, & needles. These will be used to make the necessary measurements (ruler), to standardize the testing methods in Step 3 of the Methods/Protocol (weight set), and to prepare the samples in Step 2 of the Methods/Protocol (remaining supplies & equipment). Newly Purchased Equipment: Rubber from McMaster-Carr (Serial No: 2633T14), costing $38.35 for 12” by 12” piece. Necessary because it has a thickness of ¼”, allows test subjects to be partially cut through. Provides appropriate firmness, stretch limit (70%), & tensile strength (200 psi). New Clamps from Instron (2710-004 ), costing $1000. Necessary to hold the wider test subjects and meet the needed load requirements. Surgical stapler & 5 pre-loaded staples, costing $15 from Wilderness Medical. Necessary to apply & test the staples. Ryan Stuckert