Embedded Files
In order to ensure the device would work as we were expecting, the materials we were using (mainly resin and sutures) underwent testing to verify their chemical and material properties.
Mechanical Testing
Mechanical Testing
Suture Loading Test
Suture Loading Test
One of the first mechanical test was to ensure the sutures would not break under the intended load. Since these sutures are currently used in the DVJ lab to perform biaxial testing, we expected that these results would yield the sutures did not deform, but we were wrong.
Suture load testing results showed a consistent trend of increases in length with respect to time
The suture testing revealed that under a load of 100g (~5 times the expected load) the sutures stretched ~0.25mm every 12 hours. This was not something we were expecting. We re-evaluted our design to use wire instead of sutures since the deformation shown here is on the same order of magnitude as the amount of biaxial displacement we were attempting to apply.
Load Arm FEA Analysis
Load Arm FEA Analysis
Before we printed, an FEA analysis was done in Solidworks on the loading arm to ensure it would not break. We had assume the most vulnerable part would be the small posts, however from the results we saw it was actually the center arch of the arm.
SolidWorks FEA Analysis. After inputting the properties of the resin we were using from the published data sheet, a factor of safety on the order of 103 was determined, which is more than high enough to conclude the part was safe and should not break during the defined use.
Load Arm Testing
Load Arm Testing
We then confirmed our FEA analysis results by performing load testing on the arm. It was hung vertically with about 40g of weight to simulate the load distribution in the device.
Load arm testing set up. Images and measurements were taken every 12 hours for a total of 72 hours and no changes were observed.
Ratchet and Pawl Loading Test
Ratchet and Pawl Loading Test
Similar to the load arm testing set up, the ratchet wheel, and a full quarter of the device prototype, were load tested in a vertical orientation. This was to account for the direction the forces would be felt when the full device was built. A weighboat was used to apply about 40g of load and the device was clamped in place for 72 hours.
Measurements and images were taken every 24 hours and no changes were observed. The ratchet wheel did not slip and no other part of the device broke, so this test was considered as proof the pieces were designed to be strong enough to withstand the load required during biaxial loading.
Testing to Confirm Linear to Angular Displacement Conversion
Testing to Confirm Linear to Angular Displacement Conversion
The gears were designed such that a movement of one gear tooth or one click of the ratchet wheel, would move aobut 0.3mm. This was decided upon because we were aiming for a 10% biaxial stretch of a 6mm sample, which is equivalent to 0.6mm.
It was designed such that each tooth movement is half of that amount to allow for greater control and "zero-ing" of the device. The act of "zero-ing" ensures that the sutures holding the sample are taut and aligned correctly, but no major forces are being applied to the tissue.
Each movement of a gear tooth was approxiamtely 0.33mm. As such, for 1 tooth it moves less than 1mm, or about 0.33mm. For 3 gear teeth it moves 1mm. Jumping up to 9 teeth, we can see it moves 3mm. These results can be interpolated to prove that the 1 tooth movement is in fact about 0.33mm.
This data was collected using a tripod to hold the camera in place and with a ruler attached to the bottom of the device. This ensured that neither the user or camera greatly influenced or caused variation in the results. Repeated testing showed consistent results each time.
Chemical Testing
Chemical Testing
Formalin Interaction Testing
Formalin Interaction Testing
Measurement of Resin Piece with Calipers. All pieces we used for testing were measured before being submerged in resin and then every 24 hours for 72 hours total.
Results were graphed as percent change in length. Each of the 4 panels shows the changes undergone by 4 different locations on one of the resin tubes measured. Marker color designates the user that measured; magenta for AZ, green for AB, and cyan for DKD.
From the results, it can be seen that for most locations there was a net positive change over 72 hours, however the variation between the different time points (and thus the users) made this test inconclusive. So while we were not able to say that formalin does not affect the resin, it also cannot be said it does. From a qualitative standpoint, the resin pieces and sutures did not appear to become more malleable or brittle or otherwise change.
Created by: Delaney K. Donnelly
Page updated
Report abuse