A Study of Tensile Degradation of Bioresorbable Materials Used for ...

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Degradation of Bioresorbable Tensile Bars Conclusions Exposure to water affects tensile degradation in ways that were unexpected prior to this research. Originally, it was believed that the tensile strength of bioresorbable tensile bars would decrease linearly with respect to the time they were exposed to water. After examining the data, it became clear that tensile strength does not decrease due to exposure to water. A Student T Test was used to compare tensile strength found after different intervals of water exposure to the control tensile strength of no water exposure. The T Test demonstrated that the tensile strength after zero days of exposure to water was not significantly different to the tensile strength recorded at five, twelve, seventeen, or 22 days. Although the tensile strength did not decrease, the time of fatigue before failure decreased greatly as the time of exposure to water increased. The Student T Test confirmed that the times of fatigue were significantly different for intervals of twelve to twenty-two days. The time of fatigue for the interval of five days was not significantly different from the control time. These results illustrate that although the tensile strength in term of force per unit area did not decrease, the tensile bars are still susceptible to breaking. The tensile bars can withstand the same amount of force no matter how long they are placed in water, but they cannot withstand that force for the same amount of time. Once the maximum load is applied to each tensile bar, the bars that have been exposed to water longer will fatigue quicker and therefore break first. Bioresorbable tensile bars are a sufficient option for internal bone fixation because throughout their time in the body, they will be able to withstand the same amount of force. The average tensile strength of titanium alloy is roughly 830 MPa, whereas the average tensile strength of PLA 2.4 bioresorbable tensile bars is approximately 73.85 MPa. Although the tensile strength of bioresorbables is so much less than titanium, it is strong enough to maintain the necessary position to heal bones. As long as the strength stays the same throughout the healing process, bioresorbable materials are a contender with titanium for bone fixation. Even during the last weeks of healing, the tensile bars will remain intact under pressure. The forces will not be able to be applied for long periods of time, but the tensile bars will still hold up against internal forces. These bioresorbable materials are a great option for facial or non-weightbearing fractures because external forces are not as common to an area of the body that is non-weightbearing. Despite the lower tensile strength than titanium, bioresorbable tensile bars are an acceptable replacement to titanium fixation without the hassle of a removal surgery. 17
Degradation of Bioresorbable Tensile Bars Limitations and Assumptions In order to complete the research concerning bioresorbable tensile bars, several assumptions were made before experimentation. It was assumed that PURAC Biomaterials shipped the correct tensile bars to be tested. All the tensile bars had the same intrinsic viscosity of 2.4 and did not lose any tensile strength during the shipping process. It was also assumed that the container in which the tensile bars were stored did not affect the tensile strength. All tensile bars of equivalent intrinsic viscosities and dimensions are assumed to have the same tensile strength when not exposed to water or any other liquid. It was assumed that the Instron 5544 provided accurate data throughout experimentation. Another assumption was that temperature did not affect the tensile strength of bioresorbable materials. A larger assumption was that water was a component in causing the breakdown of the bioresorbable tensile bars. This research was limited due to time constraints. The total time period necessary for healing bones was unable to be tested during experimentation because an eight week time frame was unavailable. The number of trials was also limited because of the difficulty in obtaining bioresorbable tensile bars. Throughout conducting tests, several aspects of the experiments were controlled. The amount of time each tensile bar was exposed to water was controlled within each trial. The containers that stored the tensile bars in water remained constant during all trials of experimentation. The Instron 5544 that was used to test the tensile bars was the same for each test. All tensile bars used in this experiment had the same intrinsic viscosity and were shipped from the same company. Although the results collected from this research are consistent, several sources of error could have altered the data. The Instron being used throughout the experimentation could have been inaccurate, even though it was precise. The time intervals chosen could have been too close together and therefore did not display an accurate representation of tensile strength degradation. If bacteria were able to enter the water that the biomaterials were being tested in, then the bacteria could have caused degradation to speed up or slow down. These limitations and assumptions could have altered the results minutely, but the data is still precise. 18
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