Week 10, Final Presentation

After the culmination of our project, we presented our findings on Wednesday, June 5 to staff and students of Drexel University. Our presentation was a success and gained much appreciation. The entire 10 week journey was eye-opening and extremely informative. The group gained much insight into the inner workings of a Three-Point Bending Test, understood the relationships between mechanical properties of bones, and improved their skills at analyzing data. Below is the link to access our final report and view our presentation. Thank you to all who supported and followed us along the way!

http://sdrv.ms/11vCM69

Week Nine

The bones that we requested in Week 8 were received this week. They are shown in the picture below. As a recap, we printed four pairs of bones: a set of healthy bones with no modifications, another set of bones with minimal modification, one more pair with slightly more modification, and a final pair of bones that had the most modified dimensions.

4 set of bones printed in red ABS plastic. As laid out above, the bones
decrease in scale of modification. The bones farthest to the right have not been modified at all.

The majority of the time in lab was spent in treating the bones with acetone. Out of the eight bones, all of the modified bones as well as one healthy bone were soaked in acetone for sixty seconds. The remaining healthy bone, which was not treated, will serve to be a control group. Furthermore, the data that we collect after testing this bone will serve as a back-up set of data to the original data we have. This way we can check for any outliers, if they should so arise. Further testing of data and data-analysis will follow on Friday of this week (5/31/13).

Pouring 100% in a soap dish

Bone undergoing treatment for 60seconds

--- FRIDAY UPDATE---

After waiting a couple days for the acetone treated bones to dry, we went back to the lab today and tested the eight bones. Though the data we received was consistent, it was surprising to find that these bones, unlike the ones printed several weeks ago, were not hollow. Instead, they had a second layer of thick plastic inside the bone. 

Week Eight

           Between last week and the beginning of this week, we have collected the results from the Three Point Flexural Test, figured out the Bending Stiffness and Young's modulus, and analyzed data. 

             We noticed that the Young's modulus and the Bending Stiffness decrease as the amount of time that the bones are submerged in 100% acetone increases. This holds true for the hollow cylindrical, normal bones and the scaled bones. However, there is one exception: in the loading test #8, the data we obtained for the modified femur that is treated with acetone for 60 seconds did not turn out as expected. The obtained Young's modulus and Bending Stiffness increased. As we examined this modified bone model after the test, we noticed that the breaking point was not in the middle of the bone's length. Instead, it was between the mid-shaft and the trochanter of the bone. Meanwhile, in the remaining models, the breaking point happened to be in the middle. This error may have affected the accuracy of our data in loading test #8. So, we've decided to overlook the result from loading test #8. 

             At the end of this week's lab, we returned to our bone model on AutoCad to re-modify the dimensions of its frontal and transversal planes. We sent out the adjusted model with the new dimensions for 3D printing. 

Week Seven

Between the last week's lab and this week's lab, we developed two Matlab programs to aid in the analysis and redesign of our bones.  The first is called Find_Modulus.m, and it prompts the user for specifications on the geometry of the cross section, the span of the supports, the data from the three point flexural test, and two user defined numbers.  Once the the first few portions were entered, the program graphs the data and requests a threshold.  The threshold determines where the program recognizes that the bone broke.  If the distance between two adjacent points is larger than the threshold, then the program separates the data at that point.  The second number it asks for is the number points to skip at the beginning of the test.  This is so that if the applicator isn't contacting the bone at the beginning of the test, it won't affect the data.    

The program's prompt for a threshold, showing the graph of the data.

Once the data is input, the program generates a graph of the approximate cross section, and a second graph of the data showing what section was used for the analysis.  The final outputs are the bending stiffness and the modulus.

The approximate cross section, and the graph of the data from the test as displayed by the Matlab program.

In this week's lab we tested all of the bones we printed and modified in the previous week.  We will analyze the data later this week.

Week Six

This week we were given most of our requested printing.  We had asked for four cylinders, but received only two.  We tested a normal bone and a hollow cylinder to give us healthy moduli.  After these initial tests, we began to investigate exactly how acetone affects the bones.  This was met with some initial difficulties, as acetone dissolves most plastic containers.  Finally, we figured out that the Biomed Kitchen five floors up had paper cups which could hold the acetone.  Armed with containers capable of holding acetone, we were able to begin our degradations.  We broke the second hollow cylinder to give us four halves, and treated three with acetone.  The first bone, we submerged in 100% acetone for 15 seconds, the second for 30 seconds, and the third was submerged twice for thirty seconds each time.  The bones became very gooey until the acetone dried, and the models seemed significantly weakened even after just 15 seconds.  The data obtained from these four tests will help us estimate the effects on the moduli of the bones when they are treated with acetone.

Materials printed: three normal bones (left), two capped hollow cylinders (bottom), & three modified bones (right).

Three point flexural test of test cylinder

Three point flexural test of healthy bone

Broken parts after the tests

Week Five

We received word that there will be a slight modification to the project specifications. Because the 3D printer's plastic tensile strength cannot be changed to one that is weaker, the "mutated" bone must be rendered weak manually. In order to do this, the "mutated" bone geometry will be printed on the same plastic as the healthy bone. However, it will be degraded by being submerged in a solution of acetone. Acrylonitrile butadiene styrene (ABS) plastic, the material that is used to print all the bones, is very soluble in acetone. What remains unclear is how much acetone will be needed for the process, and for how long the bone models will need to be immersed in the solvent to be properly degraded. Because ABS plastic is soluble in acetone, leaving it in the solution for too long may lead to total dissolution of the plastic. Thus, in lab this week, we designed a hollow cylinder (Figure 1), capped with two hemispheres, that will receive the acetone treatment next week.

Figure 1: Hollow Bone design which will undergo acetone treatment.
Length= 100 mm
Cross Sectional Diameter= 8.6mm
Extruded Cut= 6.0m

Also in lab, the group was able to figure out how to modify bone geometry in CREO by using the Warp tool. Shown below are the original femur bone as well as the modified bone. As can be seen, the thickness has been increased by approximately 8mm. The bones shown are scaled to 100mm from their original lengths of 14.6mm. 

Figure 2: Left: Original bone, scaled to 100mm
Right: Modified bone with increased thickness. 

Week Four

We received one of the three bones printed from the .stl file that we converted last week. We measured the length, and the cross section length of the different parts of the bone (including cross sections at the hip, lower hip, flattened, mid-shaft  lower mid-shaft, above the knee, and the lump).

We then applied the Three Point Bending test to the bone, and figured out the distance between 2 loads to be 0.226 in (8.5 mm)

Since the length of our bone is too small (14.6 mm) comparing to the width of the force applicator, our result might not be accurate. We were advised to scale the dimensions of the bone to 100 mm for the subsequent bones.

Index finger comparison showing the printed model

The printed model on the Three Point Flexural Machine showing that the width of the force applicator is larger than the length of the printed model

The .stl file of our bone is saved as facet feature in Creo; it is not a solid that has definite volume and shape. We are trying to convert the facet feature to a real solid so that we can adjust and modify the geometry of the bones.

Unfortunately, it appears that using a facet feature will prove impossible for the nature of this project. We have tried multiple programs to edit and/or convert the file into a form that can be edited more easily within Creo. Since we have to be able to edit the geometry of the bone, the group is trying a brute force approach to modeling the bone within Creo by creating a series of sketches that match the axial geometry of the bone and then using the swept blend tool to create a 3D model of the bone from the sketches. While this method is extremely labor intensive, we are very confident that it will create a successful, accurate model of the bone.