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.