Cancer Nanotech Outreach Module
One of the outreach modules I worked on as an engineering education developer showed students how nanotechnology is being used to develop targeted cancer treatments that would result in less collateral damage to other parts of the body.
To help explain how the targeted treatment works, an activity was designed to model the molecular process that allows the drug to be released at a particular organ. In the activity, students make different sized sodium alginate beads and roll them down a ramp with different sized slotted holes. The goal is to figure out what size to make the beads in order to get them into a particular hole. My role was to design and manufacture the ramp.
Design and Construction
The material was selected as HDPE for cost and machinability. The assembly consists of a base, a ramp, and two columns to hold up the ramp. The base and the ramp were machined from sheets of .75" HDPE. Weight was not really an issue so we did not add any operations to remove excess material. I learned a lesson in DFMA with the columns. I decided to make the columns from square rod stock - mistake number 1. I should have machined the rods out of a sheet just like everything else. Yes, it would have wasted a lot more material, but it would have saved several hours of labor.
I also should have figured out a way to fix the columns to the base in a way that didn't require threaded holes in the ends of the columns. For the prototype, this was fine. But we had to manufacture around 15 of these assemblies. That's 30 columns I needed to centerdrill, drill, tap, and chamfer in the lathe. To add to my frustration, I quickly learned that the tolerances of the square shaft were quite large, which meant that it was very difficult to get many of the square rods to fit in the 1/2" square collet.
My friend Russell finished up the assemblies by machining little recesses in the ramps for clear acrylic covers to prevent the beads from bouncing out.
After all the ramps were assembled, we collected a lot of data to see if there was any correlation between the size of the bead and which hole it went into. I realized that because the probability of falling into further holes was dependent on how the beads interacted with the earlier holes, the further down a hole was, the more unlikely it was that a bead would fall into it.
This reminds me of the game Plinko, which has been used to demonstrate the meaning of the normal distribution curve. In the video, the balls are very unlikely to reach the tails of the curve because it requires a very unique and improbable combination of moves. It is much more likely that the balls will fall in the center, as many combinations of moves can take the ball to that central location on the curve.
Similarly, only a few combinations of bounces will allow the beads to land in the last hole, whereas just about every other combination of bounces will make the bead miss the hole. The more holes there are, the total number of combinations of bounces increases much more than the number of combinations of successful bounces, so the overall probability that the bead will land in the hole decreases with the number of holes it has to pass first.