Yeah, not too happy about the title either. Not a great pun,

and the Vader quote is technically “No, I am your father.”

For this midterm project, my group (me, Gabby, Meilani, and Symone) needed to replicate a set of four LUCIA cancer models twice — once using 3D printing, and again using molding and casting.

 

LUCIA (Low-cost, universal cervical cancer instructional apparatus) was developed by the Richards-Kortum lab and Rice360 as a teaching tool for cervical cancer screening and prevention. The full set of cervixes cervices is on the right, and includes different morphologies: normal, acetowhite changes (following application of acetic acid to cells, where white areas on the cervix indicate abnormal cells), cysts, high-grade cervical precancer with abnormal vasculature, and findings consistent with invasive cervical cancer.

 

We chose the cancerous models to replicate (1-2H and 1-2G). Our first task was printing them. Luckily, the files were on the canvas, so all we had to do was hit print. Symone printed our first batch, and upon further inspection we found unsightly ridges. So we reprinted, changing the layer height from 0.16 mm to 0.10 mm to our desired model finish.

 

 

 

 

 

 

 

Next was hand painting. This was difficult for  a few reasons:

1. The vasculature of the cancerous models have tiny, but important details that were hard to paint.
   1. solution: I taped a tiny pin (from the fasteners cabinet) to a paintbrush for fine detail work
2. We are not artists, so color matching was difficult, made even harder by the acrylic paint drying down a few shades darker
   1. solution: match color shades exactly, then add white paint (+1/3 the total paint volume)
3. The original LUCIA models have a high gloss finish. This was hard to achieve, even with multiple coats of clear gloss paint
   1. solution: ignore proper spray paint etiquette. Spray close and directly (no sweeping motion) for 3-4 thick coats

We decided to paint outside for the spring weather and natural light to try to color match as closely as possible. Then we applied many thick coats (at least 4) of clear spray paint to achieve a glossy  finish. That’s one set complete. On to molding and casting.

We printed a positive (twice — we think someone mistakenly took our first one from the print bed), poured silicone into it to create a negative (mixing parts A and B 1:1 of TC-5130 from BJB materials, scraping the sides), and got incredibly lucky that the bubbles in the negative mold did not congregate around important details (the few bubbles that existed were around the letters, which we decided to post process post casting).

On to demolding. Unlike our intro molding and casting project, the container was not flexible, so it was pretty difficult to remove the positive from the negative. We needed to dig in with a flat head screwdriver (pictured below). Luckily the silicone is pretty robust, so it just ate anything we threw at it.

 

 

Then, we filled the negatives with quick cast polyurethane (Smooth-Cast 300). We first applied mold release lubricant to our negative, as the polyurethane directions specified this was absolutely necessary (it was not), then mixed together 40 mL of parts A and B (80 mL total) with a popsicle stick. This cured in about three minutes, which was crazy to watch. We had our casts! Unfortunately, we saw a few defects caused by air bubbles, so we recast. This time we placed our rig on a belt sander, since the vibrations from the platform would shake the mold during the setting process and release the bubbles.

 

 

 

 

 

 

 

This second round of casting went well. The belt sander, after threatening to jiggle our rig off the platform, eliminated the bubble problem. We had to sand down about 2 mm off the bottom because we overpoured, corrected the small defects around the lettering, and used a bit of filler to fix some details. Now to paint (again).

We hand painted again, facing some difficulty to color match once more. It was a bit easier since we knew how to anticipate the dry-down shade. Once again, we coated the models with a few layers of clear gloss, and everything was good to go.

 

 

 

 

 

 

 

 

 

It was fun to iterate through this design process, and optimize conditions for 3D printing and molding and casting. Ideally, for any other high fidelity mold-and-cast projects, a proper vacuum setup would  be used, but I think our improvised vibration table worked just fine.

 

 

Cost breakdown

materials cost: $72.30
tools cost: $7.43
labor cost: $320

total cost $399.73

Cost source list:

silicone kit

white PLA filament

Smooth-Cast 300

acrylic paint set (12 colors)

gloss spray paint

fast dry filler

mold release spray

paint brushes

plastic mixing cups

popsicle sticks

sandpaper

prototype engineer wage

design engineer wage