For our midterm project, we (Gabby, Symone, Nico, and I) were tasked with using 3D printing and mold casting to create 2 sets of LUCIA cancer models as teaching tools for low-resource settings.
First, we imported the STL file for the models provided on Canvas and printed them using a Bambu 3D printer. We had to re-print after adjusting the layer height from 0.16mm to 0.1mm to get the optimal surface finish on the top of the model. Once we had the 3D printed models, we used acrylic paint to recreate the anatomical models provided by the LUCIA kit. We had a lovely time enjoying the Houston spring weather outside while painting.
The hardest part of painting was color matching, as the paint would dry down darker than expected, causing us to have to do multiple layers to achieve the appropriate hue. It took 2-3 work sessions to fully paint and gloss coat the models, making this step the lengthiest and most labor intensive portion of production. We also noticed that the gloss coat was not as glossy as the LUCIA models, prompting us to do 2-3 layers to achieve extra-shininess. Symone noted, however, that added layers of gloss could also cause discoloration and yellowing of the paint so for future models we only did 2 coats of gloss. 
To create the models using molding, we first generated a positive mold of the cervixes in a box in TinkerCAD and uploaded this STL file to the Bambu printer. By using the same layer height as before, we got a high fidelity positive mold with our first print!
We then generated a negative silicone mold using TC-5130 from BJBmaterials by mixing 1:1 ratios of part A and B and stirring vigorously, making sure to scrape the sides of the cup. We estimated the volume of silicone needed to make the mold by using water and a measuring cup to ensure we did not waste silicone – which is very costly.
We poured the silicone over the positive mold and let it set overnight. We noticed some air bubbles but hoped they would be minor or not noticeable on the surfaces. After they finished curing, we used a flathead screwdriver to pry the mold from the box. It was surprisingly difficult but the silicone mold was very sturdy!
We noted some small air bubbles on the edges and around the letters, but decided that the mold was good enough to proceed to the next step with some minor post-processing later on.
We poured the polyurethane positive casts using Smooth-On Smooth-Cast 300. Mixing parts A and B in 1:1 ratio very quickly and pouring into the silicone mold before they set in 3 minutes.
We sprayed mold release lubricant on the silicone negative before pouring the polyurethane, according to manufacturer’s instructions.
Time lapse of polyurethane setting: IMG_5810.MP4
The first pass at making these casts had some issues with air bubbles, so we repeated the process and used a sand belt to vibrate the air bubbles out of the molds. This process worked wonders! If we were to scale up production, a vibrating table or vacuum chamber would be necessary to ensure high quality casts.
We sanded off excess polyurethane using 40-grit sandpaper and did some minor post processing to fill any air bubbles.
We finished the polyeurthane casts by painting with acrylics in the same manner as the 3D prints. This time, we had learned some tricks about color matching and anticipating the color after drying which sped up the painting process. We finished with the same gloss as before.
my final models:
left-to-right: LUCIA, 3D print, mold cast
In conclusion, we had a great time iterating throughout the 3D printing and mold casting process. Each fabrication method has pros and cons, which you can weigh for your use case (see our paper for details!). In our experience, the painting process is the most time consuming and laborious part of the production. To scale up production, hand-painting would be the limiting factor. To recreate an anatomically realistic model in large volumes, a stamp or hydro-dip method might be necessary.
Cost analysis:
| Cost Type | Cost | Price | Source | Quantity | Total |
| Materials | Silicone | $75/2lbs | link | 250mL | $41.33 |
| PLA Filament | $0.51 / Ounce | amazon link | 190.36 g | $3.42 | |
| Polyurethane Part A + Part B | $108.22/gal | link | 40ml each | $9.55 | |
| Acrylic Paint (24 colors) | $6.99 | link | 1 | $6.99 | |
| Paint Brushes | $6.99 | link | 1 | $6.99 | |
| Gloss Spray Paint | $5.98 | link | 1 | $5.98 | |
| Fast Dry Filler | $32/half gallon | 3M link | 1 gram | $0.01 | |
| Mold release lubricant | $7.79/can | link | 1 can | $7.79 | |
| Plastic Cups | $22.99/36-pack | link | 6 cups | $3.83 | |
| Popsicle sticks | $0.97/50 pack | link | 4 sticks | $0.78 | |
| Sand Paper | $13.99/pack | link | 1 | $13.99 | |
| Labor | Prototyping Engineer (You!) | $36/hr | link | 8 | $288 |
| Design | Engineering and Development | $32/hr | link | 1 | $32 |
| 3d print Iterations (PLA material) | $0.51 / Ounce | amazon link | 41.63 g | $0.75 |
Total $421.41
Assumptions:
- 3D printer is already available
- Only 1 3D printer or silicone mold
Clean bench:
