For this project, we created LUCIA cervix models, a low-cost training tool for cervical cancer screening. We produced two sets of LUCIA model cervixes: one using 3D printing and the other through molding and casting.
3D Printing
For 3D printing, we began by downloading our STL cervix files from Canvas, which already had the correct sizes for the models. We uploaded them to Bambu and left the default options, changing only the layer height to 0.2 mm. However, this resulted in cervixes with very visible layer lines, so we decided to change the layer height to 0.09 mm, as recommended by another group. This time, we prepared the file in TinkerCAD, including both the box and cervixes, to minimize the number of prints and facilitate post-processing. Once we transferred that file to Bambu, we were ready to print! However, we observed something none of us had ever seen before—what appeared to be an odd spaghettification effect:
We decided to restart the print, and it worked the second time around! Well… at least the cervixes turned out well. The box itself, on the other hand, was too small and needed to be resized. At this point, we entered a phase of several rounds of reprinting the box. The first reprint, which was smaller than the original, had a space between one of the inner and outer walls that we needed to address. We corrected this in TinkerCAD and reattempted the print. This version would have turned out well—except somehow, we accidentally made the cervixes larger. So, on our final attempt, we ensured that we addressed all previous errors: making the box the proper size, eliminating any spacing between the inner and outer walls, and ensuring the cervixes were the correct size. Now, we were ready to move forward with casting!
Creating a Cast
To create our final Smooth-Cast positives, we first needed to create a silicone negative. For this, we mixed a 1:1 ratio of Silicone A to Silicone B, pouring only as much as necessary since silicone is expensive! To determine the required amount, we filled our box and cervixes with water, measured the volume, and subtracted the volume taken up by the cervixes. We ended up needing approximately 220 mL of silicone in total. We combined, mixed, and then poured the silicone into the mold:
We let the silicone sit for a day before removing it. The removal process was much more difficult than expected—we had to use a spatula and a flathead screwdriver to pry it out! The trick was to create an air pocket between the silicone and the edge of the mold, allowing us to wiggle the cast out little by little. After about 20 minutes and a team of people cheering us on, we managed to extract the silicone negative!
But we still had one more step—creating our final Smooth-Cast positive. This step wasn’t nearly as high-stakes since Smooth-Cast 300 only takes 10 minutes to solidify and is relatively inexpensive. The setup was simple: we determined the volume needed to fill the cervix portion of the negative, added a little extra for leeway, and then divided the total into equal parts of Smooth-Cast A and B. We poured each part into separate cups, quickly combined and mixed them with a popsicle stick, and then poured the mixture into the cervix negative. We had to complete this entire process within three minutes, before the Smooth-Cast hardened!
We repeated this process multiple times, as our first two attempts resulted in bubbles. We finally resolved this issue by placing the system on a rotating belt for vibration, which helped push the bubbles out.
Post-Processing and Finishing
We were finally ready for post-processing and finishing. We sanded down the edges and bottom of the cervixes and then painted them using a mix of pink, red, white, and yellow acrylic paint. We applied two coats before adding red details using either red paint or a pen for higher precision. Finally, we finished with a clear coat to give the models a smooth finish, similar to the actual ones.
This project was fun and provided insight into different fabrication techniques for achieving the same outcome. For this application, 3D printing proved to be far superior to molding and casting, as it is quicker, simpler, and more cost-effective.
3D printing method:
| Cost Type | Cost | Price | Source | Quantity | Total |
| Materials | PLA filament | $19.99 / kg | Bambu Lab | 0.04 kg | $ 0.80 |
| Paint | $14.99 / set | Amazon.com | 0.5 set | $ 7.495 | |
| Clear Spray Paint | $0.5 / Oz | Homedepot | 0.2 Oz | $ 0.1 | |
| Labor | Prototyping Engineer (Intern) | $17 / hour | ZipRecruiter.com | 1 hr (set up + monitor 3D printing) + 16 hr (post-processing)
= 17 hrs |
$ 17
$ 281 |
| Overhead | Brush | $3.99 / set | Amazon.com | 1 set | $ 3.99 |
| Electricity | $ 0.36/day | 0.167 day | $ 0.06 | ||
| Paper Towel | $0.051 / Sheet | Amazon.com | 10 sheets | $ 0.51 | |
| Quality control | 27.5/ hour | LinkedIn.com | 0.25 h | $ 6.875 | |
| Design | Engineering and Development | $17 / hour | ZipRecruiter.com | 0.5 h | $ 8.5 |
| Misc. | Waste and Scrap | $0.17 / L | Houstontx.gov | 0.05 L | $ 0.0085 |
Sum: $ 326.34
| Cost Type | Cost | Price | Source | Quantity | Total |
| Materials | PLA filament | $19.99 / kg | Bambu Lab | 0.12 kg | $1.4112 |
| Silicon | $0.48 / Oz | Amazon.com | 220 ml | $3.571 | |
| Polyurethane | $68.92 / Gallon | Amazon.com | 90 ml | $1.654 | |
| Paint | $14.99 / set | Amazon.com | 0.5 set | $7.495 | |
| Waterproof Pen | $2.49 / count | Unibrands.co | 1 count | $2.49 | |
| Clear Spray Paint | $0.5 / Oz | Homedepot | 0.2 Oz | $ 0.1 | |
| Labor | Prototyping Engineer (Intern) | $17 / hour | ZipRecruiter.com | 1 hr (set up + monitor 3D printing) + 0.25 hr (pouring silicon) = $1.25
0.25 hr (demolding) + 0.5 hr (casting) + 2 hr (sanding) + 16 hr (painting) = $14.75 |
$ 21.25
$ 318.75 |
| Overhead | Flathead screwdriver and spatula | $3.25 for one
$4.99 for one |
Amazon.com | 1 count
1 count |
$ 3.25
$4.99 |
| Brush | $3.99/ set | Amazon.com | 1 set | $3.99 | |
| Electricity | $ 0.36/day | 0.33 day | $ 0.12 | ||
| Paper towel | $0.051 / Sheet | Amazon.com | 10 sheets | $0.51 | |
| Plastic cup with mixing sticks | $0.18 / count | Amazon.com | 3 counts | $0.54 | |
| Sandpaper | $0.20 / piece | Amazon.com | 1 piece | $0.20 | |
| Quality control | $27.5/ hour | LinkedIn.com | 0.25 h | $6.875 | |
| Design | Engineering and Development | $17 / hour | ZipRecruiter.com | 0.5 h | $ 8.5 |
| Iterations | $17 / hour | ZipRecruiter.com | 1 h | $ 17 | |
| Misc. | Waste and Scrap | $0.17 / L | Houstontx.gov | 0.05 L | $ 0.0085 |
Sum: $ 402.70
Clean work station!
