To begin, as a team (Sradha, Abby, Jayashri, and I), had to select a cervical model to fabricate using two different methods: 3D printing and polyurethane casting.
Out of the five LUCIA Models currently used, we chose to replicate the CYSTS Model types (1C, 1D, 2C, and 2D) using both fabrication techniques.
Image of five LUCIA Models currently used
Once we selected the model type, we exported the necessary 3D print model files from Canvas under LUCIA Files > Cyst_Polyps. We used STL print files and SOLIDWORKS files (SLDPRT) to proceed with fabrication. We initiated the 3D printing process using Bambu PLA printers, which printed four cervical models in PLA white.
Simultaneously, we worked on creating a 3D-printed positive mold of a box containing a set of cervixes. This mold would be used to cast a silicone negative mold, allowing us to create polyurethane replicas of the cervix models.
We were introduced to Computer-Aided Design (CAD) platforms: SolidWorks and TinkerCad. Our TA provided a tutorial on creating the 3D model for the mold using SolidWorks, and Dr. Wettergreen introduced us to TinkerCad, a simpler, more user-friendly platform.
While half the team experimented with TinkerCad, we ultimately chose SolidWorks due to a team member’s prior experience with the interface. The positive mold design included slanted internal angles using right-angled triangles, ensuring easy removal of the silicone mold. Additionally, we smoothed the edges to facilitate sanding post-printing.
Once finalized, we printed the box mold on Bambu printers using white PLA filament.
We then attempted to paint the 3D-printed cervical models using acrylic paints provided by Dr.Wettergreen. One challenge was achieving accurate coloration, as the paint dried unevenly and patchy. To correct this, we adjusted our painting technique by applying multiple even coats. We added 2-3 coats of gloss to give a finishing touch.
With the 3D-printed positive mold completed, we proceeded to create the silicone negative mold using Silicone Part A and Part B in a 1:1 ratio (brand and type in Cost Analysis table). We stirred the mixture and poured from the corner of the box.
Volume Calculation:
Volume of 1 Cervix: π × r^2 × h = 13.54 cm^3
Total for 4 Cervixes: 13.54 cm^3 × 4 = 54.16 cm^3
Volume of Box: 10 cm × 3.5 cm × 10 cm = 350 cm^3
Required Silicone Volume: 350 cm^3 – 54.16 cm^3 = 295.84 cm^3
We allowed the silicone to cure for 24 hours before attempting to remove the mold.
Once the silicone mold was ready, we moved on to polyurethane casting.
We followed the class instructions to mix and pour Polyurethane Parts A and B, using 80mL based on what the class was using (average amongst all of our volumes). The brand and type in cost analysis table. The bottles had stated a reaction time of 3 minutes. We timed this task accurately and had to stir the mixture quickly once we poured Part A into Part B. We pour it into the mold within the remaining time. The reaction was almost instant, and when we removed the casts, they were still warm to the touch.
We noticed a couple of differences at this point between the two models when we took them out. The polyurethane models were heavier than the 3D-printed models + the surface resolution was lower; the letters and numbers on the polyurethane models were not as sharp as on the PLA prints.
When we proceeded to painting the polyurethane models, we noticed more differences. The paint dried darker than expected + the polyurethane surface absorbed paint unevenly, requiring 1-2 shades lighter for accurate coloration. We also added a finishing gloss to this model.
However we persevered and tried shade matching as close as possible and have our finished products below!
Below is our cost analysis and all the materials we used for this project!
| Cost Type | Cost | Price | Source | Quantity | Total |
| Materials | PLA Filament | $25.99/ 1 kg | amazon.com | 0.2 kg | $5.20 |
| Silicon
|
$31.42/500 mL | amazon.com | 400 mL | $25.14 | |
| Polyurethane Part A + Part B | $25.09 /1 pint | amazon.com | 80 ml | $4.27 | |
| Acrylic Paint (24 colors) + Paint Brushes | $25.99 – ($0.54/fl oz) | amazon.com | 2 fl oz | $1.08 | |
| Gloss Spray Paint | $5.98 per 12 oz can | Home Depot | 0.25 oz | $0.12 | |
| Plastic Cups | $14.99 for 25 | amazon.com | 4 | $2.40 | |
| Popsickle sticks | $4.98 for 100 | amazon.com | 5 | $0.25 | |
| Ruler | $1.96 for 1 | amazon.com | 1 | $1.96 | |
| Labor | Prototyping engineer | $36/hour | ziprecruiter.com | 2 hours | $72 |
| 3D Printing Operator | $23/hour | ziprecruiter.com | 3 hours | $57 | |
| Total | $169.42 |
Feasibility for Mass Production
| Number of products | 3D Printing | Mold Casting ( Silicon + Polyurethane) |
| 50 | Time: Much Faster
Quality: Higher Cost: $0.70 for 4 cervixes. $0.175 for 1 cervix print |
Time: Slower
Quality: Lower Cost: 2) $7.90 per 1 cervix 3) $7.90 * 50 = $394.875 total to print 50 cervixes |
| 100 | Time: Much Faster
Quality: Higher Cost: $0.70 for 4 cervixes. $0.70*25=$17.50 total for 100 cervixes |
Time: Slower
Quality: Lower Cost: $4.27*25=$106.75 total for 100 cervixes |
| 1000 | Time: Much Faster
Quality: Higher Cost: $0.70 for 4 cervixes. $0.175 for 1 cervix print |
Time: Slower
Quality: Lower Cost: |
Assumptions made:
- 3D printer is already purchased/access to a 3D printer is available
- There is no time constraint or deadline for creating the number of products
- Cost of creating 4 cervixes with 3D printing is $0.70
- Cost of creating 4 cervixes with Polyurethane casting is $31.59 (first time only and includes the 3D printed box, silicone, and polyurethane)
- Cost of creating 4 cervixes with Polyurethane is $4.27 every time following the first
- Assuming that we only make the 3D printed box and silicone mold once for all products made (50-1000)
Reflection on Fabrication Method Comparison and Cost Analysis Reflection:
3D printing proved to be more efficient for mass production, while polyurethane casting required more labor and materials, making it unsuitable for large-scale manufacturing. Additionally, the silicone mold had a limited lifespan of only 10-30 casts according talking to a TA, so this necessitated frequent replacements.
In terms of ease of production, 3D printing required fewer materials and less manual labor, whereas polyurethane casting was more time-consuming. Surface quality and detailing was also better in 3D printing, which produced smoother surfaces similar to commercial LUCIA model numbers, while polyurethane models had rough spots and color inconsistencies post-painting, making it difficult to perfect.
Cost-wise, 3D printing was significantly cheaper, especially for large-scale production, while polyurethane casting costs increased gradually due to material and labor needs as well.
Ultimately, while both fabrication methods produced viable cervical models for the LUCIA apparatus, 3D printing came out as the superior method in terms of efficiency, cost, ease of production, and surface quality.
In conclusion, this project provided great insights into fabrication methods, allowing me to assess feasibility for different clinical applications!
Clean table:
