Sterilizing PLA for Medical Use – How PLA Survived Autoclaving

DtM-v3.1 Face Shield published an article a few days ago concerning research on using PLA filament for objects in the “sterile surgical field.” I can barely contain my excitement!

Last week, I printed a mask using Atomic’s Clear “No Yellow” PLA. In order to thermoform the nose portion to my face, I dipped that part in boiling water. As you may be able to see from the photograph to the right, that section looks a lot like molded plaster. I thought to myself that this process may be able to waterproof models. I have not taken the time to try it yet, so I was happy to see that other people had been experimenting with the process.

I have had difficulty printing face shield models as most require filaments other than PLA and I only print with PLA/PLA+ filament. I am working on designing a face shield band that I will hot water anneal into shape once I figure out how to place knobs for holding the plastic sheet. If I owned a pressure cooker, I could autoclave the band as well.

I would like to dissect the entire research paper, however, in this post I will simply list what I thought were key points:

Four 30mm cubes with different infill geometries were designed with the software Tinkercad™ (Autodesk®, Inc.), and were exported as a standard tessellation language (STL) file. The STL file was then imported into Ultimaker Cura LulzBot® Edition software (Ultimaker B.V., version 21.08, Aleph Objects, Inc.), where adjustments for wall thickness of 1.5 mm and different infill geometries, “tetrahedral”, “triangles”, “zig-zag”, and “grid”, were selected (Fig. 1). The cubes were printed 20% infill…LulzBot® Mini 3D printer (Aleph Objects, Inc.).

The four cube designs were printed simultaneously with 0.38mm layer height utilizing a 0.5mm printhead nozzle. Print bed and printhead nozzle temperatures were selected according to manufacturer specifications for each print material using the highest recommended nozzle temperatures, defaulting to 60 °C for bed temperature (Table 1). Higher temperatures have been shown to optimize layer adhesion and strength for FDM printing. Filament materials were selected based on consumer accessibility.

The seven materials tested were colorFabb Woodfill (ColorFabb BV, Netherlands), Dragons Metallic PLA in All That Glitters Gold (Maker Geeks, USA), Essentium PLA in Gray (Essentium Materials LLC, USA), Maker Series PLA in Food Safe FDA OK Clear (MatterHackers, Inc., USA), Maker Series PLA in White HOT White, Proto-Pasta HTPLA in White (Protoplant, Inc., USA), and Raptor Series PLA in HD Vivid Blue (Maker Geeks, USA).

Cubes were subjected to a hot water-bath annealing treatment… for 30 mins at 100 °C. The cubes were removed from the hot water-bath and allowed to cool to room temperature without interference.

Following the hot water-bath annealing treatment, the cubes were placed in Chex-all® II Instant Sealing autoclave sterilization pouches… and subjected to surgical grade autoclaving … for 45 mins at 134 °C and a pressure of 375 PSI… The packages were removed from the autoclave and the cubes were allowed to cool to room temperature.

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