An alternative filament fabrication method as the basis for 3D-printing personalized implants from elastic ethylene vinyl acetate copolymer

In this work, a novel tool for small-scale filament production is presented. Unlike traditional methods such as hot melt extrusion (HME), the device (i) allows filament manufacturing from small material amounts as low as three grams, (ii) ensures high diameter stability almost independent of the viscoelastic behavior of the polymer melt, and (iii) enables processing of materials with rheological profiles specifically tailored toward fused filament fabrication (FFF).

Hence, novel materials, previously difficult to process due to HME limitations, become easily accessible for FFF for the first time. Here, we showcase the production of highly flexible drug-free, and drug-loaded filaments based on ethylene-vinyl acetate polymers with a vinyl acetate content of 28 w% (EVA28) and unprecedented high melt flow rates of up to 400 g/10 min. Owing to their low viscosity, FFF with low print nozzle sizes of 250 μm was achieved for the first time for EVA28.

These small nozzle diameters facilitate 3D-printing of high-resolution structures in small-dimensional dosage forms such as subcutaneous implantable drug delivery systems, which can later be used for personalization. Consequently, the material portfolio for FFF is tremendously broadened, allowing material and formulation optimization toward FFF, independent of a preliminary extrusion process.

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Materials

Ethylene-vinyl acetate polymers (EVAs) with a vinyl acetate (VA) content of 28 wt% and a melt flow rate (MFR; determined according to ASTM D 1238 at 190 °C and 2.16 kg load) of 150 g/10 min (Ateva 2830 A; EVA28/150) and of 400 g/10 min (Ateva 2842 A; EVA28/400) were kindly donated as powders by Celanese Corp. (Irving, TX, USA). EVA with a VA content of 28 wt% and an MFR of 25 g/10 min (Greenflex XS70; EVA28/25; Eni Versalis, San Donato, Milanese, Italy) that was previously used for filament fabrication via HME²¹ served as a reference. Micronized progesterone (P4) was used as received from Euro OTC & Audor Pharma GmbH (Bönen, Germany). As the first layer adhesive aid during 3D-printing, the black rubber mat P-surface 141 (PP-Print GmbH, Bayreuth, Germany) was applied.

Brandl, B., Eder, S., Hirtler, A. et al. An alternative filament fabrication method as the basis for 3D-printing personalized implants from elastic ethylene vinyl acetate copolymer. Sci Rep 14, 22773 (2024). https://doi.org/10.1038/s41598-024-73424-6