Taguchi Optimization of Additively Manufactured PEKK and Silicon Nitride Loaded PEKK for Medical Device Applications

Silicon nitride (Si₃N₄) is reported to exhibit antibacterial properties and support osteoblast maturation, while polyetherketoneketone (PEKK) is considered to potentially have antibacterial and osseointegrative properties while offering favorable manufacturability through extrusion-based additive manufacturing compared to traditional ceramics manufacturing. Incorporating silicon nitride into PEKK is hypothesized to enhance its bioactivity while maintaining processability, making Si₃N₄-PEKK composites promising for medical implants. Our objective was to determine optimal fused filament fabrication (FFF) parameters for PEKK and Si₃N₄-PEKK. Taguchi optimization (L9 array, n = 5) was performed on PEKK and 15 vol.% Si₃N₄-PEKK to assess the impact of printing parameters (layer height: 0.1, 0.2, and 0.3 mm; nozzle temperature (PEKK/Si₃N₄-PEKK): 340/380, 370/400, and 400/420; bed temperature: 130°C, 150°C, and 170°C; and chamber temperature: 110°C, 130°C, and 150°C) on ultimate tensile strength (UTS). Z-directional tensile specimens were printed on a medical FFF printer. Specimens underwent tensile testing according to ASTM D638. Signal/noise ratios for UTS were calculated and ANOVA (Minitab 21.4.2) was used to assess statistical significance (p < 0.05). Layer height had the greatest impact on UTS for both PEKK and Si₃N₄-PEKK. Optimal nozzle and chamber temperatures were 400°C and 130°C, respectively, while the optimal layer height was 0.1 mm for both materials. The optimal bed temperature for PEKK and Si₃N₄-PEKK was 150°C and 170°C, respectively. For PEKK, differences in all parameters were significant except for bed temperature, while for Si₃N₄-PEKK all parameters were significant except for nozzle temperature. The specimens with optimum statistically significant parameters showed the highest UTS for both PEKK (91 ± 2 MPa) and Si₃N₄-PEKK (76 ± 3 MPa). Layer height is the most influential printing variable for both PEKK and Si₃N₄-PEKK. The optimal PEKK printing condition has a comparable UTS, while Si₃N₄-PEKK achieved 84% of the injection-molded value for neat PEKK.