Taguchi-based optimization and comparative analysis of filament and direct powder FFF for biomedical UHMWPE composites

Fused Filament Fabrication (FFF) has become a key additive manufacturing technique for producing biomedical components with complex geometries and reduced material waste. However, the processing of ultra-high molecular weight polyethylene (UHMWPE) remains challenging due to its high melt viscosity and poor interlayer adhesion. This study aims to optimize FFF parameters and evaluate an alternative direct powder extrusion approach for UHMWPE composites reinforced with hydroxyapatite (HAP) and titanium dioxide (TiO₂). A low-cost, single-screw filament extruder was developed in-house to fabricate UHMWPE/HAP/TiO₂ filaments for conventional FFF printing. The same extruder was later modified to operate as a direct powder extrusion head, eliminating the filament fabrication step. A Taguchi L16 orthogonal array was used to optimize four key process parameters (extrusion temperature, bed temperature, infill percentage, and number of outer perimeters) with ultimate tensile strength (UTS) as the response variable. ANOVA and signal-to-noise ratio analyses were employed to determine parameter significance. Subsequently, a second-order polynomial regression model was developed based on the experimental dataset to predict UTS as a function of the dominant FFF parameters, effectively capturing the non-linear behavior of the process. Extrusion temperature and infill percentage were identified as the most influential parameters affecting tensile strength. The refined regression model demonstrated robust predictive reliability, achieving an adjusted $$\:{R}^{2}$$ of 75.04% and a predictive $$\:{R}^{2}$$ of 66.38%, ensuring its suitability for process optimization. Comparative mechanical testing showed that direct powder-printed samples achieved a maximum UTS of 50.15 MPa, nearly identical to filament-based prints, confirming the feasibility of direct extrusion for UHMWPE composites. The study establishes a cost-effective route for manufacturing biomedical-grade UHMWPE composites, demonstrating that direct powder extrusion (DPE) is a viable, high-performance alternative to filament-based FFF. The results identify infill percentage and the quadratic effect of perimeters as the most critical factors influencing mechanical integrity. The validated second-order model provides a reliable framework for reaching a peak UTS of 50.15 MPa, effectively bridging the gap between low-cost fabrication and industrial-grade performance. These findings establish a foundation for advancing bio-additive manufacturing of orthopedic components through simplified, low-degradation processing stages.