Optimization and biocompatibility analyses of fused filament fabrication-printed polylactic acid-silicon nitride scaffolds with enhanced mechanical properties.

Fused filament fabrication (FFF) in additive manufacturing has emerged as a potential technology in the development of tissue engineering scaffolds of precise, complex geometries. The choice of material and process parameters is significant in determining their properties, such as mechanical strength. Polymer-ceramic composites with exceptional bioactivity have the potential for FFF applications in fabricating scaffolds. In this study, polylactic acid (PLA) composite scaffolds reinforced with silicon nitride (Si₃N₄) particles in various weight ratios (97:03, 95:05, and 93:07 weight%) were developed using FFF technology. Taguchi's orthogonal array and grey relational analysis were employed to optimize three parameters (polymer-reinforcement ratio, infill density, and layer thickness) to analyze mechanical strength - through tensile, compressive, flexural, and impact tests - surface morphology using scanning electron microscopy, and biocompatibility through 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT assay). The optimal formulation of 95:05 wt.%, 0.17 mm layer height, and 100% infill density demonstrated superior mechanical properties with a tensile strength of 47.52 MPa, flexural strength of 67.3 MPa, compressive strength of 71.57 MPa, and impact strength of 2.63 kJ/m². Analysis of variance revealed layer thickness as the most influential factor (41.7%) impacting mechanical properties, followed by PLA: Si₃N₄ ratio and infill density. MTT assay and immunofluorescent staining analysis revealed that the optimal formulations enhanced cell viability and proliferation compared to controls.