Polylactic acid/silicon nitride biodegradable and biomedical Nanocomposites with optimized rheological and thermomechanical response for material extrusion additive manufacturing

Silicon nitride (Si₃N₄) is a well-known bio-ceramic that is widely used for medical and healthcare purposes, due to its biocompatibility and superior chemical, physical and mechanical properties, which make it suitable for implants. Due to its unique features, examining its efficiency as a cost-effective reinforcement agent for thermoplastics in material extrusion (MEX) Additive Manufacturing (AM) seems promising for the development of composites for biomedical applications. The mainstream thermoplastic in MEX AM is the biodegradable and biocompatible Polylactic Acid (PLA). Herein, a biomedical grade PLA was used as a matrix for Si₃N₄ nanopowder in various filler loadings. Filaments were prepared with melt extrusion, whereas MEX 3D printing was engaged to prepare specimens for mechanical evaluation, according to standardized tests. The effect of the Si₃N₄ nanoparticles loading and its optimization was carried out by means of fifteen (15) different tests. The nanocomposites were fully characterized with Raman, Thermogravimetric Analysis, and Scanning Electron Microscopy, among others. Aspects of the process, such as rheology and processability, were also assessed and quantified. A more than 40% increase in both flexural and tensile strength of the samples was found, proving the hypothesis for the effectiveness of Si₃N₄ nanoparticles as a compelling alternative reinforcement agent in MEX AM of biomedical PLA-based parts.