The microstructural evolution of material extrusion based additive manufacturing of polyetheretherketone under different printing conditions and application in a spinal implant

With the advances in additive manufacturing, polyetheretherketone (PEEK), a biocompatible polymer, can be used in biomedical applications such as spinal implants. This paper aims to investigate the evolution of the microstructure of PEEK parts manufactured by material extrusion (MEX)-based additive manufacturing with different printing parameters. The effect of layer thickness (LT) and nozzle diameter on mechanical properties was investigated using tensile, Charpy impact, and short beam strength (SBS) tests. Two different LTs, 0.1 and 0.2 mm, and two different nozzle diameters, 0.6 and 0.8 mm, were used as printing parameters. By increasing the LT, tensile strength dropped by around 24%, and impact strength by almost 55%. Moreover, altering the LT resulted in a 15% decrease in interlaminar shear strength (ILSS) from the SBS test. In addition, increasing the nozzle diameter also led to a significant reduction in all of the results as tensile strength, Charpy impact strength, and ILSS. The results were also consolidated by scanning electron microscopy. The main findings were that increasing LT leads to an increase in microstructural defects that act as stress concentrators. Following the tests, response surface methodology (RSM) was used to determine optimal printing parameters. In the end, using the optimum printing parameters from the RSM study, a structural analysis of a MEX-printed spinal implant was conducted through finite element method, considering the loading cases mimicking daily human body motions. Highlights: As layer thickness increased, tensile and impact strength dropped. Tensile and impact strength dropped truly with increasing nozzle diameter. SEM revealed that increasing layer thickness causes more microstructural flaws. FEM analysis showed that PEEK-based implant provides structural integrity.