Achieving injection molding interlayer strength via powder assisted hot isostatic pressing in material extrusion polyetheretherketone

Polyetheretherketone (PEEK), as fabricated by material extrusion, has the unique advantages of strength-to-mass ratio and biocompatibility in medical applications, yet its practical application is severely hindered by the insufficient interlayer adhesion, typically in the ranges of 5-20 MPa, far below the strength requirement of bone replacement of ~100 MPa. In this study, we present a novel powder-based hot isostatic pressing (PHIP) treatment to enhance the tensile strength of PEEK manufactured through the material extrusion method. By combining it with material extrusion printing parameters optimization, we successfully achieved a remarkable improvement in interlayer adhesion and tensile strength. Specifically, the tensile strength in the Z-XY was measured to be 102.6±0.7 MPa, 423.5% higher than that of the state-of-the-art PEEK extrusion specimens (19.6±6.1 MPa), 3.5% higher than the optimized X-YZ specimen reported in the literature (98.9±2.3 MPa), and comparable to the tensile strength of injection molded PEEK with a value of 107.7±0.7 MPa. The improvement in mechanical properties was attributed to the improved molecular diffusion and crystallinity of PEEK, as observed through scanning electron microscope (SEM) and differential scanning calorimetry (DSC) analysis. Microcomputer tomography (micro-CT) results confirmed the extensive and deep fusion between the extruded filaments and the elimination of most voids. Additionally, the PHIP method demonstrated superior shape retention stability compared to regular thermal annealing. These findings demonstrate the viability of significantly improving the mechanical properties of material extrusion PEEK via PHIP towards its bulk limit and offer a promising solution for enhancing the practical applications of PEEK manufactured through material extrusion.