Investigating the Impact of Fused Filament Fabrication Process Parameters on the Compressive Properties of Porous PEEK and PEKK Biomaterials

Abstract

Additive manufacturing (AM) can create orthopedic devices with integrated porosity that enables bone fixation post-implantation. While porosity is key in promoting bone ingrowth and long-term fixation, the device must provide adequate mechanical strength and functionality. Since AM process parameters dictate the final mechanical performance of printed parts, identifying key process parameter levels that preserve or improve such behavior in load-bearing devices with integrated porosity is essential. Using a Taguchi design of experiments, gyroid-structured polyether-ether-ketone (PEEK) and polyether-ketone-ketone (PEKK) specimens were fabricated via fused filament fabrication (FFF) AM to examine the impact of nozzle temperature (T_N), chamber temperature (T_Ch), and layer height (LH) on their compressive mechanical behavior. In addition to compression testing, the printed specimens were analyzed using optical microscopy, scanning electron microscopy, and micro-computed tomography. Elevated processing conditions, specifically high T_Ch combined with thick LH, can enhance heat retention, slow crystallization, increase strut thickness, and improve bonding at strut junctions, enabling porous PEEK and PEKK to withstand higher compressive loads. The elastic moduli of all the porous specimens were more sensitive to variations in processing conditions than their yield strength. Notably, the more amorphous PEKK specimens achieved over 87%–88% of PEEK's calculated elastic modulus in this study and 87%–90% of the yield strength without undergoing annealing. These results are promising, considering that, like PEEK, the elastic modulus of the porous PEKK fell within the range of trabecular bone, while its yield strength surpassed that of trabecular bone.