Effects of porogen morphology on the architecture, permeability, and mechanical properties of hydroxyapatite whisker reinforced polyetheretherketone scaffolds.

Porous polyetheretherketone (PEEK) and bioactive hydroxyapatite (HA) reinforced PEEK scaffolds have attracted recent interest for enabling biologic fixation of orthopaedic and spinal implants, such as interbody spinal fusion cages. Porous PEEK and HA-PEEK scaffolds have been prepared by compression molding and leaching a fugitive porogen, most commonly NaCl salt crystals which exhibit a cubic morphology. Ellipsoidal or spherical porogen particles have been suggested to improve pore interconnectivity and permeability in scaffolds through improved porogen particle contact compared with a cubic porogen, but a direct comparison without concomitant effects from other factors is lacking. Therefore, the objective of this study was to investigate the effects of the porogen morphology on the architecture, permeability, and mechanical properties of bioactive HA whisker reinforced PEEK scaffolds. HA whisker reinforced PEEK scaffolds were prepared using a cubic or ellipsoidal NaCl porogen of equivalent size at multiple, equivalent levels of porosity and a constant level of HA reinforcement. Scaffolds prepared with an ellipsoidal porogen exhibited greater pore interconnectivity, indicated by a lower specific surface area measured by micro-computed tomography, and greater permeability than scaffolds prepared with a cubic porogen at 75-85% porosity. Compressive mechanical properties were not affected by the porogen morphology. Thus, an ellipsoidal porogen facilitated improved pore interconnectivity and permeability without compromising mechanical properties, and offers a means to circumvent an otherwise inherent design tradeoff between the benefit of increased porosity on permeability and the detriment of increased porosity on mechanical properties.