Strategic Placement of Pores to Modulate Toughness in Hydroxyapatite Bone Scaffolds Fixation

Hydroxyapatite-based ceramic scaffolds are attractive for bone tissue engineering but are prone to brittle fracture during screw fixation. This study addresses the challenge of tuning local toughness in the peri-screw region of brittle ceramic scaffolds. Inspired by the presence of voids in many load-bearing biological materials, we explored how micro-pores interact with cracks to modulate fracture toughness. A circular scaffold is considered, featuring a central hole to accommodate the screw and a notch to trigger fracture. The scaffold was analysed under radial compression, using finite element simulations based on a phase field formulation for brittle fracture. The influence of notch size on crack propagation was first investigated and compared with the behavior of a plate under mode I failure. Subsequently, the influence of micro-pore shape and spatial arrangement on strength and toughness was examined. Results showed that the circular scaffold attenuates notch sensitivity when compared to the plate-like scaffold, due to the interplay between circumferential tension and radial compression. Circular pores increased energy dissipation through crack deflection and they decreased the strength due to stress concentration. Elongated pores preserved strength by mitigating these stress peaks. These findings identify key geometric parameters for optimizing the mechanical reliability of ceramic scaffolds requiring screw fixation.