Anisotropic mechanical behaviour and microstructural characterization of 3D-printed hydroxyapatite composite reinforced with alumina plate-like particles

Hydroxyapatite (HA) is promising for bone-replacement applications, but its structural use is limited by low fracture toughness and defect-sensitive brittle failure. Here, DLP printed HA containing 1 vol% Al 2 O 3 plate-like particles was evaluated in three build orientations. XRD showed an HA-dominated phase composition with minor β-TCP and no evidence of extensive bulk degradation. All specimens reached similar relative densities of 92–93% t.d., yet microscopy revealed pronounced local changes: the particles aligned within the printed layers, were surrounded by microporous halos, and were locally associated with MgAl 2 O 4 and CaAl 2 O 4 phases. The mechanical response was strongly orientation dependent. Al 2 O 3 addition did not improve flexural strength or clearly enhance fracture toughness because potential crack-deflection mechanisms were offset by particle-associated porosity and interfacial defects. Microporous halo formation, rather than bulk densification or phase stability, was therefore identified as the main barrier to effective low-volume reinforcement of DLP printed HA.