Two-step freeze casting fabrication of hydroxyapatite porous scaffolds with bionic bone graded structure

Hydroxyapatite (HA) porous scaffolds with bionic bone graded structure were fabricated by a two-step freeze casting. The phase, porosity, pore morphology, and compressive strength of the fabricated HA scaffolds were characterised. The HA scaffolds did not decompose after sintering at 1250 °C. The porosity of the inside and outside of the graded-porosity HA scaffolds was controlled by adjusting the initial HA content of the casting slurries. Cylindrical HA scaffolds with a radially aligned porosity gradient from the inside (highly porous) to the outside (less porous) were prepared, and a natural transition was found at the interface because partial melting–recrystallization occurred between the two sides. The compressive strength of the graded HA scaffolds depended on the porosity of the inner part. A compressive strength of 22.2±4.1 MPa was achieved at an average porosity of 42.3% and outer thickness of about 2 mm.