Physico-Chemical, In Vitro, and In Vivo Evaluation of a 3D Unidirectional Porous Hydroxyapatite Scaffold for Bone Regeneration

The unidirectional porous hydroxyapatite HAp (UDPHAp) is a scaffold with continuous communicated pore structure in the axial direction. We evaluated and compared the ability of the UDPHAp as a three-dimensional (3D) bone tissue engineering scaffold to the interconnected calcium porous HAp ceramic (IP-CHA). To achieve this, we evaluated in vitro the compressive strength, controlled rhBMP-2 release behavior, adherent cell morphology, cell adhesion manner, and cell attachment of UDPHAp. As a further in vivo experiment, UDPHAp and IP-CHA with rhBMP-2 were transplanted into mouse calvarial defects to evaluate their bone-forming ability. The Results demonstrated that the maximum compressive strengths of the UDPHAp was 7.89 ± 1.23 MPa and higher than that of IP-CHA (1.92 ± 0.53 MPa) (p = 0.0039). However, the breaking energies were similar (8.99 ± 2.72 vs. 13.95 ± 5.69 mJ, p = 0.055). The UDPHAp released rhBMP-2 more gradually in vivo. Cells on the UDPHAp adhered tightly to the surface, which had grown deeply into the scaffolds. A significant increase in cell number on the UDPHAp was observed compared to the IP-CHA on day 8 (102,479 ± 34,391 vs. 32,372 ± 29,061 estimated cells per scaffold, p = 0.0495). In a mouse calvarial defect model, the percentages of new bone area (mature bone + trabecular bone) in the 2x field were 2.514% ± 1.224% for the IP-CHA group and 7.045% ± 2.055% for the UDPHAp group, and the percentage was significantly higher in the UDPHAp group (p = 0.0209). While maintaining the same strength as the IP-CHA, the UDPHAp with 84% porosity showed a high cell number, high cell invasiveness, and excellent bone formation. We believe the UDPHAp is an excellent material that can be applied to bone regenerative medicine