Unidirectional porous beta-tricalcium phosphate and hydroxyapatite artificial bone: a review of experimental evaluations and clinical applications

Abstract

In Japan, where allograft bone transplantation is not widespread, prospects for artificial bones are very high. Therefore, artificial bones with various compositions, porous structures, and porosities have been developed and employed for clinical use. Both Affinos^® and Regenos^® (made of beta-tricalcium phosphate and hydroxyapatite, respectively) are artificial bones with a unique unidirectional porous structure, in which pores with a diameter suitable for tissue penetration (25-300 μm) are aligned in one direction. The unidirectional porous structure allows rapid penetration of blood deep into the materials by a capillary effect. In animal experiments, Affinos^® showed well-balanced resorption and was replaced with the host's own bone from an early stage after implantation and new bone formation and remodeling were observed in the cortical bone and medullary cavity. When implanted for clinical situation, resorption from an early stage and good replacement with the patient's own bone were also observed. Regenos^® has an internal osteon-like material and a vascular-like structure that is maintained within the pores even after long-term implantation, as noted in an animal experiment. When implanted for clinical situation, good osteoconductivity was observed from an early stage of implantation. In addition, the material was observed to be slowly absorbed over time in some cases. We have discussed the beneficial effects of combining teriparatide and platelet-rich plasma impregnation and the potential prospects of these artificial bones.

Keywords: Artificial bone; Beta-tricalcium phosphate; Bone grafting; Hydroxyapatite; Unidirectional porous structure.

Fig. 1

Three-dimensional micro computed tomography image of Affinos^®, unidirectional porous β-TCP. The pores, 25–300 μm in diameter, are lined up in one direction. The porosity is 57%, and its initial compression strengths of 8 and 1.5 MPa are applied in the directions parallel and perpendicular to the pores, respectively

Fig. 2

Three-dimensional micro computed tomography image of Regenos^®, unidirectional porous HAp. The pores, 100–300 μm in diameter, are lined up in one direction. The porosity is 75%, and its initial compression strengths of 14 and 1.0 MPa are applied in directions parallel and perpendicular to the pores, respectively