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.

Radially Porous Nanocomposite Scaffolds with Enhanced Capability for Guiding Bone Regeneration In Vivo

“…[17] Previous studies have certified that scaffolds with oriented porous structure are more favorable for infiltration and migration of surrounding cells, exchange of nutrients and wastes, and also deposition of extracellular matrix, compared with scaffolds with random porous structure. [18][19][20] Among a variety of methods, [2,3] the burgeoning 3D printing [21,22] and directional freeze-casting techniques [23,24] are the most powerful approaches to engineer TE scaffolds with oriented porous structure, which both have their own advantages. 3D printing, for example, can spatially control the structure and composition of scaffolds to an unprecedented degree.…”

Reconstruction of rabbit mandibular bone defects using carbonate apatite honeycomb blocks with an interconnected porous structure

“…Regenos ® is widely used in the orthopedic field in Japan for bone defects of the arm, leg, and vertebra, bearing large loads [ 40 , 41 ]. It has already been applied in clinical cases to intra-articular calcaneal fractures with large bone defects and distal radius fractures and has yielded good results [ 42 , 43 ].…”

Freeze Casting with Bioceramics for Bone Graft Substitutes

“…Freeze-cast HA has shown great potential as a bone graft substitute. Unidirectional porous HA with pores averaging 300 μm have been studied in vivo with animal models [103,104] and clinical cases [96,105] with success in orthopedic applications [106] and Japanese Pharmaceuticals and Medical Devices Agency (PMDA) approval for use in human cases [107].…”

“…One benefit of β-TCP over HA is its improved osteoinductivity, with many reports on successful osteoinduction through its usage [109]. While also readily accepted by the body, TCP resorbs much faster than HA, with partial resorption occurring within ten weeks [95,110] and full resorption of a porous β-TCP implant occurring within 1-1.5 years leading to potential implant loosening [106,111]. Along with faster resorption, TCP exhibits lower mechanical strength, which can limit the material's use in loading applications [110,112].…”

“…The major advantages of this technique are its versatility for material fabrication and many methods of structural control. Freeze casting has shown flexibility in working with a variety of biocompatible ceramic and ceramic composite materials with success in vitro and in vivo [106]. This technique's affinity with bioceramics means bone growth and osteoconduction are also achievable.…”