Formation of osteon‐like structures in unidirectional porous hydroxyapatite substitute

Abstract

Unidirectional porous hydroxyapatite (UDPHAp) bone substitute comprises a microstructure of cross‐sectionally oval pores with diameters ranging from 30 to 300 µm. Bone remodeling within the UDPHAp is expected upon implantation into bone; however, the mechanism and factors influencing this bone growth remain unclear. The objectives of the present study were to assess the vasculature and microstructure of newly formed bone and to determine how bone formation is affected by load transfer and UDPHAp pore size. Formation of osteon‐like structures, defined by the presence of lacunae, canaliculi and a central lumen containing capillaries, was observed within the implanted UDPHAp material in all animals after six weeks. The number of osteocytes and osteon‐like structures in areas adjacent to the cortex of recipient bone was significantly higher than in areas next to the medullary cavity throughout the recovery period. Notably, osteon‐like structures tended to form in smaller diameter pores. Continuous bone remodeling might be promoted by the rapid formation of unidirectional capillaries and the osteocyte lacunae‐canalicular system. Load transfer and smaller pore size could positively affect cortical bone regeneration. © 2018 The Authors Journal of Biomedical Materials Research Part B: Applied Biomaterials Published by Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 2665–2672, 2018.

Radiographic and clinical assessment of unidirectional porous hydroxyapatite to treat benign bone tumors

“…Bone defects < 3 cm in longitudinal diameter were generally filled with granule-type UDPHAp alone. Block-type UDPHAp was grafted in the cavity with its pores parallel to the longitudinal direction of bone, as shown in previous reports 8 , 10 . The average volume of implanted UDPHAp was 7.5 g (range 1–46 g).…”

“…UDPHAp is a bone filling material with 75% porosity and 99.9% purity that also possesses an interconnected porous structure consisting of unidirectional oval pores toward the horizontal direction (approximately 100–300 µm in the longest diameter) that completely penetrate through the material 9 . The pore size and microstructure of UDPHAp facilitated the invasion of cells and fluids necessary for osteogenesis 8 . Owing to these features, histological analysis showed good bone regeneration and remodeling within UDPHAp 8 , 9 , and good clinical outcomes of UDPHAp implantation in various bone defects have been also reported 10 , 12 .…”

“…The pore size and microstructure of UDPHAp facilitated the invasion of cells and fluids necessary for osteogenesis 8 . Owing to these features, histological analysis showed good bone regeneration and remodeling within UDPHAp 8 , 9 , and good clinical outcomes of UDPHAp implantation in various bone defects have been also reported 10 , 12 . We therefore began to use UDPHAp in the treatment of benign bone tumors, which to our knowledge has not been reported.…”

“…Furtehrmore, osteogenic cells are able to penetrate deeply and easily into UDPHAp due to the unidirectional orientation with diameters of 100–300 µm 5 , 7 . These features facilitate new bone formation and remodeling within UDPHAp 8 , 9 . UDPHAp has been used to fill bone defects in orthopedic surgeries for high tibial osteotomy and cervical decompression 10 , 11 .…”

Effects of teriparatide on bone formation in novel unidirectional porous beta-tricalcium phosphate

“…An animal model of a cortical bone defect was created as previously described. 22,23 For this study, 12 skeletally mature male Japanese white rabbits (28 weeks old, 3.0–3.5 kg body weight) were used. Throughout the experimental study, the rabbits were maintained in separate cages under a 12-h light/dark cycle with free access to water and food.…”