Bone Regeneration and Remodeling within a Unidirectional Porous Hydroxyapatite Bone Substitute at a Cortical Bone Defect Site: Histological Analysis at One and Two Years after Implantation

Abstract

Unidirectional porous hydroxyapatite (UDPHAp) is an artificial bone substitute with a unique microstructure consisting of 100–300-µm oval pores that present the material unidirectionally. UDPHAp has a compression strength of 14 MPa and a porosity of 75%, which promotes cell migration and capillary formation within the material. Despite these advantageous properties, bone remodeling and bone formation with UDPHAp remain unclear. To examine long-term remodeling and differences in bone formation based on the defect site, trapezoidal prism-shaped UDPHAp blocks were implanted into rectangular-shaped cortical bone defects in the proximal tibia of Japanese white rabbits. Histological analysis performed at 52 and 104 weeks after implantation revealed that bone and capillaries had formed within the implanted UDPHAp material. Bone formed within the UDPHAp implanted in the cortical defect of rabbit tibia and remodel up to two years. The percentage of new bone area within UDPHAp was larger in cortical lesions than that in medullary lesions. These findings suggest that UDPHAp is a promising material for the repair of non-critical-sized cortical bone defects.

Formation of osteon‐like structures in unidirectional porous hydroxyapatite substitute

“…Iwasashi et al analyzed bone formation within UDPHAp blocks implanted into the same animal bone defect model used in the present study and found that bone formation was greater in the cortical regions of the UDPHAp compared to medullary areas. Consistent with this previous finding, more lacunae and osteon‐like structures were found in the cortical areas in the present study.…”

“…In a previous study, we implanted UDPHAp blocks into a rectangular cortical bone defect in rabbit tibia and reported statistically greater new bone formation after 12 weeks in cortical areas than in the medullary cavity . This difference of bone growth between the cortical area and medullary cavity was also observed throughout the 2‐year period of recovery . Based on these findings, we speculated that the unique structure of UDPHAp promotes cortical bone formation under the mechanical stress of weight bearing.…”

“…7 This difference of bone growth between the cortical area and medullary cavity was also observed throughout the 2-year period of recovery. 8 Based on these findings, we speculated that the unique structure of UDPHAp promotes cortical bone formation under the mechanical stress of weight bearing. However, the mechanism by which bone remodeling occurs within UDPHAp remains unclear.…”

New description of gradual substitution of graft by bone tissue including biomechanical and structural effects, nutrients supply and consumption

“…Numerical simulation was performed using FEM software COMSOL Multiphysics v.5.2.®. The geometry model is similar to the fragment of rabit tibia investigated in experimental work performed by Iwasashi et al [19]. A 4.5 mm × 7 mm rectangular defect was made in proximal tibia of rabbit and then fitted with a piece of rectangular prism of porous biomaterial.…”

Development and Characterization of Gear Shape Porous Scaffolds Using 3D Printing Technology

“…The simplest structure of scaffold with mechanical optimization is the unidirectional porous structure where continuous pores and struts are constructed in the loading direction. Actually, this kind of unidirectional porous structure has effectively been utilized for a bone substitute, where bone growth takes place in the direction of the pores and maximized stiffness and strength are obtained in that direction [1], [2].…”