Bone neo-formation and mineral degradation of 4Bone. ® Part I: Material characterization and SEM study in critical size defects in rabbits

Objective: This study reports the characterization process and in vivo application of a new high-porosity biphasic calcium phosphate (4Bone^® - HA 60%/β-TCP 40%) inserted into the critical size defect of a rabbit tibiae. Material and methods: Two critical size defects of 6 mm diameter were created in each tibia of 15 New Zealand rabbits, and a total of 60 defects were divided into a test group filled with 4Bone^® (n = 30) and a control group (n = 30). The material and the implants were characterized by scanning electron microscope (SEM) fitted with energy-dispersive X-ray spectroscopy (EDX). Results: The biomaterial's grain size decreased progressively with the graft integration process over the 60-day study period. Element analysis revealed increased percentages of Ca/P (2.86 ± 0.32 vs. 1.97 ± 0.59) in new bone and at the interface (P < 0.05). Element mapping showed that Ca and P were concentrated in the medullary and cortical zones in the test group but were concentrated only in cortical zones in the control group. Conclusions: Critical size defects in a rabbit tibia model can be sealed using this highly porous biphasic calcium phosphate; it supports new bone formation, creates a bridge between defect borders, and facilitates bone in growth.