Influence of hydroxyapatite granule size, porosity, and crystallinity on tissue reaction in vivo. Part B: a comparative study with biphasic synthetic biomaterials

Objective: The aim of this study was to compare the influence of the physical-chemical properties of synthetic hydroxyapatite (HA) and biphasic commercial materials on the biological behavior of study materials through material characterization and SEM analysis before and after application in rabbit tibias.

Materials and methods: Two defects were performed in each tibiae for a total of 180 defects: Group I HA granules (2000-4000 μm), Group II HA granules (1000-2000 μm), Group III HA granules (600-1000 μm), Group IV Ossceram^® nano (Bredent medical GmbH & Co. KG, Senden, Germany), Group V 4Bone^® granules (MIS Implants Technologies Ltd, Shlomi, Israel), and Group VI: empty defect acted as control. Comparison was performed by mean of material characterization, SEM, and EDX.

Results: 4Bone: Pores between 300 μm and 100 μm with intra- and interparticle spaces. Ossceram show also interparticle and intraparticle pores, between 100 μm and 26 μm, but the proportion of interparticles in the 4Bone is clearly minor than in the Ossceram. Related with pure HA, Group III has the greatest porosity (69.3%). For Group I, the intraparticle pores (0.71 μm) are about 8 times larger than those of the other two samples. The analysis of the images of in vivo SEM shown as biphasic groups has presented a more gradual resorption of the material.

Conclusion: HA-based biomaterials, both pure and biphasic, are an effective means for bone regeneration processes; of these, materials with higher initial and secondary porosimetry allow greater cell colonization and therefore more effective substitution by new bone. The two-phase materials have a higher ion release to the environment in the early stages and thus allow greater colonization by collagen fibers that can be matured into new bone.