Enhanced mechanical properties and osseointegration features of CaNb2O6-PNb9O25-Ca3(PO4)2 triphasic nanostructured bioceramics derived by optimised sinterization of Nb2O5 and natural hydroxyapatite-β-tricalcium phosphate

The aim of this work was to evaluate the effects of sintering temperature over the structural, physical and mechanical properties in addition to the in vivo biological performance of nanostructured biocomposites obtained from the mixture between calcined fish bone (hydroxyapatite + beta-tricalcium phosphate) and niobium pentoxide. The sintering temperatures varied from 650 to 1150 degrees C, in steps of approximately 50 degrees C. The results showed the formation of a stable triphasic nanostructured bioceramic with almost constant relative proportions between the CaNb2O6 , PNb9O25 and Ca-3(PO4)(2) phases. Special attention was given to the sintering temperature at 1080 degrees C because there was occurrence of a liquid phase, and the sample showed localised maximisations of linear shrinkage, density and Vickers hardness. This niobium-biphasic calcium phosphate 1080 (Nb-BCP-1080) nanostructured biocomposite presented measured values for compressive strength (242 +/- 29 MPa), Young's modulus (19.63 +/- 3.5 GPa), Poisson's ratio (0.248 +/- 0.016) and flexural strength (24 +/- 5.9 GPa) close to those of some human bones. Then, to further explore these characteristics, in vivo studies were performed by implanting 8.0-mm diameter discs of this material in calvaria of rats. Histological observation showed the occurrence of osseointegration between the neo-formed bone and the triphasic bioceramic just 45 days after implantation. In conclusion, the observations of this work unambiguously show that CaNb2O6-PNb9O25-Ca-3(PO4)(2) triphasic bioceramics are candidates for bone replacements where high and medium loads are demanded.