EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

The regeneration of load-bearing bone segments is a critical need, still unmet due to the lack of bone scaffolds capable of inducing extensive osteogenesis and vascularization, and with appropriate mechanical performance. Indeed, conventional fabrication methods do not allow accurate control of compositional and structural changes, particularly during the consolidation of calcium phosphate bioceramics, where irreversible crystal growth and chemical stabilization occurs, reducing the scaffold bioactivity. The present work describes the unique properties of a large hydroxyapatite (HA) scaffold obtained by biomorphic transformation of natural wood structures, obtained thanks to the application of heterogeneous gas–solid reactions acting in the 3-D state. Thanks to this unpreceded approach, the scaffold shows enhanced bioactivity, induced by the synergistic effect of bone-like composition, lamellar nanostructure and hierarchical osteon-mimicking architecture exhibiting wide interconnected porosity from the nano to the macro scale. We found that these features enable continuous exchange of bioactive ions from and to the scaffold when soaked in physiological body fluids, as chemical signals supporting osteogenic cell differentiation. In this respect, bioreactor studies show overexpression of various osteogenic genes with the biomorphic scaffold in comparison with sintered hydroxyapatite scaffold with similar porosity extent. Moreover, the hierarchical, channel like porosity, closely resembling the osteon structure, was found to facilitate the crosstalk between mesenchymal and endothelial cells, very promising to promote vascularization in the whole scaffold volume. Furthermore, such a hierarchical architecture was found to induce damage-tolerant mechanical performance, unusual for a pure ceramic material, permitting the use of fixating screws during implantation in bone defects. We observe that such mechanical properties make biomorphic ceramics as unique materials laying between ceramics and woods, when depicted in Ashby maps. The biologic and mechanical performance so far observed are very promising for application as scaffolds to regenerate load-bearing segmental bone defects.