Some biomaterials are osteoinductive, that is, they are able to trigger the osteogenic process by inducing the differentiation of mesenchymal stem cells to the osteogenic lineage. Although the underlying mechanism is still unclear, microporosity and specific surface area (SSA) have been identified as critical factors in material-associated osteoinduction. However, only sintered ceramics, which have a limited range of porosities and SSA, have been analyzed so far. In this work, we were able to extend these ranges to the nanoscale, through the foaming and 3D-printing of biomimetic calcium phosphates, thereby obtaining scaffolds with controlled micro- and nanoporosity and with tailored macropore architectures. Calcium-deficient hydroxyapatite (CDHA) scaffolds were evaluated after 6 and 12 weeks in an ectopic-implantation canine model and compared with two sintered ceramics, biphasic calcium phosphate and β-tricalcium phosphate. Only foams with spherical, concave macropores and not 3D-printed scaffolds with convex, prismatic macropores induced significant ectopic bone formation. Among them, biomimetic nanostructured CDHA produced the highest incidence of ectopic bone and accelerated bone formation when compared with conventional microstructured sintered calcium phosphates with the same macropore architecture. Moreover, they exhibited different bone formation patterns; in CDHA foams, the new ectopic bone progressively replaced the scaffold, whereas in sintered biphasic calcium phosphate scaffolds, bone was deposited on the surface of the material, progressively filling the pore space. In conclusion, this study demonstrates that the high reactivity of nanostructured biomimetic CDHA combined with a spherical, concave macroporosity allows the pushing of the osteoinduction potential beyond the limits of microstructured calcium phosphate ceramics.

BACKGROUND: Current therapies for bone cancers -either primary or metastatic -are

No abstract

Immune cells are sensitive to the microstructural and textural properties of materials. Tuning the structural features of synthetic bone grafts could be a valuable strategy to regulate the specific response of the immune system, which in turn modulates the activity of bone cells. The aim of this study was to analyse the effect of the structural characteristics of biomimetic calcium deficient hydroxyapatite (CDHA) on the innate immune response of macrophages and the subsequent impact on osteogenesis and osteoclastogenesis. Murine RAW 264.7 cells were cultured, under standard and inflammatory conditions, on chemically identical CDHA substrates that varied in microstructure and porosity. The impact on osteogenesis was evaluated by incubating osteoblastic cells (SaOS-2) with RAW-CDHA conditioned extracts. The results showed that macrophages were sensitive to different textural and structural properties of CDHA. Under standard conditions, the impact of inflammatory cytokine production by RAW cells cultured on CDHA played a significant role in the degradation of substrates, suggesting the impact of resorptive behaviour of RAW cells on biomimetic surfaces. Osteoblast differentiation was stimulated by the conditioned media collected from RAW cells cultured on needle-like nanostructured CDHA. The results demonstrated that needle-like nanostructured CDHA was able to generate a favourable osteoimmune environment to regulate osteoblast differentiation and osteogenesis. Under inflammatory conditions, the incubation of RAW cells with less porous CDHA resulted in a decreased gene expression and release of pro-inflammatory cytokines.

Low temperature self-setting ceramic inks have been scarcely investigated for solid freeform fabrication processes. This work deals with the robocasting of alpha-tricalcium phosphate/gelatine reactive slurries as a bioinspired self-setting ink for the production of biomimetic hydroxyapatite/gelatine scaffolds. A controlled and totally interconnected pore network of $300 mm was obtained after ink printing and setting, with the struts consisting of a micro/nanoporous matrix of needle-shaped calcium deficient hydroxyapatite crystals, with a high specific surface area. Gelatine was effectively retained by chemical crosslinking. The setting reaction of the ink resulted in a significant increase of both the elastic modulus and the compressive strength of the scaffolds, which were within the range of the human trabecular bone. In addition to delaying the onset of the setting reaction, thus providing enough time for printing, gelatine provided the viscoelastic properties to the strands to support their own weight, and additionally enhanced mesenchymal stem cell adhesion and proliferation on the surface of the scaffold. Altogether this new processing approach opens good perspectives for the design of hydroxyapatite scaffolds for bone tissue engineering with enhanced reactivity and resorption rate.

Rough implant surfaces have shown improved osseointegration rates. In a majority of dental implants, the microrough surfaces are obtained by grit blasting and/or acid-etching. The aim of this contribution was to evaluate the effects of acid-etching, after the grit-blasted treatment in titanium dental implants, on surface wettability, surface energy, osteoblast responses and its osseointegration behavior. Four surfaces were studied: as-machined, acid-etched, micro-rough by grit-blasting and the combination grit-blasted surface with acid-etched. The surfaces with increasing roughness show more osteoblastic adhered cells. This effect was most pronounced on samples blasted and blasted with acid-etching. The roughness obtained by grit-blasting is the main factor in comparison with the acid etching treatment in the biological response. These results were confirmed in vivo tests and histological analysis. The results demonstrated that the combination of the grit-blasted and acid-etched accelerated lightly bone regeneration at the different periods of implantation in comparison with the grit-blasted implants.

Bacterial infection in dental implants along with osseointegration failure usually leads to loss of the device. Bioactive molecules with antibacterial properties can be attached to titanium surfaces with anchoring molecules such as silanes, preventing biofilm formation and improving osseointegration. Properties of silanes as molecular binders have been thoroughly studied, but research on the biological effects of these coatings is scarce. The aim of the present study was to determine the in vitro cell response and antibacterial effects of triethoxysilypropyl succinic anhydride (TESPSA) silane anchored on titanium surfaces. X-ray photoelectron spectroscopy confirmed a successful silanization. The silanized surfaces showed no cytotoxic effects. Gene expression analyses of Sarcoma Osteogenic (SaOS-2) osteoblast-like cells cultured on TESPSA silanized surfaces reported a remarkable increase of biochemical markers related to induction of osteoblastic cell differentiation. A manifest decrease of bacterial adhesion and biofilm formation at early stages was observed on treated substrates, while favoring cell adhesion and spreading in bacteria-cell co-cultures.Surfaces treated with TESPSA could enhance a biological sealing on implant surfaces against bacteria colonization of underlying tissues. Furthermore, it can be an effective anchoring platform of biomolecules on titanium surfaces with improved osteoblastic differentiation and antibacterial properties.

No abstract