Multiscale porous geopolymer-hydroxyapatite composite scaffolds fabricated via hollow-core bead assembly for bone tissue engineering

• Fabrication of geopolymer–hydroxyapatite scaffolds via a bead–assembly approach. • Shear-thinning viscosity supports droplet sphericity and shell integrity. • Calcination at 900°C enhanced formation of β-Ca 2 P 2 O 7 /Ca 4 P 2 O 9 phases. • Higher calcium and phosphorus content supports osteogenic differentiation. • Gradual colonization of the materials without cytotoxic effect. This work reports the first fabrication of porous geopolymer–hydroxyapatite (GH) scaffolds via a spherical bead–assembly approach. The resulting composite represents a novel class of materials composed of a sodium aluminosilicate matrix modified with calcium silicate phases. The shear-thinning viscosity of ∼3 Pa·s at 100 s - ¹ in the GH mixtures supports droplet sphericity and preserves shell integrity. Furthermore, combined thermogravimetric and thermomechanical analyses (TGA, TMA) define a sintering window at 900°C, corresponding to a viscous-flow transition without vitrification. The assembled scaffolds exhibit hierarchical porosity, with macrodomains of tens to hundreds of micrometres and interconnected millimetre-scale voids, visualized by computed tomography and electron microscopy (micro–CT and SEM). The combination of mesopores and macropores closely mimics the spatial heterogeneity of trabecular bone, resulting in compressive strength values of 16–24 MPa. X-ray diffraction (XRD) results evidenced the enrichment of the microstructure with pyrophosphate phases β-Ca 2 P 2 O 7 , Ca 4 P 2 O, formed as intermediates products during surface redistribution of Ca 2+ and PO 4 3- ions from hydroxyapatite. GH scaffolds exhibited consistent cell proliferation and viability with minimal cytotoxicity. Biological assessment after immersing the scaffolds in simulated body fluid (SBF) revealed that the materials increase the solution’s pH, which is beneficial for promoting osteoblast proliferation and alkaline phosphatase (ALP) activity. ALP enzymatic activity gradually increased on the scaffolds, as confirmed by staining. All tests performed thus indicate favorable biocompatibility and optimal interaction between the scaffold and the host.