Graphene-filled nano-hydroxyapatite for printable hydrogels

Hydroxyapatite-graphene oxide (HA-GO) nanocomposites are promising materials for bone repair. However, conventional synthesis methods often lack the control necessary for uniform dispersion and reliable performance. This study employs a microfluidic platform informed by computational fluid dynamics (CFD) to regulate precursor mixing and nucleation under stable creeping-flow conditions. This approach avoids recirculation and heterogeneities in the formation process. Structural and morphological analyses demonstrate that microfluidic synthesis results in finely distributed, semi-crystalline hydroxyapatite domains that are closely interfaced with graphene oxide. This forms a continuous, hierarchical architecture that is distinct from that obtained by hydrothermal or mechanical blending methods. These structural features directly improve functional behavior, including reduced swelling, slower degradation, and pronounced shear thinning with rapid recovery, all of which are beneficial properties for minimally invasive injection and extrusion-based bioprinting. All nanocomposites exhibit good cytocompatibility; the 90% hydroxyapatite microfluidic formulation achieves the most favorable balance of mechanical reinforcement, structural uniformity, and biological response. These results clarify how controlled microfluidic synthesis influences the structure-function relationship in HA-GO systems. They also provide a pathway for tailoring performance according to the demands of bone regeneration. This integrated approach enhances the reproducibility and translational potential of HA-GO composites for advanced orthopedic applications. Microfluidic creeping flow guides particles from random injection to fully aligned downstream transport, with no recirculation. Controlled streamlines and velocity gradients ensure homogeneous mixing and reproducible HA–GO nucleation. • Microfluidic processing engineers HA/GO nanocomposites with controlled nucleation and dispersion. • Confined laminar mixing yields finely distributed semi-crystalline HA domains on GO templates. • Hierarchical interfaces enhance mechanical reinforcement and viscoelastic performance in hydrogels. • Strong shear-thinning and rapid recovery enable injectable and 3D-printable composite architectures. • Balanced stiffness, stability and cytocompatibility achieved at 90% HA loading for bone repair applications.