Physicochemical properties of carbon/hydroxyapatite/fibrin-based composite scaffolds

Hydroxyapatite (HAp) is widely used in bioactive scaffold development because of its mineral composition, biocompatibility, and capacity to support surface-mediated ion interactions. However, monolithic or highly mineral-dominated HAp ceramic scaffolds exhibit low fracture toughness, flaw-sensitive failure, and brittle mechanical behaviour, which limit their use in mechanically demanding applications. This study compared structurally distinct carbon components within a common HAp/fibrin scaffold platform to identify a lead formulation for further optimisation. Four formulations, HAp/fibrin (HAp/F), graphene oxide/HAp/fibrin (GO/HAp/F), functionalised graphite/HAp/fibrin (fG/HAp/F), and functionalised multiwalled carbon nanotube/HAp/fibrin (fMWCNT/HAp/F), were fabricated by freeze-drying using the same HAp/fibrin base and evaluation protocol. This controlled design enabled formulation-dependent effects to be assessed without major differences in composition or fabrication conditions. The scaffolds were characterised by scanning electron microscopy with energy-dispersive X-ray spectroscopy, Fourier transform infrared spectroscopy, dry compression testing, short-term simulated body fluid (SBF) weight-loss testing, and an indirect umbilical cord-mesenchymal stem cell MTS assay. All formulations exhibited micropore-dominated structures, with pore sizes of 0.5–14.4 μm and apparent porosities of 0.50–9.99%. FTIR supported the coexistence of carbon-associated, mineral, and organic functional groups. Dry compressive strengths ranged from 11.09 to 17.13 MPa. Among the formulations, GO/HAp/F showed the highest apparent porosity, the lowest early SBF weight loss, and the highest MTS response among the scaffold-conditioned groups, giving it the most favourable overall screening profile. Nevertheless, the low apparent porosity and micropore-dominated architecture remain major limitations. GO/HAp/F should therefore be considered a lead formulation for pore-architecture and hydrated-mechanical optimisation rather than a final tissue-regenerative construct.