Novel mixed mode I/II fracture load prediction of chitosan polymer-infiltrated hydroxyapatite ceramic scaffolds using ICIM/GMTS theory in bone scaffold additive manufacturing

• First application of ICIM with GMTS for mixed-mode fracture load prediction in polymer-infiltrated scaffolds. • Novel triphasic calcium phosphate bio-ink for DIW 3D printing in bone scaffold manufacturing. • Unique use of Voronoi Compact Beam Bending (VCBB) samples for mixed-mode I/II fracture testing. • Significant toughness enhancement using chitosan infiltration, closely matching trabecular bone properties. • Validated fracture behavior with FEA and experimental results, achieving a prediction error of 23%. In modern surgery, ceramic scaffolds are favored for their biocompatibility, osteoconductivity, and bioactivity, enhancing osseointegration and bone regeneration. Despite this, the mechanical response of such constructs requires further advancement. This study introduces a novel approach by synthesizing an advanced triphasic calcium phosphate-based powder, utilized as a bio-ink for Direct Ink Writing (DIW) Additive Manufacturing (AM). Scaffolds, designed with varying irregularities and relative densities through Voronoi tessellation, are 3D printed as Voronoi Compact Beam Bending (VCBB) mixed mode I/II fracture samples and infiltrated with chitosan polymer to enhance their toughness. Parallel Brazilian Disk (BD) testing assesses the tensile strength of the infiltrated scaffolds as a reference. The Infiltrated Composite Isomorphism Model (ICIM), integrated with the Generalized Maximum Tangential Stress (GMTS) criterion, is employed to explore the fracture loads of these bi-material, anisotropic constructs. Detailed finite element analysis derives fracture parameters for the theoretical framework. Experimental results, validated against numerical and theoretical approaches, reveal an average error of 23 % across various crack geometries, loading modes, boundary conditions, scaffold irregularities, and relative densities. The fracture toughness of the polymer-infiltrated ceramic network (PICN) ranges from 28 to 382 KPa ( m 0.5 ) , closely aligning with the properties of trabecular bone.