Synthesis of PCL/PHB/FHAp/PP composites and preliminary structural, mechanical, and biological evaluation for...

Long-bone critical-size bone defects are clinically problematic, and there are limitations in conventional methods of treating these defects (autografts, allografts), because of donor site morbidity, limited availability, and possible immune rejection. To promote osteogenesis and functional integration, bone tissue engineering scaffolds need to mimic the mechanical characteristics (100-230 MPa compressive strength) and electroactive properties of normal cortical bone. The paper presents quaternary composite scaffolds composed of polycaprolactone (PCL), polyhydroxybutyrate (PHB), fluorapatite (FHAp), and polypyrrole (PP), fabricated through solvent-cast 3D printing (SlC-3DP). To determine the best compositional ranges, 29 different formulations with different compositional ratios were characterised systematically with mechanical, electrical and biological properties. The compressive strengths of the selected formulations (S13, S17, S24) reached 100-105 MPa, which is close to the lower end of cortical bone. Tensile strength was 38-39 MPa, and flexural strength was 49-51 MPa. Electrical conductivity of the samples with 2.5%-5% PP was between 0.015 and 0.0345 S m^-1, which were within the literature ranges of electroactive bone tissue engineering samples.In vitrodegradation assessment in PBS at 37 °C over 60 d revealed compositionally tunable mass loss (5.5%-13.8%), with PHB content and FHAp. These are identified as key determinants of degradation rate. Cytocompatibility evaluation using the MTT assay on MG-63 osteoblast-like cells showed that representative formulation S1 achieved ∼140% cell viability relative to control at day 8. The haemolysis percentages of all tested formulations remained below the 2% threshold defined by ASTM F756-17, confirming non-haemolytic behaviour. These initial findings indicate that PCL/ PHB/ FHAp/ PP composites can be compositionally tuned to produce mechanical properties that are comparable to native bone and retain biocompatibility and electrical conductivity. Additional confirmation onin vivoresearch, thorough degradation, osteogenic differentiation evaluation with or without electrical stimulation, as well as quantitative porosity analysis, is necessary before being translated clinically.