Chitosan-quinoxaline Schiff base hydroxyapatite composite with antimicrobial properties for bone regeneration

Implant-associated infections remain a major challenge in bone regeneration, often compromising the long-term success of hydroxyapatite-based biomaterials. A new sulfonated quinoxaline aldehyde, 2-ethoxy-4-formylphenyl 2,3-dioxo-1,2,3,4-tetrahydroquinoxaline-6-sulfonate (B6), was synthesized and covalently grafted onto chitosan via Schiff base condensation to yield derivatives with controlled degrees of substitution (d1-d4). Which were subsequently incorporated into hydroxyapatite to form composite systems (dH0-dH4). Structural characterization using Fourier-transform infrared spectroscopy (FTIR), nuclear magnetic resonance (NMR), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) confirmed successful Schiff base formation, while thermogravimetric analysis (TGA) indicated enhanced thermal stability. Scanning electron microscopy with energy-dispersive X-ray analysis (SEM-EDX) and Brunauer-Emmett-Teller (BET) analyses revealed homogeneous hydroxyapatite dispersion and a mesoporous architecture (44.8 m² g^- 1, ~ 20 nm pores) for the optimized composite. Among the investigated formulations, dH2 exhibited the most balanced physicochemical and biological performance. The dH2 composite exhibited pronounced antimicrobial activity, achieving biofilm inhibition of 89.65% against Bacillus cereus and 86.65% against Staphylococcus aureus, with MIC values lower than those of reference antibiotics under the tested conditions. Cytotoxicity assessment using Vero and MG-63 cells demonstrated excellent biocompatibility, with > 99% cell viability at ≤ 125 µg/mL and IC₅₀ values of 344.99 and 156.62 µg/mL, respectively. These findings indicate that the developed chitosan-quinoxaline Schiff base hydroxyapatite composite represents a multifunctional, infection-resistant platform suitable for bone regeneration applications.