Injection moulded biodegradable hydroxyapatite–kaolin geopolymer scaffolds with enhanced mechanical strength, biocompatibility, and antibacterial activity for bone regeneration

This study explored the synthesis and optimization of biodegradable scaffolds composed of bovine-derived hydroxyapatite (HA) and uncalcined kaolin, specifically formulated for extrusion-based injection moulding. The mixture contained geopolymeric solids (kaolin and silica sand, GP) activated with varying concentrations of sodium hydroxide (NaOH) to form a paste compatible with low-temperature curing processes. Characterizations included X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, field emission scanning electron microscopy- energy dispersive X-ray spectroscopy (SEM-EDS), the specific surface area and porosity analysis, and mechanical testing, alongside evaluations of biodegradability, cytotoxicity, and antimicrobial activity. Results demonstrated that a composition of 15 % GP and 1.5 % NaOH achieved an optimal balance of mechanical strength (7 MPa), porosity (55 %), Young`s modulus (5.6 GPa), and acceptable biocompatibility. The materials also exhibited effective antimicrobial activity, with the strongest inhibition observed against Staphylococcus aureus (31 mm zone at 1000 μg/mL) and the weakest against Pseudomonas aeruginosa (7 mm at 125 μg/mL). In addition, they demonstrated a suitable degradation behavior over 21 days in both phosphate buffer solution (PBS) and simulated body fluid (SBF) media. The cytotoxicity results showed a dose-dependent cytotoxic response; however, all tested concentrations maintained cell viability above 70 %, suggesting moderate biocompatibility. These findings suggested promising applications in bone tissue engineering, particularly for trabecular bone regeneration.