Eggshell waste derived nano-hydroxyapatite/metakaolin composites for bone scaffold applications

Area of Science:

• Biomaterials Science
• Materials Chemistry
• Nanotechnology

Background:

• Biomedical applications require advanced biomaterials with specific mechanical and biological properties.
• Eggshells are a readily available, low-cost source of calcium carbonate for hydroxyapatite synthesis.
• Metakaolin offers potential for reinforcing bioceramic composites.

Purpose of the Study:

• To develop a zero-waste synthesis method for eggshell-derived nano-hydroxyapatite (HA) reinforced with metakaolin (MK).
• To evaluate the structural, mechanical, bioactive, and antimicrobial properties of the fabricated HA/MK composites.
• To assess the biocompatibility of the composites for potential use in bone tissue engineering scaffolds.

Main Methods:

• Zero-waste wet chemical precipitation using calcined eggshell-derived calcium oxide and metakaolin.
• Incorporation of metakaolin at varying weight ratios (25-100% of HA mass).
• Characterization using XRD, FTIR, SEM-EDX, BET, mechanical testing, in vitro bioactivity, antimicrobial assays, and cytotoxicity tests.

Main Results:

• Successful synthesis of rod-like nano-hydroxyapatite crystals reinforced with metakaolin.
• Increasing metakaolin content reduced crystallinity and crystallite size.
• Cold pressing enhanced bulk density and mechanical strength (compressive strength: 16.4 MPa, diametral tensile strength: 11.8 MPa).
• Composites demonstrated significant in vitro bioactivity with apatite layer formation.
• Broad-spectrum antimicrobial activity and excellent biocompatibility with MC3T3-E1 pre-osteoblasts (>95% viability).

Conclusions:

• The developed eggshell-derived HA/MK composites possess favorable mechanical, bioactive, and antimicrobial characteristics.
• These composites show significant potential for application in bone tissue engineering scaffolds.
• The zero-waste synthesis approach offers a sustainable route for producing advanced biomaterials.