Synthesis of macro and micro porous hydroxyapatite (HA) structure from waste kina (Evechinus chloroticus) shells

• Conversion of the waste kina shells (Evechinus chloroticus) into hydroxyapatite.
• Synthesis step carried out at ambient pressure and at a low temperature of 100 °C.
• The shell porous and interconnected structure was preserved.
• HA layer was formed on the surface of the calcium carbonate structure of the shells.

The aim of this study was to investigate the conversion of waste kina shells (Evechinus chloroticus) into hydroxyapatite (HA, Ca10(PO4)6(OH)2), while preserving its porous and interconnected structure. The shells were subjected to a pyrolysis process followed by a chemical synthesis step at ambient pressure and at a low temperature of 100 °C under alkaline condition. The obtained HA had a porous structure with large pores ranged 300–500 µm and small pores of 10–20 µm, which is considered beneficial for bone repair materials to ensure blood and nutrient circulation required for bone regeneration. The samples also had high concentrations of magnesium (3.44%) which is an important component of HA used in bone grafting. X-Ray Diffractometer results indicated that a HA layer was formed on the surface of the calcium carbonate structure of the shells. The synthesized HA had no toxicity to the osteoblast cells and the porous and interconnected microstructure of the shells was preserved during an incubation period of 3 days. The obtained HA may have potential applications in bone tissue enegineering.

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