# Nano-Hydroxyapatite Derived from Biogenic and Bioinspired Calcium Carbonates: Synthesis and In Vitro Bioactivity

## TL;DR

This paper explores using natural calcium carbonate sources to make hydroxyapatite for bone regeneration, finding that eggshell-derived materials support better cell growth.

## Contribution

The study introduces novel synthesis of hydroxyapatite from biogenic calcium carbonate sources and evaluates their bioactivity for bone regeneration.

## Key findings

- Eggshell-derived hydroxyapatite sintered at 900°C showed the best cell adhesion and proliferation.
- Cuttlebone and amorphous calcium carbonate sources resulted in poorer cell interconnection and round-shaped cells.
- Materials derived from different sources exhibited variable densification and sintering behavior due to doping elements.

## Abstract

Biogenic calcium carbonates naturally contain ions that can be beneficial for bone regeneration and therefore are attractive resources for the production of bioactive calcium phosphates. In the present work, cuttlefish bones, mussel shells, chicken eggshells and bioinspired amorphous calcium carbonate were used to synthesize hydroxyapatite nano-powders which were consolidated into cylindrical pellets by uniaxial pressing and sintering 800–1100 °C. Mineralogical, structural and chemical composition were studied by SEM, XRD, inductively coupled plasma/optical emission spectroscopy (ICP/OES). The results show that the phase composition of the sintered materials depends on the Ca/P molar ratio and on the specific CaCO3 source, very likely associated with the presence of some doping elements like Mg2+ in eggshell and Sr2+ in cuttlebone. Different CaCO3 sources also resulted in variable densification and sintering temperature. Preliminary in vitro tests were carried out (by the LDH assay) and they did not reveal any cytotoxic effects, while good cell adhesion and proliferation was observed at day 1, 3 and 5 after seeding through confocal microscopy. Among the different tested materials, those derived from eggshells and sintered at 900 °C promoted the best cell adhesion pattern, while those from cuttlebone and amorphous calcium carbonate showed round-shaped cells and poorer cell-to-cell interconnection.