Apatite formation abilities of various carrageenan gels in simulated body environment

Organic–inorganic hybrids with apatite-forming abilities in physiological environments offer possibilities for building flexible bone-bonding bioactive materials; several functional groups are known to induce apatite nucleation. Here, bioactive organic–inorganic hybrids from κ-carrageenan and λ-carrageenan containing sulfonic groups were prepared. Carrageenan hydrogels were made by cross-linking with CaCl2. The apatite-forming abilities of each kind of carrageenan hydrogel were examined using simulated body fluid (SBF); λ-carrageenan was found to be superior to κ-carrageenan for this purpose. The former swelled significantly in aqueous conditions, releasing a large amount of Ca2+ ions into the SBF, contributing to rapid apatite formation.