Mineralization of chitosan rods with concentric layered structure induced by chitosan hydrogel

Ca ions and P ions absorbed by chitosan hydrogel with a molar ratio of 1.19 were converted into carbonated apatite under ambient condition, by alternate soaking in combination with alkali treatment within a few hours. The alkali treatment helped to convert amorphous calcium phosphate in chitosan hydrogel into carbonated apatite. The bending strength of mineralized chitosan with a concentric layered structure varied from 62.7 MPa to 92.5 MPa, which was 45.8-67.5% as strong as that of rabbit femur. During the process of alternate soaking and alkali treatment, chitosan hydrogel not only provided a medium for the carbonated apatite coating reaction which helped to form the concentric layered structure due to the Liesegang rings phenomenon, but also induced absorption of Ca and P ions in the hydrogel framework via chelation or electrostatic interaction rather than the diffusion model originated from the concentration gradient.