Effects of surface carboxylic acid groups of cerasomes, morphologically stable vesicles having a silica surface, on biomimetic deposition of hydroxyapatite in body fluid conditions

Biomimetic mineralization of supramolecular scaffolds consisting of biomolecules or their analogues has received much attention recently from the viewpoint of creation of novel biomaterials. This study investigated biomimetic deposition of hydroxyapatite (HAp) on cerasomes, morphologically stable organic-inorganic hybrid vesicles. Scanning electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray diffraction studies revealed that the pristine cerasomes induced heterogeneous nucleation of HAp when they were immersed in 1.5SBF, a solution having 1.5 times higher ion concentration than that of a simulated body fluid (SBF). The HAp deposition was further accelerated when dicarboxylic and monocarboxylic acid groups were displayed on cerasome surfaces. These carboxylic acid groups are expected to enhance calcium ion binding to the cerasome surface, causing an increase of HAp nucleation sites. At lower surface concentrations on the cerasome surface, the dicarboxylic acid group is apparently more effective for HAp deposition than the monocarboxylic acid group. The resultant HAp-cerasome hybrids are useful as biocompatible materials having unique properties deriving from the lipid bilayer structure of the cerasomes.