Morphological control of calcium phosphate nanostructures using lyotropic liquid crystals

Abstract

Organisms use “soft” organic compartments to control the morphology of the embedded “hard” minerals. Here we present a simple method using liquid crystal (LC) phases as “soft” and “inert” templates to prepare nanostructured calcium phosphates (CaPs), which are inorganics of known bioefficacy. Specifically, 6 nm-thick CaP nanowires and CaP sheets that precisely replicate reverse hexagonal (H₂) and lamellar (L_α) LCs have been successfully synthesized and we attribute this to the sufficient spatial regulation offered by the negative (H₂) or flat curvature (L_α) of the aqueous domain. A normal hexagonal (H₁) phase possesses a positive curvature of the aqueous domain, therefore limited spatial restriction. For this reason, precise replication of the H₁ phase by CaP has not been possible. Interestingly, the dynamic nature of the template allowed the construction of micron-sized brushite objects with a laminated structure decorating a specific facet, possibly as a result of epitaxial overgrowth of nano-sized brushite subunits.