Morphological, chemical and kinetic characterisation of zein protein-induced biomimetic calcium phosphate films

This study examines zein protein-induced growth of calcium phosphate (CaP) thin films at air-liquid interfaces. The results demonstrate that zein protein films in contact with simulated body fluids (SBF) promote the growth of hemispherical CaP particles of 150 nm radius, which combine to form a film. The CaP films formed on zein were less continuous than those obtained using a hexadecanoic acid monolayer self-assembled at the air-liquid interface. In situ ellipsometry measurements were used to follow the nucleation and growth of CaP in these systems. The kinetic parameters extracted from the ellipsometry data were dependent on the organic layer and also the SBF concentration. The mineralisation process was slower and final CaP film thicknesses smaller when zein films were used. XPS analyses revealed the presence of zein protein only on the air-facing side of the CaP films, confirming that the zein protein is involved in nucleating the unusual hemispherical CaP morphology. The zein protein-induced CaP thin films showed iridescence with a distinct range of colours as a function of CaP film thickness. Templated CaP mineralisation with zein protein is a simple and chemically facile method for synthesising CaP films with novel morphologies and controllable thicknesses.