Preparation of transparent hydroxyapatite/citric acid particle films

Transparent hydroxyapatite/citric acid (Cit/HA) particulate film formation and the stability in biological solution were investigated. Negatively charged Cit/HA nanoparticles were synthesized, and the particulate films were prepared by a spin-coat method through water or ethanol dispersion. As a result, the crack-free and transparent Cit/HA films were prepared from water dispersion, which exhibited the better optical properties as compared with the films prepared from ethanol dispersion. The Cit/HA films exhibited higher optical transmittance with increasing the hybridized Cit amount, and the highest transmittance in the visible light region exceeded 80%. Moreover, the calcined film had long-term stability in phosphate-buffered saline while maintaining high transparency, which is expected to be used as a candidate coating film for cell culture substrates. [Display omitted] •Negatively charged hydroxyapatite/citric acid nanoparticles were synthesized.•Transparent hydroxyapatite/citric acid particle films were prepared by spin coating.•The homogeneity of films depends on the citric acid amount and dispersant type.•Film stability in a biological solution can be improved after calcination.•The film can be used as a candidate coating film for cell culture substrates.