Reverse micelle-mediated synthesis of calcium phosphate nanocarriers for controlled release of bovine serum albumin

Calcium phosphate (CaP) nanoparticles with a calcium to phosphorus (Ca:P) molar ratio of 1.5:1 were synthesized using reverse microemulsion. Ca(NO3)2·4H2O and H3PO4 were used as the aqueous phase, cyclohexane as the organic phase and poly(oxyethylene)12 nonylphenol ether (NP-12) as the surfactant. Depending on the calcination temperature between 600 and 800 °C, CaP nanoparticle showed different phases of calcium-deficient hydroxyapatite (CDHA) and β-tricalcium phosphate (β-TCP), particle size between 48 and 69 nm, and a BET specific average surface area between 73 and 57 m2 g−1. Bovine serum albumin (BSA) was used as a model protein to study loading and release behavior. The adsorptive property of BSA was investigated by the change in BET surface area of these nanoparticles and the pH of the suspension. At pH 7.5, the maximum amount of BSA was adsorbed onto CaP nanoparticle. The release kinetics of BSA showed a gradual time-dependent increase in pH 4.0 and 6.0 buffer solutions. However, the amount of protein released was significantly smaller at pH 7.2. The BSA release rate also varied depending on the presence of different phases of CaPs in the system, β-TCP or CDHA. These results suggest that the BSA protein release rate can be controlled by changing the particle size, surface area and phase composition of the CaP nanocarriers.