Hydroxyapatite nanoparticles synthesized via reverse microemulsions and their adsorption/desorption properties with enrofloxacin

Abstract

Calcium phosphates are regularly used in biomedical materials, such as bone cement, bone replacement material and drug carriers, as they are the major inorganic constituents of human hard tissue. Different pH conditions were tested to obtain calcium phosphate materials. In acidic conditions, the brushite or monetite phases with bulk structures were synthesized even while keeping a constant Ca/P ratio of 1.67; by contrast, at alkaline conditions, the hydroxyapatite phase was found to exhibit a needle-like shape. An annealing process on the hydroxyapatite phase generated nanoparticles featuring improved crystallinity and a quasi-spherical shape. The results showed that the pH bears a direct effect on the resulting calcium phosphate phase, and only in alkaline conditions it was possible to reach the hydroxyapatite phase; also, the Ca/P ratio in the starting reagents plays an important role in the morphology of the final product. An analysis of the efficiencies of adsorption and desorption of the antibiotic enrofloxacin was carried out on the quasi-spherical hydroxyapatite nanoparticles. It was demonstrated that these nanoparticles could be loaded with 92% of the enrofloxacin in solution and they can also deliver 74% of the antibiotic during the first 12 h, which could prove useful if these nanoparticles are used as coatings for dental or orthopedic implants.