Controlled release from hydroxyapatite nanoparticles incorporated into biodegradable, soluble host matrixes

We report in this paper a strategy to prepare nanocomposite fertilizers based on the dispersion of hydroxyapatite (Hap) into urea and thermoplastic starch at nanoscale, where Hap was assumed as a model for poorly soluble phosphate phases, such as phosphate rocks. Our experiments revealed the role of particle agglomeration on the effective phosphate release, showing that Hap dispersion within two water-soluble matrices (urea and thermoplastic starch/urea) is an effective strategy to increase Hap solubility. Aspects such as matrix solubility, morphology and Hap loading were detailed studied. Also, these structures showed an interesting slow-release of urea, i.e., the materials were at the same time a system for faster release of poorly soluble phosphate phases and slow release of very soluble nitrogen source (urea). Our results support the development of a new class of smart fertilizers, with release properties tailored by nanostructure.