Release of DL- leucine by biomaterials: Apatitic calcium phosphates analogous to bone mineral

The interaction of DL-leucine, an essential amino acid having a hydrophobic character with poorly crystalline calcium phosphate apatites, synthesized at the physiological temperature (37 °C), is studied. These apatites of atomic ratio Ca/P between 1.33 and 1.67 are analogous to bone mineral. Their surface reactivity is indeed linked to the existence of a metastable hydrated surface layer containing labile ionic species. This study shows that the kinetics of release is slow and experimental release profiles corresponding to these phosphates are similar. The chemical composition of the apatites has an influence on the release. The release rate is more important for apatite containing more HPO42- ions. It is found that the incubation of apatite after fixation of the amino acid DL-leucine in the de-ionized water solution depends on the R (ml/mg) = volume/mass. The adsorption and release properties of poorly crystalline apatites are essentially dependent on the maturation, the chemical composition of the hydrated layer and the composition of the adsorbate solution. The understanding of adsorption and desorption mechanisms with respect to active molecules can be exploited for the development of drug delivery applications.