Spectroscopic investigation of adsorbed lactoferrin onto hydroxyapatite nanocrystals.

Biomimetic hydroxyapatite (HA) nanocrystals represent an ideai bone-substitute material; thè elucidation of their interaction with proteins is centrai to understanding thè integration of an implanted material with biological tissues and to develop new materials with a bioactive surface for biomedicai applications [1]. Thus, thè adsorption mechanism of lactoferrin (LF), a protein of blood plasma and milk with antioxidant, cariostatic, anticarcinogenic and anti-inflammatory properties [2], onto biomimetic hydroxyapatite nanocrystals at two different pH values (7.4 and 9.0) has been studied. The interaction has been investigated for thè most part by spectroscopic techniques, but thermal and microscopie procedures were used as well. The study of protein structure by means of vibrational spectroscopy (Raman and IR) has been practised since thè '70s, when thè specific band assignments of secondary structures and of side chain environments have been established [3]. The positive electrostatic surface potential of LF at pH 7.4 allows a strong surface interaction with thè slightly negative FIA nanocrystals and avoids thè protein-protein interaction, leading to thè formation of a coating protein monolayer. In contrast, at pH 9.0 thè surface potential of LF is a mix of negative and positive zones favouring thè protein-protein interaction and reducing thè interaction with HA nanocrystals, as a result a thè doublé layer of coating protein has been formed. These experimental findings are supported by thè good fittings of thè adsorption isotherms by different theoretical models according to Langmuir, Freundlich and Langmuir-Freundlich models. The nanosized HA does not affect appreciably thè conformation of thè adsorbed protein. In fact, using FT-Raman and FT-IR, we found that after adsorption thè protein was only slightly unfolded with a small fraction of thè a-helix structure being converted into turn, while thè p-sheet content remained almost unchanged. Not only does this study relative to LF binding on HA nanocrystals allow a better understanding of thè protein adhesion mechanism, but could also favour thè development of a bone-implantable biomaterials for hard-tissue engineering and regeneration technologies with a bioactive surface coating.