COLAGEN / HYDROXYAPATITE INTERACTIONS IN COMPOSITE BIOMATERIALS The aim of this study is to investigate the interaction between pure collagen and mineral phases like hydroxyapatite. For that purpose, collagen fibers were mineralized starting from hydroxyapatite aqueous precursors. The mineral phase identification was made by XRD, the collagen-hydroxyapatite interaction was studied by IR spectroscopy, the microstructure of the composite materials was investigated by SEM and the amount of mineral phases’ deposition was evaluated by ATD-TG. Ultrasonication was used in order to evaluate the strength of the collagen-hydroxyapatite bond. The obtained results showed that it was obtained a collagen – hydroxyapatite composite material, characterized by a strong interaction between the collagen fibers and the hydroxyapatite crystals, which can be successfully used as a bone substitute.