Hydroxyapatite-gelatin films: a structural and mechanical characterization

Composite films of gelatin and hydroxyapatite were prepared and characterized by mechanical tests, scanning electron microscopy and X-ray diffraction investigation. The mechanical properties of the films are greatly affected by the presence of hydroxyapatite and change as a function of inorganic phase content. On stretching, the long axis of the collagen molecular portions align parallel to the direction of deformation and the gelatin coarse layered structure becomes more evident and ordered. Furthermore, under deformation the inorganic crystals, which are embedded in the gelatin layers, seem to squeeze out in the interlayer spaces and assume a preferential orientation parallel to the force trajectories. Thus, as the inorganic phase stiffens the gelatin films, the macromolecular matrix distributes the stress promoting the preferential orientation of the apatitic crystals. The results indicate that this experimental approach can be used to prepare composites with anisotropic properties, which can be modulated through variation in composition and mechanical deformation in order to get biomaterials suitable to fulfill specific mechanical functions.