Growth, structure and mechanical properties of phosphate based bio-composites studied by ex situ and in situ Raman spectroscopy

This study contains the investigation of the formation of carbonate apatite (cAp) from a citrate-stabilized amorphous calcium phosphate (cit-ACP) phase in various ionic solutions. This is primarily realized via in situ Raman spectroscopy by studying the variation of the v1 phosphate stretching mode as a function of maturation time. The transition is complemented by ex situ transmission electron microscopy (TEM) for microstructural characterization. These observations shed light on the possible pathway regulating in vivo formation of cAp in bone. Further, the impact of titanium substitution on the electronic properties of apatite was assessed via structural characterization of titanium substituted hydroxyapatite (Ti/HA) composites performed by ex situ Raman spectroscopy and TEM. Raman studies revealed the formation and evolution of titanium oxide and calcium phosphate related phases, whereas TEM studies showed the morphological evolution of particles. Following cit-ACP transformation, the mechanical and molecular properties of collagen/cAp bio-inspired structures are studied by in situ Raman spectroscopy under mechanical stress. The impact of cAp content on the molecular response of these structures is highlighted by a wavenumber shift of collagen related Raman bands. This interplay between cAp and collagen is associated to the mechanical properties of bone.