Thermal characterization of hydroxyapatite or carbonated hydroxyapatite hybrid composites with distinguished collagens for bone graft

Bone remodeling for spontaneous regeneration might be achieved by a combination of collagen and hydroxyapatite (HA). The aim of the present study is to synthesize and characterize hybrid composites of HA and carbonated hydroxyapatite (CHA) with different types of collagen. For these hybrid composite synthesis, HA or CHA precursors were precipitated in solutions containing either hydrolyzed collagen (HC) or type II collagen (COL). For control, pure HA and CHA were synthesized in the absence of collagen. During the HA-based materials synthesis, in addition to HA, another calcium phosphate phase, brushite, was also produced, as confirmed by X-ray diffraction and scanning electron microscopy (SEM). In the composites, HA presented preferential crystalline growth on the (211) crystallographic plane due to the influence of both collagens. On the other hand, CHA was precipitated in its pure form, although a reduction in the crystallinity was observed with the incorporation of the carbonate groups. Calcium/phosphorous (Ca/P) mass ratios determined by energy dispersive spectroscopy (EDS) were very close to those expected for HA, 1.67, and brushite, 1.00, confirming the formation of two calcium phosphate phases. SEM/EDS results showed higher values of Ca/P for CHA than for HA, which indicates that some phosphate groups were replaced by carbonated ones.