Microstructure and composition of biosynthetically synthesised hydroxyapatite

Biosynthetic hydroxyapatite (HA) manufactured utilising the bacterium Serratia sp. NCIMB40259 was characterised using X-ray diffraction (XRD), Fourier transform infra-red spectroscopy (FTIR), energy dispersive X-ray analysis (EDX) scanning electron microscopy (SEM), transmission electron microscopy (TEM) and electron diffraction (ED). SEM/EDX showed that the non-sintered material consisted mainly of calcium-deficient HA (CDHA) with a Ca/P ratio of 1.61 ± 0.06 and crystal size (from TEM) of 50 ± 10 nm. ED analysis of non-sintered powder showed resolvable ring patterns ascribed to (0002), (\( 11\overline 2 2 \)) and (0006) planes of crystalline HA. The crystallinity of the samples improved with heat treatment from approximately 9.4% (non-sintered) to 53% (1,200°C). Samples heated at 600°C and sintered at 1,200°C were identified by XRD and FTIR as mainly CDHA with some sodium calcium phosphate in the sintered samples. Ca/P ratios (SEM/EDX) were 1.62 and 1.52, respectively. Single crystal spot patterns characteristic of HA were seen with commercial HA and Serratia HA heated at 600°C. After sintering at 1,200°C the material consisted of needle-like crystals with a length between 86 and 323 nm (from TEM) or 54–111 nm (from XRD) and lattice parameters of a = 9.441 A and c = 6.875 A. This study indicated that the material produced by Serratia bacteria was initially mainly nanophase calcium deficient hydroxyapatite, which sintered to a more highly crystalline form. With further refinements the method could be used as an inexpensive route for hydroxyapatite production for biomaterials applications.