Microstructure and composition of biosynthetically synthesised hydroxyapatite

Biomaterials research often focuses on the synthesis and characterization of calcium phosphate-based materials like hydroxyapatite (HA), which are widely used in bone regeneration and tissue engineering. Traditional HA production methods rely on chemical processes that can be costly and energy-intensive. In contrast, biosynthetic approaches using microorganisms offer a potentially more sustainable and economical alternative. However, the structural and compositional properties of biosynthetic HA remain underexplored. Prior research has demonstrated that bacteria can produce calcium phosphate materials, but the extent of their crystallinity and phase composition is not fully understood. This gap motivated the investigation of HA produced by Serratia sp. NCIMB40259. The study aimed to determine whether this biosynthetic HA could match or improve upon conventional HA in terms of crystal structure and purity. Understanding the microstructure and composition of such materials is essential for evaluating their suitability in biomedical applications. The lack of comprehensive data on biosynthetic HA's thermal stability and phase transformation under heat treatment remains a key limitation in the field. This research sought to address these uncertainties by employing multiple analytical techniques to characterize the material in detail.

The primary aim of this study was to investigate the microstructure and composition of hydroxyapatite produced biosynthetically using Serratia sp. NCIMB40259. The researchers sought to determine whether this method could yield a material with desirable properties for biomedical applications. A specific problem addressed was the lack of detailed characterization of biosynthetic HA, particularly regarding its crystallinity and phase composition. The motivation stemmed from the potential of microbial synthesis to offer a cost-effective and environmentally friendly alternative to traditional HA production methods. By analyzing the material's properties under various heat treatments, the study aimed to assess its thermal stability and transformation behavior. The researchers also sought to compare the biosynthetic HA with commercial HA to evaluate structural similarities. This work aimed to provide a foundation for optimizing the biosynthetic process for industrial use. The study's findings could help bridge the gap between microbial synthesis and practical biomaterials applications.

The researchers employed a range of analytical techniques to characterize the biosynthetic hydroxyapatite. X-ray diffraction (XRD) was used to determine the crystal structure and phase composition of the material. Fourier transform infra-red spectroscopy (FTIR) provided insights into the molecular structure and functional groups present. Energy dispersive X-ray analysis (EDX) combined with scanning electron microscopy (SEM) was used to assess elemental composition and morphology. Transmission electron microscopy (TEM) allowed for detailed imaging of crystal size and shape. Electron diffraction (ED) was applied to identify crystallographic planes and confirm structural features. The samples were analyzed in both non-sintered and sintered forms to evaluate the effects of heat treatment. These methods collectively enabled a comprehensive assessment of the material's properties. The combination of multiple techniques ensured a robust characterization of the biosynthetic HA.

The non-sintered biosynthetic HA was found to consist mainly of calcium-deficient hydroxyapatite (CDHA) with a Ca/P ratio of 1.61 ± 0.06 and a crystal size of 50 ± 10 nm. EDX analysis confirmed the presence of calcium and phosphorus as primary elements. Electron diffraction patterns revealed ring structures corresponding to (0002), (1122), and (0006) planes of crystalline HA. Heat treatment significantly increased the material's crystallinity, rising from approximately 9.4% in the non-sintered state to 53% after heating at 1,200°C. XRD and FTIR analysis of sintered samples indicated the presence of sodium calcium phosphate alongside CDHA. The Ca/P ratio of the 600°C-heated sample was 1.62, while the 1,200°C-sintered sample had a ratio of 1.52. TEM imaging showed needle-like crystals with lengths ranging from 86 to 323 nm. Lattice parameters of a = 9.441 Å and c = 6.875 Å were measured, consistent with HA crystal structure.

The study demonstrated that Serratia sp. NCIMB40259 can produce a material primarily composed of nanophase calcium-deficient hydroxyapatite (CDHA). Heat treatment significantly improved the crystallinity of the biosynthetic HA, with sintering at 1,200°C yielding a more crystalline form. The material's crystal structure and lattice parameters were comparable to those of commercial HA. The presence of sodium calcium phosphate in sintered samples suggests a compositional shift with increasing temperature. The findings suggest that biosynthetic HA could be a viable alternative to conventional HA in biomedical applications. The method's potential for cost-effective production was highlighted as a key advantage. Further refinements to the biosynthetic process may enhance its suitability for industrial use. The study's results support the feasibility of microbial synthesis as a route for HA production.