Synthesis of hydroxyapatite and sericin nanocomposites

Hydroxyapatite (HAp) and sericin (SS) nanocomposites represent a new class of biomaterials with unique properties. On one hand, nanometric hydroxyapatite (nano-HAp) is the primary constituent of hard tissues, exhibiting properties of biocompatibility, bioactivity and osteonductivity. On the other hand, SS has shown an improvement in cell proliferation when used as an organic matrix or as a medium for cell growth. These characteristics make these materials excellent candidates for biomedical applications, namely for bone tissue engineering. In this context, the objective of the present work consisted in the synthesis of HAp/SS nanocomposites with controlled properties (purity, size, size distribution and morphology) through a simple methodology. For this, precipitation of HAp with different SS concentrations was studied in batch, in a stirred tank (ST) and in a meso oscillatory flow reactor (meso-OFR). The performance of both reactors was compared by monitoring the pH profile and characterizing the particles produced. These were evaluated in terms of purity and crystallinity (Fourier transform infrared (FTIR), X-ray diffraction (XRD)), size distribution (laser diffraction), as well as size and morphology (scanning electron microscopy (SEM), transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM)). Nanoparticles of HAp and HAp/SS were successfully synthesized in both reactors. Although the hydrodynamic conditions of the two reactors were not directly comparable, the results demonstrate the best performance of the meso-OFR when compared to the ST, since the precipitation process was about four times faster. The obtained particles present both rod and plate-like shape, and have low crystallinity and calcium deficiency, characteristics which are similar to biological HAp. The results further demonstrate that the concentration of SS had an influence on the size, morphology, aggregation and crystallinity of HAp particles. In fact, there was an increase in the mean particle size and a larger number of plate-like particles with increasing SS concentration. In addition, the presence of SS increases the aggregation of the formed particles and decreases their crystallinity. Due to their characteristics, these nanocomposites represent a biomaterial with potential for application in regeneration of bone tissues, generating an improved biological response in terms of cell differentiation and proliferation and allowing the study of the biomineralization process.