Unravelling the nature-inspired silk sericin - Calcium phosphate hybrid nanocomposites: A promising sustainable biomaterial for hard tissue regeneration applications

Calcium phosphates (CPs) are widely utilized as biomaterials for bone tissue repair due to their osteoinductive and osteoconductive properties. Hydroxyapatite (Ca10 [PO4]6OH2, HAp) and Monetite (CaPHO4, DCPA) are the two different phases of calcium phosphate that have triggered the interest of researchers due to their exceptional properties like bioactivity, biocompatibility, high crystallinity, good mechanical as well as biological characteristics. Current investigations focus on combining CPs with natural proteins to offer innovative biomaterials that accommodate various functional requirements. In the current study, we explore the biomedical relevance of the association of CPs with natural protein silk sericin (SS) composite with calcium phosphate (SCP) at room and low temperatures. The effect of silk sericin concentration and mineralization time on the formation of apatite nanocrystals, including their biocompatibility, were investigated for hard tissue regeneration. The fabricated CP and SCP nanocomposites at room and low temperature were subjected to an X-Ray diffraction technique, revealing a dual phase of calcium phosphate - hydroxyapatite and monetite with hexagonal and triclinic crystal system. Further, the presence of SS and SCP had been confirmed with Fourier-transformed infrared spectroscopy (FTIR) that showed the characteristic bands of amide I at 1642 cm-1 and the dominant phosphate group stretching at 1017 cm-1. Further, nanostructures with rods and tiny blossoms of flower-like enhanced morphologies have been observed for SCP at room and low temperatures. Moreover, the bioactivity of SCPs at low and room temperature materials exhibited apatite layer formation from day 7 of immersion which was confirmed with structural and morphological analysis. The cell viability assay demonstrated that the SCP nanocomposites have over 130% of viable cells. Therefore, fabricated SCP nanostructures are proven to be highly biocompatible with a rapid rate of mineralization capability, which will be a promising candidate for hard tissue applications.