Mineralization of nacre-like structures mediated by extrapallial fluid on pearl nucleus

Nacre is renowned for its fascinating iridescence and superior mechanical properties owing to their hierarchically ordered structures at multiscale levels. However, mechanisms for constructing these ordered structures and bottom-up strategies to synthesize nacre-like materials are still lacking. Here, we developed a CaCO3 deposition system in vitro to mimic biomineralization process in vivo. Strikingly, in the presence of extrapallial fluid (EPF) from the pearl oyster Pinctada fucata, a multilevel layered nacre-like structure was formed on pearl nucleus. Particularly, aragonite nanocolumns with diameters of 30-60 nm aggregated by a parallel pattern and assembled into polygonal tablets in each layer. Moreover, linkers between adjacent laminated layers were observed, resembling mineral bridges in natural nacre. Thus, we found that EPF could induce the mineralization of nacre-like structures on pearl nucleus in vitro, which would be helpful for better understanding the mechanism for assembling layered structures, pearl production, as well as biomimetic synthesis of nacre-like materials.