Cellular orchestrated biomineralization of crystalline composites on implant surfaces by the eastern oyster, Crassostrea virginica (Gmelin, 1791)

• Outer mantle epithelium (OME) and hemocytes participate in prismatic and foliated shell formation.
• Auto-fluorescent prismatic extracellular matrix (ECM) walls appear to originate from the OME.
• Cells, exosome-like vesicles, and cellular products including crystals and ECM are present at the mineralization front.
• Laser scanning microscopy reveals the spatial orientation of the prismatic ECM.

The phylum Mollusca is unmatched in the mastery of cellular-engineered shell microstructures, producing shells that are visually elegant, structurally complex and fracture resistant. Shell formation in the eastern oyster, Crassostrea virginica is a process that involves both hemocytes (blood cells) and the outer mantle epithelial cells (OME). This study reports the secretion of an extracellular matrix (ECM) and cellular activity during shell layer formation by observing folia and prismatic development on different metal alloy surfaces (Ti6Al4V titanium, 7075-T6 aluminum, and 316 L stainless steel) implanted under the OME. During prism formation, a close association was observed between the ECM surrounding the prisms, the OME, and hemocytes. The prismatic ECM walls appeared to originate from the OME surface and were auto-fluorescent. During folia formation, an initial infiltration response of hemocytes to the implant surface was observed followed by the formation of a thin translucent ECM membrane onto which exosome-like vesicles, some containing crystals, deposited. These structures progressively organized into well-defined folia mineral. It is proposed that molluscan shell is formed through a series of coordinated events involving cells and cell products whereby both organic and mineral phases are secreted, organized, and simultaneously formed. The coordination of cells and cell products for shell synthesis opens a new realm of cellular control not previously explored in shell formation.