Biomineralization – Biocolors

The main objective of our research topic ‘BioColors’ is to understand the relationship between biomineralization and pigmentation mechanisms in sea urchins and to take inspiration from these biological phenomena to produce biocolorants that will exhibit a large palette of chemical and photo-stable colors.

  • Vaskar Sardhalia (PhD student):

« The colors of sea urchin spines towards the synthesis of bio-inspired hybrid colorants »

Sea urchins show diverse colours from purple to green due to the presence of a family of organic molecules, the polyhydroxylated naphthoquinones (PHNQ). In sea urchins, it is believed that the incorporation of the PHNQ molecules within the crystalline biogenic calcite protects the organic pigments from the external environment as isolated PHNQ molecules are otherwise sensitive to sunlight, high temperature and solvents. The incorporation of the PHNQ molecules takes place during the coupled biomineralization and pigmentation processes. Biomineralization in sea urchins involves the presence of amorphous calcium carbonate (ACC) precursors that further crystallize into calcite. During ACC crystallization, diverse macromolecules (proteins, lipids, polysaccharides, metabolites) and likely the PHNQ molecules are incorporated within the biogenic calcite. 

The objectives of this PhD are to 1) identify the physico-chemical mechanisms at the origin of the colours of sea urchin spines and 2) synthesize bio-inspired coloured hybrid CaCO3 based materials.

The PHNQ molecules are biosynthesized in the so-called red-spherule cells, progressively integrate the growing mineral that becomes first light pink and then takes different hues according to sea urchins and the biomineralization stages. However, the mechanisms at the origin of the colour and its variations are unknown. 

During the course of this Ph.D., the pigments will be extracted from the spines and the red-spherule cells. We are also planning to carry out the synthesis of the organic pigments. CaCO3 crystals will be then synthesized from an ACC precursors in the presence of macromolecules and pigments extracted or synthesised. The crystallization of the ACCs will be induced by humidity or by heating during which the possible colour changes will also be studied. The chemical interactions between the pigments, the mineral phases and the macromolecules in the biogenic as well as in the synthetic samples will be studied.

PhD director: Dr. Marie Albéric and Dr. Thierry Azaïs. Collaborators: Dr. Frédéric Marin