Biomineralization – Composite Self-assembly

  •  Camila Bussola Tovani (PhD student):

“Exploring the synergistic effect between collagen and Sr2 + towards new insights of apatite formation in bone mineralization”

Strontium is a trace element in human body which accumulates preferentially in the bone tissue by means of Ca2+ substitution in the bone lattice. It is well known that Sr promotes bone remodeling through a dual action: increasing osteoblasts activity and decreasing osteoclasts activity. Nevertheless, the role played by this ion in the mechanism of bone mineralization remains unknown.
In this sense, my PhD deals with the bioinspired synthesis of Sr2+ substituted phosphates and carbonates, aiming not only the design of osteoinductor materials but also the investigation of the Sr role in the process of bone formation including kinetics and thermodynamics aspects. Towards new insights on the biomineralization process related to phosphates and carbonates, I have dealt with the synthesis of these materials in confined medium advised by Dr. Ana Paula Ramos at University of São Paulo, Brazil.
Now, in my third year of PhD, I am working at the laboratory « Chimie de la Matière Condensée de Paris » advised by Dr. Nadine Nassif focusing on the study of hydroxyapatite mineralization in the presence of Sr2+ at the organic/inorganic interface by using collagen matrices as a model of confinement to a fundamental understanding of bone apatite formation.

PhD director: Dr. Ana Paula Ramos ; 3th year supervisor: Dr. Nadine Nassif, Collaborators: Dr. Thierry Azaïs

  • Elora BESSOT (PhD student):

“Design of cylindric and spongious units of bone”

Bone is a composite material which closely associates a dense and organized collagen organic matrix (mainly type I collagen fibrils) with an apatite mineral network. From nanometers to millimeters and beyond, bone is hierarchically structured to provide maximum strength with a minimum of material. Although the structure/function relationship in bone is central, little attention has been paid to the long-range collagen/hydroxyapatite (HA) structure in in vitro models. Despite being one of the most studied living materials, bone structures are still not reproducible in vitro. Recently, the cholesteric geometry where the characteristic “collagen fibrils /apatite co-alignement” is observed in bone  was reproduced in the laboratory ; the structure of the synthetic platelets and their related behavior in water mimicking the biological one.

The new challenge in my PhD work focus on reaching higher levels of bone hierarchical organization enlarging the relevance and applications of bone models. Two organizations are aimed in parallel: the spongy bone and the cylindrical motif (osteons). Both imply the texturization of the liquid-crystalline phase made of a mixture of highly concentrated acidic collagen with the HA precursors.

The resulting hybrid collagen-apatite biomimetic materials and their hierarchical organization require various characterization techniques (e.g. in-situ observations by polarized optical microscopy (birefringence) and investigation by SAXS/WAXS of the directed co-assembly of the organic/inorganic phases, electronic microscopies, mechanical tests etc).

The resulting materials will provide original models to advance in the understanding of the fundamental questions on bone biomineralization. More specifically, we propose a physicochemical point of view of the development of anisotropic textures in living tissues. Additionally, the development of biomimetic hierarchically-structured materials offers a remarkable substrate to study the impact of hierarchical organization, for example, on mesenchymal stem cells’ or bone-forming cells’ (osteoblasts) behavior (adhesion, differentiation, specific cellular functions).

PhD director: Dr. Nadine Nassif; Collaborators: Dr. Franck Artzner, Dr. Marco Faustini, Pr. Clément Sanchez