Biomimetic Composites With Amorphous Calcium Carbonate: Linking Microstructure to Mechanical Response

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Recent discoveries have revealed that many organisms produce amorphous calcium carbonate not as a precursor for more stable calcite but as a mineral of choice. The crucial role of amorphous calcium carbonate in morphological and structural control of biominerals has thus been recognized. However, the determining factors for the formation, stabilization and transformation of the amorphous phase are still in debate and the mechanical response of the resulting composite has not been investigated yet. This award supports fundamental research to investigate the mechanical response of amorphous-crystalline organic calcium carbonate composites as a function of the microstructure using a combination of experimental and modeling work. Tuning and optimizing the mechanical properties of this material opens new opportunities for the development of biomimetic materials with superior properties. In parallel, this research addresses major questions regarding biomineralization, a topic of primary biogeochemical, environmental, and economic significance. This research involves several disciplines including mechanics, engineering, materials science, colloidal science, and chemistry. This multi-disciplinary approach provides a wide range of research opportunities. It will help broaden participation of underrepresented groups through several undergraduate students in the involved research groups and a K-12 Outreach program offering introductory lectures, field trips, and hands on research. The knowledge gained in this project will be integrated in various lectures and therefore it will positively impact engineering education. The biomimetic composites with amorphous calcium carbonate are synthesized in the laboratory. This research aims at establishing design parameters to tune their microstructure, to scrutinize their microstructure-mechanical response relationship, and to study their failure mechanisms. The experimental work involves adsorption and force measurements to study mineral formation, nanoindentation to study microstructure-mechanical response relationship and atomic force microscopy to investigate interfacial properties and amorphous-to-crystalline transformation. The modeling work is based on the Shear Transformation Zone Theory, a statistical thermodynamic framework for modeling failure deformation in amorphous materials, and cohesive finite element simulations. Correlation between experiments and modeling will enable to uncover fundamental phenomena underlying the mechanical response of the novel hybrid composites including (i) multiscale toughness mechanisms through a combination of hierarchical geometry and microstructure design, (ii) transition from ductile behavior with distributed deformation to brittle response and strain localization, (iii) glass transition, and (iv) interfacial separation and healing.