Role of mineral proximity on mechanics of organic macromolecules in a bio-nanocomposite

Nacre, the iridescent inner layer of seashells, is a material exhibiting extraordinary mechanical properties. Nacre is a laminated nanocomposite composed of pseudohexagonal platelets that are 2 micrometer to 3 micrometer in diameter and 250 nm to 500 nm tall with an organic phase about 20 nm thick between the platelets. Although nacre is composed of about 95% aragonitic calcium carbonate and 5% organics (mainly proteins), the fracture toughness exhibited by nacre is 3000 times higher than aragonite. Nacre has been studied as an inspiration for design of the next generation of high-performance biomimetic nanocomposites. In this research, the influence of the close proximity of mineral aragonite on mechanical response of the organic phase is studied for the first time.; The major focus of this research is to study the influence of mineral proximity on the mechanical properties of proteins in a natural bio-nanocomposite nacre. This work seeks to understand the fundamental mechanisms behind unfolding of protein at mineral proximity. The results and knowledge from this research will help in designing the next generation of high-performance materials, particularly with hybrid organic and inorganic phases.; The influence of mineral proximity on the mechanical property of a protein is found by pulling a model protein domain at mineral proximity and without the presence of mineral. The "Glycine-Serine" domain of a nacre protein, Lustrin A, has been used as a model system. Steered Molecular Dynamics has been used for our simulations. The CHARMm potential parameters necessary for aragonite are derived. The protein is pulled at three different velocities and for same duration of time in the presence and absence of the mineral. It is concluded that several times more energy are required to unfold a protein in the presence of the mineral compared to unfolding the protein alone. A detailed quantitative analysis to understand reasons for the enhancement of the load deformation response in the proximity of the mineral is conducted, and mechanisms leading to the enhanced properties are described. This work provides useful information for designing biomimetic nanocomposites as well as to further our understanding of the mechanical response in natural biological composites.