Experimental investigation of nanomechanics of the mineral-protein interface in nacre

Nacre, the inner layer of molluscan seashells is a model biomimetic nanocomposite system that has been an inspiration for design of novel composites. The organic phase present in nacre is believed to play an important role in enhancing the toughness of nacre. The understanding of the adhesion forces of the organic matrix on to the mineral phase is essential for the fundamental assessment of the toughening properties in nacre. Our prior work using molecular dynamics simulations revealed that a very large force is needed to pull the protein molecules when in close proximity with the aragonite phase. In the current work, we have experimentally described the mechanical response of the organic phase in proximity of aragonite using force mode atomic force microscopy. Our results indicate that a very large force is required (>5–6 nN) to pull the proteins away from the aragonite. Our experiments show that the molecular interactions at the organic–inorganic interface in nacre are substantial and may play a significant role on the overall toughness of nacre. Thus, molecular interactions albeit weak and non-bonded play a significant role on the mechanics of hybrid nanocomposite systems.