Nano-hierarchical structure and electromechanical coupling properties of clamshell

Electromechanical coupling is a nearly universal property of biomaterials, and may play an important role in many physiological and functional phenomena. The intrinsic or externally-generated electric field within biomaterials may also contribute to their predominant mechanical properties. Mollusc shells are well known for their outstanding mechanical properties, which are generally believed to originate from their hierarchical structures in multi-levels. This paper is therefore focused on the studies of the hierarchical structures and electromechanical coupling behaviors of clamshell from micro- to nano-levels, and in particular, the biopolymer concentrated regions. Detailed studies are performed to characterize the piezoelectric and ferroelectric properties of clamshell. It was found that the piezoresponse of clamshell is originated from the biopolymers between the mineral grains, as well as those intercalated within the mineral crystalline structure after the biomineralization process. Local ferroelectric hysteresis loops of clamshell have also been observed and analyzed on the samples with different orientations, biopolymer contents, or moisture contents. It is believed that the overall functioning of the clamshell or even other mollusc shells may incorporate many mechanisms interacting together, rather than originate from the hierarchical structure alone. This study of the electromechanical coupling effects of clamshell can be a path to have more comprehensive understandings of the properties and behaviors of mollusc shells.