In situ transmission electron microscopy observation of reversible deformation in nacre organic matrix

The deformation behavior of the organic polymer matrix of the biocomposite nacre structure in abalone shell was investigated by in situ straining during transmission electron microscopy (TEM). We observed strong adhesion to mineral plates and high ductility of the organic matrix, confirming a crack-bridging toughening mechanism. In addition, direct observation of reversible mechanical behavior was made in the viscoelastic reformation of matrix ligaments after failure. Crystalline β-sheet structures identified through electron diffraction suggested the presence of protein structures similar to spider or cocoon silk, and the reversible mechanism was attributed to hydration-induced unfolding and refolding of domains in these silklike proteins. This work provides further insight into the molecular and nanoscale behavior of nacre organic matrix and its contribution to bulk mechanical performance.