What is the mechanism behind biological ferroelectricity?

Biological tissues are soft, amorphous and often appear to possess a high degree of material symmetry. This would appear to preclude a phenomenon like ferroelectricity which, in the world of hard materials, only occurs in selected crystalline materials that are non-centrosymmetric. Recent experiments, however, indicate the presence of ferroelectricity in soft biological entities such as the protein elastin—a large biopolymer found in the extracellular domains of most tissues. In this letter, we present a model and an explanation for this intriguing observation. Based on a very simple physical hypothesis, we develop an analytical statistical mechanics model that, coupled with insights from molecular dynamics, provides a plausible mechanism underpinning biological ferroelectricity. Furthermore, we predict for the first time, piezoelectric properties of tropoelastin, a precursor/monomer of elastin—properties that are not easily obtained from experiments. Specifically we find that the piezoelectric constant of tropoelastin is larger than any known polymer.