Liquid crystalline filamentous biological colloids: Analogies and differences

Amyloid fibrils, nanocellulose and filamentous viruses are three important families of filamentous biological colloids exhibiting a rich phase behavior in two and three dimensions. Similarly to the entropy-driven crystallization of hard spheres into crystals, also in their case entropy triggers order-order transitions at increasing concentrations, but their high aspect ratio, semi flexible and chiral nature bring additional complexity to the phase diagram and in some cases, system-specific features. Some of the differences among these three classes of filamentous colloids arise from their own constitutive nature and their mesoscopic structure; however, other features are universally shared among them and can be understood by applying general liquid crystal theories in bulk or confined geometries. In this manuscript we review the main analogies and differences among these three classes of biological filamentous colloids, starting from a discussion on their chemical composition and progressing across length scales to discuss first their mesoscopic structure and then their colloidal behavior, with particular emphasis to their lyotropic liquid crystalline features. By doing so, we highlight the main tools available to tune the colloidal properties, from the onset of the isotropic-nematic transition and the width of its biphasic region, to the shape transformations and director field distribution in the ensued liquid crystalline droplets, to the way chirality is transferred from the constitutive colloidal particles to the final macroscopic liquid crystalline phases.