Biomimetic mechanically adaptive nanocomposites

The development of a new class of mechanically adaptive nanocomposites has been inspired by biological creatures such as sea cucumbers, which have the ability to reversibly change the stiffness of their dermis. Several recent studies have related this dynamic mechanical behaviour to the distinctive nanocomposite architecture of the collagenous tissue, in which interactions among rigid collagen fibrils, embedded in a viscoelastic matrix of fibrillin microfibrils, are regulated by neurosecretory proteins. Here we review the development of a new family of artificial polymer nanocomposites that mimic the architecture and the mechanic adaptability of the sea cucumber dermis. The new materials are based on low-modulus matrix polymers that are reinforced with a percolating cellulose nanofiber network. Owing to the abundance of surface hydroxyl groups, the cellulose nanofibers display strong interactions between themselves, causing the evenly dispersed percolating nanocomposites to display a high stiffness. The nanofiber-nanofiber interactions can be largely switched off by the introduction of a chemical regulator that allows for competitive hydrogen bonding, resulting in a significant decrease in the stiffness of the material.