Cytoskeletal organization and elasticity are greatly influenced by molecular stiffness and sterics as well as externally imposed and internally generated stresses or so it might be hypothesized. These dynamic networks are generally composed of stiff filaments of actin and flexible crosslinkers. Recent experiments have identified not only isotropic, nematic and raft phases of such structures but also affine and non-affine elastic regimes of protein-crosslinked actin networks. Synthetic materials lack the complexity of biological tissues, and man-made materials that respond to external stresses through a permanent increase in stiffness are uncommon. Here we report for the first time, the systems of nanotube-polydimethyl siloxane(CNT-PDMS) soft nanocomposite and analogous liquid crystalline elastomer (LCE) that mimic the actin filaments in muscle tissues. Polydomain nematic LCEs increase in stiffness by up to 90% when subjected to a low amplitude (5%), repetitive dynamic compression. Elastomer stiffening is influenced by liquid crystal content, the presence of a nematic liquid crystal phase and the use of a dynamic as opposed to static deformation. Rheological and X-ray diffraction measurements reveal that the stiffening can be attributed to a mobile nano-scale nematic director that rotates in response to dynamic compression. Dynamic stiffening, not previously observed in liquid crystal elastomers may pave the way for useful development of self-healing materials and for the development of biocompatible, adaptive materials for tissue replacement
