Biological liquid crystalline polymers are found in cellulosic, chitin, and DNA based natural materials. Chiral nematic liquid crystalline orientational order is observed frozen-in in the solid state in plant cell walls and is known as a liquid crystal analogue characterized by a helicoidal plywood architecture. The emergence of the plywood architecture by directed chiral nematic liquid crystalline self assembly has been postulated as the mechanism that leads to optimal cellulose fibril organization. In natural systems, tissue growth and development takes place in the presence of inclusions and secondary phases leaving behind characteristic defects and textures, which provide a unique testing ground for the validity of the liquid crystal self-assembly postulate. In this work, a mathematical model, based on the Landau-de Gennes theory of liquid crystals, is used to simulate defect textures arising in the domain of self assembly, due to presence of secondary phases representing plant cells, lumens and pit canals. It is shown that the obtained defect patterns observed in some plant cell walls are those expected from a truly liquid crystalline phase. The analysis reveals the nature and magnitude of the viscoelastic material parameters that lead to observed patterns in plant-based helicoids through directed self-assembly. In addition, the results provide new guidance to develop biomimetic plywoods for structural and functional applications.

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A systematic computational and scaling analysis of defect textures in polygonal arrangement of cylindrical particles embedded in a cholesteric (Ch) liquid crystal matrix is performed using the Landau de Gennes model for chiral self assembly, with strong anchoring at the particles' surface. The defect textures and LC phases observed are investigated as a function of chirality, elastic anisotropy (monomeric and polymeric mesogens), particle polygonal arrangement and particle size. The presence of a polygonal network made of N circular inclusions results in defect textures of a net charge of -(N-2)/2 per unit polygonal cell, in accordance with Zimmer's rule. As the chirality increases, the LC matrix shows the following transition sequence: weakly twisted cholesterics, 2D blue phases with non-singular/ singular defect lattices, cholesteric phases with only disclinations, and finally fingerprint cholesteric textures with disclinations and dislocations. For monomeric mesogens at concentrations far from the I/Ch phase transition and low chirality, for a given symmetry of the LC phase, the particle with weaker (stronger) confinement results in a phase with lower (higher) elastic energy, while at high chirality the elastic energy of a LC phase is proportional to the number of particles that form the polygonal network. Thus, hexagonal (triangular) particle arrangement results in low elastic energy at low (high) chirality. For semiflexible polymeric mesogens (high elastic anisotropy), defect textures with fewer disclinations/ dislocations arise but due to layer distortions we find a higher elastic energy than monomeric mesogens. The defects arising in the simulations and the texture rules established are in agreement with experimental observations in cellulosic liquid crystal analogues such as plant cell wall and helical biological polymeric mesophases made of DNA, PBLG and xanthan. A semi-quantitative phase diagram that shows different LC phase and defect textures as a function of chirality and elastic anisotropy is obtained. The inclusion of particles has a stabilizing effect on the LC phases, as they occupy λ +1 disclination cores, thereby reducing the free energy cost associated with these disclinations. The findings provide a comprehensive set of trends and mechanisms that contribute to the evolving understanding of biological plywoods and serve as a platform for future biomimetic applications.

This review on self-assembly in biological fi brous composites presents theory and simulation to elucidate the principles and mechanisms that govern the thermodynamics, material science, and rheology of biological anisotropic soft matter that are involved in the growth/self-assembly/material processing of these materials. Plant cell wall, a multi-layered biological fi brous composite, is presented as a model biological system to investigate self-assembly mechanisms in nature's material synthesis. In order to demonstrate the universality of the presented models and the mechanisms investigated, references to other biological/ biomimetic systems are made when applicable. The integration of soft matter physics theories and models with actual biological data for plant cell walls provides a foundation for understanding growth, form, and function in biological material and offers a fi rm platform for biomimetic innovation.

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In this work the mechanisms leading to the enhancement of optical nonlinearity of nematic liquid crystalline material through localized heating by doping the liquid crystals (LCs) with gold nanoparticles (GNPs) is investigated. We present some experimental and theoretical results on the effect of voltage and nanoparticle concentration on the nonlinear response of the GNP-LC suspensions. The optical nonlinearity of these systems is characterized by diffraction measurements and the second order nonlinear refractive index, n 2 is used to compare systems with different configurations and operating conditions. A theoretical model based on heat diffusion that takes into account the intensity and finite size of the incident beam, the nanoparticle concentration dependent absorbance of the GNP doped LC systems and the presence of bounding substrates is developed and validated. We use the model to discuss possibilities of enhancing further the optical nonlinearity.