Session F18: Non-Equilibrium Bioinspired Modes of Assembling Materials

Bioinspired liquid crystal patterns to command living matter

Microscale biological systems such as swarms of swimming bacteria and cell tissues demonstrate fascinating out-of-equilibrium dynamics. This dynamics is difficult to control by factors other than transient gradients, such as gradients of nutrients; visual, acoustic and tactile communication channels that humans use to control large animals are not effective. To establish communication with microscale biological systems, we propose to use special class of nontoxic lyotropic chromonic liquid crystal with a long-range orientational order. The anisotropy axis of the liquid crystal can be designed as uniform or be pre-patterned into various structures. We describe how the patterned liquid crystals can be designed to command dynamics of two systems, (i) swimming bacteria; (ii) tissues formed by human dermal fibroblast cells. Topological defects in liquid crystals are demonstrated to impact the biological microstructures most strongly, causing spatial variation of bacterial concentration and cell phenotype. The control of active matter by patterned liquid crystals might result in new approaches to harness the energy of collective motion for micro-robotic, biomechanical, and sensing devices.   

Reaction-Diffusion Driven Pattern Formation in Soft Materials

Reaction-diffusion processes are versatile, yet underexplored methods for manufacturing that provide unique opportunities to control the spatial properties of materials, achieving order through broken symmetry. The mathematical formalism and derivation of equations coupling reaction and diffusion were presented in the seminal paper by Alan Turing [Phil. Trans. R. Soc. Lond. B 237, 37,1952], which describes how random fluctuations can drive the emergence of pattern and structure from initial uniformity. Inspired by reaction-diffusion systems in nature, this talk will describe a new processing strategy predicated on the exploitation of an advancing polymerization front sustained through coupled reaction and thermal diffusion. The system uses the exothermic release of energy to provide a positive feedback to the reaction. In turn, this stimulates further exothermic energy release and a self-propagating reaction “front” that rapidly moves through the material – a process called frontal polymerization. We recently reported the frontal ring-opening metathesis polymerization (FROMP) of dicyclopentadiene (DCPD) that exhibits the high energy density, high reactivity, relatively long pot life, and low viscosity required for the synthesis of high-performance thermosetting polymers and composites [Robertson et al., Nature, 557 (2018)]. This talk will describe several novel methods to control thermal transport in this system, giving rise to symmetry breaking events that enable complex, emergent pattern formation and control over growth, topology, and shape.   

Colour with a Twist: Engineering Optical Appearance with Chiral Noematic Architectures

The most brilliant colours in nature are obtained by structuring transparent materials on the scale of the wavelength of visible light. By controlling/designing the dimensions of such nanostructures, it is possible to achieve extremely intense colourations over the entire visible spectrum without using pigments or colorants. Colour obtained through structure, namely structural colour, is widespread in the animal and plant kingdom [1]. Such natural photonic nanostructures are generally synthesised in ambient conditions using a limited range of biopolymers.
In this seminar, I will review our recent advances to fabricate bio-mimetic photonic structures with cellulose and chitin and I will give examples of how to fabricate novel photonic materials based on chiral noematic architectures using low cost polymers in
ambient conditions [2-7].

References:
[1] Kinoshita, S. et al. (2008). Physics of structural colors. Rep. Prog. Phys. 71(7), 076401.
[2] Narkevicius A, et al. (2019). Controlling the Self-Assembly Behavior of Aqueous Chitin
Nanocrystal Suspensions, Biomacromolecules 20, 2830
[3] Chan C. L. et. al. (2019) Visual Appearance of Chiral Nematic Cellulose-Based
Photonic Films: Angular and Polarization Independent Color Response with a Twist, Adv
Mater 31, 1905151
[4] Frka-Petesic et al. (2019) Angular optical response of cellulose nanocrystal films
explained by the distortion of the arrested suspension upon drying. Physical Review
Materials 3, 045601
[5] Parker R. et al. (2018) The Self-Assembly of Cellulose Nanocrystals: Hierarchical
Design of Visual Appearance. Adv Mat 30, 1704477
[6] Parker R. et al. (2016). Hierarchical Self-Assembly of Cellulose Nanocrystals in a
Confined Geometry. ACS Nano, 10 (9), 8443–8449
[7] Liang H-L. et al. (2018). Roll-to-roll fabrication of touch-responsive cellulose photonic
laminates, Nat Com 9, 4632   

Programming dynamic pathways to colloidal self-assembly using DNA nanotechnology

DNA is not just the stuff of our genetic code; it is also a means to build new materials. For instance, grafting DNA onto small particles can, in principle, 'program' the particles with information that tells them exactly how to put themselves together--they 'self-assemble.' Recent advances in our understanding of how this information is compiled into specific interparticle forces have enabled the assembly of crystalline phases. However, programmable assembly of other user-prescribed structures, such as aperiodic solids, liquids, or other mesophases remains elusive. Furthermore, the dynamic pathways by which DNA-based materials self-assemble are largely unknown. In this talk, I will present experiments showing that: (1) combining DNA-grafted particles with free DNA oligomers dispersed in solution can create suspensions with new types of assembly pathways; and (2) we can quantify the dynamic pathways to self-assembly, such as nucleation and growth, using a combination of microfluidics, video microscopy, and image analysis. Whenever possible, I will describe attempts to understand and model our observations using simple physical arguments. In the future, this work could prove especially useful in nanomaterials research, where a central goal is to manufacture functional materials by growing them directly from solution.