Session T16: Engineered Soft Materials: New Approaches, Mechanisms and Structures III

Multiscale Acoustic Holography of Soft Materials by Optimal Tarzan Scanning

Acoustic holograms capture both the amplitude and phase profiles of the sound scattered by small objects and therefore encode more information than conventional optical holograms that record only the intensity. Extracting that information can proceed either by reconstructing the three-dimensional sound field that generated the recorded hologram or by treating the hologram as an input to a high-dimensional inverse problem whose solution yields characterization and tracking data for the distribution of scatterers. Either analysis involves numerical reduction of massive data sets. We introduce an acoustic camera that acquires holograms by efficiently scanning a microphone across an arbitrarily large field of view in a pattern designed to provide full-field coverage with spatial resolution that improves with time. The scan pattern is generated with an iterative map that can be optimized for continuously improving sampling uniformity. We demonstrate the efficacy of this novel measurement technique through multiscale acoustic characterization of complex materials. This analysis reveals dynamical properties of the insonated systems, as well as their three-dimensional structure.

    

Encoding Textures into Liquid-Crystalline Materials Using Structured Magnetic Fields

Liquid-crystalline block copolymer (LCBCP) systems self-assemble into microphase-separated structures that are magnetically anisotropic and can be aligned by the imposition of a sufficiently strong magnetic field. The balance between magnetostatics, elasticity, and interfacial block interactions governs the resultant morphology. We propose a methodology for using microstructured magnetic materials, appropriately patterned, to precisely control LCBCPs using spatially varying magnetic fields. Here we show that these fields can govern the local orientational order in LCBCPs. We simulate the field patterns created when a unique geometry of ferromagnetic material embedded into and around LCBCPs is brought into the presence of a weak background magnetic field. Then, we use software based on the tensorial Landau-de Gennes theory to describe how variations in the field and the newly imposed boundary conditions, alter the local nematic director orientation of the mesogenic and elastic components of the LCBCP. These steps allow us to engineer ferromagnetic inclusions to program methodical arrangements of mesophase grain orientation (textures) into these LC systems. We anticipate that these bespoke textures in the LCBCP systems can be coupled to thermomechanical, thermochromic, and optical abilities and will enable a new paradigm for geometric actuation in soft stimuli-responsive materials. This development will lay the groundwork for the invention of materials with tunable properties for industries like soft robotics, smart wearables, and photonics.   

Sequence-defined oligocarbamates binding in solution: multiscale modeling and experimental study

Our understanding of the rules of DNA base pairing has opened new avenues of research in materials design. The deployment of DNA technologies on a commercial scale, however, is limited due to constraints in processing conditions such as the need for operating in aqueous solutions. Hence, it is of interest to develop synthetic molecules that mimic the programmable hybridization strength of DNA strands but are able to selectively associate in organic solvents. We present a computational framework to facilitate the rational design of synthesizable sequence-defined oligocarbamates (SeDOC) for improved fidelity and stability. We show that our novel SeDOCs bind specifically through sequence-defined binding sites. This specific binding is both enthalpically and entropically favorable. We show through multiscale molecular simulations that the positive change in entropy associated with the binding of two complementary SeDOC arises from the competition between intramolecular and intermolecular binding. By augmenting the multiscale molecular simulations platform with a machine learning framework, we are able to efficiently unveil correlations between sequence space and binding thermodynamics to propose molecular design criteria to achieve target binding characteristic. In the future, we plan to leverage our sequence-defined molecules in the self-assembly of nanoparticles for photonic and electronic applications.   

3D Printed Methacrylate-modified Chitosan / Methylcellulose Blend Hydrogel Scaffolds for Body Tissue Regeneration

In tissue engineering, 3D scaffolds serve as temporary extracellular matrices to support cell growth, proliferation and differentiation. But a scaffold made from a single biopolymer has limited functionalities. Scaffolds can be tailored to possess desired properties by using two or more biopolymers. UV-crosslinkable methacrylate-modified chitosan (CSMA) is based on cell-compatible chitosan and methylcellulose (MC) is a non-toxic polymer. Blends of CSMA and MC are attractive materials for tissue engineering scaffolds with good biocompatibility and mechanical properties. 3D printing is powerful and can fabricate customized scaffolds according to clinical needs. In this study, polymer blends of CSMA and MC were prepared for 3D printing of hydrogel scaffolds. Rheological properties of blend hydrogel inks were studied, and optimized inks were used for 3D printing. The morphology and structure of 3D printed blend hydrogel scaffolds were examined. Also, mechanical properties, thermal stability, water absorption, etc. of 3D hydrogel scaffolds were investigated. It was found that the addition of MC to CSMA provided required viscoelastic behavior and hence good printability, which allowed 3D printing of multi-layered porous structures without collapsing and ensured structural integrity of printed scaffolds. In addition, the blended networks of CSMA and MC resulted in good mechanical strength of scaffolds. Biological tests revealed good biocompatibility of the blend hydrogel scaffolds.

    

Associative Liquid-in-Liquid 3D Printing Induced by Surfactants Self-Assembly

Structuring oil-water interfaces to create hierarchical functional structures between fluidic interfaces has been a significant area of study in various material sciences and engineering fields. In the current research, we will introduce a new liquid-in-liquid 3D printing approach that utilizes self-assembly at the interface of surfactants in the aqueous phase and cosurfactants in the oil phase to create interfacial assemblies that are highly ordered, which makes the work distinguishable from other traditional 3D printing techniques or liquid-in-liquid printing methods. In this technique, extruding an aqueous solution of various surfactants into a stabilizing lipid bath can generate gel-like constructs with internal nanostructures. When the prepolymers are added into one of the phases followed by photopolymerization, the ordered nanostructures induced by surfactant self-assembly are persevered, confirmed by small-angle X-ray scattering (SAXS). Tunable mechanical properties are observed by changing constituent concentrations and types. We present the phase behavior and structure-properties relationship using shear rheometry, tensile measurements, microscopy, and SAXS. We will further explain the underlying stabilization phenomena and morphological phase transitions using experiments and dissipative particle dynamics (DPD) simulation.

    

Peptide ‘bundlemer’ design for model protein nanoparticle creation and hierarchical solution assembly

A new solution assembled system comprised of computationally designed coiled coil bundle motifs, also known as ‘bundlemers’, will be introduced as model nanoparticles.  The molecules are not natural sequences and provide opportunity for controlled solution behavior and arbitrary soft matter creation with peptides.  With control of all amino acid side chain display (both natural and non-natural) throughout the bundles, desired physical and covalent (through ‘click’ chemistry) interactions have been designed to control solution interparticle interactions in both individual bundlemers as well as polymers and networks of connected bundlemers.  One-dimensional nanostructures span rigid rods that produce a wide variety of liquid crystal phases to semi-flexible chains, the flexibility of which are controlled by the interbundle linking chemistry. The particles and chains are also responsive to salt and pH since computational design is used to design bundlemers with different net charged character in order to manipulate their interactions in solution.  Finally, other patches of interaction can be designed on the surface of the particles to dictate their interaction in solution and the control of particle assembly (e.g., crystalline lattice vs. amorphous aggregate). 

    

Asymmetric Functionalization of Colloidal Microcapsules

Cell mimics are microstructures engineered to emulate the features and behavior of biological cells. Their development can help expand our fundamental understanding of cell biology and create countless opportunities in nanotechnology. While some cell mimics made of bio-materials can recreate certain cell functions and structures, fully abiotic cell mimics remain rudimentary in their design and lack functionality. In my talk, I will describe a synthetic process for fabricating colloidal microcapsules with well-defined geometries and tunable internal chemistry.

    

Detailed control of mesoscopic droplets through temperature-driven phase transtions

Temperature serves as a switch capable of regulating molecular function in living systems. Molecules with temperature-responsive domains can trigger reversible phase separations that can change the properties of the bulk even at low concentrations. We will present an experimental tool that captures the phase transitions driven by temperature changes in colloidal mesoscale droplet mixtures. Temperature is used as a continuous control over droplet internal forces, driving changes in density and size. We will offer an assessment of how molecular conformations effectively control droplet structural changes with high resolution; aspect of broad importance in living and physical systems.   

Design of active and informative display with liquid crystal modulator

Informative, clear and active properties are important factors in the field of display. Hologram shows visible signal as 3D display and structural color has a potential with high resolution, environmental protection and high durability against chemical pigments. Metasurface which is composed of nano-structures with subwavelength scale is a method to realize a variety of information such as hologram and structural color. Each of them is called ‘metahologram’ and ‘meta-color’. Herein, we add liquid crystals (LCs) modulator for active platform to replace using responsive materials on metasurface. As LCs are used broadly as stimuli-responsive materials, the reorientation of LCs by stimuli enables to control actively the properties of the light passed by the LCs.

In this work, we demonstrated that the tunable meta-system combined with metasurface and LC modulator. The system is consisted of polarization dependence metasurface and LCs modulating polarization of the light. Consequently, we realized the active system to change the hologram and gray scale of color by specific stimuli (e.g. electrical field, heat, pressure, gas). [1-3] Additionally, for more informative system, we add the orbital angular momentum to represent more hologram in one system. Design of meta-system with LCs will be useful for future integrated display.

This work was supported by the Korea National Research Foundation (NRF-2021R1A4A1030944, 2021R1A2C2095010) and Samsung Electronics Co., Ltd (4.0024479).   

Double-Gyroid Network Morphology formed by Asymmetric Magic-Ratio Block Oligomers

Amphiphilic block oligomers self-assemble into thermotropic liquid crystals with a variety of morphologies, such as lamellae, hexagonally-packed cylinders, and ordered spherical micelle packings. Among these phases, three-dimensional network structures are seldom found due to narrow composition and temperature phase windows over which they form. In this work, we designed a family of amphiphilic triblock oligomers comprising two asymmetric hydrophobic tails based on geometric analysis and assess their self-assembly in molecular dynamics simulations. With a comprehensive exploration, stable double gyroid morphologies are observed in the self-assembly of oligomers with a "magic" 1:2 tail length ratio. By changing the lengths of the tails while keeping the same headgroup, systematic explorations of the morphologies formed at different volume fractions indicate that this magic ratio for double gyroid stability is a robust molecular design across many volume fractions. This work demonstrates a new approach for designing amphiphilic block oligomers and stabilizing cubic network structures, which could lead to insights into the shape-filling mechanism of network phase formation and amphiphilic self-assembly.   

Making highly elastic and tough hydrogels from doughs

A hydrogel is often made from preexisting polymers by covalently crosslinking them into a polymer network. The crosslinks make the hydrogel swell-resistant but brittle. We present a method to resolve this conflict, making a hydrogel from a dough. The dough is formed by mixing long polymer chains with a small amount of water and photoinitiator. It is homogenized by kneading and annealing at elevated temperatures, during which the crowded polymer chains densely entangle. The polymer chains are then sparsely crosslinked into a polymer network under UV, and then swollen to equilibrium. The resulting hydrogel is both swell-resistant and tough, and shows near-perfect elasticity, high strength, high fatigue resistance, and low friction. We demonstrate the method with poly(ethylene glycol) and cellulose. The method is generally applicable to synthetic and natural polymers, and is compatible with industrial processing technologies, opening doors to the development of sustainable, high-performance hydrogels.

    

Reducing polymorphism in the self-assembly of tubules through soft-modes

Biological systems can create complex self-limited structures, such as viral capsids and microtubules, by controlling the valence and binding angles of biomolecular interactions. Inspired by this strategy, we create DNA origami subunits with specific interactions and prescribed binding angles that assemble into tubules whose self-limited width is much larger than the subunit size. Although we target a single tubule geometry, we find that thermal fluctuations can produce a variety of assemblies close to the target structure. This challenge is compounded by the fact that specific, valence-limited interactions localize subunit binding and limit their mobility within an assembly. Therefore,  the tubule structures are unable to relax to equilibrium even as they continue to grow. To circumvent this challenge, we tweak the interactions to have softer localization that enables the subunits to slide along one another, creating soft modes within the assemblies. These soft modes allow the tubules to anneal towards their equilibrium structure, reducing the overall polymorphism we observe in our assemblies. These results show how including degrees of freedom for assemblies to anneal out of kinetics traps can help reduce polymorphism as we strive to make more complex structures.   

Reacting dislocations drive chirality and shape transitions in tubular crystals

Natural and synthetic tubular crystals, such as microtubules and single-walled carbon nanotubes, often contain dislocation point-defects. When dislocations move through a tubular crystal, they alter the chirality of the lattice, and they may stabilize deformed tube geometries if the crystal is freestanding. In order to elucidate the complex feedback between topological defects, lattice chirality, and tube geometry, we conduct molecular dynamics simulations of patchy spherical particles assembled into free-standing tubular structures with preexisting defects. We demonstrate that stable patterns of dislocations, which are specific to tubular crystals, significantly deform the macroscopic shape of the crystal. In addition, we find dislocation reaction behaviors unique to tubular crystals, with the reacting defects, located several lattice spacings apart, effectively changing their orientations and thus altering the chirality of the lattice. We show that externally applied torsion can be used to control the dislocation motion and even initiate a sequence of elementary defect reactions, resulting in a target defect pattern. Our findings suggest routes to colloidal crystal assemblies with switchable mechanical and electro-optic behaviors.   

Exploring the Self-assembly of Glycolipids into Three-dimensional Network Phases

Glycolipids are intriguing molecules comprising a glycan head group and a lipid moiety, which self-assemble into a number of ordered phases. Their ability to form 3D network phases, such as double gyroid and double diamond, has drawn much attention due to their useful bicontinuous structures. However, the specific inter- and intra- molecular interactions underlying this useful self-assembly behavior remain obscure. In this work, we developed a molecular dynamics simulation workflow to predict the formation of network phases in glycolipids for concurrent experimental studies. Specifically, a multi-step simulation strategy featuring a guiding-field method was used to investigate the stability of four network structures, including double gyroid, double diamond, single gyroid and single plumber’s nightmare (single primitive). The two Guerbet glycolipids, disaccharide-based β-maltose-C₁₄C₁₀ and monosaccharide-based β-galactose-C₁₄C₁₀, are thus shown to exhibit distinct phase behavior. Their predicted thermotropic liquid crystalline phase behavior is corroborated by experimental results based on small-angle X-ray scattering of analytically pure samples of these glycolipids.

    

Hierarchal coatings for biological building blocks via electrospray deposition

Electrospray deposition (ESD) is a spray coating process that utilizes a high voltage to atomize a flowing solution into charged microdroplets. These self-repulsive droplets evaporate as they travel to a target grounded substrate, depositing the solution solids as thin films. These thin films can be utilized in biomedical applications including drug and therapeutics delivery in addition to the fabrication of medical implants and biosensors. Our lab has categorized various modes of ESD, including self-limiting electrospray deposition (SLED). In SLED, the material arrives onto a target as a dried spray, carrying a charge that eventually begins to repel itself over time. The charged spray is redirected to regions that are uncoated such that manipulation of the electrostatic repulsion, hydrodynamic forces, and evaporation kinetics can be employed to conformally cover 3D architectures with micro-coatings. The generated coatings are hierarchical, possessing either nano-shell, nanoparticle, or nanowire microstructure, which can be smoothed through further post processing. We envision SLED as being a replacement for dip or conventional-spray coating, where its greatest advantage would be the potential for much higher materials utilization. While many studies have presumed high efficiency in ESD, this is rarely quantified. Here, we show how architecting the local charge landscape can lead to SLED coatings approaching 100% deposition efficiency on microneedle arrays and other complex substrates of relevant therapeutics with the building blocks and signals for synthetic biology, including DNA vaccines, proteins, amino acids, bioactive small molecules, and biocompatible conductors.