Session Y56: Mechanisms of Macromolecular Self-Assembly

3D Printing-guided Chiral Self-assembly in Cellulose-based Constructs

The chiral or helical arrangement found in biomolecules is known as the origin of the superior fracture resistance in the "smasher-type" mantis shrimp's dactyl club and the vivid metallic colors in beetles. In this talk, I present how combining the "bottom-up" molecular self-assembly with a "top-down" 3D printing technology can be exploited to program nano/microscale chiral arrangements in intricate geometries. Our inks are designed based on cellulosic materials enabling the formation of chiral nano/microstructures. We exploit the coupling of chiral twist energy, 3D printing flow dynamics and filaments' curved confinement to direct and tailor the hierarchical chiral self-assembly in printed constructs. Our biomimetic concept will open the way to developing materials with programable photonic responses and enhanced mechanical properties, naturally emerging from their nanostructure, and transferred into the larger scale printed architectures. This will expand 3D printing material technologies well beyond what has been conceived and attempted so far, into a new generation of nanocomposite and process design.   

Controlling Chain Conformation in Amorphous Polymers through Liquid Crystal Confinement

This presentation introduces a novel approach to control the conformations of polymer chains in intrinsically amorphous materials using non-reactive liquid crystals (LCs). The focus is on achieving alignment in polymers like PMMA and polystyrene, known for their rapid, irreversible transition into random coil conformations upon heating. The solution lies in low-temperature polymerization within LC solvents, which preserves the nematic phase, providing effective nanoconfinement for highly aligned conformations. By utilizing specific LC removal solvents, these aligned chains can be kinetically trapped, enabling remarkable shape memory behaviors. The implications extend beyond polymers into liquid crystal elastomers, shape memory materials, and other fields.   

Quantifying hydropathy of self-assembling biomaterials

Self-assembly is ubiquitous and, unsurprisingly, central to life. In biological systems, the interactions of protein, lipid, glycoproteins, and nucleic acids lead to the micro and macromolecular structures essential to life functions. All these interactions are related to the relative hydropathy of the interacting molecules. Several research articles on amino acid hydropathy have attempted to describe protein folding and assembly. However, self-assembly is more intricate than the chemical nature of the aggregating molecule. Our recent work showed that the molecule's three-dimensional structure is a critical determinant in self-assembly. We have developed a computational tool called PARCH (Protocol for Assigning a Residue's Character on a Hydropathy) Scale, which makes no assumptions about the chemical nature of the molecule to quantify its hydropathy. We have calculated parch values of residues in nucleic acids, biomimetics, and amino acid residues in more than 1,000 folded proteins. This work will feature several examples of macromolecular self-assembly that manifest from the chemical and topological heterogeneity of the molecule.   

Revealing the Molecular Language of Protein Phase Separation Using Physics-Based Computational Approaches

The molecular language of protein phase separation refers to the specific rules and interactions governing the formation of biomolecular condensates within cells. This process has been deemed crucial for the proper functioning of cells, as it allows for the organization of membraneless compartments of different proteins and other biomolecules. In the first part of the talk, I'll discuss the relative merits of currently utilized mechanistic approaches to describe protein phase separation, from a general description based on physical principles to system-specific tools based on experimental input. The latter part of the talk will focus on applying physics-based approaches my group and others developed to several important biological systems of interest. In closing, I'll present results that highlight the limitations of currently accepted biophysical rules or the lack of general principles to describe important aspects of protein self-assembly.